TiB2在球磨中的氧化行为

用行星球磨对TiB2原粉进行处理,并用X射线光电子能谱仪,X射线衍射仪,能量色散X射线荧光光谱仪等对TiB2在球磨过程中的氧化行为进行分析.结果表明:在室温下TiB2粉末存在表面氧化,而球磨加速TiB2粉末氧化,随着球磨时间的延长,TiB2粉末的氧化程度加大;酸洗及离心作用造成硼的流失,使B和Ti的摩尔比失调,最终形成TiO2和少量硼酸包覆TiB2结构;通过改变不同球磨工艺,发现湿磨加Ar保护工艺使TiB2被氧化程度明显降低.     

高温氧化对再结晶碳化硅陶瓷断裂强度的影响

研究了在1500℃空气中的高温氧化对再结晶碳化硅(recrystallized silicon carbide,RSiC)陶瓷断裂强度的影响。用X射线衍射仪、扫描电镜分析了RSiC样品氧化后表面的物相组成及显微结构。结果表明:在1500℃下RSiC陶瓷的氧化质量增加遵循抛物线规律,氧化速率常数为3.77×10-5g2/(cm4·h1),其线性相关系数r2为0.998。RSiC陶瓷的室温抗弯强度随氧化时间增加呈现出先升后降的变化趋势,当氧化21h时,材料的室温抗弯强度最高,达到87MPa。氧化初期由于样品表面生成致密的非晶态SiO2,对样品表面的缺陷起到了钝化作用,导致材料室温断裂强度升高;氧化后期由于非晶态SiO2膜的析晶而产生裂纹以及循环氧化导致裂纹扩展,从而使材料的断裂强度降低。     

TiB2 陶瓷材料氧化动力学研究

采用Ф函数法,计算了TiB2陶瓷在空气中氧化时的ΔG°R值。计算表明,在700~1 100℃的温度区间内,TiB2陶瓷将会发生氧化。在硅碳棒高温炉中进行了TiB2陶瓷的氧化试验,并推导了TiB2陶瓷的氧化动力学公式。研究表明,TiB2陶瓷在空气中中温氧化时,其氧化行为表现为氧化增重随时间的变化服从抛物线规律;在研究的温度范围内,TiB2陶瓷的氧化活化能为44 982.8 J/mol;TiB2陶瓷材料的氧化主要由氧通过氧化层的向内扩散所控制。     

Si_3N_4陶瓷材料的氧化行为及其抗氧化研究

研究了Si3N4陶瓷材料的氧化行为 ,同时探讨了通过表面处理使Si3N4陶瓷材料表面形成一层Si2 N2 O对其抗氧化性能的影响。实验结果表明 ,Si3N4陶瓷材料在空气中的氧化行为服从抛物线规律。另外 ,用X射线衍射分析 (XRD)和X光电子能谱 (XPS)分析验证了Si2 N2 O层的存在。由于形成了Si2 N2 O层 ,Si3N4陶瓷材料在 130 0℃下氧化 10 0h后 ,氧化增重从原来的 0 .4 2mg/cm2 降低到 0 .2 4mg/cm2 ,其抗氧化性能有了明显的提高。同时 ,表面处理后Si3N4陶瓷材料的强度也有一定的提高 ,其中室温强度从原来的62 1MPa提高到 662MPa。     

原位合成TiB2-TiCx复相陶瓷的显微组织

应用光学显微镜(OM)、X射线衍射(XRD)、透射电镜(TEM)和扫描电镜(SEM)对原位合成的TiB2-TiCx复相陶瓷显微结构进行了分析。并分析了Ti-B4C反应的原位生成机理。结果表明,Ti3B4相稳定存在于生成物中,其形态与形成温度和反应机理有关。     

TiB_2-TiSi_2复相陶瓷的氧化行为研究

采用等温氧化增重法,研究了1650℃热压烧结的TiB2-TiSi2复相陶瓷的高温氧化行为。通过XRD、SEM等分析手段,研究了高温氧化层的物相组成与显微结构,并结合热力学计算,探讨了TiB2-TiSi2复相陶瓷高温抗氧化机理。研究表明:TiB2-TiSi2复相陶瓷的氧化增重随时间变化符合抛物线变化规律;随着在空气中氧化时间延长,氧化增重初期增加较快,进而增加较为平缓,进入钝化氧化阶段;TiB2-TiSi2复相陶瓷的高温抗氧化机理为TiSi2先于TiB2与氧发生反应形成TiO2与SiO2保护层,阻碍了氧气与材料的进一步接触,使材料具有高温自愈合抗氧化性,提高了TiB2-TiSi2复相陶瓷的高温使用温度。     

