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High Temperature XRay Diffraction Camera A. E. Austin, N. A. Richard, and C. M. Schwartz Citation: Review of Scientific Instruments 27, 860 (1956); doi: 10.1063/1.1715396 View online: http://dx.doi.org/10.1063/1.1715396 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/27/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in High Temperature Camera for XRay Topography Rev. Sci. Instrum. 38, 638 (1967); 10.1063/1.1720788 A High Temperature XRay Diffraction Camera Rev. Sci. Instrum. 20, 343 (1949); 10.1063/1.1741529 High Temperature XRay Diffraction Camera Rev. Sci. Instrum. 18, 367 (1947); 10.1063/1.1740951 High Temperature XRay Diffraction Camera Rev. Sci. Instrum. 17, 558 (1946); 10.1063/1.1770431 An XRay High Temperature Camera Rev. Sci. Instrum. 13, 481 (1942); 10.1063/1.1769946 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 129.120.242.61 On: Fri, 28 Nov 2014 15:52:19

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Page 1: High Temperature X-Ray Diffraction Camera

High Temperature XRay Diffraction CameraA. E. Austin, N. A. Richard, and C. M. Schwartz Citation: Review of Scientific Instruments 27, 860 (1956); doi: 10.1063/1.1715396 View online: http://dx.doi.org/10.1063/1.1715396 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/27/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in High Temperature Camera for XRay Topography Rev. Sci. Instrum. 38, 638 (1967); 10.1063/1.1720788 A High Temperature XRay Diffraction Camera Rev. Sci. Instrum. 20, 343 (1949); 10.1063/1.1741529 High Temperature XRay Diffraction Camera Rev. Sci. Instrum. 18, 367 (1947); 10.1063/1.1740951 High Temperature XRay Diffraction Camera Rev. Sci. Instrum. 17, 558 (1946); 10.1063/1.1770431 An XRay High Temperature Camera Rev. Sci. Instrum. 13, 481 (1942); 10.1063/1.1769946

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Page 2: High Temperature X-Ray Diffraction Camera

THE REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 27, NUMBER 10 OCTOBER, 1956

High Temperature X-Ray Diffraction Camera*

A. E. AUSTIN, N. A. RICHARD, AND C. M. SCHWARTZ'

Battelle Memorial Institute, Columbus 1, Ohio (Received May 23, 1956)

A. high:temperature x-ray powder diffrac;tion car~era has been designed and constructed. The design speCificatIOns were as follows: (1) to permit operatIOn at temperatures up to at least 2000°C in a high vacuun;t, (2) to be able to work i~ controlled atmosphere at somewhat lower temperatures, and (3') to permit succ:sslve exposures of the specImen held at temperature. The completed apparatus appears to meet these reqUirements.

INTRODUCTION

T HE increased demand for high-temperature mate­rials has required more extensive knowledge of

physical properties and phase transformations of both metals and ceramic materials. The determination of existence regions of phase stable at high temperature frequently requires observation at temperature, rather than to rely upon quenched specimens, in which the phase stable at high temperature is not always retained at room temperature. An excellent means of obtaining such data is by direct examination at temperature, using x-ray diffraction. High temperature phases may be observed, and phase transformations detected. From precision lattice parameter measurements at tempera­ture, the limits of solid solubility may be determined.

Since previous designsH of high-temperature x-ray diffraction cameras failed to fulfill the needs of this laboratory in the study of active metals, a camera was designed to meet the following requirements: 1. A sample temperature of at least 2000°C should be at­tainable, in high vacuum. 2. It should be possible to convert to operation in controlled atmosphere, probably at some sacrifice in temperature attainable. 3. It should be possible to record successive x-ray diffraction patterns while maintaining temperature, and without loss of vacuum. 4. Construction of camera should be such as to minimize outgassing problems. To this end, the photographic emulsion was to be placed outside the vacuum, and the use of ceramic supports, insulators, and exposed rubber was to be avoided. S. The design of the vacuum system and the camera was to provide optimum pumping speed, with efficient trapping. 6. The specimen temperature was to be measured by optical pyrometer or by thermocouple, depending upon the temperature required.

DESIGN

Figure 1 shows schematically the camera with speci­men mount and film cassette. The camera body is

* Work performed under U. S. Atomic Energy Contract w-7405-eng 92.

1 Edwards, Speiser, and Johnston, Rev. Sci. Instr. 20 343 (1949). '

2 J. R. Johnson, Ind. Lab. 4, 84 (April, 1954). 3 H .. J. G~ldschmidt in X-Ray D~fTraction by Polycrystalline

Mater~als, edited by Peiser, Rooksby, and Wilson (The Institute of Physics, London, 1955), Chap. 9.

supported on the table top with three levelling and positioning screws. The camera body projects through the table top, the extension containing an internal liquid nitrogen trap, plus water-cooled vapor baffles. A two-inch self-fractionating 3-stage metal oil diffusion pump is attached directly below. Water cooling is provided for the power leads, the camera body and the specimen holder and its bushing. The water-cooling channels were milled on the outside of the camera body and enclosed by means of cylindrical sleeves soldered in place before final machining of the reference surfaces.

In order to reduce eccentricity errors in obtaining precision lattice-constant measurements, it is necessary to design so that the specimen and film axes are main­tained concentric. To accomplish this, alignment of specimen mount and camera body was obtained by machining to close tolerances the lower cylindrical flange of the specimen holder and the upper cylindrical surface of the camera body. The film cassette was then aligned by making its inner upper cylindrical surface a sliding fit with the outer cylindrical surface of the specimen holder. The tolerance specification for these surfaces was ±0.0002S in. in 4-in. diameter.

