Black high thermal conductivity aluminum nitride ceramic and method of making same

Abstract

The present application belongs to the technical field of aluminum nitride ceramic manufacturing, and discloses a black high-thermal-conductivity aluminum nitride ceramic and a preparation method thereof. The black high-thermal-conductivity aluminum nitride ceramic is formed by uniformly mixing and sintering aluminum nitride powder, sintering aids and coloring aids in a mass ratio of 90-98:1-5:1-5, and has a reflectivity of not more than 14% and a thermal conductivity of more than 180 W / m·k. The preparation method provides black modification for the aluminum nitride based on the coloring aids, and through precise control of the oxygen content in the degassing sheet obtained by degassing, the multi-stage temperature end point in the sintering process, and the different atmospheres in the degassing and sintering processes, the adverse effects of the coloring aids on the thermal conductivity improvement are hindered, and the obtained aluminum nitride ceramic has both black color and high thermal conductivity. The raw materials required by the preparation method are conventional and easy to obtain, the process is simple and the cost is low, and the method is convenient for popularization in the field of high thermal conduction and special light requirements.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of aluminum nitride ceramic manufacturing, and particularly relates to a black high-thermal-conductivity aluminum nitride ceramic with black color and high thermal conductivity, and a preparation method thereof. BACKGROUND

[0002] Currently, aluminum nitride ceramics are mostly translucent, with a slightly yellow or slightly gray color. Ordinary aluminum nitride ceramics are mostly used in LED packaging substrates, and a small amount of high-thermal-conductivity aluminum nitride ceramics are used in the field of laser heat sinks.

[0003] Black ceramics currently mainly refer to alumina black ceramics, which are applied to the fields of multilayer ceramic circuits, optoelectronics, digital integrated circuits, microwaves, optical communications, and crystal oscillator device ceramic housings. However, black alumina ceramics have low thermal conductivity, and cannot meet the heat conduction needs of high-power, high-density devices and power devices with special requirements for heat absorption and light avoidance.

[0004] Although there are currently related researches on high-thermal-conductivity aluminum nitride ceramics and black aluminum nitride ceramics, the dual performance of high thermal conductivity and black color cannot be considered in aluminum nitride ceramics. Therefore, an aluminum nitride ceramic with high thermal conductivity and black color can meet the needs of high heat conduction and be applied in fields with special requirements for light. It is necessary to further study the preparation of black high-thermal-conductivity aluminum nitride ceramics. SUMMARY

[0005] In view of the problem in the prior art that the modification of aluminum nitride ceramics is only for single performance of high thermal conductivity or black color, the present inventors have found, on the basis of long-term research on aluminum nitride ceramics, that the main reason why the two cannot be considered together is that the preparation of black ceramics often needs to add a colorant, but the colorant will have an adverse effect on thermal conductivity under conventional preparation processes, hindering the improvement of thermal conductivity. Therefore, through improvement of the preparation process, a black high-thermal-conductivity aluminum nitride ceramic and a preparation method thereof are provided. The preparation method realizes the modification of aluminum nitride ceramics in high thermal conductivity and black color by precisely controlling the atmosphere sintering, while ensuring high thermal conductivity of the aluminum nitride ceramic.

[0006] The present application specifically adopts the following technical solutions:

[0007] A black high-thermal-conductivity aluminum nitride ceramic is prepared by uniformly mixing and sintering aluminum nitride powder, sintering aids, and coloring aids in a mass ratio of 90-98:1-5:1-5, and has a reflectivity of not more than 14% and a thermal conductivity of not less than 180 W / (m·K).

[0008] Obviously, the reflectivity of not more than 14% ensures that the aluminum nitride ceramic has obvious black color, belonging to the category of black ceramics.

[0009] Wherein, the aluminum nitride powder as raw material can be AlN powder with oxygen content not more than 0.7%. The aluminum nitride powder before sintering is controlled to have oxygen content not more than 1.9%.

[0010] Wherein, the sintering aid is selected from a mixture of at least two of Y2O3, CaF2, CaO, MgO, ZnO, SiO2. For example, it can be a mixture of two such as Y2O3 and CaF2, or Y2O3 and MgO, or a mixture of three such as Y2O3 and CaO and MgO, or Y2O3 and ZnO and SiO2, which will not be repeated here.

[0011] Wherein, the coloring aid is selected from any one of CeO2, MnO2, MoO2, MoO3, Fe2O3, Fe3O4, Cr2O3, NbO2, HfO2, DyO2, TiO2, Co3O4, GaO2, or a mixture of at least two. For example, it can be a single MnO2, MoO3, etc., or a mixture of two such as NbO2 and Mo2O3, or MnO2 and MoO3, or a mixture of three such as TiO2 and Cr2O3 and Ga2O3, or Co3O4 and Cr2O3 and NbO2, which will not be repeated here.

[0012] Preferably, the black high-thermal-conductivity aluminum nitride ceramic further comprises a dispersant, which can be selected from one of oleic acid, herring oil, acrylate, phosphate, etc. The addition of the dispersant does not affect the thermal conductivity and color development of the final aluminum nitride ceramic, etc. Generally, the addition amount of the dispersant is controlled to be 1% to 5% of the total mass of the aluminum nitride powder, the sintering aid and the coloring aid, which can be implemented according to the general description in the prior art.

[0013] The present application also provides a preparation method of the above-mentioned black high-thermal-conductivity aluminum nitride ceramic, comprising the following steps:

[0014] S1, mixing and ball-milling the sintering aid, the coloring aid, the aluminum nitride powder, the binder and the solvent to obtain a casting slurry;

[0015] S2, vacuum debubbling the casting slurry until the viscosity is 5000 mPa·s to 18000 mPa·s, and then casting to obtain a green sheet;

[0016] S3, heating the green sheet to 300℃ to 600℃ under inert gas or inert-air mixed gas, and controlling the process from the start of heating for at least 10 h to perform degassing to obtain a degassing sheet with oxygen content not more than 1.9%;

[0017] S4, heating the glue-removed sheet to 1400℃-1600℃ at one time, and before reaching the temperature, passing in inert-reducing mixed gas for at least 60 min to perform color development reaction, then heating to 1650℃-1950℃ at two times for at least 90 min, and finally keeping for 3 h-100 h, and ensuring that the total time of the two-time heating and keeping is not less than 10 h, to complete sintering, and obtain black high-thermal-conductivity aluminum nitride ceramic.

