Structure and Magnetic Properties of Fe1-xCx Solid Solution Prepared by Mechanical Alloying

Supersaturated solid solutions Fe1-xCx （0≤x≤0.9 ） of wide composition range have been prepared by mechanical alloying process. Nanocrystalline phase was formed for 0 ≤ x ≤ 0.67 and a large grain phase for 0.75 ≤ x ≤ 0.9. The large fraction of graphite volume puts off formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows simple magnetic dilution, and eoereivity He is mainly due to dissolution of carbon at grain boundaries. In the nanocrystalline phase the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for x ≤ 0.5, suggesting that the high carbon concentration may enhance diffusion of carbon into the Fe lattice. It shows a discontinuity in the Hc variation with a grain size D of nanocrystalline phase. For small grain D below the critical value, Hc increases with D. For a large grain D, Hc decreases with increasing D. The solubility limit of carbon in a-Fe extended by nanocry- stalline phase formation is discussed.     

在室温和常压下用机械合金化方法制备Fe5C2金属间化合物

Single phase Fe5C2 intermetallic compound was prepared by mechanical alloying method. The phase and crystal structure of sample were analyzed with X-ray differaction spectrum. The decomposing temperature of the Fe5C2 compound is 596.4℃ determined by the DSC curve. It is further shown that the size of nanometer crystal grain is an important condition for carrying out the solid state reaction at room temperature and normal pressure.     

Preparation and characterization of metakaolin-phosphate cement

We prepared cold-setting cement with metakaolin from kaolin dehydrated at 800 ℃ and phosphate, and studied the phase composition, microstructure and setting reaction mechanism of the cementing material by means of infrared spectroscopy, thermogravimetry, X-ray diffraction, and scanning electron microscopy. The metakaolin-phosphate cement is predominantly amorphous, where the phases responsible for chemical setting are mainly amorphous aluminophosphate hydrates. The reactivity of metakaolin depends on the particle size. Metakaolin particles of 1.75 μm in D50 have an acid dissolution index up to 18.45%, and the reaction with phosphate at room temperature to form metakaolin-phosphate cement takes only 6 h. The so obtained cement shows a compressive strength of 92.5 MPa after 7 d and keeps its amorphous phase at 1 000 ℃, demonstrating better bonding and mechanical properties and higher stability at a medium or high temperature.     

Preparation and application of supported amorphous alloy catalyst CoP/TiO2

A new supported amorphous catalyst CoP/TiO2 was prepared by chemical reduction and characterized by ICP, XRD, TEM, BET and DSC Its application in decomposing PH3 to high purity phosphor and its catalytic activity were studied. The decomposition rate is over 95% at 450 ℃. For comparison, unsupported CoP amorphous catalyst was prepared by the same method. The result suggests that CoP/TiO2 exhibits higher thermal stability and catalytic activity than CoP, which is attributed to the high dispersion of CoP alloy particles on the support-TiO2.     

Magnetic Properties of Nanocrystalline Fe60Cr40 Powders Prepared by Mechanical Alloying in Vacuum and Air

Magnetic properties of nanocrystalline Fe60 Cr40 powders prepared by mechanical alloying in vacuum and air were investigated by utilizing the measurements of magnetization, X-ray diffraction, and ^67Fe M（oe）ssbauer spectrum. The results show that the Fe60 Cr40 powders keep the bcc structure during milling in air and vacuum. The saturation magnetization of the Fe60 Cr40 powders milled in vacuum and air decreases with the increase of the milling time up to 45 h. The decrease of saturation magnetization of the Fe60Cr40 powders milled in vacuum is due to the formation of Fe-Cr solid solution, while in air it is due to the formation of paramagnetic disorder structure and solid solution.     

