CN108516814A - A kind of method of low temperature preparation high strength mullite ceramics - Google Patents

Abstract

The invention provides a method for preparing high-strength mullite ceramics at low temperature. Using kaolin, aluminum sol and alumina as raw materials, under the action of mineralizers and sintering aids, first synthesize acicular whisker-containing ceramics at low temperature. Mullite porous ceramics, using the pores inside the material to provide space for the growth of whiskers to fully develop, and then impregnating mullite precursors with high reactivity, and finally obtained by secondary low-temperature sintering, the beneficial effects of the present invention The reason is that the raw material is cheap, the sources are widely available, and the cost is low; the preparation temperature is low, which greatly reduces the production energy consumption; the process is simple and the equipment requirements are low; the in-situ self-generated whiskers realize the simultaneous improvement of material strength and toughness ; During the sintering process, the shrinkage of the product is small, and the net size molding can be realized.

Description

A method for preparing high-strength mullite ceramics at low temperature

technical field

The invention relates to the technical field of ceramic material preparation, in particular to a method for preparing high-strength mullite ceramics at low temperature.

Background technique

Mullite (3Al ₂ O ₃ 2SiO ₂ ) is a stable binary compound in the Al ₂ O ₃ -SiO ₂ system, which has a high melting point (1830°C), low thermal conductivity, small thermal expansion coefficient, and chemical stability Good and good thermal stability and so on. Dense mullite ceramics has outstanding mechanical properties and can maintain high strength at high temperatures, making it an excellent high-temperature structural material.

At present, no matter what kind of material system is used, the mullite reaction temperature in the sintering process is often lower than its densification temperature, and the difficulty of sintering of mullite leads to the preparation of dense mullite ceramics requires extremely high sintering temperature, and the production energy consumption Higher, there are higher requirements for production equipment. At the same time, the intrinsic brittleness of ceramic materials limits its application. In actual use, it is very important for ceramic materials to maintain high strength while maintaining high fracture toughness. Therefore, it is important to develop high-strength mullite ceramics at low temperature. meaning.

In view of the above-mentioned defects, the creator of the present invention has proposed the present invention through long-term research and practice.

Contents of the invention

Aiming at the shortcomings of high sintering temperature and poor mechanical properties of dense mullite, the present invention adopts a technical solution to provide a method for preparing high-strength mullite ceramics at low temperature, which includes the following steps:

The first step: Put kaolin, alumina, and industrial aluminum sol with a mass ratio of 1:0.2-0.6:1.2-3.1 in the mixing tank, add mineralizers and sintering aids at the same time, mix, dry and sieve, Obtain mixed powder;

The second step: put the mixed powder described in the first step in a mold, press and form it in an isostatic pressing device, the pressure is 100-300MPa, and the pressure holding time is 1-5 minutes. After the pressing is completed, the mold is demoulded to obtain ceramic green body;

The third step: placing the ceramic green body described in the second step in a sealed alumina crucible, sintering in an air furnace, and obtaining a porous mullite preform after cooling down;

Step 4: Slowly add the silica sol dropwise to the same volume of aluminum sol, and stir and reflux at 60°C for 1-2 days to obtain the mullite precursor sol;

The fifth step: immerse the porous mullite prefabricated body described in the third step into the mullite precursor sol described in the fourth step, and immerse it in a vacuum environment for 0.5-2h. After the immersion is completed, take it out, and Dry at 130°C for 2-5 hours, then repeat the above steps 3-10 times;

Step 6: Place the impregnated mullite preform in step 5 for secondary sintering in an air furnace, and then obtain high-strength mullite ceramics after cooling down.

Preferably, the kaolin in the first step needs to be calcined at a high temperature of 900°C and ball milled to make the particle size distribution between 0.2-1 μm.

Preferably, the alumina in the first step is α-Al ₂ O ₃ , and the particle size of the powder is 1-2 μm.

Preferably, the solid phase content of the industrial aluminum sol is 20-30%, and the particle size of the colloid in the industrial aluminum sol is about 20-80nm.

Preferably, the mineralizer in the first step is anhydrous aluminum fluoride with a particle size of 5-10 μm, and the added amount of the mineralizer accounts for 8-12% of the total mass of the mixed powder; The sintering aid in the first step is molybdenum trioxide with a particle size of 5-10 μm, and the added amount of the sintering aid accounts for 8-16% of the total mass of the mixed powder.

