Silver–carbon electrocatalyst for air cathodes in alkaline fuel cells

A method for producing electrocatalysts containing silver supported on different carbons was developed. The catalysts were investigated in air (oxygen) diffusion electrodes in alkaline electrolyte (7 M KOH). Depending on the carbon support used, up to a threefold improvement in electrode performance was achieved compared with the activity of the uncatalysed carbon in this media. At ambient temperature and atmospheric pressure, a current density of 150 mA/cm^–2 was obtained at electrode potential 1.2 V vs zinc (0.75 vs HE). A correlation between electro catalytic activity and wetted surface area of the electrocatalysts was found.     

Polyamide‐6‐b‐polybutadiene block copolymers: Synthesis and properties

Polyamide‐6 (PA6)/polybutadiene (PB) block copolymers were synthesized with macroactivators (MAs) based on hydroxyl‐terminated polybutadiene functionalized with diisocyanates and having three N‐acyllactam chain‐growing centers per molecule. Two different diisocyanates, hexamethylene diisocyanate and isophorone diisocyanate, were applied as precursors for the MAs. The sodium salt of ε‐caprolactam was chosen as an initiator. The influence of the MA type and concentration on the anionic ring‐opening polymerization of ε‐caprolactam at 180°C was studied. A large percentage of the gel fraction in the copolymers was estimated, indicating crosslinked macromolecules. The structure and phase behavior of the copolymers were investigated with differential scanning calorimetry, wide‐angle X‐ray scattering, thermogravimetric analysis, and dynamic mechanical thermal analysis. In the copolymers, only the PA6 chains crystallized, and the crystallinity depended on the PB content. Different glass‐transition temperatures for the PB blocks and PA6 blocks were observed, indicating microphase separation in the copolymers. The mechanical properties of the copolymers were studied by notched impact testing and hardness measurements. The impact strength increased linearly with the soft component concentration up to 10 wt % and reached values six times higher than those of the PA6 homopolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 711–717, 2003     

Strength properties of chamotte concretes based on phosphate binders

Conclusions The authors have investigated the strength properties of chamotte concretes based on phosphate binders over a wide range.They have shown the dependence of the compressive strength of the concretes on the type of phosphate binder used, the heat treatment temperature of the concrete, and its test temperature. Maximal compressive strength is exhibited by concretes roasted at 1450°C.They have established a relation between the physicochemical transitions taking place in a phosphate binder during heating and the strength characteristics of the concrete.Simultaneous introduction of phosphate binder and clay to the extent of 10–20% into chamotte concretes increases their strength at 20°C and during heating.Translated from Ogneupory, No. 6, pp. 32–36, June, 1979.     

Synthesis of Titanates with a Ramsdellite-Type Tunnel Structure Crystallizing in the Li<Subscript>2</Subscript>O-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> System in Different Gaseous Media

The ramsdellite-type phases crystallizing in the Li₂O-Fe₂O₃-TiO₂ system in the course of synthesis in gaseous media at different oxygen partial pressures are studied. Solid solutions based on the ramsdellite structure with the composition Li₂Ti_3?xFe _x O_{7 ? δ} (0 ≤ x ≤ 0.7) are prepared in an oxidizing medium (P_O2 = 1 atm) for the first time. Analysis of the results obtained by electron paramagnetic resonance and Mossbauer spectroscopy revealed that, in these solid solutions, all iron ions are in the oxidation state Fe⁺³.     

Influence of pitch composition and surface properties of petroleum coke on their interaction during the preparation of carbon/carbon composites

The influence of pitch composition and surface properties of petroleum coke on the interaction of pitch and coke in the composite is studied. The adsorption results and EPR data indicate that recombination of paramagnetic centers and interaction of oxygen functional groups occur during the preparation of the composite. As a result of interaction between petroleum coke and pitch, polar compounds are concentrated in the adsorption layer. The baking criterion is used for the characterization of the baking ability of the pitches obtained as a result of different oxidation treatments of commercial coal tar pitch. It is determined that physico-chemical properties of the obtained pitches influence the value of the “baking criterion”. The kind of thermo-oxidation treatment of the parent pitch should be chosen hence achieving the maximum value of the baking criterion. For this purpose, the maximal part of the pitch has to take part in the adsorption layer.     

Andreev reflections in a Bi<Subscript>1.8</Subscript>Pb<Subscript>0.3</Subscript>Sr<Subscript>1.9</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>x</Subscript> break junction

The current-voltage characteristic (CVC) of a break junction made from polycrystalline Bi_1.8Pb_0.3Sr_1.9Ca₂Cu₃O_x is investigated. The experimental CVC has a hysteretic feature that reflects part of the curve with a negative differential resistance. The CVC is discussed within the framework of the Kümmel-Gunsenheimer-Nicolsky theory that takes into account multiple Andreev reflections in superconductor/normalmetal/superconductor junctions.     

Numerical modeling of wave processes in layered media in the Arctic region

The aim of this work is the numerical simulation of wave propagation in media with linear-elastic and acoustic layers as exemplified by the seismic prospecting problems in the Arctic region and the explosive impact on an iceberg. The complete system of equations describing the state of a linearly elastic body and the system of equations describing the acoustic field are solved. The grid-characteristic method is used to provide the contact and boundary conditions, including the contact condition between acoustic and linear-elastic layers, to be correctly described.     

Dynamic model of proximity of positions of social network users

A mathematical model is proposed for the proximity dynamics of political positions of interacting individuals which form a closed group. The model is described as a system of ordinary differential equations. The results of numerical experiments for the system are presented and a number of substantial conclusions are formulated. It is shown that in the case of two individuals the system has an asymptotically stable zero steady state. In the case of two individuals and two themes we get an infinite number of stationary states, all except the zero state being unstable.