Influence of stress concentrators on the temperature dependence of the liquid metal embrittlement of Armco iron

We study temperature dependences of the effects of liquid indium and lead-bismuth eutectics on the ultimate strength and tensile elongation of Armco iron. Tests were performed on Armco iron cylindrical specimens with stress concentrators and with square cross section under active strain with a rate of 8.3 · 10^–4 s^–1. It was found that, under identical test conditions, the decrease in the ultimate strength of the specimens with concentrators caused by the effect of melts occurs in a broader temperature range than the embrittlement of specimens without concentrators. The effect of liquid metal also depends on the size of the grains in iron (26 – 110 µm) but its character is different for specimens with and without concentrators.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 5, pp. 65–72, September–October, 1993.     

Sintering of powder mixtures and the growth of ferrous powder metallurgy

Advances in the understanding of sintering of powder mixtures contributed significantly to the growth of ferrous powder metallurgy industry. Solid-state sintering and liquid-phase activated sintering play an important role in the sintering of powder mixtures. In this paper, sintering of iron powder with graphite; iron powder with copper and graphite; iron powder with nickel and graphite; iron powder with phosphorus; and iron powder with boron is discussed. Mechanical properties of the sintered parts are presented along with application of these parts.     

Effect of hydrogen on phase and structural transformations in titanium alloys of different classes

We study the laws of phase and structural transformations in titanium alloys under the action of dissolved hydrogen and in the course of subsequent degassing. We show the possibility to control structure formation in them with the help of alloying with hydrogen and to obtain structures that cannot be obtained by conventional technological methods. It has been established that the alloying system determines the character of interaction of these alloys with hydrogen in the course of hydrogenation. After additional alloying with hydrogen, intermediate hydrides are formed in titanium alloys with β-isomorphic stabilizers (V, Nb), Ti Cr₂ intermetallic compound appears in alloys with β-eutectoid stabilizer (Cr), and Ti₃Al compound is formed in alloys with high aluminum content. After vacuum annealing of hydrogen-containing specimens at 600°C, a composite heterophase (α + β + α₂) or (α + β + TiCr₂) structure is formed, and intermetallic particles in it have an incoherent boundary. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 33–39, May–June, 2006.     

Investigation of stress corrosion cracking of low-alloy steel in water

For four low-alloy steels with a wide range of tensile strength, the dynamical processes of the nucleation and propagation of stress corrosion cracking (SCC) in water with various polarization conditions and in a 0.1 N K₂Cr₂O₇ solution were traced with an optical microscope. The results show that if the tensile strength of the steel is higher than a critical value that is different in different polarization conditions and K_IK_ISCC, the plastic zone in front of a loaded crack tip is enlarged with time i.e. the delayed plastic deformation occurs in all the environments used. The nucleation and propagation of SCR will proceed when this delayed plastic deformation develops to a critical condition. Neither anodic and cathodic polarization nor the inhibitor can change the feature of the delayed plasticity and the nucleation and propagation of SCC in water.In all the environments used, K_ISCC is increased and $\text{da}\text{dt}$ is decreased with the decrease in the strength of the steel. K_ISCC is increased and da/dt is decreased with the anodic polarization and the addition of the inhibitor, but the cathodic polarization has the opposite effect.     

Assessment of critical material attributes of polyethylene oxide for formulation of prolonged-release tablets

Abstract

Physicochemical evaluation of polyethylene oxide (PEO) polymers with various molecular weights was performed at molecular (polymeric dispersion) and bulk level (powders, polymeric films, and tablets) with the aim of specifying polymer critical material attributes with the main contribution to drug release from prolonged-release tablets (PRTs). For this purpose, grades of PEO with low, medium, and high viscosity were used for formulating PRTs with a good soluble drug substance (dose solubility volume 15?ml). The results revealed a good correlation (r²=0.88) between in?vivo data (pharmacokinetic parameters: C_max and AUC) and the elastic property of PEO films determined with the nanoindentation method, demonstrating that film level can also be used for the in?vivo prediction of drug dissolution. The study confirmed that polymer molecular weight and its viscosity are the most important critical material attributes affecting drug dissolution (in?vitro) and in?vivo bioavailability (e.g. C_max and AUC). Our research revealed that the nanoindentation technique can distinguish well between various types of polymers, classifying PEO as the most ductile and polyvinyl alcohol as the most brittle. Finally, our study provides an approach for the determination of exact physical attributes of PEO as a critical material attribute from clinically relevant data, and it therefore fulfills the basic principles of product development by Quality by Design.     

