不同运动方式KDP单晶生长流动与物质输运数值分析

针对两种不同运动方式下的KDP单晶生长,进行了流动与物质输运模拟。分析和比较了不同运动方式下,晶面附近溶液流动及晶面过饱和度分布特征。研究了晶体尺寸对晶面过饱和度场的影响。结果表明:二维运动法中,晶面遭受的水动力学条件较为复杂,使得其过饱和度分布不如转晶法规则;二维运动法锥面过饱和度明显高于转晶法;单位周期内,转晶法晶面平均过饱和度存在较大波动,而二维运动法过饱和度随时间变化较小;总体上看,小尺寸晶体时,二维运动法晶面过饱和度梯度小于转晶法;大尺寸晶体时,二维运动法晶面过饱和度梯度大于转晶法。     

二维平移法小尺寸KDP单晶生长溶液流动与传质模拟

二维平移法是一种新型的晶体生长方法.在该方法中,晶体不再作正反转运动,而是沿着特定轨迹作周期性的平移运动.本工作对二维平移法小尺寸磷酸二氢钾(KDP)单晶生长过程进行了数值模拟研究,获得了不同平移速度、不同平移距离以及不同迎流角度下晶体附近溶液流动与晶面过饱和度分布.结果表明:增加平移速度,晶面过饱和度随之增加,但流场结构并无明显变化;增大平移距离,晶面的过饱和度反而降低,标准差则有逐渐增大的趋势,这不利于提高过饱和度均匀性;不同迎流角度下,柱面的过饱和度分布差异较大,对流的不对称性也更加明显,当迎流角度为45°时,对晶体生长更有利.此外,台阶推移结果表明,不均匀的过饱和度会造成台阶弯曲和聚并,二维平移法更利于台阶稳定推移,有望提高形貌稳定性和晶体质量.     

喷流转晶法KDP晶体生长系统的流动与传质模拟

提出了一种通过锥顶喷流改善KDP锥面过饱和度的晶体生长方法。采用有限体积法和滑移网格技术,对传统转晶法及喷流转晶法的KDP晶体生长过程进行了数值模拟。展示了两种生长方式下晶体表面过饱和度时均分布云图及均方差,分析了不同转速、不同喷流速度、不同晶体尺寸对晶面时均过饱和度及均方差的影响。结果表明:相比于传统转晶法,喷流转晶法晶体的锥面过饱和度提高且表面均匀性增加。提高喷流速度可以进一步提高锥面过饱和度,但其均方差却呈现先减小后增大的变化。旋转速度的增加能提高锥面过饱和度并减小其均方差。此外,晶体尺寸也会在一定程度上影响喷流的效果。     

pH值对ADP晶体(100)面生长的影响

通过对40℃、不同pH值和过饱和度下ADP晶体(100)面法向生长速度的研究,发现在同一过饱和度下,改变pH值后晶面的生长速度明显加快。实验数据显示,在过饱和度较低时,(100)面的生长以螺旋位错生长机制为主;过饱和度较高时,以二维成核生长机制为主,而且pH值的改变会促使ADP晶体在较低的过饱和度下就从位错生长机制向二维成核生长机制转变。利用实验数据计算出了不同pH值下、二维成核生长机制控制晶体生长时的台阶棱边能。最后,运用原子力显微镜(AFM)非实时观察了不同过饱和度、不同pH值下生长的ADP晶体(100)面的微观形貌,发现与正常pH值相比,在较低的过饱和度下,pH=2.5和5.0的晶面上就出现了二维核。     

简立方晶体（001）晶面生长的蒙特卡罗模拟

通过对简立方晶体(001)晶面生长的蒙特卡罗模拟,获得了不同晶体表面热粗糙度,不同过饱和度,不同平均扩散距离以及不同表面尺寸下晶体生长速率;同时,应用舍维数法,计算了表面分形维数;并对表面形貌及描述表面特性的相关参量作了分析.结果表明,法向生长模式和二维核生长模式,包括单核和多核生长模式,都可能出现,其主要取决于热粗糙度和过饱和度的大小.晶体生长速率与表面的微观特性紧密相关,如扭折、台阶、台面和吸附基元的百分比.     

