Mechanical properties of Nb2O5 and Ta2O5 prepared by different procedures

We have studied the mechanical properties of niobium pentoxide and tantalum pentoxide ceramics prepared by a conventional ceramic processing technique and by exposure to high-intensity light (HIL). The results demonstrate that, after HIL exposure in an optical furnace, the niobium pentoxide and tantalum pentoxide ceramics possess enhanced microhardness and improved mechanical properties (strength, fracture toughness, and brittle microstrength) owing to the formation of fractal micro- and nanostructures. With increasing exposure intensity, the strength of the Nb₂O₅ and Ta₂O₅ ceramics increases.     

Influence of Nb2O5 doped amount on the property of BCTZ lead-free piezoelectric ceramics doped with Li2CO3

Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ (BCTZ) lead-free piezoelectric ceramics doped with Nb₂O₅ (0.1, 0.3, 0.5, 0.7, 0.9 wt%) and Li₂CO₃ (0.6 wt%) were prepared by conventional solid-state reaction method. Influence of Nb₂O₅ doping amount on the piezoelectric property, dielectric property, phase composition and microstructure of prepared BCTZ lead-free piezoelectric ceramics doped with Li₂CO₃ were investigated by X-ray diffraction and scanning electron microscopy and other analytical methods. The results showed that the sintered temperature decreased greatly when the BCTZ lead-free piezoelectric ceramics were co-doped with Nb₂O₅ and Li₂CO₃; a pure perovskite structure of BCTZ lead-free piezoelectric ceramics co-doped with Nb₂O₅ and Li₂CO₃ sintered at 1,020 °C could be also obtained. The grain size decreased when Nb₂O₅ doping amount increased. The piezoelectric constant (d₃₃), the planar electromechanical coupling factor (k_p), the relative dielectric constant (ε_r) of BCTZ ceramics doped with Li₂CO₃ increased firstly and then decreased, the dielectric loss (tanδ) decreased firstly and then increased when Nb₂O₅ doping amount increased, indicating that Nb₂O₅ was “soft” additive. When Nb₂O₅ doping amount (z) was 0.7 wt% and Li₂CO₃ doping amount was 0.6 wt%, the BCTZ ceramics sintered at 1,020 °C possessed the best piezoelectric property and dielectric property, which d₃₃ was 238 pC/N, k_p was 29.33 %, ε_r was 4,691, tanδ was 2.07 %.     

Nb_2O_5对碲铅铋铌系玻璃结构和性能的影响

采用熔融法制备不同Nb2O5含量的TeO2-PbO-Bi2O3-Nb2O5系玻璃粉,研究了Nb2O5的加入量对TeO2-PbO-Bi2O3-Nb2O5系玻璃热膨胀系数、软化温度和热稳定性的影响。利用傅里叶变换红外光谱仪检测玻璃粉的结构,通过热机械分析仪和综合热分析分别测试玻璃的膨胀系数和析晶温度,采用场发射扫描电镜观察太阳能电池Ag/Si接触界面。结果表明,随着Nb2O5含量的增加,玻璃的热膨胀系数和软化温度逐渐降低,玻璃化温度和析晶温度逐渐升高,玻璃的热稳定性逐渐增强。添加Nb2O5的玻璃粉所对应的太阳能电池正面电极中,Ag/Si接触界面存在大量的纳米银粒子,这将更有利于晶硅太阳能电池的光电子传导。     

Synthesis and characterization of γ-Bi2O3 based solid electrolyte doped with Nb2O5

γ-phase bismuth oxide is a well known high oxygen ion conductor and can be used as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). This study aims to determine new phases of Bi₂O₃-Nb₂O₅ binary system and the temperature dependence of the electrical transport properties. The reaction products obtained in open air atmosphere were characterized by X-ray powder diffractions (XRD). The unit cell parameters were defined from the indexes of the powder diffraction patterns. The γ-Bi₂O₃ crystal system were obtained by doping 0.01 < mole% Nb₂O₅ < 0.04 at 750 °C for 48 and 96 h. Thermal behaviour and thermal stability of the phases were investigated by thermal analysis techniques. Surface and grain properties of the related phases were determined by SEM analysis. The temperature dependence of the electrical properties of γ-Bi₂O₃ solid solution was measured by four-point probe d.c. conductivity method. In the investigated system, the highest value of conductivity was observed for σ _T = 0.016 ohm^?1 cm^?1 at 650 °C on 4 mole% Nb₂O₅ addition. The electrical conductivity curves of studied materials revealed regular increase with temperature in the form of the Arrhenius type conductivity behaviour.     

