JPH02160699A - Purification of magnesia whisker - Google Patents

Abstract

PURPOSE:To facilitate the production of MgO whiskers of high purity which are free from MgO particles and gives whisker composites of high strength by treating MgO whiskers containing MgO particles with hydrochloric acid. CONSTITUTION:A magnesium salt and a halide is allowed to react under heating and the formed salt melt is calcined to prepare MgO whiskers containing a small amount of MgO particles (shots) as a by product. Then, the whiskers are treated with dilute hydrochloric acid to dissolve shots. The concentration of the dilute hydrochloric acid is suitably in the range from 0.5 to 2N. Then, the MgO whiskers are separated by filtration, washed with water and dried to give MgO whiskers of high purity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for refining magnesia whiskers, and in particular, magnesia whiskers useful as compounding materials for composite materials such as FRC can be purified to high purity. This invention relates to a method for refining magnesia whiskers.

[Prior Art] In recent years, with the progress of space exploration technology, heat-resistant and high-strength inorganic fibers have been developed, and today Aj! 203, C, SiC%
Sis N4. Whiskers such as AILN are being used as constituent materials for composite materials, fireproofing, and insulation materials. Further, MgO whiskers are also being considered.

Whiskers are thin fibrous single crystals and are also called whisker crystals. A characteristic of whiskers is that the thinner they are, the fewer crystal defects (such as dislocations) there are, and in the presence of helical dislocations, the integrity of the crystal can be detected by the occurrence of kinks and the low elastic limit. Therefore, it has high strength and is therefore extremely effective as a fiber reinforced material in various composite materials.

Conventionally, the following methods for producing MgO whiskers have been used:
Method (2) has been proposed.

■ Molar ratio of magnesium salts and halogen compounds is 0.
．． 5-5. O
A first step of forming a molten salt by heating at 700 to 900°C to generate whiskers;
A method consisting of a second step of washing and separating this (patent application 1986)
1-314804).

■ The first step is to prepare a crude magnesium mineral salt solution by dissolving various magnesium crude ore raw materials containing 80% or more of MgO in mineral acids (sulfuric acid, hydrochloric acid, nitric acid), and adding alkali ( The second step is to precipitate and remove impurities by adding ammonium hydroxide, caustic soda), then insert the reaction solution into an autoflavve, introduce oxygen, and seal it for 10 to 30 minutes.
A third step of high temperature and high pressure curing at 15 to 8/Crr1';
Furthermore, a method consisting of a fourth step of washing and dehydrating the product cured at high temperature and high pressure, and a fifth step of baking the dehydrated product at 1,100 to 1,200°C to form a fibrous material (Japanese Patent Application Laid-Open No. 81
-26511).

When manufacturing such MgO whiskers, granular Mg
O (hereinafter referred to as "shot") is produced as a by-product, and a method for classifying and purifying MgO whiskers from the shot is required.

By the way, conventional methods for classifying and refining whiskers include dispersing whiskers in a liquid, allowing it to stand for a certain period of time, and then forcefully filtering the resulting whisker aggregates in a plurality of layers in a direction perpendicular to the filtration direction. A dividing method has been proposed (Japanese Patent Laid-Open No. 143900/1983).

[Problems to be Solved by the Invention] However, when the method described in JP-A-62-143900 is applied to the purification of magnesia whiskers, it is not possible to completely separate the "shot" produced as a by-product during whisker production. As a result, the conventional MgO whisker product was found to have a very small amount of shot mixed in.

Therefore, when such MgO whiskers are used in various composite materials, the characteristics of the MgO whiskers cannot be fully exhibited, and there are problems in terms of strength and the like.

The present invention solves the above conventional problems and uses chemical means to completely separate and remove shot in MgO whiskers, which could not be achieved with conventional mechanical methods. High purity MgO free
The object is to provide a method for purifying MgO whiskers that makes it possible to obtain whiskers.

[Means for Solving the Problems] The method for purifying MgO whiskers according to claim (1) is characterized in that magnesia whiskers are treated with hydrochloric acid. ) is characterized in that 0.5-2N hydrochloric acid is used as the hydrochloric acid.

The present invention will be explained in detail below.

