US2556167A - Crystal analysis apparatus - Google Patents

Description

J. E. COLEMAN CRYSTAL ANALYSIS APPARATUS Original Filed May 18, 1945 Z-AXIS INVEN TOR.

JOSEPH E. COLEMAN M Patented June 12, 1951 CRYSTAL ANALYSIS APPARATUS Joseph E. Coleman, Red Bank, N. J., assignor to the United States of America, as repr'esented' by the Secretary of War Original application May 18., 1945, Serial No.

594,468. Divided and this application December 18, 1945, Serial No. 635,828

3 Claims. '(Cl. 12535) (Granted under the act of :March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

.The invention relates to an apparatus for determinin the locations of the axes in crystals and, more particularly, to X-ray crystal analysis apparatus and auxiliary jigs which are used for facilitating proper orientation of unfaced quartz crystals, and subsequent cutting of the oriented crystal.

This application is a division of my parent application entitled Crystal Analysis Apparatus, Serial No. 594,468, filed May 18, 1945. Optical apparatus for orienting crystals are shown by my Patent No. 2,418,463, filed May 18, 1945, issued April 8, 1947, and entitled Crystal Analysis Apparatus, and by my Patent No. 2,497,070, filed May 18, 1945, issued February 14, 1950, and entitled Crystal Analysis Apparatus Having a Removable Holder.

The manufacture of the piezo-electric vibrator plates used in the radio industry for stabilizing the frequencies of the oscillators and band-pass filters depends upon the state of the quartz crystal, i. e., whether it is a perfect or a partially perfect crystal, whether it has crystal faces or areas on the surfaces that have a well-defined pattern, or whether the crystal pattern has been obliterated because of the external erosive action. The faced quartz has crystal faces which at once define the location of certain guiding lines through the crystal called reference axes for crystal cutting, and it is comparatively sim plc to determine the positions of these guiding lines in the faced quartz. The bulk of the raw material, however, comes in irregular masses broken out of large mother crystals, with no evidence of any of the crystal faces. This is known as "unfaced quartz, and in the manufacture of oscillator plates from the quartz, it becomes necessary to locate the reference axes accurately by some other means in order that the final plate will have a definite pre-selected relationship with respect to these reference axes. This is known as orientation of the oscillator plate.

Three methods of procedure are used at the present time. These methods are:

(1) The direct watering method in which wafers are sawed directly from the mother crystal and diced into blanks;

' (2) The Z section-Y bar method in which sections are out perpendicular to the Z axis, then sawed into bars, and finally sliced intoblanks;

3) The X block method in which blocks are cut perpendicular to the X-axis, are sawed into bars or wafers, and sliced into blanks.

The choice of method depends upon the size of the quartz to be out, whether it is faced or unfaced, and the available testing equipment.

The direct wafering method is usually used with small faced quartz; unfaced quartz can be used if X-ray equipment is available. Wafers are sawed directly from the mother crystal.

The Z section-Y bar method? is suitable .for quartz weighing more than 500 grams. It is believed that if the quartz is electrically twinned, there is less salvage than in the X block method. It can be used with face quartz or withunfaced quartz. With faced quartz, the location of the Z axis and one of the X direc tions is comparatively simple, since the growth lines on the m, faces or intersection of a rhom; bohedral and an m faceshow these directions, and quartz cuts can be readily made at either end and perpendicular to the X axis to produce an X block.v a

' The steps that are followed in obtaining prop-,- erly oriented oscillator-plates from an irregular mass of raw ,unfaced quartz are: the identificae tion of thereference axes or the Z, X and Y axes, the handedness of the quartz, and electrical polarity of, the X axis.

The invention discloses improvements in the apparatus for identifying the reference axes of the quartz crystal, when it is in the form of an irregular mass of unfaced quartz. More specifically,'the invention relates to an X-ray crystal analysis apparatus and a jig used with the X-ray apparatus and the cutting saw which facilitates the determination of the X-axes and the angle of cut of the unfaced crystal.

