Title:
Fixed abrasive grinding/polishing tool
Kind Code:
A1


Abstract:
A fixed abrasive grinding/polishing tool containing cerium oxide particles each being in the plate shape and having an average particle size in an in-plane direction of the plate-form particles of 10 nm to 200 nm, which are bonded together with a water-soluble polymer.



Inventors:
Kishimoto, Mikio (Osaka, JP)
Oshita, Tadashi (Osaka, JP)
Ikeno, Junichi (Saitama-shi, JP)
Application Number:
11/065452
Publication Date:
10/20/2005
Filing Date:
02/25/2005
Assignee:
HITACHI MAXELL, LTD.;
Junichi IKENO
Primary Class:
International Classes:
B24D3/00; B24B1/00; B24D3/20; B24D3/32; B24D11/00; C09K3/14; (IPC1-7): B24B1/00
View Patent Images:



Primary Examiner:
MICALI, JOSEPH
Attorney, Agent or Firm:
BIRCH, STEWART, KOLASCH & BIRCH, LLP (FALLS CHURCH, VA, US)
Claims:
1. A fixed abrasive grinding/polishing tool for grinding or polishing a substrate, wherein said tool comprises cerium oxide particles having an average particle size of 10 nm to 200 nm and a binder comprising a water-soluble polymer.

2. The fixed abrasive grinding/polishing tool according to claim 1, wherein each of the cerium oxide particles in plate form and a ratio of the maximum length in the in-plane direction of the plate-form particle to a thickness thereof is from 2 to 20.

3. The fixed abrasive grinding/polishing tool according to claim 1, comprising said cerium oxide particles as a main component and further comprising additional oxide particles which are at least one selected from the group consisting of zirconium oxide particles, aluminum oxide particles and iron oxide particles.

4. The fixed abrasive grinding/polishing tool according to claim 3, wherein said additional oxide particles have an average particle size of 10 nm to 200 nm.

5. The fixed abrasive grinding/polishing tool according to claim 3, wherein said additional oxide particles are in the plate form and have a ratio of the maximum length in the in-plane direction of the plate-form particle thereof to a thickness thereof of from 2 to 20.

6. The fixed abrasive grinding/polishing tool according to claim 3, wherein a content of the additional oxide particles is from 1 to 50% by weight relative to a weight of the cerium oxide particles.

7. The fixed abrasive grinding/polishing tool according to claim 1, wherein a content of the water-soluble polymer is from 0.5 to 30% by weight and a content of the cerium oxide particles is from 50 to 99% by weight based on the total weight of the particles and binder.

8. The fixed abrasive grinding/polishing tool according to claim 1, wherein the binder further comprises an organic solvent soluble polymer.

9. The fixed abrasive grinding/polishing tool according to claim 1, wherein the cerium oxide particles have a narrow particle size distribution.

10. The fixed abrasive grinding/polishing tool according to claim 3, wherein the zirconium oxide particles, aluminum oxide particles and/or the iron oxide particles have a narrow particle size distribution.

11. The fixed abrasive grinding/polishing tool according to claim 1, wherein the water-soluble polymer is a metal alginate.

12. The fixed abrasive grinding/polishing tool according to claim 11, wherein the metal is an alkali or alkaline earth metal.

13. A method of producing a fixed abrasive grinding/polishing tool, comprising a step of combining cerium oxide particles having an average particle size of 10 nm to 200 nm with a binder comprising a water-soluble polymer.

14. The method according to claim 13, further comprising: dissolving the water-soluble polymer with a solvent to form a solution, dispersing the cerium oxide particles each being in the shape of a plate into said solution into which the water-soluble polymer is dissolved to form a dispersion, forming said dispersion into a specific shape to form an intermediate product so that said plate-shaped cerium oxide particles are aligned substantially in a specific direction.

15. The method according to claim 13, further comprising: combining additional oxide particles which are at least one selected from the group consisting of zirconium oxide particles, aluminum oxide particles and iron oxide particle, each being in the shape of a plate, with the cerium oxide particles.

16. The method according to claim 14, further comprising: removing solvent in the dispersion to increase the concentration of binder and particles in the dispersion, aligning the orientation of the particles using electrophoresis.

17. The method according to claim 15, further comprising: dissolving the water-soluble polymer with a solvent to form a solution, dispersing the cerium oxide particles and the additional oxide particles each being in the shape of a plate into said solution into which the water-soluble polymer is dissolved to form a dispersion, forming said dispersion into a specific shape to form an intermediate product so that said plate-shaped oxide particles are aligned substantially in a specific direction, removing solvent in the dispersion to increase the concentration of binder and particles in the dispersion, aligning the orientation of the particles using electrophoresis.

18. The method according to claim 13, wherein the water-soluble binder comprises a metal alginate.

19. The method according to claim 18, wherein the metal is an alkali or alkaline earth metal.

20. A method of increasing the smoothness of a surface of a substrate, comprising contacting the fixed abrasive grinding/polishing tool according to claim 1 with the surface of the substrate to smoothen said surface.

21. The method according to claim 20, wherein the substrate is silica.

22. A product made by a process comprising contacting the fixed abrasive grinding/polishing tool according to claim 1 with a surface of the product to smoothen said surface.

23. The product according to claim 22, wherein the smoothened surface of the product is made of silica.

Description:

This application claims priority to Japanese Patent Application No. 2004-108946, which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fixed abrasive grinding/polishing tool for grinding or polishing a workpiece, and particularly, to a fixed abrasive grinding/polishing tool using cerium oxide particles as main abrasive grains.

2. Description of the Background Art

It is increasingly desired to decrease the thickness of a silicon wafer, and various methods are proposed to this end. A grinding stone using diamond abrasive grains is commonly used because of its high grinding efficiency, but grinding marks remain on a workpiece after grinding and it is necessary to carry out mirror polishing with a different grinding means using slurry abrasive grains to remove the grinding marks. That is, totally different methods should be used to perform grinding, which makes the grinding process complicated. As a result, the grinding efficiency is reduced and thus grinding costs increase.

In the grinding method using slurry abrasive grains, good surface smoothness is obtained after grinding, but grinding speed is low and thus grinding efficiency is low.

In decreasing the thickness of a quartz crystal wafer, a slurry containing cerium oxide particles having a particle size of about 1 μm dispersed therein is used. However, further improvement of the grinding efficiency is required. In this connection, it may be a great problem from the environmental view to treat a great amount of the waste slurry discharged in the polishing process.

Despite the demand for the further improvements in grinding efficiency, currently, any fixed abrasive grinding/polishing tool meeting the needs in the market has not been developed because of the problem arising from the fact that the surface smoothness is decreased after grinding as a grinding efficiency is increased.