Thresholds of optical limiting in solutions of nanoscale compounds of zinc phthalocyanine with galactopyranosyl radicals

The optical limiting (OL) of nanosecond laser pulses in solutions of newly synthesized dyes in dimethyl sulfoxide (DMSO) has been investigated. These dyes are compounds of zinc phthalocyanine (ZnPc) with D-galactopyranosyl radicals (Gal) located in the peripheral (p-GalZnPc) and nonperipheral (n-GalZnPc) positions with respect to the ZnPc macrocycle. Experiments have been performed using laser radiation with a wavelength of 532 nm, at which the optical absorbance of solutions of ZnPc, p-GalZnPc and n-GalZnPc dyes is four orders of magnitude lower than the absorbance in the peaks at wavelengths of 671, 680, and 701 nm, respectively. It is established that solutions of p-GalZnPc and n-GalZnPc in DMSO have a much lower OL threshold in comparison with ZnPc solution; the nonlinearity of p-GalZnPc solutions exceeds that of n-GalZnPc solutions. OL thresholds for the dyes under study in a wide concentration range are determined.     

An investigation into the capability of unconventional amount of aluminum and nano-alumina to alter the mechanical response of magnesium

In the present study, magnesium aluminum alloys with aluminum content exceeding conventional alloying limit (Mg–10Al, Mg–15Al, and Mg–20Al) and the composite of Mg–10Al alloy with 1.5 volume percentage of nano-alumina particulates are created using the technique of disintegrated melt deposition. Significant improvements in microstructure and mechanical properties compared with pure magnesium are obtained. Intermetallic phase Mg₁₇Al₁₂ was detected in all the materials. The increase in amount of aluminum in magnesium led to a reduction in coefficient of thermal expansion and a marginal increase in porosity. Yield strength, ultimate tensile strength, and hardness increased significantly with an increasing amount of aluminum. The 0.2% yield strength increased from 140 to 394 MPa (181%) in the case of Mg–20Al. Ductility reduced with progressive addition of aluminum. However, the addition of both Al and nano-alumina particulates significantly increased not only strengths, but also ductility of pure Mg. The overall tensile properties assessed in terms of work of fracture increased by almost 143% in the case of composite sample. An attempt is made in this study to correlate the tensile response of alloys and composite with their microstructural characteristics.     

Ionic control of the rupture of fetal membranes

Preterm premature rupture of the chorioamniotic membrane frequently leads to preterm birth and perinatal mortality. To ascertain whether the rupture of these membranes is influenced by variations in environmental pH and sodium concentration, we punctured 180 specimens from 9 membranes that were equilibrated in solutions of different pH, and 196 specimens from 10 membranes that were equilibrated in solutions with different sodium concentrations. Whole-membrane mechanical characteristics—strength, stiffness, toughness and ductility—were measured. These characteristics were defined based on a variant of the weakest-link theory: from a pool of three to five specimens, the specimen that had the lowest values of strength and concomitant values of stiffness, toughness, and ductility represents the mechanical characteristics of the entire membrane section. Strength-related mechanical characteristics—strength, stiffness and toughness—correlated negatively with pH (p<0.001, p<0.001, and p<0.02, respectively), while ductility did not correlate significantly with pH. Membrane hydration and thickness correlated positively with pH (p<0.001). The greatest increase in hydration accompanied by the greatest drop in strength, stiffness and toughness was observed between pH values of 3.68 and 5.58, suggesting that insufficient quantities of vaginal H⁺ could cause—as well as mark—premature rupture of the chorioamniotic membrane. No whole—membrane mechanical characteristics correlated significantly with changes in sodium concentration. Membrane hydration and thickness had slight positive correlations with sodium concentration (p<0.05). Changes solely in the sodium concentration of the amniotic fluid during normal pregnancy are not sufficient to facilitate rupture at term.     

