氧化木素磺酸盐的热缩合机理

本文主要介绍了木素磺酸盐及其氧化衍生物的热缩合反应的缩合途径和主要的影响因素:木素磺酸盐的含量,pH、反应温度、时间以及木素磺酸盐的氧化程度等等,从中推导出该反应的缩合机理——木素磺酸盐的碳水化合物中的羟基与木素磺酸盐分子中的羧基、磺酸基以及羰基适过酯键和(半)缩醛或酮的结构缩合,氧化木素磺酸盐较未改性的木素磺酸盐有更高的反应活性和缩合速率,本试验结果表明:缩合产物具有优良的抗水性能和抗碱性能,这将大大扩大木素利用的途径。

负热膨胀材料研究进展

本文介绍了负热膨胀材料的制备技术、结构、性能、应用及热缩机理研究的主要进展。分析了负热膨胀材料合成及其应用中存在的主要问题,讨论了刚性单元模模型及其局限性,给出了热缩机理理论和实验特别是第一性原理声子谱计算和拉曼光谱研究的最新进展、存在问题及发展趋势。指出了负热膨胀材料研究中应重点解决的一些重要问题。

负热膨胀材料的研究及应用

综述了近年来发现的负热膨胀材料的种类及负热膨胀机理,着重介绍正负膨胀材料的复合,制备可控膨胀、低膨胀、近零膨胀材料及其应用前景。

Fabrication and mechanical properties of Ti_(2)AlC/TiAl composites with co-continuous network structure

Ti_(2)AlC/TiAl composites with different volume fractions were prepared by hot pressing technology,and their reinforced structural characteristics and mechanical properties were evaluated.The results showed that when the reinforced phase volume fraction of Ti_(2)AlC was 20%,three-dimensional interpenetrating network structures were formed in the composites.Above 20%,Ti_(2)AlC phase in the composites accumulated and grew to form thick skeletal networks.The microplastic deformation behavior of Ti_(2)AlC phase,such as kink band and delamination,improved the fracture toughness of the composites.Comparative analysis indicated that the uniform and small interconnecting network structures could further reinforce the composites.The bending strengths of composites prepared with 20 vol.%Ti_(2)AlC reached(900.9±45.0)MPa,which was 25.5% higher than that of TiAl matrix.In general,the co-continuous Ti_(2)AlC/TiAl composite with excellent mechanical properties can be prepared by powder metallurgy method.

Mechanism of high pressure roll grinding on compression strength of oxidized hematite pellets

The mechanism of high pressure roll grinding on improvement of compression strength of oxidized hematite pellets was researched by considering their roasting properties. The results indicate that oxidized hematite pellets require higher preheating temperature and longer preheating time to attain required compression strength of pellets compared with the common magnetite oxidized pellets. It is found that when the hematite concentrates are pretreated by high pressure roll grinding （HPRG）, the compression strengths of preheated and roasted oxidized hematite pellets get improved even with lower preheating and roasting temperatures and shorter preheating and roasting time. The mechanism for HPRG to improve roasting properties of oxidized pellets were investigated and the cause mainly lies in the increase of micro-sized particles and the decrease of dispersion degree for hematite concentrates, which promotes the hematite concentrate particles to be compacted, the solid-phase crystallization, and finally the formation of Fe203 bonding bridges during subsequent high temperature roasting process.

Effect of synthesis parameters on structural and mechanical properties of Ti_(3)Al-Nb-Mo intermetallic compound obtained by powder metallurgy techniques

The influence of microstructure,heat treatment and alloying addition on mechanical and fracture properties of Ti3Al-basedintermetallic at room and elevated temperatures was studied.Ti3Al?11Nb?1Mo(mole fraction,%)alloy was consolidated viapowder metallurgy processing by mechanical alloying(MA)and hot pressing(HP).MA powders were characterized using XRD andSEM-EDS.Optimum MA duration was25h and HP conditions of1350°C,2h,35MPa.After HP,solution treatment at1050°C for1h and water quenchingα2+βWidmanst?tten microstructure is present,while subsequent aging at800°C during24h induces smallcontent of O-phase.High fraction ofβ-phase is a direct consequence of Mo.Compression tests were performed from roomtemperature to750°C in vacuum.The yield strength of compacts increases with temperature up to250°C(pyramidal slip systemsactivation),after which it decreases.Ductility increases throughout the whole temperature range.The presence of O phasecontributed to ductility increase in aged alloys,while negligibly lowering yield strength.Registered drop in the yield strength of agedalloys compared with non-aged ones was mostly influenced by precipitation ofα″2particles.Mixed fracture modes are operative atall temperatures.

Blowup mechanism for viscous compressible heat-conductive magnetohydrodynamic flows in three dimensions

We investigate initial-boundary-value problem for three-dimensional magnetohydrodynamic （MHD） system of compressible viscous heat-conductive flows and the three-dimensional full compressible Navier-Stokes equations. We establish a blowup criterion only in terms of the derivative of velocity field, similar to the Beale^Kato-Majda type criterion for compressible viscous barotropic flows by Huang et al. （2011）. The results indicate that the nature of the blowup for compressible MHD models of viscous media is similar to the barotropic compressible Navier-Stokes equations and does not depend on further sophistication of the MHD model, in particular, it is independent of the temperature and magnetic field. It also reveals that the deformation tensor of the velocity field plays a more dominant role than the electromagnetic field and the temperature in regularity theory. Especially, the similar results also hold for compressible viscous heat-conductive Navier-Stokes flows, which extend the results established by Fan et al. （2010）, and I-Iuang and Li （2009）. In addition, the viscous coefficients are only restricted by the physical conditions in this paper.