JP2003509579A - Al2O3 / SiC-nanocomposite abrasive particles, their production and use - Google Patents

Abstract

(57) Abstract: The present invention, aluminum oxide-containing sol is mixed with SiC nanoparticles, then gelled this, dried, calcined, of Al ₂ O ₃ / SiC nanocomposite abrasive particles to sinter The present invention relates to a production method, and the Al ₂ O ₃ / SiC nanocomposite abrasive particles.

Description

Detailed Description of the Invention

The invention relates to sintered Al ₂ O ₃ / based on the preamble of claim 11.
The invention relates to SiC nanocomposite abrasive particles (abrasive particles), a process for their production according to claim 1 and their use as abrasives.

Abrasive particles based on Al ₂ O ₃ are industrially processed in large quantities as abrasives because of their high hardness, their chemically inert properties and their high temperature resistance. In addition to fused corundum, which can be produced in an arc discharge furnace at a comparatively favorable price, reinforced sintered corundum, which is obtained by a ceramic or chemical method, has recently been used for certain fields of application. The abrasive technical advantage of sintered corundum is obtained by its microcrystalline structure, which also accounts for the special wear mechanism of the abrasive particles in the polishing process. Especially in applications where high contact pressure is required, for example in the processing of special steels, hardened steels or alloys that are difficult to machine, the use of sintered corundum can significantly improve the polishing properties.

Particles of sintered corundum having a microcrystalline structure for this application have substantially higher wear resistance than fused corundum having a microcrystalline structure. In addition, polishing with corundum, which has a microcrystalline structure, causes small areas to protrude from the grains, which creates new cutting edges, which again participate in the polishing process. Such self-polishing action of particles does not occur in the case of molten corundum having a microcrystalline structure. This is because in this case the cracks caused by the mechanical loading of the particles in the polishing process cannot be redirected and travel along the crystal planes throughout the particles, which results in the destruction of the abrasive particles.

When using sintered abrasive particles having a microcrystalline structure, the abrasive particles tend to behave more favorably in the polishing process in many applications as the structure becomes finer when hardness and density are comparable. In particular, a fine structure can be obtained by the sol-gel method. In this case, for example, when very finely dispersed boehmite type aluminum oxide monohydrate is used as a raw material, it becomes a gel after it is colloidally dissolved, and then dried. After being calcined and sintered, it is converted into a dense and dense α-Al ₂ O ₃ sintered body. Next, preparation into abrasive particles is performed. The advantage of the sol-gel method for producing corundum with a microcrystalline structure is that it uses fine, highly reactive raw materials and densifies the resulting green compact at relatively low sintering temperatures. Is possible, which is advantageous for producing fine structures.

European Patent No. B-0 152 768 was produced by the sol-gel process with the addition of certain crystallization seeds at a sintering temperature of about 1400 ° C., with the primary crystallites being largely or completely formed. Microcrystalline corundum with a diameter of less than 1 μm is described.

Since the sintering temperature is low and seeds for crystallization are added, crystal growth during the sintering process is significantly suppressed. European patent B-0 408 771 describes a fine structure with both high density and high hardness. The European patent B-0
No. 408 771, according to sol-gel method, particularly fine seeds for crystallization were added, and the average size of the crystals obtained according to a specific temperature program and sintering program was less than 0.2 μm. Abrasive particles are described, in which the program is carried out in the temperature range from 900 to 1100 ° C. for less than 90 seconds, then the material is briefly heated to a temperature at which the maximum temperature does not exceed 1300 ° C. and then 1000 Sinter and densify at a temperature lower than the maximum temperature in the range of ˜1300 ° C. This temperature program is chosen so that the resulting sinter or its precursor is not exposed for a long time to a temperature that favors crystal growth, resulting in a high densification.

In order to obtain a structure having a crystal structure as fine as possible, in addition to using seeds for crystallization, crystal growth is inhibited or the sintering process is promoted, thereby indirectly suppressing the generation of large crystals. A sintering additive is used. The influence of individual additives on the sintering process and crystal growth during the sintering of Al ₂ O ₃ is described in “Journal of the
American Ceramic Society, Vol. 39, No. 10, 1
956 ”. Some examples among numerous patents describing the use of sintering additives and combinations of sintering additives in combination with seeds for crystallization to produce abrasive particles by the sol-gel method Is as follows.
European Patent B-0 024 099 describes spinels or their precursors which have been transformed during the manufacturing process of spinels. European Patent B-02
No. 00 487, α-Fe ₂ O ₃ crystallization seeds, at least one modified component selected from the group consisting of oxides of magnesium, zinc, cobalt, nickel, zirconium, hafnium, chromium and / or titanium. It is described to be used in combination with. European patent B-0 373 765 also has the same
The use of yttrium and neodymium oxides and their compounds as modifying components in combination with -Fe ₂ O ₃ crystallization seeds is described. Abrasive particles made by the above method have advantages over the current state of the art for certain applications.