JP-A-2003-73656 discloses active abrasive grains and a grinding stone or the like comprising the same capable of grinding a workpiece by a mechanochemical action. The abrasive grains and the grinding stone have been developed by one of the present inventors, and the grinding stone is produced by mixing glass beads and a water-soluble polymer binder such as sodium alginate and processing the obtained mixture to a desired state using electrophoresis. JP-A-2003-73656 also describes that the active abrasive grains constituting the grinding stone exhibit an excellent grinding ability by the mechanochemical action and, an excellent mirror surface can be formed although the grinding method using the grinding stone exerts grinding rather than polishing.

Furthermore, JP-A-2003-049158 and JP-A-2003-206475 disclose cerium oxide particles each of which has a plate form and an average particle size of 10 to 200 nm in the direction of the plate plane. The description of how to make the cerium oxide particles as both generically and specifically taught in these references is herein incorporated by reference.

The conventional fixed abrasive grinding/polishing tools, as described above, generally have a problem that the tools easily cause marks on the surface of a workpiece despite the high grinding efficiency exhibited by the tools, which leads to poor smoothness on the ground surface. On the other hand, the slurry abrasive grain used in a wet method has a defect that the slurry has low and inferior grinding efficiency although it can easily form the smoothly ground surface. In the current state of the art, there has not yet been provided any fixed abrasive grinding/polishing tool that has an excellent grinding ability and can achieve excellent surface smoothness on the workpiece after grinding.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a fixed abrasive grinding/polishing tool capable of realizing excellent surface smoothness after grinding, which has never been obtained with a conventional grinding stone, while maintaining the excellent grinding ability of grinding stones by employing cerium oxide particles having specific particle shapes and specific particle sizes as abrasive grains and binding the cerium oxide particles with a water-soluble polymer.

According to the present invention, it has been found that an excellent grinding performance, which has never been obtained with the conventional tool of this kind, can be achieved by employing the cerium oxide particles having a plate-shape and an average particle size of 10 to 200 nm in the direction of a plate plane as abrasive grains in a fixed abrasive grinding/polishing tool. Preferably the average particle size of the cerium oxide particles is from 20 to 180 nm, more preferably from 40 to 160 nm. Such cerium particles are described in JP-A-2003-049158 and JP-A-2003-206475.

That is, usually, as the particle sizes of abrasive grains are smaller, the smoothness of a ground surface is usually better, but the grinding efficiency is lower. On the contrary, the abrasive grains of the present invention are fine particles and have an average particle size of 10 to 200 nm, and when the particles are plate shaped, they exhibit an excellent grinding ability by using the edges of the plate-form particles, although the particles are fine particles. In this way, the present inventors, for the first time, have succeeded in rendering two seemingly contradictory characteristics of a grinding stone, that is, both a high grinding efficiency and excellent surface smoothness after grinding can be obtained together by employing the cerium oxide particles having a specific shape and specific particle sizes.

Cerium oxide particles each having a plate shape, which are employed in the present invention, are characterized in that they not only exhibit an especially excellent grinding action with using their edges, but also show a large chemical grinding action. The present invention, for the first time, achieves simultaneously the excellent mechanical grinding ability with using their edges and the excellent chemical grinding ability owned by cerium oxide.

In the fixed abrasive grinding/polishing tool of the present invention, the cerium oxide particles further comprise other particles formed of at least one oxide selected from the group consisting of aluminum oxide, zirconium oxide and iron oxide, wherein the cerium oxide particles remain as the main component according to a kind of a workpiece to be ground or polished, grinding conditions, etc. The use of the additional oxide in the particles can improve the grinding ability of the tool in comparison with the tool using only the cerium oxide particles each of the present invention, since the mechanical grinding ability of the additional oxide particles is added.

For example, the fixed abrasive grinding/polishing tool of the present invention may be produced as follows:

The particles of the oxides each having a plate shape as the abrasive grains are dispersed in the solution of a water-soluble polymer such as sodium alginate so that the abrasive grains are bonded together with the water-soluble polymer. Then, water is removed from the dispersion, and the residual bound abrasive grains are shaped in the specific form of the tool. When the tool of the specific shape is shaped using an electrophoresis phenomenon, the plate-shaped particles are orientated in a specific direction so that their edges align well, and they are easily closely packed. Therefore, the fixed abrasive grinding/polishing tool can exert better performance.

Accordingly, the fixed abrasive grinding/polishing tool of the present invention is used as a grinding stone and can realize the excellent grinding efficiency and surface smoothness simultaneously. In addition, the fixed abrasive grinding/polishing tool of the present invention can also be used in the presence of water like the conventional slurry abrasive grains. In this case, the chemical polishing action of cerium oxide is enhanced by the presence of water. When water is used, even a trace of water has a great effect and an amount of water can be adjusted arbitrarily depending on an application or a purpose of the use. The fixed abrasive grinding/polishing tool of the present invention can be used either as a grinding stone or in the presence of water, which enables the fixed abrasive grinding/polishing tool to be a tool used in a wide variety of applications.

While the advantages of the use of the plate-form cerium oxide particles have been mainly explained in the above description, the use of cerium oxide particles each having a plate shape exerts the mechanical grinding ability induced by the edges of the particles as described above. Furthermore, with a construction in which the cerium oxide particles having an average particle size of 10 nm to 200 nm of the present invention are bound together with the water-soluble polymer, the inherent chemical grinding ability induced by the fine particles is emphasized to exert the excellent grinding and polishing properties, which have never been achieved with the conventional fixed abrasive grinding/polishing tools. Therefore, the fixed abrasive grinding/polishing tool of the present invention is not limited to the use of the plate-form cerium oxide particles, but the important characteristics of the present invention resides in that cerium oxide particles having an average particle size of 10 nm to 200 nm are bound together with a water-soluble polymer.

In the case of the fixed abrasive grinding/polishing tool of the present invention, the cerium oxide particles as constituent particles not only exert an excellent mechanical grinding ability when the edges of the particles are effectively used, but also exert an excellent chemical grinding ability based on the chemical characteristic thereof. Since the particle size is small and from 10 to 200 nm, excellent surface smoothness is obtained after grinding of a workpiece. Accordingly, the present invention can provide a grinding stone which is excellent in grinding efficiency and also in surface smoothness after grinding simultaneously. Here, the term “plate-shape” or “plate-form” means that a ratio of the maximum length in the in-plane direction of the plate-form particle to the thickness thereof is from 2 to 20. Preferably the ratio is from 3 to 18, more from 5 to 15. A particle diameter or size herein used is an average of the diameters of 100 particles the photograph of which is taken with a high resolution transmission electron microscope. The thickness thereof is measured by dispersing particles in a binder, coating the dispersion on a sheet and then observing the sections thereof with a high resolution transmission electron microscope.

