On the Subsolidus Structure in the CaAl4O7 – Ca7Al6ZrO18 – CaAl2O4 – CaZrO3 – SrZrO3 – SrAl2O4 Region of the CaO – SrO – Al2O3 – ZrO2 System

The subsolidus structure of the CA₂ – C₇A₃Z – CA – CZ – SrZ – SrA region of the CaO – SrO – Al₂O₃ – ZrO₂ system is studied. The occurrence of the solid-phase reaction between strontium aluminate and calcium zirconate is considered from the standpoint of thermodynamics. The conodes, three-component sections, and elementary tetrahedrons are studied in the given region. A promising region for the production of special cements is determined, and rapidly hardening, high-strength, and refractory binding materials are obtained in it.     

Structural evolution of β – iPP during uniaxial stretching studied by in–situ WAXS and SAXS

Polymorphism and crystal transition are of great significance for property mediation in polymer materials. Isotactic polypropylene (iPP) with β – crystal has been widely utilized for the preparation of high performance plastics or films. In the present work, the structural evolution of initially isotropic β – nucleated iPP (β – iPP) during uniaxial stretching at different temperatures was investigated by in–situ X – ray scattering using synchrotron radiation. The wide – angle X – ray scattering (WAXS) results confirmed that the β – crystal transformed either to the mesophase at lower temperature (30 °C) or to the α – crystal at higher temperature (60, 100 and 120 °C) during stretching. An interesting orientation of β – crystal with molecular chains perpendicular to the tensile direction was identified. As revealed by small – angle X – ray scattering (SAXS), cavitation took place in β – iPP stretched at temperatures lower than 120 °C. The size and shape of the cavities were observed by scanning electron microscope. A deformation mechanism of β – iPP combining the crystal transition, cavitation and orientation was proposed.     

Alkaliinduzierte Bildung von ortho-Semidinen aus 3-Nitro- und 3-Azo-carbazolen – Synthese von 8,16-Dialkyldiindolo[3,2-a,d]phenazinen

Alkali-induced Formation of ortho-Semidines from 3-Nitro- and 3-Azocarbazoles – Synthesis of 8,16-Dialkyldiindolo[3,2-a,d]phenazines The ortho-semidines 9-alkyl-4-(9-alkylcarbazol-3-ylamino)-3-aminocarbazoles ( 2a – d ) are formed either by reduction of 9-alkyl-3-nitro-carbazoles ( 1a – d ) or of the azo-( 6 ) or the azoxycarbazoles ( 7 ) with zinc in alkaline alcoholic solution. It could be shown by cross experiments that the semidines 2 result from an intramolecular rearrangement. The compounds 2a – d are oxidized by air or H₂O₂ to the 8,16-dialkyldiindolo[3,2-a,d]phenazines ( 3a – d ). Reduction of 1a – c with Raney-alloy affords the 9-alkyl-3-azoxycarbazoles 7a – c in good yields.     

Preparation of Sn‐Doped Zinc Phosphate Amorphous Thin Film and its Emission Properties

Using liquid‐phase synthesis, SnO – ZnO – P₂O₅ amorphous coating films exhibiting broad emission of Sn²⁺ center were prepared. It is found that the P – O – Zn bonds of the film were generated during the heat‐treatment. The emission property due to Sn²⁺ depended on the heat‐treatment temperature, which correlated with the residual chloride ion content. Although the peak position of the photoluminescence (PL) excitation band was almost constant, that of PL red‐shifted with increasing amount of SnO, which was quite different from the result observed for SnO – ZnO – P₂O₅ bulk glass containing Sn²⁺ center.     