The X-ray crystal analysis apparatus is used for locating precisely one of the electrical or X-axes of the Z block. When X-rays fall upon the atomic structure of the crystal at definite angles, secondary X-ray waves are produced around each diffracting center. These centers lie in planes, and from each plane secondary waves are diffracted which interfere with each other. by annuling when they are out of phase, and adding when they are in phase. The waves add and reinforce each other only in certain well defined directions, giving rise to X-ray beams in those directions. The direction of the incident beam and the diffracted beam have a definite angular relation to the diifh'acting atomic planes in the crystal. These angles are commonly called the glancing angles." There to measure the diifracted rays, and a means for measuring the amount of rotation of. the specie ment under examination. Rotation is required to meet fully the angular relations between the incident and difiracted beams :for the atomicplane used in the examination. The X-ray detecting chamber is knownas the ionization chamber" since the X-ray will .i'onize-and-make certain gases conduct an electrical current.

4 the well upon the determination of the X-axis of the crystal.

These and other features of the invention will be more clearly understood from the following detailed description and-the accompanying drawings, in which;

Figure 1 illustrates a plan view of the X-ray apparatus and the lie;

taken along line 33 illustrated in Fig. 2;

The ionization chamber is connected to a direct current amplifier, and the resultant current is used to actuate a milliameter, maximum reading of the latter indicating proper orientation of the crystal with respect to the impinging beam of the X-ray radiation, The input and output glancing angles are measured by means of a goniometerwhich is an arc of a circle that has been dividedinto degrees with a rotating Vernier to read the minutes between the degrees. Suitable types of X-ray crystal analysis apparatus are well known in the art, .for example, one such type is manufactured by Philips Metali'x Corporation, New .York, New York, and is known. in trade as Philips XRay Crystal Analysis Apparatus, Type 40,000.

The invention resides in the improvements of this apparatus and the provision of a jig which can-be used with the X-ray apparatus of the ing the position of the-atomic :planesinthe crystal. -Such method is inferior to the one outlined in this specification since it introduces two errors destroying the precision of the X-ray determinations. One error takes place durin the actual drawing of the line, and the second during alignin of the drawn line with the blade of the cutting saw. The invention automatically-eliminatesthese errors. I

e It is, therefore, an :object of this inventionto provide an X'-ray crystal analysis apparatus with the instrumentalities which make it possible to orient the unfaced quartz crystal in 'the'proper manner with respect to the X-ray radiation for determining the X-axes of the crystal, these 'instrumentalities i'ncludinga reference plane in the X-ray apparatus which matches the reference plane of the jig, and a corresponding reference plane on the turntable of acutting saw, whereby the electrical axes determinations obtained in the X-ray apparatus can be'conveniently transferred to the saws turntable without the loss of precision in determinin the X-axes which is possible in the X-ray'apparatus, g

It .is an additional object of this. invention .to provide ajig suitable for orienting the unfaced crystals in. the .X-ray machine which includesa flat, rectangular plate provided. with a circular well, a disk. mounted in the well,- instrumentalitieswfor turning this disk, and for locking it in Figure 4 illustrates a piece of unfaced quartz, and Y Figure 5 is a perspective view of the cutting saw, its turntable, and the jig mounted on the turntable of the saw.

Referring to Fig. 1, the X-ray apparatus is mounted on a table, top 10 of which is illus trated in the figure. The source of X-rays is mounted under the protective hood [2 which protects the operators from the scattered X-ray radiation. Onl that side of the .X-ray equipment which is used for determining the vX-axis isillustrated in the drawing. The protective ,hood' [2 is provided with an X-ray window and filter It, so that the X-rays of only one wave length emerge from the window. The X-ray beam im-' pinges upon the unfaced crystal I6, mounted on a .jig I1. The jig, itself, is mounted on a turntable 13. provided with areference edge 20 which matches one of the reference edges 2| of the jig. TheX-rays, after impingin upon the lattice structure of the crystal, are reradiatedand, if the-setting of the-goniometer is -correct,=the reradiated beam will be intercepted by an ion 'ization chamber 22. The ionization chamber is connected. to a direct current amplifier which is mounted below top I!) of the table, and its output is connected to a meter 24 which indicates the degree of-ionization produced in the ionization chamber. When this is maximum, the crystal .16 .is properly oriented with respect to the X-ray beamand the reference edges 20 and 21; It .now remains only to remove jig H from the turntable of the .X-ray machine and mount it on a turntable .500 of the cutting machine, reference edge v2i matching reference edge 502 provided. on the turntable of the cutting machine. The-crystal, upon its mountingon the turntable of the cutting machine, is ready for its cutting by means of a diamond saw 506.