Preferably, the sintering process in the third step is to raise the temperature to 800-1000° C. at a rate of 3-8° C./min and keep the temperature for 1-3 hours.

Preferably, the preparation method of the aluminum sol in the fourth step is to add the inorganic aluminum salt to absolute ethanol, prepare an aluminum salt ethanol solution with an aluminum ion concentration of 1.5 mol/L, and stir and reflux at 60°C for 24 hours .

Preferably, the inorganic aluminum salt is one of aluminum nitrate nonahydrate or aluminum chloride hexahydrate.

Preferably, the silica sol in the fourth step is prepared by adding tetraethyl orthosilicate into a certain amount of absolute ethanol to prepare an ethanol solution with a concentration of 0.5 mol/L, and stirring at 60° C. for 2 hours.

Preferably, the second sintering process in the sixth step is to raise the temperature to 1200-1400° C. at a rate of 1-4° C./min and keep the temperature for 2-4 hours.

Compared with prior art, the beneficial effect of the present invention is:

1. Using natural mineral kaolin and industrial aluminum sol as raw materials, the price is low, the source is widely available, and the cost is low;

2. Reduce the reaction temperature of mullite, greatly reduce the energy consumption of production, and use the holes inside the material at low temperature to provide space for the growth of mullite whiskers, so that they can fully develop and obtain needle-like whiskers. Mullite porous ceramics;

3. By impregnating mullite precursor sol multiple times, the process is simple and the equipment requirements are low; and mullite ceramics can achieve higher density at low temperature;

4. The second low-temperature sintering promotes the regrowth of whiskers and improves the strength and fracture toughness of mullite ceramics;

5. During the sintering process, the sintering shrinkage of the green body is extremely small, and the net size molding can be realized.

Detailed ways

The above-mentioned and other technical features and advantages of the present invention will be described in more detail below in conjunction with the embodiments.

Example 1

A method for preparing high-strength mullite ceramics at low temperature provided in this embodiment comprises the following steps:

The first step: put kaolin, alumina, and industrial aluminum sol (solid phase content 24%) with masses of 100g, 52g, and 154g respectively in the mixing tank, and add 18.90g of mineralizer anhydrous aluminum fluoride at the same time and molybdenum trioxide as a sintering aid with a mass of 22.68g, and then add 400g of alumina balls and 150ml of absolute ethanol as grinding media, after continuous mixing for 24 hours, dry in an oven at 60°C and sieve to obtain a mixed Powder;

The second step: put the mixed powder described in the first step in a mold, press and form it in an isostatic pressing equipment, the pressure is 200 MPa, keep the pressure for 2 minutes, demould after the pressing is completed, and obtain a ceramic green body;

The third step: the ceramic green body described in the second step is placed in a sealed alumina crucible, and sintered in an air furnace. 2h, obtain porous mullite prefabricated body after cooling down;

Step 4: Add aluminum nitrate nonahydrate to a certain amount of absolute ethanol, configure an aluminum salt ethanol solution with an aluminum ion concentration of 1.5 mol/L, and stir and reflux at 60°C for 24 hours to fully hydrolyze it to obtain aluminum sol; Add tetraethyl orthosilicate to a certain amount of absolute ethanol to prepare an ethanol solution with a concentration of 0.5mol/L, stir at 60°C for 2 hours to obtain silica sol; slowly add the silica sol to the same volume In the aluminum sol, the mullite precursor sol was obtained after stirring and refluxing at a temperature of 60° C. for 1-2 days;

The fifth step: immerse the porous mullite preform described in the third step into the mullite precursor sol described in the fourth step, and immerse it in a vacuum environment for 0.5h, so that the impregnation process is fully carried out. After the impregnation is completed, take it out, And dry in an environment of 120°C for 2-5 hours, and repeat the above steps 6 times;

Step 6: Place the impregnated mullite prefabricated body in step 5 in an air furnace for secondary sintering. The process condition for the secondary sintering is to raise the temperature to 1300°C at a rate of 3°C/min , heat preservation for 2 hours, and high-strength mullite ceramics can be obtained after cooling down.

