Tin oxide refractory and method for its production

Abstract

To provide a tin oxide refractory which prevents volatilization of SnO.sub.2 in a high temperature zone from an early stage and which also has high erosion resistance to glass. A tin oxide refractory comprising SnO.sub.2, SiO.sub.2 and ZrO.sub.2 as essential components, wherein the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 in the tin oxide refractory is at least 70 mass %, and, based on the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2, the content of SnO.sub.2 is from 32 to 98 mol %, the content of SiO.sub.2 is from 1 to 35 mol % and the content of ZrO.sub.2 is from 1 to 35 mol %.

Claims

1. A tin oxide refractory comprising SnO.sub.2, SiO.sub.2 and ZrO.sub.2 as essential components, wherein the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 in the tin oxide refractory is at least 70 mass %, and, based on the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2, the content of SnO.sub.2 is from 76 to 98 mol %, the content of SiO.sub.2 is from 1 to 12 mol % and the content of ZrO.sub.2 is from 1 to 35 mol %, and wherein when heat treatment at 1,300 C. for 350 hours is conducted, a ZrSiO.sub.4 phase and a ZrO.sub.2 chase are formed on a sintered body surface of the tin oxide refractory.

2. The tin oxide refractory according to claim 1, wherein the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 is at least 95 mass %.

3. The tin oxide refractory according to claim 1, wherein, based on the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2, the content of ZrO.sub.2 is from 1 to 12 mol %.

4. The tin oxide refractory according to claim 1, further comprising at least one component selected from the group consisting of CuO, Cu.sub.2O, ZnO, Mn.sub.2O.sub.3, CoO, Al.sub.2O.sub.3, Sb.sub.2O.sub.3 and Li.sub.2O.

5. The tin oxide refractory according to claim 1, wherein after heat treatment at 1,300 C. under 700 mmHg for 350 hours, a volatilization rate of SnO.sub.2 is at most as compared with a SnO.sub.2 sintered body having a SnO.sub.2 content of at least 99 mol %.

Description

DESCRIPTION OF EMBODIMENTS

(1) The present invention is characterized in that SnO.sub.2, SiO.sub.2 and ZrO.sub.2 are incorporated so that their contents in the tin oxide refractory would be in the prescribed amounts. Now, the present invention will be described in detail.

(2) SnO.sub.2 to be used in the present invention has high resistance to erosion by molten glass and high heat resistance, and thus is incorporated as the main component of the refractory.

(3) SiO.sub.2 to be used in the present invention is a component to form matrix glass and to provide a stress relaxation function. Further, it is a component having a function to prevent volatilization of SnO.sub.2 being the main component in the refractory.

(4) ZrO.sub.2 to be used in the present invention is a component having high resistance to erosion by molten glass and also having a function to prevent volatilization of SnO.sub.2 being the main component in the refractory.

(5) In the present invention, the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 contained in the refractory is adjusted to be at least 70 mass %. The reason is such that if other components are contained in the refractory too much, the content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 decreases, and particularly, the excellent erosion resistance of SnO.sub.2 to glass tends to be impaired. In order to bring the erosion resistance to be good, the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 is preferably at least 85 mass %, more preferably at least 95 mass %. Further, the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 is preferably from 97 to 99.5 mass %.

(6) Further, in the present invention, when the total content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 being essential components is regarded to be 100 mol %, SnO.sub.2 is contained in an amount of from 32 to 98 mol %, SiO.sub.2 is contained in an amount of from 1 to 35 mol %, and ZrO.sub.2 is contained in an amount of from 1 to 35 mol %.

(7) In the present invention, by adjusting the content of SnO.sub.2, SiO.sub.2 and ZrO.sub.2 in the refractory to be within the prescribed range as mentioned above, and further adjusting the relation of these components to have the prescribed relation, it is possible to obtain a tin oxide refractory which prevents volatilization of SnO.sub.2 in a high temperature zone from an early stage and which also has high erosion resistance to glass.

(8) As a result of a study on the contents of SnO.sub.2, SiO.sub.2 and ZrO.sub.2, the present inventors have found that in a case where two components of SnO.sub.2 and ZrO.sub.2 are used as the main components without incorporating SiO.sub.2, ZrO.sub.2 to exhibit an effect to prevent volatilization of SnO.sub.2 is present as solid-solubilized in SnO.sub.2. And, the characteristics of the obtainable refractory are influenced by the firing temperature and the temperature lowering rate at the time of producing the refractory, but, for example, in a case where firing was carried out at 1,400 C. for 5 hours and the temperature lowering was carried out at a rate of 300 C./hr, the solid solubility limit concentration of ZrO.sub.2 in SnO.sub.2 was from about 20 to 25 mol %.

