Chromium oxide product

Abstract

A sintered refractory product having a granulate bonded by a matrix and comprising, in percentages by mass based on the oxides, more than 40% chromium oxide Cr.sub.2O.sub.3, less than 50% aluminium oxide Al.sub.2O.sub.3, 1% or more zirconium oxide ZrO.sub.2, of which at least 20% by mass is stabilised in the cubic and/or quadratic form, 0.1% or more yttrium oxide Y.sub.2O.sub.3, acting as a stabiliser for the zirconium oxide ZrO.sub.2, less than 1.9% hafnium oxide HfO.sub.2, the total content of chromium, aluminium and zirconium oxides Cr.sub.2O.sub.2+Al.sub.2O.sub.3+ZrO.sub.2 being greater than 70%.

Claims

1. A sintered refractory product exhibiting an aggregate bonded by a matrix wherein the sintered refractory product comprises, as percentages by weight on the basis of the oxides: more than 40% of chromium oxide Cr.sub.2O.sub.3, less than 50% of aluminum oxide Al.sub.2O.sub.3, 1% or more of zirconium oxide ZrO.sub.2, at least 20% by weight of which is stabilized in the cubic and/or tetragonal form, 0.1% or more and less than 2.0% of yttrium oxide Y.sub.2O.sub.3, acting as stabilizer for the zirconium oxide ZrO.sub.2, less than 1.9% of hafnium oxide HfO.sub.2, the total content of chromium oxide, aluminum oxide and zirconium oxide Cr.sub.2O.sub.3+Al.sub.2O.sub.3+ZrO.sub.2 being greater than 70%, said product comprising a codopant, acting or not acting as stabilizer for the zirconium oxide, selected from the group consisting of CaO, MgO, TiO.sub.2, and mixtures thereof, a sum of the contents of calcium oxide, magnesium oxide, and titanium oxide Cao+MgO+TiO.sub.2 being less than 6.0% and greater than 0.5%, as percentages by weight, and more than 50% of the yttrium oxide and of the codopant being present in the matrix, as percentage by weight.

2. The product as claimed in claim 1, in which: the content of chromium oxide Cr.sub.2O.sub.3 is greater than 65%, and/or the content of aluminum oxide Al.sub.2O.sub.3 is less than 35%, and/or the content of zirconium oxide ZrO.sub.2 is greater than 3%, and/or the content of yttrium oxide Y.sub.2O.sub.3 is greater than 0.2%, and/or the total content of chromium oxide, aluminum oxide and zirconium oxide Cr.sub.2O.sub.3+Al.sub.2O.sub.3+ZrO.sub.2 is greater than 80%, as percentages by weight on the basis of the oxides.

3. The product as claimed in claim 2, in which: the content of chromium oxide Cr.sub.2O.sub.3 is greater than 75%, and/or the content of aluminum oxide Al.sub.2O.sub.3 is less than 10%, and/or the content of zirconium oxide ZrO.sub.2 is greater than 4.5%, and/or the content of yttrium oxide Y.sub.2O.sub.3 is greater than 0.3%, and/or the total content of chromium oxide, aluminum oxide and zirconium oxide Cr.sub.2O.sub.3+Al.sub.2O.sub.3+ZrO.sub.2 is greater than 90%, and/or the sum of the contents of chromium oxide Cr.sub.2O.sub.3, aluminum oxide Al.sub.2O.sub.3, zirconium oxide ZrO.sub.2, yttrium oxide Y.sub.2O.sub.3, calcium oxide CaO, silicon oxide SiO.sub.2, magnesium oxide MgO, titanium oxide TiO.sub.2 and hafnium oxide HfO.sub.2 is greater than 95%, as percentages by weight on the basis of the oxides.

4. The product as claimed in claim 3, in which: the content of chromium oxide Cr.sub.2O.sub.3 is greater than 80%, and/or the content of aluminum oxide Al.sub.2O.sub.3 is less than 5%, and/or the content of zirconium oxide ZrO.sub.2 is greater than 5%.

5. The product as claimed in claim 1, in which more than 50% of the zirconium oxide is stabilized in the cubic and/or tetragonal form, as percentage by weight.

6. The product as claimed in claim 1, in which the only zirconium oxide present in the matrix represents more than 2.5% of the total weight of the product.

