CN1334362A

CN1334362A - Self-spread high-temp synthesis process for preparing beta-silicon nitride whisker

Info

Publication number: CN1334362A
Application number: CN 01126400
Authority: CN
Inventors: 陈殿营; 张宝林; 庄汉锐; 李文兰
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2001-08-03
Filing date: 2001-08-03
Publication date: 2002-02-06
Anticipated expiration: 2021-08-03
Also published as: CN1157506C

Abstract

A process for preparing beta-Si3N4 whisker by high-temp self-spread synthesis includes mixing Si powder with alpha-Si3N4 powder in a ratio of (5-9):(1-5), adding whisker growing aid, loading in porous graphite crucible with inner surface coated with boron nitride, igniting the raw materials, and reaction in nitrogen atmosphere under 3-10 MPa for 2-10 min. Its advantages are 7-10 of length/diameter ratio, complete structure and smooth surface of crystal, no environmental pollution, and high yield (near 100%).

Description

The synthetic method for preparing the beta-silicon nitride whisker of self propagating high temperature

Technical field

The present invention relates to β-Si ₃N ₄The preparation method of whisker is particularly with self propagating high temperature synthetic (SHS) preparation β-Si ₃N ₄The method of whisker belongs to the ceramic powders preparation field.

Background technology

Stupalith is with series of advantages such as its hot strength are big, high temperature resistant, wear-resistant, anticorrosive, in light weight, successful application has been obtained in fields such as parts in aerospace, metallurgy, electronics, motor car engine, but the fragility of stupalith is an one deadly defect, just be easy to expansion in case crack, cause calamitous fracture.In order to improve the toughness of stupalith, investigators have done a large amount of work in this respect both at home and abroad, and particle dispersion is toughness reinforcing as adopting, transformation toughening, fiber or crystal whisker excess weld metal are toughness reinforcing.Wherein, the toughness reinforcing best results of crystal whisker excess weld metal.

β-Si ₃N ₄Whisker is a kind of strengthening and toughening agent of ceramic material of function admirable owing to have the combination of high strength, high-modulus, high dielectric property, high temperature resistant, good series of advantages such as chemical stability.

So far, β-Si ₃N ₄The preparation of whisker mainly is the method that adopts the long-time insulation of high temperature, such as " β-the Si of people's inventions such as Japanese Ruo Benzhuo looks ₃N ₄The preparation of whisker " (clear 63-222099), select non-crystalline silicon and silicon diimine, 1200 ℃ of-1700 ℃ of lower temperature-gradient methods, reach 16 hours N total time ₂Synthetic under the atmosphere." the β type Si of river, Japan Pu wise man Lang Faming ₃N ₄The preparation method of whisker " (clear 59-147000), be with SiO ₂+ C+ ice crystal is raw material, at N ₂And NH ₃Under the mixed atmosphere, 1250 ℃-1450 ℃ of temperature were reacted the β-Si of preparation 24 hours ₃N ₄Whisker Content is between 80～95wt%.

Although above two kinds of technologies can both prepare β-Si ₃N ₄Whisker, but common shortcoming is that the production cycle is long, needs simultaneously to consume the more energy.In addition, NH in the technology that adopted of river, Pu wise man youth ₃Use not only be harmful to the healthy of staff, and pollute whole Working environment.

Self propagating high temperature synthesis method (self-propagating high-temperature synthesis is called for short SHS) is put forward in first official in 1967 by USSR (Union of Soviet Socialist Republics) scientist Merzhanov, its main points are to utilize the energy of high thermopositive reaction that chemical reaction is continued automatically, thereby reach the purpose of synthetic materials.People have used the SHS method and have prepared multiple material and powder thereof at present, such as carbide TiC, ZrC, SiC, WC, and silicide MoSi ₂, TaSi ₂, ZrSi ₂, nitride TiN, BN, AlN, α-Si ₃N ₄, β-Si ₃N ₄Etc., but not yet have from spreading the standby β-Si of legal system ₃N ₄The report of whisker.

Summary of the invention

The objective of the invention is to utilize the synthetic advantage of self propagating high temperature provide a kind of easy, quick, energy-conservation, prepare β-Si efficiently ₃N ₄Whisker and method thereof.

Main implementation process of the present invention is:

(1) with silica flour and α-Si ₃N ₄Powder is the reaction initiation material, and both mixed proportions are 5～9: 1～5, α-Si ₃N ₄The α phase content of powder is 83wt%, and particle diameter is 0.3～30 μ m; Silica flour purity＞98wt%, particle size range is 0.5～50 μ m.Best proportioning is 1: 1 (weight ratio).

