Study of insulating electrical conductivity in hydrogenated amorphous silicon-nickel alloys at very low temperature

On the insulating side of the metal-insulator transition (MIT), the study of the effect of low temperatures T on the electrical transport in amorphous silicon-nickel alloys a-Si_1−yNi_y:H exhibits that the electrical conductivity follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T^−1/2. This behaviour showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at the Fermi level and creates the Coulomb gap (CG). For T higher than a critical value of temperature T_C, we obtained the Mott Variable Range Hopping regime with T^−1/4, indicating that the DOS becomes almost constant in the vicinity of the Fermi level. The critical temperature T_C decreases with the content of nickel in the alloys.     

Nonlinear dynamics and chaos in shape memory alloy systems

Smart material systems and structures have remarkable properties responsible for their application in different fields of human knowledge. Shape memory alloys, piezoelectric ceramics, magnetorheological fluids, and magnetostritive materials constitute the most important materials that belong to the smart materials category. Shape memory alloys (SMAs) are metallic alloys usually employed when large forces and displacements are required. Applications in aerospace structures, rotordynamics and several bioengineering devices are investigated nowadays. In terms of applied dynamics, SMAs are being used in order to exploit adaptive dissipation associated with hysteresis loop and the mechanical property changes due to phase transformations. This paper presents a general overview of nonlinear dynamics and chaos of smart material systems built with SMAs. Oscillators, vibration absorbers, impact systems and structural systems are of concern. Results show several possibilities where SMAs can be employed for dynamical applications.     

Synergistic Spectrophotometric and Atomic Absorption Spectrometric Analysis of Zinc in Alloys and Environmental Samples with N-p-MEthoxyphenyl-2-Furylacrylohydroxamic Acid and Pyridylazo Reagents

Abstract

Zinc (II) was selectively extracted from aqueous solutions of pH 7.8–8.5 into chloroform with N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA). 1-(2-pyridylazo)-2-naphthol (PAN) or 2-[(5-nitro-2-pyridyl)azo]-1-naphthol (NPAN) were added to the extract to form intensely coloured ternary complexes measurable spectrophotometrically at 550 nm (? = 6.03 × 10⁴ 1 mol^?1 cm^?1) and 625 nm (? = 8.15 × 10⁴ mol^?1 cm^?1) respectively. For atomic absorption spectrometric analysis, methyl isobutyl ketone (MIBK) was used as extracting solvent instead of chloroform and the zinc-MFHA-MIBK extract was aspirated directly into an air-acetylene flame. The absorbance was measured at the 213.9 nm resonance line with a detection limit of 0.05 ppb, which was significantly better than the limit of 1.0 ppb achieved for zinc previously with flame AAS. The method tolerated a large number of anions and cations normally occurring with zinc in environmental samples, and was applied to the trace analysis of zinc in alloys, coal, plant tissues, animal tissues and natural waters. The combinations of MFHA and PAN/NPAN were chosen from eleven hydroxamic acids and nine pyridylazo reagents as detailed in the paper.     

蛇形通道制备半固态A380铝合金浆料组织的演变

采用石墨质蛇形通道制备半固态A380铝合金浆料,并研究浆料制备过程中浆料组织的演变. 结果显示,合金熔体在蛇形通道内发生一次凝固,在其通道内壁的激冷和异质形核作用下形成大量的初生自由晶,半固态浆料的剩余液相在收集坩埚内发生二次凝固形成二次非枝晶. 初生晶粒的游离模型表明一部分初生自由晶直接生长为球晶,其他部分则成长为枝晶,枝晶在"自搅拌"的作用下发生缩颈和熔断,通过"自旋转"在蛇形通道内得到初步球化和熟化. 二次凝固形成的二次非枝晶在收集坩埚内得到初步球化和熟化,同时初生晶粒在收集坩埚内得到进一步球化、熟化和均匀分布.     

Effect of Sr on microstructure and aging behavior of Mg-14Li alloys

The as-cast and as-extruded Mg-14 wt％Li-xSr (x=0.14,0.19,0.39 wt％) alloys were,respectively,prepared through a simple alloying process and hot extrusion.The effects of Sr addition on microstructure and...     

A review on the research progress of push-out method in testing interfacial properties of SiC fiber-reinforced titanium matrix composites

Experimental analysis of single-fiber push-out for SiC fiber-reinforced titanium matrix composites (TMCs) is complicated by the incorporation of large thermal residual stresses, strong chemical bond of the fiber/matrix interface and matrix plastic deformation. This paper summarizes the development of push-out test and the characteristics of push-out test for TMCs such as crack initiating at the bottom face and theoretical analysis of the test. Moreover, it deeply analyzes the progresses of interfacial shear strength and fracture toughness, and work focus is pointed out in future.     

Diffusion and precipitation phenomena across layer interfaces in a roll bonding composite of Al(Si) and Al(Cu)

Layered composite structures can be generated in metallic sheets by roll bonding of dissimilar metals/alloys. In this investigation, heat treatable (Al(Cu)) and non-heat treatable (Al(Si)) aluminium alloys are roll bonded in sheet form. Large hardness differences between layers poses significant bonding challenges in the form of multiple necking within the hard Al(Cu) layers. For successful processing, it is vital to choose the candidate materials in a state of marginal hardness differences during rolling, but being capable of altering properties through subsequent heat treatments. Atomic diffusion takes place during heat treatment of the composite sheet and results in gradual hardness variation across sheet thickness. The Al(Cu) layers contribute to strength, whereas the Al(Si) layers provide protection from corrosion/wear-related degradation in the newly developed hybrid sheet. The overall mechanical properties of the heat-treated composite fall between the base alloys. The bonding interfaces are noted as the potential spots for initiating failure.