CN101104516A - Method for synthesizing high pure and ultra-fine beta-SiC powder by self-spread burning - Google Patents

Abstract

A method for preparing high-purity ultrafine beta-SiC powder through self-propagating combustion synthesis relates to the silicon carbide preparation technical field. The process is that silicon power, carbon black or activated carbon are mixed based on a 0.3-2 C/Si mole ratio and added with PTFE which is 3-25% in mass fraction and then ball-milled for 10 to 15 hours taking anhydrous alcohol as medium and finally dried in an air drying box; the dried mixed power is placed in a combustion synthesis reactor which is 5 to 60 litres in volume; 0.5 to 8 MPa nitrogen gas is charged into the reactor after the reactor is pumped vacuum, then titanium powder is pre-positioned on the end part of the reaction mixture as an igniter; a tungsten wire is electrified to ignite the titanium powder to trigger combustion reaction of the reaction mixture to generate the product. The invention has the advantages that the reaction only happens in a thermal wave region, thus the temperature can be easily controlled and the thermal waves spread fast, and also the reaction is highly efficient, so that the fine-grained and high-activity powder can be obtained. The PTFE additive content required by the invention can reach 2 percent in minimum, while the volume of the reactor can reach 60 litres in maximum.

Description

With the synthetic method for preparing high pure and ultra-fine beta-SiC powder of self-propagating combustion

Technical field

The invention belongs to the ceramic preparing technical field, provide a kind of with the synthetic method for preparing high pure and ultra-fine beta-SiC powder of self-propagating combustion, this method is simply efficient.

Background technology

Silicon carbide is a kind of advanced ceramics material, has that resistance of oxidation is strong, wearability good, thermostability is high, thermal expansivity is little, thermal conductivity is big, hardness is high and premium propertiess such as anti-thermal shock and resistance to chemical attack.Relative α-the SiC of β-SiC has better sintering character and semiconducting behavior, shows better use properties.High purity, small particle size are the basic demands of high-performance ceramic powder.The Acheson method is mainly adopted in the production of preparation ultra-fine beta-SiC at present, and the problem of existence is long reaction time (generally reaching tens hours), need subsequent technique such as pickling impurity removal, and preparation cycle is long, and production process complexity, cost are higher.Explore energy-efficient low-cost preparation technology is hot research in recent years always.

Self-propagating combustion synthetic (SHS) is an advanced technology of preparing of utilizing reaction self heat release synthetic materials, after reaction mixture is lighted, forms the combustion wave that spreads voluntarily, and combustion wave is fast to the unreacted regional spread, and after the combustion wave, reactant is converted into product; Reaction process does not need the external world that energy is provided, and is an energy-saving technique; Speed of response is fast, efficient is high; The high temperature of combustion wave can make volatile impunty effectively decompose, the product purity height; Equipment is simple, with low cost.These a series of advantages make SHS obtain widespread use in preparation ceramic powder, intermetallic compound and prepare composite.At present SHS still of no use prepares the patent of high-purity β-SiC, but the pertinent literature report is arranged, as Wang Tiejun etc. (Wang Tiejun, Wang Shenghong. preheating SHS prepares the mechanism and the technology of SiC powder. powder metallurgy technology, 1997,15 (2): 106-110; Wang Tiejun, Wang Shenghong. preheating SHS legal system is equipped with the research [J] of β-SiC micro mist. steel research journal, 1997,9 (supply): 26-31.) prepared SiC from climing burning method, but preheating increases the complexity of equipment with preheating.People such as Nersisyan (G.A.Nersisyan, V.N.Nikogosov, S.L.Kharatyan, A.G.Merzhanov, Combust.Expl.Shock Waves, 1991,7:720) in argon gas atmosphere, prepared thin silicon carbide with burning synthesis method, add the tetrafluoroethylene of 18wt% in the reaction mixture as chemical promoter.(J.Zhang such as Zhang, J.C.Jeong, J.H.Lee, C.W.Won, D.J.Kim, C.O.Kim, The effect of carbon sources and activative additive on the formation of SiCpowder in combustion reaction.Mater Res Bull, 2002,37:319-329.) mix as additive with tetrafluoroethylene and magnesium powder, with Si, be pressed into piece after C and the additive mixing and ball milling drying thereof, prepared β-SiC with the SHS method, wherein the addition of tetrafluoroethylene is up to 25%, and residual have a MgO, needs pickling just can dispel residue.People such as C.C.Chen (Chien-Chong Chen, Chia-Ling Li, Keng-Yuan Liao, A cost-effective processfro large-scale production of submicron SiC by combustion synthesis, Materials Chemistry and Physics, 2002,73,198-205) right cylinder of material powder compacting journey 120mm * 120mm * 60mm is carried out the composite granule that burning synthesis for preparing is equipped with α-SiC and β-SiC.Have not yet to see and carry out at large size reactor (volume reaches 5kg, powder raw material cloth in 60 liters, the single batch materials) that burning synthesis for preparing is high-purity fully, the report of ultra-fine beta-SiC powder.

