共查询到20条相似文献,搜索用时 46 毫秒
1.
提出一种以电火花放电加工技术对半导体硅材料进行铣削加工的方法,建立了半导体放电加工电路模型,测量了半导体放电加工放电通道的维持电压,其值为18V.在此基础上,从放电能量和ANSYS仿真两个方面对单晶硅电火花铣削的蚀除机理进行了研究.通过单位能量蚀除量的计算,并与45钢比较,得出单位能量单晶硅的蚀除量是45钢的4倍,由此提出了单晶硅蚀除是热蚀除和热应力剥落综合作用的结果;通过仿真分别计算出单脉冲放电温度场和热应力场的蚀除量,其热应力剥落是热蚀除的4.6倍,与基于能量计算的分析结果基本吻合.最后实验验证了分析结果的正确性. 相似文献
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在利用电火花线切割(WEDM)加工锗晶体时,会出现回路放电电流逐渐减少,并伴随着进电材料与锗晶体间有钝化物的生成,最终导致放电切割无法延续.本实验对放电切割状态进行了实验模拟并生成了钝化物,运用XRD技术对钝化物进行了分析,提出了一种防范钝化物产生的方法,最后采用这种方法利用改进的线切割机床对N型锗进行了放电切割,高效稳定地加工出了工件,从而验证了这种防钝化物产生方法的可行性,为进一步提高锗晶体的放电加工工艺指标奠定了基础. 相似文献
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分别采用超声振动冲击和脉冲激光加热技术对开槽金刚石砂轮断续磨削加工聚晶金刚石过程中的机械冲击和热冲击进行了模拟实验研究.研究结果表明,在断续磨削加工过程中,由于开槽砂轮和工件之间接触面积变化引起的磨削力周期性变化,有利于聚晶金刚石材料加工表面上的晶粒产生脆性微细破碎去除;由于开槽砂轮和工件之间接触面积变化引起的热冲击,有利于聚晶金刚石材料加工表面上的晶粒产生微细裂纹和疲劳破碎.实验结果表明,开槽金刚石砂轮磨块切入部分的磨粒以破碎损耗为主,磨块切出部分的磨粒以机械磨耗、氧化、石墨化损耗为主. 相似文献
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硬脆晶体材料如SiC、Ge和Si等,由于具有极高的硬度和脆性,普通线锯切割很难进一步提高硬脆材料晶片的切割效率和表面质量.本研究把超声振动应用到金刚石线锯切割单晶SiC.基于超声振动切削加工的特点,分析了柔性线锯横向振动切割单晶SiC的必要条件;建立了横向超声激励下柔性金刚石线锯对SiC工件的动态切割过程模型,研究分析了超声振动对线锯间歇切割弧长及切割速度的影响,得到横向超声振动线锯切割速度增量的数学表达式.基于压痕裂纹模型,讨论了横向超声振动线锯切割和普通线锯切割对切割速度、切割力和表面粗糙度的影响.以单晶SiC为切割对象,对普通线锯切割和超声振动线锯切割进行了对比实验,结果表明在相同条件下,超声振动线锯切割使晶片的表面粗糙度有明显改善,超声振动线锯的切割速度比普通线锯切割的速度提高了约45;,锯切力减少28;~53;.实验结果与理论分析具有良好的一致性. 相似文献
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超声辅助线锯切割SiC单晶实验研究 总被引:1,自引:1,他引:0
针对单晶SiC切割过程切割效率低,加工表面粗糙度和表面不平度差以及线锯磨损和断裂严重等问题,提出采用线锯横向施加超声振动的方法切割单晶SiC.通过实验对比研究了普通切割与超声辅助切割两种切割工艺,结果表明:与普通切割相比,超声辅助切割单晶SiC,锯切力减小37;~52;,且减小趋势随工件进给速度的增大更明显;切片表面粗糙度降幅约为26;~55;,晶片表面形貌均匀,无划痕,明显优于普通切割方法所获得的表面;线锯磨损降低约近40;;切割效率提高近56;. 相似文献
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利用钎焊金刚石线锯,在恒进给速度的方式下对单晶硅材料进行切割加工,探讨切割参数对切割力及表面粗糙度的影响机制.建立了金刚石线锯的切割力模型,推导线锯横截面不同位置处金刚石磨粒的法向力与线锯总法向力之间的关系式,依据单晶硅材料的压痕断裂力学性能,探讨钎焊金刚石线锯切割单晶硅时线锯横截面不同位置金刚石磨粒去除材料的机理.分析表明,随着磨粒位置的变化,其法向力值经历了一个从最大值到零的变化过程,并存在脆塑性转变角,其值的大小决定了工件表面材料的去除方式. 相似文献
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在晶体加工中,特殊晶向及晶体棱镜的切割一直是困扰加工者的一大难题.虽然通过一边研磨一边测量修正能够制作出器件,但是,要付出很大的工作量,而且晶体损失严重.又由于误差积累致使加工精度很难提高.另外,在晶体抛光过程中,平行度要达到1″~2″,光洁度在3级以上时,传统的光学玻璃加工工艺也是无法达到的.本文介绍一种解决这两个难题的新方法. 相似文献
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研磨过程中机械去除作用与化学去除作用的有效分离是实现研磨过程可控调节及提高加工表面质量的前提.本文通过尖晶石在不同介质中的材料去除速率,对其在不同研磨液中化学与机械作用的材料去除率进行了分离和计算;采用微/纳压痕仪测量了不同研磨液作用下工件表面的显微硬度,依此分析了其软化层厚度.结果表明:研磨液对镁铝尖晶石工件具有一定的化学去除作用,研磨过程中材料去除以机械作用下的脆性去除为主;研磨液的化学作用主要体现在工件表面形成了一层软化层,其中乙二醇产生的软化层最厚,三乙醇胺最薄. 相似文献
