JPH0154300B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses chemical ceramic technology to create an abrasive mineral based on synthetic non-fusible aluminum oxide with a microcrystalline structure of irregularly oriented crystallites consisting of a continuous phase of the main component and a second phase, which is α-alumina. The present invention relates to abrasive products made from abrasive minerals. Alumina, commercially produced by fusing and sintering techniques, is a known abrasive mineral. Attempts to improve the abrasive performance of synthetic alumina have had varying degrees of success. In small grain abrasive materials, the combination of alumina and other mineral additives such as zirconia has been known for virtually some time. The combinations were obtained by simply blending mineral pellets or by forming pellets of eutectic or sintered blends of minerals. Melting and Eutectic Techniques Typically, a mixture of alumina and other oxide precursors is heated to 1800° C. or higher until melted to produce a eutectic blend. A commercially preferred method of producing coated abrasive materials is to pour the molten composition into a bed of steel balls or large pieces of solid minerals, such as alumina-zirconia, so-called "book molds." Alternatively, it is poured into a vessel containing a molten salt or low melting metal and allowed to cool at a controlled rate that promotes growth of the crystal size desired in the final abrasive product. The resulting molten mineral is a microcrystalline, directionally solidified composite material with distinctive grain boundaries or colonies. Such alumina:zirconia minerals are sold under the trade name " ^Norzon " by the Norton Company of Worcester, Mass. The minerals are oriented in the direction of heated flow and are non-porous. It was described as having a fused structure characterized by the presence of zirconia rods or platelets in which the regular orientation is removed and whose size depends on the cooling rate.Fused alumina: zirconia in zirconia By increasing the amount of the eutectic composition ZrO ₂ :Al ₂ O ₃ =43:57 (weight ratio) and significantly increasing the cooling rate, the size of the crystals in the composite is reduced, thus improving the abrasive performance of the resulting mineral. The crystal size of the alumina:zirconia particles produced by the fusion process is controlled both by the cooling rate and the amount of alumina and zirconia in the melt. ,
For example, it produces very fine fine crystals, while the outside of the eutectic composition produces large crystals of one component embedded in a fine crystalline molten common matrix. Even in eutectic compositions, the crystal size is generally not uniform, with areas that cooled rapidly becoming finer and areas that cooled more slowly becoming coarser. There is no known method for producing fused abrasive grains with fine, uniform crystal size that is substantially unaffected by varying the amount of alumina or cooling rate. The lack of uniform crystal size necessarily results in different mineral types in the same lot. Furthermore, mixtures containing extremely hard alumina particles, such as those obtained by melting methods, must be ground to create the desired abrasive particle size. Such grinding requires expensive and robust equipment, rather long hours, a lot of energy and a lot of work. The crushed mineral is then sorted to the desired size. Any material smaller than the desired size can only be restored by melting it again at very high temperatures. Sintering Techniques Hardened blends of powdered alumina and other powdered minerals such as zirconia, magnesia, etc. can be sintered. For preferred compositions of alumina and zirconia, the temperature required to sinter is above the monoclinic-square crystal structure deformation temperature of zirconia. Thus, the sintering temperature changes much of the zirconia from the monoclinic form to a square crystal lattice, but upon cooling of the sintered structure, the zirconia restores the monoclinic structure. This restoration creates internal stresses that weaken the resulting composite with a substantial increase in volume. Although internal stresses in sintered alumina-zirconia may be reduced by the addition of certain oxides such as silica and ceria, sintered grit or cake is typically made from fused alumina of comparable composition. -Not yet as hard as zirconia grains.
Therefore, while sintered materials are durable and useful in high pressure rough polishing operations, they are not as desirable as fused alumina-zirconia. Sintering is facilitated by the use of very fine particles that provide high surface energy and the necessary chemical activity to promote sintering between adjacent particles and impart strength to the resulting sintered product. Though thought to be a simple thermal process, sintering is actually extremely complex, involving simultaneous or sequential changes in the surface,
Includes evaporation-condensation, surface and bulk diffusion, plastic flow, hole shape, size and total hole volume, shrinkage recrystallization, grain growth and movement of grain boundaries. Other phenomena that occur during calcination processing include solid state reactions, formation of new phases, polymorphic deformation, and decomposition of crystalline compounds to form new phases or gases. Prior to the sintering process, removal of binder, water and decomposition of precursor salts occur. Many of the precursor components used in the main body of ceramic products are carbonates or hydrated compounds;
Removal of the produced CO ₂ or H ₂ O requires temperatures up to 1000°C. In addition to these technical complexities,
Since it is difficult to homogenize the starting materials by mechanical mixing, separation is permitted.
