SelfSupporting High Temperature HeaterEugene L. Hansen Citation: Review of Scientific Instruments 35, 242 (1964); doi: 10.1063/1.1718798 View online: http://dx.doi.org/10.1063/1.1718798 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/35/2?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Transport study of selfsupporting porous silicon Appl. Phys. Lett. 66, 1098 (1995); 10.1063/1.113584 Photoelectric properties of selfsupporting porous silicon Appl. Phys. Lett. 64, 3118 (1994); 10.1063/1.111366 SelfSupporting Carbon Resistance Thermometers for Use at Low Temperatures Rev. Sci. Instrum. 39, 925 (1968); 10.1063/1.1683544 SelfSupporting Heating Element Rev. Sci. Instrum. 31, 306 (1960); 10.1063/1.1716962 Preparation of Thin SelfSupporting Carbon Films Rev. Sci. Instrum. 31, 197 (1960); 10.1063/1.1716924

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242 NOTES

Self-Supporting High Temperature Heater EUGENE L. HANSEN

Sandia Corporation, Albuquerque, New Mexico

(Received 20 September 1963)

A SMALL, compact heater has been designed that is suitable for heating small areas in a vacuum or a

controlled atmosphere. The requirements that led to the heater's development were (1) a maximum temperature capability of 1000°C, (2) a high resistance, low current characteristic, and (3) a simple, compact configuration. These requisites limited the materials that could be used and made it desirable that there be a minimum of support necessary for the heater element.

Cylinder and cage designs, although simply constructed, were undesirable because of their high current require­ments. A single spiral heater has the desirable low current characteristic, but it would have required an overly com­plex support structure. Each turn must have an insulated support to prevent sagging, and the insulation must be shielded from the direct heat of the element. An additional complication is that a double heat shield is necessary at high temperatures.

In order to take advantage of the low current character­istic of the single-spiral element, but to avoid its support complexities, a double-spiral heater element was designed. It is shown in Figs. 1 and 2. The element, constructed of

FIG. 1. Double spiral element.

FIG. 2. Exploded view of element and heat shields.

molydbenum, consists of two spirals wound with the same pitch but in opposite directions. The spirals are assembled one inside the other and are spot welded where they in­tersect. The double-spiral element is the electrical equival­ent of a single-spiral element with the same length but twice the width of the strips in the double-spiral assembly. This design eliminates sag in the heater and requires support only at the ends, which are also the power-feed points.

The heater has been used successfully as a substrate heater in the evaporation of metal films. Temperatures up to 1000°C were attained with a current of 75 A.

Mechanical McLeod Gauge for Accurate Measurement of Pressures in the

5 to 500", Range* JOHN T. PARKt

University of Nebraska, Lincoln, Nebraska

(Received 6 November 1963)

I N many experiments it is necessary to make accurate and rapid pressure measurements in the pressure range 5

to 500 fJ.. The use of standard McLeod gauges in this pres­sure range is often difficult, especially if a cold trap cannot be used with the test gas. I~ addition, the use of a McLeod gauge requires considerable time if accurate measurements are desired. This article describes a simple mechanical McLeod gauge suitable for extending the sensitive range of commercially available mechanical pressure meters down to pressures as low as 5 fJ..

The pressure measuring device is shown in Fig. 1. It consists of a piston arrangement using a Bellofram rolling diaphragml to permit simple, leak tight construction of the piston assembly and a Decker pressure meter2 that is capable of measurIng pressures in the pressure range 0.03

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NOTES 243

FIG. 1. Schematic diagram of the me­chanical McLeod gauge.

BELLOFRAM ROLLING

DIAPHRAGM

DECKER

PRESSURE SENSOR

306-2F BALL VALVE

TEST

SYSTEM

to 0.6 mm Hg. The temperature of the Decker pressure meter has been held constant to ±0.06°C, and its output voltage was measured by a potentiometer making it pos­sible to obtain readings with 2% standard deviations.3

The piston assembly was fixed with stops so that its posi­tion at the extremes of its motion was accurately repeat­able. The test system was connected to the mechanical McLeod gauge by a ball valve.

With the ball valve open, the system's pressure could be read directly with the Decker pressure meter. If the pres­sure was lower than could be measured with the Decker

60r--------r--------r--------r--------~~~

50

III

~ 30

~ CL 20 ..I C(

j::: i 10

0.1 0.2 0.3 0.4 PRESSURE AFTER COMPRESSION (mm Hg.)

FIG. 2. Pressure in the test system as a function of the pressure of the compressed gas.

pressure meter, the ball valve was closed, the piston depressed, and the pressure of the compressed gas was measured.

The ratio of the pressure of the compressed gas to the original gas pressure w;J.s 7.47±0.08 (see Fig. 2). This permitted the accurate measurement of pressures as low as 5 p.. The total pressure range of the mechanical McLeod gauge system was 0.005 to 0.6 mm Hg. The standard deviation determined from the uncertainty in the Decker pressure meter's readings, the calibration of the compres­sion ratio, and the uncertainty in the standard McLeod gauges used in calibration was 3% from 0.008 to 0.05 mm Hg and 2% from 0.05 to 0.6 mm Hg.

It should be noted that the mechanical McLeod gauge was an integral part of a larger piece of apparatus, and, as a result, the volume of the compressed gas was larger than would otherwise be necessary. Careful construction, with the aim of improving the compression ratio, could greatly improve this ratio and extend further the pressure range of the device.

* Supported by the U. S. Atomic Energy Commission. t During 1963-64 at the Physics Department, University College,

London, England. 1 Class 4C-300-300 Rolling Diaphragm, Bellofram Corporation,

Burlington, Massachusetts. 2 Model 306-2F, 0 to ±O.3 in. H20, The Decker Corporation,

Bala-Cynwyd, Pennsylvania. a J. T. Park and E. J. Zimmerman, Phys. Rev. 131, 1611 (1963).

Fabrication of Epoxy Electrical Lead Insulation for Pressure Vessels*

JAMES A. CORLL

Sandia Laboratory, Albuquerque, New Mexico

(Received 7 October 1963)

IN high pressure experimentation the method of intro-ducing electrical leads into the high pressure region

often consists of a metal cone and an insulating conical shelP The difficulty involved in obtaining an initial pres­sure seal with good electrical insulation has lead to the investigation of various insulating materials, and, in recent years, the use of epoxy has been reported by several sources.2- 6 The pressure vesseF used in this laboratory was initially supplied with electrical leads having epoxy in­sulation made by dipping the metal cone in Eccocoat D30.8 This note describes a method of fabricating the electrical insulation that eliminates the problem of making an initial pressure seal. The techniques and modifications described apply to a rather large pressure chamber, but should be applicable to many pressure vessels that now use a cone and shell electrical lead.

The metal cones were machined to the shape shown in Fig. 1 from BeryIeo 25 rod and large thermocouple wire

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