JP2004339412A - Submicron diamond powder for abrasive material and method for producing the same powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain single crystal-based submicron diamond abrasive material particles having extremely narrow particle size distribution by using single crystal-based synthetic diamond abrasive material particles enabling control of these physical properties as a starting material and carrying out superfine pulverization and precise classification of these particles to particle size of submicron (>1 μm). <P>SOLUTION: The method for producing submicron diamond fine powder for abrasive materials comprises isolating a diamond converted/prepared from non-diamond carbon under ultra-high pressure by static pressurizing method and further carrying out particle size control by combination of (1) ball mill grinding operation using a steel ball with (2) crude classification by hydraulic elutriation or centrifugal treatment and (3) precise classification by repeated centrifugal treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００４６】
上記結果に見られるように両サイズとも、Ｄ_５０値については粗分級品と精密分級品との間に実質的な差がないものの、精密分級を行なうことによってＤ_９０／Ｄ_１０については３．５９及び３．１６からそれぞれ３．０以下まで低下し、またピーク値フラクションの頻度は１５％以上となっており、粒度分布幅が狭くなっていることが認められる。なお粗分級から精製品への歩留りは６５％であった。
【００４７】
上記で得られた８０ｎｍ精密分級品のダイヤモンド粉末を、窒素雰囲気中で１０００℃に１２時間保持する加熱処理を施した。得られた加熱処理ダイヤモンドは、黒色を呈しており、硫酸−硝酸混液中で煮沸する湿式酸化処理による減量から、ダイヤモンドの表面に形成された非ダイヤモンドカーボン量は、４．５質量％と見積もられた。
【００４８】
このダイヤモンドを用いた３．５インチのアルミハードディスクのテクスチュアリング加工において、加工面の面粗さとして２．７Åの値が得られ、８０ＧＢの記録密度を目指した加工砥粒として用いうることが、確かめられた。
【００４９】
【発明の効果】本発明のダイヤモンド微粉は、静圧法で合成されたダイヤモンドの特徴である単結晶質を保持しながら、１００ｎｍ以下の粒度域において狭い粒度範囲を呈することから、精密研磨その他各種の精密用途に適する。[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to single-crystal diamond abrasive particles, particularly submicron diamond abrasive particles suitable for precision polishing of electronic materials such as texturing of hard disks and polishing of thin-film magnetic heads. It relates to a manufacturing method.
[0002]
2. Description of the Related Art In recent years, optical parts, electronic parts, precision mechanical parts, and the like have been required to have higher performance and higher functions, and the materials used are metallic materials, ceramics, glass, and the like. For plastics and a wide variety of other applications, the roughness indication on the finished surface is shifting from nanometers to Angstroms.
[0003]
For precision polishing of such parts, polycrystalline diamond is widely used. Polycrystalline diamond is synthesized by shock pressure using explosives from graphite as raw material.Since the synthesis reaction time is short, primary particles of several tens of nm in diameter are welded to form sub-micron or micron-order secondary particles. are doing. In addition, it has an excellent characteristic that a fine finished surface roughness can be obtained by reflecting the fineness of the primary particles while securing a polishing rate depending on the secondary particle size.
[0004]
However, in the case of polycrystalline diamond, since the synthesis reaction is a very short time pressurization and heating reaction on the order of microseconds, it is difficult to strictly control the size of the primary particles and the welding strength between the particles, and it is difficult to use abrasives. It is said that it is difficult to keep the physical property values in a narrow area.
[0005]
On the other hand, synthetic diamonds synthesized under static ultra-high pressure using a hydraulic press have a pressure and heating holding time on the order of minutes. Although it is easier than in the case, on the other hand, since these particles are generally obtained as single crystalline particles having a diameter of several tens to several hundreds of μm, in order to use them as abrasives for fine processing, these particles are used. There is a need to establish a technology for crushing, classifying and collecting to submicron size.