Figure 1 shows also the heater arrangement, x-ray beam collimator and relative film position. Heating is acc,omplished by means of two ribbon heater loops, reSIstance heated. The heaters are made of 12-mil tantalum strips i-in. wide bent to form a cylinder of about i-in. diameter with 3\-in. gap between leads. These loops are self-supporting in the lead clamps; no ceramic support or insulation was used. A /6-in. gap between lower and upper heaters permits entry and exit of the x-ray beam. The two heater loops are in series, electrically, with the common center connection grounded to the camera body. This is possible, since the low-voltage secondary of the output transformer is isolated. Radiation baffies are provided, to conserve heat. These consist of two concentric tantalum cylinders supported from the camera body by means of a tripod of l6-in. tantalum wire.

As shown in Fig. 1, the film positioning is of the Straumanis4 type. The x-ray beam collimator was machined out of tantalum, with a 20-mil defining aperature. The beam trap was also of tantalum, and

4 M. E. Straumanis, J. App!. Phys. 20, 726 (1949).

860

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Page 3: High Temperature X-Ray Diffraction Camera

DIFFRACTION CAMERA 861

FIG. 1. High-temper­ature x-ray camera.

Lapped, Chro_·Plated

X·Ray Pinhole

Mole! lntemal channels for water a for gases are not shown

contained a slot carrying a beryllium shutter coated with fluorescent material on its external side. The shutter is movable from the exterior, through a Herme­flexs bellows seal. With the shutter up, the fluorescent image of the x-ray beam can be seen through a vacuum­tight Vycor window. This is useful for checking speci­men alignment. By moving the shutter down, the heated specimen can be sighted with an optical py­rometer. By exposing the Vycor window to the hot zone only for short periods, possible error due to change in optical transmission of the window, as a result of deposition of evaporated materials, is minimized.

6 A bellows-sealed rotary motion transmitter, made by Kearfott Engineering, Inc., Little Falls, New Jersey.

.. '-.. .. _.-./"'-

J ,/

if_H-+.. ___ 2 Cycles pet

)-1++-"""-- 1 Rev

X·Ray Shutter

The specimen holder is shown in Fig. 1. The motor rotation is transmitted through a Hermeflex bellows seal. By means of the illustrated cam and gear train, the specimen-support shaft is oscillated vertically through a i-in. translation during rotation. The rotation rate is about 8 times the rate of oscillation. The specimen rod is about 2 in. long, 0.080 in. in diameter at the chuck end, and with lower half-inch less than 0.020-in. diame­ter. It is held in a sliding nut on the end of shaft. The specimen can be aligned on the rotation axis by transla­tion of the sliding nut.

The film cassette is designed to expand the film against the inner wall, in the Straumanis position. The cassette diameter is 4.520±O.OOO5 in., so that the front

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Page 4: High Temperature X-Ray Diffraction Camera

862 AUSTIN, RICHARD, AND SCHWARTZ

FIG. 2. Power supply for high-temperature camera.

surface diameter of the film is 114.59 mm. The film is protected during handling by a cylindrical shutter which can be raised after the cassette is mounted on the camera body. The cassette has brass light traps for the incident x-ray beam and exit light beam. When the cassette is in position the light traps can be advanced into re-entrant parts in the camera body.

Vacuum seals were made with rubber O-rings seated in grooves of sufficient size to allow metal-to-metal contact. The beryllium windows were sealed by means of tempered shellac cement. The x-ray collimator port had a beryllium window sealed by an indium gasket. The exit port had a flat Vycor window sealed by an indium gasket. Thermocouple leads passed through a Stupakoff seal which entered below the x-ray beam

entrance port and is not shown in Fig. 1. A vacuum of IX 10-6 mm Hg was readily attainable.

Temperature regulation is obtained by supplying power to the step-down transformer through a Stabiline6

0.1% voltage stabilizer, while maintaining the water cooling constant by means of a pressure regulator. With constant thermal load and constant imput voltage, temperature fluctuations were negligible, without any form of feedback control. The power supply is shown in the block diagram of Fig. 2. The heaters are protected against vacuum failure or low water pressure by relays interlocking with the vacuum ionization gauge and water pressurestats. The voltage regulator, variable transformer, and step-down transformer have each a 2.5 kva rating. The step-down transformer can supply up to 250 amp to the heaters.

For use with a controlled atmosphere, the ionization gauge can be replaced by a gas inlet. The tantalum heaters and baffles may be replaced by other appropri­ate metals, if necessary. No other modifications should be required. Because of heat loss by conduction in the atmosphere, the upper temperature attainable will not be as high as in vacuum.

For measuring temperatures below the range of the optical pyrometer, a thermocouple can be placed in the heater gap next to the specimen. The couple can be clamped between heater lead strips, using suitable insulator material such as mica or a refractory oxide.

The utilization of this camera is illustrated by the x-ray diffraction photographs of tantalum at 1730°C in

(a)

(b)

FIG. 3. X-ray diffraction photographs of tantalum.

Fig. 3. The copper Ka doublet of the back-reflection lines is well resolved.

The authors wish to thank Wm. J. Scharenberg, Jr., and W. Zelinski, of the Mechanical Engineering Depart­ment, for aid in design and construction of an operating camera.

6 Superior Electric Company, Bristol, Connecticut.

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