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Liquid crystals (LC) are the state of matter intermediate between isotropic liquids and the crystalline state. LC-forming molecules have strongly anisotropic shapes (rod-like in most cases). This leads to an interaction potential that consists of distance-dependent and orientation-dependent parts. Rotational dynamics of LC molecules falls into two frequency regions. Rotations about the short axes are strongly hindered by the potential barrier and thus coupled to fluctuations of the molecular centers of mass. This in turn causes these longitudinal or “flip-flop” motions, characterized by a relatively large relaxation time τ||, to exhibit considerable temperature, pressure and volume dependences. Experimental relaxation times determined to date for various LC phases (nematic, smectic A, C, and E) for different thermodynamic conditions (isobaric, isothermal and isochoric) are discussed herein, adopting the formulae applied for characterization of the structural relaxation times of glass-formers (GF). This analysis appears fruitful; in particular, the strength parameter characterizing the steepness of the interaction potential can be determined from the relaxation times, and τ|| is independent of temperature and pressure along the nematic-isotropic transition line, similar to the behavior of the structural relaxation time along certain transitions in GFs. 相似文献
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Agata Semeniuk Justyna Kalinowska-Tluscik Wojciech Nitek Barbara J. Oleksyn 《Journal of chemical crystallography》2008,38(5):333-338
Abstract The crystal structure of hydroxychloroquine sulfate (OHClQ) was determined in order to compare its conformation and intermolecular
interactions to those in the crystalline chloroquine phosphate (ClQP) and quinine salicylate (QSal) monohydrate. The crystals
of OHClQ are monoclinic with the space group P21/c and unit-cell dimensions: a = 10.4966(1) ?, b = 8.8056(1) ?, c = 21.8603(3) ?, β = 101.074(1)°. The quinoline antimalarial drugs may interact with their putative receptors by formation
of characteristic hydrogen-bonded rings. The protonated nitrogen atoms and/or hydroxyl groups of the drug cation are proton
donors, while the oxygen atoms of anions are proton acceptors. Water molecules may intermediate in these interactions.
