THERMAL EXPANSION OF TUNGSTEN

Transcription

1 . THERMAL EXPANSION OF TUNGSTEN S515 By Peter Hidnert nd W. T. Sweeney ABSTRACT This pper gives the results of n investigtion on the therml expnsion of tungsten (99.98 per cent) over vrious temperture rnges between 100 nd +500 C. A summry of vilble dt obtined by previous observers on the therml expnsion of tungsten is included. The expnsion of tungsten is given by the following empiricl eqution: Lt = I41 + (4.28 t t 2 )10^] where L t represents the length of the metl t ny temperture t between 105 nd +502 C, nd L the length t 0 C. Averge coefficients of expnsion for vrious temperture rnges re given in tble. NTENTS Pge I. Introduction 483 II. Apprtus 485 III. Results 485 IV. Summry 487 I. INTRODUCTION The pioneer experiments of Fink on the liner therml expnsion of tungsten were followed by the work of Lngmuir, Worthing, nd other investigtors. A summry of the results 1 of these reserches is given in Tble 1 The present reserch ws undertken for the purpose of obtining relible dt on the liner therml expnsion of pure tungsten. Expnsion determintions were mde over vrious temperture rnges between -100 nd +500 C. The uthors wish to express their pprecition for the tungsten furnished by the Fnsteel Products Co., North Chicgo, 111. Acknowledgment is lso due to Dr. W. Souder, Bureu of Stndrds, for vluble suggestions. 1 With reference to determintions mde on tungsten filments, C. W. Blke, chemicl director of the Fnsteel Products Co., sttes tht most tungsten filments contin up to three-fourths of 1 per cent of thorium oxide t 483

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3 Hidnert "I Sweeney] Therml Expnsion of Tungsten II. APPARATUS 485 Figure 3 of Bureu of Stndrds Scientific Pper No. 497 shows prt of the pprtus used in this investigtion. A detiled description will pper in forthcoming scientific pper of this bureu on the Therml Expnsion of Fused Silic. III. RESULTS A rod of pure tungsten, mm in dimeter nd 300 mm in length, ws used in this investigtion. The density 3 ws C TEMPERATURE Fig. 1. Liner expnsion of tungsten (99.98 per cent) :: g/cm t 25 C. After the expnsion determintions the chemicl composition 4 of the tungsten rod ws found to be s follows : Molybdenum, per cent; copper, per cent; rsenic, less thn per cent; bismuth, ntimony, tin, nd vndium not detected; tungsten, per cent (by difference). Direct determintion of tungsten gve vlues between nd for tungsten. s For preprtion, see Jones, Chem. nd Met. Eng., 22, p. 9; " Determined by Miss E. E. Hill, of this bureu. 1 Determined by H A. Bright, of this bureu.

4 486 Scientific Ppers of the Bureu of Stndrds I Vol. BO Seven expnsion tests were mde on the rod of tungsten for the following temperture rnges: Tests 1, 2, 3, nd 5 ech from bout 23 to 300 C; test 4 from -105 to +302 C; test 6 from 21 to 402 C, nd test 7 from 21 to 502 C. All tests except 6 nd 7 were mde in the oil bth shown t the extreme right of the figure mentioned in the preceding section. The ir furnce mrked BS18625 in the sme figure ws used for tests 6 nd 7. The seventh test ws not crried beyond the mximum temperture indicted in order to prevent oxidtion of the smple. The observtions of ll tests on heting, reduced to n initil temperture of 23 C, re represented grphiclly in Figure 1. The numbers on the observtions refer to the tests. From these dt the following empiricl eqution ws derived by the method of lest squres it = L [1 + (4.28 t t 2 ) 10" 6 ] where L t represents the length of the metl t ny temperture t between -105 nd +502 C, nd L the length t 0 C. The probble error of L t is ± L. The verge coefficients of expnsion for vrious temperture rnges given in Tble 2 were computed from the preceding eqution. Tble 2. Averge coefficients of expnsion of tungsten Temperture rnge (in degrees centigrde) Averge coefficients of expnsion per degree centigrde Temperture rnge (in degrees centigrde) Averge coefficients of expnsion per degree centigrde X10-i X10-" 100 to to to 4.3 to to to to to to to to to to to to The observtions on cooling generlly lie below the expnsion curve on heting. The mximum devition between the observtions on heting nd cooling did not exceed per cent in ny test. For the fifth, sixth, nd seventh tests the devition ws less thn per cent. Figure 2 gives comprison of the expnsion curve (pplicble from 0 C.) obtined in the present investigtion with dt from previous investigtors for the temperture rnge between 100 nd C. The vlues of Gry, Schd nd Hidnert, nd Worthing gree closely with the results of this reserch. Fink's vlue lies below the curve, nd Disch's vlues t the high tempertures lie bove the curve.

5 : Sweeney] Therml Expnsion of Tungsten 487 IV. SUMMARY This pper gives the results of n investigtion on the therml expnsion of tungsten (99.98 per cent) over vrious temperture rnges between 100 nd +500 C. A summry of vilble dt obtined by previous observers on the therml expnsion of tungsten is included. Fig D0 o TEMPERATURE -Comprison of expnsion curve obtined in the present investigtion on tungsten with dt from previous observers The expnsion of tungsten is given by the following empiricl eqution Z t = -k [l + (4.28 t * 2 )10-6 ] pplicble between 105 nd C. The coefficients of expnsion increse regulrly with temperture. From to 500 C. the verge coefficient of expnsion is 4.6 X 10-6 per degree centigrde. Tble 2 gives dditionl coefficients of expnsion for vrious temperture rnges. Wshington, August 17, J*

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