DE2131538B2 - GAS POLLUTION ELEMENT - Google Patents

Description

The invention relates to a method for producing a gas detection element, in which on a Carrier material between two electrodes a first semiconductor layer, instasondcr metal oxide layer, which adsorbs - preferably flammable - gases and vapors and thereby changes their electrical conductivity, and a second semiconductor layer is applied for heating the first layer.

With known gas detection elements of this type, e.g. as in German Offenlegungsschrift 2005497 and 2007937 specified, their gas-adsorbing semiconductor body is made by sintering a metal oxide material, which has been brought into the desired shape beforehand.

The disadvantage is that because of the amalgamation phenomena during sintering, the sensitivity of the elements increases with increasing strength is reduced, since the air permeability and thus the gas-adsorbing surface is considerable and undefined is decreased. Also the use of paraffin and a coating of a porous binder in the production, none can be defined

Ensure results.

Also known from US Pat. No. 3,479,257 are gas detection elements of this type, which are largely with work homogeneous metal oxide layers on suitable substrates. These layers will be by depositing a metal layer, in particular tungsten, molybdenum, chromium, niobium, nickel, iron or Titanium obtained by vacuum evaporation and subsequent oxidation. In addition, it seems necessary

dig, the layers by applying a catalytically active element to the surface of the metal oxide to activate. This method is complex, cumbersome and difficult to use. Also for the production of the gas detection element according to the German

see laid-open specification 1648909 with an In ₂ O ₃ layer by evaporation of indium or In ₂ O ₃ in a vacuum and subsequent oxidation, the disadvantage applies in the same way. In addition, there is a significant disadvantage with these processes that they are too small

ao adhesion of the layers on their substrates.

The invention is therefore based on the object of specifying a method which enables the production of Gas detection elements with largely uniform sensitivity at a relatively low heating output.

»5 equips.

This object is achieved according to the invention in that first the second layer, then a thin insulating layer, for example made of SiO _2, and finally the first semiconductor layer on the carrier material

are applied, and that the two semiconductor layers by a reaction of metal halide solution, which are sprayed in an oven at temperatures between 300 and 700 ° C.

It should be mentioned that layers of the type according to the invention - insofar as they are transparent - are known per se are. They are used to cover glasses, for example, in order to heat them up or to prevent static charging. Layers of this kind adhere firmly to their base, they are smudge-proof and scratch-proof.

Fetner ensures that the flammable gases and / or vapors burn on the surface of the layer. This increases the temperature of the layer, which leads to an additional change in conductivity.

♦ 5 leads. The gas detection element according to the invention becomes even more sensitive.

Another advantage is that the gases adsorbent layer is heated evenly distributed over its entire surface and that because of the intimate Contact of the two layers only requires a relatively low heating power.

Further developments of the invention are described in the subclaims.

If the sensing element produced by the method according to the invention is used in an electrical circuit, e.g. a Wheatstone bridge circuit, to measure the concentration of gases and / or vapors, then a compensation element is generally provided; this can be produced in the same way as the gas sensing element, only with the The difference is that it is additionally surrounded by an insulating layer, for example made of SiO ₂ , preferably of the same thickness as the other layers, which has an influence of the gases on the compensation element

65 prevented.

In detail, you can proceed as follows, for example:

A carrier, e.g. a thin quartz plate, is

next heated in an oven to a temperature of around 600 to 650 ° C. When the temperature equilibrium is reached a certain amount of a metal salt solution is sprayed on. This can be, for example, the following Composition have:

100 parts by volume
1 to 2 parts by volume

30 to 50 parts by volume
20 to 30 parts by volume

SnCl ₄

SbCl ₃ (this serves to increase conductivity)

Methanol or ethanol as stabilizers for the SnCl ₄ glacial acetic acid as a further stabilizer for the SnCl ₄

The particles of this solution, which are deposited on the surface of the plate, react with it Surface and form an electrically conductive layer. The heating layer is now complete.

A thin insulating layer made of SiO _{2 is then} vapor-deposited onto the heating layer.

Finally, the layer which adsorbs gases and vapors is applied to the insulating layer in a similar way to how the heating layer has been applied: after putting the item in an oven A metal salt solution is sprayed into the furnace after it has been heated to 600 to 650 ° C. This can e.g. B. the following Have composition.

100 parts by volume SnCl ₄

20 parts by volume of methanol or ethanol as stabilizers for the SnCl ₄
20 parts by volume of glacial acetic acid as an additional stabilizer

for the SnCl ₄

S 2 parts by volume of gold chloride solution (the gold ion is used for doping)
(Instead of the gold chloride solution, a copper halide solution, e.g. 0.5 to 20 parts by volume of 20% aqueous CuCl ₂ lo

solution, or a nickel halide solution, e.g. B. 1 to 10 parts by volume of 10% aqueous NiCl ₂ solution are added.)
5 parts by volume of HCl

The element produced in this way is provided with electrodes by known methods, for example by electroplating or soldering electrodes. The gas detection element is now ready.
During operation, the gas detection element is heated to temperatures between 50 and 350 ° C. Higher temperatures of up to around 500 ° C can also be set. Of course, the heating can also take place in other ways than by means of the heating layer described above, for example with the aid of a platinum coil. Of course, the gas and vapor adsorbing layer can also be placed on a; Apply heating wire. In that case, however, a layer of glass, quartz or ceramic must be applied to the wire before the layer is applied.

Claims (5)

JL 21 538 * Patent claims: 1. A method for producing a gas detection element, in which on a carrier material between pei electrodes a first semiconductor layer, inside a metal oxide layer, which - preferably combustible - adsorbs gases and vapors and thereby changes their electrical conductivity, and a second semiconductor layer for heating the first layer, characterized in that the second layer is applied to the carrier material first, then a thin insulating layer, for example made of SiO ₂ and finally the first semiconductor layer are applied, and that the two semiconductor layers are applied by a reaction of metal halide solution which are sprayed in an oven at temperatures between 300 and 700 ° C, preferably at 600 to 650 ° C, are formed. 2. The method according to claim 1, characterized in that the semiconductor layers by Reaction can be formed from a tin tetrachloride solution. 3. The method according to claim 1 and 2, characterized in that the starting solution stabilizers, in particular methanol or ethanol and / or glacial acetic acid and / or hydrochloric acid are added will. 4. The method according to claim 1 to 3, characterized characterized in that the starting solution for doping the first semiconductor layer with heavy metals metal halide solutions, in particular a copper halide solution and / or a zinc halide and / or a nickel halide solution, is added. 5. The method according to claim 1 to 3, characterized in that the starting solution for doping the second semiconductor layer with heavy metals, metal halide solutions, in particular an antimony trichloride solution is added.