When the cerium oxide particles are used as main particles and the additional plate-form particles of a specific oxide such as aluminum oxide are simultaneously used in an adequate amount, the grinding properties can enhanced as compared with a case where only the plate-form cerium oxide particles are used because of the mechanical grinding ability of the additional oxide particles.

In addition, in the fabrication of the grinding stone as described above, there can be obtained a fixed abrasive grinding/polishing tool exerting the excellent grinding ability by the use of an electrophoresis phenomenon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transmission electron microphotograph of cerium oxide particles prepared in Example 1 (magnification of 2×105);

FIG. 2 is an X-ray diffraction pattern of cerium oxide prepared in Example 1; and

FIG. 3 is a transmission electron microphotograph of cerium oxide particles obtained in Example 2 (magnification of 2×105).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fixed abrasive grinding/polishing tool of the present invention uses cerium oxide particles developed independently as described above, that is, cerium oxide particles each having a plate shape and an average particle size of 10 to 200 nm, which are bonded together with a water-soluble polymer. Thus, the fixed abrasive grinding/polishing tool of the present invention simultaneously realizes a high grinding efficiency and an excellent surface smoothness of a workpiece to be ground or polished.

The cerium oxide particles each having a peculiar shape and a specific particle size used in the present invention may be produced as follows:

The aqueous solution of a cerium salt is added to an alkali aqueous solution, the obtained hydroxide or hydrate of cerium is heated in a first temperature range of 110 to 300° C. in the presence of water, followed by filtration and drying. The first temperature range is preferably from 120 to 250° C., more preferably from 130 to 200° C. This is followed by a heat treatment in a second temperature range of 200 to 1500° C. in the air. The second temperature range is preferably from 300 to 1200° C., more preferably from 400 to 1000° C.

Specifically, in the first step, the desired shapes and sizes of particles are obtained in a hydrothermal reaction treatment, in which the hydroxide or the hydrate, which has been obtained by adding the aqueous solution of the metal salt to the alkali aqueous solution, is heated in a temperature range of 110 to 300° C.

In this step, since a pH value at which the hydroxide or the hydrate are precipitated is different according to a kind of a metal, pH control is of importance. For example, since aluminum hydroxide or hydrate is dissolved and not precipitated in either an acidic or alkaline pH range, a pH value should be controlled in a neutral range. Since cerium hydroxide or hydrate is dissolved and not precipitated in a neutral region, a pH value should be controlled in the alkaline range. In order to obtain a hydroxide or a hydrate each particle of which is in a desired shape and particle size by the hydrothermal reaction, a pH control is an important factor in this reaction.

Then, in the second step, the hydroxide or the hydrate is heated in the air to obtain plate-form cerium oxide particles having an average particle size of 10 nm to 200 nm and a uniform particle size distribution. The resulting cerium oxide particles hardly suffer from sintering or agglomeration and have good crystallinity.

By employing the production method comprising the above two steps, the plate-form cerium oxide particles having an average particle size of 10 nm to 200 nm, which has been unable to obtain according to the conventional production methods, The fixed abrasive grinding/polishing tool of the present invention is fabricated as follows:

The cerium oxide particles obtained as described above are dispersed in the solution of a water-soluble polymer, and the plate-form cerium oxide particles are bonded together with the water-soluble polymer. Since the fixed abrasive grinding/polishing tool of the present invention uses a water-soluble polymer as a binder, it has an advantage that the environmental burden is small in the manufacturing process. Also, the water soluble binder is preferred over non-water soluble binders, since the substrate is preferably washed with water as the substrate is being smoothed. By using a water soluble binder, the binder slowly dissolves, leaving more cerium oxide exposed to the substrate. Also, by using a water soluble binder, the binder that scuffs off the tool during polishing is dissolved and is therefore easily handled.

Lastly, the water soluble binder is preferred to comprise a polymer having ionic character along the length of the polymer (i.e., ionic groups are part of the backbone and/or pendant groups). By having this ionic character, cerium oxide particles bound by the polymer can be physically attracted to an electrode having an opposite charge to the charge of the polymer using electrophoresis, which will be described, infra.

The kind of the water-soluble polymer is not limited. Preferred examples of the water-soluble polymer include a metal alginate, wherein the metal can be at least one of Na, K and NH3, polyvinyl alcohol, etc. Among them, sodium alginate is a material contained in seaweeds and thus is particularly preferable as a harmless polymer binder having ionic character along the length of the polymer.

However, a binder may not be specifically limited to a water-soluble polymer in the fabrication of the grinding stone according to the present invention. Needless to say, various kinds of polymer binders to be dissolved in an organic solvent may be used in combination with the water-soluble polymer. For example, polymer binders such as vinyl chloride polymers, polyurethanes, acrylic polymers, urethane polymers, and nitrocellulose may be used.

The cerium oxide particles used in the present invention are characterized in that they have an excellent mechanical grinding action and also a chemical polishing action. Furthermore, the fixed abrasive grinding/polishing tool of the present invention can have further improved mechanical grinding ability, when the additional plate-form particles of a metal oxide such as at least one of aluminum oxide, zirconium oxide or iron oxide are used together with the cerium oxide particles.

More concretely, the fixed abrasive grinding/polishing tool of the present invention can be fabricated as described below:

Firstly, a solution in which the prescribed amount of the water-soluble polymer is dissolved is prepared, and the prescribed amount of the plate-form oxide particles are dispersed in the solution. No specific limitation is imposed on a dispersing method, and a uniform dispersion is prepared using any of a ball mill, a paint conditioner, etc.

The content of the water-soluble polymer in the fixed abrasive grinding/polishing tool is preferably from 0.5 to 30% by weight, more preferably from 1 to 25% by weight and particularly preferably from 2 to 20% by weight, based on the total weight of oxide particles and binder. When the content of the water-soluble polymer is low, the plate-form particles are weakly bonded, and the particles easily drop during grinding. On the other hand, when the content of the water-soluble polymer is excessively high, the viscosity of a dispersion is high and it is difficult to uniformly disperse the particles.

The content of all of the oxide particles is preferably from 50 to 99% by weight, more preferably from 60 to 97% by weight and particularly preferably from 75 to 95% by weight based on the total weight of oxide particles and binder. When the content of the oxide particles is less than the above range, the grinding efficiency is unsatisfactory. When this content is excessively high, the bonding of the particles with the polymer deteriorates, and thus the particles easily drop off.

The content of cerium oxide particles is preferably not less than 50% by weight of all of oxide particles. When the content is less than 50% by weight, mechanochemical efficiency is unsatisfactory.

