炭黑-二氧化硅双相填料的结构与灰化性能研究

通过傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、氮吸附比表面积、透射电子显微镜(TEM)、扫描电子显微镜(SEM)和原子力显微镜(AFM)分析研究3种炭黑-二氧化硅双相填料(CSDPF)(分别为CSDPF A,CSDPF B和CSDPF C)的微观结构和灰化性能。FTIR和XPS分析结果显示,CSDPF含有炭黑和二氧化硅两种组分。SEM和TEM分析结果显示,不同CSDPF的比表面积和灰化性能存在较大差异,随着灰化温度的升高,炭黑相先从CSDPF中去除,导致CSDPF的比表面积增大,之后二氧化硅的烧结占主导,导致CSDPF的比表面积减小。SEM分析结果显示,在高温灰化时,CSDPF A和CSDPF B首先形成球形聚集体,由于二氧化硅稳定性不同,球形聚集体可烧结形成更大的球形聚集体或片状甚至网状结构,CSDPF C在灰化过程中形成蜂窝状结构且其变化较小。CSDPF A和CSDPF B中白炭黑大部分分布在其内部,CSDPF C中白炭黑大部分分布在其表面。

Surface modification of biomedical magnesium alloy wires by micro-arc oxidation

Magnesium alloy wires were processed by micro-arc oxidation （MAO） in a modified silicate-phosphate composite electrolyte containing hydroxyapatite （HA） nanopowders and NaOH. Effects of NaOH content in the composite electrolyte on the microstructure and properties of the MAO ceramic coatings on magnesium alloy wires were studied. It is found that the arc voltage of magnesium alloy wires in the micro-arc oxidation process is significantly reduced while the oxidation rate is accelerated. Addition of 2 g/L NaOH in the composite electrolyte is a better choice for improving corrosion resistance of magnesium alloy wires. During early simulated body fluids （SBF） immersion, the micro-arc oxidized magnesium alloy wires undergo a slow and stable degradation. After soaking for 28 d, the protective ceramic coating still shows no damage but significant degradation is observed for magnesium alloy wires after immersion for more than 60 d.

Lifetime prediction for tantalum capacitors with multiple degradation measures and particle swarm optimization based grey model

A lifetime prediction method for high-reliability tantalum （Ta） capacitors was proposed, based on multiple degradation measures and grey model （GM）. For analyzing performance degradation data, a two-parameter model based on GM was developed. In order to improve the prediction accuracy of the two-parameter model, parameter selection based on particle swarm optimization （PSO） was used. Then, the new PSO-GM（1, 2, co） optimization model was constructed, which was validated experimentally by conducting an accelerated testing on the Ta capacitors. The experiments were conducted at three different stress levels of 85, 120, and 145℃. The results of two experiments were used in estimating the parameters. And the reliability of the Ta capacitors was estimated at the same stress conditions of the third experiment. The results indicate that the proposed method is valid and accurate.

Preparation and sintering properties of zirconia-mullite-corundum composites using fly ash and zircon

Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.

Effect of hydroxyapatite:zirconia volume fraction ratio on mechanical and corrosive properties of Ti-matrix composite scaffolds

Ti-based scaffolds reinforced with zirconia and hydroxyapatite were produced successfully by a hybrid method with an eco-friendliness and low cost to obtain low elastic modulus(E) with sufficient physical, electrochemical and biological properties. The effect of simultaneous modification of the volume fraction of hydroxyapatite(HA) and zirconia(ZrO_(2)) on scaffolds was investigated in terms of mechanical, corrosive, and antibacterial properties. Scanning electron microscopy with attached electron dispersive spectroscopy and X-ray diffraction were used for the characterization of scaffolds. Compression and electrochemical tests were performed to determine mechanical properties with detailed fracture mechanism and in-vitro corrosion susceptibility to simulated body fluid at 37 ℃,respectively. Antibacterial tests were carried out by comparing the inhibition areas of E.coli and S.aureus bacteria. It was observed that the mechanical strength of the scaffolds decreased with increasing HA:ZrO_(2)volume fraction ratio.The lowest E was achieved(6.61 GPa) in 6:4 HA:ZrO_(2)composite scaffolds. Corrosion current density(J_(corr)) values were calculated to be 21, 337, and 504 μ A/cm^(2) for unreinforced Ti, 3:2 and 6:4 HA:ZrO_(2)reinforced scaffolds,respectively. The inhibition capacity of the 6:4 reinforced composite scaffold was found to be more effective against S.aureus bacteria than other scaffolds.

Research on the influence of the fly ash on the concrete carbonation

The influence of fly ash on the fresh properties, mechanical properties and carbonation properties were studied in this paper. The performance of a kind of curing agent which was applied to the hardened concrete surface was evaluated. Incorporating large volume of fly ash will risk the concrete carbonation. The curing agent could prevent the concrete carbonation, and the mechanism was explained.

Hydration Properties of Calcined Clay Pozzolan and Limestone Mineral Admixtures in Binary and Ternary Cements

This paper investigates the properties of hydrated binary and ternary blended cements using limestone and calcined clay pozzolan as supplementary cementitious materials. The blended cements were hydrated and their phase compositions were evaluated by thermogravimetric and powder X-ray diffraction at 28 days. The morphology of the samples was also determined. The water demand, setting time, compressive and flexural strengths of mortar and concrete samples were determined up to 365 days. The study concluded that the portlandite [Ca（OH）2] content was considerably reduced whilst ettfingite formation were enhanced as a result of admixture reactions. The water demand and setting times of blended cements were lower than OPC with 5% admixture content but higher with increasing content. The mechanical test results also showed that Class 42.5N and 32.5R cements can be produced from the binary and ternary blends containing up to 10% and 20% admixtures, respectively.