MXPA99001802A - Solid gel abrasive with reduced tita content - Google Patents

Abstract

A method for forming a sol gel abrasive comprising forming a gelled dispersion wherein the solids in the dispersion comprise from 92 to 99 weight percent alumina or alumina precursor and from 1 to 8 weight percent titanium oxide or precursor of titanium oxide. The gelled dispersion is dried to form a dry gel and heated to a temperature from about 1225 ° C to about 1500 ° C. The heating is done in a gas atmosphere in a reducing environment to create reduced titanium oxide in the finished abrasive product. The temperature scale for a heating time of ten minutes can be determined by the formula §C = 1425 ± 75 - 20 Tc, where Tc is the concentration of titania in percent by weight of the solids. The product of the invention is a sol gel abrasive containing reduced titanium oxide. The invention also includes novel gel sol grain made with the method of the invention.

Description

ABRASIVO DE SOL GEL WITH REDUCED CONTENT OF TITANIA Background of the Invention This invention relates to an abrasive grain and more particularly relates to an abrasive grain made by a sol gel process. The alumina products made by a sol gei process are known at least since 1960 when the application for United States Patent 3,106,888 was filed. Ceramic particles comprising mainly alumina were described as being made from a sol gel process in U.S. Patent 4,181,532. In U.S. Patent 4,314,827, which expires on February 9, 1999, an abrasive material based on non-molten aluminum oxide was described. We describe how this material is made from a sol gel process that uses an aluminum spinel and a precursor of at least one of zirconia or hafnia. It has been found that the sol gel abrasive materials have certain advantages over the abrasive grains formed by melting powder concretion. In particular, sol gel products can have a smaller crystal size, lower porosity and better cutting and wear characteristics compared to traditional cast and concreted abrasive products.

Unfortunately there have been problems associated with the preparation of sol gel abrasive grains. In order to obtain a consistently good product, drying and concretion conditions have had to be precisely controlled and expensive grain modifiers, such as zirconia, hafnia, beryllium, toria, yttria and cobalt compounds, have often been required, nickel and zinc and rare earth compounds such as ceria, samaria, neodymium oxide and lanthanum. Sol gel abrasives consisting of alumina and titania have been described in the literature on the date of application of this document, see for example U.S. Patent 5,114,891. The titania is not reduced.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of the sol gel abrasive cuts of air-fired samples from the examples described herein against the ignition temperature. Figure 2 is a graph of sol gel abrasive cuts of graphite lit samples from the examples of the present against the ignition temperature.

Brief Description of the Invention According to the invention there is provided a method that allows the manufacture of abrasive grains of so! gel comparable with the best alumina-containing sol gel grains available in the prior art, without the requirement to add costly modifiers, with more breadth in the control process, and without the requirement to tightly control the reaction conditions and the environment to order to obtain the nitride content. The invention also includes novel gel sol grain made by the method of the invention. It has been found that reduced titania in molten grains is beneficial, see for example U.S. Patent 5,143,522; however, no sol gel gel containing any significant amount of reduced titania has been known nor has there been any suggestion of how such a grain can be obtained in view of the stringent sol gel processing requirements. The novel gel sol grain is the first sol gel gel that contains any significant amount of reduced titania. The simple addition of reduced titania to the are prior to concretion does not result in a sol gel abrasive grain containing a reduced titania component. The presence of oxygen during concretion simply oxidizes the reduced titanium to titanium dioxide. The use of a nitrogen atmosphere causes a reaction between nitrogen and titanium to form titanium nitride, see for example European Patent Application EP 0471 389. In particular the novel method of the invention comprises forming a gelled dispersion wherein the solids in the dispersion comprise from 64 to 99 weight percent alumina or alumina precursor), 0 to 35 weight percent of zirconia or zirconia precursor and 1 to 8 weight percent of a titanium oxide and titanium oxide precursor. The gelled dispersion is dried to form a dried gel and heated to a temperature from about 1225 ° C to about 1500 ° C. The heating was effected in a gas atmosphere in a reducing environment to create a reduced titanium oxide in the finished abrasive product. The reducing environment can be formed using a reducing gas such as carbon monoxide or by mixing the feed with graphite powder. The temperature scale for a heating time of ten minutes can be determined by the formula ° C = 1425 ± 75 - 20Tc where Te is the concentration of titanium oxide in percent by weight solids. The product of the invention is a sol gel abrasive containing a reduced titanium oxide.

