Evaluation of hardness, tribological behaviour and impact load of carbon-based hard composite coatings exposed to the influence of humidity

Diamond-like composite coatings were deposited by PACVD with an interface magnetron sputtered metallic layer prepared by d.c. unbalanced magnetron sputtering onto HSS substrates. The focus of the present work was on the study of the humidity effect on the tribological properties, hardness and impact resistance of the deposited coatings. The coatings were tested under both dry and humid conditions using several testing methods, like the pin-on-disc test equipped with linear reciprocating movement, impact test and depth sensing indentation test. It was found that the humidity may substantially influence not only the results of tribological tests, but surprisingly, also the results of the dynamic wear and hardness tests. By increasing the relative humidity, the value of dynamic impact resistance increased at an equivalent stress of 1.6 GPa more than three times. On the other hand, the wear rate of the coated part increased by more than four orders of magnitude. The results of the indentation test were influenced by humidity mainly at nanometre scales. The hardness measured at dry conditions was higher by 25% than the values obtained by the measurements under humid conditions.     

Is air-drying of plant-based food at low temperature really favorable? A meta-analytical approach to ascorbic acid,total phenolic,and total flavonoid contents

The aim of this work was to review the studies that evaluated the effect of drying temperature on the content of ascorbic acid (AA), total phenolic (TPC), and total flavonoid contents (TFC) in fruits and vegetables, and quantify whether drying at 40 °C is more favorable than at higher temperatures. For the purpose of this study, AA, TPC, and TFC values for 40 °C were compared with those obtained at 50 °C, 60 °C, and 70–80 °C. A meta-analysis was performed using the weighted response ratio calculated for each experiment. Despite the fact that other variables significantly influenced the nutrient content in individual experiments, the meta-analysis provided a general view on the effect of air-drying temperature on the quality of plant-based food products from outcomes of various studies.     

Synthesis of defined polyhedral oligosilsesquioxane‐containing diblock and triblock methacrylate copolymers by atom transfer radical polymerization

Defined diblock and triblock copolymers composed of methyl methacrylate‐co‐glycidyl methacrylate block and 3‐{3,5,7,9,11,13,15‐hepta(2‐methylpropyl)‐pentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]‐octasiloxan‐1‐yl}propyl methacrylate block(s), i.e., P(MMA‐co‐GMA)‐b‐PiBuPOSSMA and PiBuPOSSMA‐b‐P(MMA‐co‐GMA)‐b‐PiBuPOSSMA, were synthesized by atom transfer radical polymerization (ATRP). First, monofunctional and bifunctional P(MMA‐co‐GMA) copolymers were synthesized by ATRP. Subsequently, these copolymers were successfully used as macroinitiators for ATRP of POSS‐containing methacrylate monomer. The process showed high initiation efficiency of macroinitiators and led to products with low dispersity. The synthesized block copolymers were characterized by size exclusion chromatography, ¹H‐NMR spectroscopy and their glass transition temperatures were determined by differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

High‐Tg,heat resistant epoxy–silica hybrids with a low content of silica generated by nonaqueous sol–gel process

The epoxy‐silica hybrids showing high T_g and thermal stability are prepared by the non‐aqueous sol–gel process initiated with borontriflouride monoethylamine. Tetramethoxysilane (TMOS) is used as a precursor of silica and 3‐glycidyloxypropyl trimethoxysilane as a coupling agent to strengthen the interphase interaction with an epoxy matrix. The basic factors governing the nonaqueous sol–gel process are studied in order to reveal the formation–structure–properties relationships and to optimize the hybrid composition as well as conditions of the nonaqueous synthesis. The formation of the hybrid, its structure, thermomechanical properties and thermal stability are followed by chemorheology experiments, NMR, DMA and TGA. The most efficient reinforcement of the epoxy network is achieved by the combination of both alkoxysilanes, showing synergy effects. The hybrids with a low content (～10 wt %) of the in situ generated silica exhibit dramatic increase in T_g and the high modulus, 335 MPa, up to the temperature 300°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40899.     

