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APPLICATION OF MICROSCOPIC FUSION METHODS TO INORGANIC COMPOUNDS DONALD G. GRABAR and WALTER C. McCRONE Armour Research Foundation of Illinois Institute of Technology, Chicago, Illinois
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GREAT deal of work has been done during the pwst several years on the application of fusion met,hods to t,he study of organic compounds (4, 6, 7, 8, 8 ) . Although fusion methods can he applied to inorganic compounds in t,he same manner as for organic compounds, less attention has been given t,o inorganio applirat,ions. This neglect has been due perhaps t.o a feeling that the. melting points of most, inorganic compounds lie above the safe operating limits of ordinary microscopic equipment.
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Melting Points of Inorganic Compounds'
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01
NO. f'omnnand*
% 17 I1 11 7 6 4
5 4 6 4 25 -
]Figure 1.
Construction of Hotstmge Showing Details of Aluminvm
Block A, B, two halves of elunlinum hluck. C, d o t for reoeivinl~slide. D. hole far viewing asmgle. 8. t h c r ~ n o o o r ~ rwell. ~ l r li, thermometer well.
peraturc measuremcnt. 'l'hr details of eonst,ruction are shown in Figures I and 2 . The most important feature of this stag? is its use with an auxiliary lens system in conjunction \I-ith the microscope SO that the hot preparation can bc kept away from the microscope
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The table shows the results of a survey based on more than 500 inorganic compounds and indicates that over 40 per cent melt below 350°C. and consequently can be handled in the same manner as described previously for organic compounds (7). Compounds melting in this low-temperature range can he handled readily with ordinary hotstages. The Kofler stage might be mentioned as one of the best where controlled temperatures are desired. Hotstages operating above 350°C. are not generally available. To fill this need two hotstages have been constructed to cover the range of temperatures up to 1000°C. The first of these hotstages is unique only in its simplicity and ease of use. I t consists essentially of an aluminum block containing a slot to receive a micromope slide, and a t right angles to this, in the center. a hole through which the sample is viewed. This block is wound with nichrome wire, wrapped with asbestos. and mounted in a frame of asbestos boards. Thermometer and thermocouple wells are provided for tem-
b u r e 2.
Construction of Hotstage Shoving Block Mounted in itSupport
A . aluminum block. 8. asbestos board. C, mirror and $upport. D. E. dot for receiving slide. Thermometer snd thernmeouple wella are omittcd fron, thir dmrinp. M e for viewing sample.
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3.
Hotstage Positioned for Use 4 t h Auxiliary Lena Sy~ttsm
objective. Figure 3 shows the stage positioned for operation. The hotstage is placed beneath the substage assembly of the microscope, which is tilted so that its axis is perpendicular to the slot in the aluminum block of the hotstage. Being tilted a t an angle of about 30' removes the microscope stage and lenses from the direct upward path of the heat. The substage condenser is removed and a 32-mm. objective centered in its place. By moving the objective upward or downward using the rack and pinion, a real image of the preparation can be focused above the microscope stage and viewed as usual r ~ i t hthe regular microscope optics. Satisfactory resolution is obtained with either a 32mm. or 16-mm. objective on the microscope, and by using 20X or even 30X eyepieces, magnifications 11p to 300X are possible. Since more than lOOX magnification is seldom required for fusion studies this arrangement is quite satisfactory. Sustained working temperatures up to 500°C. are easily obtained with this apparatus. For temperatures greater than 500°C. a modified microfurnace is used, the construction of which is illustrated in Figures 4 and 5. The furnace core (Figure 4A) is a cylinder of a zirconium refractory material having an inner shelf for supporting the preparation (made to order by Leco Company, St. Joseph, Michigan). Its dimensions are: height, S/4 inch; O.D., a/, inch; I.D., '/%inch; diameter inner