Transformations of Iron (III) Precursors in a Wave of Flameless RDX Combustion

Flameless combustion of 40% Fe₂O₃ – 40% RDX – 20% HDI (mix I) and 30% CoCO₃ – 15% iron formate – 40% RDX – 15% HDI (mix II) systems was explored by time-resolved X-ray diffraction (TRXRD). In case of mix I, the reaction was found to proceed via the formation of FeO intermediate: Fe₂O₃ → FeO → Fe₃O₄. Variation in the extent of iron reduction was associated with dynamic temperature change and a reductant content of the reaction zone. The reduction proceeded as a solid-state reaction, without amorphization of the structure. The process in system II involved the formation of CoO and FeO intermediates. Further reduction – up to metals – takes place behind the combustion front and yields a mixture of nanosized Co, Fe, and Co_0.7Fe_0.3 particles. Exposure of hot reaction products – nano-sized Co and Fe – to the air leads to their self-ignition and formation of Co₃O₄ and Fe₃O₄, respectively.     

Dithiocarbonsäuren,Dithiocarbonsäureester oder Thiocarbonsäureamide aus methylenaktiven Chlormethylverbindungen und Schwefel

Dithiocarboxylic Acids, Dithiocarboxylic Esters, or Thiocarboxylic Amides by Reaction of Methylene-active Chloromethyl Compounds with Sulfur With a mixture of sulfur and amine in DMF at room temperature halomethyl compounds ( 1 , 5 – 10 ) can be oxidized to give thiocarboxylic acids ( 2 , 11 – 16 ) and their derivatives ( 3 , 4 , 17 – 35 ). We studied this reaction in detail especially with chloroacetic derivatives ( 11 – 15 ) or chloromethyl heterocycles ( 16 ) formally derived from chloroacetic acid. The resulting thiooxalic acid derivatives ( 11 – 27 ) represent activated acids and very useful C₂-synthons, especially for the synthesis of heterocycles. Oxidation in the presence of triethyl amine leads to dithiocarboxylates ( 11 – 16 ) which can be alkylated to dithioesters ( 17 – 27 ) in high yields. As a rule, with different primary and secondary amines instead of tertiary amines these dithiocarboxylates or dithiocarboxylic esters can be transformed already at low temperatures to thioamides ( 28 – 35 ).     

Heterocyclic Synthesis with Nitriles: Synthesis of some novel pyrrolo [2,1-b]thiadiazoline,pyrrolo[2,1-b]thiadiazolo[3,2-a]pyrimidine and pyridine derivatives

α-(Bromothiocyanatomethyl)benzylidenemalononitrile ( 1 ) reacts with the hydrazides 2a – c , cyanoacethoydrazide ( 2d ,) cyanoacetamide ( 3a ) and cyanoacetanilides 3b – d to afford pyrrolo[2,1-b]thiadiazolines 5a – c , pyrrolo[2,1-b]thia-diazolo[3,2-a]pyrimidine ( 8 ) and the pyridone derivatives 11a – d . Structures and conceivable mechanisms are discussed.     

Studies on biodegradation of phenol using response surface methodology

Biodegradation of phenol was studied using Pseudomonas pictorum (NCIM 2077) immobilized on alginate and activated carbon – alginate beads. Control experiments were also performed using free cells and non‐inoculated activated carbon – alginate beads. The entrapped alginate and activated carbon – alginate beads suffer from a concentration gradient for oxygen in the interior of the beads and hence free cells showed better degradation at lower concentrations of phenol. The results on entrapped alginate beads were modeled using response surface methodology which determines the dependency of the maximum percentage of phenol degraded as a function of the independent variables, namely initial phenol concentration, initial pH, temperature, and diameter of the immobilized beads. The predicted values are in close agreement with the experimental values with the coefficient of correlation equal to 0.9999 and 0.9993 for both P pictorum – alginate beads and activated carbon – P pictorum – alginate beads respectively. © 2002 Society of Chemical Industry     

Opacified Glazes Based on Liquating Glass of Low-Alkali Compositions

The vitrification processes in the Na₂O – MgO – CaO – B₂O₃ – SiO₂ system and the effect of the heat-treatment conditions on the location of the liquation regions, the nature, the structure, and the phase composition of liquating glasses and on the kinetics of the liquation processes are studied. Physicochemical parameters of the glasses that corroborate the presence of liquation-phase inversion are identified. Compositions for liquating glazes with a minimum content of zirconium-bearing opacifying components are developed.     

