Crystallization and dielectric properties of lead-free glass-ceramic composites with Gd_2O_3 addition

Lead-free glass-ceramic composites in barium sodium niobate silica system with Gd2O3 addition were synthesized through melt-casting fol-lowed by controlled crystallization technique. Crystallization and dielectric properties of the Gd2O3 adding glass-ceramic composites were investigated. With the increase in the concentration of Gd2O3, the glass transition temperature and the crystallization temperature of the pre-cursor glass shift towards the higher temperature. The crystallization behavior that occurred during the heat treatment procedure leads to the enhancement of dielectric constant. All the three compositions of glass-ceramic composites exhibit ferroelectricity when tested at room tem-perature. Both the values of the remanent polarization and coercive field are enhanced regularly with the gradual increase in the concentration of Gd2O3 additive under the same testing field.

Recycling of Glass Fibers from Fiberglass Polyester Waste Composite for the Manufacture of Glass-Ceramic Materials

This work presents the feasibility of reusing a glass fiber resulting from the thermolysis and gasification of waste composites to obtain glass-ceramic tiles. Polyester fiberglass (PFG) waste was treated at 550℃ for 3 h in a 9.6 dm3 thermolytic reactor. This process yielded an oil (≈24 wt%), a gas (≈8 wt%) and a solid residue (≈68 wt%). After the polymer has been removed, the solid residue is heated in air to oxidize residual char and remove surface contamination. The cleaning fibers were converted into glass-ceramic tile. A mixture consisting of 95 wt% of this solid residue and 5% Na2O was melted at 1450℃ to obtain a glass frit. Powder glass samples (<63 μm) was then sintered and crystallized at 1013℃, leading to the formation of wollastonite-plagioclase glass-ceramic materials for architectural applications. Thermal stability and crystallization mechanism have been studied by Differential Thermal Analysis. Mineralogy analyses of the glass-ceramic materials were carried out using X-ray Diffraction.

Preparation and Microstructure of a Si-Mo Fused Slurry Coating on Carbon/Carbon Composites for Oxidation Protection

A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370℃.

Sand Slurry Erosive Wear Behavior of Hot Extruded Al6061-SiC Composites

Aluminum based composites are very popular in automotive and aerospace segments. In particular aluminum alloy-SiC composite systems are widely studied and seriously explored for various other applications in defense and space. However they have not been looked at as potential materials in naval and chemical applications where synergistic effects of both wear and corrosion need to be addressed to. This needs the assessment of wear behavior of composites. From the survey, it is evident that major focus is on mechanical and corrosion properties of cast composites. However, meager information is available as regards the slurry erosive wear behavior of cast and extruded metal matrix composites. In the light of the above, the present investigation is aimed at studying in detail the slurry erosive wear behavior of cast and hot extruded Al6061 and Al6061-SiC composites in sand slurry. Al6061-SiC composites have been prepared primarily by vortex method. Hot extrusion of these composites and the matrix alloy has been carried out at 550℃ using a 500T hydraulic press. Both as cast and hot extruded composites have been subjected to microstructure studies, microhardness, and slurry erosive wear tests. The hot extruded composites exhibit higher hardness, and slurry erosive wear resistance when compared with as cast alloy and its composites.

Optimization of mixing speed and time to disperse the composite conductive agent composed of carbon black and graphene in lithium-ion battery slurry

This paper proposed an optimal approach to disperse the composite conductive agent which is composed of carbon black(CB)and graphene(Gr)within lithium-ion battery(LIB)slurry with different mixing speeds and mixing times.The internal structures of LIB slurry are characterized by Electrochemical Impedance Spectroscopy,Scanning Electron Microscopy,and Raman experiment.Initially,a composite conductive solution is prepared by mixing the composite conductive agent with NMP solvent under the conditions of five different mixing speeds n_(1)(n_(1)=1000,1100,1200,1300,1400 rpm)in the case of mixing time t_(1)=10 min.Subsequently,LIB slurry is prepared by blending the composite conductive solution,LiCoO_(2)and PVDF-NMP solution under the conditions of five different mixing speeds n_(2)(n_(2)=1000±280,1100±280,1200±280,1300±280,1400±280 rpm)in the case of mixing time t_(2)=6 min.By analyzing the internal structure of different LIB slurries,it shows that in the case of n_(1)=n_(2)=1200 rpm,a conductive network structure is well formed within LIB slurry.Additionally,in order to determine the optimal time to prepare the composite conductive solution for LIB slurry,nine different t_(1)(t_(1)=0,10,20,30,40,50,60,70,80 min)are selected.By analyzing the internal structure of different LIB slurries,a well-formed conductive network structure and a uniformly distributed composite conductive agent are deduced in LIB slurry when t_(1)=50 min.Therefore,it can be concluded that the composite conductive agent composed of CB and Gr is able to be uniformly dispersed in LIB slurry by establishing a well-formed conductive network structure under the optimal mixing speed n_(1)=n_(2)=1200 rpm and the optimal mixing time t_(1)=50 min,t_(2)=6 min.This kind of the internal structure has the potential to be used to further analyze the dispersion characterizations of LIB slurry under different composite conductive agent and CB/Gr ratios with the aim of improving the final performance of LIB.

