Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

The objective of this review is to study interfacial reactions between pure Sn or Sn-rich solders, and common base metals used in Pb-free electronics production. In particular, the reasons leading to the observed interfacial reactions products and their metallurgical evolution have been analyzed. Results presented in the literature have been critically evaluated with the help of combined thermodynamic–kinetic approach based on the concept of local equilibrium and microstructural knowledge. The following conclusions have been reached: Firstly, the formations of intermetallic compounds in solid/liquid reaction couples are primarily controlled by the dissolution processes of base metals. Other factors that need be considered are the thermodynamic driving force for the formation of intermetallic compounds, their structures and concentration profiles in liquid. Secondly, annealing of solder interconnections in solid state can drastically change the microstructures formed in the solid/liquid reactions, especially if only one of the components in the solder takes part in the interfacial reactions. Thirdly, additional elements can have three major effects on the binary reactions between a base metal and Sn: (i) they can increase or decrease the reaction/growth rates, (ii) the additives can change the physical properties of the phases formed, and (iii) they can form additional reaction products or displace the binary equilibrium phases by forming new reaction products. Finally, if the local stable or metastable equilibrium is established at the interface, stability information together with kinetic considerations can provide a feasible approach to analyze interfacial reactions, which can have significant impact on the reliability of soldered electronics assemblies.

Interfacial reactions between lead-free solders and common base materials

Phase-pure TiO2(B) with microfibrous morphology was prepared via a newly developed method from amorphous TiO2. Cyclic voltammetry evidences that Li-insertion into TiO2(B) is governed by a pseudocapacitive faradaic process, whose rate is not limited by solid-state diffusion of Li+ in a broad interval of scan rates. This unusual behavior was discussed in terms of the crystal structure of the TiO2(B) host, having freely accessible parallel channels for Li+-transport perpendicular to the (010) face. The characteristic Li-insertion electrochemistry of TiO2(B) allows re-interpretation of several previous reports, which did not consider explicitly this relation or the presence of TiO2(B) in various TiO2 materials of different origin.

Pseudocapacitive Lithium Storage in TiO2(B)

Metal or metal oxide nanoparticles possess unique features compared to equivalent larger-scale materials. For applications, it is often necessary to stabilize or functionalize such nanoparticles. Thus, modification of the surface of nanoparticles is an important chemical challenge. In this survey, various possibilities are discussed how nanoparticles can be protected by organic ligands and how these ligands can be used to introduce functionalities. The preparative possibilities include grafting of an already functionalized ligand on the nanoparticle surface, exchanging part or all existing ligands on the nanoparticle surface, or grafting of a ligand on a nanoparticle followed by modification by organic chemical reactions.

Surface modification and functionalization of metal and metal oxide nanoparticles by organic ligands

Polyamide thin-film nanofiltration membranes containing TiO2 nanoparticles

Study of structural and electrical properties of grain-boundary modified ZnO films prepared by sol–gel technique

A simple spectrophotometric method for determination of the optical constants and band gap energy of multiple layer TiO2 thin films

Investigation on sol–gel synthesized Ag-doped TiO2 cermet thin films

Structural, optical and electrical studies on sol–gel deposited Zr doped ZnO films

The porous core layer deposited by modified chemical vapour deposition process has been analyzed in terms of thickness, pore size distribution, homogeneity and characteristics of the soot particles to investigate their variation with deposition temperature and input vapour composition. The compositions selected were SiO2, SiO2-GeO2 and SiO2-P2O5. Rare earth ions were incorporated into the deposit by a solution doping technique. The analysis of deposited microstructures was found to provide a quantitative indication about the rare earth incorporation and its variation with respect to process conditions. Thus the characterization provides a method of controlling rare earth doping and ultimate preform/fiber properties.

Suchitra Sen

Papers

Study of structural and electrical properties of grain-boundary modified ZnO films prepared by sol–gel technique

A simple spectrophotometric method for determination of the optical constants and band gap energy of multiple layer TiO2 thin films

Investigation on sol–gel synthesized Ag-doped TiO2 cermet thin films

Structural, optical and electrical studies on sol–gel deposited Zr doped ZnO films

Characterization of porous core layer for controlling rare earth incorporation in optical fiber