CN101445223A - Method for preparing low-oxygen high-alpha phase silicon nitride powder by auto-igniting synthesis - Google Patents
Method for preparing low-oxygen high-alpha phase silicon nitride powder by auto-igniting synthesis Download PDFInfo
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Abstract
The invention discloses a method for preparing low-oxygen high-alpha phase silicon nitride powder by auto-igniting synthesis, which is characterized in that the method comprises the processing steps of treating raw materials, compounding, mixing, reacting and finishing. The obtained product has high purity and high content of alpha phase, and the oxygen content is less than 1%.
Description
Technical field:
The invention belongs to field of inorganic nonmetallic material, be specifically related to a kind of employing and prepare the method for the high α-phase silicon nitride powder of low oxygen content from climing combustion, the silicon nitride of preparation can be widely used in fields such as fine ceramics and high-end refractory materials.
Background technology:
Because silicon nitride (Si
3N
4) pottery has unique physical and mechanical property, for example density is low, high strength, high rigidity, wear-resistant, corrosion-resistant, good thermostability (particularly low thermal expansivity), high thermal conductivity etc., has a wide range of applications in fields such as Aeronautics and Astronautics, semi-conductor, electronics, chemical industry, the energy, machinofacture, weapon industries.
Silicon nitride is typical covalent linkage compound, two kinds of crystal formations are arranged, β is acicular crystals mutually, belongs to high-temperature stable, α phase crystalline particulate body, belong to the cryostatic stabilization type, both are hexagonal system, and the internal strain of α phase structure is mutually bigger than β, so free energy is mutually higher than β, at 1400-1600 ℃ of heating, α-Si
3N
4Can be transformed into β-Si
3N
4, the transformation of α → β phase generally can take place in the sintering process of beta-silicon nitride powder, this phase transformation is separated out mechanism by dissolving and is carried out the densification of simultaneous density.Oxygen is to have maximum impurity elements in the silicon nitride powder, and a part is dissolved in the granule interior of silicon nitride powder, and the form with oxygen-rich layer exists a part on the silicon nitride powder surface.Usually the oxygen-rich layer on silicon nitride powder surface is regarded as SiO
2Film.In sintering process, the oxygen-rich layer on silicon nitride particle surface and sintering aid reaction form liquid phase, promote phase transformation and densification.Except the oxidesintering auxiliary agent of other interpolation, the oxygen-rich layer on silicon nitride powder surface also participates in the formation of liquid phase in the sintering process as sintering aid, and influences the composition and the quantity of crystal boundary phase in the silicon nitride ceramics, thereby influences its mechanical behavior under high temperature.It is also extremely important with the influence of mechanical behavior under high temperature mutually to the silicon nitride ceramics crystal boundary to adopt the α phase silicon nitride powder sintered ceramic of low oxygen content just progressively to become the surperficial oxygen-rich layer of the subject study silicon nitride powder that domestic and international scientific research institutions and enterprise competitively carry out.
The traditional method of preparation α phase silicon nitride powder can be divided into following several, and first kind is metallic silicon power (Si) direct nitridation method of industrial extensive employing, and second kind is silicon-dioxide (SiO
2) carbothermic method, the third is a chemical gas phase synthetic method, and the 4th kind is relatively advanced plasma (orifice) gas phase synthesi, and the 5th kind is from climing combustion high-temperature synthesis.
The metallic silicon power direct nitridation method is: in the atmosphere of nitrogen or ammonia, the heating of metal silica flour makes it to take place nitrogenizing reaction in electric furnace, this method is simple, and be the most effective of synthetic alpha silicon nitride powder and be relative simple method, be the method for widespread usage in the industry.But this method has its significant disadvantages, silica flour may melt in pyroreaction, cause reaction atmosphere diffusion difficulty, secondly along with the carrying out that reacts, the silicon nitride layer that coats silica flour can stop the further nitrogenize of inner silica flour, in addition, entire reaction course needs twice nitrogenize, need a couple of days this reaction time, from start to finish must strict control reaction temperature in this process, nitrogen partial pressure guarantees to generate the thermal environment that α needs mutually with gas flow, has caused the bigger energy consumption of these method needs, synthetic powder granularity skewness, foreign matter content is higher, can't satisfy preparation high-performance Si
3N
4The ingredient requirement of pottery.
