CN100395176C - Method for synthesizing isotropic silicon nitride powder adopting hollow type annular material-distribution - Google Patents
Method for synthesizing isotropic silicon nitride powder adopting hollow type annular material-distribution Download PDFInfo
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Abstract
The present invention relates to a method for synthesizing isotropic silicon nitride powder by hollow type annular material distribution, which belongs to the field of inorganic non-metal material. Silicon powder and silicon nitride powder are ground and mixed according to different proportions and are arranged in a combustion synthesis reaction apparatus with a ventilation type hollow tube after being dried in a hollow annular material distribution method; the reaction apparatus is filled with gas containing nitrogen of 1 to 20Mpa after being vacuumized; combustion synthesis reaction is induced by ignition. The present invention has the advantages that the method realizes the complete nitridation of the silicon powder in an approximate isothermal mode of whole reaction matters, and enhances the evenness of the silicon nitride powder in combustion synthesis products; the synthetic silicon nitride powder has high purity, consistent phasecontent and high sintering activity. The present invention has the advantages of high productive efficiency, energy saving, simple equipment, low cost and convenient operation.
Description
Technical field
The invention belongs to field of inorganic nonmetallic material, a kind of method of hollow type annular material-distribution synthesizing isotropic silicon nitride powder adopting particularly is provided.
Background technology
Silicon nitride is a kind of non-oxide ceramics of synthetic.Have that density is low, proportion is low, hardness is high, intensity is high, corrosion-resistant, anti-oxidant, wear-resistant, Young's modulus is big, high temperature resistant, characteristics such as thermal expansivity is little, thermal conductivity is big, heat-shock resistance and electrical insulation capability are good, its mechanical property and thermal property obviously are better than general oxide ceramics.Silicon nitride ceramics and nitride silicon based complex phase ceramic goods by different sintering process manufacturings can be widely used in cutting tool, bearing, engine parts, and required various wear-resisting, heat-resisting, the corrosion-resistant member of chemical industry, metallurgy, machinery, oil, electronics, military project, space flight and aviation, nuclear energy and light industry and shielding material, armour material etc., be one of generally acknowledge the present age most important and heat-resisting, high-strength, wear-resisting, corrosion resistant engineering ceramic material that application potential is arranged most.
The silicon nitride powder preparation of research and development mainly contains silica flour direct nitridation method, carbothermal reduction-nitridation method, chemical gas phase synthetic method, plasma method and combustion synthesis method both at home and abroad.Direct nitridation method is that silica flour is placed nitrogen (or the nitrogen/hydrogen) atmosphere that flows, and divides several stages to carry out the insulation of long period, and fully nitrogenize can obtain beta-silicon nitride powder.This method production cycle is grown (more than 40 hours), and energy consumption is bigger, needs the secondary nitrogenize, and material purity is required height, needs strict control process parameters such as temperature of reaction and nitrogen flow etc. in addition.Germany Starck company, Japanese Denka company produce the beta-silicon nitride powder of the multiple trade mark with this method.Carbothermic method exists speed of response slow, the reaction process complexity, shortcomings such as the production cycle is long, have also simultaneously that energy consumption is big, efficient is low, in the product problem chemical gas phase synthetic methods such as foreign matter content height such as carbon, oxygen owing to be gas-phase reaction, air-flow is controlled easily during reaction, the product purity height, fine size.This method can make the α phase content and be up to beta-silicon nitride powder more than 98%, is to generally acknowledge best commodity silicon nitride powder at present, and the powder of producing with Japanese UBE company is representative.But this method complex process, cost is higher, and has etching problem and the high shortcoming of product chlorinity in the production process.Plasma method is to feed the plasma body working gas (as N in plasma generator
2-H
2-Ar etc.), by injecting nitrogen-containing material (as NH behind the plasma arc heating work gas
3, N
2Deng) and silicon-containing material (as SiH
4, SiCl
4Deng) carry out chemical gas phase reaction and prepare beta-silicon nitride powder.The plasma method directly silicon nitride of preparation is unformed beta-silicon nitride powder mostly, and contains ammonium chloride impurity, need through remove ammonium chloride impurity more than 500 ℃ and more than 1400 ℃ the high temperature phase inversion handle and could obtain the α phase silicon nitride powder.Shortcomings such as also there is the equipment complexity in plasma method, and technological process is loaded down with trivial details, and need bigger energy consumption.
