CN1280955A

CN1280955A - Gas-phase synthesis process of superfine silicon nitride powder

Info

Publication number: CN1280955A
Application number: CN 99109605
Authority: CN
Inventors: 刘庆昌
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-06-30
Filing date: 1999-06-30
Publication date: 2001-01-24
Anticipated expiration: 2019-06-30
Also published as: CN1142089C

Abstract

A gas-phase synthesis process of superfine silicon nitride powder uses SiC14 and ammonia in ratio of 1:(1.5-1.9) as base materials and features that the gas-phase synthesis takes place in a sealed reactor with DC plasma arc as heat source. The resultant of reaction is quenched in settling procedure to directly become super fine powder. In the reactor by means of controlling the output power of plasma generator and the ratio of N2 and H2 to stabilize the ionic arc and keeping reaction temp. at 1000-1500 deg.C, the superfine powder is heated to remove impurities of chlorides to obtain high-purity nm-class Si3N4 powder.

Description

Gas-phase synthesis process of superfine silicon nitride powder

The invention belongs to a kind of gas-phase synthesis process of inorganic chemical industry nitride, specifically to the improvement of nitride micro mist manufacture craft.

Silicon nitride (Si ₃N ₄) ultra-fine micropowder is the desirable base-material of high-temperature structural ceramics, matrix material, heat exchange material and superhard cutter.Occupying consequence with its technical feature that can not be substituted in field of new, is the basic industry of developing high-tech industry, thereby is subjected to the generally attention of countries in the world.At present, the method for production high purity, superfine silicon nitride powder can be divided into three kinds theoretically: one is a hot reducing method, by SiO ₂Mix to place with excessive carbon dust and fill N ₂Be heated to 1400 ℃ in the environment, reduction SiO ₂Generate Si ₃N ₄At SiO ₂-C-N ₂One critical temperature (1450 ℃) is arranged under the hybird environment.If temperature control is unstable, can produce SiC is not Si ₃N ₄So, need add small amount of Fe aborning ₂O ₃The disinthibite generation of SiC utilizes hydrochloric acid to remove ferruginous compound again after the reaction.This method often contains a spot of SiO ₂Or the impurity of other form, its high purity is greatly affected.Two, silicon powder nitride method: with the silica flour of the following granularity of 10 μ m at N ₂In be heated to 1200 ℃-1450 ℃, the directly synthetic Si that obtains ₃N ₄Agglomerate grinds the Si that obtains about 1 μ m through pulverizing ₃N ₄Powder.The processing method of this mechanical type refinement fundamentally can't guarantee the refinement and the consistence of its micro mist, and the hard aggregation phenomenon is inevitable, and it is higher directly to use the cost cost of silica flour, and quality-guarantee is unstable, produces in enormous quantities to have suitable difficulty.It three is gas phase synthesis methods: with gaseous state SiCl ₄And NH ₃Under 1350 ℃-1450 ℃, synthesize amorphous Si ₃N ₄Transform into Si through aftertreatment again ₃N ₄, but wherein closing contains the Cl ionic impurity more, uses the induced with laser method at present and comes investment of production equipment too big, and the cost height is unsuitable for suitability for industrialized production.Use the low excessively economic scale that can not form of other heat-source energy utilization ratio instead.Object height is pure though it is produced, and high refinement is far superior to other method, only does systems simulation under laboratory scale in practice and fails to realize the industrial experiment of mass-producing.

The objective of the invention is to find out a Si who is applicable to suitability for industrialized production ₃N ₄Novel process, make it not only can guarantee high thin, high-purity technical requirements, and want facility investment little, processing ease, with low cost, be easy to make Si ₃N ₄Product have the rational ratio of performance to price and start its application market.

