Wear Behavior of Cooling Slope Rheocast A356 Al Alloy

In the present study, the dry sliding wear behavior of rheocast A356 Al alloys, cast using a cooling slope, as well as gravity cast A356 Al alloy have been investigated at a low sliding speed of 1 ms^?1, against a hardened EN 31 disk at different loads. The wear mechanism involves microcutting–abrasion and adhesion at lower load for all of the alloys studied in the present work. On the other hand, at higher load, mainly adhesive wear along with oxide formation is observed for gravity cast A356 Al alloy and rheocast A356 Al alloy, cast using a 45° slope angle. Unlike other alloys, 60° slope rheocast A356 Al alloy is found to undergo mainly abrasive wear at higher load. Accordingly, the rheocast sample, cast using a 60° cooling slope, exhibits a remarkably lower wear rate at higher load compared to gravity cast and 45° slope rheocast samples. This is attributed to the dominance of abrasive wear at higher load in the case of rheocast A356 Al alloy cast using a 60° slope. The presence of finer and more spherical primary Al grain morphology is found to resist adhesive wear in case of 60° cooling slope processed rheocast alloy and thereby delay the transition of the wear regime from normal wear to severe wear.     

Fabrication and characterization of 7075 Al alloy reinforced with SiC particulates

7075 aluminum (Al) alloy as matrix and silicon carbide (SiC) as reinforcement has been identified since it has potential applications in aircraft and space industries because of lower weight to strength ratio, high wear resistance and creep resistance. Thorough investigations about the microstructure and characterization of Al alloy/SiC composite are needed so that metal matrix composites (MMCs) fabricated for aircraft and space industries are defect free and have sound microstructure. Objective of this research work are the fabrication and microstructural investigations of AA7075–SiCp MMCs. 7075 Al alloy is reinforced with 10 and 15 wt.% SiCp of size 20–40 μm by stir casting process. The resulting as-cast composite structures are analyzed using scanning electron microscopy, X-ray diffraction (XRD), differential thermal analysis, and electron probe microscopic analysis (EPMA). SiCp distribution and interaction with 7075 Al alloy matrix is studied. The 7075 Al alloy–SiCp composite microstructure showed excellent SiCp distribution into 7075 Al alloy matrix. In addition to this, no evidence of secondary chemical reactions is observed in XRD and EPMA analysis. Decomposition step in derivative thermogravimetric curve is seen at temperature of 1,257, 1,210, and 1,256 °C for 7075 Al alloy, AA7075/10 wt.%/SiCp (20–40 μm) and AA7075/15 wt.%/SiCp (20–40 μm) composites, respectively. So, these composites can be successfully used for applications where temperature does not exceed beyond 1,250 °C.     

Low-frequency Raman scattering of light by silver nanoparticles

Silver nanoparticles sprayed onto a crystalline quartz substrate are characterized by means of the low-frequency Raman scattering. Contributions of silver nanoparticles of different sizes to the Raman scattering spectrum are estimated. Data of scanning electron microscopy are used to verify the validity of the results obtained.     

Retrieval of thermal properties in a transient conduction–radiation problem with variable thermal conductivity

This article reports an inverse analysis of a transient conduction–radiation problem with variable thermal conductivity. Simultaneous retrieval of parameters is accomplished by minimizing the objective function represented by the square of the difference between the measured and the assumed temperature fields. The measured temperature field is calculated from the direct method involving the lattice Boltzmann method (LBM) and the finite volume method (FVM). In the direct method, the FVM is used to obtain the radiative information and the LBM is used to solve the energy equation. With perturbations imposed on the measured temperature data, minimization of the objective function is achieved with the help of the genetic algorithm (GA). The accuracies of the retrieved parameters have been studied for the effects of the genetic parameters such as the crossover and the mutation rates, the population size, the number of generations and the effect of noise on the measured temperature data. A good estimation of parameters has been obtained.     