(9) Whereas, when the composition is made to contain SiO.sub.2 as in the present invention, the solid solubility limit concentration of ZrO.sub.2 in SnO.sub.2 decreases to a large extent to about 12 mol %, although the cause is not clearly understood. Therefore, in the composition range containing SiO.sub.2, as compared with a case where only ZrO.sub.2 is contained without containing SiO.sub.2, at the time of volatilizing SnO.sub.2 in a high temperature zone, ZrO.sub.2 solid-solubilized in SnO.sub.2 reaches the solid solubility limit in an early stage and will precipitate on the SnO.sub.2 particle surface. Thus, it becomes possible to exhibit an excellent effect to prevent volatilization of SnO.sub.2 from the initial stage after beginning of volatilization, as compared with a case where no SiO.sub.2 is contained.

(10) Further, the majority of SiO.sub.2 present in a non-crystallized state at the grain boundary of SnO.sub.2 having ZrO.sub.2 solid-solubilized therein (hereinafter referred to also as SnO.sub.2ZrO.sub.2 solid solution) will react with ZrO.sub.2 precipitated as exceeded the solid solubility limit and will be present as ZrSiO.sub.4 at the grain boundary of the SnO.sub.2ZrO.sub.2 solid solution thereby to reduce the relative surface area of SnO.sub.2. Thus, an excellent volatilization-preventing effect over a long period of time is obtainable also as compared with a case where ZrO.sub.2 is contained without containing SiO.sub.2.

(11) Further, ZrO.sub.2 not reactive with SiO.sub.2 is also present, and such ZrO.sub.2 exhibits a volatilization-preventing effect by itself. With respect to ZrSiO.sub.4 and ZrO.sub.2, their presence can be confirmed by means of an electron microscopic device such as SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Detector (manufactured by Hitachi High Technologies Corporation, trade name: S-3000H).

(12) Here, the solid solubility limit concentration was determined as an approximate solid solubility limit concentration of ZrO.sub.2 solid-solubilized in SnO.sub.2 by analyzing a sintered body structure by means of SEM-EDX with respect to a sintered body obtained by changing the amount of ZrSiO.sub.4 added.

(13) Now, the reason for limiting the refractory in the present invention to the above composition will be explained as follows.

(14) As mentioned above, when the total amount of SnO.sub.2, ZrO.sub.2 and SiO.sub.2 is regarded as 100 mol %; if the contents of the respective components satisfy the relation of from 32 to 98 mol % of SnO.sub.2, from 1 to 35 mol % of ZrO.sub.2 and from 1 to 35 mol % of SiO.sub.2, the solid solubility limit concentration of ZrO.sub.2 decreases, and ZrO.sub.2 starts to precipitate on the SnO.sub.2 particle surface at an early stage after beginning of volatilization of SnO.sub.2. Thus, an excellent effect to prevent volatilization of SnO.sub.2 can be obtained from an earlier stage as compared with a case where no SiO.sub.2 is contained. Further, the majority of SiO.sub.2 will react with ZrO.sub.2 precipitated as exceeded the solid solubility limit and will be present as ZrSiO.sub.4 at the grain boundary of the SnO.sub.2ZrO.sub.2 solid solution thereby to reduce the surface area of SnO.sub.2 exposed to the exterior environment. Thus, an excellent effect to prevent volatilization of SnO.sub.2 for a long period of time is obtainable as compared with a case where ZrO.sub.2 is contained without containing SiO.sub.2.

(15) In this composition range, ZrO.sub.2 is mainly in a state solid-solubilized in SnO.sub.2, and a portion exceeding the solid solubility limit will precipitate at the grain boundary of SnO.sub.2. The precipitated ZrO.sub.2 will react with SiO.sub.2 and will be present as ZrSiO.sub.4 at the grain boundary of the SnO.sub.2ZrO.sub.2 solid solution. However, depending upon the amount of SiO.sub.2 present, unreacted one will be partially present as ZrO.sub.2 at the grain boundary of the SnO.sub.2ZrO.sub.2 solid solution.

