CN1177761C

CN1177761C - Process for preparing alumina powder with high sinter activity

Info

Publication number: CN1177761C
Application number: CNB021110018A
Authority: CN
Inventors: 濂高; 高濂; 靳喜海
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2002-03-12
Filing date: 2002-03-12
Publication date: 2004-12-01
Anticipated expiration: 2022-03-12
Also published as: CN1369434A

Abstract

The present invention provides a method for preparing alumina powder with high sintering activity, which is characterized in that aluminium containing inorganic salt is used as principal raw material, ammonium bicarbonate is used as a precipitating agent, and NH4Al(OH)2CO3 is generated. More specially, the aluminium containing inorganic salt is one of aluminum nitrate, aluminium chloride and aluminium ammonium sulfate, the concentration of the aluminium containing inorganic salt is from 0.1 to 1 M, and the concentration of the ammonium bicarbonate is from 1 to 4 M. The reaction temperature is from 5 to 50 DEG C, and the precipitating and ageing time is from 2 to 24 hours. Precipitates are washed by deionized water until the impurity content of the inorganic salt is controlled to be 10 ppm, and then, the precipitates are dried at 50 to 150 DEG C and are finally sintered at 1100 to 1200 DEG C to change the precipitates into alpha-Al2O3 which is submicron and nanometer alumina powder with the grain size smaller than 400 nm. With the advantages of little hard aggregation and high sintering activity, the alumina powder prepared by the method is suitable for preparing high-grade alumina ceramic material.

Description

Preparation method of high-sintering-activity alumina powder

Technical Field

The invention relates to a method for preparing high-sintering activity alumina powder, belonging to the field of fine chemical engineering.

Background

The alumina ceramic has the characteristics of high hardness, high wear resistance and mechanical strength, high resistivity and good chemical stability, is widely applied to the industries of chemical industry, electronics, textile, machinery, automobiles and the like as materials of integrated circuit substrates, spark plugs, friction plates, cutters and the like, and is a ceramic material with the widest application field. Under ideal conditions, the strength of the single-phase alumina ceramic reaches about 700MPa, and when the alumina is compounded with zirconia and silicon carbide nano particles (or whiskers), the mechanical property of the material can be further improved to more than 1-1.5 GPa.

Alumina powder is industrially produced in large quantities mainly by the bayer process, the chemical precipitation process and the aluminum salt thermal decomposition process at present. In the Bayer process and the chemical precipitation process, the generated intermediate product is usually colloidal aluminum hydroxide precipitate, contains a large amount of water and hydroxyl, and is easily subjected to the condensation effect of capillary force and hydroxyl among particles in the subsequent drying and calcining processes to cause hard agglomeration of the obtained alumina powder, reduce the powder sintering property and seriously influence the microstructure and mechanical property of the sintered ceramic body. Further, although it is possible to obtain alumina powder having a high sintering activity with less hard agglomerates by ammonothermal decomposition of aluminum sulfate, this method generally releases a large amount of SO₂Harmful gas, which is not beneficial to environmental protection.

Disclosure of Invention

The invention aims to provide a preparation method of alumina powder with high sintering activity and environmental protection. The alumina powder prepared by the method has uniform particle size distribution, less hard agglomeration, capability of sintering at lower temperature, small environmental pollution and applicability to industrial production.

The object of the invention is thus achieved: firstly, using aluminium inorganic salt as main raw material and ammonium hydrogen carbonate as precipitant to respectively prepare aqueous solutions with certain concentration, and controlling dosage proportion, reaction temperature and ageing time of the two solutions to prepare NH₄Al(OH)₂CO₃Precipitating, drying and calcining at high temperature to obtain the alumina powder.

The invention can be divided into four steps:

first step NH₄Al(OH)₂CO₃Preparing a precipitate; washing the precipitate in the second step; thirdly, drying the precipitate; and fourthly, calcining and precipitating at high temperature to obtain alumina powder.

One, NH₄Al(OH)₂CO₃Preparation of the precipitate

By controlling the concentration, dosage proportion, reaction temperature and precipitation aging time of the aluminum inorganic salt and ammonium bicarbonate aqueous solution, NH is obtained₄Al(OH)₂CO₃White precipitate. The inorganic aluminum salt includes one of aluminum chloride, aluminum nitrate and ammonium aluminum sulfate, and has water solution concentration of 0.1-1M and ammonium bicarbonate solution concentration of 1-4M. The molar ratio of the inorganic aluminum salt to the ammonium bicarbonate is controlled between 5 and 20 in the whole reaction process, the reaction temperature is controlled between 5 and 50 ℃, and the aging time is 2 to 24 hours. The general formula of the whole reaction equation can be expressed as:

in the above reaction, the NH is favored by properly increasing the reaction temperature, the dosage proportion of the ammonium bicarbonate and the aluminum inorganic salt or prolonging the aging time₄Al(OH)₂CO₃And (4) generating. However, in order to obtain alumina powder with high sintering activity, the optimal dosage (molar) ratio of ammonium bicarbonate to inorganic aluminum salt should be controlled between 9-12, and the optimal reaction temperature and aging time should be controlled between 15-30 ℃ and 10-15 hours.

Secondly, washing the precipitate

The presence of inorganic ions is very likely to cause agglomeration of the precipitate during drying, and to eliminate this adverse effect, repeated washing of the NH with deionized water is necessary₄Al(OH)₂CO₃Precipitating to completely remove inorganic salt impurities contained therein, and controlling the total content of the inorganic salt impurities below 10 ppm.

Thirdly, drying the precipitate

Due to NH₄Al(OH)₂CO₃The decomposition temperature is about 200 ℃, and in order to ensure that the NH4Al (OH)2CO3 precipitate is not decomposed in the drying process, the drying temperature is controlled between 50 ℃ and 150 ℃. Before drying, the washed precipitate is filtered and dehydrated for a long time to be in a semi-dry state.

