INDUSTRIAL A N D ENGINEERING CHEMISTRY
1386
Val. 20, No. 12
Recommended Equipment of a Modern X-Ray Laboratory - for the Study of Structures of Materiais' George L. Clark D~P~BTIBX osTCRBMISIBY, Umvsnsrrv or ILLTWOIS,URBANA,ILL.
0 RAPID has been the
S
growth in i n t e r e s t among universities and industries in the new developments of x-ray science, and so numerous have been the requests for suggestions concerning the installation and e q u i p m e n t of an adequste laboratory, that it seems desirable to describe the most modern apparatus, particularly as it is utilized in the x-ray laboratory of the University of Illinois.
A detailed description is given of the various types of complete x-ray apparatus such as may be employed advantageously in the study of fine structures of materials by the diffraction method. The equipment is essentially that installed in the new x-ray laboratory at the University of Illinois. The more important improvements are special cassettes for the pinhole and oscillation methods to be used with the mnltiplediffraction apparatus; the design and set-up of gaatype, copper-target tubes with the power plant to operate these; a fine leak to regulate air pressure in these tubes: details of manipulation based upon experience; the applicability of various methods to certain types of problems; reproductions of typical diffraction patterns obtained in the study of industrial materials and processes; enumeration of useful auxiliary equipment for a laboratory of this type. In general, an effort is made to give an estimate of the present status of the problem of the most dependable and economical installation of x-ray apparatus.
CASSETTEAND HOLDBR-
As s u p p l i e d , t h e u n i t is
e q u i p p e d w i t h t h e usual c w s e t t e s f o r t h e powder straight-line crystal spectrograms (Hull method), hut no provision is made for mounting flat films sue11 as are ordinarily required for pinhole patterns. To fill this need J. B. Hayes and the writer have designed a cassette and holder which will fit on the slides that hold the powder cassettes in place on the table of the apparatus. Inasmuch Molybdenum DiBraction as the beam from the target of Unit the tube, whieh is coaxial with I n the study of chrniical the cylinder supporting the and industrial materials it is defining slits and pinholes, obviously advantageous to emerges a t an angle of 5 d e have as the first diffraction apparatus a multiple unit with gees from the horizontal, it is essential to construct the holder which it is possible to make several exposures simult~aneously so that the film in the cassette will be perpendieular to the from the same x-ray tube. The design of such a multiple beam or 5 degrees from vertical. The holder is a single castapparatus combining the Hull powder method and the mono- ing of aluminum, the base grooved to fit the usual slides chromatic pinhole method has been presented in an earlier and the sides slotted so that the flat cassette niay he slid paper.* The familiar General Electric apparatus has been into position from the top. A piece of lead sheet 3/82 inch redesimed so that (3 mm.) thick is mounted in the aluminum holder directly t h e s e v a r i o u s back of the cassette so that the x-rays, after passage through methods m a y he the film, are entirely absorbed. The cassette is similar to employcd. This those ordinarily employed in medical radiographic work. apparatus bas re- The framework consists of an aluminum casting over which movable and inter- is fastened thin aluminum foil for the side through which the chringeable s l i t s , exposure is made. narrow and wide, The removable back and pinholes con- is held in position by s t r u c t e d from astrongspring so that B a k e l i t e impreg- ample allowance is n a t e d with lead made for using intcnoxide. In the new sifying screens. Two switchboard rheo- stiff, small springs are stats are omitted also fastened to the and the whole unit b s c k so t h a t t h e is so designed that cassette will be held the regular Cool- firmly in position in idge-type molyb- t h e bolder. It has denum target dif- been found from exfraction tube may perience that for ordibe operated a t n a r y purposes an FIBure I-Film Cassette and Holder 30,000 volts and 8.255 X 10.16cm.film for Pinhole Diffrscfion M e t h o d w i t h 24 milliamneres. is sufficiently large to General Eiectrlc Multiple Appar~fue This e q u i p m e n t register complete pat3-Cassette Assembly OD Table therefore constitutes the first unit for the laboratory whose terns when the &- Flgure of mffraction ~ ~ ~ a r ~ t chief interest lis? in analysis of crystalline or ultimate struc- tance from the speciture of materials. men to the GIm is 5 em. or less. By using this size all of the twelve stations on the apparatus may be used simultaneously 1 Received July 24.1928. J. O9lirol Soc. A m , 19, a79 (1020). and, of course, the expense is much less than if 12.7 x 17.78 f
~ t ~
December, 1928
IiYDUSTRIAL A.ND ENGINEERING CHEMISTRY