7. The product as claimed in claim 1, in which more than 90% of the yttrium oxide Y.sub.2O.sub.3 is present in the matrix.

8. The product as claimed in claim 1, in which the content of aluminum oxide Al.sub.2O.sub.3 in the matrix is greater than 1% and less than 10%, as percentage by weight on the basis of the weight of the oxides of the product.

9. The product as claimed in claim 1, in which: the content of aluminum oxide Al.sub.2O.sub.3 is greater than 1%, and/or the content of silicon oxide SiO.sub.2 is greater than 0.5% and less than 6%, as percentages by weight on the basis of the oxides.

10. The product as claimed in claim 1, in which: the content of aluminum oxide Al.sub.2O.sub.3 is greater than 2%, and/or the content of silicon oxide SiO.sub.2 is less than 3%.

11. The product as claimed in claim 1, comprising, as percentage by weight on the basis of the oxides, for a total of 100%: 60%<Cr.sub.2O.sub.3<95%, 1% <Al.sub.2O.sub.3<25%, 3% <ZrO.sub.2<10%, HfO.sub.2<1.0%, 0.1% <Y.sub.2O.sub.3<2.0%, other oxides <10%.

12. The product as claimed in claim 1, wherein the codopant is CaO.

13. The product as claimed in claim 12, wherein the content of CaO is greater than 0.04%.

14. The product as claimed in claim 12, wherein the content of CaO is greater than 0.1%.

15. The product as claimed in claim 12, wherein the content of CaO is greater than 0.2%.

16. The product as claimed in claim 1, manufactured by sintering a charge comprising a zirconium oxide powder codoped with calcium oxide and yttrium oxide, and a zirconium oxide powder doped with yttrium oxide.

17. The product as claimed in claim 1, wherein the content of MgO is greater than 0.1%.

18. The product as claimed in claim 1, wherein the content of MgO is greater than 0.5%.

19. The product as claimed in claim 1, wherein the content of TiO.sub.2 is greater than 0.5%.

20. The product as claimed in claim 1, comprising, as percentage by weight on the basis of the oxides, for a total of 100%: 65%<Cr.sub.2O.sub.3<90%, 2%<Al.sub.2O.sub.3<10%, 4%<ZrO.sub.2<8%, HfO.sub.2<0.5%, 0.2% <Y.sub.2O.sub.3<2.0%, other oxides <5%.

21. The product as claimed in claim 1, wherein more than 90% of the yttrium oxide and of the codopant being present in the matrix, as percentage by weight.

22. A gasifier comprising a reactor provided with an internal wall lined, at least partially, with a refractory lining comprising a product as claimed in claim 1.

23. The gasifier as claimed in claim 22, in which said refractory product is provided in the form of a layer or in the form of a block.

24. A manufacturing process of a sintered refractory product, the process comprising the following successive stages: a) preparation of a charge, b) casting said charge in a mold and shaping so as to form a preform, c) removing the preform from the mold, d) optionally, drying the preform, e) firing the preform at a temperature of between 1300 and 1600 C., so as to form a sintered refractory product, in which process the charge is suitable for resulting, at the end of stage e), in the sintered refractory product as claimed in claim 1, the charge comprising a matrix fraction comprising a zirconium oxide powder stabilized, at least in part, with yttrium oxide.

Description

DETAILED DESCRIPTION

(1) The sintered refractory product according to the invention is composed of grains bonded and surrounded by a matrix.

(2) The grains may exhibit varied chemical analyses, in particular may comprise chromium oxide.

(3) In particular, the aggregate may be composed, for more than 80%, indeed even more than 85%, indeed even more than 90%, indeed even more than 95%, indeed even more than 97%, of its weight, of chromium oxide and/or aluminum oxide, in particular of chromium oxide.

(4) The matrix preferably comprises zirconium oxide. The only zirconium oxide present in the matrix preferably represents more than 2.5%, indeed even more than 5%, indeed even more than 10% of the total weight of the product. The zirconium oxide is stabilized by yttrium oxide and at least 20% by weight is stabilized in the cubic and tetragonal form.

(5) In particular, the matrix may be composed, for more than 90%, indeed even more than 94%, of its weight, of zirconium oxide and of yttrium oxide and/or of chromium oxide and/or of aluminum oxide and/or of silicon oxide, and optionally of a codopant chosen from CaO, MgO, TiO.sub.2 and their mixtures, the codopant acting or not acting as stabilizer for the zirconium oxide. Preferably, the codopant is CaO.