[0018] Specifically, in step S1, the casting slurry is obtained by mixing and ball-milling the composite colloid and the sintering powder.

[0019] Further, the preparation method of the sintering powder is: mixing and ball-milling the sintering aid, the coloring aid, the aluminum nitride powder and the first solvent to obtain the sintering powder.

[0020] Further, the mass ratio of the aluminum nitride powder, the sintering aid and the coloring aid is 90-98:1-5:1-5, and the mixture of the three is defined as the ceramic powder.

[0021] Generally, the mass ratio of the ceramic powder and the first solvent is controlled to be 1:0.4-0.8.

[0022] Further, the preparation method of the composite colloid is: uniformly mixing the binder and the second solvent to obtain the composite colloid.

[0023] Generally, the mass ratio of the binder and the second solvent is controlled to be 1:3-7.

[0024] The "solvent" in the above step S1 includes the first solvent and the second solvent.

[0025] In the preparation of the casting slurry in step S1, the mass ratio of the binder and the ceramic powder is 0.05-0.12:1.

[0026] In step S3, the process of glue removal can be to reach a temperature of 300℃-600℃ at one time with a slow heating rate (one-step method), or to reach a temperature of 300℃-600℃ and then to perform moderate keeping operation, or to reach a final temperature of 300℃-600℃ in stages with a fast heating rate and set a keeping period (multi-step-keeping plateau method), or to combine the one-step method or the multi-step-keeping plateau method with the keeping operation after heating, so as to ensure that the total operation time is at least 10 h and the oxygen content of the glue-removed sheet is controlled to be not more than 1.9%.

[0027] In step S4, inert gas or inert-reducing mixed gas is used during the color development reaction, the secondary temperature rising process and the subsequent holding process. In the secondary temperature rising process and the subsequent holding process, the reducing gas in the mixed gas can be used to further reduce the oxygen content, thereby improving the thermal conductivity.

[0028] The inert-reducing mixed gas refers to the mixed gas of inert gas and reducing gas.

[0029] Generally, the inert gas can be selected from conventional inert gases such as nitrogen, argon and helium, and the reducing gas can be selected from hydrogen or carbon monoxide.

[0030] Further, in step S4, the volume content of the reducing gas in the inert-reducing mixed gas introduced during the color development reaction accounts for 4% to 15% of the total volume of the inert-reducing mixed gas.

[0031] Further, in step S4, the process of the first temperature rising can be to reach the temperature of 1400°C to 1600°C at a slow rising rate (one-step method), or to reach the temperature of 1400°C to 1600°C and then perform a moderate holding operation, or to reach the final temperature of 1400°C to 1600°C in stages at a fast rising rate and set a holding section during the process (multi-step-holding plateau method), or to combine the one-step method or the multi-step-holding plateau method with the holding process after the temperature rising.

[0032] Further, in step S4, the process of the secondary temperature rising can be to reach the temperature of 1650°C to 1950°C at a slow rising rate in one step (one-step method), or to reach the final temperature of 1650°C to 1950°C in stages at a fast rising rate and set a holding section during the process (multi-step-holding plateau method), so as to reach a total secondary temperature rising time of at least 60 min.

[0033] Generally, part of the dispersing agent is added in the preparation process of the sintered powder, so that the powder materials are more uniformly dispersed.

[0034] Generally, part of the plasticizer can also be added in the preparation process of the composite colloid, which can be selected from DOP and / or DBP. The addition of the plasticizer does not affect the thermal conductivity and color development of the final aluminum nitride ceramic. Generally, the addition amount of the plasticizer is controlled to be 0.5 to 1.2 times the mass of the binder, and those skilled in the art can implement it according to the general description in the prior art.

[0035] The binder is selected from polyvinyl butyral and / or polyacrylic acid resin.

[0036] The first solvent and the second solvent are each selected from any one of xylene, toluene, methanol, ethanol, isopropanol, n-butanol, acetone, ethyl acetate, methyl ethyl ketone, trichloroethane, and cyclohexanone, or a mixture of at least two thereof. For example, the solvent can be single toluene, acetone, ethanol, isopropanol, or the like, or a mixed solvent of two kinds such as toluene and isopropanol, or butanone and ethanol, or ethyl acetate and ethanol, and the like, which will not be described one by one here.

[0037] When the first solvent and the second solvent are a mixture of two solvents, the ratio of the two solvents is not limited, such as 2:3, 3:2, 3:4, and the like.

[0038] The above black high-thermal-conductivity aluminum nitride ceramic and the preparation method thereof provided by the present application, on the basis of providing black modification for aluminum nitride by the coloring aid, through precise control of the degassing degree (oxygen content in the degassing sheet), the multi-stage temperature end point in the sintering process, and the different atmospheres in the degassing and sintering processes, the adverse effects of the coloring aid on the thermal conductivity improvement are hindered, and the obtained aluminum nitride ceramic has both black color (reflectivity not more than 14%) and high thermal conductivity of more than 180 W / (m·K).

[0039] Specifically, first, through control of the atmosphere in the degassing process, the increase of the oxygen content in the aluminum nitride after the degassing process is controlled, the proportion of the second phase of the aluminum nitride in the subsequent sintering process is reduced, and the thermal conductivity of the aluminum nitride ceramic is ensured to be higher; second, through the staged temperature rising and sintering atmosphere control in the sintering process, the doping reaction of the coloring aid and the valence adjustment of the coloring element are performed in advance, and through the control of different sintering atmospheres and time, the lattice oxygen impurity content of the aluminum nitride is reduced during the high-temperature grain growth of the aluminum nitride, the grain growth is promoted, and the thermal conductivity of the ceramic is improved. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art with creative labor before making the present application belong to the scope of protection of the present application.