Combustion synthesis technology (Combustion Synthesis, abbreviation CS) is the synthetic new preparation technology of material that obtains broad research and application in recent years.The synthetic self propagating high temperature synthetic (Self-propagatingHigh-temperature Synthesis, abbreviation SHS) that is also referred to as of burning.The basic characteristics of combustion synthesis technology are: the outside necessary energy that provides is provided, bring out the local chemical reaction (this process be called light) that takes place of high heat-producing chemical reaction system, form combustion reactions forward position (being combustion wave), after this combustion reactions is under self exothermic support, reaction is from continuing to carry out (promptly from spreading), show as combustion wave and spread whole reaction system, spread in the progressive process at combustion wave, reactant is transformed into synthetic materials.The most outstanding advantage of combustion synthesis technology be swift in response, save energy, with low cost, equipment is simple, synthetic product purity is high.So adopt the product of combustion synthesis technology production to develop into more than 500 kinds up to now.For the burning of nitrogen-silicon system is synthetic, because the reaction system between nitrogen and solid Si powder belongs to high heat release system (743.5KJ/mol), can quick at short notice synthesizing silicon nitride powder.And since cost of material cheap, be easy to obtain, with short production cycle, characteristics such as the product subsequent disposal is simple adopt combustion synthesis technology to prepare beta-silicon nitride powder just has been subjected to domestic and international investigation of materials person since the nineties from twentieth century great attention and broad research.
The domestic and international patent that relates to combustion synthesis of silicon nitride powder emphasizes particularly on different fields, and also has limitation separately respectively." preparation method of high α phase content silicon nitride " (U.S. Patent number US5032370) as inventions such as Muscovite A.G.Merzhanov, the nitrogen pressure too high (being up to 30MPa) that its combustion synthesis of silicon nitride powder needs, and ammonium salt add-on too high (be up to silica flour weight 60%), in addition, in the silica flour raw material of its use, add the unformed silicon or the silicon imide of different content, increased raw materials cost.Inventions such as U.S. J.B Holt " adopt the alkali-metal thing that iterates (as NaN with the synthetic thin brilliant α phase silicon nitride (U.S. Patent number US4944930) of combustion method
3Deng) as nitrogenous source, its NaN
3Usage quantity more (account for reactant silica flour 50%) is not suitable for the large dimension specimen large-scale production.China Chen Ke newly waits the technology of the method for alpha-phase silicon nitride powder " a kind of low-pressure combustion synthetic " (Chinese patent application number be 02100183.9) employing suspension silicon nitride powder of invention, can synthesize alpha-phase silicon nitride powder under lower nitrogen pressure.But the unformed silicon or the silicon imide that in the silica flour raw material of its use, have also added different content, and production unit and technical process are complicated, the production cycle is longer, and energy consumption is big, and production process control difficulty is bigger, finally causes production cost too high.In grand " production methods that the supercharging in a kind of silicon nitride burning building-up process is regulated and control " that wait invention of king's sound (Chinese patent application number be 03149961.9) and the production method of synthesizing silicon nitride " a kind of granulation burn " (Chinese patent application number be 200410037807.9), mainly be applicable to beta-silicon nitride.Above patent is used different additive and technology (as reducing nitrogen pressure etc.) mostly, lay particular emphasis on the α phase silicon nitride content that improves in the combustion synthesized product, do not relate to and take suitable technological measure to increase nitrogen gas permeability, the homogeneity question that solves the combustion synthesized product structure and form raw material.