The dispersion obtained as described above can also be used as slurry abrasive grains. Preferably the dispersion is shaped in a specific form using the electrophoresis phenomenon. No specific limitation is placed on the electrophoresis method. For example, an apparatus can be used, in which a cylindrical positive electrode rod is placed at the center of an electrophoresis bath and a negative electrode is installed so as to surround the positive electrode. That is, the dispersion is charged in the electrophoresis bath and a voltage is applied between the positive electrode and the negative electrode while rotating the positive electrode rod. Thereby, the plate-form cerium oxide particles which are covered with the water-soluble polymer are adsorbed and deposited on the peripheral surface of the positive electrode rod.

The orientation of the particles will now be discussed. The plate-form oxide particles of the present invention have a characteristic such that when the particles are adsorbed and deposited using the electrophoresis, the plate-form particles align on the positive electrode rod with the planes of the particles being substantially aligned in a specific direction, i.e., substantially in parallel with each other. In other words, it is preferred that the particles are not randomly oriented.

With such an alignment, since the edge faces of the plate-form particles align in a specific direction, the fixed abrasive grinding/polishing tool thus prepared exhibits improved grinding efficiency in practical use by edge-on grinding. However, it should be noted that the inventive fixed abrasive grinding/polishing tool can also be used to smooth the surface of the substrate when the particles are randomly oriented.

In another embodiment of the invention, the fixed abrasive grinding/polishing tool includes at least one other particle in addition to cerium oxide particles wherein said at least one other particle is selected from the group consisting of aluminum oxide, zirconium oxide and iron oxide. The additional aluminum oxide particles and/or zirconium oxide particles can be in the same plate-shape and having the same average particle size range and thickness range as that described herein for cerium oxide, and wherein these particles are preferably oriented in a similar fashion to the cerium oxide particles for edge-on grinding.

Once the plate-form cerium oxide particles which are covered with the water-soluble polymer are adsorbed and deposited on the peripheral surface of the positive electrode rod, the positive electrode rod is pulled out from the dispersion and then removed from the intermediate product consisting of the plate-form oxide particles bound with the water-soluble polymer to obtain the intermediate product in the prescribed shape. In this example, the intermediate product is deposited on the outer surface of the positive electrode rod. Therefore, the substantially cylindrical form intermediate product corresponding to the shape of the positive electrode rod is produced. The intermediate product is cut to pieces with an arbitrary size and dried in the air to obtain the fixed abrasive grinding/polishing tool of the present invention.

In the above example, a cylindrical intermediate product is fabricated using the electrophoresis phenomenon. Needless to say, by changing the shape of the positive electrode or the intermediate product, a grinding stone having an adequate shape such as a disk, prism or others and an adequate size may be fabricated. Furthermore, in order to obtain a closely packed grinding stone from the plate-form oxide particles, the electrophoresis phenomenon is one of useful methods, while for example, simple press molding can also fabricate a grinding stone without using the electrophoresis phenomenon. A fabricating method using the press molding only has an advantage in simplicity and ease of the fabrication process.

The fixed abrasive grinding/polishing tool of the present invention can achieve the excellent grinding efficiency and the surface smoothness at the same time when it is used as a grinding stone. Furthermore, the tool of the present invention can also be used in the presence of water. In this case, the amount of water is adjusted so that the chemical polishing action of cerium oxide is realized in the presence of water. Accordingly, the fixed abrasive polishing tool of the present invention can be used as a grinding stone or in the presence of water depending on an application and a purpose thereof. That is, the fixed abrasive grinding/polishing tool is a fixed abrasive grinding/polishing tool which can be used in a wide variety of applications.

When the cerium oxide particles according to the present invention are used, the mechanical grinding ability are exerted using the edges of the particles having the plate shape. However, only with a construction in which the cerium oxide particles having an average particle size of 10 nm to 200 nm of the present invention are bound together with the water-soluble polymer, the chemical grinding ability is enhanced because of the small particle size, so that the excellent grinding/polishing ability, which has never been achieved by the conventional fixed abrasive grinding/polishing tool, is exerted.

The important steps of the production method of the present invention will be explained further in detail.

Preparation of Plate-Form Cerium Oxide Particles, etc.

(Preparation of Precipitates)

A cerium salt such as cerium chloride, cerium nitrate, cerium sulfate or the like is dissolved in water to obtain an aqueous solution containing cerium ions (an aqueous cerium salt solution). Among the cerium salts, cerium chloride is most preferable, since cerium oxide particles with a narrow particle size distribution can be obtained. As an alkali, an aqueous solution of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia or the like is preferably used.

The aqueous cerium salt solution is drop wise added to the alkali aqueous solution to precipitate the hydroxide or hydrate of cerium. The pH value of the suspension containing the precipitate is adjusted in a range of from 8 to 11, and the suspension is preferably aged at room temperature for about one day. The pH value adjustment and aging are effective for obtaining cerium oxide particles with a higher crystallinity in the subsequent heat treatment at a relatively low temperature.

(Hydrothermal Treatment)

The suspension containing the precipitate of the hydroxide or hydrate of cerium is subjected to a hydrothermal treatment using an autoclave, etc., In the hydrothermal treatment, while the suspension containing the precipitate as such may be directly subjected to the hydrothermal treatment, preferably by-products and/or residues other than the precipitate are removed by washing with water and then the pH value is adjusted again with sodium hydroxide, etc. The pH value at this time is preferably from 7 to 11. When pH is lower than 7, crystals may insufficiently grow in the hydrothermal treatment. When it exceeds 11, the particle size distribution is broadened and it is difficult to obtain the designed particles with a small particle size.

A temperature in the hydrothermal treatment is preferably from 110° C. to 300° C. When the temperature is lower than 110° C., a hydroxide or a hydrate of cerium having a plate shape is hardly obtained. When it exceeds 300° C., an apparatus used for the hydrothermal treatment is expensive since it should withstand a high pressure generated at such a high temperature.

A time for the hydrothermal treatment is preferably from 1 hour to 4 hours. If the hydrothermal treatment time is very short, growth of particles with a specific shape is insufficient. When it is very long, a production cost increases without any merit.

(Heat Treatment)

After the hydrothermal treatment, the particles of cerium hydroxide or hydrate are filtered and dried and then subjected to a heat treatment. Prior to filtration, the pH value is preferably adjusted in a neutral range of from 6 to 9 by washing with water. When the particles are washed with water, impurities which have an adverse influence such as sintering in the heat treatment, for example, sodium, chlorine and the like are removed.

The particles are preferably treated with silica by further adding a silicon compound such as sodium silicate to the particles of cerium hydroxide or hydrate. The silica treatment is effective for maintaining the specific shape of the cerium oxide particles which are the final desired products.

