Synthesis of trimethylene carbonate/ϵ‐caprolactone copolymers initiated with zinc alkoxide: influence of copolymer chain microstructure on thermal and mechanical properties

Ethylzinc(II ) ethoxide is a highly active and efficient initiator for the bulk polymerization of 1,3‐trimethylene carbonate and its copolymerization with ? ‐caprolactone. This initiator allows one to obtain (co)polymers with high molar masses in quite a short time. Significant difference in co‐monomer reactivity and relatively low participation of intermolecular transesterification processes lead to the obtained copolymers being characterized by a gradient chain microstructure. In ¹³C NMR spectra, in all regions, we observed the presence of triads which were distinctly represented by four peaks for the carbonyl signal. Mechanical tests showed that copolymers containing 70% and more of ? ‐caprolactone presented a relatively high Young's modulus and a very high maximum elongation factor; therefore these materials are promising in many biomedical applications. Due to the high reaction rate, we also made an attempt at copolymerization using reactive extrusion which gave promising results. © 2017 Society of Chemical Industry     

Accuracy and uncertainty of single-shot, nonresonant laser-induced thermal acoustics

We study the accuracy and uncertainty of single-shot nonresonant laser-induced thermal acoustics measurements of the speed of sound and the thermal diffusivity in unseeded atmospheric air from electrostrictive gratings as a function of the laser power settings. For low pump energies, the measured speed of sound is too low, which is due to the influence of noise on the numerical data analysis scheme. For pump energies comparable to and higher than the breakdown energy of the gas, the measured speed of sound is too high. This is an effect of leaving the acoustic limit, and instead creating finite-amplitude density perturbations. The measured thermal diffusivity is too large for high noise levels but it decreases below the predicted value for high pump energies. The pump energy where the error is minimal coincides for the speed of sound and for the thermal diffusivity measurements. The errors at this minimum are 0.03% and 1%, respectively. The uncertainties for the speed of sound and the thermal diffusivity decrease monotonically with signal intensity to 0.25% and 5%, respectively.     

Structure and properties of 6061 + 26 mass% Si aluminum alloy produced via coupled rapid solidification and KOBO-extrusion of powder

Experiments on mechanical consolidation of rapidly solidified (RS) powder of 6061 + 26 mass% Si alloy were performed using the oscillating-die extrusion method. The RS powder was wrapped in thin-wall 6061-alloy cup 35 mm in diameter and vacuum-compressed by means of 100 ton press. Bars 8 mm in diameter were extruded with cross-section reduction of λ = 19 without any preheating of the charge. Tubes with a diameter/wall thickness of 14 mm/1 mm and cross-section reduction of λ = 33 were also manufactured with success. TEM/STEM observations revealed a very fine structure of as-extruded material and bimodal distribution of quasi-spherical silicon particles. Statistical analysis revealed a silicon fine fraction of 0.1–0.7 μm and a coarse fraction 2.1–2.5 μm in diameter. Examination by means of TEM did not reveal any significant changes in the morphology of the silicon particles, even when a high extrusion ratio and the material annealing after deformation were used. Hot compression tests on as-extruded rods (λ = 19) and preliminary annealed samples were performed at a constant true strain rate of 5 × 10^?3 s^?1 within the temperature range of 293–823 K. High strength of the material and relatively high ductility of samples deformed by compression up to ?_t ? 0.4 were observed. The maximum flow stress value for as-extruded material was reduced with deformation temperature from ～390 to ～3.5 MPa for 293 and 823 K, respectively. Annealing of the samples at 773 K/30 min was found to reduce the maximum flow stress by 30–40%. Tensile strengths of similar as-cast alloys and materials manufactured by means of other powder metallurgy methods were shown for the purpose of comparison.     

