JPH0329020B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a calcia sintered body having high purity, high density and excellent digestion resistance and suitable as a raw material for refractories for steelmaking furnaces, and a method for producing the same. Conventional technology In recent years, there has been a growing trend in the steel manufacturing industry towards streamlining operations, such as using higher quality steel and continuous casting, leading to the introduction of higher temperatures in converters and ladles, and the introduction of ladle smelting methods. . Therefore, it has been conventionally used for refractories used in converters and ladle smelting furnaces. Refractories that can withstand harsher conditions than magnesia-carbon, magnesia-chromium, high-alumina, and zirconia refractories are desired. As a basic refractory material, calcia has a melting point of
At a high temperature of 2580℃, it has excellent properties such as high thermal shock resistance and slag erosion resistance, as well as the ability to absorb Al ₂ O ₃ inclusions in steel. Since our country is rich in resources, it is highly anticipated as a refractory for steelmaking furnaces. Despite this, calcia refractories have not yet been put into full-scale practical use. The main reasons for this are that calcia clinker (calcia sintered compacts are called calcia clinker), which is the raw material for refractories, has low water and digestion resistance, is difficult to handle, store, and manufacture bricks, and has a high density. Since a sintered body cannot be obtained, there are problems with slag resistance and strength. Therefore, in order to utilize calcia refractories industrially, improving the digestion resistance and bulk density of calcia clinker is a major issue. There is a close relationship between digestibility and bulk density, and increasing bulk density also improves digestibility. Therefore, increasing the bulk density is one of the important requirements for increasing the digestion resistance. In addition to increasing the density, various methods have been proposed to improve the digestibility of calcia clinker. For example, calcareous raw materials
Each component is added and mixed so that Fe ₂ O ₃ is 2 to 10% by weight, MgO is 1 to 5% by weight, and SiO ₂ is 2% by weight or less. After this raw material is pressure molded, it is fired at 1350 to 1650°C. Method (Japanese Unexamined Patent Publication No. 55-95614) A method of adding calcium fluoride together with one of the compounds of Group 1 or Group 3 elements of the periodic table (Japanese Unexamined Patent Publication No. 56-14457)
Publication) CaO or CaO and MgO are the main components,
_{Fe2O3 0.4-1.2} % by weight, _TiO2 0.1-0.5% by weight,
Contains SiO ₂ 1.5% by weight or less, Al ₂ O ₃ 1.0% by weight or less,
and the total amount of Fe ₂ O ₃ , TiO ₂ , SiO ₂ , Al ₂ O ₃ is 0.5 to 3
There is a method of expressing it as weight % (Japanese Unexamined Patent Publication No. 59-35060). These methods attempt to obtain digestion resistance by adding certain impurities to CaO to lower the sintering temperature of CaO, promoting densification, and covering the surface of CaO crystals with low-melting compounds. It's a method. In addition, a method for obtaining a calcia sintered body with high digestion resistance by using slaked lime of high purity and a constant fine particle size as a starting material and firing it at a high temperature of 1800°C or higher (Japanese Patent Application Laid-Open No. 1989-1999- 51658) has been proposed. Problems to be Solved by the Invention In the above method, adding a large amount of an additive that forms a low melting point compound with CaO to CaO leads to a decrease in hot strength and high temperature stability. Although effective, it has the disadvantage of deteriorating the originally excellent properties of calcia refractories. Furthermore, the method disclosed in JP-A No. 60-51658, in which high-purity fine slaked lime is fired at a high temperature, has a high firing temperature of 1800°C or higher and requires a large amount of energy. The relative density is 90-93%, and the total porosity is 7-10%. This is the relative density (97
%), which is unfavorable in terms of slag resistance and strength. Furthermore, high digestion resistance cannot be expected at such a density. Calcia clinker is desired to have high purity and high digestion resistance, and it is also desired that the bulk density is equivalent to or higher than magnesia clinker in terms of not only digestion resistance but also slag resistance and strength. There is. An object of the present invention is to provide a calcia sintered body that has excellent digestion resistance, high density, and high purity, and a method for producing the same. Means for Solving the Problems As a result of repeated research focusing on the effects of additives on calcia sintering and the structure and digestion resistance of the obtained calcia sintered bodies, the present inventors found that
