CN100398488C - Preparation method of magnesium aluminum spinel nanometer transparent ceramics - Google Patents

Abstract

The preparation method of magnesium aluminum spinel nano transparent ceramics uses magnesium aluminum spinel nano powder with a purity >99% as a raw material, and the process steps include powder molding and high-pressure sintering. Powder molding is to put magnesium aluminum spinel nano powder with a purity greater than 99% into a mold, and form it into a green body at room temperature and under a pressure of 5-20 MPa; high-pressure sintering is to put the green body into a double-sided top press, Sintering under the pressure of 2-5GPa, the sintering temperature is 500-700°C, and the sintering time is at least 20 minutes, so that the magnesium-aluminum spinel nano-transparent ceramics can be obtained. This method is not only simple in process, but also the transmittance of the prepared transparent ceramic (MgAl ₂ O ₄ ) with absorption peak in the infrared band is increased to more than 80%, the brittleness is reduced, and the macroscopic size is increased.

Description

Preparation method of magnesium aluminum spinel nanometer transparent ceramics

technical field

The invention belongs to the field of transparent ceramics, in particular to a preparation method of magnesium aluminum spinel transparent ceramics.

Background technique

Transparent ceramics have the dual advantages of excellent physical and chemical properties of high-temperature oxide single crystals and glass, which is easy to make special-shaped devices and can be enlarged in size, so its application fields are becoming wider and wider. In recent years, people eagerly expect to prepare ceramics with better performance by synthesizing nano-ceramics.

The United States has been committed to the development of transparent magnesia-aluminum spinel (MgAl ₂ O ₄ ) ceramics since the 1970s. In 1976, US3974249 disclosed a method for preparing transparent spinel. However, due to the limitations of the method and process, the prepared material Optical transmittance is low. Subsequently, US 4930731, US 4983555, and US5244849 disclosed the preparation method and application of transparent spinel successively, but the above-mentioned methods all adopt the two-step method of hot isostatic pressing after vacuum hot pressing or atmosphere sintering. It is complicated, the equipment investment is large, and the prepared transparent spinel has no absorption peak in the infrared band, so the application range is limited.

Chinese patent ZL95117836.9 discloses a preparation method of transparent polycrystalline spinel (MgAl ₂ O ₄ ). In this method, a sintering aid LiF is added to the spinel powder, and the molding is performed at 5-10 MPa, and the heating temperature is 1000 ~1100°C, keep warm for 30 minutes, continue to heat up to 1500~1700°C (the pressure is correspondingly increased to 40~50 tons, φ100mm mold), keep warm for 2~5 hours, and then cool down at a rate of 5°C/min to obtain transparent polycrystalline spinel. Although the above preparation method reduces the investment in equipment and obtains transparent polycrystalline spinel with high transmittance, the sintering temperature is high (1500-1700°C), and the preparation method is still relatively complicated. The prepared transparent spinel is in the There is still no absorption peak in the infrared band.

"Applied Physics Letters" disclosed a low-temperature, ultra-high pressure sintering method of nano-transparent ceramics in May 2006 (Lu Tiecheng, Chang Xianghui, Qi Jianqi, Luo Xiangjie, Low-temperature high-pressure preparation of transparent nanocrystalline MgAl ₂ O ₄ ceramics, Applied Physics Letters, Vol:88, No.23120, 2006), in this method, the magnesium-aluminum spinel nano-powder is initially pressed into a green body, and then the green body is sintered under high pressure with a six-sided top press, The sintering temperature is about 600°C, and the sintering time is 20-30 minutes. Although this method provides a technical solution with a different concept for the preparation of transparent ceramics, and the prepared transparent ceramics (MgAl ₂ O ₄ ) has two absorption peaks in the infrared band, there is a problem that the prepared transparent ceramics are transparent Low transmittance (the transmittance in the infrared band with a wavelength of 760-2200nm is less than 50%, and the transmittance in the visible light band with a wavelength of 500-760nm is less than 40%), the macroscopic size is small (less than 10mm), and it is easy to crack .

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, to provide a kind of preparation method of the improved magnesia-aluminum spinel nano-transparent ceramics, this kind method not only technology is simple, and the prepared infrared band has the transparent ceramics (MgAl ₂ O ₄ ) the transmittance increases, the brittleness decreases, and the macroscopic size increases.

The technical solution of the present invention is to improve the existing low-temperature and ultra-high-pressure sintering method of transparent ceramics, and use a double-sided pressing machine instead of a six-sided pressing machine to sinter the molded green body.