Accepted practices of thermal spray technology

This is the fourth and final article in a series of articles dealing with the metallographic preparation and evaluation of thermal spray coatings. Previous articles have covered variables and best practices for the sectioning, mounting, and coarse grinding of coated components. In this article, the relationship between fine grinding and polishing practices, consumables, and resultant plasma spray coating structure are discussed.     

Improving Steam Boiler Operation by On-Line Monitoring of the Strength and Thermal Performance

The operation of steam boilers with high efficiency requires control of thermo-hydraulic and strength parameters in the on-line mode. During operation under transient conditions, there are significant temperature differences over the circumference of the horizontal pressure vessels. This occurrence is caused by the different values of heat transfer coefficients on the inner surface of the boiler drum in the water and steam region. Large thermal stresses can occur in partially filled horizontal vessels. This takes place in large steam generator drums, superheater headers, and steam pipelines. The paper presents a method for determination of thermo-flow parameters for steam boilers. This method allows performing the calculations of the boiler furnace chamber and heating flow rates absorbed by superheater stages. These parameters are important for monitoring the performance of the power unit and determining the degree of the furnace chamber slagging. Knowledge of these parameters allows determining the degree of the furnace chamber slagging. The calculation can be performed in online mode and use to monitoring of steam boiler. The presented method allows to the operation of steam boiler with high efficiency.     

Effect of pH on Apparent Viscosity of Wholemeal Oat Flour Water Dispersions

Research was undertaken to determine the effects of pH (1.5–12), stabilization time (1–3 h), and shear rate (200–1200 s^?1) on the apparent viscosity of wholemeal oat flour—water dispersions (10% w/w). Six oat cultivars, with different content of dietary fibre, especially of (1–3) (1–4) β-D-glucans, were used in this study. The study demonstrated instability of apparent viscosity of wholemeal oat flour dispersions. An increase of viscosity was observed with the increase in stabilization time. The range of viscosity changes was related with the dispersion pH level—the greatest range of changes was noted for dispersion with pH 9.5. Wholemeal oat flour dispersions, irrespective of the pH level, displayed pseudoplastic flow behaviour. A moderate to high significant linear correlations (Pearson, p ≤ 0.05) existed between the apparent viscosity and the (1–3) (1–4) β-D-glucans, soluble dietary fibre and total dietary fibre content. Measurements of apparent viscosity of wholemeal oat flour water dispersions can be used for the estimation of particular dietary fibre fractions content, especially of (1–3) (1–4) β-D glucans. With the application of suitable measurement conditions, the content of (1→3) (1→4) β—D glucans can be explained by the apparent viscosity of the oat flour dispersion (R² = 0.97–0.98).     

The Role of MgCl2 as Supporter for the New Generation of Olefin Polymerization Catalysts

Most of the research in the field of olefin polymerization is focused on TiC1, catalysts on a specially prepared MgCl, support. In order to combine a high polymer yield with good stereoselectivity, a complexed cocatalyst is used. Most frequently it is a mixture of AIEtzCl or AlEt, with an electron donor such as tetrahydrofuran (THF) or ethyl benzoate for ethylene and propylene polymerization, respectively.     

Ion bombardment of MoS2 nanoplateletcoatings deposited by electrospraying

The present paper reports on a novel process for deposition ofMoS₂ lubricating coatings by electrospraying aball-milled platelet suspension of stoichiometric MoS₂particles. Ultralow friction coefficients in the range of0.010-0.020, in a dry-nitrogen atmosphere, were obtained with areciprocating ball-on-disk tribometer for a stainless-steel ballsliding on a MoS₂-coated silicon substrate. Thesliding endurance for MoS₂, as deposited, was measuredfor thicknesses ranging from 0.28 to 1.00 m tobe between 0.6 and 44 m. The effect of a low-dose, high-energy,argon-ion bombardment was studied. Thus an ion bombardment with400 keV argon ions to a dose of 18 x 10¹⁵ions/cm² increased the sliding endurance by a factorof about thirty, for a coating thickness of 0.3m.