Advanced Materials Research Vol. 704

Abstract: Density functional theory calculations have been performed for sulfur atom adsorption on the Fe(111) surface at 0.5 and 1.0 ML. The geometry structures, density of the state, charge population and adsorption energy were calculated. It is found that the most favored adsorption site for sulfur atom is the hollow site, and the interaction between Fe and S comes in large part from the hybridization of Fe 3d orbital and S 3p orbital. Our results have shown that the force between iron atom and sulfur atom is very small.

Abstract: Mechanical properties and fatigue behavior of die cast AlMg5Si2Mn alloy are studied to broaden its application. Results indicate that the microstructure consist of coarse α₁-Al crystals, fine α₂-Al and eutectic [Al+Mg₂S region. Dilatant shear band and surface layer are observed in the surface and sub-surface of the die castings. Ultimate tensile strength, yield strength and elongation of as-cast AlMg5Si2Mn alloy are 333MPa, 191MPa and 10.7% respectively. Age treatment significantly improves the strength and slightly decreases the elongation. Fatigue limit of AlMg5Si2Mn is 56MPa and the fatigue lives of as-cast and age treat specimens are similar to each other. Uniform fatigue striations and tear ridges are observed in the fatigue fracture.

Abstract: The aesthetic characteristics and mechanical properties of a new raw glaze of the matt type, developed for porcelain tiles, referenced SG, were determined and compared with those of a commercial matt glaze for porcelain tiles, referenced RG. Glaze SG was formulated by introducing boron as calcined borate E4972 [1]. In contrast, glaze RG contained a frit (30%) that included boron among its constituents. Despite the different chemical and mineralogical characteristics of these glazes, their chemical and mechanical properties, as well as their aesthetic characteristics, were appropriate. The dissolution of crystalline particles and the crystallisation and sintering phenomena in glaze SG were studied. The effective viscositytemperature curve of this glaze was experimentally obtained by hot stage microscopy (HSM). A model describing the effective viscosity of a glaze, based on Kriegers equation for concentrated colloidal suspensions, was developed in this study. The agreement between the experimental data and the calculated values was quite good.

Abstract: Magnesium is demanded increasing in aerospace, electronics industry and medical field requires the surface treatment method. That allows increasing the corrosion resistance in order to put to practical use as products. The spark anodized treatment method in this study used was anodized depending on the various times to 1-4 minutes with a current density of 300 mA/cm2 in the constant-current mode that duty cycle is 50% and frequency is 125 Hz by a bipolar pulse power. And the characteristics of the film were evaluated. This treatment method is to obtain the uniform film by reducing the applied voltage on the surface by adding 0.1 M Sodium silicate (Na₂SiO₃) in the mixed solution of 2.0 M Sodium hydroxide (NaOH) and 0.1M Sodium phosphate (Na₃PO₄). It aims to express brown or dark brown color by adding Potassium permanganate, and to improve the corrosion resistance. After anodization treatment, the surface characteristics were analyzed using SEM, XRD and illuminance meter, and Vickers hardness was measured. In order to evaluate of corrosion resistance, the corrosion potential and corrosion current were measured by potentiodynamic method in 3.5 wt. % NaCl electrolyte. The critical voltage required to generate the oxidized layer could be lower depending on the addition of (Na₂SiO₃) and (KMnO₄). The size of a pore was reduced depending on the processing time, and the thickness of the film was grown in proportion to it. As the result of XRD, a new peak of Mg0.9Mn0.1O was formed, and the peak of parent metal was reduced by the increase of the oxide. By the potentiodynamic polarization behavior, the value of corrosion potential was increased and the corrosion current density was decreased and the corrosion resistance was improved.

