CN109384468B - Preparation method of boron nitride-aluminum nitride composite powder - Google Patents
Preparation method of boron nitride-aluminum nitride composite powder Download PDFInfo
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Abstract
The invention provides a preparation method of boron nitride-aluminum nitride composite powder, which comprises the following steps: a, uniformly mixing boric acid or anhydride thereof and melamine, reacting in an atmosphere furnace, cooling and crushing to obtain a boron nitride semi-finished product; b, mixing, dispersing and drying the alumina powder, the carbon powder, the boron nitride semi-finished product, cane sugar or glucose and water which are prepared by dehydrating the alumina powder to prepare a reaction material; c, in a flowing nitrogen atmosphere, heating the reaction materials to 1400-1600 ℃ for reduction nitridation reaction to obtain a boron nitride-aluminum nitride semi-finished product; d, performing charcoal burning and crushing treatment on the boron nitride-aluminum nitride semi-finished product to prepare boron nitride-aluminum nitride composite powder; the boron nitride and the aluminum nitride in the obtained composite powder are uniformly dispersed, and when the composite powder is used for preparing products only containing the boron nitride and the aluminum nitride, the products can be directly molded and sintered without a grinding and mixing process for increasing the oxygen content of the powder, so that the ceramic product with higher heat conductivity is prepared.
Description
Technical Field
The invention belongs to the field of inorganic non-metallic materials, and particularly relates to a preparation method of boron nitride-aluminum nitride composite powder.
Background
The composite ceramic containing boron nitride and aluminum nitride is one of the fine ceramic materials with the application development faster in recent years.
The hexagonal boron nitride has a layered structure similar to graphite, has a relatively stable structure in the lamellae, is relatively weak in combination between the lamellae, is easy to peel into the lamellae, and has excellent insulation and dielectric properties in the direction of the lamellae and the direction vertical to the lamellae; can still keep stable at about 2000 ℃ in non-oxidizing atmosphere; can be used as high-temperature lubricant and electric insulating material. The sintered body of hexagonal boron nitride has a mohs hardness of about 2 and is easy to machine, and a ceramic material containing 15% or more of hexagonal boron nitride can also be machined.
The aluminum nitride has a hexagonal wurtzite structure, and has high thermal conductivity, insulating property and chemical stability. Can be kept stable at about 1500 ℃ in non-oxidizing atmosphere and is not infiltrated and corroded by metals such as aluminum, copper, silver, lead and the like, can be used as basic ingredients of vacuum aluminizing evaporation boats, metal melting crucibles and sintering casting molds, and can be used for manufacturing GaAs crystal melting crucibles. The thermal conductivity of the properly prepared aluminum nitride ceramic can reach more than 180 w/m.k, the thermal shock resistance is good, and the aluminum nitride ceramic can be used as a high-power circuit substrate; thermally conductive ceramics containing aluminum nitride have also been marketed. Pure aluminum nitride ceramics have a mohs hardness of 7 or more and are difficult to machine, limiting the applications of such ceramics.
The composite ceramic containing boron nitride and aluminum nitride integrates the excellent performances of two materials, boron nitride endows the composite ceramic with machinability, aluminum nitride endows the composite ceramic with high heat conductivity, and the boron nitride-aluminum nitride composite ceramic is generally prepared by powder mixing, hot-pressing sintering or cold pressing and then high-temperature sintering molding. When the boron nitride powder and the aluminum nitride powder are respectively prepared, the oxygen content is generally about 1% or more, the oxygen content brought into a mixture is about 1% or more, the thermal conductivity of the ceramics obtained by directly sintering and molding or adding other ceramic raw materials such as titanium diboride is lower, and the negative influence of oxides contained in the ceramics on the thermal conductivity is usually eliminated and sintering is assisted by adding yttrium oxide, calcium oxide and the like to form a low-melting point yttrium boroaluminate calcium salt; meanwhile, the mixed materials of boron nitride, aluminum nitride and a small amount of yttrium oxide and calcium oxide which need to be added are difficult to realize uniform dispersion, or the process is complicated, and the quality and the performance of the prepared boron nitride-aluminum nitride composite ceramic are fluctuated.
In the prior art, hexagonal boron nitride can be prepared from boric acid and melamine in an atmosphere furnace at a temperature of above 850 ℃, and alkali metal salt can be added in the ingredients as an auxiliary agent. The preparation process has the advantages of easily available raw materials, low cost and capability of preparing products with the particle size of 1-20 mu m. Common preparation methods of aluminum nitride powder include a direct aluminum powder nitriding method, an alumina carbothermic reduction method, and an aluminum chloride or alkyl aluminum gas phase reaction method, wherein the alumina carbothermic reduction method is widely applied. The basic process for preparing aluminum nitride powder by alumina carbothermic method comprises the steps of dispersing and mixing alumina or its precursor with carbon powder or its precursor, reacting the mixture in nitrogen at 1500 deg.C or higher, and oxidizing and decarbonizing the reaction product at 800 deg.C such as 600 deg.C and 800 deg.C. The method has the advantages of mature process and capability of preparing the aluminum nitride powder with the grain diameter of less than 1 mu m and higher sintering activity.
In the production process of the powder containing the hexagonal boron nitride and the aluminum nitride, the particle size, the specific surface area and the oxygen content are not easy to realizeAnd a suitable balance of carbon content. The average particle diameter of the aluminum nitride powder is more than 1 μm, or the specific surface area is less than 5m2At/g, it is generally more difficult to make dense, high thermal conductivity ceramic articles. The aluminum nitride contains a proper amount of oxygen to facilitate sintering, but if the oxygen content is more than 1.2m%, the heat conductivity of the aluminum nitride-containing ceramic is reduced; for example, carbon residue of 0.2m% or more, not only makes the aluminum nitride powder darker in color, but also may reduce the electrical insulation properties of the prepared ceramic. When the grain size of the hexagonal boron nitride is too small, the machinability of the ceramic material can be easily realized only by adding a little higher additive amount; the thermal sintering forming of the ceramic material is not facilitated by the excessively small specific surface area and the excessively low oxygen content. The roasted material in the preparation process of hexagonal boron nitride generally needs to be washed and acid-washed to remove boron-containing substances and carbon-containing nitrogen substances which are not converted into boron nitride, the boron-containing compounds and the carbon-containing nitrogen compounds which can be washed can account for 15-30% of the input amount, and the washing removal wastes B, C/N with higher reaction activity and generates wastewater to be treated and discharged.
