Marzia Pentimalli

Reactive Pellets for Improved Solar Hydrogen Production Based on Sodium Manganese Ferrite Thermochemical Cycle

Hydrogen production by water-splitting thermochemical cycle based on manganese ferrite/sodium carbonate reactive system is reported. Two different preparation procedures for manganese ferrite/sodium carbonate mixture were adopted and compared in terms of material capability to cyclical hydrogen production. According to the first procedure, conventionally synthesized manganese ferrite, i.e., high temperature (1250°C) heating in Ar of carbonate/oxide precursors, was mixed with sodium carbonate. The blend was tested inside a temperature programed desorption reactor using a cyclical hydrogen production/material regeneration scheme. After a few cycles, the mixture resulted rapidly passivated and unable to further produce hydrogen. An innovative method that avoids the high temperature synthesis of manganese ferrite is presented. This procedure consists in a set of consecutive thermal treatments of a manganese carbonatel sodium carbonateliron oxide mixture in different environments (inert, oxidative, and reducing) at temperatures not exceeding 750°C. Such material, whose observed chemical composition consists of manganese ferrite and sodium carbonate in stoichiometric amounts, is able to evolve hydrogen during 25 consecutive water-splitting cycles, with a small decrease in cyclical production efficiency.

Effects of substrate treatment and growth conditions on structure, morphology, and luminescence of homoepitaxial ZnTe deposited by metalorganic vapor phase epitaxy

The structure, morphology, and luminescence of homoepitaxial ZnTe layers grown by metalorganic vapor phase epitaxy on (100)ZnTe:P wafers are reported as function of substrate surface treatment and growth conditions. Epilayers grown on substrates in situ H2 treated at temperatures above 240 °C exhibit long range crystalline perfection comparable to the substrate, but their structure rapidly degrades at lower temperatures, an effect ascribed to the incomplete removal of native oxides from the wafer surface. Instead, the material microscopic structure improves monotonically by annealing the wafer up to 350 °C. A nearly featureless surface morphology is obtained for epilayers grown within a narrow temperature interval around 350 °C, corresponding to the transition between surface kinetics and mass transport limited growth. Surface ridging along a 〈110〉 in-plane direction is observed at lower temperatures, while large pyramidlike hillocks occur randomly on the surface of samples grown above 350 °C. Besides the...

Metal Hydride-Based Composite Materials with Improved Thermal Conductivity and Dimensional Stability Properties

To address the issues of poor thermal conductivity and fragmentation of metal hydride particles undergoing hydriding/dehydriding reactions, a metal hydride-based composite material was developed. The active metal phase was embedded in a silica matrix and a graphite filler was incorporated by ball milling. A set of compact pellet samples at different composition were prepared and tested. Experimental data obtained from the thermal conductivity measurements shown that using powder graphite produced a quite linear increase in the thermal conductivity of the metal hydride – silica composite. Ongoing studies include composition optimization as well as long-term testing upon cycling of such metal hydride composites to evaluate their potentiality in technological hydrogen storage applications.

Structural Characterization of Hybrid Organic–Inorganic Nanocomposites: X-ray

The properties of hybrid composites result from a complex cooperation between the organic and inorganic species constituting the nanocomposites. A continuous, increasing demand of the detailed knowledge of such properties at the nanoscale has contributed to the development of the characterization techniques. The chapter provides an overview on two specific characterization tools widely used in nanocomposites research: X-ray scattering (XRS) and Solid-State Nuclear Magnetic Resonance spectroscopy (SSNMR). We briefly describe some fundamentals of both the methods and present several relevant results from the literature in this field. Specific emphasis is devoted to nanoparticle polymer nanocomposites and polymer-layered silicate nanocomposites.

Structure of Nanocomposite films of CdS nanoparticles in a polymer matrix

A thiolate precursor was dispersed in a polymer solution and a precursor/polymer film was obtained by casting. Thermal annealing of the precursor/polymer film leads to the formation of a nanocomposite of nanometer-sized CdS dispersed in the polymer (thermolytic process). Different polymers were used as matrix material; in particular we employed a cyclo-olefin copolymer for its good optical properties and extremely low water absorption. After annealing with a temperature between 230 and 250°C in vacuum (pressure of about 6×10 −3 mbar) the CdS nanoparticles are found to be crystalline with a diameter of about 2nm in size. The nanoparticle size can be increased up to 15nm by annealing at higher temperatures (300°C). The details of the structural properties of the nanocomposite films have been investigated by small and wide angle x-ray scattering (SAXS and WAXS, respectively). A simple dependence of the nanoparticle dimensions on the annealing temperature was found. Furthermore, SAXS measurements indicate that the separation between the nanoparticles compares with their diameter.