3,868 Matching Results

Search Results

Advanced search parameters have been applied.

The effects of moisture on the microstructure of cement-based materials. Progress report

Description: New information about shrinkage at the microstructural level has been acquired. Experiments and computer analysis serve as a basis for modeling. Some highlights: C-S-H (shrinking phase) shrinks and values for dimensional change are being determined. There may be two types of C-S-H, only one of which shrinks. All other phases serve as restraints to shrinkage. Pores expand on drying and therefore may be a mechanism for the ``size effect``, in addition to microcracks.
Date: July 15, 1993
Creator: Jennings, H. M.
Partner: UNT Libraries Government Documents Department

Microstructurally based mechanisms for modeling shrinkage of cement paste at multiple levels

Description: Shrinkage of cement paste is controlled by a number of mechanisms that operate in various parts of the microstructure and at various length scales. A model for creep and shrinkage can be developed by combining several models that describe phenomena at each of several length scales, ranging from the nanometer to the meter. This model is described and preliminary results are discussed.
Date: July 15, 1993
Creator: Jennings, H. M. & Xi, Yunping
Partner: UNT Libraries Government Documents Department

Nonstoichiometry of Al-Zr intermetallic phases

Description: Nonstoichiometry of metastable cubic {beta}{prime} and equilibrium tetragonal {beta} Al-Zr intermetallic phases of the nominal composition Al{sub 3}Zr in Al-rich alloys has been extensively studied. It is proposed that the ``dark contrast`` of {beta}{prime} core in {beta}{prime}/{sigma}{prime} complex precipitates, in Al-Li-Zr based alloys, is caused by incorporation of Al and Li atoms into the {beta}{prime} phase on Zr sublattice sites, forming nonstoichiometric Al-Zr intermetallic phases, rather than by Li partitioning only. {beta}{prime} particles contain very small amounts of Zr, approximately 5 at.%, much less than the stoichiometric 25 at.% in the Al{sub 3}Zr metastable phase. These particles are, according to simulation of high resolution images, of the Al{sub 3}(Al{sub 0.4}Li{sub 0.4}Zr{sub 0.2}) type. Nonstoichiometric particles of average composition Al{sub 4}Zr and Al{sub 6}Zr are observed also in the binary Al-Zr alloy, even after annealing for several hours at 600{degree}C.
Date: June 1, 1994
Creator: Radmilovic, V. & Thomas, G.
Partner: UNT Libraries Government Documents Department

Characterization of Phase and Emulsion Behavior, Surfactant Retention, and Oil Recovery for Novel Alcohol Ethoxycarboxylate Surfactants

Description: This semi-annual technical progress report describes work performed at Clark Atlanta University under DOE Grant No. DE-FG26-97FT97278 during the period October 01, 1997 to April 01, 1998 which covers the first six months of the project. During this reporting period, laboratory space to set up the surfactant characterization measurement system in the Research Science Center was made available. A Ph.D. student in Chemistry was identified and is supported as a Graduate Research Assistant in this project. Her contribution towards this project will form her Ph.D. thesis. The test matrix to perform salinity and temperature scans was established. Supply requests to obtain refined hydrocarbon, surfactant, and crude were processed and supplies obtained. A temperature bath with a control unit to perform temperature scans was obtained on loan from Federal Energy Technology Center, Morgantown, WV. The setting up of the temperature control unit, and associated chiller with water circulation lines is in progress. Tests were conducted on several hybrid surfactants to identify the best surfactants for future experimental work that yield almost equal volumes of top, middle, and bottom phases when mixed with oil and water. The student reviewed the current literature in the subject area, and modeling efforts that were established in previous studies to predict electrical conductivities and inversion phenomena. These activities resulted in one published conference paper, and one student poster paper during this reporting period.
Date: May 1, 1998
Creator: Moeti, Lebone T. & Sampath, Ramanathan
Partner: UNT Libraries Government Documents Department


Description: This semi-annual technical progress report describes work performed at Clark Atlanta University under DOE Grant No. DE-FG26-97FT97278 during the period April 01, 1998 to October 01, 1998 which covers the second six months of the project. Presently work is in progress at the EOR Laboratory, Clark Atlanta University (CAU), to characterize phase and emulsion behavior for a novel, hybrid (ionic/non-ionic), alcohol ethoxycarboxylate surfactant (NEODOX 23-4 from Shell Chemical Company). During this reporting period, salinity scans were completed for 0, 5, 10, 20, 50, 100, 250, 500, 1000, 2000, 3000, 4000, 5000, and 6000 mM salt concentrations at 20, 25, and 30 °C to identify optimal salinity intervals in which all three phases coexist for this surfactant. Temperature scans were also performed at 20 mM salt concentration for various surfactant concentrations ranging from 0 to 60 weight percent at temperatures ranging from 5 to 50 °C to identify optimal surfactant concentration and temperature intervals in which all three phases coexist. This resulted in an "alpha" curve with an interval of temperature in which all three phases coexisted. Presently, temperature scans are being repeated at 100, 250, 500, 1000, and 5000 mM salt concentrations to see whether increase in salt concentration has any effect on the temperature interval. This will provide us better understanding and experimental control of the many variables involved in this research in the future. Following completion of the temperature scans, phase studies will be conducted at CAU, and coreflooding experiments at the facility of our industrial partner, Surtek, Golden, CO.
Date: November 1, 1998
Partner: UNT Libraries Government Documents Department