(16) SiO.sub.2 reacts with SnO.sub.2, ZrO.sub.2 and other components and is present in a non-crystallized state at the grain boundary of a SnO.sub.2ZrO.sub.2 solid solution, and when ZrO.sub.2 precipitates at the grain boundary, it will react with ZrO.sub.2 to form ZrSiO.sub.4.

(17) As described above, the tin oxide refractory of the present invention exhibits an excellent effect to prevent volatilization of SnO.sub.2, because from an early stage in volatilization of SnO.sub.2, the solid solubility amount of ZrO.sub.2 in SnO.sub.2 reaches the solid solubility limit concentration, and ZrSiO.sub.4 and ZrO.sub.2 are formed on the SnO.sub.2 surface of the sintered body.

(18) According to the tin oxide refractory of the present invention, for example, after heat treatment at 1,300 C. for 350 C., on the sintered body surface, a ZrSiO.sub.4 phase and a ZrO.sub.2 phase are formed. Further, in a case where the SiO.sub.2 content is at least about 5 mol % based on the total amount of SnO.sub.2, ZrO.sub.2 and SiO.sub.2, a SiO.sub.2 phase also remains. Thus, if such high temperature treatment is done before use, it is possible to produce and use a refractory capable of exhibiting an excellent volatilization-preventing effect immediately after use.

(19) At that time, if the content of SiO.sub.2 is small at a level of less than 1 mol % based on the total content of SnO.sub.2, ZrO.sub.2 and SiO.sub.2, a phenomenon of decrease in the solid solubility limit concentration of ZrO.sub.2 in SnO.sub.2 will not be observed, and development of the volatilization-preventing effect in the initial stage after beginning of volatilization of SnO.sub.2 tends to be delayed to a certain extent, and since the SiO.sub.2 content is small, even if ZrO.sub.2 precipitates, formation of ZrSiO.sub.4 will be less, whereby improvement in the volatilization-preventing effect will be small.

(20) If the content of ZrO.sub.2 is small at a level of less than 1 mol % based on the total content of SnO.sub.2, ZrO.sub.2 and SiO.sub.2, the volatilization-preventing effect by ZrO.sub.2 and ZrSiO.sub.4 will be very small.

(21) If the content of SiO.sub.2 is large at a level of exceeding 35 mol % based on the total content of SnO.sub.2, ZrO.sub.2 and SiO.sub.2, the content of SiO.sub.2 is too much, whereby the content of SnO.sub.2 tends to be small, and the erosion resistance to glass tends to decrease.

(22) If the content of ZrO.sub.2 is large at a level of exceeding 35 mol % based on the total content of SnO.sub.2, ZrO.sub.2 and SiO.sub.2, the content of ZrO.sub.2 is too much, whereby the content of SnO.sub.2 tends to be small, and the erosion resistance to glass tends to decrease.

(23) Here, in the tin oxide refractory of the present invention, the content of ZrO.sub.2 is preferably within a range of from 1 to 12 mol % based on the total content of SnO.sub.2, ZrO.sub.2 and SiO.sub.2. Further, the content of SiO.sub.2 is also preferably within a range of from 1 to 12 mol % based on the total content of SnO.sub.2, ZrO.sub.2 and SiO.sub.2. Accordingly, the content of SnO.sub.2 is preferably within a range of from 76 to 98 mol % based on the total content of SnO.sub.2, ZrO.sub.2 and SiO.sub.2.

(24) Further, irrespective of the above conditions, sintering treatment is carried out usually by heat treatment at from 1,200 to 1,600 C. for from 3 to 5 hours. Therefore, depending upon the sintering conditions in actual treatment, the blend amounts of SnO.sub.2, ZrO.sub.2 and SiO.sub.2 in the refractory composition may be adjusted.

(25) Further, the above-mentioned other components are not particularly limited so long as they are ones not to impair the characteristics as the refractory of the present invention, and they may be known components which are used in tin oxide refractories.

(26) Such other components may, for example, be oxides such as CuO, Cu.sub.2O, ZnO, Mn.sub.2O.sub.3, CoO, Li.sub.2O, Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5, CeO.sub.2, CaO, Sb.sub.2O.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3, UO.sub.2, HfO.sub.2, etc.