The preparation method of magnesium-aluminum spinel nano-transparent ceramics of the present invention uses magnesium-aluminum spinel nano-powder with a purity >99% as a raw material, comprising the following steps:

(1) Powder molding

Put the magnesium aluminum spinel nanopowder with a purity greater than 99% into a mold, and shape it into a green body at room temperature and under a pressure of 5 to 20 MPa for 1 to 5 minutes;

(2) High pressure sintering

The biscuit is put into a double-sided top press, sintered under a pressure of 2-5GPa, the sintering temperature is 500-700°C, and the sintering time is at least 20 minutes, and the magnesium-aluminum spinel nano-transparent ceramics are obtained.

The raw material described in the above method—magnesium-aluminum spinel nanopowder with a purity>99% is prepared from analytically pure (>99%) magnesium salt and aluminum salt, and the proportioning ratio of magnesium salt and aluminum salt is based on Mg and Al The molar ratio is 1:2, and the preparation method is to add magnesium salt and aluminum salt to deionized water to form a mixed solution (the amount of deionized water is not strictly required, just flood the magnesium salt and aluminum salt), and then mix The solution is put into a heating furnace, heated to 1100-1150°C under normal pressure at a rate of 5-10°C/min and roasted, kept at this temperature for at least 2 hours and then allowed to cool naturally to room temperature to obtain a white and fluffy magnesium-aluminum spinel Stone (MgAl ₂ O ₄ ) powder is ground and sieved with a sample sieve to obtain MgAl ₂ O ₄ nanometer powder. The magnesium salt is MgSO ₄ or Mg(NO ₃ ) ₂ or MgCO ₃ , and the aluminum salt is NH ₄ Al(SO ₄ ) ₂ or Al(NO ₃ ) ₃ or NH ₄ Al(CO ₃ ) ₂ .

The raw material used in the method of the present invention (magnesia-aluminum spinel nanopowder with a purity >99%) can also be prepared by a bimetallic alkoxide method, and the specific process can be found in Chinese patent ZL 95117836.9.

The present invention has the following beneficial effects:

1. There is no need to add a sintering aid to the magnesium aluminum spinel nanopowder, which can not only simplify the process, but also reduce the cost.

2. The molded blank is directly put into the two-sided top press for sintering, that is, the magnesium-aluminum spinel nano-transparent ceramics are obtained, and the process is very simple.

3. The sintering temperature is low (500-700°C), and the sintering time is short (at least 20 minutes), which can save electric energy.

4. Compared with the existing low temperature and ultra-high pressure sintering method, the transparency of the prepared magnesium-aluminum spinel nano-transparent ceramics with two absorption peaks in the infrared band is significantly improved, and the transmittance of the infrared band with a wavelength of 760-2200nm is greater than 70%, and the transmittance in the visible light band with a wavelength of 500-760nm is greater than 50% (see Figure 2).

5. The brittleness of the prepared magnesium-aluminum spinel nano-transparent ceramics is reduced, and the cracking phenomenon of the ceramics is obviously improved.

6. The prepared magnesium-aluminum spinel nano-transparent ceramics increase in macroscopic size, and the macroscopic size can reach more than 30 mm.

7. The prepared magnesia-alumina spinel nano-transparent ceramics have an absorption peak near the wavelength of 1430nm and 1970nm respectively in the infrared band, so its application range is expanded, and it has broad application prospects in the fields of infrared detection and infrared photography.

Description of drawings

Fig. 1 is the photo of the magnesium aluminum spinel nano-transparent ceramics (MgAl ₂ O ₄ ) prepared by the method of the present invention, which is taken by placing the magnesium aluminum spinel ceramics on the grid substrate with text , to show the transparency of magnesium aluminum spinel ceramics.

Fig. 2 is the transmittance curve of the magnesium aluminum spinel nano-transparent ceramics (MgAl ₂ O ₄ ) prepared by the method of the present invention. The transmittance curve is measured with a thickness of magnesium aluminum spinel of 2 mm. The instrument is an ultraviolet/visible/infrared spectrophotometer, model Lambda 950, produced by PerkinElmer.

Fig. 3 is the transmission electron microscope picture of the magnesium aluminum spinel nano-transparent ceramics (MgAl ₂ O ₄ ) prepared by the method of the present invention, which picture shows that the average grain size of the transparent ceramics is less than 100 nanometers, and the test instrument model for JEOL 3011.

