Influence of the content of a surrogate of iron aluminate high-level wastes on the phase composition and structure of glassy materials for their immobilization

Alkali borosilicate glassy materials with high iron and aluminum oxide concentrations, which simulate vitrified high-level wastes from the Savannah River Site (United States) at their content ranging from 50 to 70 wt %, have been investigated using X-ray powder diffraction, optical and electron microscopy, and infrared spectroscopy. Quenched and slowly cooled samples containing 50 wt % wastes are glasses. Samples containing 60 and 70 wt % wastes, which were quenched on a metal slab, are predominantly glasses with an insignificant content of the spinel formed in a trevorite-magnetite solid solution. The slowly cooled samples also contain nepheline, and its amount increases with an increase in the waste content in the glassy materials.     

Thermoplastic Forming of Bulk Metallic Glasses

Metallic glasses display interesting mechanical properties including high mechanical resistance and large capacity to store elastic energy. Since metallic glasses can now be produced in bulk conditions, they can be used for structural applications. In this new context, thermoforming of metallic glasses can be a particularly well adapted technique for production of small size components with good surface finish. As for other glasses, metallic glasses can be preferentially thermoformed in their supercooled liquid region. However, since metallic glasses are still emerging materials, the mechanisms of high temperature deformation remain not completely understood and intensive work is currently carried out to identify the elementary mechanisms of deformation. Moreover, since thermoforming is performed in the supercooled liquid region, the thermal stability of the glass to be formed is a key point for the success of the thermoforming process. Finally, it is also shown that thermoforming conditions can be used to produce multi materials associating metallic glasses and conventional metallic alloys.     

Calcium and Zinc Containing Bactericidal Glass Coatings for Biomedical Metallic Substrates

The present work presents new bactericidal coatings, based on two families of non-toxic, antimicrobial glasses belonging to B₂O₃–SiO₂–Na₂O–ZnO and SiO₂–Na₂O–Al₂O₃–CaO–B₂O₃ systems. Free of cracking, single layer direct coatings on different biomedical metallic substrates (titanium alloy, Nb, Ta, and stainless steel) have been developed. Thermal expansion mismatch was adjusted by changing glass composition of the glass type, as well as the firing atmosphere (air or Ar) according to the biomedical metallic substrates. Formation of bubbles in some of the glassy coatings has been rationalized considering the reactions that take place at the different metal/coating interfaces. All the obtained coatings were proven to be strongly antibacterial versus Escherichia coli (>4 log).     

Transformations of molecules and secondary building units to materials: a bottom-up approach

A variety of complex inorganic solids with open-framework and other fascinating architectures, involving silicate, phosphate, and other anions, have been synthesized under hydrothermal conditions. The past few years have also seen the successful synthesis and characterization of several molecular compounds that can act as precursors to form open-framework and other materials, some of them resembling secondary building units (SBUs). Transformations of rationally synthesized molecular compounds to materials constitute an important new direction in both structural inorganic chemistry and materials chemistry and enable possible pathways for the rational design of materials. In this article, we indicate the potential of such a bottom-up approach, by briefly examining the transformations of molecular silicates and phosphates. We discuss stable organosilanols and silicate secondary building units, phosphorous acids and phosphate secondary building units, di- and triesters of phosphoric acids, and molecular phosphate clusters and polymers. We also examine the transformations of metal dialkyl phosphates and molecular metal phosphates.     

Stabilized gold clusters: from isolation toward controlled synthesis

Bare metal clusters with fewer than ～100 atoms exhibit intrinsically unique and size-specific properties, making them promising functional units or building blocks for novel materials. To utilize such clusters in functional materials, they need to be stabilized against coalescence by employing organic ligands, polymers, and solid materials. To realize rational development of cluster-based materials, it is essential to clarify how the stability and nature of clusters are modified by interactions with stabilizers by characterizing isolated clusters. The next stage is to design on-demand function by intentionally controlling the structural parameters of cluster-based materials; such parameters include the size, composition, and atomic arrangement of clusters and the interfacial structure between clusters and stabilizers. This review summarizes the current state of the art of isolation of gold clusters stabilized in various environments and surveys ongoing efforts to precisely control the structural parameters with atomic level accuracy.     

