Roles of titanium-rich precipitates as inoculants during solidification in low carbon steel

The effect of titanium on the as-cast structure and the growth form of titanium precipitates, and the effect of cooling rate on the size and distribution of titanium precipitates were studied. It is shown that Ti-rich precipitates acting as heterogeneous nucleation sites play an important role in refining the grain size and increasing the equiaxed grain ratio. Cooling rate has a great effect on the size and distribution of precipitates. The number of precipitates increases and the size decreases with the increase of cooling rate. Ti-rich particles acting as heterogeneous nucleation sites at the onset of solidification are observed in the experiment. This result suggests that TiN nucleated on Ti₂O₃ is an effective inoculant for δ-ferrite during solidification in low carbon steel.     

氧化铝树枝晶形核机理初探

本文利用快速冷却试样研究了铝脱氧钢液中氧化铝树枝晶的形核机理。通过理论分析认为:氧化铝具有很高的表面能,只能通过非均质过程形核。而硅酸盐夹杂物的表面能只为氧化铝的10~(-8),具备在钢液中均质形核的条件。通过实验研究发现,当钢液加铝脱氧时,溶解铝和硅酸盐夹杂物发生反应,生成部分反应的硅酸盐夹杂物。这些夹杂物具有高铝质的外壳和高硅质的内核,其外壳由于转变应力而开裂。这些裂缝随后则作为基底而形核、生长出氧化铝树枝晶。     

无氦重复频率TEACO_2激光器

本文报道了采用增装气体循环、冷却装置和扩大腔体贮气体积与放电体积之比方式,实现了 TEACO_2激光器无氦、高气压、重复频率长时间稳定工作。得到在每秒5次重复频率时激光脉冲输出能量为1焦耳;激光器的最高重复频率可达每秒10次以上;一次充气输出1.1× 10~5个脉冲后,能量没有出现下降的趋势。     

SO2-4/ZrO2-SiO2超强酸催化剂研究(Ⅲ)(英文)——酸性及比表面积

系统地研究了SO2-4/ZrO2-SiO2催化剂的酸性和比表面积,采用吸附吡啶的红外光谱法、BET法以及指示剂法考察了催化剂的组成、温度以及其他处理条件对催化剂酸强度以及催化剂比表面积的影响.实验结果表明:在硅锆比小于10时,SO2-4/ZrO2-SiO2催化剂的比表面积随催化剂中硅锆比的增高而增大;在硅锆比为10左右时,比表面积可高达440m2/g,数倍于SO2-4/ZrO2催化剂的比表面积.在相同处理条件下,SO2-4/ZrO2-SiO2催化剂的酸强度低于SO2-4/ZrO2的酸强度.吸附吡啶的红外光谱证明该催化剂的表面酸点多为Lewis酸点.     

高速列车空调冷凝风机的变频应用研究

列车在高速运行中表面产生的负压使冷凝风量相继减小.通过数值模拟计算不同车速下冷凝风机入口的平均负压值和冷凝风量,结果表明,高速工况下的负压影响冷凝风机正常运行.选取大容量冷凝风机并采取变频调节方式,建立以冷凝温度为反馈信号的PID控制方式,比较不同车速下定频与变频运行所消耗的功率,得出变频运行冷凝风机在列车低速运行时具有良好的节能效果和一定的变工况适应性,为变频技术在列车冷凝风机上的应用提供了技术依据.     

Preparation and characterization of SiO2 non-catalytic nucleation coating for the solidification of undercooled melt

SiO2 non-catalytic nucleation films were coated onto a ceramic substrate and the inner surface of a ceramic crucible by the Sol-Gel method. The surface morphology of the coatings was characterized with an atomic force microscope and a scanning electronic microscope. The non-catalytic effect of the coating on the heterogeneous nucleation of metal melts was tested through measuring the nucleation undercooling. Investigation results indicated that the prepared coating could act as a baffle-wall to prevent the metal melt from nucleating heterogeneously on the inner surface of the crystalline crucible. The tiny holes with a diameter below 2 μm and heaves on the coating surface have no evident effect on the undercooling of metal melts. For a poly-layer coating, the super-layer can cover the cracks in the sub-layers, which prevents the cracks in the coating from spreading in the direction vertical to the coating layers and thus eliminates the effect of cracks on the coating.     

