Process for producing a body of sintered TiO.sub.2 for resistive gas sensor
AssigneeGeneral Motors Corporation
InventorAdolph L. Micheli
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Abstract
A titanium oxide resistive-type exhaust gas oxygen sensor having a unique microstructure of interlocked highly irregular, flake-like particles forming a highly durable porous body preferably having a surface area greater than about 3 square meters per gram. A method for producing such particles and forming them into such a high surface area body is also described.
Claims3
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.
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.
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.sub.4 Cl in solution by adding NH.sub.4 OH to an aqueous titanium tetrachloride solution;
- filtering the gel from said NH.sub.4 Cl solution to provide a titanium oxide hydrate residue;
- rinsing the residue substantially free of NH.sub.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.degree.-920.degree. C. to provide a body of high mechanical strength without decreasing said high surface area significantly below about 3 square meters per gram.
Dependencies are inferred from the claim text.