And it's a tough problem. Sintering mixed alumina-zirconia powders, even with additives such as MgO, CaO, _CaF2, etc., results in fine crystal size, low pore volume as defined here. It is not possible to produce abrasive grains of In the absence of additives that slow crystal growth to some extent, the crystals will grow to relatively large sizes over the long periods and high temperatures necessary for densification. Even with such additives, the resulting particles are not of superior abrasive quality. Chemical Ceramics Technology Chemical Ceramics Technology is a colloidal dispersion in solution or mixing with other sol precursors into a gel or other physical state that suppresses the migration, drying and calcination of the components to obtain ceramic (ceramic) materials. or converting it into a hydrosol (sometimes referred to as a sol). Sols include precipitation of metal hydroxides from aqueous solutions followed by peptidation, dialysis of anions from metal salt solutions, solvent extraction of anions from metal salt solutions, hot water extraction of metal salt solutions containing volatile anions, etc. It can be produced by action decomposition. Sols contain metal oxides or their precursors, which are converted into semi-rigid solid states of limited mobility, such as gels, by partial extraction of solvents, for example. Chemical ceramic techniques have been used to produce ceramic materials such as fibers, films, flakes, and microspheres, but not to produce dense minerals for abrasive products. The present invention is characterized by a highly non-calcium and alkali metal ion-free alumina main continuous phase and a substantially homogeneous microcrystalline structure of crystallites present in a random orientation of the modifying component. A granular abrasive mineral based on fused synthetic aluminum oxide is provided. The energy required to produce the present non-fusible minerals is relatively moderate energy as opposed to the production of fused minerals which require very high peak electrical energies to melt. The mineral of the present invention is based on (1) a continuous α-alumina phase as a main component and (2) a calcined solid content, with at least 10% by volume of zirconia, hafnia, or a combination of zirconia and hafnia, alumina and cobalt oxide, and oxidized cobalt oxide. at least 1% by volume of at least one spinel derived from a reaction with at least one metal oxide selected from the group consisting of nickel, zinc oxide and magnesia; at least 1% by volume of at least one spinel as defined above; and 1-45% by volume of a metal oxide selected from the group consisting of zirconia, hafnia, and a combination of zirconia and hafnia;
It consists of a second phase substantially homogeneously dispersed within the alumina phase. The term "calcium ion and alkali metal ion free" means that the mineral contains less than about 0.05% by weight of total calcium and alkali metal ions, such as lithium, sodium, potassium, rubidium and cesium. As used herein, the terms "microcrystal,""crystallite," and "microcrystalline size" mean that the apparent diameter of the crystal is on the order of 3000 Å or less. The term "dense" means virtually no holes when viewed under a light microscope at 500x magnification.
The term "major component" means the largest single phase by volume in a mineral. Modifying components can also be derived from precursors that produce metal oxides and/or other reaction products that form the second phase of the abrasive minerals of this invention. The amount of a modifying ingredient in an abrasive mineral is hereby calculated by weight or volume of its fully oxidized form as determined by metallurgical analysis, regardless of the actual form added or present as such in the mineral. show. The process of the present invention produces aluminum oxide-based minerals not previously obtained by conventional methods such as calcining or melting blended powders. The mineral of the present invention is a granular abrasive mineral based on a dense synthetic aluminum oxide having a substantially homogeneous microcrystalline structure of alumina as the main continuous phase and randomly oriented crystallites as a modifying component. It is. The minerals of the present invention are generally of fine crystalline size regardless of the varying relative amounts of alumina and modifying components. Room temperature electron microscopy and
Linear diffraction analysis shows that the modified components are dispersed in a primary matrix of microcrystalline alumina that is almost more homogeneous than that obtained with conventional sintered and consolidated formulations of the same modified components or their eutectic compositions as powdered alumina. Indicates that the The method of the present invention involves first combining an alumina source compound, such as a colloidal dispersion or hydrosol of alumina, in a liquid medium with a precursor of a modifying component such as calcium ions and an alkali to a concentration in a calcined mineral as described above. It consists of producing a homogeneous mixture free of metal ions. The liquid mixture is then turned into a gel and dried to produce a porous solid material that is vitreous and can be crushed (vitreous means that the material exhibits a friable shell-like fracture under 50x magnification and is usually (meaning transparent). The solid material is then heated at a controlled rate and at least
Calcining in non-reducing conditions (preferably oxidizing conditions) at a temperature of 1250 °C but not higher than the melting point of the final mineral, first driving out volatile materials (e.g. liquids and anions) and then forming a porous It breaks down the aluminum oxide material and converts it non-destructively into a mineral based on high-density alpha-aluminum oxide. The liquid medium containing the raw material compound for alumina and the precursor of the modifying component is thoroughly mixed to form a homogeneous mixture and then gelled. Gelling inhibits or limits the mobility of the components without substantially separating them on a macroscopic scale, thereby preserving the homogeneity of the mixture in the semi-rigid solid state. By mixing the ingredients in the liquid state and then suppressing their mobility, aluminum oxide can be produced after sintering with very fine crystal sizes not previously available by melting or conventional sintering processes. Abrasive minerals based on The mixture may be formed into flakes, spheres, rods, pellets before drying, or may be dried in any convenient form and then crushed or crushed to form particles that can be used as abrasive grains and grains after firing. can. The smaller the original particle size, the better if particle growth inhibitors are added, typically in alumina.