Specific features of the interaction of alloys of the didymium-iron-boron system with hydrogen

We study the interaction of alloys of the Dd-Fe-B system [M-82, M-83, M-84, and M-85 alloys with a mass content of 33–40% didymium, up to 0.5% aluminum, and 1–1.25% boron (the rest is iron)] with hydrogen using volumetric, X-ray phase, and differential thermal analysis. If the initial hydrogen pressure is 1.0 MPa, hydrides with 0.4–0.6 mass % of hydrogen are formed. The saturation of these alloys with hydrogen is accompanied by an increase in the spacing a of an elementary cell by 1.2–1.4% and in c by 0.8–1.1% (the general increase in volume is 3.2–3.9%). If the initial pressure is 0.15–0.2 MPa, the time of complete saturation with hydrogen is 15–20 min for most alloys. At 973–1033 K, the alloys under study in hydrogen disproportionate into DdHx didymium hydride (a = 0.5449 – 0.5458 nm), -iron (a = 0.2864 – 0.2866 nm), and Fe2 B iron boride (a = 0.5112 – 0.5117 nm, c = 0.4228 nm). An increase in the initial hydrogen pressure from 0.1 to 5.0 MPa is accompanied by a decrease in the disproportionation temperature to 930 K.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 2, pp. 105–112, March–April, 2004.     

Simulation of Non-Isothermal Turbulent Flows Through Circular Rings of Steel

This article is intended to examine the fluid flow patterns and heat transfer in a rectangular channel embedded with three semi-circular cylinders comprised of steel at the boundaries. Such an organization is used to generate the heat exchangers with tube and shell because of the production of more turbulence due to zigzag path which is in favor of rapid heat transformation. Because of little maintenance, the heat exchanger of such type is extensively used. Here, we generate simulation of flow and heat transfer using non-isothermal flow interface in the Comsol multiphysics 5.4 which executes the Reynolds averaged Navier stokes equation (RANS) model of the turbulent flow together with heat equation. Simulation is tested with Prandtl number (Pr = 0.7) with inlet velocity magnitude in the range from 1 to 2 m/sec which generates the Reynolds number in the range of 2.2 × 10⁵ to 4.4 × 10⁵ with turbulence kinetic energy and the dissipation rate in ranges (3.75 × 10⁻³ to 1.5 × 10⁻²) and (3.73 × 10⁻³−3 × 10⁻²) respectively. Two correlations available in the literature are used in order to check validity. The results are displayed through streamlines, surface plots, contour plots, isothermal lines, and graphs. It is concluded that by retaining such an arrangement a quick distribution of the temperature over the domain can be seen and also the velocity magnitude is increasing from 333.15% to a maximum of 514%. The temperature at the middle shows the consistency in value but declines immediately at the end. This process becomes faster with the decrease in inlet velocity magnitude.     

Enhancement of dielectric and electrical properties of NaNbO3-modified BiFeO3

Solid solutions of BiFeO₃ (BFO) and NaNbO₃ [i.e., (Bi_1?xNa_x) (Fe_1?xNb_x)O₃] for x = 0.1, 0.2, 0.3 were prepared by a mixed-oxide method. X-ray diffraction analysis confirms the formation of a single-phase system within a certain limit of x, and indicates that with increase in concentration of NaNbO₃ there is structural transformation of BFO from the rhombohedral to the tetragonal phase. The dielectric constant and loss-tangent of samples increase with rise in temperature. It is found that with increase of concentration of NaNbO₃ in the solid solution, tangent loss of BFO is greatly reduced that can be useful for some industrial applications. The appearance of hysteresis loops of the samples at room temperature confirms the ferroelectric properties of the materials. As the electrical conductivity of the above system increases with rise in temperature, it follows the Arrhenius relation. The frequency and temperature dependence of conductivity of the above system obeys Joncher’s universal power law. Some voltage is induced with the application of magnetic field confirming the existence of multiferroics properties in the materials. Leakage current reduces with increase in content of NaNbO₃ in the solid-solutions.     