The starting point of the present invention is the improvement to gas phase synthesis method technology, and its key point is that choosing plasma body in the gas phase synthesis technique is thermal source, gas phase is synthesized in the reactor that is provided with plasma arc of sealing finish.Concrete technical process is to be based upon on the theoretical basis of plasma chemical industry, and the major technology target is to guarantee Si under the high purity ₃N ₄Specific surface area.Use the advantage of gas phase synthesis method exactly to be to utilize the gas phase synthesising reacting speed fast and evenly, if controlled temperature and reaction times just can obtain the building-up process of high quality and less energy-consumption exactly.Under the common energy, can't realize, though synthetic can the realization under the laser, but uncontrollable cost, have only the plasma arc of utilization just might realize the temperature precise control for thermal source, rate of heating is fast, special process environments such as reaction zone internal and external temperature gradient is big, to be subjected to the big restraining effect of reaction zone internal and external temperature gradient difference obvious for the synthetics grain growth when realizing that resultant velocity is fast, and thermosteresis is little.Thereby to select plasma arc to be that the thermal reactor of thermal source does be key of the present invention.The synthetic phase feed is injected in the thermal reactor exactly, controlled well proper technical conditions, promptly the building-up reactions of dozens of minutes in the technical process at ordinary times even several hours can be finished in second in some thousandths of, finish synthetic Si ₃N ₄Automatically breaking away from the ion arc by the guiding of the air-flow in gravity and the reactor is the thermal reaction area freedom of entry sedimentation quenching refinement at center.Follow-up gas-phase reaction material constantly replenishes into reaction zone, the or else disconnected introducing of resultant negative area quenching is collected, thereby form the technological process that a serialization is produced, the equipment that this technology adopted can design with reference to the direct current-arc plasma thermal reactor, this equipment is by applicant's formal application national patent, application number: 99205853.8, name is called: plasma method is produced the reactor of ultra-fine micropowder, the related master operation of this technology all can be finished in this equipment, and concrete technical process and control condition are as follows:

A, nitrogenizing reaction device environment: keep forming negative pressure in the reactor, negative pressure value is the 50-110cm water column, mainly is to form negative pressure, nitrogen environment, gets rid of the foreign gas of reactor, carries out environmental preparation for purifying reaction, guarantees synthetics purity.

The evaporation of b, liquid raw material and quantitatively transmission: with liquid silicon tetrachloride and NH ₃By weight 1: 1.5-1.9, insert respectively in the vaporizer, be converted into gaseous state and inject synchronously in the plasma reactor, because NH by weight the throughput ratio that transforms ₃Boiling point lower, can finish under the normal temperature gasification thereby NH ₃Need not special evaporator unit, SiCl ₄Boiling point be higher than liquefied ammonia for guaranteeing SiCl ₄Can the temperature in the vaporizer must be transferred to 110 ℃-135 ℃ to set flow steady input reactor, pressure is 0.4MPa-0.5MPa.

C, to finish silicon nitride under design temperature synthetic: the setting of temperature is one of key of this Technology with adjusting, Si ₃N ₄Synthesis temperature between 1000 ℃-1500 ℃, often kind and the purity according to raw material has bigger difference, when using liquid Si Cl ₄Synthesis temperature is higher during raw material, can be on the low side when using chlorosilane, add in the raw material effective ingredient and change and can directly influence synthesis temperature, this often batch materials must test next strictly determined parameter by pre-production after entering factory.The conciliation of temperature and setting can be obtained by the variation of following processing parameter: regulate the output rating of plasma arc generator, and fit adjustment stabilising arc gas N ₂And H ₂Drainage flow ratio in the input reactor.N ₂And H ₂The input flow rate ratio is: 1: between the 2.8-3.5.

D, the resultant quenching refinement after synthetic: directly formation is solid-state through quenching for the synthetic resultant down of gas phase, not only can reduce energy expenditure, and prevent to generate the increase of article grain, the fine structure of formation superfineization.For effectively resultant being introduced settling pocket, can make part N ₂Gas is introduced from reactor head and is formed the trend that the local malleation of reactor upper container impels logistics formation to move down, and finishes the purpose that drainage enters the quenching settling vessel smoothly with combining from resedimentation of resultant.In order to guarantee the technological effect of quenching, utilize the forced water cooling circulation in the sedimentation wall outside sandwich, make and form the ideal thermograde in the settling vessel, this gradient serves as with reference to 1/4th seconds temperature of every free setting 0.8-1.2 standard(thermodynamic)scale that should descend with the free setting process.Quenching processing through this gradient can make resultant reach nano level fine structure, and is very good.For guaranteeing normal technical process, the N that introduces from the top ₂Airshed should the 20-60 liter/minute between.The bottom-up liter of water coolant is squeezed into high pressure, and water pressure is as the criterion with the thermograde that can realize processing requirement and suitably regulates.