We have discovered that by sintering Al ₂ O ₃ and ZrO ₂ in the coexistence, a calcia sintered body with high density and large crystals, which could not be obtained conventionally, can be obtained. Furthermore, they discovered that this sintered body has much better resistance to digestion than conventional sintered bodies, and established a method for producing it. and,
Its structure is as described in the claims. For the purpose of the invention, the purity of the calcia sintered body of the present invention is set to be 97.5% by weight or more as CaO. The bulk density is
3.20 g/cc or more, preferably 3.26 g/cc or more is required, and the average diameter of calcia crystals must be 60 μm or more, preferably 80 μm or more.
Unless the bulk density and the average diameter of calcia crystals are simultaneously satisfied within the above ranges, high digestion resistance, high slag corrosion resistance, and strength cannot be obtained. The calcia sintered body of the present invention is
Contains Al ₂ O ₃ 0.05% by weight or more and 0.5% by weight or less, ZrO ₂ 0.1% by weight or more and 1.0% by weight or less, preferably
Al ₂ O ₃ more than 0.1% by weight and less than 0.2% by weight,
Contains ZrO ₂ 0.1% by weight or more and less than 0.5% by weight.
Even if Al ₂ O ₃ exceeds 0.5% by weight based on scorching heat, the effect on bulk density and grain size of calcia crystals is saturated;
There is also no change in digestion resistance. However, Al ₂ O ₃ reacts with CaO and forms CaO at around 1400℃.
- Formation of an Al ₂ O ₃ -based liquid phase leads to a decrease in strength and fire resistance, so the upper limit is set at 0.5% by weight.
The lower limit is 0.05% by weight of Al ₂ O ₃ based on scorching heat, and if Al ₂ O ₃ is less than that, calcia crystals with an average grain size of 60 μm or more cannot be obtained. If ZrO ₂ exceeds 1.0% by weight on a scorching heat basis, calcia crystals with an average particle size of 60 μm or more cannot be obtained due to the grain size suppressing effect of ZrO ₂ on calcia crystals. If ZrO ₂ is less than 0.1% by weight on a sintering basis, a high-density sintered body with a bulk density of 3.20 g/cc or more cannot be obtained. In addition, the effect on the bulk density of the calcia sintered body and the average grain size of the calcia crystals is
The effects of Al ₂ O ₃ and ZrO ₂ only work when both coexist, and the above composition range is limited to Al ₂ O ₃ and ZrO ₂
Even if either one of them comes off, the bulk density is 3.20g/cc.
As described above, a calcia sintered body having an average grain size of calcia crystals of 60 μm or more and sufficient strength cannot be obtained. Al ₂ O ₃ exceeds 0.1% by weight on scorching heat basis
0.3% by weight or less, and ZrO ₂ is 0.1% by weight or more, 0.5
When the amount is less than % by weight, the obtained calcia sintered body has a higher density and the average grain size of the calcia crystals becomes larger. Conventionally, Al ₂ O ₃ has been considered to be effective as a sintering aid and anti-digestion agent during calcia clinker firing, but the present inventors have found that Al ₂ O ₃
It was found that in order to promote the grain growth of CaO particles, which are harmful to sintering, from around 1200°C, it actually works in the direction of lowering the density in high-density regions where the relative density exceeds 97%. Furthermore, the inventors found that ZrO ₂ does not form a low-melting point compound with CaO, and that the calcia sintered body produced by adding and firing ZrO ₂ to suppress the grain growth of calcia particles and calcia crystals has a very high density. It was found that However, at this time, the average particle size of the calcia crystals becomes small, and high digestion resistance cannot be obtained. The present inventors have discovered that Al ₂ O ₃ and ZrO ₂ have completely different effects as described above.
It has been discovered that by simultaneously adding and firing a calcia sintered body, a calcia sintered body having a high density and large crystals, which has never been seen before, can be obtained. The reason why high density and large crystallization of the calcia sintered body are achieved at the same time is that ZrO ₂ suppresses grain growth and network formation that are harmful to densification near the temperature at which CaO densifies, and after densification. In the high temperature range, CaO−Al ₂ O ₃ system liquid phase or CaO−Al ₂ O ₃ −
It is presumed that a small amount of ZrO ₂ -based liquid phase is generated and promotes the growth of calcia crystals. FIGS. 1 and 2 show the influence of Al ₂ O ₃ and ZrO ₂ on the particle size and bulk density of calcia crystals depending on the firing temperature. FIG. 1 is a graph showing the relationship between the average particle diameter of calcia crystals, firing temperature, and content of Al ₂ O ₃ and ZrO ₂ in a calcia sintered body containing Al ₂ O ₃ and ZrO ₂ . FIG. 2 is a graph showing the relationship between each firing temperature and bulk density for the same sample. The lines drawn in these graphs each represent Al ₂ O ₃
