Crystal I i zat i o n

GREGORY D. BOTSAWfS EDWARD G. DENK GUN S. ERSAN DONALD J. KIRWAN GEOFFREY MARGOLIS MAKOTO OHARA ROBERT C. REID JEFFERSON TESTER

CrystalIization Part 11. Crystallization Processes

his second part of the Crystallization Review deals with T processes and techniques of crystallization as well as with the investigation of process operating parameters. The opening section of the review, page 86, October I&EC, was concerned with the transport phenomena involved in crystal growth and nucleation. Part I11 which follows in December is directed toward investigators whose interests lie in the crystallization of a particular product. (For details on subdivision, see Introduction and Outline in Part I . ) This review covers a two-year period from Spring 1967 to Spring of the current year, 1969. Crystallization Processes Involving Suspensions of Crystals

A significant factor in the study of continuous crystallizers has been the application of population balances as an aid to the analysis of the crystallizer performance. Nyvlt (56H) has discussed this aspect from a general point of view and the effects of classified product removal on the crystallizer operation has been reported on by Miyauchi and Imai (50H) and H a n and Shinnar (28H). Application of such analyses to the determination of growth and nucleation rates from particle size distributions has been studied by Bransom et al. (7IH, 12H), -4begg et al. ( 7 H ) , Estrin et al. (21H),and Han (25H, 26H). Theoretical computations utilizing population balance mechanics, on the other hand, have been done by Randolph ( 6 8 H ) on the effects of crystal breakage on crystal size distribution in a mixed suspension crystallizer and Larson et al. (39H) on the effects of suspension density on crystal size distribution. Fluidized bed crystallizers have been extensively reported on particularly in the Russian literature. Razumovskii et al. (70H) has developed equations for characterizing crystals grown under fluidized conditions, and in another paper (72H) reports on the size distributions characteristics of KzCr207, NazCrz07, NaN03, and CuSO4 grown in fluidized beds. Parkash (60H, 6 1 H ) has measured suspension densities and particle residence times in fluidized bed crystallizers, and the crystallization of aluminum potassium sulfate has been comprehensively studied by Mullin and Garside (52H, 53H) and Garside and Mullin ( 2 3 H ) with the objective of assessing the validity of the use of simple laboratory scale measurements for the design of fluidized bed crystallizers. T h e effect of operating conditions and in particular of mixing on the growth of crystals has been studied by Petrenko and Arabova (64H),Korobitsin et al. (35H),Micek et al. (49H), and Babayan et al. (7H). Many papers have been published on the effects of operating conditions on the crystallization (continuous or batch) of specific compounds such as tartaric acid (XH, 83H) calcium sulfate ( 2 H ) , alumino silicates (31H),and ammonium titanyl sulfate (34H). 92

I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY

Coprecipitation and Puriflcation in Crystallization Processes from Solution

T h e two major areas of interest in cocrystallization have been the determination of the factors affecting the impurity content during growth and the measurement of distribution coefficients. Gorshtein ( 6 J )has obtained data on the capture of isomorphic impurities by the solid phase during crystallization and has shown that the data agree well with theory, indicating that the process is determined by distribution coefficients, mass transfer properties, and solution supersaturation. I n a similar manner Rogalla and Schmalzried (7XJ) found the precipitation of SrClz from supersaturated KCl to be diffusion controlled. However, Novobilsky et al. (145)showed that cocrystallization of di- and trivalent iron during the crystallization of ammonium sulfate was affected by a n adsorption process. Novobilsky ( 7 4 J ) has found further that the Fe3+ distribution coefficients increase with supersaturation during cocrystallization of trivalent iron with ammonium sulfate. The equilibrium distributions of impurities during the crystallization of NaC1, KC1, and KBr from aqueous solutions have been measured by Andreev ( Z J ) , and Shvartsval'd ( 1 9 5 ) has reported on the distribution of nonisomorphic impurities between mother liquor and the crystals. Kirgintsev and Shavinskii ( 7 J ) report distribution coefficients for KCl, CaC12, CdIz, NaxOs, (NH4j~S04,and " 0 3 . Industrial Crystallizers and Development of large-Scale Crystallization Processes from Solution

The papers presented in this section of the review deal with crystallization on an industrial scale. These papers are listed in Tables I-K, 11-K, and 111-K as patents relating to industrial crystallization, experimental studies of commercial crystallizers, and mathematical models describing industrial crystallizers.

AUTHORS Robert C. Reid is Professor of Chemical Engineering at M I T . Cambridge, Mass., and Gregory D . Botsaris is Associate Professor of Chemical Engineerang at T u f t s University, Medford, M a s s . Other coauthors are Donald J . Kirwan, Momanto co.,St. Louis, Mo.; Geoffrey Margolis, Assistant Professor of Chemical Engineering, and Makoto Ohara and Jefferson Tester, Ph.D. Chemical Engineering Candidates, all M I T ; and Edward G. Denk and Gun S. Ersan, Ph.D. Candidates in Chemical Engineering, T u f t s . W i t h the exception of D r . Kirwan, all the authors are members of the i M I T - T u f t s Crystallization Study Grouf .

Besides the papers presented in these tables, some general reviews of industrial crystallization have also appeared recently. Bamforth’s text on industrial Crystallization ( 3 A ) has already been mentioned in Part I of this report. Nitschmann, in an annual review (38K),covers many aspects of crystal growth. One of the ten sections of his review deals with recent developments in commercial crystallizers, while another section is concerned with the techniques employed in the production of crystals on a large scale. A review by Hufnagel (72K) treats the theory of industrial crystallization processes, and includes discussions of nucleation, crystal growth, and secondary processes that influence crystallizer design. Paasikoski (48K)outlines the theory and practice used to obtain large, uniform crystals in the chemical industry. Mucskai (36K)discusses the information needed to design modern industrial crystallizers. Messing, in two papers, shows how different crystal requirements dictate different plant designs (33K),and presents a review of the theory of crystallization and a description of the modern crystallizers presently in use in Germany (34K). Barduhn reviews the state of the crystallization equipment and processes used in desalination ( 3 K ) ,while Kang ( 7 6 K )summarizes the design criteria for a Krystal-Oslo crystallizer. The general trend of all the papers in this section seems to indicate that the design and operation of industrial crystallizers is gradually becoming less of an art and more of a science. Even though crystallization has yet to achieve the scientific level of some of the other unit operations, the task of raising its status is a t least well under way. Production of Single Crystals from Melt

Techniques for growing single crystals from the melt, including the Czochralski, Bridgman-Stockbarger, Verneuil, Flux, and Floating Zone methods, were the subject of a great many articles. Here we consider only those papers whose primary purpose is a process improvement or a n explanation of phenomena occurring rather than the application of the process to a specific material. Laudise (48L) has reviewed developments in the techniques of producing crystals from the melt. A number of Russian papers have reviewed developments in the method of growing crystals from the melt (77L, 28L, 47L, 79L). Luzhnaya (52L) has discussed single crystal growth from metal solutions and Cockayne (6L, 22L) has discussed the growth and perfection of high meltingpoint oxides. The Czochralski technique continues to be the most popular and versatile technique fbr growing single crystals. A number of patents and papers dealt with improvements in the apparatus for pulling crystals from the melt (77L, 33L, 34L, 43L, 46L, 64L, 67L, 77L, 89L). Methods are described for controlling the diameter of the crystal by controlling the drawing rate (4ZL) or the power supplied to the furnace (5L). The capillary seed technique for use in crystal pulling was described in a paper by Hiscocks (37L). Another paper discussed the transfer of defects from a deformed seed crystal to the growing crystal (26.L). Papers by Mullin (58L) and Hiscocks and West (38L) dealt with the use of liquid encapsulation techniques to allow the pulling of crystals containing a volatile constituent. Papers by Reed (66L),Vigdorovich and Uglov (88.L)and Brice (73L) analyzed heat flow during growth by the Czochralski method. Two papers by Turovskii (85L, 86L) experimentally evaluated the effect of seed crystal rotation on axial temperature gradients along the ingot. Other Russian papers (35L, 75L, 76L) considered the effect of crystal pulling rate and crystal diameter on axial temperature gradients during the growth of silicon crystals by the Czochralski method. Impurity striations or banding in crystals pulled from the melt are generally considered to be the result of temperature oscillations in the melt. Two papers by Carruthers (78L, 19L) found that temperature oscillations could be attributed to thermal convection and crucible rotation rather than crystal rotation. A series of papers by Morizane, Witt, and Gatos (56L, 57L, 9215) related impurity heterogeneities in the core of the crystal to thermal asymmetry. Oscillations in the crystallization front during crystal pulling were experimentally observed by Shashkov (77.L, 78L). A number of papers presented improvements in the apparatus or techniques for the growth of single crystals by the Stockbarger or Bridgman method (2415, 40L, 50L, 7 3 0 , SOL). A Russian paper (70L) described the growth of mixed organic crystals for scintillation counters by the Stockbarger technique. Wolfson and Kobes (93.L) grew large mixed crystals of NaCI-KCl by the

