Low temperature specific heat and thermal stability of Fe-B ultrafine amorphous alloy particles

Fe-B ultrafine amorphous alloy particles (UFAAP) were prepared by chemical reduction of Fe3+ with NaBHO4 and confirmed to be ultrafine amorphous particles by transmission electron microscopy and X-ray diffraction. The specific heat of the sample was measured by a high precision adiabatic calorimeter, and a differential scanning calorimeter was used for thermal stability analysis. A topological structure of Fe-B atoms is proposed to explain two crystallization peaks and a melting peak observed at T=600, 868 and 1645 K, respectively.

Calorimetric study of Wood alloy

The heat capacities of Wood alloy have been measured with an automatic adiabatic calorimeter over the temperature range of 80 similar to 360 K. The thermodynamic data of solid-liquid phase transition have been obtained from the heat capacity measurements. The melting temperature, enthalpy and entropy of fusion of the substance are 345.662 K, 18.47 J.g(-1) and 0.05343 J.g(-1).K-1, respectively. The necessary thermal data are provided for the low temperature thermodynamic study of the alloy.

An investigation of the roles of surface aluminum and acid sites in the zeolite MCM-22

Ammonia adsorption studies reveal that the observed Lewis acidity in the zeolite MCM-22 is derived from at least two types of framework aluminum sites (Al(F)), that is, octahedral Al(F) and three-coordinate Al(F). Comparative ammonia or trimethylphosphine (TMP) adsorption experiments with MCM-22 confirm that octahedral Al species gives rise to the signal at delta(ISO) approximate to 0 in the (27)Al NMR spectrum; this is a superposition of two NMR signals from the different Al species on the water-re constructed zeolite surface. A sharp resonance assigned to framework Al reversibly transforms on ammonia adsorption to delta(ISO) (27)Al approximate to 55 from tetrahedral Al(F), while the broad peak is assigned to nonframework aluminium which results from hydrothermal treatment. This study also demonstrates the effectiveness of (27)Al magic angle spinning (MAS) and multiple quantum (MQ) MAS NMR spectroscopy as a technique for the study of zeolite reactions.

Epoxidation of propylene with dilute H2O2 over titanium silicalite containing trace aluminum

Titanium silicalite (TS-1) was successfully synthesized by using TPABr as the template and silica sol as silicon source in a 100 l stainless steel autoclave. IR, XRD, UV--vis, elemental analysis, and (2)7Al and (3)1P MAS NMR were used to characterize the synthesized products. The results show that the synthesized material has an MFI structure with high crystallinity and large crystal size and two kinds of titanium species. Trace aluminum in silica sol is also incorporated into the zeolite framework. The synthesized TS-1 exhibits high activity in the epoxidation of propylene with dilute H2O2 with high selectivity to methyl mono-ethers and low selectivity to propylene oxide (PO). The low selectivity toward PO is due to the residual acidity onto TS-1. The selectivity of PO can reach up to 90% through adjusting the pH of the reaction mixture. Extra amounts of base decrease the H2O2 utilization and the H2O2 conversion. However, in over acid-treated TS-1 in which part removal of extra-framework titanium takes place, the utilization of H2O2 is quite different: for the low Si/Ti ratio of TS-1, the H2O2 utilization increases. But the utilization of H2O2 does not change for the high Si/Ti ratio TS-1. Thermal analysis shows that the as-synthesized TS-1 exhibits high activity and thermal stability in the calcined range 540-900 degreesC.

Stable tetrahedral aluminum sites in hexagonal mesoporous aluminosilicates

A unique templating approach for the synthesis of hexagonal mesoporous aluminosilicates via self-assembly of pre-formed aluminosilcate nanoclusters with the templating micella formed by cetyltrimethylammonium bromide (CTAB) is described. The obtained materials of MAS-5 are hydrothermally stable, which is shown by X-ray diffraction (XRD) analysis. Furthermore, as characterized by NMR technique, MAS-5 has stable tetrahedral aluminum sites that is the major contributions to the acidity of aluminosilicate molecular sieve, and on non-framework aluminium species in the samples was observed.

The effect of tungsten additive on the surface characteristics of amorphous Ni-P alloy

The variation of surface compositions on amorphous Ni80.4W1.5P18.1 alloy by O-2 oxidation and H-2 reduction treatments have been studied by XPS, UPS and ISS. It shows that addition of tungsten in the amorphous Ni-P alloy leads to dramatic changes of the relating component distributions in the surface layers before and after these treatments. Oxidation of a Ni80.4W1.5P18.1 amorphous alloy in 1 bar of oxygen at 513 K caused a significant segregation of nickel in different oxide states at the surface. The subsequent reduction of the oxidized surface with I bar hydrogen at 553 K resulted in only a small portion of Ni and P being reduced into elemental states, while most of them was found to combine to form a kind of nickel phosphate compound. On the other hand, under the same conditions, the oxidation and reduction of a Ni80P20 alloy gave rise to metallic Ni and elemental P as the predominate species on the alloy surface. The addition of W in the amorphous alloy might act as nuclei for a favorable formation of the phosphate structure which was proposed to be an active species for hydrogen-relating catalytic reactions. (C) 1999 Elsevier Science B.V. All rights reserved.

Characterization and thermodynamic study of ultra-fine particle of Ni-B amorphous alloy

Ultra-fine particle of Ni-B amorphous alloy was prepared by chemical reduction of Ni2+ with NaBH4 and characterized with TEM and XRD. The heat capacity and thermal stability were measured with a high-precision automatic adiabatic calorimeter and DTA. The upper limit of applied temperature of the substance was found to be 684 K for use as catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.

Preparation and characterization of Pd-Ag alloy composite membrane with magnetron sputtering

A Pd-Ag (24 wt%) alloy composite membrane was prepared by the magnetron sputtering. A gamma-Al2O3 membrane was synthesized by the sol-gel method and used as substrate of the Pd-Ag alloy film. The process parameters of the magnetron sputtering were optimized as a function of the compactness of the Pd-Ag alloy film. The best membrane with a thickness of 1 mu m was produced with a sputtering pressure of 2.7 Pa and a substrate temperature of 400 degrees C. The membrane had an H-2/N-2 permselectivity of 51.5-1000 and an H-2 permeation rate of 0.036-1.17 x 10(-5)cm(3)/cm(2).s. Pa, depending on operating conditions.

XRD and XPS studies on the ultra-uniform Raney-Ni catalyst prepared from the melt-quenching alloy

We present a novel method for preparing an ultra-uniform Raney-Ni catalyst, which includes melt-quenching, hydrogen treatment and leaching in an alkali solution. The resultant catalyst shows superior activity in the reaction of cyclohexanone hydrogenation. X-ray diffraction (XRD) and XPS have been employed to characterize the catalysts. As demonstrated, the pretreatment with hydrogen caused a distinct phase transfer of the Ni-Al alloys, forming more of the Ni2Al3 component. In the subsequent leaching process, the Ni2Al3 component shows high activity and the resultant catalyst exhibits high surface areas and small pores. Moreover, metallic Al in the hydrogen-pretreated alloy appeared to be leached more easily and thus the aluminium species remaining on the catalyst surface is aluminium oxide predominantly, which serves as a matrix to stabilize active Ni species on the surface. Copyright (C) 2001 John Wiley & Sons, Ltd.