JP4177908B2 - Manufacturing method of high purity powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high-purity powder obtained by heating at a high temperature.
[0002]
[Prior art]
Conventionally, various heat treatment methods have been proposed in the production of high-purity powders obtained by heat treatment at high temperatures, such as high-purity ceramic powders and high-purity rare earth powders. For example, the method of continuously processing with a rotary kiln and the method of heat-processing batchwise in heat-resistant containers, such as a crucible, are mentioned. In particular, in high-purity powders, contamination from the heating device may become a problem, and measures are taken by means such as using a heat-resistant and high-purity furnace core tube.
[0003]
[Problems to be solved by the invention]
In the above-described heat treatment, for example, in an application that promotes an oxidation reaction while ventilating an oxygen-containing gas, it is preferable to distribute the gas as uniformly as possible. However, when the powder to be heated is charged in a crucible or the like and heat-treated, the gas does not diffuse easily at the bottom of the crucible even if the gas is circulated only on the surface layer portion, and it takes a long time for firing. In some cases, the obtained heat-treated powder may have uneven quality. In order to avoid this, for example, a method of performing a heat treatment while providing a gas from the bottom of the crucible by providing a porous plate at the lower part of the crucible or inserting a diffuser tube can be considered. However, if heat treatment is performed while supplying gas from the bottom of the crucible, the gas can flow uniformly in the powder due to fluctuations in the flow rate of the supply gas, changes in the gas linear velocity during the heating process, changes in powder properties, etc. However, there is a problem that uneven flow occurs or a powder spills out from the crucible, resulting in poor quality and reduced productivity.
[0004]
In particular, synthetic silica glass powder, which is a high-purity powder, has many uses such as semiconductor jigs and crucibles for pulling single crystals and is used at high temperatures of 1000 ° C. or more, and is required to be resistant to thermal deformation. Silanol groups remain in the synthetic quartz glass powder obtained by this method, which causes a decrease in viscosity at high temperatures. For this reason, by carrying out heat treatment at a high temperature of 1100 to 1300 ° C. for a long time (usually several hours to several tens of hours) while circulating a gas having a low dew point, the residual silanol concentration is reduced and the high temperature viscosity is reduced. It is necessary to improve. Incidentally, the residual amount of silanol required in applications used at high temperatures (1000 ° C. or higher) is 100 ppm or less, preferably 50 ppm or less.
[0005]
However, when emphasizing productivity, when heat treatment is performed with a certain amount of powder, even if the gas on the powder surface is controlled with a low dew point, this replaces the water vapor generated from the inside of the powder by diffusion. It takes time to do so, and as a result, a very long heat treatment is required. In order to solve this problem, conventionally, for example, as a method for introducing a low dew point gas at the time of heat treatment, a method for shortening the firing time by introducing a low dew point gas into the powder layer (JP-A-4-83711). In addition, by controlling the amount of introduced gas within a certain range, non-uniform silanol concentration due to the location of the obtained powder in the crucible due to gas drift (short path) inside the powder. And a method (Japanese Patent Laid-Open No. 9-118513) has been devised that suppresses powder spillage due to bubbling and enables uniform silanol reduction in a shorter time. Under such conditions, low silanol synthetic silica glass powder can be produced in a large amount in a short time, but the control range of the gas amount described above is narrow, due to fluctuations in the gas source pressure, etc. It was difficult to completely suppress silanol concentration non-uniformity due to gas drift (short path) and powder spillage due to bubbling.
[0006]
[Means for Solving the Problems]
The present inventors have intensively studied in view of the above problems. As a result, the powder preparation layer height and the diameter of the heat-resistant container are set to a specific ratio, that is, the powder to be heated is heated to a temperature higher than the diameter of the heat-resistant container. They found that the problem could be solved and at the same time the productivity could be greatly improved.
[0007]
With the present invention, it has been found that stable operation can be continued without any loss due to drifting of aeration gas and spilling of powder, and the present invention has been achieved. That is, the present invention uses a heat-resistant container composed of a member having a bottom and a ring-shaped member on the bottom, and the charged layer height of the powder is 1.1-5. The present invention resides in a method for producing a high-purity powder characterized by including a step of performing heat treatment while supplying a gas to a powder to be heated in a batch type in a state of 0 times.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
First, examples of the high-purity powder that is an object of the present invention include high-purity ceramics, rare earth powder, phosphor powder, and synthetic silica glass powder.
Moreover, as the powder to be heated to be subjected to the heat treatment in the present invention, these high-purity powder precursors are typical. For example, precursors of high-purity ceramics, precursors of rare earth oxide powder, carbonates, nitrates, hydroxides of various metals, alumina, silica, silica-alumina, silica-zirconia, which are various heat-resistant glasses and ceramics, Examples thereof include a gel body obtained by a sol-gel reaction, which is a precursor of a composite oxide such as silica-titania.
[0009]
Among these, the present invention is extremely useful in producing synthetic silica glass powder by heating the silica gel powder to make it nonporous by batch-type firing.
In particular, in synthetic silica glass powder derived from silica gel powder obtained by the sol-gel method, residual silanol groups cause a decrease in viscosity at high temperatures as described above. Processing is required. However, efficient gas diffusion at this time while suppressing gas drift and powder spillage inside the powder depends on factors related to the silanol elimination reaction, the shape and physical properties of the treated powder. However, it is difficult to control with the prior art because it can be influenced depending on the situation. When heat treatment is performed according to the present invention, the above problems can be solved and efficient heat treatment can be performed, and thus industrial value is extremely high.