The variety of various Al ₂ O ₃ sintered abrasive particles is that polishing itself is a particularly diverse process, and widely changes raw materials to be processed and processing conditions (contact pressure, cooling conditions, etc.). Explained by what can be done. Various processing raw materials (various types of steel, alloys and metals, synthetic resins, wood, rock, ceramics, etc.) have a set purpose (
Surface treatment, material cutting, etc.) according to a variety of different conditions. The demands placed on the abrasive particles used correspondingly also differ, with the utility and performance of abrasive particles being characterized only by such quantities as hardness, density and crystal structure for a given polishing process. You cannot do it. Other criteria, such as chemically inertness, thermal conductivity, oxidation resistance and temperature resistance, toughness, etc., play a large role as well, depending on the application.

Other variables in the polishing process are the degree of bond and the specifications of the abrasive, which can be further modified by adding additives (polishing aids, pore formers, etc.).

Therefore, in the past, the performance of abrasive particles produced by the sol-gel method was studied not only for making the crystal structure finer, but also for imparting particularly advantageous properties for certain applications. . European Patent A-0 228
No. 856, yttrium is added to a dispersion of α-aluminium oxide monohydrate in the form of yttrium salt of an anion (nitrate, acetate, etc.) that volatilizes easily in the sol-gel method, and the At this time, it is described that yttrium-aluminum garnet (3Y ₂ O ₃ -5Al ₂ O ₃ ) is reacted with aluminum oxide. This material has particular advantages in the processing of simple structural steels as well as stainless steel, titanium, nickel alloys, aluminum and other difficult-to-machine alloys. Obviously, the inclusion of the crystal structure of garnet gives the abrasive particles extra wear resistance for this application, which is reflected in the high polishing performance. In addition to Y ₂ O ₃ or its precursor, the addition of seeds for crystallization and / or other sintering additives is described. Furthermore, European Patent B-0 293 164 is to add a rare earth element selected from the group consisting of praseodymium, samarium, ytterbium, neodymium, lanthanum, gadolinium, cerium, dysprosium, erbium and / or some combination thereof. Is listed. These rare earth elements form hexagonal aluminates with Al ₂ O ₃ , which obviously increases the wear resistance of the abrasive particles when included in the Al ₂ O ₃ matrix. European Patent B-0
No. 368 837 describes that the toughness is increased by the formation of whisker-like crystals obtained by adding a cerium compound. In this case as well, the toughness is increased because the structure is strengthened. German patent A-196
No. 07 709 describes a composite obtained by the sol-gel method,
This is different from the above-mentioned compounds in that, in addition to the Al ₂ O ₃ matrix, there are at least two discontinuous structural portions whose average particle diameters differ from each other by at least 10 times. European Patent No. B-0 491 184 describes Al ₂ O ₃ -based composites containing a hard isometric material that is at least 10 times larger than the primary crystals that make up the matrix.

All of the above methods and materials are based on the sol-gel method and have at the same time succeeded in achieving very fine, preferably submicron, crystal structures with sintering additives. Abrasive particles are often tuned and optimized for some applications by further doping.

Abrasives or particles are generally simply divided into two major groups. Corundum, together with SiC, belongs to the so-called conventional abrasives and has been produced and used in large quantities in a relatively well known and cost-effective way for a long time. In addition to these, so-called superabrasives such as diamond and cubic boron nitride are often found recently. The manufacturing cost is 1000 to 10,000 times higher than that of a normal abrasive, but due to its performance, the down time of the machine associated therewith is reduced, and the abrasive itself is less consumed, or In order to increase the number of products produced per unit time,
It provides a particularly favorable price / performance relationship for many polishing operations.

The use of superabrasives requires special mechanical equipment, which is subject to corresponding investment, so that the field of application of this high-performance abrasive is still limited.

Therefore, the main purpose in the development of new abrasive particles is set to obtain abrasive particles which can be used in conventional machines but have a performance level between that of conventional abrasives and superabrasives. This aim can be achieved, in part, with corundum by the sol-gel method described above, which can use very favorable price / performance relationships in many polishing operations. In particular, corundum by the sol-gel method should be classified not only in terms of manufacturing cost but also in performance, which is close to the types of ordinary abrasives, and in the case of polishing operations in which the use of superabrasives is not considered appropriate. Very suitable to use the normal corundum type.

