Fabrication and Microstructure of Composite Metal-Clad Ceramic Superconducting Wire

Sheathed high- T _c superconducting ceramic wire composites have been fabricated by wire drawing. Superconducting powders of YBa₂Cu₃O_7-x (Y-123) and Bi₄(Sr, Ca)₆Cu₄O_16+x (Bi-464) have both been prepared and successfully fabricated into continuous wire form. Under certain circumstances, a displacement reaction occurs at the interface between the ceramic superconductor and the containment tube; the nature of this displacement reaction and its prevention are discussed. Microcracking of the ceramic core is attributable predominantly to relative shrinkage effects during sintering. Failure of the metal wall during wire fabrication is attributed to drawing conditions and the mechanical properties of core and cladding.     

膨胀珍珠岩对镁钙质陶瓷热震稳定性的影响

以煅烧白云石、工业氧化镁为主要原料,通过添加膨胀珍珠岩制备镁钙质陶瓷试样;探讨膨胀珍珠岩含量对试样显气孔率、体积密度、抗热冲击性能及热冲击对试样抗折强度的影响。试验结果表明：添加适量的膨胀珍珠岩能有效地提高镁钙质陶瓷的抗热冲击性能。     

SiC/莫来石复相多孔陶瓷气孔率和强度的影响因素

以煅烧高岭土、Al(OH)3粉末、SiC粉末为主要原料,以石墨为造孔剂制备了SiC/莫来石复相多孔陶瓷,研究了造孔剂含量、碳化硅颗粒粒径以及烧结温度对SiC/莫来石复相多孔陶瓷抗弯强度和气孔率的影响,并分别用XRD和SEM分析晶相组成和断面显微结构.结果表明:当SiC粒径为60 μm,造孔剂含量为15％时,在1400℃下保温3h制备的样品综合性能最佳,其孔隙率为30.3％,抗折强度达到58.0 MPa.     

碳化硅/堇青石复相多孔陶瓷的制备及性能研究

采用碳化硅、烧高岭土、氢氧化铝、滑石为主要原料,石墨为造孔剂制备了碳化硅/堇青石复相多孔陶瓷.研究了烧结温度和烧结助剂二氧化铈对碳化硅/堇青石复相多孔陶瓷气孔率和强度的影响,并分别用XRD和SEM分析晶相组成和断面显微结构表明:制备出的SiC多孔陶瓷的主相是SiC,结合相是堇青石与方石英,多孔陶瓷具有相互连通的开孔结构;在1350℃烧结,并保温3h,当造孔剂含量为15％时,碳化硅/堇青石复合多孔陶瓷性能最佳,其气孔率31.80％,相应的弯曲强度为63.74 MPa.在1200℃下,添加不同含量的CeO2,对烧结样品的相组成有影响,能够降低生成堇青石的温度,在CeO2含量为3％的样品中,堇青石的峰最明显,但是过量的氧化铈会抑制了堇青石的生成;随着CeO2加入量的增加,其气孔率和弯曲强度也会随之变化,1200℃下,在CeO2加入量为4％时其弯曲强度最优.但随着CeO2的含量的增加,其气孔率逐渐下降.     

Strength Degradation of Nonrandom Porous Ceramic Structures under Uniaxial Compressive Loading

Nonrandom porous mullite ceramics with controlled pore geometry have been fabricated using a lost mold process, where the molds were fabricated using the fused deposition process from CAD data. The pore geometry of molds was varied to achieve different pore sizes and shapes. These porous ceramic structures were then tested under uniaxial compression to evaluate their strength degradation for different pore volumes created by varying pore sizes and shapes. The finite element method (FEM) has been used to understand the effect of these porosity parameters based on stress concentrations along pore boundaries. Strength degradation of porous ceramics was found to be related to the increase in stress concentration along the pore boundaries in three-dimensional nonrandom porous ceramics.     

