GB2567660A

GB2567660A - Refractory material

Info

Publication number: GB2567660A
Application number: GB1717157.0A
Authority: GB
Inventors: Dukes Gary; Joseph Handley Stuart; James Zampell Brian; Michael Heffeman John
Original assignee: VULCAN REFRACTORIES Ltd
Current assignee: VULCAN REFRACTORIES Ltd
Priority date: 2017-10-19
Filing date: 2017-10-19
Publication date: 2019-04-24
Also published as: WO2019077318A1; GB201717157D0

Abstract

A refractory material and a method of the making the same is described. The refractory material includes silicon carbide reactively sintered with silicon metal in a nitrogen atmosphere to form the silicon nitride bound silicon carbide and further includes an additive comprising vanadium pentoxide. The fired refractory includes at least 96.5 weight % silicon carbide, silicon nitride and vanadium pentoxide, and the silicon carbide is in the range of 65‑ 90 weight %, silicon nitride is in the range of 10-35 weight %, and the additive is in the range of 0.1 - 4 weight %. The refractory material may have a weight gain of less than 2.5% upon exposure to an oxidation environment at 1000ºC. The refractory material may be used in a boiler, incinerator, heat exchanger, kiln furniture, autoclave part, exhaust gas heat exchanger or high temperature nozzle.

Description

REFRACTORY MATERIAL

FIELD OF INVENTION

This invention relates to SiC bonded with S13N4 refractory material with improved oxidation resistance and a method of manufacturing it.

BACKGROUND

Silicon carbide (SiC) bound by a matrix of silicon nitride (S13N4) was developed at the end of the 1970s as described, for example, in U.S. Pat. No. 2,752,258, to be used as refractory material. Silicon carbide (SiC) bound by a matrix of silicon nitride (S13N4) is obtained by reactive sintering of a mixture of silicon carbide and silicon, with nitrogen deriving from firing in a nitrogen atmosphere.

Silicon carbide (SiC) bound by a matrix of silicon nitride (S13N4) materials material facilitates a compromise between oxidation resistance, mechanical strength (erosion), and thermal conductivity which is superior to that of carbon blocks. The improvement in abrasion resistance these materials offer is particularly advantageous in applications where this property is required. However, the usefulness of the material is limited by degradation as a consequence of oxidation when held at high temperatures (over 800°C) in the presence of oxygen. The oxidation leads to the conversion of the carbide to oxide. This deleteriously alters the material properties and ultimately leads to product failure.

The invention is aimed at reducing the rate of oxidation which in turn extends the useful life of the silicon carbide (SiC) bound by a matrix of silicon nitride (S13N4) materials in service.

SUMMARY OF INVENTION

In an aspect a refractory material includes silicon carbide reactively sintered with silicon metal in a nitrogen atmosphere to form silicon nitride bound silicon carbide, further including an additive; wherein, the additive comprises vanadium pentoxide; and wherein, in the fired refractory, there is present in total at least 96.5 weight % silicon carbide, silicon nitride and vanadium pentoxide, and the silicon carbide is present in the range of 65 — 90 weight %, silicon nitride is present in the range of 10 — 35 weight %, and the additive is present in the range of 0. 1-4 weight %.

In some embodiments, the silicon carbide and silicon nitride are present in a ratio ranging between 2:1 to 9:1.

In some embodiments, the silicon nitride is present in a beta form and alpha form having a ratio of ranging between 1 :99 to 99: 1.

In some embodiments, the porosity is between 5-30%.

In some embodiments, silicon carbide is present in the amount of around 70 85 % by weight, silicon nitride is present in the amount of around 15 - 35% by weight, vanadium pentoxide is present in the amount of around 0.1 - 2.5% by weight.

In some embodiments, the silicon carbide is reactively sintered with silicon metal at a temperature above 1400 °C.

In some embodiments, the reactive sintering at 1400 °C continues for around 5 days.

In some embodiments, a boiler includes an interior surface lined with the refractory material described above. In some other embodiments, the refractory material is configured to be exposed to a temperature above 800 °C.

In some embodiments, an incinerator includes an interior surface lined with the refractory material described above. In some other embodiments, the refractory material is configured to be exposed to a temperature above 800 °C.

In some embodiments, a heat exchanger includes an interior surface made of the refractory material described above. In some other embodiment, the refractory material is configured to be exposed to a temperature above 800 °C.

