CuO-TiO_2复合助剂低温烧结氧化铝陶瓷的机理(Ⅱ)

固定CuO(0.4%)和TiO_2(4%)的添加量、改变TiO_2(0-32%)和CuO(0-3.2%)的添加量(质量分数,下同),研究了CuO-TiO_2复合助剂对氧化铝陶瓷烧结性能、微观结构、物相组成以及烧结激活能的影响,以揭示复合助剂的低温烧结机理。结果表明,在1150-1200℃TiO_2固溶入Al_2O_3生成Al_2Ti_7O_(15)相,并生成大量正离子空位提高了扩散系数,从而以固相反应烧结的作用机理促进了氧化铝陶瓷的致密化;TiO_2在Al_2O_3中的极限固溶度为2%-4%,超过固溶极限的TiO_2对陶瓷烧结没有促进作用;添加适量的CuO(0.4%)可将TiO_2在Al_2O_3中的固溶温度降低到1100℃以下,并以液相润湿作用促进氧化铝陶瓷的致密烧结。陶瓷烧结激活能的计算结果定量地印证了上述烧结机理;当在Al_2O_3中添加4%的TiO_2和2.4%的CuO,可将烧结激活能降低到54.15 kJ·mol~(-1)。     

CuO-TiO_2复合助剂低温烧结氧化铝陶瓷的机理(Ⅰ)

向氧化铝陶瓷中添加总量固定,但m(CuO)/m(Ti02)不同的CuO-TiO2复合助剂,研究其对氧化铝陶瓷烧结性能、微观结构以及物柑组成的影响,揭示复合助剂的低温烧结机理.结果表明,CuO与Ti02不易发生化合反应,分别以液相烧结和固相反应烧结来促进氧化铝陶瓷的致密化进程;Ti02与Al2O3反应生成Al2Ti7O15的固相烧结,比CuO的液相烧结更能有效地促进陶瓷的晶粒生长与致密化.在Ti02固相烧结的基础卜适当引入CuO液相,能够最大程度地降低氧化铝陶瓷的烧结温度;当在50gA12O3粉体中添加总量为0.025mol的CuO-TiO2复合助剂,并使m(TiO2)/m(CuO+TiO2)为0.80时,氧化铝陶瓷在1250℃烧结后其密度达到理论密度的98%以上.     

烧结助剂对反应热压烧结B4C基复合材料性能的影响

以微米级B₄C粉体为原料,通过与TiO₂葡萄糖原位反应制备TiB₂颗粒增韧B₄C复合材料。研究了烧结温度和烧结助剂对材料烧结行为及力学性能的影响。在1950℃反应热压下获得了相对密度为97.7%的TiB₂/B₄C复合材料,断裂韧性达到5.3 MPa·m1/2。添加Al₂O₃和Si烧结助剂后,分别在1950℃和1900℃ 获得了接近致密的(TiB_2,Al₂O₃)/B₄C和(TiB_2,SiC)/B₄C复合材料,断裂韧性分别提高到7.09和6.35 MPa·m1/2。显微组织分析表明,增韧作用主要来自残余应力引起的裂纹偏转。     

氧化铝纳米晶陶瓷研究进展

Al₂O₃陶瓷由于具有独特的物理化学特性而被普遍应用于结构材料、光学材料、电子材料等领域,但脆性严重限制了其更广泛的应用。近年来,人们对Al₂O₃纳米晶陶瓷的制备进行了不懈探索。Al₂O₃纳米晶陶瓷的制备主要包括α-Al₂O₃纳米颗粒的制备、素坯的烧结两个方面。本文综述了α-Al₂O₃纳米颗粒的主要制备方法,包括喷雾热解法、溶胶-凝胶法、沉淀法和机械球磨法;总结了Al₂O₃纳米晶陶瓷的主要烧结方法,包括放电等离子烧结、微波烧结、热压烧结和无压烧结;归纳了Al₂O₃纳米晶陶瓷力学性能的初步研究进展。最后展望了Al₂O₃纳米晶陶瓷研究的发展趋势。     

