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An early method of vacuum— melting tantalum
Ipri/, 1952
;'acu.m,
portions which had been anodised varied with the thickness of the oxide coating. Those anodised at low voltage were identical to the untreated aluminium whereas those anodised at I lOV remained substantially undamaged except for numerous pinholes. T h e reflectivities o f the bare aluminium and the mirror anodised at l l 0 V measured at 12 ° angle of incidence, after exposure were (in ";~ reflection) : 4,60o ~, 5,3oo x 5,7ooA 6,oook Untreated Aluminium 32 Anodised iIoV .. 86~-
35 84~
36 83
I'./. l l
N.. .'
MAY I SUPPLEMENT Dr. G. L. Miller's comprehensive and well balanced article on Applied Vacuum Metallurgy in ' Vacuum ' J a n u a r y , 1952, 19-32 by a few historical comments on the production and use of tantalum metal, in the development of which I have taken a modest part as a junior scientist and assistant to Dr. W. Von BoRon, the inventor o f the first method of the production of ductile vacuummelted tantalum in 19021 . T h e development o f the
36 83
T h e oxide layer must have remained substantially intact because when viewed at glancing incidence the interference colours were the same as those on treated unexposed mirrors. L. HOLLANI) N. SUTHERI.AND Research Laboratories, W. Edwards & Co. (London) Limited, Lower Sydenham, London, S.E.26. England. 5th September, 1952
References HASS, G:, J. Opt. Soc. Amer., 39 (July 1949) 532-54 o. LOMER, P. D., Proc. Phys. Soc., 63 (Oct. 195o) 8!8-819. WEISKIRCHNER, W., Z. Natmforsch., 6A (Sept. I95I) 5o9-5IO. WALKENHORST,W., Naturwiss., 34 (1947) 373. w~Beo
~
An Early Method of V a c u u m Melting Tantalum Sommaire L'AUTEURRAPPELLEUNE TECHNIQUEde fusion sous vide, d6j&
ancienne, due it O. A. Simpson et W. Von Bolton et employ6e par Siemens et Halske it Berlin de I9o3 it 1912 pour la fabrication de filaments de tantale pour les lmalpes it incandescence. II donne des d&ails du proc6d6 et un croquis de l'appareil de fusion alors employ6. L'auteur est d'avis que cette m6thode classique offre toujours des possibilit6s pour le laboratoire de recherche moderne.
VACU U M FU I~NACF__.0005) A.O..~1 M I)SON ~W~. B O L T O N
15~J
melting technique as well as the rolling and drawing for production purposes was due to the late electrical and mechanical engineer Otto Archibald Simpson, and it was used between 1903 and 1912 for the manufacture of filaments for incandescent lamps in the Siemens & Halske factory at Berlin-Charlottenburg (now Osram, Berlin). Apart from lamp filaments, dental and surgical instruments as well as special laboratory tools like dishes were made from • vacuum-melted tantalum metal. The vacuum sintering process was used at a later date for a multiplicity of technical purposes, but not for lamp filaments (the lamp became obsolete and was gradually replaced by the tungsten lamp since 1911)2 ,More than 60 million tantalum lamps with filaments ranging between 0.03mm. and 0.08 ram. diameter were produced between 1903 and 1912~, requiring an amount of ductile, vacuum-melted tantalum of the order of one ton 4. A sketch showing the principle of the melting apparatus, which was used in the Siemens & Halske factory'~ is to be found in the book on powder metallurgy by Kieffer and Hotop ~. The sketch attached to this note has been made from memory by the writer. It has been repeatedly shown as a lantern slide in lectures on industrial applications of vacuum techniques within the last few years. Though the sketch is essentially self-explanatory, I may mention a few points. The pressed tantalum powder pellet, weighing 80-100 grams, was resting on a tantalum sheet of about 2mm. thickness. The ' a r c stabilizing' cathode of the direct current arc (50-80 Volts, 50-300 Amps.) consisted of a mixture of Ta and TaO~ (the dissociable browrr oxide) or according to a later suggestion 7 of a mixture of W and BaO ; the first mentioned having remained the standard procedure, The pressure at which the arc was started was about 5 × 10 3 mm. Hg (two-stage reciprocating oil pump). It then went through a maximum as a result of degassing an:t oxide dissociation, and at the end of the melting cycle was about 5 ~: 10 2 mm. Hg. The melting took a few minutes and the pellet, which had a considerable surface tension, was kept liquid for one to two minutes. This could be observed by the vibrations of its surface. The melting cycle was then broken
