JPH04119959A - Production of low-density heat insulating structural material - Google Patents

Abstract

PURPOSE:To obtain a low-density heat-insulating structural material excellent in heat resistance, etc., by mixing specified three kinds of inorg. fibers, an org. fiber and boron oxide by a specified weight ratio in water, dehydrating, molding, drying and calcining in order to join the inorg. fibers with boron oxide. CONSTITUTION:To the total amount of three kinds of inorg. fibers consisting of 100 pts.wt. silica-type fiber of 0.3-3mum average fiber diameter, 5-100 pts.wt. of alumina fiber of 1-5mum average fiber diameter, and 5-30 pts.wt. of aluminoborosilicate fiber of 3-15mum average fiber diameter, 5-30wt.% of org. fiber and 0.5-10wt.% of boron oxide are blended by dispersing in water. Then the obtd. slurry is dehydrated, molded, dried and calcined at the temp. at which boron oxide melts. Thereby, the org. fiber is removed by burning, while the inorg. fibers are joined with boron-contg. glass to form a three-dimensional mesh structure. Thus, the low-density heat-insulating structural material is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a material having high heat resistance and thermal shock resistance that is suitable as a heat insulating material used under severe temperature conditions exceeding 1200°C. The present invention relates to a method of manufacturing a low density insulation structure.

[Conventional technology]

It is required to withstand extremely high temperatures and severe thermal shock, to have low density and excellent insulation properties, such as the surface protection material of the US NASA Space Shuttle, and to have strength and machinability above a certain level. A porous molded body mainly made of heat-resistant inorganic fibers is known as a typical heat-insulating structure.

The first material of this kind to be used was formed by molding high purity silica fibers in the presence of colloidal silica as a binder at temperatures of about 1300'C! It is a material called silica tile made by firing. This material has low strength, deteriorates quickly, and has the disadvantage of chipping or peeling of adhesives due to mechanical impact during use. In order to eliminate the above-mentioned drawbacks of silica tiles caused by the use of a binder, the invention of JP-A No. 55-37500 discloses a mixture of silica fiber, aluminosilicate fiber and boron oxide, or a mixture of silica fiber and aluminoborosilicate fiber. We have proposed a mixture in which fibers are fused together by molding and firing the mixture. Further, the invention of JP-A-60-151269 discloses a method in which silica fibers and alumina fibers having a specific fiber diameter are fused together using boron oxide.

[Problem to be solved by the invention]

The low-density insulation structures made by the inventions mentioned above have already achieved a fairly high level of performance, but as space development progresses, there is a growing demand for high-performance structures with lower density, strength, and durability. ing.

An object of the present invention is to meet such demands and provide a method for manufacturing a heat insulating structure that has excellent strength, heat resistance, thermal shock resistance, etc. at a waste paper density.

[Means to solve the problem]

The present invention, which has succeeded in achieving the above object, consists of 100 parts by weight of siliceous fibers with an average fiber diameter of 0.3 to 3.07+m, 5 to 100 parts by weight of alumina fibers with an average fiber diameter of 1 to 5 μm, 5 to 30 parts by weight of aluminoborosilicate fibers with a diameter of 3 to 15 μm, and 5 to 30% by weight of organic fibers based on the total amount of the above three types of inorganic fibers and 0
．． Production of a low-density heat insulating structure characterized by dispersing and mixing 5 to 10% by weight of boron oxide in water, dehydrating the resulting slurry, drying, and firing at a temperature at which the boron oxide melts. It is the law.

[Effect]

When compared with the conventional manufacturing method, the main points of the manufacturing method of the present invention are that the blend of inorganic fibers has been improved and that a homogeneous porous structure is formed using organic fibers that are ultimately burned out. That's what I did.