In the method of the present invention, MgO whiskers containing a small amount of shot produced by various conventional methods are treated with hydrochloric acid, preferably 0.5-2N hydrochloric acid. That is, for example, M150 whiskers are added to 0.5-2N diluted hydrochloric acid and stirred. Then, when the dissolution of the shot in dilute hydrochloric acid is completed, the remaining whiskers are filtered, washed with water, and dried.

In this case, the concentration of hydrochloric acid is too low, and if it is 0.5N, it takes time to dissolve the shot, and operations such as heating are required. On the other hand, if the hydrochloric acid concentration is too high, exceeding 2N, the whisker surface will also be etched in addition to the shot, which is not preferable. Therefore, it is optimal that the hydrochloric acid concentration is in the range of 0.5 to 2N.

The amount of hydrochloric acid used varies depending on the amount of shot, the concentration of hydrochloric acid, etc., but usually MgO whisker 10 containing shot
It is set to be about 500 to 5000 mλ with respect to g. The time required to finish dissolving the shot is usually about 10 to 30 minutes. This treatment with hydrochloric acid can be carried out at room temperature to 100°C.

In the present invention, the method of treating MgO whiskers with hydrochloric acid is not limited to the above-mentioned stirring method, but a method of passing dilute hydrochloric acid through a net containing MgO whiskers can also be adopted.

The method of the present invention is based on the MgO whisker manufacturing method disclosed in JP-A-63-166715, that is, by heating and melting a mixture of magnesium chloride and a halide at 650°C or higher, and using the resulting molten salt. MgO whiskers produced by heating at 650 to 10,000°C in a steam atmosphere or patent application 1986-
It can also be suitably applied to MgO whiskers produced in Japanese Patent Application No. 141146, Japanese Patent Application No. 145468/1982, and Japanese Patent Application No. 145469/1983.

[Function] The present invention does not use the conventional principle of separation by gravity sedimentation to purify MgO whiskers, but by chemically processing them by utilizing the difference in crystal surface properties between MgO whiskers and shot. , 11tPi.

That is, the crystal shape of the MgO whisker is a single crystal, and its surface is a chemically inert (1,O,O) plane. On the other hand, shot is made of polycrystalline or amorphous material, and therefore is not chemically stable like whiskers. Utilizing this difference between the two, it is possible to completely separate the whiskers by chemical treatment. In the present invention, the shot is dissolved by treatment with dilute hydrochloric acid, making it possible to completely separate the whisker component.

In the present invention, more effective purification can be achieved especially by using 0.5 to 2N hydrochloric acid.

[Example]゛ EXAMPLES The present invention will be explained in more detail with reference to Examples below.

Example 1 1 g of MgO whiskers containing a small amount of shot was mixed and dispersed in 300 mf of a hydrochloric acid solution having a concentration shown in Table 1 by stirring with a magnetic stirrer. After stirring for the time shown in Table 1, the suspension was filtered and washed with water, and the whiskers collected on the filter paper were observed by SEM to examine the dissolution state of the shot and the residual rate of whiskers. The shot dissolution status and whisker residual rate are shown in Table 1. As is clear from Table 1, the shot was completely dissolved when the hydrochloric acid concentration was IN or higher and the treatment time was 10 minutes or longer. Furthermore, when considering the whisker residual rate within this range, it is recognized that treatment for IN and 30 minutes or less is appropriate.

Table 1 ○: No shot ×: Shot remaining [Effects of the invention] As detailed above, according to the MgO whisker refining method of the present invention, MgO whiskers containing a small amount of shot are completely removed. It is possible to obtain MgO whiskers of extremely high purity, which is unprecedented. Therefore, when a whisker composite is manufactured using MgO whiskers purified according to the present invention, performance such as strength can be significantly improved compared to when conventional MgO whiskers are used.

In particular, by the method of claim (2), as hydrochloric acid, 0.5 to
By using 2N hydrochloric acid, the purification efficiency is significantly increased.

Agent Patent Attorney Tsuyoshi Shigeno

Claims (2)

[Claims] (1) A method for purifying magnesia whiskers, which comprises treating magnesia whiskers with hydrochloric acid. (2) The method according to claim 1, wherein the concentration of hydrochloric acid is 0.5 to 2N.