Effect of γ-irradiation on the melting behaviour of poly(trioxane)

Poly(trioxane) obtained by radiation-induced polymerization in the solid state, was subjected to 1 Mrad -rays and the change in melting behaviour and the thermogravimetric curve examined. Little structural change in the X-ray scattering patterns was observed. The heating curve of as-polymerized poly(trioxane) exhibited a double endothermic peak under a high polymer yield, but the endotherm on the higher temperature side disappeared at a heating rate lower than 8° C min^–1. On irradiating over 25 krad, or rolling, the endotherm was again absent even at heating rates above 16° C min^–1. The endotherm at higher temperatures is interpreted as being due to superheating caused by entropy restriction. The irradiation or rolling causes chain scission at a selective point in the crystallites. These scissions reduce the superheatability of a poly(trioxane) with a high polymer yield. The lamellar-type poly(oxymethylene) crystal was also studied for comparison.     

Investigation on the martensitic transformation in γ-Fe(n) nanoparticles

γ-Fe(5.90–10.9 at.% N) nanoparticles ranging in diameters from 30 to 100 nm were prepared by laser-induced pyrolysis of mixtures of Fe(CO)₅ and NH₃. During the quenching from high temperature to room temperature and even down to 4.2 K, no martensitic transformation occurred in these particles. Based on the effects of surface tension and refinement of grain size on the yield strength of the nanoparticles, the dependencies of nucleation driving force and the martensite-start temperature on the particle size was revealed, from a viewpoint of thermodynamics of martensitic transformation in the γ-Fe(N) nanoparticles. It is suggested that the yield strength increment due to the surface tension and to the very fine crystallite grains is probably the predominant aspect responsible for inhibiting the nucleation of martensite and drastic decrease of the martensite-start temperature of the nanoparticles. High pressure of 0.5–4.0 GPa were adopted to induce the martensitic transition of the γ-Fe nanoparticles. It is found that the extent of martensitic transformation increased with the increasing pressures, most individual γ-Fe particles were partially transformed to martensite after pressurization.     

Effect of γ-irradiation on the physical and mechanical properties of chitosan powder

In this study, locally produced chitosan powder was irradiated with pre-determined doses of γ-ray (Co-60) of 10 kGy, 25 kGy, 50 kGy and 100 kGy respectively. The properties of both chitosan powder and the chitosan film were examined and compared with unradiated chitosan. Physical characteristic of the irradiated powder and film was studied using stereo microscope. It was observed that the γ-ray induces a noticeable colour tone intensity change to the chitosan. Further investigation using Fourier Transformed Infrared Spectroscopy (FT-IR) analysis has confirmed that the chain scission reaction was occurred as a result of γ-ray exposure through the depolymerization mechanisms. Interestingly, the degree of deacetylation (DD) of chitosan measured using FT-IR showed a negligible effect due to the exposure of γ-ray radiation. Further investigation on the viscosity average molecular weight (M_v) showed a reduction of M_v from 577 kD of pure chitosan to 458 kD, 242 kD, 159 kD and 106 kD for 10 kGy, 25 kGy, 50 kGy and 100 kGy of γ-radiated chitosan respectively. In addition, the tensile strength and elongation at break showed a similar decreasing trend with increasing dosage of γ-ray.     

Effect of addition of tin on the microstructure and machinability of α-brass

This study was aimed at developing lead-free brass alloys with the goal of substituting lead element with tin. For this purpose, lead-free alloys with tin were developed and the microstructure, hardness and machining behaviour of the Cu–30%Zn alloy was compared with Cu–30%Zn–x%Sn (x?= 1.2, 3.2, 5.4, 8, 11.4, 13.9, 17.4). The results showed that the addition of Sn to single-α phase brass led to the formation of duplex (α?+?β′) brass and then the formation of (β′?+?? ) brass both with increased hardness. In addition, the addition of Sn to Cu–30%Zn alloy led to the decrement of equivalent machining forces (F_m), surface roughness and also the promotion of chip fragmentation due to the formation of the β′ phase, which is an improvement in machinability.     

Effect of cooling rate on phosphorus segregation behavior and the corresponding precipitation of γ″ and γ′ phases in IN718 alloy

Effect of segregation behaviors of P at different cooling rates on the precipitation of γ″ and γ′ phases and the corresponding strength are investigated. The precipitation of γ″ and γ′ phases during cooling is sensitive to P concentration. With increasing the concentration of P, the amount of γ″ and γ′ particles increases after air cooling. With decreasing the cooling rate, the accelerating effect of P on the precipitation of γ″ and γ′ phases decreased first and then increased, which demonstrates the concentration of P dissolved in the grain interior decreases first and then increases. The different effects of P on γ″ and γ′ phases with different cooling rates were analyzed by the kinetic characteristic of nonequilibrium grain-boundary segregation. The characteristic of nonequilibrium grain-boundary segregation of P in superalloy is further confirmed, and the phenomenon caused by critical cooling rate is captured.     

