JP2003206476A - Heat-treated diamond fine powder and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diamond fine powder having excellent separability, settling an unavoidable and rigid cohesion problem of conventional single crystal submicron diamond powders, especially of heat-treated ones. <P>SOLUTION: The heat-treated diamond fine powder is one comprising an aggregate of single crystal submicron diamond particles having heat affected structure, wherein the substantially whole diamond particles of the aggregate are separated from each other through a carbon layer having a non-diamond structure. The method for producing the diamond fine powder comprises soaking the powder into a solution or suspension of a non-diamond structure carbon- generating agent to make the carbon-generating agent adhere to at least a part of the particle surface, heating the powder in an inert gas atmosphere at a treating temperature to carbonize the surface of the diamond particles to obtain non-diamond carbon, simultaneously decomposing the carbon-generating agent to produce non-diamond carbon and, thereby, separating adjacent diamond particles from each other with the non-diamond carbon. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a submicron diamond fine powder suitable for use as a slurry-like abrasive suspended in a dispersion liquid, particularly a diamond fine powder suitable for processing a hard disk or a magnetic head, and a method for producing the same.

[0002]

2. Description of the Related Art Due to the demand for rapid increase in recording capacity of hard disks in recent years, fine processing defined in units of angstrom is required for processing hard disks and magnetic heads.

For such fine processing, a slurry in which submicron-sized diamond is suspended in an aqueous or oil-based dispersion medium is widely used. And as a preferable slurry, there are three requirements: a large amount of processing per unit time, no deep scratches on the polishing surface, and no leaving a particle that digs into the polishing surface for a soft work material. Listed.

The present inventors have used the fine powder of single crystalline diamond synthesized under static ultrahigh pressure as a raw material and added various steps of grinding, chemical treatment and heat treatment to meet the above three requirements. At the same time, a fine powdery abrasive to be filled was completed, and a patent application was previously filed (Japanese Patent Laid-Open No. 2000-136376).

The fine powder recovered from this heat treatment, if left as it is, immediately settles when it is poured into water, and has a surface state that makes it impossible to form a slurry. The reason for this is
The loss of hydrophilic functional groups on the powder surface due to heating, and the formation of a strong bond between the powder particles during heating, resulting in agglomerated particles.

[0006] In spite of the above-mentioned drawbacks, the heat-treated submicron diamond fine powder has a peculiarity that the processing speed is high and the finished surface roughness is small at the same time in the processing of a hard disk or a magnetic head as compared with an untreated product. It has been found to exhibit excellent performance. This peculiar performance is considered to be derived from the non-diamond carbon layer formed on the diamond powder surface. Due to these advantages, heat-treated submicron diamond is used on a trial basis in some finishing departments, but it is widely used because it is difficult to deagglomerate particles. The situation has not been reached.

[0007]

In order to obtain a larger recording capacity in a hard disk and to create a finer polished surface, it is necessary to use finer diamond fine powder as an abrasive. However, when the raw material diamond fine powder has an average size of 150 nm or less, strong agglomeration occurs between the fine powders during the heat treatment. There is a drawback that a step of mechanically crushing the particles is required, and as a result, a large number of steps and time are required.

Further, it was also recognized that the non-diamond carbon layer on the surface of the diamond powder is destroyed by the crushing operation for a long time, and as a result, the peculiar performance as the heat treated particles is deteriorated.

Further, since the binding force between the powder particles generated during the heat treatment is large, the powder particles are supplied to the user without being sufficiently crushed and used as agglomerated, apparently coarse particles in the processing to cause scratches. Inevitable troubles were unavoidable, and it was necessary to develop a method for producing heat-treated particles without aggregation.

Therefore, the main object of the present invention is to solve the problem of strong agglomeration, which is unavoidable in the conventional single crystal submicron, especially such diamond fine powder which has been heat-treated, and which has good separability. Is to provide.

[0011]

Means for Solving the Problems The present inventors have clarified the aggregation mechanism that occurs between fine powder particles during heat treatment. Thus, the above disadvantages of the conventional fine powder, prior to the heat treatment, the separation agent (spacer) consisting of a substance capable of forming non-diamond carbon or non-diamond carbon in situ between the fine powder constituent particles in advance. It has been found that the problem can be solved essentially by separating them. That is, by depositing a separating agent material on the opposing surfaces of substantially the entire set of adjacent particles, keeping each particle individually separated,
During heating, the constituent particles are kept in an isolated state, and binding between the particles is prevented.

First, the gist of the present invention is a powder comprising an aggregate of single crystalline submicron diamond particles having a heat-affected structure, wherein substantially all diamond particles of the aggregate have a non-diamond structure. A heat-treated diamond fine powder characterized by being separated from each other through a carbon (non-diamond carbon) layer.