Detailed description of the invention _ The sol gel abrasives as used herein represent abrasives formed from gelled dispersions that are dried and calcined. Dispersions are dispersions containing mainly hard substances or hard substance precursors suitable for abrasive applications, especially alumina (to aluminum oxide). Another suitable hard substance is zirconia. In accordance with the present invention the titanium oxide or the titanium oxide precursor is included in the sol gel to subsequently obtain a reduced titanium oxide in the finished product to obtain improved properties with the broader permissible processing parameters. Dispersions are stable dispersions in the literal sense, ie the solids in the dispersion do not settle easily. Such dispersions are intended to include colloidal dispersions and real solutions and mixtures thereof. In the present invention, such dispersions can include alumina colloids, zirconia, and various titanium oxides, for example titanium dioxide, titanium monoxide, titanium sesquioxide and mixtures thereof, and substances which will convert to such materials during processing of the soi gel. The colloidal materials are prepared by acidifying water-insoluble agglomerated crystalline materials which usually have an average particle size (50%) of less than 200 and preferably less than about 150 microns and desirably less than 25 microns. Such materials can be made by chemical precipitation or by crushing or milling the larger sized material, for example bauxite. The precursors include organic and inorganic compounds of metals that will be converted to the desired hard material or a desired additive during processing. Examples of such precursor compounds include aluminum oxide hydrates, aluminum chloride, aluminum nitrate, zirconium chloride, titanium alkoxides such as titanium IV isopropoxide, titanium butoxide and titanium ethoxide; titanium chloride, lanthanum nitrate and magnesium nitrate. The dispersions used in the invention contain alumina and reduced alumina precursors in an amount which results in from about 64 to 99 weight percent alumina, 0 to 35 weight percent zirconia and about 1 to 8 weight percent reduced titania in the finished product. Unless otherwise indicated, the weight percent of the alumina oxide and titania colloids and precursors is stated in percent by weight solids calculated exclusive of any solid reducing agent. In a preferred dispersion, the alumina precursor is provided in an amount of from about 5 to about 40 percent combined alumina precursor and colloidal alumina and from about 1 to less than about 2 weight percent of the titanium oxide solids. combined and precursor of titanium oxide. In order to form the gelled dispersion (sol gel), colloidal sized materials and precursors are dispersed in the form of 60 to 90 weight percent of the dispersion, of a suitable liquid medium comprising mainly water. Tai dispersion can be done using a high shear blender. The components can be mixed simultaneously or the components can be dispersed independently and the resulting independent dispersions subsequently mixed with other components. A gelation additive is included in the dispersion either at the time of initial dispersion or after. The gelling additive is usually a mineral acid which reacts with the aluminum hydrate in the dispersion to form a gel. A particularly suitable mineral acid is nitric acid. Such acid is used in a usual manner in an amount of about 0.08 to 0.1 mol of acid per molecule of alumina. The reducing agent may be included in the sol gel or may surround the gel sol to provide a reducing environment during concretion (heating up to 1225 ° C to 1500 ° C). Such reducing agents include colloidal carbon, usually in the form of graphite and water-soluble organic carbon, for example isopropanol, n-butanol and various soluble sugars. Other reducing agents include easily oxidizable colloidal metals whose oxides are compatible with the abrasive composition, for example aluminum. The amount of the reducing agent used is often sufficient to react with 40 to 125 percent oxygen by weight of solids in the sol gel, for example 20 to 50 weight percent of carbon. A reducing atmosphere can be used alone or in conjunction with the reducing agent in or around the gel sol. The reducing atmospheres are carbon monoxide and hydrogen. Other additives may be included in the sol gel for various purposes, for example, grain growth and grain boundary modifiers, densification agents, dispersing agents and solvents, for example, lanthanum oxide, iron oxides, surfactant and isopropanol . After the gel is formed, it is dried and crushed. Drying can be done by any suitable means such as film evaporation and grinding can also be done by known methods, for example roll crushing. After trituration the dried gel sol is calcined at 500-600 ° C and then concreted at a temperature from about 1225 ° C to about 1500 ° C for a time of about 2 seconds to about 60 minutes. The best temperature in degrees Celsius has been determined empirically to be usually 1425 ± 75 -20 TC where TC is the concentration of titania in percent by weight of solids excluding carbonaceous materials (eg free reactive metals, carbon and compounds organic compounds such as aluminum, graphite, alcohols and sugars). Time depends in some way on the size of the batch of material being heated, since longer times are required to heat larger quantities of materials to the desired temperature. In general small batches and short heating times are preferred since they result in a more uniform product having a smaller average glass size. Heating can be done in crucibles in a standard oven; however, a tube furnace is preferable as it results in faster heat transfers by making the heating times as short as possible. In an ideal situation the individual grains of crushed material pass through a tube furnace in a matter of seconds. After heating, the grain can be cooled rapidly, for example below 900 ° C in less than ten seconds. Shorter cooling times can be used. The titanium in the finished product is combined with oxygen in an average titanium valence of minus +3.5 resulting in a desirable and superior product.

