3
Differential Expansion Diffusion Couple Welding Device Dilip K. Das Citation: Review of Scientific Instruments 29, 70 (1958); doi: 10.1063/1.1716008 View online: http://dx.doi.org/10.1063/1.1716008 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/29/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Electron plasma expansion rate studies on the Electron Diffusion Gauge experimental device Phys. Plasmas 12, 072310 (2005); 10.1063/1.1952828 Thermocouple buttwelding device Rev. Sci. Instrum. 63, 5485 (1992); 10.1063/1.1143375 Adiabatic expansions of solutions of coupled secondorder linear differential equations. II J. Math. Phys. 20, 1202 (1979); 10.1063/1.524171 Adiabatic expansions of solutions of coupled second−order linear differential equations. I J. Math. Phys. 16, 875 (1975); 10.1063/1.522592 A Determination of the Thermal Expansion of Pure Ge and a Measurement of the Differential Thermal Expansion of a Ge–GaAs ThinLayer Couple J. Appl. Phys. 43, 3114 (1972); 10.1063/1.1661668 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: 128.192.114.19 On: Thu, 18 Dec 2014 06:23:44

Differential Expansion Diffusion Couple Welding Device

  • Upload
    dilip-k

  • View
    213

  • Download
    1

Embed Size (px)

Citation preview

Page 1: Differential Expansion Diffusion Couple Welding Device

Differential Expansion Diffusion Couple Welding DeviceDilip K. Das Citation: Review of Scientific Instruments 29, 70 (1958); doi: 10.1063/1.1716008 View online: http://dx.doi.org/10.1063/1.1716008 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/29/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Electron plasma expansion rate studies on the Electron Diffusion Gauge experimental device Phys. Plasmas 12, 072310 (2005); 10.1063/1.1952828 Thermocouple buttwelding device Rev. Sci. Instrum. 63, 5485 (1992); 10.1063/1.1143375 Adiabatic expansions of solutions of coupled secondorder linear differential equations. II J. Math. Phys. 20, 1202 (1979); 10.1063/1.524171 Adiabatic expansions of solutions of coupled second−order linear differential equations. I J. Math. Phys. 16, 875 (1975); 10.1063/1.522592 A Determination of the Thermal Expansion of Pure Ge and a Measurement of the Differential ThermalExpansion of a Ge–GaAs ThinLayer Couple J. Appl. Phys. 43, 3114 (1972); 10.1063/1.1661668

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:

128.192.114.19 On: Thu, 18 Dec 2014 06:23:44

Page 2: Differential Expansion Diffusion Couple Welding Device

70 NOTES

correction can be neglected in most cases. Assuming an error of ±O.S mm in reading the position of the mercury in the McLeod, the accuracy of the hydrogen analysis for this particular design can range from ±O.OS fJ. for one micron pressure of the mixture to ± 2 fJ. for 2000-fJ. pressure of the mixture.

With normal use the mercury never contacts the stop­cock lubricant because the stopcock is placed slightly above barometric height on the mercury column. As a consequence of the stopcock position and the large bore of the capillary, this particular design is not too convenient for measuring pressures below the micron range. Rough estimates of the pressures in lower ranges can be obtained by applying pressure to the mercury reservoir, but these measurements are obtained at the risk of mixing the mercury and stopcock lubricant. The stopcock must be lubricated lightly so that no grease enters the capillary. If this does happen, the bore is large enough to be cleaned with a pipe cleaner with the stopcock core removed.

The speed of hydrogen separation with this design results from at least three factors. First, only an aliquot part of the collected gas is analyzed. In the particular system in which this gauge is employed, the aliquot portion is one tenth of the total. Second, the gas mixture is close to the palladium tube so that the hydrogen does not have to diffuse a great distance through other gas. Third, the McLeod gauge compresses the hydrogen about 200-fold when the mercury is immediately below the stopcock. According to diffusion theory, this should increase the permeation rate through the palladium 14-fold. If a graded seal with an inside diameter of 2 mm had been available, the compression ratio might have been made as high as high as 1000 to 1 in which case the permeation increase would have been 32-fold.

A convenient and inexpensive heater for the palladium tube can be constructed from a 50-ohm wire-wound power resistor of 100-w capacity with an outside diameter of 1t in. and a length of 6! in. The heater is run continuously at 3S0-400°C from a l1S-v variable autotransformer.

1 J. L. Brandt and C. N. Cochran, J. Metals 8, 1672 (1956). 2 Juenker, van Swaay, and Birchenall, Rev. Sci. Instr. 26, 888

(1955).

Differential Expansion Diffusion Couple Welding Device

DILIP K. DAS*

Raytheon Manufacturing Company, Waltham 54, Massachusetts

(Received October 2, 1957; and in final form, October 16, 1957)

ONE of the experimental difficulties encountered in the study of intermetallic diffusion is the preparation of

diffusion couples. Among other methods, pressure welding has been used quite successfully.l The equipment used for the pressure welding, however, has been specialized

FIG. 1. The diffusion couple welding jig, with a sandwich couple in place, ready for the furnace.

and elaborate. A simple device has therefore been designed and built, which takes advantage of the differences in thermal expansion of different high-temperature melting metals and alloys. With the aid of this simple apparatus, the existing furnace facilities of most metallurgicallabora­tories can be profitably utilized for the purpose.