Microstructure and isothermal oxidation of 3Al_2O_3·2SiO_2/SiC coating on high and low density carbon-carbon composites

Carbon-carbon composite （C/C） materials are prone to severe oxidation and volatilization problems. To address these issues, mullite （3Al2O3.2SiO2）/silicon carbide （SIC） coatings were deposited on C/C composite substrates characterized into high and low densities. The coatings were applied by a two-step approach： pack cementation and silica sol based slurry coating processes. The relationship between the microstructure of 3Al2O3·2SiO2/SiC coatings and C/C substrates during isothermal oxidation cycle at 1 500 ℃ was investigated using X-ray diffractometer （XRD） and scanning electron microscope （SEM） mounted with energy dispersive spectrometer （EDS）. The results indicate that the density of the substrates has a marked effect on the coatings. Dense, thick and well-bonded coatings are obtained in the high density substrate. After 106 h of isothermal oxidation, the high density substrate with 3Al2O3-2SiO2/SiC coating offers effective protection as compared to low density substrate suffering recession.

Microstructural characteristics of in situ Mg_2Si/Al-Si composite by low superheat pouring

To control the morphology and size of the primary and eutectic Mg2Si phases in in situ Mg2Si/Al-Si composite and achieve a feasible and reliable technique to produce appropriate feedstock for the thixo-casting and rheo-casting of this type of material, three AI-Si matrix composites reinforced by 5wt.%, 9wt.% and 17wt.% Mg2Si with hypoeutectic, eutectic and hypereutectic compositions were prepared by the low superheat pouring （LSP） process. The effects of the pouring temperature （superheat） on the morphology and size distribution of primary phases （primary e-AI and Mg2Si）, binary （a-AI ＋ Mg2Si） eutectic cell and eutectic Mg2Si were investigated. The experimental results show that low pouring temperature （superheat） not only refines the grain structure of the primary e-AI and binary （e-AI ＋ Mg2Si） eutectic cell in three composites and promotes the formation of more non- dendritic structural semi-solid metal （SSM） slurry of these phases; but also refines the primary and eutectic Mg2Si phases, which seems to be attributed to the creation of an ideal condition for the nucleation and the acquisition of a high survival of nuclei caused by the LSP process.

Oxidation behavior of oxidation protective coatings for C/C-SiC composites at 1500 ℃

Porous carbon/carbon preforms were infiltrated with melted silicon to form C/C-SiC composites. Three-layer Si-Mo coating prepared by slurry painting and SiC/Si-Mo multilayer coating prepared by chemical vapor deposition(CVD) alternated with slurry painting were applied on C/C-SiC composites, respectively. The oxidation of three samples at 1 500 ℃ was compared. The results show that the C/C-SiC substrate is distorted quickly. Three-layer Si-Mo coating is out of service soon due to the formation of many bubbles on surface. The mass loss of coated sample is 0.76% after 1 h oxidation. The sample with SiC/Si-Mo multilayer coating gains mass even after 105 h oxidation. SiC/Si-Mo multilayer coating can provide longtime protection for C/C-SiC composites and has excellent thermal shock resistance. This is attributed to the combination of dense SiC layer and porous Si-Mo layer. Dense SiC layer plays the dual role of physical and chemical barrier, and resists the oxidation of porous Si-Mo layer. Porous Si-Mo layer improves the thermal shock resistance of the coating.

Some Studies on Wear and Corrosion Properties of Al5083/Al₂O₃/Graphite Hybrid Composites

Advanced technology has put an increasing demand on the composite materials, particularly more in the areas of dynamic structures. Among the several types of aluminum alloys being used, Al5000 series are widely used in marine and aerospace applications due to their superior corrosion resistance, excellent formability and good welding characteristics. Al5083, a non-heat treatable high Mg-Al wrought alloy, is extensively used for the marine applications. Hence, an attempt has been made in the proposed work to study the effects of Graphite (Gr) and Aluminium oxide (Al2O3) on aluminum hybrid composites involving both hard and soft reinforcements on wear and corrosion properties. The synthesis of hybrid metal matrix composite used in the present study has been carried out by stir casting method. The effects of reinforcement, time duration and particle size on prepared samples of composites have been studied on slurry erosive wear. The static and accelerated corrosion tests have been performed and the microhardness of the developed composites was also investigated. The experimental results on Al5083-Al2O3-Gr hybrid composites revealed that the addition of reinforcement improves the hardness and reduces corrosion and wear rates.

