Crystal structure and thermoelectric properties of Cu2Cd1−xZnxSnSe4 solid solutions

Cu₂Cd_1–xZn_xSnSe₄ solid solutions were synthesized, and their phase constitutions and thermoelectric properties were investigated. The solid solutions crystallized in the stannite-type structure for Zn contents x up to 0.65 and in the kesterite-type structure for 0.7 ≤ x ≤ 1.0. The lattice parameter a and cell volume V of the compounds decreased linearly with increasing x for both the stannite-type (0 ≤ x ≤ 0.65) and the kesterite-type (0.7 ≤ x ≤ 1) structures. The lattice parameter c decreased with increasing x for the compounds with the kesterite-type structure but increased for the compounds with the stannite-type structure. The c/a ratio increased with increasing Zn content, which indicated an weakening of the lattice distortion. The Seebeck coefficient tended to decrease with increasing Zn content, whereas the electrical conductivity and thermal conductivity increased. The figure of merit ZT increased with increasing x over the composition range of 0 ≤ x ≤ 0.60 and then fluctuated with a further increase in x. A maximum ZT of 0.23 was achieved for Cu₂Cd_0.4Zn_0.6SnSe₄ at 720 K.     

Determination of particle size distributions and the degree of dispersion in nanocomposites

Objective of this study was the investigation of measurement techniques to determine the quality of the dispersion process of nanoparticles in polymer composites. In order to prepare the matrix suspension, alumina nanoparticles were dispersed applying shear mixing techniques in a high performance laboratory kneader. The product quality in liquid state was determined by means of dynamic light scattering (DLS) and centrifugal sedimentation analysis (CSA). However, particle measurements in carrier fluids like epoxy resin are complex and challenging. Measuring values like particle size distribution and grade of homogeneousness are strongly influenced by the sample preparation and adjustments of the measuring device. Within this study the machine settings and the formulation was analysed systematically. Hereby an identification of the key parameters and an optimisation of the measuring process were possible. Additionally, the composite was cured and analysed by scanning electron microscopy (SEM). Finally all measuring techniques were evaluated and compared among each other. Thus, DLS is the fastest method to measure spherically particles in the liquid matrix, CSA allows a certain deviation from the spherical shape and SEM gives a qualitative impression of the final particle size in cured composite condition.     

Some optical,magnetic and transport properties of CdMoO4:Nd3+

Single crystal of new cadmium and neodymium molybdate solid solution (Cd_0.958Nd_0.028□_0.014MoO₄, where □ denotes cationic vacancies) has been successfully grown by the Czochralski method. The X-ray diffraction analysis confirmed that this solid solution crystallizes in the scheelite type structure, the Nd³⁺ ions do not show long-range order and they are randomly distributed in the unit cell, substituting the Cd²⁺ ions. As a consequence, the unexpected properties of CdMoO₄:Nd³⁺ are observed such as the energy gap (~1.77 eV) twice smaller than that of the matrix CdMoO₄, a paramagnetic state with the short-range ferromagnetic interactions, behavior related to the electrical conductor with p–n transition along the 〈100〉 axis, the semiconducting behavior with n–p transition along the 〈001〉 axis and the diode-like behavior found to be of Schottky- or Maxwell-Wagner type. Therefore, we predict great potential of this single crystal for technical applications in electronic devices.     

Chemical and thermal shrinkage in thermosetting prepreg

A methodology for predicting residual cure deformation and stresses in composite laminates during cure is proposed. The technique employs an unbalanced cross-ply strip denoted as a “bi-lamina” strip to measure the in situ development of chemical and thermal shrinkage deformation during a specified thermal cycle. The constitutive model of the composite material was developed based on self-consistent micro-mechanical homogenization with variable resin thermo-mechanical material properties during the cure cycle. The resin properties were determined as a function of cure and temperature using different experimental techniques, including differential scanning calorimetry, digital image correlation, rheometry and dynamic mechanical analysis. The predicted bending deflection profiles of the strip agreed closely with experimental observations. The proposed methodology can be used to validate the material model of the resin and composite during the cure cycle.     

Cure cycle optimization of an inorganic polymer matrix material for high temperature fiber reinforced composites

We investigated the potential effects of inorganic polymer processing conditions on the residual stress generation of fiber reinforced inorganic polymer matrix composites. By optimizing various stages of processing it was found that process-induced shrinkage can be reduced by as much as 20%, while simultaneously, the compression strength can be improved by over 30% compared to baseline processing parameters. Further with the optimization of the process parameters, the pore diameter reduced by over 65%, while the relative density increased by a little over 5%. These results suggest high temperature dimensional stability and reduced pore content. Also SEM images indicate a continuous thermodynamic transformation in the bonding strength between the precipitated particles. Thus, it is demonstrated that, through the process modification, a path exists to reduced cure shrinkage, high mechanical strength and thermodynamic stability that results in a potential reduction in residual stresses in continuous fiber reinforced, inorganic matrix composites.     

