JPH0212894B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a calcium silicate molded body, particularly a lightweight calcium silicate molded body having a density of 130 kg/m ³ or less and suitable as a heat insulating material used at high temperatures. It is. Conventional Technology Calcium silicate molded bodies are becoming lighter and lighter year by year, and ultra-lightweight products with a bulk density of 130 kg/m ³ or less have already been commercialized. There are various purposes for reducing the weight of calcium silicate molded bodies, such as making them easier to cut, transport, and fixing them to furnaces and buildings, but one of the most important purposes is to improve heat insulation performance. Therefore, it can be said that conventional weight reduction has been progressing while achieving its purpose. However, it has been found that reducing the weight so that the bulk density is 130 Kg/m ² or less does not necessarily lead to improved insulation performance. In other words, the thermal conductivity of calcium silicate molded bodies generally increases as the temperature rises, but especially in lightweight products, the radiation heat transfer that passes through the pores has a large effect on the thermal conductivity of the entire insulation material. Therefore, weight reduction depending on an increase in porosity does not improve the heat insulation performance beyond a certain limit, and may even worsen it. Naturally, this tendency becomes more pronounced at higher temperatures where heat radiation becomes stronger, and when the operating conditions are approximately
At high temperatures above 300°C, lightweight products become inferior to medium-density products in terms of insulation performance. Furthermore, not only does the thermal conductivity increase, but the increase in thermal conductivity as the temperature rises becomes steep and exponential (for example, at a density of 210 kg/m ³ between 200°C and 500°C). JIS A9510-1984 No. 1
An example of a calcium silicate molded body with a density of 110 Kg/m ³ shows an increase in thermal conductivity of about 120%, whereas a product equivalent to 22 shows an increase in thermal conductivity of about 55%. ) Materials that exhibit large fluctuations in thermal conductivity due to such slight temperature changes can make the performance of furnaces, etc. that use them as heat insulating materials unstable, or make it difficult to design the entire device. Therefore, although conventional lightweight products have the advantages of sufficient heat resistance and light weight, they are difficult to use in high-temperature regions. As a means to reduce the amount of radiant heat transfer in a calcium silicate molded body, there is a method of incorporating a powder having a large thermal radiation shielding effect into the molded body as a shielding material (JP-A-58-49654, JP-A-60- 112663, etc.), but with this method, adding a shielding material significantly reduces the strength of the product, and if the shielding material is added from the hydrothermal synthesis reaction stage, it becomes difficult to control the reaction. There was a problem. Problems to be Solved by the Invention The purpose of the present invention is to solve the above-mentioned problems with lightweight calcium silicate molded bodies, and to produce calcium silicate which has a low density but whose thermal conductivity does not increase much even at high temperatures. Molded objects, specifically
A calcium silicate molded body that exhibits almost the same thermal conductivity temperature dependence as JIS A9510-1984 No. 1 22 (density 220 Kg/m ³ ) is produced without any significant adverse effect on the hydrothermal synthesis reaction or product strength. The purpose is to provide a manufacturing method. Means for Solving the Problems The method for producing a calcium silicate molded body provided by the present invention involves heating and reacting a slurry mixture consisting of a silicic raw material, a calcareous raw material, and water under pressure while stirring. A slurry of calcium silicate hydrate crystals in which calcium silicate hydrate crystals form spherical aggregates is produced by mixing silicon carbide powder with the slurry, followed by molding and drying. In the method for manufacturing molded objects, the average particle size of silicon carbide is 1 μm.
It is characterized by using the following and reacting the silicic raw material and calcareous raw material so that the average diameter of the calcium silicate hydrate crystal aggregate is 20 times or more the average particle diameter of the silicon carbide used. shall be. Hereinafter, the method for manufacturing a calcium silicate molded body according to the present invention will be explained in order of steps. In the production method of the present invention, first, a silicate raw material, a calcareous raw material, and a large amount of water are stirred and hydrothermally reacted in an autoclave in a conventional manner to prepare a calcium silicate hydrate crystal slurry. As the silicic acid raw material, it is desirable to use a crystalline material, such as a fine powder of silica stone with an average particle size of about 5 to 15 microns, but the material is not limited thereto.
Although any calcareous raw material can be used, a particularly preferred calcareous raw material is quicklime with a CaO crystal size of 0.3 μm or less. In addition,
“Quicklime with a CaO crystal size of 0.3μ or less” is
The average diameter of microcrystalline grains in the form of granules or fused particles observed when a fresh fracture surface is observed with a scanning electron microscope (if particles are found to be fused, the size of the primary particles can be determined based on their shape) Refers to quicklime that has a particle size of 0.3μ or less. There are no particular restrictions on the conditions for digesting the quicklime, and it may be carried out using a conventional method using about 10 to 40 times the amount of water or hot water. The CaO/SiO ₂ molar ratio of the raw materials is preferably about 0.9 to 1.1. The hydrothermal reaction is carried out at a pressure of 12 to 20 kg/cm ² and for a period of about 4 to 8 hours. This reaction yields a slurry consisting of spherical aggregates of calcium silicate hydrate crystals. There is a difference between the size of the calcium silicate hydrate crystal aggregates produced at this time and the reaction conditions. Since there is a relationship that the crystal aggregates become larger, it is desirable to make the crystal aggregates generated as large as possible by selecting these conditions, and at least increase the average particle size of the silicon carbide used.
