Critical phenomena in electrical resistance of binary liquids: A study of the frequency dependence

The electrical resistance is measured in two binary liquid systems CS2 + CH3NO2 and n-C7H16 + CH3OH in the critical region as a function of frequency from 10 Hz to 100 kHz. The critical exponent b ≈ 0.35 in the singularity of dR/dT α (T - Tc)−b near Tc has no appreciable dependence upon the frequency. Thus any contribution from dielectric dispersion to the critical resistivity is not appreciable. The universal behaviour of the dR/dT anomaly does not seem to be followed in binary liquid systems.

Wide Ranged La Modification in CCTO Ceramics Through Sol-Gel: Effect on Microstructure and Dielectric Properties

Sol-Gel method was employed to synthesize pure and wide ranged La-modified CaCu3Ti4O12 ceramics using mixed acetate-nitrate-alcoxide individual metal-ion precursors. SEM pictures revealed that grain size monotonously decreases with the extent of La incorporation. All the prepared ceramics manifested dielectric constant in the range similar to 10(3)-10(4). Dielectric loss was found to decrease with La incorporation and got optimized for 20% La3+ while retaining its high dielectric constant which may be industrially important. Room temperature Impedance spectroscopy suggested that decrease in grain resistance is responsible for reduction in dielectric loss according to Internal Barrier Layer Capacitor (IBLC) model.

A PEFC With Pt-TiO2/C as Oxygen-Reduction Catalyst

Carbon-supported Pt-TiO2 (Pt-TiO2/C) catalyst with varying atomic ratio of Pt to Ti, namely, 1: 1, 2: 1, and 3: 1, is prepared by sol-gel method and its electrocatalytic activity toward oxygen-reduction reaction (ORR) is evaluated for the application in polymer electrolyte fuel cells (PEFCs). The optimum atomic ratio of Pt to Ti in Pt-TiO2/C and annealing temperature are established by cyclic voltammetry and fuel-cell-polarization studies. Pt-TiO2/C annealed at 750 degrees C with Pt and Ti in atomic ratio of 2: 1, namely, 750 Pt-TiO2/C (2: 1), shows enhanced electrocatalytic activity toward ORR. It is found that the incorporation of TiO2 with Pt ameliorates both electrocatalytic activity and stability of cathode in relation to pristine Pt cathode, currently being used in PEFCs. A power density of 0.75 W/cm(2) is achieved at 0.6 V for the PEFC with 750 Pt-TiO2/C (2: 1) as compared with 0.62 W/cm(2) at 0.6 V achieved with the PEFC comprising Pt/C as cathode catalyst while operating under identical conditions. Interestingly, carbon-supported Pt-TiO2 cathode exhibits only 6% loss in electrochemical surface area after 5000 potential cycles while it is as high as 25% for Pt/C. DOI: 10.1115/1.4002466]

Alloy design for fracture resistance

Several methods for improving the strength of metallic materials are available and correlations between strength and various microstructural features have been established. The purpose of this paper is to review parallel developments favouring improved fracture resistance. Resistance to fracture in monotonie loading, cyclic loading and when fracture is environment-aided have been considered in steels, aluminium alloys and anisotropic materials. Finally, the question of optimising alloy behaviour is discussed.

A2MoTiO7−x (Atriple bond; length as m-dashrare earth or Y): a new series of oxide pyrochlores prepared by topochemical reduction of A2MoTiO8 scheelites

A series of anion-deficient pyrochlore oxides of the formula A2MoTiO7−x (xless-than-or-equals, slant0.5), where Atriple bond; length as m-dashSm, Gd, Tb, Dy, Ho, Er, Lu and Y, has been prepared by reduction of A2MoTiO8 scheelites. The scheelite-to-pyrochlore conversion is reversible, indicating that the reaction is likely to be topochemical. The oxidation states of molybdenum and titanium are most probably Mo(III) and Ti(IV) for the limiting composition of the pyrochlores A2MoTiO6.5. The new pyrochlores are non-metallic and paramagnetic as expected.

A Convenient Methodology for the Selective Reduction of Carboxylic Acids With Benzyltriethyl-Ammonium Borohydride—Chlorotrimethylsilane

A combination of benzyltriethylammonium borohydride and chlorotrimethylsilane (1:1) in dichloromethane (0-25°C) has been found to be a convenient reagent system for the selective reduction of carboxylic acids to alcohols.