In some embodiments, a kiln furniture, an autoclave part, an exhaust gas heat exchanger or a high temperature nozzle comprises the refractory material described above. In some other embodiments, the kiln furniture, the autoclave part, the exhaust gas heat exchanger or the high temperature nozzle is configured to be exposed to a temperature above 800 °C.

In some embodiments, the refractory material is configured to have a percentage weight gain less than 2.5% upon exposure to an oxidation environment at 1000°C.

In an aspect a method of making a refractory material includes providing a raw material to be blended; wherein the raw material solely comprises of silicon carbide, silicon metal, vanadium pentoxide, a temporary binder and water; blending the raw materials to form a mix; shaping the mix into a formed shape; drying the formed shape to eliminate moisture; firing the formed shape that has dried at a temperature in a nitrogen atmosphere.

In some embodiments, silicon carbide is in the range of 65 — 90 weight %, silicon metal powder is in the range of 4 — 20 weight %, vanadium pentoxide is in the range of 0.1 — 2%, the temporary binder is in the range of 1 - 4 weight % and water is in the range of 1-5 weight %. In some other embodiments, silicon carbide powder is provided in the form of a dry powder comprising of black refractory grade SiC or high purity SiC. In some other embodiments, the black refractory grade SiC has a purity of 97% SiC content.

In some embodiments, the silicon carbide powder comprises of particles having a blocky grain having an aspect ratio ranging from 1.0 - 3.0mm.

In some embodiments, the particle size distribution of the silicon carbide powder comprises 50 % of the particles having a particle size in the range of 0.5 — 1.5 mm, 10 % of the particles having a particle size in the range of 0.25 — 0.5 mm, 15 % of the particles having a particle size in the range of 0.1 — 0.2 mm, and 10 % of the particles having a particle size less than 75 pm.

In some embodiments, silicon metal powder is provided in the form of a dry powder having purity of about 98.5 % silicon content.

In some embodiments, the particle size of the silicon metal is less than 0.5 mm

In some embodiments, the particle size of the silicon metal is less than 250 pm.

In some embodiments, 95% of the silicon metal particles have a particle size less than 100 pm.

In some embodiments, vanadium pentoxide is provided in the form of a dry powder having a particle size less than 0.5 mm.

In some embodiments, the particle size of the vanadium pentoxide is less than 250 pm.

In some embodiments, the d90 of the vanadium pentoxide is 45 — 50 pm and the d50 of the vanadium pentoxide particles is 10 — 20 pm.

In some embodiments, at least one of the temporary binders is a solution of modified starch derivatives, an aqueous solution of dextrin or of lignone derivatives, a polyvinyl alcohol, a phenol resin, an epoxy type resin, a furfuryl alcohol, or a mixture thereof. In some other embodiments, the lignone derived binder is calcium lignosulfonate powder. In some other embodiments, calcium lignonsulfonate powder is added to about 2.5 % by weight of the mix. In some other embodiments, the temporary binder is starch. In some other embodiments, starch is added to about 0.5 weight % of the mix. In some other embodiments, the quantity of temporary binder is in the range 0.5 % to 7 % by weight relative to the particulate mixture of the charge.

In some embodiments, silicon carbide is in the range of 75 — 85 % by weight, silicon metal powder is in the range of 10 —15% by weight, vanadium pentoxide in the range of about 0.75 - 1% by weight, the temporary binder includes calcium lignosulfonate in the range of about 2.3 — 2.5% by weight and starch in the range of about 0.3 — 0.5% by weight and water is in the range of 0.75 — 5 weight %.

In some embodiments, the mixing is carried out using a planetary mixer, spiral mixer, vertical cutter mixer, V-blenders, Marion Mixers, or Hobart Mixers.

In some embodiments, the mix is formed in to a formed shape by hydraulic pressing, vibratory pressing, impact pressing, or slip casting. In some other embodiments, the pressing is carried out uniaxially or isostatically.

In some embodiments, the formed shape is dried at a temperature ranging from 105 - 210 °C and for around 1-5 days to remove the water. In some other embodiments, the formed shape is dried at a temperature of about 120 ⁰ C and for around 3 days to remove the water.

In some embodiments, the residual moisture content of the formed shape after drying is less than 1.0%, or less than 0.5%.

In some embodiments, the firing is carried out at 1400°C. In some other embodiments, the firing at 1400 °C continues for around 5 days.

