CN103242044B - Gel-casting preparation method of BN/Si3N4 composite ceramics - Google Patents
Gel-casting preparation method of BN/Si3N4 composite ceramics Download PDFInfo
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- 239000000919 ceramic Substances 0.000 title claims abstract description 88
- 239000002131 composite material Substances 0.000 title claims abstract description 60
- 238000005266 casting Methods 0.000 title claims abstract description 29
- 238000002360 preparation method Methods 0.000 title claims abstract description 28
- 229910052581 Si3N4 Inorganic materials 0.000 title abstract description 7
- 239000000843 powder Substances 0.000 claims abstract description 101
- 239000002002 slurry Substances 0.000 claims abstract description 40
- 238000005245 sintering Methods 0.000 claims abstract description 31
- 238000001746 injection moulding Methods 0.000 claims abstract description 13
- 239000007787 solid Substances 0.000 claims abstract description 13
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- 238000001035 drying Methods 0.000 claims abstract description 7
- 238000002156 mixing Methods 0.000 claims abstract description 3
- JEIPFZHSYJVQDO-UHFFFAOYSA-N ferric oxide Chemical compound O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 31
- 239000003795 chemical substances by application Substances 0.000 claims description 24
- 239000007788 liquid Substances 0.000 claims description 20
- 239000000463 material Substances 0.000 claims description 20
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- 238000000034 method Methods 0.000 claims description 15
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- 239000000203 mixture Substances 0.000 claims description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 13
- 239000000080 wetting agent Substances 0.000 claims description 12
- 239000008367 deionised water Substances 0.000 claims description 11
- 229910021641 deionized water Inorganic materials 0.000 claims description 11
- 238000001354 calcination Methods 0.000 claims description 8
- 150000003839 salts Chemical class 0.000 claims description 8
- 239000000725 suspension Substances 0.000 claims description 8
- 238000000498 ball milling Methods 0.000 claims description 7
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 6
- 238000009413 insulation Methods 0.000 claims description 6
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 5
- 238000007873 sieving Methods 0.000 claims description 5
- 238000003756 stirring Methods 0.000 claims description 5
- 239000011248 coating agent Substances 0.000 claims description 4
- 238000000576 coating method Methods 0.000 claims description 4
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- 230000001681 protective effect Effects 0.000 claims description 4
- 238000004062 sedimentation Methods 0.000 claims description 4
- 238000002791 soaking Methods 0.000 claims description 4
- HRPVXLWXLXDGHG-UHFFFAOYSA-N Acrylamide Chemical group NC(=O)C=C HRPVXLWXLXDGHG-UHFFFAOYSA-N 0.000 claims description 2
- 239000004160 Ammonium persulphate Substances 0.000 claims description 2
- 101100493705 Caenorhabditis elegans bath-36 gene Proteins 0.000 claims description 2
- 229920002125 Sokalan® Polymers 0.000 claims description 2
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 2
- ROOXNKNUYICQNP-UHFFFAOYSA-N ammonium persulfate Chemical compound [NH4+].[NH4+].[O-]S(=O)(=O)OOS([O-])(=O)=O ROOXNKNUYICQNP-UHFFFAOYSA-N 0.000 claims description 2
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- ZIUHHBKFKCYYJD-UHFFFAOYSA-N n,n'-methylenebisacrylamide Chemical group C=CC(=O)NCNC(=O)C=C ZIUHHBKFKCYYJD-UHFFFAOYSA-N 0.000 claims description 2
- -1 poly(oxyethylene glycol) Polymers 0.000 claims description 2
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Abstract
The invention relates to a gel-casting preparation method of BN/Si3N4 composite ceramics and aims at solving the problems that when the exiting BN/Si3N4 composite ceramics is subjected to gel casting, the solid content of slurry is low, and homogeneous dispersion of BN in a Si3N4 matrix is difficultly realized during gel casting. The preparation method comprises the steps of: 1, preparing a BN coated powder; 2, preparing a hybrid ceramic powder; 3, preparing the slurry; 4, adding an initiator and a catalyst into the slurry, mixing and carrying out injection molding to obtain a cured ceramic wet green body, and then drying the cured ceramic wet green body to obtain a dried green body; and 5, carrying out degreasing treatment on the dried green body in an air furnace, and then sintering the dried green body after degreasing treatment to obtain the BN/Si3N4 composite ceramics. The gel-casting preparation method is applied to the field of ceramic materials.