Effectiveness of the use of steel fibres on the torsional behaviour of flanged concrete beams

The behaviour under torsion of reinforced concrete beams with steel fibres as mass reinforcement is experimentally investigated. Short hooked-ended steel fibres with aspect ratio l_f/d_f = 37.5 are used. Test results of 35 beams with rectangular, L-shaped and T-shaped cross-sections tested in pure torsion are presented and discussed. Various configurations of conventional and fibre steel reinforcement are examined. The experimental program includes (i) plain concrete beams (control specimens), (ii) specimens with longitudinal reinforcing bars and (iii) specimens with bars and stirrups. All cases are examined with 0%, 1% and 3% steel fibre volume fractions. The use of steel fibres as the only shear torsional reinforcement is also reported herein, in an attempt to examine the effectiveness of fibres as a potential replacement of stirrups. Test results indicated that fibrous concrete beams exhibited improved overall torsional performance with respect to the corresponding non-fibrous control beams. The addition of steel fibres was essential to the tested beams without or with inadequate conventional steel reinforcement. Fibres prevented the sudden brittle failure of both rectangular and non-rectangular beams and proved to be under some circumstances adequate to provide for enhanced torsional moment capacities, even in the case of full replacement of stirrups with steel fibres.     

Preparation of high-density small grain size compacts of lead tin telluride

High-density compacts of lead tin telluride with grain sizes,L, in the range 25<L<60 µm, 10<L<25 µm, 5<L<10 µm andL<5 µm and with good mechanical properties have been prepared using a two-stage pressing technique. Preliminary measurements of the thermoelectric transport properties of cold-compacted and hot-pressed material are reported. The lattice thermal conductivity decreases with a reduction in grain size. In the cold-compacted material this reduction more than offsets the accompanying reduction in the electrical power factor and results in a significant improvement in the thermoelectric figure of merit.     

Effect of O-acylmenthol and salt formation on the skin permeation of diclofenac acid

Purpose: To enhance the transdermal delivery of diclofenac acid (DA) by using O-acylmenthol as a penetration enhancer and complexing with amines, or by a combination of the two methods. Methods: The skin permeability of diclofenac was tested in vitro across rat skin with each of the evaluated permeants in a saturated isopropyl myristate (IPM) donor solution. Results: A 4.5-fold increase in the flux of diclofenac was observed by ion-pair formation with diethylamine; however, the cations with hydroxyl groups had negative effects on the transdermal delivery of diclofenac. 2-isopropyl-5-methylcyclohexyl 2-hydroxypanoate and 2-isopropyl-5-methylcyclohexyl heptanoate produced significant increase in the permeation of diclofenac potassium (D-K); however, both of them were ineffective for the other diclofenac salts, including diclofenac diethylamine (D-DETA), diclofenac ethanolamine (D-EA), diclofenac diethanolamine (D-DEA), diclofenac triethanolamine, and diclofenac N-(hydroxylethyl) piperidine. 2-isopropyl-5-methylcyclohexyl tetradecanoate was effective on the penetration of D-K, D-DETA, D-EA, and D-DEA. Also, it is exciting to note that the combined use of diethylamine with 2-isopropyl-5-methylcyclohexyl tetradecanoate produced a 9.74-fold increase in accumulation amount of diclofenac compared with DA in IPM. Conclusions: The use of ion pair in combination with O-acylmenthol is necessary to further increase the diclofenac flux to provide better compliance for the patients undergoing clinical therapy.     

Adjuvant properties of a biocompatible thermo-responsive polymer of N-isopropylacrylamide in autoimmunity and arthritis

To evaluate the thermo-responsive poly(N-isopropylacrylamide) (PNiPAAm) polymer as an adjuvant, we synthesized PNiPAAm through free radical polymerization and characterized it both in vitro and in vivo. The polymer when mixed with collagen type II (CII) induced antigen-specific autoimmunity and arthritis. Mice immunized with PNiPAAm–CII developed significant levels of CII-specific IgG response comprising major IgG subclasses. Antigen-specific cellular recall response was also enhanced in these mice, while negligible level of IFN-γ was detected in splenocyte cultures, in vitro. PNiPAAm–CII-immunized arthritic mouse paws showed massive infiltration of immune cells and extensive damage to cartilage and bone. As determined by immunostaining, most of the CII protein retained its native configuration after injecting it with PNiPAAm in naive mice. Physical adsorption of CII and the high-molecular-weight form of moderately hydrophobic PNiPAAm induced a significant anti-CII antibody response. Similar to CII, mice immunized with PNiPAAm and ovalbumin (PNiPAAm–Ova) induced significant anti-ovalbumin antibody response. Comparable levels of serum IFN-γ, IL-1β and IL-17 were observed in ovalbumin-immunized mice with complete Freund, incomplete Freund (CFA and IFA) or PNiPAAm adjuvants. However, serum IL-4 levels were significantly higher in PNiPAAm–Ova and CFA–Ova groups compared with the IFA–Ova group. Thus, we show for the first time, biocompatible and biodegradable thermo-responsive PNiPAAm can be used as an adjuvant in several immunological applications as well as in better understanding of the autoimmune responses against self-proteins.     

