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357. Composition for obtaining conducting coatings on a ceramic
Classified abstracts 354-362 37 354. Properties of krypton 85 labelled metals used in industry. (Hungary) Experiments with krypton 85 gas labelled aluminium and nickel-base metals were carried out. Ion bombardment in vacuum was used to introduce krypton, every plate being bombarded for 10 rain at 8 kV negative voltage with 90/~A ion current density at pressure of 10-3 torr. The specific activities achieved varied between 0.2 and 1.0 /~Ci/cm2. Desorption of krypton atoms was followed by measurement of the decrease in activity over several months. Experimental results are discussed. I Ury, Kemiai Kozlemenyek, 32 (2), 1969, 137-144 (in Hungarian).
IV. Materials and techniques used in vacuum technology 42. GLASS, CERAMICS AND REFRACTORY OXIDES 42 355. Method of preparing a cermet heater. (USSR) A n improved technique for the manufacture of cermet heaters used in vacuum technology is described. The distinguishing feature of this process is that a current is passed through the heater in the final stages of sintering; the electrical resistance of the heater is determined from the applied voltage and the current passing, and sintering is ended when a specified resistance is achieved. In order to realise this process in practice, an arrangement for rapidly lowering the heater into a furnace, passing a specified current, and extracting equally rapidly as and when required is provided. In this way, the large-scale production of heaters with negligible deviations from the specified electrical resistance may readily be ensured. Allowance has to be made for the fact that the current passing through the heater in the final stages of sintering (several amperes) itself provides additional heating. This is advantageous rather than otherwise, as it helps remove contamination deposited from the furnace and stabilizes the properties of the heater material. S I Faifer et al, USSR Patent, No 258,469, appl 1st March 1969, publd 12th May 1970. 42 356. A suspension for depositing an oxide coating. (USSR) A new form of suspension for depositing oxide coatings, differing from conventional varieties in respect of its plasticizing and binding component (3-4 per cent of polymethylmethacrylate and polyvinylacetate in a 1:10 ratio), is proposed; the suspension contains carbonates of the alkaline-earth metals with a grain size of 2/~ (20-30 per cent), with acetone as a dispersing medium (66-76 per cent). The coating may be deposited, for example, by means of a syringe, passing through an aperture of 50/~ or under. The polymethylmethacrylate is introduced before milling in order to improve the dispersion of the carbonates; the polyvinylacetate is added later to improve stability and ductility. G I Fridgant et al, USSR Patent, No 254,665, appl 6th May 1968, publd 21st April 1970. 42 357. Composition for obtaining conducting coatings on a ceramic. (USSR) A new composition for producing conducting coatings on ceramic surfaces is proposed; in contrast to its predecessors, this composition contains 20-60 per cent of manganese compounds, and is particularly suitable for high-alumina ceramic parts. The manganese compounds are mixed with titanium oxide and hydride before sintering; the resultant material has a high degree of adhesion and a specific resistance of 10s-1012 ohm.era, depending on the precise conditions of formation. The properties of the coating remain constant up to 800°C in a reducing medium and at voltages up to 60 kV. A convenient method of deposition lies in the use of a powder mixture in an organic binder, followed by sintering in hydrogen for up to 60 rain at 1200-1500°C. L I Milenysheva and V A Krestov, USSR Patent, No 248,088, app127th May 1968,publd 9th Dee 1969. 42 : 33 358. An electrical ceramic material. (USSR) A ceramic material of considerable mechanical strength and vacuum tightness, with a fair thermal conductivity and an electrical resistivity of 105-10n ohms,cm at 20°C, having a dielectric loss factor of tan 198
6<0.01, is proposed. The material contains Al~O3 (93-99 per cent) with traces of MgO and Ti203. The MgO is introduced to combat the rapid growth of A1203 crystals attributable to the Ti20.~ while sintering. The absence of SiO2 makes control of the composition and properties easier. Mouldings of this material are sintered at 1500-1600°C in order to ensure vacuum tightness, final annealing taking place in a reducing atmosphere. V N Batygin et al, USSR Patent, No 256,003, appl 31st May 1967, pubM 7th April 1970. 45. SOLDERING, WELDING, BRAZING, SOLDERS 45 359. A solder for joining parts of electrical vacuum apparatus. (USSR) A new type of solder for joining parts of electrical vacuum apparatus at a reasonably low temperature is proposed. The solder contains 35-50 per cent gold, 1-3 per cent palladium, and 5-7 per cent germanium, the remainder being copper; it is ductile and convenient in application, providing excellent working conditions at 850-900°C. The solder wets molybdenum, copper, Kovar, German silver, nickel, and carbon steel in a hydrogen atmosphere; it gives vacuum-tight joints between copper on the one hand and copper, molybdenum, Kovar, nickel, and carbon steel on the other. In the annealed state the tensile strength is 41 kg/mm 2 and the relative elongation 59 per cent. This material is far superior to conventional compositions, which either require much higher working temperatures or incorporate silver, which gives porous joints. R E Kovalevskii et al, USSR Patent, No 252,833, appl 13th July 1968, pubM 18th Feb 1970. 