160
off and after cooling down air was admitted, whereupon the pellet was turned upside down and melted again. During the melting the cathode was manually moved around the pellet in a few mm. distance and the current was controlled carefully by a variable series resistance in order to keep the pellet at the required even temperature. This was carried out by specially trained ' unskilled ' operators. The finished malleable ' lenses ,8 consisted of one to six crystallite,~ and were rolled down on hexagonal-profile steel rollers, to about 1.5mm. and then drawn through drawing plates made of steel to about 0.3mm. and then through diamonds. I vividly remember the earlv times, when 1,000 metres of 0.05ram. wire were a day's target. I think that with obvious adjustments to the present 'state of the a r t ' the ' classical' vacuummelting method I have sketched has still some potential applications in the modern research laboratory. M. PIRANI 2, The Clone, Kingston Hill Surrey, England. 3rd January, 1952
References J BOLTON, W. VON., Z. Electrochem., No. 3, (19o5), 45-5 l ' D a s Tantal Seine Darstellung und Seine Eigenschaften.' 2 GANSWlNDT, S., WerkstoJy Handbuch der NichteisenMeta~le, Vol. 4, (Beuth-Verlag, Berlin, 1931). ;* STROBEL, W., Metall, 6, No. I Z I 8 , (1952), 560-563 .
' Metalle im Dienste der Glfihlampe.' * SIEMENS,A., Engineering, 87, (April 30, 19o9), 6ol. ' German Patent I55,548 (19o3).
'~ KIEFFORS, R., HOTOP, W., Pulvermetallurgie und Sinterwerkstoffe, 2nd Edition, (Springer-Verlag, Berlin, I948), 250. U.S. Patent 873,958 (19o7) SIEMENS & HALSKE, LAMPWORKS, (P'let in English), Tantalum and Its Technical and Scientific Applications, (1912), 6, Fig. 4.
;'acu.m,
portions which had been anodised varied with the thickness of the oxide coating. Those anodised at low voltage were identical to the untreated aluminium whereas those anodised at I lOV remained substantially undamaged except for numerous pinholes. T h e reflectivities o f the bare aluminium and the mirror anodised at l l 0 V measured at 12 ° angle of incidence, after exposure were (in ";~ reflection) : 4,60o ~, 5,3oo x 5,7ooA 6,oook Untreated Aluminium 32 Anodised iIoV .. 86~-
35 84~
36 83
I'./. l l
N.. .'
MAY I SUPPLEMENT Dr. G. L. Miller's comprehensive and well balanced article on Applied Vacuum Metallurgy in ' Vacuum ' J a n u a r y , 1952, 19-32 by a few historical comments on the production and use of tantalum metal, in the development of which I have taken a modest part as a junior scientist and assistant to Dr. W. Von BoRon, the inventor o f the first method of the production of ductile vacuummelted tantalum in 19021 . T h e development o f the
36 83
T h e oxide layer must have remained substantially intact because when viewed at glancing incidence the interference colours were the same as those on treated unexposed mirrors. L. HOLLANI) N. SUTHERI.AND Research Laboratories, W. Edwards & Co. (London) Limited, Lower Sydenham, London, S.E.26. England. 5th September, 1952
References HASS, G:, J. Opt. Soc. Amer., 39 (July 1949) 532-54 o. LOMER, P. D., Proc. Phys. Soc., 63 (Oct. 195o) 8!8-819. WEISKIRCHNER, W., Z. Natmforsch., 6A (Sept. I95I) 5o9-5IO. WALKENHORST,W., Naturwiss., 34 (1947) 373. w~Beo
~
An Early Method of V a c u u m Melting Tantalum Sommaire L'AUTEURRAPPELLEUNE TECHNIQUEde fusion sous vide, d6j&
ancienne, due it O. A. Simpson et W. Von Bolton et employ6e par Siemens et Halske it Berlin de I9o3 it 1912 pour la fabrication de filaments de tantale pour les lmalpes it incandescence. II donne des d&ails du proc6d6 et un croquis de l'appareil de fusion alors employ6. L'auteur est d'avis que cette m6thode classique offre toujours des possibilit6s pour le laboratoire de recherche moderne.
