A thermally stable alumina ceramic and its preparation method

Abstract

The present invention discloses a thermally stable alumina ceramic and a preparation method thereof. The thermally stable alumina ceramic is obtained by first uniformly mixing alumina powder, Cr2O3 and an auxiliary agent, and then performing pressing, debinding, sintering, ion implantation and annealing treatments. The present invention is beneficial to improving the fluidity of the alumina powder through three times of ball milling and stirring, so that the internal consistency of the green body formed by pressing is better; the organic matter is removed through debinding to avoid the reduction of the sintering quality in the later stage; the thermal expansion coefficient of the alumina ceramic can be reduced by controlling the sintering temperature of the ceramic green body and the dosage of Cr2O3; by introducing element Mg and performing high-temperature treatment, the corundum phase of the original high-purity alumina is changed into the magnesium aluminate spinel phase. The magnesium aluminate spinel phase has more space for atoms to move compared with the corundum phase. Therefore, in repeated heat treatments, the displacement caused by the thermally vibrated atoms will be absorbed by the pores, so that the alumina ceramic has better thermal shock stability and the thermal expansion coefficient is further reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of alumina ceramic preparation, and particularly relates to a thermally stable alumina ceramic and a preparation method thereof. Background Art

[0002] Alumina ceramics have many advantages such as high strength, high hardness, and wear resistance, and are widely used in the fields of electronic appliances (such as electronic components, electronic insulators, microwave components, etc.), chemical industry (such as the inner lining of chemical equipment, pumps, valves, pipelines, etc.), environmental protection (such as purifiers, filters, catalyst carriers, etc.), medical treatment (such as medical implants, prostheses, etc.), industry (such as refractory materials, stove utensils, furnace linings, grinding media, grinding tools, etc.).

[0003] In practical applications, the applicant uses alumina ceramics as the firing plate of the product and as a carrier during the ceramic sintering process. The required sintering temperature of the ceramic is relatively high. After repeated high-temperature heat treatment, most of the existing firing plates are prone to cracking, deformation and other phenomena, which greatly affect the sintering quality of the product. Summary of the Invention

[0004] In order to solve the technical problems existing in the prior art, the purpose of the present invention is to provide a thermally stable alumina ceramic and a preparation method thereof.

[0005] In order to achieve the above purpose and reach the above technical effects, the technical solution adopted by the present invention is:

[0006] A thermally stable alumina ceramic is obtained by first mixing alumina powder, Cr2O3 and additives evenly, and then performing pressing, debinding, sintering, ion implantation, and annealing treatments.

[0007] Furthermore, the thermal expansion coefficient of the thermally stable alumina ceramic is 4.7 - 5.5 μm / m·°C.

[0008] Furthermore, the weight parts of the alumina powder and Cr2O3 are 40 - 100 parts and 1 - 30 parts respectively;

[0009] The additives include the following components in weight parts:

[0010] Dispersant 3 - 5 parts

[0011] Defoamer 0.002 - 0.003 parts

[0012] Binder 1 - 3 parts

[0013] Lubricant 0.2 - 2 parts.

[0014] Furthermore, the alumina powder is α-phase high-purity alumina powder, and the particle size of the α-phase high-purity alumina powder is 1 - 2 μm.

[0015] The present invention also discloses a preparation method of a thermally stable alumina ceramic, comprising the following steps:

[0016] First, mix alumina powder, Cr2O3 and additives evenly, and then perform compacting, debinding, sintering, ion implantation, and annealing treatments to obtain the required thermally stable alumina ceramic.

[0017] Further, the preparation method comprises the following steps:

[0018] 1) By weight, add 40 - 100 parts of alumina powder, 1 - 30 parts of Cr2O3, 3 - 5 parts of dispersant, and 0.002 - 0.003 parts of defoamer into a ball mill, and mix evenly by ball milling;

[0019] 2) Continuously add 1 - 3 parts of binder into the ball mill, and mix evenly by ball milling;

[0020] 3) Continuously add 0.2 - 2 parts of lubricant into the ball mill, and mix evenly by ball milling. At this time, the particle size D50 of the slurry is 300 - 400 nm; then granulate;

[0021] 4) Compacting:

[0022] The compacting pressure is 1.5 - 2.0 T, and the pressure holding time is 3 s or more;

[0023] 5) Debinding;

[0024] 6) Sintering of the ceramic green body;

[0025] 7) Ion implantation;

[0026] 8) Annealing.

