Method for preparing a semi-conductive ceramic material, semi-conductive ceramic material and ignition plug using this ceramic material

1. Method for preparing a semi-conductive ceramic material, characterised in that:

in a receptacle containing a liquid, there are mixed from 30 to 90% by weight of a conductive phase based on Z 1-x M x CrO 3 for 0≦×≦0.3, with Z being able to be an element of the lanthanide group or a mixture of elements of this type, and M being able to be calcium, strontium, magnesium, aluminium, titanium, yttrium or a mixture of two or more of these elements; from 8 to 60% by weight of an insulating phase based on fine grains of alumina or tabular alumina or mullite or a mixture of two or more of these compounds; and from 0 to 10% by weight of sintering additives;

operations are carried out for milling, drying and sieving this mixture;

this mixture is pressed;

and this mixture is sintered in order to obtain a ceramic material having a porosity less than or equal to 25%.

2. Method according to claim 1 , characterised in that Z is lanthanum.

3. Method according to claim 1 , characterised in that the porosity of the ceramic material obtained is between 0 and 15%.

4. Method according to claim 1 , characterised in that one or more plasticising compounds are added to the mixture and in that a de-binding operation is carried out after the pressing and before the sintering.

5. Method according to claim 4 , characterised in that the milling is carried out in two steps, in that the addition of the plasticising agent is effected between the two steps, and in that the second milling step is less energetic than the first step.

6. Method according to claim 1 , characterised in that the sintering additives are selected from silicates, alkaline and alkaline-earth oxides Na 2 O, K 2 O, BaO, CaO, MgO, alkaline-earth carbonates BaCO 3 , CaCO 3 , MgCO 3 , dolomite, rare earth compounds, such as La 2 O 3 , transition metal compounds, such as Y 2 O 3 , thermoemissive compounds, such as BaTiO 3 , or a mixture of these compounds.

7. Semi-conductive ceramic material, characterised in that it comprises from 30 to 90% by weight of a conductive phase based on a compound of the type Z 1-x M x CrO 3 for 0≦X≦0.3, Z being able to be an element of the lanthanide group or a mixture of elements of this type, and M being able to be calcium, strontium, magnesium, aluminium, titanium, yttrium or a mixture of two or more of these elements, from 8 to 60% by weight of an insulating phase based on alumina or mullite or a mixture of these compounds or the high temperature reaction products thereof, and from 0 to 10% by weight of sintering additives or the high temperature reaction products thereof, and in that the porosity thereof is less than or equal to 25%.

8. Ceramic material according to claim 7 , characterised in that Z is lanthanum.

9. Semi-conductive ceramic material according to claim 8 , characterised in that the porosity thereof is between 0 and 15%.

10. Semi-conductive ceramic material according to claim 7 , characterised in that the sintering additives are selected from silicates, alkaline-earth oxides BaO, CaO, MgO, Na 2 O, K 2 O, alkaline-earth carbonates BaCO 3 , CaCO 3 , MgCO 3 , dolomite, rare earth compounds, such as La 2 O 3 , transition metal compounds, such as Y 2 O 3 , thermoemissive compounds, such as BaTiO 3 , or a mixture of these compounds.

11. Semi-conductive ceramic material according to claim 7 , characterised in that, after sintering, it contains compounds of the type Al x Si y O z , with y being able to be equal to 0, lanthanide aluminate and optionally lanthanide silicate, Z 1-x M x CrO 3 , with M being able to be Ca, Sr, Mg, Al, Ti, Y or a mixture of several of these elements, and an amorphous phase based on oxygen and one or more elements from Al, Si, Ca.

12. Ignition plug of the high-energy, low-voltage type comprising a semi-conductive ceramic material between the electrodes thereof, characterised in that the ceramic material is of the type according to claim 7 .