(6) In one embodiment, the product comprises, as percentage by weight on the basis of the oxides, for a total of 100%, 60%<Cr.sub.2O.sub.3<95%, preferably 65%<Cr.sub.2O.sub.3<90%, 1%<Al.sub.2O.sub.3<25%, preferably 2%<Al.sub.2O.sub.3<10%, preferably Al.sub.2O.sub.3<5%, 3%<ZrO.sub.2 <10%, preferably 4% <ZrO.sub.2 <8%, HfO.sub.2<1.0%, preferably HfO.sub.2<0.5%, 0.1%<Y.sub.2O.sub.3<4.0%, preferably 0.2%<Y.sub.2O.sub.3<3.0%, other oxides <10%, preferably other oxides <5%.

(7) Use may be made, in order to manufacture a block made of a sintered refractory product according to the invention, of a process comprising stages a) to e) above.

(8) Stages a) to e) are stages conventionally employed to manufacture sintered products.

(9) In stage a), a charge is prepared comprising: a particulate mixture composed of particles of the oxides intended to form the sintered refractory product and/or of particles of precursors of these oxides, optionally one or more additives, optionally water.

(10) The composition of the particulate mixture of the charge is determined as a function of the final composition of the block.

(11) Preferably, the particulate mixture is composed, for more than 90%, more than 95%, indeed even substantially 100%, by weight, of particles having a size of less than 20 mm.

(12) Preferably, the grains represent more than 60%, indeed even more than 70%, and/or less than 90%, less than 80%, of the weight of the particulate mixture, the remainder to 100% being composed of the matrix particles.

(13) The way of determining the amounts of the oxides or precursors of oxides in the charge is fully known to a person skilled in the art. In particular, a person skilled in the art knows that the chromium oxide, aluminum oxide and zirconium oxide present in the starting charge are reencountered in the refractory product manufactured. Some oxides may also be contributed by the additives. For one and the same amount of the constituents of the sintered refractory product, the composition of the starting charge may thus vary, in particular as a function of the amounts and of the nature of the additives present in this charge.

(14) The chromium oxide may be contributed in the form of a mixture of sintered or fused particles of chromium oxide optionally comprising aluminum oxide.

(15) Preferably, the source of zirconium oxide comprises more than 80%, preferably more than 90%, by weight of zirconium oxide.

(16) The zirconium oxide is contributed in the form of a stabilized zirconium oxide powder, preferably stabilized by means of yttrium oxide. At least 20% by weight of the zirconium oxide is stabilized in the cubic and/or tetragonal form. The zirconium oxide may comprise a codopant. Preferably, the codopant is chosen from CaO, MgO, TiO.sub.2 and their mixtures. Preferably, the codopant is CaO.

(17) Preferably, the zirconium oxide is doped to more than 3%, indeed even more than 4%, indeed even more than 5%, with yttrium oxide and optionally a codopant, preferably chosen from CaO, MgO, TiO.sub.2 and their mixtures, as a percentage by weight on the basis of the total weight of the zirconium oxide, yttrium oxide and codopant. Preferably, the codopant is CaO and its content in the zirconium oxide powder is between 2% and 4%, on the basis of the total weight of the zirconium oxide, yttrium oxide and calcium oxide.

(18) The stabilized zirconium oxide is preferably introduced, for more than 70%, more than 80%, more than 90%, indeed even substantially 100%, of its weight, in the form of matrix particles.

(19) The hafnium oxide HfO.sub.2 is always naturally present in the sources of zirconium oxide, at contents generally less than 2%. In one embodiment, the hafnium oxide is introduced only as impurities, in particular with the source of zirconium oxide.

(20) The aluminum oxide may in particular be contributed in the aggregate in the form of a mixture of sintered or fused particles of chromium oxide and aluminum oxide or in the matrix fraction in the form of a mixture of particles of calcined or reactive alumina, indeed even of white corundum.

