CN103951433A - A method for preparing MgO-Y2O3 nano-ceramics by microwave two-step sintering - Google Patents

Abstract

The invention relates to a method for preparing MgO-Y2O3 nanoceramics by two-step microwave sintering. The method comprises the steps of proportioning, ball-milling and granulating, pressing a green piece, placing the green piece in an aluminum-oxide-made sagger of which the outer surface is coated with a heating-assistant material, then placing into a microwave sintering furnace, carrying out microwave sintering in two steps, and cooling to obtain MgO-Y2O3 nanoceramics, wherein in the first sintering step, the first-step sintering temperature T1 is 1320-1400 DEGC and the heat preservation time is 1-10 minutes, and in the second sintering step, the second-step sintering temperature T2 is 1250-1300 DEGC and the heat preservation time is 10-90 minutes. The method disclosed by the invention has the advantages of simple preparation process, short firing cycle and low energy consumption and can be used for preparing samples with larger size and complex shapes and is suitable for industrial production.

Description

A method for preparing MgO-Y2O3 nano-ceramics by microwave two-step sintering

technical field

The invention relates to a method for preparing MgO-Y ₂ O ₃ nanometer ceramics by microwave two-step sintering, which belongs to the field of inorganic non-metallic materials.

Background technique

MgO-Y ₂ O ₃ nano-ceramics has excellent mid-wave infrared transmittance, high mechanical properties, good impact resistance and erosion resistance, and is a new type of infrared window material. At present, the preparation methods of MgO-Y ₂ O ₃ nano-ceramics mainly include spark plasma sintering (SPS) and hot isostatic pressing (HIP). However, both processes have their own problems. SPS is limited by equipment, it is difficult to prepare samples of large size and complex shape, and it is easy to cause carbon pollution to samples; HIP preparation process is complicated, production efficiency is low, and production cost is high.

Compared with the traditional sintering process, microwave sintering for ceramic preparation has the advantages of rapidity, high efficiency, energy saving and environmental protection, and is a technology with great potential. For example, CN103360040A discloses a low-temperature microwave sintering method for high thermal conductivity alumina ceramic materials, adding 3-10wt% sintering aids ZrO ₂ , SiO ₂ , Y ₂ O ₃ , TiO ₂ and a mixture of MgO to the alumina powder , sintered at a low temperature of 1400-1600°C in a microwave sintering furnace, and kept for 0.5-2h. However, the disadvantage of this method is that the addition of sintering aids to achieve low-temperature dense sintering will form new phases and easily lead to grain growth. In the preparation process of MgO-Y ₂ O ₃ infrared transparent ceramics, the formation of new phases (the third phase except MgO and Y ₂ O ₃ ) and large grains will lead to a significant decrease in infrared transmittance.

Contents of the invention

Aiming at the deficiencies of the existing technology, in order to solve the problems of carbon pollution and high cost in the preparation of MgO-Y ₂ O ₃ nano-ceramics in the prior art, the present invention provides a method for preparing MgO-Y ₂ O ₃ nano-ceramics by microwave two-step sintering.

Technical scheme of the present invention is as follows:

A kind of microwave two-step sintering prepares the method for MgO-Y ₂ O ₃ nanometer ceramics, comprises the following steps:

(1) Mixing nano-MgO powder with a purity greater than 99.9% and a particle size of less than 30nm and Y ₂ O ₃ powder in proportion, the proportion of MgO powder is 40-45wt%, and the proportion of Y ₂ O ₃ powder is 55-60wt%; Mixture;

(2) Put it into a ball mill tank for wet ball milling; dry the obtained slurry, add polyvinyl alcohol (PVA) solution with a concentration of 3-5wt%, granulate, and pass the granules through a 40-100 mesh sieve;

(3) Molding the pellets obtained in step (2) into a billet, and then carrying out isostatic pressing to obtain a compact;

