Greater Diffusion Rate Research Articles

Interface dissolution kinetics and porosity formation of calcite and dolomite (1 1 0) and (1 0 4) planes: An implication to the stability of geologic carbon sequestration

Geologic carbon sequestration (GCS) via injecting CO2 into deep carbonate reservoirs (mainly calcite and dolomite) is a promising strategy to reduce CO2 level. However, the dissolution or precipitation of calcite/dolomite planes on minerals/solution interface during long-term GCS process develops intergranular porosity and thus affects the permeability and stability of reservoirs. To investigate this process, both calcite and dolomite were dissolved in acetic and carbonic acids. A diffusion-controlled process was identified, with greater diffusion rates in acetic acid than that in carbonic acid. Quantified planes activity of both minerals follows (110) > (116) > (101) > (113) > (018) > (104) through density functional theory. Accomplished with preferential dissolution of calcite (110) planes in carbonic acid, calcite crystals precipitated with (104) planes at 423.15 K, under which, more calcite crystals were observed on dolomite surface, producing Ca-deplete surface. Molecular dynamic calculations showed higher dissolution rates of calcite/dolomite (110) planes than (104). In addition, the dissolution coefficients of Ca2+ were approximately triple of that Mg2+. Therefore, this study reveals the interface dissolution mechanisms of calcite and dolomite, especially on (110) and (104) planes at an atomic level, for the first time, providing better understanding for the stability of long-term GCS process.

Atomic Layer Deposition of Metal Sulfide Materials

CONSPECTUS: The field of nanoscience is delivering increasingly intricate yet elegant geometric structures incorporating an ever-expanding palette of materials. Atomic layer deposition (ALD) is a powerful driver of this field, providing exceptionally conformal coatings spanning the periodic table and atomic-scale precision independent of substrate geometry. This versatility is intrinsic to ALD and results from sequential and self-limiting surface reactions. This characteristic facilitates digital synthesis, in which the film grows linearly with the number of reaction cycles. While the majority of ALD processes identified to date produce metal oxides, novel applications in areas such as energy storage, catalysis, and nanophotonics are motivating interest in sulfide materials. Recent progress in ALD of sulfides has expanded the diversity of accessible materials as well as a more complete understanding of the unique chalcogenide surface chemistry. ALD of sulfide materials typically uses metalorganic precursors and hydrogen sulfide (H2S). As in oxide ALD, the precursor chemistry is critical to controlling both the film growth and properties including roughness, crystallinity, and impurity levels. By modification of the precursor sequence, multicomponent sulfides have been deposited, although challenges remain because of the higher propensity for cation exchange reactions, greater diffusion rates, and unintentional annealing of this more labile class of materials. A deeper understanding of these surface chemical reactions has been achieved through a combination of in situ studies and quantum-chemical calculations. As this understanding matures, so does our ability to deterministically tailor film properties to new applications and more sophisticated devices. This Account highlights the attributes of ALD chemistry that are unique to metal sulfides and surveys recent applications of these materials in photovoltaics, energy storage, and photonics. Within each application space, the benefits and challenges of novel ALD processes are emphasized and common trends are summarized. We conclude with a perspective on potential future directions for metal chalcogenide ALD as well as untapped opportunities. Finally, we consider challenges that must be addressed prior to implementing ALD metal sulfides into future device architectures.

Na and Li ion diffusion in modified ASTM C 1260 test by Magnetic Resonance Imaging (MRI)

In the current study, MRI was applied to investigate lithium and sodium ion diffusion in cement paste and mortars containing inert sand and borosilicate glass. Paste and mortars were treated by complying with ASTM C 1260. Lithium and sodium distribution profiles were collected at different ages after different treatments. Results revealed that sodium ions had a greater diffusion rate than lithium ions, suggesting that Na reaches the aggregate particle surface before Li. Results also showed that Na and Li ions had a competitive diffusion process in mortars; soaking in a solution with higher [Li] favored Li diffusion but hindered Na diffusion. In mortars containing glass, a substantial amount of Li was consumed by the formation of ASR products. When [Li] in soaking solution was reduced to 0.37 N, a distinctive Na distribution profile was observed, indicating the free-state Na ions were continuously transformed to solid reaction products by ASR. Hence, in the modified ASTM C 1260 test, [Li] in the storage solution should be controlled at 0.74 N, in order to completely prevent the consumption of Na ions and thus stop ASR.