Intragranular nanocomposite powders as building blocks for ceramic nanocomposites

A powder-based bottom-up processing scheme is introduced for the production of ceramic nanocomposites. Internal displacement reactions between solid solution powders and metallic reactants proceeding via gaseous intermediates are utilized to generate nanostructured building blocks for the synthesis of ceramic nanocomposites. Subsequent rapid sintering results in ceramic nanocomposites, whose microstructures are inherited from the building blocks. This processing scheme is demonstrated for the production of titanium carbide nanocomposites featuring up to 28 wt.% intragranular tungsten inclusions derived from titanium-tungsten mixed carbide powders. Heat treatment of mixed carbide powders in evacuated ampoules containing titanium sponge and iodine at 1000°C for 24 h resulted in nanocomposite powders featuring tungsten precipitates within titanium carbide grains that were subsequently consolidated via spark plasma sintering at 1300°C for 10 min to produce titanium carbide/metallic tungsten nanocomposites. Transformation of mixed titanium–tungsten carbide powders to titanium carbide/metallic tungsten nanocomposite powders was analyzed via X-ray diffraction. Electron microscopy observations of microstructures pre- and post- sintering showed that the intragranular character of nanocomposite powders can be retained in sintered ceramic nanocomposites. The building block approach demonstrated in this work represents an improved method to make ceramic nanocomposites with majority intragranular character.     

Structural Relaxation in Amorphous Magnetic Screens

The structural relaxation is studied in amorphous magnetic screens produced by plasma deposition and explosive compacting from an amorphous metallic ribbon. Investigations are performed by different methods, such as differential scanning calorimetry (DSC), measurements of magnetic hysteresis properties, X-ray powder diffraction analysis, and electron probe X-ray microanalysis. It is found that the structural relaxation in the objects studied proceeds in the same way as in rapidly quenched glasses.     

Progress in non-traditional machining of amorphous alloys

Amorphous alloys are a new type of multi-functional advanced material with the properties of general metal materials and glass, which are also called metallic glasses. They have good comprehensive properties, such as a wide application range, low cost, and high reusability. Using reasonable process parameters, non-traditional machining can not only realize the machining of complex amorphous parts, but also avoid the crystallization and oxidation of amorphous alloys, realizing tasks that cannot be accomplished by traditional machining. Therefore, this review systematically summarizes the research status and development potential of amorphous alloys fabricated using non-traditional machining methods. First, we introduce the principles of laser machining, ultrasonic machining, electrical discharge machining, electrochemical machining, and other non-traditional machining methods for amorphous alloys. Subsequently, the influence of the machining parameters and other external conditions on the machining effect is summarized. The machining cost, machining efficiency, and environmental impact of these non-traditional machining methods were compared. Finally, non-traditional machining technology for amorphous alloys is summarized and discussed.     

Solution combustion synthesis of metal nanopowders: Nickel—Reaction pathways

Nanopowders of pure nickel were directly synthesized for the first time by conventional solution combustion synthesis (SCS) method. In this article, a specific reaction pathway is suggested to describe the metallic phase formation during SCS. It is proposed that the exothermic reaction between NH₃ and HNO₃ species formed during the decomposition of glycine and nickel nitrate acts as the source of energy required to achieve the self‐sustained reaction regime. A thermodynamic analysis of the combustion synthesis reaction indicates that increasing glycine concentration leads to establishing a hydrogen rich reducing environment in the combustion wave that in turn results in the formation of pure metals and metal alloys. TGA of reaction systems and XRD analysis of products in the quenched combustion wave show that the formation of oxide phases occurs in the reaction front, followed by gradual reduction of oxide to pure metallic phases in the postcombustion zone. A methodology for SCS of pure metals and metal alloys nanoparticles can be inferred from the results presented. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Electrochemical and XPS studies of Ni-based metallic glasses in boiling nitric acid solutions