Eu3+掺杂Nb2O5-La2O3-P2O5-Na2O-BaO玻璃的光谱性质

制备了χNb2O5-(10-χ)La2O3-60P2O5-10Na2O-19BaO-Eu2O3(以mol%记χ=9、7、5)的玻璃,测定了玻璃的吸收光谱、发射光谱、激发光谱、声子边带谱和差热分析曲线.从发射光谱出发获得了Eu3 光学跃迁的J-O参数Ω2、Ω4,并计算了Eu3 离子5DO→7FJ(J=1,2,4)的自发辐射跃迁几率A以及受激发射截面σp.结果显示,随着La2O3的增加和Nb2O5的减少,玻璃样品的热稳定性降低,强度参数Ω2减小,表明材料的对称性提高,共价性减弱,Eu-O键强减弱;随着La2O3的增加,电-声子偶合减弱,受激发射截面σp减小.     

Performance of mortar prepared with recycled concrete aggregate enhanced by CO2 and pozzolan slurry

One of the most promising strategies to manage the large volume of construction and demolition (C&D) waste is recycling and utilizing it for the production of new concrete. However, recycled concrete aggregate (RCA) derived from C&D waste possesses relatively higher porosity and water absorption capability, which often limits its wild utilization. In this study, pozzolan slurry (includes silica fume, nano-SiO₂, and fly ash slurries) and CO₂ treatments as enhancement methods for RCA were investigated. Test results showed that CO₂ treatment was more effective in reducing water absorption and enhancing fluidity, whereas pozzolan slurry treatment could decrease fluidity. Mortars prepared with treated RCA exhibited better mechanical strength and higher resistance towards carbonation and chloride-ion diffusion than those with untreated RCA. Both pozzolan slurry and CO₂ treatments enhanced not only the properties of RCA, but also the old and new interfacial transition zones (ITZs) as demonstrated in the measured micro-hardness and SEM observation.     

Cu-ZnO@Al2O3 hybrid nanoparticle with enhanced activity for catalytic CO2 conversion to methanol

A facile approach is demonstrated for the fabrication of Cu-ZnO-based hybrid nanostructures for the catalytic CO₂ conversion to methanol. The method combines colloid stabilization of Al₂O₃ nanoparticles (as support material) and controlled co-precipitation of Cu (active metal) and ZnO (promoter) onto the Al₂O₃ nanoparticles. Complementary approaches, including X-ray diffractometry, Brunauer-Emmett-Teller surface area analysis, N₂O pulse chemisorption, CO₂-based temperature-programmed desorption, transmission electron microscopy coupled with energy dispersive spectroscopy, inductively coupled plasma optical emission spectrometry and thermal gravimetric analysis are employed for the characterization of catalyst materials. The results show a successful synthesis of ultrafine Cu-ZnO nanocrystallites deposited on the Al₂O₃ nanoparticle clusters (Cu-ZnO@Al₂O₃). Hybridization with Al₂O₃ nanoparticles enhanced metal dispersion and number of basic sites of the Cu-ZnO-based nanocatalyst. Aminosilane-based surface functionalization on the Al₂O₃ nanoparticle increased metal surface area in the hybrid nanostructure. The CO₂ conversion catalyzed by the synthesized Cu-ZnO@Al₂O₃ was shown to be proportional to active surface area of the hybrid nanostructure. An optimum selectivity of the synthesized catalyst was identified (≈47–49%) when the mass fraction of Al₂O₃ was (35–36) %, in correspondence to the highest moderate basicity of the synthesized hybrid nanostructures. The highest yield of methanol achieved 12989 ± 2007 µmolg^?1 h^?1 by the developed Cu-ZnO@Al₂O₃. Our work demonstrates a prototype study of fabricating high-performance hybrid nanocatalyst with the support of mechanistic understanding in material synthesis for the synergistic catalysis of CO₂ hydrogenation to methanol.     

