Intern. Plastics 134, 827-9 (1958). Statistics as applied in rubber industry. Application of statistics in rubber factory. (202) Ibid., 134, 903-4, 906 (1958). (203) Tingev, F. H., I n d . Eng. Chem. 50, 1017-20 (1958). Identification of estimation of variation in process measurements. (204) Tingle, \V. H., Matocha, C. I4-78.4 (Dec. 1958). Circumstances alter cases. (234) Ibid., 51, 81.1-82A (Fell. 1959). What is a measurement. (235) Zbid., 51, 81.4-824 (April 1959). I
,
Sampling study-Complex
processing
of alloys poses special sampling prob-
lem. (236) Ibid., 51, 79.4-80.4 (June 1959). Evolutionary operation. (237) Zbid., 51, 65‘4-66A (-4iig. 1959). Experiments in experimentation. (238) Touden, W. J., Znd. Qualitu Control 14, 24-8 (5Iav 1959). Graphical diagnosis of interinborntorv test reSllltl.
(239) Touden, JV. J., Condor, JV. S., Severo, S. C., Technoinetrzcs 1, 101-9 (1959). Measurements made by niatching with knon-n standards. (240) Tuker, H. E., “ A Guide to Statistical Calculations,” Putnam’s Sons, Kew York, 1958. (241) Zelen, hl., Connor, JV. S., Znd. Quality Control 15, 14-17 (llarch 1959). Multifactor experiments. Additional References (242) .4nscombe, F. J., Technometrics 1, 195-209 (1959). Quick analysis methods for random balance screening experiments. (243) Batchelor, J. H., “Operations Research-.innotated Bibliography,’J 2nd ed., St. Louis Univ. Press, St. Louis, hlo., 1959. (244) Box, G. E. P., i l p p l . Statistics 6, 81-101 (1957). Evolutionary operation, Vethod for increasing- industrial productivity. (245) Box, G. E. P., Hunter, J. S., Technometrics 1, 77-95 (1959). Condensed calculations for evolutionary operation programs. (246) Lurie, W.,A m . Scientist 46, 57-61 (March 1958). Impertinent questioner: Scientists guide to statistician’s mind. (247) hlandelsohn, J., I n d . Quality Control 13, 31-4 (hlay 1957). Relation between engineer and statistician. (248) hlayne, J. W.,Scz. Monthly 84, 26-33 (Jan. 1957). Role of statistics in scientific research.
Review of Fundamental Developments in Analysis
Differential Thermal Analysis C. B. Murphy Generol Electric Co., Schenecfady,
T
N. Y.
review covers the period from the last review on differential thermal analysis (45)until the end of August 1959. It is again impossible to include all published works in this field. Accordingly, m a n y worth-while papers are not included. It is intended t h a t significant trends be covered. Smothers and Chiang (70) have published a book on the theory and practice of differential thermal analysis. Mackenzie has published the “Differential Thermal Investigation of Clays” (49). A well documented review has been written by West et al. (79). Application of the technique in mineralogy and geological prospecting has HIS
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been the subject of a review by FoldvariVogl (21). Papers b y Sauman (67) and Lehman (41) discuss experiences with differential thermal analysis encountered in their respective laboratories. INSTRUMENTATION
Several new concepts in differential thermal analysis instrumentation have occurred. Although equipment capable of producing thermograms in the range -150” t o 300” C. has been reported (%’), other types have been developed for low temperature work of the more conventional type. Haighton
and Hannewijk (27) have employed a n electrically heated copper block, coppercylinder sample holders, and ironconstantan thermocouples mounted in a Dewar flask for excellent results below 100” C. Hill and Murphy (SO) have devised a simple, inexpensive system employing an infrared lamp as a heating element with conventional detection equipment for low temperature organic studies, Pakulak and Leonard ( 5 3 ) have employed matched thermistors for measuring and controlling temperature in the 20’ t o 300’ C. range. Lloyd and Murray (42) have automatic equipment for high vacuum (10-6 mm.) heated by a molybdenum
element. I n addition to conventional sample sizes, the equipment is also capable of handling 20- to 80-gram samples in crucibles. Apparatus capable of high sensitivity with variable heating rates from 6" to 20" C. per minute has been described (81). Siske and Proks (69) have described a new method in which the sample and standard material are moved a t a regulated speed into a heated furnace. Pave1 a n d Fojtik (57) have used a single thermocouple embedded in the sample. On programmed heating, a recorder simultaneously plots e.m.f. to give the tcmperature and its derivative with time. Advantages over conventional techniques are claimed to exist in speed, in requiring no inert sample, and in use of a single thermocouple; disadvantage exists in dependence on linearity of heating rate. Equipment capable of application to 1550" C. has been described by Xewkirk (@). Borchardt (8)has developed apparatus capable of registering thermogiams to 1750" C. t h a t includes a rhodium-wound furnace, Ir-Ir 607, R h temperature-measuring thermocouple, Pt 20% Rh-Pt 40% R h differential thermocouple, and Pt-107, R h foil sample holders similar to those described by West and Sutton (80). Arseneau ( 1 ) has modified equipmcnt originally described by Borcliardt (6) to contain molten samples. Freeman a n d Edelman ($3) have described a simple method for derivative differential thermal analysis. T h e advantages of this last method were given by Campbell and Gordon (13).
