JPS60200847A - Manufacture of alpha type hemihydrate gypsum - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an improved method for producing α-type hemihydrate, more specifically, an economically advantageous method for producing α-type hemihydrate by contacting sanmizu ceracola with steam in an open container. It concerns a method of converting it into gypsum.

Although the crystal structure is extremely similar to hemihydrate Ceracola,
There are α and β types, which have different water binding states and crystal external shapes, and have significantly different water usage characteristics. Table 1 shows an example of the difference in hydration properties between α-type hemihydrate gypsum and β-type hemihydrate gypsum.

Table 1 As can be seen from this table, α-type semi-hydrated gypsum is used with a smaller amount of water than β-type semi-hydrated gypsum, has a shorter setting time, and the resulting aggregates are extremely strong. It has the following characteristics. Therefore, while the β-type semi-hydrated polyester is used for Ceracola boards, plasters for painting, ceramic molds, etc., the α-type polyester is mainly used for precision molds for dentistry and mold bonding materials for casting. has been done.

Conventionally, this α-type semi-hydrated slag is produced by heating a block of dihydrated slough with a diameter of 2 to 3α at a temperature of 120°C in an autoclave.
A pressurized steam method in which the treatment is carried out for 5 to 8 hours at a temperature of ~140°C and a water vapor pressure of 2 to 4 atm. In an autoclave, powdered Ceracola trihydrate is treated in an aqueous solution at a temperature of 120 to 140°C and a pressure of 2 to 4 atm. Pressurized aqueous solution method, treated for 1 to 4 hours;
It is produced by a method such as a normal pressure aqueous solution method in which powdered Ceracola trihydrate is treated under normal pressure in an aqueous solution of an inorganic salt such as a sulfate, hydrochloride, or ammonium salt at a temperature close to the boiling point of the aqueous solution.

However, the pressurized steam method and the pressurized aqueous solution method require a pressure-resistant container, which is disadvantageous as an industrial method, and the normal-pressure aqueous method does not require a pressure-resistant container, but uses inorganic salts. Therefore, it is disadvantageous in terms of cost, and it also has the disadvantage of causing wastewater problems.
These methods were not always satisfactory.

By the way, regarding the production mechanism of α-type hand water gypsum in the pressurized steam method and the pressurized aqueous solution method, conventionally, Sansui Ceracola first dissolves in the presence of liquid water or saturated steam to exhibit a supersaturated state, and then becomes stable at high temperatures. The so-called elution precipitation mechanism, in which α-type hand-washing gypsum is precipitated, has become a well-established theory. Similarly to the pressurized steam method and the pressurized aqueous solution method, the normal pressure aqueous solution method, in which treatment is carried out in an aqueous inorganic salt solution, is based on the dissolution precipitation mechanism in which trihydrate ceracola is first dissolved and then α-type hemihydrate gypsum is precipitated. However, since the precipitation temperature, that is, the transition temperature, of α-type hemihydrate gypsum decreases to below 100°C in the presence of inorganic salts, even at normal pressure, if α-type hemihydrate gypsum is above its transition temperature, It is said that it can exist stably in an aqueous inorganic salt solution.

In this way, the production of α-type hemihydrous gypsum is said to be based on the dissolution precipitation mechanism in all six conventional methods, and therefore,
It was thought that the presence of liquid water or saturated steam was required for the production of α-type hemihydrous gypsum.

As a result of extensive research into an economically advantageous method for producing α-type hemihydric gypsum, the present inventors surprisingly discovered that it was possible to process trihydric gypsum in the presence of water vapor in an open container. The inventors have found that α-type hemihydrate can be easily obtained, and have completed the present invention based on this knowledge.

That is, the present invention provides a method for producing α-type hemihydrate gypsum, which is characterized by treating trihydrate ceracola in an open container at a temperature of 110 to 150°C in the presence of steam with a partial pressure of 600 to 7601111H9. This is what we provide.

In the method of the present invention, the trihydric ceracola used as a raw material is represented by the chemical formula 〇 a S Q4°2H20, which includes natural ceracola and chemical ceracola obtained by synthesis or by-product. Natural ceracola includes transparent gypsum, which is colorless and transparent plate-like crystals, glaucoma ceracola, which is pure white fine crystals, fibrous ceracola, which has a silky luster, and its leafy, granular, and raw forms. On the other hand, chemical ceracola includes, for example, phosphoric acid gypsum, titanium ceracola, fluoric acid gypsum, by-product ceracola such as ceracola obtained by desulfurization of heavy oil or flue gas desulfurization, and synthetic ceracola.

In the method of the present invention, any of these three-hydroceracola can be used, and it may be used in either lump or powder form, dry state, or wet state.

