SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

ROTATING MACHINES FOR EXTREME ENVIRONMENTS

D. Irani - C. S. SmithAiResearch Manufacturing Company*

Torrance, Cal ifornla

ABSTRACT

This paper is an approach to materials selection anddesign considerations of rotating machines subjectedto difficult environmental conditions.

INTRODUCTION

Modern space travel and exploration has made revolu-tionary changes in the environmental requirements ofrotating machinery. In the past five years require-ments for operation in hard vacuums (10'9 TORR),5000Cambients, high radiation levels, alkali atmospheres,have become commonplace in the aerospace industry.

This paper attempts to describe the problems affect-ing the design of a rotating machine. Such problemsas relate to conductor and magnetic materials, insu-lation systems, bearings, and performance.

CONDUCTORS

Table I shows the advantages and disadvantages ofseveral commercially available high temperature con-

ductors. The aging characteristics of these conduc-tors are shown in Figure I.

TAI

We have successfully used 28 percent nickel-clad cop-per conductors in ambients over 3000C. For tempera-tures over 5000C, Cufenic or nickel-iron-clad copperis the most suitable.

MAGNETIC MATERIALS

A number of magnetic materials, comrnercially avail-able, are suitable for use as stator and rotor lami-nations in high-temperature rotating machines. Cobaltalloys have the most stable high-temperature, magne-tic properties and the highest Curie temperatures,but are radioactive in the presence of an irradiatedenvironment. Unoriented silicon steels also have ex-cellent high-temperature properties and do not be-come radioactive.

TEMPERATURE EFFECTS ON MAGNETIC MATERIALS

The greatest influence of temperature on magneticproperties occurs just below the Curie point or nearthe temperature of a phase transformation. The in-tensity of magnetization of a magnetic material de-creases when the temperature increases.

Table II shows the Curie temperature of various mag-netic materials and discusses the feasibility ofoperation in a 5000C ambient.

BLE I

COMPARISON OF HIGH TEMPERATURE CONDUCTOR MATERIALS

*A Division of THE GARRETT CORPORATION

620

Resistivity Upper TemperatureName of Ohm-Cir i - iC Advantages DisadvantagesConductor Mil-ft at°C 12-20 Awg 21-40 Awg

Nickel-plated 11.5 400 Not High conductivity; Low oxidationcopper Recommended good ductility resistance

Nickel-clad [3.5 500 400 Good oxidation resist- Resistance changescopper ance good ductility in fine sizes at

high temperature

Stainless 14.3 650 650 Stable electrical 30 Awg, fine wiresteel clad (21-30 Awg) resistance at high limit; chemicalcopper temperature; good resistance

oxidation resistance

Cufenic, 13.1 650 650 Stable electrical None in temperature(nickel-iron- resistance; good rangeclad copper) oxidation resistance;

good ductility

Nickel-clad 11.7 750 750 Stable electrical High cost in largesilver resistance; high sizes; radioactive

conductivity, good after exposure toductility, good radiation; mechan-oxidation resistance Ical fatigue; high

expans ion

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

\\\ /~~~NO. 1'8 NICKEL-CLAD SILVE'R0.3

| | . ~~~~~NO. 30 NICKEL-CLAD SILVER

NO. 18 CUFEN IC(NICKEL-IRON-CLAD COPPERR)>

3 wNO. 30 STAINLESS STEEL-CLAD COPPERNO. 18 STAINLESS STEEL-CLAD COPPER

Ol I 200 300 400 500 6 0

AGING TIME - HOURS AT 500 C

Figure 1. Percent Change in Resistance vs Aging Timeat 5000C for Two Sizes of Five Magnet Wire Conductors

It is generally found that saturation induction, resi-dual induction (Bres) and coercive force (Ho) de-creased with temperature. Figure 2 shows the reduc-tion in Brys and Ho and Figure 3 shows the reductionin saturat?on for 27 percent cobalt Iron. Figure 4shows the hysteresis loops at various temperaturesfor 3 percent silicon iron. Figures 2 and 3 when re-lated to Figure 4 show the high temperature stabilityof Cobalt alloys.

There is a significant reduction in core loss withIncrease in temperature. This is demonstrated byFigure 5 for 27 percent cobalt Iron.

Magnetic materials undergo aging at high temperaturessimilar to that experienced with conductor materials.Figure 4 shows the change in the hysteresis loop atroom temperature (240C) after exposure of 3 percentsilicon iron to 8000C.