Preparation of composite abrasives by electrostatic self-assembly method and its polishing properties in Cu CMP

The adsorption characteristics of cationic polyelectrolyte poly dimethyl diallyl ammonium chloride （PDADMAC） and anionic polyelectrolyte poly （sodium-p-styrenesulfonate） （PSS） on benzoguanamine formal- dehyde （BGF） particles are investigated. The charging characteristics of BGF particles are changed and con- trolled using electrostatic self-assembly method. A variety of PE,-BGF/SiO2 composite abrasives are obtained. The as-prepared samples are analyzed by zeta potential analysis, transmission electron microscope （TEM） and thermogravimetric （TG） analysis. The composite abrasive slurries are prepared for copper polishing. The poli- shing results indicate that it is SiO2 abrasives, not only coated SiO2 abrasive on polymer particles but also free SiO2 abrasive in slurry, that offer the polishing action. The material removal rates of copper polishing are 264 nm/min, 348 nm/min and 476 nm/min using single SiO2 abrasive slurry, PE0-BGF/SiO2 mixed abrasive slur- ry and PE3-BGF/SiO2 composite abrasive slurry, respectively. The surface roughness Ra of copper wafer （with 5μm×5μm district） is decreased from 0.166 μm to 3.7 nm, 2.6 nm and 1.5 nm, and the surface peak-valley values Rrv are less than 20 nm, 14 nm and 10 nm using these kinds of slurries, respectively. Key words ： chemico-mechanical polishing; polishing slurry; composite abrasives ; polyelectrolyte ; copper

装配式叠合楼板后浇带接缝处细节施工研究

叠合楼板因整体性能好、构造简单、弹性好以及使用便捷等优势在装配式建筑中具有广泛的应用价值,装配式叠合楼板后浇带接缝处因模板与后浇带叠合板存在空隙等导致其存在漏浆通病问题,其不仅影响装配式建筑的整体美观,而且还增加施工成本。鉴于此,以某装配式项目为例,针对传统施工模式下后浇带接缝处存在的漏浆通病,提出在模板底部采取螺杆反吊和利用废钢筋焊接形成自拉加固体系,加固接缝处模板,以此减少叠合板后浇带接缝空隙,控制叠合板后浇带接缝漏浆通病。

沼液滴灌条件下不同类型灌水器的堵塞特征

为了探求不同类型灌水器在沼液滴灌中的抗堵塞性能,研发适用于沼液滴灌的灌水器,明确沼液滴灌条件下灌水器的堵塞类型。选用内镶贴片式灌水器(1.38、2、3 L/h)、内镶圆柱式灌水器(2、3 L/h)、压力补偿式灌水器(2、4、6 L/h)三类灌水器,在灌水压力0.08 MPa、水沼液配比4∶1(体积比)条件下进行周期性间歇灌水试验,比较不同灌水器的堵塞情况,并使用扫描电镜分析堵塞物的粒径大小及各粒径占比情况,同时结合堵塞物的傅里叶红外光谱图分析堵塞物的组成成分。结果表明,8种灌水器(E1~E8)达到堵塞标准所需的时间分别为108、126、141、111、132、84、102和117 h;灌水器堵塞物在出水口、进水口以及过水流道内均有分布,进水口处为黄色泥沙沉积,出水口及过水流道拐角处为黑色絮状物;堵塞物成分为沙粒、碳酸盐、硫酸盐、磷酸盐等无机化合物以及烃类、蛋白质、脂类等有机物;堵塞物中88.42%的颗粒物粒径集中在0.2~1.4μm的粒径范围内,其余11.58%为大絮状物。综上所述,同类型灌水器中,额定流量越大的灌水器达到堵塞标准所需的时间越长,抗堵塞性能越好;同额定流量的灌水器,内镶贴片式灌水器的抗堵塞性能最佳;额定流量3 L/h的内镶贴片式灌水器的抗堵塞性能最佳;灌水器发生的堵塞类型为物理-化学-生物三者协同作用导致的复合型堵塞。