In the case of MgO, it is clear that if less than 0.25% by weight is added, the particles of the produced sintered ceramic product will be larger.Considering that the technology is contrary to what the technology teaches, the size of very fine crystals is That's surprising. Among minerals consisting of alumina:zirconia = 70 = 30 (weight ratio), alumina is about 1000Å or
A matrix is formed containing a zirconia phase characterized by zirconia crystallites having an apparent average diameter of less than about 2500 Å that are substantially uniformly separated from center to center by 3000 Å. Preferred substantially eutectic alumina-zirconia mineral compositions have zirconia crystallites with an apparent diameter of less than about 2500 Å and alumina crystallites with an apparent diameter of less than about 3000 Å. It must be understood that the relative amounts of alumina and modifying components affect the average crystallite diameter and separation, and the same crystalline scale cannot be applied to all of the mineral products of the present invention. Although the synthetic abrasive materials of the present invention are dense, the composition and/or method of manufacture may be modified to increase pore volume for certain purposes. The pore volume is increased if the calcination temperature is lowered or if appropriate volatile organic materials are added. The synthetic aluminum oxide-based minerals of the present invention are characterized by shell-like fractures as a result of crushing or crushing the dry material prior to calcination to produce particles particularly suitable for use as abrasive grains. The abrasive grains may be used to make any of a variety of abrasive products, such as coated abrasive products, shaped abrasive wheels, low density nonwoven abrasive products, and the like. The invention will be further illustrated in the accompanying drawings. Figures 1-6 relate to alumina-zirconia minerals produced in accordance with the present invention. Figure 1 is a Laue X-ray photograph, Figure 2 is a transmission electron micrograph magnified at a magnification of 33,000 times, and Figure 3 is a photomicrograph taken with a scanning electron microscope at a magnification of 30,000 times. Figure 4 is an optical micrograph of air-dried particles taken at 30x magnification, and Figure 5 is an optical micrograph of air-dried particles taken at 30x magnification.
Figure 6 is a photomicrograph of particles of a gel precalcined at 1000°C; Figure 6 is a photomicrograph of the particles taken with an optical microscope at 30x magnification; Figure 7 shows a preferred method of producing the minerals of the invention. This is a flowchart. As shown in FIG. 7, a preferred method of the invention involves dispersing alumina monohydrate in acidified water to produce a relatively stable hydrosol or colloidal dispersion of peptidized alumina monohydrate, e.g. Undispersed particles are removed by separation, the resulting dispersion is mixed with a modifying component precursor, such as zirconyl acetate or other alkanate, the mixture is gelled, the gel is dried to a glassy state, and the dried gel is Grinding to the desired particle size, the ground material is calcined at a temperature of at least 1250°C, but below the mineral melting temperature, to form a close contact of fine crystal sized alumina and random orientation of the modified components. This includes producing mixtures of different types. Methods for making alumina monohydrate are well known in the art. Commercially available α useful in the present invention
-Alumina monohydrate is a by-product of the Ziegler process for producing primary alcohols, and is available under the trade names " ^Dispal® M,"" ^Dispural® ," and "Catapal®. ^"
Sold at SB. These products have special purity, high surface area (e.g. 250-320m ² /g)
and very small crystallite size (approximately 50
Å). Alumina monohydrate can also be obtained by hydrolysis of aluminum alkoxides. Monobasic acids or acidic compounds that may be used to peptide alumina monohydrate, and the resulting hydrosol or colloidal dispersion, include acetic acid, hydrochloric acid, and nitric acid.
Nitric acid appears to provide the most stable alumina monohydrate hydrosol or colloidal dispersion. That is, when the peptide is peptided with nitric acid, there is little or no precipitation of alumina. Acetic acid, although still useful, appears to be the least stable. (The term "relatively stable hydrosol or colloidal dispersion" refers to a dispersed aqueous mixture of fine particulate material that remains in suspension for extended periods of time.)