[0041] Embodiment 1

[0042] The present embodiment provides a preparation method of a black high-thermal-conductivity aluminum nitride ceramic, which comprises the following steps:

[0043] First, 1.5 g of Y2O3 powder and 0.5 g of CaF2 powder are mixed as a sintering aid, and 0.3 g of NbO2 powder and 0.7 g of Mo2O3 powder are mixed as a coloring aid.

[0044] Then, the sintering aid, the coloring aid and 1.5 g of oleic acid were mixed with 45 g of a toluene-isopropyl alcohol mixed solvent and wet-pre-milled and dispersed for 2 h, and 97 g of the aluminum nitride powder (oxygen content: 0.65%) was added and milled and dispersed to obtain the sintering powder.

[0045] That is, the ratio of the total amount of the ceramic powder composed of the sintering aid, the coloring aid and the aluminum nitride powder to the mass of the toluene-isopropyl alcohol mixed solvent for dispersing the same was 1:0.45.

[0046] Again, 8 g of the polyacrylic acid resin and 4 g of DBP were dissolved in 28 g of a toluene-isopropyl alcohol mixed solvent to prepare a polyacrylic acid solution as the composite colloid.

[0047] In the fourth step, the composite colloid was added to the sintering powder, and the aluminum nitride ceramic slurry was obtained by milling and sufficiently dispersing the same.

[0048] That is, the ratio of the total amount of the ceramic powder composed of the sintering aid, the coloring aid and the aluminum nitride powder to the mass of the polyacrylic acid resin in the composite colloid was 100:8.

[0049] In the fifth step, the aluminum nitride ceramic slurry was vacuum-deaerated to have a viscosity of 11000 mPa·s, and was cast to obtain a green sheet.

[0050] In the sixth step, the green sheet was subjected to a de-binding process in stages to obtain a de-binding sheet having an oxygen content of 1.6%.

[0051] Specifically, the de-binding was completed by increasing the temperature to 300°C at a temperature increasing rate of 0.5°C / min under a nitrogen gas flow of 800 L / min and maintaining the temperature for 1 h, and then increasing the temperature to 350°C at a temperature increasing rate of 0.05°C / min under a nitrogen-hydrogen mixed gas flow (600 L / min of nitrogen gas + 200 L / min of air) and maintaining the temperature for 1 h.

[0052] Finally, the de-binding sheet was subjected to a sintering process in stages to obtain a black high-thermal-conductivity aluminum nitride ceramic.

[0053] Specifically, the sintering was completed by increasing the temperature to 1000°C at a temperature increasing rate of 6°C / min under nitrogen gas, then increasing the temperature to 1600°C at a temperature increasing rate of 2°C / min under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen gas to hydrogen gas: 9:1), and finally increasing the temperature to 1750°C at a temperature increasing rate of 0.3°C / min under nitrogen gas and maintaining the temperature for 12 h under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen gas to hydrogen gas: 9.6:0.4).

[0054] The black high-thermal-conductivity aluminum nitride ceramic obtained in the embodiment is obtained by uniformly mixing 97% aluminum nitride, 2% sintering aids (including 1.5% Y2O3 and 0.5% CaF2) and 1% coloring aids (including 0.3% NbO2 and 0.7% Mo2O3) and sintering.

[0055] Embodiment 2

[0056] The embodiment provides a preparation method of black high-thermal-conductivity aluminum nitride ceramic, which comprises the following steps:

[0057] Firstly, 4 g of Y2O3 powder, 0.5 g of CaO powder and 0.5 g of MgO are weighed and mixed as sintering aids, and 1.5 g of TiO2 powder, 2 g of Cr2O3 powder and 0.5 g of Ga2O3 powder are weighed and mixed as coloring aids.

[0058] Then, the sintering aids, the coloring aids and 4 g of phosphate ester are mixed with 75 g of butanone-absolute ethanol mixed solvent, and wet pre-ball-milling dispersion is performed for 3 h, and then 91 g of aluminum nitride powder (oxygen content is 0.65%) is added and ball-milling dispersion is performed, to obtain sintering powder.

[0059] That is, the mass ratio of the total amount of ceramic powder composed of the sintering aids, the coloring aids and the aluminum nitride powder to the butanone-absolute ethanol mixed solvent used for dispersing the ceramic powder is 1:0.75.

[0060] Again, 5.5 g of polyacrylic acid resin and 6 g of DOP are dissolved in 38 g of butanone-absolute ethanol mixed solvent to prepare a polyacrylic acid solution as a composite colloid.

[0061] Fourthly, the composite colloid is added to the sintering powder, and ball-milling is performed to sufficiently disperse the sintering powder, to obtain aluminum nitride ceramic slurry.

[0062] That is, the mass ratio of the total amount of ceramic powder composed of the sintering aids, the coloring aids and the aluminum nitride powder to the polyacrylic acid resin in the composite colloid is 100:10.

[0063] Fifthly, the aluminum nitride ceramic slurry is vacuum degassed to a viscosity of 5000 mPa·s, and is flow-cast to obtain a green sheet.

[0064] Sixthly, the green sheet is subjected to staged degassing treatment to obtain a degassed sheet with an oxygen content of 1.85%.

[0065] Specifically, the degassing is completed by increasing the temperature to 250℃ at a temperature increasing rate of 0.3℃ / min under a nitrogen gas flow rate of 600 L / min and maintaining the temperature for 1 h, and then increasing the temperature to 580℃ at a temperature increasing rate of 0.15℃ / min under a nitrogen gas flow rate of 600 L / min and maintaining the temperature for 1 h.

[0066] Finally, the green sheet is subjected to a sintering process in stages to obtain the black high-thermal-conductivity aluminum nitride ceramic.

[0067] Specifically, the temperature is raised to 1400°C at a temperature raising rate of 10°C / min under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 8.5:1.5), and then the temperature is kept at 1400°C for 30 min. Finally, the temperature is raised to 1700°C at a temperature raising rate of 0.6°C / min under a nitrogen gas atmosphere, and then the temperature is kept at 1700°C for 100 h under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 9.5:0.5) to complete the sintering.