ADP晶体{100}面族二维成核生长微观形貌的AFM研究

ADP晶体{100}面族微观形貌的非实时AFM(atomic force microscopy,AFM)成像表明,过饱和度σ=0.053时,晶面上出现二维成核生长;随σ增加至0.11,二维岛数量急剧增加,尺寸减小,分布渐趋均匀,二维成核生长逐渐增强,界面呈现出由光滑向粗糙转变的特征;各二维岛形状趋近于长条形,表现出各向异性,长轴平行于[001]晶向;二维岛上有单分子高度的台阶和台阶聚并后高度为2～3nm的大台阶;二维岛间融合时取向相同;σ=0.053时,融合后所形成的较大二维岛的生长呈现出周边快中心慢的情况,将可能导致产生晶体缺陷.     

柠檬酸钠对半水石膏不同晶面结晶习性及力学性能的影响

本工作采用X射线衍射(XRD)分析方法,研究了在不同柠檬酸钠掺量下半水石膏在蒸压时不同晶面的结晶习性.运用Materials Studio 2017软件进行分子动力学模拟,研究了柠檬酸钠吸附在半水石膏晶体不同晶面的结晶习性.基于等温等容系统(NVT)对柠檬酸钠吸附于半水石膏晶体不同晶面的最低能运动轨迹进行模拟,研究了半水石膏晶体不同晶面的力学性能.XRD分析结果表明:柠檬酸钠的掺量为0.06％(质量分数,下同)时,半水石膏晶体的(200)晶面、(020)晶面和(400)晶面衍射峰强度最高,即晶面发育较好.分子动力学模拟结果表明:从柠檬酸根离子与半水石膏晶面距离来看,(200)晶面和(400)晶面是柠檬酸根离子与Ca2+的主要结合位点;相互作用能从小到大的顺序为ΔE(400)<ΔE(200)<ΔE(111)<ΔE(204)<ΔE(020),则柠檬酸钠更易于与半水石膏晶体的(200)晶面、(400)晶面作用,从而抑制半水石膏晶体在C轴方向上生长;从弹性模量(E)、体模量(K)和剪切模量(G)等力学性能的参数可知,柠檬酸根离子与(200)晶面和(111)晶面上钙离子之间主要有较强的结合力,即柠檬酸根离子易于吸附在C轴方向的晶面上.柠檬酸根离子使半水石膏晶体在垂直于C轴方向上的尺寸变大,对半水石膏晶体在C轴方向上的强度的影响显著.试验所得的晶面分析结果与模型研究的结果具有互证性.     

水热法合成ZnO单晶生长工艺研究

采用水热温差法进行ZnO晶体的生长研究,分析在不同温度压力和矿化剂条件下分别合成几十纳米ZnO晶体和径向尺寸和高度到毫米级的ZnO晶体的生长工艺,探讨了晶体不同晶面生长速度和质量的一般规律及晶体生长机制.     

ADP晶体的生长丘、台阶微观形貌及台阶棱边能

ADP晶体{100}面族生长的实时与非实时AFM(atomic force microscopy,AFM)研究表明,过饱和度σ处于0.005～0.04,生长温度介于293～313K之间时,晶面上观察到位错生长丘和其它晶体缺陷所形成的生长丘,晶面主要为台阶推进方式生长;位错生长丘上空洞的出现与位错弹性理论相符;随过饱和度σ降低,台阶形貌会发生相应变化;生长温度为298K时,台阶棱边能不小于6.2×10-7J/cm2.     

对流效应和溶质浓度对KNbO3晶体界面形貌稳定性的影响

研究了在不同对流形态对KNbO3晶体生长形貌的影响。在温度梯度较小的扩散-平流区域,晶体以枝蔓晶的形态生长;而在温度梯度的较大的扩散-对流区域,生长出的晶体呈现光滑晶面。通过测定不同区域KNbO3晶体界面附近的溶质浓度分布,从对流效应降低晶体界面附近的溶质浓度分布的不均匀性的角度研究了对流效应对晶体界面形貌稳定性的影响,证明对流效应提高了晶体界面形貌稳定性,与晶体界面弥散度的理论计算相一致。同时解释了扩散-对流区域的晶体尺寸大于扩散-平流区域的晶体尺寸的原因。观察并定性地解释了不同溶质浓度KNbO3形成不同的界面非稳定形貌,当KNbO3重量百分比为20wt%时形成骸晶,30wt%时形成枝蔓晶。     