Among them, the kaolin in the first step needs to be calcined at a high temperature of 900°C, and the particle size distribution is between 0.2-1 μm after ball milling; the alumina is α-Al ₂ O ₃ , and the particle size of the powder is 1 -2 μm; the solid phase content of the industrial aluminum sol is 20-30%, and the particle size of the colloid in the industrial aluminum sol is about 20-80nm. The mineralizer is anhydrous aluminum fluoride with a particle size of 5-10 μm, and the sintering aid is molybdenum trioxide with a particle size of 5-10 μm.

A mullite ceramic prepared in this example has a porosity of 9%, a flexural strength of 160 MPa, a fracture toughness of 2.9 MPa·m ^1/2 , and a heat-resistant temperature of 1600°C.

Therefore, a low-temperature method for preparing high-strength mullite ceramics provided in this example uses natural mineral kaolin and industrial aluminum sol as raw materials, which are cheap, widely available, and low in cost; the reaction of mullite is reduced. The temperature greatly reduces the production energy consumption, and the pores inside the material at low temperature are used to provide space for the growth of mullite whiskers, so that they can fully develop and obtain mullite porous ceramics containing needle-like whiskers; Impregnation of mullite precursor sol has simple process and low equipment requirements; and can achieve higher density of mullite ceramics at low temperature; secondary low-temperature sintering promotes whisker regrowth and improves the strength of mullite ceramics and fracture toughness; during the sintering process, the sintering shrinkage of the green body is extremely small, and the net size molding can be realized.

Example 2

The difference between this example and Example 1 is that the inorganic aluminum salt in the fourth step is aluminum chloride hexahydrate.

The porous mullite prepared in this example has a porosity of 10%, a flexural strength of 140 MPa, a fracture toughness of 2.3 MPa·m ^1/2 , and a heat-resistant temperature of 1500°C.

Example 3

The difference between this example and Example 1 is that the masses of the kaolin, the alumina powder, and the industrial aluminum sol (solid phase content: 27%) in the first step are 100g, 20g, and 309g, respectively;

The molding pressure described in the second step is 100MPa, and the holding time is 3min;

The process condition of the sintering in the third step is to raise the temperature to 900° C. at a rate of 3° C./min and keep the temperature for 3 hours.

The porous mullite ceramic prepared in this example has a porosity of 30%, a flexural strength of 67 MPa, a fracture toughness of 1.1 MPa·m ^1/2 , and a heat-resistant temperature of 1500°C.

Example 4

The difference between this embodiment and embodiment 1 is:

The quality of the kaolin, the alumina powder and the industrial aluminum sol (30% solid content) in the first step is respectively 100g, 60g and 120g;

The molding pressure described in the second step is 300MPa, and the holding time is 2min;

The process condition of the sintering in the third step is to raise the temperature to 1000°C at a rate of 6°C/min and keep the temperature for 3h;

The process condition of the sintering in the sixth step is to raise the temperature to 1400° C. at a rate of 4° C./min and keep the temperature for 4 hours.

The porous mullite ceramic prepared in this example has a porosity of 3%, a flexural strength of 230 MPa, a fracture toughness of 4.3 MPa·m ^1/2 , and a heat-resistant temperature of 1700°C.

Example 5

The difference between this embodiment and embodiment 1 is:

In the first step, the mineralizer anhydrous aluminum fluoride and the sintering aid molybdenum trioxide quality are respectively 21.68g and 28.34g;

The process condition of the sintering in the third step is to raise the temperature to 800°C at a rate of 4°C/min, and keep the temperature for 3h;

The process condition of the sintering in the sixth step is to raise the temperature to 1200° C. at a rate of 2° C./min and keep the temperature for 2 hours.

The porous mullite ceramic prepared in this example has a porosity of 24%, a flexural strength of 110 MPa, a fracture toughness of 1.3 MPa·m ^1/2 , and a heat-resistant temperature of 1500°C.

Example 6

The difference between this embodiment and embodiment 1 is:

The inorganic aluminum salt described in the 4th step is aluminum chloride hexahydrate;

The number of times of the dipping in the fifth step is 10 times;

The process condition of the sintering in the sixth step is to raise the temperature to 1300° C. at a rate of 1° C./min and keep the temperature for 2 hours.