The above relationship is shown for samples containing ZrO 2 and ZrO ₂ as shown below. Note that (%) below is based on weight. Line Al ₂ O ₃ (%) ZrO ₂ (%) Solid line 10.02 - Solid line 20.02 0.2 Dotted line 30.06 - Dotted line 40.06 0.2 From this figure, Al ₂ O ₃ and ZrO ₂ are present in the calcia sintered body. It is clear that the calcia sintered body having high density and large crystals according to the present invention can be obtained only when it is present at the same time and in a small amount. The calcia sintered body according to the present invention has a composition expressed in weight percent based on scorching heat, such that CaO is 97.5 or more, Al ₂ O ₃ is 0.05 or more, 0.5 or less, ZrO ₂ is 0.1 or more and 1.0 or less, and the balance is composed of unavoidable impurities (a ) Calcium hydroxide with a particle size of 44 μm or less accounting for 98% by weight or more and a CO ₂ content of 5.0% by weight or less based on Ca(OH) ₂ (b) Al ₂ O ₃ or Al ₂ O ₃ by thermal decomposition Aluminum compound (c) By mixing ZrO ₂ or a zirconium compound that thermally decomposes to become ZrO ₂ , the raw material whose composition has been adjusted is either as it is or pressurized to form a molded product, which is then fired at 1500℃ or higher. It can be manufactured by Calcium hydroxide, one of the raw materials, must contain particles with a diameter of 44 μm or less at least 98% by weight. Such calcium hydroxide is produced by sintering quicklime obtained by calcining limestone or synthetic calcium carbonate in water, preferably warm water, and then using a wet sieve or a liquid cyclone to slake the resulting slurry. Obtained by classification. Particles larger than 44 μm are harmful to sintering, and must be removed in order to obtain a high-density sintered body. Furthermore, quicklime contains impurities such as SiO ₂ , Al ₂ O ₃ , MgO,
Although it often contains a large amount of Fe ₂ O ₃ , CaCO _{3 ,} etc., it is possible to remove a large amount of these impurities by the above operation. The calcia sintered body according to the present invention contains 97.5% by weight or more of CaO, preferably 98.0% by weight or more, but in order to obtain such a composition, the purity of calcium hydroxide must be 99% by weight or more as CaO on a sintering basis. There must be. Additionally, calcium hydroxide has a _CO2 content of 5.0 based on Ca(OH) _2.
Must be less than % by weight. When the _CO2 content of calcium hydroxide exceeds 5.0% by weight, the bulk density
A high-density calcia sintered body of 3.20 g/cc or more cannot be obtained. This means that CO ₂ in calcium hydroxide
This is presumed to be because it is contained as CaCO ₃ and decomposes at around 900°C during firing, forming voids due to the generation of CO ₂ gas and volumetric contraction. Calcium hydroxide easily reacts with CO ₂ in the air, and CaCO ₃ generated in this way is difficult to remove by classification, so care must be taken. The aluminum and zirconium compounds used in the present invention must be oxides or compounds that become oxides upon thermal decomposition. That is, aluminum compounds include Al ₂ O ₃ and Al
(OH) ₃ , AlCl ₃ , Al(NO ₃ ) ₃ , Al ₂ (SO ₄ ) _3, etc. Zirconium compounds include ZrO ₂ ,
These include ZrOCl ₂ , zirconyl acetate, zirconyl nitrate, and zirconyl carbonate. The compound used may be a commercially available industrial chemical, but it is desirable that the purity is high and that the powder is fine. Normally, slaked lime contains Al ₂ O ₃ as an impurity as mentioned above.
It is possible that the Al ₂ O ₃ content defined in the present invention can be achieved even in classified and purified slaked lime that contains Al 2 O 3 . In such a case, only the zirconium compound is mixed. In the present invention, as a manufacturing process up to baking, the cake obtained after filtering the raw material slurry is (1) directly baked, (2) after drying, pressure molded and baked, and (3) calcined. Any one of the three steps of subsequent pressure molding and firing can be used. In either step, it is desirable that the calcium hydroxide, aluminum compound, and zirconium compound be mixed sufficiently uniformly.
Mixing by stirring in a calcium hydroxide slurry, mixing by kneading in a filter cake, etc. are preferred. When taking step (2), it is also possible to dry mix the calcium hydroxide slurry after filtering and drying it. Further, when taking the step (3), there is no problem even if calcium hydroxide is calcined to form calcium oxide and then mixed. However, in this case, the aluminum and zirconium compounds used are preferably oxides. In any of the above steps, a commonly used filter, such as a vacuum filter or a pressure filter, can be used for filtration. When taking step (2), a drying step is necessary, and a commonly used dryer can be used. However, when fossil fuel combustion gas is used for drying, the absorption of CO ₂ needs to be reduced to 5.0% by weight or less based on Ca(OH) ₂ . Drying in an air atmosphere is preferable since there is no absorption of CO ₂ . Further, it is desirable to reduce the moisture content by drying to 10% by weight or less based on Ca(OH) ₂ in order to obtain a high-density sintered body.
