Preparation and characterization of zirconia and mixed zirconia/titania in ionic liquids

Zirconia and mixed zirconia/titania were synthesized in two different ionic liquids, namely, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP]TFSA) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide ([EMIm]TFSA) using sol–gel methods. The synthesized oxides were characterized by means of X-ray diffraction, scanning electron microscopy with energy dispersive X-ray (SEM-EDX)), thermogravimetric and differential thermal analyses (TGA–DTA). The results show that the as-synthesized ZrO₂ powders obtained either in [BMP]TFSA or in [EMIm]TFSA show amorphous behaviour, and calcination at 500 °C yields t-ZrO₂ which is subject to further phase transformation to m-ZrO₂ at 1000 °C. The type of the ionic liquid influences the morphology of the synthesized zirconia as the sample obtained from [BMP]TFSA showed a porous morphology with very fine particles in the nanometer regime, whereas micro-rods were obtained from [EMIm]TFSA. ZrO₂-TiO₂ nanorods with an average diameter of about 100 nm were synthesized in [EMIm]TFSA. The presence of zirconia in the mixed oxides stabilizes the anatase phase and elevates the temperature at which the phase transformation to rutile occurs.     

硼化锆粉体的制备与表征

采用碳热还原法,在氩气气氛下1750℃保温1h制备出ZrB2粉体,反应物ZrO2、B2O3和C物质的量比为1:1:10,其中ZrO2以凝胶形式加入,ZrO2凝胶通过NaBH4滴定ZrOCl2溶液制备,C分别以活性炭和炭纤维形式加入,聚乙二醇(PEG)作分散剂,乙醇作为混合介质.用XRD、SEM和EDS分析方法对所得粉体进行了表征.结果表明,用活性炭作为还原剂制备的ZrB2,颗粒细小、均匀,平均粒径在80nm左右,粒子为球形;用炭纤维作为还原剂制备ZrB2粉体,由于炭纤维活性差,反应不彻底.     

ZrB2粉体制备的研究进展

随着高温技术的快速发展,高温材料的需求日益增大,同时对高温材料的性能也提出了更高的要求.ZrB2作为一种重要的高温结构材料,具有较高的化学稳定性、高的电导率和热导率、良好的阻燃性及高的耐腐蚀性等优点,因此应用前景广阔,逐渐引起了科研工作者的关注.主要介绍了ZrB2粉体的制备技术,综述了ZrB2陶瓷的主要应用,详细分析了各种制备方法的特点,最后展望了ZrB2粉体的应用前景.     

TiB2基复合材料的制备及其研究近况

TiB2因其优良的综合机械性能而备受关注.但是由于难以获得致密的TiB2,使其难以被广泛应用.加入金属基、陶瓷基材料是增强TiB2材料的有效方法.本文从材料制备方面简述了TiB2基复合材料的研究进展.     

机械力化学法制备滑石-TiO_2复合粉体的颜料性能

采用机械力化学法,在水介质中采用滑石研磨和滑石与TiO_2共混研磨方式制备滑石-TiO_2复合粉体,探讨影响复合粉体颜料性能的工艺因素,表征复合粉体的颜料性能与显微结构。结果表明:滑石的颗粒粒径随研磨强度的增加呈先减小后增大、再逐渐趋于稳定的规律,可满足与TiO_2复合的基体要求;滑石-TiO_2复合粉体表面滑石颗粒紧密包覆TiO_2颗粒层,具有与钛白粉相似的颜料性能;TiO_2质量分数为70%的滑石-TiO_2复合粉体的遮盖力为10.45 g/m~2,TiO_2质量分数为66%的复合粉体的遮盖力为12.50 g/m~2,2种复合粉体的遮盖力分别达到金红石型TiO_2的105.26%和88%;滑石-TiO_2复合粉体紫外线屏蔽性能与金红石钛白粉相当。     

二硼化钛基陶瓷涂层的制备研究进展

TiB2是具有高熔点、高耐磨、高耐腐蚀以及优异抗氧化争陛能的陶瓷材料。详述了国内外TiB2基陶瓷涂层的制备工艺,着重介绍了有关国内外热喷涂法和SHS法制备含陶瓷相涂层的情况,并指出了不同工艺的优缺点。最后阐述了涂层的成功应用情况及未来的涂层制备的发展趋势。     

Preparation and electrical erosion resistance of TiB2/Cu nanocomposites

A procedure is described for producing nanocomposite TiB₂/Cu powders containing up to 57 vol % TiB₂. Using shock compression of composite powders, we have prepared electrode materials offering enhanced electrical erosion resistance at high arc discharge currents. The effect of titanium diboride nanoparticles embedded in the copper matrix on the erosion behavior of the nanocomposites is examined. The nanoparticles are shown to suppress the copper droplet entrainment during the service of the electrode. TiB₂/Cu nanocomposite electrodes containing more than 10 vol % TiB₂ retain their shape and dimensions in the course of electrical erosion tests and offer enhanced service life.     