Polybasic acids such as sulfuric and phosphoric acids should be avoided because they cause the alumina monohydrate to gel very quickly and are difficult to mix with the modifier precursor. The amount of acid required may be determined by conductometric titration to the apparent equivalence point and is directly related to the surface area of the alumina. The pH of the peptide sol is generally 1-2.
Although it is only a small amount, it increases to about 3 if left alone. Insufficient amounts of acid inhibit particle dispersion. Excess acid will quickly gel the mixture upon addition of the modifying component precursor, making mixing difficult, but if uniformity is achieved, there will be no adverse effect on the product. The concentration of alumina monohydrate in the hydrosol or colloidal dispersion can vary widely from 2-3% by weight to concentrations as high as 40% by weight or more. Mixtures made with hydrosols or colloidal dispersions containing less than 5% by weight alumina monohydrate when combined with a modifier precursor solution generally do not undergo gelation without preliminary dehydration of the mixture. Concentrations of alumina monohydrate greater than 30% tend to gel too quickly and are therefore somewhat difficult to mix with the modifying component source compound. Therefore, the preferred concentration of alumina monohydrate is about 15% by weight to about
It is 30% by weight. During firing, the modifying component precursor utilized in the present invention produces metal oxides, some of which react with alumina to form spinel. Spinel is produced by reacting alumina with oxides of metals such as cobalt, nickel, zinc and magnesium. Zirconia and hafnia do not form spinels with alumina. The precursor for the modifying component preferably has a volatile monovalent organic or inorganic anion. Certain precursors with multivalent ions, such as carbonate and oxalate, do not cause premature gelation and do not interfere with homogeneous mixing;
or their decomposition does not result in excessive bubbles or porosity in the gel and the resulting mineral. Such multivalent anion-containing compounds are particularly useful in promoting gelation of dilute sols. Useful precursors of the modifying components are zirconyl acanate and zirconium nitrate which yield zirconia upon calcination, nickel nitrate and nickel acetate which yield nickel oxide, zinc nitrate and zinc acetate which yield zinc oxide and cobalt nitrate which yields cobalt oxide. include. It must be understood that the above list of exemplary precursors is not exhaustive and that other compounds can also be used. Additionally, a single precursor may provide more than one modifying component. Certain metal oxides (eg, magnesia) may be dissolved directly in the alumina-containing acidic medium. It must be understood that many precursors may contain small amounts of impurities or intentionally added components that do not interfere with the production of useful minerals in many cases. For example, zirconium compounds generally contain about 1-2% hafnium as an impurity that does not have an adverse effect on the final abrasive mineral. Therefore, useful abrasive minerals are produced when other metal oxides or their precursors are included in addition to the above modifying components. Examples of such minerals are zirconia and samaria (the latter obtained, for example, from samarium acetate or samarium nitrate),
and a second phase consisting of alumina-magnesia spinel with titania, ceria, zirconia and mixtures thereof. Preferred modifying component precursors are zirconyl alkanates, particularly zirconyl formate or zirconyl acetate, available from Ventron Corporation.
Alpha Division
and Harshaw Chemical Co.
Chemicals Company). The empirical formula for zirconyl alkanate in the product literature from co-suppliers is HZrOOH-
(OOCR) ₂ where R is H or CH ₃ . Zirconyl acetate is the most preferred zirconyl alkanate because it has a long shelf life and is currently readily available. Other zirconyl alkanates are also useful. Zirconyl acetate is a water-soluble solid that may contain sodium ions. The presence of calcium or alkali metal ions in the alumina-zirconia minerals of the present invention tends to make them undesirably porous, soft, and brittle, possibly due to the formation of beta-alumina. Therefore, when the alumina-zirconia minerals of the present invention are used as abrasive grains, a step of removing substantially all traces (less than about 0.05% by weight) of calcium ions, sodium ions, and any other alkali metal ions is required. Must be taken in. Excess calcium and alkali metal ions may be removed by passing the zirconyl alkanate solution through a column containing a cation exchange resin or by simply mixing the solution with such a resin. Alumina monohydrate hydrosol dispersions contain zirconyl alkanates (or other precursors to modifying components)
to obtain a homogeneous mixture which is mixed with gel. The amount of time required to form a gel depends on the ratio of the precursor components to each other in the solution or dispersion, their respective solids content, acid content, acid content and the size of the colloidal particles. Some low solids content mixtures do not gel without first being partially dehydrated. The alumina monohydrate hydrosol dispersion and the modified compound precursor solution may be mixed at any convenient temperature so long as they do not solidify, gel, or rapidly evaporate the solvent. Typical mixing temperature is 10
The temperature range is from 0.degree. C. to 80.degree. C., preferably from 30.degree. C. to 60.degree. The mixing equipment in which the two liquids must be brought into a homogeneous blend is batch or preferably continuous equipment. The most preferred systems are rapidly compounding and