Examples 1-52 An Al203-Ti02 system was produced from boehmite (aluminum oxide hydrate) under the DISPERSAL brand owned by Condea Chemie GMBH of the Federal Republic of Germany. The following formulation was used: 97 grams of Al203 from DISPERSAL-boemita (97 + .745 to respond for chemical water) 3 grams of T02 from 10.7 grams of titanium IV isopropoxide, and 120 ml of HN03 (0.1 mols HN03 per mole of boehmite). With a lit blender 130.2 grams of boehmite in 400 ml of water were added. 5 ml of concentrated nitric acid were diluted in 30 ml of water and added to the boehmite paste. The acid dispersed the boehmite to a colloidal state to form a sol. 10.7 grams of Ti IV isopropoxide were added to 450 grams of isopropyl alcohol and then added to a mixture of 30 ml of water and 4 ml of concentrated nitric acid. The resulting mixture was added to the sun. The rest of the acid (3 ml) was added to 40 ml of water and added to the soi which then forms the gel. The gel is dispersed on a plastic sheet and left to dry in the air. The air-dried gel is then dried in an oven at 100 ° C and crushed and sieved. The material was then calcined at 550 ° C for 45 minutes and was ready for ignition. The procedure was repeated for various concentrations of Titanium propoxide to provide calculated titania concentrations of 0 (with .06 and .14 mols of acid), 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 8.0 percent. As the amount of titanium isopropoxide was increased, the amount of acid added to the titanium isopropoxide was increased accordingly. Samples of 100 grams in four increments of 25 grams of the compositions were fired for ten minutes at various temperatures from 1200 to 1525 ° C both not protected in air and protected by mixing with graphite and covered by a layer of graphite to form a reducing environment . Each of the samples of ignited material was graded to 36 grit and coated using standard procedures on a 20.32 cm by 20.32 cm fiber backing material using phenolic resin, calcium carbonate and cryolite. For comparison purposes, a commercial alumina gel sol that incorporates approximately one percent of each magnesia oxide, yttrium oxide, lanthanum oxide and neodymium oxide was also coated on a support using the same procedures. The 20.32 cm square coated products were cut into 17.78 cm diameter discs and were tested by grinding on 1018 steel samples having a cross section of 2.54 by 30.48 cm. Tables 1 and 2 show the results in grams of the material removed during the life of the disk. As can be seen from tables 1 and 2 and the graphs developed therefrom shown in Figures 1 and 2, the products of the invention that incorporate as little as one percent reduced titania have cuts comparable to those that use at least 3% of titania in air and also with sun commercial gels that include expensive rare earth components. In addition, it is clear from the graphs that products made in a reducing atmosphere are more tolerant to processing conditions.

Table 1. ASG's and Cutoff for each sample turned on air On Air rv > * This court is considered invalid. There was edge wear on the disk

Claims (18)

1. A method for making a sol gel abrasive composition comprising: forming a gelled aqueous dispersion wherein the solids in the dispersion, excluding the carbonaceous material, comprises 64 to 99 weight percent alumina or alumina precursor, from 0 to 35 per cent. weight percent zirconia or zirconia precursor, and 1 to 8 weight percent of a titanium oxide or titanium oxide precursor; drying the dispersion to form a dry gel; heating the dried gel to a temperature of about 1225 ° C to about 1500 ° C for a time of about 2 seconds to about 60 minutes, the temperature for a heating time of ten minutes which is determined by the formula ° C = 1425 ± 75 - 20 TC, where Te is the concentration of titania in percentage by weight excluding carbonaceous materials, characterized in that the heating occurs in a gaseous atmosphere in a reducing environment, to form an abrasive composition of sol gel containing titanium combined with oxygen to an average titanium valence of less than +3.5.

The method of claim 1, characterized in that the dried gel is heated to the temperature for less than about one minute.

3. The method of claim 1, characterized in that the reducing environment comprises an atmosphere containing carbon monoxide.

4. The method of claim 1, characterized in that the reducing environment is obtained by including a reducing agent in the sol gel.

The method of claim 4, characterized in that the reducing agent is selected from the group consisting of colloidal carbon, oxidizable organic compounds and aluminum.

The method of claim 5, characterized in that the reducing agent is from about 20 to 50 percent of the solids and is graphite powder.

The method of claim 1, characterized in that the alumina precursor is provided in the form of colloidal aluminum hydrate in an amount of from about 5 to about 40 weight percent of the combined alumina precursor and colloidal aluminum hydrate.

8. The method of claim 1, characterized in that the titania precursor is in the form of titanium IV propoxide.

The method of claim 1, characterized in that less than 2 weight percent of the solids, excluding the reducing agent, is used from the combined titanium oxide and titanium oxide precursor.

10. A sol gel abrasive characterized in that it is made according to the method of claim 1, the sol gel abrasive comprising from 64 to 99 weight percent alumina, or up to 35 weight percent zirconia and from 1 to 8 weight percent of titanium oxide reduced in an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

11. A sol gel abrasive characterized in that it is manufactured according to the method of claim 2, the sol gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

12. A sol gel abrasive characterized in that it is manufactured according to the method of claim 3, the sol gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

13. A sol gel abrasive characterized in that it is manufactured according to the method of claim 4, the soi gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

14. A sol gel abrasive characterized in that it is manufactured according to the method of claim 5, the sol gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

15. A sol gel abrasive characterized in that it is manufactured according to the method of claim 6, the sol gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

16. A sol gel abrasive characterized in that it is manufactured according to the method of claim 7, the sol gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

17. A sol gel abrasive characterized in that it is manufactured according to the method of claim 8, the sol gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.

18. A sol gel abrasive characterized in that it is manufactured according to the method of claim 9, the sol gel abrasive comprising from 92 to 99 weight percent alumina and from 1 to 8 weight percent oxide of titanium reduced to an average titanium valence of less than +3.5, the sol gel abrasive that is essentially free of titanium nitride.