JPS6272527A - Production of chromium oxide - Google Patents

Abstract

PURPOSE:To obtain the titled oxide usable as a thermal spraying material by adding a specific metal oxide and/or its precursor to the chromium oxide, and by heating it in an oxidative atmosphere thereby growing a crystal size thereof. CONSTITUTION:Ten or less percent of any one kind or more than two kinds of oxides selected from among Ti, Ni, Pb, Bi, Zr, W and Cu and/or its precursor are added to the chromium oxide powders, and heated in the oxidative atmosphere at the temp. of from 1,300 deg.C to a melting point of the chromium oxide, preferably 1,450-1,600 deg.C, thereby growing the crystal size of the chromium oxide to 5-50%. Thus, the chromium oxide having 10-50mum a mean particle size and a sphere or a polygonal shape and having an excellent fluidity is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing chromium oxide, and an object thereof is to provide chromium oxide suitable for thermal spraying materials.

[Prior Art] Conventional chromium oxide for thermal spraying is made by heating ordinary chromium oxide powder to a high temperature of -L above the melting point of approximately 2400°C, melting it, cooling it to solidify it, and then pulverizing it. This method was manufactured by sieving and recovering the desired particle size, but since it has a shortening point as described below, the inventors of the present invention added an alkali metal salt or alkaline earth to chromium oxide in order to solve this problem. Invented and applied for a method for producing chromium oxide for thermal spraying by heating and baking a mixture containing one or more metal salts selected from similar metal salts (Japanese Unexamined Patent Publication No. 1980-85727). are doing.

[Problems to be solved by the invention] In the conventional method, chromium oxide powder is heated and melted at high temperatures, which tends to cause contamination due to corrosion of the furnace material and electrodes, and a decrease in chemical purity. Classification tends to increase contamination and reduce yield, and microscopic observation shows that the particles are all angular, irregularly shaped fragments, with irregular and rough crushed surfaces. There were problems such as poor fluidity as a body, making it inconvenient for use as a thermal spray material.

Although the method disclosed in Japanese Patent Application Laid-Open No. 80-65727 was able to improve the problem described in L to a certain extent, it had the secondary problem that the additives tended to corrode the container.

[Means for solving the problem] In order to solve the problem mentioned in L, the inventor of the tree
The invention of Japanese Patent No.-85727 was further improved to arrive at the present invention.

That is, the present invention is a method for producing chromium oxide with a grown crystal grain size by heating and firing chromium oxide powder in an oxidizing atmosphere at a temperature from 1300°C to a temperature below the melting point of chromium oxide, in which titanium is added to the chromium oxide powder. , nickel, lead, bismuth, zirconium, tungsten and copper.
This is a method for producing chromium oxide, characterized by carrying out heating and firing in the presence of a metal oxide or two or more metal oxides or their precursors.

The raw material chromium oxide is usually [commonly commercially available powdered chromium oxide, but its precursors such as chromic anhydride, chromium hydroxide, ammonium chromate, or ammonium dichromate are also available. Alternatively, a part of the chromium oxide recovered by the production method of the present invention can be reused.

On the other hand, titanium is added to chromium oxide.

The oxide is one or more oxides selected from nickel, lead, bismuth, zirconium, tungsten, and copper, and may be a precursor thereof. Precursors include, for example, carbonates, hydroxides, nitrates or organic acid salts.

The amount of the above-mentioned oxides etc. to be added is at most 10% by weight, preferably at most 5% by weight based on the oxides, based on the total amount. The reason for this is that, although it is expected that chromium oxide crystals will grow and become spheroidal with addition, if the amount exceeds about 10% by weight, a phenomenon is observed in which the particle size decreases compared to that without the addition.

The above raw material mixture is heated and baked in an a-oxidizing atmosphere,
The firing time is carried out at a temperature of 1300° C. to below the melting point of chromium oxide, preferably 1450° C. to 1600° C., for a desired period of time. The firing time is not particularly limited, but the longer it is, the greater the crystal growth, so it is set in consideration of energy efficiency. do it.