A feature of the present invention is that the above-mentioned Sansui Ceracola is made into a lump or powdered form and placed in an open container, and the secondary Ceracola is heated to 11% using water vapor at a partial pressure of 300 to 760 mrttHjj.
The point is that the process is carried out in a temperature range of 0 to 150°C. If the treatment temperature is less than 110°C, α-type semi-hydrated gypsum is difficult to form and the treatment takes a long time, making it impractical;
If it exceeds 50%, the resulting hand water ceracola will contain a large amount of β type, which is not preferable. When the partial pressure of water vapor is less than 10011 M Hg, α-type hemihydrate gypsum is difficult to produce, and β-type hemihydrate gypsum is produced in large amounts. Note that since the treatment is carried out in an open container, the partial pressure of water vapor does not exceed 760 mmHg. The treatment time depends on the partial pressure of water vapor and the treatment temperature, but is generally about 1 to 240 hours.

In addition, regarding the treatment method, for example, a lump or powdered Sanhydric Ceracola is placed in a processing container communicating with a steam generator, and the heating temperature of the steam generator is adjusted so that the partial pressure of the steam becomes the desired value. There is a method in which the treatment vessel is heated to a desired treatment temperature, or a tower-type treatment vessel is filled with bulk or powdered industrial water Ceracola, and the partial pressure of water vapor is adjusted to a desired temperature. By generating water vapor with a water vapor generator to reach the desired value, transporting the water vapor using air or nitrogen gas, heating this vapor to the processing temperature, and introducing it into the processing container. A multi-processing method can be used.

The α-type hemihydrate obtained in this way has a hexagonal crystal system, and the aggregate obtained by hydration has extremely high strength and hardness, so it can be used for precision molding for dentistry and for casting. Used for casting joint materials, etc.

According to the method of the present invention, there is no need to use a pressure-resistant container or an aqueous inorganic salt solution unlike the conventional method for producing α-type hemihydrate, and therefore it is economically advantageous and does not cause waste water problems. is of high practical value.

Next, the present invention will be explained in more detail with reference to Examples.

The content of α type in the obtained hemihydrate Ceracola was determined according to the following method.

In other words, the α-type hemihydrate crystal (hexagonal system) is 190°C.
Nearby, β-type chezumi settsukou (hexagonal crystal system) is 650℃
Since there is a transition point to the orthorhombic system in the vicinity, the obtained hemihydrate Ceracola was heated at a temperature of 200°C for 24 hours and the transition rate to the orthorhombic system was measured by X-ray diffraction. , from this value α
The content of the mold half-water settsukou was calculated.

Example 1 As an apparatus, a ball cooling tube (length 5ocm) was attached to the top of a 10cc flask with branches, and an adapter and an eggplant-shaped flask were attached to the tip of the flask's branches, and the opening was inserted into the flask. The one with only the upper cooling pipe was used.

About 50 cc of water and a boiling stone were put into a flask with a branch, and a 5 cc container containing about 2 cc of water and about 1 og of trihydric ceracola powder was put into an eggplant-shaped flask at the end of the branch. Only the cooling part of the ball cooling tube of this device is exposed to the outside, and all other parts are placed in a dryer (40 x 40 x 40 CIn, 100 V, 1
01'), and the temperature of the dryer was adjusted so that the inside of the eggplant-shaped flask reached a predetermined temperature. The temperature inside the eggplant-shaped flask was measured using a thermocouple sealed in advance.

In addition, the temperature inside the dryer is about 10 to 15°C higher than the temperature inside the eggplant-shaped flask, so the water in the side flask is always in a boiling state, so the water vapor pressure in the system changes with the heating temperature. Regardless, it always maintains 760 mm1-J.

The content ratios of α-type and β-type hemihydrate gypsum in the hemihydrate ceracola thus obtained are calculated, and the results are shown in Table 2.

Example 2 An experiment was conducted using the same equipment as used in Example 1, and placing the flask part with plate and the eggplant-shaped flask part in separate dryers. went.

The dryer in the eggplant-shaped flask section is adjusted so that the temperature and humidity inside the eggplant-shaped flask are 110 to 130°C, and -
The dryer in the flask section with plate has a water vapor partial pressure of 500 mm.
Adjusted to be HIF.

The total content ratio of α-type and β-type hemihydrate in the hemihydrate ceracola thus obtained was determined, and the results are shown in Table 3.

Table 3 Note 2) Temperature is the temperature inside the eggplant-shaped flask.

Claims (1)

[Claims] 1 In an open container, bring Sansui Ceracola to a partial pressure of 300
Temperature 110 in the presence of ~760 flmHll water vapor
1. A method for producing α-type hemihydrate snail, characterized by processing at ~150°C.