Disclosure of Invention
In order to solve the technical problem, the invention provides a preparation method of boron nitride-aluminum nitride composite powder, which comprises the following steps:
A. mixing 100 parts of boric acid or its dehydrate powder and 50-80 parts of melamine, and reacting at 850-1100 deg.C for 2-5 hr; cooling and crushing the generated material to obtain a semi-finished product of boron nitride;
B. mixing 100 parts of alumina powder prepared by roasting and dehydrating the alumina powder at the temperature of 350-;
C. in a flowing nitrogen atmosphere, heating the reaction material to 1400-1600 ℃ to carry out reduction nitridation reaction for 2-10 hours to obtain a boron nitride-aluminum nitride semi-finished product;
D. and (3) carrying out charcoal burning and crushing treatment on the boron nitride-aluminum nitride semi-finished product to prepare the boron nitride-aluminum nitride composite powder.
In the preparation method of the boron nitride-aluminum nitride composite powder, the atmosphere furnace in the step A is a reducing atmosphere which is mainly formed by thermal decomposition of melamine or intermediate products generated by melamine, boric acid and boric acid dehydrate, the discharged gas can be ignited when the temperature is high, the main reducing components comprise carbon monoxide and ammonia gas, and the gas emission amount is larger; the atmosphere furnace can be used for isolating air smoldering, and can also be used for introducing nitrogen, ammonia or the mixed gas of the nitrogen and the ammonia. The temperature of 900-950 ℃ in the last reaction stage or high temperature section of the atmosphere furnace in the step A is better, the cost of the furnace is lower, the power consumption is lower, the yield of the boron nitride is higher, and the obtained boron nitride semi-finished product is suitable for the operation or the reaction in the steps B-D. The proportion of boron contained in boric acid or the dehydrated product thereof to generate boron nitride is 60-85%, the obtained boron nitride semi-finished product contains 60-80m% of boron nitride, and the balance of boron-containing compounds and carbon-containing nitrogen compounds which can be washed by hot water, wherein the boron-containing compounds and the carbon-containing nitrogen compounds except the boron nitride can be better activated after being added with water in the step B and can be further reacted in the high-temperature reduction nitridation reaction of the step C, wherein the boron-containing compounds except the boron nitride are basically converted into the boron nitride except a small amount of volatilization.
The alumina powder prepared by roasting and dehydrating the alumina powder at the temperature of 600 ℃ in the step B is large in specific surface area and internal pore volume, high in reaction activity, easy to disperse, process and form and good in effect in the high-temperature reduction nitridation reaction in the step C. The aluminum hydroxide powder is preferably pseudo-boehmite dry powder, and the alumina powder prepared by roasting and dehydrating the pseudo-boehmite dry powder has higher specific surface area and internal pore volume, and the specific surface area is generally more than or equal to 280m2The volume of an inner hole is more than or equal to 0.6 ml/g; particularly, the pseudoboehmite dry powder containing less impurities is selected so as to ensure that the aluminum nitride powder has lower impurity content, and the pseudoboehmite dry powder adopted in the embodiment has Na300mg/kg, Fe47mg/kg and Si260 mg/kg; the Na, Fe and Si contents of the other pseudo-boehmite dry powder are all below 10 mg/kg.
The carbon powder added in the step B is more than 30% of the amount required for generating the metallic aluminum intermediate and the carbon monoxide by reacting with the alumina in the high-temperature nitridation reaction process in the step C, and the excessive carbon also contributes to further reduction nitridation of boron compounds contained in the boron nitride semi-finished product. The specific surface area of the carbon powder is more than or equal to 300m2Preferably,/g, in the reactionThe material is heated to the reduction nitridation temperature and still has a relatively large specific surface area during reaction, so that high reactivity is shown, and the temperature of the reduction nitridation reaction is reduced or the reaction time is shortened. Carbon black prepared from low-carbon alkane and olefin such as natural gas and carbon four is preferably selected, and the carbon black has the advantages of simple raw material components, stable process control, less introduced impurities and better quality guarantee in production. Other carbon blacks prepared by using heavy oil and fuel oil as raw materials contain more metal impurities, which affect the preparation process of aluminum nitride and the purity and performance of the prepared aluminum nitride. The carbon powder is preferably water-soluble carbon black, and is more easily dispersed in the water-based ingredient or slurry of the invention due to surface treatment, simple mixing equipment and shorter mixing time are adopted, and organic media with higher cost and safety problems and complicated mixing and dispersing processes are not needed.
And step B, in the process of mixing and dispersing materials, part of sucrose or glucose enters the inner hole of the alumina powder with larger specific surface area and inner hole volume, is decomposed to generate highly dispersed carbon-containing substances and carbon in the heating process of the boron nitride-aluminum nitride semi-finished product, is dispersed between the inner surface and the outer surface of the alumina particle with large specific surface area and inner hole and particles, separates most of the alumina particles, and remarkably lightens sintering in the alumina particles and among the particles in the subsequent heating and high-temperature stages, so that the alumina particles still have larger reaction area in the high-temperature reduction nitridation stage, and are in close contact with the alumina particles, good in dispersion and high in activity, thereby reducing the temperature of nitridation reaction or shortening the reaction time. A small part of sucrose or glucose enters the inner hole of the boron nitride semi-finished product powder particle and is decomposed to generate highly dispersed carbon-containing substances and carbon in the subsequent heating process, and the reduction effect can be realized on the boron-containing compounds except the boron nitride in the boron nitride semi-finished product powder particle by converting the boron-containing compounds into the boron nitride; under the 1400-1600 ℃ reduction nitridation reaction condition, neither boron nitride in the boron nitride semi-finished product powder nor newly generated boron nitride reacts with the carbon-containing substance and carbon generated by the thermal decomposition of the carbon powder, the sucrose or the glucose to generate the boron-carbon compound.
