JPH01197315A - Calcium hydroxide - Google Patents

Abstract

PURPOSE:To produce calcia sintered compact suitable as raw material for refractory for steel-making furnace, having high purity, high density and excellent consumption-resisting property, by contg. impurities in the amt. below a specified amt. and by making a specified particle size. CONSTITUTION:The calcium hydroxide for calcium sintered compact, having high purity and density, having >=95% 325 mesh undersize particle and having the composition (by weight %) of >97.5 CaO and as impurities, <1.0 MgO, <0.2 SiO2, <0.1 Fe2O3, <0.1 Al2O3 and <0.05 B2O3 when incandesced, is produced. The calcium hydroxide is produced by digesting quicklime obtd. by calcining limestone, calcium carbonate, etc., in water, by classifying the aq. dispersion of the produced calcium hydroxide with a centrifuge, etc., to remove particles having >=325 mesh particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to calcium hydroxide. For more details,
The present invention relates to calcium hydroxide suitable for producing high-purity, high-density calci and sintered bodies (calcia clinker) suitable as raw materials for large-sized products for steelmaking furnaces.

Conventionally, high-purity, high-density magnesia clinker or magnesia-calcia-based talin is often used as a raw material for refractories for steelmaking furnaces.

However, in recent years, the steelmaking field has been moving towards clean tailing, and hot metal pretreatment methods and out-of-furnace refining methods have been adopted in steelmaking technology, and operating conditions have become more severe. There is a demand for the development of refractories that can withstand use in such fields.

Calcia refractories are known to have dephosphorization and desulfurization properties, low vapor pressure in high temperature ranges, and high spalling resistance, and are used in hot metal pretreatment methods, out-of-furnace refining methods, etc. Research has been underway for some time as a possible refractory.

However, since calcia refractories have the disadvantage of low digestibility, it is necessary to improve their digestibility in order to expand the field of industrial use of calcia refractories. Various methods have been proposed to improve digestion resistance, but all of them involve adding an anti-digestion agent. For example, ・F e , O, -MgO-S i O, a method of adding system components (see JP-A-4-9-118706), S i OH-F e 203-A t,,
o, or Sin, -Fe103-MgO-based component and B10
．． Method of adding ingredients together (Japanese Patent Application Laid-Open No. 57-14985
(See Publication No. 3), T u O! ,SIO! ,
AI! Os and B, one of Or skin components and Ca
This is a method of adding F (see Japanese Unexamined Patent Publication No. 14457/1983). It is thought that such anti-digestion agents produce a low melting point compound with CaO, turn into a liquid phase by high temperature heating, and coat the surroundings of calcia crystals as a thin film, thereby improving the digestibility of calcia.

However, calcia refractories manufactured by adding anti-digestion agents have new drawbacks due to the presence of low melting point compounds present as impurities, namely a decrease in hot strength and high temperature stability. Although the addition of additives improves the digestibility of calcia refractories, it results in deterioration of the originally excellent properties of calcia refractories.

An object of the present invention is to provide calcium hydroxide suitable for producing a high-purity, high-density calcia sintered body (calcia clinker).

Another object of the present invention is to provide calcium hydroxide that provides a calcia sintered body with high purity, high density, and excellent digestion resistance.

Still another object of the present invention is to provide calcium hydroxide that provides a calcia sintered body with high purity and high density and excellent hot strength and high temperature stability.

Yet another object of the invention is to have a CaO content of at least 97.5% by weight on a scorching basis and a bulk density of 3.0 g/cm.
The object of the present invention is to provide calcium hydroxide suitable for producing a high-density calcia sintered body having the above properties.

Further objects and advantages of the present invention will become apparent from the description below.

According to the invention, the objects and advantages of the invention described above are such that the composition, on scorching basis, expressed in weight %, contains CaO97,5
Above M g O 1,0 below 5i02 0.2 or below Fe, 0. 0.1 or less Al2O30,1 or less BzOx O,05, and 95% or more of the total weight is achieved by high purity calcium hydroxide having a particle size that passes through 325 mesh.

According to the present invention, high-purity calcium hydroxide having the above composition is calcium hydroxide obtained by digesting quicklime or calcium oxide obtained by calcining raw materials for lime, such as limestone or calcium carbonate, in water. It can be produced by classifying an aqueous dispersion and removing particles having a particle size larger than 325 mesh (Tyler mesh) from the aqueous dispersion. According to the research of the present inventor, as described above, by calcining limestone, digesting and classifying the obtained quicklime, impurities contained in limestone, which is the initial starting material, such as Mg, can be removed by scorching heat.
It is a fine, high-purity calcium hydroxide that can remove a large amount of impurities that give O, A I 203 , S i 0H1Fe103, etc., and can be observed under a microscope as a concatenation of fine spherical crystal grains, most of which are about 0.2μ or less. It was revealed that a dispersion was produced.

