基于离散单元法的锥形双螺杆输送及混合机理分析

锥形双螺杆挤出机结构模型与其他普通螺杆挤出机相差很大且构成独特,近年来在聚合物加工行业中发挥了很大的作用。设计螺槽深度与螺杆半径比为1∶2、2∶5、1∶3的三种锥形双螺杆挤出机,通过离散单元法模拟了锥形双螺杆挤出机挤出LDPE、HDPE两种颗粒的过程,分析了锥形双螺杆挤出机螺槽内颗粒速度的变化,同时在不同参数下对三种锥形双螺杆挤出机的输送效率进行了比较。利用EDEM软件对LDPE和HDPE颗粒进行离散元分析,得出不同时刻两种颗粒在三种锥形双螺杆挤出机内的混合情况。结果表明,螺槽深度与螺杆半径比为1∶2的锥形双螺杆挤出机的混合效率优于螺槽深度与螺杆半径比为2∶5、1∶3的锥形双螺杆挤出机。     

Modulation on the electrical and optical properties of Na and Rh co-doped Ruddlesden-Popper layered Ca3Ti2O7

Layered perovskite Ca_2.91Na_0.09Ti_2-xRh_xO₇ (x?=?0.00, 0.02, 0.04, 0.06) were synthesized by a conventional solid-state reaction. Room temperature ferroelectricity has been confirmed. The remanent polarization increases with an increase of Rh content, which is due to a larger oxygen octahedral distortion by Rh doping. The coercive field increases with Rh doping as the pinning effect of oxygen vacancies reduce the mobility of domain wall. Remanent polarization and coercive field are caused by different mechanisms, so it is possible to modulate them independently to meet the requirement of application in ferroelectric field. The concentration of oxygen vacancy increased with Rh doping, leading to the significant increase of leakage current density. The bandgap of samples doped with Rh drastically decrease and the visible light response of the sample was improved by Rh doping due to the formation of impurity energy levels within the band gap.

     

Improved electric insulation ability and ferromagnetic property in Nb2O5 doped BiFeO3-based multiferroic ceramics

Journal of Electroceramics - 0.675BiFeO3-0.3BaTiO3-0.025LaFeO3-x mol% Nb2O5 (x?=?0–1.25) multiferroic lead- free ceramics, fabricated by conventional solid-state reaction, were...     

表面工程技术在导弹武器装备维修中的应用

本文主要介绍铝/F_(46),协合涂层新技术、复合电刷镀Ni—PTFE新工艺、DJB—823电接触保护剂及三防电子器件绝缘清漆在二炮导弹武器装备维修中的应用。     

冷热循环工艺中冷热转移速率对LY12铝合金尺寸稳定性的影响

研究了冷热转移速率对LY1 2铝合金微屈服强度和残余应力的影响。结果表明 ,提高冷热转移速率易使材料中形成稳定的位错组态 ,从而有利于提高微屈服强度 ;对于圆柱和圆环试样 ,提高冷热转移速率不利于降低残余应力。分析认为 ,冷热转移速率应根据工件几何形状和尺寸进行相应调整。     

关于超耐候性BA01—02钛白粉的研制

采用高温淬火方法制备了Ｔｃ在２７．４Ｋ至９２．４Ｋ之间的一组不同氧含量的ＰＭＰ（粉末熔融工艺）法ＹＢＣＯ超导体。通过对这些超导体样品的磁滞回线及不可逆线的研究发现，随着氧空位的增加，超导体的磁通钉扎力减小     

真空磁压缩等离子弧焊接方法的研究

本文介绍了一种新的焊接方法——真空磁压缩等离子弧焊接。真空磁压缩等离子弧是将低真空中的自由电弧用与电极同轴向的磁场压缩后获得的。实验表明,随着气压的降低,自由电弧会越来越扩展,弧根区的电流密度越来越低,直至产生“旁弧”,不能稳定燃烧而熄灭。而且这种低真空自由电弧难以用和普通等离子弧相似的机械方法压缩。采用轴向磁场可以有效地压缩真空电弧。磁压缩的效果随气压的降低趋于明显,气压低于1.33×10~2Pa 时,几十分之一特斯拉(T)的磁场就可获得略粗于电极、上下直径近似相等的弧柱,我们称之为真空磁压缩等离子弧。使用真空磁压缩等离子弧作为热源,可以焊接一般金属和活泼金属,其熔透工件的能力可超过大气氩弧,并可用调节磁场强度的方法,调节电弧的能量分布。与常规氩弧焊、等离子孤焊、电子束焊相比,真空磁压缩等离子弧焊接有其独到的优点,可望在不久的将来获得广泛的应用。     

钨酸铵溶液浓度对超微钨粉形貌的影响

以钨酸铵溶液为原料，采用超声喷雾干燥法制备了超微钨粉。研究了该方法中钨酸铵浓度对超微钨粉形貌的影响。结果表明，当溶液中钨酸铵的浓度为10%时，得到了球形度很好的非完全结晶的前驱体。当钨酸铵浓度达25％时，得到了层片状的晶态前驱体。钨酸铵溶液浓度对干燥时晶体生长速度具有重要的影响。分别采用这2种前驱体在630℃，保温30min和氢气流莆4L／min条仲下能够完全还原，得到超微α—W粉。所制得的钨粉形貌完全遗传了其前驱体的形貌，分别得到球状和层状钨粉。球状钨粉由纳米颗粒聚集而成。片层状钨粉的厚度在1mm以下。     

在铸造过程中实施渗碳的效果及机理

采用在铸型中放置石墨片，然后浇注低碳合金钢的方法，制造表面耐磨材料。分析了铸造过程中渗碳的效果及机理，讨论了影响组织和渗层深度的因素。     

STRUCTURAL DETERMINATION OF TITANIUM-OXIDE NANOPARTICLES BY X-RAY ABSORPTION SPECTROSCOPY

As a potential application of titanium-oxide nanoparticles, it is extremely important to investigate a detailed picture of the surface and interior structural properties of nanocrystalline materials, such as rutile and anatase with diameters 7.0 and 4.5nm, respectively. X-ray absorption spectroscopy has been used to identify the local Ti environment and related electronic structure. We combine the experimental results at the Ti edge in both bulk and nano-crystals to determine the lattice distortion in terms of differently characteristic preedge features and the variation in the multiple-scattering region of X-ray absorption near-edge structure (XANES) spectra. The relationship between the transition peaks and the surface-to volume ratio is also discussed.