The aluminum oxide powder prepared by roasting and dehydrating the aluminum hydroxide powder at the temperature of 400-450 ℃ in the material preparation in the step B has better effect, the alumina powder prepared under the temperature condition still has more micropores with the diameter of less than 2nm, and cane sugar or glucose enters the part of micropores with the diameter of less than 2nm to be further decomposed to generate carbon-containing substances and carbon which are dispersed on the surfaces and among the particles of the small-size alumina particles forming the part of micropores, the sintering of the small-size alumina particles is obviously reduced in the subsequent high-temperature stages of temperature rise and reduction nitridation, so that the small-size alumina particles still have larger reaction area and activity in the high-temperature reduction nitridation stage, more aluminum nitride crystal nuclei are favorably formed, the particle size of aluminum nitride in the prepared boron nitride-aluminum nitride composite powder is smaller, and the obtained boron nitride-aluminum nitride composite powder or the boron nitride-aluminum nitride composite powder which is added into the boron nitride-aluminum nitride composite powder is easier to sinter.
In the preparation process of the reaction material in the step B, the mixing and dispersing treatment of the alumina powder, 55-80 parts of the carbon powder and the boron nitride semi-finished product powder can be realized by high-speed shearing, ball milling and other modes, and the oxidation of boron nitride in the boron nitride semi-finished product is not required to be considered, so that the reaction material with uniform mixing can be realized. In the high-temperature nitridation reaction process in the step C, newly generated boron nitride and aluminum nitride particles are uniformly dispersed among other particles, so that the boron nitride and aluminum nitride can be uniformly dispersed in the generated boron nitride-aluminum nitride semi-finished product and the finally prepared boron nitride-aluminum nitride composite powder, and the dispersion degree of the boron nitride and the aluminum nitride can be obviously higher than the level which can be achieved by mixing and dispersing boron nitride powder and aluminum nitride powder by a dry method and a wet method, and the scanning electron microscope photos of the powder can be contrasted; the prepared boron nitride-aluminum nitride composite powder is directly hot-pressed and molded to obtain the boron nitride-aluminum nitride composite ceramic, the heat conductivity of the boron nitride-aluminum nitride composite ceramic is higher than that of the boron nitride powder and the aluminum nitride powder which are mixed, dispersed and hot-pressed and molded by a dry method and a wet method, and the dispersion uniformity of the boron nitride and the aluminum nitride is very critical except for different oxygen contents.
C, strong reduction nitridation reaction is carried out in the high-temperature reaction process of the step C, and the aluminum oxide is reduced by excessive carbon powder, carbon-containing substances generated by thermal decomposition of cane sugar or glucose and carbon and reacts with nitrogen to generate aluminum nitride; and B, basically reducing and nitriding boron-containing compounds except the boron nitride contained in the boron nitride semi-finished product, converting the boron-containing compounds into boron nitride, carrying out recrystallization to a certain degree along with the boron nitride generated in the step A, growing along the direction of a wafer, reducing the oxygen content, improving the graphitization degree, and allowing most of the contained carbon and nitrogen compounds to participate in the reduction nitridation reaction and a small part of the contained carbon and nitrogen compounds to be thermally decomposed. The oxygen content of the prepared boron nitride-aluminum nitride semi-finished product can be lower than 0.5m%, even lower than 0.2m%, except the boron nitride and the aluminum nitride which are used as main products, the rest is mainly carbon which can be burnt in the charcoal burning treatment process in the step D; boron other than boron nitride generally has a boron oxide content of less than 0.1 m%.
C, in the step D, in the charcoal-burning treatment process under the conditions of proper temperature and oxygen-containing gas such as air or carbon dioxide, the contained boron nitride and aluminum nitride are basically stable, and the rest carbon and O2Reacting to form CO and/or CO2Or with CO2CO is generated by the reaction and is basically removed, and the content of residual carbon can be lower than 0.2m percent and even lower than 0.1m percent; but the oxygen content of the boron nitride-aluminum nitride composite material after the carbon burning is slightly improved, but the oxygen content can be controlled to be below 1.2m percent, even below 1.0m percent, even below 0.8m percent; boron other than boron nitride generally has a boron oxide content of less than 0.1 m%.
And C, adopting a sagger with holes or directly stacking and burning, or having a better ventilation effect, so that the structure of the high-temperature nitriding reaction furnace is simple, the processing capacity is higher, or a better nitriding reaction effect is obtained. And part of the aluminum paste is transferred and dispersed to the particle outer surfaces and the particle inner holes of the boron nitride semi-finished product powder and the carbon powder in the forming and drying processes, and more aluminum nitride crystal nuclei can be formed in the initial stage of the high-temperature reduction nitridation stage, so that the finally generated aluminum nitride particles are finer, and are better dispersed after being mixed with the boron nitride particles.
1-5 parts of auxiliary agents such as polyacrylamide, polyacrylic acid or ammonium salt thereof can be added into the ingredients in the step B to play roles in lubrication, pore forming, bonding and dispersion; the molecular weight of the added auxiliary agent is 2000-5000. When the reaction material is prepared by adopting a spray granulation mode, the water adding amount of the material is large, and the dispersion uniformity of alumina powder and carbon powder in slurry can be improved by adding polyacrylic acid or ammonium salt thereof.