[0068] The above black high-thermal-conductivity aluminum nitride ceramic obtained in the embodiment is obtained by uniformly mixing 91% aluminum nitride, 5% sintering aids (including 4% Y2O3, 0.5% CaO and 0.5% MgO) and 4% coloring aids (including 1.5% TiO2, 2% Cr2O3 and 0.5% Ga2O3) and sintering.

[0069] Example 3

[0070] The embodiment provides a preparation method of a black high-thermal-conductivity aluminum nitride ceramic, which comprises the following steps:

[0071] First, 2 g of Y2O3 powder and 0.8 g of MgO are weighed and mixed as sintering aids, and 0.4 g of Co3O4 powder, 0.4 g of Cr2O3 powder and 0.2 g of NbO2 powder are weighed and mixed as coloring aids.

[0072] Then, the sintering aids, the coloring aids and 2 g of oleic acid are mixed with 80 g of ethyl acetate-anhydrous ethanol mixed solvent, and wet pre-milling and dispersion are performed for 3 h, and then 96.2 g of aluminum nitride powder (oxygen content is 0.5%) is added for ball milling and dispersion to obtain sintering powder.

[0073] That is, the mass ratio of the total amount of ceramic powder composed of the sintering aids, the coloring aids and the aluminum nitride powder to the ethyl acetate-anhydrous ethanol mixed solvent used for dispersing the ceramic powder is 1:0.8.

[0074] Again, 5 g of polyacrylic acid resin and 4 g of DBP are dissolved in 25 g of ethyl acetate-anhydrous ethanol mixed solvent to prepare a polyacrylic acid solution as a composite colloid.

[0075] Fourthly, the composite colloid is added to the sintering powder, and ball milling is performed to obtain aluminum nitride ceramic slurry.

[0076] That is, the mass ratio of the total amount of ceramic powder composed of the sintering aids, the coloring aids and the aluminum nitride powder to the polyacrylic acid resin in the composite colloid is 100:5.

[0077] In the fifth step, the aluminum nitride ceramic slurry is vacuum degassed to a viscosity of 18000 mPa·s, and is cast into a green sheet.

[0078] In the sixth step, the green sheet is subjected to a staged degumming treatment to obtain a degummed sheet with an oxygen content of 1.35%.

[0079] Specifically, the degumming is completed by heating to 250°C at a heating rate of 0.7°C / min under a nitrogen flow of 600 L / min and holding for 1 h, and then heating to 450°C at a heating rate of 0.15°C / min under a nitrogen flow of 600 L / min and holding for 3 h.

[0080] Finally, the degummed sheet is subjected to a staged sintering treatment to obtain a black high-thermal-conductivity aluminum nitride ceramic.

[0081] Specifically, the sintering is completed by heating to 800°C at a heating rate of 10°C / min under nitrogen, then heating to 1600°C at a heating rate of 3°C / min under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 8.5:1.5), and finally heating to 1780°C at a heating rate of 0.3°C / min under nitrogen and holding for 20 h under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 9.5:0.5).

[0082] The above black high-thermal-conductivity aluminum nitride ceramic obtained in this example is obtained by uniformly mixing and sintering 96.2% aluminum nitride, 2.8% sintering aids (including 2% Y2O3 and 0.8% MgO), and 1% coloring aids (including 0.4% Co3O4, 0.4% Cr2O3, and 0.2% NbO2).

[0083] Example 4

[0084] The present example provides a method for preparing a black high-thermal-conductivity aluminum nitride ceramic, which comprises the following steps:

[0085] First, 2.5 g of Y2O3 powder and 0.5 g of CaF2 powder are weighed and mixed as sintering aids, and 0.3 g of NbO2 powder and 0.7 g of Mo2O3 powder are weighed and mixed as coloring aids.

[0086] Then, the above sintering aids, coloring aids, and 2 g of oleic acid are mixed with 60 g of a toluene-isopropyl alcohol mixed solvent, and wet pre-milling and dispersion are performed for 2 h, and then 96 g of aluminum nitride powder (oxygen content is 0.65%) is added for ball milling and dispersion to obtain a sintering powder.

[0087] That is, the mass ratio of the total amount of ceramic powder composed of sintering aids, coloring aids, and aluminum nitride powder to the toluene-isopropyl alcohol mixed solvent used for dispersing it is 1:0.6.

[0088] Again, 7 g of polyacrylic acid resin, 6 g of DBP were dissolved in 42 g of toluene-isopropyl alcohol mixed solvent to prepare a polyacrylic acid solution as a composite colloid.

[0089] In the fourth step, the composite colloid was added to the sintering powder, and ball milling was performed to obtain an aluminum nitride ceramic slurry.

[0090] That is, the ratio of the total amount of the sintering aid, the coloring aid, and the aluminum nitride powder to the mass of the polyacrylic acid resin in the composite colloid was 100:7.

[0091] In the fifth step, the aluminum nitride ceramic slurry was vacuum degassed to a viscosity of 11000 mPa·s, and was cast to obtain a green sheet.

[0092] In the sixth step, the green sheet was subjected to a staged degassing process to obtain a degassed sheet with an oxygen content of 1.5%.

[0093] Specifically, the degassing was completed by heating to 250°C at a heating rate of 1°C / min under a nitrogen flow of 600 L / min and maintaining the temperature for 1 h, and then heating to 500°C at a heating rate of 0.8°C / min under a nitrogen-air mixed gas flow (600 L / min of nitrogen + 100 L / min of air) of 700 L / min and maintaining the temperature for 1 h.

[0094] Finally, the degassed sheet was subjected to a staged sintering process to obtain a black high-thermal-conductivity aluminum nitride ceramic.

[0095] Specifically, the sintering was completed by heating to 1000°C at a heating rate of 10°C / min under nitrogen, then heating to 1550°C at a heating rate of 8°C / min under a nitrogen-hydrogen mixed gas (the volume ratio of nitrogen to hydrogen was 9.5:0.5), and finally heating to 1850°C at a heating rate of 0.5°C / min under nitrogen and maintaining the temperature for 20 h under a nitrogen-hydrogen mixed gas (the volume ratio of nitrogen to hydrogen was 9.5:0.5).

