Surface generation mechanism of ceramic matrix composite in ultrasonic assisted wire sawing

Ceramic matrix composites (CMC) are highly required in many fields of science and engineering. However, the CMC parts always have poor surface finish. This study attempts to improve cutting performance of CMC material by combing the advantages of ultrasonic assisted cutting and diamond wire sawing. Cutting force, surface roughness, machined edge and tool wear are analyzed based on experimental results. It shows that the oscillatory movement of tool edges provides positive effect on particle ejection and residual material reduction. Ductile chip formation can be achieved due to the small tip radius of grits. Obvious decrease in cutting force, surface roughness and tool wear are obtained. Moreover, burrs, fuzzing and fracture are reduced. Meanwhile, both the surface characteristics and shape accuracy are significantly improved. These results provide a valuable basis for application of ultrasonic assisted wire sawing and understanding of CMC cutting mechanisms.     

Influence of Different Additives on the Interaction of Quinolone Antibiotic Drug with Surfactant: Conductivity and Cloud Point Measurement Study

Conductometric and cloud point (CP) measurement studies have been performed to investigate the interaction of tetradecyltrimethylammonium bromide (TTAB) and Triton® X-100 (TX-100) with ciprofloxacin hydrochloride (CFH) in different solvents over the temperature range of 295.15–315.15 K. CFH is used for the treatment of various bacterial infections. The observed critical micelle concentration (CMC) values of TTAB were found to be reduced in the presence of electrolytes (Na₂SO₄/Na₃PO₄), and this reduction proceeds with the elevation of salt concentration. The order of the CMC of TTAB follows the trend: > >. The observed CMC values of TTAB were found to increase with increasing temperature and decrease with increasing concentration of CFH in aqueous medium. The values of Gibbs free energy of micellization () for the TTAB/TTAB + CFH mixture were found to be negative, implying spontaneous micellization. The estimated CP of TX-100 decreases with increasing concentration of TX-100 in aqueous medium. The CP values first decrease with increasing concentration of CFH and then increase at higher concentration of CFH almost in all cases investigated. The values of free energy of clouding were found to be positive in all cases studied implying that phase separation of TX-100 was nonspontaneous. The other thermodynamic parameters associated with the micellization of TTAB and the phase separation of TX-100 were estimated and explained.     

Synthesis of hexacelsian barium aluminosilicate by film boiling chemical vapour process

An original oxide/oxide ceramic-matrix composite containing mullite-based fibers and a barium aluminosilicate matrix has been synthesized by the film boiling chemical vapour infiltration process. Alkoxides were used as liquid precursors for aluminum, silicon and barium oxides. The structure and microstructure of the oxide matrix were characterized by Scanning Electron Microscopy, Energy Dispersive Spectroscopy and X-ray diffraction. Apart from small residual mullite and amorphous phase amounts, the oxide matrix is composed of the hexacelsian phase, conferring to the material interesting perspectives for high-temperature electromagnetic and structural applications.     

Mullite-bonded SiC-whisker-reinforced SiC matrix composites: Preparation,characterization, and toughening mechanisms

A novel mullite-bonded SiC-whisker-reinforced SiC matrix composite (SiCw/SiC, SiC whisker-to-SiC powder mass ratio of 1:9) was designed and successfully prepared. Before preparing the composite, the inexpensive lab-made SiCw was first modified by an oxidation/leaching process and then coated with Al₂O₃. The kinetics results indicate that the oxidation process can be described by improved shrinking-cylinder models. The aspect ratio of SiCw improved after modification. Subsequently, raw materials with a SiC–SiO₂–Al₂O₃ triple-layered structure were obtained after the Al₂O₃-coating process and used as feedstocks during the subsequent hot-pressing sintering. Finally, the characterization of the composites indicates that the mullite-bonded sample performs better (relative density of 93.8?±?1.4%, flexural strength of 533.3?±?18.2?MPa, fracture toughness of 13.6?±?2.1?MPa?m^1/2, and Vickers hardness of 20.6?±?2.5?GPa) than the reference sample without the mullite interface. The improved toughness could essentially be attributed to the moderately strong interface bonding and effective load transfer effects of the mullite interface.     