45 360. A solder for joining electrical-vacuum parts. (USSR) The disadvantages of conventional solders employed for joining tungsten, nickel, and molybdenum parts of electrical vacuum apparatus are discussed; these solders are frequently of low mechanical strength, eg only half that of soft copper. The new solder here proposed contains 9-11 per cent of both silver and germanium, 1-5 per cent nickel, and the remainder copper (the nickel may be replaced by palladium); it provides reliable fluxless soldering of large or small parts in any media, including vacuum. The new solder interacts with none of the materials in question but ensures excellent wetting of each of them at 940-97ffC. The mechanical strength derives largely from the nickel or palladium constituent. In this way molybdenum, tungsten, iron, and iron alloy parts may be soldered without any preparation such as galvanic gold or copper plating. The joints are corrosion resistant under tropical conditions. N N Tutorskaya et al, USSR Patent, No 255,014, app128th Aug 1968, publd 2nd April 1970. 46. GLASS BLOWING, GLASS-TO-METAL AND CERAMICTO-METAL SEALING TECHNIQUES 46 361. Adhesion of graphite to glass. (Hungary) It is found that adhesion of graphite to glass can be increased by adsorption of ions in the graphite suspension, which are also well adsorbed by glass. An interface layer containing alkaline ions on the glass surface is efficient in such a process. I Baranyas and F Kardos, Tavkozlesi Kutato lntezet Kozlemenyei, 14 (1), 1969, 29-42 (in Hungarian). 46 362. Metailizing alumina ceramics and sealing them to metals. (Czechoslovakia) Results of experiments, which were performed in connection with processes of metallizing and sealing the ceramic vacuum envelopes of transmitting electron tubes, are reported. A two-step ceramic-tometal sealing technology is used; first, the ceramic parts are metallized with a mixture of molybdenum powder, manganese and titanium hydride, then the deposited metals are fired on in an atmosphere of humidified hydrogen whereupon the fired layer is electroplated with nickel. Finally, the ceramic part prepared in this way is brazed to the metal using a silver or copper solder. Special hydrogen furnaces with programme control facilities had to be developed, enabling the plated metal to be fired and the ceramics to be brazed to the metal. Using differential thermal and x-ray analyses, the physico-chemical reactions developing when thin layers of metal powder are fired on to an alumina body are analyzed. During firing the molybdenum and manganese powder are slightly oxidized, titanium hydride is converted and tile metallic titanium thus formed is also oxidized. The
IV. Materials and techniques used in vacuum technology 42. GLASS, CERAMICS AND REFRACTORY OXIDES 42 355. Method of preparing a cermet heater. (USSR) A n improved technique for the manufacture of cermet heaters used in vacuum technology is described. The distinguishing feature of this process is that a current is passed through the heater in the final stages of sintering; the electrical resistance of the heater is determined from the applied voltage and the current passing, and sintering is ended when a specified resistance is achieved. In order to realise this process in practice, an arrangement for rapidly lowering the heater into a furnace, passing a specified current, and extracting equally rapidly as and when required is provided. In this way, the large-scale production of heaters with negligible deviations from the specified electrical resistance may readily be ensured. Allowance has to be made for the fact that the current passing through the heater in the final stages of sintering (several amperes) itself provides additional heating. This is advantageous rather than otherwise, as it helps remove contamination deposited from the furnace and stabilizes the properties of the heater material. S I Faifer et al, USSR Patent, No 258,469, appl 1st March 1969, publd 12th May 1970. 42 356. A suspension for depositing an oxide coating. (USSR) A new form of suspension for depositing oxide coatings, differing from conventional varieties in respect of its plasticizing and binding component (3-4 per cent of polymethylmethacrylate and polyvinylacetate in a 1:10 ratio), is proposed; the suspension contains carbonates of the alkaline-earth metals with a grain size of 2/~ (20-30 per cent), with acetone as a dispersing medium (66-76 per cent). The coating may be deposited, for example, by means of a syringe, passing through an aperture of 50/~ or under. The polymethylmethacrylate is introduced before milling in order to improve the dispersion of the carbonates; the polyvinylacetate is added later to improve stability and ductility. G I Fridgant et al, USSR Patent, No 254,665, appl 6th May 1968, publd 21st April 1970. 