(27) It is preferred to contain, among these oxides, at least one oxide selected from the group consisting of CuO, ZnO, Mn.sub.2O.sub.3, CoO, Al.sub.2O.sub.3, Sb.sub.2O.sub.3 and Li.sub.2O. Further, CuO, ZnO, Mn.sub.2O.sub.3, CoO, Li.sub.2O or the like effectively serves as a sintering assistant. If such a sintering assistant is incorporated, the strength of the refractory may be more improved, for example, as densified by firing at 1,400 C. for 5 hours. Accordingly, it is more preferred to contain at least one oxide selected from the group consisting of CuO, ZnO, Mn.sub.2O.sub.3, CoO and Li.sub.2O, and particularly preferred to contain CuO.

(28) A preferred tin oxide refractory of the present invention is a refractory wherein after heat treatment at 1,300 C. under 700 mmHg for 350 hours, the volatilization rate of SnO.sub.2 is at most as compared with a SnO.sub.2 sintered body having a SnO.sub.2 content of at least 99 mol %. At that time, the comparison is carried out by adjusting the open porosity difference between them to be at most 1%. Here, the open porosity is calculated by a known Archimedes method.

(29) The tin oxide refractory of the present invention may be produced by uniformly mixing powder raw materials, forming the mixture into a desired shape and subjecting the formed mixture to sintering treatment at a high temperature of at least 1,200 C., preferably from 1,300 to 1,450 C. More specifically, fine powder raw materials are weighed in required amounts so that the components in the obtainable refractory would be in the above-mentioned contents, e.g. the components such SnO.sub.2, SiO.sub.2, ZrO.sub.2, CuO, etc. would be in the prescribed blend amounts, and put in a rotary ball mill or a vibration ball mill, followed by mixing and pulverization by the pulverizer using an organic solvent such as ethanol as a medium. The obtained slurry is dried under reduced pressure, followed by press molding by means of metallic mold pressing or isostatic pressing, and the obtained molded product is sintered, for example, at 1,400 C. for 5 hours, to obtain a tin oxide refractory.

(30) The raw materials are not limited to the above-mentioned combination of powders, and for example, a ZrSiO.sub.4 powder may be used as a raw material for ZrO.sub.2 and SiO.sub.2 being volatilization-preventing components.

(31) Further, a powder of a simple substance metal such as Zr, Si or Cu, a metal salt compound containing such a metal, Zr(OH).sub.2, CuZrO.sub.3, CuCO.sub.3, or Cu(OH).sub.2 may, for example, be used. Among them, CuZrO.sub.3 or CuCO.sub.3 is preferred.

(32) In a case where a ZrSiO.sub.4 powder is used as a raw material for ZrO.sub.2 and SiO.sub.2 being volatilization-preventing components, within a range wherein the solid solubility amount of ZrO.sub.2 in SnO.sub.2 is at most 12 mol %, SnO.sub.2 serves as a dissociation accelerator of ZrSiO.sub.4, and therefore, for example, by firing at 1,400 C. for 5 hours, it is possible to let ZrSiO.sub.4 be dissociated to ZrO.sub.2 and SiO.sub.2, thereby to produce a tin oxide refractory of the present invention.

(33) Further, in the case where a ZrSiO.sub.4 powder is used as a raw material, it is not necessary, for example, to put raw material powders of ZrO.sub.2 and SiO.sub.2 dividedly into a mixing apparatus, whereby the production process can be simplified. Further, mixing of the raw material powders is simplified, and a uniform mixture is obtainable, which contribute to shortening of the production process and stability of the product quality.

EXAMPLES

(34) Now, the present invention will be described specifically with reference to Examples and Comparative Examples, but it should be understood that the present invention is by no means restricted by such descriptions.

Ex 1 to 26

(35) Firstly, as raw materials for producing tin oxide refractories, powder raw materials having average particle sizes, chemical components and purities as shown in Table 1 were prepared. Then, so that a tin oxide refractory would have a composition as shown in Table 2, powders of SnO.sub.2, ZrO.sub.2, SiO.sub.2, ZrSiO.sub.4, Al.sub.2O.sub.3, Sb.sub.2O.sub.3, CuO, Mn.sub.2O.sub.3, etc. were blended in the proportions as shown in Table 3.

(36) In Table 2, in Ex (Ex 1, 2, 4 to 6, 11 to 17, 23 and 25) wherein the molar ratio of ZrO.sub.2 to SiO.sub.2 is 1:1, a ZrSiO.sub.4 powder was used. Whereas, in Ex wherein the molar ratio of ZrO.sub.2 to SiO.sub.2 is not 1:1, a ZrO.sub.2 powder and a SiO.sub.2 powder were used.