Accordingly, it is an object of the present invention to provide abrasive particles and methods of making the same that have better potential performance as compared to the techniques of the art described above. According to the invention, this problem of the invention is solved by the features of claims 11 and 1. Claim 20 relates to a suitable use of the abrasive particles of the invention.

The concept of nanocomposite is a concept that has been adopted in the field of ceramics for about 10 years, and is composed of at least two solid phases, and the particle size of at least one phase is in the nanometer (nm) range. Means the system in.

[0017]   SiC particles are made of Al for reinforcement₂O₃Al incorporated in the matrix ₂ O₃/ SiC composites are described in European Patent B-0 311 289.
Materials, eg ceramic materials for use in motor or turbine structures
Is considered as. In this case, SiC in a proportion of 2 to 10 mol% in the composite.
Diameter of particles is less than 0.5 μm, while Al₂O₃The diameter of the particles exceeds 5 μm
must not. Al₂O₃These materials with SiC particles dispersed in
Characterized by very high breaking strength and toughness, it has a
It can be used as a structural ceramic material in a motor structure.

Similar Al ₂ O ₃ / SiC nanocomposites, which are distinguished by their good high temperature resistance and oxidation resistance among the composites reinforced with known whiskers, fibers or platelet-shaped materials, are described in Journal of the Ceramic Society of
Niiha, Japan, 99 (10), 974-982 (1991).
Ra's paper. The effect of very fine SiC particles on the growth and sintering behavior of Al ₂ O ₃ matrix particles is described in Journal of the E
European Ceramic Society, Volume 10 (1992) 4
73-477, Zhao and Harmer. Al ₂
The mechanical properties of O ₃ / Sic nanocomposite are Journal of the Ame
rican Ceramic Society magazine, Volume 76 (No. 2) 503-51
Zhao, Harmer, Chan, Miller, page 0 (1993).
And Cook. The nanocomposite produced by the sol-gel method is a Journal of the Ceramic Society.
of Japan, Volume 102, pages 312-315 (1994).
En Xu, Nakahira and Niihara.

The above cited references are mostly concerned with composites with a proportion of SiC greater than 2 mol%, but the authors are Wilhelm and Wruss, cfi / Ber.
, DGK 75, 40-44 (1998) describe the mechanical properties of hot pressed Al ₂ O ₃ / SiC composites with a low proportion of SiC. In addition to the documents cited above, among many other publications, Al ₂ O ₃ / SiC nanocomposites are described in the Journal of the European Ceramic So.
Cerity, Volume 17 (1997), 1061-1082, Sternizk.
e is summarized in the overview. This paper also states the speculation that Al ₂ O ₃ / SiC nanocomposites serve as abrasive particles to fill the void between conventional and superabrasives. However, in contrast to these speculations, the properties of almost all publications cited in this paper and the materials cited from them are clearly related to their use as structural ceramic materials. Such properties include microstructure, thermodynamic stability, density, hardness, breaking strength, crack toughness, wear properties, and creep rate. All these quantities definitely play an important role in the polishing process,
It is not valid to make a statement alone about the usefulness of a material as abrasive particles. High hardness, for example, is a reliable assumption that a material can be used as abrasive particles. However, although B ₄ C, which is often quoted in the professional world, has a high hardness, but due to its insufficient chemical and thermal properties and high brittleness, it has found great use as an abrasive. As can be seen from the above, the whole property must be observed to recognize its suitability as an abrasive. Hard materials with hardnesses in the range between normal and superabrasives are likewise not widely accepted as abrasives. This is because these materials lack additional properties such as toughness, thermal and chemical stability, or other important requirements for the polishing process. Thus, while the nanocomposite materials described in the literature exhibit certain properties necessary for the polishing process, they have hitherto not been successfully used as abrasive particles. These materials behave very much like Al ₂ O ₃ -based ceramics, which have great success when used, for example, for milling machines or lathes, but when processed into particles the usual melting It exhibits unsatisfactory wear properties at corundum or lower levels.

To that extent, observing only certain material properties that are known to have an effective effect on the polishing process, and on the basis of which to characterize the availability or expected polishing behavior properties of the abrasive particles. Is currently found to be extremely difficult in practice. The theory of the actual wear that occurs when a material is abraded by an abrasive tool has heretofore been developed only on the basis of changes in the work product and the abrasive tool after the abrading process. Since the influence on the polishing behavior characteristics depends not only on the abrasive particles but also on the condition of the polishing tool (bondability, porosity, additive substance, etc.) and the product itself to be processed, a certain polishing result can be obtained according to a certain abrasive particle It is often difficult later to relate material properties. For the first time, through an applied technical test of abrasives,
Alternatively, the final conclusions can only be reached by practical or field tests, which are quite financially and time consuming.