MULTIPURPOSE EQUIPMENT
The need for equipment capable of providing d a t a simultaneously with diffmential thermal analysis has been matie very apparent by Kotz and Jaffe (60). Although air is used in both differential thermal analysis and therniogravimetric analysis of uranyl sulfate and pitchblende, the variation in sample packing in both cases resulted in different sample atmospheres in the immediate vicinity of the specimens. Results were obtained t h a t would have confused less competent investigators. V u r p h y and Hill (46) have modified conventional differential thermal analysis equipment so t h a t a gas sampling bottle can be attached, evacuated, and fillrd with evolved gases associated with registration of thermogram peaks. Blazek (4)has improved the technique further by devising apparatus t h a t permits simultaneous differential thermal and thermogravimetric analysis a n d gas analysis. Equipment has been described t h a t provides simultaneous differential thermal and thermogravimetric analysis (75). Paulik, Erdey,
et ul. ( 5 4 , 5 5 )have described the Derivatograph. This equipment is capable of siniultaneously recording differential thermal, thermogravimetric, and derivative thermogravimetric curves and is being marketed by Metrinipes, Budapest.
termined the heat of oxidation of ten minerals, sulfides and arsenides of iron, nickel, and cobalt. B y using the heat of combustion, the concentraticn of graphite was determined in geological deposits (35).
PHASE EQUILIBRIA
SOLID STATE REACTIONS
T h e calcium-strontium metal system was determined, iri part, b y differential thermal analysis (68). Uranium phase transitions have also been investigated by Lloyd and Murray (42) employing this technique. Bellot, Henry, and Cabane (3) have applied the method not only to uranium, but to zirconium of differcnt purities, uranium-zirconium, and uranium-molybdenum systems. K a t 0 has determined phase transitions occurring in the lithium oxide-ferric oxide system (36) and in lithium ferrospinel-lithium aluminospinel solid solutions (37). Variations were found in the thermograms of lithium ferrospinel as a function of quenching. Differential thermal analysis and quenching techniques were employed by Sastry and Hummel 166) to investigate the lithium oxide-lithium borate system. The transitions occurring in nickel and magnesium heptahydrates have been investigated (24) by differential thermal and thermogravimetric techniques. Reisman and Karlak (63) have investigated the transitions involved in the thermal treatment of copper sulfate pentahydrate. A new phase transition has been reported (5'9) in the sodium carbonate system. Differential thermal analysis was also employed to study the nitric acid-rubidium nitrate system (59). Hogan and Gordon have studied the potassium perchlorate-barium nitrate (32) a n d the barium perchloratepotassium nitrate (33) systems. Evidence has been presented for the metathetical reaction between barium chlorate and potassium nitrate. Transition temperatures and melting points for n-tricontane and n-ditricontane and the melting point of neicosane have been reported (48). Sakurai and Yabe (65)have applied the technique to n-hexadecanamide.