After filtration and drying, the particles of cerium hydroxide or hydrate can be heat treated to form cerium oxide particles. No specific limitation is placed on an atmosphere in the heat treatment. Preferably, the heat treatment is carried out in the air since the production cost can be made lowest. The heat treatment temperature is preferably from 300° C. to 1200° C. When the temperature is lower than 300° C., crystalline cerium oxide particles are hardly obtained. When it exceeds 1200° C., particle sizes grow larger by sintering or a particle size distribution is broadened. While the cerium oxide particles are obtained by the heat treatment, the cerium oxide particles with higher purity are obtained if unreacted materials are removed by washing with water. Therefore, the cerium oxide particles are preferably washed with water in the final step for use as an abrasive.

The cerium oxide particles obtained are particles having an average particle size of 10 nm to 200 nm and each having a plate shape and thus the optimal particles for use in the fixed abrasive grinding/polishing tool.

In an embodiment of the invention, the cerium oxide particles have a narrow particle size distribution. Preferably, 50% of the particles have an average particle size which is within ±50% of the mean average particle size. More preferably, 60% of the particles have an average particle size which is within ±50% of the mean average particle size. Most preferably, 70% of the particles have an average particle size which is within ±50% of the mean average particle size.

In the X-ray diffraction of the cerium oxide particles according to the present invention, peaks corresponding to the crystalline structure of CeO2 having the CaF2 (fluorite) structure are clearly observed. Furthermore, crystal boundaries are clearly observed with an electron microscope, which means that the particles are plate-form particles having an extremely good crystallinity, which has never been obtained according to the conventional method.

The above description relates to the preparation of the plate-form cerium oxide particles. However, plate-form particles of aluminum oxide, zirconium oxide and iron oxide can also be prepared by a method analogous to the above-described method (see JP-A-2003-049158 and JP-A-2003-206475).

Preparation of Dispersion for Fixed Abrasive Grinding/Polishing Tool:

Hereinafter, one example of the preparing method of a dispersion for fabricating a fixed abrasive grinding/polishing tool will be explained using the cerium oxide particles prepared by the above method according to the present invention.

Sodium alginate is dissolved in a prescribed amount of water. The amount of sodium alginate is preferably from 0.1 to 2% by weight based on the amount of water. When the amount of sodium alginate is less than 0.1% by weight, it is difficult to disperse cerium oxide particles uniformly in water and the cerium oxide particles easily settle. When the amount of sodium alginate exceeds 2% by weight, the viscosity increases, and the dispersibility of the cerium oxide particle worsens.

Then, the cerium oxide particles are added to and dispersed in the aqueous solution of sodium alginate. The amount of cerium oxide particles to be added is preferably from 1 to 20% by weight based on the prescribed amount of water. When the amount of the cerium oxide particles is less than 1% by weight, a high grinding efficiency as the fixed abrasive grinding/polishing tool may hardly be obtained. When the amount of the cerium oxide particles exceeds 20% by weight, the cerium oxide particles are hardly be dispersed uniformly and thus a uniform dispersion may not be obtained.

No specific limitation is placed on a dispersing method, and various dispersing apparatuses such as a ball mill, a paint conditioner, a disper and the like can be used. Among them, a paint conditioner is preferable. A dispersing time may depend on a dispersing machine. For example, when a paint conditioner is used, a dispersion time is preferably from 1 to 10 hours.

Then, the dispersion in a container is placed on a hot plate and heated while stirring to evaporate water and to concentrate the dispersion. A weight after the evaporation and concentration is preferably from a half to one tenth of the weight of the dispersion prior to the evaporation of water. When the concentration is less than the range, the filling property of the cerium oxide particles may be low in the fabrication of an intermediate product using an electrophoresis phenomenon described later or the cerium oxide particles in the dispersion tend to settle. When the concentration exceeds the range, the transfer of the cerium oxide particles by the electrophoresis phenomenon is difficult, and thus the productivity of the intermediate product decreases.

When the contents of sodium alginate and cerium oxide particles in the dispersion after evaporation and concentration are adjusted in a range of from 0.2 to 5% by weight and of 2 to 60% by weight, respectively, based on the total weight of the dispersion, the efficiency in the production of the intermediate product using the electrophoresis phenomenon is greatly increased, and the fixed abrasive grinding/polishing tool fabricated using the intermediate product has the excellent balance between the grinding ability and the retention of the cerium oxide particles in the tools.

Fabrication of Intermediate Product from Cerium Oxide and Water-Soluble Polymer Mixture Using Electrophoresis:

The dispersion obtained by evaporation and concentration as described above is charged in a glass beaker. A metal positive electrode rod is inserted in the dispersion, and a metal negative electrode is positioned so that it spirally surrounds the positive electrode. A direct-current voltage is applied between the electrodes while rotating the positive electrode rod. The applied voltage differs according to the sizes and shapes of the electrodes and a distance between the electrodes. Preferably, the voltage is from 1 to 20 V. An electric current is usually from about 0.1 to 3 A. In this step, the cerium oxide particles covered with the water-soluble polymer are electrically attracted to the positive electrode rod and deposited thereon, and the thickness of the layer of deposited particles increases as time passes.

Fabrication of Fixed Abrasive Grinding/Polishing Tool:

The cerium oxide particles covered with the water-soluble polymer are deposited to a proper thickness according to the above-described method. Thereafter, the positive electrode rod is pulled out from the dispersion, the positive electrode rod is then removed from the cylindrical deposit of the cerium oxide particles, and the deposit is cut at a proper length. The cut piece is dried at room temperature in the air. Then, the dried piece is polished to smoothen its outer surface to finally finish the dried piece into a desired tool.

EXAMPLES

Hereinafter, the present invention will be illustrated by the following examples, which do not limit the scope of the invention in any way.

Example 1

Preparation of Plate-Form Cerium Oxide Particles:

In 800 ml of water, 0.90 mole of sodium hydroxide was dissolved to prepare an alkali aqueous solution. Separately, 0.074 mole of cerium chloride (III) heptahydrate was dissolved in 400 ml of water to prepare the aqueous solution of cerium chloride. The latter solution of cerium chloride was drop wise added to the former alkali aqueous solution at about 25° C. to prepare precipitates containing cerium hydroxide. The pH value of the mixture at this time was 10.5. The precipitate was aged for 20 hours in the state of a suspension.

Then, the supernatant liquid was removed and thereafter, the suspension of the precipitate was placed in an autoclave and subjected to a hydrothermal treatment at 180° C. for 2 hours.

The product from the hydrothermal treatment was washed with water, filtered and dried at 90° C. in the air. The dried product was slightly crushed with a mortar and then heat treated at 600° C. for 1 hour in the air to obtain cerium oxide particles. After the heat treatment, the particles were washed with water using a supersonic wave dispersing apparatus to remove the unreacted products and residues, followed by filtration and drying.