AiResearch uses Silicon steel for temperatures up to4000C. Cobalt alloys are preferable for temperaturelevels above 400° and up to 8500C.

EFFECT OF NUCLEAR IRRADIATION ON MAGNETIC MATERIALS

Nuclear irradiation causes appreciable changes instructure sensitive properties, viz: permeability,coercive force, and residual induction. Saturationinduction, a structure insensitive property, exhibitsnegligible change. Materials with high initial per-meability and low coercive forces (superalloy) aremost affected. The initial and maximum permeabilitiesof these alloys decrease and their coercive force in-creases. Materials of relatively low initial perme-ability and higher coercive forces (silicon-irons andsilicon-aluminum-iron exhibit little or no change.

TABLE II. FEASIBILITY OF OPERATION OF SOFT MAGNETIC MATERIALS

Materi al

Silicon-Iron 2 Si4 Si8 Si

II Si

50 Co,49 Co,Coba l t

3 Mn (Permendur)2 V (2 V Permendur)Iron 27 Co

Nickel-Iron65 Ni (65 Permalloy)

79 Ni (Permalloy)

45 Ni, 25 Co, 7.5 Mo.(Permi nvar)

79 Ni, 4 Mo (modified P-alloy)79 Ni, 5 Mo (Supermalloy)4 7 N i, 3 Mo (Monimax)43 Ni, 3.25 Si (Sinimax)76 Nii, 1.5 Cr, 4 Cu (Mumetal)36 Ni, (Invar)42 Ni50 Ni (Deltamax)

Iron

Cobalt

Nickel15 Al, 3.3 Mo (Thermenol)

ICurie Tempera-ture, Deg C

756752720690

980980980

620

580

535

460400510510450275400510

770

130

358400

I

Comment on operationat 500 C ambient

Usable, subject to degradation of properties

Usable when part not subject to irradiation

Usable, highly strain sensitive, should beceramic cased

May have limited application where there isno temperature rise

Higher resistivity at the expense of lowerCurie point

Curie temperature too low

Must be protected against oxidation

Long half life; may be undesirable for radiation

Curie temperature too lowCurie temperature too low

621

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SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

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00 200 300 400 500A.10052

TEMPERATURE, DEGREES CENTIGRADE

Figure 2. Residual Induction and Coercive Force vsTemperature for 27-Percent Cobalt Iron

t6A-10054

Figure 4. Effect of Temperature on Magnetic GrainOriented 3-Percent Silicon-Iron (Curie TemperatureCirca 7500C)

Magnetic data taken periodically during irradiationshows progressive changes in properties with increas-ing dosage. The initial characteristics of magneticmaterials may be restored to the prior conditionsby reannealing but this technique poses difficultiesfor wound cores.

Table II shows the classification of Magnetic Materi-als for high radiation and high temperature stability.

1oMAGNETIZING FORCE - OERSTEDS

A -5952Figure 3. Normal Magnetization Curves for 27-Percent Cobalt Iron

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SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

O 100 2Q0 300 u00 500

TEMIPERATVRE - DEGREES CENTIGRADE

Figure 5. Core Loss vs Temperature for 27-PercentCobalt Iron

TABLE III

CLASSIFICATION OF MAGNETIC MATERIALS FOR HIGHTEMPERATURE AND HIGH RADIATION LEVEL ENVIRONMENTS

VG = very good

U = usable

P - poor

NU = not usable* = becomes radioactive

INSULATION

The insulation system for an electrical machine con-tains many different, interrelated and compatiblecomponents. The insulation may be required to with-stand extreme temperature, hard vacuum, radiation,and exposure to alkali vapor.

AiResearch has attained satisfactory systems withthe use of ceramic coated wire, ceramic based encap-sulant, glaze, and glass bonded mica as slot materi-al, In applications where the temperature is lessthan 4000C. However, where severe vibration Is en-countered, a bore seal Is recommended since the en-capsulant and glaze flake under these conditions andcause bearing contamination.

TEMPERATURE EFFECTS

Insulation resistance decreases very rapidly with in-crease in temperature. The general results of hightemperature exposure include: chemical and physicalchange, thermal expansion, thermionic emission,andthermal shock. The principal chemical and physicalchange is actual breakdown of the structure. Theprincipal electrical change is severe lowering of thedielectric strength and breakdown voltage of thematerials.