The burning synthesizing silicon nitride belongs to gas-solid system combustion synthesis reaction.One of reactant wherein is a kind of porous medium, i.e. the mixture of forming by silica flour and additive, and another kind of reactant is a nitrogenous gas.The gas of this porous medium and infiltration therein takes place keeps thermopositive reaction certainly to be called the infiltration burning synthetic.The infiltration burning is synthetic to be that gas-permeable is gone into exothermic chemical transformation and the structural transformation process that takes place in the porous medium.In the combustion synthesis reaction process, because combustion reactions has consumed a large amount of nitrogen, the nitrogen concentration in combustion wave forward position reduces rapidly, and pressure descends, thereby formed combustion wave forward position and atmosphere surrounding pressure difference, need to replenish nitrogenous gas from outside atmosphere to the combustion wave forward position continuously.Therefore the effect of the rate of permeation of nitrogen in the burning synthesizing silicon nitride is extremely important, is to influence the nitriding velocity of reactant silica flour and the important factor of nitridation.And the rate of permeation of nitrogen depends on that the pressure of nitrogenous gas and the ventilation property condition of reactant powder base comprise its constructional feature, interior porosity and hole characteristics etc.In addition, for combustion synthesis of silicon nitride powder, its products of combustion may be the α phase silicon nitride, also may be beta phase silicon nitride, and this depends primarily on the temperature of combustion of Si-N combustion reactions.Lower temperature of combustion helps the generation of α phase silicon nitride, helps the generation of beta phase silicon nitride when temperature of combustion is too high.The height of temperature of combustion depends on that to a great extent the one-tenth of reactant is grouped into the radiating condition with reaction zone.
Products of combustion layering or sandwich phenomenon often appear during the routine combustion synthesis of silicon nitride powder.On apparent, outer color is greyish white, and is softer, and the hard caking that its centre often has thickness not wait exists.From the thing phase composite, top layer α phase content is higher, and center lump β phase content is higher.This phenomenon is to cause burning owing to powder base internal-combustion temperature is too high, finally causes inner with the outside α phase content of synthetic product to differ bigger.The particularly important is, because the high temperature burning, reactant inside often occurs being difficult to broken fine and close lump, and the powder sintering performance after this burning is also relatively poor relatively.(single stove charge amount is greater than 4Kg) this phenomenon is more outstanding under the condition of large-scale production.Because each charge amount is bigger, the inner and outer radiating condition and the difference of nitrogen infiltration condition when the synthetic autoreaction of burning takes place of reactant powder base is more obvious.Mainly be because reactant powder base is outer big with the nitrogen contact area, and nitrogen gas permeability is good, thereby nitrogenizing reaction is rapid, main is that temperature of combustion is lower, is suitable for the generation of α phase silicon nitride because the outer radiating condition of reactant powder base is good.And reactant powder base is inner little with the nitrogen contact area, nitrogen gas permeability is poor, thereby nitrogenizing reaction is slow relatively, be prone to back nitrogenize phenomenon, it is poor to add reactant powder base internal heat dissipating condition, the heat that reaction discharges can't scatter and disappear rapidly, causes reactant powder base internal-combustion temperature higher, thereby makes the easier generation of beta phase silicon nitride of high-temperature stable.The α phase silicon nitride that has generated at high temperature also undergoes phase transition easily and is converted into beta phase silicon nitride.In a word, the inhomogeneous ununiformity that easily causes synthetic product of heat distribution in the combustion synthesis reaction process.Be mainly reflected in the inner and outside bigger ununiformity of existence aspect thing phase composite, foreign matter content, microtexture and grain size of products of combustion.The ununiformity phenomenon of this synthetic product often occurs in the combustion synthesis of silicon nitride powder process, the production efficiency and the product purity of combustion synthesis of silicon nitride powder have greatly been influenced, also increased the difficulty that later separation is handled, seriously limited the large-scale industrialized production of combustion synthesis of silicon nitride powder and use.
The objective of the invention is to: the method that a kind of hollow type annular material-distribution synthesizing isotropic silicon nitride powder adopting is provided, solved the temperature field problem of uneven distribution that conventional combustion synthesis method exists owing to lost different each position of reaction mixture system that cause of heat with the heat accumulation condition, composition and microscopic appearance non-uniformity problem, especially synthetic product inner and the outer thing phase composite of product, grain form and the bigger problem of foreign matter content difference of the synthetic product of conventional combustion synthesis method existence have been overcome.Make the beta-silicon nitride powder thing phase composite of preparation even, sintering activity is good, and powder granule is tiny evenly, and foreign matter content is low.And easy to operate, equipment is simple, the production efficiency height.