The X-ray diffraction of the obtained cerium oxide particles was measured and the obtained spectrum corresponded to that of cerium oxide having the fluorite structure.

The shapes of the particles were observed with a transmission electron microscope (a field emission electron microscope HF-200 of Hitachi Ltd.) at a magnification of 2×105, and it was found that each particle had a plate shape and the particles had an average particle size of 21 nm. Here, an average particle size was obtained by taking a transmission electron microphotograph of 100 particles, measuring the maximum particle size of each particle and then averaging the measured particle sizes of 100 particles.

The ratio of the maximum length in the in-plane direction of the plate-form particles to the thickness thereof was about 5. This ratio was obtained by observing the section with the same electron microscope as used above at a magnification of 5×106.

FIG. 1 shows the photograph of the cerium oxide particles of this Example taken with a transmission electron microscope at a magnification of 2×105 and FIG. 2 shows the X-ray diffraction pattern of the cerium oxide particles of this Example.

(Preparation of Dispersion Using Plate-Form Cerium Oxide Particles and Water-Soluble Polymer)

In 560 g of water, 3 g of sodium alginate as a water-soluble polymer was dissolved. To the solution, 37 g of the plate-form cerium particles (abrasive grains) prepared in the previous step were added, and the mixture was dispersed for 2 hours using a paint conditioner. Further, 200 g of zirconia beads each having a diameter of 1 mm as a dispersion medium was added to the pot for the paint conditioner. With the dispersing treatment applied, the individual cerium oxide particles were dispersed in the aqueous solution of sodium alginate to obtain a uniform dispersion.

Then, the dispersion was taken out from the pot, 300 g of the dispersion was charged in a 500 cm3 glass beaker, and water was evaporated from the dispersion while stirring on a hot plate until the total weight of the content in the pot decreased to 75 g.

Fabrication of Intermediate Product From Plate-Form Cerium Oxide Particles and Water-Soluble Polymer Using Electrophoresis:

The concentrated dispersion from the previous step was transferred into a 100 cm3 glass beaker and a positive electrode rode and a negative electrode were set therein. The positive electrode rod was a brass rod having a diameter of 4 mm and a length of 10 cm. The negative electrode was a spirally shaped brass rod and disposed along the inner wall of the beaker.

A voltage of 10 V was applied between the positive electrode and the negative electrode using a direct current power supply with a low voltage. A current flowing between the electrodes was from about 0.7 to 0.1 A. In this state, the positive electrode rod was rotated and the direct-current voltage was applied for 30 minutes to deposit the cerium oxide particles each having a plate shape covered by sodium alginate on the outer surface of the positive electrode rod. The thickness of the layer of deposit particles was about 4 mm and the diameter thereof was about 12 mm.

Fabrication of Fixed Abrasive Grinding/Polishing Tool:

The positive electrode rod was pulled out from the deposit prepared in the previous step, and the hollow cylindrical deposit was cut with a disposable blade so that a height of the cut piece was about 1 cm. The cylindrical intermediate product was dried at room temperature in the air for about one day. The intermediate product shrank due to drying to obtain a cylindrical product having a diameter of about 8 mm and a height of about 7 mm, which consisted of the plate-form cerium particles bound with sodium alginate. The circumferential surface and end surfaces were smoothed using a polishing tape to complete a fixed abrasive grinding/polishing tool.

Example 2

A precipitate containing cerium hydroxide was produced in the same way as that in Example 1 except that, in preparation of plate-form cerium particles in Example 1, conditions for a hydrothermal treatment of the suspension of the precipitate were changed to 200° C. and 2 hours from 180° C. and 2 hours and conditions for heat treatment in the air were changed to 800° C. and 1 hour from 600° C. and 1 hour, and then washing with water, filtration and drying followed and further, a heat treatment followed to prepare cerium oxide particles.

The obtained cerium oxide particles were measured on X-ray diffraction pattern to observe a spectrum corresponding to cerium oxide having the fluorite structure, similar to that in Example 1. Observation on shapes with a transmission electron microscope was conducted with findings that the particles were of an average particle size of 58 nm each having a plate shape. FIG. 3 shows a transmission electron microphotograph of cerium oxide particles at a magnification of 2×105. A ratio of the maximum length the in-plane direction of a plate-form particle to a thickness thereof was about 8.

A dispersion was prepared using the cerium oxide particles and a water-soluble polymer in the same method as that adopted in Example 1 and an intermediate product was produced from the plate-form cerium oxide particles and the water-soluble polymer using electrophoresis, from which a fixed abrasive grinding/polishing tool was fabricated.

Example 3

A dispersion was prepared and concentrated in the same way as that adopted in Example 1 except that in preparation of the dispersion using the plate-form cerium oxide particles having an average particle size of 21 nm and the water-soluble polymer in Example 1, the amount of sodium alginate added as a water-soluble polymer into 560 g of water was changed to 1.5 g from 3 g. An intermediate product was prepared from the mixture of plate-form cerium oxide particles and the water-soluble polymer under the same conditions as in Example 1 to complete a fixed abrasive grinding/polishing tool.

Example 4

A dispersion was prepared and concentrated in the same way as that adopted in Example 1 except that in preparation of the dispersion using the plate-form cerium oxide particles having an average particle size of 21 nm and the water-soluble polymer in Example 1, the amount of sodium alginate added as a water-soluble polymer into 560 g of water was changed to 4.5 g from 3 g. An intermediate product was prepared from the mixture of plate-form cerium oxide particles and the water-soluble polymer under the same conditions as in Example 1 to complete a fixed abrasive grinding/polishing tool.

Example 5

A dispersion was prepared and concentrated in the same way as that adopted in Example 1 except that in preparation of the dispersion using the plate-form cerium oxide particles having an average particle size of 21 nm and the water-soluble polymer in Example 1, the amount of cerium oxide particles added into 560 g of water was changed to 18.5 g from 3.7 g. An intermediate product was prepared from the mixture of plate-form cerium oxide particles and the water-soluble polymer under the same conditions as in Example 1 to complete a fixed abrasive grinding/polishing tool.

Example 6

A dispersion was prepared and concentrated in the same way as that adopted in Example 2 except that in preparation of the dispersion using the plate-form cerium oxide particles having an average particle size of 58 nm and the water-soluble polymer in Example 2, an amount of sodium alginate added as a water-soluble polymer into 560 g of water was changed to 4.5 g from 3 g. An intermediate product was prepared from a mixture of plate-form cerium oxide particles and a water-soluble polymer under the same conditions as in Example 2 to complete a fixed abrasive grinding/polishing tool.