Phase precipitation and isothermal crystallization kinetics of FeZrB amorphous alloy

The crystallization process of Fe78ZrTBls （at%） amorphous ribbon was investigated by Xray diffraction （XRD）, differential scanning calorimetry and scanning electron microscopy （SEM）. The fully amorphous structure of asquenched （Aq） ribbons was confirmed by XRD pattern. The saturation magnetization （Ms） and Curie tem perature of the Aq ribbon were measured as 124.3 （A.mZ）＆g and 305 ℃ with vibrating sample magnetometer （VSM）, respectively. When the ribbons was annealed at 550 ℃ near the first onset temperature （Txl = 564.9 ℃）, the Ms was increased by 17 %, which was caused by the formation of a dual phase structure. The isothermal crystallization kinetics and crystallization mechanism of primary ctFe phase in the dual phase structure were studied by Arrhenius and JohnsonMehlAvramiKolmogorov equations respectively. The results showed that the crystallization of Fe phase was a diffusioncontrolled surface nucleation growth process, and the nucleation rate decreased with longer crystallization time.     

Fabrication and characterization of VO2 thin films by direct current facing targets magnetron sputtering and low temperature oxidation

Low valence vanadium oxide（VO2-x） thin films were prepared on SiO2/Si substrates at room temperature by direct current facing targets reactive magnetron sputtering, and then processed through rapid thermal annealing. The effects of the annealing on the structure and phase transition property of VO2 were discussed. X-ray photoelectron spectroscopy, X-ray diffraction technique and Fourier transform infrared spectroscopy were employed to study the phase composition and structure of the thin films. The resistance-temperature property was measured. The results show that VO2 thin film is obtained after annealed at 320℃ for 3 h, its phase transition temperature is 56 ℃, and the resistance changes by more than 2 orders. The vanadium oxide thin films are applicable in thermochromic smart windows, and the deposition and annealing process is compatible with micro electromechanical system process.     

CoNi/CoO 双层膜磁化反转机制与温度的依赖关系

Exchange coupling and magnetization reversal mechanism in two series of Co_xNi_(1-x)/CoO(30 nm)(x=0.2 and 0.4)bilayers are studied by vector magnetometer.Two components of magnetization are measured parallel and perpendicular to the applied field.At low temperatures,coercivity H_c∝(t_(FM))~(-n),n=1.5 and 1.38 for x=0.2 and 0.4,respectively,in agreement with the random field model.At room temperature,the coercivity is nearly proportional to the inverse FM layer thickness.In addition to the exchange field and the coercivity,the characteristic of the magnetization reversal mechanism was found to change with temperature.At temperatures below 180 K,magnetization reversal process along the unidirectional axis is accompanied only by nucleation and pinning of domain wall while magnetization rotation is also involved at high temperatures.     

Influence of Magnetic Field on the Rectification Process of Binary Heterogeneous Azeotrope

To improve separate effect of binary heterogeneous azeotrope in the magnetic field with different magnetic induction intensity, the influence of magnetic field on the rectification process of binary heterogeneous azeotrope was investigated with l-butanol-water system. The results show that the composition of liquid-liquid phase equilibrium of l-butanol-water system has definitely changed, the composition of l-butanol in light phase （l-butanol layer） increases by 1. 17%-1.63% and the composition of water in heavy phase （water layer） increases by 1.21%-1.58% under the influence of magnetic field. By separation of magnetization, the composition of l-butanol increases by 0.8%-1.2% and the recovery ratio of 1 -butanol increases by 1.6%-2.5%. Magnetic field has positive effect, however, the magnetized effect is not in proportion to magnetic induction intensity and has an optimum condition, in the range of 0.25 T-0. 3 T.     

Microstructures and mechanical properties of SiBCNAl ceramics produced by mechanical alloying and subsequent hot pressing

Amorphous SiBCNAl powders were prepared via a mechanical alloying (MA) technique using crystalline silicon (Si), hexagonal boron nitride (h-BN), graphite (C), and aluminum (Al) as starting materials. SiBCNAl powders were consolidated by a hot pressing (HP) technique at 1800 °C under a pressure of 30 MPa in argon and nitrogen. The sintering atmosphere had a great influence on the microstructures and mechanical properties of the ceramics. The two ceramics had different phase compositions and fracture surface morphologies. For the ceramics sintered in argon, flexural strength, fracture toughness, elastic modulus and Vickers hardness were 421.90 MPa, 3.40 MPa·m1/2, 174.10 GPa, and 12.74 GPa, respectively. For the ceramics sintered in nitrogen, the mechanical properties increased, except for the Vickers hardness, and the values of the above properties were 526.80 MPa, 5.25 MPa·m1/2, 222.10 GPa, and 11.63 GPa, respectively.     