It is necessary to have a diameter 20 times or more. Further, in order to obtain a calcium silicate molded body having a low specific gravity, it is desirable to generate a calcium silicate hydrate having as large a sedimentation volume as possible at this stage of the hydrothermal reaction. For this reason, it is desirable to carry out the reaction with strong stirring for at least a period of time. Sedimentation volume refers to the volume of the calcium silicate hydrate layer that settles when 500ml of slurry with a solid concentration of 2% by weight is placed in a 500ml measuring cylinder with an inner diameter of 50mm and left to stand at 20°C for 2 hours. do.
Setting this value to 450 ml or more is essential in order to produce a calcium silicate molded body that has a density of 130 Kg/m ³ or less and has sufficient strength even if a sufficient amount of thermal radiation shielding material is mixed. Next, silicon carbide as a thermal radiation shielding material is added to the obtained calcium silicate hydrate crystal slurry. Silicon carbide must be fine particles with a particle size of 1μ or less. By using such fine particulate silicon carbide and generating calcium silicate hydrate crystal aggregates with a diameter of 20 times or more than the particle size, it is possible to significantly reduce strength such as bending strength for the first time. Thermal radiation shielding material can be contained in the calcium silicate molded body without any heat radiation shielding material. The appropriate amount of silicon carbide added is 10 to 30% by weight (based on the weight of the final product). In addition, at the stage of mixing silicon carbide, reinforcing fibers and other auxiliary materials can be added as necessary. As reinforcing fibers, those commonly used for reinforcing calcium silicate molded bodies, such as pulp, glass fiber, rayon cloth, and asbestos, can be used. The slurry of hydrated calcium silicate with silicon carbide and other additives is then dehydrated and shaped. Finally, by drying the obtained molded product, the desired calcium silicate molded product can be obtained. In the above manufacturing method, the silicon carbide fine particles mixed into the calcium silicate hydrate crystal aggregate adhere to the needle-like crystals on the surface of the crystal aggregate. Therefore, the silicon carbide particles are uniformly introduced into the molded body during molding without being separated due to differences in specific gravity, and are useful for shielding heat radiation passing through the pores. However, if the particle size of silicon carbide is too large or the calcium silicate hydrate crystal aggregate is not large enough,
The silicon carbide powder interposed between the crystal aggregates separates the crystal aggregates from each other, creating structural weaknesses and extremely reducing bending strength. If the grain size of the crystal aggregates is sufficiently large compared to the size of the silicon carbide particles, even if silicon carbide particles are present, the crystal aggregates will deform in a concave manner and come into contact with each other, so that the structure will not change. It is not a weakness of the above,
A product with sufficient bending strength can be obtained. EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. Example 1 Quicklime with a CaO crystal size of 0.26 μm was
The mixture was poured into twice the amount of hot water and digested for 1 hour while stirring. Silica stone powder with an average particle size of 10 μm was added to the obtained milk of lime so that the CaO/SiO ₂ molar ratio was 1.0.
Add water so that the amount of water is 30 times the total amount of quicklime and silica stone to make a homogeneous slurry, and while stirring in an autoclave, adjust the temperature.
The reaction was carried out at 197° C. and a pressure of 15 kg/cm ² for 4 hours. The calcium silicate hydrate formed in this reaction consists of xonotrite, and the average diameter of the crystal aggregates is 50
mm, and the sedimentation volume was 410 ml. The above zonolite slurry has an average particle size of 0.47μ.
m of silicon carbide fine powder and glass fiber at 15% and 4 m, respectively, based on the weight of the molded body after drying.
% and mixed. The mixed slurry was molded using a dehydration press and then heated to 130°C for 18 hours.
By drying for a period of time, a hardened calcium silicate molded body was obtained. Comparative Example 1 A calcium silicate molded body was produced in the same manner as in the above example except that silicon carbide was not mixed. Comparative Example 2 A calcium silicate molded body was produced in the same manner as in the above example except that silicon carbide having an average particle diameter of 5 μm was used. Table 1 shows the performance values of the calcium silicate molded bodies obtained in each of the above examples. The thermal conductivity values shown in the table are based on JISA1412 "Measurement method of thermal conductivity of heat insulating materials (flat plate comparison method)".

[Table] Effects of the Invention According to the present invention, by combining large-diameter calcium silicate hydrate crystal aggregates and ultrafine silicon carbide particles as described above, the strength can be improved without causing almost any decrease in strength. The temperature characteristics of thermal conductivity in lightweight calcium silicate molded bodies, which has been a problem in the past, can be significantly improved. As a result, it has become possible to use lightweight calcium silicate molded bodies even in high-temperature areas that were previously difficult to use, expanding the range in which the excellent properties of lightweight calcium silicate insulation materials can be utilized.
It can make a major contribution to promoting energy conservation.

Claims (1)

[Claims] 1 Calcium silicate water in which calcium silicate hydrate crystals form spherical aggregates by heating and reacting a slurry mixture consisting of a siliceous raw material, a calcareous raw material, and water under pressure while stirring. In the method for producing a calcium silicate molded body, which involves producing a slurry of hydrate crystals, mixing silicon carbide powder with the slurry, and then molding and drying the slurry, silicon carbide having an average particle size of 1 μm or less is used. , and a calcium silicate molding characterized in that a silicate raw material and a calcareous raw material are reacted so that the average diameter of the calcium silicate hydrate crystal aggregate is 20 times or more the average particle diameter of the silicon carbide used. How the body is manufactured.