The valence electron structure and property analysis of TiC

The valence electron structure of TiC was calculated by using the empirical electron theory of solids and molecules. The calculated results show that with the increase of temperature the number of common electrons of TiC increases, which indicates that TiC has a good thermal stability; and there exists a close relationship between hardness and brittleness of TiC. According to the number of lattice electrons, the differences among the crystals with different structures can be explained qualitatively. Using the “bond- strengthening factor”, the differences of hardness among the crystals with different structures can also be qualitatively explained to some extent.     

Hardness estimation for covalent crystals using empirical electron theory

Covalent electrons substantially determine the intrinsic hardness of inorganic crystals. A hardness model is presented on the basis of the Empirical Electron Theory generated from Pauling’s covalent bond length equation and the bond length difference method. The calculated hardness values of inorganic crystals are in good agreement with experimental and other theoretical values. Covalent bond energy with polarity correction can be used as an intrinsic indicator linking microscopic electronic structure to macroscopic hardness. A simple mathematical processing of bond energy is performed to extend the model to multi-bonding or multi-component systems. It is also found that spatial distribution of covalent bonds has a great influence on the hardness of inorganic crystals.     

Ni掺杂AlN铁磁性的第一性原理研究

采用密度泛函理论(DFT)的总体能量的平面波超软赝势方法,结合广义梯度近似(GGA),对Ni掺杂AlN32原子超原胞体系分别进行了几何结构优化,计算和分析了Ni掺杂AlN的结构、能带、电子态密度、集居数及体系总能.结果表明,Ni掺杂AlN会产生自旋极化,能带结构显示6.25%Ni掺杂AlN呈现半金属性质,有铁磁性,铁磁性可以用Ni和相邻的N之间的p-d杂化机制来解释.Ni掺杂的AlN应该是一种有应用前景的稀磁半导体DMS.     

高电场下聚酯薄膜中陷阱捕获电子的特性研究

本文用表面电位测试技术研究了固体介质在强电场作用下陷阱捕获电荷的动力学特性.作者在考虑了碰撞电离退陷阱化后,获得的一级捕获动力学方程,定性地解释了电荷的捕获随施加电场的时间而变化的关系和捕获电荷稳态值随电场的增强而下降的现象。利用这个动态平衡模方程,经实验分析表明:这种捕获电荷稳态值随电场的增强而下降的现象是由于自由电子与陷阱化电子碰撞电离退陷阱化的结果,而不是陷阱化电子隧道效应或Poole-Frenkel效应的结果。当电场增强使碰撞电离退陷阱化达到一定程度时,介质便发生击穿。     

Microstructural evolution of titanium matrix composite coatings reinforced by <Emphasis Type="Italic">in situ</Emphasis> synthesized TiB and TiC by laser cladding

Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles were successfully fabricated on Ti6Al4V by laser cladding using Ti-B₄C-Al or Ti-B₄C-C-Al powders as the precursor materials. The microstructural and metallographic analyses were made by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The results show that the coatings are mainly composed of α-Ti cellular dendrites and a eutectic transformation product in which a large number of coarse and fine needle-shaped TiB and a few equiaxial TiC particles are homogeneously embedded. A thin dilution zone with a thickness of about 100 μm is present at the interface, and it consists of a few TiB and TiC reinforcements and a large number of lamella grains growing parallel to the heat flux direction in which a thin needle-shaped microstructure exists due to the martensitic transformation. The microstructural evolution can be divided into four stages: precipitation and growth of primary β-Ti phase, formation of the binary eutecticum β-Ti+TiB, formation of the ternary eutecticum β-Ti+TiB+TiC, and solid transformation from β-Ti to α-Ti.     

Microstructure and mechanical properties of Ni-based composite coatings reinforced by in situ synthesized TiB2 + TiC by laser cladding

A Ni-based composite coating reinforced by in situ synthesized TiB₂ and TiC particles was fabricated on Ti6Al4V by laser cladding. An attempt was made to correlate the thermodynamic predictions and experimental observation. The microstructure and the microhardness profile across the coating were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and a hardness tester. It is found that the coating mainly consists of a large number of reinforcements (black blocky TiB₂, flower-like or equiaxial TiC, and fine acicular CrB) and the γ matrix. The hardness of TiB₂, TiC, and CrB reinforcements is much higher than that of the γ matrix. The dispersive distribution of such high hardness reinforcements causes the increase in hardness of the whole coating. The average value of the hardness is approximately Hv_0.2 700 in the coating. The hardness of the coating is obviously higher than that of the substrate due to the dispersion strengthening of reinforcements.     