Structural dependence of ionic motion at interfaces between NaCl crystal surfaces and supersaturated solutions in crystallization process

The effects of surface structure and solution concentration on crystal morphology have been investigated through molecular dynamics (MD) simulation in the NaCl crystallization process. Four types of crystal surface structures were prepared for simulation. The probability of ion existence suggests that the solute ions were hardly taken into flat surfaces, while they were easily taken into roughs with some kinks and steps. This is because solute ions are more stable at a kink than at a terrace. The present simulated results suggest that the mechanism of crystal growth is dependent on the solution concentration. It was demonstrated that some ions are slotted on the crystal surface at low supersaturation after moving to the crystal surface. Under high supersaturation, the clusters are formed and adsorbed on the crystal surface. When comparing the crystal growth rates of Na⁺ and Cl⁻, the attractive force of Na⁺ from the crystal surface was found to be larger than that of Cl⁻. Moreover, the repulsive force of Na⁺ from the crystal surface was smaller than that of Cl⁻ in approaching the crystal surface. The adsorption of Na+ was also found to occur before that of Cl⁻.     

不同过饱和度下DKDP晶体生长和缺陷的研究

过饱和度是影响DKDP晶体生长和质量的关键因素. 本文采用“点籽晶”快速生长技术在不同的过饱和度下从氘化程度为75%的溶液中生长DKDP晶体并选取部分样品进行同步辐射X射线形貌术和粉末X射线衍射测试. 研究了不同过饱和度下DKDP晶体的生长和缺陷. 实验证明, DKDP晶体可以在的过饱和度下实现快速生长, 但晶体的缺陷随着过饱和度的增大而增加.     

Vibrations of an infinitely long flowing liquid jet—Influence of spin and axial flow

For an infinitely long liquid column the influence of axial flow velocity and spin has been investigated. The results are exhibited for axisymmetric mode m=0 and asymmetric modes m=1 and 2. A frictionless liquid shows with the increase of axial flow an increase of the frequency in flow direction and a decrease of the oscillation frequency in the opposite flow direction for axisymmetric motion. It also means that a larger surface tension, larger diameter or larger density of the liquid column exhibit the same behavior. For asymmetric motions the effect of axial velocity w₀ is the opposite. With increasing axial wave length the natural frequencies decrease. At certain axial speed magnitudes both waves move in flow direction with different magnitude. The effect of increasing spin is a decrease of natural frequencies and an instability for smaller axial wave lengths. Viscous effects show usually smaller oscillation frequencies.     

Band Gap Characteristic and Transmission Spectrum of Ring-shaped Holes Photonic Crystal in THz Range

采用平面波展开法研究了2D三角晶格空气孔型光子晶体的带隙结构和空气环型光子晶体的完全带隙。结果发现空气孔半径R从0.41a到0.49a之间变化时,空气孔型的完全带隙会越大;在同一空气孔半径(R=0.41a~0.47a)下空气环型结构都能得到比空气孔结构更宽的完全带隙,得到最优参数R=0.47a,r=0.133a下的完全带隙为0.1698THz,是空气孔结构的1.15倍。使用时域有限差分法研究了空气环型结构的透射谱,根据计算结果设计了(0.7198~0.8655)THz波段的滤波器。     

A reliable in vitro approach to assess the stability of acetabular implants using digital image correlation

The main cause of failure of the hip acetabular component is aseptic loosening. Preclinical test methods currently used to assess the stability of hip acetabular implants rely on crude simplifications. Normally, either one component of motion or bone strains are measured. We developed a test method to measure implant 3D translations and rotations and bone strains using digital image correlation. Hemipelvises were aligned and potted to allow consistent testing. A force was applied in the direction of the load peak during level walking. The force was applied in 100‐cycle packages, each load package being 20% larger than the previous one. A digital image correlation system allowed measuring the cup‐bone relative 3D displacements (permanent migrations and inducible micromotions) and the strain distribution in the periacetabular bone. To assess the test repeatability, the protocol was applied to six composite hemipelvises implanted with very stable cups. To assess the suitability of the method to detect mobilisation, six loose implants were tested. The method was repeatable: the interspecimen variability was 16 μm for the bone/cup relative translations, 0.04° for the rotations. The method was capable of tracking extremely loose implants (translations up to 4.5 mm; rotations up to 30°). The strain distribution in the bone was measured, showing the areas of highest strain. We have shown that it is possible to measure the 3D relative translations and rotations of an acetabular cup inside the pelvis and simultaneously to measure the full‐field strain distribution in the bone surface. This will allow better preclinical testing of the stability of acetabular implants.     