纳米-Al2O3/SiO2加入量对MgO-Al2O3-SiO2复相陶瓷烧结机理的影响

为了探究纳米-Al₂O₃/SiO₂加入量对MgO-Al₂O₃-SiO₂复相陶瓷烧结行为的作用机理。以微米级MgO、纳米级Al₂O₃和SiO₂为主要原料制备陶瓷基复合材料。通过XRD和 SEM等检测手段对烧后试样的物相组成和微观结构进行测试与表征,重点研究Al₂O₃/SiO₂的加入对复相陶瓷物相组成、微观结构及烧结性能的影响。结果表明:随着Al₂O₃/SiO₂加入量的增大,试样烧后相对密度和烧后线变化率呈先增大后减小再增大的趋势,加入15%Al₂O₃/SiO₂(质量分数)的试样经1 500 ℃烧结后,其相对密度可以达到94%。引入的Al₂O₃/SiO₂与基体中的MgO生成镁铝尖晶石与镁橄榄石相,原位反应伴随的体积膨胀,抵消部分烧结过程中的体积收缩。Al₂O₃/SiO₂加入量为75%(质量分数)的试样经1 400 ℃烧结后,基体中有大量堇青石相生成,随着煅烧温度提高到1 500 ℃,堇青石分解所产生的高温液相促进了试样的烧结收缩。     

原位Al2O3片晶/Ce-TZP和SrO·6Al2O3棒晶/Ce-TZP复合材料的制备与显微结构

通过在Ce-TZP基体中加入AlOOH及矿化剂TiO₂或反应剂SrCO₃制备了原位Al₂O₃片晶/Ce-TZP复合材料和原位SrO·6Al₂O₃棒晶/Ce-TZP复合材料。在烧结过程中TiO₂促进Al₂O₃晶粒发生显著的各向异性生长原位生成的片晶、Al₂O₃与SrCO₃发生反应,原位生成的高度各向异性的棒晶,它们在基体中分布均匀,具有较大的纵横比。烧结温度对片晶/棒晶的大小和含量有明显影响。通过在基体中原位形成片晶或棒晶,材料的力学性能有明显的改善。     

共沉淀法合成近零膨胀ZrW2O8/ZrO2复合陶瓷的致密化

采用化学共沉淀法合成前驱体,经1150℃ 烧结3.5 h得到近零膨胀26 wt% ZrW₂O₈/ZrO₂复合陶瓷,并利用X射线衍射仪、扫描电镜和热膨胀仪研究了原料中加入Al(NO₃)₃·9H₂O对26 wt% ZrW₂O₈/ZrO₂复合陶瓷的相组成、致密度和热膨胀性能的影响。研究结果表明,少量添加Al(NO₃)₃·9H₂O可有效提高复合材料致密度,所得复合陶瓷的组分仍为立方结构的α-ZrW₂O₈和单斜的m-ZrO₂,其中添加2.21 wt% Al(NO₃)₃·9H₂O的复合材料的致密度达到理论密度的98.67%,且对复合陶瓷的热膨胀性能影响不大。其促进致密化机制为晶界处低熔点液相物质Al₂(WO₄)₃提高了复合材料的烧结性能,消除气孔促进致密化。     

SiO2玻璃原位反应合成Al/Al2O3复合材料

利用SiO₂玻璃具有易近成型、致密及各向同性的特点,通过SiO₂玻璃与铝熔体间的反应合成了Al/Al₂O₃复合材料,克服长期以来在合成Al/Al₂O₃复合材料时均采用颗粒反应物的局限。反应产物是一种组织均匀致密的Al 与Al₂O₃互为网络的Al/Al₂O₃陶瓷基复合材料。反应温度升高,整个反应产物中的Al的体积分数上升。Al/Al₂O₃复合组织在三维空间的真实形态中存在着Al相被Al₂O₃完全包围的形态,证明了网络状Al₂O₃组织形成的烧结机理。与合成Al/Al₂O₃的其它工艺相比,本工艺可在1000℃的较低温度进行,并具有反应速度快、断裂韧性和抗弯强度值高的特点。     