TABLE I-K. PATENTS ON INDUSTRIAL CRYSTAL L I2 A T I0 N Descriplzon of Patent

Process for continuous crystallization of alkali metal aluminum acid orthophosphates Method using additives to give intergrowth-free KCI product crystals Continuous crystallizer using a circulating suspension adiabatically evaporated with air--suitable for production of basic phosphates or crystallization of (NH4)rSOd from HzS04 production waste gases Continuous crystallizer to convert saline water to potable water Apparatus for freeze concentration of comestibles such as orange juice, apple juice, coffee extract, etc. Two methods suitable for separation of p-xylene from mixtures containing 0-, m-,and p-xylene and ethyl benzene Process for production of sodium perborate crystals Process for production of large ammonium perchlorate crystals Process for continuous countercurrent crystallization of sulfur from toluene solutions Apparatus in which crystalline hexamethylene tetramine is produced by reacting formaldehyde and ammonia Process for freeze concentration of solutions containing a volatile component-especially suited for the concentration of beer Apparatus for making ultrafine calcium sulfate dihydrate crystals Crystallizer in which deposits on circulating pump and shaft and on exposed surfaces are minimized -suitable for crystallization of organic salts Apparatus for producing salts from solutions Process for producing crystallized granules of a crystalloid such as starch hydrolyzate Crystallizer with a special heater and a second device, both of which control the number of fine crystals in the product Process for controlling size range of borax decahydrate crystals Technique for crystallization of pyrophosphoric acid from seeded, nonaqueous solutions System for controlling cooling process for crystallizing and viscous products Technique for crystallization of salts from solution by countercurrent introduction of a cooling agent Crystallizer for caprolactam Fractional crystallizer suitable for production of potable water from brine and concentration of fruit juices, vegetable juices, and beverages Technique for crystallization of materials from solutions in which solubility of solute is highly temperature-dependent Apparatus for production of crystals of uniform dimensions Vacuum cooling crystallizer for production of dust free, coarse crystalline products such as KCl Multisection crystallizer with separate heat exchangers in each section Apparatus for vacuum crystallization of salt solutions Continuous, cooling crystallizer whose cooling area can be easily changed Vacuum crystallizer that gives large, uniform crystals

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TABLE I l - K . STUDIES ON INDUSTRIAL CRYSTALL I 2 ERS Subject of Study

Factors which affect size of NaN08 crystals produced in a vacuum crystallizer with circulating suspension Continuous vacuum crystallizer for production of K2Cr20, Effect of biuret on size of urea crystals produced in a n Oslo crystallizer Compact, low-temperature refrigeration unit for use in a crystallizer Production of large ammonium phosphate and ammonium sulfate crystals in fluidized bed Equipment used for crystallization of sodium chlorate in fluidized bed Process for separation ofp-xylene from its isomers, which employs countercurrent heat transfer Factors which affect size of crystals obtained in a vacuum crystallizer with circulating suspension Crystallizer for production of potassium bichromate and sodium bichromate crystals in which incrustation is minimized Factors which affect size of NaNO3 crystals produced in a suspension circulation vacuum crystallizer with propeller pump Crystallizer for production of sodium sulfate and sodium chloride crystals in which incrustation is minimized Effect of stirring on product crystal size in both batch and continuous crystallizers Effect of MgC12 content on crystallization of carnallite in a vacuum crystallizer Vacuum crystallization of ferrous sulfate from pickling liquor Crystallizer in which large KC1 crystals were obtained by suppression of spontaneous nucleation

Bridgman and the Czochralski techniques. In contrast to the Bridgman method, the crystals grown by the Czochralski technique were strain-free and homogeneous. A paper by Pastor and Pastor (59L) described the use of the Verneuil method of crystal growth above 22OOOC. Other experimental papers described the use of plasma heat transfer with the Verneuil method (X, 4L, 97L) and a means of automating the Verneuil process (68L). Popova ( 6 2 L ) prepared solid solutions of rare earth oxides using the Verneuil method. Roy and White (69L)reviewed the flux (high temperature solution) method of crystal growth. Brice et al. (15L) obtained a patent on a method of growing crystals in volatile solvents. Another paper (54L) generally reviewed the preparation of high melting single crystals by the flux method. Chase and Wilcox (27L) described temperature fluctuations and the resulting impurity striations during flux growth and Perry, Hutchins, and Cross (60L)observed such inhomogeneity in the growth of (Ba, Pb)TiOs in two different flux systems. In a variation of the flux method, Brixner and Babcock (76.5) used a flux-reaction technique for the preparation of inorganic single crystals in which a salt melt serves both as a flux and a reactant. Floating zone refining is used to prevent contamination by a crucible during the production of single crystals of high melting materials. A floating zone technique using an electron beam is described in two articles (8L, 87L). A German patent (29L)was obtained on floating zone melting in a vacuum chamber. Harkness et al. (36L) grew large single crystals by controlling zone formation with focused light. Solid solutions of Cd,Hgl-,Te were grown by a vertical zone melting method (27L) while single crystals of Pb,Srl- .(TiOa) were grown by passing solvent zones 94

INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY

through polycrystalline rods of the same composition (25L). A Russian paper (47L) discusses the effect of growth conditions on the orientation, purity, and perfection of tantalum crystals grown by zone melting without a crucible. Axial temperature gradients during vertical zone melting of silicon were measured as a function of crystal diameter and zone passage rate (45L). A French paper ( I L ) describes a method of crystallization from the melt without mechanical displacement. The technique consists of slow cooling of a furnace containing a crucible in a region of high temperature gradient. A Russian paper (84L) describes a preparation technique for solid solution single crystals in which the components strongly segregate upon solidification. Hurle, Mullin, and Pike (39L)presented the basic principles of the thin alloy zone crystallization technique in which crystallization of a substance is achieved via diffusion through a thin alloy zone separating the crystal from the source material.

Purification by Melt Crystallization

Processes effecting purification by crystallization from the melt include zone refining, normal or directional freezing, and column crystallization. On the laboratory scale, increased interest is being shown in the use of zone refining and normal freezing for the purification of organic compounds, while column crystallization retains its potential as a large-scale purification method for organic compounds under the appropriate conditions. Gouw ( 15M) has reviewed the basic principles of purification by normal freezing. Pfann ( 3 7 M ) has described an improved apparatus for the zone refining of organic compounds. I t employs tube rotation and direct contact of the tube with coolant to minimize zone length and maximize the separation per zone pass. A Russian paper ( 3 3 M )discusses the limitations in the application of zone refining to organic compounds. Perrin ( 3 5 M ) noted that zone crystallization is preferred to zone melting for substances that are liquids a t room temperature. A comparison of the purification and separation of inorganic salts by zone refining and column crystallization was made by von Ammon ( Z M ) . A number of papers (27M, 29M, 37M, 40M, 43M) dealt theoretically with the effect of operating variables such as zone travel rate on the impurity distribution during zone refining or zone leveling. A Russian paper by Lozovskii and Nikolaeva (30M) dealt with impurity distribution during temperature gradient zone melting. Another paper ( 3 6 M )analyzes a method of obtaining a n effective distribution coefficient from zone melting experiments. Except for a few examples, no attempt will be made here to list the many applications of zone refining to the purification of metals and inorganic and organic compounds reported in the literature in the past two years. Three papers (24iM, 47M, 47M) dealt with the purification of molybdenum by electron-beam zone refining. I n a study of the purification of niobium by zone melting in a vacuum, the most important contribution to purification was found to be the vacuum pressure (79M). Diehn, Rowland, and Wolf (8M) described the separation of radioactive trace components from organic compounds by zone refining. A Russian paper (4M) dealt with zone-melting in the acetonitrile-benzene system. Li, in a series of papers (26M-28M), has computed concentration profiles during normal freezing in systems having variable segregation coefficients. A paper by Evans, Bogan, and Battino (77M)described the production of (>99.9970)pure hexafluorobenzene by directional freezing. In another paper ( 3 8 M ) the purification of krypton by directional freezing was observed. A technique for the removal of inclusions from crystals by applying a temperature gradient across the crystal was presented and analyzed by Wilcox (46M). The steady development of countercurrent column crystallization on an industrial scale is reflected mainly in a number of U S . and foreign patents ( 6 M , IOM, 73M, 74M, 77M). A Russian paper ( 7 M ) describes the purification of sulfur in a column crystallizer. Diffusion in the solid phase was found to be the factor limiting purification. A British patent (3ZM) and a Russian paper ( 3 4 M ) describe cascade-type crystallization processes.

TABLE I Il-K. MATHEMATICAL MODELS DESCRIBING INDUSTRIAL CRYSTALLIZERS Subject of Model

Relation between height of a Krystal crystallizer and size of product crystals obtained from it Modification of usual equation by which thickness of the solidified crystal layer on a rotary, cooled, drum crystallizer is calculated-the modification considers viscous effects Equations for describing the behavior of a twin crystallizer (a pair of connected crystallizers operating under different conditions) Mathematical relations by which median size of product crystals obtained from both batch and continuous, stirred crystallizers may be predicted Relations by which particle size distribution of product crystals coming from a cascade of mixed crystallizers may be predicted-experimental data for Ca(N08)2, FeS04, and urea were used as checks on theoretical values Relations by which saturation rate in a continuous, mixed crystallizer may be calculated Relations by which residence time and output characteristics of a mixed crystallizer with classified product removal can be predicted-predicted values were checked by experiments with NazSzO8 Equations for calculating optimal temperature distribution in a cascade of cooling crystallizers Equations for calculating temperature in each member of a cascade of cooling crystallizers Equations for predicting output of a batch, mixed crystallizer Nomographs by which mean crystal size and other output characteristics of both batch and continuous crystallizers may be estimated Relations for characterizing product obtained from an ideally mixed crystallizer Equations giving distribution of particle sizes in a real, mixed crystallizer and a cascade of crystallizers Equations describing operation of industrial crystallizers under conditions of diffusion controlled crystal growth

Ref.

