JPS5841104B2 - Surface treatment method for porous articles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface treatment method for improving the lubricity of porous articles or articles having porous surfaces, and more specifically, the present invention relates to a surface treatment method for improving the lubricity of porous articles or articles having porous surfaces. The present invention relates to a surface treatment method for improving lubricity by impregnating with sulfide or tungsten sulfide.

Generally, solid lubricating molybdenum disulfide powder, tungsten disulfide powder, powdered polyfluoroethylene, or colloidal carbon is impregnated into the pores of porous articles or articles with porous surfaces to reduce the coefficient of friction and lubricate. These porous articles have been used in mechanical parts such as bearings to improve their properties.

By the way, conventional methods for impregnating solid lubricant into the pores include immersing the object to be treated in solid lubricant powder, or dispersing solid lubricant powder in a liquid and then adding it to the dispersion. Methods have been adopted in which the object to be treated is immersed, but since the solid lubricant in these methods has a tangible size, it is not sufficient when the pore size is small or has a complex shape. There are problems in that impregnation cannot be carried out, or even if impregnated, the amount of impregnation is insufficient.

The purpose of the present invention was to solve these problems, and it aims to improve porous articles or articles with porous surfaces (hereinafter referred to as "porous articles"), which have conventionally been impossible or difficult to impregnate with solid lubricants. It is an object of the present invention to provide a method for impregnating a solid lubricant deep into the pores of a solid lubricant in a sufficient amount.

The present invention will be explained below.

The present invention provides lubricity by producing and filling a sufficient amount of molybdenum sulfide or tungsten sulfide, which is known for its excellent properties as a solid lubricant, in the pores of a porous article through chemical reaction and heat treatment. , which aims to significantly improve wear resistance.

The porous articles according to the third aspect of the present invention include porous metal bodies produced by sintering, porous ceramics, porous plastics, porous chromium plating, microcrack chromium plating, and the like.

These porous articles are degreased and cleaned using an organic solvent such as perchlorethylene or trichlorethylene.

Next, it is immersed in an aqueous solution in which at least one of ammonium salt, alkali metal salt, alkaline earth metal salt of thiomolybdic acid, antinium salt, alkali metal salt, and alkaline earth metal salt of thiotungstic acid is dissolved.

Next, an inorganic acid such as sulfuric acid, nitric acid, hydrochloric acid, acetic acid, or oxalic acid, an organic acid, or a salt of these acids is dissolved to adjust the pH to at least 4.
Immerse in an acidic aqueous solution prepared as follows.

By repeating this series of alternate dipping operations, molybdenum trisulfide or tungsten trisulfide can be formed and impregnated into the pores of the porous article.

The chemical reaction in this case is, in the case of thiomolybdate,
It is shown as follows.

MoS: + 2 H-+Mo53↓+H2S At this time, most of the generated hydrogen sulfide (H2S) dissolves in water, and some of it becomes bubbles and is removed from the pores, forming molybdenum trisulfide, which is insoluble in water. only remains in the hole.

After impregnating molybdenum trisulfide or tungsten trisulfide into the holes through the above series of operations, thoroughly rinse with water.
Moisture is evaporated and then, if the object to be treated has heat resistance, heat treatment is performed to produce crystalline terepden disulfide or tungsten disulfide.

This reaction is expressed in the case of molybdenum as follows.

Heating MoS3-+ MoS2+S In this way, a sufficient amount of molybdenum disulfide or tungsten disulfide with a layered crystal structure, which is a solid lubricant, can be generated and filled deep into the pores of the porous article. It became.

To explain the treatment method of the present invention more specifically, when a porous article is immersed in a thiomolybdate or thiotungstate aqueous solution, thiomolybdate ions or thiotungstate ions penetrate into the pores by diffusion. I will do it.

The immersion time at this time is the time required for thiomolybdate ions or thiotungstate ions to reach the bottom of the hole by diffusion, for example, about 1 to 10 minutes.

At this time, adding methanol, ethanol, or a surfactant to the aqueous solution to lower the surface tension of the aqueous solution has the effect of improving permeability into the pores and shortening the immersion time.

The same applies to the case of immersion in an acidic aqueous solution, and the immersion only needs to be performed for the time required for hydrogen ions to reach the bottom of the pores.

In this case as well, methanol, ethanol, or a surfactant can be added to the acidic aqueous solution to improve permeability.

The hydrogen ion concentration of the acidic aqueous solution is preferably a concentration sufficient to react with thiomolybdate ions or thiotungstate ions, usually 10' mol/ or more (pH 4 or less).