(37) TABLE-US-00001 TABLE 1 Raw material powder Purity, mass % Average particle size m SnO.sub.2 99.0 2.7 ZrO.sub.2 99.9 0.1 SiO.sub.2 99.9 4.0 ZrSiO.sub.4 99.5 1.1 Al.sub.2O.sub.3 99.9 0.3 Sb.sub.2O.sub.3 99.9 1.1 CuO 99.9 1.0 Mn.sub.2O.sub.3 99.9 5.1 Li.sub.2O 99.0 3.0 ZnO 99.9 1.0

(38) TABLE-US-00002 TABLE 2 Content [mol %] based on (SnO.sub.2 + SiO.sub.2 + ZrO.sub.2) Composition [mol %] SnO.sub.2 SiO.sub.2 ZrO.sub.2 SnO.sub.2 ZrO.sub.2 SiO.sub.2 Al.sub.2O.sub.3 CuO Mn.sub.2O.sub.3 Li.sub.2O ZnO Sb.sub.2O.sub.3 CaO Na.sub.2O content content content Ex 1 95.1 2.0 2.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 96.0 2.0 2.0 Ex 2 89.1 5.0 5.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 89.9 5.0 5.0 Ex 3 69.1 5.0 25.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 69.7 25.2 5.0 Ex 4 75.1 12.0 12.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 75.8 12.1 12.1 Ex 5 63.1 18.0 18.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 63.7 18.2 18.2 Ex 6 49.1 25.0 25.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 49.5 25.2 25.2 Ex 7 56.1 25.0 18.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 56.6 18.2 25.2 Ex 8 85.1 2.0 12.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 85.9 12.1 2.0 Ex 9 79.1 2.0 18.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 79.8 18.2 2.0 Ex 10 71.1 10.0 18.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 71.7 18.2 10.1 Ex 11 89.1 5.0 5.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 89.9 5.0 5.0 Ex 12 75.1 12.0 12.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 75.8 12.1 12.1 Ex 13 79.1 5.0 5.0 10.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 88.8 5.6 5.6 Ex 14 69.1 5.0 5.0 20.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 87.4 6.3 6.3 Ex 15 88.6 5.0 5.0 0.0 0.9 0.0 0.0 0.0 0.5 0.0 0.0 89.9 5.1 5.1 Ex 16 87.6 5.0 5.0 0.0 0.0 0.0 2.4 0.0 0.0 0.0 0.0 89.8 5.1 5.1 Ex 17 89.1 5.0 5.0 0.0 0.0 0.0 0.0 0.9 0.0 0.0 0.0 89.9 5.0 5.0 Ex 18 99.1 0.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 100.0 0.0 0.0 Ex 19 94.1 0.0 5.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 95.0 5.0 0.0 Ex 20 95.1 4.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 96.0 0.0 4.0 Ex 21 74.1 25.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 74.8 0.0 25.2 Ex 22 59.1 5.0 35.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 59.6 35.3 5.0 Ex 23 29.1 35.0 35.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 29.4 35.3 35.3 Ex 24 57.1 40.0 2.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 57.6 2.0 40.4 Ex 25 49.1 5.0 5.0 40.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 83.1 8.5 8.5 Ex 26 0.0 0.0 1.3 92.6 0.0 0.0 0.0 0.0 0.0 0.5 5.6 0.0 100.0 0.0

