阅读说明：本技术 烧结助剂、钛酸铝陶瓷前体料和钛酸铝陶瓷及其制造方法 (Sintering aid, aluminum titanate ceramic precursor, aluminum titanate ceramic, and method for producing same ) 是由 陈长龙 魏玉玲 于 2020-08-05 设计创作，主要内容包括：本发明公开了钛酸铝陶瓷的烧结助剂、钛酸铝陶瓷前体料和钛酸铝陶瓷及其制造方法。所述烧结助剂包括金属微粉和氧化硅微粉,金属微粉选自镍微粉、锌微粉、铟微粉中的至少一种。钛酸铝陶瓷前体料包括以下质量百分数的原料：含铝化合物47～60％、含钛化合物35-55％、烧结助剂0.5-10％。将钛酸铝陶瓷前体料与助剂混合得到坯料,将坯料通过等静压、模压或注凝成形得到生坯体；将生坯体进行烧制,得到钛酸铝致密陶瓷。本发明的钛酸铝陶瓷制备步骤简单、成本低、制备过程中不排放三废或三废排放少,并且制备得到的钛酸铝陶瓷致密性好、抗热震性高、热膨胀系数小且抗弯强度高。(The invention discloses a sintering aid for aluminum titanate ceramics, an aluminum titanate ceramic precursor material, aluminum titanate ceramics and a method for producing the same. The sintering aid comprises metal micro powder and silicon oxide micro powder, wherein the metal micro powder is at least one of nickel micro powder, zinc micro powder and indium micro powder. The aluminum titanate ceramic precursor comprises the following raw materials in percentage by mass: 47-60% of aluminum-containing compound, 35-55% of titanium-containing compound and 0.5-10% of sintering aid. Mixing an aluminum titanate ceramic precursor material with an auxiliary agent to obtain a blank, and carrying out isostatic pressing, mould pressing or injection-coagulation forming on the blank to obtain a green body; and firing the green body to obtain the aluminum titanate compact ceramic. The aluminum titanate ceramic provided by the invention has the advantages of simple preparation steps, low cost, no three wastes discharge or less three wastes discharge in the preparation process, and the prepared aluminum titanate ceramic has good compactness, high thermal shock resistance, small thermal expansion coefficient and high bending strength.)

1. A sintering aid characterized by: the material comprises the following raw materials in percentage by mass:

2-15% of metal micro powder and 75-98% of silicon oxide micro powder.

2. The sintering aid according to claim 1, characterized in that: the metal micro powder is at least one of nickel micro powder, zinc micro powder and indium micro powder; preferably, the nickel micro powder, the zinc micro powder and the indium micro powder have a particle size distribution that 90 percent of particles have the size less than or equal to 600nm and the median particle size less than or equal to 500 nm; the silica micropowder has a particle size distribution with a median particle size of less than or equal to 500 nm.

3. The method for producing a sintering aid according to claim 1 or 2, characterized in that: the preparation method comprises the following steps:

at least one of nickel micro powder, zinc micro powder and indium micro powder is uniformly mixed with silicon oxide micro powder, and then the mixture is fired for 1 to 3 hours at the temperature of 650-900 ℃ in the air atmosphere to obtain the sintering aid.

4. The production method according to claim 3, characterized in that: the mixing is selected from one of ball milling, jar milling and grinding.

5. Use of the sintering aid of claim 1 or 2 in the preparation of an aluminum titanate ceramic.

6. An aluminum titanate ceramic precursor material characterized by: the material comprises the following raw materials in percentage by mass:

47-60% of aluminum-containing compound, 35-55% of titanium-containing compound and 0.5-10% of sintering aid as claimed in claim 1 or 2.

7. The aluminum titanate ceramic precursor material of claim 6, wherein: the aluminum-containing compound is industrial-grade high-temperature alumina, and the purity is more than or equal to 98 wt%; the titanium-containing compound is industrial titanium oxide, including rutile, anatase or amorphous titanium oxide, and the purity is more than or equal to 96 wt%.