It is therefore worthwhile to find an independent measuring method and quantity that can be directly mentioned with regard to the availability of a material. In recent years, the so-called single particle test (Fig. 1: single particle scratch test) has become more and more practical in practice. This test is conducted under conditions that are as close as practical to those imposed during the polishing process.
The test equipment is a modified milling machine polishing machine in which a scratch disk is mounted on the polishing spindle instead of the grinding wheel for polishing. From a practical standpoint, a scratch disk made of a processing material (eg aluminium) which is relatively light and easy to machine has a holding device around which a support with soldered abrasive particles is mounted. . When scratching, the work piece is mounted on the support of the scratch device and moved below the rotating scratch disk in the x direction relative to the direction of rotation. Abrasive particles protruding beyond the circumference of the disk based on a predetermined Zustellung in the y-direction scratch the work piece with each revolution. As the scratch length and scratching time increase, the scratch depth and cross section decrease due to abrasive particle wear, and finally the abrasive particle tip rubs by the amount of feed in the y direction. It will decrease and no scratch marks will remain. Traces of scratches can be inspected and evaluated with a surface measuring device. The measuring principle is shown in FIGS. 1 and 2 and will be described below using the reference numbers.

FIG. 1 shows a scratch disk (1) and particles for scratching (2), x
Fundamental structure of a tester with axles (3, 4, 5) movable in the y, z and z-directions, workpieces (6), tester stand (7) and polishing spindle head (8) Indicates. In order to perform the measurement itself, the cutting speed v _c according to the possibility of polishing operation,
For the workpiece speed v _w and the feed a _e , we define the standard conditions that we will later use for the abrasive particles. In addition, the use of machined parts and cooling lubricants must be decided.

The rationale for the evaluation will be understood by reference to an exemplary run curve (FIG. 2) for various abrasive particle types. In this figure, the change in scratch cross-section A _Rn / A _R0 is plotted against the scratch length I _R. Here, A _R0 is the cross section of the scratch when the scratch is first made, and A _Rn is the cross section of the scratch after the scratch having a length of n mm is made.

The performance factor LF ₂₅ for a single particle is obtained from the point of intersection of the characteristic curve for a single particle type with the vertical axis at a scratch length of 25 mm, the change in the cross section of the scratch A _R0 / A Equivalent to _R25 . The performance factor is expressed as a% for the theoretical case where no wear of the particles occurs and A _R25 = A _R0 . A typical curve shape was chosen for evaluation at a scratch length of 25 mm, as it contains a region of the first part of the curve where the particle wears most severely and has a significantly steeper slope. This region is similar to the actual polishing process in terms of the feed a _e , and the performance of the polishing particles can be represented very well. As you go further, the curve becomes flat. This is because the particles are not used so much due to the reduced feed and do not wear too fast. To obtain typical results for abrasive particles, at least 2 for each particle type.
Zero particles must be measured and the wear curve must be constructed from the average of the individual measurement points.

The single particle scratch test is able to evaluate the suitability of abrasive particles in good agreement with actual results, where all quantities associated with the polishing process, such as hardness, toughness, density, Since strength, creep rate, thermal and chemical stability, crystal structure, etc. come indirectly into the whole, there is no need to know if a property or combination of properties is known. Nor do they have to be considered accordingly.
Of course, certain minimum requirements must be met for all properties, so that one material is generally problematic as abrasive particles. For example, a material whose hardness is significantly less than the normal hardness of the abrasive would not be suitable for polishing, despite all other properties.

Surprisingly, S made directly by the sol-gel method with the addition of seeds for crystallization
For Al ₂ O ₃ / SiC in which the proportion of iC is less than 5 mol%, the performance factors found by the above method are the performances conventionally found for Al ₂ O ₃ / SiC nanocomposites. It was clearly superior to the factor. The performance values of the nanocomposites of the present invention are superior to the known values of pure or doped sol-gel-corundum and are therefore in the target range between conventional abrasive particles and superabrasives. .

A known Al ₂ O ₃ nanocomposite produced by mixing the raw materials using powder technology, followed by densification (eg by hot pressing, pressureless sintering and hot isostatic pressing) and sintering. In contrast, the abrasive particles of the present invention are produced wet-chemically using the direct sol-gel method with the addition of seeds for crystallization. Xu, Nakahira and Niihara are Journal Ceramic Society o
f Japan magazine, in their paper 1994,102,312～315 page Shosai sol in the production of Al ₂ O ₃ / SiC nanocomposite - describes the use gel method. However, they simply use this technique to mix the nanopowder as homogeneously as possible over the pre-made colloidal solution of particles. The sol is then dried and calcined to give a mixture of ultrafine Al ₂ O ₃ and SiC powders, which is then subjected to a pressure of 30 MPa and 1 N under nitrogen as in conventional powder technology.
The hot press is performed at a temperature of 600 ° C.