(21) The additives may be added to the charge in order to provide it with sufficient plasticity during the shaping stage b) and in order to confer sufficient mechanical strength on the preform obtained at the end of stages c) and d). Mention may be made, as examples of usable additives well known to a person skilled in the art, without implied limitation, of: temporary (that is to say, removed in all or in part during the drying and firing stages) organic binders, such as resins, cellulose derivatives or lignone, or polyvinyl alcohols; preferably, the amount of temporary binder is between 0.1 and 6% by weight, with respect to the weight of the particulate mixture of the charge; shaping agents, such as magnesium stearate or calcium stearate; hydraulic binders, such as a cement of CaO aluminate type; deflocculants, such as alkali metal polyphosphates or methacrylate derivatives; sintering promoters, such as titanium dioxide or magnesium hydroxide; additions of clay type which will facilitate the processing and help in the sintering. These additions contribute alumina and silicon oxide, and a few alkali metal or alkaline earth metal oxides, indeed even iron oxide, depending on the type of clay.

(22) The amounts of additives are not limiting. In particular, the amounts conventionally employed in sintering processes are appropriate.

(23) Preferably, the content of clay in the starting charge is greater than 0.5%, greater than 1.0%, greater than 1.5%, and/or less than 5.0%, less than 3.0%, as percentage by weight on the basis of the oxides.

(24) The sources of zirconium oxide conventionally comprised traces of hafnium oxide.

(25) If appropriate, if an additive contributes one or more of the oxides participating in the composition of the refractory product, this contribution is preferably taken into account in determining the composition of the particulate mixture.

(26) Preferably, the charge comprises, as percentage by weight: more than 60% and preferably less than 90% of grains; less than 40% of matrix particles; less than 7% of one or more shaping additives.

(27) Preferably, the grains and the matrix particles together represent more than 94%, preferably more than 95%, of the weight of the charge.

(28) The mixing of the different constituents of the charge is continued until a substantially homogeneous mass is obtained.

(29) Preferably, between 1% and 5% of water, as a percentage by weight on the basis of the particulate mixture, is added.

(30) The charge is preferably conditioned. Advantageously, it is thus ready for use.

(31) The invention also relates to a particulate mixture as described above and to a charge prepared or capable of having been prepared during a stage a).

(32) In stage b), the charge is placed in a mold and then shaped.

(33) In the case of a shaping by pressing, a specific pressure of 400 to 800 kg/cm.sup.2 is appropriate. The pressing is preferably carried out in a uniaxial or isostatic manner, for example using a hydraulic press. It may advantageously be preceded by a manual or pneumatic ramming and/or vibrating operation.

(34) In stage c), the preform thus obtained is removed from the mold.

(35) In stage d), the drying may be carried out at a moderately high temperature.

(36) Preferably, it is carried out at a temperature between 110 C. and 200 C. It conventionally lasts between 10 hours and a week, depending on the format of the preform, until the residual moisture content of the preform is less than 0.5%.

(37) The invention also relates to a preform obtained in stage c) or in stage d).

(38) In stage e), the dried preform is fired. The duration of the firing, of between 3 and 15 days approximately from cold to cold, may vary according to the composition but also according to the size and the shape of the preform. The firing cycle is preferably carried out conventionally, under air, at a temperature of between 1300 C. and 1600 C.

(39) Preferably, the sintered refractory product obtained on conclusion of stage e) exists in the form of a block having a weight of greater than 1 kg and/or for which all the dimensions are greater than 100 mm.

(40) Surprisingly, the sintered refractory product obtained on conclusion of stage e) has proved to be particularly resistant to the stresses encountered inside gasifier reactors, in particular resistant to infiltration by the slags or the molten ashes.

(41) The firing stage e) may be carried out, in all or in part, after assembly of the preform in the reactor.

(42) The blocks are assembled by means of appropriate expansion joints, according to techniques well known to a person skilled in the art.

(43) The manufacture of a product according to the invention is not limited to the process described above. In particular, the invention also relates to a refractory product according to the invention in the form of a lining of a reactor, in particular of a gasifier. To this end, a charge, for example manufactured according to stage a) above, may be applied as a layer on the internal surface of the wall of the reactor, for example by casting, vibro-casting or spraying, according to requirements and with great flexibility, and then sintered in situ during the preheating of the reactor, so as to produce a lining made of a refractory product according to the invention. The sintering preferably takes place at atmospheric pressure, preferably under an oxidizing atmosphere, and preferably at a temperature between 1300 and 1600 C.

