Fabrication and characterization of multi-scale coated boron powders with improved combustion performance:A brief review

Boron has high mass and volume calorific values,but it is difficult to ignite and has low combustion efficiency.This literature review summarizes the strategies that are used to solve the above-mentioned problems,which include coatings of boron by using fluoride compounds,energetic composites,metal fuels,and metal oxides.Coating techniques include recrystallization,dual-solvent,phase transfer,electrospinning,etc.As one of the effective coating agents,the fluorine compounds can react with the oxide shell of boron powder.In comparison,the energetic composites can effectively improve the flame temperature of boron powder and enhance the evaporation efficiency of oxide film as a condensed product.Metals and metal oxides would react with boron powder to form metal borides with a lower ignition point,which could reduce its ignition temperature.

WHR （Waste Heat Technology） Method in Tri-generation Model

This paper is focused on description of cool production in using WHR （Waste Heat Technology） Technology-a new method of centralized production of heat by using the waste heat from generated exhaust gas, which has been in 2009 developed and operated by companies HELORO s.r.o, and COMTHERM s.r.o.

Characterization and Magnetic Properties of Nickel Ferrite Nanoparticles Prepared by Ball Milling Technique

Nickel ferrite nanoparicles with various grain sizes are synthesized using annealing treatment followed by ball milling of its bulk component materials. Commercially available nickel and iron oxide powders are first mixed, and then annealed at 1100~C in an oxygen environment furnace and for 3h. The samples are then milled for different times in an SPEX mill. X-ray diffraction pattern indicates that in this stage the sample is single phase. The average grain size is estimated by scanning electron microscopy （SEM） and x-ray diffraction techniques. Magnetic behavior of the sample at room temperatm＇e is studied using a superconducting quantum interference device （SQUID）. The Curie temperature of the powders is measured by an LCR meter unit. The x-ray diffraction patterns clearly indicate that increasing the milling time leads to a decrease in the grain size and consequently leads to a decrease in the saturation magnetization as well as the Curie temperatures. This result is attributed to the spin-glass-like surface layer on the nanocrystalline nickel ferrite with a ferrimagnetically aligned core.

Effects of H on Electronic Structure and Ideal Tensile Strength of W： A First-Principles Calculation

We investigate the structure, energetics, and the ideal tensile strength of tungsten （W） with hydrogen （H） using a first-principles method. Both density of states （DOS） and the electron localization function （ELF） reveal the underlying physical mechanism that the tetrahedral interstitial H is the most energetically favorable. The firstprinciples computational tensile test （FPCTT） shows that the ideal tensile strength is 29.1 GPa at the strain of 14% along the [001] direction for the intrinsic W, while it decreases to 27.1 GPa at the strain of 12% when one impurity H atom is embedded into the bulk W. These results provide a useful reference to understand W as a plasma facing material in the nuclear fusion Tokamak.

Properties of the Collision Efficiency of Nanoparticles in Brownian Coagulation

The collision efficiency of nanoparticles with diameters from 100nm to 750nm in the Brownian coagulation is studied by building and solving＂ numerically the equations of particle collision in the presence of the van der Waals force, the elastic deformation force, the Stokes resistance, the lubrication force and the electrostatic force. The results show that the collision efficiency decreases overall with the increasing- particle diameter. It is found that there exists an abrupt increase in the collision efficiency when the particle diameter is equals to 550nm. Finally a new expression for the collision efficiency is presented.

Trimeric Hydrogen Bond in Geometrically Frustrated Hydroxyl Cobalt Halogenides

The mid-infrared absorption spectra of geometrically frustrated hydroxyl cobalt halogenides Co2 （OH）3 CI and Co2 （OH）3Br are measured by FTIR spectrometers, and the stretching vibrational modes of hydroxyl groups are found to be 3549 cm-1 and 3524 cm-1 respectively. Through finding their true terminal O II group stretching vibration frequencies, we obtain 107cm-1 and 99cm-1 red shift caused by the corresponding O-H...Cl and 0 H...Br hydrogen bonds. Rarely reported trimeric hydrogen bonds （Co3≡O H）3….C1/Br are pointed out to demonstrate the relative weakness of this kind of hydrogen bond which may have a critical effect on the lattice symmetry and magnetic structures.

