Patent GB-813828-A (GB)
Title: Improvements relating to the production of metallic bonds between surfaces
IPC: C04B37/00
Filed: 1955-10-21
Abstract: 813,828. Soldering. GENERAL ELECTRIC CO. Oct. 21, 1955 [Oct. 22, 1954], No. 30120/55. Class 83 (4). [Also in Group XXXVI] In forming a metallic bond between members of metal or ceramic or between a member of metal and a member of ceramic, the members are heated to degas them, subsequently cooled and then contacted by solder which bonds them together. In an embodiment metal parts 10, 12, 13, 15, 16, 18 and refractory parts 11, 14, 17 of an electric discharge device are assembled together after a slurry including at least one hydride of titanium, zirconium hafnium or thorium preferably of titanium hydride powder or zirconium hydride powder or a mixture of these powders in an amyl acetate and nitrocellulose binder solution has been painted on interfacing surfaces. The metal parts may be of copper, nickel, iron, chromium, molybdenum, cobalt, tantalum, titanium, zirconium or alloys thereof but in the embodiment are of copper and the refractory parts may be of ceramic material such as aluminas, forsterites, steatites or beryllias but in the embodiment are of alumina. The assembled parts are placed in a jig 21, having contact members 23, 24 loaded by a spring 25, over a bath of solder, e.g. lead on an extendable support 35 and a tantalum or titanium oven 26 is placed over the assembly. A bell jar 29 is placed over the oven to rest on a table 30 of an evacuating apparatus. The bell jar is exhausted and the temperature of the discharge device is raised to 850‹ C. by an induction heating coil 32 about the bell jar when the hydride decomposes to form metal layers between the parts. When the device is degased the heating is stopped, the temperature of the device is allowed to fall to 700‹ C. and the solder bath which has been heated to below 600‹ C. is raised into contact with the copper parts of the device to effect bonding of the parts of the device. The cathode of the discharge device can be activated during the degasing and sealing. If the metal parts are of tantalum and the refractory parts are of a high-temperature ceramic the degassing temperature may be 1350‹ C. and to allow better access to the parts, for degassing, the parts need not be tightly assembled until just before the solder is applied. Instead of using the solder bath a solid stick of solder may be raised from the base of the apparatus to contact the discharge device and to avoid preliminary titanium &c. hydride coating a solid solder stick coated with titanium hydride may be made to contact the parts. The solder used may include at least one of lead, tin and aluminium. In a modification the parts are assembled as before but after powdered titanium alloy in nitrocellulose, instead of a hydride coating, has been painted on the parts. The assembly is degassed and evacuated and a solder, formed by heating to 800‹ C. in a vacuum 95 per cent soft solder, e.g. lead with 5 per cent titanium hydride to liberate all the hydrogen of the hydride, is applied in solid or molten form to the assembly parts. Aluminium may be used instead of lead. If the metal parts are of titanium or zirconium no painting of these parts is necessary when a solder consisting of lead, tin, aluminium or mixtures thereof is used Specification 755,985, [Group XL (a)], is referred to.