Preparation and characterization of a novel solid solution of aluminum in tungsten carbide by mechanically activated high-temperature reaction

In this work, a novel substitutional solid solution (W0.8Al0.2)C was synthesized by mechanically activated high-temperature reaction. X-ray diffraction was used for phase identification during the whole reaction process. Environment scanning electronic microscopy-field emission gun and energy dispersive x-ray were used to investigate the microstructure and the quantitative material composition of the specimen. (W(0.8)A(10.2))C was found to crystallize in the WC-type, and the cell parameters were a = 2.907(1) angstrom and c = 2.837(1) angstrom. The hardness of (W0.8Al0.2)C was tested to be 19.3 +/- 1 GPa, and the density was 13.19 +/- 0.05 g cm(-3).

Diluting thiol-derivatized oligonucleotide monolayers on Au(111) by mercaptohexanol replacement reaction

Surface replacement reaction of thiol-derivatized, single-stranded oligonucleotide (HS-ssDNA) by mercaptohexanol (MCH) is investigated in order to reduce surface density of the HS-ssDNA adsorbed to Au(111) surface. Cyclic voltammograms (CVs) and scanning tunneling microscopy (STM) are employed to assess the composition and state of these mixed monolayers. It is found that each CV of mixed self-assembled monolayers (SAMs) only shows a single reductive desorption peak, which suggests that the resulted, mixed SAMs do not form discernable phase-separated domains. The peak potential gradually shifts to negative direction and the peak area increases step by step over the whole replacement process. By analyzing these peak areas, it is concluded that two MCH molecules will replace one HS-ssDNA molecule and relative coverage can also be estimated as a function of exposing time. The possible mechanism of the replacement reaction is also proposed. The DNA surface density exponentially reduces with the exposing time increasing, in other words, the replacement reaction is very fast in the first several hours and then gradually slows down. Moreover, the morphological change in the process is also followed by STM.

Crystallization and characterization of substoichiometric compound (W0.5Al0.5)C-0..5 obtained by solid-state reaction

(W0.5Al0.5)C-0.5 substoichiometric compound is synthesized by a combination of mechanical milling and high-pressure reactive sintering. X-ray diffraction is used to monitor the phase changes and crystallization of (W0.5Al0.5) C-0.5 during the whole reaction process. As a result, (W0.5Al0.5) C-0.5 is identified as the hexagonal WC-type belonging to the P-6m2 space group (No. 187), and the lattice parameters of (W0.5Al0.5)C-0.5 are calculated to be a = 2.907 (1) angstrom, c = 2.838 (1) angstrom, which are very similar to those of WC even if there are approximately 50 pct carbon vacancies in the cell of (W0.5Al0.5)C-0.5 as compared with WC. The substoichiometric (W0.5Al0.5)C-0.5 compound has a Vickers microhardness of 2385 +/- 70 kg mm(-2), which is as high as that of WC, while its density is far lower than that of WC.

Syntheses and properties of novel polyimides derived from 2-(4-aminophenyl)-5-aminopyrimidine

2-(4-Aminophenyl)-5-aminopyrimidine (4) is synthesized via a condensation reaction of vinamidium salts and amidine chloride salts, followed by hydrazine palladium catalyzed reduction. A series of novel homo- and copolyimides containing pyrimidine unit are prepared from the diamine and 1,4-phenylenediamine (PDA) with pyromellitic dianhydride (PMDA) or 3,3',4,4'-biphenyl tertracarboxylic dianhydride (BPDA) via a conventional two-step thermal imidization method. The poly(amic acid) precursors had inherent viscosities of 0.97-4.38 dL/g (c = 0.5 g/dL, in DMAc, 30 degrees C) and all of them could be cast and thermally converted into flexible and tough polyimide films. All of the polyimides showed excellent thermal stability and mechanical properties. The glass transition temperatures of the resulting polyimides are in the range of 307-434 degrees C and the 10% weight loss temperature is in the range of 556-609 degrees C under air. The polyimide films possess strength at break in the range of 185-271 MPa, elongations at break in the range of 6.8-51%, and tensile modulus in the range of 3.5-6.46 GPa. The polymer films are insoluble in common organic solvents, exhibiting high chemical resistance.