[0096] The black high-thermal-conductivity aluminum nitride ceramic obtained in this example was obtained by uniformly mixing and sintering 97% aluminum nitride, 2% sintering aid (including 1.5% Y2O3 and 0.5% CaF2), and 1% coloring aid (including 0.3% NbO2 and 0.7% Mo2O3).

[0097] Example 5

[0098] The present example provides a method for preparing a black high-thermal-conductivity aluminum nitride ceramic, which comprises the following steps:

[0099] Firstly, 2.5 g of Y2O3 powder and 0.5 g of CaF2 powder are mixed as sintering aids, and 0.3 g of NbO2 powder and 0.7 g of Mo2O3 powder are mixed as coloring aids.

[0100] Then, the sintering aids, coloring aids and 3 g of oleic acid are mixed with 60 g of a mixed solvent of toluene-isopropyl alcohol, and wet pre-milling dispersion is performed for 2 h, and then 96 g of aluminum nitride powder (oxygen content: 0.65%) is ball-milled and dispersed to obtain sintering powder.

[0101] That is, the mass ratio of the total amount of ceramic powder composed of sintering aids, coloring aids and aluminum nitride powder to the mixed solvent of toluene-isopropyl alcohol used for dispersing the same is 1:0.6.

[0102] Again, 7 g of polyacrylic acid resin and 6 g of DBP are dissolved in 42 g of a mixed solvent of toluene-isopropyl alcohol to prepare a polyacrylic acid solution as a composite colloid.

[0103] Fourthly, the composite colloid is added to the sintering powder, and ball-milling is performed to obtain an aluminum nitride ceramic slurry.

[0104] That is, the mass ratio of the total amount of ceramic powder composed of sintering aids, coloring aids and aluminum nitride powder to the polyacrylic acid resin in the composite colloid is 100:7.

[0105] Fifthly, the aluminum nitride ceramic slurry is vacuum degassed to a viscosity of 11000 mPa·s, and is cast to obtain a green sheet.

[0106] Sixthly, the green sheet is subjected to a staged degassing process to obtain a degassed sheet having an oxygen content of 1.35%.

[0107] Specifically, the degassing is completed by increasing the temperature to 250°C at a temperature increasing rate of 0.7°C / min under a nitrogen gas flow of 600 L / min and maintaining the temperature for 1 h, and then increasing the temperature to 450°C at a temperature increasing rate of 0.15°C / min under a nitrogen gas flow of 600 L / min and maintaining the temperature for 3 h.

[0108] Finally, the degassed sheet is subjected to a staged sintering process to obtain a black high-thermal-conductivity aluminum nitride ceramic.

[0109] Specifically, the sintering is completed by increasing the temperature to 800°C at a temperature increasing rate of 10°C / min under nitrogen gas, then increasing the temperature to 1600°C at a temperature increasing rate of 3°C / min under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen gas to hydrogen gas: 8.5:1.5), and finally increasing the temperature to 1800°C at a temperature increasing rate of 0.3°C / min under a nitrogen-hydrogen mixed gas (volume ratio of nitrogen gas to hydrogen gas: 9.5:0.5) and maintaining the temperature for 3 h.

[0110] The black high-thermal-conductivity aluminum nitride ceramic obtained in the embodiment is obtained by uniformly mixing 97% aluminum nitride, 2% sintering aids (including 1.5% Y2O3 and 0.5% CaF2) and 1% coloring aids (including 0.3% NbO2 and 0.7% Mo2O3) and sintering.

[0111] Example 6

[0112] The embodiment provides a preparation method of black high-thermal-conductivity aluminum nitride ceramic, which comprises the following steps:

[0113] Firstly, 4 g of Y2O3 powder and 1 g of CaF2 powder are mixed as sintering aids, and 0.3 g of NbO2 powder and 0.7 g of Mo2O3 powder are mixed as coloring aids.

[0114] Then, the sintering aids, the coloring aids and 1.5 g of oleic acid are mixed with 45 g of a toluene-isopropyl alcohol mixed solvent, and wet pre-ball milling dispersion is performed for 2 h, and then 94 g of aluminum nitride powder (with an oxygen content of 0.65%) is ball milled and dispersed to obtain sintering powder.

[0115] That is, the mass ratio of the total amount of ceramic powder composed of the sintering aids, the coloring aids and the aluminum nitride powder to the toluene-isopropyl alcohol mixed solvent used for dispersing the ceramic powder is 1:0.45.

[0116] Again, 8 g of polyacrylic acid resin and 4 g of DBP are dissolved in 28 g of a toluene-isopropyl alcohol mixed solvent to prepare a polyacrylic acid solution as a composite colloid.

[0117] Fourthly, the composite colloid is added to the sintering powder, and ball milling is performed to sufficiently disperse the sintering powder to obtain aluminum nitride ceramic slurry.

[0118] That is, the mass ratio of the total amount of ceramic powder composed of the sintering aids, the coloring aids and the aluminum nitride powder to the polyacrylic acid resin in the composite colloid is 100:8.

[0119] Fifthly, the aluminum nitride ceramic slurry is vacuum degassed to a viscosity of 11000 mPa·s, and is flow-cast to obtain a green sheet.

[0120] Sixthly, the green sheet is subjected to staged degassing treatment to obtain a degassed sheet with an oxygen content of 1.75%.

[0121] Specifically, the degassing is completed by heating to 300°C at a heating rate of 0.5°C / min under a nitrogen gas flow of 800 L / min and maintaining the temperature for 1 h, and then heating to 350°C at a heating rate of 0.05°C / min under a nitrogen-air mixed gas flow of 800 L / min (750 L / min of nitrogen gas + 50 L / min of air) and maintaining the temperature for 1 h.

[0122] Finally, the green sheet is subjected to a sintering process in stages to obtain black high-thermal-conductivity aluminum nitride ceramic.

[0123] Specifically, the temperature is raised to 1000°C at a rate of 6°C / min under nitrogen, then raised to 1600°C at a rate of 2°C / min under nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 9:1), and finally raised to 1750°C at a rate of 1.5°C / min under nitrogen and kept for 30 hours under nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 9.6:0.4) to complete sintering.

