饱和度对纳米AlOOH水热结晶形貌的影响

由结晶理论可知，过饱和度是结晶的驱动力，对晶体生长速度、质量和晶体外形都有很大影响。本文采用单注、双注、添加不同组分的添加剂等对比试验，制备了试验样品。通过对试验数据的分析、归纳和整理，揭示了前躯体制备方式以及饱和度状态对结晶形貌的影响，探讨了纳米AlOOH晶体成长的结晶机制和成核机理，为制备各种理想形貌的AlOOH的过程控制提出了新的思路。     

基于蔗糖结晶过程的图像采集与控制研究

针对大多数蔗糖结晶工艺装备技术与自动化煮糖要求的相距甚远的矛盾,本文设计一种基于蔗糖结晶过程的图像采集与控制系统.通过对蔗糖结晶过程模型化描述,利用COMS图像传感器采集图像并进行处理,得到单位面积内蔗糖结晶颗粒面积、周长、形状指数等控制参数,送工控机与原有控制参数数据融合,再将控制命令通过无线传感器向控制结点发送以实现自动控制.系统能够达到节约能耗,降低生产成本,提高白砂糖产量和质量的目的.     

氯乙酸生产过程控制系统

针对氯乙酸生产过程中氯化和结晶工序的特点及控制系统的要求,选择A-B公司的ControlLogix系统构成过程控制系统,系统通过现场总线网形成由过程控制级和监督管理级构成的二级分层体系结构.在氯化工序中采用由釜内温度、夹套循环水温度和氯气流量构成的前馈-串级复合控制;结晶工序中采用预热水温度的自适应Smith预估补偿控制.     

硫酸盐结晶的MVR控制系统设计

针对某企业的硫酸盐溶液蒸发结晶项目,介绍了MVR技术的应用及原理,并根据MVR技术原理,提出了将MVR技术应用于硫酸盐溶液蒸发结晶的工艺流程,同时对MVR技术的自动控制系统进行整体设计及硬件设计。控制系统通过PLC与变频器相结合的控制方式,对机械式蒸汽压缩机、进料泵、出料泵、强制循环泵等实现自动控制,同时可对硫酸盐溶液的浓缩、蒸发、结晶过程中的液位、温度及流量等工艺参数进行监测控制。     

用于芒硝矿一种经济的耐腐蚀泵的探讨

言引生产芒硝最主要的工艺流程之一是芒硝未结晶前高温Na_2SO_4水溶液的强制循环,其过程需要多台水泵。采用一般水泵在这种腐蚀性介质下工作,腐蚀严重,泄漏利害,使用周期极短;采用不锈钢或优质不锈钢材料如1Cr18Ni9Ti、1Cr13、2Crl3、1Cr18Ni12Mo2Ti、Cr15Mo3等来制造水泵,又不太理想。因为首先价格比用灰铸铁提高几倍至十多倍。另外,生产制造水泵的厂,用不锈钢铸造时需要电炉等一套昂贵铸钢设备,多数厂家只得委托加工不锈钢铸件。且     

永磁同步电机双向检测启动控制的研究

针对永磁同步电机(PMSM)启动控制的设计与实现过程,以数字信号处理芯片TMS320LF2812为核心控制单元,采用霍尔传感器与增量式光电编码器等位置反馈元件,提出了通过粗测与双向精准检测来测量确定启动位置的方法.用该方法控制启动电流,可以避免过流或欠流等问题.最后,利用Matlab建立了模型,通过仿真验证了该方法的应用对启动电流等方面的控制优点.试验表明,该方法能实现对电机转子启动位置的精确控制.     

芒硝水玻璃在熔模铸造中的应用

介绍了芒硝水玻璃的工艺性能及其在熔模铸造生产中的应用，实践证明，通过对水玻璃涂料的工艺性能及质量的有效控制，可以提高型壳质量，降低铸件废品率。     

运用小波模极大值滤波算法消除光电容积脉搏波中的运动干扰

在通过光电容积脉搏波(PPG)测量血氧饱和度的过程中,PPG信号易受到被测者身体移动的影响产生运动伪迹,这些无规律的运动伪迹影响了血氧饱和度测量的稳定性和准确性.首先利用朗伯-比尔(Lamber-Beer)定理和指尖半球形模型,分析了运动干扰与正常信号之间的关系,分析表明运动干扰信号与正常信号约成线性叠加关系.并利用分析结果引入小波模极大值重构滤波算法去除信号中的运动干扰,而后通过初步实验将该算法与常规快速傅里叶(FFT)算法进行了比较.实验结果表明, 此方法较FFT法有更高的准确性和稳定性.     