This work systematically reports the electrochemical properties and surface characteristics of Ni-based metallic glasses in boiling nitric acid solutions. The Ni-based glassy alloys demonstrate high corrosion resistance in boiling 6 N HNO₃ solutions with and without Cr⁶⁺ ions, which may be of great potential for nuclear fuel reprocessing applications. X-ray photoelectron spectroscopy analysis reveals that the high corrosion resistance of the alloys is due to the formation of the passive film composed exclusively of Nb⁵⁺ and Ta⁵⁺ cations after immersion in the solution without Cr⁶⁺ ions, and Nb⁵⁺, Ta⁵⁺ and Cr³⁺ cations after immersion in the solution with Cr⁶⁺ ions.     

Influence of Alkyl Chain Length on Thermal Properties,Structure, and Self-Diffusion Coefficients of Alkyltriethylammonium-Based Ionic Liquids

The application of ionic liquids (ILs) has grown enormously, from their use as simple solvents, catalysts, media in separation science, or electrolytes to that as task-specific, tunable molecular machines with appropriate properties. A thorough understanding of these properties and structure–property relationships is needed to fully exploit their potential, open new directions in IL-based research and, finally, properly implement the appropriate applications. In this work, we investigated the structure–properties relationships of a series of alkyltriethylammonium bis(trifluoromethanesulfonyl)imide [TEA-R][TFSI] ionic liquids in relation to their thermal behavior, structure organization, and self-diffusion coefficients in the bulk state using DSC, FT-IR, SAXS, and NMR diffusometry techniques. The phase transition temperatures were determined, indicating alkyl chain dependency. Fourier-transformed infrared spectroscopy studies revealed the structuration of the ionic liquids along with alkyl chain elongation. SAXS experiments clearly demonstrated the existence of polar/non-polar domains. The alkyl chain length influenced the expansion of the non-polar domains, leading to the expansion between cation heads in polar regions of the structured IL. ¹H NMR self-diffusion coefficients indicated that alkyl chain elongation generally caused the lowering of the self-diffusion coefficients. Moreover, we show that the diffusion of anions and cations of ILs is similar, even though they vary in their size.     

Anodic dissolution of rapidly quenched amorphous Ni81P19 alloys of different initial melt temperatures

The anodic behaviour of rapidly quenched Ni₈₁P₁₉ samples prepared at different melt temperatures was investigated in 1.0 mol dm^–3 aqueous HCl solution. The electrochemical properties of the alloys kept in melt at different temperatures are significantly influenced by the initial melt temperature. X-ray diffractometry suggests that this behaviour is associated with the presence of different quantities of crystalline secondary phase(s). On the basis of potentiodynamic polarization curves and potential-time functions recorded at constant current the alloys were characterized by a charge per surface unit amount proportional to the secondary phase content. A new model was proposed to characterize the anodic dissolution of alloys containing crystalline clusters.     

Effect of secondary structural relaxation on the onset of crystallization in amorphous alloys Fe69Ni9Si9B13 and Fe61Co20Si5B14

In rapidly quenched amorphous alloys, relaxation phenomenon known as the secondary structural relaxation, together with the structural relaxation occurring in all amorphous materials is observed below the temperature of glass transition. This paper investigates the effect of annealing in the range of secondary structural relaxation on the onset of crystallization. The relationship between the fundamental laws governing the structural relaxation and nanocrystallization in alloys is established.     