Furthermore, it is desirable to pulverize the dried product obtained in these steps using a ball mill, Henschel mixer, etc. in order to obtain the next best molded product. In steps (2) and (3), molding is performed under pressure of about 1 t/cm ² . As the molding machine, a commonly used briquetting machine or the like can be used. Calcination in step (3) must be performed at a temperature between 600°C and 1000°C. At temperatures lower than 600°C, the effect of calcination is small, and at temperatures higher than 1000°C, the specific surface area decreases, resulting in a decrease in sinterability. The calcination carried out here can be carried out using a commonly used light furnace, rotary kiln, etc., but even in this process, it is necessary to suppress CO ₂ absorption as low as possible, and it is necessary to suppress CO ₂ absorption as low as possible. It is particularly preferable to carry out under an air atmosphere. The filter cake, dry molded body, or pre-fired molded body obtained as described above must then be calcined at a temperature of 1500°C or higher, preferably 1650°C or higher. At this temperature, sintering progresses sufficiently, and a calcia sintered body having a high bulk density and large crystals can be obtained. At temperatures lower than 1500°C, calcia crystals are insufficiently developed and high digestion resistance cannot be obtained. For firing, a firing furnace that is normally used for firing magnesia clinker can be used, such as a rotary kiln. In this case, since fuel such as heavy oil is used, the atmosphere inside the furnace is different from an air atmosphere, and is an atmosphere with high partial pressures of CO ₂ and H ₂ O. Since the composition of the present invention facilitates sintering in such an atmosphere, there is no problem with firing in such an atmosphere, but if possible, an atmosphere with a low CO ₂ partial pressure
It is preferable to bake in an air atmosphere. According to the present inventors, by performing calcination in an atmosphere with a high partial pressure of CO ₂ , carbon dioxide occurs at a relatively low temperature near the surface of the calcium hydroxide cake or molded body.
It was discovered that as a result of the two processes of CaCO ₃ generation and CaCO ₃ decomposition that occur at around 900°C, the resulting calcia sintered body has many pores and a low bulk density. In addition, CaCO ₃ due to these CO ₂
It has also been revealed that the formation of can be significantly reduced by calcining calcium hydroxide to form calcium oxide. Therefore, when firing is performed in an atmosphere with a high partial pressure of CO ₂ , it is desirable to perform the calcination forming step (3) among the above steps. Next, Examples and Comparative Examples of the present invention will be given and specifically explained. In addition, various measuring methods in the present invention are as follows. (1) Bulk density JSPS method 2 “Magnesia clinker apparent porosity,” proposed by the 124th Committee of the Japan Society for the Promotion of Science
It was measured according to the method for measuring apparent specific gravity and bulk specific gravity. (2) Average crystal diameter According to the Fullman method (J.of.Metals 447 1953). That is, a straight line was arbitrarily drawn on a photograph of the polished surface, and the value obtained by multiplying the average value of the length of the line segment cut by the grain boundary by 1.5 was defined as the average diameter grain.
In addition, for the measurement, five or more clinker grains were selected, and more than 100 crystals were measured for each piece of paper. (3) Chemical composition JSPS method 1 “Chemical analysis method of magnesia clinker” proposed by the 124th Committee of the Japan Society for the Promotion of Science
Measured according to. (4) Weight increase rate As a guideline for digestion resistance, calcia sintered bodies classified into 2.00 to 4.47 mm were left standing in air at a relative humidity of 65% and a temperature of 20°C for two weeks, and the weight increase was measured. The amount of increase relative to the original weight is expressed as a percentage. (5) Calcium hydroxide particle size It was determined from the weight of calcium hydroxide remaining on the sieve after classifying the water slurry using a sieve. Examples Examples 1 to 3, Comparative Examples 1 to 4 Quicklime was slaked with warm pure water at 60°C and then classified to obtain calcium hydroxide having the chemical composition and particle size shown in Table 1. To this, predetermined amounts of Al ₂ O ₃ and ZrO ₂ were added and mixed in a slurry. Here Al ₂ O ₃
was a high-purity γ-Al ₂ O ₃ powder, and ZrO ₂ was added and mixed as a zirconyl acetate solution (reagent). The obtained mixed slurry was filtered, dried, and pulverized, and then molded under pressure of 1 t/cm ² . By crushing these molded bodies, 3.66 ~
Adjusted to a particle size of 5.66mm and heated at 1650℃ under air atmosphere.
It was fired in Table 2 shows the physical properties of the calcia sintered body obtained by cooling.