Detailed ways

Example 1

The processing steps of the present embodiment are as follows:

(1) Preparation of magnesium aluminum spinel nanopowder

Using analytically pure MgSO ₄ ·7H ₂ O (purity ≥99.0%) and NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O (purity ≥99.5%) as raw materials, MgSO ₄ ·7H ₂ O and NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O is measured according to the molar ratio of Mg to Al of 1:2. Put the measured MgSO ₄ 7H ₂ O and NH ₄ Al(SO ₄ ) ₂ 12H ₂ O into the container, add deionized water and stir to form a mixed solution (the amount of deionized water added is not strictly required, and the MgSO ₄ · 7H ₂ O and NH ₄ Al(SO ₄ ) ₂ · 12H ₂ O), put the mixed solution in a quartz cup and place it in a muffle furnace, heat it at 5°C/min to 1150°C under normal pressure and bake it. Keep it warm at this temperature for 4 hours, then allow it to cool naturally to room temperature to obtain a white and fluffy MgAl ₂ O ₄ powder, grind it and sieve it with a sample sieve to obtain magnesium aluminum spinel (MgAl ₂ O ) with a purity greater than 99%. O ₄ ) Nanopowder;

(2) Powder molding

10 grams of magnesium-aluminum spinel nano-powder prepared in step (1) are packed into a steel mould, held at room temperature and under a pressure of 10 MPa for 3 minutes to form a green body;

(3) High pressure sintering

Put the biscuit into the double-sided top press, raise the pressure to 4GPa in 5 minutes, slowly raise the temperature while maintaining the pressure, raise the temperature to 500°C in 5 minutes, sinter at 500°C for 20 minutes, and then The temperature is lowered to room temperature in 5 minutes, and the pressure is lowered to normal pressure in 5 minutes to obtain a magnesium-aluminum spinel nano-transparent ceramic. The photo of the ceramic after polishing is shown in Figure 1, and the transmittance curve is shown in Figure 2. The transmission electron microscope image is shown in Figure 3.

Example 2

(1) Preparation of magnesium aluminum spinel nanopowder

Using analytically pure MgSO ₄ 7H ₂ O (purity ≥99.0%) and NH ₄ Al(CO ₃ ) ₂ (purity ≥99.5%) as raw materials, the formulation of MgSO ₄ 7H ₂ O and NH ₄ Al(CO ₃ ) ₂ The ratio is measured by the molar ratio of Mg and Al being 1:2. Put the measured MgSO ₄ 7H ₂ O and NH ₄ Al(CO ₃ ) ₂ into the container, add deionized water and stir to form a mixed solution (the amount of deionized water added is not strictly required, and the MgSO ₄ 7H ₂ O and NH ₄ Al(CO ₃ ) ₂ ), put the mixed solution in a quartz cup and place it in a muffle furnace, heat it to 1150°C at normal pressure at 10°C/min, and keep it at this temperature for 2 hours. Then allow it to cool naturally to room temperature to obtain a white and fluffy MgAl ₂ O ₄ powder, grind it and sieve it with a sample sieve to obtain a magnesium aluminum spinel (MgAl ₂ O ₄ ) nanopowder with a purity greater than 99%;

(2) Powder molding

10 grams of magnesium-aluminum spinel nano-powder prepared in step (1) are packed into a steel mould, held at room temperature and under a pressure of 5 MPa for 5 minutes to form a green body;

(3) High pressure sintering

Put the biscuit into the double-sided top press, raise the pressure to 3GPa in 3 minutes, raise the temperature slowly while maintaining the pressure, raise the temperature to 700°C in 3 minutes, sinter at 700°C for 30 minutes, and then The temperature is lowered to room temperature in 3 minutes, and the pressure is lowered to normal pressure in 3 minutes, so that the magnesium-aluminum spinel nano-transparent ceramic is prepared.

Example 3

(1) Preparation of magnesium aluminum spinel nanopowder

Using analytically pure Mg(NO ₃ ) ₂ (purity ≥99.0%) and NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O (purity ≥99.5%) as raw materials, Mg(NO ₃ ) ₂ and NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O is measured according to the molar ratio of Mg to Al being 1:2. Put the measured Mg(NO ₃ ) ₂ and NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O into the container, add deionized water and stir to form a mixed solution (the amount of deionized water added is not strictly required, and the Mg( NO ₃ ) ₂ and NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O), put the mixed solution in a quartz cup and place it in a muffle furnace, heat it at 8°C/min at normal pressure to 1150°C for calcination, Keep it warm at this temperature for 6 hours, then allow it to cool naturally to room temperature to obtain a white and fluffy MgAl ₂ O ₄ powder. After grinding, sieve it with a sample sieve to obtain magnesium aluminum spinel (MgAl _{2 )} with a purity greater than 99%. O ₄ ) Nanopowder;