It involves pumping the two liquids sequentially and simultaneously into a small-volume, high-action in-line mixer that thoroughly mixes and discharges. The resulting gel is then dried at a temperature and pressure that does not cause the water to boil or bubble. Characteristically, drying results in stubby pieces of gel due to low cohesion and significant shrinkage of the gel. If the produced mineral is to be used as an abrasive grain, the dry material must be a solid mass larger than the desired abrasive grain. If a virtually void-free, dense baked product is desired, drying conditions that cause the gel to foam or create voids or bubbles must be avoided. Preferably, it is dried slowly with or without stirring. The preferred method is to spread the gel to a thickness of approximately 2-3 cm, with approximately 1
This involves sun drying or removing all free water (ie, water not chemically bound) from the gel, leaving a particulate, glassy material. Although the individual pieces of dried gel appear to be solid and dense, they are actually brittle and can be crushed with finger pressure. FIG. 4 shows an optical micrograph of the air-dried material. X-ray diffraction examination of the dry gel shows the same diffraction pattern as the wet gel. The dried gel should preferably be sufficiently porous to allow rapid calcination. 150
Without heating above 0.degree. C., the dried gel can be completely dispersed in water to form a sol that can be recycled. When the dry particulate material is too fine to be used as abrasive grains,
This feature has economic benefits since it can be easily recycled. The dry material is then ground to reduce the particle size to the desired size of the abrasive particles. Since calcination typically causes shrinkage of 20%-40% by volume, the milled material must be slightly larger than the desired granules. Since the material is very hard and brittle, grinding is relatively easy and can be carried out by any grinding device, preferably a hammer mill or a ball mill. Consideration must be given to maximizing the yield of the usable size range and producing the desired particle morphology. The crushed material is sorted to extract the size of the particles that will become useful abrasive grains.
The remaining bulk material can be recycled. Large unusable size material may be reground and small unusable size material may simply be redispersed in water. It must be noted that due to the large surface area, after drying, the vitreous particulate material absorbs a large amount of water vapor and other gaseous materials from the atmosphere if cooled at room temperature under ambient conditions. The absorbed material is generally driven off by the time the firing temperature reaches 150°C. Optimal firing conditions will depend on the particular composition, but can be easily determined by those skilled in the art since this technology has been disclosed. The dried gel or vitreous particulate material is heated in the presence of oxygen (eg, in air) during an operation described herein as calcination. chemically bound water and the remainder of the acid used to produce the alumina sol by heating, decomposing the organic zirconyl alkanate to zirconium dioxide, and oxidizing;
Remove volatile reaction products, convert alumina and zirconia to the desired crystal structure, break the composite,
Essentially eliminating vacancies and producing a dense, solid alumina-zirconia mineral consisting of an intimate mixture of small zirconia and alumina crystallites present in random orientation. Care must be taken in the calcination to avoid destroying the composite before driving out all volatile materials and to provide sufficient oxygen during the oxidation of the zirconyl alkanate to zirconium dioxide and gaseous products. While heating the composite, care must be taken to raise the temperature slowly enough to allow volatile materials to escape as they evolve without creating significant internal pressure within the composite. Zirconyl alkanates are carbonized or charred at around 250°C and oxidized to zirconium dioxide at 450°C. At approximately 600°C, essentially all chemically bound water is released from the hydrated alumina. The temperature at which the remaining portion of the acid is driven off depends of course on the particular acid used, but is generally around 1000°C.
It is as follows. All minerals at least 1250℃, typically
Continue firing until the temperature reaches 1300℃ or higher.
At this point, the porous, high surface area structure of the dry gel breaks down to form independent free-flowing particles of a solid, dense body of alumina-zirconia, and various deformations occur in the crystal structure of the alumina and zirconia. The transformation of alumina and zirconia into various crystal structures is very complex and not completely understood. The first identifiable crystallographic species of zirconia obtained during calcination of the dry gel is identified by X-ray diffraction as having a tetragonal crystal structure. As the firing temperature increases, the X of the produced mineral at room temperature increases.
Linear diffraction examination shows the presence of some monoclinic zirconia. The amount of conversion depends on the zirconia content, firing rate, firing conditions and type of equipment used. if,
Firing at 1300°C for several hours with a high zirconia content, say around 40%, will produce a crystal structure that is primarily monoclinic with a small amount of tetragonal crystal structure ^* ( ^* if X-ray If the diffraction lines are diffuse, they will include some cubic zirconia).