42 357. Composition for obtaining conducting coatings on a ceramic. (USSR) A new composition for producing conducting coatings on ceramic surfaces is proposed; in contrast to its predecessors, this composition contains 20-60 per cent of manganese compounds, and is particularly suitable for high-alumina ceramic parts. The manganese compounds are mixed with titanium oxide and hydride before sintering; the resultant material has a high degree of adhesion and a specific resistance of 10s-1012 ohm.era, depending on the precise conditions of formation. The properties of the coating remain constant up to 800°C in a reducing medium and at voltages up to 60 kV. A convenient method of deposition lies in the use of a powder mixture in an organic binder, followed by sintering in hydrogen for up to 60 rain at 1200-1500°C. L I Milenysheva and V A Krestov, USSR Patent, No 248,088, app127th May 1968,publd 9th Dee 1969. 42 : 33 358. An electrical ceramic material. (USSR) A ceramic material of considerable mechanical strength and vacuum tightness, with a fair thermal conductivity and an electrical resistivity of 105-10n ohms,cm at 20°C, having a dielectric loss factor of tan 198
6<0.01, is proposed. The material contains Al~O3 (93-99 per cent) with traces of MgO and Ti203. The MgO is introduced to combat the rapid growth of A1203 crystals attributable to the Ti20.~ while sintering. The absence of SiO2 makes control of the composition and properties easier. Mouldings of this material are sintered at 1500-1600°C in order to ensure vacuum tightness, final annealing taking place in a reducing atmosphere. V N Batygin et al, USSR Patent, No 256,003, appl 31st May 1967, pubM 7th April 1970. 45. SOLDERING, WELDING, BRAZING, SOLDERS 45 359. A solder for joining parts of electrical vacuum apparatus. (USSR) A new type of solder for joining parts of electrical vacuum apparatus at a reasonably low temperature is proposed. The solder contains 35-50 per cent gold, 1-3 per cent palladium, and 5-7 per cent germanium, the remainder being copper; it is ductile and convenient in application, providing excellent working conditions at 850-900°C. The solder wets molybdenum, copper, Kovar, German silver, nickel, and carbon steel in a hydrogen atmosphere; it gives vacuum-tight joints between copper on the one hand and copper, molybdenum, Kovar, nickel, and carbon steel on the other. In the annealed state the tensile strength is 41 kg/mm 2 and the relative elongation 59 per cent. This material is far superior to conventional compositions, which either require much higher working temperatures or incorporate silver, which gives porous joints. R E Kovalevskii et al, USSR Patent, No 252,833, appl 13th July 1968, pubM 18th Feb 1970. 45 360. A solder for joining electrical-vacuum parts. (USSR) The disadvantages of conventional solders employed for joining tungsten, nickel, and molybdenum parts of electrical vacuum apparatus are discussed; these solders are frequently of low mechanical strength, eg only half that of soft copper. The new solder here proposed contains 9-11 per cent of both silver and germanium, 1-5 per cent nickel, and the remainder copper (the nickel may be replaced by palladium); it provides reliable fluxless soldering of large or small parts in any media, including vacuum. The new solder interacts with none of the materials in question but ensures excellent wetting of each of them at 940-97ffC. The mechanical strength derives largely from the nickel or palladium constituent. In this way molybdenum, tungsten, iron, and iron alloy parts may be soldered without any preparation such as galvanic gold or copper plating. The joints are corrosion resistant under tropical conditions. N N Tutorskaya et al, USSR Patent, No 255,014, app128th Aug 1968, publd 2nd April 1970. 46. GLASS BLOWING, GLASS-TO-METAL AND CERAMICTO-METAL SEALING TECHNIQUES 46 361. Adhesion of graphite to glass. (Hungary) It is found that adhesion of graphite to glass can be increased by adsorption of ions in the graphite suspension, which are also well adsorbed by glass. An interface layer containing alkaline ions on the glass surface is efficient in such a process. I Baranyas and F Kardos, Tavkozlesi Kutato lntezet Kozlemenyei, 14 (1), 1969, 29-42 (in Hungarian). 46 362. Metailizing alumina ceramics and sealing them to metals. (Czechoslovakia) Results of experiments, which were performed in connection with processes of metallizing and sealing the ceramic vacuum envelopes of transmitting electron tubes, are reported. A two-step ceramic-tometal sealing technology is used; first, the ceramic parts are metallized with a mixture of molybdenum powder, manganese and titanium hydride, then the deposited metals are fired on in an atmosphere of humidified hydrogen whereupon the fired layer is electroplated with nickel. Finally, the ceramic part prepared in this way is brazed to the metal using a silver or copper solder. Special hydrogen furnaces with programme control facilities had to be developed, enabling the plated metal to be fired and the ceramics to be brazed to the metal. Using differential thermal and x-ray analyses, the physico-chemical reactions developing when thin layers of metal powder are fired on to an alumina body are analyzed. During firing the molybdenum and manganese powder are slightly oxidized, titanium hydride is converted and tile metallic titanium thus formed is also oxidized. The