Organobentonite as Efficient Textile Dye Sorbent

Domestic bentonite clay was modified using cationic surfactant – hexadecyltrimethylammonium bromide (HDTMA‐bromide) in order to obtain more efficient sorbent. Removal of Acid Orange 10 from aqueous solution at different dye concentrations, adsorbent doses, and pH was studied. These studies were carried out under unaltered pH value in order to prove that adjusting pH as an additional operation in wastewater treatment is not entirely necessary. The results obtained confirmed the adsorption capacity is significant even for unaltered pH. The adsorption isotherm data were well fitted with both the Freundlich and Langmuir model and the latter was shown as more appropriate. Dynamical data were well represented with the pseudo second‐order kinetic model. The results indicate that HDTMA‐bentonite could be employed as low‐cost sorbent in textile dye wastewater treatment.     

Ultimate strength of I-girders under eccentric patch loading: Derivation of a new strength reduction coefficient

In structural applications I-girders are subjected to eccentric patch loading since even a small eccentricity of applied loads relative to the web plane is unavoidable in practice. Experimental research shows that the behaviour of eccentrically loaded girders differs from that of concentrically loaded girders. A reduction in ultimate strength due to eccentricity is evident, and some expressions for the reduction have been proposed. We show that these expressions overestimate the reduction in capacity for large eccentricities. In this paper, results of 102 tests on I-girders subjected to eccentric patch loading are presented and the variables involved in the phenomenon are evaluated based on a parametric study of experimental data and the results of several finite element models. The parametric study confirms that the parameters previously identified for evaluating the effect of small eccentricities are sufficient for addressing cases with larger eccentricities. New mathematical expressions are proposed herein to represent the reduction in strength across the full range of eccentricities considered.     

A model of ultrafine microstructure evolution in materials deformed by high-pressure torsion

The proposed crystal plasticity model outlines a possible mechanism of a material response under severe plastic deformation as observed in high-pressure torsion experiments. A simplified version of the model based on an assumption of uniform deformation of plane-strain double slip reveals rotations of slip systems caused by the imposed shear strain. An axial compression and a shear stress of twist govern this process. The accompanied continuous reconstruction of the deformation substructure is probably one of the main reasons for the observed strengthening. Local variations in the crystal lattice orientation are responsible for the microstructure fragmentation.     

High performance concrete containing lower slag amount: A complex view of mechanical and durability properties

A wide set of parameters of concrete containing 10% of ground granulated blast furnace slag as Portland cement replacement involving basic material characteristics, mechanical and fracture-mechanical properties, durability characteristics, hydric and thermal properties and chloride binding characteristics is determined and compared with the parameters of reference Portland cement concrete with otherwise the same composition. The experimental results show that the replacement of Portland cement by even such a low amount of ground granulated blast furnace slag as environmental more friendly and still valuable alternative binder either affects positively or at least does not worsen in a significant way the substantial properties of hardened concrete mix. The mechanical and fracture-mechanical properties are found to be very similar as compared to the reference mix, the liquid water transport parameters of the mix containing slag are significantly better, the basic durability characteristics such as the frost resistance and corrosion resistance similar and very good, the resistance against de-icing salts slightly worse. These findings may be significant for the future use of slag in the countries where its available amount is decreasing and its more efficient use as a binder than it was common to date can appear necessary.     

Comparison study for Level set and Direct Lagrangian methods for computing Willmore flow of closed planar curves

The main goal of this paper is to present results of comparison study for the level set and direct Lagrangian methods for computing evolution of the Willmore flow of embedded planar curves. To perform such a study we construct new numerical approximation schemes for both Lagrangian as well as level set methods based on semi-implicit in time and finite/complementary volume in space discretizations. The Lagrangian scheme is stabilized in tangential direction by the asymptotically uniform grid point redistribution. Both methods are experimentally second order accurate. Moreover, we show precise coincidence of both approaches in case of various elastic curve evolutions provided that solving the linear systems in semi-implicit level set method is done in a precise way, redistancing is performed occasionally and the influence of boundary conditions on the level set function is eliminated. The authors were partly supported by the following projects and grants: the project HPC-EUROPA(RII3-CT-2003-506079), the NCMM project LC06052, VEGA 1/3321/06 grant, the project MSM 6840770010 and APVV-0247-06, APVV-RPEU-0004-06 grants.     

Distribution of titanium and aluminium in sintered mullite

The distribution of TiO₂ and Al₂O₃ in mullite and the glassy phase of samples obtained by sintering kaolin and Al₂O₃ with O to 3 wt% TiO₂ has been studied. Quantitative phase analysis was performed by means of X-ray diffraction and by successive dissolution of the glassy phase and mullite in HF. The microstructure and microanalyses of the samples were determined using scanning electron microscopy and by analytical electron microscopy. With samples containing >1 wt% TiO₂, not only two morphologically and compositionally different mullites have been determined (the large prismatic mullites and the small needle-shaped ones, embedded into the glassy matrix) but also rutile in the form of needle-shaped crystals embedded in the glassy matrix. In addition on the surface of prismatic mullites, an exsolution of the phase enriched in titanium and iron has been detected. However, the formation of tialite, Al₂TiO₅, has not been proved either by X-ray diffraction or by analytical electron microscopy. Using energy dispersive X-ray analysis a greater Al/Si ratio has been determined for needle-shaped mullites than for prismatic ones. Prismatic mullites have constant Al₂O₃ values, not dependent on the sintering temperature and on TiO₂ added. The solubility of TiO₂ in prismatic mullites is due to the decrease in SiO₂.     

Free material optimization for stress constraints

Free material design deals with the question of finding the lightest structure subject to one or more given loads when both the distribution of material and the material itself can be freely varied. We additionally consider constraints on local stresses in the optimal structure. We discuss the choice of formulation of the problem and the stress constraints. The chosen formulation leads to a mathematical program with matrix inequality constraints, so-called nonlinear semidefinite program. We present an algorithm that can solve these problems. The algorithm is based on a generalized augmented Lagrangian method. A number of numerical examples demonstrate the effect of stress constraints in free material optimization. Dedicated to Pauli Pedersen on the occasion of his 70th birthday.     

On the discontinuous Galerkin method for the simulation of compressible flow with wide range of Mach numbers

The paper is concerned with the numerical simulation of compressible flow with wide range of Mach numbers. We present a new technique which combines the discontinuous Galerkin space discretization, a semi-implicit time discretization and a special treatment of boundary conditions in inviscid convective terms. It is applicable to the solution of steady and unsteady compressible flow with high Mach numbers as well as low Mach number flow at incompressible limit without any modification of the Euler or Navier–Stokes equations.     

Correlation between fracture toughness and microstructure of seeded silicon nitride ceramics

Microstructure development and fracture toughness of Si₃N₄ composites were studied in the presence of seeds and Al₂O₃ + Y₂O₃ as sintering aids. The elongated β-Si₃N₄ seeds were introduced into two different α-Si₃N₄ matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure. The maximum fracture toughness of 9.0 MPa m^1/2 was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 °C for 6 h.