Summary of the invention

The object of the present invention is to provide and a kind ofly realized powder raw material cloth rather than block material cloth, simplified preparation technology with the synthetic method for preparing high pure and ultra-fine beta-SiC powder of self-propagating combustion; Reduce the usage quantity of additive, reduced cost; In the large size reactor, prepared high performance β-SiC powder with SHS technology first.

Concrete technology of the present invention is:

With silica flour, carbon black (or gac) mixes with certain mol proportion, adds certain mass fractional tetrafluoroethylene again.The scope of the mol ratio of C/Si is 0.3～2, and the massfraction scope that tetrafluoroethylene adds is 2%～25%; With reaction mixture ball milling 10～15h, 70～150 ℃ of oven dry in the air drying baker; Dried mixed powder is placed the reactor of 5 liters to 60 liters, charge into the nitrogen of 0.5～8MPa pressure, place titanium valve the reaction mixture end as priming mixture in advance, the titanium valve consumption will cover tungsten filament, light titanium valve with the tungsten filament energising, the combustion reactions of initiation reaction mixture obtains product.

Raw mix of the present invention is with the powder shaped cloth, does not need to be pressed into block.

Tetrafluoroethylene of the present invention is an additive, for reaction provides primary heat.An end titanium valve of reactor is lighted in the tungsten filament energising, and the thing that induces reaction reacts.React after lighting, do not need external heat source, the reaction liberated heat can continue to propagate to keep reaction to the unreacted district, and entire reaction is finished smoothly.

Based on foregoing, under the prerequisite that does not break away from basic fundamental thought of the present invention,, modification, replacement or the change of various ways can also be arranged to its content according to the ordinary skill knowledge and the means of this area, can continue to increase as the volume of reactor.

The present invention adopts burning synthetic method to prepare high-purity β-SiC.SHS is that a kind of keeping by reaction self liberated heat reacted a kind of synthetic method of carrying out, not needing extraneous lasting heating or insulation.When reacting once lighting, by self heat release formation heat wave, heat wave is propagated voluntarily by whole reactor, thereby reactant is changed into product.To be that burning is synthetic can rely on self heat release to keep entire reaction to carry out the characteristics of this technology maximum, in case in the end points combustion of reactor, heat wave can transmit to the unreacted district; Reaction only takes place in the heat wave zone, and the zone that heat wave does not propagate into remains the low-temp reaction thing; This feature makes system temperature be easy to control, can obtain fine particle, high reactivity powder; Reaction process does not need to continue heating simultaneously, and speed of response is fast, is a high-efficiency energy-saving technology; This is the essential distinction of this patent and above-mentioned publication.

