Porous ceramic as well as preparation method thereof, air-floating bearing and application

[0023] like figure 1 As shown, a method for preparing a porous ceramic according to an embodiment, the porous ceramic prepared by the method is a silicon carbide porous ceramic. The preparation method of the porous ceramic comprises the following steps:

[0024] Step 110: Mix the raw materials to form a mixture.

[0025] Wherein, in terms of mass percentage, the raw materials include: 55% to 70% of silicon carbide, 5% to 15% of seaweed mud, 10% to 20% of additives and 10% to 15% of lubricants.

[0026] The main component of diatom mud is silica. There are many pores in the structure of diatom mud, which is beneficial to increase the porosity of porous ceramics and improve the permeability of ceramics.

[0027] The additive is selected from at least one of bauxite, industrial alumina and activated alumina. The alumina in the above additives can form mullite with the silica component in the diatom mud, so as to improve the strength, hardness and wear resistance of ceramics.

[0028] The mass percentage content of aluminum oxide in the bauxite is more than 85%, which can ensure that the porous ceramic has higher strength, hardness and wear resistance. If the content of aluminum oxide in bauxite is low, the content of metal oxides (such as calcium oxide, iron oxide, etc.) in bauxite is high, and too much metal oxide will not only increase the glass phase content, but also cause mullite to decompose at high temperature, reducing the porosity and mechanical properties of porous ceramics. By controlling the mass percentage of alumina in the bauxite to be more than 85%, so that the bauxite contains an appropriate amount of metal oxides, it can not only play a role in promoting sintering, reduce the sintering temperature, but also The porous ceramics can have higher strength, hardness and wear resistance.

[0029] Further, the mass percentage content of aluminum oxide in the bauxite is 85% to 90%, so that the obtained porous ceramic has higher strength, hardness and wear resistance.

[0030] Specifically, the total mass percentage content of metal oxides in bauxite is 3% to 5%, and the content of metal oxides can enable the mixture to obtain higher strength, hardness and resistance at lower sintering temperature. grinding performance.

[0031] Specifically, the metal oxides in bauxite include ferric oxide, titanium oxide, calcium oxide, magnesium oxide, sodium oxide and potassium oxide. More specifically, in bauxite, the mass percentage of ferric oxide is 1% to 1.5%, the mass percentage of titanium oxide is 1.5% to 2%, calcium oxide, magnesium oxide, sodium oxide and oxide The total mass percentage of potassium is 0.5% to 1.5%.

[0032] Industrial alumina is made of bauxite (Al 2 O 3 ·3H 2 O) and diaspore, the main component is γ-Al 2 O 3 , industrial alumina has a lower sintering temperature than ordinary pure alumina, and can also be compatible with SiO in diatom mud 2 Mullite is formed. Therefore, using industrial alumina as a sintering aid can not only improve the strength of porous ceramics, but also reduce the sintering temperature of ceramics, so that porous ceramics can obtain higher strength and hardness at lower sintering temperatures. and better wear resistance.

[0033] Activated alumina powder, also known as activated bauxite, has a porous structure and has a lower sintering temperature than ordinary pure alumina. At the same time, activated alumina powder can interact with SiO in diatom mud. 2 Mullite is generated. Therefore, using activated alumina powder as an additive can not only increase the porosity of porous ceramics, improve the permeability of porous ceramics, but also increase the strength of porous ceramics and reduce the sintering temperature of ceramics, so that the porous ceramics can be Better permeability, higher strength, hardness and better wear resistance are obtained at lower sintering temperatures.

[0034] Lubricants can reduce the wear of porous ceramics and help prolong the service life of porous ceramics. The lubricant is selected from at least one of graphite and molybdenum disulfide.

[0035] Further, the lubricant is graphite, which has better lubricity and can more effectively reduce the wear of the porous ceramic. Specifically, the graphite is selected from at least one of spherical graphite and flake graphite. Further, the lubricant is spherical graphite, which has good fluidity and can be more uniformly dispersed in the mixture, so that the entire porous ceramic has better lubricity, so that the porous ceramic has better wear resistance. .

[0036] Specifically, the step of mixing the raw materials to form a mixture includes: mixing a dispersant and a solvent to form a premix; mixing the raw materials and the premix to form a slurry; and drying the slurry to obtain a mixture.