[0006]
SUMMARY OF THE INVENTION Accordingly, one of the main objects of the present invention is to use the above-mentioned monocrystalline synthetic diamond abrasive particles whose physical properties can be controlled as a starting material, and to use submicron (less than 1 μm) particles. The object of the present invention is to obtain single-crystal submicron diamond abrasive particles having an extremely narrow particle size distribution by subjecting them to ultrafine pulverization to a particle size and precision classification.
[0007]
Another object of the present invention is to provide abrasive particles which cover the surface of such diamond particles with non-diamond carbon converted from base diamond, thereby enabling a finer polished surface to be achieved in the polishing process. That is.
[0008]
In the present invention, in order to solve the problems], subjecting the single crystalline diamond particles to pulverization and classification steps, D ₅₀ average particle size (median) is at 500nm or less, and a particle size classification in showing the most frequently Submicron diamond abrasive particles are prepared, characterized in that the particles comprise more than 15% of the total. However, the particle size value is a dynamic light scattering particle size distribution analyzer having 44 channels, in which Microtrack UPA, the value of the second channel is 5.500 μm, and the particle size ratio between channels is the reciprocal of the square root of 2 Of the detection frequency for each size.
[0009]
In the present invention, essentially, a single crystal submicron diamond abrasive particle having a narrow particle size distribution is obtained by a combination of an impact crushing technique using a ball mill or the like and a repetitive classification technique using a centrifuge. In particular, a repetitive classification technique capable of effectively removing coarse components and fine components far away from the central particle size constitutes a main part of the present technology.
[0010]
It is recognized by SEM observation of the pulverized particles that the cleavage of cracks is dominant in the refinement of diamond. Therefore, it can be said that impact crushing of the prior art using steel balls is a preferable method for crushing in terms of both crushing efficiency and operation cost.
[0011]
In the pulverization process, the diamond crystal is cleaved and the parts with defects and foreign matter in the crystal are destroyed preferentially, and the foreign matter exposed on the fracture surface is removed in the purification process by chemical treatment in post-processing. As a result, the amount of defects and the content of impurities are reduced as the powder becomes finer or the particle size is reduced, so that the original characteristics of diamond can be obtained.
[0012]
In the present invention, a general elutriation technique utilizing a phenomenon in which the sedimentation speed of particles in water depends on the particle size is used in the step of classifying the fine diamond particles according to a predetermined size region, that is, the classification step. However, like other substances, the surface of diamond becomes active and becomes easily aggregated with the pulverization, so that the surface of the diamond particles is made hydrophilic prior to the elutriation step, and the dispersibility of the dispersion medium in water is increased. It is preferable to perform a pretreatment. As this pretreatment method, a surface oxidation treatment technique of Japanese Patent No. 2691884 can be exemplified.
[0013]
Elutriation is generally used in the classification of diamond powder as a technique suitable for sizing with a narrow particle size distribution width, but the sedimentation speed in water slows down as the particles to be classified become finer. The productivity decreases. That is, from the Stokes' rule, which is the basis of elutriation classification, the sedimentation rate of diamond particles at room temperature is 0.2 mm / h for particles having a particle size of 0.2 μm, and 0.11 mm / h for particles having a particle size of 0.15 μm. Calculated, which is already close to the limits of elutriation classification techniques.
[0014]
As a classifying method with high productivity, a technique of using a centrifugal separator to move particles by a large gravitational acceleration and recovering the particles in a slurry state or as a cake attached to the wall surface of a rotor is widely used.
[0015]
By the way, for use as a precision abrasive, it is required that the particles are separated with a difference of 0.1 μm or less, particularly a narrow particle size difference of 0.02 μm or less, as an average particle diameter (median value). The present inventors, as a method of achieving such a narrow particle size difference, in addition to making the slurry supplied to the centrifuge a dilute slurry having a small diamond content, the concentrated slurry collected by centrifugation or It has been found that it is very effective to disperse the cake again in a large amount of water to make a dilute slurry, supply it to a centrifugal separator, and repeatedly classify it. The present invention is based on such findings.
