JPH032811B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for refining ceramic raw materials. In general, many ceramic raw materials are naturally produced, such as aluminum hydroxide represented by bauxite, kyanite, aluminum silicate represented by Kibushi clay, or artificial raw materials made by combining and firing these natural raw materials. For example, mullite (3Al ₂ O ₃・2SiO ₂ ), cordierite (3MgO・
Artificial raw materials such as Al ₂ O ₃ 3SiO ₂ ) generally contain impurities (Fe ₂ O ₃ , TiO ₂ ,
Contains small amounts of CaO, Na ₂ O, etc.). Especially Fe ₂ O ₃ ,
If a large amount of TiO ₂ is contained, the product value will be significantly impaired, such as significantly reducing the fire resistance and corrosion resistance of products made from this raw material, and making it impossible to use them in a reducing atmosphere. . The present invention relates to a method for removing impurities from ceramic raw materials containing such undesirable impurities and increasing their industrial value. The present applicants previously disclosed a method for purifying zirconium oxide in JP-A-56-32328. The invention described in JP-A No. 56-32328 involves heating baddellite ore to 400 to 1400°C and contacting it with a sublimated gas of ammonium chloride to remove impurities such as Fe ₂ O ₃ , TiO ₂ , After converting CuO to chloride, it is dissolved and removed, or the heating temperature of baddellite ore is set to a high temperature side (800 ~
1400℃) to volatilize and remove chloride. The present inventors applied this method to other ceramic raw materials and attempted to remove the contained impurities, but surprisingly found that the reaction rate was slower than expected and the impurity removal rate was low. Various problems arose, including large variations in the removal rate due to differences in type and lot, and some raw materials that sintered throughout during heat treatment and became integrated, making subsequent processing difficult. After intensive research to elucidate the cause of this, we found that the cause of the slow reaction rate was thought to be due to the oxygen present in the surrounding atmosphere of the raw materials, which reacts with the oxygen and produces reducing carbon monoxide (CO). It has been found that the addition of combustible substances to convert into carbon dioxide (CO ₂ ) and carbon dioxide (CO 2 ) is extremely effective in increasing the reaction rate. Furthermore, the reason for the low impurity removal rate is that the dissolution removal rate of chloride converted from impurities is low, or the volatilization removal rate is low when trying to volatilize chloride by setting the heating temperature to a high temperature. In addition, we found that the dissolution removal rate or volatilization removal rate depends on the particle size of the raw material, and the optimum value was determined.
The inventors have determined that the diameter is 0.1 mm or more, and have devised the present invention. According to the method of the present invention, almost all ceramic raw materials can be efficiently purified.
That is, in the method of the present invention, ceramic raw materials are prepared in advance.
When the particle size is adjusted to a range of 0.1 mm to 3 mm and then brought into contact with a sublimated ammonium chloride gas while heating at 400 to 1400°C with a combustible material, the chloride converted from the product impurity will be dissolved later. The efficiency of removal or volatilization removal by setting high temperatures is significantly increased, and stable values can always be obtained. In particular, when the particle size is 0.1 mm or more, the effect is remarkable, and furthermore, even during high-temperature treatment, the entire body becomes hard and does not sinter, making subsequent processing easier. This is because ammonium chloride converts impurity oxides in the raw materials into chlorides.
It has the property of volatilizing and moving from the inside of the particle to the surface of the particle, and once it is deposited at a high concentration on the surface, particles with a large diameter are related to the surface area and small size.
This is thought to be because the subsequent dissolution and volatilization of chloride is easy. The ceramic raw materials used in the present invention include diaspore (Al ₂ O ₃ .H ₂ O), gypsite (Al(OH) ₃ ), bauxite (Al ₂ O ₃ .2H ₂ O), which is a mixture of diaspore and gypsite, etc. Aluminum hydroxide minerals and their calcined products, kyanite, kibushi clay,
Contains aluminum silicate minerals such as frog's eye clay and shale clay, and calcined products of these minerals. Furthermore, natural minerals other than alumina-containing minerals such as zircon sand (Zr・SiO ₄ ), silica sand (SiO ₂ ), forsterite (Mg ₂・SiO ₄ ), steatite (Mg・SiO ₄ ), spinel (MgO・
( _Al2O3 ), mullite ( _{3Al2O3 ・ 2SiO2} ) _, cordierite (3MgO・_Al2O3・_3SiO2 ), silicon carbide ( _SiC ), zirconium carbide (ZrC),
It also includes artificial raw materials such as stabilized zirconia and silicon nitride (Si ₃ N ₄ ), as well as recycled ceramic raw materials that have been used once and contain impurities. First, the ceramic raw materials mentioned above are pretreated to make the particle size uniform. That is, the diameter of the particle size is 0.1mm
For smaller fine powders, use water or starch, an appropriate water-soluble adhesive such as polyvinyl alcohol (PVA), an organic solvent-soluble adhesive such as ethyl cellulose or wax, or ammonium chloride to be used in the subsequent process with water or alcohol. Using an aqueous solution dissolved in a suitable solvent such as as an adhesive, powder mist drying method,
By an appropriate method such as the tablet method, the diameter of the particle size is 0.1.
Adjust the particle size so that it is within the range of ~3mm. On the other hand, lump-like raw materials made from pre-calcined shale clay like shale clay are crushed into pieces with a diameter of 0.1 to 3 mm.
Adjust the grain size within the range. Alternatively, the particles may be pulverized to a size smaller than 0.1 mm and then granulated to a diameter of 0.1 to 3 mm using the adhesive described above. It seems that the rate at which impurities are converted to chloride is faster in the latter than in the former, but there are cases where the rate is exactly the same. In addition, if the finely ground material of the raw material becomes dry during granulation and granulation is difficult, an appropriate amount of plastic clay such as the above-mentioned Kibushi clay may be mixed and granulated. After adjusting the particle size of the raw materials in the range of 0.1 to 3 mm in this way, the particle size of the raw materials is adjusted to 400 to 1400 mm with an appropriate amount of carbon powder.
The impurities contained in the raw material are brought into contact with sublimated ammonium chloride gas while heating to ℃.
Fe ₂ O ₃ and TiO ₂ may be converted into chlorides and removed by washing or volatilization in a later step.
This reaction is understood to be that impurity oxides are reduced by ammonia, metallized, and easily react with chlorine gas. The reason why the particle size of the raw material is limited to 0.1 to 3 mm in the present invention is that if it is smaller than 0.1 mm, the cleaning removal rate and volatilization removal rate will decrease and variations will occur depending on the lot. If the particle size is larger than 3 mm, it is not desirable because it takes too much time to react with the sublimated ammonium chloride gas to the inside of the particles. Regarding the heating temperature, if it is lower than 400℃, impurities in the raw materials cannot be sufficiently converted to chloride, so the heating temperature should be 400℃ or higher, and if it is higher than 1400℃, the reaction tube should be closed. It is uneconomical because it cannot be constructed from economical quartz glass and alumina tubes. Furthermore, the ceramic raw material used as the raw material is easily sintered, which is inconvenient for subsequent handling. Therefore, the heating temperature is preferably 1400°C or less. In addition, when the heating temperature is set to 400 to 800℃, chloride converted from impurity oxides in the raw materials is not volatilized and removed, so it is necessary to dissolve and remove it by washing. When set, the generated chloride is vaporized, so it has the advantage that it can be removed by volatilization and cleaning treatment can be omitted. The amount of combustible materials added, such as sawdust, paper chips, and carbon powder, should be in the proportion necessary to consume the oxygen present around the raw materials and convert them into CO and CO ₂ , so the internal volume of the equipment and the filling of the raw materials should be adjusted accordingly. It must be determined by the rate etc. . In the present invention, the following method can be adopted as a means for contacting the sublimation gas of ammonium chloride. (1) Add and mix carbon powder and ammonium chloride to the ceramic raw material whose particle size has been adjusted, and heat it at 400 to 1400℃.
A method in which the ammonium chloride in the mixture is sublimated and gasified by heating to a temperature of 100°C to bring it into contact with the coexisting ceramic raw materials. A method similar to this method is to add and mix an appropriate amount of ammonium chloride as a binder when preparing granules from fine powder of ceramic raw materials. (2) Particle size-adjusted ceramic raw materials are mixed with combustible materials and filled in the upper part of the reaction tube divided into upper and lower parts by air-permeable plates, ammonium chloride is filled in the lower part, and the reaction tube is heated at 400 to 1400℃. A method in which sublimated gas from ammonium chloride is introduced into and contacted with the ceramic raw material above. (3) A reaction tube is filled with a mixture of ceramic raw materials and combustible materials whose particle size has been adjusted, and sublimation gas of ammonium chloride is generated in a separate location, and this sublimation gas is transferred to the reaction tube using a carrier gas such as air or nitrogen. Method of introduction and contact with ceramic raw materials. Next, examples of the present invention will be described. Example 1 Iwate clay, a type of shale clay, having a chemical composition shown in Table 1 below was prepared. All of this dry powder passed through a sieve with an opening of 0.077 mm (200 mesh). Add 45g of water to 300g of this dry powder and make it into a clay-like shape, then granulate it with a granulator to a diameter of 2 to 3mm, put it in an enameled dish, and put it in a hot air dryer kept at 110℃. It was dried for 5 hours to obtain dry particles. Next, there is an inner diameter of 50 mm with a breathable plate in the center.
Prepare an alumina tube with a length of 300 mm, stand this alumina tube vertically, and place the dry particles 200 gr on the top.
and 10g of carbon powder with a diameter of 0.5 to 1mm were mixed well and packed, and the bottom was filled with 40g of ammonium chloride.
This alumina tube was placed in an electric furnace, and the temperature of the alumina tube was raised to 500°C. At this time, the ammonium chloride sublimated in the lower part rose as a gas, passed through the permeable plate, and flowed into the dry particles in the upper part. After the generation of sublimated ammonium chloride gas from the alumina tube stopped, the alumina tube was taken out of the electric furnace and the purified product inside was taken out. The purified product was white, the particles were not sintered, and could be easily taken out from the alumina tube. No granulation instead of dry particles for comparison
The dry powder that had passed through a 200-mesh sieve was packed into an alumina tube, heated to 1000°C, and brought into contact with sublimation gas of ammonium chloride. This refined product was gray in color and slightly sintered inside the alumina tube, making it difficult to remove. The analytical values of these purified products are shown in Table 1.