[0037] Specifically, the dispersant is selected from at least one of polymethacrylamide, sodium hexametaphosphate and sodium tripolyphosphate. The mass ratio of the dispersant to the solvent is 0.5:100 to 1:100.

[0038] The solvent is distilled water. It should be noted that the solvent is not limited to distilled water, but may also be tap water, deionized water, ultrapure water or ethanol. Using distilled water as a solvent can not only minimize impurities in the mixture, but also be affordable.

[0039] Specifically, the method of mixing the raw material with the premix to form the slurry is ball milling mixing. And when the ball mill is mixed, the mass ratio of the raw material to the grinding medium is 1:1 to 1:3; the mixing speed is 200 rpm to 300 rpm; the mixing time is 3 hours to 6 hours.

[0040]Specifically, the step of drying the slurry is: drying at 100° C. for 8 hours to 16 hours.

[0041] Further, the median particle size of the silicon carbide is 5 microns to 15 microns, the median particle size of the seaweed mud is 10 microns to 20 microns, the median particle size of the additives is 10 microns to 20 microns, and the median particle size of the lubricant is 10 microns to 20 microns. The diameter is 15 microns to 25 microns. By controlling the particle size of each component in the above range, the pore size of the porous ceramic can meet the requirements of the air bearing; if the pore size is too large, the strength will be affected, and the ceramic is easy to wear, the permeability is unstable, and the pore size is too small, resulting in permeability Low, can not meet the use requirements.

[0042] Step S120: The mixture is made into a green body.

[0043] Specifically, the method for making the mixture into a green body is compression molding or gel injection molding.

[0044] Further, before the step of making the mixed material into a green body, it also includes the step of crushing the mixed material and then passing through a 40-mesh sieve. Specifically, the crushing method is ball mill crushing, the crushing speed is 250 rpm to 350 rpm, and the time is 1 hour to 2 hours.

[0045] Step S130: sintering the green body to obtain porous ceramics.

[0046] Specifically, the step of sintering the green body is carried out under vacuum conditions to avoid oxidative volatilization at high temperature using graphite as a lubricant.

[0047] Specifically, the sintering temperature is 1200°C to 1300°C.

[0048] Specifically, the step of sintering the green body includes: heating the green body to 400°C to 500°C at a rate of 10°C/hour to 30°C/hour, and then to 900°C at a rate of 30°C/hour to 90°C/hour ℃~1000℃, then increase the temperature to 1200℃~1300℃ at a rate of 30℃/hour~60℃/hour, and keep sintering for 1 hour~5 hours.

[0049] The above-mentioned preparation method of porous ceramics has at least the following advantages:

[0050] (1) The algae mud in the raw material of the above-mentioned preparation method of porous ceramics has a porous structure, which is beneficial to increase the porosity of the porous ceramics and improve the permeability of the ceramics; at the same time, since the additives are selected from bauxite, industrial alumina and active oxidation At least one kind of aluminum, and the mass percentage of aluminum oxide in the bauxite is more than 85%, and the mass percentage of aluminum oxide is more than 85% of bauxite, industrial alumina and Activated alumina can play the role of promoting sintering and lowering the sintering temperature, avoiding the problem of porosity reduction caused by high temperature sintering. At the same time, the above additives can also react with diatomite to form mullite to improve the strength and hardness, and make it have good wear resistance, which is not only conducive to improving its service life, but also can reduce the amount of grinding debris generated during machining of porous ceramics, and reduce the penetration of porous ceramics caused by blocked pores. rate reduction problem.

[0051] (2) At the same time, by controlling the median particle size of silicon carbide to be 5 microns to 15 microns, the median particle size of seaweed mud to be 10 microns to 20 microns, the median particle size of additives to be 10 microns to 20 microns, and the lubricants to be 10 microns to 20 microns. The median particle size of the porous ceramic is 15 microns to 25 microns, so that the pore size of porous ceramics can meet the requirements of air bearing; if the pore size is too large, it will affect the strength, and the ceramic is easy to wear, the permeability is unstable, and the pore size is too small, resulting in low permeability , can not meet the requirements of use.