[0010]
In the present invention, a powder to be heated such as a precursor of these high-purity powders is charged in a heat-resistant container and heat-treated. The material and shape of the heat-resistant container are not particularly limited, but a material that does not cause contamination to the object to be heated by heating is desirable. A typical example of the heat-resistant container is a crucible.
What is necessary is just to select the temperature of a heating suitably with the prior art regarding manufacture of the target high purity powder. For example, in order to produce synthetic silica powder, the temperature is generally 1000 to 1300 ° C, preferably 1100 to 1300 ° C. Further, the steps other than heating in the production of the high-purity powder may be performed by appropriately selecting conventional techniques, and are not particularly limited.
[0011]
In the present invention, in the heat treatment, the charged layer height of the powder to be heated is set within a specific range. That is, the height exceeds the diameter of the heat-resistant container.
The diameter of the heat-resistant container here refers to the inner diameter of the heat-resistant container. The powder layer height is a vertical distance from the bottom surface in the heat-resistant container to the highest part of the powder surface layer part.
When the cross section of the heat-resistant container is not a circle, the longest distance connecting two points on the circumference of the horizontal section of the heat-resistant container is regarded as the diameter of the heat-resistant container.
[0012]
If the height of the powder layer is larger than the diameter, the length of each is not particularly limited, but preferably the height is 1.1 to 5.0 times, preferably 1.2 to 3.0 times the diameter. good.
If the powder layer height is less than the diameter, the operating range of the gas introduction amount becomes narrow, the effect of the present invention is not sufficiently obtained, and if the powder layer height is too high, the crucible itself when firing at a high temperature. Thermal deformation / durability becomes a problem, and ancillary facilities such as crucible support materials are required.
[0013]
Further, the size of the crucible to be used is preferably about 150 to 1200 mm, particularly preferably about 200 to 1000 mm in diameter in consideration of productivity, work efficiency, and the like.
As described above, in order to perform heating with the charged layer height of the powder higher than the diameter of the heat-resistant container according to the present invention, it is assumed that a heat-resistant container having a longer height than the diameter is used. The container does not necessarily have to be a single object. For example, the bottom of the powder charging layer height setting method (FIG. 1) by setting a donut-shaped ring on a low crucible A heat-resistant container can also be configured from a member having a ring-shaped member and a brick-like member riding on the member. In FIG. 1, 1 is a member having a bottom, and 2 is a ring-shaped member.
[0014]
By setting the shape of the heat-resistant container according to such an embodiment and specifying the charged layer height of the powder, gas drift, powder spillage, etc. due to fluctuations in the gas pressure introduced into the powder, etc. Therefore, it is possible to stably and uniformly produce a low silanol synthetic silica glass powder. Such an effect is presumably because the low dew point gas introduction tube can be inserted deeper into the powder layer, so that the powder pressure increases and as a result, the operating range of the introduced gas amount is expanded. Further, by increasing the crucible height, the baking ability per batch can be greatly improved.
[0015]
Hereinafter, the present invention will be described in detail by way of examples.
[0016]
【Example】
(Example)
Tetramethoxysilane was hydrolyzed and gelled, and this was pulverized, dried and classified to obtain silica gel powder having a particle size distribution of 100 to 500 μm and an average particle size of 230 μm. 110 kg of this powder was charged in a quartz glass crucible having an inner diameter of 550 mm and a height of 850 mm from the bottom to a height of 750 mm, and as shown in FIG. A blow tube was inserted and set in an electric furnace. FIG. 2 is a schematic view showing an embodiment of the heat treatment in the example. In FIG. 2, 3 is a crucible, 4 is a lid, 5 is silica gel powder, 6 is a gas blowing tube, and 7 is dry air.
[0017]
Through this gas blowing tube, while supplying dry air with a dew point of −45 ° C. at 1.1 liter / min, the temperature was raised to 1200 ° C. over 10 hours and kept at 1200 ° C. for 45 hours for heat treatment. Under the same conditions, heat treatment was carried out with a total of 100 crucibles, but when the powder state inside the crucible after heat treatment was confirmed, there was no evidence of gas drifting. In addition, for the powder obtained by each heat treatment, the silanol concentration at each location in the crucible indicated by a black circle in FIG. 3 was measured by infrared absorption, but both were within the range of 45 to 55 ppm, The variation was small.
(Comparative example)
The silica gel powder obtained by the same method as in Example 1 was charged into a quartz glass crucible having an inner diameter of 550 mm and a height of 600 mm up to a height of 500 mm from the bottom. Firing treatment was performed under the conditions. When heat treatment was performed with a total of 100 crucibles under these conditions, cracks and unevenness in the powder layer where gas drift was thought to have occurred were confirmed for the powders in all three crucibles. Regarding the powders in these three crucibles, when the silanol concentration at the position indicated by the black circle in FIG. 3 was measured, the variation was as large as 45 to 75 ppm.
[0018]
FIG. 3 is a diagram showing silanol measurement sites in Examples and Comparative Examples.
[0019]
【The invention's effect】
According to the present invention, heat treatment of high-purity powder can be performed efficiently.
[Brief description of the drawings]
FIG. 1 is a diagram showing a method for increasing a powder charge layer height. FIG. 2 is a schematic diagram showing an aspect of heat treatment in Examples. FIG. 3 is a diagram showing silanol measurement sites in Examples and Comparative Examples. Explanation】
3 Crucible 4 Lid 5 Silica gel powder

Claims (2)

Using a heat-resistant container composed of a member having a bottom and a ring-shaped member riding on the member, in a state where the charged layer height of the powder is 1.1 to 5.0 times the diameter of the heat-resistant container A method for producing a high-purity powder, comprising a step of performing a heat treatment while supplying gas to a powder to be heated in a batch type.   The method for producing a high-purity powder according to claim 1, wherein the heat-resistant container has a diameter of 200 to 1000 mm.

Images