(44) In order not to needlessly expand the present description, not all the possible combinations according to the invention of the various embodiments are given. However, it is clearly understood that all the possible combinations of the initial and/or preferred ranges and values described above as regards the product, the matrix or the aggregate or also the process are envisaged.

EXAMPLES

(45) The examples which will follow make it possible to nonexhaustively illustrate the invention. For these examples, the following starting materials were used: sintered chromium oxide powder comprising approximately 98% of Cr.sub.2O.sub.3 and 2% of TiO.sub.2 by weight and composed of at least 90% by weight of particles having a size of greater than 20 microns but less than 5 mm (powder G1), sintered chromium oxide powder comprising approximately 88% of Cr.sub.2O.sub.3, approximately 6% of Al.sub.2O.sub.3, approximately 3.5% of SiO.sub.2 and approximately 1.8% of TiO.sub.2 by weight and composed of at least 90% by weight of particles having a size of greater than 20 microns but less than 5 mm (powder G2), sintered chromium oxide powder comprising approximately 45% of Cr.sub.2O.sub.3, approximately 52% of Al.sub.2O.sub.3, approximately 1.1% of SiO.sub.2 and approximately 1.6% of TiO.sub.2 by weight and composed of at least 90% by weight of particles having a size of greater than 20 microns but less than 5 mm (powder G3), pigment chromium oxide powder (>98% of Cr.sub.2O.sub.3), the median size (D.sub.50) of which is less than 2 microns (powder P1), zirconium oxide powder (>98% by weight of ZrO.sub.2) stabilized with 4.2% by weight of CaO, the size of the particles being less than 50 microns, the median size being approximately 12 m, and said particles comprising approximately 70% of zirconium oxide in the tetragonal and/or cubic form (powder P2), alumina powder (>98% by weight of Al.sub.2O.sub.3), the median size (D.sub.50) of which is less than 10 microns (powder P3), zirconium oxide powder (>91% by weight of ZrO.sub.2) stabilized with approximately 3.2% by weight of CaO and approximately 1.1% by weight of Y.sub.2O.sub.3, comprising approximately 70% of zirconium oxide in the tetragonal and/or cubic form, as a percentage by weight on the basis of the zirconia, the size of the particles being less than 60 microns (D.sub.90=47 m) with a median size of approximately 13 m (powder P4), zirconium oxide powder (>91% by weight of ZrO.sub.2) stabilized with approximately 6.4% by weight of Y.sub.2O.sub.3, comprising approximately 70% of zirconium oxide in the tetragonal and/or cubic form, as a percentage by weight on the basis of the zirconia, the size of the particles being less than 50 microns (D.sub.90=34 m) with a median size of approximately 8 m (powder P5a), or being less than 50 microns (D.sub.90=8 m) with a median size of approximately 3 m (powder P5b), yttrium oxide powder (>99% of Y.sub.2O.sub.3), the median size (D.sub.50) of which is between 5 and 10 microns (powder P6), additives: RR40 clay comprising approximately 40% of Al.sub.2O.sub.3, approximately 55% of SiO.sub.2, approximately 2.3% of TiO.sub.2, approximately 2% of Fe.sub.2O.sub.3 and approximately 0.6% of CaO.

(46) The products tested were manufactured according to stages a) to e) described above.

(47) In stage a), the starting materials as shown in table 1 were mixed with from 0.5 to 2% of RR40 clay and approximately 3% of water and also from 0.3 to 0.7% of binders (magnesia stearate and Bretax C) were added to the particulate mixture, as a percentage on the basis of said particulate mixture.

(48) The silicon oxide originates essentially from the addition of clay.

(49) In stage b), compacting of the charge inside the mold at a pressure of 600 kg/cm.sup.2 was carried out so as to form a preform.

(50) In stage d), the firing was carried out under air at a temperature of between 1400 and 1600 C. so as to form a sintered refractory product.

(51) The bulk density (Bd) and open porosity (Op) measurements were carried out according to the standard ISO 5017 on the products before any corrosion.