In step C, the reaction material can be treated at 800 ℃ for 1-5hr under nitrogen or oxygen-free conditions to decompose and carbonize organic substances such as sucrose, glucose, acetic acid, citric acid, polyacrylamide, polyacrylic acid and the like or aluminum salt generated by the reaction, and then the temperature is raised to 1400 ℃ and 1600 ℃ for reduction nitridation reaction; the low-temperature coking can be carried out in a kiln outside the 1400-1600 ℃ reduction nitriding furnace, and has low cost and easy control.
In the step C, the reduction nitridation reaction of the reaction material can be carried out in two steps, firstly, the reaction is carried out at the temperature of 1400 ℃ and 1500 ℃ for a period of time, then the temperature is raised to the temperature of 1500 ℃ and 1600 ℃ for further reaction, so that the nitridation reaction is carried out more thoroughly, the purity is improved, the oxygen content of the prepared product is lower after the obtained boron nitride-aluminum nitride semi-finished product is subjected to carbon burning treatment in an air atmosphere at the temperature of 550 ℃, and the particle size of the aluminum nitride is slightly smaller, so that the reduction nitridation reaction is directly carried out at the temperature of 1500 ℃ and 1600 ℃. The invention adopts the reduction nitridation temperature below 1600 ℃ to avoid the overlarge crystallization of aluminum nitride and the reduction of the sintering property of the prepared composite powder, and avoid the reaction of boron nitride and carbon to generate boron-carbon compounds which can reduce the heat conduction and insulation properties of the ceramic material prepared by sintering the composite powder.
In the step D, the conventional 650-700 ℃ oxygen-containing atmosphere charcoal burning treatment temperature of the boron nitride-aluminum nitride semi-finished product can be adopted, and the advantages are that the charcoal burning speed is high, the carbon residue content is low, but the defect is that the oxygen content of the product is high; in the method of the invention, when the lower temperature of the reduction nitridation reaction is adopted, such as 1400 ℃ plus 1500 ℃, the activity of the residual carbon powder is still higher, the carbon powder is processed at 500 ℃ plus 550 ℃ in the air atmosphere, only the time is slightly longer, but the oxygen and carbon contents of the product can be simultaneously controlled to lower levels, such as boron nitride-aluminum nitride O0.8m% and C0.12m% after the carbon burning processing at 500 ℃ under the air atmosphere for 15hr in an embodiment. When the temperature of the reduction nitridation reaction is higher, such as 1400 ℃ for 1500 ℃ reaction for a period of time, and then the temperature is raised to 1500 ℃ for 1600 ℃ for further reaction, the activity of the residual carbon powder in the reaction is slightly lower, and the carbon can be oxidized and burned at 550 ℃ in the air atmosphere.
In the step D, the carbon burning treatment of the boron nitride-aluminum nitride semi-finished product can also be carried out under the conditions of pure carbon dioxide gas flow and the temperature of 700-2And the carbon which is not reacted reacts to generate CO so as to realize carbon removal. The method has the advantages that boron nitride and aluminum nitride are not oxidized basically, and the oxygen content of the product is low.
In the step B, the forming method of the boron nitride-aluminum nitride semi-finished product comprises extruding, briquetting and pelleting; the process has the advantages that the water adding amount of the materials is large, the materials can be granulated in a spray granulation mode when being made into slurry, the slurry has large treatment scope when the process is adopted, the slurry can be treated to be in an ideal state by adopting methods of ball milling, sequential feeding and the like, and the quality of the obtained granulated powder is good. The advantages of extruding and briquetting are that the requirements for a stacking mode and a saggar are lower during high-temperature reduction nitridation, and granulated powder is generally filled into the saggar.
In conclusion, the preparation method of the boron nitride-aluminum nitride composite powder omits the water washing process after the preparation of the boron nitride and avoids the boron loss in the water washing process, the boron-containing compound and the carbon-containing nitrogen compound except the boron nitride contained in the boron nitride semi-finished product can be better activated after absorbing water in the step B, and further react in the high-temperature reduction nitridation reaction in the step C, wherein the boron-containing compound except the boron nitride is basically converted into the boron nitride after being volatilized in a small amount; the boron nitride and the aluminum nitride in the finally prepared composite powder are uniformly dispersed, when the composite powder is used for preparing products only containing the boron nitride and the aluminum nitride, the products can be directly molded and sintered without a grinding and mixing process for increasing the oxygen content of the powder, and the ceramic product with higher heat conductivity can be prepared, and when a small amount of yttrium oxide and calcium oxide auxiliary agents are required to be added, the ceramic product can be simply soaked in a non-aqueous solution; the following features are also included.
1. In the step B, in the material preparation, a part of sucrose or glucose enters the inner hole of the alumina powder with larger specific surface area and inner pore volume, is decomposed to generate highly dispersed carbon-containing substances and carbon in the temperature rising process of the boron nitride-aluminum nitride semi-finished product, and is dispersed on the surface of the alumina particle and among the particles forming the inner hole to separate most of the alumina particles, and the sintering of the alumina particles is obviously reduced in the subsequent temperature rising and high temperature stages, so that the alumina particles still have larger reaction area in the high temperature reduction nitridation stage, more aluminum nitride crystal nuclei are favorably formed, the particle size of the aluminum nitride in the composite powder prepared by the method is smaller, the particle size is easily below 1 mu m, and the sintering activity is higher.
2. By adopting the alumina powder dehydrated at the low temperature of 400-450 ℃ and still provided with more micropores with the diameter of less than 2nm, the sucrose or the glucose enters the part of micropores with the diameter of less than 2nm and is further decomposed after the temperature is raised to generate highly dispersed carbon-containing substances and carbon which are dispersed on the surfaces and among the particles of the small-size alumina particles forming the part of micropores, the sintering of the part of small-size alumina particles is obviously relieved in the subsequent temperature raising and high temperature stages, so that the small-size alumina particles still have larger reaction area and activity in the high-temperature reduction nitridation stage, and the temperature of the reduction nitridation reaction is reduced.
