MOVABLE PLPER CLAMP
-r
I
53tm
1
flXED PIPER
CLAMP
FRONT V I E W
steel (other suitable materials can be used) and its dimensions have been selected to accommodate 35.6 X 43.2 em. (14 x 17 inch) x-ray films. The over-all height of the frame is 53 cm. and its n'idth is 36.2 Cm. The support plate of the frame is 35.6 em. wide and 45'5 high and slightly curved, the center being 2 em. higher than both ends, on both sides, the plate is bordered by a stainless steel strip 2 em. wide t o facilitate centering and aligning of the film and chromatography paper,
REAR VIEW
The steel side strips are continued 7 . 3 em. beyond the lower end of the plate t o form the legs of the frame and s u p p r t a fixed clamp. TITO right-angle extensions, 7.0 cI11. long on each side, are fused to the upper ends of the side strips and serve as legs when the frame is used horizontallS for loading. To the upper end of the side strips are attached backward two rails, 1.7 cm. ! d e and 17.5 cm. long, on which rides a second movable clamp which can be fastened, by
a spring, to a hook in the back of the support plate. The frame can be used in two positions, horizontally during part of the loading process, and vertically during exposure. The chromatography paper is inserted in both the stationary and floating clamps, but without fastening the latter. This step is carried out in the darkroom under ordinary light. Using only the safety light (Kodak filter, Wratten Series IA), the film (Kodagraph Contact Standard, Eastman Kodak Co.) is then removed from its protective box and slipped between the loose chromatography paper and the support plate of the frame. The filter paper is then tightened against the film by fastening th(' floating clamp to the hook on the buck of the plate. ThP spring of the floating clanip takes up all nvailablc slack, yet prevents tearing the paper. The loaded frame is then placed a t the desired distance from the ultraviolet lamp (%watt germicidal lamp, Sylvania Electric Co.) and the automatic timer (GraLab Universal timer, Dimco-Gray Co.) started to give the preset timed exposure. This contact printing frame is easy to use in the darkroom and gives excellent results.
Extrusion of Cylindrical Specimens for X-Ray Powder Diffraction Analysis L. J. E. Hofer, A. Damick', A. F. Headrick, F. Fauth, E. H. Bean, and P. Branch o f Coal-to-Oil Research, Bureau of Mines, Bruceton, Pa. specimen in the Debye-Scherrer Tdiffraction camera has two features HE
important to analytical chemistry. First, it can be small, of the order of 2 to 3 mg. in weight, for organic compounds (6-8). (Because of greater density, inorganic specimens will in general be heavier.) This suggests that the Debye-Scherrer diffraction camera can be used as a microanalytical tool. Secondly, the specimen can in principle be prepared without any binder (2, 11I S ) . Thus the problems of sample contamination, important to the chemist, and of interfering background scattering from the binder, important to the diffraction analyst, are avoided. With crystalline organic specimens, background scattering is troublesome, because the scattering power of the binder is of the same order of magnitude as that of the specimen itself. Diffuse scattering from an amorphous binder when used on an amorphous specimen is even more confusing, because the contribution of the binder, such as a resin, gum, or plastic, to the diffraction pattern, cannot be distinguished from that of the specimen. These potential advantages of the binderless, extruded specimen have only partly been realized (1). The first major obstacle was overcome with the
L.
Golden,
introduction of loading devices, by which very small samples could be completely transferred into a n extrusinn tube with little loss (3, 5, IO). These loading devices are essentially convenient funnels or similar devices for directing the specimen into the extrusion tube, but the funnel does not solve the problem of extrusion. Hitherto, extrusion has been manual, and success depended upon the skill with which the specimen had been consolidated prior to extrusion and upon the nature of the material to be extruded. No matter how skillful the manual extrusion, a certain shock always occurred a t the moment of extrusion, which was sufficient to shatter fragile samples. A mechanical extrusion device providing more control was required. Together with the loading device previously described, such an apparatus provides a very reliable method for preparing binderless extruded specimens from sample materials of 3 to 5 mg.
The details of the loading equipment and the manual extrusion procedure have been described (9). However, certain aspects of this procedure should be emphasized and amplified. The extrusion tubes used are sections of 19-gage hypodermic needle tubing of Type 304 stainless steel. The specifications for this tubing are 0.042 inch outside diameter X 0.0075 inch wall with +0.0005-inch tolerances on both the outside diameter and the wall. The inside diameter of this tubing is about 0.7 mm. Before use, burrs in the ends of the tubes must be removed by filing. A device by which this can be readily accomplished (Figure 1) consists of a hardened steel block resting upon a steel surface containing a hole just the right size to hold the block. After filing, the tubes must be further dressed with either a reaming tool or a No. 73 twist drill (0.024 inch in diameter). Stainless steel tubing which meets the above requirements can be obtained commercially (I).
Figure 1. Jig for preparing x-ray specimen tubes
Present address, U. S. Steel Corp. Research Laboratories, Monroeville, Pa. VOL. 2 9 , NO. 10, OCTOBER 1957
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Thorough grinding of the sample to 325-mesh or smaller particle size is very important. Consolidation of the specimen in the extrusion tube must proceed by very small increments, of about 0.1 mg. each. This ensures uniform density and cohesion throughout the length of the specimen. Introduction of a tiny drop of n-ater, of the order of 0.1 cu. mm., into the extrusion tube by the plunger used in consolidation of the specimen prior to the introduction of sample material into the extrusion tube is sometimes very ht.lpful. This small amount of water readily evaporates under normal conditions, especially if the specimen is placed in a vacuum camera. This technique is usable only if the specimen is insoluble in water. K h e n the extrusion tube has been loaded and the specimen properly consolidated within the tube, it may be extruded manually by a rod held in a pin vise and a pair of pliers to hold the extrusion tube. If the length of plunger projecting from the pin vise is made shorter than t h p extrusion tube by approximately 0.5 mm., the specimen cannot be pushed completely out of the tube. The tube can then be used as a convenient holder for mounting in the diffraction camera. Unfortunately, considerable force (20 to 30 pounds, 8) is necessary to start extrusion of the specimen, and as a result there is poor control over the process. T o avoid this difficulty, the mechanical extrusion device shown in Figure 2 was developed.