Special features of heat transfer under conditions of heat protection of high-temperature firing walls of components of modern power-generating units by way of tangential injection

In order to more precisely define the characteristics of heat transfer under conditions of protection of firing wall by means of tangential injection in the case of its high temperature (in particular, higher-thanadiabatic temperature) and to assess the effect of degree of turbulence of the incoming gas flow on heat transfer, a numerical investigation is performed under conditions of parameters typical of combustors of gas-turbine plants (GTP) with high parameters of the working medium. In so doing, the heat flux distribution, the profiles of turbulence intensity, the distribution of turbulent viscosity in the injection zone region under study, and other characteristics are determined. The low-Reynolds k-ε model with wall functions and a new model of turbulent viscosity without wall functions are employed. It is found that a maximum of turbulent viscosity takes place behind the exit section of the injection slit with a shift to the main flow under conditions of tangential injection on an isothermal surface with a temperature much in excess of injection temperature (in a more general case, T _w > T _ad). This causes impairment of heat protection by injection, i.e., an increase in heat fluxes in the computational domain compared to heat fluxes calculated using integral methods.     

Overview of the first AGILE catalog of high-confidence gamma-ray sources

AGILE is an Italian Space Agency mission launched in April 2007, devoted to γ-ray observations in the 30 MeV–50 GeV energy range, with simultaneous X-ray imaging capability in the 18–60 keV band. During its first year in orbit AGILE surveyed the γ-ray sky and detected many galactic and extragalactic sources. The first catalog of high-confidence γ-ray sources detected by AGILE during observations performed from July 9, 2007 to June 30, 2008, for energies greater than 100 MeV was recently published [1], and preliminary versions of the catalog were published on the AGILE Data Center webpage to allow AGILE Cycle-2 guest observers to benefit of the Catalog in the preparation of their proposals. We present here the main results of the final catalog, that includes 47 high-confidence sources, 21 of which are associated with confirmed or candidate pulsars, 13 with Blazars (7 FSRQ, 4 BL Lacs, 2 unknown type), 2 with HMXRBs, 2 with SNRs, 1 with a colliding-wind binary system, 8 with unidentified sources.     

Oxidation of Hydrazine during Evaporation of Nitric Acid Solutions

The processes of hydrazine oxidation with nitric acid on heating and at continuous evaporation were compared. The latter process was performed in a titanium vessel equipped with an external heating chamber and three removable sieve overflow plates. At evaporation, the yield of HN₃ and primarily NH₄NO₃ decreases with increase in the acidity of the bottoms and decrease in the concentration and feeding rate of hydrazine; the presence of plates in the evaporator and their spraying with the reflux decrease the yields of HN₃ and NH₄NO₃ to a still greater extent.     

The influence of different porogens with halogen substituents on the pore structure of polydivinylbenzene beads

Polydivinylbenzene (PDVB) beads with high surface area and porosity were prepared via suspension polymerization in the presence of solvents with halogen substituents as porogens. The porogens employed in the present work were p-dichlorobenzene, chlorobenzene, bromobenzene, benzyl chloride, and tetrachloroethane. The porogens were used in a 1/1 volume ratio with divinylbenzene (DVB). As predicted from previous knowledge of porogen with halogen substituents possessing strong capacity to construct porosity, the surface area of PDVB beads prepared with the above porogens reached 647.1–744.6 m² g⁻¹, which mainly depended on the difference of solubility parameter of the porogens and PDVB networks. The smaller the difference, the larger the surface area of PDVB beads was. Overall, research results of the present study indicated that in comparison with other types of porogen, solvent with halogen substituent could generate larger surface area and construct higher porosity in PDVB beads.