[Table] Example 2 Australian bauxite having the chemical composition shown in Table 2 below was prepared. This bauxite had a diameter of 1 mm or more, and most of the bauxite had a spherical shape of 5 to 7 mm. The sample with this particle size distribution as it is, that is, the sample without treatment, was designated as A. Next, it was sifted through a sieve with an opening of 3 mm, and those with a diameter larger than 3 mm were labeled B, and those with a diameter smaller than 3 mm and larger than 1 mm were labeled C. Separately, a part of this bauxite was milled into a fine powder with a diameter of 0.1 mm or less using a roll mill. Add 40g of 3% starch solution to 600g of this finely ground powder.
The mixture was added and mixed well to form a clay-like mixture, which was then granulated into particles with a diameter of 2 to 3 mm using a granulator. Next, the granulated particles were placed in an enameled dish and placed in a hot air drying oven set at 110°C and dried for 5 hours. The dry particles thus obtained were designated as D. Next, add 100gr of ammonium chloride to 500gr each of A, B, C, and D and carbon powder with a particle size of 0.5 to 1.0mm.
20gr each was added and mixed, placed in aluminium crucibles and placed in an electric furnace maintained at 1200°C. After the generation of sublimated ammonium chloride gas was completed, the alumina crucible was taken out from the electric furnace to obtain purified bauxite. The analytical values of these purified products are shown in Table 2.