Al2O3颗粒增强纯铝基复合材料的研究

本文探讨了用粉末冶金法,采用常规的冶金加工设备和工艺,制造Al₂O₃颗粒增强纯铝基复合材料的可行性。研究了不同Al₂O₃体积含量复合材料的显微组织及力学性能。初步试验了二次热挤压变形对颗粒分布和对基体强化的影响。结果表明,Al₂O₃颗粒与纯铝粉混合,加压烧结制备的复合材料,组织致密,颗粒分布均匀,随Al₂O₃含量增加,复合材料强度、硬度及弹性模量大大提高,Al₂O₃含量小于10%时,塑性不降低。二次热挤压有助于提高颗粒分布的均匀性;并使基体显著强化。     

烧成温度对Al2O3/Ni复合材料的致密化、物相组成和显微结构的影响

首先采用非均相沉淀合成出Ni包裹Al₂O₃粉体,然后热压烧结包裹粉体制备了Al₂O₃/Ni复合材料。本文作者主要研究了不同烧成温度对复合材料致密化、物相组成和显微结构的影响。结果表明:在1400℃保温1h,烧结体获得了最大相对密度,而致密度随Ni含量的增加反而降低;高于1350℃时,除Al₂O₃和Ni相外,在烧结体的表层生成一种由Al,Ni,O,C四种元素组成的新相;随着温度的升高,包裹层的纳米Ni颗粒聚合、长大,并退缩至三角晶界处,在适当的烧结温度(1400℃),少数小的纳米Ni颗粒被卷入Al₂O₃晶内,大的位于三角晶界,当烧成温度为1450℃时,不仅观察到Al₂O₃/Ni界面存在空隙,也发现了Al₂O₃晶粒异常长大现象。     

Effect of CuO addition to Nd(Zn1/2Ti1/2)O3 ceramics on sintering behavior and microwave dielectric properties

The microwave dielectric properties and microstructures of CuO-doped Nd(Zn_1/2Ti_1/2)O₃ ceramics prepared by the conventional solid-state route were investigated. The prepared Nd(Zn_1/2Ti_1/2)O₃ exhibits a mixture of Zn and Ti showing 1:1 order in the B-site. As an appropriate sintering aid, not only did CuO lower the sintering temperature, it could effectively hold back the evaporation of Zn in the Nd(Zn_1/2Ti_1/2)O₃. Moreover, CuO only resided in boundaries, which was confirmed by EDX analysis. The measured lattice parameters of CuO-doped Nd(Zn_1/2Ti_1/2)O₃ (a = 5.4652 ± 0.0005 ?, b = 5.6399 ± 0.0007 ?, c = 7.7797 ± 0.0008 ? and β = 90.01 ± 0.01°) retained identical to that of the pure Nd(Zn_1/2Ti_1/2)O₃ in all cases. In comparison with the pure Nd(Zn_1/2Ti_1/2)O₃ ceramics, specimen with 1 wt.% CuO addition possesses a compatible combination of dielectric properties with a ε_r of 30.68, a Q × f of 158,000 GHz (at 8 GHz) and a τ_f of − 45 ppm/°C at 1270 °C. It also indicated a 60 °C lowering in the sintering temperature. The proposed dielectrics can be a very promising candidate material for microwave or millimeter wave applications requiring extremely low dielectric loss.     

A new method for surface modification of TiO2/Al2O3 nanocomposites with enhanced anti-friction properties

In this paper, the TiO₂/Al₂O₃ composite nanoparticles were prepared by a hydrothermal method and in situ modified with acrylic acid. It was found that the mean particle size of modified TiO₂/Al₂O₃ composite nanoparticles was about 80 nm with a uniform distribution by the particle size analysis. The modified TiO₂/Al₂O₃ composite nanoparticles can disperse in lubricating oil homogenously for several weeks. The dispersion stabilization of modified TiO₂/Al₂O₃ composite nanoparticles in lubricating oil was significantly improved in comparison with the as-prepared nanoparticles, which was due to the introduction of grafted polymers by surface modification. The formation of covalent bands was identified by Fourier transform infrared spectrum. Under an optimized concentration of 0.1 wt%, the averaged friction coefficient was reduced by 14.75%, when the modified TiO₂/Al₂O₃ composite nanoparticles were used as lubricating oil additivities.     

