Production of porous ceramic materials using nanodisperse SiC powder

Porous ceramic materials were produced by hot pressing of a nanocrystalline (19 nm) silicon carbide powder synthesized by a hybrid method that combined the sol–gel processing of a finely divided and chemically reactive SiO₂–C system and the carbothermic synthesis at moderate (1400°C) temperature in a vacuum. It was studied how such characteristics as density, porosity, sizes of crystallites and aggregates of SiC particles, specific surface area, and compressive strength depend on pressing temperature (1400, 1500, 1600, and 1700°C).     

Specific features of the defect structure of metastable nanodisperse ceria, zirconia, and related materials

Models of the defect structure and microstructure of the CeO₂, ZrO₂, Ce-Me¹-O (Me¹ = La, Sm, Zr), and Zr-Me²-O (Me² = Ca, Sr, Ba) nanomaterials are discussed. For ceria-based fluorite, the appearance of weakly bound oxygen and the mobility of bulk oxygen are due to distortions in the Ce-O coordination sphere and the appearance of interstitial oxygen atoms. For pure and doped zirconia, the phases forming in the intermediate temperature range are characterized by metastable structural networks differing from those observed in the equilibrium phases. The change in the local environment of the Zr cations (eight-atom coordination sphere) from a square antiprism in the initial salts to a distorted fluorite-like polyhedron in zirconia and the principle of structural conformity between hydrolyzed cations and the terminal hydroxyls of the Zr complexes in solution are the factors determining the genesis and structural features of the metastable phases. The defect structure and microstructure of the complex fluorite-like oxides have an effect on the state of the supported active component, favoring the formation of clustered species in the vicinity of extended defects in the support. Some examples of this effect in different types of reactions are provided.     

Thermal and structural characterization of superfine down powder

The thermal degradation of down fiber and down powder was studied using TG, DSC, TG-FTIR, and ATR-FTIR as a function of mass loss. For both down fiber and down powder, two evident mass loss stages were observed. Compared to down fiber, down powder had higher moisture and lower thermal stability. The oxygen in air weakened the mass loss of superfine down powder in the temperature range of 300–530 °C, and accelerated the oxidation–reduction reaction between oxygen and powder when the temperature was over 530 °C. The microstructures of down fiber and down powder were investigated on the analysis of DSC results. As the decrease in the average particle size of down powder, the absorbed energy of the destruction of crystallinity, rupture of crosslinks and thermal degradation of peptide bonds decreased, respectively. The gases evolved during thermal degradation of superfine down powder were inspected by in situ FTIR, and then the solid residues collected at different temperature were analyzed using ATR-FTIR. The color evaluation of superfine down powder hot-pressed at high temperature was discussed to confirm the best hot-processing condition.     

An X-ray electron study of nanodisperse hydroxyapatite

Two states of surface valence electrons localized on faces with different molecular reliefs were observed for nanodisperse hydroxyapatite. Thermal treatment of nanocrystals caused a shift ΔE _b = 0.5 eV of the spectrum of valence electrons on molecularly rough faces and a shift of 0.8 eV of the spectrum from smooth faces. Similar electron spectrum shifts were observed for sorption, in particular, of sodium succinate. These results are of importance for the diagnostics of various hydroxyapatite kinds, since hydroxyapatite is a constituent mineral component of living organisms, and for the synthesis of medicines with enhanced biological activity used in treatment of various bone diseases.     

超微粉Ga-BETA沸石的水热合成及其结构研究

本文报道了新型杂原子BETA沸石,Ga-BETA沸石超微粉的水热合成研究, 讨论了原始反应物配比对产物粒度的影响因素.利用TEM,X荧光,XRD,IR,DTA,XPS 等手段对样品进行SiO~2/Ga~2O~3比测定及结构特征表征.由于Ga的掺入,产物的晶胞参数,红外光谱以及Ga3d电子的电子结合能都发生明显变化.     

