CN1433959A

CN1433959A - Process for combustion synthesizing high alpha phase superfine silicon carbide powder and silicon nitride whisker

Info

Publication number: CN1433959A
Application number: CN 02100195
Authority: CN
Inventors: 葛昌纯; 曹永革
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2002-01-22
Filing date: 2002-01-22
Publication date: 2003-08-06
Anticipated expiration: 2022-01-22
Also published as: CN1209281C

Abstract

The present invention provides a SHS process for preparing high alpha-phase Si3N4 powder and Si3N4 whiskers. For preparation of high alpha-phase powder the additive alpha-Si3N4 content is 10-100 wt% of silicon powder, NH4F+NH4Cl+CaF2 content is 1-60 wt% of silicon powder content, the nitrogen gas pressure for retaining SHS reaction is 1-30 MPa, the specific surface area of the obtained ultrafine Si3N4 powder body is in the range of 2-6 sq.m/g, and its equivalent grain size of adjustable in the range of 0.3-0.9 micrometer. For preparation of Si3N4 whiskers beta-Si3N4 whisker reactant component is Si powder, beta-Si3N4 powder is 5-15 wt% of silicon powder content, NH4Cl is 1-60 wt% of silicon powder content and analytically pure Al powder is 0.5-5 wt% of silicon powder content.

Description

Method with combustion synthesizing high alpha phase superfine beta-silicon nitride powder and silicon nitride crystal whisker

The present invention relates to a class by the ultra-fine Si of high α phase content of synthetic (self-propagatinghigh-temperaturesynthesis, SHS) method preparation of self propagating high temperature ₃N ₄Powder and α-Si ₃N ₄Whisker and β-Si ₃N ₄Whisker.

Since The former Russian scholar A.G.Merzhanov in 1967 and I.P.Borovinskaya found the SHS phenomenon, SHS was one of most active research direction in Materials Science and Engineering field always.Its basic characteristics 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 chemical reaction forward position (being combustion wave), after this chemical reaction is under self exothermic support, continue to move ahead, show as combustion wave and spread whole reaction system, last synthetic materials.The most outstanding advantage of SHS synthesis technique be save energy, with low cost, synthetics purity is high.So adopt the product of SHS explained hereafter to develop into more than 500 kinds so far.But mainly by solid-solid reaction, its reaction mechanism is fairly simple for these products, and the technology ratio is easier to control.And the burning of gas-solid system is synthetic, and particularly the burning of nitrogen-silicon system is synthetic, reacts under condition of high voltage by gas phase N ₂Reaction is carried out with solid phase Si, and intrapore gas is not enough can to carry out fully in the impact reaction, and the thawing of solid phase can hinder the infiltration of gas.Its reaction mechanism is more complicated, and technology is restive, is difficult to especially obtain the ultra-fine Si of high α phase content ₃N ₄Powder.

Silicon nitride is a kind of non-oxidized substance mineral of synthetic.Because silicon nitride has characteristics such as proportion is low, thermal expansion is little, hardness is big, Young's modulus is high, good heat resistance, its mechanical property and thermal property obviously are better than general oxide ceramics.Can produce various performance requriementss by technologies such as reaction sintering, hot pressed sintering, pressureless sintering and heavy sintering, difform silicon nitride ceramics and nitride silicon based complex phase ceramic goods, silicon nitride ceramics and nitride silicon based complex phase ceramic goods have become a kind of important heat-resisting, high-strength, wear-resisting, corrosion resistant engineering ceramic material.

Relate to the ultra-fine Si of combustion synthesizing high alpha phase content ₃N ₄The international monopoly of powder has SHS inventor A.G.Merzhanov academician at " preparation method of high α phase content silicon nitride " (the US Patent5032370) by name of various countries applications, is CN1017609B in the patent No. of China.But the synthetic sample weight of this patent is very little, is not suitable for the large dimension specimen large-scale production, can not be used for the ultra-fine Si of high α phase content ₃N ₄The production of powder.The United States Patent (USP) of U.S. Holt J.Birch etc. is " with the synthetic thin brilliant α-Si of burning synthesis method ₃N ₄(US4944930).This patent adopts the alkali-metal thing that iterates as nitrogenous source, and the basic metal of synthetics influences high-temperature behavior.These patents all only relate to powder, do not relate to Si ₃N ₄Whisker.