基于煤颗粒−结合水复合相的水煤浆导热系数预测模型

水煤浆气流床气化是目前大型先进煤气化技术之一,提升水煤浆气化效率有助于推动煤炭清洁高效利用。水煤浆预热技术被认为是提高煤气化能源利用效率的关键技术之一。目前,复杂液固悬浮液导热系数的变化规律和内在机理仍未被完全认识。导热系数是介质流动换热的重要基础参数,表征着其在稳态导热过程的导热能力。利用瞬态热线法测定不同温度下相同质量分数水煤浆的导热系数,实验结果表明:温度越高,导热系数越高。在室温下测定不同质量分数下水煤浆的导热系数,实验结果表明可以分为2个阶段:质量分数从51%增大到58%时为下降区,导热系数快速下降,由0.401 W/(m·K)降至0.358 W/(m·K);而质量分数继续增加,从58%到67%时为恒定区,导热系数基本保持在0.358 W/(m·K)。基于实验结果,综合考虑平行模型、麦克斯韦模型、广义自洽模型等复合材料模型,提出煤颗粒−结合水复合的水煤浆导热系数平行预测模型。水煤浆中的水分包含自由水和结合水,结合水会和煤颗粒形成煤颗粒−结合水复合相,将水煤浆视为复合相和自由水相组成的两相复合材料。在下降区,随着煤颗粒质量分数的增加,自由水相减少,复合相不变,水煤浆导热系数快速降低;在恒定区,随着煤颗粒质量分数的进一步增加,复合相中的结合水量减少,但复合相的导热系数基本维持稳定。

浆料浸渍辅助PIP工艺制备C/HfC-SiC复合材料的微观结构及性能研究

针对高速飞行器对于防热/承载一体化超高温陶瓷基复合材料的迫切需求,以及现有反应型HfC先驱体存在的成本高、效率低和致密效果差等不足,本研究将HfC亚微米粉体配制成稳定的陶瓷浆料,利用浆料加压浸渍辅助先驱体浸渍裂解(PIP)工艺制备了HfC基体均匀分布的C/HfC-SiC复合材料,探讨了HfC含量对于复合材料微观结构、力学与烧蚀性能的影响。结果表明,当HfC实际体积分数为13.1%~20.3%时,复合材料密度为2.20~2.58 g·cm^(-3),开孔率约为5%。通过单层碳布加压浸渍陶瓷浆料,HfC颗粒能够分散到纤维束内部,且在复合材料中分布比较均匀。提高HfC含量会降低复合材料纤维含量,其力学性能也呈现出降低趋势。当HfC体积分数为20.3%时,复合材料的密度、拉伸强度和断裂韧性分别为2.58 g·cm^(-3)、147 MPa和9.3 MPa·m^(1/2);经氧乙炔焰烧蚀60 s后,复合材料的线烧蚀率和质量烧蚀率分别为0.0062 mm/s和0.005 g/s,烧蚀过程中形成的熔融相Hf_(x)Si_(y)O_(z)能覆盖在材料表面,起到良好的保护作用。

单晶碳化硅电化学机械抛光液的组分设计与优化

单晶碳化硅具有高硬度和高化学惰性,化学机械抛光方法难以同时保证其加工效率和表面质量。电化学机械抛光具有较高的材料去除率,是加工碳化硅的一种有效方法。然而,目前针对碳化硅电化学机械抛光液的相关研究还较为缺乏。为此,首先通过单因素实验确定电化学机械抛光液中导电介质和磨粒种类,然后分析导电介质和磨粒浓度以及抛光液pH值对材料去除率和表面粗糙度的影响规律,最终确定抛光液的最佳参数。结果表明:在抛光液以NaCl为导电介质,SiO_(2)为抛光磨粒时,碳化硅具有较好的抛光效率和表面质量,其材料去除率和表面粗糙度随着NaCl浓度的增大而增大,随着磨粒浓度的增加先增大后趋于稳定;当NaCl浓度为0.6 mol/L、SiO_(2)质量分数为6%、抛光液pH值为7时,可以兼顾碳化硅抛光的材料去除率和表面粗糙度Sa,其值分别为2.388μm/h和0.514 nm。