1387
em. or larger films were used. It is advantageous, however, mounting is designed so that it may be raised or lowered to to have one or two holders and 12.7 X 17.78 em. cassettes take care of various thicknesses of specimens, and it may also be rotated in a horizontal plane in case a study is made available for special requirements. A photograph of this simple but sturdy holder and cassette of directional properties. This flat table may be entirely is shown in Figure 1. Figure 2 shows several of these units removed and a goniometer head substituted. A single crystal in position on the apparatus table, together with the quad- may be mounted on this head and oriented optically, then rant cassettes for the powder method supplied with the ap- placed in position in the spectrograph. It may be held paratus and a special spectrograph described below. I n fixed when a Laue photograph is made or rotated for obtainFiirrure 3 is shown the nat- ing a complete diagram, a method now in very great favor teLn obtained with a speci- for unique analysis of space group structnre. I n Figure 5 the new spectrograph is shown in two positions. men of a s b e s t o s . T h e small piece of the fibrous As an example of the first type of application-namely, with mineral was placed over the specimen held at a fixed grazing angle with respect to the pinhole and the film in the x-ray beam-the diffraction patterns for the extremely its holder adjusted a t a dis- thin layer of a complex aluminum borate electrodeposited tance of 5 em. With this npon sheets of cold-rolled aluminum are illustrated in Figure simple arrangement it has 6. The marked fiber structure of the aluminum foil itself been possible to compare is evident in Figure 7. It was necessary, therefore, to adquantitatively samples of just the coated aluminum specimens a t an extremely small a s b e s t o s from numerous grazing angle so that the x-ray beam would penetrate only sources. The pattern for the outer a m and not the underlying aluminum. That black diamond showing this has been successfuily accomplished is shown by the Figure %-Pinhole Dihaction fairly large crystal grains fact that there are no traces of the fibered aluminum in Pattern of Rhodesian Chrysotile habeafos Fibera cemented together in ran- Figure 6. The two specimens are clearly distinguishable doni orientation is repro- by the considerable difference in the size of the crystal grains. duced in Fignre 4. The The deposited film was so extremely thin that no satisfactory g r e a t a d v a n t a g e of the measurement could be made microscopically. The spectrograph when employed in its oscillating form h o l d e r c o n s i s t s in its rigidity and in the possi- has been very sucoessfully used in the study of the thin films bility of rapidly adjusting of paraffin wax, fatty acids, soaps, and numerous other orbhe holder at precisely the ganic compounds, porcelain, nitrocellulose, resins, waxes, same distance from t.he linseed-oil films, adhesives, and other materials ordinarily specimen in simultaneous applied in thin layers. The detailed study of fundamental differentiation betnreen paraffin waxes will be presented in or successive exposures. OSCILLATING SPECTRO-another paper. This spectrograph may he used equally CJRAPH4ne Of the most interesting developments in the study of structure of materials has been in the analysis of s u r f a c e s and thin films. In order to make n r o v i s i o n f o r this application, another apparatus has been-designed which will also fit directly upon tho diffraction apparatus. This spectrograph has a double utility. The specimen may be placed upon a small mounting table for surface examination. This table may be tilted a t a known angle, read on a scale, so that the x-ray beam emerging through the slit or pinhole will strike the specimen a t a definite angle. It is obvious that the zero angle at which the beam grazes the surface in a parallel direction is actually 5 degrees from 6he horizontal. The film holder in this apparatus is so designed that it will move through twice the angle of incidence and thus be in the most favorable position in accordance with the IRN of Bragg to receive the reflected rays. This apparatus is somewhat similar to one previously described,j which, however, was used with a perpendicular slit rather than the horizontal beam definition used in the multiple-diffraction apparatus. By a very simple adjustment, requiring only a few seconds, the spectrograph may be converted into the oscillating type such as is required for the study of single crystals and thin films, particularly of longchain carbon compounds. I n other words, the apparatus becomes a regular Bragg spectrograph. The film holder is held fixed while the crystal table upon which is mounted the specimen oscillates through a known angle which is determined by the size of the driving cam. The flat table FIBure 5-A New Oscillating Specuomph for Use w i t h Ckk,‘’AppUed X-Rsyga? P. 183. New York. 1921.