(52) The change in the flexural modulus of rupture of products which have been subjected to a thermal shock between 800 C. and 20 C. was evaluated according to the standard ISO 5014. The residual flexural modulus of rupture value after a thermal shock test is denoted MOR res and the loss in MOR (MOR res with respect to the initial MOR measured at 20 C.) is denoted MOR in table 1. The MOR res has to be as high as possible. A lower AMOR (of at least 20% in absolute value) indicates a greater stability of the properties of the product. Likewise, the residual flexural modulus of rupture value after three thermal shock tests is denoted MOR res 3 and the loss in MOR (MOR res 3 with respect to the initial MOR measured at 20 C.) is denoted MOR 3 in table 1.

(53) The other measurements were carried out on products subjected, after sintering, to a corrosion representative of the operating conditions experienced by the hot face of the gasifier linings. This corrosion was obtained in the following way. Eight test specimens of the product to be tested, with a length of 200 mm and with a trapezoidal section, the bases of which measure 63 mm and 90 mm respectively and the height of which measures 33 mm, are placed in a metal hoop in order to form a rotary furnace in which the molten slag is placed, at a temperature of 1600 C., for 5 hours. The test specimens and the hoop are rotated at a speed of 2 revolutions per minute.

(54) The slag used exhibits the following composition by weight: SiO.sub.2: approximately 30-50% Al.sub.2O.sub.3: approximately 10-20% Fe.sub.2O.sub.3 or FeO: 15-25% CaO: approximately 10-20% Other entities, such as MgO: remainder to 100%.

(55) The basicity index B of this slag, that is to say the (CaO+MgO+Fe.sub.2O.sub.3)/(SiO.sub.2+Al.sub.2O.sub.3) ratio by weight, was typically of the order of 0.6. The CaO/SiO.sub.2 ratio by weight was of the order of 0.4.

(56) The depth of penetration of CaO originating from the slag is measured by virtue of a microprobe analyzer carried out on a metallographic section. The indicator of penetration (Ip) is equal to the ratio of the depth penetrated of the test specimen of the reference example (example 1 for examples 2 to 8, example 9 for examples 10, 13 and 14, example 11 for example 12 and example 15 for example 16) to the depth penetrated of the test specimen of the example under consideration, multiplied by 100. Ip is thus 100 for the reference product and a value of greater than 110 indicates a better resistance to the penetration of the slag. The values of greater than 165 are representative of a very significantly improved resistance to the penetration of the slag (+50%).

(57) The results obtained are summarized in table 1 below.

(58) The HfO.sub.2 content is substantially equal to 0.1%.

(59) TABLE-US-00001 TABLE 1 No. 1 2 3 4 5 6 7 8 Components of the charge G1 74.5 74.5 74.5 74.5 74.5 74.5 74.5 74.5 P1 14.7 14.7 14.7 14.7 14.7 14.7 14.7 14.7 P2 6.9 5.9 3.4 P3 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 P4 6.9 3.4 3.4 P5a 3.4 6.9 3.4 P5b 6.9 3.4 P6 1.0 Chemical analysis, calculated on the basis of the starting materials (as % by weight) Cr.sub.2O.sub.3 87.6 87.6 87.7 87.7 87.6 87.7 87.7 87.7 ZrO.sub.2 + HfO.sub.2 6.5 5.6 6.4 6.4 6.4 6.4 6.4 6.4 SiO.sub.2 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Al.sub.2O.sub.3 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 TiO.sub.2 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6 CaO 0.3 0.3 0.2 0.2 / / 0.1 0.1 Y.sub.2O.sub.3 / 1.0 0.2 0.1 0.5 0.4 0.3 0.3 Other properties of the sintered product (before corrosion) Bd (g/cm.sup.3) 4.2 4.2 4.3 4.2 4.3 4.2 4.2 4.2 Op (%) 14.3 13.1 11.8 14.0 13.4 13.6 14.1 14.2 Resistance to thermal shocks MOR res 11 9 13 13 16 9 11 14 (MPa) MOR (%) 72 80 67 63 60 82 74 42 MOR res 3 3 3 8 5 3 2 4 13 (MPa) MOR 3 (%) 91 94 80 86 92 96 90 46 Measurements of resistance to the penetration of CaO due to the corrosion Ip 100 109 207 164 249 328 295 193