(QK)

Miscellaneous Crystallization Procorses and Techniques

VAPOR-LIQUID-SOLID GROWTH. The vapor-liquid-solid (VLS) growth technique is a relatively new method of producing pure single crystals of a number of new compounds. Ellis, Pfann, and Wagner ( 7 N a ) mention in their patent that the VLS method can be used for semiconductors, superconductors, high melting refractory and ceramic materials, luminescent materials, magnetic oxides, and optical maser compounds. Filby et al. (ZNa) grew epitaxial layers of Si in the presence of Au by the VLS method. Heuer and Burnett ( 3 N a ) discuss the VLS mechanism in accounting for MgO whisker growth. Sickafus and Barker (8Na)explained spike growth of NiBrz crystals by a VLS mechanism. Ryan et al. ( 7 N a ) discuss VLS and melt growth of silicon carbide. Komatsu, Higuchi, and Niina (4Na, 5 N a ) used the VLS method to grow single crystals of Si. Niina and Higuchi ( 6 N a ) also employed this technique to grow silicon single crystals. Wagner and his associates (9-72%”) discuss the mechanistic aspects of VLS growth including branching and kinking and defect formation. GEL GROWTH. Although crystallization in gels is one of the oldest crystal growth techniques (about 50 years old), only recently has this method of crystallization been used to any extent. Gel growth can be used to prepare crystals that cannot be grown by the conventional techniques; for example, it can be used to produce crystals that have very low solubilities (e.g. 10-7 weight %), and for the preparation of crystals of metastable phases. Gel growth can be successfully applied for the growth of whiskers, dendrites, and optical quality single crystals. Chemical reactions which form crystals can be adjusted by controlled diffusion of the

reactants into the gel. The growth process is simple, whereas the chemical and diffusive processes are not. The apparatus used is also simple and inexpensive. There are two general techniques used in gel growth. One is the “Diffusion” technique where one reagent is already in the gel and the other reagent diffuses into the gel where a chemical reaction takes place to form the product crystals. The second method is the “Decomplexation” method where a soluble complex of the crystal is diffused into the gel where a simultaneous decomplexation and dilution yielding the product crystals take place. T o grow larger crystals, a reseeding procedure is used in which the crystals formed in one gel are transferred to a new nutrient gel where they grow larger. Care must be taken to avoid contamination and damage of the crystal surface during the transfer, since this could lead to polycrystalline materials. Gel growth has certain advantages over solution growth. There is an absence of convective currents and turbulence in gel growth. The suppression of nucleation allows crystals to grow in selected sites under controlled environmental conditions and in a n inert media. The solute and growing surface is self-adjusting, so there is a more orderly growth. The reduction of competition for solute leads to larger and more perfect crystals. Gel growth also has advantages over melt growth. Metal crystals can be grown a t ambient temperatures and a t rapid growth rates. The large thermal stresses and crystal imperfections caused by thermal vibrations, contamination by impurities, and point imperfections are absent. The gel structure plays a very important role in gel growth, but u p to now the structures of the gels have not been well established because of their complexity. The density, pH, and temperature of the gel are also very important. Silica gels, gelatin, carpopol acrylic polymer, styrene, and maleic anhydride are the most common gelling agents. Halberstadt and Henisch (73Nb) have given a general review on recent experiments on crystal growth and nucleation in gels. Henisch (75Nb) gives a n historical and technical survey of crystal growth in gels with a description of the methods used. Dennis and Henisch (70Nb) have given a review of nucleation in gels-how it occurs, and how it can be controlled. O’Connor and Armington ( 7 9 N b )presented a review of crystal growth in gels with special emphasis on reseeding methods used to grow larger crystals. Atkinson et al. ( 5 N b ) give a description of the growth of iron oxides nucleated and grown in Fe(II1) hydroxide gels. CuCl is one of the most common crystals produced by gel growth. Armington and O’Connor report the growing of clear, tetrahedral CuCl and CuBr crystals 6 mm on a n edge by decomplexation. These authors have also measured the saturation ratio (ratio of cuprous ion found in solution to the amount soluble a t the same acid concentration) (ZNb). The same authors in another paper (3Nb) reported the growth of CuCl crystals by a decomplexation. The tetrahedral crystals were 0.3 mm on a side, and contained some physical defects. Armington, O’Connor, and their coworkers have also given the conditions for the growth of clear, perfect CuCl crystals in silica gels (7Nb). O’Connor, DiPietro, and others (20Nb) reported the growth of CuCl crystals, but the crystals formed were neither clear nor perfect. Blank, Speyer, and others (QNb) reported the growth of alkali halides in silica gels. AgI crystals were easily formed by decomplexation of their corresponding acid complex H +[AgIz] yielding hexagonal platelets 10-12 mm in diameter. AgBr crystals were prepared by decomplexation of H +(AgI2)- yielding cubic crystals 1 mm on an edge, AgCl could be prepared from its ammonia complex [Ag(NH~)z]+cl-in the form of octahedra 6 mm per edge. Halberstadt (72Nb) reported the growth of AgI crystals by a modified dilution method a t 25’ and 45OC. The crystals formed were not clear. Kratochvil and Sprusil (76Nb) grew hexagonal and triangular Au single crystals a t ambient temperatures, thus avoiding the disadvantages of melt growth. Blank, Brenner, and Okamoto (81Vb) grew Se single crystals a t room temperature by diffusion of a selenium solution in carbon disulfide into a gel of styrenemaleic anhydride copolymer. The crystals formed were monoVOL. 6 1

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clinic, 1.5-2 mm in diameter, and were of high quality. Blank and Brenner have also prepared single crystals of Cu20 a t room temperature in silica gel by controlled reduction of cupric sulfate with hydroxylamine hydrochloride and hypophosphorus acid, the latter giving more uniform and larger crystals ( 6 N b ) . After equilibrium was reached the crystals were unavoidably contaminated by copper. Blank, Brenner, and Okamoto ( 7 N b ) reported the growth of PbS single crystals a t room temperature in silica gels. Murphy, Kues, and Bohandy (78,Vb) were able to prepare a-HgS and P-HgS by using a cosolute in silica gels. They also reported the growth of silver halides in gels by using cosolutes. The crystals they obtained had reasonable crystal perfection. Single crystals of calcium tartrate have been prepared by controlled diffusion in silica gels ( I 7 N b ) . Nd doped calcium tartrate crystals over one inch in length have also been prepared (4Nb). Matsumoto (77Nb) reports the growth of NaCl whiskers in silica gels. Polytypism in gel grown PbIz are presented in 14Nb, 20Nb. Gel crystal growth is still a novel crystal growth technique. The crystal perfection that the method promises has not as yet been achieved. HYDROTHERMAL GROWTH. Hydrothermal crystallization refers to the growth of crystals in solutions which are under high pressures. Quartz crystals have been produced commercially by this technique for a number of years. Literally, hydrothermal growth implies aqueous solutions and high-water pressures, but the technique is not restricted to the use of water as the solvent. Perhaps a better name would be high pressure solution (HPS) growth (341Vc). The elevated pressures allow the system to be operated a t higher than ambient temperatures without evaporation of the solvent. Temperatures on the order of 5OOOC and pressures in the kilobar range are typical. At these higher temperatures, materials which are relatively insoluble in most solvents a t room temperature ( e g . , quartz) become soluble enough to be prepared by solution growth techniques. I n addition, the rate of crystallization a t these higher temperatures is considerably faster (up to 1000 times greater) than it would be under the same conditions but a t room temperature. Ideally, this technique is capable of producing large, single crystals relatively free from defects and impurities. For example, hydrothermally grown crystals usually contain lo4 dislocations/cm2 as compared with l o 5 for flux grown crystals and 106 for crystals grown from the melt. I n addition, the growing crystals tend to reject metal cation impurities and, therefore, are apt to be purer than crystals grown by most other techniques. Since many crystals can be prepared by hydrothermal growth a t temperatures below their melting point, they tend to be freer from thermal strains than they would be if grown from the melt. Obviously hydrothermal growth offers many significant advantages; unfortunately, it also carries with it several disadvantages. For one thing, a suitable solvent must be available; for another, crystallization must be carried out in equipment capable of operating a t several thousand pounds per square inch of pressure. T h e biggest problem a t the present time, however, lies in the manner by which the solutions are seeded. Unless well formed, carefully prepared, and properly oriented seed crystals are used, flawed growth and spontaneous nucleation are likely to result. Excellent general reviews outlining all of these problems are presented by Liptai, Lloyd, and Friddle (22hrc),and by Roy and White (341Vc). T h e problem of finding a suitable solvent that was just mentioned is usually not a severe one, and lately there has been a trend away from the use of strictly aqueous solutions (5Arc, 7ivC, 17.%'c, 12Nc, 741\'c, 15AVc, 16,Vc, 17:Vc, 18,\7~, 201Vc, 27Nc, 29A7c, ~ILVC, 32iVc, 40Nc). Recent developments in equipment design have led to systems capable of operating a t ultrahigh pressures (more than 20 kilobars). Systems that could operate a t 30 kilobars pressure were reported (2"). Other very high pressure systems have also been described (e.g., 27Nc). (These pressures are still somewhat lower than those used to produce synthetic diamonds.) Much work has also been done in establishing the phase equilibria of systems under these temperatures and pressures. For 96

INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY

example, Marshall nd Laudise (23,Vc) determined the phasea diagrams for the KZO-Nb205 and K20-Taz0: systems under hydrothermal conditions. Other improvements have come about through the use of additives. Laudise (27:Vc) reported that Li ions added to zinc oxide solutions tended to suppress both spontaneous nucleation and dendritic growth of the seed and led to better product crystals. Li was also reported to result in a n improvement in the quality of synthetic quartz crystals grown hydrothermally (39.V~). Other studies employing additives include 4'Vc, 74:Vc, and 77A'c.