the Multiple Diffrecfion Apparatus or w i t h Other Specini Unit#
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1383
well with another apparatus employing copper x-radiation which is now described. Unit Using Copper Rays
It is now essential in any laboratory devoted to the study of materials to haye ayailable a diffraction unit in which the characteristic ra,ys of copper or iron with wave lengths more than twice aslong asmolybdenumraysmaybeemployed. For d i f f r a c t i o n patterns in which good resol u t i o n a n d definition are essential for quantitative measurements, c o p p e r - r a d i a t i o n is preferable with materials with large unit cell dimensions, a8 are to he found in practically all organic materials such FMuro 6-Surface ReRectIDn Diffrscfion Patterns for Very Thin EJecfraas rubber, cellulose, deposited Layers on Rolled Aluminum p r o t e i n s , and related Foil materials. I n the writer's experience the most satisfactory tube for the generation of copper radiation has been found to be an all-metal Hadding-Siegbahn type tube. (Figure 8) This tube has replaceable targets and may be entirely dismantled and reassembled. The tube is a gas-type tubo and thus has no hot wire cathode. For proper operation, therefore, it is essential to have the amount of residual air exactly adjusted. The tube is continuously exhausted by means of 3 rotary oil pump and mercury diffusion pump of the Iangmuir type. These pumps reduce the pressure far below that required for operationm d y , 0.011 t o 0.012 mm. Consequently a fine leak must he used. An extraordinarily satisfactory t.ype of needle valve has been const.moted from Pyrex glass. Into 3 eon-
L
..
.
sprina and lever ar-
on the pump side df tlie x-ray t.ube, although it may also be sealed directly to the opposite side of the tube, this arrangement givingsmoother operation. It has been found unnecessary to use liquid air or cooling traps t o condense mercury vapor from the diffusion pump. In this installation a large 1- or 2-liter bulb serves very satisfactorily in the train to prevent entrance of deleterious amounts of mercury vapor. A McLeod gage mounted on the table and sealed in the pumping train is very useful in measuring and controlling air pressure. The tube is nsed in the reverse position from that usually employed; in other 1 Nolurc.
118.28 (1928)
Val. 20, No. 12
words, the porcelain insulator on the cathode end is below. The tube is held in position on the top of tlie table through which the porcelain insulator passes. In an enc.losed space under t.he table lined with lead for x-ray protection is placed the transformer of the x-ray power plant, so that the only high-tension lead running to the cathode in the tube is a few centimeters in length and is entirely insulated from possible contact from the outside. In this tube the target and cathode ends of the tube must be cooled. Since the
very suieessful cooling system consists in 3 slow but continuous flow of light t r a n s f o r m e r oil. A bottle holding about a gallon of oil is placed about six feet ( 2 meters) above t h e l e v e l Figure %-Diagram of which is to be cooled so that cironlation to the cathode takes place by gravity. I n the exit tube is plaoed 3 T-tube jot which is connected with the compressed air line. The column of oil is therefore lifted by the air pressure and is returned to the bottle. Because the oil gradually attacks wax and rubber connections which must be made with the metal tube through which the cooling of the cat.hode is accomplished, an experiment was tried of simply blowing a stream of air through this tube. This has proved very satisfactory and entirely a d o q u a t e inasmuch as eontinuous runs of 250 hours or more have been made. The air cooling is sufficient to keep the wax joints of the tube from melting. By far the most satisfactory wax for sealing the metal part of the tube to the porcelain insulator is pieein, which may now be purchased in this country. T h e t u b e operates in a very constant fashion for p e r h a p s 150 hours. On account of sputtering and pitting it is desirable to replace thealu~,inumeathode after o p e r a t i o n f o r this length of t,ime. It is essential that this cathode he made of pure aluminum free from slag or gas inclusions, since otherwise the operation of the tube will be spasmodic. As ordinarily desigued and constructed in Ger- Fiwre 9-Desim of Fine Leak for Gas-Type many, the tube has only ~ ~ ~ ~ ~ ~
$~~2.$&;54~f~ahn
&
i
r
December, 1928
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1389
three windows for the emergent x-ray beam, since the face
volts and 50 milliamperes as 8 factor of safety. A Wappler plant in the writer's laboratory is giving good service. The unit may he used eit.her with the Coolidge-type tube, since i t provides a filament transformer, or with the gas-type sorption of the x-rays by this light material is negligible. tube, in which case the cathode is connected to the binding post of the filament circuit which is metallically joined to the secondary of t,he transformer. A small cylindrical lead shield may be placed around the x-ray tube for protection and to hold the pinholes or slits. These may be constructed readily in lead plugs in the ends of brass tubes 4 em. long. Cassettes and holders similar to those described for use with the multiple apparatus may be used for the exposures; the beam, of course, emerges from this type of tube perfectly horizontal so that the films are placed vertically. Cassettes made with the face of aluminum foil are not satisfactory for use with copper radiation inasmuch as the longer rays are absorbed considerably. The films are therefore wrapped in paper; cardboard holders supplied by the Eastman Kodak Company are also quite satisfactory. A photograph of the installation (Figure 10) shows the pumping system, fine leak, tube support, and lead protective cylinder with pinholes and cassettes. I n the writer's laboratory a new Miiller Universal spectrograph manufactured by Hilger is being used with this unit. This Figure iU-PhofegiBph of APscmhlyfor O ~ e r a f i o nof X-Ray U n i t spcctrograph, of course, cannot he used with General Electric Employing Copper X-Radiation apparatus, since it requires vortical slits, wliile the new The great advantage of the tube lies not only in the fact instrument photographed in Figure 5 may be used with either that it may he entirely dismantled and reassembled and is a unit. Figure 11is an example of the type of results obtained permanent equipment but also in the very large radiation with the gas-type tube, the diffr:ictiou patterns of two saniintensity afforded. The windows absorb practically none ples of rayon prepared by thc? same process except for differof the energy and the specimen may be mounted vithin 2 or ences in mechanical details. 