Valence electron structure analysis of refining mechanism of Sc and Ti additions on aluminum

The mechanism of the difference of refining effect between Sc and Ti adding to aluminum can not be explained substantially with traditional theory. Valence electron structures of Al-Ti and Al-Sc alloys have been studied by using the empirical electron theory of solids and molecules (EET). The covalent bond electron numbers and interfacial electron density differences are calculated. The conclusion is that, in the two alloys, different covalent bond electron numbers of nucleation particles, and different electron densities on the interface between the second phase particles and the matrix, fundamentally lead to the difference of refining effect between Sc and Ti adding to aluminum. Supported by the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050003042)     

Experimental measurement of valence electron concentration of icosahedral AlPdMn quasicrystal

The valence charge density distribution for the icosahedral AlPdMn (i-AlPdMn) quasicrystal was obtained with the structure factors of the nine strongest symmetry inequivalent reflections, which were refined by using the quantitative convergent beam electron diffraction (QCBED) technique. It shows that the bonding charge is localized. The enhanced charge density in the middle of the aluminum-transition-metal (Al-TM) bond shown in the valence charge density distribution is the characteristic of covalent bonding. Assuming that the shape of an atom is a sphere with covalent radius, the number of electrons that each atom gains or loses in 55 different pseudo-Mackay clusters (PMCs) was calculated based on the obtained valence charge density distribution. It indicates that almost all the atoms lose electrons except a few Pd atoms that are in some particular shells. It also shows that the atoms of an identified element could have different valences because of chemically and/or structurally different local environments in which the atoms situate. Regardless of the topology and chemical occupancy, the number of valence electrons per atom in a cluster is close to 1.69. This strongly suggests that the pseudo-Mackay clusters are stabilized at a certain electron concentration. Biography: YU Fengmei (1965–), female, Professor, Ph.D., research direction: quasicrystal physics.     

ZTA—SiCw—TiC复相陶瓷材料强韧化机理研究

四方氧化锆相变增韧、碳化硅晶须补强、碳化钛粒子弥散强化，同时引入一个新的陶瓷基复合材料系统中产生了叠加的强韧化效果。热压ＺＴＡ－ＳｉＣｗ－ＴｉＣ复相陶瓷材料与Ａｌ２Ｏ３－ＳｉＣｗ－ＴｉＣ相比具有更高的综合机械性能。碳化钛在基体中形成连续的骨架阻碍晶粒的长大，随着碳化钛含量的增加，基体的硬度明显增加。主要强韧化机理有相变增韧、晶须拔出、载荷转移、裂纹偏转等。基体的主要断裂方式为穿晶解理断裂。     

Dynamical decoupling of electron spins in phosphorus-doped silicon

Quantum coherence is an important enabling feature underpinning quantum computation. However, because of couplings with its noisy surrounding environment, qubits suffer from the decoherence effects. The dynamical decoupling (DD) technique uses pulse-induced qubit flips to effectively mitigate couplings between qubits and environment. Optimal DD eliminates dephasing up to a given order with the minimum number of pulses. In this paper, we first introduce our recent work on prolonging electron spin coherence in γ-irradiated malonic acid crystals and analyze different decoherence mechanisms in this solid system. Then we focus on electron spin relaxation properties in another system, phosphorous-doped silicon (Si:P) crystals. These properties have been investigated by pulse electron paramagnetic resonance (EPR). We also investigate the performance of the dynamical decoupling technique on this system. Using 8-pulse periodic DD, the coherence time can be extended to 296 μs compared with 112 μs with one-pulse control.     

超重元素Uus（Z=117）在酸溶液中标准电极电势的理论预测

基于Born-Haber热力学循环理论,利用多组态Dirac-Fock方法计算的超重元素Uus及其同族元素Cl,Br,I和At的离化势和亲和势及已有的标准电极电势的实验值,拟合得到了Uus的元素电势图.结果表明：在酸溶液中Uus的0价态能够稳定存在,而1,1＋和5＋价态不能稳定存在;在同族元素中,随原子序数Z的增大,0价态和1＋态的稳定性逐渐增加,1价态的稳定性逐渐降低;而5＋价态的稳定性随原子序数变化并不是单调的.对于这种稳定性随原子序数变化的规律,我们从价电子能级的相对位置以及电子电离或亲和的过程作了定性的解释.     

