Process for producing a body of sintered TiO2 for resistive gas sensor

Claim 2

In a method of making a body of sintered titanium dioxide for a resistive-type exhaust gas oxygen sensor, the improvement comprising: precipitating a titanium oxide gel by alkalinizing an aqueous titanium choloride solution; mechanically separating the gel from its solution to provide a titanium oxide hydrate residue which retains microstructure attributes imparted by the gel; freeze drying the residue to produce unagglomerated minute, highly irregular and interlockable flake-like particles of anatase titanium dioxide; forming the particles into a low density, porous body having a high surface area; and sintering the particles under conditions sufficient to strongly bond the particles together but insufficient to reduce said high surface area significantly below about 3 square meters per gram, whereby said body has a high strength and permits said sensor to be operated at lower temperatures without compensation.

Claim 3

In a method of making a body of sintered titanium dioxide for a resistive-type exhaust gas oxygen sensor, the improvement comprising: precipitating a titanium oxide gel by alkalinizing an aqueous titanium tetrachloride solution; mechanically separating the gel from its solution to provide a titanium oxide hydrate residue which retains microstructure attributes imparted by the gel; rapidly freezing the residue; freeze drying the residue to produce unagglomerated minute, highly irregular and interlockable flake-like particles of anatase titanium dioxide; without significant grinding, pressing the particles into a low density, porous body having a high surface area; and sintering the particles under conditions sufficient to strongly bond the particles together but insufficient to reduce said high surface area significantly below about 3 square meters per gram, whereby said body has a high strength and permits said sensor to be operated at lower temperatures without recalibration.

Claim 4

In a method of making a body of sintered titanium dioxide for a resistive-type exhaust gas oxygen sensor, the improvement comprising: precipitating a titanium oxide gel by alkalinizing an aqueous titanium tetrachloride solution; mechanically separating the gel from its solution to provide a titanium oxide hydrate residue which retains microstructure attributes imparted by the gel; rapidly freezing the residue; freeze drying the residue to produce unagglomerated minute, highly irregular and interlockable flake-like particles of anatase titanium dioxide; without significant grinding, pressing the particles into a low density, porous body having a high surface area; and sintering the particles under conditions sufficient to strongly bond the particles together but insufficient to reduce said high surface area significantly below about 3 square meters per gram, whereby said body has a high strength and permits said sensor to be operated at lower temperatures without recalibration.

Claim 5

In a method of making a body of sintered titanium dioxide for a resistive-type exhaust gas oxygen sensor operating at lower temperatures without recalibration, the improvement comprising: precipitating a titanium oxide gel and forming NH 4 Cl in solution by adding NH 4 OH to an aqueous titanium tetrachloride solution; filtering the gel from said NH 4 Cl solution to provide a titanium oxide hydrate residue; rinsing the residue substantially free of NH 4 Cl only with solvents that do not alter the flake-like crystal-forming characteristics of the residue; applying liquid nitrogen to the residue to quickly freeze it; freeze drying the residue to produce unagglomerated minute highly irregular flake-like particles of anatase titanium dioxide; pressing such unagglomerated flake-like particles, without significant prior grinding, into a low density porous body having a high surface area; providing electrodes for said body to measure electrical resistance change in said body in response to atmosphere change; and sintering the body in an oxidizing atmosphere for a time and at a temperature generally equivalent to about one hour at 800°-920° C. to provide a body of high mechanical strength without decreasing said high surface area significantly below about 3 square meters per gram.

Claim 6

In a method of making a body of sintered titanium dioxide for a resistive-type exhaust gas oxygen sensor operating at lower temperatures without recalibration, the improvement comprising: precipitating a titanium oxide gel and forming NH 4 Cl in solution by adding NH 4 OH to an aqueous titanium tetrachloride solution; filtering the gel from said NH 4 Cl solution to provide a titanium oxide hydrate residue; rinsing the residue substantially free of NH 4 Cl only with solvents that do not alter the flake-like crystal-forming characteristics of the residue; applying liquid nitrogen to the residue to quickly freeze it; freeze drying the residue to produce unagglomerated minute highly irregular flake-like particles of anatase titanium dioxide; pressing such unagglomerated flake-like particles, without significant prior grinding, into a low density porous body having a high surface area; providing electrodes for said body to measure electrical resistance change in said body in response to atmosphere change; and sintering the body in an oxidizing atmosphere for a time and at a temperature generally equivalent to about one hour at 800°-920° C. to provide a body of high mechanical strength without decreasing said high surface area significantly below about 3 square meters per gram.