Graphical Abstract Hydroxychloroquine sulfate is a drug used in the treatment of malaria and rheumatic diseases. The X-ray structure analysis
shows an important role of intermolecular hydrogen bonds in the crystal architecture. Comparison with chloroquine phosphate
and quinine salicylate indicates that the organization of the drug cations is determined by the anions.
相似文献
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Three Zn-doped InSb crystals were directionally solidified under microgravity conditions at the International Space Station (ISS) Alpha. The distribution of the Zn was measured using SIMS. A short diffusion-controlled transient, typical for systems with k >1 was demonstrated. Static pressure of ∼4000 N/m2 was imposed on the melt, to prevent bubble formation and de-wetting. Still, partial de-wetting has occurred in one experiment, and apparently has disturbed the diffusive transport of Zn in the melt. 相似文献
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Impurity distributions in semiconductor melts and crystals grown from these melts are experimentally and numerically studied on an example of Ga-doped Ge crystals. It is shown that inhomogeneous dopant distribution is observed in the form of striations and is caused by the convective flows in the melt and their nonstationary rearrangement in the vicinity of the crystallization front. The character of heat and mass transfer under the microgravity conditions is predicted. The necessity of precision experiments under terrestrial and, especially, space conditions is emphasized. 相似文献
16.
《Journal of Non》2006,352(6-7):500-504
Random hole optical fibers (RHOFs) represent a new class of holey fiber, which utilizes randomly sized and spaced porosity in the cladding region to confine light to the core region of the fiber. The porosity in the cladding region acts to lower the average refractive index relative to that of the core region. This paper presents studies on silicon induced in situ hole formation in optical fibers. Silicon powder was added to the optical fiber preform and during drawing of the optical fiber, the silicon powder caused the formation of bubbles which were subsequently drawn into tubes in the fiber. 相似文献
17.
Dietmar Möbius 《Molecular Crystals and Liquid Crystals》2013,570(1):235-238
Quenching of fluorescence due to electron transfer is observed in monolayer assemblies when electron donor D and electron acceptor A are either at the same interface or separated by one spacer monolayer. When the donor and acceptor monolayers are separated by two or more fatty acid interlayers no fluorescence quenching is detected. 相似文献
18.
《Journal of Non》2007,353(47-51):4541-4545
We found that dc conductivity percolation process typical for low hydrated porous materials shows up in bulk viable blue-green algae, Arthrospira (Spirulina) platensis (strain Laporte 1963/M-132/2b) at unusually low hydrations, more than an order of magnitude lower than in, e.g., hydrated yeast [D. Sokolowska, A. Krol-Otwinowska, J.K. Moscicki, Phys. Rev. E 70 (2004) 052901]. The critical exponent is characteristic for two-dimensional network. Comparison with results for yeast and other similar materials shows that the hydration percolation threshold is a sensitive indicator of wettability of water accessible surface in porous bio- and abiotic materials. 相似文献
19.
A. M. Parshin V. G. Nazarov V. Ya. Zyryanov V. F. Shabanov 《Crystallography Reports》2009,54(7):1191-1196
The phase transition from the bipolar structure to the homogeneous structure in droplets formed from the nematic liquid crystal
4-n-pentyl-4′-cyanobiphenyl in poly(vinyl butyral) in the presence of a magnetic field has been investigated. The phase transition
is associated with the expansion of the regions with a tilted orientation of the director in the vicinity of defects (the
disappearance of boojums) and with the alignment of the nematic director lines in the bulk of the droplet in the direction
of the magnetic field. In the temperature range T = 24−34°C, cyclic mutual transformations between the bipolar configuration of the nematic director and the homogeneous structure,
which have a period of ∼0.5–3.5 s and result from thermal fluctuations of the order parameter, are observed in droplets 3–15
μm in size after the forming field is switched off. 相似文献
20.
《Journal of Non》2007,353(13-15):1221-1225
We present a simple mathematical model of glass transition based on the analysis of molecular agglomeration in overcooled liquids. With simple assumptions concerning local configurations and their and bonding energies, and with elementary combinatorics we are able to derive the dependence of the glass transition temperature on chemical composition in non-organic covalent glasses. 相似文献