The goniometer of the X-ray machine con sists of a graduated are" 26, andwith the gear teeth disposed along its outer periphery, a vernierggear 22 engagin the gear teeth of arc 26 and mounted on a vertical axis at the'outer end of a Vernier. arm 30. Arm 30 is'mounte'd on a vertical axis positioned at the center of arc 26. Turntable l 8 'is fixedly connected to the inner end of arm '30, so that turntable I8, together with its reference edge 20' and jig I1, is rotated when gear 28 is turned. Ionization chamber '22 is rotatively mounted on-an" arm 32, the vertical axis of which is the same vertical axis used for supporting turntable l8 and arm 30. Angular p'ositio'ning' of the ionization chamber 22 does not disturb the position of turntable f8 or arm 30, since it is rotatively mountedon the "vertical axis of the goniometer.

The X-ray jig is illustrated more fully in Figs. 2 and 3. The jig consists of a rectangular, fiat plate 200' provided with the previously mentioned reference edge 2| which, with the crystal properly' oriented, is exactly parallel to a line All}! il-' lustrated in Fig. 4, this line being perpendicular to the 1010 atomic planes of the crystal (at right angles to the paper) which are parallel to the X directions of the crystal; these planes are llustrated in Fig. 4 as a series of dotted lines 1010. A shallow counter bore, forming a circular well 300, Fig. 3, is provided in the plate of the jig and a glass-topped, steel, circular disk 202 is fitted into the well, the disk, when unlocked, freely rotatin in the well. The glass top is used for mounting the crystal.

I The lower portion of disk 202 is beveled, with the result that the side surfaces 302, 304 of the disk are slanting, as illustrated more clearly in Fig. 3. The disk is provided with two beveled shoes B and 2|0, shoe 208 being in fixed position with respect to plate 200 by a set screw 209, while shoe 2 I0 is movable. The two sides of the slots made in plate 200 for holding shoes 208 and 2| 0 are also beveled, as illustrated at 203 and 205, so that the shoes are held down to the mounting plate. Thus the disk is held in fixed relationship with respect to the bottom portion 300 of the well and against rotation by means of fixed shoe 208 and movable shoe 2 l0, mounted on the diametrically oppositeside of well 300 when shoe 2|0 is moved into its locked position. The locking shoe 2 I0 is attached to a locking arm 2 by a set screw 2|2. The locking arm is pivoted at One end by means of a pivot pin 2 M which is slidingly mounted in plate 200, the sliding movement of the pin being resisted by a spring 2 I6 inserted in the well provided for this purpose in plate 200. The reason for making pin 2|4 slightly movable will be apparent from the description that is to follow. The opposite end of the locking arm 2| terminates in a bifurcated portion provided with the extensions 2|! and H8 which engage a cam 220 during the unlocked and locked positions of the cam, respectively. Cam 220 is rotatively mounted on a pin 222, and is provided with a handle 224 which makes it possible to rotate cam 220 around pin 222. The possible movement of arm 224 is illustrated in the drawing by an arrow 225. The arm is in locked position in Fig. 2, with the result that cam 220 engages arm 2 I 8, thus shifting the entire locking arm 2 to its extreme left position as seen in Fig. 2. Since locking shoe 2|0 is attached to the locking arm by set screw 2 I2, the locking shoe will move with the arm, and thus engage the beveled surface of the disk, as illustrated in Fig. 3. Since pin 2|4 represents a spring control fulcrum, the pressure exerted on the beveled edge 304 of the disk is controlled by spring 2|6; it is more convenient when pin 2|4 has a slidable type of mounting, than a fixed mounting, since the outside diameters of the disks vary due to the manufacturing tolerances, and by making the pin spring controlled it is possible to move arm 224 into its extreme locked position with the disks of slightly different diameter, without shearing off the pin when the disk is of large diameter, or leaving it unlocked when it is of slightly smaller diameter. The locking device is also self-compensatory for the wear of the disks and 0f the locking device. In order to protect the operator from injury by the X-rays, the crystal which is mounted on disk 202 is partly covered by a lead shield which makes it necessary to rotate the disk and lock it from outside the shield. Therefore, the disk should be higher than the depth of the counter bore, as illustrated in the figures. The projecting portion of the disk is provided with holes 204 equally spaced around the periphery of the part of the disk projecting above the base plate. Wrench 206, consisting of a bent rod, is placed into one of these holes and provides a convenient means for rotating the disk during the orienting process of the crystal. The rod wrench is of sufiicient'length to turn the disk with the operator remaining outside the region of the scattered X-rays. The jig is also provided with a handle 226 permanently attached to plate 200, this handle being used for handling the jig without exposing the operator to the X-rays.

