JPH09124361A - Production of cristobalite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain cristobalite capable of carrying out phase transition of silica at a relatively low temperature without using a phase transition temperature-lowering agent by baking powdery and/or bulky diatomaceous earth at a high temperature. SOLUTION: Diatomaceous earth containing >=85%, especially >=90% silica component is preferably used as diatomaceous earth. The particle size can selected according to uses of cristobalite. When the resultant formed article is used as a template, average particle diameter of the particle is 5-50μm and when the resultant formed article is used as a filter, average particle diameter of the particle is 2-30μm. A method for forming a kneaded material of diatomaceous earth with water is selected by physical properties required for the formed article. An amount of water added is controlled so that the kneaded material has 5-30cP viscosity in casting and 20-50cP viscosity in extrusion molding. The pressure is controlled by physical properties of the objective formed article in compression molding. The pressure is preferably usually 15-30kg/cm<2> . The baking temperature is preferably 80-1100 deg.C, especially preferably 900-1050 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cristobalite and a method for producing a cristobalite molded body.

[0002]

2. Description of the Related Art Cristobalite has been widely used as an excellent raw material for castings, decorations and the like for dental and industrial purposes by the lost wax method, bricks and other refractory materials. This cristobalite is produced by using silica stone or silica sand as a raw material and changing its silica SiO ₂ phase to a cristobalite phase. However, in order to cause this phase transition, the raw material containing silica must be fired at a high temperature of 1470 ° C. or higher, and even if lithium carbonate is added in order to lower the phase transition temperature, it takes 1
A high temperature of 210 ° C is required. Therefore, the cristobalite manufacturing equipment requires furnace materials and equipment that can withstand high temperature firing, is expensive, and requires a large amount of thermal energy during production, resulting in high operating costs. Further, when lithium carbonate is used as the phase transition temperature lowering agent, the calcined product becomes alkaline, so that a large amount of washing water must be used to remove the alkaline component or a neutralizing agent must be added, resulting in a decrease in purity. Such a harmful effect occurs. Further, in order to produce a molded product of cristobalite, it is essential to add calcined gypsum, ammonium phosphate, polyvinyl alcohol, starch, etc. as a solidified binder, and the binder selected according to the application is added to cristobalite and kneaded with water. After doing
It had to be molded or compression molded in a mold, then cured and dried. Therefore, when the cristobalite molded body is used as a mold material, a refractory material, or the like, its performance is limited by the temperature at which the binder used can withstand. For example, when calcined gypsum was used as a binder, it could be used only at a temperature lower than 800 to 1000 ° C. at which the cured product decomposes.

[0003]

DISCLOSURE OF THE INVENTION The present invention, in order to solve the problems associated with the conventional production of cristobalite, does not use a phase transition temperature lowering agent, and a method for producing cristobalite in which silica undergoes a phase transition at a relatively low temperature, And a method for producing a cristobalite molded body that does not use a binder.

[0004]

Means for Solving the Problems As a result of the inventors of the present invention conducting research to solve the above problems, the ambient temperature is 800 ° C.
It was found that the silica contained in the diatomaceous earth is transformed into the cristobalite phase by firing as described above. Therefore, the present invention provides a method for producing cristobalite, which comprises firing diatomaceous earth in the form of powder and / or lumps in a high temperature range, for example, at an ambient temperature of 800 to 1100 ° C. The present invention also provides a method for producing a cristobalite compact, which comprises kneading powdery diatomaceous earth and water, shaping the mixture, and firing the mixture at an ambient temperature in a high temperature range.
Next, the present invention will be described in detail. The diatomaceous earth used in the present invention contains 85% or more of silica component SiO ₂ , and particularly preferably 90% or more. Further, the particle size of the diatomaceous earth can be variously selected according to the use of cristobalite. When the molded product of cristobalite is used as a mold, the average particle size is preferably 5 to 50 μm in order to impart appropriate smoothness and air permeability to the surface of the molded product,
When used as a filter, the thickness is preferably 2 to 30 μm in order to maintain the adsorptivity.

In the production of a cristobalite molded body, the kneaded material of diatomaceous earth and water may be molded by any of casting molding, extrusion molding and compression molding, and can be appropriately selected depending on the physical properties required for the molded body. The amount of water added to the diatomaceous earth is adjusted to give the kneaded product an appropriate viscosity according to each molding method. When cast, the viscosity is 5
The viscosity is preferably 30 cp for extrusion molding and 20 to 50 cp for extrusion molding, and 30 to 100 cp for compression molding. In compression molding, the pressure is adjusted according to the physical properties (especially strength) of the target molded product, but usually 15 to 30 kg / c
m ² is appropriate. If it is less than 15 kg / cm ^2, it is difficult to obtain sufficient strength for a mold, and if it is 30 kg / cm ² or more, it is difficult to obtain sufficient air permeability. In particular, the cristobalite molded product produced by compression molding at ²⁰ to 25 kg / cm ² has a tubular or pleated crystal having a large specific surface area, and has a large specific surface area. Most suitable as a highly filtering material. A small amount of a binder such as ethylene vinyl alcohol, polyvinyl alcohol, methyl cellulose, starch or the like may be added in order to increase the initial tackiness of the kneaded product of diatomaceous earth and water and to facilitate the molding. In this case, it is preferable to select the type and amount of the binder so that the binder does not remain in the molded body after firing. Further, the above-mentioned molded body can be used as a covering material for steel frames, and since it retains its shape up to a high temperature of 1710 ° C. in the event of a fire, it is optimal as a fireproof covering material. In addition, the molded body can be used as a fire-resistant building material with a plate shape or a curved surface shape. The firing temperature of the present invention is preferably 800 to 1100 ° C, particularly 900 to 1050 ° C. This is because if the temperature is lower than 800 ° C., the silica in the diatomaceous earth may not be completely transformed into cristobalite. In order to obtain high hardness cristobalite, it is preferable to calcine at 900 ° C. or higher.