[0016]
In the classification operation, it is understood that it is important to ensure that as much of the fine diamond particles contained in the dispersion medium, especially water, as possible are dispersed in the form of single particles. Accordingly, the lower the concentration of diamond in the slurry, the better, but because of the balance with productivity, the trapping of an average particle diameter (median value) of 0.1 μm has a diamond concentration of 0.5% or less, especially 0.1 μm. It is preferably at most 2%.
[0017]
Although not essential, it is preferable to reduce the slurry concentration in the second and subsequent repeated centrifugations as compared to the first centrifugation. On the other hand, as for the operating conditions of the centrifuge, the same conditions as in the first operation can be used for the second time and thereafter.
[0018]
In the method of the present invention, the centrifugation operation basically collects particles (fraction) in a specific range including a target elutriation device or centrifugal separator and a target particle size, which essentially removes coarse particles. It is carried out in three types of equipment: a main centrifuge, and a device for collecting and processing a slurry containing fine particles coming out of the centrifuge without being collected by the main centrifuge.
[0019]
In the first centrifugation operation (hereinafter referred to as “coarse classification”), the concentrated slurry or cake collected by the centrifugal separator of the main body has a large amount of coarse particles and fine powder removed, but the coarse particles are removed. Generally, the particle size distribution width is wide because fine powder adheres or aggregation of fine powder is observed.
[0020]
Therefore, the collected product is poured into a large amount of water and sufficiently stirred to be essentially dispersed in primary particles, that is, in an aggregated state of individual particles or a very small number of particles, and centrifuged in the same manner as in the first coarse classification. By performing the separation operation (hereinafter referred to as "refining and classification"), it is possible to obtain a product having a narrower particle size distribution width from which coarse particles and fine powder components have been further removed. If the same operation is further added, the particle size distribution width can be narrowed. However, by repeating the operation, the collection amount of the product of the target size is sequentially reduced and the efficiency is reduced. Three times is the industrially practical number of repetitions.
[0021]
The effect of the repeated classification can be evaluated using the particle size distribution data. The particle size distribution data is obtained by integrating the number of particles present in the divided size region (range) as a (relative) frequency indicated as a ratio to the total number of measured particles, and a histogram aggregated for each size region and the frequency. A method of displaying a cumulative particle size distribution curve is widely used.
[0022]
The evaluation means of the particle size distribution, the figure representing the particle size distribution, the peak height, and a method of displaying a half-value width, and a method of using the ratio of the ₂₅ value and the D ₇₅ value D in a cumulative particle size distribution curve is there.
[0023]
According to the method of the present invention, narrow significantly the size range as compared with the prior art, i.e. near the size frequency value of the median or average particle diameter D ₅₀ is high, rapid frequency decreases the now spaced, as a whole A submicron diamond powder having a particle size configuration exhibiting a sharp mountain shape is obtained. Such properties are ensured even in _{D 50} average particle size 100nm or less diamond powder.
[0024]
The particle configuration and the particle size distribution characteristics of the diamond powder according to the present invention are as follows: the value of the second channel is 5.500 μm, and the particle size ratio between the channels is the reciprocal of the square root of 2; The display is defined by the size values and their ratios. Thus, in the case where the particles in the particle size division having the highest detection frequency account for 15% or more of the whole, the ratio of D ₉₀ / D ₁₀ read from the cumulative particle size distribution curve is 3.0 or less, particularly 2.5 or less. And a particle configuration with a narrow particle size distribution width is obtained, in which the ratio of D ₁₀ / D ₅₀ is larger than 0.6 and the ratio of D ₉₀ / D ₅₀ is 1.8 or less.
[0025]
The particle size measurement of the present invention is based on a laser diffraction scattering method, and the measurement is based on a particle size distribution measuring device UPA of Microtrac Co., Ltd. There is no difference.