Description
Technical field
The present invention relates to a kind of gel casting forming preparation method of BN/Si3N4 complex phase ceramic.
Background technology
Silicon nitride (Si
3n
4) stupalith has high atom bonding strength, is one of best stupalith of over-all properties.It not only has excellent mechanical property and high thermostability (decomposition temperature is over 1900 ℃), and can regulate and control density by the control of porosity, and specific inductivity is adjustable (2～7).Its dielectric properties are very stable within the scope of room temperature to 1000 ℃, and thermal shock resistance is excellent, are very suitable for flight Mach number and are the manufacture of 6～7 high-speed flight guided missile broadband wave transparent radome.In addition, by Si
3n
4the prepared BN/Si of introducing portion BN in pottery
3n
4composite ceramics can be in conjunction with Si
3n
4the high-mechanical property of pottery and the low-k of BN pottery and the advantage such as can process, and composite ceramics can show fabulous chemical stability, high thermal shock resistance and very in wide temperature range, have lower and stable specific inductivity and dielectric loss.Thereby, BN/Si
3n
4composite ceramics has become at present one of most potential broadband wave transparent candidate material in the world.But, due to Si
3n
4and the low reliability of composite ceramics and expensive tooling cost have limited the application process of its mass-producing.
Colloidal formation technology not only can be used for near-net-shape complicated shape ceramic green, reduce ceramic component subsequent machining cost, and can also be used to reduce or eliminate the reunion of the ceramic particle in material, macroscopical pore, defects i.e.cracks, and then promote reliability of material.Gel casting forming is a forming technique that has potentiality in colloidal formation technology, and it can prepare the uniform high-strength ceramic green compact of microstructure, can to framework, carry out mechanical preprocessing in green article stage.
Prepare high solid loading, low viscous slurry is the prerequisite of gel injection molding and forming technology, but and obtained the gel casting forming of the oxide ceramics of extensive application, Si
3n
4the gel casting forming suitability of pottery is poor, particularly introduces BN and prepares BN/Si
3n
4during composite ceramics, adding of BN makes the rapid variation of slurry fluidity.This is mainly because nitride powder easily produces some organo-functional groups in surface in process of production, the cause of the alkalimetal ion of easy lingering section facile hydrolysis in powder.Thereby have to realize BN/Si by reducing the method for slurry solid load
3n
4the gel casting forming preparation technology of composite ceramics, but during slurry solid load step-down, cause wet base shrinking percentage in drying process to increase, easily produce warpage, be unfavorable for realizing the near-net-shape of member.
In addition, at preparation BN/Si
3n
4during composite ceramics, because BN is at Si
3n
4in more difficult dispersion, prepared material is difficult to realize uniform heterogeneous microstructure, and the existence of BN also can hinder the mass transfer in liquid phase process in liquid sintering process, is unfavorable for densification and the α-Si of material
3n
4to β-Si
3n
4phase transition, thereby can cause very macrolesion to the mechanical property of material.
Summary of the invention
The present invention will solve present BN/Si
3n
4during the gel casting forming of complex phase ceramic, the low and BN of slurry solid load is at Si
3n
4more difficultly in matrix realize homodisperse problem, a kind of BN/Si is provided
3n
4the gel casting forming preparation method of complex phase ceramic.