Lightweight geopolymer made of highly porous siliceous materials with various Na2O/Al2O3 and SiO2/Al2O3 ratios

The syntheses of lightweight geopolymeric materials from highly porous siliceous materials viz. diatomaceous earth (DE) and rice husk ash (RHA) with high starting SiO₂/Al₂O₃ ratios of 13.0-33.5 and Na₂O/Al₂O₃ ratios of 0.66-3.0 were studied. The effects of fineness and calcination temperature of DE, concentrations of NaOH and KOH, DE to RHA ratio; curing temperature and time on the mechanical properties and microstructures of the geopolymer pastes were investigated. The results indicated that the optimum calcination temperature of DE was 800 °C. Increasing fineness of DE and starting Na₂O/Al₂O₃ ratio resulted in an increase in compressive strength of geopolymer paste. Geopolymer pastes activated with NaOH gave higher compressive strengths than those with KOH. The optimum curing temperature and time were 75 °C and 5 days. The lightweight geopolymer material with mean bulk density of 0.88 g/cm³ and compressive strength of 15 kg/cm² was obtained. Incorporation of 40% RHA to increase starting SiO₂/Al₂O₃ and Na₂O/Al₂O₃ ratios to 22.5 and 1.7 and enhanced the compressive strength of geopolymer paste to 24 kg/cm² with only a marginal increase of bulk density to 1.01 g/cm³. However, the geopolymer materials with high Na₂O/Al₂O₃ (>1.5) were not stable in water submersion.     

The effect of Sb2O5 additions on the dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics

The sintering behavior and dielectric properties for perovskite Ag(Nb_0.8Ta_0.2)O₃ ceramic with Sb₂O₅ doping was explored. A small amount of Sb₂O₅ (2.5 wt.%) led to high densification at temperatures < 1060 °C. The dielectric constant increased and the temperature coefficient decreased with increasing concentration of Sb₂O₅, and the dielectric constant reached 673, combined with a low temperature coefficient of 147 ppm/°C, and dielectric loss of 0.0044 (at 1 MHz) for the sample with 3.5 wt.% Sb₂O₅ sintered at 1080 °C.     

Photocatalytic effects for the TiO2-coated phosphor materials

This study investigated the photocatalytic behavior of the coupling of TiO₂ with phosphorescent materials. A TiO₂ thin film was deposited on CaAl₂O₄:Eu²⁺,Nd³⁺ phosphor particles by using atomic layer deposition (ALD), and its photocatalytic reaction was investigated by the photobleaching of an aqueous solution of methylene-blue (MB) under visible light irradiation. To clarify the mechanism of the TiO₂-phosphorescent materials, two different samples of TiO₂-coated phosphor and TiO₂–Al₂O₃-coated phosphor particles were prepared. The photocatalytic mechanisms of the ALD TiO₂-coated phosphor powders were different from those of the pure TiO₂ and TiO₂–Al₂O₃-coated phosphor. The absorbance in a solution of the ALD TiO₂-coated phosphor decreased much faster than that of pure TiO₂ under visible irradiation. In addition, the ALD TiO₂-coated phosphor showed moderately higher photocatalytic degradation of MB solution than the TiO₂–Al₂O₃-coated phosphor did. The TiO₂-coated phosphorescent materials were characterized by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photon spectroscopy (XPS).     

