An analysis of concentration profiles for fluxes,diffusion depths,and zero-flux planes in multicomponent diffusion

Concentration profiles developed during isothermal, multicomponent diffusion for a single-phase, solid-solid diffusion couple are expressed on the basis of a relative concentration variable for each component and analyzed for the determination of interdiffusion fluxes. The individual concentration profiles intersect at a common cross-over composition where the relative concentrations of all components are identical. New relations are developed for describing internal consistency among the concentration profiles of the various components. A link is made between the cross-over composition and the depths of the diffusion zone on either side of the Matano plane for a diffusion couple. The cross-over composition is interpreted as the average relative concentration of each component over the diffusion zone. The identification of a zero-flux plane from concentration profiles is also described. The analysis offers several advantages in presenting as well as checking the self-consistency of results as illustrated with a single phase Cu-Ni-Zn diffusion couple annealed at 775 °C.     

Interdiffusion between U-Zr fuelvs selected cladding steels

To better understand fuel-cladding compatibility issues as affected by diffusion processes in Argonne National Laboratory’s Integral Fast Reactors, interdiffusion studies were carried out with solid-solid diffusion couples assembled with a U-23 at. pct Zr alloy and cladding steels, such as 316, D9, and HT9. All diffusion couples were annealed at 700 °C and examined metallographically and by scanning electron microscopy-energy-dispersive spectroscopy analysis for diffusion structure development. The development of diffusion layers in the couples for various cladding steels is compared and discussed in light of the relative diffusion behavior of the individual elements, intermetallic formation, and experimental diffusion paths. In the context of fuel-cladding compatibility, HT9 is considered superior to 316 and D9, as it develops the smallest diffusion zone with the fewest number of phases. Formerly Graduate Student, School of Materials Engineering, Purdue University     

Diffusion-limited sulfidation of wustite

The sulfidation of wustite in H₂S−H₂O−H₂−Ar atmospheres has been studied at temperatures of 700, 800, and 900°C with thermogravimetric techniques. Polycrystalline wustite wafers were equilibrated in a flowing H₂O−H₂−Ar gas stream and then sulfidizedin situ. During an initial transient stage a protective layer of FeS formed on the sample, and an intermediate layer of Fe₃O₄ formed between the FeO and FeS layers. Subsequently, the reaction followed a parabolic rate law. The parabolic rate constant varied from 0.22×10⁻² mg² cm⁻⁴ min⁻¹ at 700°C to 6.5×10⁻² mg² cm⁻⁴ min⁻¹ at 900°C. The reaction rate was limited by the diffusion of iron through the intermediate Fe₃O₄ layer which grew concurrently with the FeS layer and at the expense of the FeO core. After the FeO core was completely converted to Fe₃O₄, the process entered a passive stage during which no further mass changes could be detected. SCOTT McCORMICK, formerly Graduate Student, Purdue University is currently Assistant Professor, Department of Metallurgical and Materials Engineering, Illinois Institute of Technology, Chicago, Illinois 60616.     

Interdiffusion structures and paths for multiphase Fe-Ni-Al diffusion couples at 1000 °C

Diffusion studies were carried out in the Fe-Ni-Al system at 1000 °C using solid-solid diffusion couples assembled with β (B₂), γ (fcc) single phase, and (β + γ) two-phase alloys. The diffusion couples were encapsulated in quartz tubes under vacuum and annealed for 48 hours. The diffusion structures were examined by optical and scanning electron microscopy. For all β vs (β + γ) couples, growth of the β phase was observed as the (β + γ) two-phase region recessed with the dissolution of the γ phase. For multiphase couples assembled with two (β + γ) terminal alloys, demixing of the (β + γ) two-phase alloys occurred with the formation of single-phase β and γ layers. The development of an interphase boundary between the (β + β′) two-phase region and the γ phase is reported for the first time for a Fe-Ni-Al diffusion couple assembled with single-phase, β, and γ terminal alloys. Various diffusion structures for the couples were related to their diffusion paths constructed from concentration profiles determined by electron probe microanalysis. Interdiffusion fluxes of individual components were determined directly from the experimental concentration profiles and examined in light of diffusional interactions and the development of zero-flux planes and flux reversals. In addition, the boundaries for the miscibility gap between the ordered β and disordered β′ phases of the Fe-Ni-Al system at 1000 °C were determined with the aid of diffusion couples that developed β and β′ phases in the diffusion zone.     

