反应烧结制备Si3N4-BN复合材料

以Si粉和BN粉为原料,Fe2O3为烧结助剂,采用反应烧结法于1450℃氮气气氛下制备了Si3N4-BN复合材料. 利用XRD研究了不同烧结制度和BN含量下复合材料的物相组成,利用SEM对材料断面形貌进行了观察,并测定了不同BN含量材料的显气孔率、体积密度和常温抗折强度,同时探讨了Fe2O3的助烧机理和b-Si3N4的形成机理. 研究结果表明,当氮化温度为1450℃、保温时间为45 h时,Si可完全氮化,材料中主晶相仅为Si3N4和BN. 随着BN含量的增加,相对密度和常温抗折强度下降,b-Si3N4含量增多. 当BN含量为30%时,其相对密度为73.3%,抗折强度可达52.5 MPa,同时b/a相比为3.4.     

β-Si3N4及添加β-Si3N4的α-Si3N4的气氛加压烧结

介绍了β－Ｓｉ３Ｎ４及添加β－Ｓｉ３Ｎ４的α－Ｓｉ３Ｎ４的气氛加压烧结,β－Ｓｉ３Ｎ４在ＧＰＳ中具有低于α－Ｓｉ３Ｎ４的烧结活性而且陶瓷显微结构更容易调节,由ＧＰＳβ－Ｓｉ３Ｎ４制备的陶瓷材料晶粒比较均匀,具有较高的力学性能,尤其是高的韦泊模数,添加于α－Ｓｉ３Ｎ４中的β－Ｓｉ３Ｎ４对陶瓷材料显微结构具有明显的调控作用。     

原位合成MoSi2反应烧结SiC-MoSi2复合材料

将Mo粉和Si粉按12的摩尔比,在聚乙烯球磨罐中球磨混合4 h,然后与SiC粉按不同的比例配料,加入少量的Al2O3微粉和活性炭粉,再共磨混合24 h;然后在20 MPa的压力下压制成型,在1650℃下、氮气气氛中烧结,保温1 h后自然冷却至室温.采用XRD、SEM和EDAX等手段对反应产物的物相组成、组织结构和微区成分进行了分析,结果表明原位合成MoSi2反应烧结SiC-MoSi2复合材料由SiC、MoSi2以及少量的残余硅组成;其显微组织结构疏松,颗粒堆积呈蜂窝状.根据实验结果,讨论了复合材料显微结构的形成机制,并着重对MoSi2颗粒聚集区中的空心粒子及其周围分散的小气孔的形成机制进行了阐述.     

NbN/MoSi2/Si3N4陶瓷复合材料氧化性能的研究

以NbN/MoSi2/Si3N4复合材料作为研究对象,研究了其在不同温度下的氧化性能.利用X射线衍射分析、扫描电镜分析和X光能谱分析,对复合材料的氧化产物进行了测定.结果表明试样在1150～1400 ℃温度范围内氧化出现了2个阶段,即0～15 h线形快速氧化阶段,A、B氧化活化能分别为98kJ/mol和132kJ/mol,而15h以后为抛物线缓慢氧化阶段,A、B氧化活化能分别为426kJ/mol和492kJ/mol;气孔率越高,氧化越严重,快速氧化阶段持续时间越长.     

低氧分压下β-Si3N4制品的氧化烧结

以闪速燃烧氮化法合成的β-Si3N4粉为主要原料,在w(β-Si3N4粉)为80%、w(α-Al2O3粉)和w(Y2O3粉)分别为10%的混合粉料中,外加3%金属铝粉,混练、成型后,在1 600℃的弱氧化气氛(氮气中配入体积分数分别为0、10%、20%、30%的空气)中实现了β-Si3N4制品的逆氮化反应烧结.结果表明:空气配入量为10%时,得到的Si3N4烧结体指标较好;金属铝粉首先发生氧化,新生成的高活性Al2O3可促进烧结的进行;弱氧化气氛烧成时,通过氧分压来控制氧化物的生成量,既避免了Si3N4的过度氧化,又形成了活性烧结.     

高性能透波Si3N4-BN基陶瓷复合材料的研究

采用气氛压力烧结工艺(GPS)研制出了高性能透波Si3N4-BN基陶瓷复合材料.研究了BN含量对复合材料力学和介电性能的影响规律,分析了该材料的显微结构特点.实验结果表明:含有30%BN的Si3N4-BN复合材料,其室温抗弯强度(σRT)为160MPa,弹性模量(E)为99GPa,介电常数(ε)为4.0左右.     

