Conversion of calcium aluminate cement hydrates at 60°C with and without water

There have been different hypotheses about the transformation mechanisms of calcium aluminate cement hydrates and this work aims to clarify the long‐running debate about the conversion approaches. In this work, CAH₁₀ and C₂AH₈ were produced from the pastes of calcium aluminate cement (CAC) cured for 24 hours at 10 and 20°C separately. And the cured pastes were continually cured at 60°C for 3 days with water and without water, respectively. The hydration of the pastes was halted by freeze‐drying, and the phases and microstructure of hydrates were investigated by XRD and SEM, respectively. The results indicate that CAH₁₀ and C₂AH₈ converted into C₃AH₆ and AH₃ in water presence at 60°C, but did not transform into C₃AH₆ and AH₃ without water. It is confirmed that the conversion of CAH₁₀ and C₂AH₈ to C₃AH₆ and AH₃ happens through preceding solution of CAH₁₀ and C₂AH₈ and subsequent precipitation of C₃AH₆ and AH₃.     

Effect of K2SO4 additions on properties of porous fibrous alumina ceramics prepared by DCC and lost‐mold method

Flawless porous fibrous alumina ceramics with high performance were fabricated via a novel approach involving direct coagulation casting and lost‐mold method. Stable alumina suspensions were prepared by adding sodium tri‐polyphosphate as dispersant using alumina fibers as raw material and K₂SO₄ as sintering aid. Resin‐coated sand molds with designed shapes for suspension casting were fabricated through 3D printing with subsequent post‐treatments. Alumina green bodies were obtained by in situ coagulation of the suspension after treating at 90°C within 40 minutes. Porous alumina ceramics were obtained after direct furnace sintering of green bodies without demolding, in which the molds would collapse automatically at around 650°C with less exhaust emission. The effect of various K₂SO₄ contents and sintering temperatures on mechanical properties of porous ceramics was investigated. The SEM results showed that the fibers interconnected with obvious interfacial bondings on junctions when sintered at 1450°C. The XRD patterns showed that the sample sintered with various K₂SO₄ additions consisted of different phases, mainly including aluminosilicates. Porosity of ceramic samples increased slightly whereas the compressive strength enhanced significantly with increasing K₂SO₄ addition. The density of sintered samples with different K₂SO₄ contents was in accord with the porosity variation tendency. The ceramic samples had uniform pore size distribution with average size from 3.18 to 7.24 μm as increasing K₂SO₄ addition to 40 wt%. This approach may provide a convenient and general route to fabricate various dense and porous advanced ceramics with complex shapes and good composition homogeneity.     

Preparation and properties of pure crystalline perovskite CeFeO3 thin films with vanadium doping

Cerium ferrite (CeFeO₃) thin films doped with vanadium (V:CeFeO₃) were grown on SiO₂ quartz glass and <100>‐oriented SrTiO₃ (STO) crystal substrates by the radio‐frequency magnetron sputtering method in this study. The effects of crystallization, substrate, and V‐doping on the quality, the magnetic property and the magneto‐optical property of as‐prepared films are investigated. V:CeFeO₃ film grown on STO substrate has better crystallinity and has better lattice integrity due to the higher lattice matching between substrate and film. The magnetic hysteresis loop and the magnetic circular dichroism spectra show that the magnetization strength and the magneto‐optical properties of V:CeFeO₃ films have the significant anisotropy. Moreover, V‐doping and the stress lead to the change in easy magnetization direction of film. It shows that the perovskite B‐site doping with transition‐metal ion has significant influence on the magnetic and the magneto‐optical properties of CeFeO₃ thin films.     

不同相对分子质量聚丁二酸丁二酯的合成及表征

以丁二酸、1,4–丁二醇为原料,采用溶液–熔融法合成了不同相对分子质量的聚丁二酸丁二酯(PBS),并研究了4种不同催化剂合成PBS反应的催化性能。采用凝胶渗透色谱(GPC)、傅里叶变换红外光谱(FTIR)、核磁共振氢谱(1H–NMR)、差示扫描量热(DSC)、热重(TG)分析和力学拉伸仪对产物的结构、热稳定性、相对分子质量、力学性能等进行表征。结果表明,不同催化剂催化合成的PBS相对分子质量大小顺序为:对甲苯磺酸钛酸异丙酯氯化亚锡醋酸锌无催化剂。相对数均分子质量最大值为5.57×10~4,最小值为2.54×10~4。所有合成的PBS的热分解温度均大于250℃,都具有较好的热稳定性。其中以钛酸异丙酯和氯化亚锡为催化剂时,得到的PBS具有良好的力学性能。综上结果,钛酸异丙酯为催化剂时合成的PBS最优,相对分子质量为5.50×10~4,拉伸强度为34.5 MPa,断裂伸长率高达201%。     

