纳米SiO2和丁苯胶粉复合改性水泥基材料的强度及抗渗性能

本文研究了单掺丁苯胶粉(SBR)和复掺SBR/纳米SiO₂(NS)对水泥基材料抗折强度、抗压强度、吸水率、抗氯离子渗透系数的影响规律,并采用XRD、DSC-TG、FTIR、SEM-EDS、MIP等手段对水泥基材料水化产物和微观结构进行分析,探究单掺SBR和复掺SBR/NS对水泥基材料强度及抗渗性能的影响机理。结果表明,复掺SBR/NS显著改善了由单掺SBR引起的水泥基材料早期强度下降的问题,单掺SBR和复掺SBR/NS均可降低试样的吸水率、吸水速率和非稳态氯离子迁移系数,且复掺效果优于单掺。微观测试表明:单掺SBR可降低Ca(OH)₂的含量,减少有害孔和多害孔的数量,增加结构整体性;复掺SBR/NS可进一步降低Ca(OH)₂的含量,促进水化反应生成更多C-S-H,提高C-S-H的聚合度,降低最可几孔径,减少少害孔、有害孔和多害孔的数量,降低水化产物的钙硅比,从而增强试样的抗折强度和抗压强度并提高其抗渗性能。     

二氧化硅气凝胶常压干燥工艺的研究进展

二氧化硅气凝胶因具有低密度、高比表面积、稳定的物理化学性质等特性在吸附分离、隔热保温等领域表现出巨大的应用潜力。但长耗时、高成本的制备工艺限制了它的发展,尤其是湿凝胶向气凝胶转变的干燥工艺。本文介绍了二氧化硅气凝胶在常压干燥的过程中面临的主要难点及解决方法,虽然常压干燥方法工艺简单、过程安全、对设备要求低且可连续制备,成为近年来的研究热点,但也存在制备周期长、体积收缩大、需要消耗大量有机溶剂和改性剂等不足。文中从凝胶基体增强与优化、降低毛细管力与减少不可逆收缩两种角度,介绍了二氧化硅气凝胶常压干燥的改进方法及其发展现状,分析归纳了不同改进方法的优缺点,总结了二氧化硅气凝胶常压干燥目前面临的技术挑战。并且,立足于目前二氧化硅气凝胶基体增强和表面改性技术发展的趋势,对今后二氧化硅气凝胶常压干燥过程中结构可控、成本降低以及产品多功能化的发展路线进行了展望。     

多孔网幕泡破压力预测模型的建立及实验验证

金属多孔网幕具有比表面积大、物理稳定性好等诸多优点,广泛应用于推进剂在轨气液分离及相变传热等领域。泡破压力是衡量其相分离性能的关键参数,可根据多孔介质的有效泡破孔径确定。然而多孔网幕的孔隙结构极其复杂,泡破孔径计算仍未有通用且高效的方法。建立了一种基于三维孔隙结构的多孔网幕泡破压力的通用型解析模型。该模型仅依赖于多孔网幕的几何结构参数,无须实验即可有效预测多孔网幕的泡破压力。模型预测结果与本文实验及文献实验中不同网幕规格、低温及常温工质数据吻合良好,平均误差仅为8%,表明该解析模型具有普适性和准确性,可为基于多孔网幕的液体获取装置的设计与性能预测提供参考。     

EPS颗粒对超轻水泥基复合保温材料性能的影响

聚苯乙烯泡沫塑料颗粒(EPS颗粒)作为水泥基复合保温材料的超轻骨料,对水泥基复合保温材料力学性能、热工性能影响显著。以水泥为胶凝材料,EPS颗粒、混合材、泡沫剂和改性剂、水等为主要原料,采用物理发泡工艺制备干表观密度不大于120 kg/m³的超轻水泥基复合保温材料(UCIM)。通过设计不同体积掺量的EPS颗粒,分析EPS颗粒掺量对泡沫混凝土基体孔结构、超轻水泥基复合保温材料强度和热工性能的影响规律。结果表明,适宜掺量EPS颗粒可显著提高超轻水泥基复合保温材料抗压强度和抗拉强度,并确保超轻水泥基复合保温材料具有良好的热工性能,即通过EPS颗粒与泡沫混凝土基体的协同作用,协调力学性能和热工性能,制备出高性能超轻水泥基复合保温材料。     