Summary of the invention
The present invention is to be raw material with silica flour and inert diluent silicon nitride powder, preparation obtains the reaction mixture of required proportioning component after the ground and mixed drying, reaction mixture is carried out the hollow type annular material-distribution in the porous reaction container, its distributing mode is for to be arranged in the reactant powder in the porous reaction container that has the permeability type hollow tube, in the annular region that is the reactant powder between the inwall of the outer wall of permeability type hollow tube and porous reaction container, permeability type hollow tube both ends open, communicate with the environmental gas in the combustion synthesis reaction device, then the porous reaction container behind the cloth is placed the combustion synthesis reaction device, after vacuumizing, reaction unit charges into nitrogen or ammonia or nitrogen and other gas (ammonias, argon gas, hydrogen fluoride, hydrogenchloride, hydrogen bromide, hydrogen iodide, hydrogen etc.) mixed gas, gaseous tension in the combustion synthesis reaction device is controlled between suitable pressure range 1～20MPa, light priming mixture then and bring out reaction mixture and carry out combustion synthesis reaction, its product was aided with aftertreatment technology such as fine grinding and promptly obtains isotropic silicon nitride powder after reaction was finished.May further comprise the steps:
The raw material of 1 configuration different components:
By weight with silica flour 40%～90%, inert diluent silicon nitride 10%～60% mixes respectively by different ratios, obtains the reaction mixture of one group of different components proportioning;
Wherein said silica flour purity is 95～99.99%, and preferred purity is more than 97%, and particle size range is 0.1～90 μ m, preferable particle size 0.1～30 μ m;
Wherein said inert diluent silicon nitride can be by burning synthesis method or the preparation of other traditional methods, and purity is 90～99.9%, and preferred purity is 95%～99.9%; Particle size range is 0.05～50 μ m, preferable particle size 0.05～10 μ m; Oxygen level is 0.01～10%, and preferred oxygen content is 0.01～3%; The α phase content is 80～99.9%, and preferred α phase content is more than 90%;
2 raw material ground and mixed:
The reaction mixture of one group of different components proportioning that preparation is obtained carries out ground and mixed on grinding plant; Wherein said ground and mixed can be under the air atmosphere or wet grinding under nitrogen atmosphere or the ammonia atmosphere or dry grinding; Wherein said wet grinding medium can be wherein a kind of such as methyl alcohol, ethanol, isopropylcarbinol, acetone, water, liquid nitrogen;
3 dry reaction mixtures:
The reaction mixture of one group of different components proportioning after the ground and mixed is carried out drying on drying plant, drying temperature is between 30～90 ℃;
Wherein said drying can be the drying of carrying out under air atmosphere or nitrogen atmosphere or vacuum condition;
4 hollow type annular material-distributions:
Reaction mixture behind the mill-drying is carried out the hollow type annular material-distribution according to the size and the shape of porous reaction container.Its distributing mode is for to be arranged in the reactant powder in the porous reaction container that has one or several permeability type hollow tube, promptly in the annular region of reactant powder between the inwall of the outer wall of permeability type hollow tube and porous reaction container.Permeability type hollow tube both ends open, the environmental gas outer with the porous reaction container communicates.The big or small thickness of permeability type hollow tube can be adjusted as required.
Wherein said porous reaction container can be the reaction vessel of the arbitrary shape made of a kind of materials wherein such as carbon felt, paper material, woven asbesto, porous graphite, porous ceramics;
Wherein said permeability type hollow tube can be made by a kind of materials wherein such as carbon felt, paper material, woven asbesto, porous graphite, porous ceramicss;
The cross-sectional shape of wherein said permeability type hollow tube can be a kind of in the arbitrary shapes such as circle, semicircle, square, rectangle, rhombus, trilateral;
5 combustion synthesis reactions:
The porous reaction container that step 4 is carried out behind the hollow type annular material-distribution is put into the combustion synthesis reaction device, after vacuumizing, charge into nitrogen or ammonia or nitrogen and other gas (ammonias, argon gas, hydrogen fluoride, hydrogenchloride, hydrogen bromide, hydrogen iodide, hydrogen etc.) mixed gas, make the gaseous tension in the combustion synthesis reaction device be controlled at suitable pressure range (within 1～20MPa), lighting priming mixture then brings out reaction mixture and carries out combustion synthesis reaction, combustion synthesis reaction continues to finish after the dozens of minutes, after being cooled to room temperature and releasing reactor internal pressure, can obtain Powdered or loose block product, behind aftertreatment technologys such as levigate classification, obtain isotropic silicon nitride powder;
Wherein said combustion synthesis reaction device is meant the resistant to elevated temperatures high pressure vessel of being made by materials such as stainless steels, and its volume is 1～60 liter;
When using the mixed gas of nitrogen and other gases, wherein said other gases are a kind of of ammonia, argon gas, hydrogen fluoride, hydrogenchloride, hydrogen bromide, hydrogen iodide, hydrogen etc. or its combination, 1～50% of other gas comprises nitrogen volumes;
Wherein said gaseous tension scope is between 1～20MPa, between preferred 2～15MPa;
Wherein said lighting can be a kind of in the sparking mode such as electrical spark, arc-over, tungsten filament, laser, microwave, infrared heat source;
Wherein said priming mixture can be Ti, Ti+C, Fe
3O
4A kind of in the priming mixtures such as+Al.