hole, '/a inch. To mind the core with resistance wire for heating, nichrome ribbon is wrapped around a 1/4-inchbolt which is then inserted through the inner hole in the core (Figure 4B). This serves as a firm support on which a coil of B & S No. 30 ashestoscovered nichrome wire is wound (Figure 4C). This coil is then coated lightly with Sauereisen, pulled into tho core and, after removing the bolt, sealed over completely with Sauereisen (Figure 40). The winding is completed by an additional layer of wire around the outside of the core a short distance above and below the inner shelf (Figure 4E). If desired, the wall of the cylinder can be ground thinner at this point to receive the wire. The casing for the furnace is a box made of asbestos board with a '/,-inch hole drilled through the center of the bottom board (Figure 5). The core is cemented in place over the hole and the sides coated with Sauereisen. The remaining space in the box is packed with asbestos for insulation. The top cover for the case is made with a removable section for access to the furnace. Windows for covering the top and bottom hole of the case are made of Vycor or fused silica and cemented in place. Since the high temperatures attained are confined to a relatively small space inside the furnace the outer casing remains only moderately hot when the stage is used for short heating cycles. For this reason the casing is made as large as the dimensions of the microscope stage permits, and the furnace may he used in the conventional manner on the
DECEMBER. 1950
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microscope stage for periods of about one-half hour without excessive heating of the microscope. For longer periods of time the furnace is best used with an auxiliary lens system similar to the one described for the previous stage. The hotstage is supported on a tripod and a light source placed directly beneath. A 32-mm. objective is again used as an auxilialy lens and is centered above the stage by a clamp and ringstand arrangement. The microscope body tube is conveniently supported by a stand such as the Spencer Model shown in Figurc 6. With this setup a magnification of 50X is obtained with the auxiliary lens placed 6 cm. above the furnace. F i y r e 6 shows the stage set up for use with a binocular microscope. Temperature control for both hotstages is obtained by means of a voltage regulator in the circuit. For approximate temperature measurement the dial of the voltage regulator or an ammeter can be calibrated rising compounds of known melting point; for more accurate measurement a thermocouple can be used. Finding a suitable material for use as slides and cover glasses a t high temperatures presents some d5cnlties. Glass is not both because of itslowsoftening point and its high coefficient of expansion, which causes frequent breakage on cooling. Figure 5. Caring for Micraiurnasa chemical reaction also frequently takes pl;m a t elevated temperatures resulting either in contamination of the preparation or etching of the slide, thus making observations difficult. Since there is very little information on reactions and solubility a t temperatures around 1000°C., the problems of the slide and cover glass resolves into a trial and error process to find one suitable for the particular system being studied. Several substances have been found most satisfactory. Fused silica slides of the same size as ordinary microscope slides can be obtained from many supply houses. They are excellent for use with the inclined stage and may be cut down for use with the microfurnace, although their thickness is object,ionable. Thin plates about 1 inch by I/, inch cut from boules of artificial sapphire have been obtained through the courtesy of R. G. Waindle, Aurora National Watch Company, Auorora, Illinois, and are very satisfactory for most systems. However, unless cut exactly perpendicular to the optic axis they are not
65 1
Fisvw 6.
Microfumace Set UP f o ~use ~ i t h AUX~II~FYL~~~ sgstem
suitable for use with polarized light. Optical quality "Magnorite" (periclase) can be obtained from the Norton Company, Chippawa, Ontario, in limited quantity. Its melting point is about 2800°C. and a t temperatures near 100O0C. it is quite inest. MgO belongs to the cubic system and is therefore isotropic. Furthermore, i t exhibits perfect cubic cleavage and can therefore be cleaved to give thin cover glass and slides having dimensions up to I/, X '/g X '/a% inch. I t transmits without appreciable absorption between 2200 and 60,000 A. (3). A synthetic mica has been
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EUTECTIC: COMPOSIT~ON TEMPERATURE
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I Sn14 Z Sbh COMPOSITION F~.u- 7. phma ~i~~~~
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for snh+bb
reported recently in which the hydroxyl groups havebeen replaced by fluorine (6). This eliminates the objection to natural mica of opaqueness caused by liberation of water a t higher temperatures. Parallel plane cleavage is still obtained, as with the natural mica, making this substance desirable for some systems. Almost colorless flakes of carbomndum can be ob-
JOURNAL OF CHEMICAL EDUCATION
Figure 8.
Figure 10.