HEATS OF REACTION
Sakurai and Yabe (65) have calculated the heat involved for the solid phase transition of n-hexadecanamide t o be 4.0*0.3 kcal. per mole and the corresponding entropy change to be 12.4A0.9 cal. per degree mole. T h e corresponding values for the melting process were found to be 15.7~k0.3kcal. per mole and 4 6 . 6 k 0 . 8 cal. per degree mole, respectively. Asensio and Snbatier (2) have de-
T h e oxidation of uranium dioxide t o triuranium octaoxide, below 500" C., has been shown by differential thermal analysis to be a two-step process, and, with the aid of thermogravimetric analysis. the unstable intermediate compound n as found to be triuranium heptaoxide ( 1 4 ) . Borchardt ( 7 ) has investigated the interaction of triuranium octaovicle in 50-50 weight 7,with the metals iron, nickcl, chromium, and niobium in a static argon atmosphere. The thermograms indicated the reduction to uranium dioyide and oxidation of the respective nictal. I n the ease of c h r e mium, further reaction between triuranium octaohide and chromium trioxide was observed, leading to the formation of a n unidentified phase. Uranium boride and nickel, under the same conditions, also reacted to form a n identified phase. Templeton and Pask ( 7 4 ) have investigated the formation of barium metatitanate from barium carbonate and titania in air and carbon dioxide. T h e barium orthotitanate formation was suppressed in carbon dioxide because of its rapid reaction with t h e gas to form the metatitanate and barium carbonate. The thermal stability of the sulfates of the bivalent ions of manganese, iron, cobalt, nickrl, copper, zinc, cadmium, lead. magnesium, calcium, and strontium has been studied by the differential thermal and thermogravimetric methods (61). Spinedi and Gauzzi have used differential thermal and thermogravimetyic analysis to study the oxides of lead (71) and of tin (7'2). Borchardt and Thompson (10) have investigated the interaction of barium oxide with calcium and magnesium carbonates and the bivalent sulfates of calcium, magnesium, zinc, and copper, as well as t h e reaction of barium oxide with strontium carbonate and sulfate. I n a continuation of this work, differential thermal analysis has been applied to reactions of calcium oxide with magnesium carbonate and the bivalent sulfates of copper, zinc, and magnesium, and t h e reactions of magnesium oxide with copper(I1) sulfate and zinc sulfate (11). These studies have led to a reexamination of the Hedvalk effect (18) and it was concluded t h a t the originst experiments on which the Hedvall rule is based were misinterpreted (89). The increased reactivity noted in the cited VOL. 32,
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experiments is due to the formation of a liquid phase and is unrelated to the phase transition. These investigators have concluded that unambiguous evidence for a Hedvall effect is lacking. Reisman and his coworkers have continued their work on the reactions of thP group V oxides. Investigation of the compounds formed in the niobium oxide-potassium oxide (62) and niobium oxide-lithium oxide, sodium oxideniobium oxide, and silver oxide-niobium oxide (61) systems has been conducted. Studies have also been made (60) on the potassium metaniobate-sodium metaniobate and potassium metatantalatepotassium metaniobate systems. KINETICS
The variable temperature of inversion of cristobalite has been the subject of two investigations (31, 7 7 ) . Walker and his coworkers h a r e advanced evidence to show that the variability can be rationalized in terms of three rate processes dependent on the temperature of heat treatment: nucleation of the cristobalite phase from the source material, a n ordering effect. producing small, strain-free crystallites, and grain groa t h from n-ell ordered crystals. -4 significant development occurred with Blumberg's ( b ) extension of the method of Borchardt and Daniels (9) t o heterogeneous kinetics. For the reaction of vitreous silica with hydrofluoric acid in the range 0" to 35" C. the frequency factor, k , was determined to be 0.12010.022 and the activation, A,!?, to be 9 i 1 kcal. The heat of reaction determined was 33 i 2 kcal per mole of silica, which compared favorably with the value of 38 kcal. per mole of silica reported in the literature (19). Borchardt ( 7 ) has assumed t h a t t h e kinetic equations derived for liquid systems (9) hold, a t least approximately, for solid state differential thermal analysis and also that the actual thermal gradients are appi oximated by linear gradients. Applying these assumptions, rate data obtained for the decomposition of magnesium carbonate. calcium carbonate, and kaolinite have been found to agree Tithin a few per cent with data obtained by thermogravimetric analyses. ORGANIC APPLICATIONS
A study of the picrates and styphiiates of hydrazine, guanidine, aminoguanidine, guanylurea, N-methylguanidine, and N-ethylguanidine, the pyromelliates of guanidine and aminoguanidine, guanidine sulfate, guanidine nitrate, N-ethylguanidine sulfate, and nitroguanidine was reported b y F a u t h and Gallant (20). 170 R *
ANALYTICAL CHEMISTRY
Haighton and Hannewij k (27) have applied the differential thermal technique to palm oil and peanut oil in various stabilized stages. I n the latter case it mas easy to differentiate among quickly cooled, stabilized, and partially stabilized material. Lavery (40) investigated several mono-oleyl disaturated glyccrides and \I as able not only to differentiate among them, but reported finding new polymorphic modifications. Cocoa butter, margarine blends. sesame oil, peanut oil, safflov er oil, olive oil, and a number of other oils have been investigated (28) and it has been found that the shape of the curves depends largely on the pretreatment of the fat. The ferrous and ferric chrlatcs of salicylaldehyde salicyloylhydrazone have been subjected to differential thermal analysis (34). Several zinc chelates, including zinc 4,4'-bisthiopicolinaniidodiphenyl, were investigated by Doyle and Hill (17). Perkins and Mitchell (58) have obtained thermograms for a number of sugars, starchrs, amino acids, and proteins. They have suggested t h a t the method could he applied to indicate the degree of decomposition of soil organic matter, and aid in identifying soil types, changes that had occurred during the dehydration of alfalfa, and changes in other organic matter during storage and treatment.