Superconducting properties of a new oxysulfate superconductor

We report the effects of thermal treatment and La doping on the Sr site in the newly discovered intergrowth superconductor TlSr₄Cu₂O_z(SO₄), whose zero-resistivity temperature is found to be above 70?K. This new phase crystallizes in the tetragonal system (p4/mmm, a = 3.83?Å, c =16.6?Å). Resistivity and room-temperature thermoelectric measurements for the TlSr₄Cu₂O_z(SO₄) samples heat-treated at temperatures below 500?°C in Ar atmosphere suggest that the as-prepared sample is under a nearly optimal hole-doped state. In the Tl(Sr_4-xLa_x)Cu₂O_z(SO₄) (x?=?0–1.0) system, superconductivity is suppressed as the La doping content increases, and the decrease in transition temperature with the increase in La doping content above 0.1 is accompanied by increased formation of the TlSr₂CuO_z phase and decomposition of the TlSr₄Cu₂O_z(SO₄) phase, suggesting that the formation of the TlSr₄Cu₂O_z(SO₄) phase is strongly affected by La doping on the Sr site compared with that of the TlSr₂CuO_z phase.     

Ceramic microspheres with controlled porosity by emulsion-ice templating

Silicon Carbide porous microspheres were fabricated using a preceramic polymer by emulsion-ice templating. An oil-in-water macroemulsion was prepared by adding an organic solution, comprising polycarbosilane and cyclohexane, to the aqueous phase containing a nonionic surfactant. Upon directional freezing and freeze drying, microspheres with aligned pores were obtained. The influence of processing parameters was assessed. In particular, the solidification temperature affected size and morphology of the macroporosity. Our strategy enables an independent control of macro and nanoporosity. Indeed, the thermal treatment can be optimized to tune the micro-porosity at the nanoscale as well as the specific surface area of the samples.The emulsion-ice templating technique was optimized to produce microspheres with multimodal macroporosity up to 90 vol.% in the range 1–30 μm, with micro- and meso-pores with diameter up to 6 nm, and specific surface area as high as 117 m² g⁻¹.     

Preparation of Superconductor/Polymer Composite with Resistive Transition Temperature [Tc) above 77 K

A technique for preparing Y₁, Ba₂Cu₃O_7-x/polymer composites showing superconducting resistive transition above liquid-nitrogen temperature has been developed. A sintered Y₁Ba₂Cu₃O_7-x disk was impregnated with a low-viscosity 2-ethylhexyl acrylate monomer containing benzoyl peroxide and dicumyl peroxide as polymerization catalysts. The impregnation of sintered disks was carried out under moderate vacuum for 30 min followed by an overnight soaking. The polymerization treatment consisted of a heat treatment at 60°C for 24 h followed by a second heat treatment at 80°C for 8 to 10 h. The superconductorlpo1ymer specimens exhibited superconducting resistive transition at ≃80 K. The scanning electron micrograph reveals excellent welting, infiltration, and polymerization of the monomer into the superconducting material.     

Glass Strengthening by Polymer-Derived Ceramic Coatings

Polysilazane-derived ceramic coatings in the form of thin films (0.1 to 4 μm) — fabricated by dipcoating soda-lime rods with preceramic polymer solutions, followed by pyrolysis — increased the strength of the glass rods. Strengths up to 414 ± 57 MPa were obtained, 2.3 and 3.3 times higher than the strengths of uncoated/annealed and as-received rods, respectively. As-received coated glass was stronger than coated annealed glass. Microstructural damage was not observed in the optimal coatings.     

Successful Application of Simplex Methods to the Optimization of Textured Superconducting Ceramics

The fabrication of ceramic materials implies dealing with a great number of processing variables with clear interaction, which prevents straightforward optimization of the processes. In this paper, we report the optimization process applied to improve the properties of LFZ-textured Bi-2212 superconducting thin rods. In this process, based on Simplex optimization methods, four growth and four annealing parameters were taken as control variables to obtain high critical currents and short processing times. As a result, the critical current values increased by a factor of 3 after only 30 trials.     