8. The aluminum titanate ceramic precursor material according to claim 6 or 7, wherein: the preparation method comprises the following steps:

weighing an aluminum-containing compound, a titanium-containing compound and the sintering aid of claim 1 or 2 in percentage by mass, uniformly mixing, and performing ball milling or grinding to obtain the aluminum titanate ceramic precursor material.

9. The method for producing an aluminum titanate dense ceramic using the aluminum titanate ceramic precursor material according to any one of claims 6 to 8, characterized in that: the method comprises the following steps:

(1) mixing the aluminum titanate ceramic precursor material of any one of claims 6 to 8 with an auxiliary agent to obtain a blank, and forming the blank into a green body;

(2) firing the green body obtained in the step (1) according to a firing system: raising the temperature from room temperature to 1000 ℃ at the heating rate of 5-10 ℃/min, raising the temperature from 1000 ℃ to the temperature of 1450-minus 0 ℃ at the heating rate of 2-5 ℃/min, preserving the heat for 3-6h at the temperature of 1450-minus 0 ℃, naturally cooling to 1000 ℃, preserving the heat for 1-2h at the temperature of 1000 ℃, and finally naturally cooling to room temperature to obtain the aluminum titanate dense ceramic.

10. The method of claim 9, wherein: the auxiliary agent is selected from one or more of a binder, a solvent, a gel monomer, a cross-linking agent, a dispersing agent, an initiator and a catalyst.

11. The method of claim 10, wherein: the blank forming method comprises isostatic pressing, mould pressing or injection solidification forming; when the blank forming method is isostatic pressing or die pressing forming, the auxiliary agent is a binder; when the blank forming method is injection-setting forming, the auxiliary agent is gel monomer, cross-linking agent, dispersant, initiator, catalyst and solvent.

12. The method of claim 11, wherein: the binder is polyvinyl alcohol; the gel monomer is acrylamide; the cross-linking agent is N, N' -methylene bisacrylamide; the dispersant is ammonium polymethacrylate; the initiator is ammonium persulfate; the catalyst is N, N, N ', N' -tetramethyl ethylene diamine; the solvent is water.

13. The aluminum titanate dense ceramic prepared by the method of any one of claims 9 to 12, wherein the aluminum titanate dense ceramic has the following characteristics:

(1) apparent porosity is less than or equal to 3.8%;

(2) the volume density is more than or equal to 3.2g/cm³；

(3) The bending strength at normal temperature is more than or equal to 30 MPa;

(4) coefficient of thermal expansion less than or equal to 1.5 x 10^-6/℃；

(5) Continuous cycle thermal shock for at least 20 times without cracking.

Technical Field

The invention relates to the technical field of ceramic preparation, in particular to a sintering aid, an aluminum titanate ceramic precursor material, an aluminum titanate ceramic and a manufacturing method thereof.

Background

As an excellent material integrating a high melting point and a low thermal expansion coefficient, aluminum titanate ceramics can be used as a conduit or vessel through which molten metal flows, for example, a molten metal riser pipe and a sprue bush used in antigravity casting, a molten metal bath, a crucible for molten metal, a hopper for transferring molten metal, and the like. In such applications, aluminum titanate ceramic articles can be exposed to large temperature differences of up to a thousand degrees celsius and as low as room temperature in a short period of time. This requires that the aluminum titanate ceramic article have a high thermal shock resistance to withstand the impact of frequent high and low temperature transitions. On the other hand, as a conduit or vessel through which the molten metal flows, the aluminum titanate ceramic article should have high density and low apparent porosity so that the molten metal does not leak therein.