(39) TABLE-US-00003 TABLE 3 Composition [mass %] Total content of SnO.sub.2, SiO.sub.2 and SnO.sub.2 ZrO.sub.2 SiO.sub.2 Al.sub.2O.sub.3 CuO Mn.sub.2O.sub.3 Li.sub.2O ZnO Sb.sub.2O.sub.3 CaO Na.sub.2O ZrO.sub.2 in refractory [mass %] Ex 1 97.0 1.7 0.8 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 2 93.1 4.3 2.1 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 3 82.7 4.9 11.9 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 4 83.3 10.9 5.3 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 5 73.9 17.2 8.4 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 6 61.4 25.6 12.5 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 7 66.7 24.3 8.5 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 8 92.5 1.8 5.2 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 9 89.5 1.9 8.1 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 10 81.8 9.4 8.3 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 11 92.7 4.2 2.1 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 12 82.9 10.8 5.3 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 13 85.6 4.4 2.2 7.3 0.5 0.0 0.0 0.0 0.0 0.0 0.0 92.2 Ex 14 77.5 4.6 2.2 15.2 0.5 0.0 0.0 0.0 0.0 0.0 0.0 84.3 Ex 15 92.1 4.3 2.1 0.0 0.5 0.0 0.0 0.0 1.0 0.0 0.0 98.4 Ex 16 92.9 4.3 2.1 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 99.3 Ex 17 93.1 4.3 2.1 0.0 0.0 0.0 0.0 0.5 0.0 0.0 0.0 99.5 Ex 18 99.5 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 19 97.4 0.0 2.1 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 20 96.2 3.3 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 21 78.0 21.5 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 22 76.2 5.3 18.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 23 40.4 39.7 19.4 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 24 62.7 35.9 0.9 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 25 59.4 5.0 2.4 32.7 0.5 0.0 0.0 0.0 0.0 0.0 0.0 66.8 Ex 26 0.0 0.0 0.8 94.9 0.5 0.0 0.0 0.0 0.0 0.3 3.5 0.8

(40) The blended raw material powders were mixed and pulverized for 48 hours by means of a rotary ball mill (trade name: AN-3S, manufactured by Aichi Electric Co., Ltd.) using ethanol (400 ml) as a medium, whereupon the obtained slurry was dried under reduced pressure and formed into a molded product by isostatic pressing (the pressing machine was manufactured by Nikkiso Co., Ltd., trade name: CL15-28-20) with 1,500 kg/cm.sup.2. The obtained molded product was held at 1,400 C. for 5 hours in the atmospheric air atmosphere for firing and then cooled at a rate of 300 C./hr to obtain a tin oxide refractory.

(41) A test piece having a diameter of 15 mm and a height of 5 mm was cut out from a part of the obtained tin oxide refractory and heat-treated at 1,300 C. in an environment of 700 mmHg for from 10 to 400 hours, whereby the mass reduction in each case was measured (using GH-252, trade name, manufactured by A & D Company, Limited), and the volatilization amount (unit: mg) and the volatilization rate (unit: mg/hr) were calculated.

(42) Further, a test piece of 15 mm25 mm50 mm (verticalhorizontallengthwise) cut out from the obtained tin oxide refractory was immersed in soda lime glass (trade name: Sun Green VFL, manufactured by Asahi Glass Company Limited) at 1,300 C. for 100 hours in the atmospheric air atmosphere, whereupon the erosion degree was measured, and the erosion resistance was investigated.

(43) The data of the volatilization rate and the erosion degree obtained as described above are summarized in Table 4.

(44) TABLE-US-00004 TABLE 4 Volatilization rate After 10 hr of After 350 hr of Erosion degree heat treatment heat treatment (1,300 C., 100 hr) Ex 1 15 7.6 11 Ex 2 10.5 4 12 Ex 3 12.6 7.1 14 Ex 4 14.7 1.6 11 Ex 5 10.4 1.3 12 Ex 6 20.4 9.3 16 Ex 7 13.6 5.7 14 Ex 8 36.9 3.6 11 Ex 9 37.7 3 15 Ex 10 16.8 6.7 14 Ex 11 14.2 5.8 12 Ex 12 11.5 4.9 12 Ex 13 18.7 6.2 17 Ex 14 20.2 6.5 19 Ex 15 11.2 5.1 15 Ex 16 37.6 7.9 15 Ex 17 20.1 4.2 9 Ex 18 100 100 11 Ex 19 167.7 113 11 Ex 20 55.3 13.1 13 Ex 21 47.3 11.9 8 Ex 22 21.2 7.3 30 Ex 23 30.5 11.5 33 Ex 24 40.1 8.8 29 Ex 25 22.3 4.9 35 Ex 26 0 0 100

(45) In Tables 2 to 4, Ex 1 to 17 are Examples of the present invention, and Ex 18 to 26 are Comparative Examples.

(46) The erosion resistance to glass in each of Examples and Comparative Examples was compared with the alumina fused cast brick (trade name: MB-G, manufactured by AGC Ceramics Co., Ltd.) in Ex 26 which is widely used in glass production apparatus and was represented by an erosion degree relative to the maximum erosion depth being 100, of the eroded portion after the erosion test of MB-G.