The silicon-dioxide carbothermic method is with SiO 2 powder and carbon dust thorough mixing, utilizes carbon reduction SiO under flowing nitrogen atmosphere
2, Si that is reduced out and SiO and nitrogen further react and generate Si
3N
4, this method has that equipment is simple, cost of material is low, and the alpha-silicon nitride powders of generation has high α phase, and residual C can remove through 600 ℃ of calcinings, and powder need not characteristics such as ball milling.But this method need add excessive carbon to guarantee SiO
2Complete reaction, the SiO that pilot process produced causes the loss of raw material easily, simultaneously at SiO
2-C-N
2Reaction system speed of response when low temperature is slow; And when high temperature, may cause generating silicon carbide, directly have influence on the productive rate and the purity of silicon nitride.
Chemical gas phase synthetic method is that siliceous compound is (as SiH
4, SiCl
4) and the raw material of nitrogen or ammonia surface reaction takes place in reactor generates Si (NH
2)
2, NH is removed in washing then
4Behind the Cl this product is heated to 1200 ℃ and generates the amorphous phase silicon nitride, generate the alpha silicon nitride powder more than the reheat to 1500 ℃, the beta-silicon nitride powder of this method preparation has high α phase purity, characteristics that sintering activity is good, this method can be controlled the oxygen level of powder preferably, but this powder has raw material costliness, equipment complexity, shortcoming that energy consumption is bigger.Plasma method is to use direct current-arc plasma producer or high-frequency plasma generator to produce plasma body, silica flour or gas-phase silicon source are transported in the plasma flame district, in the high-temperature zone of temperature up to more than 10,000 degree, powder melts volatilization immediately, becomes Si with the rapid chemical combination of nitrogen
3N
4The method of powder.Silicon grain nearly all in plasma generator all is in high-octane state, reacts with very high speed and nitrogen, so this method can effectively shorten the reaction times, and the synthetic Si of institute
3N
4Powder mostly is amorphous phase, contain higher oxygen, have higher chemically reactive and good sintering activity, therefore need in preparation and storage process, take certain safeguard procedures, the α of Zhi Bei beta-silicon nitride powder is mutually on the low side simultaneously, the shortcoming of this method is the energy consumption height, equipment complexity, production cost costliness.
From climing combustion high temperature synthetic technology (Self-propagation High-temperature Synthesis, abbreviation SHS), also claim combustion synthesis technology (Combustion Synthesis, the CS that writes), be to utilize a kind of mode that exothermic heat of reaction and conduction mode are certainly come synthetic materials between the reactant.When in a single day reactant is ignited, just can be from the still unreacted regional spread of trend, until reacting completely, whole process needs the external world to provide any energy and reaction times very fast hardly, be a kind of method of the synthetic powder that receives much attention, it is simple to have technology, and energy consumption is low, the product purity height, the characteristics of less investment.With from climing combustion high temperature synthesizing silicon nitride ceramic powder purity height, fillibility is good, and stable performance is with low cost.