RADIATION EFFECTS

Radiation exposure affects both the mechanical andelectrical properties of a dielectric. Mechanicaldegradation takes the form of embrittlement, loss offlexibility, and change of thermal conductivity. Theelectrical characteristics (insulation resistance anddielectric constant) are adversely affected. In addi-tion, the breakdown of the surrounding atmosphere may

give rise to corona.

Not all effects of high energy radiation on materialsare necessarily degrading. For instance, the insulat-ing characteristics of polymers are actually improvedwhen subjected to intense radiation fields. This phe-nomena has opened up a new field for improvino exist-ing dielectric materials and synthesizing new materi-als by means of radiation exposure.

EFFECTS OF HARD VACUUM

If the pressure is reduced to less than the vapor pres-sure of any constituent material of the insulationsystem, outgassing occurs. This reaction may cause

structural degradation and change in the electricalproperties, particularly dielectric strength. In addi-tion, the volatile matter given off may attack othermaterials, especially the bearing lubricants.

Ceramic and glass-based materials do not exhibit out-gassing characteristics and are therefore, excellentmaterIals for hard vacuum environments.

In actual designs for extreme environments, it isnecessary to employ volatile materials as binders forthe slot insulation and magnet wire lubricants. Thesematerials must be completely removed prior to encap-

sulat ion.

ALKALI VAPOR EFFECTS

Alkali vapors are extremely deleterious to insulatingmaterials. In some instances, the physical state ofthe insulating material changes from a solid configu-ration to a powdered form. It is general practice toshield the insulation from the alkali environment

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Probablestabili ty

Radiation Temperature instability stab i ity combined

(10i" fast nvt) (500 C) environment

Magnetic cores

Silicon-iron(unoriented) VG VG VG

Silicon-iron(grain oriented; VG G G

27 cobalt-iron _* VG G

35 cobalt- iron - G G

2 V Permendur VG* G G

Supermendur P P

16 aluminum-iron VG NU NU3 Mo-Thermenol - NU NU12 aluminum-iron - P p

Supernal loy NU NU NU4-79 Mo-Permalloy NU NU NUMu-metal NU _

50 nickel -iron P NU NU50 nickel I-ron

(oriented) P NU NUFerrites VG NU NUPowder cores VG NV NU

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

with bore seals. This method has proven very effec-tive for sodium and potassium pumps.

MATERIALS

Inorganic Insulation materials such as glass, mica,ceramic, asbestos, etc. must be used In equipmentwhere the operating temperature exceeds 250 C. Attemperatures above 7500C, refractory oxides, such asberyllia and alumina have to be considered.

Conductor Insulation. Fibrous glass coveredconductors are Impregnated with a ceramic and glasspigmented low temperature binder. After the windingIs in place, firings up to 7000C remove all organicresins and fuse the powdered glass and ceramic, with-out disturbing the fibrous form of insulation. Thismaterial Is convenient to handle but requires greaterwinding space because of the thickness of the fibrousglass.

Enamel covered conductors are available in two types.The first type has a flexible ceramic covering whichhas already been fired and only the lubricant mate-rial must be driven off. The other type has ceramicor glass material in a flexible binder and Is firedafter the conductor is wound in place.

The pre-fired material is difficult to handle, withthe consequence that the reject rate has been highIn production. AlResearch Is presently evaluatingthe post-fired enamelled wire. The results lookpromising.

Slot Insulation. Sandwich-type insulationmaterials consist of a fragile layer of excellent in-sulation (mica) covered on one or both sides withglass cloth, and impregnated with a low-temperaturebinder, which is later removed. This type of materialhas been successfully used at temperatures upto500°C.At temperatures around 6000C, mica loses its waterof crystallization and crumbles to a powder.

Molded-type slot liners of various ceramic materialsshow the greatest promise for extremely high tempera-tures. There are severe limitations however, as tothe sizes and shapes which can be molded. Aluminahas been successfully used and Beryllia, althoughexpensive, has excellent thermal conductivity.

A third method of providing slot insulation is tocoat the slots directly by a process similar to por-celain-enameling. The principal problem with thismethod has been that of maintaining a uniform Insu-lation thickness over all parts of a stator. Theceramic coating process has the greatest potentialin small machines where neither sandwich nor moldedslot liners are suitable.