The obtained fired product is often a powder consisting of spherical or polyhedral particles with uniform particle size, and the particle size can be adjusted and used as is, or if necessary, it can be further classified to the desired particle size and made into a product. As the L stage for particle size adjustment, various methods such as sieving, dry or wet cyclone, and dosing can be used.

In addition, if multiple crystal grains are sintered during the crystal growth process by heating and firing, resulting in a "clumped" shape, mechanical crushing treatment is performed prior to grain size adjustment in order to separate the crystal grains from each other. It is desirable to separate the particles so that they have sufficient fluidity.

The crushing treatment may be either dry crushing or wet crushing, but it is not necessary to crush the chromium oxide crystal particles themselves, and it is sufficient to separate or loosen the crystals based on impact force or shear force. It is best to use a grinder such as a Henschel mixer with the mixture suspended in a suitable amount of water.

According to the production method of the present invention, the product has particle size characteristics suitable for commercially available chromium oxide for thermal spraying, and has a spherical to polyhedral shape, so it has good fluidity. In order to further increase fluidity, acidic phosphoric acid ester,
By adding a silane coupling agent and a lubricant such as metal soap to the surface, the fluidity can be further improved, making it suitable for use as a thermal spray material.

This will be specifically explained below by giving examples.

[Example] Examples 1 to 17, Comparative Examples 1 to 3 Commercially available chromium oxide powder (average particle size 1.
2ILm) and various additives shown in Table 1 were added, and after step 4, the material was placed in a siliconite electric furnace, baked at 1500°C in an air atmosphere for 5 hours, and left to cool until the next day 11. A fired product was obtained. The calcined product was made into a slurry by adding water, loosened using a household mixer, and the particle size was adjusted using the gravity sedimentation classification method.The liquid was then separated and dried to obtain chromium oxide.

The obtained chromium oxides all had good fluidity, and their average particle diameters and particle growth rates are as shown in Table 1.

゛・Table 1 (Note 1) The average particle size was measured by the Coulter counter method.

Examples 18 to 23 Ichisaka's chromium oxide powder (f average particle size = 1
．． 2μff1) and various additives shown in the 7JSZ table were added, put in a siliconite electric furnace with a lid, baked at 1800℃ for 6 hours in an air atmosphere, and left to cool until the next day. A fired product was obtained. The calcined product was made into a slurry by adding water, loosened with a household mixer, and further adjusted in particle size using gravity sedimentation classification, followed by solid-liquid separation and drying to obtain chromium oxide.

All of the 1rI chromium oxides had good fluidity, and their average particle diameters and grain growth rates are shown in Table 2.

Table 2: Effects of the Invention According to the method of the present invention, the crystal grain size of chromium oxide can be grown to about 5 to 50% in a relatively short firing time, and furthermore, the crystal grain size of chromium oxide can be grown to about 5 to 50% by firing in a relatively short time. 1 in 2 for thermal spraying with an average grain size of 10 to 50 gm and a spherical to polyhedral shape at a low firing temperature below the melting point.
Chromium oxide with good fluidity can be obtained without the problem of corrosion of the container cap, which is commercially advantageous.

[Brief explanation of drawings]

FIG. 1 shows Reference Example 1, FIG. 2 shows Example 3, FIG. 3 shows Example 9, and FIG. 4 shows Example 12. FIG. 5 is an electric J'-micrograph showing the structure of the crystal grains -f Jm obtained in each of Example 13, and the magnification is 100,047 in each case. Applicant: 11 Hon Kagaku Nigyo Co., Ltd. Agent: Fll Miyu 4J Month 10, P- toP% 10p@Lol, -＾J 101* Qpx

Claims (2)

[Claims] (1) A method for producing chromium oxide with a grown crystal grain size by heating and firing chromium oxide powder in an oxidizing atmosphere at a temperature of 1300°C or below the melting point of chromium oxide, the chromium oxide powder containing titanium and nickel. , lead, bismuth, zirconium, tungsten and copper, and/or a precursor thereof. (2) The amount of one or more metal oxides and/or their precursors selected from titanium, nickel, lead, bismuth, zirconium, tungsten, and copper is at most oxide based on the total amount. The method for producing chromium oxide according to claim 1, wherein the content is 10% by weight.