3. When the lower temperature of 1400-1600 ℃ for the reduction nitridation reaction is adopted, the activity of the residual carbon powder in the boron nitride-aluminum nitride semi-finished product is higher, the carbon burning can be finished under the condition of 500-550 ℃ low-temperature air, the temperature runaway cannot occur, the air flow rate can be high or low, and the oxygen and carbon contents of the obtained product can be controlled to lower levels at the same time.
4. When the boron nitride-aluminum nitride semi-finished product is subjected to carbon burning treatment under the conditions of pure carbon dioxide gas flow and the temperature of 700-850 ℃, unreacted carbon and CO2CO generated by the reaction is removed, and the boron nitride-aluminum nitride composite powder product with low oxygen content can be prepared.
Detailed Description
The technical solution of the present invention will be specifically described and illustrated with reference to the following examples, but the present invention is not limited thereto.
Example 1
The boron nitride-aluminum nitride composite powder is prepared by the following steps:
A. mixing 6.2kg of boric acid and 3.78kg of melamine (the mass ratio of the substances is 1: 0.3) in a 30L ball milling tank, and grinding for 3 hr; polyurethane is lined in the ball milling tank, and 12kg of alumina ceramic ball material with the diameter of 10mm is filled; the ground material can completely pass through a 80-mesh sieve by sampling detection; pressing into medium phi 100x80mm blocks in oil press, taking 8 blocks, and reacting in furnace with silicon nitride tube atmosphere at 950 deg.C for 4 hr; the flow rate of ammonia gas is 20L/min, and the heating rate is 250 ℃/hr; cooling the furnace to 500 ℃ after the reaction at 950 ℃, switching ammonia gas to nitrogen gas with the flow rate of 20L/min (the purity is 99.9%), taking out the material block after 0.5hr, cooling and crushing the material block, grinding the material block for 8hr by using the 30L ball milling tank and the alumina porcelain balls, and then sieving the material block by using a 325-mesh sieve to obtain a boron nitride semi-finished product;
B. collecting certain pseudo-boehmite dry powder M8kg (average diameter of 1.6 μ M), subpackaging in stainless steel disc with a material layer thickness of 30-35mm, dehydrating in electric heating roaster at 400 deg.C for 4hr to obtain alumina powder containing Al2O393.1m%, pore volume 0.61ml/g, specific surface area 385 m2(ii)/g, volume of micropores having a diameter of 2nm or less is 0.16 ml/g; na300mg/kg, Fe47mg/kg, Si260 mg/kg; 2148g of the alumina powder (containing Al) is taken2O32000g) Carbon powder X1200g (Water soluble carbon Black, Ash 180mg/kg, specific surface area 460 m)215 nm) of boron nitride, placing the boron nitride semi-finished product 1200g in a high-speed shearing machine for processing for 90min, crushing and mixing, transferring to a kneading machine, adding 5000g of aqueous solution containing 700g of cane sugar, kneading for 1hr, taking a part of wet material blocks, extruding strips with the diameter of 8mm by a hydraulic plunger, and drying the extruded strips in an oven at the temperature of 125 ℃ for 4 hr;
C. in a horizontal medium-frequency induction heating carbon tube furnace, distributing 450g of the dry strips into open microporous graphite bowls, introducing 99.999% nitrogen gas at a flow rate of 2L/min, heating to 1450 ℃ at a speed of 8-10 ℃/min, reacting at a constant temperature for 5 hours, cooling to below 300 ℃ along with the furnace, and taking out to obtain strip-shaped semi-finished products containing the carbon boron nitride-aluminum nitride;
D. placing about 100g of the strip-shaped semi-finished product containing boron nitride and aluminum nitride into an alumina box with holes, and carrying out charcoal-burning treatment in a muffle furnace at 500 ℃ and air atmosphere for 12hr until all the surfaces and the cross sections of the strips are light in color, wherein the strips with gray cross sections are inspected after the charcoal-burning treatment for 8 hr; the light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder, but are easy to twist and break;
E. and crushing the light-color boron nitride-aluminum nitride strips and materials after the carbon burning in a high-speed shearing machine to prepare the boron nitride-aluminum nitride composite powder.
700g of sucrose should contain about 210g of carbon in the thermal decomposition product in the temperature rising process of the step C, and volatile matters such as water, CO and the like are also generated in the thermal decomposition process.
Example 2
Pressing a part of the wet material block kneaded for 1hr in the step B in the embodiment 1 into a columnar block with phi 40 x60 mm by a hydraulic press, and drying in an oven at 125 ℃ for 10 hr; performing reductive nitridation and charcoal firing operation basically according to the steps C-E, wherein the main difference is that the reaction is performed for 6 hours at the constant temperature of 1480 ℃ in a nitrogen atmosphere of a carbon tube furnace, and the charcoal firing is performed for 16 hours at the temperature of 500 ℃ in a muffle furnace and an air atmosphere until all the blocks are taken out and inspected to have light surface and section colors; the light-color boron nitride-aluminum nitride block obtained after carbon burning does not fall off powder, but is easy to twist and break.
Example 3
The procedure of example 1 was substantially repeated to prepare a boron nitride-aluminum nitride composite powder, except that: in the step B, the alumina powder, the carbon powder and the boron nitride semi-finished product powder are mixed and processed in a high-speed shearing machine, then 5300g of aqueous solution containing 1000g of cane sugar is added, and in the step C, the dried strips are reacted for 5 hours at the constant temperature of 1450 ℃. And (D) burning the boron nitride-aluminum nitride semi-finished product in a muffle furnace at 500 ℃ in an air atmosphere for 12 hours, taking out, checking that the surfaces and the sections of all the strips are light in color, do not fall powder, but are easy to twist and break.
1000g of sucrose added should contain about 300g of charcoal in the thermal decomposition product in the temperature raising process of step C.