TABLE I-N.

HYDROTHERMAL SYNTHESIS

O F VARIOUS MATERIALS Material

Material

Re/.

'%

(corundum) A1203 (ruby) .41203

AS

Au Be0 BP C (diamond graphite) Ca3AlzSi3012 (garnet) CaFz (fluorite) CdS CdSe CdTe co CunO CUI cus

+

CUBS5

GeOz HfOz HgS Hg3S2Cl z HoFeOs KNb03 KNd(W04)2 K ( T a , Nb)Oa (KTN) KTa08

(322% ) ( S N c , 7 7i\'C, 78?7c) ( IgA'c, 24:Vc) (321%'~ )

(32A'c) ( 7" ) (27iVc) (371Vc)

(41Vc) ( 5'VC )

(37iVC) ( I2Nc ) (721Vc) ( 321Vc ) ( I I'VC)

(31Nc) (31Nc) ( 37 N c ) (61Vc)

( 2 0 N c) (31Nc) ( 37 N C ) (75Nc) (361Vc) (QNC) (23.V~)

(36iVc)

LiCe(\VOe)z LiNd(WO4)z LiPr(W04)2 LiV201 NaNd(WO4)z Na zeolite Nd2(W04)3 Ni

P PbS Pt Pu SbzSa SbSI S i o s (quartz) SnOz TbFeOs Te Ti02 U YsALOiz YFe03 YbFeOa

Yzoa ZnO ZnS ZnSe ZnTe ZrOz

Re/.

( IOlVC) (QlVC, l O I % ~ C )

( IO'VC)

(33Nc) (9NC) (35Nc) (9'VC ) (32.V~) (2Nc) ( 37 N C ) (32Nc) (22'VC ) (31Nc) (ZSNc, 3 1 N c ) ( I N c , 76Nc, I8Nc, 28;1'c, 39Nc) (6A-c ) (15iV~)

(31Arc,32Ai) (61Vc ) (22NC )

(3ONc) ( 151Vc ) ( 75hJc) (40Nc) (13.V~~74Nc, 781Vc, 21Nc) ( 4 O N c) (12Nc,371Vc) (12Nc) (ZOIVC)

A review paper (34Nc) reported that a special pretreatment of the seed (by etching away 0.05-0.07 m m of damaged surface layer) tended to significantly reduce the number of surface flaws of zinc oxide crystals. I n concluding, hydrothermal growth is a technique that offers great promise. I t is also a technique whose full potential is yet to be realized. Because of this potential, further studies will undoubtedly lead to refinements in the solvents and equipment used, and in the methods of seeding employed. If these further studies enjoy any measurable success, hydrothermal growth will become one of the most useful of the crystal growth techniques. REFERENCES Crystallization Processes Involving Suspensions of Crystals (1H) Abcgg, C . F., Stevens, J. D., Larson, M. A,, Crystal Size Distribution in Continuous Crystallizcrs When Growth Rate Is Size Dependent, A.I.Ck.E. J . , 14, 118 (1768).

(2H) Amin A. B., Larson M. A,, Crystallization of Calcium Sulfate from Phosphoric Aiid, IND.ENG.CLEM.,PROCESS DES.DEVELOP., 7,133 (1963). (3H) Anikin A. G . Theoretical Calculation of Cr stal Flow in Crystallizing Column, hoscow d i u . BulietinSer. Chem., 1, 14 (1967f. (4H) Arkenbout, G. J., Smit, W. M., A Mathematical Description of Countercurrent Crystallization, Separation Sci., 3, 501 (1968). (5H) A erst R. P., Phillips, M. I., Crystallization from Agitated Ammonium Perc!;fora& Solutions: Some Aspects of Nucleation and Growth, Symposium on Industrial Crystallization, The Institution of Chemical Engineers, p 58, London, April 1969. (6H) Ayerst, R. P., Phillips, M. I., A Study of thc Operation of a Pilot-Scale Forced Circulation Evaporating Crystallizer for Ammonium Perchlorate, Symposium on Industrial Crystallization, The Institution of Chemical Engineers, p 129, London, April 1969. (7H) Babayan, S. G . , Isakhanyan, S. S., Manvelyan, M. G., Kinetics of the Crystallization of Sodium Metasilicate Nonahydrate. 11. Arm. Khim. Zh., 21, 467 (1968). (8H) Bakhanov, V. P., Yanchuk, R. A,, Initial Stage of Bulk Crystallization in Supersaturated Solutions of Tartaric Acid. 11. Theoretical Study of Kinetics of the Process, Kolloid. Zh., 29, 29 (1967). (9H) Baranov, G. P., Matusevich, L. N., Influence of Certain Factors on the Size of Crystals Formed in Vacuum Crystallizeys with Circulation of the Suspension, J. Appi. Chem. USSR, 40, 2147 (1967). (10H) Bennett, R . C., Houghton, J., Crystallization of Potash, Symposium on Industrial Crystallization, The Institution of Chemical Engineers, London, April 1969. (11H) Bransom, S. H., Brown, D. E., Heeley, G. P., Crystallization Studies in Continuous Flow Stirred Tank Crystallizers. Part I : Crystal Growth Rates, Symposium on Industrial Crystallization, The Institution of Chemical Engineers, p 26, London, April 1969. (12H) Bransom, S. H., Brown, D. E., Heeley, G . P., Crystallization Studies in Continuous Flow Stirred Tank Crystallizers, Part 11: Heterogeneous Nucleation Rates, Symposium on Industrial Crystallization, Thc Institution of Chemical Engineers, p 45, London, April 1969. (13H) Bransom, S. H., Brown, D . E., Watts, P., The Effect of Impeller Speed on Growth Rates in a Stirred Vessel Crystallizer Symposium on Industrial Crystallization, The Institution of Chemical Engine&, p 89, London, April 1969. (14H) Bujac, P. D. B., Mullin, J. W., A Rapid Method for the Measurement of Crystal Growth Rates in a Fluidised-Bed Crystallizer, Symposium on Industrial Crystallization, The Institution of Chemical Engineers, p 101, London, April 1969. (15H) Canning, T. F., Randolph, A. D., Some Aspects of Crystallization Theory: Systems that Violate McCabe’s Delta L Law, A.Z.Ch.E. J.,13,5 (1967). (16H) Cartwright, P. F. S., The Preci itation of Bismuth Basic Acetate from Homogeneous Solution, Talanta, 14, 698 (1 967). (17H) Claes, F. 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(London), 46, T11 (1 968). (24H) ,Gcrasimenko, W. S. Lyubov B Y. Transient Growth of Crystals under Nonisothermal Condition:, Dokl. Aiad.‘Na;k SSSR,178, 577 (1968). (25H) Han C. D. A Control Study on Isothermal Mixed Crystallizcrs, IND.ENG. CHEM.PLOCESS DES.DEVELOP., 8, 150 (1969). (26H) Han, C . D., Determination of Crystal Growth Ratc by Analog Computer Simulation, Chem. En,?. Sci., 22, 611 (1967). ( 2 7 H ) Han, C. D., Evaluation of Somc of the Kinetic Parameters in Crystallization, tbzd., 23, 321 (1968). (28H) Han, C. D., Shinnar, R., T h e Steady State Behavior of Crystallizers with Classified Product Removal, A.I.Ch.E. J., 14, 612 (1968). (29H) Hanitzsch, E., Kahlweit, M., On the Aging of Precipitates, Symposium on Industrial Crystallization, The Institution of Chemical Engineers, London, April 1969. (30H) Huige, N. J. J., Thijssen, H . A. 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Effect of the Mixing Rate on the Size of bodiu; Fluoride ‘Crystais durjng th; Decomposition of Sodium Fluorosilicate by Sodium Carbonate, T r . Ural. Nauch.-Zsrled. Khim. Inst., 17, 118 (1968). (36H) Koziol, K., Bandrowski, J., Multiple Crystallization with Interstage Eva o ration. 11. Actual Efficicncy of the Process, Chem. Stosow. Ser. B, 5,49 (19685. (37H) Krishna Rao, B. S., Hileman, Jr., 0. E., Preci itation of Nickel Salicylaldoximatc from Homogenous Solution, Taianta, 14, 29!: (1967).