PEMFC电催化剂利用率研究方法的探讨

提高电催化剂的利用率以降低质子交换膜燃料电池(PEMFC)的成本，是加速其商业化的一个重要途径。文中讨论了现有的CV法在研究PEMFC电催化剂利用率时存在的一些问题，如CV法扫描速度的影响及Pt理论比表面积难于准确确定等，为了较好地解决这一问题，提出了一种以单位质量电催化剂产生电池功率或电能来表示膜电极中电催化剂利用率的方法。     

SCR法烟气脱硝催化剂的制备实验研究

通过溶胶-凝胶法制备脱硝催化剂的主体二氧化钛,系统研究了原料配比对二氧化钛形貌的影响。结果显示:当V(TBT)∶V(乙醇)为1∶4时得到平均粒径为60nm的二氧化钛球形颗粒。采用浸渍法制备了不同V2O5和WO3负载量的催化剂,并对其进行BET表征,得出在一定范围内,当保持WO3含量不变时,随着V2O5含量增加催化剂比表面积有减小的趋势;而当V2O5含量不变,随着WO3含量增加时,比表面积有增加的趋势。此外,进一步研究了不同比例的黏合剂和结构助剂对催化剂机械强度的影响。     

复合负载金属-支撑水相催化剂上1-己烯氢甲酰化反应性能

利用均相催化剂和多相催化剂各自的特点，首先在高比表面大孔硅胶负载金属催化剂上担载水相络合催化剂制备复合负载金属－支撑水相催化剂。同时，对负载金属催化剂、支撑水相催化剂和复合负载金属－支撑水相催化剂上的1－己烯氢甲酰化进行了考察。结果表明，多相金属组分对提高复合负载金属－支撑水相催化剂上1－己烯氢甲酰化的活性和选择性具有明显促进作用，复合催化剂中均相组分和多相组分具有协同作用。     

Undercooling evolution of pure Sn droplets in various atmospheres based on fast scanning calorimetry

Undercooling of Sn droplets in different atmospheres was studied by fast scanning calorimetry （FSC） at cooling rate of 1,000 K/s. It is found that the undercooling decreased with increasing partial pressure of oxygen. Randomly distributed SnO2 islands were observed to form on the droplet surface, which likely has promoted the heterogeneous surface nucleation. As the partial pressure of oxygen changes, the nucleation rate and growth of SnO2 led to different oxide islands, which resulted in various potential catalytic sites for the nucleation of the molten Sn droplet. The results showed that the nucleation process of the Sn droplets was sensitive to the solidification environment, and therefore the atmosphere should be taken into account in the study of the nucleation behavior of the single Sn droplets.     

2,3,5-三甲基氢醌连续合成工艺中失活催化剂的表征

通过对2,3,5-三甲基氢醌(TMHQ)连续合成工艺中失活催化剂活性组分、硫含量、比表面积及孔容的变化、催化剂表面形貌等进行分析以及对失活催化剂进行再生处理,研究催化剂失活的原因.研究结果表明:催化剂在运转前后活性组分含量、比表面积和孔容变化不大,不足以引起催化剂活性大幅度地下降;催化剂中的硫含量随催化剂运转时间的延长而增加,但对于贵金属催化剂属无毒物;运转后催化剂的沉积物只是疏松地吸附在催化剂的表面,对其比表面积和孔客的影响不大.催化剂失活的一个主要原因是催化剂表面沉积了TMHQ和少量的2,3,5-三甲基苯醌.     

多电极测氡脉冲电离室对氡探测效率的模拟研究

脉冲电离室的多个因素(几何形状、体积和电极数目)影响着其测氡探测效率,现采用蒙特卡罗程序Geant4模拟了这些因素与测氡探测效率之间的关系。模拟结果表明:脉冲电离室测氡探测效率与其表面积体积比成反比关系;同一表面积体积比下脉冲电离室测氡探测效率与其电极数目(或电极/电离室体积比)成负指数关系。该模拟结果的有效性为文献报道的多电极脉冲电离室测氡实验结果所检验,可用于提高多电极脉冲电离室测氡探测效率的快速优化设计。     

零维液态金属快速凝固过程的热力学和动力学

分析了零维液态金属快速凝固过程中的热流规律,计算了零维数滴在真空条件下的冷却速度,并建立了零维液滴单晶形核的过冷度方程,结果表明,零维液滴的凝固过程由形核前所达到的过冷和系统向环境 散热共同控制,零维液滴在真空条件下的冷却速度在１０＾５～１０＾８Ｋ／ｓ之间。     

金属一绝缘颗粒复合介质逾渗阈值的研究

在金属—绝缘颗粒复合介质中 ,当金属颗粒的浓度达到渗流阈值时 ,复合介质发生金属—绝缘体转变 采用有效介质近似 (EMA)研究了颗粒系统中阈值与颗粒形状、分布的关系 ,讨论了逾渗阈值与退极化因子的关系     

Suppression of crystal nucleation in polydisperse colloids due to increase of the surface free energy