However, if the zirconia content is low, for example around 15%, the main crystal structure is tetragonal with a small amount of monoclinic form. Under these conditions essentially all alumina is converted to the α-crystalline structure. Alumina exhibits numerous crystal structures or morphologies,
It progresses through a series of such structures as the temperature increases. After 3 to 5 hours at 1250°C, essentially all of the alumina is converted to the α-form, which is the crystalline structure of alumina commonly used as abrasive grains. However, it has been found that minerals suitable for use as abrasive grains can be produced by heating the product for 2-3 minutes at temperatures above 1250°C, even though the conversion of alumina to the alpha form is not complete. are doing. Addition of magnesia to alumina-zirconia based products creates an identifiable spinel crystal structure in addition to alumina and zirconia crystallites. Moreover, if the magnesia precursor is added directly to the alumina sol, the final product contains identifiable spinel in addition to alumina crystallites. The rate at which the temperature is increased to achieve the above objectives depends on several factors, including the chemical composition of the mineral (eg, alumina-zirconia ratio), particle size, and oxygen accessibility. If firing is done in a static bed, bed depth, heat transfer and air supply are also factors. If the minerals are agitated and exposed to air, the firing time may be substantially reduced, but since the minerals are used in the form of abrasive grains, agitation during firing is particularly important in the early stages, when they are still brittle. It must be controlled to avoid dulling or rounding the grain edges. Firing under static conditions typically requires several hours. Firing under dynamic conditions can also be achieved for 2-3 minutes. The rate of heating must be controlled so that volatiles can escape from the interior of the mineral without creating excessive internal pressure that would crack the mineral. Experimentation is required to determine the optimal firing conditions for a particular situation. Firing at very high temperatures for long periods of time can lead to undesirable crystal growth and should be avoided. For example, the growth of coarse crystals was noted in minerals heated at 1,650°C for several hours. Minerals with finer crystal structures, on the other hand, are less desirable, but are still useful as abrasive grains. After firing, the mineral may be cooled quickly to room temperature without damaging it. Preferred minerals are Knoop hardness (load 500g)
ranges from about 1200 to 1800 Kg/mm ² , and hardness is generally directly related to α-alumina content. The photograph of the Lauer X-ray pattern of the mineral of the present invention containing alumina-zirconia = 64:36 (weight ratio) in Figure 1 shows that the orientation in the alumina-zirconia mineral is substantially lacking, and the zirconia and alumina crystallites are shows the random orientation of both. The transmission electron micrograph in Figure 2 confirms this analysis and shows that the gray α-
Showing dark crystallites of zirconia in alumina with random orientation. Figure 3 is a scanning electron micrograph at 30,000x magnification of a petrographically produced sample of the mineral of the present invention, further showing the random orientation of zirconia crystallites shown as bright spots in dark α-alumina. and to check the morphology (the white dots near the center of the micrograph are extraneous particles that were used only to focus the microscope, and to confirm the focus and to confirm that the crystallite outlines or terminals are actually obscured). (It serves only to show that there is). Figure 5 is an optical micrograph of the material pre-fired at 1000°C, showing a shell-like surface. The photomicrograph of the calcined product taken with an optical microscope in FIG. 6 shows that the shell-like surface of the alumina-zirconia mineral of the present invention is still present. It should be noted that the mineral shown in Figure 6 is opaque, but is transparent to visible light if short firing times are used. The ability to produce transparent minerals from gels is evidence of the very fine crystallite size of the minerals of the present invention and the absence of gross inhomogeneities or defects. Clear or opaque calcined minerals exhibit glassy shell behavior when viewed at low magnification. The addition of magnesium oxide has been found to increase the hardness, toughness, and abrasive ability of the resulting mineral product even in small amounts, on the order of about 0.2% to about 20% by weight. Magnesium oxide may be added by dissolving or reacting a precursor such as magnesium nitrate or magnesium oxide in the zirconyl alkanate prior to addition to the alumina hydrosol. The preferred aluminum oxide-based abrasive minerals of the present invention are about 40%-99% alpha-alumina (preferably 50%-98%), about 0%-60% zirconia (preferably 0%), based on oxide equivalent weight. -45%) and about 0%-25% (preferably 1%-12%) magnesia, which is a spinel formed by the reaction of magnesia and alumina. Based on the volume in alumina-zirconia, this is approximately 49
%-90% (preferably 59%-98%).