[0027] Further, in step 5), the parameters required for debinding are:

[0028] Raise the temperature from room temperature to 650 - 700 °C, with a heating rate of 0.3 - 1 °C / min, and a heat preservation time of 30 - 120 min.

[0029] Further, in step 6), the parameters required for sintering the ceramic green body are:

[0030] Raise the temperature from room temperature to 1450 - 1680 °C, with a heating rate of 2 - 15 °C / min, and a heat preservation time of 120 - 240 min.

[0031] Further, in step 7), the steps of ion implantation are:

[0032] The target material for ion implantation is high-purity magnesium oxide;

[0033] First, evacuate the reaction chamber to a vacuum of no more than 10 Bar; subsequently, perform ion implantation with a suitable dose and energy of Mg ions. The Mg ion implantation dose is 8×10 14 -10×10 14 cm -2 , the implantation energy is 150 - 350 keV, and the Mg ion implantation time is 5 - 15 min.

[0034] Furthermore, in step 8), the parameters required for annealing are as follows:

[0035] Heat from room temperature to 1300 - 1800 °C at a heating rate of 2 - 15 °C / min, and hold for 90 - 120 min.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] The present invention discloses a thermally stable alumina ceramic and its preparation method. Through three - time ball milling and stirring, it is beneficial to improve the fluidity of alumina powder, making the internal consistency of the green body formed during pressing better; through degumming, it is convenient to remove the additives mixed in the granulation stage and avoid the reduction of the sintering quality in the later stage; by controlling the sintering temperature of the ceramic green body and the amount of Cr2O3, the thermal expansion coefficient of the alumina ceramic can be reduced; by introducing element Mg and performing high - temperature treatment, the original corundum phase of high - purity alumina is transformed into the magnesium aluminate spinel phase. The corundum phase is hexagonal close - packed, while the magnesium aluminate spinel phase has more space for atom movement compared with the corundum phase. Therefore, during repeated heat treatment, the displacement caused by the thermally vibrating atoms will be absorbed by the pores, making the alumina ceramic have good thermal shock stability, further reducing the thermal expansion coefficient, and further improving the sintering quality and efficiency. Specific embodiments

[0038] The present invention will be elaborated in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making the protection scope of the present invention more clearly defined.

[0039] The following gives a brief overview of one or more aspects to provide a basic understanding of these aspects. This overview is not an exhaustive survey of all contemplated aspects, and is neither intended to identify key or decisive elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description to follow.

[0040] A preparation method of a thermally stable alumina ceramic, comprising the following steps:

[0041] 1) Add 40 - 100 parts of alumina powder, 1 - 30 parts of Cr2O3, 3 - 5 parts of dispersant, and 0.002 - 0.003 parts of defoamer by weight to a ball mill, and ball mill and mix evenly.

[0042] 2) Continuously add 1 - 3 parts of binder to the ball mill, and ball mill and mix evenly.

[0043] 3) Continuously add 0.2 - 2 parts of lubricant to the ball mill, and ball mill and mix evenly. At this time, the particle size D50 of the slurry is 300 - 400 nm; then granulate.

[0044] Through steps 1) to 3), it is beneficial to improve the fluidity of the alumina powder, making the internal consistency of the green body formed during later compaction better.

[0045] 4) Compaction:

[0046] The compaction pressure is 1.5 - 2.0 T, and the pressure holding time is 3 s or more.

[0047] 5) Slowly heat up and slowly degum:

[0048] Heat up from room temperature to 650 - 700 °C, with a heating rate of 0.3 - 1 °C / min, and a heat preservation time of 30 - 120 min.

[0049] The function of this step is to remove organic substances such as dispersant, binder, and lubricant mixed in during the granulation stage. Without this step, the quality of the subsequent sintered body will be greatly reduced and it will easily break.

[0050] 6) Sintering of ceramic green body:

[0051] Heat up from room temperature to 1450 - 1680 °C, with a heating rate of 2 - 15 °C / min, and a heat preservation time of 120 - 240 min.

[0052] 7) Ion implantation:

[0053] The target material for ion implantation is high-purity magnesium oxide.

