Robert Schulz

Bio: Robert Schulz is an academic researcher from Hydro-Québec. The author has contributed to research in topics: Nanocrystalline material & Hydrogen. The author has an hindex of 45, co-authored 193 publications receiving 7640 citations. Previous affiliations of Robert Schulz include Université du Québec à Montréal.

Mechanically alloyed metal hydride systems

Abstract: Mechanosynthesis of metal hydrides is a new field in which important progress has been reported. In this paper, we present recent developments in mechanosynthesis of magnesium-based hydrides for storage applications. The effect of intense milling on magnesium and magnesium hydrides is presented. The influence of various additives on hydrogen-sorption properties is discussed with special emphasis on nanocomposite MgH2+5 at. % V, where hydrogen-storage characteristics, cycling properties and the mechanism of hydrogen desorption are presented. The production of novel nanocrystalline porous structures by mechanical alloying followed by a leaching technique is discussed. Hot ball-milling, as a new method for rapid synthesis of alloys, is also presented. Finally, two other methods of production of metal hydrides are discussed. One is reactive milling where metal hydrides are synthesized by mechanical alloying under hydrogen pressure, while the other is milling elemental hydrides to produce complex hydrides.

Mechanical Alloying And Milling

Abstract: 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.

Charge Storage Mechanism of MnO2 Electrode Used in Aqueous Electrochemical Capacitor

Abstract: The charge storage mechanism in MnO2 electrode, used in aqueous electrolyte, was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy. Thin MnO2 films deposited on a platinum substrate and thick MnO2 composite electrodes were used. First, the cyclic voltammetry data established that only a thin layer of MnO2 is involved in the redox process and electrochemically active. Second, the X-ray photoelectron spectroscopy data revealed that the manganese oxidation state was varying from III to IV for the reduced and oxidized forms of thin film electrodes, respectively, during the charge/discharge process. The X-ray photoelectron spectroscopy data also show that Na+ cations from the electrolyte were involved in the charge storage process of MnO2 thin film electrodes. However, the Na/Mn ratio for the reduced electrode was much lower than what was anticipated for charge compensation dominated by Na+, thus suggesting the involvement of protons in the pseudofaradaic mechanism. An important finding o...

Bulk Glass-Forming Metallic Alloys: Science and Technology

Abstract: The following article is based on the MRS Medal talk presented by William L. Johnson at the 1998 MRS Fall Meeting on December 2, 1998. The MRS Medal is awarded for a specific outstanding recent discovery or advancement that has a major impact on the progress of a materials-related field. Johnson received the honor for his development of bulk metallic glass-forming alloys, the fundamental understanding of the thermodynamics and kinetics that control glass formation and crystallization of glass-forming liquids, and the application of these materials in engineering.The development of bulk glass-forming metallic alloys has led to interesting advances in the science of liquid metals. This article begins with brief remarks about the history and background of the field, then follows with a discussion of multicomponent glass-forming alloys and deep eutectics, the chemical constitution of these new alloys, and how they differ from metallic glasses of a decade ago or earlier. Recent studies of deeply undercooled liquid alloys and the insights made possible by their exceptional stability with respect to crystallization will then be discussed. Advances in this area will be illustrated by several examples. The article then describes some of the physical and specific mechanical properties of bulk metallic glasses (BMGs), and concludes with some interesting potential applications.The first liquid-metal alloy vitrified by cooling from the molten state to the glass transition was Au-Si, as reported by Duwez at Caltech in 1960. Duwez made this discovery as a result of developing rapid quenching techniques for chilling metallic liquids at very high rates of 105–106 K/s.