Cu surface segregation in Ni/Cu system

We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150-220 °C range as a function of time initially shows linear mass transfer. By solving Fick's equation and taking empirical diffusion coefficient, 125 ± 20 kJ/mol is obtained for activation enthalpy of effective diffusion.     

Solid state amorphization of Mg-Zn-Ca system via mechanical alloying and characterization

Magnesium based bulk metallic glasses have attracted significant attention of researchers due to better mechanical and corrosion properties when compared to their crystalline counterparts especially for biomedical applications. Scaling up the part size and production volumes of such materials through liquid metallurgy route is challenging. In this work amorphous Ca₅Mg_60+xZn_35?x (X = 0, 3 and 7) alloys have been successfully synthesized through solid state amorphization using a high energy planetary ball mill. X-ray diffraction was used to identify the crystalline phases of the powder during reaction. Evolution of amorphous phase was analysed using a parameter involving the ratio of integral area of peaks to the integral area of background (I_PB) obtained from XRD patterns. Results showed reaction time increases with decreasing Zn content in Ca₅Mg_60+xZn_35?x (X = 0, 3 and 7) alloy to obtain maximum amorphous structure with a small amount of residual crystalline phase. Prolonged milling of these powders, to eliminate residual crystalline phases, resulted in the nucleation of Mg_102.08Zn_39.6 phase. The composition dependent characteristic temperatures and thermal stabilities were studied using differential scanning calorimetry.     

Solid state phase transition in Zn3As2

Static vapour-pressure investigation of the three-phase equilibrium S($\text{α}$-Zn_$\text{3}$As_$\text{2}$)S($\text{β}$-Zn_$\text{3}$As_$\text{2}$)V is reported, which describes the $\text{α-β}$ phase transition in Zn_$\text{3}$As_$\text{2}$ at the vapour pressure of the system. Isothermal sections of the P-T-X phase transition region are presented. Temperature and composition ranges of the $\text{α-β}$ transformation are found to be within 0,01 at·% and 937–948 K. Two pressure minima are experimentally registered in the phase transition range. The $\text{α-β}$ transition is shown to be of incongruent type.     

Solid state microdosimetry in hadron therapy

A report of recent developments in silicon microdosimetry is presented. SOI based microdosemeters have shown promise as a viable alternative to traditional tissue-equivalent proportional counters. The application of these silicon microdosemeters to such radiation therapy modalities as boron neutron capture therapy (BNCT), boron neutron capture synovectomy (BNCS), proton therapy (PT), and fast neutron therapy (FNT) has been performed. Several shortcomings of the current silicon microdosemeter were identified and will be taken into account in the design of a second-generation device.     

Solid state spectroelectrochemistry of redox reactions in polypyrrole/oxide molecular heterojunctions

To understand the mechanism of bias-induced resistance switching observed in polypyrrole (PPy) based solid state junctions, in situ UV-vis absorption spectroscopy was employed to monitor oxidation states within PPy layers in solution and in PPy/metal oxide junctions. For PPy layers in acetonitrile, oxidation led primarily to cationic polaron formation, while oxidation in 0.1 M NaOH in H(2)O resulted in imine formation, caused by deprotonation of polarons. On the basis of these results in solution, spectroelectrochemistry was used to monitor bias-induced formation of polarons and imines in PPy layers incorporated into solid state carbon/PPy/Al(2)O(3)/Pt junctions. A positive bias on the carbon electrode caused PPy oxidation, with the formation of polaron and imine species strongly dependent on the surrounding environment. The spectral changes associated with polarons or imines were stable for at least several hours after the applied bias, while a negative bias reversed the absorbance changes back to the initial PPy spectrum. These results indicate that PPy can be oxidized in nominally solid state devices, and the formation of stable polarons is dependent on the tendency for deprotonation of the polaron to the imine. Since PPy conductivity depends strongly on the polaron concentration, monitoring its concentration is critical to determining resistance switching mechanisms. Furthermore, the importance of ion mobility and OH(-) generation through H(2)O reduction at the Pt contact are discussed.     