Abstract: This paper studied the change regulation of the electrical resistivity of alkali-free boro-aluminosilicate glasses with the rate of SrO/(CaO + SrO) in the range 600~1600°C.The results showed that a mixed alkaline effect was observed with the increase of SrO content in alkali-free aluminoborosilcate glasses: the maximam resistivity of 178Ωcm appeared at SrO/(CaO+SrO) ratio =0.24, which is much larger than 108Ωcm at SrO=0. Meanwhile, the experiment results showed that the SrO makes stronger influence on the resistivity of the glass than CaO does. The Arrhenius plots, which showed the change of the resistivity with temperature in range of 1100~1625°C, present nonlinear variation, and an inflection at about 1100°C. It proved that the electrical resistivity of the alkali-free aluminoborosilcate glasses were controlled by the ionic radius of alkaline earth metals and the viscosity of glass melts.

Abstract: Titanium and its alloy are materials with great application in the aeronautic and biomedical area. These applications have grown in the last decade due to high resistance to corrosion and biocompatibility of the Titanium alloys. However, Titanium and its alloys are classified as hard-to-machining materials that increase the production costs due to the highest tool wear. Thus, the finishing of components made of Titanium alloys can be impaired due to the complex shearing mechanism. This work shows a study of the influence of cooling systems and the input parameters on the turning of the Ti-6Al-4V alloy. Two depths of cut, two feed rates, new and worn tools, and three cooling systems were used as input parameters. The response was the surface roughness measured according to the Ra parameter. According to the results, it can be supported that the variation of all input parameters has influence on response. However, the most important input parameter on surface roughness was the feed rate. Thus, it can be concluded that the correct choice of the cutting parameters is relevant to produce high-quality components.

Abstract: Cobalt ferrite CoFe₂O₄ tabular crystals were synthesized via two-step coprecipitation using non-equilibrium crystallization conditions by supplying a solution of CoCl₂6H₂O and FeCl₃6H₂O and a solution containing NaOH at a later crystallization stage. Mean particle size of ~16.5 nm CoFe₂O₄ primary particles synthesized by coprecipitation showed non-oriented structure. Effect of heat treatment temperature on the microstructures of the final CoFe₂O₄ crystal was examined, orderly arranged plate-like tabular CoFe₂O₄ crystals were formed under calcination at 800 °C. Magnetic hyspersis loops measured at 300 and 5 K indicated the anisotropy in the tabular crystals.

Abstract: Low temperature co-fired glass-ceramic-Ag metal electrode systems were investigated in relation to Ag diffusion and micro structural development during firing. Sintering temperature was in a range of 800°C-900°C. At lower temperature of 800°C, Ag ion was diffused through in the LTCC substrates. However, Ag diffusion was not observed at 850°C below. Simultaneously, the densification of the electrode was greatly improved. With increasing sintering temperature, glass-ceramic to the electrode does not occur due to increase of the densification of the sample. The glass-ceramics exhibited good dielectric properties: ε_r=7.74, tanδ=0.7×10^-3 at 850°C for 0.5h.

Abstract: The aim of this work is to assemble the computer models of phase diagrams (PD) for the typical ternary systems and to examine the processes of crystallization on its base. Spatial schemes of mono-and invariant equilibria have been used for it. Analysis of concentration fields, obtained by the projection of the surfaces on the Gibbs triangle, allows establish the boundaries of phase regions (located above the considered fields), the sequence of phase transformations and microstructural elements for the solidification of the initial melt at equilibrium condition. Concentration fields have been analyzed by means of mass balances for their centers of masses. Based on this technology, the research identifies concentration fields with coinciding sets of phase reactions and microconstituents, and the fields with individual characteristics.

Abstract: The SiCOH film has been prepared by using a new precursor of trimethoxy [2-(7-oxabicyclo [4.1.hept-3-yl) ethy silane via sol-gel and spin-coating methods. The resulting films were characterized by SEM, TGA, AFM, FTIR, nanomechanical testing, and electrical measurements. The TGA result shows that the SiCOH film has good thermal stability, and no obvious thermal decomposition can be observed before 400°C. After being annealed at 350°C for 2 hours, the resulting SiCOH film exhibits a smooth surface (RMS=0.222nm), and a significant reduction of CH_n groups in the film. Further, the film exhibits a novel high k value of 15.6, a leakage current density of 2.72 × 10^-6 A/cm² at 1 MV/cm, and good mechanical properties of E_r ~ 12.61 GPa and H ~ 3.80 MPa.