多孔陶瓷的制备、应用及其研究进展

多孔陶瓷材料是一类重要的陶瓷材料,由于其特有的三维多孔结构使其具有高孔隙率、良好的化学稳定性、小体积密度及低导热性等特点,从而被广泛应用于众多领域。本文回顾了多孔陶瓷材料的几种传统制备方法,并介绍了多孔陶瓷制备工艺的新进展,同时阐述了各种制备方法的特点,指出了今后多孔陶瓷的发展趋势和发展前景。     

捣固焦高温碳素溶损反应行为研究

选择有代表性的捣固焦炭,在连续热反应装置内,考察不同温度下焦炭与CO2反应行为,揭示捣固焦炭在高炉内的劣化机理.结果表明,等温条件下,不同焦炭与CO2反应至30％的水平时,转化率随时间总体呈线性规律变化,反应动力学符合零级反应特征,表观活化能为89 kJ/mol～151 kJ/mol,碳溶反应后粉化程度与焦炭显气孔率及表观活化能有关,且粉化主要以扩孔和开孔为主.     

Effects of calcining conditions of kaolinite on pore structures of mesoporous materials prepared by the selective leaching of calcined kaolinite

This paper describes the effects of calcining conditions of kaolinite on pore structures of the porous materials obtained from the selective leaching of calcined kaolinite using KOH solution. Mesoporous -Al₂O₃ was the predominant crystalline phase in the samples calcined in the temperature range between 950°C and 1050°C for 24 h. The mean specific surface area of these samples was approximately 250 m² · g^–1 and the mean total pore volume was approximately 0.8 ml · g^–1. The pore size distribution curves of these samples showed a sharp peak at around 2–3 nm pore radius. This peak was sharper for the sample calcined at 1000°C for 24 h. On the other hand, the pore sizes of the sample calcined at 1100°C for 24 h increased abruptly to 10–20 nm and this change corresponded to the formation of mullite in the sample. The pore sizes of the samples calcined at 1100°C varied with calcining time. The specific surface area and total pore volume decreased, the longer the calcining time of the samples, and this was correlated with an increase in the amount of mullite in the samples.     

Three‐dimensional modeling of porosity development during the gasification of a char particle

This work is devoted to the three‐dimensional, direct modeling of porosity and specific surface development during the gasification of a char particle. The model was developed for heterogeneous reactions occurring inside a char particle in a kinetically controlled regime. The main goal of this work is to analyze the impact of different pore size distributions on the particle carbon conversion rate. In particular, it is shown that under certain conditions the outer particle surface can influence the specific surface area. In this context the possible adaptation of the parameter ψ from the random pore model (RPM) developed by Bhatia and Perlmutter is explained. The results of simulations are compared against the RPM and discussed. Additionally, based on the results of simulations, the physics behind several input parameters used by the RPM are explored. Finally, the possible fragmentation of a chemically reacting char particle during its gasification in dependence of instantaneous porosity was investigated numerically. It was shown that the earliest fragmentation occurs at a carbon conversion of about 0.5–0.6 due to the disaggregation of the pore walls. The results are discussed and compared implicitly with data published in the literature. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1638–1647, 2017     

电脉冲处理对FeMnSiCrNiNbC合金NbC析出及记忆效应的影响

研究了电脉冲处理对FeMnSiCrNiNbC合金形状记忆效应的影响,并对其微观机理进行初步探讨.结果表明,Fe17Mn5Si8Cr5Ni0.5NbC合金经5%预变形,300 V,1 Hz电脉冲处理13次后形状回复率达到80%,比800℃时效1000s获得的最大值提高12%.SEM分析表明,电脉冲处理可在极短的时间内加速诱导大量、细小的NbC颗粒在基体内析出,进而有效地改善了合金的记忆性能并提高了效率.     

Microstructure and martensitic transformation of Ni–Fe–Ga–Si ferromagnetic shape memory alloys

The effects of the fourth element Si on the martensitic transformation and magnetic properties of Ni–Fe–Ga magnetic shape memory alloys were investigated. A complete thermoelastic martensitic transformation in Ni–Fe–Ga–Si alloys was observed in the temperature range of 218–285 K. The martensitic transformation temperatures of Ni–Fe–Ga alloys are obviously decreased by the substitution of Si for Ga element, that is, the substitution of 1 at.% Si for Ga leads to a decrease of martensitic transformation temperature of about 39.6 K. Moreover, the substitution of Si for Ga leads to a decrease of the saturation magnetic field and the magnetic anisotropy constant K₁ obviously.