Diffusion rates of positron emitters in pion irradiated patients

Results are presented which indicate that for these specific cases the biological half-life of the activated beta +-emitting radionuclides depends on the anatomical site, varying from 38 to 79 min for the sites measured. The abdominal tumours had greater diffusion rates than the more solid tumours in the other sites. This result is consistent with the expectation that increased vascularity should increase diffusion. The longevity of the biological half-lives should not cause significant reduction in count rates during the 15 min counting intervals planned for patient tomograms. However, the results suggest that solid tumours may have a biological half-life different from that of surrounding healthy tissue. If this difference is large, some problems might arise in interpreting positron tomograms, as the data will represent some time-averaged strength depending on the biological half-life.

Diffusion processes of small spots of electrostatically charged molecules in subsonic grid turbulence

A technique has been developed for the production of small spots or volumes of ionized gas and the processes of diffusion of these spots have been investigated for the case of emission in a nearly non-turbulent flow (wind-tunnel) as well as in the turbulent flow created behind a square mesh-grid. The diffusion of these charged molecules has been related to the decreasing electrical potential induced at the top of an antenna placed on the main flow axis. The study has shown different phases of dispersion in non turbulent flows; in a strongly turbulent flow, the homogeneisation of diffusion of random molecular motions is illustrated by a uniform law for decreasing induced potentials along the flow-axis; A greater diffusion rate is also observed in that case. An analysis of the transversal expansion of the small ionized clouds has been developed from which the charge density has been deduced. Finally, the charge dispersion rate has been related to the local relative kinetic energy of agitation.

Diffusion of Three Chloros-Triazines in Soil

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triaazine] diffused at a rate of 15.2 × 10−8sq cm/sec at 25 C which was faster than the diffusion rate of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) in the same soils. Diffusion rates were highly correlated with total surface area of the soil. Increasing soil moisture content, soil pH, and soil temperature resulted in greater diffusion rates. A relative indication of herbicide mobility may be obtained from some of the physical and chemical properties of the soils and herbicides involved; however, rate of diffusion appears to be governed by a combination of soil and herbicide properties.

SORPTION OF METHACRYLIC ACID BY NYLON. II. THE RATES OF SORPTION AND DESORPTION BY DRAWN NYLON 6.6 FIBRES

The rates at which methacrylic acid is sorbed and desorbed from aqueous solution by drawn nylon 6.6 fibres have been measured at 30°, 45°, and 60°C. Desorption is faster than the first sorption, and the second sorption proceeds initially at the same rate as desorption. On first sorption only, there is a very short induction period, and supersorption occurs, the amount sorbed passing through a maximum before falling to the equilibrium value. The rates of change of fibre length on sorption and desorption have been correlated with the sorption and desorption rates themselves. They are roughly proportional for desorption (decrease in length) and for sorptions beyond the second (increase in length) On first sorption, there is a relatively long induction period before the irreversible decrease in length begins. It is considered that the first sorption produces an irreversible relaxation in the fibres, allowing greater diffusion rates subsequently. This process is completed on second sorption. The sorption rates...

Observations of the Reaction between Gaseous Ammonia and Hydrogen Chloride as a Teaching Aid

In a short time, depending upon the length of the tube and the temperature, a white cloud appears. This cloud deposits a ring in the tube. The position of the ring is marked. From this position, the relative diffusion rate of the two gases may be calculated. The observing group now watches the surging of the white cloud. The movement is roughtly comparable to waves breaking against the beach and welling back as an undertow. The ammonia gas, being appreciably lighter than hydrogen chloride, appears to fall on the heavier gas and forms the white cloud of ammonium chloride. The formation of white rings in the tube is another item of interest to the observing student. Because of the greater diffusion rate of ammonia, the cloud moves toward the hydrgen chloride end of the tube. Students who have difficulty in visualizing a chemical reaction in which precipitates are produced or gases evolved, appreciate our demonstration because they feel that in this case they are able to observe more clearly how a chemical reaction progresses.