By separating the powder as an intermediate product and then subjecting it to the usual powder-technical work-up, certain advantages of the sol-gel process which are important for the production of abrasive particles are lost. The abrasive technical properties of the composites produced by the above method therefore correspond to the properties of the previously expected nanocomposites. A further economic perspective is added to this.
This is because the hot press method cannot realize economically advantageous mass production of abrasive particles in a large-scale industry.

In contrast, the direct sol of the present invention for producing an Al ₂ O ₃ / SiC nanocomposite-
In the gel method, first, an Al ₂ O ₃ sol is manufactured by a usual method. As a solid component for a sol containing aluminum oxide, boehmite-type aluminum oxide monohydrate, aluminum alkoxide, aluminum halide and / or aluminum nitrate which is vigorously stirred using a dispersing device or finely dispersed by using ultrasonic waves is used. Is advantageous. The solid content of the suspension is preferably 5 to 60% by weight. In order to disperse in this suspension as uniformly as possible, Al ₂
SiC is added in an amount of greater than or equal to 0.1 mol% and less than 5 mol%, preferably in the range 0.3 to 2.5 mol%, based on the aluminum content of the mixture calculated as O ₃ . Of course, SiC can also be added as a solid to a preformed suspension. As shown in the examples in Table 3, good results are obtained with relatively small amounts of SiC. As the SiC raw material, finely powdered SiC powder obtained by the Acheson method or manufactured by a reaction supported by heat and laser in a gas phase or various plasma methods is used.

Seeds for crystallization before gelling in order to have a positive effect on the subsequent sintering process,
It is advantageous to add further sintering additives in the form of crystal growth inhibitors and / or other modifying components. For this purpose, in particular all known sintering additives for Al ₂ O ₃ , such as spinel-forming oxides of Co, Mg, Ni and Zn, Ce, Cu, B.
, Ba, Hf, K, Li, Nb, Si, Sr, Ti, Y, Zr or an oxide of a rare earth element or a precursor thereof, and Fe ₂ acting as a seed for crystallization, for example.
Oxides having a corundum-like structure, such as O ₃ , Cr ₂ O ₃ , and Al ₂ O ₃ can be used. Of course, combinations of these can also be used to obtain certain properties of the abrasive particles.

Prior to the addition of SiC, it is preferred to mix the Al ₂ O ₃ sol with an aqueous suspension of particulate α-Al ₂ O ₃ . The maximum particle size of α-Al ₂ O ₃ particles used as seeds for crystallization is preferably smaller than 0.2 μm. The amount of seed material used is 0.5 to 10% by weight, based on the Al ₂ O ₃ content in the final product. In addition to the fineness, the number of seeds is important, so that in very fine cases a small amount of seeds is already sufficient to accelerate the sintering process.

The suspension formed is then heated to boiling and preferably gelled by addition of acid.
Also in this case, any other known gelation method (aging, addition of electrolyte, increase in temperature, concentration of suspension, etc.) can be used. Drying gel (after cooling) is 50-120 ℃
At a temperature in the range. Then, calcination is performed in a temperature range of 500 to 800 ° C. to evaporate residual water and acid. After calcination, the composite becomes a green compact with a diameter of up to a few mm, which is then sintered. The advantage of the method of direct densification is that the dried and calcined green compact has a particularly high sintering activity, the raw materials being already chemically bound to one another in this green compact. The densification and hardening are carried out substantially effectively and advantageously and a finished composite is obtained.

In addition to this, the use of sintering additives or seeds for crystallization makes it possible to improve this step and thus the product quality. Sintering of the calcined gel is preferably carried out at a temperature of 1300 to 1600 ° C., preferably under inert conditions (for example in a nitrogen atmosphere), particularly preferably in a hermetically sealed rotary tube furnace, to give the product Heat as quickly as possible so that the sintering takes place in a short sintering time. It has been observed that this has a particularly advantageous effect on the structure of the abrasive particles and thus on their performance. Alternatively, any known type of furnace that provides rapid heating rates and high temperatures can be used. Sintering is so rapid that it is possible to work under vacuum or even in an oxidizing atmosphere. Because most of the SiC nanoparticles are confined in the matrix and thus protected from oxidation.

Conventional atomizing equipment can be used before or after sintering to atomize to the desired particle size. It is advantageous to prepare the calcined gel in the raw state. This is because, after sintering, a substantial amount of energy must be consumed in order to reduce the size of the densified and hardened composite material.