我国汽车部件等离子喷涂涂层研究及应用进展

结合汽车耐损、腐蚀和表面抗氧化要求,对采用等离子喷涂涂层进行修复再制造和强化的汽车部位的实践进行了总结。重点介绍等离子喷涂技术在汽车发动机上的实践应用,并针对汽车零部件等离子喷涂涂层应用现状提出了相应改进方法。     

MIL-53(Fe)金属有机骨架材料对刚果红的高效吸附

通过水热法制备规则外形的MIL-53(Fe)金属有机骨架材料(MOF),并通过傅里叶红外光谱(FT-IR)、X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对材料进行表征。以刚果红作为目标物,研究所制得的MOF材料对其的吸附行为。结果表明,MIL-53(Fe)对刚果红的吸附动力学符合准二级动力学,吸附模型符合Langmuir吸附模型。MIL-53(Fe)材料对刚果红的最大吸附量为1 482 mg/g,是可望用于去除染料废水刚果红的高效吸附材料。     

微波法处理剩余污泥的研究进展

近几年来运用微波法处理剩余污泥成为研究热点,剩余污泥具有产量大,处理处置费用高等特点,并且当中含有包含大量未稳定的致病微生物与有毒有害元素,微波应用到污泥处理处置技术上,一方面会让污泥更高效的加热水解,脱水性能和厌氧消化性能得到改善;另一方面微波处理技术不需要投加任何化学药剂,不会对污泥的后续处理带来二次污染。本文总结了目前国内外微波处理污泥技术的一些具有代表性的研究成果,主要包括:微波热解污泥技术、微波破解污泥细胞壁技术、微波污泥脱水干化技术、微波辐照与碱联合处理污泥技术。并针对微波法处理处置污泥技术的发展前景提出了自身的见解,以期促该方法的工业化推广应用。     

An improved cutting force model for micro milling considering machining dynamics

Micro milling, as a versatile micro machining process, is kinematically similar to conventional milling; however, it is significantly different from conventional milling with respect to chip formation mechanisms and uncut chip thickness modelling, due to the comparable size of the edge radius to the chip thickness, and the small per-tooth feeding. Considering tool runout and dynamic displacement between the tool and the workpiece, the contour of the workpiece left by previous tool paths is typically in a wavy form, and the wavy surface provides a feedback mechanism to cutting force generation because the instantaneous uncut chip thickness changes with both the vibration during the current tool path and the surface left by the previous tool paths. In this study, a more accurate uncut chip thickness model was established including the precise trochoidal trajectory of the cutting edge, tool runout and dynamic modulation caused by the machine tool system vibration. The dynamic regenerative effect is taken into account by considering the influence of all the previous cutting trajectories using numerical iteration; thus, the multiple time delays (MTD) are considered in this model. It is found that transient separation of the tool-workpiece occurring at a low feed per tooth, caused by MTD and the existing cutting force models, is no longer applicable when transient tool-workpiece separation occurs. Based on the proposed uncut chip thickness model, an improved cutting force model of micro milling is developed by full consideration of the ploughing effect and elastic recovery of the workpiece material. The proposed cutting force model is verified by micro end milling experiments, and the results show that the proposed model is capable of producing more accurate cutting force prediction than other existing models, particularly at small feed per tooth.     

固定化酶催化制备乙酸正丁酯及动力学

酯交换反应可用南极假丝酵母脂肪酶B（CALB）作催化剂,采用溶胶-凝胶法固定脂肪酶CALB得到的催化剂颗粒可用于乙酸乙酯和正丁醇的酯交换反应。首先探究了固定化酶的稳定性和重复使用性,然后在间歇反应釜内进行反应动力学实验,考察了转速、催化剂用量、酯醇比、温度等因素对反应的影响,确定了适宜的操作条件。在328.15～343.15 K下,将实验数据拟合得到反应的动力学方程,通过实验值与计算值的比较,验证此宏观动力学方程合理,可用于模拟计算。