Solid state reactions in the Fe2O3-CaCO3-In2O3 system

The kinetics of solid-state reactions of powdered reactants were investigated by X-ray and by differential thermogravimetry in a magnetic field. Measurements revealed mutual diffusion of the Fe³⁺ and In³⁺ ions in the Fe₂O₃-In₂O₃ system heat treated for 3 h at 700 to 1400° C. Diffusion of indium into the Fe₂O₃ lattice caused a shift of the Curie temperature of the antiferromagnetic iron oxide towards lower temperatures. Only Caln₂O₄ was found between CaCO₃ and In₂O₃ up to 1400° C. Also, in the Fe₂O₃-CaCO₃-In₂O₃in system, the reaction started with the mutual diffusion of iron and indium and the forming of CaFe₂O₄. End-products were the magnetic -Ca₄Fe₁₄O₂₅ and CaFe₄O₇, and the non-magnetic CaFe₅O₇, depending on the In³⁺ concentration. Indium stabilized the magnetic calcium-iron oxide structures, shifting their Curie temperatures towards lower values.     

Solid state nuclear track detectors

The materials science aspects of the use of both polymeric and inorganic solids as detectors for energetic particles are reviewed. The various models proposed to explain the formation of an etchable track by a penetrating particle are discussed, as is the nature and the geometric consequences of the etching process itself. An account is given of the wide-ranging applications of solid state detectors in science and technology.     

Solid state actuators energy comparisons

Victor Giurgiutiu and Radu Pomirleanu of the Laboratory for Active Materials and Smart Structures, University of South Carolina, have co-authored a paper on ‘Energy based comparison of solid state actuators’. An abbreviated version of the study is presented here. Although this gives only US-manufactured actuator details, the data provide a valuable insight into off-the-shelf, induced strain actuators capacities and capabilities.     

Solid state transformations in Fe-Ni supercooled alloys

The effect of supercooled microstructures and composition in the solid state transformation of the Fe-Ni system was investigated utilizing transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Irrespective of the supercooling degree, Fe-Ni samples containing between 7 and 28 wt % Ni underwent a martensitic transformation above room temperature. The martensite morphology is superimposed on the sub-grain microstructure obtained by supercooling. Indications exist that alternative nucleation is activated if the samples are supercooled below the -T₀ curve. The impact of alternative nucleation on the martensitic transformation is discussed. Coherent precipitation was observed in Fe-33 wt % Ni alloys. The precipitate dimensions depend on the solidification path. The results are discussed in terms of current supercooling theories.     

Solid state reactions in the system Al2O3Nd2O3CaO: A system pertinent to radioactive waste disposal

High alumina ceramic phases are promising crystalline hosts for containment of radioactive wastes. The distribution of lanthanons in the calcia-alumina rich compositions, e.g., in CaAl₁₂O₁₉LnAl₁₁O₁₈ type solid solutions, has been explored by using Nd as a model 4f element. The remaining phase compatibilities and solid solution ranges have been examined at 1300°C.     

The steady state fracture kinetics of crack front spreading

The kinetics study is based on the energetically favourable crack propagation mechanism of double kink nucleation and its subsequent sideways spreading. The analysis was carried out on linearly elastic solids for the case when kink spreading is the rate controlling mechanism. The kink spread distribution is described by a differential equation that is identical with the mass and heat transport equations. The solutions of the differential equation represent the distribution function and the crack propagation velocity as a function of the bond breaking energy G, the work W contributed by the applied stress, and of the temperature. When WG/2 the crack velocity increases exponentially with increasing work, decreases steeply with decreasing work, and reduces to zero when WG/2. The theory represents well the behavior of ceramic materials and some metals in Region 1 and at the threshold region of stress corrosion cracking. It is of special interest for stress corrosion cracking designs that the threshold stress intensity is independent of the temperature under the conditions of the present investigation.     

Solid state behaviour and properties of plasticized cellulose acetobutyrate/phenoxy blends

Blends of commercial plasticized cellulose acetobutyrate (CAB) and the polyhydroxypropylether of bisphenol A (Phenoxy) were obtained in order to study the possibility of the plasticizer of the CAB to be distributed in the blend and to change the miscibility behaviour and the mechanical properties of the blends. During melt mixing the plasticizer of the CAB migrated to the phenoxy and changed the positions of the transitions of the blends. This change in the T_g values did not show any influence on the miscibility level. An antiplasticization process was evident, giving rise to higher modulus but poor ductilities in the blends.     