Mixed Fusmn of SnI ( U p p e r Right1 and S b l (Lower Left). Before Solidification of Eutectic
tained, which are resistant to most nonoxidizing melts. Using one of the hotst,ages described above (depending upon the t,emperat:nrr range), all of the fusion techniques previously drscrihrd as applicable for organic compounds (7) may h~ extended to inorganic ompo pounds having melt,ing point.8 up t,o 1000°C. 'I'he technilrues and theorv for the determination of i(lcnt,ity, purit,y, optiwl propert,ies, polymorphism. phase l a g r a m s ~trystal grnwth mechanisms, r:tc., remain unchanged. Specifir example of t,he application of t,hese methods to inorganic rompounds are illust,rated by Figures 7 to 13. l'hc phase diagram for t.hr binary system Sn14ShIJ (Figure 7) was drterminrd by the usual microrcopic t,echniqur. 'I'emprratl~les wrrc determined by the IinRnr hotstagr, and the c u t ~ r t , iaumposit,ion ~. hy follo\ving melt,ing of miztnrw 01' known romponition. 'l'hc pri:lin~inary mixwl fnsiou 11sd t ~ ~lt!terrnine ) the general type nf dkgram is shown in Fignres 8 and 9. F11sion preparat,ious o f SnI,, ShI:,, urmyl nilrat,e Irexahydrate (2) and zinc, nwt,at,c! ilihydratr (1) illust,ratr \w11 t,he similn.rity in appearanre b e t ~ ~ einn organir ~vmpunndsan11 irrganir ~wrnpnunrlsas grown from thc melt. In Figure 10 potassium ihlorirl~and silver chloride a1.e shosr-n as grown from thr melt. In this case the silvcr r h l ~ ~ r i d\\.as e melted at thr rdge of t,he cover glass so that i t ran under and into rontai? wit,h the pot,assium chloride which had solidifid. 'I'he preparation was then c:oolrd quickly 11p removing from the hotstage before any appreciahlr si~lntion had taken place. Figure 11 sholw t,he prepi~rat,ionaft,er remelting and cooling again. Both compounds have cryst,allieed in hhin transparent films except in the zone of mixing, where the dendritic hahit can he seen heneath t,he nearly opaque eutect,ie. T h e melting point of this cutect,ir (AgCI-KC1) determined on the Kofler hotst,age is 31i°C:., differing from the 30ii°C. value given in the literature (10). The eutetbtic composition was found to be 30.3mol per rent potassium chloride, mhirh agmrs well with the- aiwpled ~ a h wof 30.5 per cent.
C r y s t d s of KC1 (Left) and AgCI (Right) G r o w n from Melt
The hne.xrained allpearanvc of the KC! is dun to snldi~nodol.ystals on the Figure 11.
Mired Fusion of KC1 ( h f t ) and AgCl (Right)
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DECEMBER. 1950
653
Isotropic compounds which tend to crystallize in transparent films without conspicuous markings can often be rendered visible and sometimes recognized by the shrinkage cracks which appear when the preparation is cooled quickly. The preparation of sodium chloride shown in Figure 12 illustrates this behavior well. An interesting note on the behavior of KC1 and NaCl is that both compounds sublime rather readily at,temperatures near t,heir melting points.
formations of sodium sulfate from the rhombic t o monoclinic (100°C.) to hexagonal (500°C.) forms are more subtle, being evidenced only by a slight change in polarization colors when viewed by polarized light between crossed nicols.
Figure 13.
P ~ l y m a p h i cTransformation of Hglz horn Its Rhombic CYenow1 to I* Tetragonal (Red) Forms
The photoiaicmgraph on the right was taken about 10 second- after the one on the left, after the pre~arsrt~on had cooled throuah the transition temperature.