(38H) Larson, M . A,, A paratus for the Study of Crystallization Kinetics, Ckem. Eng. Progr. Symp. Ser., 58 (1967). (39H) Larson, M . A,, Timm, D. C., Wolff, P. R., Effect of Suspension Density on Crystal Size Distribution, A.1.Ch.E. J., 14, 448 (1968). (40H) Lauritzen, J. I., Passaglia, E., Di Marzio, E. A,, Kinetics of Crystallization in Multicomponent Systems, J.Res. Nut. Bur. Stand., 71A, 245 (1967). (41H) Lederer, E., Nyvlt, J., others, Crystallization. XXVII. A Mathematical Model of a Twin Crystallizer, Chem. Prum., 17, 640 (1967). (42H) Lidster, F. A,, A Continuous Classifying Circulatin Liquor Crystallizer-A Case Study, Sym osium on Industrial Crystallization, ?he Institution of Chemical Engineers, p f16, London, April 1769. (43H) Liu, S. L., Continuous Process of Zeolite A Crystallization, Chem. Eng. Sci., 24. 57 (1967). . . (44H) Lyle, S. J Maghzian, R., Precipitation of Nickel Dimethylglyoximate, Taianta., 14., lOZi’11967). . , (45H) L ubehenko T V. K O ylev, B. A,, Pozin, M. E., Crystallization of C a s 0 4 from x a P 0 4 SolAion, J: Appr. Chem. USSR, 40,2142 (1967). (46H) Matusevich, L. N., Baranov, G. P., Effect of Crystallization Ratc on Actual Su er Saturation Level and Quality of Crystals, Tear. O m . Khim. Tekhnol., 1,

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(47H) McKay D L. Goard H. W. Crystal Purification Column with Cyclic Solids Moveken;, I ~ DENC..’CHEM., . ~ R O C E S SDES.DEVELOP., 6,16 (1967). (48H) Melikhov I. V Pechnikov V. G., Methods of Studying Crystallization, Tear. Osn. Khi;. Tekh’hol., 2,42 (1668). (49H) Micek, F., Nyvlt, J., Sura, J., Crystallization. XXXV. Effect of Stirring on Crystal Size, Chem. Prum., 18, 285 (1968). (50H) Miyauchi, T., Imai, H., Crystal Size Distributions in a Continuous, SteadyState, Mixed Suspension Crystallizer. Effect of Classified Product Removal, Kagaku Kognku, 91, 36 (1967). (51H) Mullin, J. W., Amatavivadhana, ‘A,, Growth Kinetics of Ammonium and Potassium-Dihydrogen Phosphate Crystals, J. Appl. Chem., 17,151 (1967). (52H) Mullin 3. W., Garside J. Thc Crystallization of Aluminum Potassium Study in the )Asskssment of Crystallizer Design Data. Part I : Sulphate: Single Crystal Growth Rates, Trans. Inst. Chem. Engrs. (London), 45, T285 (1967). (53H) Muilin, J. W., Garside, J., The Crystallization of Aluminum Potassium Sulphate: A Study in the Assessment of Crystallizer Design Data. 11. Growth in a Fluidized Bed Crystallizer, Trans. Inst. Chem. Engrs. (London), 45, T291 (1967). (54H) N vlt J. Crystallization. XXVI. Distribution of Temperatures in a C a s c a 6 ok Cdoling Crystallizers with Nucleation in all Sections, Chem. Prum., 17, 329 (1967). (55H) Nyvlt J Crystallization XXXVI. Nomographs for Estimating the Output of Disc)on;inuous and Con’tinuous Mixed Crystallizers, ibid., 18, 494 (1968). (56H) Nyvlt, J., Crystal!ization as, a Unit Operation in Chemical En ineering, Symposium on Industrial Crystallization, The Institution of Chemical jngineers, p 3, London, April 1969. (57H) Packter A. Precipitation of Sparingly Soluble Alkaline-earth Metal and Lead Salts: ’ Ndcleation and Growth Orders during the Induction Period, J. Chem. Sac., Sect. A , 859 (1968). (58H\ Palmrr K. Product S i x Prrformancc from Oslo-Krysiil C!rvs!aIlizw5, Symposium )on Ihdurrrial Crvrralliz..irion, The Insrirution of Chemical Encinecrs, p 142, London, April 1969. (59H) Palmer, R. C., Batchelor, J., On the Crystallization of Paraffinsfrom Hydrocarbon Solution, Symposium on Industrial Crystallization, Thc Institution of Chemical Engineers, p 179, London, April 1969. (60H) Parkash, S., Residence Time of Crystals in a Fluidized Bed Crystallizer, Chem. Ind., 22, 919 (1967). (61H) Parkash, S., Suspension Dcnsities of Crystais in Fluidized Beds, Chem. Age India, 18, 434 (1967). (62H) Parkash, S., Lele, P. S., A Laboratory Oslo Crystallizer, Chem. Age India, 18,647 (1967). (63H) Penney, W. R., Crystallization on a Constant Temperature Surface, A.Z.Ch.E. J., 14, 661 (1968). (64H) Petrenko D . S. Arabova, L. M., Effects of Temperature, Acidity and Mixing of the’Mothei Liquor on the Increase Grain Size of Ammonium Sdlfatc, Koks Khim., 2, 22 (1967). (65H) Pozin M. E. Kopylev B. A. Talmud M. M. Crystallization of Dicalcium Phosphate’in the’ System MgO-baO-P*ds-HzO,’ J . Appl. Chem. USSR, 40, 2137 (1967). (66H) Prener, J. S., The Growth and Crystallographic Pro erties of Calcium Fluoride and Chlorapatite Crystals, J.Electrochem. Soc., 114, 7\3 (1967). (67H) Pylkova E. V. Crystallization of Ice during Coolings of Supersaturated NaC1-KCl-H;O Soldtions, J.Appl. Cham. USSR, 40,420 (1967). (68H) Randolph, A. D., Effect of Crystal Breakage on Crystal Size Distribution in a Mixed Suspension Crystallizer, IND.ENG.CHEM.,FUNDAM., 8, 58 (1969), (69H) Rangarajan, K., Electrocrystallization and Surface Diffusion: Effect of Chemical Reaction in the Solution, Can. J . Chem., 46, 1803 (1968). (70H) Razumovskii, L. A,, Crystallization of Salts from Solutions in a Fluidized Bed, Izu. Vyssh. Ucheb. Zaued., Khim. Ichim. Tekhnol., 10,231 (1967). (71H) Razumovskii, L. A,, Strel’tsov, V. V., Calculation of the Residence Time of a Suspension in a n Apparatus during Crystallization of Some Salts from Solutions in a Fluidized Bed, ibid., p 475. (72H) Razurnovskii L. A. Strel’tsov V. V., Particle-size Characteristice of Crystals during the Ciystadation of Shlts from Solutions in a Fluidized Bed, ibid., 11, 835 (1968). (73H) Razumovskii, L. A,, Strel’tsov, V. V., Size Distribution Characteristics of Crystals Grown in a Fluidized Bed, Tear. O m . Khim. Tekhnol., 1, 360 (1967). (74H) Rul’nova, A. Z., Shneerov, M. S., D’yachko, A. G., Mathematical Modcl of the Crystallization of Aluminum Hydroxide during the Carbonation of Aluminate Solutions, Tsud. Metal., 41, 58 (1968). (75H) Sastin M . N. Prasod T. P. Study of Beryllium Oxinate by the Homogeneous Prbcipitatibn Metiod, Taianta, 14, 481 (1967). (76H) Savage, H. R., Butt, J. B., Tallmadgc, J. A., Kinetics of Rcaction and Crystallization in Condensed Phases: T h e Aqueous Potassium Dipicrylaminc System, A.1.Ch.E. J., 14, 226 (1968).