A kind of BN/Si of the present invention
3n
4the gel casting forming preparation method of complex phase ceramic, realizes according to the following steps:
One, adopt inorganic salt sedimentation to prepare Y/Al salt coating at BN powder surface, after calcining, sieving, obtain BN coated composite powder;
Two, by volume umber takes Si
3n
4, BN coated composite powder and sintering aid, obtain hybrid ceramic powder; Si wherein
3n
4volume parts be greater than 60 parts and be less than 100 parts, the volume parts of BN coated composite powder is greater than 0 part and is less than 40 parts, the volume parts of sintering aid is greater than 5 parts and is less than 10 parts;
Three, in deionized water, add organic monomer, linking agent, wetting agent and dispersion agent, obtain premixed liquid, then with quality percentage composition, be that 28% ammoniacal liquor and quality percentage composition are pH value to 9～11 that 10% hydrochloric acid regulates premixed liquid, add again hybrid ceramic powder, then ball milling mixes, and obtains slurry; Wherein in slurry, the solid load of ceramic powder is 35～45vol.%; The add-on of organic monomer is 3～8wt.% of ceramic powder total mass, the add-on of dispersion agent is 0.2～0.6wt.% of ceramic powder total mass, the add-on of wetting agent is 2～6wt.% of ceramic powder total mass, and the mass ratio of organic monomer and linking agent is (5～15): 1;
Four, in the slurry obtaining in step 3, add initiator and catalyzer, after stirring, carry out injection molding, obtain curing ceramic wet blank, be then dried, obtain dried green compact;
Five, dried green compact are carried out in air furnace to skimming treatment, then carry out sintering, obtain BN/Si
3n
4complex phase ceramic, completes BN/Si
3n
4the gel casting forming preparation of complex phase ceramic.
The present invention introduces BN by the form with BN coated powder, and can realize solid load is 44vol.%, and the BN/Si of the very applicable gel injection molding and forming technology of viscosity
3n
4the preparation of composite mortar, has solved gel injection molding and forming technology and has prepared BN/Si
3n
4during composite ceramics, the introducing of BN causes the problem of the rapid variation of slurry viscosity; And by BN, with the form of coated powder, introduce, realized dispersed in slurry of BN, solved BN at Si
3n
4more difficultly in matrix realize homodisperse problem, finally prepare the uniform BN/Si of heterogeneous microstructure
3n
4composite ceramics, and material has excellent mechanical property and lower specific inductivity, can be used as carrying, wave transparent, thermally protective materials under severe condition, for fields such as aerospace, mechanical industries.
Accompanying drawing explanation
The shear viscosity that Fig. 1 is slurry in test 1 control group is with the variation relation of shearing rate;
for the add-on of the original powder of BN prepared slurry when by volume umber is 5 parts;
for the add-on of the original powder of BN prepared slurry when by volume umber is 10 parts;
for the add-on of the original powder of BN prepared slurry when by volume umber is 15 parts;
for the add-on of the original powder of BN prepared slurry when by volume umber is 20 parts;
Fig. 2 is the projection light field phase photo of BN coated composite powder in test 1 test group;
The shear viscosity that Fig. 3 is slurry in test 12 test group is with the variation relation of shearing rate;
for the add-on of BN coated composite powder prepared slurry when by volume umber is 5 parts;
for the add-on of BN coated composite powder prepared slurry when by volume umber is 10 parts;
for the add-on of BN coated composite powder prepared slurry when by volume umber is 15 parts;
for the add-on of BN coated composite powder prepared slurry when by volume umber is 20 parts.