Example 4
1074g of alumina powder (containing Al) prepared in step B of example 1 was added2O31000g) Putting 300g of carbon powder X600g and boron nitride semi-finished product into a ball mill, adding 4500g of aqueous solution containing 400g of sucrose, 20g of addition polyacrylic acid and 40g of polyacrylamide, carrying out ball milling treatment for 15hr, adding 60g of acetic acid, continuing ball milling for 1hr, and carrying out spray granulation at 200-250 ℃ to obtain granulation powder with the average particle size of 139 mu m; granulation powder preparation of nitridation essentially following the procedure of example 1, Steps C-EThe boron-aluminum nitride composite powder is subjected to reduction nitridation reaction, and then is subjected to carbon burning operation until the boron nitride-aluminum nitride powder is taken out and inspected, and the ground colors of the boron nitride-aluminum nitride powder are all light; the light-color boron nitride-aluminum nitride powder obtained after carbon burning is easy to twist and crush.
400g of sucrose added should contain about 120g of charcoal in the thermal decomposition product in the temperature raising process of step C.
Example 5
The procedure of example 1 was substantially repeated to prepare a boron nitride-aluminum nitride composite powder, except that: in step B, dehydrating boehmite dry powder M in a roasting furnace at 600 deg.C for 2.5hr to obtain alumina powder containing Al2O399.6m%, pore volume 0.65ml/g, specific surface area 290 m2In terms of/g, no micropores having a diameter of 2nm or less can be detected. And C, performing the operations and the phenomena in the steps C-E are basically the same, in the step D, treating the semi-finished product containing the carbon boron nitride-aluminum nitride in a muffle furnace at 500 ℃ in an air atmosphere for 12 hours to finish the carbon burning, checking that the surfaces and the section colors of all the strips are light, and taking out the strips with the gray sections for checking when the carbon burning is carried out for 9 hours. The light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder, but are easy to twist and break.
Example 6
The boron nitride-aluminum nitride composite powder was prepared by substantially repeating steps D to E of example 1 except that the treatment was carried out in a muffle furnace and air atmosphere at 550 ℃ and as a result, charring was completed within 9 hr; the light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder, but are easy to twist and break.
Example 7
The steps C-E of example 1 are basically repeated to prepare the boron nitride-aluminum nitride composite powder, except that the operation in the carbon tube furnace is controlled in two steps, the reaction is carried out at a constant temperature of 1420 ℃ for 4 hours, and then the constant temperature treatment is carried out at a temperature of 1550 ℃ for 4 hours; the charcoal burning treatment temperature in muffle furnace and air atmosphere is 550 deg.C, and results in 12hr to complete charcoal burning; the light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder and are easy to twist and crush.
Example 8
The procedure C-E of example 3 was basically repeated to prepare boron nitride-aluminum nitride composite powder, except that the operation in the carbon tube furnace was controlled in two steps, the reaction was carried out at 1420 ℃ for 4hr, and then the temperature was raised to 1550 ℃ for 4 hr; the charcoal burning treatment temperature in muffle furnace and air atmosphere is 550 deg.C, and results in 10hr to complete charcoal burning; the light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder and are easy to twist and crush.
Example 9
The semi-finished product of boron nitride-aluminum nitride containing carbon of example 1 was sampled, crushed to a particle size of about 1-2mm, and about 10g of the semi-finished product was placed in a stainless steel tube reactor with an inner diameter of phi 16mm of a tube furnace, and then passed through a CO 99.99% purity reactor with a flow rate of 300ml/min2And performing charring treatment at 800 deg.C for 12hr, cooling, taking out, and checking to remove charcoal completely, wherein the obtained light-colored boron nitride-aluminum nitride strip has no powder falling and is easy to twist.
Example 10
The method of example 1 was substantially repeated to prepare boron nitride-aluminum nitride composite powder, except that: in the step B, after alumina powder, carbon powder and boron nitride semi-finished product powder are processed in a high-speed shearing machine, 5000g of aqueous solution containing 700g of cane sugar is added, 60g of acetic acid is additionally added, the intensity of the kneaded wet material block, the extruded strip and the dried strip is high, and the extruded strip and the dried strip are not easy to break; the operation and the phenomenon of other steps are basically the same, in the step D, the semi-finished product of boron nitride and aluminum nitride containing carbon is treated in a muffle furnace at 500 ℃ and air atmosphere for 12 hours to finish the carbon burning, and the color of the surface and the section of all the strips is checked to be light; the light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder and are easy to twist and crush.
Example 11
The method of example 1 was substantially repeated to prepare boron nitride-aluminum nitride composite powder, except that: in step B, another pseudo-boehmite dry powder N (average diameter 1.1 μm) is adopted and calcined at 430 ℃ for 6hr to prepare alumina powder containing Al2O397.8m%, pore volume 0.76ml/g, specific surface area 320 m2(ii)/g, volume of micropores having a diameter of 2nm or less is 0.19 ml/g; the content of Na, Fe and Si is below 10 mg/kg; the operation and the phenomenon of other steps are basically the same, in the step D, the semi-finished product of boron nitride and aluminum nitride containing carbon is treated in a muffle furnace at 500 ℃ and air atmosphere for 12 hours to finish the carbon burning, and the color of the surface and the section of all the strips is checked to be light; the light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder and are easy to twist and break。
Example 12
The method of example 11 was substantially repeated to prepare a boron nitride-aluminum nitride composite powder, except that: in the step A, the roasting temperature of the boron nitride semi-finished product in an atmosphere furnace is 900 ℃,
the ingredient in step B is 2148g of alumina powder (containing Al) prepared by roasting the pseudo-boehmite dry powder N at 430 ℃ for 6hr2O32000g) Placing the carbon powder X1200g and the boron nitride semi-finished product 600g in a high-speed shearing machine for processing for 90 min; the operation and the phenomenon of other steps are basically the same, in the step D, the semi-finished product of boron nitride and aluminum nitride containing carbon is treated in a muffle furnace at 500 ℃ and air atmosphere for 12 hours to finish the carbon burning, and the color of the surface and the section of all the strips is checked to be light; the light-color boron nitride-aluminum nitride strips obtained after carbon burning do not fall off powder and are easy to twist and crush.