Synthesis and Characterization of Sulfanilamide-Based Nonionic Surfactants and Evaluation of Their Nano-Vesicular Drug Loading Application

Nonionic surfactants are highly stable and cost-effective and receiving acceptance for applications in many diverse fields including drug delivery, due to their distinctive properties. Here, we report on the synthesis and characterization of sulfanilamide-based nonionic surfactants for nanoscale vesicular drug loading applications. Nonionic surfactants were synthesized through alkylation of sulfanilamide with alkyl halides that possessed diverse degrees of lipophilicity. They were explored for their nanovesicular drug loading with Cefixime as a hydrophobic model drug. Drug-loaded nanovesicles were characterized for surface morphologies, size, size distribution, surface charge, and drug loading efficiency using atomic force microscopy (AFM), dynamic light scattering (DLS), and UV–visible spectrophotometry. All of the synthesized nonionic surfactants revealed their CMC values in 0.055–0.035 mM range depending upon the lipophilic chain length of surfactants. They caused a decreased hemoglobin release and low toxicity against cell culture. They self-assembled and loaded an increased amount of drug in the form of nanorange spherical shape niosomal vesicles. Results of the current study verify these synthesized nonionic surfactants are hemocompatible, nontoxic, and capable of self-assembling into nanorange niosomal vesicles. These niosomal vesicles can be suggested as safe and highly efficient nanocarriers for hydrophobic drug loading and delivery.     

多糖抑制剂的化学成份和分子量对滑石浮选的影响

选矿工业中经常使用多糖抑制剂报制具有天然可浮性的脉石来提高精矿品位。微浮选研究结果表明，在10^-3mol/L KNO3离子浓度下，多糖抑制剂的用量、分子量和化学组成等会影响多糖抑制剂对滑石的抑制作用。对4种羧甲基纤维素（CMC）和3种改性的古尔胶药剂的黏度数据进行了测试，并对各种CMC的分子量进行了估算。当体系中加入了含古尔胶的聚合物之后，滑石的天然可浮性不仅会降低，而且滑石受到的抑制作用也会随着古尔胶分子量的增大而增强。较低用量的古尔胶可强烈抑制滑石，进一步增大古尔胶用量不会再增强它对滑石的抑制作用。在10^-5mol/L KNO3条件下，CMC不是滑石的有效的抑制剂。CMC分子量的改变对滑石抑制体系没有产生任何变化，但增大CMC的浓度会使抑制作用稍稍得到增强。本文根据以上这些研究和有关的文献提出了聚合物与滑石相互作用的机理。     

合成瓦斯水合物诱导时间的研究

通过研究利用模拟瓦斯合成瓦斯水合物的诱导时间,以寻找缩短诱导时间的主要因素.结果表明：分别使用SDS（十二烷基硫酸钠），SDBS（十二烷基苯磺酸钠）及吐温-80等表面活性剂可在煤矿井下温度和中高压的条件下生成瓦斯水合物，同时使用已融化的水合物进行重复实验可显著缩短诱导时间；而且温度越高，诱导时间越长.     

用陶瓷复合材料的概念设计人工骨生物材料

现有人工骨陶瓷材料存在的主要缺点是脆性大,抗疲劳性差。由于生物陶瓷材料的弹性模量较小,很难采用添加氧化锆引起的相变增韧来解决上述缺点。采用添加纤维制成陶瓷纤维复合材料,并控制基质相中的气孔率分布呈梯度倾斜,是一个合理而有前途的新颖人工骨材料。     

Novel oxide fiber composites by freeze casting

A freeze casting process with gelatine as gelling agent is presented to manufacture novel oxide fiber composites. The growth of ice crystals causes an in situ densification of the green matrix when the composite is frozen after the lamination of 2D-fabrics. This freeze casting process leads to a porous matrix with a cellular morphology, showing no shrinkage during sintering. The porous structure is suitable for a subsequent infiltration with a precursor to densify the matrix. As the matrix is crack-free, the sintered composites have high mechanical properties. The processing is demonstrated by manufacturing laminated Nextel™610/YAG-ZrO₂ oxide fiber composites.     

UHTC-based matrix as protection for Cf/C composites: Original manufacturing,microstructural characterisation and oxidation behaviour at temperature above 2000 °C

In space propulsion applications, the development of new ceramic matrix composites with improved resistance to oxidation and ablation at high temperature is needed and ultra-high temperature ceramics-based ones appear the most suitable. Combination of both powder impregnation (ZrB₂, C) and liquid silicon infiltration enabled manufacturing of UHTC based matrices in C_f/C preforms with less than 10 vol% open porosity and various proportions and homogeneous distribution of C, ZrB₂, SiC and Si. Oxidation behaviour was evaluated on composite structures using an oxyacetylene torch at temperatures higher than 2000 °C. Chemical analyses and microstructural observations before and after oxidation testing evidenced the protection ability of ZrB₂-SiC-Si matrices thanks to the formation of multi-oxide scales which resisted even tested durations of 6 min and pointed the unharmful presence of residual 12 vol% silicon on the composite for use at high temperature under high gas flows.