(60) TABLE-US-00002 TABLE 2 No. 9 10 11 12 13 14 15 16 Components of the charge G1 75.2 75.2 75.2 75.2 81.2 81.2 G2 42 42 G3 34 34 P1 17.0 17.0 15 15 17.0 17.0 11.9 11.9 P2 4.5 7.0 4.0 P3 2.3 2.3 2.0 2.0 2.3 2.3 2.0 P4 2.3 1.5 1.0 P5a 4.5 7.0 2.2 3.0 3.0 Chemical analysis, calculated on the basis of the starting materials (as % by weight) Cr.sub.2O.sub.3 90.7 90.9 65.2 65.2 90.7 90.7 91.4 91.4 ZrO.sub.2 + HfO.sub.2 4.3 4.3 6.9 6.5 4.2 4.2 3.7 3.7 SiO.sub.2 0.6 0.3 2.4 2.4 0.6 0.6 0.6 0.6 Al.sub.2O.sub.3 2.7 2.7 23.7 23.7 2.7 2.7 2.4 2.4 TiO.sub.2 1.5 1.5 1.2 1.2 1.5 1.5 1.7 1.7 CaO 0.19 / 0.4 / 0.05 0.08 0.17 0.04 Y.sub.2O.sub.3 / 0.29 / 0.5 0.21 0.17 / 0.20 Other properties of the sintered product (before corrosion) Bd (g/cm.sup.3) 4.2 4.3 4.0 4.0 4.2 4.2 4.2 4.2 Op (%) 14.6 13.1 13.4 12.5 16.3 15.8 15.0 15.5 Resistance to thermal shocks MOR res 10 11 11 10 17 19 9 16 (MPa) MOR (%) 71 76 51 63 32 27 71 43 MOR res 3 ND ND ND ND 12 19 7 11 (MPa) MOR 3 (%) 50 54 79 60 Measurements of resistance to the penetration of CaO due to the corrosion Ip 100 487 100 151 258 248 100 235

(61) The tables make it possible to confirm that the addition of zirconium oxide doped with yttrium oxide has a very favorable effect for the resistance to the penetration of the slag (Ip) once the content of yttrium oxide in the product has reached 0.1% by weight, in particular for the products having a higher content of chromium oxide (in particular of greater than 70% by weight), which results in a reduction in the phenomenon of spelling, thus making it possible to improve the lifetime of products of this type.

(62) This addition also makes it possible to retain, indeed even to improve, the resistance to thermal shocks, all the more so when the zirconium oxide powder doped with yttrium oxide introduced into the matrix fraction exhibits a median size of greater than 5 m, as is shown by the comparison of examples 5 and 6 or 8 and 7.

(63) The resistance to thermal shocks is also improved in a noteworthy way when a zirconium oxide power codoped with calcium oxide and yttrium oxide is used in synergy with a zirconium oxide powder doped with yttrium oxide, as is shown by the comparison of example 8 with examples 4 and 5 or also by the comparison of example 13 or 14 with example 10 or, finally, by the comparison of example 16 with example 15.

(64) A comparison of examples 1 and 2 shows that the addition of yttrium oxide independently of the zirconium oxide does not improve the performance. It is thus important for the zirconium oxide to be stabilized, at least in part, indeed completely, by the yttrium oxide before the sintering.

(65) In an application in a gasifier, examples 5 to 8, 13 and 14 are regarded as the best, and in particular examples 8, 13 and 14 offer a very good compromise between the resistance to the penetration of CaO, the resistance to thermal shocks and the manufacturing cost (CaO being cheaper than Y.sub.2O.sub.3).

(66) A comparison of examples 11 and 12 also illustrates the advantage of the addition of a powder formed of particles of zirconium oxide stabilized with yttrium oxide for improving the resistance to the penetration of CaO with regard to sintered products, the aggregate of which is composed of chromium oxide and aluminum oxide, while retaining a good resistance to thermal shocks. A comparison of these examples also confirms that a stabilization with yttrium oxide is more effective than a stabilization with calcium oxide.

(67) An analysis with a scanning electron microscope (SEM) coupled with an EDS (Energy Dispersive Spectrometry) analysis makes it possible to confirm that, in the products of the invention, the yttrium oxide (and, if appropriate, the calcium oxide) is indeed combined with the zirconium oxide of the matrix.

(68) Of course, the present invention is not limited to the embodiments described, provided as illustrative and nonlimiting examples.

(69) In particular, the application of the sintered refractory product according to the invention is not limited to a gasifier.