Si3N4/TiC纳米复合陶瓷刀具材料氧化行为

在微米Si3N4基体中加入纳米Si3N4及TiC颗粒,以Al2O3和Y2O3作为助烧结剂,通过热压烧结制备了Si3N4/TiC纳米复合陶瓷刀具材料,研究了该材料在800～1 250℃时的氧化行为.结果表明:该类材料的氧化特性符合抛物线规律;随TiC含量的增加,材料的抗氧化性能降低.由氧化后样品的X射线衍射谱分析可知:氧化表面生成SiO2和TiO2,表面仅余微量的Si3N4和TiC成分,表明经1 250℃,100h氧化后,样品表面几乎被氧化物覆盖.Si3N4/TiC(含有10%纳米Si3N4和15%TiC,质量分数)纳米复合材料在经过900℃,100h氧化后,其强度无明显下降;但经过1000℃,100h的氧化后,材料的强度已经降至氧化前的41%.扫描电镜观察表明裂纹的生成及扩展是引起强度降低的主要原因.     

原位合成碳化硅-硼化钛复相陶瓷的高温摩擦性能及其磨损机理

以SiC为基体,用TiC和B4C为原料反应生成TiB2,原位合成了SiC-TiB2复相陶瓷.通过测试SiC和SiC-TiB2的高温摩擦系数和比磨损率与温度、外加载荷的关系,研究了SiC-TiB2复相陶瓷的高温摩擦学性能.在空气中,外加载荷为0.2 MPa,摩擦速度为0.3 m/s时,SiC-TiB2复相陶瓷自对偶(SiC-TiB2/SiC-TiB2)高温摩擦呈现较好的高温自润滑性能.温度对SiC-TiB2/SiC-TiB2摩擦系数和比磨损率的影响与载荷有关.载荷为0.4 MPa时,比磨损率最大.用X射线衍射测试了SiC-TiB2/SiC-TiB2磨屑的组成,用扫描电子镜观察了SiC-TiB2/SiC-TiB2磨损断面,发现高温摩擦氧化是TiB2-SiC/SiC-TiB2磨损的主要机理.磨损断面包含摩擦氧化层、过渡层和基体亚表面3层,氧化层和过渡层接触紧密.磨屑具有典型包裹结构,其主要氧化物是无定形氧化硅.平滑的氧化层改进了摩擦表面的塑变性能,缓冲了摩擦应力,减小了高温比磨损率.     

原位合成TiB2-SiC基复相陶瓷及其高温摩擦学性能的研究

本研究以SiC为基体，用TiC和B4C为原料，采用新的反应原理生成TiB2，原位合成了TiB2-SiC基复相陶瓷，提高了SiC陶瓷的物理性能和高温摩擦学性能：随着材料中TiB2物相重量百分比的增加，材料的高温摩擦学性能提高。在以下摩擦环境参数下TiB2（wt25％）SiC基复相陶瓷自对偶在空气中高温摩擦磨损性能较好，呈现良好的高温自润滑性能：在升温状态下、空气中、环境温度为200℃-1000℃、外加载荷为0．2MPa、摩擦速度为0．3m／s，温度和外加载荷对TiB2-SiC基复相陶瓷自对偶比磨损率的影响具有依存性。高温摩擦氧化是TiB2-SiC基复相陶瓷自对偶高温磨损主要机理，磨损试样磨损断面包含摩擦氧化层、过渡层和基体亚表面三层。氧化层和过渡层接触紧密；磨屑具有典型包裹结构。     

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0～15h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。     