Adopt the hollow type annular material-distribution utilize mobile nitrogenous gas in the hollow tube strengthened to the combustion reactions forward position for nitrogen, played the two-way effect in the inside and outside both sides of reactant for nitrogen, improved the radiating condition of reactant silica flour inside simultaneously, the combustion synthesis reaction process and the temperature of reaction thereof of entire reaction thing powder base have been controlled effectively, synthetic beta-silicon nitride powder purity height, α phase content height, thing phase composite uniformity, uniform particles are tiny.At different sites temperature field characteristics pockety in the reaction mixture system, by composition design and hollow type annular material-distribution to the reaction mixture system, make full use of mobile nitrogenous gas in the hollow tube strengthened to the combustion reactions forward position for nitrogen, played the two-way of the inside and outside bilateral of reactant for the nitrogen effect, greatly increased the perviousness of nitrogenous gas, improved the nitriding velocity and the nitridation of reactant silica flour inside to the combustion reactions forward position.Simultaneously, owing to adopted ventilative hollow tube design, the nitrogenous gas of internal flow has improved the radiating condition of reactant silica flour inside well, the heat accumulation of having avoided reactant powder base centre to cause owing to weak heat-dissipating, reduced reactant powder base internal-combustion temperature, can greatly improve the stability of synthesis technique, improve the qualification rate of product.
The present invention's advantage compared with the prior art:
1) the present invention is by composition design and hollow type annular material-distribution to the reaction mixture system, realized the complete nitrogenize of silica flour under the nearly isothermal pattern of W-response thing, improved the homogeneity of beta-silicon nitride powder in the combustion synthesized product, institute's synthetic beta-silicon nitride powder purity height, the phase content unanimity, the sintering activity height.
2) the invention solves in the conventional burning building-up process because the reaction that temperature of reaction temperature field skewness too high or the reaction mixture system causes not exclusively or the composition and the uneven problem of microscopic appearance of synthetic product, has especially overcome the problem that synthetic product exists layering and sandwich and burn-off phenomenon.By composition design and hollow type annular material-distribution to the reaction mixture system, make full use of mobile nitrogenous gas in the hollow tube strengthened to the combustion reactions forward position for nitrogen, played the two-way of the inside and outside bilateral of reactant for the nitrogen effect, greatly increased the perviousness of nitrogenous gas, improved the nitriding velocity and the nitridation of reactant silica flour inside to the combustion reactions forward position.
3) the present invention is by composition design and hollow type annular material-distribution to the reaction mixture system, adopted ventilative hollow tube design, the nitrogenous gas of internal flow has improved the radiating condition of reactant silica flour inside well, the heat accumulation of having avoided reactant powder base centre to cause owing to weak heat-dissipating, reduced reactant powder base internal-combustion temperature, the combustion synthesis reaction process and the temperature of reaction thereof of entire reaction thing powder base have been controlled effectively, thereby reach the purpose of control products of combustion microscopic appearance and homogeneity of ingredients, make finally that different sites has thing phase composite uniformity in the burning synthetic beta-silicon nitride powder, particle size is tiny characteristics evenly.
