Poison resistant combustible gas sensor

Claim 1

A method for producing a poison resistant active element for a combustible gas sensor comprising the steps of: forming a filament of electrically conductive material having a resistance which varies with temperature into a helical coil; coating said helical coil with a refractory material and heating said refractory material until sintering takes place to produce a dense gas-tight sheath; applying a first layer in liquid mixture form of a combination ceramic material and catalytically active material to said sheath on the helical coil; curing said first layer at a temperature in the range of 800° C. to 1100° C. from 2 minutes to 3 minutes; applying a plurality of alternating layers in liquid mixture form of a non-catalytic ceramix material and a catalytically active material to said first cured layer on said helical coil; curing the non-catalytic ceramic liquid mixture material of said plurality of alternating layers at a temperature in the range of 800° C. to 1100° C. from 2 minutes to 3 minutes, and curing the catalytically active liquid mixture material of said plurality of alternating layers at a temperature in the range of 800° C. to 900° C. from 2 minutes to 3 minutes; applying a final layer of a liquid mixture containing aluminum chloride and aluminum oxide to the final one of the alternating layers; and curing said mixture layer of aluminum chloride and aluminum oxide at a temperature in the range of 800° C. to 1100° C. from 2 minutes to 3 minutes to form a cured final layer of non-catalytic porous aluminum oxide.

Claim 2

A method for producing a poison resistant active element for a combustible gas sensor comprising the steps of: forming a filament of electrically conductive material having a resistance which varies with temperature into a helical coil; coating said helical coil with a refractory material and heating said refractory material until sintering takes place to produce a dense gas-tight sheath; applying a first layer in liquid mixture form of a combination ceramic material and catalytically active material to said sheath on the helical coil; curing said first layer at a temperature in the range of 800° C. to 1100° C. from 2 minutes to 3 minutes; applying a plurality of alternating layers in liquid mixture form of a non-catalytic ceramix material and a catalytically active material to said first cured layer on said helical coil; curing the non-catalytic ceramic liquid mixture material of said plurality of alternating layers at a temperature in the range of 800° C. to 1100° C. from 2 minutes to 3 minutes, and curing the catalytically active liquid mixture material of said plurality of alternating layers at a temperature in the range of 800° C. to 900° C. from 2 minutes to 3 minutes; applying a final layer of a liquid mixture containing aluminum chloride and aluminum oxide to the final one of the alternating layers; and curing said mixture layer of aluminum chloride and aluminum oxide at a temperature in the range of 800° C. to 1100° C. from 2 minutes to 3 minutes to form a cured final layer of non-catalytic porous aluminum oxide.

Claim 6

A method for producing a poison resistant active element for a combustible gas sensor comprising the steps of: forming a filament of electrically conductive material having a resistance varying with temperature into a helical coil; applying a refractory material to said helical coil and heating said refractory material until sintering takes place to produce a dense gas-tight sheath; applying a first layer in a liquid mixture form of a combination ceramic material and catalytically active material to said sheath on the helical coil; curing said first layer; applying a plurality of alternating layers in a liquid mixture form of a non-catalytic ceramic material and a catalytically active material to said first cured layer on said helical coil; curing the non-catalytic ceramic material of said plurality of alternating layers and curing the catalytically active material of said plurality of alternating layers to form alternating cured layers of a non-catalytic porous ceramic material and a catalytically active material; applying a final layer of a liquid mixture containing aluminum chloride and aluminum oxide to the final one of the alternating layers; and heating said liquid mixture layer containing aluminum chloride and aluminum oxide to produce a reaction forming a ceramic layer of aluminum oxide.

Claim 7

A method for producing a poison resistant active element for a combustible gas sensor comprising the steps of: forming a filament of electrically conductive material having a resistance varying with temperature into a helical coil; applying a refractory material to said helical coil and heating said refractory material until sintering takes place to produce a dense gas-tight sheath; applying a first layer in a liquid mixture form of a combination ceramic material and catalytically active material to said sheath on the helical coil; curing said first layer; applying a plurality of alternating layers in a liquid mixture form of a non-catalytic ceramic material and a catalytically active material to said first cured layer on said helical coil; curing the non-catalytic ceramic material of said plurality of alternating layers and curing the catalytically active material of said plurality of alternating layers to form alternating cured layers of a non-catalytic porous ceramic material and a catalytically active material; applying a final layer of a liquid mixture containing aluminum chloride and aluminum oxide to the final one of the alternating layers; and heating said liquid mixture layer containing aluminum chloride and aluminum oxide to produce a reaction forming a ceramic layer of aluminum oxide.