Thermal explosion in mechanically activated Ti-Ni powders: Relationship between process parameters and product composition

Upon variation in the duration of mechanical activation, characteristic temperatures of thermal explosion (TE) in Ti-Ni powder mixtures and phase composition of products were explored by electron microscopy, optical metallography, and XRD. The results shed new light on the mechanism of structure formation during TE and on the relationship between process parameters and product composition.     

Heat of combustion of coal: Basic principles and new calculation methods

Stepwise changes in the heat of combustion of Donetsk Basin coal and vitrinites during metamorphism are implied by correlation analysis of a sample including data regarding the composition and properties of bed specimens. On the basis of the relative rates of oxidation processes with the liberation of oxygen-bearing gases and carbon accumulation, as well as the rate of subsequent carbon-ring formation, we note the difference in rate and direction of change in the heat of combustion within three successive intervals: 32–36, 36.3 ± 0.3, and 36–34 MJ/kg. The yield of volatiles may be employed as a predictive parameter in the regression equation for preliminary calculation of the heat of combustion with mean square deviation 0.325 MJ/kg.     

Radioactivity of coal and ash

The radioactivity of Kuznetsk Basin coal and ash is considered, in relation to other regions.     

More efficient operation of the dust-free coke-discharge modules at OAO Zaporozhkoks coke batteries 5 and 6

Two types of dust-free coke-discharge modules are generally employed. The modules employed at OAO Zaporozhkoks are described and analyzed. Methods are proposed for determining their operational efficiency and testing their performance in plant conditions. Recommendations are made for improving the operational efficiency of dust-free coke-discharge modules mounted on door-opening machines.     

Short-range and long-range aggregation of particles in the γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> sol: II. Photometric and ultramicroscopic investigation of the aggregate stability of the positively charged γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> sol

The aggregate stability of the positively charged γ-Al₂O₃ (alundum) sol has been investigated using photometry and flow ultramicroscopy over a wide range of KCl concentrations. The data on the sol stability have been compared with the results of the calculations in the framework of the extended Derjaguin-Landau-Verwey-Overbeek theory. The parameters of the long-range structural forces for γ-Al₂O₃ particles have been evaluated. The role of the far potential minimum in the sol stability has been discussed.     

Modification of carboxyl groups of poly(ethylene-co-acrylic acid) via facile wet chemistry method: A kinetic study

In this work, we present the results of a kinetic study of the surface modification of the carboxyl group of poly(ethylene-co-acrylic acid) into acyl chloride. Reaction temperature and time, concentration of the reactants, kind of agitation have been changed in order to understand their effect on the conversion. A study on the penetration of the reaction inside the sample bulk was also performed. The results indicate that, when short reaction times are adopted, the reaction limits to the outer layers of the samples and, in this case, on increasing the temperature, the concentration of the reactants and the stirring allows having a faster kinetic. At longer reaction times, the reaction penetrates deep inside the sample (several tens of microns) and the influence of the above mentioned variables on the kinetic is very low.The results, obtained by direct FTIR, ATR-FTIR, SEM–EDX and contact angle measurements, were confirmed and corroborated by theoretical estimations.     

Biguanide-, imine-, and guanidine-based networks as catalysts for transesterification of vegetable oil

Polycationic systems based on poly(hexamethylene biguanide) (PHMBG), branched polyethyleneimine (PEI) and poly(N-vinylguanidine) (PVG) have been evaluated as heterogeneous catalysts for the transesterification of sunflower oil by methanol. Insoluble networks are synthesized via cross-linking of PHMBG by either 4,4′-methylenebis(N,N-diglycidylaniline) or polyisocyanate prepolymer, PEI with sebacoyl chloride, and PVG with 1,4-butanediol diglycidyl ether. PHMBG and its cross-linked networks appeared to be remarkably efficient catalysts, enabling 80–100% triglyceride conversion within 0.5 h at 70 °C. PEI-based networks catalyzed triglyceride transesterification with rates 8- to 12-fold slower than their PHMBG-based counterparts. The PVG-based networks, which were devoid of hydrophobic moieties, appeared to be inefficient catalysts due to limited accessibility of the basic guanidine groups to reactants. The PHMBG networks were shown to be recyclable by a simple centrifugal filtration. After 15 cycles of recovery and reuse, only 10–15% decline in performance was observed.     

The physical–chemical study of detonation nanodiamond application in adsorption and chromatography

In the present work, the study on detonation nanodiamond (DND) powders modifications in gaseous media was carried out. The surface properties of DND were studied by TGA, IR-spectroscopy, pH-potentiometry and chromatography methods. It was determined that modifying the DND surface reduces specific retention volumes and retention times of adsorbates. At the same time, specific and dispersion interactions have decreased. Such phenomena are significant for gas chromatographic separation of complex mixtures. The study of DND in contact with water and water solutions showed that chemical modification of DND produces on its surface oxygen-containing groups with acidic character. The latter stipulates its ion-exchange properties and applicability to liquid chromatography. In summary, the performed research provides significant perspective toward new-generation adsorbent creation with controlled surface identification for gaseous and liquid chromatography purposes.     

Diamond-like carbon deposited by plasma technique as a function of methane flow rate

Diamond-like carbon (a-C:H) prepared by plasma enhanced chemical vapor deposition (PECVD) as a function of methane gas flow rate is reported. Films deposited at zero flow rate, i.e., without the use of vacuum pumps during the deposition, are also investigated. For that purpose, the reactor chamber was baked and pumped down to about 10^?8 Torr to reduce contamination released from the reactor walls. The films were analyzed by visible, infrared and Raman spectroscopes. It was observed that the deposition rate, hydrogen concentration and optical gap depend on the methane gas flow rate. A maximum for deposition rate found at methane flow was much smaller than the flow usually adopted in conventional procedures.     

Surface analysis of CVD diamond exposed to fusion plasma

Microcrystalline undoped and heavily boron-doped polycrystalline diamond layers have been deposited on various substrates by hot filament CVD and exposed to hydrogen plasma in a linear plasma reactor (Pilot-PSI, The Netherlands) that simulates the high flux and high density plasma conditions of tokamak divertors, as well as in the DIII-D tokamak (US). Pre- and post-exposure analysis by SEM and Raman spectroscopy characterised the surface appearance and the sp³ and sp² components of the diamond films respectively. Surface roughness variation was measured by AFM. Hardness and Young's modulus were assessed by nanoindentation in order to characterise the effect of the plasma on the mechanical properties. HRTEM and EELS have been used to evaluate the nature of the modification induced at the diamond surface by the plasma exposure. The measurements have shown that, despite some surface amorphisation of the exposed layers, further long-term exposure studies are warranted as neither delamination, dramatic film failure nor entire erosion of the film were observed.