That is, silica fiber, alumina fiber,
A novel formulation using three types of heat-resistant and aluminoborosilicate fibers creates a unique three-dimensional network of three types of heat-resistant fibers, each with distinct physical properties, thereby creating a low-density thermal insulation structure. However, it has an extremely high level of strength, heat resistance, and thermal shock resistance. The structure of the above-mentioned novel heat insulating structure has uniform void sizes between the constituent fibers, resulting in a molded body with no local density fluctuations, providing a tough and excellent heat insulating structure, but it is not included in the manufacturing raw materials. The organic fibers are homogeneously mixed with the inorganic fibers, shaped and then burned off in the firing process, thereby facilitating the formation of much more uniform voids than if no organic fibers were used. Also, by burning out the fibers and leaving voids behind, it is possible to form a low-density molded body that would not be possible to produce a side sole when molding a raw material mixture consisting only of inorganic fibers and boron oxide. .

The manufacturing method of the present invention will be explained in detail below.

As mentioned above, the raw material inorganic fiber has an average fiber diameter of 0.3 to 3.
These include silica fibers with an average fiber diameter of 0 μm, alumina fibers with an average fiber diameter of 1 to Sμ, and aluminoborosilicate fibers with an average fiber diameter of 3 to 15 μm. Therefore, it is desirable to use high-purity silica fibers with a 5102 content of 98% or more.

As the alumina fiber, A1. O, about 72-100%,
About 0 to 28% of 5i02 is preferred. In addition, as aluminoborosilicate fiber, A I,0, about 62
~70%, 5i02 approx. 24-28%, B20. Approximately 2-1
It is preferable to have a composition of 4% and an average fiber length of 0.5 to 15 m. If fibers shorter than this range are used, the strength of the heat insulating structure will be low, and it will be difficult to obtain a molded article with a low specific gravity. On the other hand, if longer fibers are used, these rigid fibers tend to have their strength oriented in the direction parallel to the pressing surface during the molding process, and other fibers will also be oriented in the same direction, resulting in delamination. It provides a molded product that is easy to use and has low compressive strength in the thickness direction.

The amount ratio of each inorganic fiber is as described above, but if the amount of alumina fiber is less than 5 parts by weight based on 100 parts by weight of Rica fiber, the heat resistance and strength of the product will be low;
If it exceeds 0.00 parts by weight, the coefficient of thermal expansion and thermal conductivity will increase. A particularly preferred amount of alumina fiber is about 5 to 70 weight fiffFi. In addition, if the amount of aluminoborosilicate fiber is less than 5 parts by weight, the product will still have poor strength and heat resistance, and if it exceeds 30 parts by weight, it will have an adverse effect on heat resistance, such as increasing heat shrinkage at high temperatures, and Increase expansion coefficient and thermal conductivity.

Organic fibers used together with the above three types of inorganic fibers include:
Suitable materials include wood pulp for papermaking or rayon production, linter pulp, rayon staple, etc., which burn out without melting when fired.

When using pulp, it is treated in advance with a mixer, pulper, etc. to crush it and disperse the fibers. When using rayon stable, it is desirable that the fiber length is about 15+am or less; if it is too long, it will become tangled when mixed with inorganic fibers, making it difficult to mix uniformly. If organic fiber is used in excess, it will interfere with the bonding between inorganic fibers and reduce the strength of the product, so it should be
The amount shall be 5% by weight.

Boron oxide is further mixed into the mixture of inorganic fibers and organic fibers as described above. The amount thereof is 0.5 to 10% by weight based on the total amount of inorganic fibers. If boron oxide is not used in sufficient amounts, the interfiber bonding will be poor, giving a product with low strength, but if too much boron oxide is used, the glass it forms coats the fibers, allowing each inorganic fiber to develop its properties to the best of its ability. This impairs heat resistance.

Inorganic fibers, organic fibers, and boron oxide are mixed uniformly and then dispersed in water. The resulting slurry is dehydrated to an appropriate concentration, and the final bulk density is approximately 0.08 to 0.15 g/c.
It is press-molded into a desired shape under conditions such that a molded product of ra' can be obtained. After drying the resulting molded product, it is fired in air to first burn out the organic fibers, then raised in temperature, and finally fired at a high temperature of about 1100 to 1400°C to melt the boron oxide and the resulting fibers. Causes interfusion. After cooling, cutting is performed as necessary to obtain the desired low-density heat insulating structure.