The optical properties of nanodisperse silica in hydrothermal solutions

The optical properties of aqueous solutions of colloidal silica were studied by photon correlation spectroscopy and spectrophotometry. Photon correlation spectroscopy measurements were taken at a 633 nm wavelength of monochromatic laser radiation. Autocorrelation function and scattered light amplitude plots were constructed, and the mean radii and diffusion coefficients of particles were determined. Spectrophotometric measurements were taken over the electromagnetic radiation wavelength range 200–1000 nm. The positions of optical density maxima were determined. The influence of various factors, including concentration, the size of nanoparticles, temperature, and pH, on the optical properties of aqueous solutions of silica was estimated.     

神木半焦粉末萃取物的组成特征

依次用石油醚、CS₂、CH₂Cl₂、丙酮和甲醇在索氏萃取器中萃取了神木半焦粉末,得到了五级萃取物(E_1-5)和最终的萃余物,总萃取率为1.76%。分别用气相色谱/质谱联用仪(GC/MS)、大气压固体探针/飞行时间质谱仪(ASAP/TOF-MS)和电喷雾电离/飞行时间质谱仪(ESI/TOF-MS)分析了各级萃取物。用GC/MS分析的结果表明,在E₁中C_15-24的直链烷烃和E₂中3与4环的芳烃比较丰富,在E_3-5中含杂原子有机化合物较丰富,特别是E₄和E₅中含氧有机化合物的含量最高。与用GC/MS分析的结果相比,用ASAP/TOF-MS和ESI/TOF-MS从E_3-5中检测出更多的含杂原子有机化合物。     

The structural model for liquid-solid reaction of mesoporous powder

The reaction kinetics of the mesoporous powder, MCM-TP, anchored with synergistic extractant TOPO-P204, with Pd²⁺ in spent fuels have been investigated. The results showed that the reaction rate was independent of pellet size, which suggested that the powder pellet was highly porous and was composed of plate-like “grains”. This analysis was confirmed by observing the surface and cross section of the pellet with SEM. It provided the physical basis for establishing the liquid-solid reaction model of mesoporous powders: P-G^* model. The calculated curves from the model were in good agreement with the experimental results.     

Synthesis and structural features of 2-halo-2,2-dinitroacetamidoximes

Nitro compounds in which the halodinitromethyl group is bonded to the formamidoxime or halohydroxyiminomethyl moiety were obtained for the first time and characterized. The structures of some amidoximes were studied by experimental (X-ray diffraction) and theoretical methods.     

Synthesis, reactions and structural features of monofluorinated cyclopropanecarboxylates

Monofluorinated cyclopropanecarboxylates are available in racemic or optically active form by transition metal-catalyzed reactions of vinylfluorides with diazoacetates. From α-fluorostyrene and tert-butyl diazoacetate in the presence of 2 mol% of an enantiopure bis(oxazoline) copper complex, a 81:19 mixture of tert-butyl trans- and cis-2-fluoro-2-phenylcyclopropanecarboxylates was obtained with high enantiomeric excess (ee) of 93 or 89%, respectively. The corresponding racemic ethylesters were used as starting materials for the synthesis of carboxamides, of the cis- and trans-isomers of analogues of tranylcypromine, an anti-depressive drug and several of its homologous fluorinated cyclopropylmethyl and cyclopropylethyl amines. Corresponding enantiopure cyclopropylmethanols and several of their derivatives were synthesized also. Solid state structures of a selection of these compounds were examined by X-ray crystallography. Particularly, the cis-configurated fluorinated phenylcyclopropane derivatives showed extremely close intermolecular CH?FC contacts. The shortest of such distances (2.17 Å) was found in the N-(4-bromophenyl)carbamate of (1S,2R)-(2-fluoro-2-phenylcyclopropyl)methanol.     