Relaxation effects in shock-induced transitions in bismuth

Description: The indication given by the baratol experiments is that as the shock in the mixed region progresses and decays, the lead state does not change along a stable Hugoniot but appears to change from a sort of metastable Hugoniot, in accordance with Romain's data, to a stable Hugoniot reminiscent of the earlier results. If this is so, then the Bi I-III transition is exhibiting a relaxation effect similar to that seen in the Sb I-III transition. The transition detected by Romain could then be interpreted as the II-III transition seen in the metastable region. The few experiments outlined here merely hint at an explanation. Additional precision work in the stress range 6-10 GPa, some with thin samples, is needed to resolve this behavior.
Date: January 1, 1981
Creator: Neal, T.R.
Partner: UNT Libraries Government Documents Department

Neutron diffraction studies on recrystallization of solution derived lead zirconate titanates

Description: We performed neutron powder diffraction on solution-derived lead zirconate titanates (PZT). Three compositions, PZT 45/55, PZT 20/80 and PbTiO{sub 3}, were investigated. The materials were annealed so that the perovskite phase had just begun to grow from the precursor phase. In our materials this precursor phase is the pyrochlore rather than fluorite phase. The results show that in the pyrochlore phase, the (Ti,Zr) and the Pb are ordered in their crystallographic sites while the O are essentially disordered in both of the two usual pyrochlore anion sites.
Date: December 31, 1994
Creator: Morosin, B.; Tuttle, B. A.; Voigt, J. A.; Lawson, A. C. & Kwei, G. H.
Partner: UNT Libraries Government Documents Department

Metastable phases in mechanically alloyed aluminum germanium powders

Description: Aluminum and germanium form a simple eutectic system with no stable intermetallic phase, and limited mutual solubility. We report the formation of a metastable rhombohedral,{gamma}{sub 1} phase by mechanically alloying aluminum and germanium powders. This phase, which appears for compositions between 20 and 50 at. % germanium, has also been observed in rapidly quenched alloys, but there is disagreement as to its composition. By measuring the heat of crystallization as a function of composition, we determined the composition of the {gamma}{sub 1} phase to be Al{sub 70}Ge{sub 30}. We also produced Al{sub 70}Ge{sub 30} by arc melting the pure elements, followed by splat-quenching at a cooling rate in the range of 10{sup 8} K s{sup {minus}1}. This method produced two metastable phases, one of which was found to be the {gamma}{sub 1} phase obtained by mechanical alloying. The other was a monoclinic phase reported earlier in the literature as {gamma}{sub 2}.
Date: March 1, 1993
Creator: Yvon, P. J. & Schwarz, R. B.
Partner: UNT Libraries Government Documents Department

Directional solidification studies in Ni-Al alloys

Description: Three solid phases are involved in the phase equilibria of the intermetallic compound Ni{sub 3}Al near its melting point, {beta}, {gamma}{prime}(Ni{sub 3}Al), and {gamma}. The generally-accepted phase diagram involves a eutectic reaction between {beta}{prime} and {gamma}, but some recent studies agree with an older diagram due to Schramm, which has a eutectic reaction between the {beta} and {gamma}{prime} phases. The phase equilibria near Ni{sub 3}Al compositions was evaluated using quenched directional solidification experiments, that preserve the microstructures tonned at the solidification front, and using diffusion couple experiments. These experiments show that eutectic forms between {beta} and {gamma}{prime} phases, as in the Schramm diagram. Growth and phase transformations of these three phases are also studied in the directional solidification experiments. Microstructure analysis shows that etching of Ni{sub 3}Al({gamma}{prime}) is very sensitive to small composition variations and crystallographic orientation changes. The eutectic solidification study confirms that the equilibrium eutectic is {gamma}{prime}+{beta}, and that the metastable {gamma}+{beta} eutectic might be also produced in this system according to the impurities, solidification rates, and composition variations.
Date: May 1, 1993
Creator: Lee, Je-hyun
Partner: UNT Libraries Government Documents Department