METHOD AND APPARATUS FOR PRODUCING ALUMINA MONOHYDRATE AND SOL GEL ABRASIVE GRAIN

Abstract

A new method and apparatus is applied to manufacture boehmite and sol gel abrasive grain with greatly reduced raw material cost. The raw material starts from alumina trihydrate, which is transferred to highly dispersible alumina monohydrate under hydrothermal treatment in an agitated zirconium-steel or titanium-steel cladding plate high pressure reactor. Then the highly dispersed and deionized sol is converted to sintered high-density microcrystalline ceramic abrasive grain by sol-gel process.

Claims

1. A process to make highly dispersible boehmite suitable as raw material of sol gel abrasive grain, characterized in that, the boehmite is made by converting alumina trihydrate to boehmite in an agitated zirconium-steel or titanium-steel cladding plate vessel or pure titanium vessel.

2. A sol gel abrasive grain with various shapes and sizes, characterized in that, the raw material boehmite is prepared as described in claim 1.

3. A sintered abrasive grain with various shapes and sizes, characterized in that, the alpha alumina or other form of alumina is derived from the boehmite prepared as described in claim 1.

4. A coated abrasive product, characterized in that, its grain is made as described in one of claims 2 & 3.

5. A bonded abrasive product, characterized in that, its grain is made as described in one of claims 2 & 3.

6. An autoclave or a reactor or vessel, characterized in that, it is made from titanium-steel or zirconium-steel cladding plate or pure titanium and used as hydrothermal treatment in sol gel abrasive grain manufacturing process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is zirconium-steel or titanium-steel cladding plate as autoclave material.

[0018] FIG. 2 is a zirconium-steel or titanium-steel cladding plate high pressure autoclave for alumina trihydrate hydrothermal treatment.

[0019] FIG. 3 is process for making high purity, highly dispersible boehmite.

[0020] FIG. 4 is process to make sol gel abrasive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] The invented apparatus to manufacture boehmite as raw material for sol gel abrasive grain is shown in FIGS. 1 and 2. The invented method or process to make high purity, highly dispersible boehmite is described in FIG. 3 and the invented method to make sol gel abrasive grain is described in FIG. 4.

[0022] In FIG. 1, the titanium-steel or zirconium-steel cladding plate is made by explosive welding techniques. Titanium or zirconium metal or alloy is used as corrosion-resistant material, its thickness is varied from 3 mm to 10 mm which depending on the cost and corrosion consideration. Carbon steel or stainless steel is used as structure material to make autoclave for hydrothermal treatment. Its thickness is varied from 20 to 60 mm, depending on the temperature & pressure in the vessel and the size of the vessel.

[0023] In FIG. 2, the apparatus or autoclave for hydrothermal treatment includes raw material charge port, finished goods discharge port, visual inspection/maintenance hole, safety valve or steam release device to avoid high pressure explosion caused by over-heating, dispersing/mixing blade to mix the alumina trihydrate slurry to avoid agglomeration and facilitate the conversion of Al(OH).sub.3 to microcrystalline AlOOH. Heating/cooling jacket or loop is not drawn in FIG. 2, the heating can be direct or indirect, by steam or heated oil or other methods. The cooling is circulated water cooling or by other means.

[0024] In FIG. 3, the method and process is shown, the detailed process steps are as follows:

[0025] (1) Slurry preparation: Al(OH).sub.3 particles, seeded microcrystalline boehmite or pseudo-boehmite, hot deionized water and HNO.sub.3 are mixed to homogeneity by high-shear disperser. The solid content of Al(OH).sub.3 is from 10 to 30% and its particle size is D.sub.50=1-2 micron which can be readily available from market, the added HNO.sub.3 adjusts the slurry PH to 2-5. Low PH is better for hydrothermal conversion and particle size reduction but leads to gel in reactor easily. Optionally the Al(OH).sub.3 particles can also be calcined to increase surface area to facilitate the hydrothermal conversion.

[0026] (2) Size reduction of Al(OH).sub.3: the slurry is grinded in a sand mill which using small zirconia beads to a particle size of D.sub.50=0.1-1 micron, the preferred range is D.sub.50=0.1-0.5 micron. This size reduction process can facilitate the Al(OH).sub.3 converting to microcrystalline, nano-size dispersed boehmite particles with narrow particle size distribution.

[0027] (3) Hydrothermal treatment of slurry: the grinded slurry is charged to the zirconium-steel or titanium-steel cladding plate autoclave and agitated. Then increase the slurry temperature to 170-200 centigrade and hold for 1-3 hours to convert the Al(OH).sub.3 to AlOOH. The heating rate is not specified.

[0028] (4) Ion exchange: After hydrothermal conversion, the discharged boehmite dispersion is deionized to reduce alkaline oxide to get high purity products by electrodialysis or ion exchange resin or other methods.

[0029] In FIG. 4, process to make sol gel abrasive grain use invented boehmite is described. The assignee filed another patent application, there is no need to repeat the details.

[0030] The above-mentioned hydrothermal process is conducted in a 10 liter titanium-steel cladding plate autoclave, the obtained boehmite is seeded with 1% nano-sized alpha alumina, gelled, calcined, and sintered to abrasive grain, the Vickers hardness is 20 GPa at 100 gram load and the density is 3.88, it is suitable for abrasive applications.