POLYMER APPLICATIONS
Application of differential thermal analysis to polymer chemistry has increased. Keavney and Eberlin (58) have applied differential thermal analysis to the determination of glass transition temperatures of poly(acrylonitri1e) as a function of polymer molecular weight. The method mas said to be a t least as accurate as other techniques, and is far more rapidly conducted. Thermograms of epoxydimethylenedianiline, methylphenyl silicone, poly(methyl methacrylate) and poly(viny1cyclohexane) have been studied by differentialthermal analysis in air. The last materials were also run in argon. Indications \\-ere obtained from differential thermal analysis (15) t h a t nylon and phenolic resins interact. The melting endotherm associated with nylon (ca. 260" to 280" C.) is almost absent in the thermogram of the mixture. This finding has been suggested as a basis for differentiating between nylon and glass-reinforced phenolics. Doyle (16) has also found very good correlation between differential thermal analysis and thermogravimetric analysis with several zinc chelates, poly(methy1 methacrylate), and poly(ch1orotrifluoroethylene). Otani (58) has applied differential
thermal analysis in the range 200' to 750" C. to the carbonization process, occurring in nitrogen, associated with thermal degradation of poly(viny1 chloride), saran, dibenzanthrone, cellulose, lignite, coal tar pitch, and petroleum pitch. The materials had been precarbonized in nitrogen a t 320" to 450' C Thermograms of cellulose. cellulose acetate, and cellulose nitrate, for the range 50" to 200" C., were investigated (55'). Cellulose and cellulose acetate had no characteristic peaks in this range. Cellulose nitrate could be differentiated from the other two by an exotherniic peak a t 180" C. S a k a m u r a and Atlas ($7') have applied differential thermal analysis and dilatometry to a n investigation of synthetic binders. The pyrolysis of acidcatalyzed furfuryl alcohol, phenyl formaldehyde. and coal tar pitch binders was investigated. Reactions such as the evolution of volatiles, polymerization, and condensation were recordable and reproducibly so. The magnitude and position of the peaks on a thermogram not only reflected differences between binder resins, but gave insight to partial prepolymerization, to the effect of different catalysts employed, and to mechanisms involved. FUELS
Mtchell (44) has obtained thermograms of peat of varying botanical composition and has suggested t h e possibility of predicting heating characteristics from the curacs. Peats and peat constituents have also been investigated by Paulik and Weltner (56), who have determined how the constituents affected particular peat curves. Low rank coals have been subjected t o differential thermal analysis (76) and have associated a n endotherm in t h e temperature range of 130" to 170" C. to this class of coal. Hungarian hard coals have also been subjected to this technique (26). Gebler and Iskhakov (25) have examined Russian coals and have attributed a 550" to 570" C. endotherm to elimination of water from the clay minerals in coal. RADIATION DAMAGE
Freeman, Anderson, and Campisi (22) used this technique and thermogravimetric analysis to study the physicochemical changes induced in ammonium perchlorate by x-radiation. Murphy and Hill (46) have applied differential thermal to a study of the effects of gamma radiation on biphenyl, poly(viny1 chloride), Teflon, and Versalube F-50. The radiation damage detected by differential thermal analysis was not detectable by infrared analysis
in biphenyl and ammonium perchlorate. These investigations suggest a new approach to dosimetry. CATALYSTS