[0052] The porous ceramic of one embodiment is prepared by the above-mentioned preparation method of porous ceramic, so that the porous ceramic has higher permeability, higher strength, higher hardness, better wear resistance and longer service life .

[0053] The air bearing of one embodiment is produced from the above-mentioned porous ceramics. Therefore, the air bearing has higher permeability, higher strength, higher hardness and better wear resistance, so that the air bearing has better permeability and longer service life.

[0054] The above air bearing can be used in centrifuges, blowers, steam turbines, machine tools or measuring instruments. Especially high-speed centrifuges, high-power blowers or precision machine tools. For example as bearings on centrifugal separators or drives, and as bearings in blowers, steam turbines, machine tools or measuring instruments. Because the air bearing has higher permeability, higher strength, higher hardness and better wear resistance, it is beneficial to improve the service life of the device using the air bearing.

[0056] Example 1

[0057] The preparation process of the porous ceramics of the present embodiment is as follows:

[0058] (1) According to Table 1, each component is weighed according to the mass percentage content (referred to as content in the table) to obtain raw materials. Among them, the median particle size of silicon carbide is 10 microns, the median particle size of seaweed mud is 15 microns, the median particle size of additives is 15 microns, and the median particle size of lubricants is 20 microns. Among them, in bauxite, the mass percentage of aluminum oxide is 89%, the mass percentage of iron oxide is 1.2%, the mass percentage of titanium oxide is 1.8%, calcium oxide, magnesium oxide The total mass percentage of , sodium oxide and potassium oxide is 1%.

[0059] (2) mixing the dispersant and distilled water for 2 hours to form a premix; the raw material and the premix are ball milled to form a slurry, and when the ball mill is mixed, the mass ratio of the raw material to the grinding medium is 1:2, and the mixing speed is 250 rev/min, the mixing time was 4.5 hours; the slurry was dried at 100° C. for 12 hours to obtain a mixture. Wherein, the dispersant is polymethacrylamide, and the mass ratio of the dispersant to distilled water is 0.8:100.

[0060] (3) The mixture is placed in a ball-milling tank to be crushed by ball milling at a speed of 200 rpm for 1.5 hours, and then passed through 40 meshes; the mixture is then molded into a green body.

[0061] (4) Under the condition of vacuum bar, the green body is heated to 450°C at a rate of 20°C/hour, then heated to 950°C at a rate of 60°C/hour, and then heated to 1250°C at a rate of 45°C/hour, And heat preservation and sintering for 3 hours to obtain porous ceramics.

[0062] Table 1

[0063]

[0064]

[0065] Example 2

[0066] The preparation process of the porous ceramics of the present embodiment is as follows:

[0067] (1) According to Table 1, each component is weighed according to the mass percentage content (referred to as content in the table) to obtain raw materials. Among them, the median particle size of silicon carbide is 5 microns, the median particle size of seaweed mud is 20 microns, the median particle size of additives is 20 microns, and the median particle size of lubricants is 15 microns. In bauxite, the mass percentage of aluminum oxide is 88%, the mass percentage of iron oxide is 1.5%, the mass percentage of titanium oxide is 2%, calcium oxide, magnesium oxide, oxide The total mass percentage of sodium and potassium oxide is 1.5%.

[0068] (2) mixing the dispersant and distilled water for 2 hours to form a premix; the raw material and the premix are ball milled to form a slurry, and when the ball mill is mixed, the mass ratio of the raw material to the grinding medium is 1:1, and the mixing speed is 200 rev/min, the mixing time was 6 hours; the slurry was dried at 100° C. for 8 hours to obtain a mixture. Wherein, the dispersant is sodium hexametaphosphate; the mass ratio of the dispersant to distilled water is 0.5:100.

[0069] (3) The mixture is placed in a ball-milling tank to be crushed by ball milling at a speed of 50 rpm for 2 hours, and then passed through 40 meshes; the mixture is then molded into a blank.

[0070] (4) Under the condition of vacuum bar, the green body is heated to 400°C at a rate of 10°C/hour, then heated to 900°C at a rate of 30°C/hour, and then heated to 1200°C at a rate of 30°C/hour, And heat preservation and sintering for 5 hours to obtain porous ceramics.