基于电子车牌的交叉口感应信号控制方法研究

提出了一种基于电子车牌的交叉口感应信号控制方法,该方法通过设置在交叉口处的阅读器与装有有源电子标签车辆互动,得到路段区间上的车辆信息。以车辆密度作为感应控制绿灯是否延长的评价标准,车辆密度高于阈值则绿灯延续,反之,切换相位。通过仿真对比分析表明,改进后的感应控制策略能够在高饱和度路口实现实时有效交通信号控制,克服了以车辆间隔时间作为绿灯延长标准的感应控制在高饱和度下失效的弊端,提高了城市交叉口绿灯利用率。     

钯镍合金镀层特性研究

钯镍合金具有较高的硬度、较低的孔隙性与良好的焊锡性且价格低廉,可作为替代金的电镀层。但钯镍合金镀层的镍含量会随着电流密度的增加而增加,镀层结晶也会随着电流密度的增加而变得粗糙,因此在使用钯镍合金进行电镀时必须充分掌握其特性。本文通过改变电镀制造过程中的电流密度来了解钯镍合金镀层的组成与结晶状态,对钯镍合金镀层的特性作了深入的研究,对镀层质量的控制具有较大的参考价值。     

核级手动截止阀Ω焊缝凝固缺陷成因研究

采用显微硬度测量、金相和扫描电镜(SEM)观察对不锈钢手动截止阀焊接接头各微区的硬度进行测量;对Ω焊缝、热影响区(HAZ)和母材的显微组织进行观察;对接头的断口形貌进行观测分析。结果表明:接头各区域的硬度分布差异不大,分布较为均匀,而2#试样HAZ的硬度高于1#。Ω焊缝金属柱状晶粗大,晶粒(柱状和胞状晶)的方向性强,晶间存在偏析,焊缝已形成沿晶界开裂。主要原因是:Ω焊缝装配间隙部位在冷却结晶时因液态填充不够,形成缩松、缩孔。在焊接应力/应变场作用下,拉伸应变或应变率超过此时材料的临界塑性和临界应变率时则产生焊接凝固裂纹。     

Cholesterol crystals rupture biological membranes and human plaques during acute cardiovascular events--a novel insight into plaque rupture by scanning electron microscopy

Plaque rupture and/or erosion are considered the leading cause of cardiovascular events. To elucidate this process, we demonstrated that during cholesterol crystallization the occupied volume increases rapidly and sharp-tipped crystals cut through thin biological membranes in their path. The amount of cholesterol correlated directly with both peak level and rate of crystal growth (r = 0.98; r = 0.99; p < 0.01, respectively). These observations suggest that crystallization of cholesterol in atherosclerotic plaques can induce cap rupture and/or erosion. Observations by scanning electron microscopy confirmed similar findings of cholesterol crystals perforating the lumen surface in human coronary artery segments with ruptured plaque.     

镁合金液态模锻动力学与数学分析

利用合金凝固动力学基本理论,研究了镁合金ZM5在液态模锻时的结晶过程、结晶过程中的力学分析和压力对结晶晶核形成的影响,并通过试验观察结晶过程中压力的变化和压力对制件内缩孔和缩松的影响,得出了合理压力和制件相对尺寸之间关系,并通过试验进行了验证。     

聚四氟乙烯复合材料烧结过程温度控制研究

研究了PTFE复合材料烧结成型过程中内外部位的温度变化过程,探讨了升温、降温速度和晶型转变点附近的保温控制.结果表明,聚四氟乙烯材料在烧结过程中内外部位容易产生温差,这个差异在晶型转变点附近进一步增大,生产过程中应通过升、降温速度与保温控制来尽量减少各部位之间的差异.     