【table】
weight%

[Table] Example 4 An experiment was conducted under the same conditions as Example 1 except that the firing was performed at 1550°C. Table 3 shows the physical properties of the calcia sintered body obtained by cooling.

[Table] Example 5, Comparative Example 5 The firing was performed under the same conditions as in Example 1 except for the composition and the firing at 1700° C. using a firing furnace using propane and oxygen as fuel. Table 4 shows the composition and physical properties of the calcia sintered body obtained by cooling.

[Table] Example 6 The raw material powder used in Example 1 was treated in an air atmosphere.
After calcination at 800°C, the molded body is molded under a pressure of 1 t/cm ² and the resulting molded body is crushed to a size of 3.36 to 5.66 mm.
The process was carried out under the same conditions as in Example 4, except that the firing was carried out after adjusting the particle size to . Table 5 shows the physical properties of the calcia sintered body obtained by cooling.

[Table] Effects of the Invention The present invention provides a digestible material having a high purity chemical composition of 97.5% by weight or more of CaO, a bulk density of 3.20 g/cc or more, and an average grain size of calcia crystals of 60 μm or more. Calcia sintered bodies with excellent properties are Al ₂ O ₃ ,
It can be obtained by a relatively easy method of simultaneously mixing a small amount of ZrO ₂ and firing. As seen in Example 1, even when left in air with a relative humidity of 65%, the
The weight increase after a week was extremely low at 0.13%, and no change was observed with the naked eye. Therefore, the product of the present invention is expected to significantly improve digestion resistance, which has been a major hindrance when using calcia industrially, and is also expected to have high bulk density and purity, as well as slag resistance and mechanical strength.
It has become possible to fully utilize it in the industrial field.

[Brief explanation of drawings]

Figure 1 is a graph showing the average particle diameter of calcia crystals at each firing temperature of a calcia sintered body containing predetermined amounts of Al ₂ O ₃ and ZrO ₂ , and Figure 2 is a graph showing the bulk density of the same sample at each firing temperature. The graph and FIG. 3 are microphotographs showing the structure of the polished surface of the calcia sintered body of Example 1, and FIG. 4 is a microphotograph showing the structure of the polished surface of the calcia sintered body of Comparative Example 1.

Claims (1)

[Scope of Claims] 1. The composition is based on scorching heat and expressed in weight percent: CaO 97.5 or more, Al ₂ O ₃ 0.05 or more, 0.5 or less ZrO ₂ 0.1 or more and 1.0 or less, and the remainder consisting of unavoidable impurities, and has a bulk density of 3.20 g. /cc or more, and the average grain size of calcia crystals is 60 μm or more. 2. The calcia sintered body according to claim 1, which has a composition of 98.0 or more CaO, more than 0.1 Al ₂ O ₃ , and less than 0.3 ZrO ₂ 0.1 or more and less than 0.5 expressed in weight percent on a sintering basis. 3. The calcia sintered body according to claim 1 or 2, which has a bulk density of 3.26 g/cc or more. 4. The calcia sintered body according to any one of claims 1 to 3, wherein the average grain size of the calcia crystals is 80 μm or more. 5. The composition is expressed in weight percent based on scorching heat: CaO 97.5 or more, Al ₂ O ₃ 0.05 or more, 0.5 or less ZrO ₂ 0.1 or more and 1.0 or less, and the balance consisting of unavoidable impurities (a) 98% by weight or more of particles of 44 μm or less (b) Al _{2 O 3 or} an aluminum compound that thermally decomposes to become Al _{2 O 3} (c) ZrO ₂ or By mixing a zirconium compound that thermally decomposes to become ZrO ₂ , the raw material whose composition has been adjusted can be made into a molded body as it is or after being pressurized to form a molded body.
A method for producing a calcia sintered body characterized by firing at a temperature of 1500°C or higher. 6. The method for producing a calcia sintered body according to claim 5, wherein the raw material whose composition has been adjusted is calcined at a temperature of 600°C or more and 1000°C or less, and then pressurized to form a compact. 7. The method for producing a calcia sintered body according to claim 6, wherein the atmosphere during calcination is air. 8. The method for producing a calcia sintered body according to any one of claims 5 to 8, wherein the firing temperature is 1650°C or higher.