Prepare aspect the beta-silicon nitride powder adopting from climing combustion synthetic technology, existing a large amount of patents and research paper report, these results respectively have relative merits." a kind of method " nitrogen pressure higher (6-30MPa) of (patent US5032370), " preparing silicon nitride " (patent RU2257338) and " improving beta-silicon nitride powder α technology mutually " (patent RU2149824) needs for preparing alpha-phase silicon nitride as inventions such as Merzhanov from climing burning method from climing combustion, to the equipment requirements harshness, be unfavorable for scale operation, a large amount of ammonia salt that contains Cl, F of Cai Yonging simultaneously, can produce a large amount of HCl, HF gas after the reaction, to the seriously corroded of equipment, simultaneously operator have been brought bigger actual bodily harm; There is same problem in " method of the synthetic α phase silicon nitride powder of temperature control activation self-propagating combustion " (the patent CN1673070A) of people such as the Lin Zhiming of Physical Chemistry Technology Inst., Chinese Academy of Sciences invention; The Chen Ke of Tsing-Hua University newly waits the suspension nitrogenize technology of the silica flour of people's invention " method of the synthetic alpha-phase silicon nitride powder of a kind of low-pressure combustion " (patent CN1362358A) employing, the following step of main branch is finished: 1. pair silica flour carries out pickling and ultrasonic pretreatment, 2. add promoting agent, thinner and additive, 3. the pellet that mixes was ground 15-30 hours, 3. the material behind the ball milling is 50～70 ℃ of oven dry, put into reactor, be blown into the nitrogen of 0.1-1MPa after vacuumizing from the powder bottom, bring out material combusting simultaneously.Though this method can reduce nitrogen gas pressure, whole operation is various and consuming time, and the production cycle is long, introduces other impurity easily, and energy consumption is relatively large, has driven the raising of whole production cost; People's such as the Ge Changchun of University of Science ﹠ Technology, Beijing " with the method for combustion synthesizing high alpha phase superfine beta-silicon nitride powder and silicon nitride crystal whisker " (patent CN1433959A) adopts and adds CaF2, caused the Ca content of synthetic back powder to increase, and influences the use properties of powder; People's such as the Ge Changchun of University of Science ﹠ Technology, Beijing " a kind of method of synthesizing isotropic silicon nitride powder adopting layer type material-distribution " (patent CN179995A), raw material ground and mixed and drying step are consuming time loaded down with trivial details, and the stratiform cloth is consuming time, is unfavorable for large-scale production; There is HCl in people's such as the Yang Jun of Physical Chemistry Technology Inst., Chinese Academy of Sciences " method of the synthetic α phase silicon nitride powder of controlled temperature combustion " (patent CN1696076A) in the reacted tail gas; Above patent lays particular emphasis on and improves α phase silicon nitride content in the combustion synthesized product, does not relate to the problem of synthetic powder Control for Oxygen Content.
Summary of the invention:
The objective of the invention is to overcome the deficiency of above-mentioned prior art, mainly solve the general oxygen level of prior art synthetic powder higher problem, a kind of method of efficiently synthesizing low oxygen content, alpha-phase silicon nitride powder from climing combustion is provided, the powder of preparation contains higher α phase, oxygen level is less than 1%, sintering activity is good, and whole operation is simple and reliable, is easy to realize scale operation.
In order to achieve the above object, the present invention is achieved in that the method for preparing the high α-phase silicon nitride powder of low oxygen content from climing combustion, and its special character is that it comprises raw material processing, proportioning, mixing, reacts, gets finished product, and concrete processing step is as follows:
(1) raw material is handled: to granularity is that 100-300 purpose metallic silicon powers carried out ball-milling processing 12-16 hours, reduces the granularity of powder, increases a spot of amorphous silicon to improve the activity of silica flour, the wherein purity of silica flour〉99.5%.Silica flour is done through mechanize and is mixed (comprising in three-dimensional motion mixer, the agitating ball mill any), with Si
3N
4Ball is a ball-milling medium, is placed in the Polyurethane jar material: ball weight is than being 1:5～10;
(2) batching: with the metallic silicon power after the above-mentioned processing is raw material, adds thinner, additive, and its weight percent proportioning is:
Metallic silicon power (behind the high speed ball milling): 35-50wt%,
Thinner 35-45wt%,
Carbon black 0-2wt%,
Additive 10-20wt%,
Above-mentioned thinner can be the synthetic or additive method synthetic alpha silicon nitride powder from climing combustion, the α phase content of α phase silicon nitride powder〉94%, median size is 3-20 μ m, additive is NH
4Cl, NH
4Among the F any one or its combination;
(3) mix: the mixture of batching step was stirred 1-4 hours, make its thorough mixing even, take out the back and sieve with 40-60 eye mesh screens, it is mixed that described stirring is that mechanize is done, promptly adopt in planetary ball mill, the jar mill any, with Si
3N
4A kind of in ball, the steel ball or be mixed into ball-milling medium, material: ball weight is than being 1:5～10;
(4) from climing combustion reaction: the powder after above-mentioned the sieving is contained in the half-terete graphite boat, be placed on again in climing combustion reactor, after vacuumizing, fill high pure nitrogen, pressure remains on 4-8MPa, igniting guiding high temperature is synthetic from climing combustion, can be wound in spirrillum by the nichrome wire of 0.6mm, feed the direct current of 25A, make coil heating, temperature has reached the temperature of reaction of silica flour and nitrogen in the raw mix, and chemical reaction mode with climing combustion in material successively advances then, finish the logical recirculated water cooling of synthetic post-reactor until building-up reactions;
(5) finished product: between the reaction period, owing to emit heat, the pressure in the reactor rises, and reaction post-reactor internal pressure can reduce, and when the pressure of reactor drops to 5-9MPa, finishes from climing combustion reaction.Pressure in the releasing reactor, the gas of release is eliminated remaining small amount of N H by water
3Pollute to reduce, then reactor is filled 1-5 minute high pure nitrogen, reduce the temperature of reaction mass.Open the low oxygen content, the alpha-phase silicon nitride powder finished product that obtain loosening behind the reactor.