During sintering, nanoscale SiC acts as a crystallization seed for the Al ₂ O ₃ matrix, but at the same time delays the densification of the green compact, so that a pure aluminum oxide-based sol. -For gel materials, preferably high sintering temperatures must be used so that the material is sufficiently densified and crystal growth does not occur insignificantly. At about 1400 ° C. large crystals are formed, which are already enhanced. This phenomenon has already been described in US Pat. No. 4,623,364. In this patent, the undesirable phenomenon of the appearance of large crystals in an otherwise fine matrix is attributed to impurities. The patent aims to obtain a matrix of crystallites with the greatest possible proportion, which is also disclosed in the patent cited at the beginning and corresponds to the state of the art.

Surprisingly, in the present invention, the maximum length in the matrix is 20 μm.
It has been found that the polishing performance of the nanocomposite abrasive particles of the present invention is particularly high when a large proportion of large crystals having a m, average diameter of more than 2 μm, preferably more than 5 μm are present. Its polishing property is a pure sol-gel method of fine crystals having an average crystal size of 0.2 to 0.3 μm and the whole crystal in the range of submicron, preferably 0.4 μm or less. Clearly higher than the Al ₂ O ₃ abrasive particles according to. This is very surprising. This is because it is known by experts in the art that the polishing properties of sintered corundum increase significantly as the structure becomes finer, especially when the d ₅₀ region is smaller than 0.5 μm.

The performance curves of Al ₂ O ₃ / SiC nanocomposites are linear as shown in Examples 1-6 and Controls 7-11 which describe the effect of sintering conditions on the structure and polishing strength of sintered corundum. However, the maximum value is shown between 1400 and 1450 ° C. In this temperature range, the first coarse crystals and stalk-like crystals are formed in the matrix when the holding time (Haltezeit) is 30 minutes. The coarse Al ₂ O ₃ crystals preferably exhibit elongated shapes with a length to width ratio of 2: 1 to 10: 1, particularly preferably 4: 1 to 6: 1. A typical view of a matrix containing coarse crystals is shown as an electron micrograph in Figures 3 and 4 of the accompanying drawings. At temperatures below 1400 ° C., pure submicron structures are produced, where the total particles are in the range of less than 1 μm, preferably less than 0.5 μm. The polishing strength of this material is still greater than that of pure sol-gel corundum according to the state of the art, but surprisingly the material obtained in the above temperature range contains coarse crystals. Smaller than. At higher sintering temperatures, where more coarse crystals are formed, the polishing strength decreases again.

However, even in the temperature range of 1500 ° C. where a large proportion of coarse crystals are present, the level of polishing performance of the best pure sol-gel corundum is reached. On the other hand, in the pure sol-gel corundum, the polishing ability was found to be almost linearly related to the fineness of the structure, and the average crystal size d ₅₀ was 0 in the region of micron or less.
． Good performance is reached only below 4 μm.

[0039] Apparently in the case of nanocomposites, the coarse crystals exert some kind of structure-enhancing effect which positively influences the polishing behavior properties of the particles, and also the expected degradation of performance based on particle growth. Not only does it offset, but in combination with the included nanoscale SiC particles, it clearly helps improve performance over abrasive particles.

As can be seen from the example in Table 4, the improvement of the product by including the SiC particles is not limited to the case of using the nano-scale SiC powder, and the use of the particles including the relatively coarse SiC is also excellent. Excellent polishing performance can be obtained. However, it is clear that the finer the SiC powder used, the more the polishing performance tends to be improved. From an industrial point of view and availability, when producing the abrasive particles of the present invention, Ach
Only the powders mentioned in the examples below, which are obtained by grinding the industrial SiC obtained by the eson method as finely as possible, are used exclusively. However, one can start with the fact that the above tendency persists when using finer powders.

The SiC particles in the nanocomposite of the present invention are arranged as intraparticles in the Al ₂ O ₃ matrix particles and as interparticles at the boundaries between the Al ₂ O ₃ particles, in this case It has been observed that particles smaller than this are preferably incorporated as intraparticles. What kind of inclusion of SiC affects the polishing performance is the subject of further study and at present only speculative considerations are possible.

Some theories discussed in the publications cited above again relate only to one property of the composite material and do not consider the effect of the overall property on the polishing performance. . In particular, Examples 14-17 clearly show a tendency for polishing performance to increase as the size of the included particles decreases. From this, it can be concluded that the SiC contained in the particles greatly contributes to the improvement of the polishing performance.