Synthetic Mlca. Synthetic Mica has produced thegreatest improvement in high temperature insulation,since it has a dielectric strength of 7000 volts/milas compared with natural mica which Is 4500 volts/mil. Synthetic Mlca can be used up to temperaturesof 600°C. When combined with molded glass, thismaterial is recommended for applications up to 9000C.It is moldable and machinable.

Encapsulants. The physical, thermal, chemical,and electrical properties of the encapsulating com-pound virtually control the success of a high-tem-perature electrical machine. The requirements foran encapsulant are: (I) posses good dielectricstrength, (2) bind the conductors and the statorslots together for vibration resistance, (3) conduct

the heat losses to the cooling surfaces; (4) protectthe conductors against chemical attacks from externaland Internal environments; (5) withstand the environ-mental temperatures and chemicals, and (6) preventthermal stresses due to temperature gradients in vari-ous parts of the machine.

The encapsulating material found best to date hasbeen ceramic cement. It has excellent thermal sta-bility up to 8000C. Since the cured ceramic is hygro-scopic it is necessary to seal the surface with aglaze.

BEARINGS

Both ball and journal bearings have been consideredfor extreme environment applications.

BALL BEARINGS

The most attractive choice is the self-lubricatedball bearing since it requires no auxiliary equip-ment or lubricating system.

Tests by a bearing manufacturer have demonstratedbearing operation at 5000C with a radial load of35-pounds at 7500 rpm for 125 hours. At the con-clusion of the tests, the bearings had not failed.Improvement in the ball separator design provideanticipation of 500-hr life in the near future.

Dry bearings with consumable separators have beenrun in our laboratory, continuously for 8000 hours.These bearings were one-half (1/2) inch diameterand lightly loaded.

Figure 6. Motor Assembly, 1/2 HP, 180,000-RPM, HighTemperature, Solid Rotor, Induction Motor

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SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

JOURNAL BEARINGS

Gas Lubricated. Extreme temperatures and highspeeds favor gas bearings. Gas bearings can beeither hydrostatic or hydrodynamic.

The hydrostatic bearing uses pressurized gas. Thisbearing is less expensive to manufacture but in-creases system complexity due to the auxiliaryequipment required. Hydrodynamic bearings areself-pressurizing and self sustaining above a crit-ical speed.

We have successfully operated a 1/2-hp motorequipped with hydrodynamic bearings at 180,000 rpm,where the bearing temperatures reached values over

4000C. The motor is shown in Figure 6.

Dry Lubrication. A dry-lubricated journal Is a

promising approach for short-term operation. Thematerials which appear to be most appropriate forsuch a bearing are: tungsten carbide or tool steelfor shaft, and the Westinghouse silver-teflon-tung-sten diselenide composite material as the journal.Graphite and lead monoxide films are also to be con-sidered, since these have a higher temperature limitthan the composite. Finally, carbide on MoS2-silicatefilm treated carbide with an oil-lubricated break-inand run dry should run to 13000C before gallingoccurs.

PERFORMANCE

The method of design for a rotating machine underextreme environment remains the same; however, thebehavior of the various materials require a changeIn design philosophy.

It is very Important that the internal temperatures ofthe machine be computed accurately to properly definethe environment for the materials chosen.

ELECTRICAL DESIGN

For magnetic materials operated well below the Curietemperature the permeability is not affected but theiron losses decrease with increasing temperature.At high temperature the lower density of the air andat high altitude the lower pressure of the air re-sult in a reduction in windage losses. The only los-ses that significantly increase are the 12R losses.The Increased temperature and the lower conductivityof the magnet wire used cause the increase in 12Rlosses. Thus, laminations of high ambient tempera-ture motors are designed to incorporate a larger con-ductor area by an Increase in slot size and a reduc-tion in tooth dimension.

HEAT TRANSFER

The general approach to motor cooling Is to definethe high temperature points in the system and tolocate them where they will be cooled by radiationmost efficiently, or to provide a path for thermalconduction to a radiating surface. Heat transfer ina hard vacuum must be almost entirely by radiation.Convective heat transfer to the surroundings Is in-

significant because of the extremely low density airin the intervening space. The extent to which heattransfer from the shell can take place by conductionwill depend on the type of mounting used.

Heat rejection by radiation obeys the Stefan-Boltz-mann equation.

Q = ca 0 A e (T14 - T24)where Q = heat transfer rate, Btu/hr

C = Stefan-Boltzman Constant = 0.1714 x10 8 Btu/(hr)(ft)2(R)

0 = Shape factorA = Area of radiating surface, sq ft

e = emissivity

TI and T2 are the absolute temperature

(Rankine) of the radiating and receivingsurfaces respectively.