[0124] The above black high-thermal-conductivity aluminum nitride ceramic obtained in this example is obtained by mixing 94% aluminum nitride, 5% sintering aids (including 4% Y2O3 and 1% CaF2) and 1% coloring aids (including 0.3% NbO2 and 0.7% Mo2O3) uniformly and sintering.

[0125] Example 7

[0126] This example provides a method for preparing black high-thermal-conductivity aluminum nitride ceramic, which comprises the following steps:

[0127] First, 1 g of Y2O3 powder and 0.5 g of CaF2 powder are mixed as sintering aids, and 0.5 g of NbO2 powder, 2 g of Mo2O3 powder and 2.5 g of Cr2O3 powder are mixed as coloring aids.

[0128] Then, the sintering aids, coloring aids and 1.5 g of oleic acid are mixed with 45 g of toluene-isopropyl alcohol mixed solvent and wet-pre-milled and dispersed for 2 hours, and then 93.5 g of aluminum nitride powder (oxygen content is 0.65%) is ball-milled and dispersed to obtain sintering powder.

[0129] That is, the mass ratio of the total amount of ceramic powder composed of sintering aids, coloring aids and aluminum nitride powder to toluene-isopropyl alcohol mixed solvent used for dispersing is 1:0.45.

[0130] Again, 8 g of polyacrylic acid resin and 4 g of DBP are dissolved in 28 g of toluene-isopropyl alcohol mixed solvent to prepare a polyacrylic acid solution as a composite colloid.

[0131] Fourthly, the above composite colloid is added to the sintering powder, and ball-milling is performed to obtain aluminum nitride ceramic slurry.

[0132] That is, the mass ratio of the total amount of ceramic powder composed of sintering aids, coloring aids and aluminum nitride powder to polyacrylic acid resin in the composite colloid is 100:8.

[0133] Fifth step, the aluminum nitride ceramic slurry was vacuum degassed to a viscosity of 11000 mPa-s, and was cast into a green sheet.

[0134] Sixth step, the green sheet was subjected to a staged degassing process to obtain a degassed sheet with an oxygen content of 1.9%.

[0135] Specifically, the temperature was raised to 300°C at a rate of 0.5°C / min under a nitrogen flow of 800 L / min and held for 1 h, then raised to 350°C at a rate of 0.05°C / min under a mixed nitrogen and air flow (750 L / min nitrogen + 50 L / min air) of 800 L / min and held for 1 h, completing the degassing.

[0136] Finally, the degassed sheet was subjected to a staged sintering process to obtain a black high thermal conductivity aluminum nitride ceramic.

[0137] Specifically, the temperature was raised to 1000°C at a rate of 6°C / min under nitrogen, then raised to 1600°C at a rate of 2°C / min under a mixed nitrogen and hydrogen flow (volume ratio of nitrogen to hydrogen is 9:1), and finally raised to 1800°C at a rate of 0.3°C / min under nitrogen and held for 12 h under a mixed nitrogen and hydrogen flow (volume ratio of nitrogen to hydrogen is 9.6:0.4), completing the sintering.

[0138] The above black high thermal conductivity aluminum nitride ceramic obtained in this example was obtained by uniformly mixing and sintering 93.5% aluminum nitride, 1.5% sintering aids (including 1% Y2O3 and 0.5% CaF2), and 1% coloring aids (including 0.5% NbO2, 2% Mo2O3, and 2.5% Cr2O3).

[0139] To verify the precise control of the multi-stage and different atmospheres in the degassing and sintering processes in the above preparation method, the importance of improving the inhibitory effect of coloring aids on the improvement of thermal conductivity was verified by several comparative experiments.

[0140] Comparative Example 1

[0141] The same as Example 1 is not described here, only the difference with Example 1 is described. The preparation method provided by the present comparative example is different from the preparation method in Example 1 in that, in the sixth step of degassing, the degassing process is as follows: the temperature is raised to 300°C at a temperature raising rate of 1°C / min under a nitrogen gas flow of 800 L / min and kept for 1 h, then the temperature is raised to 350°C at a temperature raising rate of 0.18°C / min under a nitrogen-air mixed gas (600 L / min of nitrogen gas + 200 L / min of air) flow of 800 L / min, the degassing is completed, and a degassed sheet with an oxygen content of 1.92% is obtained. The rest is described with reference to Example 1, and a first comparative black high-thermal-conductivity aluminum nitride ceramic is obtained.

[0142] Comparative Example 2

[0143] The same as Example 1 is not described here, only the difference with Example 1 is described. The preparation method provided by the present comparative example is different from the preparation method in Example 1 in that, in the sixth step of degassing, the degassing process is as follows: the temperature is raised to 300°C at a temperature raising rate of 0.5°C / min under a nitrogen gas flow of 800 L / min and kept for 1 h, then the temperature is raised to 550°C at a temperature raising rate of 0.05°C / min under a nitrogen-air mixed gas (500 L / min of nitrogen gas + 300 L / min of air) flow of 800 L / min, the degassing is completed, and a degassed sheet with an oxygen content of 2.1% is obtained. The rest is described with reference to Example 1, and a second comparative black high-thermal-conductivity aluminum nitride ceramic is obtained.

[0144] Comparative Example 3

[0145] The same as Example 4 is not described here, only the difference with Example 4 is described. The preparation method provided by the present comparative example is different from the preparation method in Example 4 in that, in the last step of sintering, the sintering process is as follows: the temperature is raised to 1000°C at a temperature raising rate of 10°C / min under nitrogen, then the atmosphere is adjusted to nitrogen-hydrogen mixed gas (the volume ratio of nitrogen to hydrogen is 9.5:0.5) and the temperature is continuously raised to 1550°C, then the temperature is raised to 1850°C at a temperature raising rate of 0.5°C / min under nitrogen, and kept for 20 h under nitrogen-hydrogen gas (the volume ratio of nitrogen to hydrogen is 9.5:0.5), the sintering is completed. The rest is described with reference to Example 4, and a third comparative black high-thermal-conductivity aluminum nitride ceramic is obtained.