For minerals formed from alumina and MgO,
The alpha-alumina content is between 11% and 99%, preferably between 55% and 96%. Volume % ratios of other mineral compositions may be calculated from the weight % and density of phases known to be present. Particulate minerals may be used as unbound pellets or used to make coated abrasive products, abrasive wheels, nonwoven abrasive products, and other products in which abrasive particles are typically used. good. The invention will be further illustrated by the following examples.
This is not intended to limit the invention. All parts and percentages are by weight unless otherwise indicated. The compositions of the examples are summarized in Tables 1 and 2. Example 1 Water, 16N nitric acid and product name “Dispar R”
α-Alumina monohydrate powder sold by ``Dispal M'' was charged into a 6 stainless steel mixing vessel of a ``Waring'' industrial type compounder.
Dispersion was performed at high speed for 30 seconds. The dispersed solids were removed by passing the dispersion through a continuous centrifuge that generates 3000 times the force of gravity. The produced dispersion and 50% zirconyl acetate aqueous solution were metered and injected through an in-line blender to produce a mixed dispersion, and a 5 cm x 46 cm
Collected in a x61 cm aluminum dish, the mixed dispersion gelled in less than 5 minutes. The gel was dried in a forced air oven at 90°C until the volatile content was less than 10% and pelletized to approximately 0.5 cm in diameter. The small grains are crushed in a 20cm hammer mill, sieved and calcined so that the average particle size is between 0.5mm and approx.
It had a range of mm. The part of the particles with an average diameter smaller than 0.5 mm was retained for Example 3. The sieved and ground material was then transferred to a non-reactive 5 cm x 10 cm x 20 refractory dish, heated in an oxidizing atmosphere at a heating rate of 100°C/hour, and calcined at 550°C. The material was held at 550° C. for 20 hours, during which time it became a uniform translucent yellow color. Then the temperature
Raise to 1350℃ at a rate of 200℃/hour, and increase to 1350℃ for 5 minutes.
Holds time. The furnace was then cooled to room temperature and the resulting fired material was removed. The fired material was small opaque white particles consisting of 60% alumina and 40% zirconia. The following Examples 2-10 are substantially the same as Example 1 except for the changes noted. Example 2 Firing was carried out using a shorter firing time than that described in Example 1. 13cm diameter with a 30cm heated sol rotating at 7rpm at an angle of 3° to the horizontal.
The ground dried gel was fed to the end of a 700° C. kiln, which was a 1.2 mm mullite tube, and the residence time was approximately 5 minutes.
The calcined product from the 700°C kiln was fed directly to a 1350° kiln of similar construction and configuration, and the residence time was approximately 1 minute. The product was cooled to room temperature for 5 minutes to obtain a clear mineral. Opaque minerals were also produced in the same manner except that the residence time in the 1350°C kiln was approximately 3 minutes. Example 3 1 piece of dry gel fine powder pulverized as in Example 1
3 kg of water was added to 3 kg of fine powder, mixed in a Waring blender, and redispersed in water. The resulting dispersion was transferred to an aluminum dish and allowed to gel for approximately 5 hours. Example 4 MgO (reagent grade powder MgO obtained from Mallinckrodt Chemical Co.) was dispersed in a zirconyl acetate solution and reacted directly. Inserting dispersions and solutions
It was metered through an on-line compounder, dried, ground and calcined as in Example 1. Example 5 Adjusting the metering rate of dispersions and solutions;
A final composition _of 80% _Al2O3 and 20% _ZrO2 was produced. Example 6 MgO was reacted directly with a zirconyl acetate solution. Example 7 Dispersion and solution metering injection Al ₂ O ₃ 70% - ZrO ₂ 30
% product. Example 8 MgO was reacted directly with a zirconyl acetate solution. Example 9 Acetic acid was used as the acid source requiring a fairly large amount of dilute dispersion. Example 10 MgCl ₂ .6H ₂ O was dissolved in zirconyl acetate solution. Example 11 In this example, a 50% solution of zirconyl acetate was mixed with 25% water.
Same as Example 2 except that magnesium nitrate was dissolved therein. Zirconia crystallites are measured using a transmission electron microscope, and the apparent diameter is
It was shorter than 300 Å. Example 12 This example is the same as Example 2 except that magnesium nitrate was dissolved in water and the resulting solution was added to the alumina sol. Example 13 This example is a control example that is the same as Example 1 except that zirconyl acetate is omitted, and alumina
A product was produced that was 100%. Examination by optical microscopy (750x) of etched samples with only calcined particles showed that the crystal size of α-alumina was clearly finer than that of the modified mineral of the present invention, and the crystal structure was not as observed. I couldn't do it.
