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Transformation of meta-stable calcium silicate hydrates to tobermorite: reaction kinetics and molecular structure from XRD and NMR spectroscopy
Jacqueline R Houston, Robert S Maxwell, Susan A Carroll
Geochemical Transactions , 2009, DOI: 10.1186/1467-4866-10-1
Abstract: Burning of fossil fuels is believed to be the largest contributor to anthropogenic CO2 emissions and global climate change [1,2]. To reduce emissions and subsequently offset global warming, one solution is to inject CO2 into well-bores of depleted oil and gas reservoirs. Well- bores, however, are lined and plugged with Portland-based cement, which can chemically degrade in the presence of CO2 and water over time [3,4]. This presents a problem for long-term CO2 storage if reservoirs have the potential to leak through abandoned well sites. Deleterious effects can occur from leakage, including contamination of groundwater and subsurface resources and drastic changes to ecosystems [5-8]. In order to predict these processes and subsequently assess the long-term fate and storage of CO2, we need experimental data coupled with accurate simulations to identify reaction rates and pathways for cement dissolution and growth. However, there are few rate data on precipitation reactions and even fewer studies that derive growth mechanisms for cement-based minerals.Calcium silicate hydrates are key components in cement minerals and have been suggested as precursor solids for the growth of stable minerals such as tobermorite and gyrolite [9,10]. Calcium silicate hydrates include many meta-stable and amorphous disordered structures, from which stable and highly crystalline materials such as tobermorite can form when heated. The mineral tobermorite is stable over a temperature range of ~80°C to ~150°C but can be produced at temperatures greater than 200°C as a meta-stable solid [9]. Orthorhombic tobermorite can be found as either a 9 ?, 11 ? or 14 ? polytype depending on the number of water molecules present in the structure. The structure of 11 ? tobermorite consists of layers of hydrated calcium ions bonded to repeating silicate chains that have bridging and non-bridging Si (Q2) and branching Si (Q3) sites [10-13]. The silicate chains repeat every third tetrahedron, giving rise to t
Stable Occupancy of Hydrogen Molecules in Clathrate Hydrates and + THF Clathrate Hydrates Determined by Ab Initio Calculations  [PDF]
Prasad Yedlapalli,Sangyong Lee,Jae W. Lee
Journal of Thermodynamics , 2010, DOI: 10.1155/2010/651819
Abstract: Structure II clathrate hydrates of pure hydrogen and binary hydrates of THF
Top decays into lighter stop and gluino  [PDF]
Lian You Shan,Shou Hua Zhu
Physics , 1998,
Abstract: We have calculated the decay width of the process $t \to \tilde{g} \tilde{t}_1$ including one loop QCD corrections. We found that the decay width of the such process could be comparable with that of the standard channel $t \to b W^+$, and, its QCD correction could enhance the widths over 30% in a very large mass range of the lighter stop.
Observation of Sintering of Clathrate Hydrates  [PDF]
Tsutomu Uchida,Toshiki Shiga,Masafumi Nagayama,Kazutoshi Gohara
Energies , 2010, DOI: 10.3390/en3121960
Abstract: Clathrate hydrates have recently received attention as novel storage and transportation materials for natural gases or hydrogen. These hydrates are treated as powders or particles, and moderate storage temperatures (around 253 K) are set for economic reasons. Thus, it is necessary to consider the sintering of hydrate particles for their easy handling because the hydrates have a framework similar to that of ice, even though their sintering would require guest molecules in addition to water molecules. We observed the sintering process of clathrate hydrates to estimate the rate of sintering. Spherical tetrahydrofuran (THF) hydrate particles were used in observations of sintering under a microscope equipped with a CCD camera and a time-lapse video recorder. We found that THF hydrate particles stored at temperatures below the equilibrium condition sintered like ice particles. The sintering part was confirmed to be not ice, but THF hydrate, by increasing the temperature above 273 K after each experiment. The sintering rate was lower than that of ice particles under the normal vapor condition at the same temperature. However, it became of the same order when the atmosphere of the sample was saturated with THF vapor. This indicates that the sintering rate of THF hydrate was controlled by the transportation of guest molecules through the vapor phase accompanied with water molecules.
Using a lighter to heat a cautery
Brian Savage
Community Eye Health Journal , 2011,
Abstract: Those of us who are extracapsular cataract surgeons have all experienced delays in cauterizing the eye due to difficulty in lighting a spirit lamp containing methylated spirit with too much water mixed in it. We have found that using a cigarette lighter for heating is a viable alternative.
Formation of porous gas hydrates  [PDF]
Andrey N Salamatin,Werner F Kuhs
Physics , 2015,
Abstract: Gas hydrates grown at gas-ice interfaces are examined by electron microscopy and found to have a submicron porous texture. Permeability of the intervening hydrate layers provides the connection between the two counterparts (gas and water molecules) of the clathration reaction and makes further hydrate formation possible. The study is focused on phenomenological description of principal stages and rate-limiting processes that control the kinetics of the porous gas hydrate crystal growth from ice powders. Although the detailed physical mechanisms involved in the porous hydrate formation still are not fully understood, the initial stage of hydrate film spreading over the ice surface should be distinguished from the subsequent stage which is presumably limited by the clathration reaction at the ice-hydrate interface and develops after the ice grain coating is finished. The model reveals a time dependence of the reaction degree essentially different from that when the rate-limiting step of the hydrate formation at the second stage is the gas and water transport (diffusion) through the hydrate shells surrounding the shrinking ice cores. The theory is aimed at the interpretation of experimental data on the hydrate growth kinetics.