Uptake of various cations by amorphous BaAl2Si2O8 prepared by solid-state reaction of kaolin with BaCO3

The uptake of various ions by amorphous and crystalline BaAl₂Si₂O₈ was investigated. The BaAl₂Si₂O₈ samples were prepared by solid-state reaction of kaolin ground with BaCO₃ for periods from 1 to 24 h followed by firing at temperatures of 800–1200 °C for 24 h. Uptake experiments were performed at room temperature (25 °C) using a solid/solution ratio of 0.1 g/50 ml, with a cation concentration of 10⁻³ M and reaction time of 24 h. The cations used for the uptake experiments were alkaline earth ions (Mg²⁺, Ca²⁺ and Sr²⁺) and transition metal ions (Ni²⁺, Co²⁺, Cu²⁺ and Zn²⁺). The uptake of alkaline earth ions was low in all the samples while the transition metal ion uptakes were higher in the amorphous BaAl₂Si₂O₈ sample than crystalline BaAl₂Si₂O₈ samples. The high uptake of transition metal ions by the amorphous sample was further enhanced by prolonging the grinding time. Since the amorphous sample appears from the ²⁹Si and ²⁷Al NMR spectra to have a similar local structure to crystalline hexacelsian (double-layered structure consisted of alternatively corner shared AlO₄ and SiO₄ tetrahedra), the uptake of transition metal ions is suggested to occur by release of interlayer Ba ions in the vicinity of edge sites with the adsorption of transition metal ions from the solution.     

Microwave dielectric properties of Li2ZnTi3O8 ceramics prepared by reaction-sintering process

Li₂ZnTi₃O₈ (LZT) microwave dielectric ceramics prepared by reaction-sintering process were investigated. Li₂CO₃, ZnO and TiO₂ powders were mixed, pressed and sintered directly into ceramic pellets without any calcination stage involved. Pure LZT phase was obtained after sintering at temperatures above 1,100 °C for 2 h. LZT ceramic with the maximum bulk density of 3.81 g/cm³ (96.2 % of the theoretical value) and excellent microwave dielectric properties of ? _r  = 25.8, Q × f = 78,216 GHz and τ _f  = ?10.5 ppm/°C was obtained after sintering at 1,100 °C for 2 h. The results show that the reaction-sintering process is a simple and effective method to produce LZT ceramics.     

Synthesis of Co/SiO2 hybrid nanocatalyst via twisted Co3Si2O5(OH)4 nanosheets for high-temperature Fischer-Tropsch reaction

A cobalt-silica hybrid nanocatalyst bearing small cobalt particles of diameter ～5 nm was prepared through a hydrothermal reaction and hydrogen reduction.The resulting material showed very high CO conversion (＞82％) and high hydrocarbon productivity (～1.0 gHc·g-1cat,·h-11) with high activity (～8.5 x 10-5 molco·g-1Co·S-1) in the Fischer-Tropsch synthesis reaction.     

Bi2O3掺杂对Nb2O5-TiO2电容-压敏双功能陶瓷的影响

研究了Bi2O3掺杂对Nb2O5-TiO2电容压敏双功能陶瓷材料的烧结温度,相对介电常数,非线性,压敏电压的影响.实验发现,烧结温度为1200℃,Bi2O3掺杂量为0.2%时,非线性系数α高达6.6148;Bi2O3掺杂量为1.0%时,相对介电常数εr高达1.3733×104.烧结温度在1450℃时,压敏电压最低,Eb=1.979 V·mm-1.     