Lead thioarsenate system PbS–As2S3: Glass formation,macroscopic, and electric properties

Lead thioarsenate glasses are promising materials for a number of potential applications in far infrared optics, chemical sensing, nonlinear photonics, etc. Electronic properties of the PbS–As₂S₃ glasses were studied in the past, however, the relationship between the glass and crystal characteristics have not been established. Here we compare the glass-forming domain in the pseudo-binary system obtained by usual melt–quenching and mechanical milling. Macroscopic and electrical glass properties are analyzed in comparison with their crystalline counterparts: PbAs₂S₄, Pb₅As₉S₁₈, and Pb₂As₂S₅, and the annealed glasses yielding glassy/crystalline alloys. Although the primary crystallization phases in glasses are consistent with the phase diagram, the lead local environment seems to be different in glasses and crystals, reflected by their properties and preliminary high-energy X-ray diffraction results.     

Phosphate glasses containing monodisperse Fe3−δO4@SiO2 stellate nanoparticles obtained by melt-quenching process

The challenge to obtain stable glasses containing monodisperse magnetic nanoparticles with controlled size and shape is an exciting and almost unexplored field of research. Such new materials can be used in magneto-photonics or ultra-sensitive magnetic sensors. In this work, for the first time, colorless and transparent bulk glasses containing monodisperse 20 nm Fe_3−δO₄ nanoparticles were prepared by a melt-quenching route. Magnetic nanoparticles were synthesized by thermal decomposition and covered with a stellate mesoporous silica shell in order to protect them against dissolution during the glass melting process. The incorporation of nanoparticles into glasses and the ideal parameters obtained for this system are discussed. The new nanocomposite materials were characterized in order to investigate the structure, thermal, and magnetic properties. Such an original approach is a very promising way to incorporate a wide panel of nanoparticles, including metallic, bimetallic and metal oxide nanoparticles, into a variety of glasses providing new properties to these materials.     

Sintering of Industrial Mullites in the Presence of Magnesia as a Sintering Aid

The sinterability of two industrial mullite powders, in the presence of MgO as a sintering aid, was investigated. A glassy phase, which was generated during preparation, was present in both powders; this glassy phase had a strong influence on sintering, depending on its content, composition, and spatial distribution. MgO promoted sintering in the presence of a liquid phase, both in the as-received materials and in samples washed with HF, in which most of the pre-existing glassy phase was eliminated. Investigations using transmission electron microscopy, coupled with energy-dispersive spectroscopy, as well as dilatometric measurements and X-ray diffraction data, on washed and unwashed materials and on quenched and slow-cooled samples allowed a better understanding of the influence of MgO and the glassy phase on the sintering behavior and the formation of new phases. Most of the phases, in fact, can be explained by using the MgO–Al₂O₃–SiO₂ phase diagram, even in such complex systems.     

Glasses Formed from Molten Acetates

Glass formation in metal acetate systems was investigated; the tendency for these systems to form glasses is so great that even lithium and lead acetates are readily quenched to glass. Glass formation is favored near eutectic compositions in binary systems. Physical and optical properties of representative glasses are given.     

Production of glass–ceramics from incinerator ash using lab-scale and pilot-scale thermal plasma systems

This research employed two thermal plasma melting systems and vitrification technology to treat incinerator ash. The melted slag was used for the production of glass–ceramics via powder sintering and heat treatment. When using the pilot-scale plasma molten system, the melt was rapidly quenched in water to yield glassy slag. The properties of quenched slag glass–ceramics were superior to that glass–ceramics produced by slowly cooling the slag with air. The glass–ceramics with the best physical/mechanical properties and chemical resistance was produced by heat treatment at 1150 °C for 2 h. Diopside and gehlenite were formed as the major crystalline phases. Glass–ceramics produced from incinerator ash demonstrate great potential for reutilization as non-porous or water permeable materials.     

The Use of Polysiloxanes to Elucidate Molecular Aspects of Rubberlike Elasticity

Polysiloxanes can be formed into a variety of elastomeric networks that are of fundamental as well as commercial interest. This review, which primarily focuses on the author’s own work, illustrates the use of experiments and simulations to establish structure–property relationships for these materials. Studies of this type have been very useful in obtaining a better molecular understanding of rubberlike elasticity in general.