Effect of α-SiC on the microstructure and toughening of hot-pressed SiC-AlN solid solutions

The Effect of -SiC on the microstructure and toughening ofSiC-AlN solid solutions from powder mixtures of -SiC and AlNby hot-pressing were studied in the 1870 to 2030°Ctemperature range. The reaction of AlN and -SiC(3C) powderscausing transformation to the 2H(wurtzite) structure appeared todepend on hot-pressing temperatures and an additive of -SiC.For the composition of 49 wt% AlN/49 wt% SiC with 2 wt%-SiC and 47.5 wt% AlN/47.5 wt% SiC with 5 wt%-SiC at 2030°C for 1 h, the complete solid solutionswith a single phase of 2H could be obtained. The appreciable amountof -SiC could develop the columnar inter-grains of 4H phaseand the stable 2H phase with the relatively uniform composition andgrain size distributions. The effect of -SiC on the phasespresent and compositional microstructures with columnar inter-grainswas investigated using X-ray diffraction, scanning electronmicroscopy and transmission electron microscopy. The fracturetoughness and Vickers hardness of the hot-pressed solid solutionswere examined by the indentation-fracture-test method.     

Effect of composition on the dielectric properties and thermal conductivity of α-SiAlON ceramics

Journal of Materials Science: Materials in Electronics - In this study, a series of dense Ym/3Si12-(m+n)Alm+nOnN16-n (m?=?1.1–1.5, n?=?1.0) ceramics were prepared by...     

Effect of Mo on the thermal stability of γ′ precipitate in Inconel 740 alloy

The effect of Mo on gamma prime (γ′) coarsening kinetics of Ni–25Cr–20Co–1.8Ti–0.9Al–2Nb–0.03C–xMo (x = 0.5, 3, 6 wt.%) alloys was investigated with respect to the activation energy for γ′ precipitate coarsening. The coarsening rates were measured at temperatures of 760 °C, 780 °C, and 810 °C up to 500 h. Coarsening rate decreased with increasing Mo, and the activation energies for coarsening were determined to be 245 kJ/mol, 261 kJ/mol, and 278 kJ/mol for 0.5 wt.% Mo, 3 wt.% Mo, and 6 wt.% Mo, respectively.     

Influence of the temperature and water adsorption on the cation location in NaY zeolites

The structures of hydrated and dehydrated NaY zeolites were determined as a function of the temperature, using X-ray powder diffraction methods. No significant difference was observed between the dehydrated structures, determined at 323 K and at 723 K. In the presence of an equilibrium water pressure of 1870 Pa, an increased site I' occupancy is observed, which at 723 K, is higher than in the absence of water molecules. Neither the site I, nor the site II populations reach the level of the occupancies of the dehydrated state. In neither case could all cations be located at the sites I, I', and II.     

Mechanism on the Effect of Al upon the γ→ε Martensite Transformation in the Fe-Mn Alloys

The structure of the solid solution treated and deformed Fe-25Mn-(0-3.11)Al-0.15C alloys was examined by means of metallograph and X-ray diffraction, which has confirmed that Al restrains the γ→ε transformation in the Fe-Mn alloys. The mechanism on the restraining effect of Al has been discussed on the basis of the efFect of Al upon the stacking fault energy in the Fe-Mn alloys.Aluminium increases thermodynamically the stability of the Fe-Mn austenite and the driving force limit necessitated to be overcome for the γ→ε transformation, because the thermodynamicalcalculation indicates that Al increases the stacking fault energy in the Fe-Mn alloys at 300 K.Al will decrease the number and the size for the ε-martensite nucleus according to the stacking fault mechanism of the ε-martensite nucleation     

Effect of high pressure on diffusion reactions and phase diagram in Al–Mg system

Abstract

Diffusion reactions have been investigated under high pressures of up to 3·3 GPa in the Al–Mg system. The β-, γ-, and ε- phases appeared in the diffusion zone under vacuum, but only the γ- phase was found in the diffusion zone under high pressure. The occurrence of this phase in the diffusion zone is discussed using computed phase diagrams of the Al–Mg system under high pressure.