Line broadening of the X-ray diffraction pattern indicates that the crystallite size of this 100% α-alumina is smaller than that of modified alumina calcined under the same conditions. Each of the batches of abrasive particles prepared as described in Examples 1 to 13, 21 and 41 were separated into three conventional particle sizes and placed in a conventional coated abrasive in a filled rayon or cotton twill cloth. A manufacturing method was used to produce a bonded and coated abrasive sheet material. The make adhesive consisted of a conventional solution containing 48% phenol-formaldehyde resin solids and 52% calcium carbonate filler. The mineral weights shown in the table were adjusted to provide a relatively constant volume of mineral for all products having the same particle size. The overlay adhesive consisted of a conventional solution containing 32% phenol-formaldehyde resin and 68% calcium carbonate filler. The base resin was precured at 88°C for 75 minutes, and the top resin was precured at 88°C for 90 minutes. The coated abrasive product was final cured at 100°C for 10 hours. The coating was processed using conventional techniques. Endless abrasive belt with coated abrasive sheet,
7.6cm x 335cm, 1018 steel workpiece was continuously polished by a constant load surface sander for 30 seconds.
A 2.5 cm x 18.4 cm surface was polished, weighed and cooled after each polishing period. As for the polishing conditions, the pressure, belt speed, and work piece feeding speed shown in Table 1 were used. The work piece is placed with the long dimension in the vertical direction,
During polishing, it is moved perpendicular to the path 18.4 cm in one rotation from its original position and back again according to the number of cycles shown in the table. The polishing results are shown in the table below. As can be seen from the results shown in Table 1, the abrasive particles of the present invention abrade much better than conventional aluminum oxide and are substantially equal to or better than commercially available eutectic alumina-zirconia materials.

【table】

【table】

【table】
Abrasive quality
Al ₂ O ₃ ZrO ₂ MgO (load 500g)

Claims (1)

[Scope of Claims] 1. A method for producing a granular abrasive mineral based on a high-density synthetic aluminum oxide containing a modifying component in a continuous alumina phase consisting of alpha alumina, comprising: (a) an alumina source compound; , (i) zirconia, hafnia, or a combination of zirconia and hafnia, and (ii) alumina with cobalt, nickel, zinc,
or a spinel derived from at least one oxide of a metal selected from the group consisting of magnesium; gelling an ion-free homogeneous mixture; (b) drying said gelled mixture to form chunky pieces of solid material; and (c) subjecting said solid material to a temperature of at least 1250° C. in a non-reducing atmosphere. but comprising steps of calcination to a temperature not higher than the melting point of said mineral to remove volatile materials and non-destructively convert said solid material into a dense aluminum oxide based mineral; Also, the precursor contains a continuous alumina phase as a main component consisting of alpha-alumina in the mineral, and a volume % of the calcined solid of the mineral, (a)
A modifying component containing at least 10% of (i), (b) at least 1% of (ii), or (c) at least 1% of (ii) and 1 to 45% of (i). A method for producing a granular abrasive mineral, wherein the granular abrasive mineral is present in an amount to provide. 2 A granular abrasive mineral based on dense chemical ceramic aluminum oxide substantially free of calcium and alkali metal ions, comprising a calcined solid of said mineral in a predominantly continuous alumina phase consisting of alpha-alumina. (i) at least 10% of zirconia, hafnia, or a combination of zirconia and hafnia; (ii) alumina and at least one oxide of a metal selected from cobalt, nickel, zinc, or magnesium; (iii) 1-45% of said zirconia, hafnia, or a combination of zirconia and hafnia, and at least 1% of said spinel; A granular abrasive mineral having a substantially homogeneous microcrystalline structure with a second phase of crystallites present in a uniform orientation. 3. A granular abrasive mineral based on dense chemical ceramic aluminum oxide substantially free of calcium and alkali metal ions, comprising a calcined solid of said mineral in a predominantly continuous alumina phase consisting of alpha-alumina. (i) at least 10% of zirconia, hafnia, or a combination of zirconia and hafnia; (ii) alumina and at least one oxide of a metal selected from cobalt, nickel, zinc, or magnesium; (iii) 1-45% of said zirconia, hafnia, or a combination of zirconia and hafnia, and at least 1% of said spinel; An abrasive article comprising a particulate abrasive mineral having a substantially homogeneous microcrystalline structure having a second phase of crystallites present in a uniform orientation. 4. Granular abrasive minerals are adhered to a flexible backing sheet to form a coated abrasive product;
An abrasive article according to claim 3. 5. The abrasive article of claim 3, wherein the particulate abrasive minerals are bonded together to form a rotating abrasive wheel. 6. The abrasive article of claim 3, wherein particulate abrasive minerals are adhered onto and within the bulky nonwoven carrier web.