Embodiment
Embodiment one: a kind of BN/Si of present embodiment
3n
4the gel casting forming preparation method of complex phase ceramic, realizes according to the following steps:
One, adopt inorganic salt sedimentation to prepare Y/Al salt coating at BN powder surface, after calcining, sieving, obtain BN coated composite powder;
Two, by volume umber takes Si
3n
4, BN coated composite powder and sintering aid, obtain hybrid ceramic powder; Si wherein
3n
4volume parts be greater than 60 parts and be less than 100 parts, the volume parts of BN coated composite powder is greater than 0 part and is less than 40 parts, the volume parts of sintering aid is greater than 5 parts and is less than 10 parts;
Three, in deionized water, add organic monomer, linking agent, wetting agent and dispersion agent, obtain premixed liquid, then with quality percentage composition, be that 28% ammoniacal liquor and quality percentage composition are pH value to 9～11 that 10% hydrochloric acid regulates premixed liquid, add again hybrid ceramic powder, then ball milling mixes, and obtains slurry; Wherein in slurry, the solid load of ceramic powder is 35～45vol.%; The add-on of organic monomer is 3～8wt.% of ceramic powder total mass, the add-on of dispersion agent is 0.2～0.6wt.% of ceramic powder total mass, the add-on of wetting agent is 2～6wt.% of ceramic powder total mass, and the mass ratio of organic monomer and linking agent is (5～15): 1;
Four, in the slurry obtaining in step 3, add initiator and catalyzer, after stirring, carry out injection molding, obtain curing ceramic wet blank, be then dried, obtain dried green compact;
Five, dried green compact are carried out in air furnace to skimming treatment, then carry out sintering, obtain BN/Si
3n
4complex phase ceramic, completes BN/Si
3n
4the gel casting forming preparation of complex phase ceramic.
Present embodiment is introduced BN by the form with BN coated powder, and can realize solid load is 44vol.%, and the BN/Si of the very applicable gel injection molding and forming technology of viscosity
3n
4the preparation of composite mortar, has solved gel injection molding and forming technology and has prepared BN/Si
3n
4during composite ceramics, the introducing of BN causes the problem of the rapid variation of slurry viscosity; And by BN, with the form of coated powder, introduce, realized dispersed in slurry of BN, solved BN at Si
3n
4more difficultly in matrix realize homodisperse problem, finally prepare the uniform BN/Si of heterogeneous microstructure
3n
4composite ceramics, and material has excellent mechanical property and lower specific inductivity, can be used as carrying, wave transparent, thermally protective materials under severe condition, for fields such as aerospace, mechanical industries.
Embodiment two: what present embodiment was different from embodiment one is that in step 1, BN coated composite powder is realized according to the following steps: one, take 200mL deionized water, 15g Al (NO
3)
3, 21.16g Y (NO
3)
3with 10g urea, add in deionized water, then solution is heated to 95 ℃, insulation 1～2h, is cooled to room temperature subsequently, obtains premixed liquid; Two, take 51.9g BN, join in 800mL deionized water, through ball mill mixing 5～24h, obtain BN suspension; Three, premixed liquid is added to BN suspension, at 50～60 ℃ of stirred in water bath 36～48h, obtain the mixture of premixed liquid and BN suspension; Four, the mixture of the premixed liquid obtaining and BN suspension is dried in the baking oven of 60～120 ℃, after grinding, cross 100～120 mesh sieves, obtain the coated BN powder of Y/Al salt; Five, the coated BN powder of Y/Al salt is put into tube furnace in the N of 0.05～0.1MPa
2under protective atmosphere, 800～1200 ℃ of calcining 1～2h, obtain BN coated composite powder.Other steps and parameter are identical with embodiment one.
Embodiment three: what present embodiment was different from embodiment one or two is that in step 2, sintering aid is Al
2o
3and Y
2o
3be 1 by volume: the ratio of (1.5～3) mixes.Other steps and parameter are identical with embodiment one or two.
Embodiment four: present embodiment is different from one of embodiment one to three is that time of ball milling in step 3 is 10～24h, and ball material mass ratio is (1～1.5): 1.Other steps and parameter are identical with one of embodiment one to three.
Embodiment five: what present embodiment was different from one of embodiment one to four is that in step 3, organic monomer is acrylamide; Linking agent is N, N '-methylene-bisacrylamide; Wetting agent is poly(oxyethylene glycol) 400; Dispersion agent is polyacrylic acid.Other steps and parameter are identical with one of embodiment one to four.
Embodiment six: present embodiment is different from one of embodiment one to five is that initiator in step 4 is ammonium persulphate, and add-on is 3～8wt.% of ceramic powder total mass.Other steps and parameter are identical with one of embodiment one to five.