MST/402     

Effect of γ-irradiation on the structure of poly(ethyl acrylate-co-hydroxyethyl methacrylate) copolymer networks for biomedical applications

The effect of the sterilization process by γ-irradiation on the structure of poly(ethyl acrylate-co-hydroxyethyl methacrylate) copolymer networks, P(EA-co-HEMA) is studied for a broad dose range (7, 15, 25 and 50 kGy) and copolymer composition interval (0, 0.3, 0.5, 0.7 and 1 weight fraction of HEMA in the copolymer). γ-irradiation promotes chain scission in PHEMA homopolymer but induces new crosslinking points in PEA homopolymer. Both effects are present in the copolymers, with a net result that depends on composition. For copolymers with high HEMA fractions chain scission predominates, while, as the amount of EA in the copolymer increases, the situation changes and the net effect turns out to be an increase in the number of elastically active chains. Further, γ-irradiation strengthens the γ relaxation in PHEMA homopolymer, what suggest that the number of interchain hydrogen bonds decreases. FTIR spectroscopy reveals no oxidation as a consequence of the sterilization process.     

Effect of CuO on the sintering and dielectric characteristics of (Ba1−x Sr x ) (Ti0.9Zr0.1)O3 ceramics

In order to lower the temperature required to density (Ba_1–x Sr _x ) (Ti_0.9Zr_0.1) O₃ (BSTZ-series) and to avoid the formation of a low dielectric constant phase, copper oxide is added as liquidphase promotor after BSTZ-series are calcined. Thea-axis lattice constant at room temperature elongates with both increasing amount of CuO added and higher sintering temperature, while thec-axis lattice constant elongates only slightly under the same condition. The dielectric constant increases with sintering temperature. However, for different amounts of CuO added, the dielectric constant increases with increasing amount of CuO at lower sintering temperatures (below 1100°C). When a higher sintering temperature is used (above 1200°C), the dielectric constant reaches a maximum at 1 wt % CuO added, and decreases slightly on further addition of CuO.     

Speciation, stability, and reactions of Np(III–VII) in aqueous solutions

Published data on the structure of Np ions in acid and alkali solutions, on hydrolysis of Np ions and their complexation with anions and cations, on their redox reactions with water and with each other (disproportionation, reproportionation), and on the effect of anions on this process are analyzed. Possible directions of research in chemistry of Np ions are outlined.     

Effect of O2, H2O2, and HNO2 on the stability of Np(III–VII) in aqueous solutions

Published data on reactions of Np ions with O₂, H₂O₂, HNO₂, and HNO₃ in solutions of various compositions in a wide pH range are considered. O₂ oxidizes Np(III) in acid solution and Np(IV) and Np(V) in alkaline solutions. H₂O₂ exhibits dual behavior. In weakly acidic solutions, it converts Np(III) and (IV) to Np(V), in 0.75?C1 M NaHCO₃ it oxidizes Np(V) to Np(VI), whereas in dilute HClO₄ and HNO₃ and in carbonate and alkali solutions it reduces Np(VI), and in alkali solutions it reduces Np(VII). The first step of reduction in most cases is the formation of the Np(VI) peroxide complex, and the next step is the intramolecular charge transfer. In concentrated HNO₃ solutions, H₂O₂ converts Np(V) to Np(IV) and Np(VI) and then reduces Np(VI). Some radiation-, photo-, and sonochemical reactions occur via formation of excimers, i.e., of dimers arising from excited and unexcited Np ions. The excimer decomposes into two ions with higher and lower oxidation states. In reduction reactions, the excimer eliminates H₂O₂ (in addition to the H₂O₂ arising as primary product of water radiolysis). In HNO₃ solutions, oxidation of Np ions occurs only in the presence of HNO₂ arising as reaction product or upon radiolysis, photolysis, or sonolysis. The active species are NO ₂ ^? , NO₂, and NO⁺ present in equilibrium with HNO₂.     

Effect of Mineral Oil on the Mechanical Properties and Fractographs of Fe_3(Al,Cr,Zr) Intermetallic Alloy

The effect of mineral oil on the mechanical properties and fractographs of Fe3(Al,Cr,Zr) in termetallic alloy has been investigated. The results show that the tensile ductility of the Fe3(Al,Cr,Zr) alloy tested in oil is comparable with the results obtained in oxygen and is in sensitive to strain rate. The fracture mode of the Fe3(Al,Cr,Zr) alloy treated at 700℃/1.5 h and tested in oil, is cleavage and with dimples in some areas.