[0026]
In the method of the present invention, submicron diamond powder is converted from non-diamond carbon under ultra-high pressure by a static pressurization method such as a hydraulic press or the like, and crushed into ultrafine powder of diamond converted, prepared and isolated, and special classification. The particle size is adjusted in combination with the operation. For the pulverization, a ball mill pulverization operation using a steel ball can be used, while precision classification involves first performing coarse classification by elutriation or centrifugation, and then subjecting to one or several repeated centrifugation processes. Perform precision classification.
[0027]
The centrifugal separation operation in the coarse classification and the fine classification can be configured in the following steps. That is, (1) preparing a first aqueous slurry containing diamond, (2) supplying the first slurry to a centrifugal separator and performing a centrifugation treatment, and (3) preparing a first aqueous slurry having an increased diamond content. (4) taking out the second slurry or cake in the same manner as the first slurry by repeating the steps (2) and (3) one or more times; and (5) And recovering the final slurry or cake having a further increased diamond content.
[0028]
In the above, since the diamond content is increased in the second slurry or cake taken out, when the slurry or cake is subjected to the next centrifugation operation, by diluting the slurry or cake, the particle size range is narrower. A slurry or cake having a particle configuration can be obtained.
[0029]
In the above, the diamond content of the first slurry is preferably 0.5% or less and 0.05% or more. If it is lower than this, the productivity decreases, and if it is too high, the proportion of aggregated particles increases.
[0030]
Before forming the first slurry, the diamond is subjected to a hydrophilic treatment in advance, and a hydrophilic atom such as oxygen, a hydroxyl group, a carboxyl group, a carbonyl group, or another hydrophilic atomic group or a hydrophilic group is formed on the diamond particle surface. Is formed, the state of dispersion in water is improved, so that efficient treatment can be performed.
[0031]
The above hydrophilic treatment can be achieved by heating in a strong acid or a wet oxidizing agent such as concentrated sulfuric acid, concentrated nitric acid, and perchloric acid. Such a process is described in, for example, JP-A-2001-329252.
[0032]
On the other hand, the diamond is subjected to a heat treatment at a temperature of 800 ° C. or more after the simple or repeated classification operation, whereby a part of the surface of the diamond particles is converted into non-diamond carbon such as graphite or a turbostratic structure or amorphous carbon to thereby form diamond. Coating the crystal body is also effective.
[0033]
That is, the presence of non-diamond carbon on the surface of the diamond particles suppresses the formation of a sharp cutting edge that causes deep scratches or piercing on the polished surface, and a high-quality polished surface can be expected.
[0034]
This effect can be explained as follows. That is, since the diamond fine powder of the present invention is crushed by an impact load, it mainly consists of fragments due to cleavage cracks, and the abrasive particles have sharp edges and sharp angles, and the surface of the abrasive particles is hard. Therefore, particularly when the work material is a soft material, polishing scratches (scratch) are liable to occur during the polishing process as it is, and as a result, it is difficult to obtain a good polished surface quality.
[0035]
At this time, if the diamond powder is heated at the above temperature after the classification process, a softer non-diamond carbon (NDC: especially graphite or turbostratic or amorphous carbon) phase integrated with the main body is formed on the surface of the diamond particles. Is done. In addition, since the NDC phase is preferentially generated at the highly reactive sharp tip or edge of the diamond particles, the heat-treated diamond particles have a rounded cutting edge and a large particle surface. The configuration in which the non-diamond carbon cushion layer is formed can be expected to avoid polishing scratches.
[0036]
The heat treatment is preferably performed at a temperature of 800 to 1400 ° C. At 800 ° C. or lower, the effect of the heat treatment, that is, the amount of non-diamond carbon formed on the surface of the diamond particle is hardly recognized, and the strength of the diamond particle itself is not changed. On the other hand, when the temperature exceeds 1400 ° C., the graphitization of diamond proceeds rapidly, so that it becomes difficult to control the reaction. A more preferred heat treatment temperature is 1100 to 1300 ° C.