According to the method of the present invention, the high-purity calcium hydroxide dispersion produced as described above has a water content of 25% by weight or less, and has a particle size such that 95% by weight or more of the total weight passes through a 325 mesh sieve. A mixture containing calcium hydroxide particles is prepared, either as is or after being formed into a green compact, which is then sintered to provide a high-density, high-purity calcia sintered compact.

The above mixture having a moisture content of 25% by weight or less, preferably 15% by weight or less, may be formed into a green compact and then sintered, or may be sintered as it is without performing any forming operation as in Toku E11. . When sintering is performed by forming a green compact, it is not desirable to use a compact formed by applying too high a pressure.

The green compact is molded without any special pressure operation under normal pressure or under a pressure of at most 1 ton/am" or less, preferably 0.5 ton/cIn2 or less.

Generally, when sintering oxide particles, in order to improve the sinterability, it is necessary to increase the number of points between particles by increasing the compacting pressure when making a green compact of oxide particles as much as possible. It is known that this is desirable. For example, this is the case when magnesia or alumina sintered bodies are produced from magnesium oxide or aluminum oxide, and the same is true when calcia sintered bodies are produced by directly sintering limestone or calcium carbonate particles.

According to the present invention, unlike these conventional sintering operations, calcium hydroxide is sintered in a state where there are few interparticle contacts, rather than in the prior art, to form a high-density sintered body. give. Although the reason for this is not clear, it is believed that the calcium hydroxide of the present invention has adhesiveness, viscoelasticity, expansibility, etc. that are different from other oxides.

In other words, when a raw compact of calcium hydroxide has a high density, the water vapor generated by thermal decomposition of calcium hydroxide is thought to increase inside the compact, which causes the compact to relax and create relatively large pores in the sintered compact. This is because it generates micro-cranks and the like, giving a sintered body with a low density.

Calcium hydroxide contains compounds that do not or are difficult to form low melting point compounds with calcium oxide before sintering, such as ZrO2, MgO1NiO or Ti.
e, etc. can be mixed. Due to the use of the high purity calcium hydroxide of the present invention, such additives are believed to act as calcia sintering aids rather than as calcia digestive inhibitors. The additive can be added, for example, to a dispersion (suspension or emulsion) of classified calcium hydroxide, and then added to a cake of calcium hydroxide that has been classified and filtered through a colander and whose moisture content is adjusted to 25% by weight or less. It can be added and kneaded, or in some cases, it can be added to and mixed with classified dry calcium hydroxide powder. Preferably, it is added to the dispersion. Additives can usually be used in amounts of 0.5 to 1% by weight on a burning basis.

Sintering at 1800°C or higher, preferably 1900°C to 210°C
Performed at 0°C. This sintering allows sufficient growth of calcia crystals and achieves uniform distribution of impurities or additives present, albeit in small amounts.

Thus, according to the above sintering method using calcium hydroxide of the present invention, the composition, expressed in weight percent on a sintering basis, is as follows: Ca O97.5 or more M g O1,0 or less 5iOa O02 or less Fe,03 It is possible to produce a high-density, high-purity calcia sintered body having Al5o3 of 0.1 or less, 8103 of 0.05 or less, and a bulk density of 3.0 g/cm3 or more.

The above-mentioned calcia sintered body preferably has CaO
The CaO content is 98% by weight or more, and Fe2O3
Regarding Fe1on content is 0.05% by weight or less, A
AI regarding I, 03! 0. The content is 0.05% by weight or less.

Further, the calcia sintered body is preferably 3.059/c
m'' or more.

The calcia sintered body has characteristic aspects regarding the grain size of calcia crystals and possible pores. The calcia sintered body is preferably 60μ or more, particularly preferably 8
It has an average calcia crystal grain size of 0 μ or more, and the amount of pores with a pore diameter of 1 μ or less is preferably 4
It is 0% or more, particularly preferably 50% or more.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited by these Examples. In the examples, % means weight %.

In addition, various measurement methods and physical property values in the present invention are as follows.

l) Average grain size Measured according to the measurement method of Jakushin method 3 "Measurement of size of periclase in Danesia clinker and its description method".

The polished surface of the calcia sintered body was observed using a scanning electron microscope, and secondary electron images of three representative locations were photographed at a magnification of x200, and the diameters of approximately 50 CaO crystals included in the photographs were measured. The average value was taken as the average crystal grain size.