3 em. of the focal spot of the target. When the tube is The remarkable differences properly operating exposures of more than 5 hours are never in the ultimate structures required even with distinctly non-crystalline materials. At of these two specimens are an air pressure in the tube of 0.011 mm. a current of 15 noteworthy. One is sharply fibered ---that is, the crystal Nol-A greatly improved tnbr of the general type with n ~ontinuous grains are almost perfectly window around 360' C. lor mvlliplr exporure~even in the General Electric oriented with respect to t,he apparatus and with an automatic device for rliznins electrodes and a relflength of the fiber-and the contained fine leak has just been built in the laboratory. The porcelain insulator wa? made by the Ceramics Department of the other represents a nearly unrvrrrity 01 Illinois. chaotic arrangement of crysmilliamperes a t 50,000 volts is characteristic of the tube pro- tal grains, as condensed by ducing an x-ray beam of very great intensity. If a strongly the nearly uniform continumonochromatic beam is desired-that is, a copper IC-alpha ous rings. W-ith this e q u i p line-a very thin piece of nickel foil or a sheet of paper im- ment it has been possible to pregnated with a nickel salt solution serves as a filter. The obtain strikinr results with F l p u r e 12-Pattern f o r proteins, s i k tendons, and Stretched Highly Vulcanized other biological materials, as Rubber Obtained with Apparatus in Figure 10 well as easily mensurable uattems for chemical eomwiunds wit11 verv l o w chains of Earbon atoms. Figure 12 H i the patt.ern of a'streched highly vulcanized rubber specimen. of the target is at 45 degrees to the cathode-ray stream. These windows consist of very thin aluminum foil or, better, a foil consisting of a high percentage of beryllium, since ab-
Y
Ad,ditional Equipment
Figure 11-Patterns
for Two Types of Rayon Obtained with t h e A p p a m f ~ ein Figure 10
power plant for the operation of this tube is preferably a unit with rectification either by a Kenotron tube or a mechanical disk. Companies which manufacture medical x-ray equipment are glad to supply a complete unit a t less than 81000. It is, of course, essential to mecify that the uositive side of the transformer shall he groudded and that the transformer shall stand up under continuous operation a t 80,ooO
These two diffraction units-the one employing molybdenum rays for studies of metals: ores, inorganic compounds and mixtures of all kinds, ceramics, and so forth; and the other employing copper rays for use in the study of all organic materials with relatively large ultimate spacings between like planes, liquids, etc.-are therefore adequate equipment for any laboratory devoted to the chemical and industrial applications of diffraction analysis. These niay be placed in a small but convenient room, where abundant light and air are available, but wliich may be darkened for purposes of adjustment of x-ray beams with Ruorescent screens. The room is equipped with gas, air, water, and exit pipes for the cooling water in the x-ray tubes. Fifty-ampere power limes
INDUSTRIAL AND ENGINEERING CHEMISTRY
1390
are installed with safety switches and fuses. Automatic Mercoid switches to insure that the tubes are being supplied with an adequate stream of water are adjusted to open the primary circuit if the water pressure should fall below 20 or 30 pounds. Gages in the water line are very advantageous. These Mercoid switches operate most satisfactorily through a relay, since arcing would otherwise take place during make or break. The most satisfactory relay that has been found is the Cutler-Hammer starting box Type AAA. This box also acts as a thermal overload protection. It is essential that the source of power shall be as consistent as possible, since much of the trouble with development of gas in Coolidge tubes may be ascribed to irregular voltage. An autographic recording voltmeter placed across the line is a very valuable equipment for the x-ray laboratory. It not only serves to keep a record of the constancy of the electrical supply, but will also record the time of starting and stopping the apparatus. Both of the units described
Vol. 20, No. 12
are designed to operate continuously day and night and it is of great advantage in making exposures to know when operation ceases if an accident should occur during the night. A well-equipped x-ray laboratory will also have a convenient dark room with developing solutions in tanks. The films are clamped in the regular holders during development and are dried in racks in the same holders. A microphotometer or densitometer has a growing usefulness in connection with a research laboratory, particularly in problems of particle size, solid solutions, or in other phases where exact measurementi of positions or breadths of diffraction lines are essential. The laboratory should also be equipped with fireproof cabinets for the filing of exposed films and of specimens. Facilities should be provided for preparing specimens such as lapping machines, etching solutions, small Pyrex capillary tubes, plasticine for mounting specimens, pieces of lead glass, fluorescopes for visual adjustments, intensifying screens, filters, meters, and tools.