[0037]
This heat treatment is performed at a processing temperature of 800 ° C. or more and 1400 ° C. or less. The amount of coating (precipitation) can be controlled depending on the processing time, but it is appropriate that the amount is 0.5% or more and 30% or less (mass reduction rate by an oxidizing agent elution method) in terms of% by weight based on the entire diamond particles. If it is less than this, the effect is not remarkable, and if it is too large, the cutting edge becomes dull and the sharpness decreases.
[0038]
The heat treatment time varies depending on the size of the furnace to be treated, but is preferably about 6 to 12 hours.
[0039]
Due to the above heat treatment, the diamond crystal generates fine cracks (cracks) due to the difference in the coefficient of thermal expansion with the contained metal impurities, thereby contributing to the improvement of the friability. This improvement in friability has been quantitatively evaluated for coarse diamond abrasive grains. In the present application, the generation of cracks and the conversion of diamond to non-diamond carbon are referred to as thermal effects on the diamond crystal structure.
[0040]
EXAMPLE 1 using the slurry excluding D ₅₀ average particle size (median) 150 nm or more coarse fractions by elutriation operation. Deionized water was added to adjust the diamond concentration in the slurry to 0.2% by mass, and the mixture was passed through a 12000 G first-stage centrifugal separator, and a fraction having a particle size of 100 nm was once collected as a coarse classified cake. The effluent exiting the first-stage centrifuge was sent to a 21000 G second-stage centrifuge connected in series, and separated into a coarsely classified cake for collecting 80 nm particles and an effluent.
[0041]
The coarsely classified cake collected by the first and second stage centrifuges is put into a raw material slurry tank for precision classification for collecting 100 nm and 80 nm particles, respectively, and deionized water is added to reduce the diamond concentration. The slurry was adjusted and sufficiently stirred to obtain a 0.1% slurry.
[0042]
In the precision classification of a product having a nominal particle size of 100 nm, the above slurry is passed through a 5000 G pre-stage centrifuge to remove mixed coarse powder components, and the effluent is led to a 12000 G post-centrifuge. , And separated into a cake and an effluent containing fine components.
[0043]
The same operation was performed for a product having a nominal particle size of 80 nm. However, in the pre-stage centrifugation operation, coarse particles were removed by passing through a 12000 G centrifuge, and then the cake and the effluent containing the fine powder component were separated by the 21000 G post-centrifuge.
[0044]
The characteristic values of the coarsely classified product and the finely classified product obtained by the above operations are summarized in the following table. The measurement was based on a particle size distribution analyzer of Microtrac UPA.
[0045]
[Table 1]

[0046]
Both the size as seen in the above results, although there is no substantial difference between the coarse fraction grade and precision classification items for D ₅₀ value, for D _{90 /} D ₁₀ by performing a precise classification 3. From 59 and 3.16, each decreased to 3.0 or less, and the frequency of the peak value fraction was 15% or more, indicating that the particle size distribution width was narrowed. The yield from coarse classification to refined product was 65%.
[0047]
The 80-nm precision-classified diamond powder obtained above was subjected to a heat treatment at 1000 ° C. for 12 hours in a nitrogen atmosphere. The obtained heat-treated diamond has a black color, and the amount of non-diamond carbon formed on the diamond surface is estimated to be 4.5% by mass from the weight loss due to the wet oxidation treatment in which the mixture is boiled in a mixed solution of sulfuric acid and nitric acid. Was done.
[0048]
In the texturing of a 3.5-inch aluminum hard disk using this diamond, a value of 2.7 ° was obtained as the surface roughness of the processed surface, and it can be used as a processing abrasive aiming at a recording density of 80 GB. I was assured.