硬脂酸法制备层状K2La1.8Nb0.2Ti3O10

采用硬脂酸法在相对较低的温度下掺杂Nb制备了K2La1.8Nb0.2Ti3O10层状化合物.通过X射线衍射、透射电子显微镜、紫外-可见吸收光谱、拉曼光谱对产物进行了表征.结果表明,通过硬脂酸法在800℃可获得超细K2La1.8Nb0.2Ti3O10,颗粒尺寸为100～250 nm,经过Nb掺杂后的产物仍然保持层状结构,层间距约1.5nm.紫外-可见光谱表明掺杂前后的产物在紫外区均有较明显的吸收,但经Nb掺杂后的K2La1.8Nb0.2Ti3O10吸光度明显增强.     

Preparation and magnetic properties of SiO2-CaONa2O-P2O5-FeO-Fe2O3glass-ceramics prepared by gel-melt method

The SiO2-CaO-Na2O-P205-FeO-Fe2O3 precursors were prepared by the sol-gel method.And then two different ways were used to obtain the ferrimagnetjc glass-ceramics,j.e.,one is compression-sintering method.and the other is melt-quenching-heat treatment.The crystalline type and size of the magnetite were analyzed by XRD patterns.and the magnetism of samples were characterized by VSM.This kind of glass-ceramics shows a bioactive behavior after soaked in the Simufated body fluid test for two weeks.     

Li2CO3-B2O3-V2O5掺杂ZnO-TiO2陶瓷低温烧结的研究

以Li2CO3、B2O3和V2O53种常见的低熔点氧化物为烧结助剂,用传统固相法制备了Li2CO3-B2O3-V2O5掺杂的ZnO-TiO2微波介质陶瓷,并利用XRD、SEM等研究了ZnO-TiO2陶瓷的烧结行为、物相组成、显微结构特征及微波介电性能等。结果表明,当掺入3%(质量分数)Li2CO3-B2O3-V2O5时,在840℃烧结2h可制备出体积密度为4.99g/cm3的ZnO-TiO2陶瓷,达到理论密度的96.5%以上,εr、Q.f、τf分别约为24、22900GHz、-4×10-6/℃。     

溶液燃烧法制备Ni-Al2O3催化剂用于CO2-CH4重整研究

采用溶液燃烧法制备了Ni含量为2wt%、4wt%、6wt%、8wt%和10wt%系列催化剂, 并对反应前后催化剂进行N₂吸附-脱附、XRD、H₂-TPR、TPH、Raman、TEM和TG-DTG等表征。与等体积浸渍法(以溶液燃烧法制备的Al₂O₃为载体)制备的催化剂相比, 溶液燃烧法制备的催化剂具有较大的比表面积, 孔径分布可分为2~4.5 nm和4.5~10 nm两段, 属典型的多级孔结构; NiO高度分散在载体上, 与载体具有较强的相互作用, 这种相互作用有利于提高催化剂的稳定性。催化剂210 h稳定性试验表明, 溶液燃烧法制备的Ni含量为8wt%试样的CH₄转化率维持在90%左右, 失活速率仅为0.035%/h, 优于浸渍法制备的相同Ni含量催化剂。     

四元SCR催化剂V2O5-WO3-MoO3/TiO2脱硝性能

以锐钛型TiO2为载体,V2O5为主要活性成分,同时负载WO3和MoO3作为活性助剂,制备了四元催化剂V2O5-WO3-MoO3/TiO2,并对该催化剂的脱硝活性、催化选择性及微观表征进行了研究。结果表明,该四元催化剂脱硝性能优于相同负载量下单一负载W或Mo的三元催化剂,W可以提高催化剂高温(>400℃)活性,同时抑制Mo在高温区间导致的副反应发生,Mo可以提高低温(<300℃)活性,弥补W在低温区间的活性不足。该四元催化剂最大活性99%,温度窗口(脱硝活性>80%)为280～420℃,在180～380℃范围内SO2氧化率为零,在0～1000℃范围内存在3个失重峰,100～130℃结晶水蒸发,230～270℃有机添加剂分解,500～530℃无机盐分解,微观镜像表明该催化剂颗粒均匀致密,粒径大小一致,没有出现团聚现象,具有完整的微孔结构。