A positron annihilation lifetime spectroscopic study of nanocrystals formation in a chalcogenide glass-ceramic

The positron annihilation lifetime spectroscopic technique was applied to study nanocrystals formation during controlled crystallization of a chalcogenide glass 51GeS₂-9Sb₂S₃-40PbS, which was thermally treated at 330 °C for up to 15 h. The technique provided valuable information for in depth understanding of the nature of the material as well as the crystallization processes by showing systematic change of lifetime components (τ₁, τ₂, τ₃) and intensities (I₁, I₂, I₃) with thermal treatment time. Such change defines the time frame for nucleation and crystal growth processes; the nucleation process is dominating in the first 3 h, whereas after 3 h, the crystal growth becomes the main process. The values of lifetime components and their intensities reveal change of the size and amount of nano- and micro-defects with time and can be used to guide materials engineers for efficient composition designs and improvements of chalcogenide glass-ceramics.     

纳米AlOOH晶须生长结晶形态的“逆转”现象

晶须生长本质都是晶体在溶液中的成核与生长。按照一般常规,提高水热温度和延长水热时间,都有利于晶须的生长。但是,作者在试验过程中发现了AlOOH“逆转”生长的现象,即出现了由须状向片状方向的逆转,长纤维向短纤维甚至于向椭圆状、圆粒状的逆转。对这一现象作了深入细致的分析,结合结晶动力学理论,给予了适当的解释。此外,还建立了AlOOH晶须生长的基元模型,运用透射所得的结晶形态及X光衍射反射点阵特点,反证了关于晶须生长基元模型推断的正确性。     

超临界流体干燥技术制备纳米氧化铁及其表征

本文以氯化铁为原料,采用溶胶-凝胶法结合超临界流体干燥技术制备了氧化铁钠米粒子。借助 TEM、XRD 对其微观形貌、物相进行了表征。结果表明,超临界流体干燥技术可制得粒径均匀、晶形发育良好的氧化铁纳米粒子,实现产物的干燥晶化一步完成。经超临界流体干燥所得的氧化铁纳米粒子以 Fe_3O_4为主,在80℃焙烧时就开始有晶形转化,经400℃热处理2h 后基本全部转化为α-Fe_2O_3。     

Measuring silicon monocrystal diameters during melt growth

Measuring crystal diameters during Czochralski growth is investigated. An image of the crystallization meniscus zone is analyzed. Informative parameters are determined for finding crystal diameters. An algorithm for calculating the diameter of meniscus applied for crystal growth control is described. Results on operation of a sensor using the algorithm during real crystal growth are presented.     

The optimum solidification and crucible rotation in silicon czochralski crystal growth

Silicon crystallization is very important in many industrial processes, and it is desirable that maker should have a low cost manufacturing and high efficiency for producing semiconductors. One semiconductor process is the Czochralski (CZ) silicon melt flow and this CZ process has an excellent manufacturing feature and is utilized for silicon solidification. But CZ silicon melt flow is very complicated and this defect can be erased by the numerical analysis of the melt flow. In this paper, the optimum solidification conditions were shown for crucible rotation. This is because the solidification conditions depend on crucible rotation under the cooling process and the solidification conditions were investigated on heat generation rate on crucible wall and rotation by using numerical analysis. For the numerical validations, we verified with experimental data and showed good agreement with current numerical results. The solidification regions are classified with crystal rotation and crucible rotation. For the heat generation rate, qw, the optimum heat generation rate was estimated for 20 W/cm2 and when crystal rotation and crucible rotation is 5 rpm, the maximum solidification length can be obtained and has a stable solidification.     

Molecular dynamics study on external field induced crystallization of amorphous argon structure

A molecular dynamics study has been conducted on an external-force-field-induced isothermal crystallization process of amorphous structures as a new low-temperature athermal crystallization process. An external cyclic-force field with a dc bias is imposed on molecules selected randomly in an amorphous-phase of argon. Multiple peaks smoothed out in the radial distribution functions for amorphous states appear very clearly during the crystallization process that cannot be achieved otherwise. When the amorphous material is locally exposed to an external force field, crystallization starts and propagates from the interfacial region and crystallization growth rates can be estimated.