织构化多孔Al_(2)O_(3)-SiO_(2)复合陶瓷片-球混合浆料特性及光强分布仿真

陶瓷光固化技术在制备Al_(2)O_(3)-SiO_(2)复合陶瓷方面具有广阔前景,织构化的Al_(2)O_(3)-SiO_(2)复合陶瓷在陶瓷光固化增材制备方面亟待研究。本工作研究了添加片状氧化铝、等轴氧化铝、球形二氧化硅的片-球混合陶瓷光固化浆料的特性。针对不同固相配比,研究了浆料的黏度、沉降性、固化特性和固化精度,并针对所研究的片-球混合浆料开发了一种紫外光强分布模拟算法,对浆料在曝光中的光强分布进行了理论模拟分析,最终成功制备了具有片状氧化铝定向特征的织构化多孔Al_(2)O_(3)-SiO_(2)复合陶瓷。研究结果表明,片状氧化铝与球状粉体组合可以使浆料在高固相含量(总固相体积分数40%~45%,片状氧化铝体积分数占50%~60%)下保持低黏度和剪切稀释性。在相同总固相含量下,增大片状氧化铝或球形二氧化硅的含量能够减小浆料的黏度,从而提高浆料的沉降率。片状氧化铝相比于等轴氧化铝可以减少浆料对紫外光的阻挡和散射作用。在相同曝光能量条件下,降低等轴氧化铝、增加球形二氧化硅的含量可以增加的浆料固化厚度;而增加片状氧化铝和球形二氧化硅的含量会扩大尺寸误差。理论模拟结果表明,接近水平分布的片状氧化铝对光的阻挡和偏转作用弱,接近垂直分布的片状氧化铝对紫外光具有引导作用。模型上边界紫外光强平均值的变化与固化厚度测量值的变化接近,所建立的模型可以为浆料固化厚度的实验测试结果提供理论支持。

纤维复材浆料流变性能分析及矿混匀质量应用研究

为了提高混匀料场混匀矿质量,制备了高性能碳纤维增强复合材料,考察了SiC_(240)∶SiC_(1200)比值对碳纤维增强复合材料浆料流变性能、密度和断口形貌的影响。结果表明,碳纤维增强复合材料浆料的黏度从大至小的SiC_(240)∶SiC_(1200)比值顺序为:1∶5、1∶2、1∶1、2∶1、5∶1。碳纤维增强复合材料浆料的黏度会随着SiC_(240)∶SiC_(1200)比值减小而增大。随着SiC_(240)∶SiC_(1200)比例从5∶1减小至1∶5,碳纤维增强复合材料的密度从2.62 g/cm^(3)减小至2.06 g/cm^(3)。当SiC_(240)∶SiC_(1200)比例从5∶1减小至1∶5时,由于细颗粒SiC含量增加,碳纤维增强复合材料浆料素坯和原浆料体积百分比呈现增加的趋势。适宜的SiC_(240)∶SiC_(1200)比值为1∶1,此时浆料具有较好的流变性能和较高的密度。

带纤维背衬的TPO防水卷材在水产养殖项目防水工程中的应用

某水产养殖项目防水设计采用1.5 mm厚水泥胶浆+1.2 mm厚TPO防水卷材(L类,带纤维背衬),重点介绍了排水口、底部转角处的防水处理方法。该防水做法可与基层满粘,形成高强度的复合防水体系,且环保、易施工,防水效果良好。

土岩复合地层大直径泥水盾构穿越沉降敏感带扰动控制技术分析

地铁建设由于线路形式的特殊性,不可避免要穿越房屋、桥梁、管线、复杂地层及其他重要建筑物,因此复合地层条件下盾构施工过程中扰动控制技术分析尤其重要。针对大直径泥水盾构穿越敏感带时开挖面稳定性进行了数值模拟分析,研究了开挖面失稳流固耦合规律,并对不同支护压力下的开挖面变形进行了深入探讨。结果表明:完全流固耦合模拟开挖面失稳过程中,开挖面附近孔压下降梯度明显,远场孔压波动较小,基本保持为初始状态静水压力;并且随埋深的增大,开挖面的极限支护压力比逐渐减小,而开挖面稳定性逐渐增加。研究成果可为类似地层盾构施工提供参考。

浆料涂刷-热压法制备2D C_(f)-ZrB_(2)-SiC复合材料的力学与烧蚀性能

连续碳纤维增强ZrB_(2)-SiC复合材料以其优异的抗氧化、抗烧蚀性能在航天飞行器热防护结构材料领域备受关注。本文采用浆料涂刷−热压法制备2D C_(f)-ZrB_(2)-SiC复合材料,探索运用微米级粉末浆料制备2D C_(f)-ZrB_(2)-SiC复合材料的可行性,研究烧结温度对材料微观结构与力学性能的影响,并测试材料的抗烧蚀性能。结果表明:采用微米粉末浆料涂刷−热压法制备的2D C_(f)-ZrB_(2)-SiC复合材料于2000℃烧结后具有最高的致密度与抗弯强度,开孔率达到8.01%,抗弯强度达到191.3 MPa;复合材料表现出较好的抗烧蚀性能,材料表面响应温度达到2600℃,经300 s等离子火焰烧蚀后线烧蚀率为3.51μm/s。