Deuterium thermal desorption from Ni-rich deuterated Mg thin films

Mg–Ni multilayers and Ni-rich Mg thin films were deposited by electron gun and pulsed laser deposition, respectively. Samples were submitted to thermal treatment in deuterium or hydrogen atmosphere at 423 K and 10⁵ Pa pressure to promote the metal to hydride phase transition.The H chemical bonding in the multilayer samples, after annealing in H₂ atmosphere, was examined by Fourier transform infrared spectroscopy: the obtained spectra suggest that the samples with the Mg:Ni=2:1 atomic ratio contain the Mg₂NiH₄ phase while the samples with lower Ni concentration contain both the MgH₂ and the Mg₂NiH₄ phases.The effect of the Ni additive on the stability of the deuteride phase was studied by thermal desorption spectroscopy (TDS). The TDS spectra of the single-phase Mg₂NiD₄ samples show a TDS peak at 400 K. The TDS spectra of the two-phase samples show both the D₂ desorption peak at 400 K and a second peak at higher temperature that we attributed to the dissociation of the MgD₂ phase. The high-temperature peak shifts to lower temperatures by increasing the Ni content.It is suggested that in the two-phase samples, the lattice volumes having the Mg₂Ni structure resulting from the dissociation of the Mg₂NiD₄ phase reduce the thermodynamic stability of the MgD₂ phase.     

Application of nanostructured ZnO films for electrochemical DNA biosensor

Nanostructured zinc oxide (nsZnO) films have been fabricated onto conducting indium–tin–oxide (ITO) coated glass plate, by cathodic electro-deposition to immobilize probe DNA specific to M. tuberculosis via physisorption based on strong electrostatic interactions between positively charged ZnO (isoelectric point = 9.5) and negatively charged DNA to detect its complementary target. Electrochemical studies reveal that the presence of nano-structured ZnO results in increased electro-active surface area for loading of DNA molecules. The DNA–nsZnO/ITO bioelectrode exhibits interesting characteristics such as detection range of 1 × 10^?6 ? 1 × 10^?12 M, detection limit of 1 × 10^?12 M (complementary target) and 1 × 10^?13 M (genomic DNA), reusability of about 10 times, response time of 60s and stability of up to 4 months when kept at 4°C.     

Temperature dependence of electromechanical properties of PLZT <Emphasis Type="Italic">x</Emphasis>/57/43 ceramics

The compositions of lead lanthanum zirconate titanate PLZT [Pb(Zr_0.57Ti_0.43)O₃ + x at% of La, where x = 3, 5, 6, 10 and 12] have been synthesized using mixed oxide route. The temperature dependent electromechanical parameters have been determined using vector impedance spectroscopy (VIS). The charge constant d ₃₁ and elastic compliance s ₁₁ ^E show a peak in all the samples at a temperature T _mt much below the ferroelectric — paraelectric transition temperature, whereas the series resonance frequency f _s shows a dip at these temperatures. The Poisson’s ratio σ ^E increases with temperature T showing a broad peak at a temperature higher than T _mt . The voltage constant g ₃₁ decreases and the planar coupling coefficient K _p remains constant up to half of the T _mt and then falls sharply with T. Half of the T _mt can, therefore, be used for specifying the working temperature limit of the piezoceramics for the device applications.     

Oberflächenenergetische Charakterisierung

Surface Energetic Characterization of Nanoscale Fillers and Elastomers Almost any technically used rubber material is filled with particles in nanometer size, by which the properties of the material can be specific controlled. In modern car tires the used fillers have crucial influence on driving security (wet grip and ice grip), on fuel consumption (rolling resistance) and on the cost‐effectiveness (life time of the tire) [1].The first fillers used in rubber application were carbon blacks; actually in passenger car tires mostly surface modified silica is applied. The implementation of novel filler systems like organophilic modified layered silicates (organo‐clays) or carbon nanotubes is subject of intense research [2,3]. Surface energy and –polarity of the filler surface is a crucial, but often underestimated determining factor. All surface properties of rubber and filler have to be well balanced to get the nanoscale filler particles finely dispersed in the rubber matrix and also to obtain a good adhesion between polymer and filler surface.     

Creation and Design of Energy Center

Rural Alaskan communities have special challenges to supply dependable heat and electric power while preserving environmental quality. To help address these issues in a coherent fashion, we have established an energy center at the University of Alaska Fairbanks. Initially, we will evaluate fuel cells and reformers in a test chamber, looking at both performance and reliability. Later, we will study the integration of the electric and other utilities and focus on arctic engineering issues. In designing the test chamber, we were confronted with a number of conflicting heat balance issues related to (1) additional heat for freeze protection and (2) removal of heat generated by people and equipment. This paper discusses some of the details of how we addressed these issues.