(47) Further, the volatilization rate in each of Ex 1 to 17 and Ex 18 to 26 was represented by a volatilization rate relative to the volatilization rate being 100 after the test piece in Ex 18 was heat-treated at 1,300 C. in an environment of 700 mmHg for 10 hours and 350 hours. Here, as the respective volatilization rates after the heat treatment for 10 hours and 350 hours, an average volatilization rate per unit surface area calculated from the mass reduction during the heat treatment time of from 0 hour to 10 hours, and an average volatilization rate per unit surface area calculated from the mass reduction during the heat treatment time of from 350 hours to 400 hours, are relatively shown.

(48) Further, the open porosity of each sample was measured by an Archimedes method, and in each case, a sample with 1.0% or less was used.

(49) Ex 18 represents a tin oxide sintered body having a composition excluding ZrO.sub.2 and SiO.sub.2, whereby the erosion resistance to glass is substantially equal to Ex 1 to 17, but since no volatilization-preventing component is contained, the volatilization rate of SnO.sub.2 is very fast.

(50) Ex 19 represents a tin oxide sintered body having a composition excluding ZrO.sub.2, whereby the erosion resistance to glass is substantially equal to Ex 1 to 17, but since no ZrO.sub.2 as a volatilization-preventing component is contained, the volatilization rate of SnO.sub.2 is very fast.

(51) Ex 20 and 21 represent a tin oxide sintered body having a composition excluding SiO.sub.2, whereby the erosion resistance to glass is substantially equal to Ex 1 to 17, but since no SiO.sub.2 is contained, the solid solubility limit concentration of ZrO.sub.2 in SnO.sub.2 is high. Further, the content of ZrO.sub.2 as a volatilization-preventing component is small, whereby it takes time till ZrO.sub.2 reaches the solid solubility limit concentration by volatilization of SnO.sub.2, and the volatilization rate of SnO.sub.2 after 10 hours of heat treatment is faster than in Ex 1 to 17. Further, since no SiO.sub.2 is contained, also after 350 hours of heat treatment, the volatilization rate of SnO.sub.2 is faster as compared with Ex 1 to 17.

(52) Ex 22 represents a tin oxide sintered body having a composition wherein the amount of SiO.sub.2 is increased, whereby the volatilization rate is substantially equal to Ex 1 to 17, but since the content of SnO.sub.2 is small, the erosion resistance to glass is lower than in Ex 1 to 17.

(53) Ex 23 represents a tin oxide sintered body having a composition wherein the amounts of ZrO.sub.2 and SiO.sub.2 are increased, whereby the volatilization rate is substantially equal to Ex 1 to 17, but since the content of SnO.sub.2 is small, the erosion resistance to glass is lower than in Ex 1 to 17.

(54) Ex 24 represents a tin oxide sintered body having a composition wherein the amount of ZrO.sub.2 is increased, whereby the volatilization rate is substantially equal to Ex 1 to 17, but since the content of SnO.sub.2 is small, the erosion resistance to glass is lower than in Ex 1 to 17.

(55) Ex 25 represents a tin oxide sintered body having a composition wherein Al.sub.2O.sub.3 is incorporated as other component, whereby the volatilization rate is substantially equal to Ex 1 to 17, but since the content of SnO.sub.2 is small, the erosion resistance to glass is lower than in Ex 1 to 17.

(56) Ex 26 represents an alumina fused cast brick (trade name: MB-G, manufactured by AGC Ceramics Co., Ltd.), whereby no volatilization occurs, but the erosion resistance to glass is lower than in Ex 1 to 17.

(57) On the other hand, Ex 1 to 17 representing Examples of the present invention present results such that the volatilization rate and the erosion resistance to glass are better as compared with Ex 18 to 26. From these evaluation results, it has been made clear that as compared with the tin oxide refractories in Comparative Examples, the tin oxide refractories in Examples of the present invention are excellent tin oxide refractories each being highly effective to prevent volatilization of SnO.sub.2 and having a high erosion resistance to glass, with a good balance of both physical properties.

INDUSTRIAL APPLICABILITY

(58) The tin oxide refractory of the present invention is excellent in erosion resistance to glass and capable of effectively preventing volatilization of SnO.sub.2 and thus is suitable as a refractory for a glass melting furnace.

(59) This application is a continuation of PCT Application No. PCT/JP2012/083928, filed on Dec. 27, 2012, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-289690 filed on Dec. 28, 2011. The contents of those applications are incorporated herein by reference in their entireties.