GB966344A - Improvements in or relating to methods of and apparatus for forming light-diffusing coatings on the internal surfaces of hollow vessels - Google Patents

Abstract

<PICT:0966344/C1/1> A light-diffusing coating of titanium dioxide or silicon dioxide is applied to the inner surface of a hollow vessel, for example an incandescent lamp envelope, by subjecting a titanium or silicon compound, for example the tetrachloride to thermal hydrolysis in a hydrogen-oxygen flame, thereby depositing an oxide layer on the surface, wherein a mixture of hydrogen and the silicon or titanium compound is fed into the vessel through a burner orifice, oxygen is fed via a second orifice, and hydrogen is fed into the vessel between the two orifices to form a barrier gas, screening the gas mixture from the oxygen, such that the hydrolysis of the compound in the immediate vicinity of the burner is substantially avoided. In the drawings, a lamp envelope 3 is rotatably mounted about a burner 5, which burner comprises a central vertical tube 6, which is fed with a mixture of titanium tetrachloride and hydrogen derived by passing hydrogen through heated titanium tetrachloride in tank 8, an outer concentric pipe 11 which is fed with hydrogen to form a barrier, and an outermost concentric pipe 25 which is fed with oxygen. The supply of hydrogen-tetrachloride mixture is desirably arranged so that the supply is only on when an envelope is in position, the hydrogen barrier gas acting as a pilot flame at other times.