Embodiment seven: present embodiment is different from one of embodiment one to six is that catalyzer in step 4 is N, N, N ' N '-Tetramethyl Ethylene Diamine, the volume ratio of catalyzer and premixed liquid (2～6) mL: L.Other steps and parameter are identical with one of embodiment one to six.
Embodiment eight: present embodiment is different from one of embodiment one to seven is that drying process in step 4 is carried out in climatic chamber, and dry initial humidity is controlled at 50～100%, and temperature is controlled at 20～30 ℃; After contraction to be dried stops, humidity is reduced to 30～50%, temperature is increased to 30～60 ℃, until drying process finishes.Other steps and parameter are identical with one of embodiment one to seven.
Embodiment nine: present embodiment is different from one of embodiment one to eight is that skimming processes in step 5 is to carry out in air furnace, and skimming temp is 500～800 ℃, insulation 1～2h, temperature rise rate is controlled at 0.5～2 ℃/min.Other steps and parameter are identical with one of embodiment one to eight.
Embodiment ten: present embodiment is different from one of embodiment one to nine is that sintering in step 5 is to carry out in atmosphere sintering furnace, with the N of 0.1～0.6MPa
2for shielding gas, temperature rise rate is 10～30 ℃/min, and sintering temperature is 1700～1800 ℃, soaking time 1～3h.Other steps and parameter are identical with one of embodiment one to nine.
By following verification experimental verification beneficial effect of the present invention:
Test 1, this test are divided into test group and control group.
The BN/Si of control group
3n
4the gel casting forming preparation method of complex phase ceramic, BN introduces with the form of original powder, carries out according to the following steps:
One, by volume umber takes 75～90 parts of Si
3n
4, 5～20 parts of BN, 3.5 parts of Y
2o
3powder and 1.5 parts of Al
2o
3powder, obtains hybrid ceramic powder;
Two, in deionized water, add organic monomer, linking agent, wetting agent and dispersion agent, obtain premixed liquid, the ammoniacal liquor that is then 28% with quality percentage composition regulates the pH value to 10 of premixed liquid, then adds mixed powder, and then ball milling mixes, and obtains slurry; Wherein in slurry, the solid load of ceramic powder is 40vol.%; The add-on of organic monomer is the 5wt.% of ceramic powder total mass, and the add-on of dispersion agent is the 0.4wt.% of ceramic powder total mass, and the add-on of wetting agent is the 3wt.% of ceramic powder total mass, and the mass ratio of organic monomer and linking agent is 15: 1;
Three, in the slurry obtaining in step 2, add initiator and catalyzer, after stirring, carry out injection molding, obtain curing ceramic wet blank, be then dried, obtain dried green compact;
Four, dried green compact are carried out in air furnace to skimming treatment, then carry out sintering, obtain BN/Si
3n
4complex phase ceramic.
Drying process in this testing sequence three for being first 90% in humidity, temperature is dry 2～3d in the climatic chamber of 35 ℃, afterwards humidity is adjusted into 30%, dry 2～3d under temperature 50 C; In step 4, skimming processes is to carry out in air furnace, and calcining temperature is 600 ℃, insulation 1h, and temperature rise rate is controlled at 2 ℃/min; Sintering process is to carry out in atmosphere sintering furnace, with the N of 0.1MPa
2for shielding gas, temperature rise rate is controlled at 20 ℃/min, and sintering temperature is 1750 ℃, soaking time 1h.
In this test, when adopting rotational viscosimeter by volume umber being respectively 5,10,15 and 20 parts to the add-on of the original powder of BN, prepared BN/Si
3n
4the viscosity of composite mortar is measured, and slurry viscosity with the variation relation curve of shearing rate as shown in Figure 1.As can be seen from the figure, the increase along with BN introduction volume in raw material, all increases in the scope that the viscosity of composite mortar is 5～95r/min in shearing rate gradually.But, overall on the viscosity number of four groups of samples all in 1000mPas, be to be all relatively suitable for gel injection molding and forming technology.