Solid state bonding of Al2O3 with Cu, Ni and Fe: characteristics and properties

A solid state bonding technique under hot pressing was used for joining alumina with thin metal sheets of Ni, Cu and Fe. The microstructure and microchemistry of the ceramic–metal interface and of the fracture interface were examined using scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), in order to identify the adhesion mechanisms and the nature of strength limiting flaws. Interaction between the selected metals and alumina can be physical or physico-chemical in nature: very low amounts of interfacial compounds were formed, depending on the processing conditions and on the presence of oxygen in the system. Fracture and toughness tests indicated that high ceramic–metal interface strengths (up to 177 MPa) were achieved under the adopted processing conditions and that strength and toughness were directly related. Moreover, an increase in hardening in the metal interlayer at a distance of 2–3 m from the interface was observed in the samples with high strength values. The mechanical behaviour was related to several factors that strongly depend on the bonding conditions: plastic deformation of the metal, metal creep, metal intrusion and diffusion into alumina, and chemical reactions at the interface. © 1998 Chapman & Hall     

Solid state amorphization reactions in Ni/Ti multilayer composites prepared by cold rolling

Solid state amorphizations in mechanically deformed Ni/Ti multilayer composites have been investigated by differential scanning calorimetry and X-ray diffraction. The growth of amorphous alloy in our Ni/Ti composites was facilitated by the large number of grain boundaries and relatively large degree of disorder induced in the metal layers by the cold rolling. The formation of different products of solid-state reaction in the Ni/Ti composites has been elucidated in terms of magnetic and enthalpy analysis. It is thought that the solid state amorphization occurs first during heating, followed by the formation of intermetallic compounds through direct solid-state reaction of elemental nickel and titanium and by the crystallization of the amorphous alloy already formed by the solid state amorphization reaction. The values of the activation energy for interdiffusion and interdiffusion coefficient for the formation of amorphous alloy in the Ni/Ti composites have also been calculated.     

Solid state thin-film lithium battery systems

Thin-film rechargeable lithium batteries, less than 15 μm thick, are being developed as micro-power sources. Batteries with long cycle lives have been constructed with a variety of electrode materials and cell configurations onto thin ceramic, metal, and Si substrates. Improvements in the properties of several well-known cathode thin-film materials have been reported, while several novel thin-film anode materials have been introduced in recent papers. All recent thin-film batteries with moderate discharge powers and cycle lives rely on the amorphous lithium phosphorus oxynitride electrolyte, known as Lipon, deposited by rf magnetron sputtering.     

Structural observations of the interface of explosion-bonded Mo/Cu system

The structure of the interface of explosion-bonded Mo/Cu system has been examined by optical and electron (TEM, AEM) microscopy. Molybdenum and copper can be directly bonded along the flat interface without a diffusion zone, but only on the copper side of the interface is a thin (about 10 m thick) bond layer, which consists of very fine subgrains with an ill-defined boundary. The microstructure in the bond layer is generated by severe dynamic deformation due to jetting and subsequent recovery with frictional heating. On the molybdenum side, originally-existing and elongated subgrains are observed just adjacent to the interface, even after bonding. These results indicate that jetting can occur only on the copper side, with a strength much lower than molybdenum because bonding must be carried out at an impact pressure as low as possible to avoid cracking of molybdenum as well as melting of copper during welding.     

Interface-dominated galvanic replacement reactions in the Zn/Cu(2+) system

Galvanic replacement (GR) reactions involving active-metal nanoparticles (NPs) as seeds have a number of distinctive features and can produce various noble-metal nanoparticles. The oxide layer on the surfaces of such active-metal seeds may make a remarkable impact on the final products. Taking the Zn/Cu(2+) system as a model, we show that the GR reaction of pure Zn seeds with Cu(2+) ions leads to Cu nanodendrites, while oxide-covered Zn seeds result in ultrafine Cu NPs. We demonstrate here that the oxide layer does not block the GR reaction but slows down its rate. We also show that the growing Cu NPs can eventually detach from their ZnO substrate because of poor adhesion and disperse in the reaction liquid very well. Our studies provide detailed information on mechanisms of the GR reaction involving active-metal seeds, and therefore may be useful for further control of the morphology and properties of products prepared via this approach.