Ductility of polylactide composites reinforced with poly(butylene succinate) nanofibers

Sustainable “green nanocomposites” of polylactide (PLA) and poly(1,4-butylene succinate) (PBS) were obtained by slit die extrusion at low temperature. Dispersed PBS inclusions were sheared and longitudinally deformed with simultaneous cooling in a slot capillary and PBS nanofibers were formed. Shearing of PBS increases nonisothermal crystallization temperature by 30 °C. Tensile deformation was investigated by in-situ experiments in SEM chamber. Dominant deformation mechanism of PLA is crazing, however, there are dormant shear bands formed during slit die extrusion. Pre-existing shear bands are inactive in tensile deformation but contribute to ductility by blocking, initiating and diffusing typical craze growth. PBS nanofibers are spanning PLA craze surfaces and bridging craze gaps when PLA nanofibrils broke at large strain. Straight crazes become undulated because either dormant or new shear bands become activated between crazes. Due to interaction of crazes and shear bands the ductility increases while high strength and stiffness are retained.     

Influence of zirconium content on microstructure and creep properties of Mo–9Si–8B alloys

Mo–Si–B alloys with a molybdenum solid solution accompanied by two intermetallic phases and Mo₅SiB₂ are a prominent example for a potential new high temperature structural material. In this study the influence of 1, 2 and 4 at.% zirconium on microstructure and creep properties of Mo–9Si–8B (at.%) alloys produced by spark plasma sintering is investigated. Creep experiments have been carried out at temperatures of 1100 °C up to 1250 °C in vacuum. The samples exhibit sub-micron grain sizes as small as 450 nm due to the chosen production route. With addition of 1 at.% zirconium, formation of SiO₂ on the grain boundaries can be prevented, thereby enhancing grain boundary strength and creep properties significantly. Moreover ZrO₂ particles also enhance creep resistance of the molybdenum solid solution. Creep deformation is a combination of dislocation creep in the grains including dislocation-particle interaction and grain boundary sliding leading to intergranular fracture surfaces. It is promising to use grain size adjustments in order to balance the creep and oxidation resistance of the investigated material.     

Evaluation of eddy current testing for quality assurance and process monitoring of automated fiber placement

Standards in energy and cost efficiency are higher the ever especially in the aerospace industry. While structures made from carbon-fiber reinforced plastics (CFRP) show significant advantages in regards to specific strength and lightweight design, further improvements in their production processes are essential in order for CFRP to be competitive in the future. The authors present eddy current (EC) testing as a means for quality assurance (QA) and process monitoring for CFRP parts produced by automatic fiber placement (AFP), which is one the most prevalent production methods in aerospace industry. Eddy current testing shows the potential for highly automated process monitoring that can reduce error correction and cycle time in AFP.     

十二烷基二羟乙基氧化胺在0.5 mol·L~(-1) H_2SO_4中对A3钢的缓蚀性能

通过失重法、电化学方法和量子化学计算法研究了十二烷基二羟乙基氧化胺(OAE-12)在0.5mol·L~(-1)H_2SO_4中对A3钢的缓蚀性能和作用机理。结果表明,在0.5mol·L~(-1)H_2SO_4中OAE-12能同时抑制A3钢的阴、阳极反应,缓蚀性能显著,当OAE-12质量浓度仅为200mg·L-1时,失重试验所得缓蚀率可达93.59%,且失重法、动电位极化曲线法、电化学阻抗谱法测试结果具有一致性;通过量子化学计算结果可知,OAE-12缓蚀作用机理可能是源于其分子内的氮、氧与钢表面的铁的相互作用。     

Characterising the loading direction sensitivity of 3D woven composites: Effect of z-binder architecture

Three different architectures of 3D carbon fibre woven composites (orthogonal, ORT; layer-to-layer, LTL; angle interlock, AI) were tested in quasi-static uniaxial tension. Mechanical tests (tensile in on-axis of warp and weft directions as well as 45° off-axis) were carried out with the aim to study the loading direction sensitivity of these 3D woven composites. The z-binder architecture (the through-thickness reinforcement) has an effect on void content, directional fibre volume fraction, mechanical properties (on-axis and off-axis), failure mechanisms, energy absorption and fibre rotation angle in off-axis tested specimens. Out of all the examined architectures, 3D orthogonal woven composites (ORT) demonstrated a superior behaviour, especially when they were tested in 45° off-axis direction, indicated by high strain to failure (∼23%) and high translaminar energy absorption (∼40 MJ/m³). The z-binder yarns in ORT architecture suppress the localised damage and allow larger fibre rotation during the fibre “scissoring motion” that enables further strain to be sustained by the in-plane fabric layers during off-axis loading.