Features of the reconstruction of the lost elements in the museum practice on silver items

The purpose of the article is to develop a methodological basis and solve the problem of the peculiarities of the addition of lost elements in works of precious metal in the restoration process. In practice, it has been established that the insulation of additions with materials that are widely used in modern museum restoration is not able to create a completely inert layer and insulate the anode-cathode system between the added parts and the original. As a result of corrosion caused by atmospheric influences, the metal is destroyed, galvanic corrosion is accelerated, the additions are eventually destroyed due to oxidation, and the original loses its historical appearance. The article organizes information on the study of epoxy resins, the use of which in the restoration of silver objects is not universal due to their complicated reversibility. The methodology is based on scientific and experimental methods, analytical – to reveal the essence of each of the functions, generalization – to clarify the international requirements for modern scientific restoration of metal works. The scientific novelty of the research is to develop a restoration technique and create a tool for the restoration of works of decorative and applied art from silver of non-archaeological origin in museum restoration. Conclusions. Restoration measures, such as the addition of losses on works of decorative and applied art made of silver in museum practice, need careful research and optimization. The use of lead and tungsten as a filler has a number of advantages in the chemical-physical, ethical and aesthetic fields of modern scientific museum restoration. The article has significant theoretical and practical significance, as it explores the features of the addition of losses, the possibility of using the tool as a material for casting the lost element, mastication of cracks and minor gaps. The study of the peculiarities of the addition of silver objects can have a successful practical implementation in museum restoration.

Synthesis and modification of beta zeolite for use in toluene disproportionation reaction

<p>In this paper zeolite Beta was synthesized and characterized by XRD, ATG, ATD, XRF and SEM. Subsequently various modifications were made using a surface passivation process in liquid phase with tetraethylorthosilicate (TEOS), using two loads of TEOS and three passivation cycles, in order to obtain six catalysts. These materials were characterized by NH3-TPD and tested in tolune disproportionation reaction, under different conditions of pressure and temperature. As modification cycles were increased for each catalyst, there was a change in the acidity of the solids, mainly due to deposition of an inert layer of silica on the external surface. These results were confirmed with the improvement in para-selectivity and decreasing in conversion. Despite zeolite Beta is a large pore zeolite, an improvement of the para-selectivity was obtained, achieving almost stable values for the entire range of temperature and pressure conditions.</p>

Magnetic and dielectric properties study of cobalt ferrite nanoparticles synthesized by co-precipitation method

Cobalt ferrite nanoparticles were prepared by co-precipitation method and were heat treated at 100 oC, 200 oC, 400 oC and 600 oC for 2 h to increase the particle size. Phase purity of samples was confirmed by X-ray diffraction. Scherrer formula calculations showed crystallite size varied from 12 to 24 nm when heated from 100 oC to 600 oC. Transmission electron microscopy reveals a uniform and narrow particle size distribution about 12 nm for as-prepared cobalt ferrite particles. Room temperature saturation magnetization was found to vary from 40.8 to 67.0 emu/g as the particle size increased from12 nm to 24 nm. Increase in saturation magnetization with increase in particle size was attributed to the presence of magnetic inert layer on the surface of nanoparticles. Inert layer thickness calculated at 10 K and 300 K was 6 Å and 11 Å respectively. The dielectric properties ε’, tanδ, Z and θ have been studied as a function of frequency and particles size. For the 12 nm grain size, the dielectric constant is one order higher than that of bulk cobalt ferrite. Increase in the grain size showed an increase in the dielectric constant. The increase in the conductivity with grain size is mainly due to the grain size effects. The present study shows that the dielectric properties can be tailor-made to suit the requirement of a particular application by controlling the grain size.

Size-dependent melting of matrix-embedded Pb-nanocrystals

ABSTRACTWe report calorimetric data for the size-dependence of the melting temperature as well as the enthalpy and entropy of melting for nanoscale Pb particles in an Al matrix, prepared by high energy ball-milling. The results are discussed with respect to various models for the melting of small confined systems. We can rule out models based on a temperature-independent Gibbs excess free energy of the particle-matrix interface, and a model based on an increased meansquare displacement of the interfacial layer. The best agreement to the data is provided by modeling the interface as an inert layer of finite thickness, which does not participate in the phase transition.