llagnesium silicate and magnesium aluminosilicate catalysts activated with magnesium sulfate and aluminum sulfate have been investigated (18). T h e 135” t o 150” C. endotherm was associated with separation of adsorbed water, and its precise temperature was found to increase with increased amounts of activator. A high temperature exotherm rras related t o the temperature of sintering and quantity of activator. Rode and Balandin (64) have applied differential thermal analysis to chromium oxide catalysts before and after poisoning in decomposition of isopropyl alcohol, butyl alcohol, cyclohexanone, and xylenes. I t was shown that the carbon film has two forms, one of which involves a higher decomposition temperature and is more difficult to regenerate. Differential thermal analysis has been used by Webb and van der TTalt (78) to determine the reactivity of calcium oxide. LITERATURE CITED
(1) Arseneau, D. F., J . Chum. Educ. 35, 130 (1959). (2) Asensio, J., Sabatier, G., Bull. SOC. fran5. mineral. crist. 81, 12 (1958). (3) Bellot, J., Henry, J., Cabane, G., Commissariat a 1’Energie Atomique, Centre d’Etudes Nucleaires de Saclay, Gif-sur-Yvette, France, Rept. 765 (1958). (4) Blaaek, A., HutnickS listy 12, 1096 (1957). (5) Blumberg, A. A., J . Phys. Chem. 63, 1129 (1959). (6) Borchardt, H. J., J . Chem. Educ. 33, 103 (1956). (7) Borchardt, H . J., J . Znwg. Nuclear Chem., in press. ( 8 ) Borchardt, H. J., personal communication. (9) Borchardt, H. J., Daniels, F., J . Am. Chem. SOC.79, 41 (1957). (10) Borehardt, H. J., Thompson. B. A., Ibid., 81,4182 (1959). (11) Zbid., in press. (12) Borchardt, H. J., Thompson, B. A,, unpublished results. (13) Campbell, C., Gordon, S., Abstracts, 135th Meeting, ACS, p. 23B, Bostan, Mass., April 5-10, 1959. (14) DeMarco, R. E., Heller, H. A,, Abbott, R. C., Burkhardt, W., Bull. Am. Ceram. Soe. 38, 360 (1959). (15) Doyle, C. D., personal cornmunication.
(16) Doyle, C. D., General Engineering Laboratory on WADC Contracts, Progress Rept. 5, Project 734, Contract AF33(616)-5576 (Sept. 15, 1959). (17) Doyle, C. D., Hill, J. A,, Zbid., 1st Quart. Rept., Project 8-(&7371), Contract AF33(616)-5576 (July 15, 1958). (18) Efendiev, R. M., Izvest. Akad. Nauk Azerbaidzhan. S.S.R., Ser. Fiz. Tekh. i Khim. Nauk 1959,89. (19) Evstrop’ev, K. S., Skornyakov, M. M., Akad. Nauk S. S . S . R. 1949, 182. (20) Fauth, M. I., Gallant, M. K. A., Abstracts, 134th Meeting, ACS, p. 9B, Chicago, Ill., Sept. 7-12, 1958. (21) Foldvari-Voel. 11.. iicta Geol. .kcad. ‘ Sci. Hung. 5, lo(i958j. (22) Freeman, E. S., Anderson, D. -4., Campisi, J. J., iihstracts, 135th Meeting, ACS, p. 26R, Boston, Mass., April 5-10, 1959. (23) Freeman, E. S.,Edelman, D., XSAL. CHEM. 31,624 (1959). (24) Fruchart, R., Michel, A., Compt. r a d . 246, 1222 (1958). (25) Gebler, I. V., Iskhakov, Kh. A., Koks i Khim. 1958, 16. (26) Glodi, A., Hegedus, B., Kossuth, S., Kohhzati Lupok 91,438 (1958). .. (27) Haighton, A. J., Hannewijk, J., J . Am. Oil Chemists’ SOC.35,344 (1958). (28) Hannewijk, J., Haighton, A. J., Ibid., 35,457 (1958);, (2g) Hedvall, J. A., Einfuhrung in die Festkorper Cheniie,” p. 180, Fr. Vieweg end Son, Braunschweig, 1952. (30) Hill, J. A., Murphy, C. B., ANAL. CHEM.31,1443 (1959). (31) Hill, V. G., Roy, R., J . Am. Ceram. SOC.41,532 (1958). ( 3 2 ) Hogan, V. D., Gordon, S., J . Phys. Chem. 62, 1433 (1958). (33) Zbid., 63, 93 (1959). (34) Hovorka, V., Kral, M., Chem. listy 52, 1710 (1958). (35) Jager, E., Streckeisen, A., Schweiz. mineral. petrog Mitt. 38,375 (1958). (38) Kato, E., Bull. Chem. Soe. Japan 31,108, 113 (1958). (37) Ibid., 32, 51 (1959). (38) Keavney, J. J., Eberlin, E. C., Abstracts, 135th Meeting, ACS, p. 28S, Boston, Mass., April 5-10, 1959. (39) Khlapova, A. N., Proc. Acad. Sci. IJ.S.S.R., Sect. Chem. (Engl. trans ) 116, 979 (1957). (40) Lavery, H., J . A m . Oil Chemists’ SOC. 35,418 (1958). (41) Lehman, H., Ceramica (Siio Paulo) 3, 50 (1957). (42) Lloyd, S. J., Murray, J. R., J . Sci. Znstr. 35,252 (1958). (431 Mackenzie, It. C. “Differential 1h e m a l Analysis of &lays,” Central Press, Aberdeen, Scotland, 1957. (44) Mitchell, B. D., Nature 180, 1414 (i957). ’ (45) Murphy, C. B., ANAL.CHEM.30,867 i \ 19.58). ~.__,
(46) Murphy, C. B., Hill, J. A., unpublished results. (47) Nakamura, H. H., Atlas, L. M., Preprint, 4th Conf. on Carbon, Buffalo, N.Y., June 15-19, 1959.
