Comparative cavitation erosion test on steels produced by ESR and AOD refining

Cavitation erosion studies of steels produced by Electroslag Refining (ESR) and Argon Oxygen Decarburization (AOD refining) have been carried out. The experiments were conducted using the modified ultrasonically induced cavitation test method. Erosion rates were measured and the morphology of damages under cavitation action was studied by scanning electron microscopy and optical microscopy techniques. The present work is aimed at understanding the cavitation erosion behaviour of electroslag refined steel (ESR) compared with the steel produced by Argon Oxygen Decarburization (AOD refining), commonly used in the production of hydraulic machinery parts (Pelton blades). The results exhibited lower cavitation rate of ESR steel compared with AOD steel, as a consequence of its better mechanical properties and homogeneous and fine-grained microstructure.     

Study of the dielectric relaxation of poly(phenylpropyl acrylate) and poly(phenylpropyl methacrylate): effect of slight differences in chemical structure

A comparative study of the dielectric relaxational behaviour of two structurally close polymers, containing aromatic side groups, was carried out in order to analyse how slight differences in the chemical structure affect the molecular responses to perturbation field. Specifically, poly(phenylpropyl acrylate) (P3Ph1PA) and poly(phenylpropyl methacrylate) (P3Ph1PM) were studied using differential scanning calorimetry and dielectric relaxation spectroscopy in the frequency range 10^?2–10⁶ Hz and temperature window of ?80 to 120 °C. Both techniques show one glass–rubber transition for P3Ph1PA and two for P3Ph1PM, which evidence the great effect of the methyl groups on the segmental motions of the polymer. Phenomenological analysis of the data was carried out in order to establish the strength, width and fragility parameters of the glass–rubber transitions. In the case of P3Ph1PA, the strength is found to be larger than for P3Ph1PM, pointing out that the methyl group disturbs the mobility. Conductive processes dominate the dielectric spectra at high temperatures and low frequencies. © 2015 Society of Chemical Industry     

Characteristics of Wastewater Streams Within the Bor Copper Mine and Their Influence on Pollution of the Timok River,Serbia

Wastewaters produced by mining and metallurgical treatment of polymetallic sulfide ores have polluted the Timok River in Serbia for more than 100 years. We have characterized seven different wastewater streams within the RTB Bor facilities, investigating their influence on pollution of the Timok River before its confluence with the Danube River. Their relative contribution was calculated by considering the contaminant load of each wastewater stream and non-conservative transport along their flow paths. Three sampling spots in the Timok River, before and after its confluence with the Borska River, were also monitored.     

Validation of data on polycyclic biomarkers,naphthalenes, phenanthrenes,and alkyldibenzothiophenes obtained by gas chromatographic-mass spectrometric analysis of hydrocarbon concentrates

The possibility of using the data on the hydrocarbon composition obtained by analysis of hydrocarbon concentrates for geochemical studies has been shown on the example of Pannonian Basin (Serbia) crude oils of different genetic types and different degrees of thermal maturity and biodegradation. A high convergence of the values of geochemical parameters calculated on the basis of the composition of steranes and terpanes, alkylnaphthalenes, phenanthrenes, and dibenzothiophenenes in hydrocarbon concentrates and chromatographic fractions isolated from them has been found by correlation analysis.     

Droplet Size Distribution Obtained by Atomization with Two‐Fluid Nozzles in a Spray Dryer

The possibility of predicting the droplet size distribution from the particle size distribution was investigated. For that purpose, suspensions of different types of materials were dried in a laboratory‐scale spray drier. Drying of suspensions was performed with different sizes of two‐fluid nozzles. Droplet size distribution was evaluated from the data obtained for spray drying of bismuth molybdate suspension. The method was validated experimentally with other tested materials. Investigated systems involve processes of drying, crystallization, and coating. The proposed methodology can be applied when nonagglomerated particles, spherical particles, or spherical agglomerates were obtained by spray drying.     

The structure characterization of thermosensitive poly(N‐isopropylacrylamide‐co‐2‐hydroxypropyl methacrylate) hydrogel

The goal of this work was to investigate a possible way of crosslinking polymer chains and the potential formation of intramolecular hydrogen bonds in thermosensitive poly(N‐isopropylacrylamide‐co‐2‐hydroxypropyl methacrylate) (p(NIPAM‐HPMet)) hydrogels obtained by radical polymerization. The chemical structure of the synthesized hydrogels was investigated by Fourier transform infrared (FTIR) spectroscopy and XRD. The FTIR spectrum confirmed the presence of hydrogen bonds formed between the chains in the copolymer. XRD analysis confirmed the amorphous ? crystalline structure of the copolymer. A three‐glass transition and two melting temperatures were detected by DSC. It was found that the addition of HPMet increased the glass transition and melting temperatures of the p(NIPAM‐HPMet) copolymer. The swelling transport mechanism of p(NIPAM‐HPMet) changed from non‐Fickian at 20 °C to case III or zero‐order time‐independent kinetics characterized by a linear mass uptake with time with increasing temperature at 40 °C. © 2013 Society of Chemical Industry     

Determination of pK a Values of Oxocholanoic Acids by Potentiometric Titration

The pK _a and the maximum solubility values of cholic, deoxycholic salts and their oxo-derivatives have been measured by the method of potentiometric titration. In the monomer phase (under the critical micellar concentration, CMC), the bile salts have different pK _a values, as a result of their structural differences (the number of hydroxyl and oxo groups in the steroid skeleton) and different hydration properties of the acid anions. In the micellar phase (above the CMC), the bile salts have higher pK _a values than in the monomer phase (under the CMC). This increase in the pK _a values is greater in more hydrophobic bile salts (cholate and deoxycholate), than in less hydrophobic oxo derivatives, which can be explained by the different aggregation numbers of these bile salts. The oxo-derivatives are more likely to form dimeric micelles, where the carboxylic groups are situated on the two sides of the micelle, not causing any electrostatic repulsion. In the more hydrophobic bile salts, aggregation numbers are higher, which causes electrostatic repulsion of the nearby situated carboxylic anions and consequential protonation of these anions (which leads to the stabilization of the micelle). The maximum solubility values are higher for the oxo-derivatives. If the steroid skeleton of the bile salt is more hydrophobic, the capacity to solubilize the unionized bile acid is higher, i.e. a smaller amount of the bile acid anion is needed for the solubilization of the bile acid monomer. The oxo-derivatives are less hydrophobic, but alongside their hydrophobicity, the structure of the micelle determines the solubilization capacities.