(2) the whisker growth auxiliary agent that adds is a kind of in the lanthanide rare earth oxide, such as Y ₂O ₃, La ₂O ₃, Gd ₂O ₃In a kind of, addition is silica flour and α-Si ₃N ₄0.5～10wt% of gross weight (preferentially recommended addition 2～5wt%) after powder mixed.

After mixing, the powder that (3) will be mixed with the whisker growth auxiliary agent do not need briquetting to be directly mounted loosely in the porous graphite crucible that inwall scribbles BN, place then high-pressure bottle, under the nitrogen pressure of 3～10Mpa, synthetic through energising igniting self propagating high temperature, generated time is 2～10 minutes, generally be no more than 5 minutes, synthetic β-Si ₃N ₄Whisker cools off with stove.The density of pine dress is 0.6～1.3g/cm ³

The present invention carries out similar in self propagating high temperature synthetic high pressure vessel and the general SHS method, need not particular requirement.Available reactant and the mixed uniformly crucible of whisker growth auxiliary agent deposited, inwall scribbles BN, at high temperature reacts to prevent reactant and graphite, its shape can be any, as square, cylindrical etc., but consider from economic angle, with cylindrical easy processing, cost is low and frequent use.

Obviously, the synthetic β-Si of self propagating high temperature provided by the invention ₃N ₄Whisker and existing β-Si ₃N ₄The preparation method of whisker compares, and has following advantage:

(1) energy consumption is low, except starting combustion synthesis reaction, does not need any energy;

(2) do not need special installation, generally get final product from spreading equipment, the container that bears 10MPa gets final product;

(3) easy to operate, output is big, productive rate is high, environmentally safe, be suitable for large-scale production, productive rate is near 100%, the whisker length of preparation is 3～25 μ m; diameter 0.5～3 μ m, length-to-diameter ratio is fit to reinforcement and uses greater than 5 or near 10; and crystalline structure is complete, the smooth surface zero defect.

Description of drawings

Fig. 1 is from spreading used crucible synoptic diagram.

Fig. 2 is the β-Si of embodiment 1 preparation ₃N ₄Whisker SEM photo (draw ratio～10).

Fig. 3 is the β-Si of embodiment 2 preparations ₃N ₄Whisker SEM photo (draw ratio～10).

Fig. 4 is the β-Si of embodiment 1 preparation ₃N ₄Whisker SEM photo (draw ratio～7).

Fig. 5-1 is the embodiment of the invention 1,2,3 corresponding β-Si ₃N ₄The XRD collection of illustrative plates of whisker.

Fig. 5-2 is the embodiment of the invention 1,2,3 corresponding β-Si ₃N ₄The XRD collection of illustrative plates of whisker.

Fig. 5-3 is the embodiment of the invention 1,2,3 corresponding β-Si ₃N ₄The XRD collection of illustrative plates of whisker.

Specific embodiment

Further illustrate characteristics of the present invention below by embodiment, but be not limited to embodiment.

Embodiment 1

With silica flour and α-Si ₃N ₄Powder mixes in 1: 1 ratio, adds then whisker growth auxiliary agent Y ₂O ₃, addition is Si powder and α-Si ₃N ₄The 5wt% of powder gross weight, the inwall that pine after the even mixing of powder is loaded on external diameter φ 60mm * internal diameter φ 55mm * high φ 60mm scribbles in the porous graphite crucible of boron nitride, and apparent density is 0.71g/cm ³, and place high-pressure bottle, be filled with 5MPa nitrogen (purity 99.9%) after vacuumizing, through the synthetic β-Si of energising igniting self propagating high temperature ₃N ₄Whisker, the reaction time is no more than 5 minutes, the synthetic rear nature cooling of adopting.

β-Si by above-mentioned technology preparation ₃N ₄The whisker productive rate is near 100%, and length is 10～20 μ m, diameter between 1～2 μ m, average aspect ratio～10, its crystal structure is complete, the smooth surface zero defect.As shown in Figure 2, its XRD figure spectrum is shown in Fig. 5-1.