E, cloth bag collect, and the cloth bag collection device is located at below the settling vessel, the Si that will cooling descends ₃N ₄Collect.

F, heating aftertreatment: owing to contain intermediate product impurity NH in the resultant ₄Cl or hydrogenchloride place 380-450 ℃ of vacuum drying oven internal heating with collecting good trickle powder, at N ₂Kept under the atmosphere 2-3 hour, and can effectively chloride impurity be separated and remove the NH of discharge ₄Cl can recycle becomes subsidiary products.

How to realize for further specifying process characteristic of the present invention and goal of the invention thereof, and provide following

Embodiment:

Embodiment 1:

Reactor negative pressure 60cm water column, plasma power 55KW, SiCl ₄Flow 240g/min, NH ₃Flow 152g/min, H ₂196 liters/min of flow, N ₂10 liters/min of flow.

Embodiment 2:

Reactor negative pressure 80cm water column, plasma generator power 70KW, SiCl ₄Flow 292g/min, NH ₃Flow 198g/min, H ₂280 liters/min of flow, N ₂90 liters/min of flow.

Embodiment 3:

Reactor negative pressure 100em water column, plasma generator power 85KW, SiCl ₄Flow 360g/min, NH ₃Flow 230g/min, H ₂Flow 1/min, N ₂Flow 1001/min.

The Si that produces according to above technology ₃N ₄Purity can be greater than 96%, contents of free si＜0.3%, and total oxygen content＜1.5%, mean particle size 50-100nm, specific surface area is greater than 30m ²/ g, and the overall cost cost has had tangible commercial value.And facility investment is little, and technology is simple, and is easy to operate, energy low consumption, and the breakthrough on the special technical indicator lays a solid foundation for nano-grade silicon nitride enters the practical stage.

Claims

1, gas-phase synthesis process of superfine silicon nitride powder, taking silicon tetrachloride and liquefied ammonia in the technology is basic raw material, it is synthetic to finish gas phase at the encloses container internal heating, obtains high purity Si through thermal treatment again ₃N ₄Crystalline flour.It is characterized in that this synthesis procedure is to finish in the sealed reactor that is thermal source with the plasma arc, concrete technical process is as follows:

A, nitrogenizing reaction device environment, keeping the reactor negative pressure is the 50-110cm water column,

The evaporation of b, liquid raw material and quantitatively transmission are with liquid NH ₃With silicon tetrachloride by weight 1: 1.5-1.9, insert in the vaporizer respectively.Be converted into gaseous state and inject plasma reactor synchronously by weight the throughput ratio that transforms,

C, to finish silicon nitride under design temperature synthetic, and setting synthesis temperature is between 1000 ℃-1500 ℃,

D, the refinement of resultant quenching: resultant of reaction is introduced the quenching settling vessel, and the envrionment temperature gradient is 0.5-1.2 standard(thermodynamic)scale of every free setting temperature decline in 1/4th seconds in the settling vessel,

E, cloth bag are collected,

F, heating aftertreatment, are kept and were removed the muriate of temperature in product in 2-3 hour to 300-450 ℃ at the vacuum drying oven internal heating.

2, according to the said gas-phase synthesis process of claim 1, it is characterized in that liquid Si Cl ₄Gasification condition be 110 ℃-135 ℃, pressure keeps 0.4MPa-0.5MPa.

3,, it is characterized in that synthetic Si according to the said gas-phase synthesis process of claim 1 ₃N ₄The time the temperature adjustment by means of the power and the stabilising arc gas N of plasma arc generator output ₂, H ₂The flow proportional of input reactor is finished.

4, according to the said gas-phase synthesis process of claim 3, it is characterized in that N ₂: H ₂The input flow rate ratio is 1: 2.8-1: 3.5.

5, according to the said gas-phase synthesis process of claim 1, it is characterized in that N by the reactor head drainage ₂Resultant is introduced the quenching settling vessel.

6, according to the said gas-phase synthesis process of claim 5, it is characterized in that from the N of top drainage ₂Flow control the 20-60 liter/minute.

7,, it is characterized in that the thermograde in the settling vessel realizes by means of from bottom to top cycle of higher pressure water-cooled in double sandwich sedimentation wall according to the said gas-phase synthesis process of claim 1.