Of the present inventionly prepare the method for low oxygen content alpha-phase silicon nitride powder, the product purity height that is obtained, α phase content height, oxygen level＜1% from climing combustion.By design and adjustment reactant system, select suitable additive, control is reflected at suitable temperature range, obtains high α phase; Add a certain amount of Si
3N
4Powder, control the temperature of reaction on the one hand, the temperature field uniform distribution at each position of control reaction mass system, prevented the generation of too much β phase, adjusted the porosity of material simultaneously, be beneficial to the nitriding reaction, realized the complete nitrogenize of silica flour, guaranteed from climing combustion reacting balance, continued, carry out fast.The main purpose that adds carbon black be with original silica flour in oxygen react, vacuumize processing simultaneously, reduced the oxygen level of synthesis gas, reduce the oxygen level of powder by above dual mode.
Compared with the prior art the method for preparing the low oxygen content alpha-phase silicon nitride powder from climing combustion of the present invention has outstanding substantive distinguishing features and marked improvement:
1) starting material are convenient can get, and need not special processing such as pickling;
2) synthesising reacting time is rapid, the production efficiency height, and entire reaction period (comprising batch mixing, building-up reactions, synthetics processing) 50-60 minutes is easy to suitability for industrialized production;
3) save energy outside ignition reaction, does not need external heat source, and building-up reactions relies on raw material id reaction liberated heat to keep from climing combustion, and save energy has reduced cost;
4) oxygen level of synthesizing the back powder reduces, and is suitable for very much the sintering of pyroceramic;
5) because temperature and speed of response when having controlled reaction preferably, the transformation efficiency height of reaction, synthetic product purity height, α phase content height (up to more than 94%), crystal grain rule.
Description of drawings
Fig. 1 is the beta-silicon nitride powder scanning electron microscope microscopic analysis figure of embodiment 1 from climing combustion synthetic product sampling.
Fig. 2 is the beta-silicon nitride powder X-ray diffractogram of embodiment 1 from climing combustion synthetic product sampling.
Fig. 3 is the beta-silicon nitride powder scanning electron microscope microscopic analysis figure of embodiment 2 from climing combustion synthetic product sampling.
Fig. 4 is the beta-silicon nitride powder X-ray diffractogram of embodiment 2 from climing combustion synthetic product sampling.
Fig. 5 is the beta-silicon nitride powder scanning electron microscope microscopic analysis figure of embodiment 3 from climing combustion synthetic product sampling.
Fig. 6 is the beta-silicon nitride powder X-ray diffractogram of embodiment 3 from climing combustion synthetic product sampling.
Fig. 7 is the beta-silicon nitride powder scanning electron microscope microscopic analysis figure of embodiment 4 from climing combustion synthetic product sampling.
Fig. 8 is the beta-silicon nitride powder X-ray diffractogram of embodiment 4 from climing combustion synthetic product sampling.
Embodiment:
In order to understand better and to implement, describe the present invention in detail below in conjunction with specific embodiment.