MoSi2增韧Si3N4陶瓷的研究

以Ｓｉ粉和Ｍｏ粉为原料,采用反应烧结－热压吉二步法得到了Ｓｉ３Ｎ４－ＭｏＳｉ２复合材料,并对材料进行了力学性能和Ｘ－射线衍射（ＸＲＤ）及扫描电子显微镜（ＳＥＭ）研究。认为：Ｓｉ３Ｎ４－ＭｏＳｉ２复合材料的高韧性与材料的相组成、显向下 结构、裂纹扩展方式及应力诱导开裂等有关。     

MoSi2对尖晶石制品烧结性能的影响

在尖晶石材料中分别加入3%、5%和10%的MoSi2细粉,分别在1000℃、1200℃、1500℃下烧成,研究了MoSi2对尖晶石材料烧结性能的影响.结果表明(1)在不合镁砂细粉的尖晶石试样中,添加剂MoSi2易发生氧化,生成膨胀系数较大的MoO3,试样容易破碎;(2)同时添加MoSi2和镁砂细粉的尖晶石试样能在较低温度下开始烧结,在1200℃下能达到一定程度的烧结,发生的反应方程式为2MoSi2+7O2+2MgO=2MgMoO4+4SiO2,但MgMoO4在＞1200℃时不稳定,易与Al2O3发生反应,反应方程式为MgMoO4+Al2O3=MoO3+MgAl2O4;(3)过多MoSi2细粉的加入会引起试样较大的体积膨胀.     

SiC含量对反应烧结SiC-Si3N4复合材料性能的影响

以粒度均≤0.044mm的工业Si粉和α-SiC粉为原料,酚醛树脂为结合剂(占总粉末质量的6.5%),配成SiC含量(质量分数)分别为10%、30%、50%和70%的4组试样,经200MPa冷等静压成型后,在N2气氛中(压力为1.25MPa)于1395℃反应烧结制备了SiC-Si3N4复合材料,并采用SEM、XRD和EDS等测试手段对试样进行了观察和测试。结果表明:随着粉料中SiC含量的增加,烧后试样的体积密度下降,显气孔率提高,抗折强度降低,以SiC加入量为10%的试样性能最优;4组试样经800℃～室温空冷热震15次后的抗折强度保持率均在90%以上,表明材料具有良好的抗热震性能。     

Additively manufactured mesostructured MoSi2-Si3N4 ceramic lattice

Lattice structures, their shape, orientation, and density make the critical building blocks for macro-scale geometries during the AM process and, therefore, manipulation of the lattice structure extends to the overall quality of the final product. This work reports on manufacturing of MoSi₂-Si₃N₄ ceramic lattices through a selective laser melting (SLM) approach. The strategy first employs the production of core-shell structured MoSi₂/(10-13?wt%)Si composite powders of 3–10?μm particle size by combustion synthesis followed by SLM assembly of MoSi₂/Si lattices and their further nitridation to generate MoSi₂-Si₃N₄ mesostructures of designed geometry. Experimental results revealed that the volumetric energy density of SLM laser has remarkable influence on the cell parameters, strength, porosity and density of lattices. Under compressive test, samples sintered at a higher laser current demonstrated a higher strength value. Selective laser melting has shown its potential for production of cellular lattice mesostructures of ceramic-based composites with a low content of a binder metal, which can be subsequently converted into a ceramic phase to produce ceramic-ceramic structure.     

The effect of different sintering additives on the electrical and oxidation properties of Si3N4–MoSi2 composites

The fabrication and properties of electrically conductive Si₃N₄–MoSi₂ composites using two different sintering additive systems were investigated (i) Y₂O₃–Al₂O₃ and (ii) Lu₂O₃. It was found that the sintering atmosphere used (N₂ or Ar) had a critical influence on the final phase composition because MoSi₂ reacted with N₂ atmosphere during sintering resulting in the formation of Mo₅Si₃. The electrical conductivity of the composites exhibited typical percolation type behaviour and the percolation concentrations depended on the type of sintering additive and atmosphere used. Metallic-like conduction was the dominant conduction mechanism in the composites with MoSi₂ content over the percolation concentrations due to the formation of a three-dimensional percolation network of the conductive MoSi₂ phase. The effect of the sintering additives on the electrical and oxidation properties of the composites at elevated temperatures was investigated. Parabolic oxidation kinetics was observed in the composites with both types of additives. However, the Lu₂O₃-doped composites had superior oxidation resistance compared to the composites containing Y₂O₃–Al₂O₃. It is attributed to the higher eutectic temperature and crystallisation of the grain boundary phase and the oxidation layer in the Lu₂O₃-doped composites.     