In order to avoid the strong bond between the adjacent diamond particles due to the diamond surface, such fine diamond powder is formed around each particle of the raw material diamond prior to the heat treatment, in the non-diamond structure carbon or during the heating. This can be effectively achieved by arranging particles of a substance that produces such carbon and maintaining each particle in a separated / isolated state in the non-diamond carbon layer during the heat treatment.

Therefore, the gist of the present invention is, secondly, by immersing a powder composed of an aggregate of single-crystal submicron diamond particles in a solution or dispersion of a non-diamond structure carbon generator (carbon generator). , At least a portion of the particle surface of the carbon generator is adhered, and then the powder is heated in an inert atmosphere at a treatment temperature to non-diamond carbonize the surface layer of the diamond particles and at the same time A method for producing fine diamond powder with improved separability, characterized in that non-diamond carbon is generated by decomposition and adjacent diamond particles are mutually separated by non-diamond carbon.

In the present invention, the non-diamond carbon is deposited on at least a part of the opposing surface of the adjacent diamond particles, more preferably on the entire surface, so that the adjacent particles do not come into contact with each other during the heat treatment. It is appropriate that the total amount of non-diamond carbon is 0.5% or more in the mass ratio with respect to the whole diamond powder. That is, if it is less than this, sufficient separation of particles cannot be obtained. Further, if it exceeds 25%, the work efficiency of the work is significantly reduced, so it is desirable that the total amount does not exceed this value.

In the present invention, the surface layer of diamond particles is partially converted into non-diamond carbon by heat during the heat treatment. The above total amount also includes non-diamond carbon obtained by the conversion of this diamond.

In the method for producing fine diamond powder of the present invention, as the raw material diamond powder, a monocrystalline diamond powder having a hydrophilic group on the surface is used, and the non-diamond carbon or carbon generator is dissolved or dispersed in the water treatment solution. To disperse the particles. On this occasion,
A solute or dispersoid is attached to or deposited on the surface of the diamond particles to coat each particle, and substantially all of the particles are brought into a state of isolated particles, and then heat treatment is performed.

Such a diamond can be generally obtained by using a press to finely pulverize and classify a diamond synthesized and isolated by conversion of graphite or the like under static ultrahigh pressure and high temperature conditions.

In general, it has been pointed out that even if chemically stable diamond is used, if it becomes fine powder of submicron grade, the reactivity of the surface cannot be ignored. Atoms and functional groups attached to or adsorbed on the surface of diamond are various such as hydrogen, oxygen, carboxyl group, carbonyl group, and hydroxyl group. In particular, the finely divided diamond that has undergone the steps of pulverization and acid washing often has a hydrophilic functional group on the surface, and therefore the stability of the aqueous slurry is governed by the type of functional group on the diamond particle surface.

When finely divided diamond particles having a hydrophilic functional group on the surface are heated, CO ₂ and CO are desorbed due to the decomposition of the functional group. Since it is considered that the part where the carbon atom is missing becomes an active point, it is presumed that in the conventional diamond fine powder, such an active point serves as a starting point and a bond is generated between adjacent particles.

The heat treatment is carried out in an inert atmosphere to avoid the oxidation of diamond. Under these conditions, the coating material on the particle surface is carbonized, but since the function as a spacer between adjacent particles is secured, it is considered that the formation of a strong bond close to a chemical bond is prevented between the diamond surfaces. . As a result, the diamond powder recovered from the heat treatment can be easily pulverized in a mortar and easily made into a slurry.

As the material for the coating layer that functions as a spacer, various substances that wet the diamond surface and decompose by heating to leave substantially only carbon can be used. For example, a nonionic surfactant such as polycarboxylic acid may be used as a material for forming a strong surrounding film.

When the surface of the diamond is hydrophilic, a material that surrounds the diamond particles through water and decomposes or carbonizes by heating in an inert atmosphere, and the heating residue becomes a carbonaceous substance is used. it can. Examples of such materials include water retention agents (PVA, polyacrylates, etc.), gelatin, starch and the like.

The hydrophilic groups present on the diamond surface are 80
It has been confirmed by surface analysis that it decomposes substantially when heated to 0 ° C, and it is considered that the activity of the surface decreases at higher temperatures. Therefore, the above coating layer components are 800 ℃
It is sufficient that the spacer function is maintained until the temperature reaches.

According to TEM observation, one to several amorphous layers are recognized on the surface of ordinary submicron diamond. On the other hand, in the heat-treated diamond, the presence of non-diamond carbon, which is similar to the lattice image of graphite, is recognized in several layers in succession to the lattice image of diamond. It is considered that the non-diamond carbon is responsible for the performance unique to the heat-treated diamond, that is, the reduction in the roughness of the work polishing surface. Since the formation of the non-diamond carbon layer becomes remarkable at a temperature of 800 ° C. or higher, 800 ° C. or higher is suitable as the treatment temperature in the present invention.