Embodiment 1, and 100 purpose metallic silicon powers (purity〉99.5%) are carried out ball-milling processing on three-dimensional motion mixer, and silica flour is done through mechanize and mixed, with Si
3N
4Ball is a ball-milling medium, is placed in the Polyurethane jar material: ball weight is than being 1:5, and the ball milling time is 12 hours; Reaction mass is per distribution ratio by weight: metallic silicon power (after the ball-milling processing) is 35%, beta-silicon nitride powder (median size 3 μ m, α phase〉94%) 45%, NH
4After mixing, Cl 20% puts into jar mill, with Si
3N
4Ball is a ball-milling medium, material: ball weight mixed 1 hour than for 1:5, made the reaction mass thorough mixing even, took out the back and sieved with 40 eye mesh screens; Material after sieving is positioned in the half-terete graphite boat of porous uniformly, put into then from climing combustion synthesis reactor, after vacuumizing, charge into the high pure nitrogen of 6MPa, nichrome wire with diameter 0.6mm is made heating element, be wound in spirrillum, feed 25 amperes electric current, make coil heating, temperature has reached the temperature of reaction of silica flour and nitrogen in the raw mix, chemical reaction mode with climing combustion in material successively advances then, finish until building-up reactions, reactor one straight-through recirculated water cooling but reacts the post-reactor internal pressure and can reduce between the reaction period, when the pressure of reactor drops to 6MPa, finish from climing combustion reaction.Pressure in the releasing reactor, the gas of release is eliminated remaining small amount of N H by water
3Pollute to reduce, then reactor is filled 1 minute high pure nitrogen, reduce the temperature of reaction mass, open the product that reactor takes out loose shape then, remove the unreacted silica flour of surperficial one deck, the product integral body that obtains is milk yellow, and the α phase content of powder is greater than 94%, contents of free si is less than 0.15%, reaction yield〉95%.
Embodiment 3, and 300 purpose metallic silicon powers (purity〉99.5%) are carried out ball-milling processing on agitating ball mill, and silica flour is done through mechanize and mixed, with Si
3N
4Be ball-milling medium, be placed in the Polyurethane jar, material: ball weight is than being 1:8, and the ball milling time is 16 hours; Reaction mass is per distribution ratio by weight: metallic silicon power (after the ball-milling processing) is 50%, silicon nitride (median size 8 μ m, α phase〉94%) 35%, NH
4F13.5%, carbon black 1.5% are put into planetary ball mill after mixing, and are ball-milling medium with the steel ball, and material: ball weight mixed 2 hours than for 1:8, made the reaction mass thorough mixing even, take out the back and sieve with 60 eye mesh screens; Material after sieving is positioned in the half-terete graphite boat of porous uniformly, put into then from climing combustion synthesis reactor, after vacuumizing, charge into the high pure nitrogen of 8MPa, nichrome wire with diameter 0.6mm is made heating element, be wound in spirrillum, feed 25 amperes electric current, make coil heating, temperature has reached the temperature of reaction of silica flour and nitrogen in the raw mix, chemical reaction mode with climing combustion in material successively advances then, finish until building-up reactions, reactor one straight-through recirculated water cooling but reacts the post-reactor internal pressure and can reduce between the reaction period, when the pressure of reactor drops to 9MPa, finish from climing combustion reaction.Pressure in the releasing reactor, the gas of release is eliminated remaining small amount of N H by water
3Pollute to reduce, then reactor is filled 5 minutes high pure nitrogen, reduce the temperature of reaction mass, open the product that reactor takes out loose shape then, remove the unreacted silica flour of surperficial one deck, the product integral body that obtains is milk yellow, and the α phase content of powder is greater than 94%, contents of free si is less than 0.15%, reaction yield〉95%.
Embodiment 4, and 240 purpose metallic silicon powers (purity〉99.5%) are carried out ball-milling processing on agitating ball mill, and silica flour is done through mechanize and mixed, with Si
3N
4Be ball-milling medium, be placed in the Polyurethane jar, material: ball weight is than being 1:7, and the ball milling time is 15 hours; Reaction mass is per distribution ratio by weight: metallic silicon power (after the ball-milling processing) is 50%, silicon nitride (median size 12 μ m, α phase〉94%) 35%, NH
4F7%, NH
4Cl 6%, carbon black 2% are put into planetary ball mill after mixing, and are ball-milling medium with the steel ball, and material: ball weight mixed 2 hours than for 1:7, made the reaction mass thorough mixing even, take out the back and sieve with 60 eye mesh screens; Material after sieving is positioned in the half-terete graphite boat of porous uniformly, put into then from climing combustion synthesis reactor, after vacuumizing, charge into the high pure nitrogen of 5MPa, nichrome wire with diameter 0.6mm is made heating element, be wound in spirrillum, feed 25 amperes electric current, make coil heating, temperature has reached the temperature of reaction of silica flour and nitrogen in the raw mix, chemical reaction mode with climing combustion in material successively advances then, finish until building-up reactions, reactor one straight-through recirculated water cooling but reacts the post-reactor internal pressure and can reduce between the reaction period, when the pressure of reactor drops to 6MPa, finish from climing combustion reaction.Pressure in the releasing reactor, the gas of release is eliminated remaining small amount of N H by water
3Pollute to reduce, then reactor is filled 4 minutes high pure nitrogen, reduce the temperature of reaction mass, open the product that reactor takes out loose shape then, remove the unreacted silica flour of surperficial one deck, the product integral body that obtains is milk yellow, and the α phase content of powder is greater than 94%, contents of free si is less than 0.15%, reaction yield〉95%.
