Effect of dispersion states (electrostatic/electrosteric stabilization) on particles arrangement in the yttria-stabilized zirconia sediments

In the present work, particle arrangement and their packing in the sediment layer of zirconia suspension were studied. To evaluate the particle settling, aqueous suspensions of zirconia nanoparticles were prepared in different dispersion states. In one state, Dolapix CE64 was used as a dispersant to provide electrosteric mechanism. In another state, pH of the suspension was adjusted at 4 to provide electrostatic mechanism. The other state was the combination of dispersant and pH adjustment which resulted in the most stable suspension. First of all, the stability of all dispersion states was evaluated by zeta potential, sediment volume (SV) and height, viscosity, and packing density (PD). Then, the sediment layers of all suspensions were characterized. Incorporation of electrostatic mechanism was resulted in a main decrease in viscosity with high surface charges, while electrosteric mechanism caused lower sedimentation of particles. Fall velocities of particles/agglomerates were estimated, and the influences of dispersion states on the particles fall velocities were characterized. The microstructural observation revealed homogeneous packing of particles in the sediment layer of the stable suspension demonstrating the proper dispersion of particles. Dolapix CE64 and pH adjustment resulted in a uniform arrangement of particles without agglomeration and spherical and regular granules with a uniform shape.     

Effect of SiC particles on rehological and sintering behaviour of alumina–zircon composites

The effect of additions of SiC particulates on rheological and sintering behaviour of slip-cast alumina–zircon composites has been investigated. Finely divided alumina, zircon and silicon carbide powders were first processed into slips, using polyacrylite dispersant (0.5 wt.%) to create highly concentrated, stable aqueous suspensions at 40 vol.% loadings, from which test specimens which were then slip cast and dried. They were subsequently sintered in air for 2 h at 1650 °C. Rheological properties of the prepared slips were evaluated and related to the amount of added SiC. After sintering, the resultant porosities, fractional densities, crystallographic phases present, and microstructures were determined.     

A general approach to the measurement of change in fuzzy concept lattices

The quantity of unstructured and semi-structured data available is growing rapidly. Adding structure to such data by grouping similar items into fuzzy categories (or granules) can be a productive approach, and can lead to additional knowledge (e.g. by monitoring association and other relations between classes). Formal concept analysis (and fuzzy formal concept analysis) enables us to identify hierarchical structure arising from similarities in attribute values. However, in an environment where source data is updated, this data-driven approach may lead to concept lattices whose structure varies over time (that is, the number of concepts and their relation to each other may change significantly as updates are processed). In this paper, we describe a novel way of measuring the distance between concept lattices. The method can be applied to comparison of lattices derived from the same set of objects using different attributes or to different sets of objects categorised by the same attributes. We prove that the proposed method is a distance metric and illustrate its use by means of examples.     

Homogeneous electrocatalytic oxidation of <Emphasis Type="SmallCaps">d</Emphasis>-penicillamine with ferrocyanide at a carbon paste electrode: application to voltammetric determination

The electrooxidation of d-penicillamine (d-PA) was studied in the presence of ferrocyanide as a homogeneous mediator at the surface of a carbon paste electrode in aqueous media using cyclic voltammetry (CV) and chronoamperometry. Under optimum pH in CV the oxidation of d-PA occurs at a potential about 380 mV less positive than that in the absence of ferrocyanide. The catalytic oxidation peak current was dependent on the d-PA concentration and a linear calibration curve was obtained in the ranges 4.0 × 10⁻⁵–2.0 × 10⁻³ M and 8.0 × 10⁻⁶–1.8 × 10⁻⁴ M of d-PA with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 1.9 × 10⁻⁵ and 3.2 × 10⁻⁶ M by CV and DPV methods. This method was also used for the determination of d-PA in pharmaceutical preparations by the standard addition method.     

CH4 reforming with CO2 for syngas production over nickel catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, BET, TPR, TPH, SEM and TPO techniques. The BET analysis showed a high surface area of 204m²g^?1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The results revealed that an increase in nickel loading from 5 to 15 wt% decreased the surface area of catalyst from 182 to 160 m²g^?1. In addition, the catalytic results showed an increase in methane conversion with increase in nickel content. TPO analysis revealed that the coke deposition increased with increasing in nickel loading, and the catalyst with 15 wt% of nickel showed the highest degree of carbon formation. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Increasing CO₂/CH₄ ratio increased the methane conversion. The BET analysis of spent catalysts indicated that the mesoporous structure of catalysts still remained after reaction.     