In an aspect a method includes lining a boiler, an incinerator, a heat exchanger or a furnace with a fired refractory including silicon carbide reactively sintered with silicon metal in a nitrogen atmosphere to form the silicon nitride bound silicon carbide, further including an additive; wherein, the additive comprises vanadium pentoxide; and wherein, in the fired refractory, there is present in total at least 96.5 weight % silicon carbide, silicon nitride and vanadium pentoxide, and the silicon carbide is present in the range of 65 — 90 weight %, silicon nitride is present in the range of 10 — 35 weight %, and the additive is present in the range of 0.1 - 4 weight %.

In some embodiments, the silicon carbide is reactively sintered with silicon metal at a temperature above 1400 °C. In some other embodiments, the reactive sintering at 1400 °C continues for around 5 days.

BRIEF DESCRIPTION OF DRAWINGS AND FIGURES

The above and other objects and advantages of the present disclosure will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout.

FIG. 1 shows the various steps employed in the production of a refractory material in accordance with this disclosure;

FIG. 2 shows a schematic of the set-up used for conducting the ASTM C863 standard use for evaluating the performance of a silicon carbide refractory in oxidation conditions;

FIG. 3 shows the oxidation, represented as a percentage weight gain, of a refractory material held at 1000 °C over a period of time for a standard SiC bonded S13N4 refractory (line X), a standard SiC bonded S13N4 refractory with 1 weight % vanadium pentoxide (line Y);

FIG. 4 shows the percentage weight increase rate per hundred hours for the two samples discussed in FIG. 3;

FIG. 5 shows the comparison of the weight increase rate per 100 hours after initial passivation of single fired and twice fired three standard types of SiC bonded S13N4 refractory material after 500 hours of oxidation at 1000°C, namely, Standard Product, twice fired Standard Product and Standard Product with 1 weight % vanadium pentoxide after 500 hours of oxidation at 1000°C; and

FIG. 6 shows the volume increase after 500 hours of oxidation at 1000°C for the samples shown in FIG. 5.

DETAILED DESCRIPTION

A refractory material includes, silicon carbide reactively sintered with silicon metal in a nitrogen atmosphere to form the silicon nitride bound silicon carbide and additional additive. The additive includes vanadium pentoxide. The fired refractory includes present in total at least 96.5 weight % silicon carbide, silicon nitride and vanadium pentoxide with the silicon carbide (SiC), present in the range of 65 — 90 weight %; silicon nitride (S13N4), present in the range of 10 — 35 weight %; and the additive, present in the range of 0.1 - 4 weight %.

In certain embodiments, the fired refractory includes 80 — 85 weight % silicon carbide (SiC). In certain embodiments, the fired refractory includes 15 — 35 weight % silicon nitride. In certain embodiments, the fired refractory includes 0.5 2.0 weight %, for example, about 1 weight % additive of vanadium pentoxide.

In some embodiments, the silicon nitride is present in a beta form and alpha form having a ratio of ranging between 1:99 to 99: 1.

In some embodiments, the porosity of the fired refractory material is between

1-30%.

Applicants have identified that the addition of vanadium pentoxide to the formulation of silicon nitride bonded silicon carbide refractory enhances resistance to oxidation in a wide range of high temperature oxidizing environments. The applications of specific interest for the material in accordance with this disclosure are refractories for use in industrial boilers and incinerators. In such applications silicon carbide materials are relied upon to protect the metal components from the deleterious effects of high temperature exposure. However, the prolonged exposure to temperatures greater than 800 °C result in the premature degradation of the refractory. These applications subject the refractory to prolonged elevated temperatures where the refractory can degrade through oxidation. Furthermore, in some of these applications the cyclic nature of heating and cooling additionally thermally shocks and stresses the refractory causing addition acceleration of the degradation. The improved oxidation resistance resulting from the addition of vanadium pentoxide containing silicon nitride bonded silicon carbide provides longer service life.

A protective glass coating on the silicon carbide can be used to reduce the rate of oxidation. It is possible to form a glass by firing at temperatures above 1000 °C or by adding glass formers. However two difficulties are encountered. Firstly, often only a surface glass is formed which can be lost during service and with it the protective effect. Secondly, using many glass forming additives is effective in producing glassy coatings, but the type of glass formed has poor protective properties. This can be due to low melting point glass that allows relatively easy oxygen transport, or poor thermal expansion characteristics which cause microcracking. Both effects allow oxygen to continue to reach the silicon carbide surfaces and therefore relatively poor passivation.