A new approach to the kinetics of size reduction in ball milling

The rate of breakage of feed in ball milling is usually represented in the form of a first-order rate equation. The equation was developed by treating a simple batch test mill as a well mixed reactor. Several case of deviation from the rule have been reported in the literature. This is attributed to the fact that accumulated fines interfere with the feed material and breaking events are masked by these fines. In the present paper, a new rate equation is proposed which takes into account the retarding effect of fines during milling. For this purpose the analogy of diffusion of ions through permeable membranes is adopted, with suitable modifications. The validity of the model is cross checked with the data obtained in batch grinding of ?850/+600 ?m size quartz. The proposed equation enables calculation of the rate of breakage of the feed at any instant of time.

An optimal parallel algorithm for sparse matrix bandwidth reduction on a linear array

A simple and efficient algorithm for the bandwidth reduction of sparse symmetric matrices is proposed. It involves column-row permutations and is well-suited to map onto the linear array topology of the SIMD architectures. The efficiency of the algorithm is compared with the other existing algorithms. The interconnectivity and the memory requirement of the linear array are discussed and the complexity of its layout area is derived. The parallel version of the algorithm mapped onto the linear array is then introduced and is explained with the help of an example. The optimality of the parallel algorithm is proved by deriving the time complexities of the algorithm on a single processor and the linear array.

The roles of nitrification and nitrate reduction pathways in nitrogen cycling of Baltic Sea

The Baltic Sea is one of the largest brackish water bodies in the world. Primary production in the Baltic Sea is limited by nitrogen (N) availability with the exception of river outlets and the northernmost phosphorus limited basin. The excess human induced N load from the drainage basin has caused severe eutrophication of the sea. The excess N loads can be mitigated by microbe mediated natural N removal processes that are found in the oxic-anoxic interfaces in sediments and water column redoxclines. Such interfaces allow the close coupling between the oxic nitrification process, and anoxic denitrification and anaerobic ammonium oxidation (anammox) processes that lead to the formation of molecular nitrogen gas. These processes are governed by various environmental parameters. The effects of these parameters on N processes were investigated in the northern Baltic Sea sediments. During summer months when the sediment organic content is at its highest, nitrification and denitrification reach their maximum rates. However, nitrification had no excess potential, which was probably because of high competition for molecular oxygen (O2) between heterotrophic and nitrification microbes. Subsequently, the limited nitrate (NO3-) availability inhibited denitrification. In fall, winter and spring, nitrification was limited by ammonium availability and denitrification limited by the availability of organic carbon and occasionally by NO3-. Anaerobic ammonium oxidation (anammox) was not an important N removal process in the northern Baltic Sea. Modeling studies suggest that when hypoxia expands in the Baltic Sea, N removal intensifies. However, the results of this study suggest the opposite because bottom water hypoxia (O2< 2 ml l-1) decreased the denitrification rates in sediments. Moreover, N was recycled by the dissimilatory nitrate reduction to ammonium (DNRA) process instead of being removed from the water ecosystem. High N removal potentials were found in the anoxic water column in the deep basins of the Baltic Proper. However, the N removal in the water column appeared to be limited by low substrate availability, because the water at the depths at which the substrate producing nitrification process occurred, rarely mix with the water at the depths at which N removal processes were found. Overall, the natural N removal capacity of the northern Baltic Sea decreased compared to values measured in mid 1990s and early 2000. The reason for this appears to be increasing hypoxia.

Effect of microstructure and hardness on the grinding abrasive wear resistance of a ball bearing steel

Grinding media wear appears to be non-linear with the time of grinding in a laboratory-scale ball mill. The kinetics of wear can be expressed as a power law of the type w=atb, where the numerical constant a represents wear of a particular microstructure at time t = 1 min and b is the wear exponent which is independent of the particle size prevailing inside a ball mill at any instant of time of grinding. The wear exponent appears to be an indicator of the cutting wear mechanism in dry grinding: a plot of the inverse of the normalised wear exponent (Image ) versusHs (where Hs is the worn surface hardness of the media) yields a curve similar to that of a wear resistance plot obtained in the case of two-body sliding abrasive wear. This method of evaluating the cutting wear resistance of media is demonstrated by employing 15 different microstructures of AISI-SAE 52100 steel balls in dry grinding of quartz in a laboratory-scale ball mill.

Evaluation of interfacial frictional resistance

Three distinct mechanisms — sliding, bonding and bearing — for the mobilisation of interfacial friction have been identified. In the light of these mechanisms, the effect of variation in reinforcement parameters, such as extensibility, flexibility and hardness on mobilisation of interfacial friction, and the mechanisms themselves has been examined. The influence of boundary effects of apparatus on the interfacial friction has been discussed and a method of estimating the same in a pull-out box has been proposed.