Film Characteristics of the Esters of the Component Fatty Acids of Linseed Oil' B. H. Thurman and W. R. Crandall AMERICAN LINSEEDCOMPANY, 297
I
N A preliminary effort to detect the factors responsible for
the varied phenomena observed in the behavior of protective coatings in which linseed oil either predominates or plays a prominent part, such as in paints, varnishes, nitrocellulose lacquers, fabric coatings, and patent leather finishes, the work briefly described in this paper was instigated. Of the component fatty acids of linseed oil about 90 per cent belong to the unsaturated series of varying degree of unsaturation while the remainder are saturated. I n order to throw some light on the properties conferred on linseed oil in protective coatings by the different kinds of its component fatty acids, it was decided to depart radically from the procedure of studying these acids in the form of the glycerides as they occur in the oil. The study of the behavior of these acids in the form of simple esters, such as the ethyl esters, was selected as a novel and informative method. The reason for this selection is that complications arising in the drying of the glycerides are eliminated. The ethyl esters of linseed fatty acids absorb oxygen at about the same rate as do the glycerides, but while in this process the glycerides set to a solid film, the esters remain liquid.2 Preparation of Esters
Various known methods were used for the preparation of ethyl and methyl esters, involving both glycerides and fatty acids as raw materials, and sodium alcoholate and hydrochloric acid, respectively, as catalysts. The following preferred methods are applicable to the preparation of methyl, ethyl, glycol, and benzyl esters. Method 2 is also applicable to the preparation of esters from diethylene glycol, glycol monoethyl ether, and furfuryl alcohol. METHOD1-Two to four volumes of anhydrous alcohol are mixed with one volume of fatty acid, and anhydrous hydrochloric acid is rapidly passed in to the point of saturation. The heat of absorption raises the mixture to the boiling point, or nearly; hence a condenser should be used. In the case of methyl or ethyl esters the reaction is practically 1 Received
May 9, 1928.
* Morrell, J . Oil Cdour Chem. Assocn., 7, 153 (1924).
FOURTHAvE., NEWYORK, K. Y.
complete a t this point, only a few per cent additional yield being secured by further heating. The upper ester layer is separated and washed first with a large volume of cold water, then with successive portions of 1 to 2 per cent sodium hydroxide in 50 per cent alcohol until the washings are strongly alkaline to phenolphthalein, warming slightly to promote settling. The entrained soap is washed out with hot 50 per cent alcohol, the esters washed with boiling water, dried, and distilled a t 40 mm. or less pressure. Comparison of the iodine numbers of linseed fatty acid ethyl ester mixture prepared by this method and the oil from which it was derived showed that the ester absorbed about 3 per cent less iodine than the calculated amount. This is accounted for, a t least in part, by the appearance of free hydrochloric acid in the distillate. This hydrochloric acid disappears upon several hours' standing, only to reappear in a subsequent distillation. It is therefore necessary to give the ester so prepared a sodium bicarbonate wash immediately after distilling. METHOD2-In 2 or more volumes of anhydrous alcohol about 0.01 part of sodium is dissolved and 1 volume of glyceride added. It is then boiled under a reflux for a few minutes. I n the case of methyl and ethyl esters, the reaction is practically complete by the time the mixture attains the boiling point. The mixture is cooled to room temperature and agitated with 2 parts of cold water, decanted, washed once with 50 per cent alcohol, then several times with boiling water, dried, and distilled. Linseed ethyl esters prepared by this method absorb the theoretical amount of iodine, calculated from the iodine number of the glycerides from which they are derived. Preparation of Films
Since the ethyl esters of the mixed fatty acids of linseed oil do not set to a solid film, 20-second lacquer nitrocellulose was used as a fixative. This was easily accomplished, since all the esters studied were soluble in the usual fat and lacquer solvents and were miscible with solutions of the 20-second lacquer nitrocellulose in volatile esters. To obtain such