VACU U M FU I~NACF__.0005) A.O..~1 M I)SON ~W~. B O L T O N
15~J
melting technique as well as the rolling and drawing for production purposes was due to the late electrical and mechanical engineer Otto Archibald Simpson, and it was used between 1903 and 1912 for the manufacture of filaments for incandescent lamps in the Siemens & Halske factory at Berlin-Charlottenburg (now Osram, Berlin). Apart from lamp filaments, dental and surgical instruments as well as special laboratory tools like dishes were made from • vacuum-melted tantalum metal. The vacuum sintering process was used at a later date for a multiplicity of technical purposes, but not for lamp filaments (the lamp became obsolete and was gradually replaced by the tungsten lamp since 1911)2 ,More than 60 million tantalum lamps with filaments ranging between 0.03mm. and 0.08 ram. diameter were produced between 1903 and 1912~, requiring an amount of ductile, vacuum-melted tantalum of the order of one ton 4. A sketch showing the principle of the melting apparatus, which was used in the Siemens & Halske factory'~ is to be found in the book on powder metallurgy by Kieffer and Hotop ~. The sketch attached to this note has been made from memory by the writer. It has been repeatedly shown as a lantern slide in lectures on industrial applications of vacuum techniques within the last few years. Though the sketch is essentially self-explanatory, I may mention a few points. The pressed tantalum powder pellet, weighing 80-100 grams, was resting on a tantalum sheet of about 2mm. thickness. The ' a r c stabilizing' cathode of the direct current arc (50-80 Volts, 50-300 Amps.) consisted of a mixture of Ta and TaO~ (the dissociable browrr oxide) or according to a later suggestion 7 of a mixture of W and BaO ; the first mentioned having remained the standard procedure, The pressure at which the arc was started was about 5 × 10 3 mm. Hg (two-stage reciprocating oil pump). It then went through a maximum as a result of degassing an:t oxide dissociation, and at the end of the melting cycle was about 5 ~: 10 2 mm. Hg. The melting took a few minutes and the pellet, which had a considerable surface tension, was kept liquid for one to two minutes. This could be observed by the vibrations of its surface. The melting cycle was then broken
160
off and after cooling down air was admitted, whereupon the pellet was turned upside down and melted again. During the melting the cathode was manually moved around the pellet in a few mm. distance and the current was controlled carefully by a variable series resistance in order to keep the pellet at the required even temperature. This was carried out by specially trained ' unskilled ' operators. The finished malleable ' lenses ,8 consisted of one to six crystallite,~ and were rolled down on hexagonal-profile steel rollers, to about 1.5mm. and then drawn through drawing plates made of steel to about 0.3mm. and then through diamonds. I vividly remember the earlv times, when 1,000 metres of 0.05ram. wire were a day's target. I think that with obvious adjustments to the present 'state of the a r t ' the ' classical' vacuummelting method I have sketched has still some potential applications in the modern research laboratory. M. PIRANI 2, The Clone, Kingston Hill Surrey, England. 3rd January, 1952
References J BOLTON, W. VON., Z. Electrochem., No. 3, (19o5), 45-5 l ' D a s Tantal Seine Darstellung und Seine Eigenschaften.' 2 GANSWlNDT, S., WerkstoJy Handbuch der NichteisenMeta~le, Vol. 4, (Beuth-Verlag, Berlin, 1931). ;* STROBEL, W., Metall, 6, No. I Z I 8 , (1952), 560-563 .
' Metalle im Dienste der Glfihlampe.' * SIEMENS,A., Engineering, 87, (April 30, 19o9), 6ol. ' German Patent I55,548 (19o3).
'~ KIEFFORS, R., HOTOP, W., Pulvermetallurgie und Sinterwerkstoffe, 2nd Edition, (Springer-Verlag, Berlin, I948), 250. U.S. Patent 873,958 (19o7) SIEMENS & HALSKE, LAMPWORKS, (P'let in English), Tantalum and Its Technical and Scientific Applications, (1912), 6, Fig. 4.