Centre National De La Recherche Scientifique

Thomson-csf

Serge Vilminot

Arvind Shroff

Jean-Claude Bernier

Paul J Poix

Jean-Luc Rehspringer

Bernard Carriere

Veronique Hebert

Dominique Brion

Gabriel G Vilmin

Disclosed are a method for the fabrication of an impregnated cathode and a cathode obtained thereby. The impregnation is obtained by applying a sol-gel method. The emissive material which impregnates the body of the cathode only partially fills the pores. This facilitates the migration of the material towards the surface and increases the lifetime of the cathode.

Method for the fabrication of an impregnated cathode and cathode

The present invention relates to a cordierite (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.2) type ceramic powder sintering at low-temperature defined in that its composition is: 60 to 50% SiO.sub.2, 5 to 20% MgO and 20 to 40% Al.sub.2 O.sub.3, and in that its specific surface area is not less than 50 m.sup.2 /g, this powder having a fritting temperature of less than 1,100.degree. C. The invention also relates to a process for the preparation of this powder, which consists in preparing a mixed alcoholic solution of an aluminum and silicon salt, in preparing a solution of an alcohol-soluble magnesium salt, in mixing the two solutions, in padding a hydrolyzing agent in the form of a totally volatile weak base to the solution, which leads to the formation of a gel, in subjecting the said gel to a first thermal treatment at a temperature not exceeding 450.degree. C., and in subjecting the said powder to a second thermal treatment at a temperature of between 450.degree. C. and 900.degree. C. By a sintering which may be carried out at a temperature lower than 950.degree. C., the powder obtained leads to dielectric ceramics which have a coefficient of expansion less than 1.10.sup.-6 C.sup.-1, and a dielectric constant less than 5.

Low-temperature sinterable cordierite type ceramic powder, preparation

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Serge Vilminot