有机蒙脱石的热性能及结构变化研究

借助热重分析(TG)、差热分析(DTA)、傅里叶红外变换分析(FTIR)、X-射线衍射分析(XRD)等分析表征手段,本文系统的研究了有机蒙脱石的热性能及其失重变化规律,对不同灼烧温度下有机蒙脱石的结构变化进行了全面的分析。研究结果表明:有机蒙脱石在200～500℃之间存在大量失重和放热过程,这预示着层间烷基铵的分解;进一步的结构分析证实了有机蒙脱石中烷基铵在500℃下灼烧2h时分解的完全和对蒙脱石的层状结构的保护作用,但900℃下灼烧2h时蒙脱石的结构已破坏,这为研究有机蒙脱石层间烷基铵的定量表征提供了依据。

Thermodynamic Performance Characteristics of a Brownian Microscopic Heat Engine Driven by Discrete and Periodic Temperature Field

A Brownian microscopic heat engine with a particle hopping on a one-dimensional lattice driven by adiscrete and periodic temperature field in a periodic sawtooth potential is investigated.In order to clarify the underlyingphysical pictures of the heat engine, the heat flow via the potential energy and the kinetic energy of the particles areconsidered simultaneously.Based on describing the jumps among the three states, the expressions of the efficiency andpower output of the heat engine are derived analytically.The general performance characteristic curves are plotted bynumerical calculation.It is found that the power output-efficiency curve is a loop-shaped one, which is similar to onefor a real irreversible heat engine.The influence of the ratio of the temperature of the hot and cold reservoirs and thesawtooth potential on the maximum efficiency and power output is analyzed for some given parameters.When the heatflows via the kinetic energy is neglected, the power output-efficiency curve is an open-shaped one, which is similar to onefor an endroeversible heat engine.

Effect of heat treatment on mechanical and wear properties of Zn−40Al−2Cu−2Si alloy

In order to determine the effect of heat treatment on the mechanical and wear properties of Zn−40Al−2Cu−2Si alloy,different heat treatments including homogenization followed by air-cooling(H1),homogenization followed by furnace-cooling(H2),stabilization(T5)and quench−aging(T6 and T7)were applied.The effects of these heat treatments on the mechanical and tribological properties of the alloy were studied by metallography and,mechanical and wear tests in comparison with SAE 65 bronze.The wear tests were performed using a block on cylinder type test apparatus.The hardness,tensile strength and compressive strength of the alloy increase by the application of H1 and T6 heat treatments,and all the heat treatments except T6,increase its elongation to fracture.H1,T5 and T6 heat treatments cause a reduction in friction coefficient and wear volume of the alloy.However,this alloy exhibits the lowest friction coefficient and wear volume after T6 heat treatment.Therefore,T6 heat treatment appears to be the best process for the lubricated tribological applications of this alloy at a pressure of 14 MPa.However,Zn−40Al−2Cu−2Si alloy in the as-cast and heat-treated conditions shows lower wear loss or higher wear resistance than the bronze.

Fabrication and Properties of Microencapsulated n-octadecane and Paraffin

Microencapsulated n-alkanes as energy- storage materials have promising application prospects. The ndcrocapsules containing 100 - 50 wt% of n - octadecane, 0 -20 wt% of paraffin and 0 - 30 wt% of cyclohexane were synthesized by in-situ polymerization using melamine- formaldehyde polymer as shell. Cyclohexane was removed after heat-treated the microcapsules at 100℃. The morphologies, cell parameters, phase change properties, thermal stable temperatures of these microcapsules were examined. The diameters of these microcapsules are lower than 5 μm. The effect of paraffin in the microcapsules on the cell parameters of n-octadecane is negligible. The paraff＇m is effectively used as a nucleating agent to decrease the degree of supercooling. The melting enthalpy is decreased from 132 J/g to 111 J/g due to the increase of the cyclohexane contents. The thermal stable temperature is enhanced 6 - 16℃ after heat-treated the microcapsules at 160℃ for 30 min.

Numerical Investigation of Base-Setting of Stator's Stagger Angles for a 15-stage Axial-Flow Compressor

A 15-stage axial-flow compressor utilized in steel industry was studied in this paper. All the stator's stagger angles of the compressor are variable to ensure the multistage compressor operate effectively within a wide range of flow rate and meanwhile satisfy the demand for sufficient pressure ratio, adiabatic efficiency and stall margin. Three in all different base-settings of stator's stagger angles were presented and commercial CFD software was applied to obtain the overall performance characteristics. The results showed that both of the optimized base-settings improved the performances both in summer and winter conditions, although the adiabatic efficiency was somewhat decreased. Taking incidence angle and stage loading into consideration, differences among the three cases were analyzed in detail. On the basis of numerical computations, the performance could be effectively improved through adjusting the base-setting of stator's stagger angles.

Copper chalcogenide thermoelectric materials

Cu-based chalcogenides have received increasing attention as promising thermoelectric materials due to their high efficiency,tunable transport properties,high elemental abundance and low toxicity.In this review,we summarize the recent research progress on this large family compounds covering diamond-like chalcogenides and liquid-like Cu2X (X=S,Se,Te)binary compounds as well as their multinary derivatives.These materials have the general features of two sublattices to decouple electron and phonon transport properties.On the one hand,the complex crystal structure and the disordered or even liquid-like sublattice bring about an intrinsically low lattice thermal conductivity.On the other hand, the rigid sublattice constitutes the charge-transport network, maintaining a decent electrical performance.For specific material systems,we demonstrate their unique structural features and outline the structure-performance correlation. Various design strategies including doping,alloying,band engineering and nanostructure architecture,covering nearly all the material scale,are also presented.Finally,the potential of the application of Cu-based chalcogenides as high-performance thermoelectric materials is briefly discussed from material design to device development.