Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe properties and the structure of colloid agregates of the silver besilcate Ag6Si2O7 in water medium
76
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The paper describes the investigation of the properties of silver besilicate salt colloids in water medium. Ag6Si2O7 was obtained in a soft conditions, in water medium, at temperatures and pressure close to room ones. The morphology and crystallinity of matter under investigations appear to depend on the growth conditions. Slow growth resulted in quasi-crystalline yellowish whiskers, while high concentration of precursors led to fast formation of the quasi-amorphous aggregates. The elemental constitution of object under study was determined with the help of Comebax-INCA set-up, and was then proved by chemical analysis. The ratio of elements was close to Ag6Si2O7, and depended a little whether the sample was taken from the sediments of reaction or from dried residue of a liquid medium. The experiments in Raman technique revile several well-resolvable bands in whisker-like samples, but only few of them were able to detect in quasi-amorphous material. In the last case the bands were broader, but the positions of weak broad bands were close to the positions of corresponding bands in whiskers. We can suggest, that the bands, common in two former cases, are due to oscillation in bepyramidal molecules of Ag6Si2O7, and the bands, seen only at whiskers, are due to long-rang order. The very special peculiarity was observed under chemical test with hydrochloric acid. The white flakes sedimentation appeared after addition of NaCl but do not appeared when HCl was added. This result can be explained if to assume the existence of silicon acid shell around the colloidal particles of silver besilicate. The model of silicon acid shell around colloids was proved by high resolution electron microscopy.
rate research
Read More
Molecular adsorption on surfaces plays a central role in catalysis, corrosion, desalination, and many other processes of relevance to industry and the natural world. Few adsorption systems are more ubiquitous or of more widespread importance than those involving water and carbon, and for a molecular level understanding of such interfaces water monomer adsorption on graphene is a fundamental and representative system. This system is particularly interesting as it calls for an accurate treatment of electron correlation effects, as well as posing a practical challenge to experiments. Here, we employ many-body electronic structure methodologies that can be rigorously converged and thus provide faithful references for the molecule-surface interaction. In particular, we use diffusion Monte-Carlo (DMC), coupled cluster (CCSD(T)), as well as the random phase approximation (RPA) to calculate the strength of the interaction between water and an extended graphene surface. We establish excellent, sub-chemical, agreement between the complementary high-level methodologies, and an adsorption energy estimate in the most stable configuration of approximately -100,meV is obtained. We also find that the adsorption energy is rather insensitive to the orientation of the water molecule on the surface, despite different binding motifs involving qualitatively different interfacial charge reorganisation. In producing the first demonstrably accurate adsorption energies for water on graphene this work also resolves discrepancies amongst previously reported values for this widely studied system. It also paves the way for more accurate and reliable studies of liquid water at carbon interfaces with cheaper computational methods, such as density functional theory and classical potentials.
The most common species in liquid water, next to neutral H$_2$O molecules, are the H$_3$O$^+$ and OH$^-$ ions. In a dynamic picture, their exact concentrations depend on the time scale at which these are probed. Here, using a spectral-weight analysis, we experimentally resolve the fingerprints of the elusive fluctuations-born short-living H$_3$O$^+$, DH$_2$O$^+$, HD$_2$O$^+$, and D$_3$O$^+$ ions in the IR spectra of light (H$_2$O), heavy (D$_2$O), and semi-heavy (HDO) water. We find that short-living ions, with concentrations reaching $sim 2%$ of the content of water molecules, coexist with long-living pH-active ions on the picosecond timescale, thus making liquid water an effective ionic liquid in femtochemistry.
We have analyzed the atomic arrangements and quantum conductance of silver nanowires generated by mechanical elongation. The surface properties of Ag induce unexpected structural properties, as for example, predominance of high aspect ratio rod-like wires. The structural behavior was used to understand the Ag quantum conductance data and the proposed correlation was confirmed by means of theoretical calculations. These results emphasize that the conductance of metal point contacts is determined by the preferred atomic structures and, that atomistic descriptions are essential to interpret the quantum transport behavior of metal nanostructures.
Molecular dynamics simulations using an interatomic potential developed by artificial neural network deep machine learning are performed to study the local structural order in Al90Tb10 metallic glass. We show that more than 80% of the Tb-centered clusters in Al90Tb10 glass have short-range order (SRO) with their 17 first coordination shell atoms stacked in a 3661 or 15551 sequence. Medium-range order (MRO) in Bergman-type packing extended out to the second and third coordination shells is also clearly observed. Analysis of the network formed by the 3661 and 15551 clusters show that ~82% of such SRO units share their faces or vertexes, while only ~6% of neighboring SRO pairs are interpenetrating. Such a network topology is consistent with the Bergman-type MRO around the Tb-centers. Moreover, crystal structure searches using genetic algorithm and the neural network interatomic potential reveal several low-energy metastable crystalline structures in the composition range close to Al90Tb10. Some of these crystalline structures have the 3661 SRO while others have the 15551 SRO. While the crystalline structures with the 3661 SRO also exhibit the MRO very similar to that observed in the glass, the ones with the 15551 SRO have very different atomic packing in the second and third shells around the Tb centers from that of the Bergman-type MRO observed in the glassy phase.
We present a detailed study of the energetics of water clusters (H$_2$O)$_n$ with $n le 6$, comparing diffusion Monte Carlo (DMC) and approximate density functional theory (DFT) with well converged coupled-cluster benchmarks. We use the many-body decomposition of the total energy to classify the errors of DMC and DFT into 1-body, 2-body and beyond-2-body components. Using both equilibrium cluster configurations and thermal ensembles of configurations, we find DMC to be uniformly much more accurate than DFT, partly because some of the approximate functionals give poor 1-body distortion energies. Even when these are corrected, DFT remains considerably less accurate than DMC. When both 1- and 2-body errors of DFT are corrected, some functionals compete in accuracy with DMC; however, other functionals remain worse, showing that they suffer from significant beyond-2-body errors. Combining the evidence presented here with the recently demonstrated high accuracy of DMC for ice structures, we suggest how DMC can now be used to provide benchmarks for larger clusters and for bulk liquid water.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