4) the present invention is by composition design and hollow type annular material-distribution to the reaction mixture system, the output capacity and the output qualification rate of beta-silicon nitride powder have been improved, avoided composition and the microscopic appearance inhomogeneous later separation dressing process that increase of conventional burning building-up process owing to synthetic product, can stablize and synthesize the purity height, the phase composite uniformity, the beta-silicon nitride powder of even particle size distribution.
5) energy consumption is little, and production cost is low.Except that bringing out reaction needed external energy hot spot combustion priming mixture, synthesizing isotropic silicon nitride powder adopting relies on the heat effect of reaction self to finish.Therefore present method has advantage aspect reduction energy consumption and the production cost.
6) reaction times weak point, the production efficiency height.Whole combustion synthesis reaction process is rapid, and the reaction times is generally several minutes to dozens of minutes according to raw material weight, proportioning etc., and is with short production cycle, can save the production technique time.
The method of the hollow type annular material-distribution synthesizing isotropic silicon nitride powder adopting that the present invention proposes is not particularly limited combustion synthesis reaction device and technological process, and the size of combustion synthesis reaction device is determined according to throughput.
Description of drawings
The hollow type annular material-distribution reactant powder base synoptic diagram that Fig. 1 is adopted for embodiment 1, wherein 1 is reactant powder base, 2 is the permeability type hollow tube.
The hollow type annular material-distribution reactant powder base synoptic diagram that Fig. 2 is adopted for embodiment 2, wherein 1 is reactant powder base, 2 is the permeability type hollow tube.
The hollow type annular material-distribution reactant powder base synoptic diagram that Fig. 3 is adopted for embodiment 3, wherein 1 is reactant powder base, 2 is the permeability type hollow tube.
Fig. 4 is the beta-silicon nitride powder scanning electron microscope microscopic analysis figure of embodiment 1 combustion synthesized product average sample.
Fig. 5 is the beta-silicon nitride powder X-ray diffractogram of embodiment 1 combustion synthesized product average position sampling.
Embodiment
Embodiment 1
The raw material that present embodiment adopts is the silica flour (purity is greater than 98.5%) of median size 25 μ m and the beta-silicon nitride powder of median size 1 μ m (purity greater than 96%, α phase content about 93%).Prepare burden and ground and mixed according to weight ratio, its ratio of components is Si: Si
3N
4=50: 50, the reaction mixture gross weight is 4.2 kilograms.Above-mentioned ground and mixed to reaction mixture is carried out in the following manner: be silica flour that the ball-milling medium ball milling carried out ground and mixed in 6 hours with the dehydrated alcohol in the ball milling bucket of agitated ball mill earlier, then carry out drying in 60 ℃ in vacuum drying oven.And then added behind the inert diluent silicon nitride powder on vibration mill ground and mixed 1 hour.Again reaction mixture is carried out the hollow type annular material-distribution according to shown in the accompanying drawing 1 in cylindric porous graphite crucible, wherein the cylindric permeability type hollow tube of Cai Yonging is the carbon felt, and its volume is 1/9th of a cylindric porous graphite crucible volume.Cylindric porous graphite crucible behind the cloth powder is put into 60 liters of combustion synthesis reaction devices, lay helically wound tungsten filament at an end of circular reactant powder base and do ignition source.After vacuumizing, charge into nitrogen, reach 5MPa up to nitrogen pressure in combustion synthesis reaction device inside.Pass to pulsed current to helical tungsten filamen, light priming mixture and bring out reaction mixture and carry out combustion synthesis reaction, priming mixture is a titanium valve.Bring out the material powder burning, after combustion reactions finishes, be cooled to room temperature, nitrogen in the release discharging combustion synthesis reaction device, the whole color and luster of the combustion synthesized product that obtains is even, do not have layering and sandwich phenomenon, be aided with aftertreatment technologys such as fine grinding and obtain promptly that purity is 97.5%, α phase silicon nitride content is that 96.26wt%, free silica are that 0.09wt%, median size are the isotropic silicon nitride powder of 0.7 μ m.