TiC/Fe cermet coating by plasma cladding using asphalt as carbonaceous precursor

A new Ti-Fe-C compound powder for plasma cladding was prepared by heating a mixture powder of ferrotitanium and asphalt pyrolyzed as carbonaceous precursor. The carbon by the pyrolysis of the asphalt acts as a reactive constituent as well as a binder in the compound powder. TiC/Fe cermet coatings were prepared by plasma cladding with the compound powder. Results show that the Ti-Fe-C compound powder has a very tight structure, which can avoid the problem that reactive constituent particles are separated during cladding. The TiC/Fe cermet coating presents a typical morphology of plasma cladding coatings with two different laminated layers: one is the composite layers in which the round fine TiC particles (<500nm) are dispersed within a Fe matrix, the other is the paragentic layers of TiC and Ti₂O₃. The coating shows high hardness and excellent wear resistance. The surface hardness of the coating is 68±5(HR30N). In the same fretting conditions, the wear area of Ni60 coating is about 11 times as much as the TiC/Fe cermet coating.     

TiC晶须对YG10F硬质合金材料硬度和韧性的影响

采用添加不同含量TiC晶须、不同制备工艺方法,研究了TiC晶须对YG10F硬质合金材料硬度和韧性的影响。结果表明:添加TiC晶须可以提高试验材料的显微硬度;采用适当的制备工艺、添加适量的TiC晶须,可以十分显著地提高试验材料的韧性。     

TiC/Fe cermet coating by plasma cladding using asphalt as carbonaceous precursor

A new Ti-Fe-C compound powder for plasma cladding was prepared by heating a mixture powder of ferrotitaniurn and asphalt pyro- lyzed as a carbonaceous precursor. The carbon by the pyrolysis of the asphalt acts as a reactive constituent as well as a binder in the compound powder. The TiC/Fe cermet coatings were prepared by plasma cladding with the compound powder. Results show that the Ti-Fe-C compound powder has a very tight structure, which can avoid the problem of the reactive constituent particles being separated during cladding. The TiC/Fe cermet coating presents a typical morphology of plasma cladding coatings with two different laminated layers： one is the composite layer in which the round fine TiC particles （〈500 nm） are dispersed within a Fe matrix, the other is the paragentic layer of TiC and Ti2O3. The coating shows high hardness and excellent wear resistance. The surface hardness of the coating is 68 ± 5（HR30N）. In the same fretting conditions, the wear area of Ni60 coating is about Ⅱ times as much as the TiC/Fe cermet coating.     

TiC晶须对YGIOF硬质合金材料硬度和韧性的影响

采用添加不同含量TiC晶须、不同制备工艺方法，研究了TiC晶须对YG10F硬质合金材料硬度和韧性的影响。结果表明：添加TiC晶须可以提高试验材料的显微硬度；采用适当的制备工艺、添加适量的TiC晶须，可以十分显著地提高试验材料的韧性。     

In situ synthesis and hardness of TiC/Ti5Si3 composites on Ti-5Al-2.5Sn substrates by gas tungsten arc welding

TiC/Ti₅Si₃ composites were fabricated on Ti-5Al-2.5Sn substrates by gas tungsten arc welding (GTAW). Identification of the phases was performed using X-ray diffraction (XRD). The microstructures were analyzed using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS) and optical microscopy (OM). The Vickers hardness was measured with a micro-hardness tester. The TiC/Ti₅Si₃ composites were obtained in a double-layer track, and the Vickers hardness of the track increased by two to three times compared with the Ti-5Al-2.5Sn substrate.     