Effect of Si3N4 Ceramic Particulates on Mechanical,Thermal, Thermo-Mechanical and Sliding Wear Performance of AA2024 Alloy Composites

Silicon - In this investigation, hybrid AA2024 – Si3N4 (0–6 wt.% @ 2%) – SiC (2 wt.%) – graphite (2 wt.%) alloy composites have been fabricated as...     

Phase Composition and Structure of Aluminum – Coating Composite

Low-melting enamel coatings for household aluminum kitchenware are synthesized. The possibility of formation of low-melting glasses in the system R₂O – Al₂O₃ – B₂O₃ – TiO₂ – P₂O₅ is studied. An optimum glass matrix composition with a decreased firing temperature (580°C) is selected.     

Characterization of extra virgin olive oils derived from the Croatian cultivar Oblica

The objective of the present research work was the characterization of extra‐virgin olive oils derived from the main cultivar at the Adriatic coast Oblica by the determination of selected organic parameters as well as of the elemental composition. Twenty elements were quantified by inductively coupled plasma – optical emission spectrometry (ICP‐OES) after acidic microwave assisted digestion. In all samples the concentrations of As, Cd, Co, Cr, Mn, Mo, Pb, and V were below the LOD. The mode of production (pressing or centrifugation) is reflected in the contents of Cu, Fe, Ni, and Si. Thus only the contents of Al, Ca, K, Mg, Na, Se, Sn, and Zn ranging from 0.02 – 0.5, 0.8 – 11, 0.1 – 2.5, < LOD – 0.2, 2.7 – 4.2, 0.6 – 2.9, <LOD – 4.8, and 2.5 – 4.0 µg/g oil, respectively, can be used for characterizing the Oblica variety. The organic quality parameters analyzed were free fatty acids (0.1 to 0.6% oleic acid), peroxide value (2.2 to 4.4 mmol O₂/kg) and specific absorbances in the UV range (K₂₃₂ 0.8 to 1.9; K₂₇₀ 0.8 to 1.9; 0.08 to 0.21; and ΔK < 0.003). Practical applications : Oil characterization by organic as well as inorganic parameters is the basis for nutritional and food technological investigations such as adulteration detection and genuineness analysis. Knowing the composition of authentic samples (reference values) is necessary in order to be able to detect differences caused by fraud in products available on the market. Since Croatia is a candidate for entering the European Union the characterization of food stuff coming from this country is of great concern.     

Separation of Ammonium Dinitramide from Reaction Mixture

To separate ammonium dinitramide from the reaction mixture obtained in the reaction between NO₂HS₂O₇ and nitramine in aceto-nitrile and subsequent neutralization with NH_{3 aqua} the following procedure was applied: – separation of the solid precipitated during the reactions; – evaporation of the acetonitrile solution; – extraction of the obtained solid with isopropanol; – evaporation of the isopropanol solution; – crystallization this way obtained crude ammonium dinitramide from ethyl acetate. According to the crude ammonium dinitramide concentration in the crystallization solvent, products with various compositions were obtained. For determined concentrations good yield and selectivity of the crystallization were attained. IR, TG, DTA and elementary analysis examined the selected products of the separations what allowed connecting the recorded spectra and thermographs with determined purity of ammonium dinitramide samples.     

Synthesis of Complex Lanthanum and Calcium Titanates with a Perovskite Structure and Their Electric Properties Studied at High Temperatures

Phase formation in the CaTiO₃ – La₂O₃ system in the concentration range 0 – 40 mol.% La₂O₃ is revisited. Conductivity, dielectric constant, and dielectric loss are measured in the temperature range of 5 – 600°C, and electric strength and the temperature coefficient for dielectric constant (TCε) of perovskite phases in the CaTiO₃ – La₂O₃ system are determined. The ceramic materials studied have a low dielectric loss depending but slightly on temperature [tan d = (1 – 6) × 10^–4], a high dielectric constant (ε = 30 – 120), and a TCε varying from – 1480 × 10^–6 deg^–1 to + 10,500 × 10^–6 deg^–1 with composition; the zero point for TCε is identified at 23 mol.% La₂O₃.     