The beta-silicon nitride powder that does not carry out the combustion synthesized product average sample of aftertreatment technology such as fine grinding in the present embodiment adopts x-ray fluorescence analysis to analyze its chemical ingredients: Si (59.32wt%), N (39.64%), Fe (0.033wt%), Ca (0.018wt%), Al (0.0519wt%), C (0.08wt%), O (0.85wt%).Adopting the X-ray diffraction analysis standard measure to calculate its α phase silicon nitride content is 96.26wt%.Its scanning electron microscope microscopic analysis figure and X-ray diffractogram are seen accompanying drawing 4,5.
Embodiment 2
The raw material that present embodiment adopts is the silica flour (purity is greater than 98%) of median size 17 μ m and the beta-silicon nitride powder of median size 2.2 μ m (purity greater than 98%, α phase content about 95%).Prepare burden and ground and mixed according to weight ratio, its ratio of components is Si: Si
3N
4=52.5: 47.5, the reaction mixture gross weight is 4 kilograms.Above-mentioned ground and mixed to reaction mixture is carried out in the following manner: earlier silica flour and inert diluent silicon nitride powder being mixed the back is that the ball-milling medium ball milling carried out ground and mixed in 8 hours with the dehydrated alcohol in the ball milling bucket of agitated ball mill, then carries out drying in 65 ℃ in Electric heat oven.Then dried silica flour and inert diluent silicon nitride powder mixture ground and mixed 2 hours on the roller ball grinding machine.Again the reaction mixture after this ground and mixed is carried out the hollow type annular material-distribution according to shown in the accompanying drawing 2 in cylindric woven asbesto container, wherein the cross section of Cai Yonging is that leg-of-mutton permeability type hollow tube is a paper material, and its volume is 1/8th of a cylindric woven asbesto container volume.Cylindric woven asbesto container behind the cloth powder is put into 60 liters of combustion synthesis reaction devices, lay helically wound tungsten filament at an end of reactant powder base and do ignition source.After vacuumizing, charge into the mixed gas of nitrogen and ammonia in combustion synthesis reaction device inside, wherein the ammonia proportion is 5vol%, reaches 9MPa up to gaseous tension.Pass to pulsed current to helical tungsten filamen, light priming mixture and bring out reaction mixture and carry out combustion synthesis reaction, priming mixture is the mixture of titanium valve and carbon black.Bring out the material powder burning, after combustion reactions finishes, be cooled to room temperature, nitrogen in the release discharging combustion synthesis reaction device, the whole color and luster of the combustion synthesized product that obtains is even, do not have layering and sandwich phenomenon, be aided with aftertreatment technologys such as fine grinding and obtain promptly that purity is 98%, α phase silicon nitride content is that 98wt%, free silica are that 0.1wt%, median size are the isotropic silicon nitride powder of 1.3 μ m.
Embodiment 3
The raw material that present embodiment adopts is the silica flour (purity is greater than 98.5%) of median size 47 μ m and the beta-silicon nitride powder of median size 1.5 μ m (purity greater than 96%, α phase content about 90%).Prepare burden and ground and mixed according to weight ratio, its ratio of components is Si: Si
3N
4=55: 45, the reaction mixture gross weight is 3.5 kilograms.Above-mentioned ground and mixed to reaction mixture is carried out in the following manner: be silica flour and inert diluent silicon nitride powder ball-milling medium ball milling 6 hours with the dehydrated alcohol in the ball milling bucket of agitated ball mill respectively earlier, then carry out drying in 60 ℃ in vacuum drying oven.Then the mixture of silica flour and inert diluent silicon nitride powder ground and mixed 3 hours on vibration mill.Reaction mixture with these three parts of different components proportionings carries out the hollow type annular material-distribution according to shown in the accompanying drawing 3 in rectangle papery container again, adopting 2 cross sections is foursquare papery permeability type hollow tube, and its volume is 1/7th of a rectangle papery container volume.Rectangle papery container behind the cloth powder is put into 60 liters of combustion synthesis reaction devices, lay a long strip shape graphite flake at an end of reactant powder base and do ignition source.After vacuumizing, charge into the mixed gas of nitrogen and hydrogen in combustion synthesis reaction device inside, wherein the hydrogen proportion is 8vol%, reaches 7MPa up to gaseous tension.Pass to pulsed current to graphite flake, light priming mixture and bring out reaction mixture and carry out combustion synthesis reaction, priming mixture is a titanium valve.Bring out the material powder burning, after combustion reactions finishes, be cooled to room temperature, nitrogen in the release discharging combustion synthesis reaction device, the whole color and luster of the combustion synthesized product that obtains is even, do not have layering and sandwich phenomenon, be aided with aftertreatment technologys such as fine grinding and obtain promptly that purity is 98%, α phase silicon nitride content is that 95wt%, free silica are that 0.08wt%, median size are the isotropic silicon nitride powder of 1.1 μ m.