Fourthly, high temperature calcination

The calcination temperature has great influence on the crystal form and the sinterability of the obtained alumina powder, the calcination temperature is usually selected between 1100-1200 ℃, the time is 0.5-1.5 hours, the temperature is high, the holding time is short, and vice versa, most or all of the obtained alumina powder is converted into α phase, and the primary grain size is below 400nm, so that the obtained alumina powder has high sinterability.

Compared with the common alumina powder making method, the method has the outstanding characteristics that:

1. obtained NH₄Al(OH)₂CO₃The precipitate is in a non-colloidal state, contains less water, has small capillary force in the drying process, and is easy to obtain NH with less aggregation and looseness₄Al(OH)₂CO₃And (3) precursor powder.

2. NH during pyrolysis₄Al(OH)₂CO₃Decompose and release a large amount of gas, and objectively play a role in expanding the obtained alumina powder, thereby being beneficial to preventing hard agglomeration in the alumina powder.

3. Compared with the common industrial alumina, the alumina powder prepared by the invention has obviously improved sintering property.

4. The raw materials used in the invention are all industrial raw materials, the raw material cost is low, the process is simple, and the obtained alumina powder has high quality and is applied to the preparation of high-grade alumina ceramic products, so that the alumina powder has good market prospect.

Drawings

FIG. 1 (A) shows NH prepared at room temperature using 0.4M aluminum nitrate and 4M ammonium bicarbonate as raw materials₄Al(OH)₂CO₃XRD pattern of the precipitate after 12 hours of aging; in FIG. 1, (B) is 0.2M aluminum nitrate and 2NH prepared at room temperature by using ammonium bicarbonate of M as raw material₄Al(OH)₂CO₃XRD pattern of the precipitate after 24 hours of aging.

In FIG. 2, (A) and (B) are NH indicated by (A) and (B) in FIG. 1, respectively₄Al(OH)₂CO₃Calcining the precipitate at 1200 ℃ for 1 hour to obtain Al₂O₃The XRD pattern of the powder shows that both the powder and the powder are crystallized to α -Al₂O₃。

In FIG. 3, (A) and (B) are α -Al indicated by (A) and (B) in FIG. 2, respectively₂O₃SEM photograph of the powder.

Curves A and B in FIG. 4 are α -Al indicated by (A) and (B) in FIG. 2, respectively₂O₃Firing of powderA knot curve. The horizontal axis represents sintering temperature (. degree. C.) and the vertical axis represents relative density (%).

Detailed Description

Example 1

To a 4M ammonium bicarbonate solution (1500ml) was added dropwise a 0.4M aluminum nitrate solution (1000ml) at room temperature while stirring, and the resulting white precipitate was aged for 12 hours and then washed 5 times with deionized water to remove free inorganicions. The obtained precipitate is in a semi-dry state after being subjected to suction filtration and dehydration for a long time, and then is transferred to an oven for drying at 50 ℃. XRD characterization is carried out on the obtained dry powder before and after calcination for 1 hour at 1200 ℃, and the uncalcined powder is completely generated into NH₄Al(OH)₂CO₃(FIG. 1A), NH after high temperature calcination₄Al(OH)₂CO₃Decomposition to α -Al₂O₃(FIG. 2A.) produced α -Al₂O₃The particle size was about 300nm (FIG. 3A), and the sintering property was good. Pressureless sintering at 1500 deg.C for 2 hours can reach 96% of theoretical density, and sintering at 1525 deg.C for 2 hours can completely densify (curve A in FIG. 4).

Example 2

The same procedure as in example 1 was repeated except that 2M ammonium bicarbonate and 0.2M aluminum nitrate were used as raw materials, and the alumina powder was prepared by aging for 24 hours and calcining at 1200 ℃ for 1 hour. FIG. 1B and FIG. 2B are the resulting NH, respectively₄Al(OH)₂CO₃Precipitation and α -Al₂O₃XRD pattern of powder FIG. 3B shows α -Al₂O₃SEM photograph of the powder. The powder shows good sintering property, 98% of theoretical density can be achieved by pressureless sintering at 1500 ℃ for 1 hour, and complete densification can be achieved by sintering at 1525 ℃ for 1 hour (curve B in figure 4).

Claims

1. A preparation method of alumina powder with high sintering activity is characterized in that:

(1) taking aluminum-containing inorganic salt as a starting material and ammonium bicarbonate as a precipitator, and carryingout precipitation reaction to obtain NH₄Al(OH)₂CO₃A precipitate; wherein the concentration of the inorganic salt containing aluminum is 0.1-1M, and the concentration of the ammonium bicarbonate is 1-4M; the reaction temperature is 5-50 ℃; the precipitation and aging time is 2-24 hours;

(2) the precipitate is washed by deionized water and is dehydrated by long-time suction filtration to be in a semi-dry state, the drying temperature is 50-150 ℃, and then the precipitate is calcined at the temperature of 1100-1200 ℃ for 0.5-1.5 hours to prepare α -Al₂O₃。

2. The method of claim 1, wherein the aluminum-containing inorganic salt is one of aluminum nitrate, aluminum chloride and aluminum ammonium sulfate.

3. The method for producing an alumina powder having a high sintering activity as claimed in claim 1, wherein the precipitate is washed with water to control the content of inorganic salts to 10ppm or less.

4. The method for preparing alumina powder with high sintering activity as claimed in claim 1, wherein the reaction temperature is 15-30 ℃ and the aging time is 10-15 hours.

5. The method for preparing alumina powder with high sintering activity according to claim 1, wherein the aluminum-containing inorganic salt and the ammonium bicarbonate precipitant are industrial raw materials.