Hylton McWhinney

A surface study of the chemistry of zinc, cadmium, and mercury in portland cement

Abstract X-ray photoelectron spectroscopy (XPS), a surface sensitive technique, is employed in the elucidation of chemical information regarding the environment of the priority metal pollutants; zinc, cadmium, and mercury, solidified in Portland cement. The metals were added as the aqueous solution of the salts [Zn(NO3)2, Cd(NO3)2, Hg(NO3)2] as 10% 3nd 20% by weight nitrate (hydrated). Standards of undoped Portland cement were prepared with cation-free water. The locations of metal ions, with respect to the bulk and surface of the cement matrix as a function of the interfacial phenomena of the alkaline medium, were probed. Bulk and topographical examinations were carried out using energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) respectively. Zinc, cadmium, and mercury are thought to exhibit dissimilar chemistries in the highly buffered alkaline medium. Their final solidification products seem to differ in how they are contained in the matrix. Mercury appears to be stabilized through physical interactions in the cement matrix, existing in mercury-rich deposits. The most impacting observation lies in the tremendous increase in surface carbonate formation in all the metal-ion doped cements.

Studies in neutron depth profiling

This paper describes first the application of neutron depth profiling (NDP) for measuring the distribution of6Li in LiAlO2 ceramics. Using a surface barrier detector for detecting3H produced in6Li(n, α)3H,6Li was profiled to a depth of 14 μm in the ceramics. Secondly, a new methodology is presented for NDP with enhanced capabilities based on measuring the energy of recoiling nuclei from (n, p) and (n, α) reactions by time-of-flight mass spectrometry. The scope of recoil nucleus time-of-flight mass spectrometry (RN-TOF-MS) includes profiling of10B,14N,17O,33S,35Cl,40K. Probe depths may be of a few tens nanometers. RN-TOF-MS complements and refines NDP based on charged particle (p or α) spectrometry.

Diffusion of lithium-6 isotopes in lithium aluminate ceramics using neutron depth profiling

Abstract Lithium Ceramics offer tremendous potential as a source for the production of tritium ( 3 H) for fusion power reactors. Their successful application will depend to a great extent upon the diffusion properties of the 6 Li within the matrix. Consequently knowledge od 6 Li concentration gradients in the ceramic matrices is an important requirement in the continued development of the technology. In this investigation, the neutron depth profile (NDP) technique has been applied to the study of concentration profiles of 6 Li in lithium aluminate ceramics, doped with 1.8%, 50% and 95% 6 Li isotopic concentrations. Specimen for analysis were prepared at Battelle (PNL) as pellet discs. Samples for diffusion studies were arranged as diffusion couples in the following manner: 1.8% 6 Li discs/85% 6 Li powder. Experiments were performed at the Texas A&M Nuclear Science Center Reactor Building, utilizing 1 MW equivalent thermal neutron fluxes 3 × 10 11 n / m 2 s . The depth probed by the technique is approximately 15 μ.m. Diffusion coefficients are in the range of 2.1 × 10 −12 to 7.0 × 10 −11 m 2 s −1 for 1.8% 6 Li-doped ceramics annealed at 1200 and 1400° C, for 4 to 48-h anneal times.

Characterization of Copper-Manganese-Aluminum-Magnesium Mixed Oxyhydroxide and Oxide Catalysts for Redox Reactions

Complex multi-metal catalysts require several stages in their preparation. These are: co-mixing, co-precipitation, milling and sol-gel, drying, dehydroxylation, and calcination and sometimes regeneration of the hydroxide by rehydration. These processes require thermal analysis (DTA, TGA, DSC) and accompanying off gas analysis, plus one or more of these: XRD, XPS, SEMEDS, FTIR and UV-VIS. In this study, hydrotalcite, hopcalite and mixed systems were prepared and guided by the above characterization techniques. The systems were initiated by mixing the chlorides or nitrates followed by hydrothermal treatments to produce the hydroxides which were further treated by washing, drying, and calcination. The thermal analysis was critical to guide the preparation through these stages and when combined with structural determination methods considerable understanding of their chemical and physical changes was obtained. The correlations between preparation and characterization will be discussed.

Electrochemical Properties Of Copper Oxide Surfaces, Buried Interfaces, And Subsurface Zones And Their Use To Characterize These Entities

Electrochemistry of oxides is an expanding area of oxide characterization. Although, interfacial characterization techniques including surface science methods have contributes substantially to our current understanding of the processes involved in the oxidation of metals and alloys. The characterization of subsurface zones and buried interfaces still remain a major challenge. Copper reactions with oxygen have been studied by high vacuum based techniques of AES, ELS, ISS, XPS. SIMS, LEED. STM, SEXAFS, HEIS and PFDMS and with optical methods, like UV-Vis-NIR, diffuse reflectance spectroscopy, FTIR and photoluminescence spectroscopes. However it has become evident that the processes that produce thermally and plasma grown oxide films on metals and alloys are electrochemical in nature and can be modeled by electrochemical concepts. Therefore, it is important that the oxide over layers, thin films and thick films be characterized by electrochemical means -with electrochemical methods, such as linear potential sweep voltammetry, cyclis voltammetry, galvanostatic reduction and coulometry which allow the identification of copper (I), copper (II) and copper (III) oxides. Interest in copper as a technologically important material needs to be met with greater understanding of the fundamental nature of copper oxide structures. In this study, the authors demonstrate the use of Linear Sweep Voltammetry (LSV) to study buried structures in the thermally grown oxide layers on copper. In particular, LSV can be used to detact reactions at buried interfaces. It also recognizes Cu 3 O 2 and the decomposition of copper oxides at the metal-oxide layers on copper. In particular, LSV can be used to detect reactions at buried interface. The two key parameters that drive oxide growth and decomposition are demonstrated to be oxygen activity and the free energies of formation of the oxides. The complex nature of the oxidation of copper, as well as other metals and alloys, will be described qualitatively using the Modified Cabrera-Mott (C-M) Model. Surface studies of oxidation of metals and alloys need to be supported and complemented by other techniques such as electrochemical methods.