Therefore, according to the present invention, there are provided Al ₂ O ₃ -based nanocomposite abrasive particles, in which SiC nanoparticles are mainly included as intraparticles, having a hardness (HV _0.2 ).
Is greater than 18 GPa, the density is greater than 95% of theoretical density, and the polishing performance is LF ₂₅ > 75%. (Here, LF ₂₅ is processing material 100
Cr6 (HRc = 62) is an average value measured 20 times. The conditions in this case are a cutting speed of 30 m / sec, a feed rate of 20 μm, a processing material speed of 0.5 mm / sec, and a 3% emulsion as a coolant. added. ) Next, the present invention will be illustrated by the following examples. These examples do not limit the invention.

Examples 1 to 6 Suspension A (boehmite sol) 10 kg of pseudoboehmite (Disperal, Condea) was added to a dispersion device (Megatron MT type 1-90, Kinematica) of about 300 ml. It was dispersed in 50 liters of distilled water whose pH was adjusted to 2.4 by adding concentrated nitric acid. A dispersant was also added to this dispersion so that the maximum particle size was d _max = 0.
Seed slurry containing 50% of 4 μm α-Al ₂ O ₃ was added. This seed slurry was obtained by wet-milling fine α-Al ₂ O ₃ powder (CS400M, Martinswer) and then centrifuging. About 2% by weight of Al ₂ O ₃ crystallization seeds were present in the sol after the seed slurry was added.

Suspension B (SiC suspension ) 1.5 g of 50% polyethyleneamine suspension (Fluka) are added to 600 ml of distilled water with vigorous stirring. Then 30 g of nanoscale SiC (UF 45, HC Starck) was added to this diluted suspension with stirring.

Suspension B was added to the boehmite sol (Suspension A) with stirring and the pH value of this mixture was adjusted to 1.8 with nitric acid. The mixture is then heated to 95 ° C. with constant stirring and nitric acid is added dropwise to initiate gelation. The gel was cooled and then dried in an oven at 85 ° C. Particle size of dried gel is 5m
Granulated until smaller than m and then calcined at 500 ° C.

In Examples 1 to 6, only the sintering temperature was changed. Table 1 shows the measured hardness, the polishing factor, and the microcrystalline structure depending on the sintering conditions.

[0048]

[Table 1]

Control Examples 7 to 11 (without SiC inclusion component) About 300 ml of concentrated nitric acid was prepared by using 10 kg of pseudoboehmite (Disperal, Condea) and a disperser (Megatron MT type, 1-90, Kinematica). In addition, it was dispersed in 50 liters of distilled water whose pH was adjusted to 2.4. A dispersant was also added to this dispersion to give a maximum particle size d _max = 0.
Seed slurry containing 50% of 4 μm α-Al ₂ O ₃ was added. This seed slurry was obtained by wet-milling fine α-Al ₂ O ₃ powder (CS400M, Martinswer) and then centrifuging. After adding the seed slurry, about 2% by weight of Al ₂ O ₃ seeds for crystallization were present in the sol.

The pH value of this mixture was adjusted to 1.8 with nitric acid. The mixture is then heated to 95 ° C. with constant stirring and nitric acid is added dropwise to initiate gelation. The gel was cooled and then dried in an oven at 85 ° C. The dried gel was granulated until the particle size was less than 5 mm and then calcined at 500 ° C.

Also in Comparative Examples 7 to 11, only the sintering temperature was changed. Table 2 shows the measured hardness, the polishing factor and the microcrystalline structure depending on the sintering conditions.

[0052]

[Table 2]

Example 12 Example 12 was manufactured in the same manner as in Examples 1-6. But 75g of nano
A scale SiC UF45 was used.

Example 13 Production was carried out in the same manner as in Example 12. But nano-scale SiC UF
150 g of 45 was used instead of 75 g. Table 3 shows performance factors depending on the concentration of SiC.

[0055]

[Table 3]

Example 14 Example 14 was manufactured in the same manner as Example 4. Instead of the SiC UF45, a slightly coarser SIC UF25 (HC Starck) was used. Sintering was performed at 1400 ° C. in a nitrogen atmosphere. The heating rate was 60 ° C. per minute and the holding time was 30 minutes.

Example 15 Example 15 was manufactured in the same manner as Example 14. Coarse SIC UF15 (HC Starck) was used instead of SiC UF25.

Comparative Example 16 Example 16 was prepared in the same manner as in Example 15. SIC UF1000 (Elektroschmelzwerk Kemp instead of SiC UF15)
(Ten company) was used.

Comparative Example 17 Example 17 was prepared in the same manner as in Example 16. SIC UF600 (Elektroschmelzwerk Chem instead of SiC UF1000)
Pten) was used.

[0060]   Table 4 shows the nanocomposite performance factors depending on the particle size of the included SiC.

[0061]

[Table 4]

Abrasive Test In addition to scratch tests, abrasive tests were conducted in the form of strip abrasives for some examples. The results of this test are summarized in Table 5.