Example 7

In preparation of the dispersion using the plate-form cerium oxide particles and the water-soluble polymer in Example 1, 3 g of sodium alginate as a water-soluble polymer was dissolved into 560 g of water. Then, to the solution, were added 29.6 g of the cerium oxide particle prepared in Example 2 having an average particle size of 58 nm and 7.4 g of plate-form aluminum oxide (γ-alumina) having an average particle size of 80 nm and a ratio of the maximum length in the in-plane direction of a plate-form particle was about 10.

The plate-form aluminum oxide particles were produced as follows:

In 800 ml of water, 0.75 mole of sodium hydroxide was dissolved to prepare an aqueous alkaline solution. Separately, 0.074 mole of aluminum (III) chloride heptahydrate was dissolved in 400 ml of water.

To the aqueous alkaline solution, the aqueous solution of aluminum chloride was drop wise added to form a precipitate containing aluminum hydroxide, and the pH of the suspension containing the precipitate was adjusted to 10.2 by the drop wise addition of hydrochloric acid. The suspension containing the precipitate was aged for 20 hours, and then washed with water in an amount of about 1,000 times volume of the suspension.

Thereafter, the supernatant was discarded and the pH of the suspension containing the precipitate was adjusted to 10.0 with an aqueous solution of sodium hydroxide. Then, the suspension was placed in an autoclave and subjected to the hydrothermal treatment at 200° C. for 2 hours. After that, the hydrothermal product was recovered by filtration and dried in an air at 90° C., slightly comminuted with a mortar and heated in the air at 600° C. for 1 hour to obtain plate-form aluminum oxide particles.

A dispersion and a fixed abrasive grinding/polishing tool were fabricated in the same methods as those adopted in Example 1.

Example 8

A dispersion and a fixed abrasive grinding/polishing tool were fabricated in same ways as those adopted in Example 7 except that 7.4 g of plate-form zirconium oxide particles having an average diameter of 20 nm and a ratio of the maximum length in the in-plane direction of a plate-form particle to a thickness thereof of about 3 was added in place of the addition of 7.4 g of plate-form aluminum oxide particles having an average particle size of 80 nm.

The plate-form zirconium oxide particles were produced as follows:

In 800 ml of water, 0.75 mole of sodium hydroxide was dissolved to prepare an aqueous alkaline solution. Separately, 0.074 mole of zirconium (IV) chloride was dissolved in 400 ml of water.

To the aqueous alkaline solution, the aqueous solution of zirconium chloride was drop wise added to form a precipitate containing aluminum hydroxide. The pH of the suspension containing the precipitate was 10.8. The suspension containing the precipitate was aged for 20 hours, and then washed with water until the pH reduced to 7.8.

Thereafter, the supernatant was discarded and the suspension was placed in an autoclave and subjected to the hydrothermal treatment at 200° C. for 2 hours. After that, the hydrothermal product was recovered by filtration and dried in an air at 90° C., slightly comminuted with a mortar and heated in the air at 600° C. for 1 hour to obtain plate-form zirconium oxide particles.

Example 9

A dispersion and a fixed abrasive grinding/polishing tool were fabricated in same ways as those adopted in Example 7 except that 7.4 g of plate-form iron oxide particles having an average diameter of 50 nm and a ratio of the maximum length in the in-plane direction of a plate-form particle to a thickness thereof of about 5 was added in place of the addition of 7.4 g of plate-form aluminum oxide particles having an average particle size of 80 nm.

The plate-form iron oxide particles were produced as follows:

In 800 ml of water, 0.75 mole of sodium hydroxide and 100 ml of 2-aminoethanol were dissolved to prepare an aqueous alkaline solution. Separately, 0.074 mole of ferric chloride hexahydrate was dissolved in 400 ml of water.

The aqueous alkaline solution and the aqueous solution of the ferric chloride were maintained at 15° C., and the aqueous solution of ferric chloride was drop wise added to the aqueous alkaline solution to form a precipitate containing ferric hydroxide. The suspension containing the precipitate was aged for 20 hours, and then washed with water in an amount of about 1,000 times volume of the suspension.

Thereafter, the supernatant was discarded and the pH of the suspension was adjusted to 11.3 with an aqueous solution of sodium hydroxide. The suspension was then placed in an autoclave and subjected to the hydrothermal treatment at 200° C. for 2 hours to obtain plate-form goethite (α-FeOOH). The goethite was recovered by filtration and dried in an air at 90° C., slightly comminuted with a mortar and heated in the air at 600° C. for 1 hour to obtain plate-form α-iron oxide particles.

Example 10

A precipitate containing cerium hydroxide was produced in the same way as that adopted in Example 1, washing with water, filtration and drying were applied, thereafter a heat treatment followed to prepare cerium oxide particles, except that conditions for the heat treatment in the air were changed to 300° C. and 1 hour from 600° C. and 1 hour without conducting the hydrothermal treatment on the suspension of precipitate. The obtained cerium oxide particles were measured on an X-ray diffraction pattern to observe a spectrum corresponding to cerium oxide particles having the fluorite structure, similar to that in Example 1. The shapes of the particles were observed with a transmission electron microscope with the result that the shapes are spherical or of other particulate shapes and an average particle size was 30 nm.

A dispersion using the cerium oxide particles and a water-soluble polymer was prepared in the same method as that adopted in Example 1 and an intermediate product was obtained from the mixture of spherical or other particulate shaped cerium oxide particles and a water-soluble polymer with electrophoresis to produce a fixed abrasive grinding/polishing tool.

Comparative Example 1

Three grams of sodium alginate as a water-soluble polymer was dissolved in 260 g of water. To the solution, was added 37 g of commercially available diamond abrasive particles (an average particle size of 0.1 μm shown in a catalogue) and the particles were dispersed while stirring for 1 hour. The dispersion was placed on a hot plate to evaporate off water till stirring is impossible.

The concentrated mixture was shaped into a cylinder and the cylinder was dried at room temperature in the same way as that adopted in Example 1 and the intermediate product was smoothed on the cylindrical surface and both end surfaces with a polishing tape or the like to complete a fixed abrasive grinding/polishing tool. That is, in Comparative Example 1, the diamond particles were used as abrasive particles and fixed with a water-soluble polymer to fabricate the tool.

Comparative Example 2

Three grams of sodium alginate as a water-soluble polymer was dissolved into 260 g of water. To the solution, was added 37 g of commercially available α-alumina abrasive grains (an average particle size of 0.2 μm shown in a catalogue) and the particles were dispersed while stirring for 1 hour. The dispersion was placed on a hot plate to evaporate off water till stirring is impossible.