In the above examples 1 to 12, the O content of the boron nitride-aluminum nitride semi-finished product containing carbon obtained in step C was less than 0.3m%, and the boron compounds other than boron nitride were boron oxide contents less than 0.1 m%; d, the content of C in the boron nitride-aluminum nitride strip after the carbon is sintered in the step D and the content of O in the boron nitride-aluminum nitride composite powder prepared in the step E are respectively lower than 0.15m percent and 1.0m percent, the content of boron other than the boron nitride is lower than 0.1m percent, the average outer diameter of aluminum nitride microparticles in the strip and the powder is lower than 1.0 mu m, and the specific surface area of the composite powder is 9-13m2(ii) in terms of/g. In examples 7 and 8, the boron nitride-aluminum nitride strips after the carbon baking in step D and the boron nitride-aluminum nitride composite powder prepared in step E have O contents slightly lower than those of the corresponding strips and powders in examples 1 and 3, respectively, and the average outer diameters of the aluminum nitride microparticles are slightly higher than those of the corresponding strips and powders in examples 1 and 3, respectively. Example 9 the boron nitride-aluminum nitride strip after the carbon firing in step D and the boron nitride-aluminum nitride composite powder prepared in step E both had an O content of less than 0.6m%, which was lower than the corresponding strip and powder of comparative example 1.
Comparative example 1
The procedure of example 1 was substantially repeated, except that: adding water in the step B without adding cane sugar, namely generating highly dispersed carbon-containing substances and carbon in alumina inner holes, changing the using amount of the carbon powder X to 1400g, kneading, extruding strips, drying, and using the dried strips in the step C; and C, the high-temperature reduction nitridation conditions are the same. In the step D, when the material is treated in a muffle furnace and an air atmosphere, the charring cannot be finished at the temperature of 500 ℃ for 12 hours, the surface and the section of the material strip are very black, the treatment is continued at the temperature of 600 ℃ for 3 hours and is still black, and the charring is finished by further treating the material strip at the temperature of 700 ℃; the material after charcoal burning does not fall off powder, is hard and brittle and is difficult to twist and crush, and the C content is measured to be higher than 0.20m by sampling. And D, measuring that the O content of the semi-finished product obtained in the step C is higher than 3m%, and the boron content except boron nitride is lower than 0.1m% of boron oxide.
Comparative example 2
The procedure of example 1 was substantially repeated, except that: in the step B, the dosage of the carbon powder X is changed into 1400g, and after the alumina powder, the carbon powder and the boron nitride semi-finished product powder are processed in a high-speed shearing machine, water and a water solution containing cane sugar are not added, and the mixture is pressed into a columnar block with phi 40 gamma of 60mm by a hydraulic machine and is used in the step C; and C, the high-temperature reduction nitridation conditions are the same. In the step D, when the material is treated in a muffle furnace and an air atmosphere, the charring cannot be finished at the temperature of 500 ℃ for 12 hours, the surface and the section of the material strip are very black, the treatment is continued at the temperature of 600 ℃ for 3 hours and is still black, and the charring is finished by further treating the material strip at the temperature of 700 ℃; the material after charcoal burning does not fall off powder, is hard and brittle and is difficult to twist and crush, and the C content is measured to be higher than 0.20 percent by sampling. And D, measuring that the O content of the semi-finished product obtained in the step C is higher than 3m%, and the boron content except boron nitride is higher than 1m% of boron oxide.
Comparative example 3
The operations of steps C to E of example 1 were substantially repeated except that the carbon tube furnace was operated at a temperature of 1650 ℃ for the isothermal reaction for 4 hr. As a result, the processing under the conditions of the muffle furnace and the air atmosphere can not finish the charcoal burning after 12hr at the temperature of 500 ℃, the surface and the section of the material strip are still black, the processing under the temperature of 550 ℃ is continued for 5hr and the charcoal burning is finished after 3hr of further processing under the temperature of 600 ℃. The prepared aluminum nitride powder has thicker particles. And D, measuring the boron yield except the boron nitride in the semi-finished product obtained in the step C to be more than 0.5m% of boron oxide, measuring the C content of the material after the carbon burning to be more than 0.5m%, and generating a due boron-carbon compound.
Comparative example 4
Steps C-E of example 7 were substantially repeated, except that after the isothermal reaction at 1420 ℃ in a carbon tube furnace for 4hr, the isothermal treatment at 1550 ℃ for 4hr was changed to the isothermal treatment at 1650 ℃ for 3 hr; as a result, the treatment at 550 ℃ for 12hr in a muffle furnace and air atmosphere failed to complete the charring, and the treatment at 650 ℃ for 4hr completed the charring. And D, measuring the boron yield except the boron nitride in the semi-finished product obtained in the step C to be more than 0.5m% of boron oxide, measuring the C content of the material after the carbon burning to be more than 0.5m%, and generating a due boron-carbon compound.
Comparative example 5
Taking pseudo-boehmite dry powder M3kg (containing Al)2O32000g) Treating in a high speed shearing machine for 15min, transferring to a kneader, adding 110g aqueous solution containing acetic acid 3100ml, kneading for 1hr, extruding with hydraulic plunger to obtain 8mm strip, and drying in oven at 125 deg.C for 4 hr; the dried strips (about 250 g) were calcined in a muffle furnace and air atmosphere at 400 deg.C, 600 deg.C, and 1200 deg.C for 3 hr. The specific surface areas of the obtained alumina strips were respectively 350 m2/g、288 m2/g、3.5m2/g。
Comparative example 6
Taking 100g of alumina strips obtained in comparative example 5 at 400 ℃ and 600 ℃, respectively soaking 60ml of water solution containing 26g of cane sugar, sealing and standing for 10hr for homogenization treatment, drying at 125 ℃ for 6hr, then placing in an oxygen-free roasting furnace, heating to 650 ℃ at the speed of 10 ℃/min, roasting for 4hr to obtain two kinds of carbon-loaded alumina, wherein the C content is about 8m percent of the alumina.