[0146] Comparative Example 4

[0147] The same as Example 4 is not described here, only the difference between Example 4 is described. The preparation method provided by the present comparative example is different from the preparation method in Example 4, and the sintering process in the last step of sintering is as follows: heating to 800℃ at a heating rate of 10℃ / min under nitrogen, then heating to 1550℃ at a heating rate of 1℃ / min under nitrogen-hydrogen mixed gas (the volume ratio of nitrogen to hydrogen is 9.5:0.5), finally heating to 1850℃ at a heating rate of 5.5℃ / min under nitrogen, and keeping for 20h under nitrogen-hydrogen gas (the volume ratio of nitrogen to hydrogen is 9.5:0.5), and completing sintering. Referring to Example 4, the fourth comparative black high-thermal-conductivity aluminum nitride ceramic is obtained.

[0148] Comparative Example 5

[0149] The same as Example 5 is not described here, only the difference between Example 5 is described. The preparation method provided by the present comparative example is different from the preparation method in Example 5, and the sintering process in the last step of sintering is as follows: heating to 800℃ at a heating rate of 10℃ / min under nitrogen, then heating to 1600℃ at a heating rate of 3℃ / min under nitrogen-hydrogen mixed gas (the volume ratio of nitrogen to hydrogen is 8.5:1.5), finally heating to 1800℃ at a heating rate of 0.3℃ / min under nitrogen, and keeping for 2.5h under nitrogen-hydrogen gas (the volume ratio of nitrogen to hydrogen is 9.5:0.5), and completing sintering. Referring to Example 5, the fifth comparative black high-thermal-conductivity aluminum nitride ceramic is obtained.

[0150] Comparative Example 6

[0151] The same as Example 2 is not described here, only the difference between Example 2 is described. The preparation method provided by the present comparative example is different from the preparation method in Example 2, and the sintering process in the last step of sintering is as follows: heating to 1400℃ at a heating rate of 10℃ / min under nitrogen-hydrogen mixed gas (the volume ratio of nitrogen to hydrogen is 8.5:1.5), then keeping for 30min at 1400℃, finally heating to 1700℃ at a heating rate of 0.6℃ / min under nitrogen, and keeping for 150h under nitrogen-hydrogen gas (the volume ratio of nitrogen to hydrogen is 9.5:0.5), and completing sintering. Referring to Example 2, the sixth comparative black high-thermal-conductivity aluminum nitride ceramic is obtained.

[0152] Comparative Example 7

[0153] The same as Example 4 is not described here, only the difference with Example 4 is described. The preparation method provided by the present comparative example is different from the preparation method in Example 4 in that, in the last step of the sintering step, the sintering process is specifically as follows: heating to 800℃ at a heating rate of 10℃ / min under nitrogen, then heating to 1550℃ at a heating rate of 8℃ / min under nitrogen, finally heating to 1850℃ at a heating rate of 0.5℃ / min under nitrogen, and keeping for 20h under nitrogen to complete sintering. The rest is referred to the description in Example 4, and a seventh comparative black high-thermal-conductivity aluminum nitride ceramic is obtained.

[0154] The black high-thermal-conductivity aluminum nitride ceramics provided by Examples 1-7 and the comparative aluminum nitride ceramics provided by Comparative Examples 1-7 are ground to a thickness of 0.5mm, put into a reflectance tester, and the reflectivity thereof is measured; the ceramic density is tested by using a drainage method density tester; the three-point bending strength is tested by using an electronic universal testing machine; and the thermal conductivity of the ceramic is tested by using an instantaneous plane heat source method; and the test results are shown in Table 1.

[0155] Table 1: Performance test results of the aluminum nitride ceramics provided by each of the examples and comparative examples

[0156]

[0157] As can be seen from Table 1, the aluminum nitride ceramics provided by Examples 1-7 all have very low reflectivity, that is, they have a darker black color and have a good visible light absorption effect; and the thermal conductivities thereof all reach above 180 W / (m·K), showing high thermal conductivity. At the same time, from the test results of the relative density and the bending strength, it can be seen that the performance of the aluminum nitride ceramic reaches an excellent level of the existing similar products.

[0158] As can be seen from Table 1, Comparative Example 1 is compared with Example 1, the glue removal time in Comparative Example 1 is shorter, and the binder is not completely decomposed and removed in the glue removal process. In the sintering process, the residual binder increases more impurities in the sintering process, thereby reducing the sintering thermal conductivity of the black aluminum nitride.

[0159] Comparative Example 2 is compared with Example 1, more air is introduced in the glue removal process, and the heating time and the holding time are both longer, so that the oxygen content in the glue removal sheet obtained after glue removal reaches 2.1%. In the sintering process, there are more oxygen impurities and oxygen defects in the aluminum nitride crystal, which increases the phonon scattering of the aluminum nitride, and the thermal conductivity is reduced more than that of Example 1.

[0160] Compared with Example 4, Comparative Example 3 experienced a rapid temperature rise during sintering, especially insufficient time for the color development reaction. This resulted in the coloring agent not being effectively incorporated into the crystal to form a color crystal, leading to insufficient absorption of visible light by the product obtained in Comparative Example 3, which in turn increased reflectivity. In other words, its blackness was not sufficient for use as a black ceramic.

[0161] Compared with Example 4, Comparative Example 4 experienced excessively rapid secondary heating during sintering, resulting in abnormal growth of aluminum nitride powder grains, decreased grain uniformity, and lower thermal conductivity. Furthermore, the uniformity of the coloring additives decreased during sintering, leading to a decrease in light absorption and an increase in reflectivity. Consequently, the product obtained was neither a black ceramic nor a high thermal conductivity ceramic.

[0162] Compared with Example 5, Comparative Example 5 had a shorter holding time after the second heating in the sintering process, resulting in insufficient crystal growth, low uniformity, increased phonon transmission loss, and thus lower thermal conductivity.