(4) Put the green compact prepared in step (3) in an alumina sagger coated with a heat-promoting material on the outer surface, and put it into a microwave sintering furnace; the heat-promoting material is graphite, carbon black or carbonized Silicon coating. the

(5) Microwave two-step sintering

Adjust and control the output power of the microwave oven, heat up to the first step temperature T ₁ =1320-1400 ℃ at a heating rate of 5-50°C/min, keep warm for a period of time t ₁ =1-10min, and then heat it at a temperature of 15-35°C/min Speed down to the second step temperature T ₂ =1250-1300°C, keep warm for a period of time t ₂ =10-90min, and cool to obtain MgO-Y ₂ O ₃ nano ceramics.

Preferred according to the present invention:

In the mixture described in step (1 ₎ , the proportion of MgO powder is 42-43wt%, and the proportion of _Y2O3 powder is 57-58wt%.

The wet ball mill described in step (2) adopts a water-added planetary ball mill, the ball mill tank is made of polyurethane, the grinding balls are zirconia balls, the ball milling speed is 200r/min, and the ball milling time is 3-10h. Mixture: grinding balls: water The mass ratio is 1:6:7. the

For the granulation described in step (2), the polyvinyl alcohol (PVA) solution with a concentration of 3-5wt% is used and the amount added is 1-2wt% of the total amount of the slurry (dried). the

The pressure of the molding blank described in the step (3) is 10-40MPa, and the pressure of the isostatic pressing is 180-250MPa. the

The heat aid material in step (4) is one of graphite, carbon black, and silicon carbide paint; all of them are commercially available powder products. Play the role of auxiliary heating. the

For the microwave two-step sintering described in step (5), the microwave frequency is 2.45GHz, and the output power is 0.1-2KW; more preferably, the heating rate is 10-30°C/min, and the temperature _T1 of the first step is 1340-1380°C, The holding time _t1 is 2-5min, the cooling rate is 18-28°C/min, the second step temperature _T2 is 1270-1290°C, and the holding time t2 is 30-60min.

The microwave two-step sintering process of the present invention prepares MgO-Y ₂ O ₃ nano ceramics, which has simple process, short firing cycle and low energy consumption; it is suitable for industrial production, and the prepared MgO-Y ₂ O ₃ nano ceramics have fine grains and uniform sizes , the grain size is 80-98nm; it can replace the existing SPS and HIP processes. The resulting product can be used to prepare samples of large size and complex shape.

Description of drawings

Fig. 1 is the SEM picture of the sample that embodiment 1 makes. the

Fig. 2 is a schematic diagram of the structure of the sagger, 1, the aluminum oxide sagger body, 2, the coating of the heat-promoting material, 3, the compact to be sintered, 4, the firing gasket, and 5, the thermal insulation material. the

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the examples, but the protection scope of the present invention is not limited thereto. the

The model of the planetary ball mill is QM-3SP4, available from Nanjing Nanda Instrument Co., Ltd. All raw materials used are commercial products. the

The microwave frequency of the microwave oven used in the embodiment is 2.45GHz, and the output power is 0.1-2KW. the

Example 1:

A microwave two-step sintering method for preparing MgO-Y ₂ O ₃ nano ceramics, the steps are as follows:

(1) Weigh 42 parts by weight of MgO powder and 58 parts by weight of _{Y2O3 powder} and mix them;

(2) Put the powder prepared in step (1) into a polyurethane ball mill tank, then add 700 parts by weight of deionized water and 600 parts by weight of zirconia balls, and mill on a planetary ball mill for 6 hours to obtain MgO-Y ₂ O ₃ slurry; the obtained slurry is dried, and the PVA solution accounting for 1wt% of the dried slurry and having a concentration of 5wt% is added, granulated, and the granules are passed through a 60-mesh sieve;

(3) Press the compact under 30MPa, and then isostatically press under 200MPa;

(4) Put the compact into an alumina sagger, coat a layer of graphite paint on the outer surface of the sagger, and then place the alumina sagger in a microwave oven;

(5) Adjust and control the output power of the microwave oven, raise the temperature to 1360°C at a heating rate of 30°C/min, hold for 2 minutes, cool down to 1270°C at a cooling rate of 18°C/min, and hold for 35 minutes. With furnace cooling, MgO-Y ₂ O ₃ nano-ceramics with a relative density of 98.4% and a grain size of 91nm were prepared. Its Vickers hardness is 9.2±0.4GPa, and the 5μm infrared transmittance is 82%.