A good approximation to the external shape of a motoris a right circular cylinder. The shape factor is 1.0for a radiating body which is relatively small com-pared to the surroundings that enclose it. An emis-sivity of 0.9 is attainable in a surface that willwithstand both high temperature (5000C) and low pres-sure (150,000 ft altitude) without significant de-terioration. A method of surface treatment withnickel oxides reputedly produces an emissivity of0.95 in this temperature range. Roughing the sur-face increases the effective emissivity considerably.These treatments will help the heat rejection problem.

For this approximation of the motor shape, togetherwith the assumptions that the heat flux and tempera-ture In the motor shell are uniform, the Stefan-Boltzmann law leads to the plotted motor shell tem-peratures of Figure 7 as a function of sheil heat re-jection (power dissipation) at ambient compartmenttemperatures of IOOOF and -65F. These curves indi-cate the shell temperature at various shell heatfluxes at the two ambient temperatures for radiationheat transfer.

Figure 8 is a similar plot, with the air at sea levelpressure. Heat dissipation is, therefore, by naturalconvection and radiation. The calculations assume ahorizontal cylinder three Inches in diameter. Theactual motor dimensions are not important becausethe curves show that free convection cooling of themotor is small relative to the heat transfer by radi-ation in the 1000 F environment where the motor tem-peratures are highest. These curves are useful inestimating the motor case temperature.

SHELL HEAT REJECTION - WATTS PER SQ IN. OF SHELL A-IWSS

Figure 7. Radiation Heat Transfer From Motor Shell

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SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

4 5 6 7 8 9 10 12 13 14 15 16 7

THFLL HEAT REJECTION - WATT S'ER SO IN. OF SHELL A-105

Figure 8. Radiation and Natural Convection HeatTransfer from Motor Shel]l

This analysis is somewhat Idealized because the heatsources within the motor are not uniformly distribu-ted and, hence, the heat flux from the shell willprobably not be uniform. Also, the radiation fromthe shaft of the motor extending from the end of theshell was not considered in the analysis and mayplay a major role in the cooling of the bearings.

In a recent space application it was necessary for a

squirrel cage Induction motor to withstand a stalledcondition for 600 seconds with full power applied ina hard vacuum. Cooling of the motor in this casewas almost entirely by radiation. Computer studies,

utilizing a passive network composed of resistanceelements representing various heat transfer coeffi-cients and capacitors representing heat capacitiesto the individual parts showed that the highest tem-perature (that of the rotor) was approaching 5200C.

GENERAL COMMENTS

There is no set solution to all environmental prob-lems. The specification requirements must be evalu-ated in the entirety before a complete system can beproposed. If only extreme temperature is involvedwithout radiation, then Hyperco is more stable thansilicon steel. With radiation, the choice is siliconsteel. The cooling medium may determine the environ-mental system; if for example, an Inert gas is present,then oxidation may not be a problem.

In a recent induction motor design, we chose copperbars over aluminum for strength at high temperatures.However, we created a major problem, namely, that ofpreventing the copper from oxidizing. Due to asmall air gap, the only practical solution turnedout to be nickel plating. We also considered seal-ing the motor and using a pressurized inert gas likehelium. Although expensive, the gas solution, inaddition to reducing oxidation, would add convectioncool ing to a rotor that was restricted to radiat Ioncooling because of the high vacuum requirements.

Extreme care must be used in the choice of housingand shaft materials so that the coefficients of ex-pansion will not cause stress and distortion. Wehave found 17-4pH to be an acceptable choice forgeneral extreme environment use.

Since the materials which are acceptable for largerotating components may not be acceptable for smallcomponents, it becomes apparent that prototype sys-tems must be assembled for specific applications.

REFERENCES

1. W. W. Pendleton, 'Advanced Magnet Wire Systems" Electrotechnology, October 1963.

2. H. S. Saunders, "The Use of Ceramic Materials in High Temperature Electrical Apparatus," Insulation,May 1963.

3. M. M. Pearcy, "High Temperature Materials for Encapsulation," Special Research Bibliography SRB-60-13,Lockheed Missiles and Space Division, Lockheed Aircraft Corporation, ASTIA-No. AD248358, November, 1960.