Magnetic anisotropy of mechanically alloyed Fe25Ni75 nanocrystallites

The magnetic anisotropy of Fe₂₅Ni₇₅ nanocrystallites in the range of 10∼20 nm was measured by the law of approach to saturation. The samples were prepared by mechanical alloying process, and the average crystal size was determined by X-ray diffraction. The effective magnetic anisotropy of these fine particles is found In an order of 10⁶ erg/cm³ that is much greater than that of normal crystal size of particles. The dependence of magnetic anisotropy on the particle size was studied. It has been demonstrated that the strain anisotropy occupies the most of the total magnetic anisotropy, and the internal strain is a critical factor for their magnetic properties. Supported by the Science Foundation of Shanghai Municipal Commission of Education (807965)     

柠檬酸含量对溶胶凝胶自燃烧法制备的钡铁氧体磁性能的影响

BaFe12O19 powders with nanocrystaUine sizes were produced by sol-gel auto-combustion method. The precursors were prepared under the molar ratios of citric acid to the metal nitrate of 0.5, 1.0 and 1.5. Appropriate ethylene diamine （C2H8N2） was added in order to adjust pH of 7. The ions distribution of citric acid at different pH explains the effect of citric acid in the starting solution. The XRD patterns of the as-burnt powders and annealing powders show different phases for different citric acid content. In addition, the lattice constants （a, c） derived from X-ray diffraction pattern were changed from 0.58881 nm to 0.58997 nm and 2.32057 nm to 2.32296 nm respectively. The data from VSM indicated that the powder with high citric acid content took on good magnetic properties. Pure single BaFe12O19 of the specific maximum magnetization M（1 T）≈ 49.73 Am^2/kg, the specific remanent magnetization Mr ≈ 30.77 Am^2/kg and the coercive force He≈ 467 kA/m was produced when the molar ratios of citric acid to the metal nitrate was 1.5.     

Dependence of nanocrystalline phase formation and magnetic properties in Fe25Ni75 on ball milling time

Nanocrystalline Fe₂₅Ni₇₅ powders were prepared by the mechanical alloying process. They were investigated by X-ray diffraction and magnetic measurements. The ball milling time dependence of grain size, internal strain and magnetic properties has been discussed. The results show that the formation of Fe₂₅Ni₇₅ alloy phase is almost completed after milling for 30 hours. The reduction of grain size accompanied by the growth of internal strain was observed after extended milling. An average grain size about 10–20 nm of alloyed powders has been determined by Sherrer formula estimation. The saturation magnetisation Ms has a slight increase when the average grain size continues to decrease by intensive milling. This fine size of mechanically alloyed powders (10–20 nm) results in a single domain magnetic structure and the formation of superparamagnetic phase.     

Curie temperature of the intergranular amorphous phase in nanocrystalline Fe89Zr7B4 alloy

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Fe-Ni系列合金超细粉末的磁性和有效磁各向异性常数

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Characteristics of bottom gate a-Si TFT array for AM-OLEDs

The authors have fabricated bottom gate amorphous silicon thin film transistor (a-Si TFT) array using five-step lithography process.The device shows a field effect mobility of 0.43 cm 2 /(V·s),on/off ratio of 7.5×10 6 and threshold voltage of 0.87 V.The instability of a-Si TFT is ascribed to the defect state in the a-Si channel and SiNx/a-Si interface.The present a-Si TFT array with SiN x insulator could be a significant step towards the commercialization of active matrix organic lighting diode (AM-OLED) te...