Summary of the invention:

The present invention solves and uses the raw material identical with prior art, adopts the simplest technology and equipment, the step that simplifies the operation, and preparation α phase content is greater than the Si of 90wt% ₃N ₄Ceramic powder, α-Si ₃N ₄Whisker and β-Si ₃N ₄Whisker.Its technical process is as follows:

(1) powder is by specifying the proportioning preparation, (2) ball milling 6 hours in the alcohol medium, and the oven dry of (3) powder is crossed 100 mesh sieves and (4) the powder combustion chamber of packing into is lighted.

Of the present invention theing contents are as follows:

For high α phase Si ₃N ₄The preparation of powder, additive α-Si ₃N ₄Content is the 10-100wt% of silica flour content, NH ₄F+NH ₄Cl+CaF ₂Content be the 1-60wt% of silica flour content, wt% is weight percentage, and keeps the nitrogen pressure 1--30MPa of SHS reaction; Prepared ultra-fine Si ₃N ₄Powder by adjustment diluent addition and proportioning, and is adjusted synthetic technological condition, Si ₃N ₄The powder specific surface is at 2-6m ²In/g the scope, equivalent grain size is adjustable in the 0.3-0.9 mu m range.

For Si ₃N ₄The preparation of whisker, β-Si ₃N ₄Whisker reactant composition is the Si powder, β-Si ₃N ₄Powder is the 5-15wt% of silica flour content, the NH of the 1-60wt% of silica flour content ₄The pure Al powder of the analysis of the 0.5-5wt% of Cl and silica flour content; α-Si ₃N ₄The reactant composition of whisker should be Si powder, α-Si ₃N ₄Powder is the NH of the 1-60wt% of the 5-15wt% of silica flour content and silica flour content ₄F, the nitrogen pressure of reaction is answered 5--20MPa.

The present invention synthesizes high α phase Si ₃N ₄Powder and Si ₃N ₄The method of whisker, the method that has adopted multicomponent reactive diluent and inert additwe to combine by addition and the synthetic technological condition of the various diluents of strict control, has made α up to 93% ultra-fine Si ₃N ₄Powder, its specific surface is at 2-6m ²In/g the scope, equivalent grain size is adjustable in the 0.3-0.9 mu m range.

Synthesize Si by further investigation with the SHS technology ₃N ₄Mechanism and control technological parameter, synthetic SHSSi ₃N ₄, they have different leading phases and the α-Si of pattern ₃N ₄Powder, α-Si ₃N ₄Whisker and β-Si ₃N ₄Whisker is to satisfy different purposes and needs.

Basic parameter: recovery rate, powder at least 95%, whisker at least 60%; Powder particle size is 0.3-0.9 μ m, and specific surface is 2-6m ²/ g; β-Si ₃N ₄Whisker, diameter 1-3 μ m, long 100-1000 μ m; α-Si ₃N ₄Whisker, diameter 0.3-1.2 μ m, long 110-150 μ m.

Ultimate principle of the present invention is summarized as follows:

Be difficult to form combustion wave after the Si powder is lighted and spread in high pressure nitrogen, and can only form on the biscuit top layer the thick grey black Si of the about 1-2mm of one deck ₃N ₄Layer, and the centre accompanies a large amount of Si beads.This is because the melting of a large amount of Si is reunited, and has hindered N ₂Thereby the infiltration to reaction front causes " stopping working ".This is a kind of Lock-in " quenching " phenomenon.Reunite for the fusion of avoiding Si, improve the α phase content in the reaction product silicon nitride, promote the crystalline growth, in silica flour, sneak into a certain amount of α-Si ₃N ₄, NH ₄F+NH ₄Cl+CaF ₂, respectively as reactive thinner and inert diluent.α-Si wherein ₃N ₄Content is the 10-100wt% of silica flour content, NH ₄F+NH ₄Cl+CaF ₂Content be the 1-60wt% of silica flour content.The nitrogen pressure of reaction should be greater than 1MPa.

Synthetic β-Si ₃N ₄The reactant composition of whisker should be Si powder, β-Si ₃N ₄Powder is the 5-15wt% of silica flour content, the NH of the 1-60wt% of silica flour content ₄The pure Al powder of the analysis of the 0.5-5wt% of Cl and silica flour content.Synthetic α-Si ₃N ₄The reactant composition of whisker should be Si powder, α-Si ₃N ₄Powder is the NH of the 5-10wt% of the 5-15wt% of silica flour content and silica flour content ₄F.The nitrogen pressure of reaction should be greater than 5MPa, the α-Si that makes ₃N ₄The whisker long axis direction is [001].

Description of drawings:

Fig. 1 is SHS of the present invention reaction chamber structural representation, ignition wire 1, reactant base substrate 2, thermometric thermopair 3, sample table 4.