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(77H) Sherwin, M . B., Shinnar, R., Katz, S., Dynamic Behavior of the Well-mixed Isothermal Crvstallizer., ibid.. 13. 1141 119671. . , (78H) Shirotsuka, T., Toyokura, K., Sugiyama, F., Design Methods of Continuous Stirred Tank Crystallizer, Kognku Kognku, 5 , 98 (1967). (79H) Simpson, P., Landau, M., Effects of Reaction Environment on the Settling Properties of Ferrous Hydroxide, Symposium on Industrial Crystallization, The Institution of Chemical Engineers, p 154, London, .4pril 1969. (8OH) Strel’tsov, V. V., Razumovskii, L. A,, Kinetics of the Change in Particle Size Composition during Crystaliization in a Fiuidized Bed, Zru. Vyssh. Ucheb. Zuved.: Khzm. Khim. Tekhnol., 11, 356 (1968). (81H) Tezak, B., Novosel, B., Coulombic Retardation Effect of “Neutral” Electrolytes on Formation of Barium Sulfate Crystallites (reversal of Schulze-Hardy Rule), Croat. Chem. Acta, 40, 53 (1968). (82H) Timm, D . C., Larson, M. A,, Effect of Nucleation Kinetics on the Dynamic Behavior of a Continuous Crystaiiizer, A.I.Ch.E. J., 14, 452 (1968). (83H) Todes, 0. M., Shimanskii, V. K.. Kinetics of Magnification of Tartaric Acid Crystals in Saturated Solutions, Krist. Tech., 2, 77 (1967). (84H) Vamey, G., Crystal Growth in Aqueous Suspensions, J. Pharm. Pfiarmacol. Suppi., 19, 19 (1967). (85H) Yakhium E. D. others Crystallization of Pol amide in Alcohol Suspensions C 7 y s h Growth, 5 , 184 (19693. of Mineral Paiticles, ,

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(13J) Murthy A. S. A., Mahadevappa, D . S., Distribution of Isomorphous Salts between AqLeous and Solid Phases in Fractional Crystallization, Curr. Sci., 57, 585 (1968). (14J) Novobilsky, V., Jaeger, L., Nyvlt, J., Crystallization. XXXI. T h e Effect of Supersaturation on the Cocrvstallization of Trivalent Iron during the Crystallization of AmmoniumSulfate, b e m . Prum., 18, 123 (1968). (15J) Novobilsky V. Nyvlt J., Jaever L., Crystallization. XXXII. Mechanism of Cocrystallizition’of Di- and TriGalint Iron during the Crystallization of Ammonium Sulfate, ibid., p 180. (16J) Pozin M. E., Kopylev B. A. Talmud M . M., Crystallization of Dicalcium Phosphatd in the M a neiium dxide-Calkurn Oxide-Phosphorus PentoxideWater System, Z h . Prik! Khim.,40,2220 (1967). (175) Przytycka R . Katural Radioisotopes as Tracers in Crystallization Studies, iVukleonika., li, 745 (1967). (18J) Rogalla W. Schmalzried, H., Precipitation Kinetics of Supersaturated, Potassium bhloride Crystals Containing Strontium Chloride, Be,. Bunsenper. Phys. Chem., 72, 615 (1968). (195) Shvartsval’d A. I. Removal of Nonisomorphic Impurities from Inorganic Salts duripg Cryshliza;ion from Solutions, Z h . Prikl. Khim., 40,2452 (1967). (205) Syromyatnikov, Trofimova, L. A,, Cocrystallization of Thorium with Barium Sulfate, Radiokhimiya, 61 (1 967). (21 J) Takiyama, K., Gordon, L., Electron Microscopy and Diffraction Studies on Coprecipitation. I. Morphological Studies on Coprecipitation, J. Electronmicrasc. (Tokyo), 16, 232 (1967).

Indusfrial Crystallizers and Developmenf of .Large-Scale Crystallization Processes from Solufion (IK) Baranov G. P Matusevich, L. N., Effect of Some Factors on the Size of Crystals Prgpared ‘in Vacuum-Crystallizers with a Circulating Suspension, J . Appl. Chem. USSR, 40, 2147 (1967) (Eng.). (2K) Biranov G. P., Matusevich L. N., Smolin, A. N., Continuous Vacuum Crystallizer: with Propeller-Pumb Circulation, Khim. Neft. Mashinosir., 6 , 8-10 (1968) (Russ.). (3K; Barduhn, A. J., The State of the Crystallization Processes for Desalting Saline Waters, Desalination, 5 , 173-84 (1968). (4K) Bennet, A. E., others, Crystallization of Urea, Chem. Process Eng., 48, 43-48 (1967).

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(48K) Paasikoski, O., Crystallization in the Chemical Industry, Kem. Teollisuur, 24, 767-71 (1967) (Finnish). (49K) Panov, V. I., Lebedenko, Y. P., Crystallizer, U.S.S.R. Patent 192,170, Feb. 6, 1967. (50K) Randolph, A. D., Process for Controlling the Mean Size Range of Borax Decahydrate Crystals, U.S. Patent 3,399,976, Sept. 3,1968. (51K) Savinkova E I Vil'nyanskii Y. E others, Effect of Magnesium Chloride Content in Hot) L i e & the Compdsition'bf Crystals Precipitating in a VacuumCrystallization Apparatus in a Carnallite Plant, Z h . Prikl. Khim., 41, 43-7 (1968) (Russ.). (52K) Shen, C. Y., Crystallization of Pyrophosphoric Acid, U.S. Patent 3,371,922, March 5, 1968. (53K) Shibko, N. A,, Zan'kov, Y. N., Shabshaevich, M. L., Controlling the Cooling Process for Crystallizing and Viscous Products, U.S.S.R. Patent 187,811, Oct. 20, 1966. (54K) Shleinkov, V. M., Usyukin, I. P., others, Crystallization of Salts from Solution, U.S.S.R. Patent 201,327, Sept. 8, 1967. (55K) Skrivanek, J., Moudry, F., Nyvlt, J., Crystallization. X X . Distribution of Particle Sizes in Real Crystallizers, Collection Czech. Chem. Commun., 32, 480-8 (1967) (Ger.). (56.K) Skrivanik J. Nyvlt J. Crystallization. XXXIV. Particle Size Distribution in a Doubie drystall&: ibid., 33, 2799-806 (1968) (Ger.). (57K) Sladky, J., Kulla, S . , Kalab, V., Crystallizer for 6-Caprolactam, Czech. Patent 126,518, March 15, 1968. (58K) Stollcr, F. L., Fractional Crystallization System, U.S. Patent 3,395,547, Aug. 6, 1968. (59K) Suzuki, H., Tanaka, S., Toyokura, K., Cr stallization of Ferrous Sulfate from Pickling Liquor in a Vacuum Crystallizer, &nku Kogaku, 31, 784-9 (1967) (Japan). (60K) Todes, 0. M., Litunovskii, N. I., Possible Physical Models of Industrial Crystallizers for Diffusion-Controlled Crystal Growth, Krirt. Tech., 1, 597-609 (1966) (Ger.). (61K) Torobin, L. B., Crystallization Process, U.S. Patent 3,294,673, Dec. 27, 1966. (62K) Tsukishimn Chemical &lachincry &lanufacturing Company Ltd., Solution Cr!stallization, French Parcnr 1,497,897, Ocr. 13, 1967. (63K) Urff, G., Focrtsch, R., Kocrber, K., A Dust-Free Coarse Crystalline Product, East German Patent 60,016, Feb. 5, 1968. (64K) Vra ov, A. P., Makhov, A. M., Multisection Crystallizer, U.S.S.R. Patent 202j873, %ept. 28, 1967. (65K) Waldlebcn W. Ap aratus for Vacuum Crystallization of Salt Solutions, German Patent'1,26?,66[ May 9, 1968. (66K) Waldleben, W., Crystallizer for Production of Coarse Granular Crystals, Freiberger Forschungsh., A436, 71-8 (1968) (Ger.). (67K) Werkspoor, N. V., Apparatus for Crystallizing Solutions by Cooling, British Patent 1,075,919, July 19, 1967. (68K) Wintershall A . 4 . Celle Apparatus for the Pre aration of Large, Uniform Crystals by Vacuum Cooling,'German Patent 1,258,8%, Jan. 18, 1968.

Techniques of Single Crystal Production from Melt (1L) Adam-Bcnvcnistc M Berge P others Apparatus for Cr stallization without Rev. >hi:. Appl.,'3, 414 (1968) ( F r j . Mechanical Displace&;, (2L) Adamski J. A Powell R. C Sampson J. L Growth of Uncommon Verneuil Crystals and T h & CharActeriiHtion by iight'kcattering, J. Crystal Growth, 3, 246 (1968). (3L) Alford W. J Bauer W H R F Plasma Growth and Cr stalline Perfcction of Si&le-Cr$stal Alimina, ?. Piys.'Chem. Solids, Suppl., 1, 71 h967). von Ardenne, M., Knebel, E. D., others, Growth of Sin IC Crystals with a (4LH)igh Frequency Plasma Burner by the Verneuil Method, h t . Tech,, 1, 437 (19661 (Ger.). - ~ , (5L) Arst, M. C., Crystal Growing Method, U.S. Patent 3,359,077 (Dec. 1967). (6L) Bardsley, W., Cockayne, B., Growth and Perfection of High Melting Point Oxides, J.Phys. Chem. Solids, Suppl., 1, 109 (1967). (7L) Barta, C., Nigrinova, J., Verneuil's Method Applied to Monocrystals of the Alkaline-Earth Metaniobates, "Growth of Crystals," 3, 302, Consultants Bureau, New York (1962). (8L) Barthel, J., Scharfenberg, R., Growing of High-Melting Metal Crystals by Electron Zone Melting, J. Phys. Chem. Solids, Suppl., 1, 133 (1967) (Ger.). (9L) Beiziter, L. K., Thin Semiconductor Film Crystallization by Zone Melting, Lntv. PSR Zinat. Aknd. Vertis, F i z . Teh. Zinnt.Ser., 6, 34 (1966) (Russ.). (1OL) Belikova, G. S . , Belyaev, L. M., Mixed Organic Crystals for Scintillation Counters, Growth Crystals, 3 , 228, Consultants Bureau, New York (1962). (11L) Bclyaev L. M Dobrzhanskii G. F Bagdasarov Kh. S Some Changes in a Method of k r o d g Cr stals frdm Mzlts, Growth krystals," 4, 73, Consultants Bureau, New York (19667. (12L) Belyaev, L. M Perl'shtein, V. A,, Use of Radioactive Tracers in Studies on Crystal Growth, arowth Crystals, 3, 232, Consultants Bureau, New York (1962). (13L) Brice J. C. Analysis of the Temperature Distribution in Pulled Crystals, J. Crystal browth,'2, 395 (1968). (14L) Brice, J. C. Whiffin P. A C. Solute Striae in Pulled Crystals of Zinc Tungstate, Brit.j.Appl. ghys., 18, 58) (1967). (15L) Brice, J. C., Wise, A. G., Page, J. L., Growing Crystals in Volatile Solvents, Brit. Patent 1,062,309 (March 1967). (16L) Brixner L. H. Babcock K Inor anic Single Crystals from Reactions in Fused Salts,'Mat. Rls. Bull., 3,'817'(19687. (17L) Bushmanov, B. N., Growth of Large Metal Monocrystals of S ecified Orientauon and the Mass-Production of Seed Crystals, Growth E)yrtaIs, 3, 285, Consultants Bureau, New York (1962). (18L) Carruthers, J. R., Radial Solute Segregation in Czochralski Growth, ibid., p 959. (19L) Carruthers, J. R., Tern erature Oscillations in Czochralski Crystal Growth, J. Electrochem. Sac., 114, 1077 (1967). \-