[0054] First, evacuate the reaction chamber, and the vacuum degree is not greater than 10 Bar; then perform ion implantation with appropriate Mg ion implantation dose and energy. The Mg ion implantation dose is 8×10 14 -10×10 14 cm -2 , the implantation energy is 150 - 350 keV, and the Mg ion implantation time is 5 - 15 min.

[0055] 8) Annealing:

[0056] The temperature is raised from room temperature to 1300-1800°C, the heating rate is 2-15°C / min, and the holding time is 90-120min, and finally the desired thermal stability alumina ceramics are obtained, and the thermal expansion coefficient is 4.7-5.5μm / m·°C.

[0057] In the present invention, the alumina powder is α-phase high-purity alumina powder, and the particle size of the α-phase high-purity alumina powder is 1-2 μm.

[0058] Compared with the prior art, the present invention has at least the following technical effects:

[0059] (1) After ion implantation, the lattice structure of alumina will be destroyed by the injected substances. In addition, the injected substances do not occupy the lattice points at this time, but only stay in the position of the lattice gaps. Only through heat treatment at a certain temperature will the ions in these gaps be given new energy to carry out particle rearrangement and crystal reconstruction;

[0060] (2) The annealing temperature after ion implantation is relatively high compared to the general annealing temperature, which is closely related to its synthesis temperature. The synthesis temperature of magnesium aluminum spinel is 1750-1850°C, and the generation of spinel at 1000-1400°C is not conducive to sintering. Therefore, the present invention controls the annealing temperature to 1300-1800°C and the holding time to 90-120min;

[0061] (3) Although traditional high-purity alumina ceramics have certain advantages in terms of wear resistance, strength and hardness, in actual applications, the heat treatment temperature is too high, exceeding 1600°C. After repeated heat treatment, the receiving plate is very likely to break. The present invention introduces the element Mg and performs high-temperature treatment to transform the original high-purity alumina corundum phase into a magnesium-aluminum spinel phase. The corundum phase is hexagonal close-packed, and the magnesium-aluminum spinel phase has more space for atoms to move than the corundum phase. In this way, during repeated heat treatment, the displacement caused by the atoms vibrating under heat will be absorbed by the pores, making it have better thermal shock stability and a lower thermal expansion coefficient.

[0062] Example 1

[0063] A method for preparing thermally stable alumina ceramics comprises the following steps:

[0064] 1) Add 77 parts of α-phase high-purity alumina powder, 20 parts of Cr2O3, 3 parts of dispersant, and 0.0025 parts of defoamer into a ball mill by weight, with a ball milling speed of 75 rom and a ball milling time of 10 h, and mix them evenly;

[0065] 2) Add 1.5 parts of binder into the ball mill, with a ball milling speed of 75 rom and a ball milling time of 90 min, and mix evenly;

[0066] 3) Continue to add 1 part of lubricant to the ball mill, with a ball milling speed of 75 rpm and a ball milling time of 90 min. After ball milling and mixing evenly, the slurry particle size D50 is 300 nm at this time; then granulation is carried out;

[0067] 4) Compacting the green body:

[0068] The compaction pressure is 1.5 T and the pressure holding time is 6 s;

[0069] 5) Slowly heating up and slowly degumming:

[0070] Heat from room temperature to 700 °C, with a heating rate of 0.5 °C / min and a heat preservation time of 60 min;

[0071] 6) Sintering the ceramic green body:

[0072] Heat from room temperature to 1450 °C, with a heating rate of 7 °C / min and a heat preservation time of 150 min;

[0073] 7) Ion implantation:

[0074] The target material for ion implantation is high-purity magnesium oxide;

[0075] First, evacuate the reaction chamber to a vacuum degree of 10 Bar; then carry out ion implantation with appropriate Mg ion implantation dose and energy. The Mg ion implantation dose is 8×10 14 cm -2 , the implantation energy is 150 keV, and the Mg ion implantation time is 10 min;

[0076] 8) Annealing:

[0077] Heat from room temperature to 1300 °C, with a heating rate of 2 °C / min and a heat preservation time of 90 min, and finally obtain the required thermally stable alumina ceramic with a thermal expansion coefficient of 5.3 μm / m·°C.

[0078] In this example, the particle size of the α-phase high-purity alumina powder is 1 μm.

[0079] Example 2

[0080] The difference between this example and Example 1 is that the sintering temperature of the ceramic green body in this example is different from that in Example 1.