[0063]

[Table 5]

[Brief description of drawings]

[Figure 1]   Principle structure of scratch tester with single particles.

FIG. 2 Abrasion curves of Al ₂ O ₃ / SiO nanocomposite compared to some typical abrasive particles.

3 and 4   An electron micrograph of a matrix of the composite abrasive particles of the present invention.

─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3C058 AA07 CB01 CB02 CB05 DA02                 4G076 AA02 AA24 AB02 BF10 CA04                       CA26 CA29 DA30

Claims (20)

[Claims] 1. A method for producing Al ₂ O ₃ / SiC nanocomposite abrasive particles, which comprises mixing an aluminum oxide-containing sol with SiC nanoparticles and then subjecting to gelling, drying, calcination and sintering. . 2. The aluminum oxide-containing sol comprises a boehmite-type aluminum oxide monohydrate, an aluminum alkoxide, which is very finely dispersed as a solid component.
A method according to claim 1, characterized in that it comprises aluminum halide and / or aluminum nitrate. 3. The aluminum content of the mixture calculated as Al ₂ O ₃ is 0.
． Method according to claim 1 or 2, characterized in that SiC nanoparticles are added in an amount of 1 mol% or more and less than 5 mol%, preferably 0.3-2.5 mol%. 4. Crystallized seeds that influence the sintering process before gelling,
Method according to claims 1 to 3, characterized in that sintering additives are added in the form of crystal growth inhibitors and / or other modifying components. 5. The method according to claim 4, characterized in that finely powdered α-aluminum oxide is used as crystallization seeds. 6. The method according to claim 1, wherein the gelation of the suspension is carried out by raising or lowering the pH value, aging, adding an electrolyte, raising the temperature and / or concentrating the solution. 7. The gel is dried in a temperature range of 50 to 120 ° C., calcination is then performed in a temperature range of 500 to 800 ° C., and sintering is performed in a temperature range of 1300 to 1600 ° C. The method according to claim 1. 8. The method according to claim 7, wherein the sintering is performed in a temperature range of 1380 to 1500 ° C. 9. The method of claim 7, wherein the sintering is performed under inert conditions. 10. The method according to claim 1, wherein the grain size reduction to a desired grain size is performed before or after sintering. 11. Al ₂ O ₃ / SiC having a hardness of more than 16 GPa, a density of more than 95% of the theoretical value, and a proportion of SiC in the Al ₂ O ₃ matrix of 0.1 mol% or more and less than 5 mol%. In nanocomposite abrasive particles, SiC particles were present as interparticle and intraparticle particles in an Al ₂ O ₃ matrix, the abrasive particles exhibiting LF ₂₅ > 75% performance in a single particle scratch test. Characteristic A
l ₂ O ₃ / SiC nanocomposite abrasive particles. 12. The proportion of SiC is between 0.3 and _{2. with} respect to the Al ₂ O ₃ matrix.
Al ₂ O ₃ / SiC nanocomposite abrasive particles according to claim 11, wherein from 5 mol%. 13. The Al ₂ O ₃ / S according to claim 11 or 12, characterized in that the SiC particles are mainly present as intraparticles in the Al ₂ O ₃ matrix.
iC nanocomposite abrasive particles. 14. The matrix Al ₂ O ₃ crystal has an average diameter of 0.2 to 20 μm.
The Al ₂ O ₃ / SiC nanocomposite abrasive particles according to claim 11, wherein m is m. 15. Al ₂ O ₃ matrix has the following structure microns, the average size is from 1 [mu] m, Al ₂ O according to claim 11 to 13, wherein preferably characterized in that less than 0.5μm ₃ / SiC nanocomposite abrasive particles. 16. The Al ₂ O ₃ / SiC nanocomposite abrasive particles according to claim 15, wherein coarse Al ₂ O ₃ crystals are formed in a submicron Al ₂ O ₃ matrix. 17. Al ₂ O ₃ / SiC nanocomposite abrasive particles according to claim 16, characterized in that the coarse Al ₂ O ₃ crystals have an average diameter of more than 2 μm, preferably more than 5 μm. 18. The Al ₂ O ₃ / SiC nanocomposite abrasive particles according to claim 17, wherein the coarse Al ₂ O ₃ crystals have an elongated shape. 19. A coarse Al ₂ O ₃ crystal having a length-to-width ratio of 2: 1 to 10: 1, preferably 4: 1 to 6: 1. Al ₂
O ₃ / SiC nanocomposite abrasive particles. 20. Use of Al ₂ O ₃ / SiC nanocomposite abrasive particles according to claims 11 to 19 for the production of abrasive tapes and disks.