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Puritleation by Growth from Melt (1M) Aleksandrov, B. S., Dobrokhotova, V. K., others, Zonc Purification of Matcrials for Usc in Monocrystal Scintillators, Growth Crystals, 3, 239, Consultants Bureau, New York (1962). (2M) von Ammon R. Purification and Separation of Inorganic Salts by Column Crystallization aAd b; Zone Melting, Chem.-Ins.-Tech., 39,428 (1967) (Gcr.). (3M) Chcrnonnordin, I. F., Krcstovnikov, A. N., Vigdorovich, V. N., New Methods and Construction of Devices for Refining by Crystallization, Izv. Vyssh. Ucheb. Zaued., Tsvet. Met., 11, 98 (1968) (Russ.). (4M) Chistozvonova, 0. S., Dupacheva, G. M., Arikin, A. G., Zone Melting and Thcrmal Analysis of AcetanitrilcBenzene Systcm, Rum. J . Phys. Chem., 41, 42 (1967). (5M) Clasen, H . , Optimum Combination of Crystallization and Rectification for

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H., A Closed-Form Equation for Normal Freezing with Variable Segregation Coeff., Brit. J . A@l. Phys., 38,359 (1967). (27M) Li, C. H., Computed Concentration Profiles in Normally Frozen Rods, ibid., p 2407. (28M) Li, C . H., Normal Freezing with Cubic Liquidus and Solidus Lines, ibid., 39, 2094 (1968). (29M) Li, C. H., Single-Pass Zone Melting with Variable Segregation Cocfficients, J . Aj$l. Phys., 38, 3793 (1967). (30M) Lozovskii, V. N., Kikolaeva, E. A., Redistribution of Impurities in the Solid Phase during Zone Melting with a Temperature Gradient, Inorg. Moter., 4, 899 (1968). (31M) Mcrzhanov, I. A., Anikin, A. G., Impurity Distribution in Sam I t s of a Finite Lcngth aftcr Zone Recrystallization, Z h . Fir. Khim., 42, 1038 (1968) (Russ.). (32M) Molinari, J. G. D., Refining Process for Crystallizable Compounds, Brit. Patcnt 1,066:032 (April 1967). (33M) Molochko, V. 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(45M) Vigdorovich V. N Vol’pyan A. E Method for Calculating Segregation Curves in Zone R;crystaiii&ation, Tlor. 0s;: K h m . Tekhnol., 1,474 (1967) (Russ.). (46M) Wilcox, W. R., Removing Inclusions from Crystals by Gradient Techniques, IYD.END.CHEM.,60 (3), 12 (1968). (47M) Yesin, V. O., others, Orientation, Purity and Perfection of Molybdenum Single Crystals Grown by Electron-Beam Zone Melting, Phys. Met. Metallog., 22, 95 (1966).

Miscellaneous Cryslallization Processes and Techniques VAPOR-LIQUID-SOLID G R O W T H (1Na) Ellis, W. , C Pfann W. G. Wagner R. S Vapor-Liquid-Solid Crystal Growth Techniq;)e, U.S. batent 3,546,414 (bl.I17:i06) (Oct. 10,1967). (2Na) Filby, J. D., Nielsen, S., others, Investigation of E itaxial Silicon Layers Grown in the Presence of Small Quantities of Gold, Phil. A&., 16, 565 (1967). (3Na) Heuer, A. H., Burnett, P., Evidence for MgO Whisker Growth by a VaporLiquid-Solid Mechanism, J . Amer. Ceram. Soc., 50, 627 (1967). (4Na) Komatsu, E., Higuchi, Y . ,Niina;T., A plication of the Va or-Liquid-Solid Method to Silicon Crystal Growth, Suiyokai-Ai, 16, 476 (1968) (&pan.). (5Na) Komatsu, E., H i uchi, Y , Niina, T., A p-n Junction in Si Whiskers Grown by VLS Methods, Appf Phys. Lett., 10,42 (1967). (6Na) Niina, T., Higuchi, T., Techniques of Growing Single Crystals. VaporLiquid-Solid Growth ofsilicon, Oyo Butsuri, 36, 125 (1967) (Jap.). (7Na) Ryan, C. E., Berman, I., others, Vapour-Liquid-Solid and Melt Growth of Silicon Carbide, J . Cryrtnl Growth, 1, 255 (1967). (8Na) Sickafus, E. N., Barker, D. B., Surface-Spike Growth on NiBrz Crystals; A VLS (Vapor-Liquid-Solid) Mode of Crystal Growth, J. Crystal Growth, 1, 93 (1967). (9Na) Wagner, R . S., Defects in Silicon Crystals Grown by the Vapor-LiquidSolid Technique, J.App. Phyr., 38,1554 (1967). (10Na) Wagner, R. S . , Branching, Kinking, and Defect Formation during VLS Growth, .I. Phys. Chem. Solidr,Suppl., 1,347 (1967). (11Na) Wagner, R. S., A Solid-Liquid-Vapor Etching Process, J. Crystal Growth, 3-4, 159 (1968). (12Na) Wagner, R. S., Doherty, C. J., Mechanism of Branching and Kinking during VLS Crystal Growth, J.Electrochem. Soc., 115, 93 (1968). GEL G R O W T H (1Nb) Armin ton A. F DiPietro, M. A,, O’Connor, J. J., Factors which Influence the 8ro;th of &Cl in Silica Gel, U S . Gout. Res.Deu. Rept, 67,123 (1967). (2Nb) Armington, A. F., O’Connor, J. J., Gel Growth of CuCl Crystals, J. Crysta Growth, 3-4, 367 (1968). (3Nb) Armington, A. F., O’Connor, J. J., Gel Growth of Clear Cuprous Chloride Crystals, Mater. Res. Bull., 2, 907 (1967). (4Nb) Armington, A. F., O’Connor, J. J., Gel Growth of Doped and Undoped CalciumTartrate Crystals, U.S. Gout. Res. Diu. Rept, 6 8 , 100 (1968). (5Nb) Atkinson, R. J., Posner, A. M., Quirk, J. P., Crystal Nucleation in Fe(II1) Solution and Hydroxide Gels, J.Inorg. Nucl. Chem., 30, 2371 (1968). (6Nh) Blank, Z . , Brenner, W., Growth of Single Crystals of CuzO in Silica Gels a t Near Ambient Temperatures, Nature, 222,79 (1969). (7Nb) Blank, Z., Brenncr, W., Okamoto, Y., Growth of Single Crystals of PbS in Silica Gels at Ambient Temperature-Preliminary Characterization and Effect of Various Organic Compounds as Sulfide Ion Donors, Mater. Res. Bull., 3, 555 (1968). (8Nb) Blank, Z., Brenncr, W., Okamoto, Y., Growth of Single Crystals of Se in Gels at Ambient Temperatures, J.Crystal Growth, 3-4,372 (1 968). (9Nb) Blank, Z., Speyer, D. M., et al., Growth of Single Crystals of Silver Halides in Silica Gels a t Near Ambient Temperatures, Nature, 216, 1103 (1967). (1ONb) Dennis, J., Henisch, H. K., Nucleation and Growth of Crystals in Gels, J . Electrochem. Soc.., 114., 263 (1967). (11Nb) DiPietro, M . A., O’Connor, 3. J., Rubin, B., Growth of Single Crystal Calcium Tartrate Tetrahydrate by Controlled Diffusion in Silica Gel, U S . Gout. Res. Den. Rept, 41, 106 (1966). (12Nb) Halberstadt, E. S., Growth of Single Crystals of Silver Iodide in Silica Gel, Nature, 216, 574 (1967). (13Nb) Halberstadt, E. S., Henisch, H. K., Experiments on Crystal Growth in Gels, J . Crystal Growth, 3-4, 363 (1968). (14Nb) Hanoka, J. I., Vedam, K., Henisch, H . K., Polytypism in Gel-Grown PbI Crystals, J . Phys. Chem. Solids, Suppl. 1, 369 (1967). (15Nb) Henisch, H. K., Crystal Growth in Gels, Helu. Phys. Acta, 41, 888 (1968) (Eng.). (16Nb) Kratochvil, P., Sprusil, B., Growth of Au Single Crystals in Gels, J . Crystal Growth, 3-4, 360 (1968). (17Nb) Matsumoto, T., Growth of NaCl Whiskers from Aqueous Solution, Kogakuin Dargaku Kenkyu Hokoku, 17, 32 (1965) (Japan.). (18Nb) Murphy, J. C., Kues, H . A., Bohandy, J., Growth of Crystals in Silica Gel Using a Co-Solute, Nature, 218, 165 (1968). (19Nb) O’Connor, J. J., Armington, A. F., A Method of Growing Larger Crystals in Gels, J. Crystal Growth, 1, 327 (1967). (20Nb) ,O’Connor, J. J., DiPietro, M . A., others, Gel Growth of Crystalline Cuprous Chloride, Nature, 212, 68 (1966). (21Nb) Vand, V., Hanoka, J. I., Epitaxial Theory of Polyty ism; Observations on the Growth of PbIz Crystals, Mater. Res. Bull., 2, 241 (196fi. HYDROTHERMAL G R O W T H (1Nc) Bihr, B., Matccha, J., others, Autoclaves for the Hydrothermal Synthesis of Quartz at 2000 Atmospheres Pressure, Krist. Tech., 1,443 (1966) (Ger.). (2Nc) Boksha S. S., Equipment for the Growth of Crystals a t Very High Gas Pressures, J:Crystal Growth, 3-4, 426 (1968) (Eng.).

