JPH01290554A - Sintered body of calcia obtained by casting and its production - Google Patents

Abstract

PURPOSE:To eliminate residual impurities such as sintering aid, etc., to improve high temp. characteristics of calcia, and to obtain a sintered body of calcia easily and inexpensively by adjusting the particle size of carbonate or organic acid salt of Ca as a base material to an appropriate particle size range, casting the base material and then calcining the casted product. CONSTITUTION:After adjusting the particle size of carbonate or org. acid salt of Ca, as base material, to an appropriate particle size range, the base material is molded to a crucible shape, etc. by a casting means, and the molded product is sintered under specified calcination conditions. The porosity of the sintered body is pref. regulated to <=30%. The sintered body of calcia is formed by prepg. a slurry by mixing a carbonate or an org. acid salt of Ca with an appropriately selected dispersant and binder, then forming the slurry to crucible shape, etc., by casting, and sintering the molded product under specified calcination conditions (pref. >=1,300 deg.C), thereafter.

Description

DETAILED DESCRIPTION OF THE INVENTION Production The present invention relates to various sintered bodies such as calcia crucibles, sprues, nozzles, and boards for refining high-purity metals and alloys such as titanium, and methods for producing the same.

Total bending and alloys such as Ti have a large tensile strength, are superior to steel or aluminum alloys in terms of specific strength, and are stable against chemicals. Despite this, it is difficult to melt due to its high activity and high melting point, and when it is made into molten metal, it has the property of causing contamination depending on the refractory furnace material.

In order to deal with the above, for example, Japanese Patent Publication No. 59-40210 and Japanese Patent Application Laid-Open No. 59-673.32 disclose a means of using a calcia container as a container for active total flexural dissolution, and In JP-A-60-186475 and JP-A-60-186547, CaCl2 is added to calcia powder having a high melting point, and
A method of obtaining a crucible by hot pressing at 1500-1800 0 C is disclosed. Furthermore, JP-A No. 62-158159 discloses that high-purity calcia is used as a base material, 0.1 to 5% of CaF2 is added to the base material, and molded.
A method of firing at a temperature of 900°C or higher, and a method in which Ca is added to the base material.
A method has been proposed in which a crucible is obtained by containing 0.01 to less than 1% by weight of Cl2 and carrying out similar molding and firing.

Problems to be Solved by the Invention However, in the case of such a conventional manufacturing method of a crucible for dissolving active metals, molding and firing treatments are performed after adding additives such as CaCl2 and CaF2, so that the completed crucible is There was a problem in that the above-mentioned additives remained in the product crucible, and these additives could not be completely removed, resulting in deterioration of the original characteristics of the calcia crucible.

In other words, these additives have the effect of reducing the strength of the crucible, and in the case of halogens in particular, even if there is only a small amount remaining, they tend to thermally dissociate at high temperatures to generate halogen compounds, and impurities can be produced in the melted crucible. It has the disadvantage that it can be mixed in.

Furthermore, calcined Cab or fused CaO is used as a base material, but not only does this require a heat source, but furthermore, calcia is chemically unstable.

During production, molding is performed in a state that prevents contact with moisture.
The disadvantage is that expensive molding equipment such as injection molding, CIP, HP, HfP, etc. must be used.

Furthermore, in order to improve moldability and waterproofness, various polymeric materials such as polystyrene must be used.
These binders have the disadvantage of complicating the manufacturing process, such as having to be degreased for a long time before the main firing. Furthermore, 820. CaO used as base material by CO2
There is also a problem in that it changes to CaCO3.

Therefore, the present invention solves various problems such as residual sintering aids that conventional calcia sintered bodies and methods for producing the same have, improves the high-temperature properties of calcia, and makes manufacturing easier. The object of the present invention is to provide an easy and low-cost calcia sintered body and a method for manufacturing the same.

Means for Solving the Problems In order to achieve the above object, the present invention uses calcium carbonate and organic acid salt as a base material, adjusts the particle size to an appropriate range, and then molds the base material into a crucible shape by casting means. etc.,
The present invention provides a calcia sintered body sintered under predetermined firing conditions and a method for producing the same, further comprising making sure that the porosity of the crucible, etc. is within a range of 30% or less, and that the sintered body is mixed into the base material. The method is characterized in that a slurry is used in which salts such as polycarboxylic acid and polyacrylic acid to be prepared are appropriately combined with a polymeric dispersant such as polyvinyl alcohol and a binder, and mixed with water. Furthermore, the present invention provides a method for producing a calcia sintered body, which involves casting into a crucible shape using a water-absorbing mold material such as gypsum, and then firing it at a temperature of 1300° C. or higher.

According to the present invention having the above configuration, a calcia sintered body such as a calcia crucible can be obtained by using chemically stable calcium carbonates and organic acid salts as the base material and applying casting and firing means. In addition, since the purity and particle size of the calcium carbonate and organic acid salt powders that serve as the base material can be adjusted, the resulting calcia sintered bodies such as calcia crucibles do not contain impurities such as sintering aids. Since no residue remains and the porosity can be adjusted, melting treatment at high temperatures is possible, and stability against highly active metals is also improved.

In addition, by adopting a cast molding method that uses water-absorbing mold materials such as plaster, it can be applied to high-mix, low-volume production and products with complex shapes. Because it does not require complicated operations,
This simplifies the manufacturing process and improves work efficiency.

Various embodiments of the calcia sintered body such as a calcia crucible and its manufacturing method according to the present invention will be described below.