不同烧结助剂制备的Si_3N_4陶瓷的氧化行为

以α-Si3N4粉末为原料,分别以Y2O3-La2O3和Y2O3-CeO2为烧结助剂,利用热压烧结法制备了Si3N4陶瓷。研究了Si3N4陶瓷样品在空气中高温下的氧化行为。结果表明:原始的α-Si3N4在烧结过程中完全转化为β-Si3N4。在1000～1350℃氧化100h后,用Y2O3-La2O3烧结助剂制备的样品表现为质量增加趋势,质量变化小于0.389mg/cm2,其氧化过程符合抛物线规律。用Y2O3-CeO2烧结助剂制备的样品,在1000℃氧化后表现为质量减小,为-0.248mg/cm2;在1230℃和1350℃表现为质量增加,分别为0.024mg/cm2和0.219mg/cm2,并且其氧化过程不符合抛物线规律。样品的氧化过程主要受2个扩散过程的控制,即稀土元素的向外扩散与氧的向内扩散。     

SiAlC ceramics from a new polyaluminocarbosilane: Synthesis,structure and oxidation behaviors

SiAlC ceramics were prepared with a new polyaluminocarbosilane (PACS-N01) which was synthesized using methylaluminoxane (MAO) and liquid hyperbranched polycarbosilane (LPCS), and had a quite high ceramic yield (around 82.7%) at 900 °C in argon after curing. The obtained SiAlC ceramics consisted of β-SiC as major building units, small amounts of α-SiC and Al-containing phases with Al–O and Al–C bonds, and stayed partially amorphous till 1600 °C. Oxidation behaviors of SiAlC ceramics and SiC ceramics prepared through the same procedure were studied in the air at 1200 °C for different times. Dense oxide scales free of pores were formed on the surface of both samples. Measurements of oxide scale thickness revealed that the oxidation followed parabolic reaction kinetics and that the oxidation rate constant was apparently smaller for SiAlC than that for SiC. Besides, –Al–O–Si– network structure could be formed in SiAlC's oxide scale, which was supposed to block the pathway of oxygen diffusion and thus lowered the oxidation rates.     

SiC-TiB2-TiCx复相陶瓷的氧化行为研究

本文采用热等静压原位合成技术制备了TiB2-TiCx和SiC-TiB2-TiCx复相陶瓷,对其高温氧化行为进行了研究.结果表明,添加SiC后陶瓷材料抗氧化性有很大提高.SiC-TiB2-TiCx陶瓷的最高有效抗氧化温度为1200℃,而TiB2-TiCx陶瓷只有700℃.在温度低于1200℃时,SiC-TiB2-TiCx陶瓷的长时间抗氧化性能也优于TiB2-TiCx陶瓷.     

Ca3Co4O9陶瓷的制备和热电性能

氧化物半导体陶瓷材料是新型的中、高温热电材料。采用传统固相合成法和溶胶－凝胶法成功地制备了Ca3Co4O9陶瓷。对它们的显微结构和热电性能（Seebeck系数、电导率和热导率）进行了研究。实验结果表明，由两种方法制备得到的Ca3Co4O9陶瓷具有类似的热电性能。Ca3Co4O9陶瓷为取向无规则片状结构，属于p型半导体热电材料，其热电品质因子随温度升高而增大。Ca3Co4O9陶瓷具有大的Seebeck系数和低的热导率，但它的电导率仍然偏低，导致了它的热电品质因子比传统热电合金的热电品质因子低。     

Oxidation Behavior of NBD 200 Silicon Nitride Ceramics

The oxidation behavior of NBD 200 Si₃N₄ containing 1 wt% MgO sintering aid was investigated in oxygen at 900°-1300°C. The oxide growth followed a parabolic rate law with an apparent activation energy of 260 kJ/mol. The oxide layers were enriched with sodium and magnesium because of outward diffusion of intergranular Na⁺ and Mg²⁺ cations in the ceramics. The 2-4 orders of magnitude higher oxidation rate for NBD 200 Si₃N₄ than for other Si₃N₄ ceramics with a similar amount of MgO could be attributed to the presence of sodium. The oxidation process was most likely rate limited by grain-boundary diffusion of Mg²⁺.     

Ultra-low shrinkage and high-strength porous TiB/TiB2 ceramics via low temperature in-situ reaction sintering combined with the freeze-drying method

Ultra-low shrinkage porous TiB₂-based ceramics reinforced by the TiB whiskers are firstly fabricated through the in-situ reaction between TiB₂ and Ti at a low temperature (1450 °C). The growth of TiB whiskers with a high aspect ratio at pore channels is achieved through a vapor-solid growth mechanism, while low aspect ratio TiB whiskers at pore walls are dominated by a solid-state reaction diffusion growth, forming bimodal distribution whiskers in porous TiB₂-based ceramics. The overlapping TiB whiskers with low-speed growth at particle contact points can significantly inhibit the shrinkage and improve the strength of porous TiB₂-based ceramics. When the solid content is fixed at 20 vol% and target TiB content changes from 0 to 80 vol%, the porous ceramics show slight sintering shrinkage (from 1.1 to 4.7%) and high porosity (from 79.3 to 73.7%) while keeping high compressive strength of 1.8–18.2 MPa, which is higher than most reported porous ceramics at the same porosity.     