On the other hand, if an excessively high heating temperature is used, the amount of non-diamond carbon converted from diamond becomes too large, and the action as an abrasive is reduced.
The upper limit of heating temperature is 1400 ℃.

The amount of non-diamond present in the fine diamond powder of the present invention can be determined by a wet or dry oxidant treatment. That is, the non-diamond carbon is a wet treatment using nitric acid or perchloric acid at 200 ° C. or higher,
Alternatively, it is easily decomposed by dry treatment with oxygen gas or the like at 350 ° C. or higher, while diamond is not substantially oxidized, so the sample is oxidized as described above,
It is evaluated by the change in mass before and after the treatment.

In order to secure the effect of separating diamond particles from each other in the present invention, an appropriate amount of non-diamond converted to a degree recognizable from diamond and non-diamond generated from particle separating agents or spacers are formed on the surface of each diamond particle. The diamond is interposed. The amount of non-diamond converted from diamond needs to be 0.5% by mass or more based on the diamond powder.

On the other hand, the T of the substance in which the separating agent (spacer) is carbonized
The EM image has no continuity with the diamond lattice and is observed as an isolated image similar to amorphous carbon or graphite. This charcoal behaves in a substantially similar manner to the oxidizer as the non-diamond (graphite) layer converted from diamond, making it difficult to distinguish between the two and, if necessary, in a blank test. Obtain quantitatively. The amount of carbon derived from the spacer material is preferably 0.2% by mass or more with respect to diamond.

The diamond particles used as a raw material in the method of the present invention are subjected to a preliminary heat treatment prior to the heat treatment in order to improve the crushability at the time of processing, or as a heat-affected structure during the heat treatment. It is possible to generate fine cracks.

The effect of using the method of the present invention is that qualitatively from a suspension state, a slurry having a concentration of about 2% prepared by throwing heat-treated diamond powder in water and dispersing it by applying ultrasonic waves is used. It can be quantitatively evaluated from the results of particle size distribution measurement.

That is, in the case of a powder having no strong bond between particles, the entire amount of the charged powder is suspended and no precipitate is observed at the bottom of the container. On the other hand, when the particle size distribution of the heat-treated powder in the slurry is measured, the result almost equal to the distribution before the heat treatment is obtained. This indicates that it contributes substantially to the polishing operation as primary particles, and in addition to avoiding the occurrence of deep polishing scratches due to agglomerated particles, it also supports a combination of polishing surface roughness and polishing speed. It is also easy to select particles having the optimum particle size range.

In the diamond powder according to the present invention,
The first merit of being easier to make into a slurry than the conventional equivalent heat-treated product is, as is obvious, an improvement in workability during slurry preparation. Since the mechanical load required for crushing the agglomerated particles is no longer required, the destruction of the non-diamond carbon layer on the diamond surface is avoided, and as a result, the polishing finish of the workpiece, which is a feature of heat-treated abrasive grains, is avoided. The improvement of the quality of the abrasive grains is ensured, that is, the surface roughness is kept small.

Next, the present invention will be described with reference to examples.

[0035]

Example 1 A surface hydrophilic submicron diamond powder MD100 made by Tomei Diamond having an average particle size (D50 value) of 105 nm
Was used as the starting material. In a 300 ml beaker, 10 g of diamond powder and 100 cc of deionized water were placed, and ultrasonic waves were used to suspend the diamond in the water.

Next, 0.5 g of gelatin powder as a separating agent was sprinkled little by little and stirred sufficiently to give a suspension. The suspension was heated and kept at 85 ° C. for 2 minutes with continuous stirring. Then, the mixture was water-cooled and further dried under reduced pressure to recover a sponge-like substance in which diamond powder was entangled with gelatin fibers.

This sponge-like substance was placed in an alumina crucible and heat-treated in a nitrogen atmosphere at 1100 ° C. for 2 hours to graphitize the diamond surface and decompose gelatin. For comparison, the starting MD100 dry powder was also heat treated.

The diamond recovered from the heat treatment had a black color. The non-diamond carbon adhering to the surface of the diamond particles was 5.5% when quantified by the wet treatment using an oxidizing agent. 110 of used gelatin
The amount of pyrolysis residue at 0 ℃ was 25%, so the carbon converted from diamond by heat treatment was estimated to be 4.3%.

1 g of the obtained heat-treated diamond according to the present invention was dispersed in 100 cc of deionized water to prepare a slurry. When the particle size distribution was measured, the D50 value was 110 nm, and it was recognized that the heat-treated diamond was a slurry in which the diamond was substantially dispersed in the state of primary particles.