2) Weight increase rate Jakushin method 7 Digestibility test method of dolomite clinker, (■
) Measured according to the autoclave method.

3) Hot flexural strength After crushing the calcia sintered body, 30% by weight of particles with a particle size of 297 to 150 μm, 15% by weight of particles with a particle size of 1.49 to 74 μm, and 55% by weight of particles with a particle size of 74 μm or less The particle size was blended so that the particle size was 500 kg/cm'', and this was press-formed at 1,700°C for 1 hour to produce a single calcia block.The hot strength of this block at 1,400°C was measured. It was defined as hot bending strength.

4) Pore size distribution This measurement was carried out by a method called mercury intrusion method. After crushing the calcia sintered body to 3 to 5+ nm, immerse it in mercury,
As the pressure applied to the mercury is gradually increased, the mercury gradually penetrates into smaller pores in response to the pressure. The pore size distribution was calculated from the relationship between the amount of penetration and pressure.

5) Bulk density (bulk specific gravity) "Method for measuring apparent porosity, apparent specific gravity and bulk specific gravity of magnesia clinker" determined by the Test Methods Subcommittee of the 124th Committee of the Japan Society for the Promotion of Science ( It was calculated using the following formula according to the 1981 Refractory Notebook.

Wl: Dry weight of clinker (g) W2: Weight of sample saturated with white kerosene in white kerosene (g) W, 2 Weight of sample saturated with white kerosene (g) S: Specific gravity of white kerosene at measurement temperature ( 9/cm") 6) Chemical composition Measured in accordance with the "JSPS method for chemical analysis of magnesia clinker" determined by the Test Methods Subcommittee of the 124th Committee of the Japan Society for the Promotion of Science (refer to the 1981 edition of the refractory notebook). did.

Especially B20. The analysis of curcumin was carried out using the absorptiometric method, which was adopted by the same committee as the Gakushin method.

Example 1 CaO 97.73%, MgO 0.61%, based on scorching heat
5tot0.84%, Fe, 0.09%, AlzO
Limestone having a chemical composition of SO, 24% and B10, 0.02% was heated at 1100° C. for 3 hours to produce quicklime. This quicklime was digested with decarboxylated tap water.

The temperature of the mixed solution at that time was 80°C. Further, the digested product was processed using a centrifuge to obtain fine calcium hydroxide with a 350 mesh passage rate of 95% or more. The chemical composition of this classified and purified product is 98.78% CaO and Mg based on scorching heat.
O0.59%, Si020.05%, Fat's
O, 02%, At, Os0.03%, 82030.02
%Met.

Reference Example 1 0.8% of Ti01 sintered body was added as an additive to the purified calcium hydroxide solution of calcium hydroxide obtained in Example 1 above.
After mixing to a water content of 10%, the mixture was dried to a moisture content of 10%. This dried product is molded at a pressure of 500 kg/cm',
It was heated and sintered at 1900°C. The chemical composition and various properties of the calcia sintered body are shown in Table 1.

Its typical microstructure is shown in the photograph attached as Figure-1.

Table 1 Reference Example 2 The same purified calcium hydroxide dry powder obtained in Example 1 was mixed at 500 kg/c without adding any anti-digestion agent.
After molding at a pressure of m2, it was sintered at 1800°C. The chemical composition and various properties of this calcia sintered body are shown in Table 2.

Table 2 Comparative Reference Example 1 A calcia sintered body was obtained in the same manner as in Reference Example 1 using calcium hydroxide having the chemical composition shown in Table 3 based on scorching heat. The properties of the obtained calcia sintered body are shown in Table 3.

Table 3

[Brief explanation of the drawing]

FIG. 1 is a micrograph showing the calcia crystal structure of the calcia sintered body from calcium hydroxide of the present invention obtained in Example 1. (1 other person)

Claims (3)

[Claims] 1. The composition is CaO9, expressed in weight percent on a scorching basis.
7.5 or more MgO 1.0 or less SiO_20.2 or less Fe_2O_30.1 or less Al_2O_30.1 or less B_2O_30.05 or less, and 95% by weight or more of the whole has a particle size that passes through 325 mesh, high purity, high density calcia sintered. Calcium hydroxide for producing aggregates. 2. The raw material for quicklime is burned to produce quicklime or calcium oxide, the quicklime or calcium oxide is digested in water to produce an aqueous dispersion of calcium hydroxide, and then the aqueous dispersion is subjected to a classification operation. The method for producing calcium hydroxide according to claim 1, characterized in that particles having a particle size larger than 325 mesh are removed. 3. The method according to claim 2, wherein the classification operation is performed by centrifugation.