Without being bound by theory, it is believed that the addition of vanadium pentoxide to the refractory formulation promotes the formation of a high quality glass layer that is both refractory and durable. This glass acts as an effective barrier between the silicon carbide and any oxygen and therefore retards the rate of oxidation. The additives and glass are homogenously distributed within the refractory material and provide effective passivation throughout the material, not just on the surface.

However, the benefits of oxidation resistant silicon carbide bonded with silicon nitride materials are not limited to incineration applications alone and extend to all applications where silicon carbide bonded with silicon nitride is used and degrades as a consequence of oxidation. Suitable applications are, but not limited to, incinerator boiler protection tiles, metal (aluminium, copper, silicon, iron) furnace linings, tiles and other kiln furniture shapes for firing of ceramics, powders and other materials requiring high temperature firing, high temperature wear resistant components, heat treatment furnace shapes, such as skid rails, autoclave parts, high temperature nozzles, and exhaust gas heat exchangers.

Tn an aspect, the method employed in production of the refractory products in accordance with this disclosure is shown in FIG. 1 and includes the following steps:

i) Blending of raw material powders and grains to form a 'mix' ii) Forming of a shape by use of pressing or casting processes.

iii) Drying to remove water from the product iv) Firing to form the ceramic bond

Blending

The various components of the raw material powders and grains are blended to form a mix. The mix includes components such as:

(i) 65-90% Silicon carbide grains and powder (ii) 4-20%

Silicon metal powder (in; u. i-4/o Vanadium pentoxide (iv) 1-3% Organic binder (v) 1-5% Water

The silicon carbide powder is provided in the form of a dry powder comprising of black refractory grade SiC or high purity SiC. In some embodiments, the black refractory grade SiC has a purity of 97% SiC content. In certain embodiments, the silicon carbide powder comprises of particles having a blocky grain having an aspect ratio ranging from 1.0 - 1.3.

Silicon metal powder is provided in the form of a dry powder having purity of about 98.5% silicon content. In some embodiments, the particle size of the silicon metal is less than 0.5 mm. In some other embodiments, the particle size of the silicon metal is less than 250 pm. In some other embodiments, 95 ^% of the silicon metal particles have particle size less than 100 pm.

In some embodiments vanadium pentoxide powder is provided in the form of a dry powder having particle size less than 0.5 mm. In some embodiments, the particle size of the vanadium pentoxide powder is less than 250 pm. In some embodiments with the particle size distribution of the silicon metal powder has a d90 of 45 — 50 pm and a d50 of 10 — 20 pm.

Any known binder or mixture of known binders may be used as the temporary binder. The binders are preferably temporary, i.e. they are completely or partially eliminated during the drying and firing steps. More preferably, at least one of the temporary binders is a solution of modified starch derivatives, an aqueous solution of dextrin or of lignone derivatives, a solution of a processing agent such as polyvinyl alcohol, a phenol resin or another epoxy type resin, a furfuryl alcohol, or a mixture thereof. In certain embodiments, the quantity of temporary binder is in the range 0.5% to 7% by weight relative to the particulate mixture of the charge. In some embodiments, the lignone derivative used as the temporary binder is calcium lignosulfonate powder. In some embodiments, calcium lignosulphonate is added to about 2.5 weight % of mix. In some embodiments, starch is used in conjunction with the calcium lignosulfonate powder. In some embodiments, starch is added to about 0.5 weight % of the mix.

In a certain embodiment, the raw material for the mix includes silicon carbide in the range of 75- 85% by weight, silicon metal powder is in the range of 10-15% by weight, vanadium pentoxide in the range of about 0.5-2% by weight, the temporary binder including calcium lignosulfonate in the range of about 2.32.5% by weight and starch in the range of about 0.3-1.0% by weight, and water is in the range of 0.75-5 weight %.

The raw materials are blended and water added to form a damp mixture and activate the binder. The additives are homogenously distributed through the mix so as to impart their protective properties throughout the finished invention. This 'mix' is then used to form in to a shape.

