Synthesis of boron nitride from boron containing poly(vinyl alcohol) as ceramic precursor

A ceramic precursor, prepared by condensation reaction from poly(vinyl alcohol) (PVA) and boric acid (H₃BO₃) in 1:1, 2:1 and 4:1 molar ratios, was synthesized as low temperature synthesis route for boron nitride ceramic. Samples were pyrolyzed at 850°C in nitrogen atmosphere followed by characterization using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).     

Effect of interface adhesion factor on the bearing capacity of strip footing placed on cohesive soil overlying rock mass

The problem related to bearing capacity of footing either on pure soil or on pure rock mass has been investigated over the years. Currently, no study deals with the bearing capacity of strip footing on a cohesive soil layer overlying rock mass. Therefore, by implementing the lower bound finite element limit analysis in conjunction with the second-order cone programming and the power cone programming, the ultimate bearing capacity of a strip footing located on a cohesive soil overlying rock mass is determined in this study. By considering the different values of interface adhesion factor (α_cr) between the cohesive soil and rock mass, the ultimate bearing capacity of strip footing is expressed in terms of influence factor (I_f) for different values of cohesive soil layer cover ratio (T_cs/B). The failure of cohesive soil is modeled by using Mohr−Coulomb yield criterion, whereas Generalized Hoek−Brown yield criterion is utilized to model the rock mass at failure. The variations ofI_f with different magnitudes of α_cr are studied by considering the influence of the rock mass strength parameters of beneath rock mass layer. To examine stress distribution at different depths, failure patterns are also plotted.     

Effect of Close-Coupled Bends in Pneumatic Conveying

Pressure drop in a close-coupled double bend in pneumatic conveying of fly ash is studied. Tests are carried out with a 6.35 cm (2.5 in) diameter 169.8 m (557 ft) long pipeline with various combinations of airflow, ash flow, phase density, and conveying velocity. The pressure drop across two close-coupled 90-degree bends is compared to the pressure drop in an isolated single 90-degree bend. Six ash samples of different physical and chemical compositions are used in the tests. Resulting bend pressure drops are correlated to the corresponding phase density and superficial air velocity at the bend inlet. The correlation pattern represented by the relationship {\Delta P_{solids} \over {SLR}} = Y1 \cdot V^{Y2} is established and found to vary with ash properties. For both single and close-coupled double bends and operating test conditions with \Delta {\rm P}_{\rm solids} / {\rm SLR} 0.15 at the bend entry, 86% of the measured test points fall within the range of - 20% of the \Delta {\rm P}_{\rm solids} / SLR calculated point. Below this threshold, the test results show that the pressure drops due to solids flow through a close-coupled double bend and single bends are often indistinguishable. Consequently, the loss through a close-coupled double bend cannot be considered as the cumulative effect of two isolated single bends.     

Sulfur Dioxide – A Leachant for Oxidic Materials in Aqueous and Non-aqueous Media

Abstract

Leaching of various oxide materials using sulfur dioxide is documented in this review. Emphasis is given to the leaching of Fe(III), Mn(IV), Mn(III) oxides/hydroxides highlighting the mechanisms and kinetics of these systems. Treatment of magnesium oxide associated with serpentinic silicate tailings, copper-zinc containing silicate slags, nickel containing waste catalysts, roasted zinc sulfide concentrate and aqueous reduction of As(V) to As(IH) are included. Acetone and aqueous SO₂ mixtures form α-hydroxy sulf⊙nic acid, which is useful for leaching phosphate and uranium ores. Aspects related to leaching of some oxidic materials in organic solvents such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) and acetonitrile in the presence of sulfur dioxide are also considered, since novel reactions in non-aqueous solvents may open up new opportunities for the treatment of complex materials.     

A model for capacity planning of flexible robotic assembly systems

This paper presents a cost-based model for capacity planning of Flexible Robotic Assembly Systems capable of handling batch assembly of multiple end products. The non-linear integer programming model is based on a specific cell design procedure that considers two important aspects, such as robot selection, and cell configuration, in forming the assembly cell. The model incorporates stochastic variations in the batch arrival rate, batch size, and processing times. The solution procedure for the model is discussed and an example problem is used to demonstrate the use of the model for real world applications.     

Optimization of process parameters for synthesis of silica–Ni nanocomposite by design of experiment

The optimum combination of experimental variable, temperature, time of heat treatment under nitrogen atmosphere and amount of Ni-salt was delineated to find out the maximum yield of nanophase Ni in the silica gel matrix. The size of Ni in the silica gel was found to be 34 and 45 nm for the two chosen compositions, respectively. A statistically adequate regression equation, within 95% confidence limit was developed by carrying out a set of active experiments within the framework of design of experiment. The regression equation is found to indicate the beneficial role of temperature and time of heat treatment.     

Sulfur Dioxide – A Leachant for Oxidic Materials in Aqueous and Non-aqueous Media

Leaching of various oxide materials using sulfur dioxide is documented in this review. Emphasis is given to the leaching of Fe(III), Mn(IV), Mn(III) oxides/hydroxides highlighting the mechanisms and kinetics of these systems. Treatment of magnesium oxide associated with serpentinic silicate tailings, copper–zinc containing silicate slags, nickel containing waste catalysts, roasted zinc sulfide concentrate and aqueous reduction of As(V) to As(III) are included. Acetone and aqueous SO₂ mixtures form α-hydroxy sulfonic acid, which is useful for leaching phosphate and uranium ores. Aspects related to leaching of some oxidic materials in organic solvents such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) and acetonitrile in the presence of sulfur dioxide are also considered, since novel reactions in non-aqueous solvents may open up new opportunities for the treatment of complex materials.     

Method of determining the admittance loading of slot coupled T-junctions

A new method is presented for inferring the real and imaginary parts of admittance loading seen by the exciting guide of an H-plane slot coupled T-junction from measurement of the magnitudes of the reflection and coupling coefficients. These quantities are measured using an HP network analyser together with a reflection and transmission test unit, which provides better accuracy of measurement. A comparison between measured data with the theoretical values determined by the authors is presented.