(48) Sechitailo, K. A., Rozenberg, L. M., Terentyera, E. hI., Topcluev, A. V., PTOC. Acad. Sci. U.S.S. R . , ij‘ect. Chem. (Engl.tmns.) 116,613 (1957). (49) Newkirk, T. F., J . Am. Ceram. SOC. 41,409 (1958). (50) Nota, K. J., Jaffe, H. H., Bull. Am. Ceram. SOC.,in press. (51) Ostroff, A. G., Sanderson, R. T., J . Inmg. Nuclear Chem. 9,45 (1959). (52) Otani, S., Kogyo Kagaku Zassha 60, 1171 (1957). (53) Pakulak, J. M., Leonard, G. W., ANAL. CHEM. 31,1037 (1959). (54) Paulik, F., Erdey, L., Gal, S., 2. anal. Chem. 163, 321 (1958). (55) Paulik, F., Paulik, J., Erdey, L., Zbid., 160,321 (1958). (56) Paulik, F., Weltner, ?*I., Acta Chim. Acad. Sci. Hunq. 16, 159 (1958). (57) Pavel, L., Fojtik, L., SbornZk CMke slw. akad. zemtdtlsk4ch vtd., Rostlinna
C m p t . r e d . 248,812 (1959). (60) Reisman, A., Banks, E., J . Am. Chem. SOC.80, 1877 (1958). (61) Reisman, A,, Holtzberg, F., Ibid., 80, 6503 (1958). (62) Reismap, .4.,Holtsberg, F., Berkenblit, M., Zbid., 81, 1292 (1959). (63) Reisman. A , . Karlak. J., ZM., 80, 6500 (1958): ‘ (64) Rode, T. V., Balandin, A. A., Zhur. Obshchd. Khim. 28,2909 (1958). (65) Sakurai. T., Yabe, M., J . Phys. sot. Japan 13, .5 (1958). (66) Sastry, S. R., Hummel, F. A., J . Am. Ceram. SOC.42, 216 (1959). (67) Sauman,,Z., Silikaty 1, 181 (1957). (68) Schottmiller, J. C., King, A. J., Kanda, F. A., J . Phys. Chem. 62, 1446 (1958). (69) Proks,, I.,. Chem. zvesti. 12, ~ -Siske. ~ V.. , 185 (1958). ’ (70) Smothers, W. J., Chiang, Y., “Differential Thermal Analysis. Theory and Practice,” Chemical Publishing Co., New York, 1958. (71) Spinedi, P., Gauzzi, F., Ann. chim. (Rome)47. 1297 11957). (72)Zbd., p: 1305.’ (73) Splitek, HutnickC listy 13,697 (1958). (74) Templeton, L. K., Pask, J. A., J . Am. Ceram. SOC.42,212 (1959). (751 Van. C.-S., Makarov, G. X., Koka i Khim. 1958, 18. (76) Vol’nova, V. A., Trudy Pmogo Sweshchaniya Tennografii, Kazan 1953 (Publ. 1955). (7’7) Walker, R. F., Zerfoss, S.,Holley, S. F., Gross, L. J., J . Research Natl. Bur. Standards 61,251 (1958). (78) Webb, T. L., van der Walt, T., Nature 181,411 (1958). (79) West, R;, R., et ul., “The Defect Solid State, Intersclence, New York, 1957. (80) West, R. R., Sutton, W. J., J . Am. Ceram. SOC.37, 221 (1954). (81) Wilburn, F. W., J . Sn’. Znstr. 35, 403 (1958). \ - - ,
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