Dean G. Grier

Rietveld quantitative X-ray diffraction analysis of NIST fly ash standard reference materials

Rietveld quantitative X-ray diffraction analysis of the fly ash Standard Reference Materials (SRMs) issued by the National Institute of Standards and Technologies was performed. A rutile ( TiO 2 ) internal standard was used to enable quantitation of the glass content, which ranged from 65% to 78% by weight. The GSAS Rietveld code was employed. Precision was obtained by performing six replicates of an analysis, and accuracy was estimated using mixtures of fly ash crystalline phases and an amorphous phase. The three low-calcium (ASTM Class F) fly ashes (SRM 1633b, 2689 and 2690) contained four crystalline phases: quartz, mullite, hematite, and magnetite. SRM 1633b also contained a detectable level of gypsum, which is not common for this type of fly ash. The high-calcium (ASTM Class C) fly ash, SRM 2691, had eleven crystalline phases and presented a challenge for the version of GSAS employed, which permits refinement of only nine crystalline phases. A method of analyzing different groups of nine phases and averaging the results was developed, and tested satisfactorily with an eleven-phase simulated fly ash. The results were compared to reference intensity ratio method semiquantitative analyses reported for most of these SRMs a decade ago.

Cobalt ferrite nanoparticles: Achieving the superparamagnetic limit by chemical reduction

An unanticipated superparamagnetic response has been observed in cobalt ferrite materials after thermal treatment under inert atmosphere. Cobalt ferrite particles were prepared via normal micelle precipitation that typically yields CoxFe3−xO4 nanoparticles (x=0.6−1.0). While samples thermally treated under oxygen show majority spinel phase formation, annealing in nitrogen gas yields materials consisting of Co-Fe alloy, FeS, and CoFe2O4 spinel. After thermal treatment, thermomagnetic studies reveal composition-insensitive, but highly treatment-sensitive, saturation magnetization, coercivity, blocking temperature, and Verwey transition temperature dependence. Extremely high saturation magnetization (159 emu/g) with low coercivity (31 Oe) was observed for one of the treated compositions, which drastically deviates from prototypical cobalt ferrite with large magnetocrystalline anisotropy. We attribute such unique magnetic response to Co-Fe alloy coexisting with FeS and CoFe2O4 spinel where the diameter of the...

Long-term stability of landfilled coal combustion by-products

Abstract Many of the by-products from coal combustion and flue gas desulfurization are cementitious, which suggests utilization in some settings replacing conventional cements. Information on the long-term stability of these materials in Nature can be obtained from studies of landfilled by-products. Five coal combustion by-products (CCBs) landfilled at four sites in the USA were characterized by X-ray diffraction. Where moisture was available during or after disposal, the materials were changed chemically, physically and mineralogically over time, in processes analogous to diagenesis of buried sediments. At three of the sites, initially formed crystalline-phase assemblages were transformed into an assemblage dominated by ettringite and thaumasite. At one site where a high-sodium by-product was landfilled, an assemblage of Na-rich phases, including a zeolite and a zeolite-related nosean-hauyne phase, as well as tobermorite, was observed. This assemblage is unique and previously unobserved in CCBs. Diagenesis associated with many of these CCBs reduced strength and increased permeability after only a few years in the natural environment. The characteristics of the altered by-products resemble those of soils more than concrete. Initially promising 7 or 28 day laboratory tests of strength and permeability may not be characteristic of these materials on exposure to the environment. Blending of CCBs with fly ash to increase the proportion of cementitious CSH, and controlling subsequent moisture additions, could minimize deleterious by-product diagenesis.

Low temperature co-pyrolysis of hexabenzylditinsulfide and selenium. An alternate route to Sn(SxSe1-x)

Benzyl-substituted tin chalcogenides (Bn{sub 3}Sn){sub 2}S (1) and (Bn{sub 3}Sn){sub 2}Se (2) yield polycrystalline-phase pure SnS and SnSe in good ceramic yields when pyrolyzed with S and Se, respectively, at 275 C. Heating mixtures of (1) and elemental selenium produce solid solutions of the formula Sn(S{sub x}Se{sub 1{minus}x}). Combustion analysis showed less than 1% residual carbon in all ceramic products. This methodology allows the complete conversion of tin-to-tin chalcogenides and eliminates the need to synthesize organosulfur and organoselenium intermediates.