[Table] Example 3 Synthetic cordierite having the chemical composition shown in Table 3 below was pulverized into powder. This powder is all 0.1
It passed through a sieve with a mm opening. This powder 600gr
40g of 3% starch solution was added to the mixture, and water was added while mixing well to form a slurry. Next, the slurry was spray-dried using a powder-fog dryer to obtain dry particles having a particle size of 0.2 to 0.3 mm. 60 gr of ammonium chloride and 20 gr of carbon powder with a particle size of 0.1 to 0.5 mm were added to and mixed with the dry particles thus obtained, and the mixture was placed in an alumina crucible and kept in an electric furnace maintained at 1000°C. After the generation of sublimation gas of ammonium chloride was completed, the product was taken out of the electric furnace to obtain a purified cordierite. For comparison, 600g of powder before granulation was mixed with 60g of ammonium chloride, and the mixture was placed in an aluminum crucible and heated in an electric furnace in the same manner as above. The analysis results of the purified product thus obtained are shown in Table 3.

【table】

Claims (1)

[Claims] 1. The ceramic raw material is crushed in advance to a diameter of 0.1 mm or more and 3 mm or less, or 3.
After being granulated to a size of 1 mm or less, the sublimation gas of ammonium chloride is brought into contact with a sufficient amount of combustible material to react with oxygen in the surrounding atmosphere and convert into CO or CO ₂ while heating at 400 to 1400°C. A method for refining ceramic raw materials. 2 The ceramic raw material is diaspore (Al ₂ O ₃ H ₂ O),
Aluminum hydroxide containing gypsite (Al(OH) ₃ ), bauxite (Al ₂ O ₃・2H ₂ O), or calcined products thereof, kyanite, Kibushi clay,
Frog-eye clay, kaolinite containing shale clay, aluminum silicate minerals whose main minerals are montmorillonite and their calcined products, zircon sand (Zr・SiO ₄ )
The method for refining a ceramic raw material according to claim 1, which is silica stone or a calcined product thereof. 3 The ceramic raw material is forsterite (Mg ₂ .
SiO ₄ ), steatite (Mg・SiO ₄ ), spinel (MgO・Al ₂ O ₃ ), mullite (3Al ₂ O ₃・2SiO ₂ ),
Claim No. 1, which is an artificial raw material containing cordierite (3MgO・Al ₂ O ₃・3SiO ₂ ), silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), zirconium carbide (ZrC), and stabilized zirconia. The method for refining ceramic raw materials according to item 1.