JPH0224779B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a sintered body having a novel composition having low porosity and low coefficient of thermal expansion using fused silica glass powder as a raw material. Quartz glass products generally have a small coefficient of thermal expansion (5 x 10 ^-7 /℃), are chemically inert (especially good acid resistance), have a high softening temperature, and have high transmittance in the ultraviolet and visible regions. Due to its unique characteristics, it is widely used in various physical and chemical instruments, lenses, prisms, heat-resistant containers, etc. However, these products require considerable high temperatures during melt-molding processing, and are therefore not only quite expensive, but also have the disadvantage that they are unsuitable for mass production due to poor moldability. On the other hand, sintered bodies made mainly from crushed fused silica glass can be produced using the same manufacturing method as ordinary refractories, so they have long been used for various purposes as industrial products that take advantage of their characteristics such as low thermal expansion. ing. Conventionally, such sintered bodies contain alumina cement and colloidal silica in the bonding part, so it is possible to obtain a product with low thermal expansion, but it is difficult to obtain a low porosity, and it is difficult to obtain a product with low porosity. A sintered body used for the joint is also known, but while this can produce a product with relatively low porosity, it has a major drawback of devitrification (crystallization) of the quartz glass due to the alkaline components in the clay. . The alkaline component contained in the sintered body of fused silica glass causes devitrification (crystallization) of the quartz glass, especially at around 1000°C. In other words, quartz glass is β
- This is because it crystallizes into cristobalite, and this part has a larger thermal expansion coefficient than the non-devitrified quartz glass part, and this difference in thermal expansion coefficient causes thermal stress, which causes cracks in the product during firing and use. . Furthermore, β-cristobalite transforms into low-temperature α-cristobalite at around 240° C., and as a result, the volume decreases by as much as 6%, which also causes cracks. Furthermore, various proposals have been made to blend small amounts of ultrafine powder or to blend acids such as nitric acid or phosphoric acid or their salts with other binders to improve sintering properties, but none of these have been proposed to improve sinterability. The reality is that it is difficult to become a rate product. In view of these points, the present inventor conducted various studies and examinations with the aim of obtaining a fused silica glass sintered body having both low porosity and low coefficient of thermal expansion. It has been found that the above object can be achieved by sintering a raw material having a specific composition containing a specific proportion of an additive such as boric acid to form a sintered body. Thus, in the present invention, the content of SiO ₂ and B ₂ O ₃ in the sintered body is reduced by adding 1 to 25% by weight of the B ₂ O ₃ component to fused silica glass powder of substantially less than 100 meshes and sintering it. is over 99%, and the alkaline component is
The proportion of R ₂ O is less than 0.1%, and 0
Thermal expansion coefficient at ~700℃ is 15×10 ^-7 /℃ or less,
The present invention provides a method for producing a dense fused silica glass sintered body characterized by having a porosity of 7% or less. In the present invention, the fused silica glass powder used as the raw material for the sintered body must have a particle size of 100 mesh or less. If the particle size is coarser than 100 mesh, the B ₂ O ₃ component contained in the sintered body may react unevenly with the silica glass powder, and in such a state, the B ₂ O ₃ component as a whole may Even if a predetermined amount is added, the object of the present invention cannot be achieved. For these reasons, the particle size of the fused silica glass powder is particularly preferably ultra-fine, the majority of which is 300 mesh or less. Further, it is necessary that the B ₂ O ₃ component contained during sintering be 1 to 25% by weight. If the content is less than the above range, a dense sintered body will not substantially be obtained, whereas if it exceeds the above range, the sintered body will easily soften and become unsuitable for high-temperature applications. Both are inappropriate. A particularly preferable sintered body can be obtained when the content of the B ₂ O ₃ component is 4 to 15% by weight.
Further, it is necessary that the content of SiO ₂ and B ₂ O ₃ in the sintered body exceeds 99% by weight. This content is
Sufficient densification (low porosity) when the content is 99% by weight or less
It is difficult to do so and often causes cracks in the sintered body, so it is unsuitable. And these contents are 99.5