Study of Pressure Effects on the Elastic Stability and Optical Treatment of Co<Subscript>2</Subscript>VAl using GGA+U

First-principles calculations of the elastic and optical properties of Co₂VAl compound under pressure are performed in the framework of density functional theory. Applying pressure causes elastic stability, hardness, Young’s modulus and Shear modulus and Debye temperature. Also, Co₂VAl shows higher ductility and anisotropy under stress. Using GGA + U method, it is found that Co₂VAl has 100 % spin polarization at the Fermi level and its spin flip gap is increased by applying pressure. The Co₂VAl response to incident light is positive only in the visible area for all pressures, and its peak is shifted to higher energies under pressure. Also, in the visible range, a peak is observed for absorption and conduction which is increased by applying pressure.     

Thermal injuries as a result of CO2 laser resurfacing

CO2 laser resurfacing of the face for fine wrinkles has gained great popularity over a short period of time. The use of the CO2 laser has proven to be effective in reducing or eliminating fine wrinkles. This tool in the surgeon's armamentarium has been added to those of dermabrasion and chemical peel. The theoretical advantage of the use of the CO2 laser for resurfacing has been better accuracy and reportedly more control of the depth of penetration. The use of the CO2 laser has been welcomed by many cosmetic surgeons. Until now, there have been few reported cases of complications with the use of the CO2 laser. To many, this would sound too good to be true; unfortunately, that is the case. The CO2 laser is a high-energy machine that can indeed cause thermal injury. This thermal injury can result in deep burns to the skin and hypertrophic scarring. We feel this is more common than is currently being reported, and we share our experience as a burn and wound care referral service. During an 18-month period, 20 consecutive patients were referred to our practice who had received injuries from the CO2 laser resurfacing laser. We present here in this review a summary of those injuries. The CO2 resurfacing laser is a very effective tool for the treatment of fine wrinkles, but it is not without the potential for serious complications. We urge caution with the use of the laser and prompt recognition and treatment of thermal injury to the skin.     

Solving nonlinear differential equations of Vanderpol,Rayleigh and Duffing by AGM

In the present paper, three complicated nonlinear differential equations in the field of vibration, which are Vanderpol, Rayleigh and Duffing equations, have been analyzed and solved completely by Algebraic Method (AGM). Investigating this kind of equations is a very hard task to do and the obtained solution is not accurate and reliable. This issue will be emerged after comparing the achieved solutions by numerical method (Runge-Kutte 4th). Based on the comparisons which have been made between the gained solutions by AGM and numerical method, it is possible to indicate that AGM can be successfully applied for various differential equations particularly for difficult ones. The results reveal that this method is not only very effective and simple, but also reliable, and can be applied for other complicated nonlinear problems.     

Development of AMZ composites via mutual attraction of particles in wet processing

In this paper, three approaches were investigated for preparing alumina-mullite-zirconia (AMZ) composites. The weight ratio of alumina to zircon was selected to be 85/15. In the first approach, common well-known reaction sintering or solid-state mixing of alumina and zircon were used. In the second approach, suspensions of the raw materials were prepared to examine the effect of wet processing method. The third approach was based on the use of aluminum alkoxide coated zircon and alumina. The sintering of samples was carried out at the temperature of 1630°C for 3 hours. Phase composition and Rietveld refinement method, microstructural observation, EDS analysis, as well as physical and mechanical properties were used and determined to characterize the sintered samples. The results showed that aluminum alkoxide coating can develop the mentioned reaction sintering and mullite formation. However, the desired mechanical properties were not obtained. Wet processing approach resulted in more interesting data about the formation of mullite and could improve the microstructure homogeneity of final composites. Higher amount of tetragonal zirconia, good densification, high hardness, and fine microstructure were obtained by the wet approach. These interesting results were attributed to the fine discrete particles provided by mutual attraction in the wet preparation method.