Methane hydrates in the Chilean continental margin
Morales G.,Esteban;
Electronic Journal of Biotechnology , 2003,
Abstract: in the coming years the worldwide energetic resources based on hydrocarbons will diminish, and methane hydrates can become an alternative source, given its huge deposits. chile does not have great amounts of energetic resources; however, during the cruise c-2901 on board the r/v conrad in 1998, seismic profiles that took place in the chilean continental margin between 35o and 45os show the presence of methane hydrates through bsr analysis. the following parameters for the hydrate layer can be assumed: thickness = 100 m, longitude e-w = 20 km, latitude n-s = 1000 km, hydrate concentration in the sediments = 10%, and 160 m3 of gas per m3 of hydrate. with these figures, the volume of estimated gas is 3.2 x 1013 m3.
More on higher order decays of the lighter top squark  [PDF]
Werner Porod
Physics , 1998, DOI: 10.1103/PhysRevD.59.095009
Abstract: We discuss the three-body decays stop_1 -> W^+ b neutralino_1, stop_1 -> H^+ b neutralino_1, stop_1 -> b slepton_i neutrino_l, and stop_1 -> b sneutrino_l l^+$ ($l =e,\mu,\tau$) of the lighter top squark within the minimal supersymmetric standard model. We give the complete analytical formulas for the decay widths and present a numerical study in view of an upgraded Tevatron, the CERN LHC, and a future lepton collider demonstrating the importance of these decay modes.
Hydrogen (H2) Storage in Clathrate Hydrates  [PDF]
Pratim Kumar Chattaraj,Sateesh Bandaru,Sukanta Mondal
Physics , 2010,
Abstract: Structure, stability and reactivity of clathrate hydrates with or without hydrogen encapsulation are studied using standard density functional calculations. Conceptual density functional theory based reactivity descriptors and the associated electronic structure principles are used to explain the hydrogen storage properties of clathrate hydrates. Different thermodynamic quantities associated with H2-trapping are also computed. The stability of the H2-clathrate hydrate complexes increases upon the subsequent addition of hydrogen molecules to the clathrate hydrates. The efficacy of trapping of hydrogen molecules inside the cages of clathrate hydrates depends upon the cavity sizes and shapes of the clathrate hydrates. Computational studies reveal that 512 and 51262 structures are able to accommodate up to two H2 molecules whereas 51268 can accommodate up to six hydrogen molecules.
Physical Properties of Gas Hydrates: A Review  [PDF]
Jorge F. Gabitto,Costas Tsouris
Journal of Thermodynamics , 2010, DOI: 10.1155/2010/271291
Abstract: Methane gas hydrates in sediments have been studied by several investigators as a possible future energy resource. Recent hydrate reserves have been estimated at approximately ? of methane gas worldwide at standard temperature and pressure conditions. In situ dissociation of natural gas hydrate is necessary in order to commercially exploit the resource from the natural-gas-hydrate-bearing sediment. The presence of gas hydrates in sediments dramatically alters some of the normal physical properties of the sediment. These changes can be detected by field measurements and by down-hole logs. An understanding of the physical properties of hydrate-bearing sediments is necessary for interpretation of geophysical data collected in field settings, borehole, and slope stability analyses; reservoir simulation; and production models. This work reviews information available in literature related to the physical properties of sediments containing gas hydrates. A brief review of the physical properties of bulk gas hydrates is included. Detection methods, morphology, and relevant physical properties of gas-hydrate-bearing sediments are also discussed. 1. Introduction Clathrate hydrates or gas hydrates are solid structures. Water molecules are linked through hydrogen bonding and create cavities (host lattice) that can enclose a large variety of molecules (guests). No chemical bonding takes place between the host water molecules and the enclosed guest molecule. The clathrate hydrate crystal may exist at temperatures below as well as above the normal freezing point of water [1]. Clathrate hydrates of current interest are composed of water and the following molecules: methane, ethane, propane, isobutane, normal butane, nitrogen, carbon dioxide, and hydrogen sulfide. However, other nonpolar components between the sizes of argon (0.35?nm) and ethylcyclohexane (0.9?nm) can also form hydrates. Clathrate hydrates, commonly called gas hydrates, form at temperatures close to 273?K and elevated pressures [2]. The discovery of gas hydrates is credited to Sir Humphrey Davy [3] in 1810. Due to their crystalline, nonflowing nature, hydrates first became of interest to the hydrocarbon industry in 1934, when they were first observed [4] blocking pipelines. Hydrates concentrate hydrocarbons: 1?m3 of hydrates may contain as much as 180?SCM (standard cubic meters) of gas. Makogon [5] indicated that large natural reserves of hydrocarbons exist in hydrated form, both in deep oceans and in the permafrost. Evaluation of these reserves is highly uncertain, yet even the most conservative
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