Synthesis and characterization of pH/temperature-sensitive block copolymers via atom transfer radical polymerization

In order to prepare well-defined pH-sensitive block copolymers with a narrow molecular weight distribution (MWD), we synthesized a pH-sensitive block copolymer via atom transfer radical polymerization (ATRP) of sulfamethazine methacrylate monomer (SM) and amphiphilic diblock copolymers by the ring-opening polymerization of d,l-lactide/?-caprolactone (LA/CL), and their sol-gel phase transition was investigated. SM, which is a derivative of sulfonamide, was used as a pH responsive moiety, while PCLA-PEG-PCLA was used as a biodegradable, as well as a temperature sensitive one, amphiphilic triblock copolymer. The pentablock copolymer, OSM-PCLA-PEG-PCLA-OSM, was synthesized using Br-PCLA-PEG-PCLA-Br as an ATRP macroinitiator. The number average molecular weights of SM were controlled by adjusting the monomer/initiator feed ratio. The macroinitiator was synthesized by the coupling of 2-bromoisobutyryl bromide with PCLA-PEG-PCLA in the presence of triethyl amine catalyst in dichloromethane. The resultant block copolymer shows a narrow polydispersity. The block copolymer solution shows a sol-gel transition in response to a slight pH change in the range of 7.2-8.0. Gel permeation chromatography (GPC) and NMR were used for the characterization of the polymers that were synthesized.     

Diffusion paths and structures in multiphase Cu−Ni−Zn couples at 775°C

Multiphase diffusion was investigated in the Cu−Ni−Zn system at 775°C for the development of diffusion structures involving two interfaces. Selected series of diffusion couples characterized by a common γ (cubic) terminal alloy joined to a set of α (fcc) alloys developed an intermediate β (bcc) phase with two interfaces, α/β and β/γ. The α/β interface showed transitions from planar to nonplanar and back to planar morphology, as the copper concentration of the α terminal alloy was decreased from 100 to about 30 at. pct. Planar β/γ interfaces were observed for all but two of the couples. The compositions on either side of planar α/β interfaces were consistent with those based on equilibrium tielines, while the compositions at nonplanar α/β interfaces differed from those of equilibrium. Selected series of couples assembled with γ and β alloys were also investigated for the development of interface instability at the β/γ interface. The diffusion paths of γ/β couples were consistent with those of γ/α couples.     

Efficacy of an anti-tobacco community education program in India

In a study on 'Assessment of Efficacy of an Anti-Tobacco Community Education Program' on Kolar District of Karnataka, India, an experimental and two control areas were chosen based on comparable population, health, and socioeconomic parameters. The two main objectives were to prevent individuals from taking up the tobacco habit among those who currently did not smoke or chew tobacco, and to stop the tobacco habit in those who did smoke or chew tobacco. A baseline tobacco-habit survey of the population was followed by anti-tobacco education of the community in the experimental area only. Two years later, a repeat survey of the population was conducted, followed by a final survey after a further three years. Methods of health education of the community included screening of films, exhibits, and personal contact with a display of photographs of the harmful effects of tobacco. The results were evaluated through changes in prevalence rates, quitters' rates, and initiation rate. The final survey showed that in the experimental area, the decline in the prevalence rate in the combined sample compared with the baseline rates was 10.2 percent in males and 16.3 percent in females, with a corresponding quitter's rate of 26.5 percent in males and 36.7 percent in females. Among men, a higher proportion (30.2 percent) had given up chewing compared with smoking (20.4 percent).     

Low Cycle Fatigue Evaluation of NiTi SESMA Thin Wires

This paper presents experimental studies on low cycle fatigue (LCF) life of super-elastic shape memory alloy (SESMA) wires. The effect of frequency of the loading and amplitude of the strain on the fatigue life has been studied individually. Various loading frequencies have been considered to study the effect of frequency, by keeping the amplitude constant. From the experimental data, it was found that the LCF life of the SESMA reduces with increase in the frequency. The effect of amplitude on the LCF life of SESMA has also been studied, and it was found that the SESMA cycled at lower net strain has more fatigue life than the one cycled at higher net strain. Further, the plastic strain accumulation is also more in the samples tested at the higher net strain loadings. The modulus of austenite is found to be by and large independent of the frequency and amplitude of the loading. Further, martensitic unloading modulus is same for all the minimum strain amplitudes.     

Characterization of shape memory behaviour of CTBN-epoxy resin system

The temperature-responsive poly(vinyl alcohol)/ poly(N-isopropylacrylamide) hydrogel was prepared as a drug delivery carrier. The vitamin B12 release behavior of hydrogel was controlled by direct oxyfluorination. The oxyfluorination of hydrogel changed the surface characteristics to have hydrophilic functional groups. On the other hand, the hydrophobicity of hydrogel increased by fluorination treatment due to the induced hydrophobic functional groups. C-O bond and C-F bond were mainly formed by oxyfluorination and fluorination, respectively. The surface morphology showed the significant variation depending on the oxyfluorination conditions. Both swelling ratio and drug release rate were strongly dependent on the oxyfluorination conditions. The swelling of hydrogel increased further by the surface modification with oxyfluorination in a higher oxygen content to give more hydrophilic properties. The drug release from hydrogel also increased as more hydrophilic functional groups were introduced by oxyfluorination because the favorable affinity at the interface resulted in a higher swelling ratio. On the other hand, the relatively low swelling ratio and slower drug release from hydrogel were observed with more hydrophobic functional groups introduced by fluorination.