Search results for "mixture"
showing 10 items of 1178 documents
Porous structure and mechanical strength of cement-lime pastes during setting
2015
Abstract The acceleration of a cement paste setting as a result of lime addition may be shown from isothermal calorimetry measurements. We investigated the underlying mechanisms through two techniques that provide information on porous structure (using Nuclear Magnetic Resonance) and mechanical properties (elastic modulus measured by rheometry). The correlation of the two sets of results on a cement paste clearly reveals the successive steps of setting, and particularly highlights the so-called induction period. We show that this induction period disappears in the presence of lime, leading to an acceleration of the setting. We also show that beyond some critical concentration of added lime …
The spectra of mixed $^3$He-$^4$He droplets
2005
The diffusion Monte Carlo technique is used to calculate and analyze the excitation spectrum of $^3$He atoms bound to a cluster of $^4$He atoms, by using a previously determined optimum filling of single-fermion orbits with well defined orbital angular momentum $L$, spin $S$ and parity quantum numbers. The study concentrates on the energies and shapes of the three kinds of states for which the fermionic part of the wave function is a single Slater determinant: maximum $L$ or maximum $S$ states within a given orbit, and fully polarized clusters. The picture that emerges is that of systems with strong shell effects whose binding and excitation energies are essentially determined over configur…
Visualizing Solubilization by a Realistic Particle Model in Chemistry Education
2019
An application for the visualization of the mixing process of two different types of structureless interacting particles is presented. The application allows to demonstrate on a qualitative basis, as well as by quantitatively monitoring the time evolution of the fractions of aggregates of different sizes, that the formation of a homogeneous mixture is the result of favorable solute-solvent interactions as well as by temperature. It is suggested that, along with the use of suitable macroscopic examples, visualizations by the present application are useful in elucidating concepts related to miscibility/solubility. The application is based on a two-dimensional realistic dynamic model where ato…
The lithium isotope response to the variable weathering of soils in Iceland
2021
Abstract This study has analysed Li isotopes ratios from well-studied soil and pore water profiles from Iceland that have the same parent material but have experienced different degrees of chemical weathering. Thus, from least to most weathered, we have analysed vitrosols (V), gleyic andosols (GA), brown andosols (BA), Histosols (H) and Histic Andosols (HA). Although the most weathered H and HA soils have the highest content in clay-sized material, they have the least fractionated δ7Lipore water values. In contrast, the least weathered GA and BA pore waters are most fractionated for Li isotopes. Given that Li isotope ratios are fractionated by clay mineral formation, this appears counter-in…
A laboratory study on the scavenging of SO2 by snow crystals
1990
Abstract A laboratory experiment is described where the uptake of SO2 by dendritic snow crystals was studied. In a first experimental series the uptake of SO2 was investigated during the growth of the snow crystals from water vapor with and without the presence of H2O2 in the air. In a second series of experiments we studied the uptake of SO2 by snow crystals which had completed their growth. The results of our experiments showed that under both conditions SO2 became scavenged by snow crystals. The uptake of SO2 was particularly pronounced during the growth of the snow crystals, and at temperatures close to 0°C where a quasi-liquid layer exists at the surface of ice. As expected, the SO2 up…
Self-assembly in surfactant-based liquid mixtures: Bis(2-ethylhexyl)phosphoric acid/bis(2-ethylhexyl)amine systems
2010
Surfactant-based liquid mixtures constitute an interesting class of nanostructured materials with promising potential in specialized applications. Here, structural and conductometric properties of liquid mixtures composed of bis(2-ethylhexyl)amine (BEEA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) have been thoroughly investigated with the aim to correlate structural features with system charge transport capability. The evolution of self-assembled local nanostructures with system composition has been investigated by FT-IR and XRD while the conductometric properties were probed by conventional AC complex impedance. Both pure components exhibit nano-segregation due to their amphiphilic natur…
Spark Plasma Sintering (SPS)-Assisted Synthesis and Thermoelectric Characterization of Magnéli Phase V6O11
2018
The Magneli phase V6O11 was synthesized in gram amounts from a powder mixture of V6O11/V7O13 and vanadium metal, using the spark plasma sintering (SPS) technique. Its structure was determined with synchrotron X-ray powder diffraction data from a phase-pure sample synthesized by conventional solid-state synthesis. A special feature of Magneli-type oxides is a combination of crystallographic shear and intrinsic disorder that leads to relatively low lattice thermal conductivities. SPS prepared V6O11 has a relatively low thermal conductivity of κ = 2.72 ± 0.06 W (m K)-1 while being a n-type conductor with an electrical conductivity of σ = 0.039 ± 0.005 (μΩ m)-1, a Seebeck coefficient of α = -(3…
EDXRF and TXRF analysis of elemental size distributions and environmental mobility of airborne particles in the city of Riga, Latvia
2004
Airborne particles were investigated in the central part of Riga during October 2000. Mass, black carbon and elemental concentrations of airborne particles were measured on Teflon filters from a dichotomous impactor, which samples fine (<2.5 µm) and coarse (2.5‐10 µm) fractions of particles. In order to obtain more detailed information on the size distributions of different elements, a seven-stage Batelle cascade impactor was used, in which quartz plates treated with silicone grease were utilized as backing for the different stages. Total reflection x-ray fluorescence (TXRF) and energy-dispersive x-ray fluorescence (EDXRF) spectrometry were used for elemental analysis on the quartz plates a…
Cr(VI) sorption by intact and dehydrated Candida utilis cells: differences in mechanisms
2001
The Cr(VI) sorption kinetics by intact and dehydrated Candida utilis cells were studied. Yeast dehydration led to enhanced Cr(VI) sorption activity by cells during the first 15–20 min of rehydration. In experiments with K2Cr2O7 as a chromium source, [Cr2O7]2− was converted into [CrO4]2− during incubation with dehydrated biomass. An effect of the considerably enhanced Cr(VI) sorption activity by dehydrated cells in the buffered media at pH≈8.0 can serve as another confirmation of the different sorption mechanisms of intact and dehydrated C.utilis cells. This effect was not revealed in water solution at pH 8.0. This phenomenon will be studied in further investigations.
Soil Carbon, Nitrogen and Phosphorus Dynamics as Affected by Solarization Alone or Combined with Organic Amendment
2006
Soil solarization, alone or combined with organic amendment, is an increasingly attractive approach for managing soil-borne plant pathogens in agricultural soils. Even though it consists in a relatively mild heating treatment, the increased soil temperature may strongly affect soil microbial processes and nutrients dynamics. This study aimed to investigate the impact of solarization, either with or without addition of farmyard manure, in soil dynamics of various C, N and P pools. Changes in total C, N and P contents and in some functionally-related labile pools (soil microbial biomass C and N, K2SO4-extractable C and N, basal respiration, KCl-exchangeable ammonium and nitrate, and water-sol…