The porous mullite ceramic prepared in this example has a porosity of 6%, a flexural strength of 190 MPa, a fracture toughness of 3.7 MPa·m ^1/2 , and a heat-resistant temperature of 1500°C.

Example 7

The difference between this embodiment and embodiment 1 is:

The fifth step becomes: immerse the porous mullite prefabricated body described in the third step into the mullite precursor sol described in the fourth step, and immerse in a vacuum environment for 2 hours to fully carry out the impregnation process. After the impregnation is completed, take out , and dried in an environment of 115° C. for 3 hours, and repeated the above steps 3 times.

The porous mullite ceramic prepared in this example has a porosity of 12%, a flexural strength of 125 MPa, a fracture toughness of 2.9 MPa·m ^1/2 , and a heat-resistant temperature of 1650°C.

The above descriptions are only preferred embodiments of the present invention, and are only illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims (10)

1. a kind of method of low temperature preparation high strength mullite ceramics, which is characterized in that it includes the following steps：

The first step：By mass ratio 1：0.2-0.6：Kaolin, aluminium oxide, the industrial Aluminum sol of 1.2-3.1 is placed in mixing tank, together When mineralizer and sintering aid is added, after mixing is dried and is sieved, obtain mixed powder；

Second step：Mixed powder described in the first step is placed in mold, the compression moulding in equal pressing equipment, pressure 100- 300MPa, dwell time 1-5min demould after the completion of compacting, obtain ceramic green；

Third walks：Ceramic green described in second step is placed in the alumina crucible of sealing, is sintered in air furnace, is dropped Porous mullite precast body is obtained after temperature；

4th step：Ludox is slowly added dropwise in the Aluminum sol of same volume, 1-2 is stirred at reflux at a temperature of 50-70 DEG C After it, mullite precursor colloidal sol is obtained；

5th step：Third is walked the porous mullite precast body to immerse in mullite precursor colloidal sol described in the 4th step, true Under Altitude, 0.5-2h is impregnated, after the completion of dipping, is taken out, and is 2-5 hours dry in 110-130 DEG C of environment, is then repeated Above-mentioned steps 3-10 times；

6th step：Mullite precast body after being impregnated described in 5th step is placed in air furnace and carries out double sintering, after cooling i.e. It can get the mullite ceramic of high intensity.

2. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that institute in the first step 900 DEG C of high-temperature calcinations need to be passed through by stating kaolin, and make its particle diameter distribution between 0.2-1 μm through ball milling.

3. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that described in the first step Aluminium oxide be α-Al₂O₃, and diameter of particle is 1-2 μm.

4. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that the industry Aluminum sol solid concentration is 20-30%, and the granular size of colloid is about 20-80nm in the industrial aluminum sol gel.

5. the method for low temperature preparation high strength mullite ceramics according to claim 2, which is characterized in that institute in the first step It is aluminum fouoride to state mineralizer, and granularity is 5-10 μm, and the addition of the mineralizer accounts for the mixed powder gross mass 8-12%；Sintering aid described in the first step is molybdenum trioxide, and granularity is 5-10 μm, and the addition of the sintering aid accounts for the mixing The 8-16% of powder gross mass.

6. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that described in third step The process conditions of sintering are to be warming up to 800-1000 DEG C with the rate of 3-8 DEG C/min, keep the temperature 1-3h.

7. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that described in the 4th step The preparation method of Aluminum sol is that inorganic aluminate is added in absolute ethyl alcohol, the aluminium salt second that configuration aluminium ion concentration is 1.5mol/L Alcoholic solution is stirred at reflux 24 hours at a temperature of 60 DEG C.

8. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that the inorganic aluminum Salt is one kind in ANN aluminium nitrate nonahydrate or Aluminium chloride hexahydrate.

9. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that described in the 4th step The preparation method of Ludox is that ethyl orthosilicate is added in a certain amount of absolute ethyl alcohol, is formulated as a concentration of 0.5mol/L second Alcoholic solution stirs 2 hours at 60 DEG C.

10. the method for low temperature preparation high strength mullite ceramics according to claim 1, which is characterized in that the 6th step institute The process conditions for stating double sintering are to be warming up to 1200-1400 DEG C with the rate of 1-4 DEG C/min, keep the temperature 2-4 hours.