(2) Powder molding

10 grams of magnesium-aluminum spinel nano-powder prepared in step (1) are packed into a steel mould, held at room temperature and under a pressure of 15 MPa for 2 minutes to form a green body;

(3) High pressure sintering

Put the biscuit into the double-sided top press, raise the pressure to 5GPa in 5 minutes, slowly raise the temperature while maintaining the pressure, raise the temperature to 600°C in 5 minutes, sinter at 600°C for 25 minutes, and then The temperature is lowered to room temperature in 5 minutes, and the pressure is lowered to normal pressure in 5 minutes, so that the nano-transparent magnesium aluminum spinel ceramic is prepared.

Example 4

(1) Preparation of magnesium aluminum spinel nanopowder

Using analytically pure MgCO ₃ (purity ≥99.0%) and Al(NO ₃ ) ₃ (purity ≥99.5%) as raw materials, the ratio of MgCO ₃ and Al(NO ₃ ) ₃ is 1:2 according to the molar ratio of Mg to Al measure. Put the measured MgCO ₃ and Al(NO ₃ ) ₃ into the container, add deionized water and stir to form a mixed solution (the amount of deionized water added is not strictly required, just submerge MgCO ₃ and Al(NO ₃ ) ₃ ) , put the mixed solution in a quartz cup and place it in a muffle furnace, heat it at 6°C/min to 1150°C at normal pressure and bake it, keep it at this temperature for 4 hours, and then let it cool down to room temperature naturally to obtain a white and fluffy The MgAl ₂ O ₄ powder is ground and sieved with a sample sieve to obtain a magnesium aluminum spinel (MgAl ₂ O ₄ ) nanopowder with a purity greater than 99%;

(2) Powder molding

10 grams of magnesium-aluminum spinel nano-powder prepared in step (1) are packed into a steel mould, held at room temperature and under a pressure of 20 MPa for 1 minute to form a green body;

(3) High pressure sintering

Put the biscuit into the double-sided top press, raise the pressure to 2GPa in 3 minutes, slowly raise the temperature while maintaining the pressure, raise the temperature to 500°C in 3 minutes, sinter at 500°C for 20 minutes, and then The temperature is lowered to room temperature in 3 minutes, and the pressure is lowered to normal pressure in 3 minutes, so that the magnesium-aluminum spinel nano-transparent ceramics are prepared.

The two-sided pressing machine used in the above examples, model DS 2×3500 tons, is commercially available; the pressurizing device used for powder molding is a jack.

Claims (3)

1. a preparation method of magnesium-aluminum spinel nano-transparent ceramics, using the magnesium-aluminum spinel nano-powder with a purity greater than 99% as raw material, it is characterized in that comprising the following steps: (1) Powder molding Put the magnesium aluminum spinel nanopowder with a purity greater than 99% into a mold, and shape it into a green body at room temperature and under a pressure of 5 to 20 MPa for 1 to 5 minutes; (2) High pressure sintering The biscuit is put into a double-sided top press, sintered under a pressure of 2-5GPa, the sintering temperature is 500-700°C, and the sintering time is at least 20 minutes, and the magnesium-aluminum spinel nano-transparent ceramics are obtained. 2. the preparation method of magnesium aluminum spinel nano-transparent ceramics according to claim 1 is characterized in that said magnesium aluminum spinel nano powder is prepared from analytically pure magnesium salt and aluminum salt, magnesium salt and aluminum The proportion of salt is measured according to the molar ratio of Mg and Al as 1:2. The preparation method is to add magnesium salt and aluminum salt to deionized water to form a mixed solution, and then put the mixed solution into a heating furnace at a temperature of 5-10°C/min. Heating at a high rate to 1100-1150°C for roasting, keeping the temperature for at least 2 hours and then allowing it to cool naturally to room temperature to obtain magnesium-aluminum spinel nanopowder. 3. The preparation method of magnesium aluminum spinel nano-transparent ceramics according to claim 2, characterized in that the magnesium salt is MgSO ₄ or Mg(NO ₃ ) ₂ , and the aluminum salt is NH ₄ Al(SO ₄ ) ₂ or Al(NO ₃ ) ₃ or NH ₄ Al(CO ₃ ) ₂ .

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