Mechanical properties and microstructure of Al2O3/TiAl in situ composites doped with Cr2O3

Al₂O₃/TiAl composites were successfully fabricated from powder mixtures of Ti, Al, TiO₂ and Cr₂O₃ by a hot-press-assisted exothermic dispersion method. The effect of the Cr₂O₃ addition on the microstructures and mechanical properties of Al₂O₃/TiAl composites was characterized, and the results showed that the Rockwell hardness, flexural strength and fracture toughness of the composites increased as the Cr₂O₃ content increased. When the Cr₂O₃ content was 2.5 wt%, the flexural strength and the fracture toughness attained peak values of 925 MPa and 8.55 MPa m^1/2, respectively. This improvement of mechanical properties was due to the more homogeneous and finer microstructure developed from the addition of Cr₂O₃ and an increase in the ratio of α₂-Ti₃Al to γ-TiAl matrix phases.     

Effect of Y3+ codoping on luminescence decays of the 4I13/2 level in Er3+-doped Al2O3 powders prepared by a sol-gel method

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er³⁺- and 0–20 mol.% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er³⁺-doped Al₂O₃ by Y³⁺ codoping. For the 0.1 mol.% Er³⁺-Y³⁺-codoped Al₂O₃ powders, the measured lifetime of Er³⁺ gradually increases with increasing Y³⁺ concentration. Consequently, codoping with 20 mol.% Y³⁺ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er³⁺ concentrations in the Al₂O₃ powders, the radiative lifetime of both the Er³⁺-doped and the Er³⁺-Y³⁺-codoped Al₂O₃ powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y³⁺ codoping does not change the-OH content in the Er³⁺-Y³⁺-codoped Al₂O₃ powders. The prolonged luminescence lifetime of the ⁴I_13/2 level of Er³⁺ in Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping is ascribed to the decrease in the energy transfer rate between the Er³⁺ ions and the Er³⁺ and -OH, respectively, due to the suppressed interaction between Er³⁺ ions.     

Fabrication of nanostructure Al2O3/ZrO2 (Y2O3) eutectic by combustion synthesis melt-casting under ultra-high gravity

A novel method for preparing Al₂O₃/ZrO₂ (Y₂O₃) eutectic was developed by combining combustion synthesis with melt-casting under ultra-high gravity (CSMC-UHG). The application of UHG = 800 g resulted in a high relative density of 99.8%, and an orientation-growth along the UHG direction. The microstructure was composed of aligned growth regimes containing a triangular dispersion of orderly ZrO₂ rods in Al₂O₃ matrix with a spacing of 300 nm. The eutectic had a high fracture toughness up to 17.9 MPa·m^1/2, which was mainly attributed to the nanostructure and the elastic bridge effects of the aligned ZrO₂ rods.     

Synthesis of Tb3Al5O12 (TAG) transparent ceramics for potential magneto-optical applications

Tb₃Al₅O₁₂ transparent ceramics have been prepared by solid state reaction and vacuum sintering. The optical quality and the microstructure of the samples were investigated. The sample sintered at 1650 °C possessed relatively good optical transparency from 400 nm to 1600 nm. The Verdet constant measured at 632.8 nm of the quasi-pore-free Tb₃Al₅O₁₂ transparent ceramic was −172.72 rad T⁻¹ m⁻¹, which was close to the counterpart of Tb₃Al₅O₁₂ single crystal. The thermal conductivity of the sample was also measured. To the best of our knowledge, this is the first time that Tb₃Al₅O₁₂ transparent ceramic with relatively good optical quality and magneto-optical property has been reported.     

The influence of the molar ratio of Al2O3 to Y2O3 on sintering behavior and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite

The influence of the molar ratio of Al₂O₃ to Y₂O₃ (i.e. M_Al2O3/M_Y2O3) on sintering densification, microstructure and the mechanical properties of a SiC–Al₂O₃–Y₂O₃ ceramic composite were studied. It was shown that the optimal value of M_Al2O3/M_Y2O3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y₃Al₅O₁₂) phase. When M_Al2O3/M_Y2O3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When M_Al2O3/M_Y2O3 was 3/2, materials existed in the two phases YAG (Y₃Al₅O₁₂) and YAM (Y₄Al₂O₉). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher.