Mechanical properties of highly toughened ZrO2Y2O3

Y-PSZ (partially stabilized zirconia) and Y-TZP (tetragonal zirconia polycrystals) containing from 1·5 to 5·0 mol% Y₂O₃ were prepared by hot isostatic pressing. The K_IC value nonlinearly increases with the decrease from 2·5 to 2·0 mol % Y₂O₃, and has a maximum K_IC value of 20 MPa √m at 2·0 mol% Y₂O₃. In order to clarify the toughness creating mechanism of the above materials, the experimental results of K_IC, σ_f and transformation zone size were examined, with emphasis on Y₂O₃ composition, Al₂O₃ additives and grain size.     

Fabrication of mesoporous Cr2O3 with highly distributed α-Fe2O3 and Pt nanoparticles for ultrafast H2 evolution rate

In the present contribution, p-n type heterojunction α-Fe₂O₃/Cr₂O₃ S-scheme system photocatalyst has been fabricated utilizing a sol-gel approach with assisted nonionic surfactant for a highly effective H₂ evolution rate under visible illumination. Pt NPs have been reduced by photodeposition during the photocatalytic reaction to collect Pt@α-Fe2O3/Cr2O3 finally. XRD analysis of Fe₂O₃/Cr₂O₃ nanocomposites verified the construction of Fe₂O₃ and Cr₂O₃ with rhombohedral phases. TEM images of Cr₂O₃ NPs were almost spherical and uniform in shape and size (20 ± 5 nm), and very small Fe₂O₃ NPs (3-5 nm) were distributed on the mesoporous Cr₂O₃ networks. The obtained α-Fe₂O₃/Cr₂O₃ photocatalyst exhibited noteworthy photocatalytic H₂ evolution with high efficiency and stability for 45 h. Interestingly, the photocatalytic H₂ evolution rate gradually boosted with the extent of Fe₂O₃ percentage up to 15% and its rate of 2215.4 μmol g^-1h^-1, which was fostered 7.25 folds larger than that of Cr₂O₃ NPs (305.7 μmol g^-1h^-1). The enhancement H₂ evolution rate of Fe₂O₃/Cr₂O₃ photocatalyst in comparison with bare Cr₂O₃ NPs was ascribed to facilitate the separation of photocarriers and existing considerable reactive sites. In addition, constructing n-type Fe₂O₃ and p-type Cr₂O₃ with close contact is essential in improving the H₂ evolution rate. The possible photocatalytic mechanism over Fe₂O₃/Cr₂O₃ nanocomposite was addressed based on electrochemical measurements. The construction of the S-scheme system of Fe₂O₃/Cr₂O₃ nanocomposite could be suggested to improve the separation of photocarriers through optimal transfer channels owing to the formation of synergistic characteristics. Our results provide avenues for constructing stable photocatalysts with high efficiency for H₂ evolution through visible exposure.     

Preparation of highly active nickel catalysts supported on mesoporous nanocrystalline γ-Al2O3 for CO2 methanation

In this study, a group of Ni catalysts supported on mesoporous nanocrystalline γ-Al₂O₃ with high surface area and with different Ni contents was prepared and employed in carbon dioxide methanation reaction. The obtained results showed increasing in nickel content from 10 to 25 wt.% decreased the specific surface area of catalysts from 177 to 130 m²/g and increased the nickel crystallite size from 12 to 24 nm. In addition, increasing in nickel content increased the reducibility of catalyst. The catalytic results revealed that the catalyst with 20 wt.% of Ni possessed high activity and stability in CO₂ methanation reaction.     

Low-temperature growth of highly crystalline β-Ga2O3 nanowires by solid-source chemical vapor deposition

Growing Ga₂O₃ dielectric materials at a moderately low temperature is important for the further development of high-mobility III-V semiconductor-based nanoelectronics. Here, β-Ga₂O₃ nanowires are successfully synthesized at a relatively low temperature of 610°C by solid-source chemical vapor deposition employing GaAs powders as the source material, which is in a distinct contrast to the typical synthesis temperature of above 1,000°C as reported by other methods. In this work, the prepared β-Ga₂O₃ nanowires are mainly composed of Ga and O elements with an atomic ratio of approximately 2:3. Importantly, they are highly crystalline in the monoclinic structure with varied growth orientations in low-index planes. The bandgap of the β-Ga₂O₃ nanowires is determined to be 251 nm (approximately 4.94 eV), in good accordance with the literature. Also, electrical characterization reveals that the individual nanowire has a resistivity of up to 8.5 × 10⁷ Ω cm, when fabricated in the configuration of parallel arrays, further indicating the promise of growing these highly insulating Ga₂O₃ materials in this III-V nanowire-compatible growth condition.

PACS

77.55.D; 61.46.Km; 78.40.Fy     

Preparation of highly dispersive solid microspherical α-Al2O3 powder with a hydrophobic surface for stereolithography-based 3D printing technology

The present research demonstrates the feasibility of the preparation of a highly dispersive, solid microspherical α-Al₂O₃ powder with a hydrophobic surface using a simple, rapid, and low-cost method for stereolithography-based 3D printing technology, including the synthesis of a precursor based on the in situ hydrothermal reaction of aluminum sulfate and urea, heat treatment, and surface modification using sodium oleate. The dependence of the morphologies of the precursors and α-Al₂O₃ powders on the type of aluminum salt, reaction time, and temperature was studied. The formation conditions of the solid spherical structure were explored. The results indicate that the formation of a solid spherical structure strongly depends on the type of aluminum salt, reaction time, and temperature. A spherical structure is only obtained by mixing aluminum sulfate with urea. Very high reaction times and temperatures facilitate the transformation of the microstructure from a solid sphere to a hollow sphere. The optimum hydrothermal reaction conditions are as follows: aluminum sulfate concentration of 0.05 mol/L, urea concentration of 0.2 mol/L, reaction temperature of 120 °C, and reaction time of 2 h. The optimum surface modification is obtained by using 3 wt% of sodium oleate, which can be used for the preparation of a 50 vol% α-Al₂O₃ ceramic UV-curable suspension with a viscosity of 1.66 Pa s at 30 s^-1. An alumina part with a sintering density of 95.5% was fabricated using stereolithography-based 3D printing technology. The analysis of the formation mechanism of the solid spherical structure indicates that the high decomposition temperature of urea, homogeneous dissolution of urea in aluminium sulfate solution, slow OH^- release by urea in the hydrothermal system, and strong coordination ability of SO₄²⁻ effectively restrain the hydrolysis of Al³⁺ and facilitate the formation of the solid spherical precursor Al₄(OH)₁₀SO₄. The solid microspherical α-Al₂O₃ powder is prepared by heat treatment of the precursor.     

Effect of Mg2+ and fluorine on the network and highly efficient photoluminescence of Eu3+ ion in MgF2–BaO–B2O3 glasses

The glass structure and photoluminescence of new oxyfluoride glasses with the composition of xMgF₂–(66.7−2x/3)BaO–(33.3−x/3)B₂O₃ (x = 10-50 mol%) were investigated in this work. The structure of the glasses was investigated by magic-angle spinning NMR, XAS, and Raman scattering spectroscopies. It was revealed that the glasses are mainly composed of BO₃ units with a disconnected borate network consisting mainly of ortho- and pyro-borate units, and ortho-borate increases with the addition of MgF₂. The fluorine atoms are surrounded by Mg²⁺ and Ba²⁺ ions. The photoluminescence of Eu³⁺-doped samples were investigated. It was indicated that asymmetry of the Eu³⁺ site increased with the addition of MgF₂. The photoluminescence quantum yield (η) of the glasses are very high and increased with MgF₂ addition; red photoluminescence is observed with η = 82% for 10MgF₂ and η = 98% for 50MgF₂ for excitation at 393 nm.     

FeAl/Al2O3 porous composite microfiltration membrane for highly efficiency high‐temperature particulate matter capturing

Journal of Porous Materials - Particulate matter (PM) pollution has raised serious concerns for public health. FeAl intermetallic porous membrane with extensive interconnected pores are potential...     

Synthesis and properties of highly branched poly(urethane–imide) via A2 + B3 approach

A series of highly branched poly(urethane–imide) (HBPUI) were synthesized via A₂ + B₃ approach using isophorone diisocyante (IPDI), polycarbonatediol (PCDL), 3,3′,4,4′-Benzophen-onetetracarboxylic dianhydride (BTDA), and poly(oxyalkylene) triamine (ATA) as materials. The structure of the products was characterized by FT-IR and ¹³C-NMR. The molecular weights were characterized by gel permeation chromatograph (GPC). The solution viscosity, thermal, and mechanical properties were measured by rotational rheometer, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), tensile tests, and dynamic mechanical analysis (DMA), respectively. The HBPUI showed lower viscosity than that of linear poly(urethane–imide) (LPUI), nevertheless T _g of HBPUI was higher than that of LPUI. TGA indicated that the thermal degradation of poly(urethane–imide) occurred above 300 °C, which was higher than conventional polyurethane. The tensile strength of HBPUI was obviously improved by increasing the content of BTDA and the molar ratio of [A₂]/[B₃]. The effects of the content of BTDA and the molar ratio of [A₂]/[B₃] on the storage modulus of the polymers were also studied.     

Novel sol–gel‐derived Ag/SiO2–Al2O3 catalysts for highly selective oxidation of methanol to formaldehyde

Novel Ag/SiO₂–Al₂O₃ catalysts with low silver content prepared by the sol–gel method exhibit excellent catalytic properties in the catalytic oxidation of methanol to formaldehyde. The silver content was as low as 2% and the yield of formaldehyde was achieved as 90.3%, which is 16% higher than that of pumice‐supported silver and even 5–6% higher than that of a commercial electrolytic silver catalyst. XRD, XPS and SEM results reveal that all silver was present as Ag⁺ before catalytic reaction and was partially reduced to the metallic state after the reaction. It was also found that silver was aggregated on the surface after its reduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

A highly active bimetallic supported Rh–Co hydroformylation catalyst prepared from RhCl3 and Co2(CO)8

The preparation of a highly active bimetallic SiO₂‐supported Rh–Co catalyst from RhCl₃ and Co₂(CO)₈ (Rh:Co= 1 : 3 atomic ratio) has been studied by IR spectroscopy and ethylene hydroformylation, etc. Two steps are involved in the preparative process: (1) surface‐mediated synthesis of Rh⁺(CO)₂/SiO₂ from calcined RhCl₃/SiO₂; (2) impregnation of Rh⁺(CO)₂/SiO₂ with a Co₂(CO)₈ solution followed by H₂ reduction at 623 K. The IR results of reductive carbonylation of calcined RhCl₃/SiO₂ have been compared to those of uncalcined RhCl₃/SiO₂ at 373 K. In situ IR observations, extraction results and elemental analysis suggest that approximately 50% of RhCl₃ are transformed to Rh₂O₃ on the SiO₂ surface and that calcined RhCl₃/SiO₂ is converted to a mixture of [Rh(CO)₂Cl]₂ and [Rh(CO)₂O₂ (O_s: surface oxygen) under CO at 373 K. When this SiO₂‐supported mixture was submitted to impregnation with a Co₂(CO)₈ solution at room temperature, IR study and elemental analysis show that [Rh(CO)₂Cl]₂ reacts easily with Co₂(CO)₈ on the surface to give RhCo₃(CO)₁₂, whereas [Rh(CO)₂O₂ does not react with Co₂(CO)₈. Catalytic study in steady‐state ethylene hydroformylation shows that a catalyst thus derived is more active than a catalyst derived from RhCo₃(CO)₁₂/SiO₂ and a catalyst derived by coimpregnation of [Rh(CO)₂Cl]₂ and Co₂(CO)₈ on SiO₂. This result suggests that the high rhodium dispersion of [Rh(CO)₂O₂ plays a crucial role in the formation of highly dispersed bimetallic Rh–Co sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Y_2O_3-Al_2O_3纤维

Ｙ2 Ｏ3-Ａｌ2 Ｏ3化合物熔点超过 1 90 0℃ ,具有优异的化学稳定性 ,因此可用作高级耐火材料。国外某文献报道了一种含有Ａｌ、Ｙ、Ｏ的连续氧化物陶瓷纤维的合成方法和性质。此种纤维中Ｙ2 Ｏ3和Ａｌ2 Ｏ3的最佳含量分别为 50 %～ 90 .7%和 9.3%～ 50 % ,而且Ｙ2 Ｏ3和Ａｌ2 Ｏ3之和应超过总量的 80 %。它由Ｙ2 Ｏ3溶胶和Ａｌ(ＯＨ) 3-ｘＤｘ 形式的铝盐溶于水形成的Ａｌ2 Ｏ3母液反应并分离制成 ,Ｄ是从氯化物、硝酸盐、羧酸盐等中选出的平衡离子。此纤维的晶相主要有Ｙ3Ａｌ5Ｏ1 2 、ＹＡｌＯ3、Ｙ4Ａｌ2 Ｏ9,还可能含有少量的Ｙ2 Ｏ3和…     

Piezoelectric properties of highly densified 0.01Pb (Mg1/2W1/2)O3–0.41Pb (Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3+0.1 wt% Y2O3+1.5 wt% ZnO thick films on alumina substrate

This paper reports on the formation of highly densified piezoelectric thick films of 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃+0.1 wt% Y₂O₃+1.5 wt% ZnO (PMW–PNN–PT–PZ+YZ) on alumina substrate by the screen-printing method. To increase the packing density of powder in screen-printing paste, attrition milled nano-scale powder was mixed with ball milled micro-scale powder, while the particle size distribution was properly controlled. Furthermore, the cold isostatic pressing process was used to improve the green density of the piezoelectric thick films. As a result of these processes, the PMW–PNN–PT–PZ+YZ thick film, sintered at 890 °C for 2 h, showed enhanced piezoelectric properties such as P_r=42 μC/cm², E_c=25 kV/cm, and d₃₃=100 pC/N, in comparison with other reports. Such prominent piezoelectric properties of PMW–PNN–PT–PZ+YZ thick films using bi-modal particle distribution and the CIP process can be applied to functional thick films in MEMS applications such as micro actuators and sensors.     

Al2O3-3Al2O3·2SiO-ZrO2耐火材料的相组成

Al<,2>O<,3>-SiO<,2>-ZrO<,2>系耐火材料应用范围广,特别被用作陶瓷辊,具有力学强度高、抗热震性能优良、耐碱类化合物侵蚀和高温蠕变率低的特性.Al<,2>O<,3>-SiO<,2>-ZrO<,2>系耐火材料性能很大程度上取决于其结晶相和玻璃相的总量和化学成分,采用定量XRPD和XRF研究了原料中Al<,2>O<,3>/SiO<,2>比和氧化铝颗粒尺寸分布对结晶相和玻璃相的总量及其化学成分的影响.耐火材料由莫来石、刚玉、ZrO<,2>的多晶体和总量各异的玻璃相组成.莫来石含量及其晶胞参数和成分随烧成温度改变,但主要受原料中Al<,2>O<,3>/SiO<,2>比的影响.     

ZrO_2-3Al_2O_3·2SiO_2-Al_2O_3系相关系和相变

本工作采用OM、XRD、SEM和EDAX诸仪器研究了ZrO_2-3Al_2O_3·2SiO_2-Al_2O_3系在缓冷和淬火条件下各组成试样的相关系。在该系的三元不变点附近选择了15个试样,其ZrO_2含量为30—35Wt％,Al_2O_3/SiO_2比(mol)为1.5—2.0。用OM和SEM观察了缓冷和淬火试样的析晶形貌特征。试样从1750℃淬火,析出细纤维状莫来石和亚显微质四方ZrO_2,在较低温度淬火或缓冷时,四方ZrO_2转变为单斜相并得到典型的莫来石-斜锆石共析体。在缓冷试样中可观察到包晶反应形貌。XRD分析表明缓冷和淬火的莫来石晶格常数的变异。用EDAX点分析,测出了莫来石和斜锆石具有组份互溶性。在本试验组成区域内不宜确定精确的三元不变点。     

A core–shell Ni/SiO2@TiO2 catalyst for highly selective one-step synthesis of 2-propylheptanol from n-pentanal

One-step synthesis of 2-propylheptanol (2-PH) from n-pentanal via a reaction integration of n-pentanal self-condensation and successive hydrogenation is of great significance for it can simplify process flow and reduce energy consumption. The key to promotion of 2-PH selectivity is to enhance the competitiveness of n-pentanal self-condensation with respect to its direct hydrogenation. For this purpose, a core–shell structured Ni/SiO₂@TiO₂ catalyst was designed and prepared. With the precise architecture of this core–shell structured catalyst, n-pentanal can be firstly in contact with TiO₂ to 2-propyl-2-heptenal (2-PHEA) while the direct hydrogenation to n-pentanol can be effectively inhibited, and then 2-PHEA diffuses into the core of Ni/SiO₂ and is hydrogenated to 2-PH. The spatial threshold of the core–shell catalyst significantly enhanced its catalytic performance; a 2-PH selectivity of 77.9% was reached with a 100% n-pentanal conversion. The 2-PH selectivity is much higher than that obtained by employing Ni/TiO₂ catalyst. Furthermore, the reaction kinetics of one-step synthesis of 2-PH from n-pentanal catalyzed by Ni/SiO₂@TiO₂ was studied and its kinetic model was established which is useful for reactor design and scale-up.     

Cr2O3-Al2O3-ZrO2高铬制品

介绍了Cr2O3-Al2O3-ZrO2制品的组成及各组成的作用、烧成气氛、制品的显微结构特征和性能指标.着重论述了影响制品性能的烧成工艺和以电熔、烧结两种Cr2O3颗粒生产的Cr2O3-Al2O3-ZrO2制品的显微结构差异,表明在还原气氛下烧成的Cr2O3-Al2O3-ZrO2制品性能优良,而采用电熔Cr2O3料生产的Cr2O3-Al2O3-ZrO2制品性能优于使用烧结Cr2O3料生产的.     

Si_3N_4添加CeO_2-Y_2O_3-Al_2O_3常压烧结

一、绪言在烧制高温结构材料的Si_3N_4时,因添加适当的烧结助剂,所以在主晶相之间残存有玻璃相或其他晶相,并已知所残存的第二相对于烧结体的特性有很大的影响。为了解决这一问题,一般采用热压或HIP等特殊方法及减少助剂用量。柘植氏等人在Si_3N_4之中添加5wt％的Y_2O_3,于1700℃烧结之后,再在N_2气体中1750℃下热压,使其在主晶相间析出耐火度高的Si_3N_4·Y_2O_3晶体,     

2CaO·2SrO·3Al_2O_3·SO_3的形成动力学

研究了一种硫铝酸锶钙矿物2CaO·2SrO·3Al_2O_3·SO_3(C_2?_2A_3$)的形成过程,采用Rietveld定量方法确定了不同温度、不同保温时间下烧成熟料中C_2?_2A_3$矿物的含量,并对C_2?_2A_3$的形成过程进行动力学分析。结果表明:在1 150–1 350℃条件下,熟料中C_2?_2A_3$的含量随着保温时间的延长而增加,在1 350℃保温180 min时C_2?_2A_3$的含量达到97.3%;在1 400℃保温超过30 min时,熟料中C_2?_2A_3$的含量开始减少;在1 450℃熟料中C_2?_2A_3$的含量随保温时间的延长而降低。形成C_2?_2A_3$的固相反应符合三维扩散模型,Jander模型具有最好的拟合效果。C_2?_2A_3$形成过程的活化能为479 kJ/mol。烧成温度主要影响C_2?_2A_3$矿物颗粒的细观形貌,但不会影响C_2?_2A_3$矿物的元素分布及组成。     

混合熔融Li2CO3-Na2CO3-K2CO3体系表面张力计算

熔融碳酸盐是一种良好的热载体和反应介质,其表面张力直接影响反应体系中熔盐分布和界面反应。在熔融盐离子半径和Butler方程的基础上,建立了熔融混合碳酸盐Li2CO3-Na2CO3-K2CO3体系的表面张力计算模型,考察了温度和熔盐组分对表面张力的影响。结果表明：模型计算的表面张力值与实际测量值比较吻合;熔融碳酸盐纯物质的表面张力随着阳离子的静电势（Z/r）的增大而逐渐减小;Li2CO3-Na2CO3-K2CO3体系中,熔盐的表面张力随着温度的升高而减小;混合熔融盐表面张力随着Li2CO3含量的增加而逐渐增大,随着K2CO3含量的增加而逐渐减小。     

CaO-SiO2-Al2O3-Fe2O3-SO3多元体系高温相变研究

实验采用石灰石、砂岩、粉煤灰和低品位铝矾土等工业原料,制备C3S相和C4A3S-相共存的水泥熟料;利用DSC-TG、高温XRD、岩相等方法对CaO-SiO2-Al2O3-Fe2O3-SO3多元体系烧制过程中高温相变进行分析,获得C4A3S-相和C3S相的变化规律,为利用废渣制备低碳排放的水泥熟料提供了理论支持.