It is now common in the industry to manufacture dense aluminum titanate ceramic articles in a solid phase two-step process by incorporating an additive strategy. The solid phase two-step method is that firstly, aluminium titanate powder is synthesized, then the powder is used for making blank, and then the aluminium titanate ceramic product is sintered at high temperature. For example, Chinese patent (CN104528817B) discloses a method for preparing aluminum titanate powder, which comprises using high-purity alumina and industrial titanium dioxide as basic raw materials, introducing magnesium oxide, cerium oxide, iron oxide, strontium carbonate and other oxides (one or more of yttrium oxide, vanadium oxide or silicon oxide) as additives, and sequentially carrying out two firing processes (respectively at 1100-. Although the above patent does not relate to the subsequent production of aluminum titanate ceramic articles, it can be seen that the solid phase two-step process of high temperature firing aluminum titanate powders in conjunction with the subsequent high temperature firing of aluminum titanate ceramic articles is a process that is energy intensive and complex. The solid phase two-step firing of dense aluminum titanate ceramic articles is commercially practiced because the reaction of titanium oxide and aluminum oxide to aluminum titanate results in a volume effect, i.e., the volume expands by about 10% (aluminum titanate ceramics and their development silicates report phase 1 of 2003, squareness, etc.). Thus, for dense aluminum titanate ceramic articles, particularly those having a thickness on the order of centimeters and above, if the titanium oxide and alumina powders are directly used for the green body, the volume effect during the subsequent firing process can cause high-density cracking and even pulverization of the ceramic, and thus dense aluminum titanate ceramic articles cannot be obtained. In addition to the above two-step solid phase process, Chinese patent (CN107500757B) discloses a method for preparing compact aluminum titanate ceramics based on a gel process, which comprises using n-butyl titanate, n-butyl silicate and aluminum nitrate as basic raw materials, using ammonia gas, ferric chloride, m-phenylenediamine and a large amount of ethanol as auxiliary raw materials, preparing gel by a reduced pressure distillation process, injecting the obtained gel into a mold to prepare a rough blank, further placing the rough blank into a reaction kettle for drying under pressure, and finally firing the obtained blank into a ceramic product at 1460 ℃. It can be seen that, the process not only uses alkoxide with high cost as raw material, but also has high equipment requirement, complex process and large amount of waste liquid, and the defects of the process for preparing the aluminum titanate ceramic are difficult to industrialize. United states corning incorporated discloses aluminum titanate compositions, aluminum titanate articles, and methods for making the same, having application numbers of 201780036774.1: mixing at least a magnesia source, a silica source, an alumina source, a titania source, and a rare earth oxide to form an inorganic batch composition; mixing together the inorganic batch composition with one or more processing aids selected from the group consisting of: plasticizers, lubricants, binders, pore formers, and solvents; on one hand, the patent uses various raw materials, and uses rare earth oxide which is an expensive raw material, so that the cost of the aluminum titanate ceramic is increased, and the aluminum titanate ceramic is not suitable for large-scale industrial application; on the other hand, this patent is specific to aluminum titanate porous ceramic articles and is not suitable for making dense aluminum titanate ceramic articles. The application numbers are: 201811082894.8 discloses a method for preparing nitride modified aluminum titanate ceramic raw material, mixing alumina powder, titanium dioxide, zirconia, magnesium carbonate and sintering aid, stirring to prepare ceramic powder, adding the ceramic powder into water, and stirring to form aluminum titanate ceramic slurry; adding silicon nitride balls into a ball mill, and performing ball milling by using water as a ball milling medium to obtain silicon nitride powder; adding nitride powder into aluminum titanate ceramic slurry to form modified slurry, drying the modified slurry to form modified powder, adding polyvinyl alcohol cementing agent into the modified powder, and fully and uniformly mixing to prepare the modified aluminum titanate ceramic raw material. The patent has more main raw materials, silicon nitride is added and dried at 450 ℃ to form modified powder, and the preparation process is complex.

Therefore, from the actual industrialization, the preparation process of the aluminum titanate ceramic with less raw material types, simple preparation process, low cost, no three wastes discharge or less three wastes discharge in the preparation process is needed, and the prepared ceramic product has good compactness, high thermal shock resistance and high stability.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides the sintering aid, the aluminum titanate ceramic precursor material, the aluminum titanate ceramic and the manufacturing method thereof, so that the aluminum titanate ceramic has simple preparation steps, low cost, no three wastes or less three wastes discharge in the preparation process, and the prepared aluminum titanate ceramic has good compactness, high thermal shock resistance, small thermal expansion coefficient and high bending strength.

The invention is realized by the following technical scheme:

the invention provides a sintering aid, which comprises the following raw materials in percentage by mass:

2-15% of metal micro powder and 75-98% of silicon oxide micro powder.

Preferably, the metal micro powder is at least one of nickel micro powder, zinc micro powder and indium micro powder.

Preferably, the nickel micro powder, the zinc micro powder and the indium micro powder have a particle size distribution that 90 percent of particles have the size less than or equal to 600nm and the median particle size less than or equal to 500 nm; the silica micropowder has a particle size distribution with a median particle size of less than or equal to 500 nm.

In a second aspect of the present invention, there is provided a method for preparing the sintering aid, comprising:

at least one of nickel micro powder, zinc micro powder and indium micro powder is uniformly mixed with silicon oxide micro powder, and then the mixture is fired for 1 to 3 hours at the temperature of 650-900 ℃ in the air atmosphere to obtain the sintering aid.

Preferably, the mixing is selected from one of ball milling, pot milling and grinding.

In a third aspect of the present invention, there is provided the use of the above sintering aid in the preparation of an aluminum titanate ceramic.

The fourth aspect of the invention provides an aluminum titanate ceramic precursor material, which comprises the following raw materials in percentage by mass:

47-60% of aluminum-containing compound, 35-55% of titanium-containing compound and 0.5-10% of sintering aid.

Preferably, the aluminum-containing compound is industrial-grade high-temperature alumina, and the purity is more than or equal to 98 wt%; the titanium-containing compound is industrial titanium oxide, including but not limited to rutile, anatase or amorphous titanium oxide, and the purity is more than or equal to 96 wt%.

Preferably, the aluminum titanate ceramic precursor material is prepared by the following method:

the aluminum-containing compound, the titanium-containing compound and the sintering aid are weighed according to mass percent and then uniformly mixed, and the mixture is selected from ball milling or grinding, so that the aluminum titanate ceramic precursor material is obtained.

Preferably, when the mixing is selected from ball milling, the milling medium ball is alumina milling medium ball, and the mass ratio of the total mass of the aluminum-containing compound, the titanium-containing compound and the sintering aid to the milling medium ball is 1: 5.5.

In a fifth aspect of the present invention, there is provided a method for preparing an aluminum titanate dense ceramic from the above aluminum titanate ceramic precursor material, comprising the steps of:

(1) preparing a blank: mixing an aluminum titanate ceramic precursor material with an auxiliary agent to obtain a blank;

(2) forming and drying the blank to obtain a green body;

(3) firing the green body obtained in the step (2), wherein the firing system is as follows: raising the temperature from room temperature to 1000 ℃ at the heating rate of 5-10 ℃/min, raising the temperature from 1000 ℃ to the temperature of 1450-minus 0 ℃ at the heating rate of 2-5 ℃/min, preserving the heat for 3-6h at the temperature of 1450-minus 0 ℃, naturally cooling to 1000 ℃, preserving the heat for 1-2h at the temperature of 1000 ℃, and finally naturally cooling to room temperature to obtain the aluminum titanate dense ceramic.

Preferably, the auxiliary agent is selected from one or more of a binder, a gel monomer, a cross-linking agent, a dispersing agent, an initiator, a catalyst and a solvent.

Preferably, the blank is formed by isostatic pressing, die pressing or injection-set forming; when the blank forming method is isostatic pressing or die pressing forming, the auxiliary agent is a binder; when the blank forming method is injection-setting forming, the auxiliary agent is gel monomer, cross-linking agent, dispersant, initiator, catalyst and solvent.

Preferably, when the method of forming the blank is isostatic pressing or press forming, the step of mixing the aluminum titanate ceramic precursor material with the auxiliary agent to obtain the blank comprises a spray drying process.

More preferably, the binder is a polyvinyl alcohol aqueous solution with the mass percentage of 1%; the gel monomer is acrylamide; the cross-linking agent is N, N' -methylene bisacrylamide; the dispersant is ammonium polymethacrylate; the initiator is an ammonium persulfate aqueous solution with the mass percentage of 5%; the catalyst is N, N, N ', N' -tetramethyl ethylene diamine; the solvent is water.

Preferably, when the blank forming method is isostatic pressing or die pressing, the mass ratio of the aluminum titanate ceramic precursor material, the binder and the grinding medium ball is 1: (1.5-2): 5.5;

preferably, when the blank forming method is injection-setting forming, the mass ratio of the aluminum titanate ceramic precursor material, the gel monomer, the crosslinking agent, the dispersant, the initiator, the catalyst and the solvent is 100: (1-4): (0.1-0.5): (0.2-0.8): (0.1-0.3): (0.1-0.3): (15-20).

In a sixth aspect of the present invention, there is provided an aluminum titanate dense ceramic prepared by the above method, which has the following characteristics:

(1) apparent porosity is less than or equal to 3.8%;

(2) the volume density is more than or equal to 3.2g/cm³；

(3) The bending strength at normal temperature is more than or equal to 30 MPa;

(4) coefficient of thermal expansion less than or equal to 1.5 x 10^-6/℃；

(5) Continuous cycle thermal shock for at least 20 times without cracking.

The invention has the beneficial effects that:

1. the sintering aid disclosed by the invention is simple and easily available in raw materials, simple in preparation method and low in energy consumption.

2. After the sintering aid is introduced, basic raw materials of alumina and titanium oxide can be directly used for preparing an aluminum titanate ceramic blank, and then an aluminum titanate compact ceramic product is obtained through one-time high-temperature sintering. The basic raw materials are not required to be sintered into aluminum titanate powder at high temperature firstly, then the blank is prepared, and then the aluminum titanate compact ceramic is sintered at high temperature for the second time. The energy consumption cost can be obviously saved, the process steps are obviously reduced, the production period is shortened, the production efficiency is improved, and the properties of the final aluminum titanate dense ceramic are basically similar to or even better than those of the traditional product. In the aluminum titanate ceramic precursor material of the present invention, the sintering aid is used in an amount of only 0.5 to 10% by mass, but the effect is remarkable even when the amount is small.

3. The apparent porosity of the aluminum titanate dense ceramic product prepared by the method is less than or equal to 3.8 percent; the volume density is more than or equal to 3.2g/cm³(ii) a The bending strength at normal temperature is more than or equal to 30 MPa; coefficient of thermal expansion less than or equal to 1.5 x 10^-6/° c; excellent thermal shock resistance and stability.

Drawings

FIG. 1 is a powder XRD pattern of the crushed and ground aluminum titanate dense ceramic prepared in example 1.

FIG. 2 is a powder XRD pattern of the aluminum titanate dense ceramic prepared in example 1 after being crushed and ground after being kept at 1000 ℃ for 30 hours.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

As discussed in the background of the invention, the current practice in the industry to fire dense aluminum titanate ceramic articles in a two-step solid phase process is due to the volume effect, i.e., the expansion of about 10% by volume, that occurs as the titanium oxide and aluminum oxide react to form aluminum titanate. Thus, for dense aluminum titanate ceramic articles, particularly those having a thickness on the order of centimeters and above, if the titanium oxide and alumina powders are directly used for the green body, the volume effect during the subsequent firing process can cause high-density cracking and even pulverization of the ceramic, and thus dense aluminum titanate ceramic articles cannot be obtained. The present invention provides a sintering aid, an aluminum titanate ceramic precursor material, an aluminum titanate ceramic, and a method for producing the same. The aluminum titanate dense ceramic is prepared by taking three compounds of aluminum oxide, titanium oxide and sintering aid as main raw materials.

The sintering aid, the aluminum titanate ceramic precursor material and the ceramic firing system can realize the solid-phase one-step method for preparing the aluminum titanate compact ceramic product. The sintering aid is prepared by firing at least one of metal micro powder nickel, zinc and indium micro powder and silicon oxide micro powder, wherein the mass percentage of the metal micro powder is only 2-15%, but the metal micro powder and the silicon oxide micro powder can form a uniform dispersion system taking the silicon oxide micro powder as a flux, and metal components in the metal micro powder are partially or completely converted into oxide and/or silicate phases. The sintering aid of the invention mainly plays a role in preparing the aluminum titanate compact ceramic: firstly, the metal ions in the sintering aid of the invention can replace Al in the process of firing ceramics at high temperature₂TiO₅Part of Al in (1)³⁺The aluminum titanate crystal lattice torsion resistance is reduced by the ions, and the effects of stabilizing the aluminum titanate and inhibiting the decomposition of the aluminum titanate are achieved; secondly, the metal component of the sintering aid can obviously inhibit the formation of aluminum titanate crystal domains, and the aluminum titanate ceramic product prepared by the traditional solid-phase two-step method and other methods by adding magnesium-based reagents can form larger crystal domains, and the existence of the crystal domains can lead the aluminum titanate ceramic product to generate cracks along the domain boundary under the working condition of frequent switching at high and low temperatures, so that the ceramic is easy to break; thirdly, the silicate phase and the silicon oxide phase in the sintering aid can be used as solid solutions to provide an ion diffusion channel for liquid phase sintering in the early sintering stage, so that the solid phase reaction of aluminum oxide and titanium oxide is promoted, and the aluminum titanate compact ceramic product is easy to sinter; fourthly, the silicate phase and the silicon oxide phase in the sintering aid are used as liquid phases, so that the volume effect generated by the reaction of titanium oxide and aluminum oxide can be effectively relieved, and the effects of bonding aluminum titanate crystal grains and reducing the internal stress of a ceramic body are achieved; fifthly, the silicon oxide and a small amount of aluminum oxide in the sintering aid generate a small amount of mullite phase in the later sintering period, and the ceramic reinforcing effect is achieved.

In addition, the ceramic firing system of the invention is beneficial to firing of compact aluminum titanate ceramic products. In the firing process, the temperature is raised to 1000 ℃ at a relatively fast temperature rise rate (5-10 ℃/min), so that the silicate phase and the silicon oxide phase in the sintering aid can quickly reach a liquid phase, ion diffusion and inoculation of aluminum titanate crystal nuclei are facilitated, and the formation and growth of the aluminum titanate crystal nuclei at a higher temperature are facilitated subsequently. The subsequent low-speed temperature rise (2-5 ℃/min) can effectively promote the nucleation and the proper grain growth of the aluminum titanate crystal nucleus, and the slow temperature rise at the section can also relieve the volume effect generated by the reaction of titanium oxide and aluminum oxide. The temperature is kept at 1580 ℃ for 3-6h at 1450 ℃, so that the aluminum titanate crystal phase can be completely formed, and the heat preservation at the section also enables the aluminum titanate crystal grains to grow into proper size and promotes the densification of the ceramic. The firing of the compact aluminum titanate ceramic product needs to be carried out for 1-2h at 1000 ℃ in the cooling stage, and the firing has the function of releasing the internal stress generated by cooling the ceramic in the high-temperature stage and enhancing the thermal shock resistance of the ceramic.

In order to make the technical solutions of the present application more clearly understood by those skilled in the art, the technical solutions of the present application will be described in detail below with reference to specific embodiments.

The test materials used in the examples of the present invention are all conventional in the art and commercially available.