Composite Ceramic Materials and Coatings for Tribological Use

The tribological properties over a broad range of sliding velocities and loads under dry friction in air of promising composite materials and coatings based on titanium carbide and carbonitride were studied. The dominating effect of secondary structures arising in the process of tribooxidation was investigated. Isomorphous oxide phases which form solid solutions and are strongly adherent to the surface of the material or coating promote the development of a continuous and dense screening film.     

Fire-retardant action of potassium nitrate in polyamide 6

The addition of 10–20 wt.-% of potassium nitrate (KNO₃) to polyamide 6 (PA 6) improves the fire retardance of the polymer. The thermal decomposition behaviour of the PA 6/KN0₃-mixture was studied using thermogravimetry, differential scanning calorimetry and thermal volatilisation analysis. Solid products of the thermal decomposition of the mixture were analysed by infrared spectroscopy, X-ray diffraction and electron paramagnetic resonance. It was found that KNO, prevents flowing and dripping of the melt and promotes charring on the surface of the polymer which decreases its fire hazard and improves its fire retardance. On the other hand, KNO₃ exothermally reacts with PA 6 in the condensed phase and supplies oxygen to the gas phase which increases the combustibility of PA 6. The mechanism of the chemical interaction of KN03 with PA 6 is discussed.     

New o-carboranyl-containing capping agents for d-metal tris-dioximates and first bis-C-carboranylboron-capped iron(II) clathrochelates: Synthesis and X-ray structure

The first use of C-carboranylboronic acid derivatives for capping of the clathrochelate complexes is reported. The initial carboranyl-containing boron dichlorides were prepared via metallation of 1-isopropyl- and 1-ethyl-o-carborane with n-butyllithium followed by borylation with boron trichloride. Their further template condensation with nonmacrocyclic iron(II) tris-nioximate afforded the C-carboranylboron-capped alicyclic iron(II) clathrochelates.     

Effect of the Polymerization Degree,Moisture Content,and Temperature on Kinetics of Hydrolysis of Corn Starch by Alpha-Amylase

Effect of the polymerization degree, moisture content, and temperature on kinetics of hydrolysis of corn starch by α-Amylase was studied. The degree of hydrolysis of the corn starch by α-amylase at low moisture content was shown to be strongly dependent on the initial starch polymerization degree and the thermodynamic activity of water in the system.     

Solid Solutions of Lindbergite–Glushinskite Series: Synthesis,Ionic Substitutions,Phase Transformation and Crystal Morphology

To clarify the crystal chemical features of natural and synthetic oxalates Me²⁺(C₂O₄)∙2H₂O (Me²⁺ = Fe, Mn, Mg, Zn), including minerals of the humboldtine group, solid solutions of lindbergite Mn(C₂O₄)∙2H₂O–glushinskite Mg(C₂O₄)∙2H₂O were precipitated under various conditions, close to those characteristic of mineralization in biofilms: at the stoichiometric ratios ((Mn + Mg)/C₂O₄ = 1) and non-stochiometric ratios ((Mn + Mg)/C₂O₄ < 1), in the presence and absence of citrate ions. Investigation of precipitates was carried out by powder X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Thermodynamic modelling was performed in order to evaluate the lindbergite–glushinskite equilibrium. It was shown that glushinskite belongs to the orthorhombic β-modification (sp. Gr. Fddd), while lindbergite has a monoclinic α-modification (sp. gr. C2/c). Mg ions incorporate lindbergite in much higher quantities than Mn ions incorporate glushinskite; moreover, Mn glushinskites are characterized by violations of long-range order in their crystal structure. Lindbergite–glushinskite transition occurs abruptly and can be classified as a first-order isodimorphic transition. The Me²⁺/C₂O₄ ratio and the presence of citric acid in the solution affect the isomorphic capacity of lindbergite and glushinskite, the width of the transition and the equilibrium Mg/Mn ratio. The transition is accompanied by continuous morphological changes in crystals and crystal intergrowths. Given the obtained results, it is necessary to take into account in biotechnologies aimed at the bioremediation/bioleaching of metals from media containing mixtures of cations (Mg, Mn, Fe, Zn).     

The Mechanism of HDS Catalysis

The mechanism of heterogeneous catalytic reactions is much more difficult to elucidate than that of homogeneous systems. Despite the facilities provided by physical methods for investigating the surface of solids, obtaining detailed information on the structure of the active component in real heterogeneous catalysts presents difficulties due to the nonuniform chemical composition of the surface species. Some of these surface species are totally inactive in catalysis, and others can catalyze the given chemical reaction by different pathways and according to different mechanisms. This results in a change of selectivity to the desired product and the appearance of intermediates and reaction by-products. Furthermore, the effect of the reaction medium on the catalyst gains importance during a catalytic process when, at high temperature and pressure, one type of surface species is transformed into another, thus changing the mechanism and direction of the catalyzed reaction.     

New Grades of Hardmetals for a Rock Cutting Tools

A concept is developed for creating hardmetals for rock cutting tools. The concept pays particular attention to increasing energy absorption and the fatigue strength of hardmetals. In order to provide high rock cutting tool efficiency it should be fitted with hardmetal inserts which exhibit high bending strength, fracture toughness, total work of deformation, and energy absorption coefficient. This has been realized in the development of new grades of hardmetals for rock cutting tools. The efficiency of rock cutting tools fitted with inserts made from the new grades of hardmetal exceeds that of similar tools fitted with standard hardmetals inserts by a factor of 2.8     

Grain-Size Composition and Coercive Force of Nd2Fe14B Alloy Powder in a Finely Divided State

The change in grain-size composition and magnetic properties of powder prepared by grinding cast alloy Nd₂Fe₁₄B in a ball mill for different times is studied. It is shown that during grinding the coercive force of the powder increases uniformly at first reaching a maximum, and then it decreases. It is established that this phenomenon is not due to powder oxidation during grinding but a reduction in the level of particle uniaxial anisotropy caused by deformation of their surface layer during grinding. The change in coercive force of Nd ₂Fe₁₄B alloy powder on grinding obeys the same features that are observed with mechanical grinding of other uniaxial magnetic materials.