Example 2:

A microwave two-step sintering method for preparing MgO-Y ₂ O ₃ nano ceramics, the steps are as follows:

(1) Weigh 43 parts by weight of MgO powder and 57 parts by weight of _{Y2O3 powder} and mix them;

(2) Put the powder prepared in step (1) into a polyurethane ball mill tank, then add 700 parts by weight of deionized water and 600 parts by weight of zirconia balls, and mill on a planetary ball mill for 4 hours to obtain MgO-Y ₂ O ₃ Slurry; Gained slurry is dried, and adding 1wt% concentration is the PVA solution of 5wt%, granulates, and granulate passes 40 mesh sieves;

(3) Press the compact under 20MPa, and then isostatically press under 220MPa;

(4) Put the compact into an alumina sagger, coat a layer of carbon black paint on the outer surface of the sagger, and then place the alumina sagger in a microwave oven;

(5) Adjust and control the output power of the microwave oven, raise the temperature to 1340°C at a heating rate of 10°C/min, hold for 5 minutes, cool down to 1280°C at a cooling rate of 25°C/min, and hold for 45 minutes. With furnace cooling, Y ₂ O ₃ -MgO nano ceramics with a relative density of 99.1% and a grain size of 87nm were prepared. Its Vickers hardness is 9.9±0.3GPa, and the 5μm infrared transmittance is 84%.

Example 3:

A microwave two-step sintering method for preparing MgO-Y ₂ O ₃ nano ceramics, the steps are as follows:

(1) Weigh 40 parts by weight of MgO powder and 60 parts by weight of _{Y2O3 powder} and mix them;

(2) Put the powder prepared in step (1) into a polyurethane ball mill tank, then add 700 parts by weight of deionized water and 600 parts by weight of zirconia balls, and mill on a planetary ball mill for 3 hours to obtain MgO-Y ₂ O ₃ Slurry; Gained slurry is dried, and adding 1wt% concentration is the PVA solution of 5wt%, granulates, and granule passes 100 mesh sieves;

(3) Press the compact at 40MPa, and then isostatically press at 180MPa;

(4) Put the compact into an alumina sagger, coat a layer of green silicon carbide coating on the outer surface of the sagger, and then place the alumina sagger in a microwave oven;

(5) Adjust and control the output power of the microwave oven, raise the temperature to 1390°C at a heating rate of 45°C/min, hold for 1 minute, cool down to 1270°C at a cooling rate of 28°C/min, and hold for 60 minutes. With furnace cooling, Y ₂ O ₃ -MgO nano ceramics with a relative density of 99.4% and a grain size of 98nm were prepared. Its Vickers hardness is 8.9±0.3GPa, and the 5μm infrared transmittance is 83%.

Example 4

A microwave two-step sintering method for preparing MgO-Y ₂ O ₃ nano ceramics, the steps are as follows:

(1) Weigh 43 parts by weight of MgO powder and 57 parts by weight of _{Y2O3 powder} and mix them;

(2) Put the powder prepared in step (1) into a polyurethane ball mill tank, then add 700 parts by weight of deionized water and 600 parts by weight of zirconia balls, and ball mill on a planetary ball mill for 10 hours to obtain MgO-Y ₂ O ₃ Slurry; Gained slurry is dried, and adding 1wt% concentration is the PVA solution of 5wt%, granulates, and granulate passes 80 mesh sieves;

(3) Press the compact under 10MPa, and then isostatically press under 250MPa;

(4) Put the compact into an alumina sagger, coat a layer of graphite paint on the outer surface of the sagger, and then place the alumina sagger in a microwave oven;

(5) Adjust and control the output power of the microwave oven, heat up to 1320°C at a heating rate of 5°C/min, hold for 5 minutes, cool down to 1280°C at a cooling rate of 20°C/min, and hold for 70 minutes. With furnace cooling, Y ₂ O ₃ -MgO nano-ceramics with a relative density of 98.0% and a grain size of 82nm were prepared. Its Vickers hardness is 10.2±0.4GPa, and the 5μm infrared transmittance is 82%.

It should be noted that the above examples are only a few specific embodiments of the present invention, and obviously the present invention is not limited to the above embodiments, and other modifications are also possible. All deformations directly derived or indirectly derived from the disclosure content of the present invention by those skilled in the art should be considered as the protection scope of the present invention. the

Claims (6)

1. a microwave two-step sintering preparation MgO-Y ₂ O ₃ methods for nano-ceramics, comprising the following steps: (1) Mixing nano-MgO powder with a purity greater than 99.9% and a particle size of less than 30nm and Y ₂ O ₃ powder in proportion, the proportion of MgO powder is 40-45wt%, and the proportion of Y ₂ O ₃ powder is 55-60wt%; Mixture; (2) Putting it into a ball mill tank for wet ball milling; drying the obtained slurry, adding a polyvinyl alcohol solution with a concentration of 3-5wt%, granulating, and passing the granules through a 40-100 mesh sieve; (3) Molding the pellets obtained in step (2) into a billet, and then carrying out isostatic pressing to obtain a compact; (4) Put the green compact prepared in step (3) in an alumina sagger coated with a heat-promoting material on the outer surface, and put it into a microwave sintering furnace; (5) Microwave two-step sintering Adjust and control the output power of the microwave oven, heat up to the first step temperature T ₁ =1320-1400°C at a heating rate of 5-50°C/min, keep warm for a period of time t ₁ =1-10min, and then heat at a temperature of 15-35°C/min Speed down to the second step temperature T ₂ =1250-1300°C, keep warm for a period of time t ₂ =10-90min, and cool down to obtain Y ₂ O ₃ -MgO nano ceramics. 2. The method for preparing MgO-Y ₂ O ₃ nano ceramics by microwave two-step sintering according to claim 1, characterized in that in the mixture described in step (1), MgO powder accounts for 42-43wt%, Y The proportion of ₂ O ₃ powder is 57-58wt%. 3. The method for preparing MgO-Y ₂ O ₃ nano-ceramics by microwave two-step sintering according to claim 1, characterized in that the wet ball milling in step (2) adopts water-added planetary ball milling, and the ball milling tank is made of polyurethane material, The grinding balls are zirconia balls, the milling speed is 200r/min, the milling time is 3-10h, and the mass ratio of mixture:grinding balls:water is 1:6:7. 4. The method for preparing MgO-Y ₂ O ₃ nano-ceramics by microwave two-step sintering according to claim 1, characterized in that the pressure of the molded blank in step (3) is 10-40MPa, and the isostatic pressing The pressure is 180-250MPa. 5. The method for preparing MgO-Y ₂ O ₃ nano-ceramic by microwave two-step sintering according to claim 1, characterized in that the heating aid material in step (4) is graphite, carbon black or silicon carbide coating. 6. The method for preparing MgO-Y ₂ O ₃ nano-ceramic by microwave two-step sintering according to claim 1, characterized in that the microwave two-step sintering described in step (5) has a microwave frequency of 2.45 GHz and an output power of 0.1 -2KW; the heating rate is 10-30°C/min, the first step temperature _T1 is 1340-1380°C, the holding time _t1 is 2-5min, the cooling rate is 18-28°C/min, the second step temperature _T2 The temperature is 1270-1290℃, and the holding time _t2 is 30-60min.