The product of above-mentioned 4 embodiment gained, its salient features such as table 1 after tested:
Table 1
Claims (5)
1, the method for preparing the high α-phase silicon nitride powder of low oxygen content from climing combustion is characterized in that it comprises raw material processing, proportioning, mixing, reacts, gets finished product, and concrete processing step is as follows:
(1) raw material is handled: to granularity is 100-300 purpose metallic silicon powers ball-milling processing 12-16 hours on high speed ball mill, with Si
3N
4Ball is a ball-milling medium, is placed in the Polyurethane jar material: ball weight is than being 1:5～10;
(2) batching: with the metallic silicon power after the above-mentioned processing is raw material, adds thinner, additive, and its weight percent proportioning is:
Metallic silicon power: 35-50wt%,
Thinner 35-45wt%,
Carbon black 0-2wt%,
Additive 10-20wt%,
Above-mentioned thinner is synthetic or additive method synthetic α phase silicon nitride powder from climing combustion, and additive is NH
4Cl, NH
4Among the F any one or its combination;
(3) mix: the mixture of batching step was stirred 1-4 hours, make its thorough mixing even, take out the back and sieve with 40-60 eye mesh screens;
(4) from climing combustion reaction: the powder after above-mentioned the sieving is contained in the half-terete graphite boat, be placed on again in climing combustion reactor, after vacuumizing, fill high pure nitrogen, pressure remains on 4-8MPa, igniting guiding high temperature is synthetic from climing combustion, can be wound in spirrillum by the nichrome wire of 0.6mm, feed the direct current of 25A, make coil heating, temperature has reached the temperature of reaction of silica flour and nitrogen in the raw mix, and chemical reaction mode with climing combustion in material successively advances then, finish until building-up reactions, reactor one straight-through recirculated water cooling but between the reaction period;
(5) get finished product: reaction post-reactor internal pressure can reduce, and when the pressure of reactor drops to 5-9MPa, finishes from climing combustion reaction.Pressure in the releasing reactor, the gas of release is eliminated remaining small amount of N H by water
3Pollute to reduce, then reactor is filled 1-5 minute high pure nitrogen, reduce the temperature of reaction mass, open low oxygen content, alpha-phase silicon nitride powder finished product that reactor obtains loosening.
2, according to claim 1ly prepare the method for the high α-phase silicon nitride powder of low oxygen content from climing combustion, it is characterized in that the purity of the metallic silicon power in the described material treatment process step 99.5%.
3, according to claim 1ly prepare the method for the high α-phase silicon nitride powder of low oxygen content, it is characterized in that mechanize in the described material treatment process step is done to mix to any in three-dimensional motion mixer, the agitating ball mill from climing combustion.
4, according to claim 1ly prepare the method for the high α-phase silicon nitride powder of low oxygen content from climing combustion, it is characterized in that the α phase content of the α phase silicon nitride powder in the described proportioning process step 94%, median size is 3-20 μ m.
5, according to claim 1ly prepare the method for the high α-phase silicon nitride powder of low oxygen content from climing combustion, the stirring that it is characterized in that described hybrid technique step is that mechanize is done and mixed, promptly adopt in planetary ball mill, the jar mill any, with Si
3N
4A kind of in ball, the steel ball or be mixed into ball-milling medium, material: ball weight is than being 1:5～10.
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