Blending may be carried out using a commercial mixer. Some of the suitable mixers that may be used are; planetary mixer where the agitator spins on an offset shaft while the bowl containing the ingredients is held stationary; spiral mixer where a stationary helix shaped agitator is used to mix the components while the bowl is moved around it; vertical cutter mixer where the mixing bowl is covered with a high powered motor and interior agitator for high output operations, V-blenders, Marion Mixers, or Hobart Mixers. A person of ordinary skill in the art would easily recognize that other methods for mixing the components are possible and contemplated in accordance with this disclosure.

Mixing of the charge is continued until the components are homogeneously distributed throughout the mix.

Forming

The mix is formed in to a formed shape by traditional ceramic forming processes, such as pressing or casting. Suitable process include, hydraulic pressing, vibratory pressing, impact pressing, slip casting and other ceramic forming processes. In some embodiments, pressing is carried out uniaxially. In some other embodiments, pressing is carried out isostatically.

Drying

The formed shape contains water, which is removed prior to firing. In some embodiments, the shape is therefore dried, typically at a temperature in the range of 105 — 210 ⁰ c and for around 1 — 5 days to remove the water. In some embodiments, the shape is therefore dried, typically at a temperature of 120 ⁰ C and for around 3 days to remove the water. In some embodiments, the residual moisture content of the dried formed shape is less than 1.0 %. In some other embodiments, the residual moisture content of the dried formed shape is less than 0.5 %

Firing

The dried shape is fired to form the S13N4 bond and to activate the additives so as to impart their protective benefits. The firing process involves firing the dried shape to abovel400 ⁰ C in a nitrogen atmosphere which convert the Si metal to S13N4. This process takes typically 5 days. The final composition of the fired refractory has been discussed above.

Examples

FIG. 2 shows a schematic for the set-up in accordance with ASTM standard, ASTM C863 used for comparing the oxidation of a silicon-carbide based refractory. Briefly, ASTM C863 requires the testing pieces 10 in the environment of 800 - 1200 °C, enough steam supply (at least 32kg/m³) for 500 hours. So the testing environment is basically a chamber (furnace) 12 with a water supply 14. As seen in

FIG. 2, a peristaltic pump 16 with a timer 18 supplies distilled water at a given rate for a given period of time matching the running time of the furnace. Flexible silicon PTFE tubes 20, 22 are used outside the furnace 12, and a solid quartz tube 24 is used to endure high temperature environment inside the furnace 12. Alumina bricks 26 are used to control the volume, otherwise too much water is required for steam supply, these bricks do not oxidise in this environment or react with testing pieces. All the samples were tested for performance under oxidation using the above described set-up.

Two samples were tested for oxidation resistance according to the ASTM standard C863 described above. Sample X contained SiC bonded with S13N4 only with no additional additives. Sample Y contained SiC bonded with S13N4 with 1% vanadium pentoxide.

FIG. 3 shows the oxidation, represented as a percentage weight gain, of a refractory material held at 1000 °C over a period of time. FIG. 4 shows the percentage weight increase rate per hundred hours after initial passivation for the two samples discussed in FIG. 3.

It is clear that Sample X, containing SiC bonded S13N4 without any additives displays poor oxidation resistance as demonstrated by the very rapid increase in weight up to about 100 hours see Fig. 4, and thereafter a continued elevated rate of weight gain as compared with Sample Y. In contrast, Sample Y, SiC bonded with S13N4 with vanadium pentoxide added to the formulation, outperformed Sample X with a lower rate of initial weight gain and a lower total weight gain as illustrated in FIG. 3. This demonstrates the improvement produced by the presence of vanadium pentoxide in the formulation over the existing formulation known in the prior art.

FIG. 5 shows the weight increase rate per 100 hours after initial passivation, for single fired (Sample X) and twice fired (Sample XZ) standard types of SiC bonded S13N4 refractory material after 500 hours of oxidation at 1000°C. Also included is the rate per 100 hours after initial passivation for single fired (Sample Y) Standard Product which is made with SiC bonded with S13N4 along with 1 weight % vanadium pentoxide. Addition of 1 weight % vanadium pentoxide reduces the weight increase rate per 100 hours after passivation for the single fired Standard Product refractory from 0.22 to 0.06%. This is a significant improvement in durability and longevity of the refractory.