Simultaneously, difference with self-propagating combustion synthetic (SHS) preparation high pure and ultra-fine beta-SiC in the present invention and the disclosed document is: first, the present invention directly carries out combustion synthesis reaction with powder raw material, and all is material powder to be pressed into block burn synthetic again in the disclosed paper of forefathers.Directly use the powder raw material cloth, not only simplified preparation technology, and effectively controlled exothermic heat of reaction, avoided the too high powder granule that causes of temperature of reaction sharply to grow up.The second, preceding is to be prepared reaction in the little reactor less than 10 liters per capita, and the weight of every batch of powder is less than 1 kilogram.The present invention has realized the preparation of high pure and ultra-fine powder first with SHS technology in the big reactor of 60 liters of pilot scale, every batch of powder weight is above 5 kilograms; Material phase analysis shows that the gained powder is simple β-SiC, no dephasign; Powder mean particle size 200 nanometers are worked as with the granulometric facies of preparation powder in the little reactor, show that amplifying preparation after product powder granule does not grow up.The success of this amplification preparation shows that can effectively control exothermic heat of reaction by the mode with the powder raw material cloth, high pure and ultra-fine beta-SiC is possible fully with the large-scale production of self-propagating combustion synthesis technique.

Embodiment

Embodiment below by the embodiment form, foregoing of the present invention is described in further detail again, but this should be interpreted as that following each embodiment is the restriction to the related scope of the above-mentioned theme of the present invention, all technology that realizes based on foregoing of the present invention all belong to scope of the present invention.

Embodiment 1

Carbon black and silica flour are made into 1: 1 mol ratio, add 2% tetrafluoroethylene then, with its mixing, ball milling is 15 hours in planetary ball mill, dries in air drying cabinet then, the powder behind institute's ball milling is placed the reactor of 10 liters.Charge into 8MPa nitrogen, place a small amount of titanium valve the reaction mixture end as priming mixture in advance, light titanium valve with the tungsten filament energising, titanium valve is swift in response and carries out once lighting, and until entire reaction still complete reaction, obtains high-purity beta-SiC.

Embodiment 2

Gac and silica flour are made into 2: 1 mol ratio, add 12% tetrafluoroethylene then, with its mixing, ball milling is 10 hours in planetary ball mill, dries in air drying cabinet then, and the powder behind institute's ball milling is placed 5 liter reactors.Charge into 0.5MPa nitrogen, place a small amount of titanium valve the reaction mixture end as priming mixture in advance, light titanium valve with the tungsten filament energising, titanium valve is swift in response and carries out once lighting, and until entire reaction still complete reaction, obtains high-purity beta-SiC.

Embodiment 3

Carbon black and silica flour are made into 0.3: 1 mol ratio, add 25% tetrafluoroethylene then, it was blended in the planetary ball mill ball milling 10 hours, in air drying cabinet, dry then, the powder behind institute's ball milling is placed 60 liter reactors.Charge into 3MPa nitrogen after vacuumizing, place a small amount of titanium valve the reaction mixture end as priming mixture in advance, light titanium valve with the tungsten filament energising, titanium valve is swift in response and carries out once lighting, and until entire reaction still complete reaction, obtains high-purity beta-SiC.

Claims (2)

1. one kind with the synthetic method for preparing high pure and ultra-fine beta-SiC powder of self-propagating combustion, and it is characterized in that: technology is:

A, with silica flour, carbon black or gac mix with the mol ratio 0.3-2 of C/Si, add the tetrafluoroethylene of massfraction 2-25% again;

B, be medium ball milling 10-15 hour with the dehydrated alcohol, 70～150 ℃ of oven dry in the air drying baker;

C, dried mixed powder is placed the combustion synthesis reaction device, reactor volume is the 5-60 liter; Charge into the nitrogen of 0.5～8MPa after reactor vacuumizes, place titanium valve the reaction mixture end as priming mixture in advance, the titanium valve consumption will cover tungsten filament, lights titanium valve with the tungsten filament energising, and the combustion reactions of initiation reaction mixture obtains product.

2. method according to claim 1 is characterized in that: raw mix is with the powder shaped cloth.