Innovative synthetical and structural features of new aryltellurenyl iodides

The syntheses and the structural characterization of the compounds [(mes)₂Te–Te(I)mes], (PyH)[mesTeI₃(I₃)] (mes = mesityl = 2,4,6-trimethylphenyl; Py = pyridine), (PyH)₃[dmephTeI₂(I₂)]₂(I₃) (dmeph = 2,6-dimethylphenyl), (PyH)₂[RTeI₄]₂·(CH₃)CO(CH₃)·C₆H₅CH₃ (R = p-tert-butylphenyl) and (PyH)₂[PhTeI₄]₂ (Ph = phenyl) are presented. Some earlier analog preparations are compared and the influence of ortho substituents in the aryl group on the oxidation state of tellurium is discussed, as well as the observed conditions for the formation of poly-iodides chains.     

Synthesis and structural features of cyclobutane-containing chiral bicyclic ureas

Efficient and stereoselective synthetic routes have been developed for the preparation of chiral N-monoprotected cyclobutane bicyclic ureas in which one of the NH groups is protected as a benzyl or tert-butyl carbamate. Ureas in both enantiomeric forms were obtained from a common chiral precursor via the selective manipulation of functional groups. These compounds have been subjected to a structural study in solution and in the solid state. NMR, IR and TEM techniques evidence a strong tendency to aggregation in solution giving regular assemblies, which is a result of intermolecular urea N–H?OC hydrogen bonding. In the solid state, X-ray analysis shows that two urea molecules interact through only one hydrogen bond yielding infinite chains. This fact and the almost complete coplanarity of both the urea and the carbamate carbonyl groups determine the crystal packing to be formed by a parallel molecular arrangement. All these structural features are well supported by theoretical calculations that allow us to conclude that the formation of a network based on hydrogen bonding is energetically favourable.     

Adiabatic compressibility and structural features of non-electrolyte aqueous solutions

Structural characteristics of the hydration complexes of non-electrolytes such as the hydration numbers h, molar adiabatic compressibility of hydration complexes β _h V _h , the molar volume of water in the hydration sphere V _1h , the solute molar volume without hydration environments V _2h and others are determined using the data on the ultrasonic velocity, the density and heat capacity of aqueous solutions of urea, urotropine, acetonitrile, and a number of amides of N-acetyl amino acids. A theoretical model of solvation is also applied. A comparison of the environments of hydrated urotropine molecules with those of urea and acetonitrile molecules in an aqueous medium shows a considerable hydrophobic interaction of urotropine with a solvent.     

Three-dimensional structural features and the toxicity of aminobenzenes and phenols

There are many organic pollutants in the environment, such as polychlorinated biphenyl, polycyclic aromatic hydrocarbons, dichlorodiphenyl-trichloroethane (DDT), and polychlorinated naphthalene. These organic pollutants are persistent,liposoluble and easily cumulated in organism; consequently, the potential toxicity will be high. Risk assessment of industrial chemicals is currently carried out using scanty experimental data, because many of these chemicals have very little or no test data. S…     

Properties and processing of cork powder filled cellulose derivatives composites

This paper deals with the use of cork powder, a by‐product from cork industry, as a filler to reinforce hydroxypropyl cellulose (HPC) matrix. Several films were prepared using HPC, as a matrix, filled with different amounts of cork powder (average diameter < 50 μm) (0.0; 0.5; 1.0 and 10.0% w/w) and in the presence or not of 1,4‐diisocyanatobutane (BDI) (7.0% w/w). Before the elaboration of these films, the surface properties of cork powder as well as that of suberin (main component of cork) were determined by Inverse Gas Chromatography (IGC). The tensile properties of the solid films obtained were studied and, as expected, for the films with BDI but without cork powder, the Young's modulus and the tensile strength increased, while the elongation decreased. However with the filled films it seemed that the Young's modulus decreased and the elongation increased. The Scanning Electron Microscopy showed that the fractured plane of samples with cross‐linking agent and cork powder displayed some nucleation points (0.3 μm) which indicates a strongly bonded interface and which could be considered as a responsible for the high mechanical properties observed.