FIG. 6 shows the volume increase after 500 hours of oxidation at 1000°C for the samples shown in FIG. 5. As can be seen from the data the single and twice fired standard refractories (Samples X and X2) showed negligible difference in volume increase after 500 hours of oxidation at 1000°C. A superior dimensional stability is observed for the Standard Product refractory (Sample Y) containing 1 weight % vanadium pentoxide

In an aspect, a method includes lining a boiler, an incinerator, a heat exchanger or a furnace with a fired refractory including, silicon carbide reactively sintered with silicon metal in a nitrogen atmosphere to form the silicon nitride bound silicon carbide, further including additives; wherein, the additives comprise vanadium pentoxide; and wherein, in the fired refractory, there is present in total at least 96.5 weight % silicon carbide, silicon nitride and vanadium pentoxide, and the silicon carbide is present in the range of 65 — 90 weight %, silicon nitride is present in the range of 10 — 35 weight %, and additives are present in the range of 0.1 -4 weight %.

Upon review of the description and embodiments provided herein, those skilled in the art will understand that modifications and equivalent substitutions may be performed in carrying out the invention without departing from the essence of the invention. Thus, the invention is not meant to be limiting by the embodiments described explicitly above.

Claims

1. A refractory material comprising:

silicon carbide reactively sintered with silicon metal in a nitrogen atmosphere to form silicon nitride bound silicon carbide, further including an additive;

wherein, the additive comprises vanadium pentoxide; and wherein, in the fired refractory, there is present in total at least 96.5 weight % silicon carbide, silicon nitride and vanadium pentoxide, and the silicon carbide is present in the range of 65 — 90 weight %, silicon nitride is present in the range of 10 — 35 weight %, and the additive is present in the range of 0.1 -4 weight %.

2. A refractory material according to claim 1, wherein, the silicon carbide and silicon nitride are present in a ratio ranging between 2:1 to 9:1.

3. A refractory material according to claims 1 or 2, wherein, the silicon nitride is present in a beta form and alpha form having a ratio of ranging between 1:99 to 99: 1.

4. A refractory material according to any of the preceding claims, wherein, the porosity is between 2 - 30 %.

5. A refractory material according to any of the preceding claims, wherein, silicon carbide is present in the amount of around 70 - 85 % by weight, silicon nitride is present in the amount of around 15 - 35 % by weight, vanadium pentoxide is present in the amount of around 0.1 - 2.5 % by weight.

6. A refractory material according to any of the preceding claims, wherein, the silicon carbide is reactively sintered with silicon metal at a temperature above 1400 °c.

7. A refractory material according to any of the preceding claims, wherein, the reactive sintering continues for around 5 days.

8. A boiler comprising an interior surface lined with a refractory material according to any of the preceding claims.

9. A boiler comprising an interior surface according to claim 8, wherein the refractory material is configured to be exposed to a temperature above 800 °C.

10. An incinerator comprising an interior surface lined with a refractory material according to any of the preceding claims.

11. An incinerator comprising an interior surface according to claim 10, wherein the refractory material is configured to be exposed to a temperature above 800 °C.

12. A heat exchanger comprising an interior surface made of a refractory material according to any of the preceding claims.

13. A heat exchanger comprising an interior surface according to claim 12, wherein the refractory material is configured to be exposed to a temperature above 800 °C.

14. A kiln furniture, an autoclave part, an exhaust gas heat exchangers or a high temperature nozzle comprising a refractory material according to any of the preceding claims.

15. A kiln furniture, autoclave part, exhaust gas heat exchanger or high temperature nozzle according to claim 14, wherein the refractory material is configured to be exposed to a temperature above 800 °cC.

16. A refractory according to any of claims 1 to 7, wherein the refractory material is configured to have a percentage weight gain less than 2.5% upon exposure to an oxidation environment at

1000°C.

17. A method of making a refractory material comprising:

providing a raw material to be blended;

wherein the raw material solely comprises of silicon carbide, silicon metal,vanadium pentoxide, a temporary binder and water;

blending the raw materials to form a mix;

shaping the mix into a formed shape;

drying the formed shape to eliminate moisture;

firing the formed shape that has dried at a temperature in a nitrogen atmosphere.

18. A method according to claim 7, wherein silicon carbide is in the range of 65 — 90 weight %, silicon metal powder is in the range of 4 — 20 weight %, vanadium pentoxide is in the range of 0.1-2%, the temporary binder is in the range of 1 — 4 weight % and water is in the range of 1 — 5 weight %.