聚羧酸减水剂/氧化石墨烯复合物的制备与性能

通过氧化石墨烯（GO）与聚羧酸系减水剂单体甲基丙烯酸聚乙二醇单甲醚（MAAPEGME）、甲基丙烯酸（MAA）及甲基丙烯磺酸盐（SMAS）进行自由基共聚反应制备了氧化石墨烯与聚丙烯酸系减水剂（PCs）单体的共聚物（GO-PCs）,旨在解决GO掺入水泥基材料时存在的分散不均匀及流动性降低的问题,制备GO-PCs时各组分的质量比为m（MAAPEGME）: m（MAA）: m（MAS）: m（GO）=17:2:1:0.2。检测结果表明GO与单体之间发生了共聚反应,GO纳米片层均匀的分布PCs中,达到了GO在水泥材料中分布均匀、不影响水泥流动性及增强增韧的目的,SEM形貌说明GO-PCs对水泥浆体的微观结构有较好的调控作用,研究结果对于制备高性能长寿命混凝土具有积极的意义。     

聚羧酸减水剂/氧化石墨烯复合物的制备与性能

通过氧化石墨烯（GO）与聚羧酸系减水剂单体甲基丙烯酸聚乙二醇单甲醚（MAAPEGME）、甲基丙烯酸（MAA）及甲基丙烯磺酸盐（SMAS）进行自由基共聚反应制备了氧化石墨烯与聚丙烯酸系减水剂（PCs）单体的共聚物（GO-PCs）,旨在解决GO掺入水泥基材料时存在的分散不均匀及流动性降低的问题,制备GO-PCs时各组分的质量比为m（MAAPEGME）: m（MAA）: m（MAS）: m（GO）=17:2:1:0.2。检测结果表明GO与单体之间发生了共聚反应,GO纳米片层均匀的分布PCs中,达到了GO在水泥材料中分布均匀、不影响水泥流动性及增强增韧的目的,SEM形貌说明GO-PCs对水泥浆体的微观结构有较好的调控作用,研究结果对于制备高性能长寿命混凝土具有积极的意义。     

Effects of Matrix Porosity on the Mechanical Properties of a Porous-Matrix, All-Oxide Ceramic Composite

The effects of matrix porosity on the mechanical properties of an all-oxide ceramic composite are investigated. The porosity is varied through impregnation and pyrolysis of a ceramic precursor solution. Mechanical tests are performed to assess the role of the matrix in both matrix-dominated and fiber-dominated loading configurations. The results demonstrate a loss in damage tolerance and tensile strength along the fiber direction as the porosity is reduced. Concomitantly, some improvements in interlaminar strength are obtained. The latter improvements are found to be difficult to quantify over the entire porosity range using the standard short beam shear method, a consequence of the increased propensity for tensile fracture as the porosity is reduced. Measurements of interlaminar shear strength based on the double-notched shear specimen are broadly consistent with the limited values obtained by the short beam shear method, although the former exhibit large variability. In addition, effects of precursor segregation during drying on through-thickness gradients in matrix properties and their role in composite performance are identified and discussed. An analysis based on the mechanics of crack deflection and penetration at an interphase boundary is presented and used to draw insights regarding the role of matrix properties in enabling damage tolerance in porous-matrix composites. Deficiencies in the understanding of the mechanisms that enable damage tolerance in this class of composites are discussed.     

劣质原料和工业废料制备高性能陶瓷制品的研究

利用工业废料粉煤灰和劣质原料风化花岗岩为主要原料,低温烧结制备高性能瓷砖,分析了原料配方、烧结温度等工艺参数对瓷砖物理性能和力学性能的影响.结果表明:所制得的全瓷砖性能良好,抗折强度达到45 MPa,吸水率低于小于0.5％,能达到国家标准,节约成本.     