Oxidation Studies of Aluminum-Implanted NBD 200 Silicon Nitride

The effects of aluminum-ion-implantation on the oxidation behavior of NBD 200 Si₃N₄ were investigated over an implant concentration range of 0–30 at.%, at 800°–1100°C, in 1 atm dry O₂. Oxidation of both unimplanted and implanted samples follows a parabolic rate law. The parabolic rate constant decreases and the activation energy increases with aluminum concentration. Smooth and crack-free oxides are formed under the combination of high implant concentrations and low oxidation temperatures. Outward diffusion of Mg²⁺ from the bulk of NBD 200 to the oxide layer remains the rate-limiting step for aluminum-implanted samples. The enhancement of the oxidation resistance of NBD 200 by aluminum implantation is attributed to the retardation of the outward diffusion of Mg²⁺.     

陶瓷-硬质合金复合刀片材料的力学性能与界面结构

采用热压烧结工艺制备了刀具用陶瓷－硬质合金复合片．复合片上层为具有一定厚度的Ａｌ２Ｏ３／ＴｉＢ２陶瓷材料，下层为ＷＣ／Ｃｏ硬质合金．结果表明：复合片综合了陶瓷材料的高硬度和硬质合金的高强度，其性能介于陶瓷材料和硬质合金之间．Ｘ射线衍射、电子探针和扫描电子显微镜分析表明：烧结过程中硬质合金和陶瓷材料中的元素在界面相互扩散，并有新相形成，增加了界面结合强度，其界面为化合物型和扩散型的混合．     

Oxidation behaviour of SiC ceramic coating for C/C composites prepared by pressure-less reactive sintering in wet oxygen: Experiment and first-principle simulation

SiC ceramic coating, for prevention of C/C composites against oxidation, was prepared by pressure-less reactive sintering to investigate the oxidation behaviour in an oxidising environment containing water vapour at 1773 K. The experimental results demonstrated that the oxidation behaviour of porous SiC ceramics could be divided into two stages, following the parabolic model, which was attributed to the variation in the contact area involved in the oxidation reactions. During the entire oxidation process, water vapour could accelerate the oxidation of the SiC ceramics, according to the weight change. By first-principle calculations, the accelerated oxidation rate of the SiC ceramics was attributed to weakened Si–O and Al–O bonds in the formed glassy scale, which were caused by hydroxide radicals from the water. Atomic thermal motions at high temperature could lead to the breakage of the network structure, promoting the diffusion and solution of oxidising gases. When the as-prepared SiC ceramics were applied as anti-oxidative coatings for the C/C composites, the SiC ceramic coating and C/C matrix could be sealed and protected faster per unit time, because water vapour was beneficial to the formation of a glassy layer. The weight loss of the C/C matrix could be attributed to unsealed microcracks inside the SiC coating in the initial stage.     

Mechanism and Kinetics of Oxidation of ZrN Ceramics

Oxidation of ZrN ceramics from 973–1373 K under static conditions reveals parabolic rate behavior, indicative of a diffusion‐controlled process. In‐situ high temperature powder XRD found the oxidation mechanism begins with destabilization of ZrN through formation of a ZrN_1?x phase with oxide peaks initially detected at around 773 K. The zirconium oxide layer was found to be monoclinic by in‐situ XRD with no evidence of tetragonal or cubic polymorphs present to 1023 K. Bulk ceramic samples oxidized at 1173 and 1273 K underwent slower oxidation than those oxidized at 973 and 1073 K. This change in oxidation rate and hence mechanism was due to formation of a denser c‐ZrO₂ polymorph stabilized by nitrogen defects. This N‐doped dense ZrO₂ layer acts as a diffusion barrier to oxygen diffusion. However, at an oxidation temperature of 1373 K this layer is no longer protective due to increased diffusion through it resulting in grain boundary oxidation.