4. G. E. Owens, "Encapsulating, Potting, and Embedding Materials for Electronic Compoents and Modules: AnAnnotated Bibliography," Special Research Bibliography SB-61-50, Lockheed Missiles and Space Division,Lockheed Aircraft Corporation, ASTIA-No. AD 265 866, August 1961.

5. H. B. Harms, J. C. Fraser, "Ultra High Temperature (5000C) Power Transformers and Inductors," SpecialtyTransformer Department, General Electric Company, WADC TR 59-348, July 1959.

6. J. Bateman, "New Ceramic Insulations," General Electric Company: Technical Survey, Vol. 16, No. 47,December 3, 1960.

7. North American Aviation, Inc., "Bi-Monthly Technical Progress Report for Development of High TemperatureAircraft Electrical Systems," Report No. 20, ASTIA No. 247 669L; Report No. 21, ASTIA No. 252 388L; andReport No. 23, ASTIA No. 261 017L.

8. J. B. Rust, C. L. Segal, M. Bart, "Development of Ultra High Temperature Dielectric Materials for Embed-ding Electronic Parts, "System Development Laboratories, Hughes Aircraft Company, Quarterly Report,ASTIA No. 240 781, 1959; Final Report, ASTIA No. 256 721, 1961.

9. General Electric Company, "Application and Performance of Insulations for 5000C Hypersonic AircraftGenerators," AIEE Aero-Space Transportation Conference, Conference Paper No. CP61-887, 1961.

10. N. E. Poulos, S. R. Elkins, J. D. Walton, "Investigation of High Temperature Resistant Materials,"Georgia Institute of Technology, Quarterly Report No. 20, ASTIA No. 256 259, 1961.

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SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE / JUNE 1965

REFERENCES (CONTINUED)

II. Synthetic Mica Company, "Development of Ultrahigh-Temperature Dielectric Materials for Embedding andEncapsulating Electronic Components,," ASTIA No. 265 499, 1961.

12. P. Lloyd, "High Temperature Transformers--A Review," Royal Radar Establishment, Ministry of Aviation,R.R.E. Technical Note No. 652, May 1959.

13. D. I. Gordon, "Environmental Evaluation of Magnetic Materials," January 1961.

14. J. F. Ahearn, M. I. Meltzer, "Development of High Temperature Transformers with New Configurations forMissiles and Aircraft," Microwave and Power Tube Division, Raytheon Company, ASTIA No. 256 785, Novem-ber 1960.

15. H. B. Harms, J. C. Fraser, "Ultra High Temperature (500C), Power Transformers and Inductors," SpecialtyTransformer Department of General Electric Company, WADC TR 59-348, July, 1959.

16. Margrave, John L., "Equilibrium Considerations for Interaction of High Temperature Materials with TheirEnvironment." Symposium: "High Temperature - A Tool for the Future," 1956 Stanford Research Institute,University of California.

17. A.Goldsmlth, T. E. Waterman, "Thermophysical Properties of Solid Materials," Armour Research Foundation,WADC TR 58-476, January, 1959.

18. R. A. Ditaranto, J. J. Lamb, "Preliminary Investigation of Hyper Environments and Methods of Simulation,"Part 1, WADC Technical Report No. 57-456, AD 142002, July, 1957.

19. C. Gazley, Jr., W. W. Kellogg, E. H. Vestline, "Space Vehicle Environment," A Paper Presented at theNational Summer Meeting of the Institute of Aeronautical Sciences, July 8-11, 1958.

20. C. F. Valach, V. D. Elarde, R. M. Soria, "Temperature Radiation and Chemical Effects." Materials Manual1, Amphenol.

21. A. 0. Allen, "Effects of Radiation on Materials," United States Atomic Energy Commission Report MDDC-962,Massachusetts Institute of Technology, Cambridge, Massachusetts, May 20, 1947.

22. E. L. Mincher, "Summary of Available Data on Radiation Damage to Various Non-Metallic Materials," UnitedStates Atomic Energy Commission Report KAPL-731, Knolls Atomic Power Laboratory, Schenectady, New York,April 2, 1952.

23. Convair, "Nuclear Radiation Damage to Aircraft Materials," Information Brochure FZM-9-035, Fort Worth,Texas, November I, 1957.

24. John W. Born, "A Study of the Effects of Nuclear Radiations on Elastomeric Compounds and CompoundingMaterials," WADC Technical Report 55-58, Part IV, November, 1958.

25. William J. Anderson, "High-Temperature Bearings," Machine Design, November 5, 1964.

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