High-Permeability Particles for Magnetic Composites

Electromagnetic shields and flux concentrators for magnetic sensors could utilize flexible and insulating composites applied using simple thin film deposition methods such as dipcoating, spin-coating, spraying, etc. As the fi rst step towards development of composites with superior performance, efforts focu sed on isolating nanoparticles with large magnetizations under low fields. In this paper, we provide the results of proof-of-concept studies for two systems: metal-functionalized silicone-based materials (metal-silicone); and, Co-ferrite (Co 2+ 1-xFe 2+ xFe 3+ 2O4) nanoparticles. The metal-silicone materials studied included a polysiloxane that containe d a pendant ferrocene where an optimum saturization magnetization of 5.9 emu/g (coe rcivity = 11 Oe) was observed. Co-ferrite nanoparticle samples prepared in this study showed unprecendented saturation magnetization (i.e., Ms > 150 emu/g) with low coercivity (H c ~ 10 Oe) at room temperature and offer potential appl ication as flux concentrators.

Residues from coal conversion and utilization: Advanced mineralogical characterization and disposed byproduct diagenesis. [Semiannual report, 1 Mar 1999--31 Aug 1999]

The goal of the project is to learn more about the phenomenon of coal conversion byproduct (CCB) diagenesis, first described by this group and co-workers at UND EERC seven years ago. CCB diagenesis is a change in the mineralogy that occurs after some CCBs are disposed in a landfill or utilized for a civil engineering application. Regulatory environmental tests and civil engineering tests are typically performed on as-generated CCBs, or on CCBs hydrated and cured for relatively short periods such as 7 or 28 days. One would like to know whether the results of these short-term tests will be valid years later. A change in mineralogy means a gain, loss or chemical redistribution of major, minor and trace elements, and alteration of physical properties. To attain this goal, two objectives were defined: (1) to develop improved methodology for quantitating mineralogy of these complex crystalline phase assemblages, and (2) to investigate the phenomenon of CCB diagenesis further by studying materials recovered from disposal landfills or civil engineering works. Objective 1--Hydrated CCBs are chemically and mineralogically complex, which makes quantitative mineralogy determination by conventional X-ray diffraction unusable or unreliable. The whole-pattern Rietveld quantitative X-ray diffraction (RQXRD) method, however, can overcome many of the problems and seems well suited to improve reliability. Two tasks were defined in the proposal: Task 1--Completion by October 1997. Prepare a reference set of CCBs for use in developing Rietveld QXRD. The reference materials will come primarily from in-house samples of advanced coal technology byproducts. The work will include SEM/EMPA characterization at UND EERC. Task 2--Completion by October 1997. Develop protocols for Rietveld QXRD analysis of CCBs. Make CCB structure data and protocols available on a Website. Determine levels of sensitivity, precision, and accuracy. Objective 2--Five types of CCBs disposed in landfills were studied between 1989 and 1994. Diagenesis was observed in three of the five materials. To obtain a more generic understanding of CCB diagenesis, additional materials and different environmental settings need to be studied. Task 3--Completion by end of project. Apply RQXRD protocols developed in Task 2 to core samples of utilized or disposed CCBs from at least five additional sites. Use results to gain a better understanding of CCB diagenesis.

RESIDUES FROM COAL CONVERSION AND UTILIZATION: ADVANCED MINERALOGICAL CHARACTERIZATION AND DISPOSED BYPRODUCT DIAGENESIS

The goals of the project are two-fold: (1) to upgrade semi-quantitative X-ray diffraction (QXRD) methods presently used in analyzing complex coal combustion by-product (CCB) systems, with the quantitative Rietveld method, and (2) to apply this method to a set of by-product materials that have been disposed or utilized for a long period (5 years or more) in contact with the natural environment, to further study the nature of CCB diagenesis. The project is organized into three tasks to accomplish these two goals: (1) thorough characterization of a set of previously analyzed disposed by-product materials, (2) development of a set of CCB-specific protocols for Rietveld QXRD, and (3) characterization of an additional set of disposed CCB materials, including application of the protocols for Rietveld QXRD developed in Task 2.