氧化结合法制备多孔碳化硅陶瓷及其特性

以不同粒径碳化硅为骨料,羧甲基纤维素钠(CMC)为粘结剂,在大气中利用碳化硅颗粒表面氧化成的SiO2粘接在一起低温合成多孔碳化硅陶瓷。分析了粒径大小、烧结温度、成型压力对氧化结合多孔碳化硅陶瓷特性的影响。用TG-DSC、XRD、SEM研究了碳化硅陶瓷的氧化性能,物相组成,微观形貌。结果表明:原始粒径越小,碳化硅陶瓷的活性越高,相应的氧化程度越高,在1μm时氧化率最高达到49.58%,但其在1000℃保温100 h质量增重也最高达7.53%;随着烧结温度升高,碳化硅氧化率增加,气孔率相应地降低;成型压力也对碳化硅陶瓷的氧化率,气孔率产生一定影响。

剧烈-温和阳极氧化结合法快速制备有序阳极氧化铝膜的研究

本研究采用剧烈–温和阳极氧化(hard anodization-mild anodization,HA-MA)结合快速制备高度有序多孔阳极氧化铝(porous anodic alumina,PAA)膜的方法,即先利用HA在铝表面快速形成有序凹坑阵列,然后再对表面留有有序凹坑的铝基进行温和阳极氧化,制备出有序PAA膜。研究了剧烈阳极氧化时氧化电压、氧化时间对所制备PAA膜有序度的影响。研究结果表明,HA-MA结合法制备PAA膜的优化HA参数为:0.3 mol/L硫酸、80 V、10 min。HA-MA结合法所制备PAA膜的有序性和机械稳定性与二步温和阳极氧化法的相近,但形成有序PAA膜所需的时间为4.5 h,约为温和阳极氧化法的1/4,极大地提高了高度有序PAA膜的制备效率。

Synthesis of Macro-Mesostructured γ-Al_2O_3 with Large Pore Volume and High Surface Area by a Facile Secondary Reforming Method

Through improving the aging process during synthesis of the support, γ-Al2O3 with large pore volume and high surface area was synthesized by a facile secondary reforming method. The synthesis parameters, such as the reaction temperature, the first aging temperature and the second aging temperature, were investigated. The textural properties of γ-Al2O3 were characterized by means of N2 adsorption-desorption isotherms, X-ray powder diffractometry （XRD）, scanning electron microscopy （SEM）, Fourier transform infrared （FTIR） spectroscopy and thermogravimetry （TG）. The experimental results indicated that AACH and amorphous A1OOH were the precursors of alumina, which were formed via precipitation from solutions after reaction of aluminum sulphate with ammonium hydrogen carbonate. The precursor nanocrystallites grew and re-assembled during the secondary reforming process, which resulted in an increased pore size and pore volume and a decreased bulk density. The as-synthesized γ-Al2O3 materials featured meso/macroporosity, large pore volume （2.175 cm^3/g）, high surface area （237.8 m^2/g）, and low bulk density （0.284 g/mL）.

A Novel Mo-Doped Compound with Graphite-Like Structure: [H_3O]_2V_3O_8

The hydrothermal reaction of Na2MoO4 . 2H(2)O, V2O5 and en in water gave rise to a graphite-shaped vanadate [H3O](2)V3O8 1, which is doped with molybdenum. Compound 1 crystallizes in tetragonal system, space group P4bm, H6O10V2.9Mo0.1, M-r = 323.37, a = 8.904(1), c = 5.573(1)Angstrom, V = 441.8(1)Angstrom (3), Z = 2, D-c = 2.431 g.cm(-3), mu = 3.137 mm(-1), F(000) = 314, the final R = 0.0477, wR = 0.0993 for 260 observed reflections. Its two-dimensional framework is built up by corner-shared ((VO4)-O-V) tetrahedra and ((VO5)-O-IV) square pyramids with all of the terminal oxygen atoms toward the same orientation and further connected inta three-dimensional framework through hydrogen bonding between the protoned water molecules.

One-dimensional iron oxides nanostructures

Iron oxides, including α-Fe2O3, γ-Fe2O3, Fe3O4, etc. are one of the most widely investigated materials for their fundamental properties and potential applications. One-dimensional （1-D） iron oxides nanostructures are the focus of recent research activi- ties because of their wide applications in magnetic refrigeration, information storage, electronics, catalysts, Li-ion battery, pigment, gas sensors, etc. This review covers the recent progress in the synthesis, properties and applications of 1-D iron oxides nanostructures. The paper begins with the introduction to 1-D iron oxides nanostructures, followed by the typical synthetic methods developed for the synthesis of 1-D iron oxides nanostructures. Then, the typical 1-D iron oxides nanostructures, in- cluding nanowires/nanorods, nanotubes, nanobelts, nanochalns, and special 3-D structures built on 1-D building blocks, are introduced in detail. The properties of 1-D iron oxides nanostructures are then discussed, focusing on the magnetic, gas sensing, and electrochemical and photocatalytic properties. Finally, we draw conclusions and look at the prospects of 1-D iron oxides nanostructures.

A simple approach to porous low-temperature-sintering BaTiO_3

Porous tetragonal BaTiO 3 ceramic was successfully prepared by a combination of hydrothermal and low-temperature-sintering method.The hollow TiO2@BaCO 3 as the sintering precursor was synthesized via a simple hydrothermal method,and then porous BaTiO 3 was generated by calcining the hollow TiO2@BaCO 3 precursor at 900 ℃ without additive.The hollow TiO2@BaCO 3 structure plays two important roles in the preparing of the porous BaTiO 3 ceramic.First,the TiO2@BaCO 3 hollow structure provides high surface areas and increases the contact points between BaCO 3 and TiO2,which can reduce the sintering temperature of the BaTiO 3 ceramic.Second,the cavity of the ordered arranged TiO2@BaCO 3 hollow sphere shows important influence on the porous structure,and the pore size of the as-prepared porous BaTiO 3 ceramic can be tuned from several nanometers to hundreds nanomters by changing the sintering temperature.The formation mechanism of the porous BaTiO 3 ceramic was proposed.

The adsorption and dissociation of multilayer CH_3OH on TiO_2(110)

The adsorption and dissociation of CH3OH on TiO2 （110） were studied using density functional theory methods. Our results suggest that CH3OH molecules can adsorb up to 3/4 ML （1 ML=5.2× 10^14 molecules/cm2） coverage at five-coordinated titanium （Tisc） sites to form the first layer. In the second layer, the CH3OH is adsorbed at bridge-bonded oxygen, and from the third layer, the CH3OH molecules form a hydrogen-bonded network with each other. The theoretical results show that dissociation of multilayer adsorbed methanol to aldehyde occurs through a stepwise pathway, with easy O-H bond dissociation and rate-determining C-H bond dissociation. The dissociation barriers for 8 or 12 CH3OH molecules on TiO2 are higher than that for low coverage by 0.15-0.21 eV; this suggests that the dissociation of multilayer adsorbed CH3OH is harder.