[0049]
The fine diamond powder of the present invention exhibits a narrow particle size range in a particle size range of 100 nm or less while retaining the single crystal characteristic of diamond synthesized by the static pressure method, so that it can be used for precision polishing and other various processes. Suitable for precision applications.

Claims (17)

In the monocrystalline diamond particles prepared through the pulverization / classification process, the particle size distribution histogram of the detection frequency by size by Microtrac UPA (the value of the second channel is 5.500 μm, and the particle size ratio between channels is 2-4) the reciprocal of the root, in the channel number 44 dynamic light scattering centrifugal particle size distribution measuring machine), D ₅₀ average particle size (median) is at 500nm or less, and a particle size within the segment that shows the most frequent particle total of Submicron diamond fine powder for abrasives, characterized in that it accounts for 15% or more. The _{D 50} average particle size is 100nm or less, the diamond powder according to claim 2. The single-crystal submicron diamond fine powder according to claim 1, wherein a particle size fraction exhibiting a maximum detection frequency in the histogram is 15% or more of the whole. In the particle size histogram, _further, the ratio of D 90 _{/ D 10} of 3.0 or less, minute diamond powder of claim 1. The ratio of the _D 90 _{/ D 10} is 2.5 or less, minute diamond powder of claim 4. In the histogram, _further, the ratio of D 10 _{/ D 50} is greater than 0.6, minute diamond powder of claim 1. In the particle size distribution histogram, _further, the ratio of D 90 _{/ D 50} is 1.8 or less, minute diamond powder of claim 1. 2. The diamond fine powder according to claim 1, wherein the surface of the single-crystal diamond particles has a heat-affected structure by a heat treatment and is coated with non-diamond carbon in a mass ratio of 0.5% or more to the entire diamond particles. . 9. The fine diamond powder according to claim 8, wherein the non-diamond carbon is graphite, a turbostratic structure or amorphous carbon. 2. The fine diamond powder according to claim 1, wherein a ratio of the non-diamond carbon to the whole diamond particles is 30% or less in a mass reduction rate by an oxidizing agent elution method. The diamond fine powder according to claim 8, wherein the diamond particles include cracks as an effect of the heat treatment. The diamond converted and prepared from non-diamond carbon under ultra-high pressure by the static pressurization method is isolated, and further (1) ball mill pulverizing operation using steel balls, (2) coarse classification by elutriation or centrifugation, and (3) The method for producing fine diamond powder according to claim 1, wherein the particle size is adjusted by a combination of precise classification by repeated centrifugation. The method for producing a diamond fine powder according to claim 12, wherein the centrifugation operation is constituted by the following steps:
(1) preparing a first aqueous slurry containing diamond;
(2) supplying the first slurry to a centrifuge to perform a centrifugation process;
(3) removing as a second slurry or cake having an increased diamond content;
(4) The second slurry or cake is subjected to the steps (2) and (3) one or more times in the same manner as the first slurry, and (5) the final slurry having a further increased diamond content. Or to collect as cake. The method for producing a diamond fine powder according to claim 12, wherein the centrifugation operation is constituted by the following steps:
(1) preparing a first aqueous slurry containing diamond;
(2) supplying the first slurry to a centrifuge to perform a centrifugation process;
(3) removing as a second slurry or cake having an increased diamond content;
(4) diluting the second slurry or cake with water to prepare a third slurry;
(5) Repeating the steps (2) and (3) one or more times in the same manner as the first slurry, and (6) as the final slurry or cake having a further increased diamond content. To collect. The method for producing fine diamond powder according to any one of claims 13 and 14, wherein the diamond content of the first slurry is 0.5% or less. 15. The method for producing fine diamond powder according to claim 13, wherein before forming the first slurry, diamond is subjected to a hydrophilic treatment in advance to form a hydrophilic group on the surface of diamond particles. The method for producing fine diamond powder according to claim 12, wherein the diamond is subjected to a heat treatment temperature of 800C to 1400C after repeated classification.