LITERATURE CITED (1) Crystallogmphic data, Anal. Chem., 21, 615 (I!IUl). (2) Ibid., 21, 1151 (1949). (3) FINLAY,G. R., Norton Company, Cbippsnn, Ontario. (Personal communication.) (4) GILPIN,V., AND W. C. MCCROW:,J . Am. Chem. Sorc, 70,208 ( l Q 4--,. R)~ (5) JACKEL, R. D., Elec. Eng., 45, I!) (11150). (6) KOFLER,L.,AND A. KOFI,R:R, "Miklm-Methoden znr Kennzeichnung orgmixher St,offc und Stoffcgernia!he," Universitasnedsg Wagner Ges. M.B.H. Innsbruck. 1948. ( 7 ) MCCRONE, W. C., Anal. Chem., 21,436 (1940). (8) MCCRONE, W. C., V. G ~ Y Nel, a!., Ind. Eng. Chem., Anal. Ed., 18, 578 (1946). (9)PICCRONE, W.C., Trans. Fcwadav Soc., 158 (1949). (10) Pann~h-AXO. X . . A N IG. I C X I . C A O I N , jilrano,p. Z P ~ ~ . Chemie, 65, I(l5110). \--
Figure 12. Crystals of NaCl Grown from Melt
Polymorphic transformations are easily recognized in many inorganic compounds. .is an example, Figure 13 shows the transforma.t,ion of mercuric iodide from the yellow rhombic form to the red tetragonal form taking place at a tempera,ture of 12G0C. The trans-
WALTER m L I u s REPPE (continued from page 648)
c
number of technical processes, all characterized by fundamentally novel technical procedures. The most important were: the hydrogenation of acetaldehyde to ethanol, of crotonaldehyde to butanol and butymldehyde; the catalytic preparat,ion of ethyl- and butylamines from acetaldehyde; the synthesis of acrylir ester from ethylene, as well as the preparation of butadiene by the classic four-stcp process. Procedures for producing ethylene by cracking of oils and by hydrogenation of acetylene were follox~edby the entire ethylene chemistry, namely ethylene chlorohydrin (new tower process), ethylene oxide, glycols, glycol ether, ete. In 1934 Dr. Reppe Iras made head of the newly created intermediate products and synthetic materials laboratory; in 1937 he was appointed Prokurist, and i n 1939 hwame a dirertor of t,he I. G. Farhenindustrie
Aktiengesellschsft. The direction of the main laborat,ory was entrusted to him in 1938, and the entire research program at the Ludvigshafen-Oppau works was pnt under his charge in 1949. His first experiments with acetylene under pressure, which formed the basis of Reppe chemistry, date from around 1928. This new domain of organic procedures embodies a large number of fundamental syntheses which, starting from the simplest building stones, make possible t.he production of homologous classes of compounds, which hitherto were not, accessible or were only so with extreme difficulty. They, together wit,h their subsequent products, span a wide domain of organic chemistry. The concurrent use of new types of catalysts resulted in a host of new reaction possibilities, which Reppe grouped in four main categories: (a) vinylation, (continued on paye 658)
DECEMBER. 1950
Isotropic compounds which tend to crystallize in transparent films without conspicuous markings can often be rendered visible and sometimes recognized by the shrinkage cracks which appear when the preparation is cooled quickly. The preparation of sodium chloride shown in Figure 12 illustrates this behavior well. An interesting note on the behavior of KC1 and NaCl is that both compounds sublime rather readily at,temperatures near t,heir melting points.
formations of sodium sulfate from the rhombic t o monoclinic (100°C.) to hexagonal (500°C.) forms are more subtle, being evidenced only by a slight change in polarization colors when viewed by polarized light between crossed nicols.
Figure 13.
P ~ l y m a p h i cTransformation of Hglz horn Its Rhombic wellowl to I* Tetragonal (Red) Forms
The photoiaicmgraph on the right was taken about 10 second- after the one on the left, after the pre~arsrt~on had cooled throuah the transition temperature.
LITERATURE CITED (1) Crystallogmphic data, Anal. Chem., 21, 615 (I!lUl). (2) Ibid., 21, 1151 (1949). (3) FINLAY,G. R., Norton Company, Cbippsnn, Ontario. (Personal communication.) (4) GILPIN,V., AND W. C. MCCROW:,J . Am. Chem. Sorc, 70,208 (lQ4R)~ --,. (5) JACKEL, R. D., Elec. Eng., 45, I!) (11150). (6) KOFLER,L.,AND A. KOFI,R:R, "Miklm-Methoden znr Kennzeichnung orgmixher St,offc und Stoffcgernia!he," Universitasnedsg Wagner Ges. M.B.H. Innsbruck. 1948. ( 7 ) MCCRONE, W. C., Anal. Chem., 21,436 (1940). (8) MCCRONE, W. C., V. G ~ Y Nel, a!., Ind. Eng. Chem., Anal. Ed., 18, 578 (1946). (9)PICCRONE, W.C., Trans. Fcwadav Soc., 158 (1949). (10) Pann~h-AXO. X . . A N IG. I C X I . C A O I N , jilrano,p. Z P ~ ~ . Chemie, 65, I(l5110). \--
Figure 12. Crystals of NaCl Grown from Melt
Polymorphic transformations are easily recognized in many inorganic compounds. .is an example, Figure 13 shows the transforma.tion of mercuric iodide from the yellow rhombic form to the red tetragonal form taking place at a tempera,turr of 12G0C. The trans-