Dendrimer‐Encapsulated Ruthenium Oxide Nanoparticles as Catalysts in Lithium‐Oxygen Batteries

Dendrimer‐encapsulated ruthenium oxide nanoparticles (DEN‐RuO₂) have been used as catalysts in lithium‐oxygen (Li‐O₂) batteries for the first time. The results obtained from ultraviolet‐visible spectroscopy, electron microscopy and X‐ray photoelectron spectroscopy show that the nanoparticles synthesized by the dendrimer template method are ruthenium oxide, not metallic ruthenium as reported by other groups. The DEN‐RuO₂ significantly improves the cycling stability of Li‐O₂ batteries with carbon electrodes and decreases the charging potential even at ten times less catalyst loading than those reported previously. The monodispersity, porosity, and large number of surface functionalities of the dendrimer template prevent the aggregation of the RuO₂ nanoparticles, making their entire surface area available for catalysis. The potential of using DEN‐RuO₂ as a standalone cathode material for Li‐O₂ batteries is also explored.     

Effect of catalyst composition on the selectivity of competitive hydrogenations of mono-olefinic reactants in the liquid state

The effect of the amount of platinum and the type of the carrier on the selectivity for competitive hydrogenation of 2-methyl-3-butene-2-ol and hex-l-ene in methanol on platinum carrier catalysts has been studied. The effect of the type of the active component and carrier on the selectivity for competitive hydrogenation of 2-methyl-3-butene-2-ol and 2-phenylpropene in methanol and cyclohexane on various types of catalyst has also been investigated. Selectivity decreased with increasing amounts of platinum on the carrier and also with decreasing polarity of the carrier. The change in selectivity was greatest for a change in the active (metal) component of the catalysts; being in most cases several times higher in cyclohexane compared with methanol.     

Gelation in the curing of epoxy resins with anhydrides

Summary The statistical theory of branching processes has been used in an analysis of gelation in the system diepoxide-cyclic anhydride-tert.-amine in step and initiated reaction mechanisms. Experimental data indicate that critical conversion depends on the concentration of tert.-amine, which suggests that a mechanism with initiation is operative.     

Activity of the Ni?CAl Mixed Oxides Prepared from Hydrotalcite-Like Precursors in the Oxidative Dehydrogenation of Ethane and Propane

The activity of Ni?CAl mixed oxides obtained by the thermal pre-treatment of Ni?CAl hydrotalcite-like precursors was studied in the ODH of ethane and propane. The activity of the Ni?CAl mixed oxide catalysts was studied with respect to (i) the role of Ni content and (ii) the role of temperature during Ni?CAl HTs thermal pre-treatment. The structure analysis and the activity of Ni?CAl mixed oxides were discussed in three groups; (A) the catalysts pre-treated at 500???C, (B) the catalysts pre-treated at 600???C and (C) the Ni2?CAl catalyst with constant Ni content pre-treated at 500?C900???C. Ni?CAl mixed oxides were active and selective catalysts in the ODH of ethane even at 450???C. On the other hand, the catalysts posses low selectivity to propene. It is supposed that the interaction of NiO with alumina phase plays the critical role in the active and selective catalysts. The Ni?CAl mixed oxides were characterized by XRD, H₂-TPR and diffuse reflectance spectroscopy.     

The effect of combinations of sodium phosphates in binary mixtures on selected texture parameters of processed cheese spreads

The dependence of hardness, adhesiveness and cohesiveness of processed cheese spreads on the composition of binary mixtures of disodium hydrogen phosphate, tetrasodium diphosphate, pentasodium triphosphate, and/or sodium salt of polyphosphate was studied. Suitable statistical models to describe the dependence of the texture parameters examined on the composition of binary mixtures were investigated. Each of the 6 types of binary mixtures was applied in 11 percentage ratios of each component. In binary mixtures of polyphosphate combined with monophosphate, diphosphate or triphosphate, hardness gradually rose with the increasing proportion of polyphosphates within the mixture. In binary mixtures of monophosphate combined with diphosphate or triphosphate, a rapid growth in hardness of the samples was observed when the proportion of diphosphate or triphosphate in the mixture increased (up to 50–60%). A further increase in diphosphate or triphosphate content (above 60%) resulted in a rapid decrease in hardness of the processed cheeses.     

Competitive Catalytic Hydrogenation in the Liquid Phase on Solid Catalysts

Abstract

Problems of heterogeneously catalyzed hydrogenation have received increased attention recently. Although the process ranks among those most widely used in the industrial practice, knowledge of it is still inadequate. One of the interesting problems, still also unexplored from the theoretical point of view, concerns competitive catalytic hydrogenations, i.e., reaction systems in which more than one compound react simultaneously. Basically, these systems can be divided into two classes: (1) various functional groups enter the reaction and (2) the reacting functional groups are the same. Competing groups capable of hydrogenation may be contained in one or several molecules.