[0006]

INDUSTRIAL APPLICABILITY In the present invention, by using diatomaceous earth as a raw material, cristobalite can be produced at a low firing temperature without using a phase transition temperature lowering agent, so that a firing furnace composed of a furnace material having a low heat resistant temperature can be used. Therefore, the facility cost can be reduced, and the cost for thermal energy can be reduced. Further, since it is not necessary to use a phase transition temperature lowering agent, cost, management and complicated post-treatment of the lowering agent are unnecessary. Furthermore, by the production method of the present invention, it is possible to produce a molded body of cristobalite at a lower cost than conventional ones,
Moreover, compared with the molded products produced by the conventional method, the obtained molded products are comparable with respect to fire resistance, strength and other physical properties. Moreover, since the molded product produced by the method of the present invention does not contain a binder, its performance is not limited by the heat resistance of the binder. Therefore, the molded product produced by the method of the present invention is not limited by the performance of the binder, and is widely used as various mold materials, plate-shaped or curved fire-resistant building materials, fire-resistant coating materials such as steel frames, and other fire-resistant materials. Can be used.
Hereinafter, the present invention will be described in detail based on examples.

[0007]

【Example】

[Example 1] SiO ₂ content of 85% or more, average particle size 10
A diatomaceous earth (FIG. 1, the structure of which was shown in the X-ray diffraction pattern) of μm was put in an electric furnace, fired at 1000 ° C. for 1 hour, and then slowly cooled to obtain a fired body. When a part of this fired body was analyzed by X-ray diffraction, it was confirmed that it was completely transformed into cristobalite as shown in FIG. That is, as a result of qualitative analysis by X-ray diffraction, as shown in FIG. 1, clear crystallinity cannot be confirmed in the raw material diatomaceous earth, but in FIG. 2, only diffraction peaks showing the presence of cristobalite crystals are found. Obtained with high strength. In addition, since no peaks of silica and tridymite as an intermediate product are confirmed in FIG. 2, it can be seen that the crystals are completely transformed into cristobalite.

[Example 2] SiO ₂ content of 85% or more,
170 parts of water was added to 100 parts of diatomaceous earth having an average particle size of 10 μm and kneaded to prepare a paste having a viscosity of 10 cp, the paste was put into a mold, and a pressure of 25 kg / cm ² was applied to remove excess water. A test member having a diameter of 50 mm and a height of 10 mm was molded. Then, this test member in an electric furnace,
After firing at 1000 ° C. for 1 hour, the body was gradually cooled to obtain a fired body. When a part of the fired body was analyzed by X-ray diffraction, it was confirmed that it was completely transformed into cristobalite as shown in FIG. Further, as shown in the electron micrograph (FIG. 4) of the fractured surface of the fired body, a tubular or pleated crystal having a large specific surface area, which is the remains of diatom, was observed.
Therefore, it can be seen that a breathable mold material was obtained by the example. In addition, when used as a filter, it showed a high adsorption capacity. The firing temperature is 800 ° C.
When it was turned on, the transformation to cristobalite was also confirmed.
The surface hardness was slightly inferior to that of the fired body at 1000 ° C.

[Brief description of the drawings]

1 shows the X-ray diffraction of the diatomaceous earth used in Example 1. FIG.

2 shows X-ray diffraction of the fired body produced in Example 1. FIG.

FIG. 3 shows X-ray diffraction of the fired body produced in Example 2.

FIG. 4 shows an electron micrograph of a fractured surface of the fired body produced in Example 2.

Claims (6)

[Claims] 1. A method for producing cristobalite, which comprises firing powdery and / or lumpy diatomaceous earth at a high ambient temperature. 2. The manufacturing method according to claim 1, wherein the ambient temperature is 800 to 1100 ° C. 3. Kneading powdery diatomaceous earth and water and molding the mixture,
A method for producing a cristobalite molded body, which comprises firing at a high ambient temperature. 4. The manufacturing method according to claim 3, wherein the ambient temperature is 800 to 1100 ° C. 5. The method for producing a cristobalite molded article according to claim 3, wherein the powdery diatomaceous earth and water are kneaded and then compression molded. 6. The method for producing a cristobalite molded article according to claim 5, wherein the pressure during compression molding is 15 to 30 kg / cm ² .