JPS5948773B2 - Fused silica and its manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to fused silica and a method for producing the same.

Fused silica is a uniform glass made of high-purity SiO2, and has a coefficient of thermal expansion of 0.5 to 1. Because it has a small temperature of OX 10-7°C and excellent heat spalling resistance, it is widely used in the electronic industry and as a material for refractories.

However, when fused silica is used for a long time in the temperature range of 1100 to 1600°C, for example as a submerged nozzle for continuous casting or as a furnace material for a coke manufacturing furnace, part or all of the fused silica is transferred to cristobalite, and the original fused silica is It had the disadvantage of impairing its characteristic heat spalling resistance, and could not be used for a long period of time.

The present inventor conducted various studies to solve these drawbacks and found that Al2O3 and R20, which were conventionally thought to be substances that promote the transition of cristobalite in fused silica,
Silica stone or silica sand containing a specific amount of components such as Na20.
The present invention was achieved based on the knowledge that even when used at a high temperature of about 1500° C., cristobalite formation is extremely small, and the material has excellent heat spalling resistance at the same temperature.

That is, the first invention of the present invention has a weight ratio of A120
30.9-3%, R200,7-2.5% and Fe2
The total amount of unavoidable components O3, MgO, CaO is 0.1~
0.5%, the balance is SiO2, and the second invention is A72030.9-3% by weight, R
200,7-2.5% and Fe2038Mg02CaO
The total amount of unavoidable components is 0.1 to 0.5%, the balance is Si
The fused silica raw material powder, which is O2, is continuously supplied to the melting furnace, and the molar ratio of hydrogen and oxygen is 1.5 to 2.0:
This is a method for producing fused silica characterized by high temperature melting using an oxyhydrogen flame.

The present invention will be explained in more detail below.

Note that percentages in the specification are expressed on a weight basis.

The fused silica of the first invention of the present invention is A12030.9
~3.0%, R200, 7~2.5%, and Fe2O
3゜The total amount of unavoidable components of MgO and CaO is 0.1 to 0.
．． It is a uniform glassy substance containing 5%.

Here, R20 is the total amount of Na2O and Ni20, and the unavoidable components are impurities contained in raw material silica stone, silica sand, etc. Fe2 o3. This is the total amount of MgOtCaO.

Table 1 shows a comparison of the chemical components of the fused silica of the present invention and conventional products.

Among the chemical components of fused silica, those containing less than 0.9% Al2O3 and those containing less than 0.7% R20 are significantly converted to cristobalite by heating.

Furthermore, if Al2O3 exceeds 3%, cristobalite formation increases, and if R20 exceeds 2.5%, the softening point of the fused silica becomes low, which is not preferable.

Next, the manufacturing method of the second invention will be explained.

The raw material used in the present invention is silica stone and/or silica sand containing specific chemical components containing 5i0295% or more, but if Al2O3 and R2O3 are less than a specific amount range, substances containing Al2O3 and R20 are added to this. Added, Al2O3 0.9-3%.

R20 is 0.7-2.5% and Fe2032Mg02
A powder is used which is adjusted to contain an unavoidable component of CaO of 0.1 to 0.5%.

A specific example of a substance containing Al2O3 and R20 is feldspar.

The content of SiO2 such as silica stone and silica sand in the raw material composition is 95%.
The reason for the above limitation is that anything less than 95% is impurity F.
Since the content of e2O3, MgO, CaO, etc. is high, Al
This is because even if substances containing 2O3 and R20 are added, the raw material composition for use in the present invention cannot be obtained.

Further, Al2O3 contained in the raw material composition is less than 0.9%,
The reason why R20 is limited to less than 0.7% is that the obtained fused silica almost transforms into cristobalite at 1400 to 1500°C, which is undesirable, while if Al2O3 exceeds 3%, cristobalite increases. This is because when R20 exceeds 2.5%, the softening point of fused silica decreases.

Also, if the unavoidable components are less than 0.1%, high purity SiO2
Since only the raw materials are melted, it is not possible to add the necessary amounts of Al1203 and R20, which play a role in suppressing crystallization (cristobalite formation) when the fused silica product is heated.

Moreover, if it exceeds 0.5%, F e 203 which is an impurity
, MgO.

Unavoidable components such as CaO increase, and since these are different substances from SiO□, when fused silica is heated, they become crystallization nuclei and promote cristobalite formation, which is not preferable.

Therefore, it is necessary to select silica stone or silica sand, and also select and adjust the type and amount of feldspar to be added.

Since the raw material of the present invention is supplied to a melting furnace and heated and melted by an oxyhydrogen flame, the particle size thereof is preferably a powder of 1 mm or less.

Next, the above-mentioned raw materials are continuously fed into the furnace together with oxygen and hydrogen from the upper burner of the melting furnace, heated and melted by an oxyhydrogen flame, and a pool of molten material is formed in the melting furnace, which is taken out as an ingot from the bottom of the furnace. In this way, the product of the present invention can be obtained.

Note that hydrogen is preferably a gas containing only hydrogen, but is not limited to this, and may be a gas containing hydrogen as a main component, which is combusted with oxygen and then heated and melted.

The molar ratio of hydrogen and oxygen in oxyhydrogen flame is 1.5:1 to 2.0
: The range of 1 is preferable.