合成温度对二氧化钛纳米管的影响

以P25纳米粉体和NaOH为原料,采用水热合成法,在不同的合成温度下制备TiO2纳米管.用XRD、TEM、BET、TG-DSC、Uv-vis等方法对TiO2纳米管的形貌、成分和性能进行了表征.结果表明,合成温度对产物有显著影响:随着反应温度的升高,纳米管的比表面积逐渐增大,长度逐渐增长,而管径基本不变,纳米管的产率也有增加的趋势.150℃反应制得粉体的比表面积为641.855m2/g,管外径为8nm.160℃反应制得的粉体经560℃处理后降解亚甲基蓝的能力要远优于市售的P25纳米粉体.鉴于以前水热处理温度对纳米管形成方面的影响研究报道较少,系统的研究了温度对纳米管形成的影响.     

Preparation and characterization of ZrB 2 -SiC ultra-high temperature ceramics by microwave sintering

ZrB₂-SiC ultra-high temperature ceramic composites reinforced by nano-SiC whiskers and SiC particles were prepared by microwave sintering at 1850°C. XRD and SEM techniques were used to characterize the sintered samples. It was found that microwave sintering can promote the densification of the composites at lower temperatures. The addition of SiC also improved the densification of ZrB₂-SiC composites and almost fully dense ZrB₂-SiC composites were obtained when the amount of SiC increased up to 30vol.%. Flexural strength and fracture toughness of the ZrB₂-SiC composites were also enhanced; the maximum strength and toughness reached 625 MPa and 7.18 MPa·m^1/2, respectively.     

碳纳米管-ZrB2-SiC陶瓷基复合材料的制备与性能研究

研究了用热压烧结方法制备的不同碳纳米管(CNTs)含量的ZrB₂-SiC- xwt% CNTs (x=0、1.0、2.5、4.0) 复合材料的工艺条件、力学性能和微观结构. 用TEM观察了试样的微观结构, 用SEM观察了试样断口形貌和裂纹扩展情况, 并对其强韧化机制进行了分析. 研究表明, 碳纳米管主要分布沉积在ZrB2颗粒内部, 形成内晶型结构, 在CNTs含量为2.5%时, 相对密度、维氏硬度和弯曲强度分别为99.6%、21.7GPa和542MPa, 断裂韧性达到6.10MPa·m^1/2. 碳纳米管加入后材料致密性提高、晶粒细化,所形成的内晶型结构是材料强度和韧性得以提高的原因.     

TiB2的含量对Al2O3／TiB2陶瓷材料的高温氧化行为的影响

研究了不同ＴｉＢ２含量的Ａｌ２Ｏ３／ＴｉＢ２陶瓷材料的高温氧化行为。用ＸＲＤ和ＳＥＭ分析材料氧化后的相组成及显微结构，探讨了该材料的氧化机理和氧化膜的破坏方式。结果表明，不同ＴｉＢ２含量的Ａｌ２Ｏ３／ＴｉＢ２陶瓷材料在１４００℃空敢中氧化３０ｈ的氧化增重符合抛物线规律。     

Preparation of homogeneous titania coating on the surface of MWNT

Preparation of homogeneous and stable inorganic coatings on the surface of multi-wall carbon nanotubes (CNTs) was studied. Precursor compounds such as titanium (IV) bromide and titanium (IV) chloride were used to cover the surface of CNTs under either solvent-free or solution conditions. As-prepared titania layers were characterized by transmission, scanning electron microscopy and X-ray diffraction techniques. Results revealed that homogenous coverage can be achieved in a controllable way.     

Preparation,composition and some properties of codeposited TiB2-TiC x -coatings

Heterogeneous TiC_x and TiB₂ containing layers have been deposited from the gas phase onto hard metal and tantalum substrates in a cold wall reactor. The process parameters were thermodynamically calculated and verified by experiments. The deposited layers have been characterized regarding the chemical composition, structure, microhardness and abrasion wear. In a large composition range a characteristic layer structure is observed. Microhardness and abrasion wear run in dependence on the layer composition through a peak factor.     

Structural modification of zirconia and its influence on the catalytic activity

X-ray diffraction, differential thermal analysis and specific surface area measurements have been employed to understand the structural properties of ZrO₂ and sulphate-modified ZrO₂ calcined at different temperatures. Calcination facilitates the transformation of ZrO₂ from cubic to monoclinic phase. Addition of SO₄ ion to Zr(OH)₄ helps to retain the cubic phase up to 550 °C, and to maintain the surface area through a surface complex formation mechanism. The modified ZrO₂ acts as a superacid catalyst and enhances the vapour-phase aniline alkylation.     