β-Si3N4对MgO-C砖高温性能的影响

研究了β-Si3N4对镁碳砖高温性能的影响及其作用机理.研究表明由于β-Si3 N4呈针状结构,热膨胀系数低,对多数熔渣和金属的润湿性小,加入β-Si3N4的镁碳砖,其高温抗折强度提高,热膨胀率降低,抗渣侵蚀性提高;另外,在反应层与原砖层之间发现有富硅层形成,这有利于抑制石墨和氮化硅的氧化以及渣的渗透.     

制备方法对Al2TiO5-Si3N4复合材料性能的影响

采用“直接法”、“反应复合法一”、“反应复合法二”3种方法制备了Al2TiO5—Si3N4复合材料。研究了3种制备方法对材料的显气孔率、吸水率、体积密度、抗折强度、烧成线收缩率、抗热震次数、显微结构等性能的影响。研究结果表明,采用“反应复合法－”制备的Al2TiO5-Si3N4复合材料的综合性能最佳,其显气孔率为16．61％、吸水率为6．01％、体积密度为2．77g/cm^2、抗折强度为45．34MPa、抗热震次数达到11次、结构最致密。     

低氮气压力下燃烧合成α-Si3N4粉体

采用机械活化的方式对原料粉体进行高能机械研磨预处理,随后在较低氮气压力下进行自蔓延高温燃烧合成反应,并对合成产品进行了X射线衍射分析和扫描电镜观察.研究表明:经机械化学活化处理的原料粉体,在低于3MPa氮气压力下燃烧合成产物主相为α-Si3N4;产物中α-Si3N4的质量分数大于90%,产物的粒度为亚微米级,粉末形貌为近球形.     

Effect of TiB2 addition on grain orientation of porous Si3N4-TiB2 composites by magnetic field alignment technology

Textured porous Si₃N₄-TiB₂ composites were prepared by gel-casting–assisted magnetic field alignment technology and subsequent pressureless sintering in the N₂ atmosphere. The effects of TiB₂ content on grain orientation and properties of composites were studied. Results showed that using the magnetic field of 6T, Si₃N₄ grains exhibited a high a- or b-axis orientation and TiB₂ grains exhibited a high c-axis orientation. In textured green bodies, the increase in TiB₂ content from 0 to 20 wt%, the degree of texture of Si₃N₄ grains showed a slight decrease from 0.78 to 0.71. However, the degree of texture of TiB₂ grains was maintained at about 0.98 regardless of TiB₂ content. After sintering, except for the Si₃N₄ and TiB₂ phases, new TiN and BN phases also appeared in the samples. Additionally, the sintering process promotes grain orientation of Si₃N₄ and TiB₂. Herein, the degree of texture of TiB₂ reached to about 1 regardless of TiB₂ content, meaning that the complete grain orientation formed for TiB₂. Owing to the reconstruction reaction between TiB₂ and N₂, new TiN and BN phases did not form the orientation. The increase in TiB₂ contents gradually increased the apparent porosity of the textured samples from 27.9% to 39.4%, thereby leading to the decrease in bending strength from 126.8 ± 18.8 MPa to 60.3 ± 11.2 MPa and from 105.3 ± 19.8 MPa to 53.6 ± 13.0 MPa in two directions, respectively.     

纳米SiO2对Si3N4/BN复合材料性能的影响

通过调整纳米SiO2含量,找出了对Si3N4/BN复合材料物理性能、力学性能、介电性能的影响规律.当纳米SiO2质量分数为5%时,复合材料的抗弯强度为174.83MPa,介电常数为4.0.     

Effect of milling energy on mechanical activation of (Mo + Si3N4) powders during the synthesis of Si3N4–MoSi2 in situ composites

Attempts have been made to study the effect of milling energy and type of grinding media on the mechanical activation during the production of MoSi₂ from a reaction between Mo and Si₃N₄. Powder mixtures of Mo and Si₃N₄ in the molar ratios of 1:1, 1:2 and 1:3 were ball milled using WC, steel, and ZrO₂ grinding media for mechanical activation. In order to evaluate the results obtained after high-energy ball milling and pyrolysis of these milled powder mixture, milling parameters have been converted to two energy parameters, namely, impact energy of the ball and total energy of milling. The optimum impact energy of ball required for mechanical activation of Mo + xSi₃N₄ (x = 3, 2, 1) powder mixtures by WC grinding media was found to be in the range of 0.145–0.173 J, which leads to a reduction of pyrolysis temperature by 100–200 °C. Samples milled with higher impact energy than the optimum range led to formation of undesirable phases, which dilutes the effect of mechanical activation. Samples milled with both steel and ZrO₂ grinding media having lower impact energies than the optimum show the presence of enormous contamination during milling and phases like ZrSi₂, Fe₃Si and Fe₅Si₃ were observed after pyrolysis without any significant reduction in pyrolysis temperature required for MoSi₂ synthesis.