Embodiment:

The pure silicon nitride of the synthetic high α phase of example 1:SHS

It is as follows to test used powder property: the Si powder, and the mass percent of impurities (down together) is: Fe (1.02), Al (＜0.01), Ca (＜0.01), Mg (＜0.01), O (0.1), granularity is 5～25 μ m.Si ₃N ₄Powder, α phase content＞93%, free Si＜0.5%, N (36.5), O (2.2), Mg (0.01), Ca (0.02), Al (＜0.005), Fe (0.012).NH ₄F, analytical pure, NH ₄F＞99.5%, SO ₄(0.005), PO ₄(0.0005), K (0.005), Na (0.005), Ca (0.001), Mg (0.001), Fe (0.0005), water-insoluble (0.005).NH ₄Cl, same NH ₄F.CaF ₂, analytical pure, CaF ₂Be no less than 98.0%, weight loss on drying (0.4%), Cl (0.01), SO ₄(0.05), N (0.005), Si (0.01), Fe (0.003), Pb (0.003).

When reactant ratio as follows: Si powder 69wt%, Si ₃N ₄Powder 20wt%, NH ₄F and NH ₄Cl is 5wt%, CaF ₂Be 1wt%.Under the 5MPa nitrogen pressure, light prepared Si ₃N ₄Powder α is up to 91%, and its specific surface is 3-6m ²/ g, equivalent grain size is 0.3-0.7 μ m.

When reactant ratio as follows: Si powder 73.4wt%, Si ₃N ₄Powder 20wt%, NH ₄F and NH ₄Cl is 3wt%, CaF ₂Be 0.6wt%.Under the 5MPa nitrogen pressure, light prepared Si ₃N ₄Powder α is up to 88%, and its specific surface is 3-6m ²/ g, equivalent grain size is 0.3-0.7 μ m.

Synthetic α-the Si of example 2:SHS ₃N ₄Whisker

Synthetic α-Si ₃N ₄The used powder of whisker is with the pure silicon nitride of synthetic high α phase.

When reactant ratio as follows: Si powder 86wt%, α-Si ₃N ₄Powder 8wt%, NH ₄F is 6wt%.Under the 7MPa nitrogen pressure, light prepared α-Si ₃N ₄The long 30-150 μ of whisker m, diameter 0.3-1.0 μ m, draw ratio 30-500.

Synthetic β-the Si of example 3:SHS ₃N ₄Whisker

Synthetic β-Si ₃N ₄Si powder and NH that whisker is used ₄Cl is with the powder of the pure silicon nitride of synthetic high α phase.β-Si ₃N ₄Powder, free Si＜0.5%, N (36.5), O (2.2), Mg (0.01), Ca (0.02), Al (＜0.005), Fe (0.012), the Al powder is pure for analyzing, Al＞99.5%.

When reactant ratio as follows: Si powder 87wt%, β-Si ₃N ₄Powder 10wt%, NH ₄F is 2wt%.Under the 7MPa nitrogen pressure, light prepared β-Si ₃N ₄Diameter of whiskers 1-3 μ m, long 300-1000 μ m.

Claims

1, a kind of from spreading synthetic high α phase Si ₃N ₄Powder and Si ₃N ₄The method of whisker is characterized in that: for high α phase Si ₃N ₄The preparation of powder, additive α-Si ₃N ₄Content is the 10-100wt% of silica flour content, additive NH ₄F+NH ₄Cl+CaF ₂Content be the 1-60wt% of silica flour content, wt% is weight percentage, and adjusts in the nitrogen pressure 1--30MPa scope of SHS reaction; Prepared ultra-fine Si ₃N ₄Powder is by adjusting additive addition and proportioning, Si ₃N ₄The powder specific surface is at 2-6m ²In/g the scope, equivalent grain size is in the 0.3-0.9 mu m range.

2, a kind of preparation method such as right 1 is characterized in that: for Si ₃N ₄The preparation of whisker, β-Si ₃N ₄Whisker reactant composition is the Si powder, β-Si ₃N ₄Powder is the 5-15wt% of silica flour content, the NH of the 1-60wt% of silica flour content ₄The pure Al powder of the analysis of the 0.5-5wt% of Cl and silica flour content; α-Si ₃N ₄The reactant composition of whisker should be Si powder, α-Si ₃N ₄Powder is the NH of the 1-60wt% of the 5-15wt% of silica flour content and silica flour content ₄F, the nitrogen pressure of reaction is answered 5--20MPa.