[Example 1] Light calcium carbonate was used as a base powder, and after adding polycarboxylic acid ammonium salt as a solid content of 0.6% of the base powder as a dispersant, the proportion of the base powder was 40%. Add water so that The thus prepared slurry is pulverized and mixed using a ball mill to prepare a slurry having an average particle size of 0.9 μm.

[Example 2] Synthetic calcium carbonate is used as a base material and polycarboxylic acid ammonium salt is used as a dispersant in a solid content of 0.00% of the base powder.
After adding 5%, water is added so that the proportion of the base powder becomes 60%. The thus prepared slurry is pulverized and mixed using a ball mill to prepare a slurry having an average particle size of 2.7 μm.

[Example 3] Heavy calcium carbonate: Light calcium carbonate was mixed in a ratio of 6=4 as a base material. 1. After adding polycarboxylic acid ammonium salt as a dispersant in a solid content of 0.2% of the base material powder, Water is added so that the proportion of the base powder becomes 65%. The thus prepared mixture is mixed using a ball mill for a predetermined period of time, and during the mixing, polymeric fine particle powder or the like is added to form a slurry.

After casting the slurry obtained in Examples 1 and 2.3 above using a plaster mold, the obtained molded body was fired in an electric furnace at a predetermined temperature and time condition. The bending strength, bulk density, and hydration rate of the sintered body were measured.

The firing conditions in each of the above examples were as follows: first heating from room temperature to 850°C at a heating rate of 800°C per hour, then heating to 1300°C at a heating rate of 50°C per hour.
In this example, the temperature is 1400°C, 1500°C,
Heating was performed under three conditions at 1650°C, and the mixture was heated in that state for 1 hour. Table 1 shows the measurement results of the bending strength, bulk density, porosity, etc. of each molded body and sintered body.

*Hydration rate: Hydration rate after being held in an atmosphere of 30°C and 100% R8 for 7 days The dispersant and water added to the base powder are all volatilized during firing, so the resulting sintered The impurities contained in the body are determined only by the constituent components of the raw material base powder. Therefore, by selecting the base material powder, the contamination of other elements can be minimized.

Further, the porosity of the sintered body can be adjusted as appropriate by adjusting the particle size of the base powder, the amount of the polymer fine particle powder added, firing conditions, etc. In the case of the present invention, the porosity is set within a range of 30% or less.

Note that an organic acid salt of calcium can be used instead of heavy calcium carbonate, light calcium carbonate, synthetic calcium carbonate, etc. used as a base material, and polyacrylic acid can be used as a dispersant instead of polycarboxylic acid ammonium salt. It is also possible to use polymeric dispersants such as salts.

As explained in detail below, according to the cast-molded calcia sintered body and the method for producing the same according to the present invention, calcium carbonate and organic acid salt are used as a base material, and the base material is cast by casting means. The present invention provides a sintered body formed into the shape of a crucible or the like and sintered by a predetermined firing means, and a method for producing the same, wherein the porosity of the crucible is within a range of 30% or less. , appropriately combining salts such as polycarboxylic acid and polyacrylic acid to be mixed and adjusted in the base material, and a polymeric dispersant such as polyvinyl acetate and a binder,
It is characterized by using a slurry mixed with water, and after casting into a crucible shape using a water-absorbing mold material such as gypsum, it is fired at a temperature of 1300°C or higher. This brings about the effects described below. In other words, since chemically stable calcium carbonates and organic acid salts are used as the base material, there is no need to use expensive molding equipment, and casting and firing methods can be applied, reducing manufacturing costs. can do.

In addition, since the calcium carbonate and organic acid salt powders that serve as the base material can be adjusted to high purity, impurities such as sintering aids may remain in the resulting sintered bodies such as calcia crucibles. Furthermore, since the porosity can be adjusted, high-purity metals and alloys such as titanium can be melted and refined at high temperatures, and stability with highly active metals is also improved.

In addition, by using water-absorbing mold materials such as gypsum during casting molding, it is possible to produce a wide variety of products in small quantities, and it can also be applied to products with complex shapes, and the setup costs are low. There is an advantage that Further, since complicated operations such as degreasing of a dispersant and a binder are not required during production, various effects such as simplifying the production process and improving work efficiency are exhibited.

Patent developer Kochi type Toyo Denka Kogyo Co., Ltd.

Claims (5)

[Claims] (1) Calcium carbonate and organic acid salts are used as a base material, and after adjusting the particle size to an appropriate range, the base material is molded into a crucible shape using a casting method, and sintered under predetermined firing conditions. A calcia sintered body produced by cast molding. (2) The cast calcia sintered body according to claim 1, which has a porosity of 30% or less. (3) Based on calcium carbonate and organic acid salt,
The method is characterized in that the base material is mixed and adjusted with appropriately selected dispersants and binders to form a slurry, the slurry is cast and formed into a crucible shape, etc., and then sintered under predetermined firing conditions. A method for producing a calcia sintered body by casting. (4) Calcia baking by cast molding according to claim 3, using a slurry prepared by properly combining salts such as polycarboxylic acid and polyacrylic acid with a polymeric dispersant and binder such as polyvinyl alcohol and mixing with water. Method for producing solids. (5) The cast-formed calcia sintered body according to claim 3, wherein the calcia sintered body is cast into a crucible shape using a water-absorbing mold material such as gypsum, and then subjected to firing treatment at a temperature of 1300°C or higher. manufacturing method.