The reason why the above-mentioned immersion time of about 1 to IO minutes is sufficient is because the reaction to generate molybdenum trisulfide or tungsten trisulfide takes only a very short time. This is because the reaction will be completely completed if the ions are allowed to diffuse to the bottom of the pore.

After each cycle of this series of alternate dipping operations (immersion in a thiomolybdate or thiotungstate aqueous solution → immersion in an acidic aqueous solution), the object to be treated is washed with water to remove any adhering products on the surface. This allows efficient impregnation.

Through the above steps, molybdenum trisulfide or tungsten trisulfide can be impregnated deep into the pores, and the pores can be filled by repeating this series of alternate dipping operations for about 5 to 20 cycles.

Then, this molybdenum trisulfide or tungsten trisulfide becomes molybdenum disulfide or tungsten disulfide by heat treatment.

The crystalline molybdenum disulfide or tungsten disulfide thus produced has a hexagonal crystal structure similar to graphite, and as is well known, has excellent lubricating properties such as a low coefficient of friction and load carrying capacity.

In addition, when heat-treating, molybdenum trioxide (Mo0
3) Alternatively, in order to prevent the formation of tungsten trioxide (WOS), it is necessary to heat the product while cutting off air, especially oxygen.

That is, it is necessary to carry out the process in an inert atmosphere such as nitrogen gas (N2) or helium (He).

Further, the heating temperature is preferably from 200° C. to 800° C., and care must be taken because if the heat treatment is performed at too high a temperature, molybdenum trisulfide or tungsten trisulfide impregnated in the pores will sublimate.

Naturally, this heat treatment cannot be performed if the porous article is made of plastic or other material that does not have heat resistance.

However, even if heat treatment is not possible, molybdenum trisulfide or tungsten trisulfide near the sliding surface may change to molybdenum disulfide or tungsten disulfide due to the frictional heat generated when the bearing is put into practical use. This provides sufficient lubricity for practical use.

Next, the present invention will be specifically explained with examples.

Example 1 Sintered alumina plate with 15% porosity 100X100X 5
A test piece of rIvrL was prepared.

On the other hand, a 1 weight aqueous solution of ammonium polythiomolybdate and a 1N aqueous sulfuric acid solution were prepared.

First, a sintered alumina plate was degreased and cleaned with trichlorethylene and air-dried.

Next, this test piece was immersed in an aqueous ammonium thiomolybdate solution for 1 minute at room temperature, then immersed in an aqueous sulfuric acid solution for 1 minute*, and then washed with water.

After repeating this series of operations 10 times, wash thoroughly with water.
It was dried for 30 minutes at ioOoC.

Next, the test piece impregnated with this molybdenum trisulfide was
Heat treatment was performed at 2000C to 800C for 30 minutes in a nitrogen gas atmosphere.

A wear test was conducted on the test piece treated as described above.

The results are shown in the table.

Wear test conditions Partner material: Hardened steel Contact area: Approx. The results are shown when the ammonium thiotungstate aqueous solution is used.0 Comparative Example The test piece of Example 1 was treated with a treatment solution in which molybdenum disulfide powder with a particle size of 3μ was dispersed in a polyvinyl alcohol aqueous solution containing 1 weight of polyvinyl alcohol at a concentration of 15 weight. The sample was immersed in the liquid while stirring at room temperature for 30 minutes.

Next, this test piece was washed with water and dried at 100° C. for 30 minutes, and the same abrasion test as in Example 1 was conducted, and the results were as follows.

As described above, if the impregnation treatment according to the present invention is carried out, molybdenum disulfide or tungsten disulfide, which has excellent lubricity, can be applied deep into the pores of a porous article and in sufficient quantity. It will be filled regardless of the
The lubricating effect of molybdenum disulfide or tungsten disulfide is retained for a very long time.

Various parts made of materials that have been subjected to such surface treatments are excellent in that they are free from "galling" and "seizing" due to their low coefficient of friction, increased load resistance, and anti-adhesion effect.

Claims (1)

[Claims] 1. An aqueous solution of at least one ammonium salt, alkali metal salt, or alkaline earth metal salt of thiomolybdic acid or thiotungstic acid, and an acidic aqueous solution of at least one inorganic acid, organic acid, or salt thereof,
A method for surface treatment of porous articles, which comprises alternately immersing porous articles or articles having porous surfaces and subjecting them to heat treatment as necessary.