Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

The search for durable dyes led several past civilizations to develop artificial pigments. Maya Blue (MB), manufactured in pre-Columbian Mesoamerica, is one of the best known examples of an organic-inorganic hybrid material. Its durability is due to the unique association of indigo molecule and palygorskite, a particular fibrous clay occurring in Yucatan. Despite 50 years of sustained interest, the microscopic structure of MB and its relation to the durability remain open questions. Combining new thermogravimetric and synchrotron X-ray diffraction analyses, we show that indigo molecules can diffuse into the channel of the palygorskite during the heating process, replacing zeolitic water and stabilizing the room temperature phases of the clay

Enhanced Thermoelectric Power and Electronic Correlations in RuSe2_2

We report the electronic structure, electric and thermal transport properties of Ru$_{1-x}$Ir$_{x}$Se$_2$ ($x \leq 0.2$). RuSe$_2$ is a semiconductor that crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe$_2$ exceeds -200 $\mu$V/K around 730 K. Ir substitution results in the suppression of the resistivity and the Seebeck coefficient, suggesting the removal of the peaks in density of states near the Fermi level. Ru$_{0.8}$Ir$_{0.2}$Se$_{2}$ shows a semiconductor-metal crossover at about 30 K. The magnetic field restores the semiconducting behavior. Our results indicate the importance of the electronic correlations in enhanced thermoelectricity of RuSb$_{2}$.Comment: 6 pages, 4 figure

Dynamic Study of N'N-dimethylparanitroaniline encapsulated in Silicalite-1 matrix using neutron spin-echo spectroscopy

International audienceThe present work focuses on the dynamic studies of N'N-dimethyl- paranitroaniline (dmpNA) encapsulated in silicalite zeolite. Quasielastic neutron scattering (QENS) experiments are carried out using neutron spin-echo technique. Polarisation of the scattered neutron beam is measured at carefully chosen values of Q=0.35, 0.9, 1.1 and 1.45 A -1 at xed T=298 K and at xed Q=0.9 A -1 at 150, 200, 250 and 298 K. This gives insight into the motion and the related activation energy of the guest dmpNA molecule. The quasielastic signal observed in the present system within the time range considered is due to fast local rotational motions of protons of the end methyl groups. The results are in good agreement with the dynamics of methyl group rotations reported in the literature by back- scattering QENS technique

X-ray diffraction studies of the effects of N incorporation in amorphous CNx, materials

The effects of nitrogen incorporation on the atomic-scale structure of amorphous CNx samples have been studied for 0, 5, 20, and 30 at. % N concentration, by x-ray diffraction. Significant differences in the structure are observed on the incorporation of only 5 at. % N, and the changes in structure continue as further N is added. From the experimental data, we are able to obtain directly the average bond distances and then calculate the average bond angles for each of the samples. The average first neighbor distance shows a gradual decrease from 1.55 Angstrom for 0 at. % N, to 1.44 Angstrom for 30 at. % N, and a similar trend is observed in the position of the second neighbor peak. This gives a corresponding increase in the average bond angle from 108 degrees to 114 degrees. The results show an increase in the fraction of sp(2) bonded carbon atoms with increasing N concentration, and there is evidence for the presence of significant numbers of C=N and C=N bonds. These results are also consistent with stress, hardness, and optical gap measurements for these samples. (C) 1998 American Institute of Physics. [S0021-8979(98)03907-3]

Association of indigo with zeolites for improved colour stabilization

International audienceThe durability of an organic colour and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidising conditions, using Raman and UV-visible spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high colour stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment

Історична наука в УРСР як предмет дослідження в англо-американській історіографії

У статті відтворено образ історичної науки в УРСР у працях англо-американських учених другої половини ХХ – початку ХХІ ст. Вивчено еволюцію ролі та функцій трьох основних акторів історіографічного процесу в Радянському Союзі – влади, істориків та пересічних громадян. Визначено сталі та змінні компоненти у загальній схемі їх взаємодії.In the article the image of historical science in the Ukrainian SSR in the works of the Anglo-American researchers published during the second half of the twentieth and the beginning of the twenty-first centuries is reconstructed. The modification of roles and functions of three main actors in Soviet historiographical process – power, historians and average citizens – is examined. The invariable and change components in the general pattern of its interaction are defined

The Structure of Hyperalkaline Aqueous Solutions Containing High Concentrations of Gallium - a Solution X-ray Diffraction and Computational Study

Highly concentrated alkaline NaOH/Ga(OH)3 solutions with 1.18 M Ga(III)T 2.32 M and 2.4 M NaOHT 4.9 M (where the subscript T denotes total or analytical concentrations) have been prepared and investigated by solution X-ray diffraction and also by ab initio quantum chemical calculations. The data obtained are consistent with the presence of only one predominant Ga(III)-bearing species in these solutions, that is the tetrahedral hydroxo complex Ga(OH)4–. This finding is in stark contrast to that found for Al(III)-containing solutions of similar concentrations, in which, besides the monomeric complex, an oxo-bridged dimer was also found to form. From the solution X-ray diffraction measurements, the formation of the dimeric (OH)3Ga–O–Ga(OH)32– could not unambiguously be shown, however, from the comparison of experimental IR, Raman and 71Ga NMR spectra with calculated ones, its formation can be safely excluded. Moreover, higher mononuclear stepwise hydroxo complexes, like Ga(OH)63–, that have been claimed to exist by others in the literature, was not possible to experimentally detect in these solutions with any of the spectroscopic techniques used

Compressibility and thermal expansion of cubic silicon nitride

The compressibility and thermal expansion of the cubic silicon nitride (c-Si3N4) phase have been investigated by performing in situ x-ray powder-diffraction measurements using synchrotron radiation, complemented with computer simulations by means of first-principles calculations. The bulk compressibility of the c-Si3N4 phase originates from the average of both Si-N tetrahedral and octahedral compressibilities where the octahedral polyhedra are less compressible than the tetrahedral ones. The origin of the unit cell expansion is revealed to be due to the increase of the octahedral Si-N and N-N bond lengths with temperature, while the lengths for the tetrahedral Si-N and N-N bonds remain almost unchanged in the temperature range 295-1075 K