[0081] A method for preparing a thermally stable alumina ceramic, comprising the following steps:

[0082] 1) By weight, add 77 parts of α-phase high-purity alumina powder, 20 parts of Cr2O3, 3 parts of dispersant, and 0.0025 parts of defoamer to the ball mill, with a ball milling speed of 75 rpm and a ball milling time of 10 h, and ball mill and mix evenly;

[0083] 2) Continuously add 1.5 parts of binder into the ball mill, with a ball milling speed of 75 rpm and a ball milling time of 90 min, and mix evenly by ball milling;

[0084] 3) Continuously add 1 part of lubricant into the ball mill, with a ball milling speed of 75 rpm and a ball milling time of 90 min, and mix evenly by ball milling. At this time, the particle size D50 of the slurry is 300 nm; then granulate;

[0085] 4) Compacting:

[0086] The compaction pressure is 1.5 T and the pressure holding time is 6 s;

[0087] 5) Slowly raise the temperature and slowly degum:

[0088] Raise the temperature from room temperature to 700 °C, with a heating rate of 0.5 °C / min and a heat preservation time of 60 min;

[0089] 6) Sintering of the ceramic green body:

[0090] Raise the temperature from room temperature to 1680 °C, with a heating rate of 7 °C / min and a heat preservation time of 150 min;

[0091] 7) Ion implantation:

[0092] The target material for ion implantation is high-purity magnesium oxide;

[0093] First, evacuate the reaction chamber to a vacuum degree of 10 Bar; then perform ion implantation with appropriate Mg ion implantation dose and energy. The Mg ion implantation dose is 8×10 14 cm -2 , the implantation energy is 150 keV, and the Mg ion implantation time is 10 min;

[0094] 8) Annealing:

[0095] Raise the temperature from room temperature to 1300 °C, with a heating rate of 2 °C / min and a heat preservation time of 90 min, and finally obtain the required thermally stable alumina ceramic with a thermal expansion coefficient of 4.7 μm / m·°C.

[0096] The rest is the same as in Example 1.

[0097] Example 3

[0098] The difference between this example and Example 2 is that the weight fraction of Cr2O3 in this example is 5 parts, and the rest is the same as in Example 2.

[0099] The thermal expansion coefficient of the thermally stable alumina ceramic in this example is 5.5 μm / m·°C.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 1 is that this comparative example does not have steps 7) and 8), and the rest is the same as Example 1.

[0102] The thermal expansion coefficient of the thermally stable alumina ceramic in this comparative example is 8.9 μm / m·°C.

[0103] Comparative Example 2

[0104] The difference between this comparative example and Example 2 is that this comparative example does not have steps 7) and 8), and the rest is the same as Example 2.

[0105] The thermal expansion coefficient of the thermally stable alumina ceramic in this comparative example is 6.3 μm / m·°C.

[0106] Comparative Example 3

[0107] The difference between this comparative example and Example 2 is that this comparative example uses α-phase high-purity alumina powder containing MgO (the content of magnesium element is 275 ppm) to replace the α-phase high-purity alumina powder in Example 2.

[0108] The thermal expansion coefficient of the thermally stable alumina ceramic in this example is 8.2 μm / m·°C.

[0109] The rest is the same as Example 2.

[0110] Comparing Examples 1-2 shows that the sintering temperature of the ceramic green body affects the thermal expansion coefficient of the thermally stable alumina ceramic. Increasing the sintering temperature of the ceramic green body is beneficial to reducing the thermal expansion coefficient of the stable alumina ceramic.

[0111] Comparing Examples 1 and 3 shows that the amount of Cr2O3 used affects the thermal expansion coefficient of the thermally stable alumina ceramic. Increasing the amount of Cr2O3 used is beneficial to reducing the thermal expansion coefficient of the stable alumina ceramic.

[0112] Comparing Example 1 with Comparative Example 1 shows that setting steps 7) and 8) is beneficial to reducing the thermal expansion coefficient of the stable alumina ceramic.

[0113] Comparing Example 2 with Comparative Example 2 shows that setting steps 7) and 8) is beneficial to reducing the thermal expansion coefficient of the stable alumina ceramic.

[0114] Comparing Example 2 with Comparative Example 3 shows that only using α-phase high-purity alumina powder is beneficial to reducing the thermal expansion coefficient of the stable alumina ceramic. Mixing α-phase high-purity alumina powder with other substances such as α-phase MgO will increase the thermal expansion coefficient of the stable alumina ceramic and is not beneficial to reducing the thermal expansion coefficient of the stable alumina ceramic.