The device, as shown in Fig. 1, consists of two 3-in. diam X !-in. thick 303 stainless steel plates, four !-in. molybdenum bolts threaded at both ends, and molyb­denum nuts. Adequate holes are provided symmetrically along the periphery of the plates to accommodate the bolts.

The metal disks of the diffusion system are machined to obtain parallel opposite faces. The surfaces to be welded to form the diffusion interface are finish polished on 4/0 emery paper. The disks are then degreased and stacked between the stainless steel plates and held snugly in place by the molybdenum nuts and bolts. The whole assembly is now heated in a furnace under a suitable atmosphere to a predetermined temperature for a desired length of time.

As the temperature of the assembly is raised, a gradually increasing pressure develops at the diffusion couple interface, because of the large difference between the thermal expansion coefficients of the stainless steel plates and the molybdenum bolts, provided of course the diffusion couple metals have thermal expansion coefficients at least comparable to that of molybdenum. In most cases, however, the diffusion couple metals will have larger coefficients of expansion than that of molybdenum, assuring adequate pressure at the interface. The pressure at the interface at welding temperature will be determined by the yield strength, at temperature, of the softest member of the couple. Since the welding temperature and the time at temperature can be readily controlled, highly

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:

128.192.114.19 On: Thu, 18 Dec 2014 06:23:44

Page 3: Differential Expansion Diffusion Couple Welding Device

NOTES 71

FIG. 2. The interface of a Mo- Ni couple welded in the present device at 1200°C for! hr and diffusion annealed at 1200°C for 32 hr (216X).

reproducible results are obtained. The sintering of the molybdenum nuts or the diffusion couples to the stainless steel plates can be prevented by the use of thin tungsten washers and disks.

The diffusion interface of a Mo- Ni couple which was welded at 1200°C for a half-hour in the welding device and then diffusion annealed for 32 hr at 1200°C is shown in Fig. 2. The diffusion zone consists of two primary solid solution bands with an Mo- Ni intermediate phase band in the middle.

* Techniques Department, Microwave and Power Tube Operations. I L. C. C. daSilva and R. F. Mehl, J. Metals 191,155 (1951).

Method of Continuous Measurement of Heart Diameter Utilizing

Sonic Energy* L. S. HIGGINS, W. H. MOWBRAY, AND D. P. WARD

Circulation Laboratory, Boston City Hospital, Tufts University School of Medicine, Boston, Massachusetts

(Received May 17, 1957; and in final form, October 10, 1957)

A METHOD has been developed at this Laboratory similar to that utilized by Rushmer,l for measuring

the transmission time of sound across the anteroposterior diameter of the left ventricle of the canine heart as a means of computing dynamic volume of this muscular pumping chamber.

The ventricular volume may be approximated by assuming a fairly constant base to apex length, as well as minimal change in wall thickness. That this assumption may be made has been well documented by Rushmer, et al.2

Two small 2.5X 12.5 mm barium titanate disk trans­ducers are first carefully shielded with fine copper mesh and waterproofed with neoprene. Electrical connections are made to the silvered flat surfaces with shielded wire.

The transducers are then affixed directly to the front and back of the left ventricle at open chest surgery and arranged to follow the contractile movement of the heart muscle. The transducers are polarized to vibrate in the thickness plane.

A sinusoidal signal is applied to one transducer (Fig. 1). The frequency is adjusted so that one-half wavelength, only, occurs between sending and receiving transducers, when the heart is contracted (systole). A frequency of about 10 kilocycles is used. The velocity of sound trans­mission through muscle and blood is very nearly that of sea water, 1.5 mm per microsecond.

The transmitted sound is received by the second transducer. The signal received is used as a reference for measurement of the time delay in the signal passing through the saline-muscle-blood medium. The two signals are amplified, clipped, and added; and the resultant finally rectified to produce a series of pulses, whose average level is proportional to the change in distance between the two transducers. The output signal may be viewed on an appropriate vacuum tube voltmeter. At this Laboratory a direct-writing instrument manufactured by Sanborn Company is used (Model 67-300 DC amplifier, a unit of the Model 67-1200 Polyviso).

Initial calibration is achieved by attachment of the transducers to the heart of a cadaver. With the heart squeezed to an approximate systolic volume, the frequency of the signal generator (Heath AG-9) is adjusted so that a null is achieved, preferably viewed on an oscilloscope connected to the output terminals. Any change in size from this point will cause an increase in voltage output. With proper adjustment of operating frequency, the trans­mitted and received signals will be just 180° out of phase, and will therefore cancel at ventrlcular systole. Since the system registers deviation from is point, any increase in volume will cause an increase iL output voltage propor­tional to this change.

FIG. 1. Circuit diagram of heart-measuring instrument.

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:

128.192.114.19 On: Thu, 18 Dec 2014 06:23:44