Taking 100g of alumina strips obtained in comparative example 5 at 400 ℃ and 600 ℃, respectively soaking 60ml of aqueous solution containing 13g of sucrose, sealing and standing for 10hr for homogenization treatment, drying at 125 ℃ for 6hr, then placing in an oxygen-free roasting furnace, heating to 650 ℃ at the speed of 10 ℃/min, roasting for 4hr to obtain two kinds of carbon-loaded alumina, wherein the C content is about 4m percent of the alumina.
Taking 100g of alumina strips obtained in comparative example 5 at 400 ℃ and 600 ℃, respectively soaking 65ml of aqueous solution containing 40g of glucose, sealing, standing for 10hr for homogenization treatment, drying at 125 ℃ for 6hr, placing in an oxygen-free roasting furnace, heating to 650 ℃ at the speed of 10 ℃/min, roasting for 4hr to obtain two kinds of carbon-loaded alumina, wherein the C content is about 8m percent of the alumina.
Before the comparative example is roasted under the oxygen-free condition, the atmosphere in the furnace is treated to be O by using normal-temperature deoxidizer2Less than 1ppm, no inert gas introduced during roasting, and high safetyAnd (4) maintaining micro positive pressure.
In the invention, the specific surface areas of the boron nitride-aluminum nitride composite powder, the alumina and the carbon powder are measured by a low-temperature nitrogen adsorption method, and the pore volume of the alumina is measured by the low-temperature nitrogen adsorption method and a saturated water absorption method; the granularity of the aluminum hydroxide and the alumina powder is measured by a laser particle sizer; the grain diameters of boron nitride and aluminum nitride microparticles in the boron nitride-aluminum nitride material block and the composite powder after the carbon burning are determined by a scanning electron microscope picture; the O, C content of the boron nitride-aluminum nitride semi-finished product and the composite powder and the C content of the carbon-loaded alumina are measured by an X-ray fluorescence spectrometry (XRF) and compared with the results of oxygen determination by a coulomb method and carbon determination by a coulomb method; the Na, Fe and Si contents of the aluminum hydroxide are measured by a solution ICP method; the boron content other than boron nitride was determined by the GJB 507-.
Claims (9)
1. A preparation method of boron nitride-aluminum nitride composite powder comprises the following steps:
A. mixing 100 parts of boric acid or its dehydrate powder and 50-80 parts of melamine, and reacting in a reducing atmosphere furnace at 850-1100 deg.C for 2-5 hr; cooling and crushing the generated material to obtain a semi-finished product of boron nitride; the obtained boron nitride semi-finished product contains 60-80m% of boron nitride;
B. 100 parts of alumina powder, 55-80 parts of carbon powder, 20-100 parts of boron nitride semi-finished product, 30-60 parts of cane sugar or glucose and 500 parts of water, which are prepared by roasting and dehydrating pseudo-boehmite dry powder at the temperature of 350-; in the mixing and dispersing treatment process, part of cane sugar or glucose enters the inner hole of the alumina powder; the specific surface area of the alumina powder is more than or equal to 280m2The volume of an inner hole is more than or equal to 0.6 ml/g;
C. in a flowing nitrogen atmosphere, heating the reaction material to 1400-1600 ℃ to carry out reduction nitridation reaction for 2-10 hours to obtain a boron nitride-aluminum nitride semi-finished product; the prepared boron nitride-aluminum nitride semi-finished product has the oxygen content of less than 0.5m percent and the boron content except boron nitride is less than 0.1m percent;
D. and (3) carrying out charcoal burning and crushing treatment on the boron nitride-aluminum nitride semi-finished product to prepare the boron nitride-aluminum nitride composite powder.
2. The method for preparing boron nitride-aluminum nitride composite powder as claimed in claim 1, wherein in the step A, the temperature of the atmosphere furnace is 900-950 ℃.
3. The method for preparing boron nitride-aluminum nitride composite powder as claimed in claim 1, wherein in step B, the calcination temperature of the pseudo-boehmite dry powder is 400-450 ℃.
4. The method for preparing boron nitride-aluminum nitride composite powder according to claim 1, wherein in step B, the carbon powder is carbon black prepared from low-carbon alkane and olefin as raw materials; and/or the specific surface area of the carbon powder is more than or equal to 300m2(ii)/g; and/or the carbon powder is water-soluble carbon black.
5. The method for preparing boron nitride-aluminum nitride composite powder as claimed in claim 1, wherein in step C, the reaction material is subjected to two-step reduction nitridation at 1400-1500 ℃ and 1500-1600 ℃ in sequence.
6. The method for preparing boron nitride-aluminum nitride composite powder according to claim 1, wherein in the step D, the conditions for the charring treatment of the semi-finished product of boron nitride-aluminum nitride are as follows: the oxygen-containing gas flow and the temperature of 500 ℃ and 550 ℃, or the pure carbon dioxide gas flow and the temperature of 700 ℃ and 850 ℃.
7. The method for preparing boron nitride-aluminum nitride composite powder according to claim 1, wherein 3-10 parts of acetic acid and citric acid and/or 1-5 parts of polyacrylamide, polyacrylic acid or ammonium salt thereof are added to the ingredients in step B.
8. The method as claimed in claim 1, wherein in step C, the reaction material is first treated at 800 ℃ for 1-5hr under nitrogen or oxygen-free conditions, and then heated to 1400 ℃ and 1600 ℃ for the reductive nitridation reaction.
9. The method according to claim 1, wherein the reaction material in the step B is formed by extrusion, briquetting or granulation.
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