(3Nc) Bonev, I., Some Instances of Change in the Faces of Crystals during Epitaxial Growth, Rost Kristallov, Akad. Nauk SSSR, Inst. Kristalloer., 8, 278 (1968) (Russ.). (4Nc) Flanigen, E. M., Taylor, A. M., ,others, Hydrothermal Garnet Crystals. Hydrothermal Crystal Growth of Calcium Aluminosilicate Garnet Containing Divalent Rare Earth Ions, U. S. Cleartnghouse Fed. Sci. Tech. Inform.,AD 646231 (1966). (5Nc) Glikin, A. E., Petrov, T. G., Crystal Growth Habit of Fluorite under Hydrothermal Conditions, Mmerol. Sb., 20, 433 (1966) (Russ.). (6Nc) Haryill, M. L., Roy, R., Habit of H drothermally Grown Rutile Structure Crystals in the Light of the Hartman Jheory and Its Extension, in “Crystal Growth,” H. Peiser, Ed., Pergamon, New York, 1967, p 563. (7Nc) Hill, V. G., Harker, R. I., T h e Hydrothermal Growth of B e 0 Single Crystals, J . Electrochem. Soc., 115, 294 (1968). (8Nc) Kashkurov K E. Nikitichev P. I others Growth of Large Corundum Crystals by th; Hyd;othermal Method: Sovie; Phys.-Cryst., 12, 837 (1 967) (.E m I. (9Nc) Kharcenko L. J., Klevcov, P. V., Hydrothermal Crystal Synthesis and Crystallogra hi: Properties of Some Rare-Earth Tungstates, Acta Cryst. (Intern.), 21, A261 (1f66) (Eng.). (10Nc) Kharcenko L. J Klevtsov P. V Hydrothermal Synthesis of Crystals of Some Double TLngsta’ies of L i t t h m aEd Rare Earth Elements, Soaiet Phys.Cryst., 12, 965 (1968) (Eng.). (11Nc) Kinoshita, A., Nakano, T., Cuprous Oxide Crystal Growth by Hydrothermal Technique, Jap. J.AppI. Phyr., 6, 656 (1967) (Eng.). (12Nc) Kolb E. D Caporaso, A. J., Laudise R A. Hydrothermal Crystallization ofSome I I l V I d m p o u n d s , J.Crystal Growti, 3-4, i 2 2 (1968). (13Nc) Kolb, E. D., Coriell A. others T h e Hydrothermal Growth of Low Carrier Concentration ZnO a t High h a t e r and Hydrogen Pressures, Mater. Res. Bull., 2, 1099 (1967). (14Nc) Kolb, E. D., Laudise R. A Hydrothermal Growth of Zinc Oxide Crystals with Ammonium Ion Addihves. ~ . SPatent . 3.353.926. Nov. - 21.> 1967. -. (15Nc) Kolb E. D. Wood D. L. Laudise R. A. The Hydrothermal Growth of Rare Earth)Orthoierrites,’J. Appf. Phyr., 36, 1362 71968). (16Nc) K O p, 0. C., Clark, G. W., Hydrothermal Synthesis, 0 tical Perfection and S u r l c c Topography of Quartz Grown in R b O H and &her Alkali Hy; droxides, J.CrysialGrowth, 2 , 308 (1968). (17Nc) Kuanctsov, V. A., Kinetics of Hydrothermal Crystallization of Corundum 11. Effect of Solvents on Crystallization, Soviet Phys.-Cryst., 12, 608 (1968j (E%.). (18Nc) Kuznetsov, V. A., On Kinetics of Hydrothermal Crystallization of Corundum, Quartz, and Zinkite, Acta Cryst. (Intern.), 21, A269 (1966) (Eng.). (19Nc) Kuznetsov, V. A., Shternberg, A. A,, Crystallization of Ruby under Hydrothermal Conditions, Souiet Phys.-Cryrt., 11,280 (1967) (Eng.). (20Nc) Kuznetsov V. A Siderenko 0. V Crystallization of ZrOz and HfOz under Hydroth&mal 6onditions, Aooviet Pzys.-Cryst, 13, 651 (1969) (Eng.). (21Nc) Laudise, R. A., Growth and Morphology of Hydrothermally Crystallized Zinc Oxide, Acta Cryst. (Intern.), 21, A262 (1966) (Eng.). (22Nc) Liptai, R . G., Lloyd, L. T., Friddlc, R. J., O n the Use of High Pressure as a Parameter in Crystal Growth, in “Crystal Growth,” H. Peiser, Ed., Pergamon, New York, 1967, p 573. (23Nc) Marshall D. J Laudise R. A T h e Hydrothermal Phase Diagrams KzONbzOa and K;O-Ta’2)0s and ;he Gr’Awth of Single Crystals of K(Ta, Nb)Oa, in “Crystal Growth,” H. Peiser, Ed., Pergamon, New York, 1967, p 557. (24Nc) Matsui, J., Shiroki, K., Hydrothermal Crystal Growth, Oyo Butsuri, 37, 579 (1968) (Japan.). (25Nc) Menkovskii, M. A., Shorygin, V. A,, Some Chemical Factors during the Hydrothermal Synthesis of Crystals, Rost Kristallou, Akad. Nauk SSSR, Inst. Kristallogr., 7, 344 (1966) (Russ.). (26Nc) Monchamp, R. R., Puttbach, R. C., Nielsen, J. W., Large Noble Metal Can Technique for Hydrothermal Crystnl Growth, J. Cryrtal Growth, 2, 178 (1968). (27Nc) Niemyski, T., Mierzejewska-Appendeimer, S., Majewski, J., High Pressure Crystallization of Boron Phosphide from Liquid Phosphorus, in “Crystal Growth,” H. Peiser, Ed., Pergamon, New York, 1967, p 58. (28Nc) Otomd, J. Hydrothermal Crystal Growth with Specral Reference to Quartz Crystals, kobutsugnki Zasshi, 8, 383 (1968) (Japan.). (29Nc) Popolitov V. I. Litvin B. N. Hydrothermal Synthesis of SbSI Single Crystals, Soaiet $hys.-C;yst., 13,’483 (19k8) (Eng.). (30Nc) Puttbach R. C., Monchamp, R. R. Nielscn, J. W., Hydrothermal Growth of YakaOit, in “Crystal Growth,’’ H . Peiser, Ed., Pergamon, New York, 1967, p 569. (31Nc) Rau, H., Rabcnau A. Crystal Synthesis and Growth in Strong Acid Solutions under Hydroth;rrn& Conditions, Solid Stnte Commun., 5 , 331 (1767) -

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(32Nc) Rau, H., Rabenau, A., Hydrothermal Growth of Some Elements, J . Crystal Growth, 3-4, 417 (1968). (33Nc) Rogers, D . B., Gillson, J. L., Gier, T. E., Hydrothermal Crystal Growth and Electrical Conductivity of the Spinel LiVzO4, Solid State Commun., 5 , 263 (1967) (Eng.). (34Nc) Roy, R . ? White, W. B., High Temperature Solution (Flux) and High Pressure Solution (Hydrothermal) Crystal Growth, J . Crystal Growth, 3-4, 33 (1968). (35Nc) Sendcrov, E. E., Bxperimcntal Study of Sodium Zeolite Crystallization under Hydrothermal Conditions, Geokhimiya, 1, 13 (1968) (Russ.). (36Nc) Shternberg, A. A., Lapsker, Y. A., Kuznetsov, V. A., Hydrothermal Synthesis of Potassium Niobate and Tantalate, Souiet Phys.-Cryst., 12, 838 (1968) (E%.). (37Nc) Strong H. M Hanneman R. E Anomalous Behavior in the Crystallization of Diadond a d Graphite,