Laminated system for gas sensors and process for producing it

Details Laminated system for gas sensors and process for producing it Laminated system for gas sensors and process for producing it

1993-04-05

1994-11-29

Niebling, John

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204424, 204426, G01N 2726

Patent

active

053687132

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a layer system and a process for producing layer systems for gas sensors in accordance with the generic class of the main claim. Such layer systems are disclosed, for example, in German Patent Specification 28 52 647.
It has been found, however, that a porous covering layer on its own cannot always adequately protect the electrode layer against contaminants from the exhaust gas such as, for example, silicon, phosphorus, zinc, lead and their compounds. EP-A2-0 331 513 therefore proposed to introduce alkaline earth metal oxides onto the surface or into the pores of the covering layer. The gaseous organic or inorganic silicon compounds are thereby trapped and converted into stable compounds which do not impair the operation of the sensor. Although alkaline earth metal oxides are able to trap the contaminant silicon effectively to form refractory reaction products, they are able to trap lead only in the presence of other coreactants such as, for example, silicon and then only to form low-melting reaction products which result in a blocking of the pores in the protective layer and, consequently, in an impairment of the sensor sensitivity.
During the initial motor run after production of a motor vehicle, the contaminant silicon may occur, in particular as a result of escape from sealing parts, whereas, during continuous operation, pollutants such as, for example, lead, phosphorus, zinc, and in exceptional cases also silicon, primarily originating from fuel and oil additives may occur.
EP-A2-0 373 745 furthermore discloses protecting the electrode layer of fuel cells or gas sensors from silicon-containing and/or aluminium-containing compounds in the test gas by depositing one or more oxides, or compounds which form oxides on heating, of the metals from the group comprising Ce, Sm, Mg, Be, Ca, Sr, Ti, Zr, Hf, Y, La, Ce, Pr, Nb, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U.
U.S. Pat. No. 4,272,349 discloses the use of an outer protective layer composed of Al.sub.2 O.sub.3 which acts as a getter for catalyst poisons, in particular for phosphorus.


SUMMARY OF THE INVENTION

The claimed layer system having the features of the main claim has the advantage that the mixed oxides are able to trap the various contaminants usually occurring in exhaust gas such as, for example, silicon, phosphorus, zinc or lead. The combination of alkali metals, on the one hand, and at least trivalent elements, on the other hand, results in mixed oxides whose reactivity and thermal stability can be matched to the pollutants. The mixed oxide getters according to the invention react with the contaminants from the exhaust gas to form reaction products having high melting points above the maximum application temperature of the layer system. The high affinity of the alkali oxides for acidic oxides results in a beneficial gettering action with respect to silicon and phosphorus. The amphoteric or weakly acidic nature of the at least trivalent mixed oxide partner also results, in particular, in the gettering action for divalent contaminants such as, for example, lead or zinc.
Compared with the known contaminant getters, the invention consequently makes it possible to cover a wide contaminant spectrum.
As a result of the measures listed in the subclaims and in the process claims, advantageous further developments and improvements of the layer system specified in the main claim are possible. It is particularly advantageous to deposit the mixed oxides by impregnation from a preferably aqueous solution, for example of the nitrates or chlorides, or from solutions of organometallic compounds. The compounds of the alkali metals and of the trivalent or higher-valency elements are chosen in such a way that they decompose at temperatures just above the application temperature of the sensor, the mixed oxides being produced in very finely dispersed, highly reactive form. The impregnation process offers the further advantage that, in addition to the mixed oxides, catalyst substances, in particular noble

REFERENCES:
patent: 4021326 (1977-05-01), Pollner et al.
patent: 4272349 (1981-06-01), Furutani et al.
patent: 4296148 (1981-10-01), Friese
patent: 4296148 (1981-10-01), Friese
patent: 4863583 (1989-05-01), Kurachi et al.
patent: 5089299 (1992-02-01), Van'T Veen et al.

Affiliated with

Also associated with

Rating

Laminated system for gas sensors and process for producing it does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Laminated system for gas sensors and process for producing it, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laminated system for gas sensors and process for producing it will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-71814