Photocatalytic reduction of NO with NH3 using Si-doped TiO2 prepared by hydrothermal method

A series of Si-doped TiO2 (Si/TiO2) photocatalysts supported on woven glass fabric were prepared by hydrothermal method for photocatalytic reduction of NO with NH3. The photocatalytic activity tests were carried out in a continuous Pyrex reactor with the flow rate of 2000mL/min under UV irradiation (luminous flux: 1.1x10(4)lm, irradiated catalyst area: 160cm2). The photocatalysts were characterized by X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrophotometer, transmission electron microscopy (TEM), photoluminescence (PL) and temperature-programmed desorption (TPD). The experiment results showed that NO conversion on Si/TiO2 at 323K could exceed 60%, which was about 50% higher than that on Degussa P25 and pure TiO2. With the doping of Si, photocatalysts with smaller crystal size, larger surface area and larger pore volume were obtained. It was also found that Ti-O-Si bands were formed on the surface of Si/TiO2 and that the surface hydroxyl concentration was greatly increased. As a result, total acidity and NH3 chemisorption amount were enhanced for Si/TiO2 leading to its photocatalytic activity improvement.     

初始应力对三维光学轮廓法测试焊接接头残余应力的影响

目的研究不同初始应力状态下,三维光学轮廓法测试焊接接头残余应力的变化规律。方法采用MIG焊分别对供货态与去应力退火态试板进行多层多道焊,焊后试板经慢走丝切割,经三维光学测量技术扫描切割面轮廓,将所得轮廓数据经所建立的数据处理平台处理,将其结果作为有限元计算的边界条件,经应力反算得到残余应力分布。最后再进行有限元模拟,计算焊接接头残余应力。结果含初始应力、去应力退火和数值模拟的焊缝中心均为拉应力区,最大拉应力分别为480, 450, 523 MPa,且都位于焊缝根部区域。三者试板两侧为压应力区域,最大压应力分别为380, 280, 157 MPa,三者数值相差较大。结论将含有初始残余应力试板、退火处理试板与数值模拟结果的残余应力分布进行对比,可以发现三者在焊缝中心处的残余应力分布较为一致,但沿着焊缝向两侧的区域内,应力差别逐渐变大。主要原因为焊接热循环温度高于金属再结晶温度时可以消除部分残余应力,而温度循环较低时对应力消除不明显,导致实验结果相差较大。     

A Coprecipitation Coating Synthesis of SiC/YAG Composites

The α-SiC in 0.5μm size powders were coated with Al_2O_3 and Y_2O_3 by a coprecipitation coating (CPC) method forfabrication of SiC/YAG composites. The same powder preparation was carried out by conventional mechanical mixing(MM) method for comparison. Two kinds of SiC/YAG composites were manufactured by pressureless sintering usingthe different powders, named CPC composite and MM composite thereafter respectively. It is shown that the CPCcomposite has the advantages of homogeneous distribution of YAG phase and of being sintered to high density ata low temperature, 100℃ lower than that of MM composite. The strength (573 MPa) and hardness (23.3 GPa) ofthe CPC composite are significantly higher than those (323 MPa and 13.5 GPa) of the MM composite, respectively.     

CF／Al复合材料的热膨胀行为

测试和分析了用热压和挤压铸造工艺制备的ＣＦ／Ａｌ复合材料热膨胀行为。指出ＣＦ／Ａｌ的热膨胀规律与其内部残余应力的存在方式密切相关，其制备方式对热膨胀过程也有影响。从热膨胀变化规律能够间接了解材料内部残余应力的生成、消亡及存在方式，为材料的尺寸稳定化处理及选择热处理制度提供理论和实验依据。