For comparison, MD100 diamond powder was heat-treated in the supplied state, and the obtained diamond was dispersed to prepare a slurry. D50 of this slurry
The value was 175 nm, indicating that agglomerated particles were formed during the heat treatment.

Using both of these slurries, an aluminum hard disk was subjected to texturing, and the roughness of the processed surface was evaluated by AFM. The finished surface using the slurry according to the present invention was 4.8Å, and the comparative product slurry. In the case of, it was 6.5Å.

[0042]

Example 2 A surface hydrophilic submicron diamond powder, MD50, made by Tomei Diamond, having an average particle size (D50 value) of 60 nm was used as a starting material. Diamond powder 2 in a 200cc beaker
0 g and 20 g of a polycarboxylic acid solution of a surfactant diluted 10 times with deionized water were added and kneaded sufficiently. 60 ° C
After drying in, it was transferred to an alumina crucible and heated to 300 ° C. to partially carbonize the polycarboxylic acid.

The contents of this crucible were heat-treated at 1000 ° C. for 2 hours in a nitrogen atmosphere to graphitize the diamond surface and decompose the surfactant. The non-diamond carbon on the surface of the diamond powder after the heat treatment was 6.3% as a result of the wet treatment using an oxidizing agent. From this, 0.14 g was subtracted from the amount of carbon derived from polycarboxylic acid, and the diamond converted non-diamond carbon amount was estimated to be 5.6%.

Regarding the obtained heat-treated diamond,
The particle size distribution was measured by the same method as in Example 1. D50
A value of 66 nm was obtained, and it was confirmed that this diamond powder was substantially dispersed in the state of primary particles.

[0045]

In the method of the present invention, a substance, a separating agent or a spacer having a function of isolating adjacent particles from each other is arranged between diamond particles prior to the heat treatment of the submicron diamond fine powder. By this method,
The agglomeration phenomenon that occurs between the diamond particles during the heat treatment is effectively avoided, and it becomes possible to obtain a slurry that is substantially composed of primary particles. As a result, it became possible to put the heat-treated submicron diamond into practical use as an abrasive for obtaining a fine finished surface of the angstrom order.

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[Procedure amendment]

[Submission date] January 10, 2002 (2002.1.1
0)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Heat treated diamond fine powder and method for producing the same

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Claims (10)

[Claims] 1. A powder comprising an aggregate of single crystalline submicron diamond particles having a heat-affected structure, wherein substantially all the diamond particles of the aggregate have a non-diamond structure carbon (hereinafter referred to as "non-diamond carbon"). "."). Heat treated diamond fines characterized in that they are separated from each other by a layer. 2. The heat-treated diamond fine powder according to claim 1, wherein the non-diamond carbon is present by being deposited on at least a part of the facing surfaces of adjacent diamond particles. 3. The heat-treated diamond fine powder according to claim 1, wherein the surface layer of the diamond particles is at least partially converted into non-diamond carbon. 4. The heat-treated diamond fine powder according to claim 1, wherein the total amount of the non-diamond carbon is 0.5% or more in a mass ratio with respect to the whole diamond powder. 5. A non-diamond structure carbon particle not originating from diamond is present between at least a part of adjacent particles of the aggregate of diamond particles, and the non-diamond structure carbon originating from diamond and the diamond originating from diamond. The heat-treated diamond fine powder according to claim 1, wherein the total amount of the non-diamond structure carbon and the non-diamond structure carbon is 1.0% or more in a mass ratio with respect to the entire diamond powder. 6. The heat-affected structure has cracks generated on the surface or inside of diamond particles, and / or the particles.
The heat-treated diamond fine powder according to claim 1, which is a deposit of non-diamond carbon generated by the conversion from the powder. 7. A powder comprising an aggregate of single crystalline submicron diamond particles is dipped in a solution or dispersion of a non-diamond structure carbon generator (hereinafter referred to as "carbon generator") to form at least a part of the powder. By attaching the carbon generator to the particle surface, and then heating the powder in an inert atmosphere at a treatment temperature, at the same time to non-diamond carbonize the surface of the diamond particles,
A method for producing fine diamond powder with improved separability, characterized in that non-diamond carbon is generated by decomposition of the above-mentioned carbon generator, and adjacent diamond particles are mutually separated by non-diamond carbon. 8. The method for producing fine diamond powder according to claim 7, wherein the carbon generator is a nonionic surfactant. 9. The carbon generator comprises at least one selected from organic water retention agents, gelatin, agar and starch.
The method for producing the fine diamond powder according to claim 7. 10. The method for producing fine diamond powder according to claim 7, wherein the treatment temperature is 800 ° C. or higher and 1400 ° C. or lower.