The add-on of the original powder of BN Si when by volume umber is 5 parts in this test
3n
4add-on by volume umber be 90 parts, the add-on of the original powder of BN Si when by volume umber is 10 parts
3n
4add-on by volume umber be 85 parts, the add-on of the original powder of BN Si when by volume umber is 15 parts
3n
4add-on by volume umber be 80 parts, the add-on of the original powder of BN Si when by volume umber is 20 parts
3n
4add-on by volume umber be 75 parts.
In this test, the add-on of the original powder of BN is respectively 5,10,15 and 20 parts, prepared BN/Si
3n
4composite ceramics is called after 5BS, 10BS, 15BS and 20BS respectively, and the density of material, bending strength and specific inductivity are characterized, and test result is as shown in table 1.As can be seen from the table, along with the increase of the original powder introduction volume of BN in raw material, BN/Si
3n
4the density of composite ceramics declines gradually, correspondingly, bending strength and specific inductivity also decline gradually, this explanation is along with the increase of BN introduction volume, the effect that hinders material sintering densification is also more and more obvious, and in expendable material Some Mechanical Properties, can bring the significantly reduction of specific inductivity.
Table 1
The BN/Si of test group
3n
4the gel casting forming preparation method of complex phase ceramic, realizes according to the following steps:
One, adopt inorganic salt sedimentation to prepare one deck Y/Al salt coating at BN powder surface, after calcining, sieving, obtain BN coated composite powder;
Two, by Si
3n
4, BN coated composite powder, Y
2o
3powder and Al
2o
3powder mixes, and obtains hybrid ceramic powder; Wherein in BN coated composite powder, contain Y
2o
3and Al
2o
3, then by Y
2o
3volume parts complement to 3.5 parts and Al
2o
3volume parts complement to 1.5 parts.
Three, in deionized water, add organic monomer, linking agent, wetting agent and dispersion agent, obtain premixed liquid, the ammoniacal liquor that is then 28% with quality percentage composition regulates the pH value to 10 of premixed liquid, then adds mixed powder, and then ball milling mixes, and obtains slurry; Wherein in slurry, the solid load of ceramic powder is 40vol.%; The add-on of organic monomer is the 5wt.% of ceramic powder total mass, and the add-on of dispersion agent is the 0.4wt.% of ceramic powder total mass, and the add-on of wetting agent is the 3wt.% of ceramic powder total mass, and the mass ratio of organic monomer and linking agent is 15: 1;
Four, in the slurry obtaining in step 2, add initiator and catalyzer, after stirring, carry out injection molding, obtain curing ceramic wet blank, be then dried, obtain dried green compact;
Five, dried green compact are carried out in air furnace to skimming treatment, then carry out sintering, obtain BN/Si
3n
4complex phase ceramic.
The method of this test BN coated composite powder adopts the method for embodiment two to carry out, drying process in this testing sequence four for being first 90% in humidity, temperature is to be dried to 2～3d in the climatic chamber of 35 ℃, afterwards humidity is adjusted into 30%, dry 2～3d under temperature 50 C; In step 5, skimming processes is to carry out in air furnace, and calcining temperature is 600 ℃, insulation 1h, and temperature rise rate is controlled at 2 ℃/min; Sintering process is to carry out in atmosphere sintering furnace, with the N of 0.1MPa
2for shielding gas, temperature rise rate is controlled at 20 ℃/min, and sintering temperature is 1750 ℃, soaking time 1h.
In this test, after BN is coated, the projection light field phase photo of powder as shown in Figure 2, in figure, the different region of shown coated BN grain edges contrast can be found out, has formed one deck be about tens nanometers to the coating layer region of up to a hundred nano thickness after coated at BN particle surface.Although the thickness of this coating layer is very uneven, and the combination of BN particle still comparatively closely, and this photo also shows that coating layer realizes BN particle completely coated substantially.