Embodiment 2

With silica flour and α-Si ₃N ₄Powder mixes in 7: 3 ratio, adds then whisker growth auxiliary agent La ₂O ₃, addition is Si powder and α-Si ₃N ₄The 0.5wt% of powder gross weight, the inwall that pine after the even mixing of powder is loaded on external diameter φ 60mm * internal diameter φ 55mm * high φ 60mm scribbles in the porous graphite crucible of boron nitride, and apparent density is 0.70g/cm ³, and place high-pressure bottle, be filled with 5MPa nitrogen (purity 99.9%) after vacuumizing, through the synthetic β-Si of energising igniting self propagating high temperature ₃N ₄Whisker, the reaction time is no more than 8 minutes, the synthetic rear nature cooling of adopting.

β-Si by above-mentioned technology preparation ₃N ₄The whisker productive rate is near 100%, and length is 8～13 μ m, diameter between 0.7～1.5 μ m, average aspect ratio～10.Its crystalline structure is complete, the smooth surface zero defect.As shown in Figure 3, its XRD figure spectrum is shown in Fig. 5-2.

Embodiment 3-self propagating high temperature synthesizes β-Si ₃N ₄Whisker

With silica flour and α-Si ₃N ₄Powder mixes in 9: 5 ratio, adds then whisker growth auxiliary agent Gd ₂O ₃, addition is Si powder and α-Si ₃N ₄The 3wt% of powder gross weight, the inwall that pine after the even mixing of powder is loaded on external diameter φ 60mm * internal diameter φ 55mm * high φ 60mm scribbles in the porous graphite crucible of boron nitride, and apparent density is 0.68g/cm ³, and place high-pressure bottle, be filled with 5MPa nitrogen (purity 99.9%) after vacuumizing, through the igniting self-propagating combustion, through the synthetic β-Si of energising igniting self propagating high temperature ₃N ₄Whisker, the reaction time is no more than 5 minutes, the synthetic rear nature cooling of adopting.

β-Si by above-mentioned technology preparation ₃N ₄The whisker productive rate is near 100%, and length is 5～10 μ m, diameter between 1～1.5 μ m, complete, the smooth surface zero defect of its crystal structure of average aspect ratio～7..As shown in Figure 4, its XRD figure spectrum is shown in Fig. 5-3.

Claims

1. a self propagating high temperature synthesizes β-Si ₃N ₄The method of whisker comprises batching, mixing, pyroreaction, it is characterized in that:

(1) with α-Si ₃N ₄Be the reaction initiation material with silica flour, both mixed weight ratios are 1～5: 5～9;

(2) the whisker growth auxiliary agent that adds is a kind of in the lanthanide rare earth oxide, and addition is silica flour and α-Si ₃N ₄0.5～10wt% of gross weight after mixing;

Pine was loaded in the porous graphite crucible that inwall scribbles BN after the powder that (3) will be mixed with the whisker growth auxiliary agent evenly mixed, and placed then high-pressure bottle, under the nitrogen pressure of 3～10MPa, the energising igniting, self propagating high temperature is synthetic, and generated time is 2～10 minutes, synthetic β-Si ₃N ₄Whisker cools off with stove.

2. by the synthetic β-Si of the described self propagating high temperature of claim 1 ₃N ₄The preparation method of whisker is characterized in that described silica flour and α-Si ₃N ₄The optimum weight proportioning of powder is 1: 1.

3. by the synthetic β-Si of the described self propagating high temperature of claim 1 ₃N ₄The preparation method of whisker is characterized in that described lanthanide rare earth oxide Y ₂O ₃, La ₂O ₃, Gd ₂O ₃In a kind of, the preferential recommended amounts of adding is 2～5wt%.

4. by the synthetic β-Si of the described self propagating high temperature of claim 1 ₃N ₄The preparation method of whisker, it is characterized in that being mixed with the whisker growth auxiliary agent to mix the apparent density that the powder pine is contained in the graphite crucible be 0.6～1.3g/cm ³

5. by claim 1 or the synthetic β-Si of 2 described self propagating high temperatures ₃N ₄The preparation method of whisker is characterized in that described silica flour purity＞98wt%, and particle diameter is 0.5～50 μ m, α-Si ₃N ₄α phase content＞the 83wt% of powder, particle diameter are between 0.3～30 μ m.

6. by the synthetic β-Si of the described self propagating high temperature of claim 1 ₃N ₄The preparation method of whisker is characterized in that the β-Si for preparing ₃N ₄Whisker length is 3～25 μ m, diameter 0.5～3 μ m, draw ratio 7～10.

7. by the synthetic β-Si of the described self propagating high temperature of claim 1 ₃N ₄The preparation method of whisker is characterized in that described high temperature generated time generally is no more than 5 minutes.