The sol–gel method for the mullite synthesis is reviewed, with particular emphasis on the characterization of monophasic and
diphasic gels at low, intermediate and high temperatures and the factors that influence the hydrolysis and condensation rate
of the sol–gel process, which in turn determine the properties of the final material. A wide range of studies about mullite
precursors synthesized via sol–gel is discussed here. 相似文献
In close to equilibrium conditions (1° per 400 min), the DSC measurements demonstrated that the melting parameters of white rat sarcoma M1 procollagen equaled to Tm?=?34.4 °C and ΔTm?=?2.7°, and the same parameters of fibers reconstructed from those solutions of procollagen were Tm?=?38.5 °C and ΔT?=?3.1°. These values were by 1.0° lower and 0.8° wider, and by 1.7° lower and 0.7° wider in comparison with the parameters of procollagen and fibers of healthy rat tissue, accordingly. The simultaneous increase in melting temperature and melting width, and a weak decrease in melting enthalpy demonstrated that sarcoma M1 procollagen had some defects. The considerable decrease by 7° in melting temperature and decrease in thermostability of procollagen fibrils in case of sarcoma M1 in comparison to the healthy norm gives a good prospective potential of using this approach as a quick DSC test to detect various sarcomas, including human sarcomas, by comparing the biopsy material or postsurgical tissues with the normal samples.
ABSTRACT Miorocrystalline cellulose stabilized emulsions (o/w) were evaluated by means of brightfield and polarized light microscopy, freeze-etch electron microscopy, droplet size analyses and rheologic measurements. These studies indicated that miorocrystalline cellulose (Avicel RC591 ) forms a network around emulsified oil droplets. This structure provides a mechanical barrier at the o/w interface which stabilizes the emulsion without the necessity for decreasing interfacial tension, as in conventional surfactant-stabilized emulsions. Rheologic studies indicated that emulsions containing Avicel RC591 had a considerable degree of thlxotropy which contributed to their stability. When Tween 80 was incorporated in this system, oil droplets coalesced indicating that the stability of the emulsion was affected adversely. 相似文献
The regioselective synthesis and characterization of a new series of 3‐aryl‐7‐trifluoromethyl[1,2,4]triazolo[4,3–a]pyrimidines from the oxidative heterocyclization of 2‐(N′‐benzylidenehydrazino)‐4‐trifluoromethylpyrimidines with copper dichloride is described. J. Heterocyclic Chem., (2011). 相似文献
Amongst the many ways of constructing the amide bond, there has been a growing interest in the use of metal-catalysed methods for preparing this important functional group. In this tutorial review, highlights of the recent literature have been presented covering the key areas where metal catalysts have been used in amide bond formation. Acids and esters have been used in coupling reactions with amines, but aldehydes and alcohols have also been used in oxidative couplings. The use of nitriles and oximes as starting materials for amide formation are also emerging areas of interest. The use of carbon monoxide in the transition metal catalysed coupling of amines has led to a powerful methodology for amide bond formation and this is complemented by the addition of an aryl or alkenyl group to an amide typically using palladium or copper catalysts. 相似文献
The photoluminescence spectra and luminescence excitation spectra of pure microcrystalline and nano-sized ZnWO4 as well as the ZnxNi1−xWO4 solid solutions were studied using vacuum ultraviolet (VUV) synchrotron radiation. The samples were also characterized by
x-ray powder diffraction. We found that: (i) the shape of the photoluminescence band at 2.5 eV, being due to radiative electron
transitions within the [WO6]6− anions, becomes modulated by the optical absorption of Ni2+ ions in the ZnxNi1−xWO4 solid solutions; and (ii) no significant change in the excitation spectra of Zn0.9Ni0.1WO4 is observed compared to pure ZnWO4. At the same time, a shift of the excitonic bands to smaller energies and a set of peaks, attributed to the one-electron
transitions from the top of the valence band to quasi-localized states, were observed in the excitation spectrum of nano-sized
ZnWO4. 相似文献
We show that the conditions defining total reflexivity for modules are independent. In particular, we construct a commutative
Noetherian local ring R and a reflexive R-module M such that ExtRi(M,R)=0 for all i>0, but ExtRi(M*,R)≠0 for all i>0.
Presented by Juergen Herzog
Mathematics Subject Classification (2000) 13D07. 相似文献
Tannin–formaldehyde cryogels (TFC) were synthesized by sol–gel polycondensation of low molecular weight and highly reactive modified tannin with formaldehyde using HCl as a catalyst. Carbon cryogels (CC) were obtained by the TFC pyrolysis at an inert atmosphere at 800 °C. Pyrolysis caused significant changes in the physical and chemical properties of the material. The pyrolysis induced the decomposition of acid superficial groups and the development of basic ones. Pyrolysis also provoked significant change in the pore volume, forming a great amount of micropores. TFC and CC showed amorphous and turbostratic structures, respectively. Unpurified samples had inorganic impurities in their compositions. 相似文献
The cheap, commercially available iron complex, Fe(NO3)3·9H2O, has been used to catalyse the formation of amides by the addition of amines to nitriles. 相似文献