When adopting rotational viscosimeter by volume umber being respectively 5,10,15 and 20 parts to the add-on of BN coated composite powder, prepared BN/Si
3n
4the viscosity of composite mortar is measured, and slurry viscosity with the variation relation curve of shearing rate as shown in Figure 3.As can be seen from the figure, the increase along with BN coated composite powder introduction volume in raw material, all increases in the scope that the viscosity of composite mortar is 5～95r/min in shearing rate gradually.But, overall on the viscosity number of four groups of samples all in 1000mPas, be to be all relatively suitable for gel injection molding and forming technology.Contrast and can find with Fig. 1, BN can significantly reduce the viscosity of slurry while introducing by the form with coated powder.
The add-on of BN coated composite powder Si when by volume umber is 5 parts in this test
3n
4add-on by volume umber be 90 parts, the add-on of BN coated composite powder Si when by volume umber is 10 parts
3n
4add-on by volume umber be 85 parts, the add-on of BN coated composite powder Si when by volume umber is 15 parts
3n
4add-on by volume umber be 80 parts, the add-on of BN coated composite powder Si when by volume umber is 20 parts
3n
4add-on by volume umber be 75 parts.The volume parts that adds BN coated composite powder in this test is to calculate by the volume parts of BN in BN coated composite powder.
In this test the add-on of BN coated composite powder by volume umber be respectively 5,10,15 and 20 parts, prepared BN/Si
3n
4composite ceramics is called after 5CBS, 10CBS, 15CBS and 20CBS respectively, and the density of material, bending strength and specific inductivity are characterized, and test result is as shown in table 1.As can be seen from the table, along with the increase of the coated BN powder introduction volume of raw material, BN/Si
3n
4the density of composite ceramics declines gradually, correspondingly, bending strength and specific inductivity also decline gradually, this explanation is along with the increase of BN coated composite powder introduction volume, the effect that hinders material sintering densification is also more and more obvious, and in expendable material Some Mechanical Properties, can bring the significantly reduction of specific inductivity.But by contrasting and can find with table 1, except the sample that BN content is 5vol.%, for other three groups of samples, when BN introduces with the form of coated powder, prepared BN/Si
3n
4the sintering characteristic of composite ceramics be improved significantly, be in particular in that the density of sample 10CBS, 15CBS and 20CBS and bending strength all will be higher than sample 10BS, 15BS and 20BS.
Table 2
Known by the test 1 in embodiment and test 2: by preparing one deck on BN ceramic powder surface containing the coating layer of Y/Al oxide compound, can to make BN/Si
3n
4the rheologic behavio(u)r of composite mortar is greatly improved, the more favourable BN/Si for preparing high solid loading
3n
4composite mortar; And when BN introduces with the form of coated powder, while introducing with former powder form with respect to the BN of same amount, sintered density and the bending strength of material all improve a lot, and the sintering characteristic of illustrative material can be greatly improved.