Fast acceleration of “killer” electrons and energetic ions by interplanetary shock stimulated ULF waves in the inner magnetosphere

Energetic electrons and ions in the Van Allen radiation belt are the number one space weather threat. Understanding how these energetic particles are accelerated within the Van Allen radiation belt is one of the major challenges in space physics. This paper reviews the recent progress on the fast acceleration of "killer" electrons and energetic ions by ultralow frequency (ULF) waves stimulated by the interplanetary shock in the inner magnetosphere. Very low frequency (VLF) wave-particle interaction is considered to be one of the primary electron acceleration mechanisms because electron cyclotron resonances can easily occur in the VLF frequency range. Recently, using four Cluster spacecraft observations, we have found that, after interplanetary shocks impact the Earth’s magnetosphere, energetic electrons in the radiation belt are accelerated almost immediately and continue to accelerate for a few hours. The time scale (a few days) for traditional acceleration mechanisms, based on VLF wave-particle interactions to accelerate electrons to relativistic energies, is too long to explain our observations. Furthermore, we have found that interplanetary shocks or solar wind pressure pulses, with even small dynamic pressure changes, can play a non-negligible role in radiation belt dynamics. Interplanetary shocks interaction with the Earth’s magnetosphere manifests many fundamental space physics phenomena including energetic particle acceleration. The mechanism of fast acceleration of energetic electrons in the radiation belt responding to interplanetary shock impacts consists of three contributing parts: (1) the initial adiabatic acceleration due to strong shock-related magnetic field compression; (2) followed by the drift-resonant acceleration with poloidal ULF waves excited at different L-shells; and (3) particle acceleration due to the quickly damping electric fields associated with ULF waves. Particles end up with a net acceleration because they gain more energy in the first half of this cycle than they lose in the second. The results reported in this paper cast a new light on understanding the acceleration of energetic particles in the Earth’s Van Allen radiation belt. The results of this study can likewise be applied to interplanetary shock interaction with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune, and other astrophysical objects with magnetic fields.     

针-板型介质阻挡放电的光电特性

设计一种针-板型介质阻挡放电装置,在大气压下以空气/氩气混合作为工作气体,研究了在混合气体流动和不流动2种情况下介质阻挡放电的光电特性.利用玻尔兹曼法计算氮分子振动温度(Tv)和谱线相对强度比值法计算电子激发温度(T_exc),实验结果表明:输入功率(P)和Tv随外加电压(Ua)增加而增大,而Texc随Ua增加有减小的趋势;当Ua一定,气体流动时,P变大,Texc变小,而Tv基本不变.通过对高能电子与工作气体发生非弹性碰撞进行定性解释,对于大气压等离子体动力学行为的深入研究具有重要意义.     

Identification of thermal effects involved in DSC experiment on Al-Cu-Mg-Ag alloys with high Cu:Mg ratio

Precipitation reactions in the differential scanning calorimetry (DSC) of an Al-Cu-Mg-Ag alloy were identified by analyzing the results from hardness test, electrical conductivity test, and transmission electron microscope (TEM) examination. It is discovered that thermal effects can be identified through selected area electron diffraction and bright-field images. The reaction peaks around 171, 231, and 276℃ can be attributed to a structural rearrangement of coherent zones, to the precipitation of Ω phases, and to the precipitation of Ω and θ' and possible combination with the transition of θ'→θ, respectively. In addition, the hardness and electrical conductivity of the alloy change proportionately with the progression of reactions during the heating process. This phenomenon can be attributed to the evolution of the microstructure.     

TiC/Fe cermet coating by plasma cladding using asphalt as a carbonaceous precursor

A new Ti-Fe-C compound powder for plasma cladding was prepared by heating a mixture powder of ferrotitanium and asphalt pyro-lyzed as a carbonaceous precursor. The carbon by the pyrolysis of the asphalt acts as a reactive constituent as well as a binder in the compound powder. The TiC/Fe cermet coatings were prepared by plasma cladding with the compound powder. Results show that the Ti-Fe-C compound powder has a very tight structure, which can avoid the problem of the reactive constituent particles being separated during cladding. The TiC/Fe cermet coating presents a typical morphology of plasma cladding coatings with two different laminated layers: one is the composite layer in which the round fine TiC particles (<500 nm) are dispersed within a Fe matrix, the other is the paragentic layer of TiC and Ti2O3. The coating shows high hardness and excellent wear resistance. The surface hardness of the coating is 68 ± 5(HR30N). In the same fretting conditions, the wear area of Ni60 coating is about 11 times as much as the TiC/Fe cermet coating.