Optimum Phase Composition Research Articles

Multicomponent Al-Si-based composites

The rapid quenching from melt was used to synthesize high-alloyed hypereutectic silumins with antimony and copper. The silumins were natural composites whose structure consisted mostly of dispersed intermetallic crystals uniformly distributed in the Al matrix. It was found that by selecting the optimum phase composition of the alloy and synthesizing multicomponent compounds, including fusible and refractory components, the linear thermal expansion coefficient can be reduced to 7.8 × 10−6 K−1, or one-third of the corresponding coefficient for unalloyed silumin.

Application of Homogeneously Precipitated Nanosized Fe‐Doped Alumina Powders to Carbon Nanotube Growth

Homogeneous precipitation of hydroxides was investigated as an alternative method to synthesize Fe‐doped aluminum oxide (α‐Al2−2xFe2xO3) particles over which carbon nanotubes (CNTs) were grown via a catalytic chemical vapor deposition (CCVD) method. Performance of the homogeneously precipitated particles for CNT growth was quantitatively compared with that of the combustion‐synthesized particles. The main advantage of the homogeneous precipitation of hydroxides and subsequent calcination process against to the combustion synthesis and other commonly practiced chemical routes is the ability to tailor the Fe‐doped Al2O3 precursor powder characteristics such as size and specific surface area (SSA) without requiring any milling step and also to control the phase composition of the oxide powder with high Fe content, and subsequently the quality and quantity of CNTs during CCVD process. The particle size of the precipitated and calcined α‐Al2−2xFe2xO3 powders varies between ∼50 and 400 nm for 5–10 cat.% Fe‐containing systems. The monodispersed particle size distribution and optimum phase composition of the homogeneously precipitated powders, particularly for a 10 cat.% Fe content in the starting oxide, and their much higher SSA than similar materials prepared by other chemical routes lead to production of high amounts of good quality CNTs.

Research on new rapid and deep plasma nitriding techniques of AISI 420 martensitic stainless steel

Cyclic plasma oxynitriding and cyclic plasma nitriding catalyzed by rare earth La of AISI 420 martensitic stainless steel were performed and compared with conventional plasma nitriding. The nitrided layers were investigated by means of an optical microscope, microhardness tester, Auger electron spectroscopy (AES), X-ray diffraction (XRD), wear machine, scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results show that the wear resistance of AISI 420 martensitic stainless steel is improved significantly by the two new rapid and deep plasma nitriding techniques. The new techniques increase the surface hardness of the nitrided layers and make the microhardness profiles gentler, which are consistent with the nitrogen concentration depth profiles. Meanwhile, the nitrided effect improves with increasing cycles. It was also found that the optimum phase compositions of nitrided layers with more γ′ phases and less ɛ phases for long-term service conditions can be obtained by the two new techniques, which is in agreement with the microstructure. In addition, traces of Fe 3O 4 were found in the cyclic plasma oxynitrided sample. Combining the SEM and EDS analysis indicated the existence of La in the nitrided layer of the sample under cyclic plasma nitriding catalyzed by rare earth La.

Application of phase optimized liquid chromatography to oligopeptide separations

Stationary phase optimized liquid chromatography (POPLC) has been applied to the separation of oligopeptides. The retention factors and theoretical plate numbers of 13 peptides were determined on five different stationary phases. Based on these values, an optimal stationary phase composition of 250 mm total length consisting of 3 segments of 20 mm octadecyl silica, 10 mm phenyl silica and 220 mm embedded polar octadecyl silica was calculated by the optimizer software. Good agreement between the calculated and experimental chromatograms was observed. In order to achieve short analysis time and baseline separation of all peptides gradient elution and optimization of the column temperature were performed. The optimized mobile phase conditions consisted of (A) acetonitrile and (B) 0.025 M aqueous sodium phosphate buffer, pH 3.0, operated at 10% A (0–12 min) followed by 10–50% A (12–32 min) at a flow rate of 0.5 mL min −1 and column temperature of 35 °C. Using these conditions all peptides could be separated in less than 30 min with good resolution and peak symmetry.

Phase optimized liquid chromatography as an instrument for steroid analysis

A new method using phase optimized LC (POPLC) for the analysis of steroids is described. The retention factors and the theoretical plate numbers of different steroids were determined for four different stationary phases. Based on these values, an optimal stationary phase composition and the resultant chromatogram have been calculated by an optimization software and compared to the measured data. It is demonstrated that these predicted data show only little differences to the experimental results. Furthermore, it is shown that the overall selectivity of the optimal stationary phase composition is much better than the selectivity of any individual stationary phase.

Glass ceramics based on spodumene glass produced in a solar furnace

The effect of the methods for introducing catalysts on phase formation in glass ceramics produced by the ceramic technology from spodumene glass melted in a solar furnace is studied. The main properties of class ceramics are identified. It is indicated that when a catalyst is introduced, the optimum phase composition determining the properties of glass ceramics is formed at lower sintering temperatures. It is established that the methods of ceramic technology can yield glass ceramics with good dielectric characteristics.

High-Temperature Nitriding of Refractory Alloys

Processes of high-temperature internal nitriding of refractory alloys based on nickel and cobalt are described. Thermodynamic backgrounds for formation of zones of internal nitriding with optimum phase compositions in alloys containing alloying elements with different affinity for nitrogen are considered. It is shown experimentally that the structures obtained in zones of internal nitriding with segregations of stable fine nitride phases depend on the ratio of concentrations of the nitride-forming elements, on the nitriding temperature, and on the composition of the saturating atmosphere. The kinetic parameters of the process of internal nitriding and the conditions of formation of through diffusion layers are determined. It is shown experimentally that the refractory characteristics of the nitrided layers are enhanced.