Claims (6)
1. the method for a hollow type annular material-distribution synthesizing isotropic silicon nitride powder adopting, it is characterized in that: with silica flour and inert diluent silicon nitride powder is raw material, prepares the reaction mixture that obtains required proportioning component through ground and mixed, dry back; Reaction mixture is carried out the hollow type annular material-distribution in the porous reaction container, its distributing mode is for to be arranged in the reactant powder in the porous reaction container that has the permeability type hollow tube, make in the annular region of reactant powder between the inwall of the outer wall of permeability type hollow tube and porous reaction container, permeability type hollow tube both ends open, communicate with the environmental gas in the combustion synthesis reaction device, then the porous reaction container behind the cloth is placed the combustion synthesis reaction device, after vacuumizing, reaction unit charges into the mixed gas of nitrogen or ammonia or nitrogen and other gases, gaseous tension in the combustion synthesis reaction device is controlled between suitable pressure range 1～20MPa, lighting priming mixture then brings out reaction mixture and carries out combustion synthesis reaction, after reaction is finished, obtain Powdered or loose block product; Through levigate stage treatment, obtain isotropic silicon nitride powder; Described other gases are ammonia, argon gas, hydrogen fluoride, hydrogenchloride, hydrogen bromide, hydrogen iodide or hydrogen.
2. method according to claim 1 is characterized in that: the reaction mixture of described one group of different components proportioning is by weight percentage with silica flour 40%～90%, and inert diluent silicon nitride 10%～60% mixes, and obtains reaction mixture; Wherein, silica flour purity is 95～99.99%, and particle size range is 0.1～90 μ m; Described inert diluent silicon nitride purity is 90～99.9%; Particle size range is 0.05～50 μ m; Oxygen level is 0.01～10%, and the α phase content is 80～99.9%.
3. method according to claim 1 and 2 is characterized in that: the ground and mixed reaction mixture is that the reaction mixture that preparation obtains is carried out ground and mixed on grinding plant; Ground and mixed is under air atmosphere or wet grinding under nitrogen atmosphere or the ammonia atmosphere or dry grinding; Wet grinding medium is a kind of in methyl alcohol, ethanol, isopropylcarbinol, acetone, water, the liquid nitrogen; Dry reaction mixture is that the reaction mixture with one group of different components proportioning after the ground and mixed carries out drying on drying plant, and drying temperature is between 30～90 ℃; The drying of under air atmosphere or nitrogen atmosphere or vacuum condition, carrying out.
4. method according to claim 1 is characterized in that: described porous reaction container is the reaction vessel that a kind of material in carbon felt, paper material, woven asbesto, porous graphite, the porous ceramics is made; The resistant to elevated temperatures high pressure vessel that described combustion synthesis reaction device is made by stainless material, its volume are 1～60 liter; When using the mixed gas of nitrogen and other gases, other gases are a kind of or its combination of ammonia, argon gas, hydrogen fluoride, hydrogenchloride, hydrogen bromide, hydrogen iodide, hydrogen, 1～50% of other gas comprises nitrogen volumes; Describedly light a kind of in electrical spark, arc-over, tungsten filament, laser, microwave, the infrared heat source sparking mode; Described priming mixture is Ti, Ti+C, Fe
3O
4A kind of in the+Al priming mixture.
5. method according to claim 1 is characterized in that: described permeability type hollow tube is made by a kind of material in carbon felt, paper material, woven asbesto, porous graphite, the porous ceramics; The cross-sectional shape of permeability type hollow tube is circle, semicircle, square, rectangle, rhombus, a kind of in triangular shaped; The quantity of permeability type hollow tube is 1～12.
6. method according to claim 1 is characterized in that: the gaseous tension scope of combustion synthesis reaction is between 2～15MPa.
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