[0115] Only by adopting the formula composition disclosed in the present invention and matching with a reasonable sintering temperature of the ceramic green body can the alumina ceramic have good thermal shock stability and a low coefficient of thermal expansion, ensuring the sintering quality and efficiency.

[0116] For the parts or structures not specifically described in the present invention, existing technologies or existing products can be adopted, and no further elaboration will be made here.

[0117] The above are only embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall similarly be included within the patent protection scope of the present invention.

Claims

1. A preparation method of a thermally stable alumina ceramic, characterized in that, The thermally stable alumina ceramic is obtained by first uniformly mixing alumina powder, Cr2O3 and additives, and then performing compacting, debinding, sintering, ion implantation, and annealing treatments; The thermal expansion coefficient of the thermally stable alumina ceramic is 4.7 - 5.5 μm / m•°C; The weight parts of the alumina powder and Cr2O3 are 40 - 100 parts and 1 - 30 parts respectively; The additives include the following components in the following weight parts: Dispersant 3 - 5 parts Defoamer 0.002 - 0.003 parts Binder 1 - 3 parts Lubricant 0.2 - 2 parts; The alumina powder uses α-phase high-purity alumina powder, and the particle size of the α-phase high-purity alumina powder is 1 - 2 μm; The preparation method includes the following steps: 1) By weight parts, add 40 - 100 parts of alumina powder, 1 - 30 parts of Cr2O3, 3 - 5 parts of dispersant, and 0.002 - 0.003 parts of defoamer into a ball mill, and ball mill and mix evenly; 2) Continuously add 1 - 3 parts of binder into the ball mill, and ball mill and mix evenly; 3) Continuously add 0.2 - 2 parts of lubricant into the ball mill, and ball mill and mix evenly. At this time, the particle size D50 of the slurry is 300 - 400 nm; then granulate; 4) Compacting: The compacting pressure is 1.5 - 2.0 T, and the pressure holding time is 3 s or more; 5) Debinding; 6) Sintering of the ceramic green body; 7) Ion implantation; 8) Annealing; In step 7), the steps of ion implantation are: The target material for ion implantation is high-purity magnesium oxide; First, evacuate the reaction chamber to a vacuum degree not greater than 10 bar; subsequently, perform ion implantation with appropriate Mg ion implantation dose and energy. The Mg ion implantation dose is 8×10 14 -10×10 14 cm -2 , the implantation energy is 150 - 350 keV, and the Mg ion implantation time is 5 - 15 min; Three times of ball milling and stirring are beneficial to improving the fluidity of the alumina powder, making the internal consistency of the green body formed during compacting better; through debinding, it is convenient to remove the additives mixed in the granulation stage and avoid the reduction of the sintering quality in the later stage; by regulating the sintering temperature of the ceramic green body and the dosage of Cr2O3, the thermal expansion coefficient of the alumina ceramic can be reduced; by introducing element Mg and performing high-temperature treatment, the original corundum phase of high-purity alumina is changed into the magnesium aluminate spinel phase. The corundum phase is hexagonal close-packed, while the magnesium aluminate spinel phase has more space for atoms to move compared with the corundum phase. Therefore, during repeated heat treatments, the displacement caused by the thermally vibrating atoms will be absorbed by the pores, making the alumina ceramic have good thermal shock stability, further reducing the thermal expansion coefficient, and further improving the sintering quality and efficiency.

2. The preparation method of a thermally stable alumina ceramic according to claim 1, characterized in that In step 5), the parameters required for debinding are: Raise the temperature from room temperature to 650 - 700 °C, the heating rate is 0.3 - 1 °C / min, and the heat preservation time is 30 - 120 min.

3. The preparation method of a thermally stable alumina ceramic according to claim 1, characterized in that, In step 6), the parameters required for sintering the ceramic green body are: Raise the temperature from room temperature to 1450 - 1680 °C, the heating rate is 2 - 15 °C / min, and the heat preservation time is 120 - 240 min.

4. The preparation method of a thermally stable alumina ceramic according to claim 1, characterized in that In step 8), the parameters required for annealing are: Raise the temperature from room temperature to 1300 - 1800 °C, the heating rate is 2 - 15 °C / min, and the heat preservation time is 90 - 120 min.