亚微米氧化铝粉体在建筑陶瓷板材中的应用研究

采用建筑陶瓷板的制备工艺,将亚微米氧化铝粉体加入到陶瓷板材坯料中,研究了其对陶瓷板材外观、烧结性能和力学性能的影响。结果表明:在常规的生产条件下,亚微米氧化铝粉体主要以α-Al₂O₃颗粒的形式均匀分布在坯体中,具有较强的增白效果。当氧化铝粉体加入量在15%(质量分数)以内时,陶瓷板材样品的吸水率低于0.1%,烧结致密化程度较高,抗弯强度随加入量增加而提高。当加入量继续增加,吸水率增大,抗弯强度下降。氧化铝粉体加入量为15%(质量分数)时,样品的抗弯强度达到最高值96 MPa,比未外加氧化铝的样品提高了30%。在白度较低的低品质原料中,通过加入亚微米氧化铝粉体可大幅度提高产品的白度和强度,既可减少优质资源的消耗,又能较好地满足陶瓷板材对装饰效果和力学性能的要求。     

Superconducting Glass-Ceramics in the Bi-Sr-Ca-Cu-O System

Bi_1.5SrCaCu₂O _z was prepared in the glassy state by rapid quenching of the melt. The recrystallization of the glass during various heat treatments was studied by differential thermal analysis, X-ray diffraction, scanning electron microscopy, and resistivity measurements. Activation energies and frequency factors for the crystallization events below 600°C were determined by nonisothermal differential scanning calorimetry. Heating at 450°C formed mainly the Bi_{2+ x} Sr_{2− x} -CuO _z solid solution ("R"). Between 765° and 845°C, R reacted slowly with the glass to form the 80 K superconductor Bi₂(Sr,Ca)₃Cu₂O _z and CuO. Heating for 7 d at 845°C, followed by slow cooling, eliminated a low-temperature resistive "tail" and raised the temperature of zero resistance to 77 K. Heating at 867°C caused partial melting, with segregation of a Bi- and Cu-rich liquid, and loss of the superconducting phases.     

CeO2增强锆莫来石泡沫陶瓷性能的研究

以氧化铝、锆英石和高岭土等为原料,稀土氧化物CeO2为添加剂,采用有机泡沫浸渍法,在1500℃烧结制备锆莫来石泡沫陶瓷,研究CeO2含量对泡沫陶瓷性能的影响,并观察其显微结构.结果表明:锆莫来石泡沫陶瓷的抗弯强度、热震性能随CeO2含量的增加先增加,而后略有下降.在CeO2含量为0.6wt％时制品的抗弯强度及抗热震性能最佳.其最高抗弯强度达1.96 MPa,1 100℃热震循环次数为12次.     

SiO2涂层对MF/Al2O3复合材料界面性能的影响

利用溶胶-凝胶法在纤维表面制备SiO2涂层,改善莫来石纤维(MF)与Al2O3基体的结合性能,通过扫描电镜观察分析研究了不同pH值、不同水硅比下制备的硅溶胶在纤维上的涂敷效果。通过三点弯曲实验等手段研究了纤维表面涂层对复合材料力学性能的影响。研究结果表明:当pH值在1～2之间,水硅比r=1时,SiO2溶胶的涂敷效果最理想,复合材料抗弯曲强度达到419.67 MPa;相对密度94.15%。     

石膏掺量对矿(钢)渣复合材料物理力学性能试验研究

通过用石膏替代部分水泥作为胶凝材料,研究了随石膏替代量的增加对以钢渣、矿渣作为粗、细骨料的复合材料强度的影响变化。试验结果表明:当石膏替代水泥总量的0~40%,水胶比为0.38时石膏最优替代水泥总量的20%,7d抗压强度最高为43.3MPa,折压比为0.15。当石膏掺量替代水泥总量的50%~80%,水胶比为0.43时石膏最优替代水泥总量为70%,其7d抗压强度为35MPa,折压比为0.3。     

BSF复合矿物掺合料对路面混凝土力学性能的影响

本文借助扫描电子显微镜、压汞测试仪和力学性能测试手段对BSF复合矿物掺合料的使用对路面混凝土力学性能的影响进行了系统研究。结果表明：（1）使用BSF复合矿物掺合料可在一定程度上提高混凝土的28 d抗折强度,大幅降低混凝土的压折比,有效改善混凝土的脆性;（2） BSF复合矿物掺合料可有效改善混凝土的界面过渡区,使浆体更加密实,并且减少有害孔的数量;（3）在水化过程中,BSF复合矿物掺合料中的砖粉和矿渣微粉会反应生成对改善混凝土抗折强度有益的纤维状晶体。