Promoter effect of La3+ on the electrochemical reaction of microperoxidase-11

The effect of La3+ on the electrochemical behavior and structure of heme undecapeptide-microperoxidase-11 (MP-11)-in the aqueous solution was investigated using cyclic voltammetry, circular dichroism (CD) and UV-vis absorption spectrometry. It was found for the first time that La3+ would promote the electrochemical reaction of MP-11 at the glassy carbon (GC) electrode. This is mainly due to the fact that La3+ would induce more beta-turn and alpha-helical conformations from the random coil conformation of MP-11 and increase the non-planarity of the heme.

Determination of gold, platinum and palladium in geological samples by inductively coupled plasma-mass spectrometry after separation and preconcentration with C-410 anion exchange resin

A method for the determination of Au, Pt and Pd in geological samples is described. Au, Pt and Pd can be separated and concentrated quantitatively by C-410 anion-exchange resin in the condition of 1.5 mol/L HCl with the adsorption rates of 91.2%, 100.0% and 95.7% respectively. No interference exists from coexisting elements except for Ge(IV), Cr(VI),Ti(IV) in inductively coupled plasma-mass spectrometry. The detection limits are 0.27 mug/L, 0.40 mug/L and 0.19 mug/L for Au, Pt and Pd respectively. The results of these elements in standard geological materials are in agreement with certified values with precision of 19.2% RSD for Au (n = 8), 28.1% RSD for Pt (n=8), and 15.6% RSD for Pd (n=8).

Silicon dioxide coating of CeO2 nanoparticles by solid state reaction at room temperature

The synthesis Of SiO2 coated CeO2 nanoparticles by humid solid state reaction at room. temperature is described. Transmission electron microscope results show that CeO2 Particles were coated with a layer Of SiO2. Binding energy of Ce 3d(5/2) was shifted from 883.8 to 882.8 eV after coating in the XPS Ce 3d spectra. This confirms the chemical bond formation between SiO32- and Ce4+. Because the surface photovoltage property of CeO2 nanoparticles that were used as core materials in the experiment approaches to that of CeO2 macroparticles, peak P2 (electron transition from 0 2p on surface to Ce 4f) disappeared in the surface photovoltage spectrum of CeO2 nanoparticles. Also, the effect Of SiO2 on the electron transition from 0 2p to Ce 4f results in the lowering of surface photovoltage response intensity of P1 peak (electron transition from 0 2p in bulk to Ce 4f).

Coating of Y2O3 : Eu3+ particles with alumina by a humid solid state reaction at room temperature

Humid solid state reaction at room temperature was utilized for the first time to coat Y2O3 : Eu3+ particles with alumina. The particles were studied with an X-ray photoelectron spectrometer (XPS), a scanning electron microscope (SEM), and an energy dispersive spectrometer (EDS). XPS results show that the yttrium and europium contents are decreased and that the aluminum content is the highest except for that of oxygen after coating. SEM and EDS results show that particles are coated with a thin shell of alumina.

Preparation of Pt/C catalyst with solid phase reaction method

The PVC catalyst was prepared with solid phase reaction method (Pt/C(S)) for the first time. Its performances were compared with that prepared by the traditional liquid phase reaction method. The results demonstrate that the electrocatalytic activity of PVC catalyst with solid phase reaction method for methanol oxidation is higher than that with liquid phase reaction method. XRD and TEM measurements indicate that the Pt/C(S) possesses low crystalline extent and small particle size.

Improved size control of large palladium nanoparticles by a seeding growth method

A new approach to the preparation of large palladium nanoparticles with diameters between 25 and 100 nm is presented. In this approach PdCl42- ions are reduced on the surface of performed 12-nm-diameter gold "seeds'' by the introduction of ascorbic acid. The resultant particles exhibit improved monodispersity relative to previous work. Interestingly, these nanoparticles possess Au-Pd core-shell structures. The method can be scaled up to produce 50-110 mg of large palladium nanoparticles.

Electron self-exchange reaction of viologen and its derivatives in poly(ethylene glycol)

The electron self-exchange rates (k(ex)) of viologen and its derivatives are estimated by using microelectrode voltammetry in poly(ethylene glycol) films. The dependences of supporting electrolyte concentration and sizes of viologen and its derivatives on k(ex) and diffusion coefficients (D) are discussed. Results show that k(ex) increases with the decrease of supporting electrolyte concentration and sizes of reactants. (C) 2000 Elsevier Science S.A. All rights reserved.