It is particularly preferable that the amount is at least % by weight because a sufficiently dense sintered body can be obtained. Furthermore, in the present invention, it is necessary that the alkaline component contained in the sintered body does not exceed 0.1% by weight as R ₂ O. If it exceeds this range, the silica glass will devitrify, causing the above-mentioned problems, and is therefore unsuitable. For this reason, it is preferable that it is substantially not contained, desirably at 0.05% by weight or less. Further, in the method for producing a sintered body of the present invention, it is easy to make the thermal expansion coefficient of the sintered body 15×10 ^-7 /°C or less at 0 to 700°C. By setting such a coefficient of thermal expansion, it is possible to prevent the sintered body from cracking during firing or use. Further, the porosity is 7% or less, making it easy to obtain a sufficiently dense sintered body. In the method for producing a sintered body according to the present invention, a raw material having the above-mentioned structure is selected and sintered to produce a dense fused silica glass powder material having a low porosity and a low coefficient of thermal expansion. Solids are obtained. Next, a preferred method for manufacturing the sintered body according to the present invention will be specifically explained. First, a predetermined amount of fused silica glass powder of 100 mesh or less and a predetermined amount of B ₂ O ₃ component are mixed. In this case, as the B ₂ O ₃ component, it is also possible to use what is already contained in the quartz glass powder, but
It is usually preferable to mix it separately from the quartz glass powder. The B ₂ O ₃ component may be an oxide in advance, but it is usually appropriate to use boric acid (H ₃ BO ₃ ) or other boron compounds that become B ₂ O ₃ by firing. It is desirable to use the B ₂ O ₃ component as a raw material in the form of a fine powder, similar to the fused silica glass powder, and it is preferable to use it as an ultra-fine powder with a particle size of substantially less than 100 mesh, and in particular, the majority of it is less than 300 mesh. preferable. These fused silica glass powder and B ₂ O _3- component powder are
Although it is formed and sintered using a conventional press, rubber press, extrusion molding, etc., the production method of the present invention allows a dense sintered body to be obtained even when sintered at a relatively low temperature. That is, it is appropriate to adopt a sintering temperature of 800 to 1400°C. If the sintering temperature is lower than 800℃, the service limit temperature will also be lower than 800℃.
On the other hand, if the temperature is higher than 1400°C, the fused silica glass tends to devitrify (crystallize) as a result, and devitrification impairs sinterability, which is not preferable. Note that this sintering temperature is required to be high if the B ₂ O ₃ component is small, and is mainly determined by the blending amount of the B ₂ O ₃ component. Further, during firing, the desirable conditions are to make the firing atmosphere free of or extremely low in alkaline components to prevent devitrification of the fused silica glass and to facilitate obtaining the desired dense sintered body. As a specific example of such a method, the molded body to be fired is housed in a pod material having an alkali component content of 1% or less, and then sintered. Place the pod material and molded body on silica sand etc. with an alkaline content of 0.1% or less, and when sintering in a dusty tunnel kiln etc. that contains alkaline components, purify the air beforehand. It is preferable to adopt a method such as putting it in place. Thus, in the method for producing a sintered body of the present invention, a dense sintered body with low porosity can be obtained while maintaining low thermal expansion. Most of the conventional main sintered bodies have a porosity of 8% or more, and most of them have a porosity of 10% or more, and those obtained by special methods rarely have a porosity of about 5% or less. Although there are reports that it has been obtained, in reality it is far from being industrialized. The sintered body according to the present invention has a coefficient of thermal expansion of 15×10 ^-7 /
℃ or lower than that of silica glass (5×10 ^-7 /
℃), and also has sufficient properties such as pressure resistance and chemical resistance, and has great value as an industrial product. [Example] After mixing fused silica glass powder that passed through a 325-mesh sieve and boric acid (H ₃ BO ₃ ) as shown in Table 1, it was prepared using an Amsler type press at 2000 kg/cm ² and 10 mmφ×
It was molded to a size of 20 mm (height), housed in a pod material containing almost no alkali component, and fired at the firing temperature shown in Table 1. The results of measuring the physical properties of the obtained sintered body are shown in Table 2.

【table】

【table】

[Table] Results of measuring expansion coefficient and porosity

Claims (1)

[Claims] 1. 1 to 25% by weight of the B ₂ O ₃ component is added to fused silica glass powder of substantially 100 mesh or less and sintered to form a sintered body of SiO ₂ and B ₂ O ₃ . The content is more than 99%, the alkaline component is less than 0.1% as R ₂ O, and the coefficient of thermal expansion at 0 to 700°C is 15 × 10 ^-7 /°C or less, and the porosity is 7% or less. A method for producing a dense fused silica glass sintered body, characterized by: 2. The method for producing a dense fused _silica glass sintered body according to claim 1, wherein 4 to 15% by weight of the _B2O3 component is added and sintered.