The concentrated mixture was worked into a cylinder and the cylinder was dried at room temperature in the same way as that adopted in Example 1 and the intermediate product was smoothed on the cylindrical surface and both end surfaces with a polishing tape or the like to complete a fixed abrasive grinding/polishing tool. That is, in Comparative Example 2, the α-alumina abrasive grains were used as abrasive particles and fixed with a water-soluble polymer to fabricate the tool.

Evaluation of Grinding Ability

To evaluate the grinding performances of the fixed abrasive grinding/polishing tools produced in the Examples and Comparative Examples described above, a workpiece was actually ground using each fabricated tool to evaluate the grinding ability thereof The evaluation of the grinding ability was conducted on a silicon wafer of 4 inch (about 10.16 mm) in diameter as a workpiece. An apparatus examining the grinding ability was a fiber polisher (SFP-120A manufactured by Seiko Giken Co., Ltd.). In grinding, four tools fabricated according to the above described method were fixed along the inner peripheral wall with a diameter of about 5 cm of a circular metal surface plate (the upper surface plate) of about 18 cm in diameter in the fiber polisher at equal intervals between adjacent tools using an adhesive. On the other hand, a silicon wafer was fixed on the lower surface plate of about 12 cm in diameter and the upper surface plate on which the tools were fixed were placed on the silicon wafer to thereby press the tools, that is, grinding stones, to the surface of the silicon wafer by the weight of the upper surface plate itself. Then, the upper surface plate was fixed and the lower surface plate was rotated at 75 rpm to grind the surface of the silicon wafer fixed on the lower surface plate.

A grinding efficiency was evaluated in a way such that a rhombic indent was formed on the surface of the silicon wafer with a Knoop hardness meter (with a model number of HM-122) manufactured by Akashi K.K. and a reduction in depth of the indent, that is a grinding depth, was measured as grinding progresses for evaluation.

A surface smoothness after grinding was measured on a surface roughness Ra (center line average height) of the silicon wafer using a non-contact surface roughness meter (New View 5000 manufactured by Zygo Corp.) and the surface smoothness was evaluated with the measured Ra.

Table 1 shows the kinds, average particle sizes and amounts of abrasive grains, and the contents of abrasive grains and of the water-soluble polymer in the grinding stones and in Table 2, there is shown evaluation the results of grinding conducted using the fixed abrasive grinding/polishing tools obtained in the Examples and Comparative Examples. Grinding depths and Ra values on the ground surfaces shown in Table 2 were measured when grinding was conducted for 30 minutes. The larger the grinding depth, the higher the grinding efficiency, while the smaller the Ra value, the better surface smoothness.

TABLE 1
Content of
Amountabrasive
ofgrains inContents of
abrasivegrindingwater-soluble
Kind of abrasive grainsgrainsstonespolymer
Ex. No.(av. particle sizes)(wt. %)(wt. %)(wt. %)
Ex. 1Plate-form cerium oxide10092.57.5
(21 nm)
Ex. 2Plate-form cerium oxide10092.57.5
(58 nm)
Ex. 3Plate-form cerium oxide10096.13.9
(21 nm)
Ex. 4Plate-form cerium oxide10089.210.8
(21 nm)
Ex. 5Plate-form cerium oxide10086.014.0
(21 nm)
Ex. 6Plate-form cerium oxide10089.210.8
(58 nm)
Ex. 7Plate-form cerium oxide80/2092.57.5
(58 nm)/plate-form
aluminum oxide (80 nm)
Ex. 8Plate-form cerium oxide80/2092.57.5
(58 nm)/plate-form
zirconium oxide (20 nm)
Ex. 9Plate-form cerium oxide80/2092.57.5
(58 nm)/plate-form iron
oxide (50 nm)
Ex. 10Spherical-particulate10092.57.5
shaped cerium oxide
(30 nm)
Comp.Diamond particles10092.57.5
Ex. 1(0.1 μm)
Comp.Particulate shaped10092.57.5
Ex. 2α-alumina (0.2 μm)

TABLE 2
Grinding efficiencySurface smoothness Ra
(grinding depth, μm)(nm)
Example 10.140.8
Example 20.222.1
Example 30.181.5
Example 40.140.9
Example 50.120.8
Example 60.201.8
Example 70.182.8
Example 80.213.1
Example 90.162.0
Example 100.101.8
Comparative Example 10.35>100
Comparative Example 20.023.6

As is clear from Table 2, it is seen that the fixed abrasive grinding/polishing tools comprising the plate-form cerium oxide particles obtained in Examples 1 to 5 are grinding stones having good balance between the grinding efficiency and the surface smoothness after grinding. The abrasive grains exhibit an excellent grinding efficiency despite the fact that the abrasive grains are fine in size based on the synergistic effect of the excellent mechanical grinding ability using the particle edges due to the plate-form shape of each of cerium oxide particles as abrasive grains and the inherent chemical grinding ability owned by cerium oxide particles. The excellent surface smoothness is achieved by the action of cerium oxide particles that are extremely fine particles having an average particle size of 20 nm to 60 nm.

The fixed abrasive grinding/polishing tools of Examples 7 to 9 used as the stones contained the plate-form cerium oxide particles as the main constituent particles, and in addition thereto, the plate-form aluminum oxide particles, plate-form zirconium oxide particles and plate-form iron oxide particles. The tools are inferior to a grinding stone using only plate-form cerium oxide particles in surface smoothness, which is because silicon wafers were used as workpieces. It was confirmed that the tools of the Examples exhibit an excellent grinding performance according to the kind of a workpiece to be ground or polished, or conditions for grinding. Therefore, the construction of a grinding stone according to the present invention can be preferably selected according to purposes or applications. While the evaluation results in the Examples were investigated about the grinding ability as the grinding stone, it is also possible to grind in the presence of water added. The conditions for grinding can be arbitrarily set: such as those for dry grinding, grinding in the presence of water or a grinding at high temperature and humidity.

Although the fixed abrasive grinding/polishing tool of Example 10 using the cerium oxide particles having other particulate shapes is slightly inferior to the tool using the plate-form cerium oxide particles in the grinding ability, the tool exhibits an excellent grinding ability in comparison with the tools using the conventional kinds of abrasive grains shown in Comparative Examples 1 and 2.

On the other hand, although the fixed abrasive grinding/polishing tool of Comparative Example 1 using the diamond abrasive grains is high in the grinding ability reflecting the high hardness of the diamond particles, grinding marks are clearly left after grinding, rendering the surface smoothness extremely poor.

Although the fixed abrasive grinding/polishing tool of Comparative Example 2 using the α-alumina particles is relatively good in surface smoothness, the grinding efficiency is very low. This is because the α-alumina particles lack an inherent chemical grinding ability while they have a comparatively high hardness.