First-Principles Investigations of the Phase Transition and Optical Properties of Solid Oxygen

Using density-functional-theory calculations, a monoclinic metallic post-ζ phase （space group C2/c） is predicted at 215 GPa. The calculated phonon dispersion curves suggest that this structure is stable at least up to 310 GPa. Oxygen remains a molecular crystal and there is no dissociation in the related pressure range. Moreover, it is found that the phase transition from （ to post-ζ phase is attributed to phonon softening, The significant change in the optical properties can be used to identify the phase transition.

Deflections of Nanowires with Consideration of Surface Effects

The elementary beam model is modified to include the surface effects and used to analyze the deflections of nanowires under different boundary conditions. Tile results show that compared to deflections of nanowires without consideration of surface effects, the surface effects can enlarge or reduce deflections of nanowires, and nanowire buckling occurs under certain conditions. This study might be helpful for design of nanowire-based nanoelectromechanical systems.

Nonlinear Optical Properties and Ultrafast Dynamics of Undoped and Doped Bulk SiC

Ultrafast third-order nonlinear optical response of bulk 6H-SiC undoped and doped with different nitrogen concentrations are investigated utilizing femtosecond Z-scan and optical Kerr effect （OKE） techniques at the wavelength of 800hm. The Z-scan measurement shows that the third-order nonlinear optical susceptibilities of the doped samples are improved in comparison to the intrinsic sample. The OKE results additionally reveal that the instantaneous nonlinear optical response of the samples can be ascribed to the distortion of the electron cloud. The ultrafast transient spectroscopic measurements with the one-color and two-color pump-probe techniques demonstrate that the ultrafast recovery process in subpicosecond domain is induced by two-photon absorption process, while the slow relaxation component reflects the carrier dynamics of the excited electrons.

Annealing Effect on Photovoltages of Quartz Single Crystals

We investigate the photovoltaic effects of quartz single crystals annealed at high temperatures in ambient atmosphere. The open-circuit photovoltages and surface morphologies strongly depend on the heating treatments. When the annealing temperature increases from room temperature to 900℃, the rms roughness of quartz single crystal wafers increases from 0.207 to 1.011 nm. In addition, the photovoltages decrease from 1.994μV at room temperature to 1.551 μV after treated at 500℃, and then increase up to 9.8μV after annealed at 900℃. The inner mechanism of the present photovoltaic response and surface morphologies is discussed.

Effect of High Temperature Annealing on Conduction-Type ZnO Films Prepared by Direct-Current Magnetron Sputtering

We experimentally find that the ZnO thin films deposited by dc-magnetron sputtering have different conduction types after annealing at high temperature in different ambient. Hall measurements show that ZnO films annealed at 1100℃ in N2 and in 02 ambient become n-type and p-type, respectiveIy. This is due to the generation of different intrinsic defects by annealing in different ambient. X-ray photoelectron spectroscopy and photolumineseence measurements indicate that zinc interstitial becomes a main defects after annealing at 1100℃ in N2 ambient, and these defects play an important role for n-type conductivity of ZnO. While the ZnO films annealed at 1100℃ in O2 ambient, the oxygen antisite contributes ZnO films to p-type.

Effect of Annealing on Microstructure and Electrical Characteristics of Doped Poly （3-Hexylthiophene） Films

The effect of annealing on the microstructure and electrical characteristics of poly （3-hexylthiophene） （P3HT） films doped with very small amounts of the electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane （F4-TCNQ） is studied. X-ray diffraction and UV-vis spectrum studies show that unlike the pure P3HT film, the thermal treatment on the doped fihns under an Ar atmosphere can effectively enhance the crystalline order of P3HT films, as well as successfully facilitate the orientation of the polymer chains. This improvement is attributed to the electrostatic force between P3HT and F4-TCNQ molecules. This force induces the polymer chains to crystallize and orient during the annealing process. As a result, annealing significantly improves performance, especially for the Ion/Ioff ratio of the TFTs based on the doped P3HT films.

Photoacoustic measurement of the thermal property of condensed matter using a strong light-absorbing surface layer

By using a strong light-absorbing surface layer and front-surface illumination with a low power He-Ne laser ( 6mW), photoacoustic measurements of the thermal effusivities of materials have been made, based on the photoacoustic theory, derived in this paper, of condensed matter with a strong light- absorbing surface layer. This method can eliminate the stray light, give full play to the power of the light irradiation, and improve the signal to noise ratio. The experiment results are in good agreement with the theoretical values.