In addition, in the manufacturing method of the present invention, a heat radiating material that blocks the transmission of radiant heat and improves insulation properties, such as silicon carbide powder,
Silicon carbide whiskers, silicon boride powder, etc. may be added to and mixed with the raw material in an amount not exceeding 20 parts by weight per 100 parts by weight of silica fibers, and may be adhered to the fiber surface of the product.

〔Example〕

Average fiber diameter: approx. 0.9μ+*, 100 parts by weight of high purity Nrica fiber (short fiber) with 5iO 198% or more, average fiber diameter: 3μ
m1A+, 0.95% alumina fiber (short fiber) 46 parts by weight, average fiber diameter 11 μm, A1.0362%, 820
．． 14% S + 0z 24%, 23 parts by weight of aluminoborosilicate fibers with an average fiber length of 6 mm, 7.7 parts by weight of boron oxide, and 0 to 30% by weight of papermaking wood pulp based on the total amount of inorganic fibers are dispersed in water. Mix until the concentration is 1.
Make a 5% slurry. This slurry is preliminarily dehydrated to a concentration of 3%, and then dehydrated and formed into a plate shape using a filter press. The obtained molded product was dried at 105°C for 16 hours and then heated to 1350°C at a heating rate of 120°C/br.
The temperature rose to 1350'C! Hold for 10 hours and bake. After cooling, cutting is performed to obtain a plate-shaped heat insulating structure having a thickness of 50 mm and a negative side of 200 mIN.

The bulk density of the product can be changed within a certain range by adjusting the degree of dehydration in the dehydration molding step of the above manufacturing method, but by manufacturing a heat insulating structure with the lowest density that can be manufactured by this method, for the product, Addition amount and density of wood pulp d
The relationship between ll1n and the tensile strength in the thickness direction was investigated, and the results are shown in FIG.

Although this type of heat insulating structure prioritizes low density over strength, the tensile strength in the thickness direction is approximately 1.5 it I/cm.
! It is said that it is desirable that the above is the same, but if pulp is added, the density is 0 or 1 while ensuring the required strength.
It can be seen that low density insulation structures of less than 5 t/cm3 can be manufactured reliably.

Table 1 shows the results of characteristic tests conducted on products of the above-mentioned heat insulating structure in which the amount of pulp added was 17.8% by weight (example of the present invention) and the case where no amount of pulp was added (comparative example). Note that the coefficient of thermal expansion is an average value at 30 to 800°C, and all other physical property values unless otherwise specified are values at room temperature.

Table 1 Room temperature → 1200°C → Room temperature 30 cycles [Effects of the invention] As described above, the present invention involves molding raw inorganic fibers together with organic fibers, burning out the organic fibers, and bonding between the inorganic fibers using boron-containing glass. , thereby forming a three-dimensional network structure, it is possible to easily produce a homogeneous porous heat insulating structure with a low specific gravity, which was previously impossible to produce.

The manufacturing method of the present invention also employs an improved and unique combination of raw material inorganic fibers, so the cooperative action of these inorganic fibers results in excellent thermomechanical properties such as strength, heat resistance, and thermal shock resistance. A structure is formed.

As a result of the synergistic effect of the above two features, according to the manufacturing method of the present invention, it is possible to easily obtain a high-performance low-density heat-insulating structure that exceeds the conventional level.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of Examples.

Claims (1)

[Claims] Siliceous fiber 100 with an average fiber diameter of 0.3 to 3.0 μm
Part by weight, 5 to 1 alumina fiber with an average fiber diameter of 1 to 5 μm
00 parts by weight, 5 to 30 parts by weight of aluminoborosilicate fibers with an average fiber diameter of 3 to 15 μm, and 5 to 30 parts by weight of organic fibers and 0.5 to 10 parts by weight based on the total amount of the above three types of inorganic fibers. % of boron oxide is dispersed and mixed in water, the resulting slurry is dehydrated and molded, and after drying, it is fired at a temperature at which the boron oxide melts.