In order to determine the position of the X-axis of crystal IE, it is first oriented in the polariscope and conoscope for determining its optical axis which coincides with the Z-axis. Upon determination of the Z-axis, the crystal is cut on two sides, thus providing two planes perpendicular to the Z-axis. The crystal is then mounted on jig IT, with the Z-axis perpendicular tothe surface of the jig. For a more detailed description of the procedure and jigs used in determining the Z-axis of the unfaced crystal, reference is made to my co-pending application for patent titled Crystal Analysis Apparatus, Serial Number 594,467, filed May 18, 1945 and which issued as Patent No. 2,497,070, February 14, 1950.

The 1010 atomic planes which are parallel to the X-axis are used for determining the position of the X-axis in the X-ray equipment. The input glancing angle is 10 38' and, therefore the goniometer arm 30 is set to that angle. The ionization chamber 22 and its arm 32 are set to 21 16' on the goniometer scale. The quartz is then moved toward the angular X-ray beam and rotated in the circular well of the jig by means of wrench 206. Moving the quartz to and from the incoming beam and rotating it slowly a. posi tion can usually be found at which a maximum current indication is obtain. When this is the case, the X-axis direction is perpendicular to the reference edge 2| of the jig and 20 of the X-ray machine. A maximum. reading will appear when the diffracting atoms 400 in Fig. 4 are closest to the surface of the specimen.

When a maximum reading is obtained, disk 202 is locked in the well by means of the lock-shoe 2|0 and lever arm 224 and the jig is transferred to the sawing table 500 with the reference edges 2| of the jig and 502 of the sawing table matching each other. This is accomplished by aligning the two surfaces 2|, 502 against each other and locking plate 200 in this position by means of a locking bar 503, which is provided with looking nuts 504. The saw-blade 506 will then cut the quartz perpendicular to the X-axis, since the plane of the saw is parallel to the plane of the reference edges 2| and 502.

From the given description, it is apparent that the directions of the X-axis obtained in the X- ray equipment are automatically transferred to the turntable of the cutting saw and, since this is accomplished by means of reference edge 2| of the jig, it is obvious that the precision with which the X-axis has been determined in the X-ray equipment will not be lost during the transfer of the jig from one machine to the other, so long as the plane of the cutting saw is parallel to the plane of the reference edge 502.. This method of transferring the determinations obtained in the X-ray machine to the cutting saw is obviously superior to the prior methods; which resorted to the use of pencil lines drawn on the window of the quartz block, since drawing of the line and its subsequent alignment on the turn-table of the cutting saw introduces a compound error which nullifies to a large extent the 7 p sion' inherently available with :the X-ray radiation method of determining theX-axis.

It is believed that the construction and opera tion of the disclosed apparatus, as well as the main advantages thereof, will be apparent from the given description. It should be understood that while I have shown and described my invention in preferred form, reasonable changes and mo ifications may be made without departing from the spirit of the invention as sought to be defined in the following claims.

Iclaim:

1. A jig for determining the X-axes of unfaced quartz crystals including, a flat plate having at least two reference surfaces, a well within said plate, a disk having a beveled rim and, rotativee ly mounted within said well, and instrumentalities for locking and unlocking said disk within said well, said instrumentalities comprisin at least two beveled locking shoes recessed in said plate and adapted to prevent rotation of said disk when in contact therewith, a bifurcated arm connected to one of said shoes and fulcrumed on said plate, cam means disposed within the bifurcated end of said arm for moving said one shoe to and from said disk a d leve me ns to tativcly connectedto said cam means formov= ing said arm toward and away from said disk;

2. A jig as defined in claim 1 in which the upper portion of said disk projects beyond the upper surface of said plate, and a wrench engaging saidupper portion for turning said disk within said well.

,3. A jig-as defined in claim 1, including spring means connected to said arm for maintaining the contact pressure between said shoes and said disk when said arm has been moved by said cam an lever means towardsaid disk.

JOSEPH COLEMAN.

REFERENCES CITE The following references are of recordin the file of this patent:

UNITED STATES PATENTS

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