The reason for this is that if the molar ratio of hydrogen to oxygen is less than 1.5 to oxygen, there will be less hydrogen and it will not be possible to obtain a high temperature, e.g., 1900°C or higher. Because you can't get it.

To explain further, hydrogen and oxygen generally burn according to the following reaction formula.

2H2+02→2H20 If the molar ratio is H210□=2, it is the theoretical molar ratio, but
If H2102<1.5, it will be a strong oxidizing flame, and 1900
Temperatures above ℃ cannot be obtained.

Therefore, it is not possible to obtain a completely glass-like product, which tends to convert into cristobalite, and it is not possible to obtain a product with excellent heat resistance and spalling properties.

In the case of H210□〉2, it becomes too much of a reduction flame, so H2
As in the case of 102=2, the temperature required to produce a completely glass-like product cannot be obtained.

As shown in Table 4 of Example 2, the fused silica of the present invention does not change into cristobalite when heated.
It occurs from around 350°C and is only about 20% even at a high temperature of 1500°C.

This phenomenon can be obtained whether the atmosphere at the time of heating is air, oxidation, or reduction, but it has a characteristic that it is difficult to convert into cristobalite especially when heated under a reducing atmosphere.

On the other hand, conventional fused silica has not been widely used because most of it transforms to cristobalite in the temperature range of 1400 to 1500°C, resulting in a decrease in heat spalling resistance.

Since the fused silica of the present invention does not convert into cristobalite at a temperature of 1200° C. or higher, it can be used alone or in combination with conventional fused silica or other refractory materials for various purposes.

Specific uses include immersion nozzles for continuous casting, furnace materials for coke manufacturing furnaces, stopper heads, coating materials for surface plates, and furnaces for the glass industry.

Furthermore, various refractory materials such as C and SiC. ZrO2, Z
r02, S102, A12o32MgO.

3A70 ・2S t 02 , S i s N1.
Addition to BN etc. 3 It is expected to be used as a material.

. The present invention will be explained below using examples.

Example 1, Comparative Example 1 Raw material C with a particle size of 1 mm or less, which is a mixture of 89 parts by weight of white silica A and 11 parts by weight of feldspar B, is continuously charged into a melting furnace, and hydrogen and oxygen with a purity of 92.24% by volume are added. and N2:0
□-1,8:1 ratio blowing temperature 1950-2000
Melted at °C.

The obtained fused silica D of the present invention was completely amorphous and so-called glass-like.

The ingredients of the raw materials and fused silica are shown in Table 1.

For comparison, a conventional product of fused silica F was obtained in the same manner as in Example 1 except that white silica E was used.

The analytical values of these chemical components are shown in Table 1.

Next, the fused silica D and F were mixed with a particle size of 297 to 149.
1200-15 in air and CO gas.
After heat treatment at 00° C. for 3 hours, the amount of cristobalite transition (total) was measured.

The results are shown in Table 2.

The measurement of cristobalite is carried out by measuring the peak of cristobalite (2θ=21.9°) using X-ray diffraction (
Ceramic Data Book 1973. "Method for measuring devitrification of quartz glass" described on page 366).

Example 2, Comparative Example 2 Fused silica H of the present invention was obtained in the same manner as in Example 1 except that silica sand G having a particle size of 200 μm or less was used.

This was all glassy. A comparison product of fused silica J was obtained in the same manner except that white silica stone (2) was used for comparison.

The analytical values of these chemical components are shown in Table 3.

Next, this fused silica was dissolved in air and CO gas at 120°C.
After heat treatment at a temperature of 0 to 1500°C for 3 hours, the amount of cristobalite transition was mlfffl.

The measurement method is the same as in Example 1.

The results are shown in Table 4.

Comparative Examples 3 to 5 The proportions of white silica A and feldspar B used in Example 1 were 80 parts by weight and 20 parts by weight in Comparative Example 3, and 7 parts by weight in Comparative Example 4, respectively.
5 parts by weight and 25 parts by weight, and in Comparative Example 5, 70 parts by weight and 30 parts by weight.
The same procedure as in Example 1 was carried out except that the parts by weight were changed.

Next, the obtained fused silica was dissolved in air and CO gas for 12
A heat treatment was performed at a temperature of 00 to 1500°C for 3 hours, and the amount of cristobalite transition was measured.

Table 5 shows the chemical analysis values of these raw materials, and Table 6 shows the amount of cristobalite transferred by heating tests.

Compared to comparative products, the fused silica of the present invention has a lower SiO2 content in its chemical components, and A A' 203
.

It is characterized by increasing the amount of chemical component 20 in Na2O, which means that the amount of transformation to cristobalite due to heating is small, especially at high temperatures of 1400 to 1600°C and in a reducing atmosphere such as CO gas. The effect is remarkable.

From this, it is possible to expect new uses for fused silica, and it is industrially useful.

Claims (1)

[Claims] 1 Weight ratio: A72030.9-3%, R200.7
2.5% and 0.1 to 0.5% of the total amount of unavoidable components Fe20a, MgO, and CaO. 2 Weight ratio A12030.9~3%, R200.7~
Fused silica raw material powder containing 2.5% and 0.1 to 0.5% of the unavoidable components of Fe2O3, MgO, and CaO in total, with the remainder being Si02, is continuously supplied to the melting furnace, and hydrogen and oxygen are A method for producing fused silica, characterized by high temperature melting using an oxyhydrogen flame having a molar ratio of 1.5:1 to 2.021.