Structure and properties of mechanically alloyed steel PK50N2M

The possibility of improving the properties of powder metallurgy nickel—molybdenum steel PK50N2M by dispersing and homogenizing the initial powders via grinding in a high-energy planetary mill, followed by single pressing and sintering, and subsequent quenching and tempering, was investigated. It was established that structural heredity provided small pore size, high homogeneity, a favorable defect density and distribution, an optimal phase composition in the heat-treated steel, and a transformation under load. These features permitted the attainment of a high level of mechanical properties, even at relatively high porosities.

Influence of structure on the crack resistance of a high-strength structural steel

The reliability and service life of parts fabricated from high-strength steels are largely determined by such characteristics as fracture toughness (K Ic ), endurance limit (σ−1), including the low-cycle region, and the rate of fatigue crack propagation (dl/dN). In recent years, there has been an upsurge of interest among investigators in the possibility of improving these parameters by imparting an optimal structure and phase composition to structural steels during their final heat treatment. This study was undertaken to see how the structure (lower bainite, retained austenite, and others) and its parameters affect the reliability and character of fracture of VKS-9 (35KhS2N3M1FA) steel.

Preparation of Ag - Bi-2223 tape by controlling the phase evolution prior to sintering

The critical current densities and microstructures of tapes prepared using various pre-sintering thermomechanical treatments were compared. The phase composition prior to sintering was found to have a strong effect on the rate of 2223 phase growth and texture and, consequently, final transport properties. The difference in optimum requisite tape sintering processes when using powder with the same stoichiometry from different powder processes or even using identical powder obtained from the same source is due to variations in the content and composition of the secondary phases in the calcinated powder and/or the different phase transformations that occur due to different thermomechanical treatments prior to the sintering procedure. The optimum phase composition before sintering is a mixture of the main phase (textured mature Pb-2212 and Pb free 2212) and a small amount of secondary phases consisting of SrCaCuO and with small particle size. BiSrCuO, CuO and CaCuO are all detrimental to final tape performance characteristics and should be minimized in precursor powder. The optimum phase composition can be prepared by appropriate pre-sintering preparation and thermomechanical procedures. The particle size of the oxide in the Ag sheath can be decreased to a large extent by the deformation process. A critical current density of and a high (1 T, 77 K)/ of 23.4% has been achieved reproducibly using short sintering times and one intermediate pressing procedure. The reproducibility is a direct consequence of controlling the phase composition of the oxide core prior to sintering.

Effect of structure on the wear of quenched martensitic cast iron for diesel cylinder liners

1. In order to obtain macrogeometrical stability and the formation of protective structures of elevated wear resistance in cylinder liners of manganese cast iron, heat treatment including high-frequency heating of the liners combined with hardening by quenching is necessary. 2. The amount of retained austenite in cast iron hardened using HFC heating must be 34–36%. Decrease or increase of this amount of Aret in the martensitic cast iron base decreases the resistance to wear and scoring of cast iron liners with a high concentration of manganese (∼2.0%). 3. The working-in regimen has a strong effect on the ability of the rubbing surfaces to form protective secondary structures of optimal phase composition. Preliminary "conditioning" of the surfaces by working-in at low specific loads, using a definite number of cycles, is necessary to guarantee compatibility of the elements of the rubbing pair.

Optimization of the composition of mixed-phase columns for gas chromatographic separation of C 1C 2 halocarbons

Mixed-phase polar and non-polar columns were used for the separation of many chloro-, bromo- and iodomethanes, ethanes and ethenes, having one or more of the same or different halogen atoms in the molecule. The optimum phase composition was determined by using the window-diagram method. A column comprising 60% of OV-1 and 40% of SP-1000 [both 10% (w/w) on Chromosorb W DMCS (80–100 mesh)] was found useful for the separation of 33 different halogenated compounds. The effect of the analysis temperature on the resolution of closely eluted groups of peaks was investigated.

Optimal Bulk Phase Composition for an Isothermal Second-Order Reaction in a Catalyst Slab-Elliptic Integral Method

Optimal Bulk Phase Composition for an Isothermal Second-Order Reaction in a Catalyst Slab-Elliptic Integral Method

Extraction of thiocyanate complexes of cobalt(II) by diphenyl-2-pyridylmethane in benzene from mineral acid solutions

Extraction of Co(II) by diphenyl-2-pyridylmethane (DPPM) in benzene form mineral acid solutions containing potassium thiocyanate has been studied at room temperature (23±2°C). Its extraction from mineral acids alone is rather poor. Optimal aqueous phase composition for the quantitative extraction of Co(II) by 0.1M DPPM is 0.1M acid+0.2M KSCN. Stoichiometric studies indicate that an ionic type complex, (DPPM·H)2·Co(SCN)4, is responsible for extraction. The metal can be back-extracted from the organic phase by aqueous acetate, citrate or oxalate solutions. Separation factors from other metals determined under optimal conditions reveal that Co(II) can be quantitatively separated from CsI), Sr(II), Cr(III), Ln(III), Zr(IV), Hf(IV), Cr(VI) and Tc(VII), Mo(VI), Zn(II), Au(III), Hg(II) and U(VI) are, however, coextracted and hence should be previously removed by other techniques or reagents.