Formation of Mullite Basedon Hydromica Clay – Aluminum Oxide Compositions

The results of studying mullite formation based on hydromica clay – Al(OH)₃ compositions are described. It is shown that formation of mullite (or a solid solution of mullite with corundum) is the most intense at temperatures of 1150 – 1200°C in compositions with a content of hydromica clay equal to 50 – 60%.     

Properties, Structure, and Application of Low-Melting Lead–Bismuth Glasses

Glass formation, crystallization, and physicochemical properties, as well as glass structure in the system PbO – ZnO – Bi₂O₃ – B₂O₃ – SiO₂, are investigated in the section with a constant molar content of glass-formers (B₂O₃ + SiO₂) equal to 20%. A nonlinear dependence of glass properties on their composition is established caused by the change of the coordination state of lead ion in glass structure. The developed glasses are recommended for joint and seals in the production of a new generation of physical parameter sensors.     

TiN – AlN-Based Hot-Pressed Composites. Part 1. Structure and Properties

Results of a study into the structure and mechanical properties of a hot-pressed TiN – AlN ceramic with the concentration of AlN in it varying from 0 to 100% are given. Composite materials with a strength of 750 MPa, a crack resistance of 4.4 MPa · m^1/2, and a hardness of 13 – 15 GPa measured over a wide range of the indenter load (50 – 100 N) are prepared. These materials exhibit an extremely high resistance to fracture under localized load. The TiN – AlN-based materials are promising for use in tribo-engineering applications — such as ceramic bearings and wear-resistant friction couples.     

Effects of Self-Etching Adhesive Systems Used in the Dental Modelling Technique on the Cohesive Strength of Composite Resin

This study evaluated the cohesive strength of composite using self-etching adhesive systems (SE) in the lubrication of instruments between layers of composite. The specimens were made by using a Teflon® device. SE were used at the interface to lubricate the instruments: Group 1(G1) – control group, no lubricant was used; Group 2(G2) – Futurabond® M; Group 3(G3) – Optibond® All-In-One; Group 4(G4) – Clearfil® SE Bond; Group 5(G5) – Futurabond® NR; Group 6(G6) – Adper® SE Plus; Group 7(G7) – One Up Bond® F. Specimens were submitted to the tensile test to evaluate the cohesive strength. Data were submitted to the ANOVA and Tukey tests. ANOVA showed a value of p = 0.00. The average means (SD): G2 = 11.33(±3.44) a, G3 = 15.36(±4.06) ab, G4 = 18.9(±4.72) bc, G7 = 19.62(±4.46) bc, G5 = 21.02(±5.09) bc, G6 = 23.39(±4.17) cd, and G1 = 28.49(±2.89) d. All SE decreased the cohesive strength of the composite, except for Adper® SE Plus.     

CFD Prediction of Flow and Homogenization in a Stirred Vessel: Part I Vessel with One and Two Impellers

A simulation of flow field and tracer homogenization was performed using the commercial CFD software FLUENT 6.1. The aim is to investigate the potential of CFD software to predict concentration distribution of added tracer in cylindrical vessels. The calculated results – dimensionless velocity profiles, power and pumping numbers, dimensionless concentration curves, and mixing times – were compared with experiments in stirred vessels. In Part I, the study was performed for vessels agitated by one or two impellers on a centric shaft. Two different impellers were used – a 6‐bladed 45° pitched blade turbine and a standard Rushton turbine. The standard k‐? turbulence model and multiple reference frames method were used for the simulations. The influence of the grid type was also investigated; three types of grid – a structured, unstructured and a special user‐defined grid – were studied.     

Interdependence of sodium and potassium substitution in tricalcium aluminate

The maximum extent of K₂O substitution in cubic Ca₃A?₂O₆ is 0.75 – 1.0 wt. % at 1000 – 1200°C. Na is required to form orthorhombic solid solutions, but these exhibit appreciably higher solubilities for K₂O, ranging up to 2.0 – 2.5 wt. %, than the cubic solid solutions.