[0163] Compared with Example 2, in Comparative Example 6, the high-temperature holding time after the second heating in the sintering process was too long, resulting in larger grain growth and higher thermal conductivity of the ceramic substrate. However, the excessively large grains would lead to reduced light absorption, thereby increasing reflectivity.

[0164] Compared with Example 4, Comparative Example 7 was sintered in a nitrogen atmosphere throughout the process. Due to the presence of factors such as coloring additives in the system that are detrimental to thermal conductivity, and the lack of a reducing atmosphere to further remove oxygen defects from the aluminum nitride crystals during the sintering process, the thermal conductivity of the substrate sintered did not reach a high level.

[0165] It is evident that in the preparation method of the black high thermal conductivity aluminum nitride ceramic provided by the present invention, the debinding and sintering under specific conditions, especially the control of oxygen content in the debinding sheet after debinding, and the control of time and atmosphere in the coloring section and crystal growth section during sintering, have an important influence on the final aluminum nitride ceramic product to overcome the adverse effects of coloring additives on improving thermal conductivity and to have both black color and high thermal conductivity characteristics.

[0166] The embodiments described above are for illustrative purposes only and do not constitute a specific limitation on the present invention. Any modifications made without departing from the basic concept of the present invention, as well as any obvious modifications derived therefrom, are within the scope of protection of the present invention.

Claims

1. A black, high thermal conductivity aluminum nitride ceramic, characterized in that, It is made by uniformly mixing aluminum nitride powder, sintering aid, and coloring aid in a mass ratio of 90~98:1~5:1~5 with binder and solvent, followed by casting, debinding, and sintering of the resulting debinded sheet, wherein the oxygen content of the debinded sheet does not exceed 1.9%; wherein the black high thermal conductivity aluminum nitride ceramic has a reflectivity of not more than 14% and a thermal conductivity of more than 180 W / (m·K); the sintering procedure is as follows: heating to 1400℃~1600℃ in one step, and inert air being introduced for at least 60 min before reaching this temperature. A reducing mixed gas is used to initiate a colorimetric reaction, followed by a second heating to 1650℃~1950℃ over a period of at least 90 minutes, and finally held at that temperature for 3 h~100 h, ensuring that the total duration of the second heating and holding is not less than 10 h to complete sintering; an inert gas is introduced during the colorimetric reaction. In the reducing gas mixture, the volume percentage of the reducing gas introduced accounts for the volume percentage of the inert gas. The reduction mixture accounts for 4% to 15% of the total ventilation volume.

2. The black high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that, The oxygen content of the aluminum nitride powder is not higher than 0.7%; the sintering aid is selected from a mixture of at least two of Y2O3, CaF2, CaO, MgO, ZnO, and SiO2; the coloring aid is selected from at least one of CeO2, MnO2, MoO2, MoO3, Fe2O3, Fe3O4, Cr2O3, NbO2, HfO2, DyO2, TiO2, Co3O4, and GaO2.

3. A method for preparing a black, high thermal conductivity aluminum nitride ceramic, characterized in that, Includes the following steps: S1. Mix the sintering aid, coloring aid, aluminum nitride powder, binder and solvent and ball mill them to obtain a casting slurry; S2. The casting slurry is degassed to a viscosity of 5000 mPa·s to 18000 mPa·s, and then cast to obtain a preform. S3. The blank is heated to 300°C to 600°C under inert gas or inert-air mixture, and the glue is removed for at least 10 hours from the start of heating to obtain a glue-removed sheet with an oxygen content of no more than 1.9%. S4. The coating sheet is heated to 1400℃~1600℃ once, and an inert-reducing mixed gas is introduced for at least 60 min before reaching this temperature to carry out a color development reaction. Then, the temperature is raised to 1650℃~1950℃ for at least 90 min, and finally held at this temperature for 3 h~100 h, and the total time for the second heating and holding is controlled to be no less than 10 h to complete the sintering and obtain the black high thermal conductivity aluminum nitride ceramic. The black high thermal conductivity aluminum nitride ceramic has a reflectivity of no more than 14% and a thermal conductivity of more than 180 W / (m·K). In the inert-reducing mixed gas introduced during the color development reaction, the volume content of the reducing gas introduced accounts for 4%~15% of the total volume of the inert-reducing mixed gas.

4. The preparation method according to claim 3, characterized in that, In the casting slurry, the mass ratio of the aluminum nitride powder, the sintering aid, and the coloring aid is 90~98:1~5:1~5; the mass ratio of the binder to the total mass of the aluminum nitride powder, the sintering aid, and the coloring aid is 0.05~0.12:

1.

5. The preparation method according to claim 3 or 4, characterized in that, In step S3, the billet is heated to 300℃~600℃ using a one-step method or a multi-step heat preservation platform method.

6. The preparation method according to claim 5, characterized in that, In step S3, the blank is heated to 300℃~600℃ and then kept at that temperature for at least 10 hours from the start of heating to the end of the holding period.

7. The preparation method according to claim 3 or 4, characterized in that, In step S4, during the heating process, the film sheet is heated to 1400℃~1600℃ in one step using a one-step method, or the film sheet is heated to 1400℃~1600℃ in one step using a multi-step heat preservation platform method. In the secondary heating process, a one-step method is used to heat the film sheet after the first heating to 1650℃~1950℃, or a multi-step-heating platform method is used to heat the film sheet after the first heating to 1650℃~1950℃.

8. The preparation method according to claim 7, characterized in that, In step S4, during the initial heating, the film is heated to 1400℃~1600℃ and then kept at that temperature. Before the end of the heat preservation, an inert-reducing mixed gas is introduced for at least 60 minutes to carry out the color development reaction.

9. The preparation method according to claim 4, characterized in that, The oxygen content of the aluminum nitride powder is not higher than 0.7%; the sintering aid is selected from a mixture of at least two of Y2O3, CaF2, CaO, MgO, ZnO, and SiO2; the coloring aid is selected from at least one of CeO2, MnO2, MoO2, MoO3, Fe2O3, Fe3O4, Cr2O3, NbO2, HfO2, DyO2, TiO2, Co3O4, and GaO2; and the binder is selected from polyvinyl butyral and / or polyacrylic acid resin.

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