Claims (8)
1. a BN/Si
3n
4the gel casting forming preparation method of complex phase ceramic, is characterized in that BN/Si
3n
4the gel casting forming preparation method of complex phase ceramic realizes according to the following steps:
One, adopt inorganic salt sedimentation to prepare Y/Al salt coating at BN powder surface, after calcining, sieving, obtain BN coated composite powder; The preparation method of described BN coated composite powder realizes according to the following steps: one, take 200mL deionized water, 15gAl (NO
3)
3, 21.16gY (NO
3)
3with 10g urea, add in deionized water, then solution is heated to 95 ℃, insulation 1～2h, is cooled to room temperature subsequently, obtains premixed liquid; Two, take 51.9gBN, join in 800mL deionized water, through ball mill mixing 5～24h, obtain BN suspension; Three, premixed liquid is added to BN suspension, at 50～60 ℃ of stirred in water bath 36～48h, obtain the mixture of premixed liquid and BN suspension; Four, the mixture of the premixed liquid obtaining and BN suspension is dried in the baking oven of 60～120 ℃, after grinding, cross 100～120 mesh sieves, obtain the coated BN powder of Y/Al salt; Five, the coated BN powder of Y/Al salt is put into tube furnace in the N of 0.05～0.1MPa
2under protective atmosphere, 800～1200 ℃ of calcining 1～2h, obtain BN coated composite powder after sieving;
Two, by volume umber takes Si
3n
4, BN coated composite powder and sintering aid, obtain hybrid ceramic powder; Si wherein
3n
4volume parts be greater than 60 parts and be less than 100 parts, the volume parts of BN coated composite powder is greater than 0 part and is less than 40 parts, the volume parts of sintering aid is greater than 5 parts and is less than 10 parts;
Three, in deionized water, add organic monomer, linking agent, wetting agent and dispersion agent, obtain premixed liquid, then with quality percentage composition, be that 28% ammoniacal liquor and quality percentage composition are pH value to 9～11 that 10% hydrochloric acid regulates premixed liquid, add again hybrid ceramic powder, then ball milling mixes, and obtains slurry; Wherein in slurry, the solid load of ceramic powder is 35～45vol.%; The add-on of organic monomer is 3～8wt.% of ceramic powder total mass, the add-on of dispersion agent is 0.2～0.6wt.% of ceramic powder total mass, the add-on of wetting agent is 2～6wt.% of ceramic powder total mass, and the mass ratio of organic monomer and linking agent is (5～15): 1;
Four, in the slurry obtaining in step 3, add initiator and catalyzer, after stirring, carry out injection molding, obtain curing ceramic wet blank, be then dried, obtain dried green compact;
Five, dried green compact are carried out in air furnace to skimming treatment, then carry out sintering, obtain BN/Si
3n
4complex phase ceramic, completes BN/Si
3n
4the gel casting forming preparation of complex phase ceramic.
2. a kind of BN/Si according to claim 1
3n
4the gel casting forming preparation method of complex phase ceramic, is characterized in that in step 2, sintering aid is Al
2o
3and Y
2o
3by volume for 1:(1.5～3) ratio mix.
3. a kind of BN/Si according to claim 1
3n
4the gel casting forming preparation method of complex phase ceramic, the time that it is characterized in that ball milling in step 3 is 10～24h, ball material mass ratio is (1～1.5): 1.
4. a kind of BN/Si according to claim 1
3n
4the gel casting forming preparation method of complex phase ceramic, is characterized in that in step 3, organic monomer is acrylamide; Linking agent is N, N '-methylene-bisacrylamide; Wetting agent is poly(oxyethylene glycol) 400; Dispersion agent is polyacrylic acid.
5. a kind of BN/Si according to claim 1
3n
4the gel casting forming preparation method of complex phase ceramic, is characterized in that the initiator in step 4 is ammonium persulphate, and add-on is 3～8wt.% of ceramic powder total mass.
6. a kind of BN/Si according to claim 1
3n
4the gel casting forming preparation method of complex phase ceramic, is characterized in that the drying process in step 4 is carried out in climatic chamber, and dry initial humidity is controlled at 50～100%, and temperature is controlled at 20～30 ℃; After contraction to be dried stops, humidity is reduced to 30～50%, temperature is increased to 30～60 ℃, keeps 2～3d, obtains dried green compact.
7. a kind of BN/Si according to claim 1
3n
4the gel casting forming preparation method of complex phase ceramic, is characterized in that the skimming processes in step 5 is to carry out in air furnace, and skimming temp is 500～800 ℃, insulation 1～2h, and temperature rise rate is 0.5～2 ℃/min.
8. a kind of BN/Si according to claim 1
3n
4the gel casting forming preparation method of complex phase ceramic, is characterized in that the sintering in step 5 is to carry out in atmosphere sintering furnace, with the N of 0.1～0.6MPa
2for shielding gas, temperature rise rate is 10～30
oc/min, sintering temperature is 1700～1800 ℃, soaking time 1～3h.
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