It consists essentially of a 10-32 screw, which can be advanced by turning a knurled knob 2 inches in diameter.
At the other end of the screw is a thrust bearing consisting of a steel ball bearing recessed into a cavity and a steel thrust base pressing upon this bearing. Solderedinto this thrust base is the extrusion pin, which bears upon the consolidated specimen within the extrusion tube. The tube is held by a pin vise, which is an integral part of the extruder. Several types of extrusion pins hare been used. Piano wire employed (4, 8) for hand extrusion is not sufficiently stiff or hard to be used in this mechanical extruder. A straight cylindrical section of a steel sewing needle proved reasonably successful. The best extrusion pin was the shank of a No. 73 twist drill cut off just below the fluted portion, so that the extrusion end was hard and the unhardened butt end was reasonably resilient. The dimensions of the pin must be chosen so that it will slide freely in the extrusion tube but without noticeable play. The loaded extrusion tube is held by a steel collet chuck to resist the extruding force bearing upon the consolidated specimen. As pressure is applied, the specimen is released and can be smoothly extruded to the desired exposure. To prevent the extruding pin from being withdrawn too far, an adjustable stop consisting of two nuts rides on the lower end of the driving screw, il stop (not shown) can also be placed on the screw to prevent the specimen from being extruded completely out of the tube. Specimens so produced are relatively sound mechanically and can be readily introduced into Debye-Scherrer cameras.
Figure 2. Extruder for preparing cylindrical binderless powder diffraction specimens
Gibons, G., Bicek, E. J., ASAL. CHEJI.20, 884 (1948). Hanawalt, J. D., Rinn, H. R., Frevel, L. K., IXD.ENG.CHEJL, ANAL. ED. 10,457 (1938).
Hofer, L. J. E., Peebles, W. C., ANAL.CHEM.23, 690 (1961). Zbid.,24, 822 (1952). Zbid.,27, 1862 (1955). Hofer, L. J. E., Peebles, IT. C . , Guest, P. G., AXAL. CHEM.22, 1218 (1950).
Jellinek, hl. H . , Fankuchen, I., Ind. Eng. Chem. 37, 158 (1945).
Kossenberg, M.,. J . Sci. Instr. 32, 117 (1955).
LITERATURE CITED
Levin, I., Ott, E., 2. Krist. 85, 305
(1) Barrett, C. S., "Structure of Rletals," p. 118, 1IcGraw-Hill, New York,
McKinley, J. B., Nickels, J. E., Sidhu, S. s., IND. ENG. CHEX.,
(19331. j - _ - -
1 Q4R
(2) Bis&i,. J., Warren, B. E., J . A p p l . Phys. 13,364 (1942).
ANAL.ED. 16, 304 (1944). Morse, J. K., J . Opt. SOC.Amer. 16, 360 (19281.
2,P-Dimethoxypropane as a Drying Agent for Preparation of Infrared Samples D. S. Erley, The Dow Chemical Co., Midland, Mich.
laboratory has often been faced T with the problem of removing water from nonvolatile samples for infrared HIS
analysis. The standard drying techniques-heating with or without vacuum -are often unsuccessful and frequently muse sample degradation. If a sample is slightly acidic, or stable in a slightly acid environment (pH < 6), however, it may be easily dried by adding excess 2,2-dimethoxypropane. This unusual reagent reacts with the water rapidly (and endothermically) to form methanol and acetone according to the reaction: CHB
I
0
1564
ANALYTICAL CHEMISTRY
Physical Properties of 2,2-Dimethoxypropane Boiling range at0760 mm., O c'. 76-82 Freezing point, C. - 47 Specific gravity at 25/25' C. 0 84!) Refractive index at 26" C. 1 37(i Flash point, tag closed cup, C. -5' Explosive limits (air), vol. yo Lower 27" C. 8 Upper 58" C. 31 Equilibrium constant at 30" C: 126 5 Heat of reaction", kcal. +3.1 a W. S . Vanderkooi, Dow Chemical Co., Midland, Mich., private communicaO
tion.
reacts at 30" C. if mixed with 2,2-dimethoxypropane in a 1 to 1 mole ratio. The resulting products as well as the excess 2,2-dimethoxypropane are volatile and'usually evaporate on standing in air. Mild heating or evacuation may be necessary. If a Sujol mull is prrpared, the grinding process often removes these products. Samples that absorb water from the air may be ground under the 2,2-dimethoxypropane and a few drops of Xujol added to the slurry. Further grinding removes the drying agent and gives a mull essentially free of water absorptions. As 2,2-dimethoxypropane presents :t cwiihustion hazard a t room teniperatiires, it should he handled with rare. 'l'his material milst br distilled a t ver? 1ov 1)rcvwrc to prertwt dcc,oi~~i)o~itioil into mctliaiiol aiid 2-11ietllosy-l-propene.