Effect of TiB2 particle size on the material transfer behaviour of Cu–TiB2 composites

Cu-5.8vol.-%TiB₂ composites reinforced with different sized TiB₂ particles were prepared by spark plasma sintering (SPS). The arc erosion resistance was examined using a JF04C electrical contact instrument. The results indicate that the TiB₂ particle size and contact currents have important effects on the material transfer mode. Both lower mass loss and relative mass transfer was observed in the Cu-5.8vol.-%TiB₂ composites reinforced with fine TiB₂ particles (10?um, 30?um) compared to those with coarse TiB₂ particles (70?um, 110?um). The investigation and analysis of the microstructure and arc erosion mechanism show uniform distribution of fine TiB₂ particles in the copper matrix can significantly improve the viscosity of the molten pool and decrease the splashing of molten Cu.     

Preparation of zirconia and silicon carbide whisker biphasic powder mixtures by carbothermal reduction of zircon powders

Carbothermic reduction of zircon powders has been studied under argon and nitrogen gas pressures of 0.15 MPa in order to obtain biphasic composite powder mixtures containing zirconia and silicon carbide whiskers. The reduction has been carried out using different mole ratios of carbon and zircon. Carbon was used in the form of activated charcoal (specific surface area 1000 m²g^–1) or carbon black (specific surface area 300 m²g^–1). Whilst complete decomposition to m-ZrO₂ was obtained in the argon atmosphere at 1700 °C, under the nitrogen atmosphere the conversion was incomplete even at 1700 °C. However, the extent of conversion to zirconia at 1650 °C under nitrogen was found to be more than that under argon gas. In a few cases, particularly under the nitrogen atmosphere, minor amounts of other forms of zirconia e.g., tetragonal (t)-ZrO₂ or orthorhombic (o)-ZrO₂ were formed along with the major monoclinic (m)-ZrO₂ phase. The rate of reaction was found in general to increase with an increase in the carbon content. The studies particularly indicate that activated charcoal is a better reducing agent than carbon black owing probably to its enormous surface area. Further, it was also noted that cobalt chloride and sodium chloride act as a catalyst and a space forming agent respectively. They aid silicon carbide whisker formation and growth and hence the reaction is appreciably accelerated and reaches completion at 1650 °C in the argon atmosphere.     

放电等离子合成Ti3AlC2/TiB2复合材料的制备及性能研究

采用放电等离子烧结方法研究了Ti3AlC2/TiB2复合材料的制备和不同TiB2含量(体积百分数)对Ti3AlC2/TiB2性能的影响.研究表明,在1 250℃,30 MPa压力和保温8 min条件下烧结,可以得到相对密度达98%以上的致密Ti3AlC2/TiB2块体材料;在Ti3AlC2中添加TiB2能大幅度提高材料的硬度;Ti3AlC2/TiB2维氏硬度达到10.39 GPa,电导率达到3.7×106 S·m-1当TiB2含量为10%时,抗弯强度为696 MPa,断裂韧性为6.6 MPa·m1/2,但当TiB2含量继续增加时,由于TiB2的团聚和TiB2抑制Ti3AlC2晶体的生长导致了材料的抗弯强度和断裂韧性的下降.     

ZrB2-Si3N4高温复相陶瓷的制备及抗氧化机理研究

由于ZrB2具有极高的熔点、强度、硬度和导电率等许多优异性能,因而其应用领域非常广泛.研究了ZrB2-Si3N4复相陶瓷的制备和高温下的氧化机理.结果表明,在1700℃、15MPa、2h烧结务件下制备的ZrB2-20%Si3N4复相陶瓷的致密度为98%左右.ZrB2-Si3N4复相陶瓷在高温氧化时生成了SiO2,并且SiO2液相容易在复相陶瓷表面富集形成一层保护膜,有望提高陶瓷在更高氧化温度下的抗氧化性能.     

Preparation and characterization of chromium oxide supported on zirconia

Chromium oxide/zirconia was prepared by dry impregnation of powdered Zr(OH)₄ with an aqueous solution of (NH₄)₂CrO₄. The characterization of prepared samples was performed using Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and differential thermal analysis (DTA), and by measurement of the surface area. The addition of chromium oxide to zirconia shifted the transitions of ZrO₂ from the amorphous to the tetragonal phase and from the tetragonal to the monoclinic phase to higher temperatures due to the strong interaction between chromium oxide and zirconia; and the specific surface area of the samples increased in proportion to the chromium-oxide content. Since the ZrO₂ stabilizes supported chromium oxide, chromium oxide was well dispersed on the surface of zirconia, and -Cr₂O₃ was only observed at calcination temperatures above 1173 K. Upon the addition of only small amounts of chromium oxide (1 wt % Cr) to ZrO₂, both the acidity and acid strength of the samples increased remarkably, showing the presence of two kinds of acid sites on the surface of CrOx/ZrO₂ (Brönsted and Lewis acid sites).