The formation of small crystallites is governed by two competing factors: the free energy gained upon transferring constituent atoms, molecules or colloidal particles from the metastable liquid to the more stable solid, and the free energy needed to create the surface area of the crystallite. Because the ratio of surface area to bulk is large for small particles, small crystallites dissolve spontaneously under conditions where larger crystallites are stable and macroscopic crystal growth occurs only if spontaneously formed crystallites exceed a critical minimum size. On theoretical grounds, the probability of forming such critical crystal nuclei is expected to increase rapidly with supersaturation. However, experiments show that the rate of crystal nucleation in many systems goes through a maximum as the supersaturation is increased. It is commonly assumed that the nucleation rate peaks because, even though the probability of forming critical nuclei increases with increasing concentration, the rate of growth of such nuclei decreases. Here we report simulations of crystal nucleation in suspensions of colloidal spheres with varying size distributions that show that the probability that critical nuclei will form itself goes through a maximum as the supersaturation is increased. We find that this effect, which is strongest for systems with the broadest particle size distribution, results from an increase with supersaturation of the solid-liquid interfacial free energy. The magnitude of this effect suggests that vitrification at high supersaturations should yield colloidal glasses that are truly amorphous, rather than nano-crystalline.     

地表水源热泵系统冷热源利用的节能评价

分析了地表水源热泵系统的冷却水温度、流量和扬程等因素对水源热泵系统能效比的影响.以空调冷负荷和冷冻水参数作为控制目标,提出了包含水源热泵机组能耗的冷却水系统能效比分析模型.利用该模型分析了地表水直接进入热泵机组的地表水源热泵系统和以板式换热器间接换热的地表水源热泵系统的运行能效.结果显示,冷却水温度变化对能效比的影响大于冷却水系统静扬程变化对能效比的影响.部分负荷工况下冷却水温度为23~24℃时系统能效比达到最大值.     

SmAlGe结构中的Al—Ge共价成键网络

用电弧熔炼法合成ＳｍＡｌＧｅ，以单晶Ｘ射线衍射法测定晶体结构．晶体学及结构修正参数：化学式ＳｍＡｌＧｅ，Ｍｒ＝２５０．０，正交晶系，ＬａＰｔＳｉ类型，（１０９）Ｉ４１ｍｄ，ａ＝０．４１９５７（３）ｎｍ，ｃ＝１．４５８８（２）ｎｍ，Ｖ＝０．２５６７９（４）ｎｍ３，Ｚ＝４，Ｄｘ＝６．４６４ｇ／ｃｍ３，μ＝３５．２７ｍｍ－１（λＭｏＫ＝０．０７１０７ｎｍ），Ｆ（０００）＝４２８，Ｔ＝２９６Ｋ，对于１２个最小二乘修正参数和１２０个独立可观察衍射点Ｒ＝０．０３０，ｗＲ＝０．０２５．此化合物中主要是Ａｌ－Ｇｅ的共价结合并形成三维网络，经典极限情况下结构式可写成Ｓｍ３＋Ａｌ２－Ｇｅ１－，可称为“ｍｅｔａｌｉｃＺｉｎｔｌｐｈａｓｅ＂．而ＹＡｌＧｅ中Ａｌ－Ｇｅ准二维网络为共价到金属结合过渡，几何堆积因素占了很重要地位．     

纱条混纺比对电容式条干均匀度仪测试信号的影响

根据电容式均匀度仪的原理,当混纺纱条在电容式传感器中的充满度很小时,提出成分、纤维和空气三者组成串联或并联介质的分析方法。这两种分析方法均可推得电容变化量与纱条混纺比之间的线性关系。但是,串联方法的结果与实验结果存在明显差异,并联方法则与实际情况较为吻合,因此,对于混纺纱条,当成分纤维介电常数的差异及混纺不匀较大时,测得的不匀率数值将大于纱条的实际条干不匀率。     

对浸渍法制备Pd／C催化剂表面积影响因素的讨论

Pc/C负载型催化剂，由活性组化Pd原子和载体活性炭组成，用于糠醛液相脱羰制呋喃。因为多相催化反应发生在催化剂表面上，所以催化剂的表面积，特别是反应可利用表面积决定催化剂的活性。根据EBT容量法，测定不同浸渍条件对Pd/C表面积的影响因素，因此选择合适的pH值和焙烧温度是使Pd/C具有较高活性的重要条件。     

IF钢凝固过程中Al_2O_3-TiN复合夹杂物的形成机理

以理论分析和实验研究相结合的方式分析了IF钢凝固过程中Al2O3-TiN复合夹杂物的形成机理.结果表明,以凝固分率0.9为界限,钢水凝固过程中Al2O3和TiN先后通过异质形核方式析出并结合形成Al2O3-TiN复合夹杂物;冷却速率越小,复合夹杂物粒径越大;在冷却速率一定时,可作为异质形核核心的夹杂物的粒径越大,凝固过程中析出的复合夹杂物的长大程度越小;复合夹杂物内层Al2O3粒径越小,外层TiN长大程度越明显.