19. A method according to claims 17 or 18, wherein, silicon carbide powder is provided in the form of a dry powder comprising of black refractory grade SiC or high purity SiC

20. A method according to claim 19, wherein the black refractory grade SiC has a purity of 97% SiC content.

21. A method according to any of claims 17 to 20, wherein the silicon carbide powder comprises of particles having a blocky grain having an aspect ratio ranging from 1.0 - 1.3.

22. A method according to any of claims 17 to 21, wherein, the particle size distribution of the silicon carbide powder comprises 50 % of the particles having a particle size in the range of 0.5 — 1.5 mm, 10 % of the particles having a particle size in the range of 0.25 — 0.5 mm, 15% of the particles having a particle size in the range of 0.1 — 0.2 mm, and 10 % of the particles having a particle size less than 75 um.

23. A method according to any of claims 17 to 22, wherein, silicon metal powder is provided in the form of a dry powder having purity of about 98.5 % silicon content.

24. A method according to any of claims 17 to 23, wherein, the particle size of the silicon metal is less than 0.5 mm.

25. A method according to claim 24, wherein, the particle size of the silicon metal is less than 250 pm.

26. A method according to any of claims 17 to 25, wherein, 95% of the silicon metal particles have particle size less than 100 um.

27. A method according to any of claims 17 to 26, wherein, vanadium pentoxide is provided in the form of a dry powder having particle size less than 0.5 mm.

28. A method according to any of claims 17 to 27, wherein, the particle size of the vanadium pentoxide is less than 250 pm.

29. A method according to any of claims 17 to 28, wherein, the d90 of the vanadium pentoxide particles is 45 — 50 pm and the d50 of the vanadium pentoxide particles is 10 — 20 pm.

30. A method according to any of claims 17 to 29, wherein at least one of the temporary binders is a solution of modified starch derivatives, an aqueous solution of dextrin or of lignone derivatives, a polyvinyl alcohol, a phenol resin, an epoxy type resin, a furfuryl alcohol, or a mixture thereof.

31. A method according to any of claims 17 to 30, wherein, silicon carbide is in the range of 70-85% by weight, silicon metal powder is in the range of ΙΟΙ 5% by weight, vanadium pentoxide in the range of about 0.75 — 1 % by weight, the temporary binder includes calcium lignosulfonate in the range of about 2.3 — 2.5% by weight and starch in the range of about 0.3 — 0.5% by weight and water is in the range of 0.75 - 5.0 weight %.

32. A method according to any of claims 17 to 31, wherein, the mixing is carried out using a planetary mixer, spiral mixer, vertical cutter mixer, V-blenders, Marion Mixers, or Hobart Mixers.

33. A method according to any of claims 17 to 32, wherein the mix is formed in to a formed shape by hydraulic pressing, vibratory pressing, impact pressing, or slip casting.

34. A method according to claim 33, wherein, the pressing is carried out uniaxially or isostatically.

35. A method according to claims 33 or 34, wherein, the formed shape is dried at a temperature ranging from 105 — 210 0 C and for around 1-5 days to remove the water.

36. A method according to any of claims 33 to 35, wherein the formed shape is dried at a temperature of about 120 0 C and for around 3 days to remove the water.

37. A method according to any of claims 17 to 37, wherein, the residual moisture content of the formed shape after drying is less than 1.0%, or less than 0.5%.

38. A method according to any of claims 17 to 37, wherein, the firing is carried out at or above 1400°C.

39. A method according to claim 38, wherein the firing or above at 1400 °C continues for around 5 days.

40. A method comprising:

lining a boiler, an incinerator, a heat exchanger or a furnace with a fired refractory comprising;

silicon carbide reactively sintered with silicon metal in a nitrogen atmosphere to form the silicon nitride bound silicon carbide, further including an additive;

wherein, the additive comprises vanadium pentoxide; and wherein, in the fired refractory,

41.

42.

there is present in total at least 96.5 weight % silicon carbide, silicon nitride and vanadium pentoxide, and the silicon carbide is present in the range of 65 — 90 weight %, silicon nitride is present in the range of 10 — 35 weight %, and the additive is present in the range of 0.1 — 4 weight %.

A method according to claim 40, wherein, the silicon carbide is reactively sintered with silicon metal at a temperature above 1400 °C.

A method according to claim 41, wherein the reactive sintering at 1400 °C continues for around 5 days.