New apparatus for DTA at 2000 bar: thermodynamic studies on Au, Ag, Al and HTSC oxides

A new DTA (Differential Thermal Analysis) device was designed and installed in a Hot Isostatic Pressure (HIP) furnace in order to perform high-pressure thermodynamic investigations up to 2 kbar and 1200C. Thermal analysis can be carried out in inert or oxidising atmosphere up to p(O2) = 400 bar. The calibration of the DTA apparatus under pressure was successfully performed using the melting temperature (Tm) of pure metals (Au, Ag and Al) as standard calibration references. The thermal properties of these metals have been studied under pressure. The values of DV (volume variation between liquid and solid at Tm), ROsm (density of the solid at Tm) and ALPHAm (linear thermal expansion coefficient at Tm) have been extracted. A very good agreement was found with the existing literature and new data were added. This HP-DTA apparatus is very useful for studying the thermodynamics of those systems where one or more volatile elements are present, such as high TC superconducting oxides. DTA measurements have been performed on Bi,Pb(2223) tapes up to 2 kbar under reduced oxygen partial pressure (p(O2) = 0.07 bar). The reaction leading to the formation of the 2223 phase was found to occur at higher temperatures when applying pressure: the reaction DTA peak shifted by 49C at 2 kbar compared to the reaction at 1 bar. This temperature shift is due to the higher stability of the Pb-rich precursor phases under pressure, as the high isostatic pressure prevents Pb from evaporating.Comment: 6 figures, 3 tables, Thermodynamics, Thermal property, Bi-2223, fundamental valu

ИЗУЧЕНИЕ ХИМИЧЕСКОЙ СБОРКИ МАКРОМОЛЕКУЛ В ПОЛИКОНДЕНСАЦИИ ДИФУНКЦИОНАЛЬНЫХ ДИМЕТИЛСИЛАНОВ

The article describes the results of a research on polycondensation “in situ” in the process of partial hydrolysis of dimethyldimetoxysilane and dimethyldiacetoxysilane as compared with similar data for the dimethyldichlorosilane and homofunctional condensation of dimethylsilandiol. The effect of the molar ratio of components on the composition of products of partial hydrolysis of the functional dimethylsilanes and dependence of the monomer conversion degree (Xm) vs. conversion of functional groups (Xf) are presented. It is shown that as the conversion of functional groups in composition products increases the share of dimethylcyclosiloxanes and reaches more than 99% (when Xf →1). It is found that among the monomers (CH3)2Si(OCH3)2 < (CH3)2Si(OCOCH3)2 ≈ (CH3)2SiCl2 the proportion of unit-to-unit assembling of oligomeric molecules, which are created by heterofunctional condensation of hydrolysis products and the proportion of organocyclosiloxanes are increasing. It is assumed that the heterophase process which is responsible for the lack of hydrolyzing agent due to its slow diffusion is the cause of the unit-to-unit assembling.В статье рассмотрены результаты исследований поликонденсации «in situ» в процессах гетерофазного частичного гидролиза диметилдиметокси- и диметилдиацетоксисиланов в сопоставлении с аналогичными данными для диметилдихлорсилана и гомофункциональной поликонденсации диметилсиландиола. Представлено влияние мольного соотношения реагентов на олигомерный состав продуктов частичного гидролиза функциональных диметилсиланов и зависимости конверсии мономеров от конверсии функциональных групп. Установлено, что в ряду мономеров (CH3)2Si(OCH3)2 <(CH3)2Si(OCOCH3)2 ≈ (CH3)2SiCl2 возрастает доля позвенной сборки олигомерных молекул путем гетерофункциональной конденсации продуктов гидролиза и доля органоциклосилоксанов. Причиной позвенности химической сборки является гетерофазность процесса, обуславливающая недостаток гидролизующего агента в зоне реакции из-за его медленной диффузии

Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.Comment: 15 pages, 11 figures. Published in European Physical Journal

THE STUDY OF CHEMICAL ASSEMBLY OF MACROMOLECULES IN POLYCONDENSATION OF DIFUNCTIONAL DIMETHYLSILANES

The article describes the results of a research on polycondensation “in situ” in the process of partial hydrolysis of dimethyldimetoxysilane and dimethyldiacetoxysilane as compared with similar data for the dimethyldichlorosilane and homofunctional condensation of dimethylsilandiol. The effect of the molar ratio of components on the composition of products of partial hydrolysis of the functional dimethylsilanes and dependence of the monomer conversion degree (Xm) vs. conversion of functional groups (Xf) are presented. It is shown that as the conversion of functional groups in composition products increases the share of dimethylcyclosiloxanes and reaches more than 99% (when Xf →1). It is found that among the monomers (CH3)2Si(OCH3)2 < (CH3)2Si(OCOCH3)2 ≈ (CH3)2SiCl2 the proportion of unit-to-unit assembling of oligomeric molecules, which are created by heterofunctional condensation of hydrolysis products and the proportion of organocyclosiloxanes are increasing. It is assumed that the heterophase process which is responsible for the lack of hydrolyzing agent due to its slow diffusion is the cause of the unit-to-unit assembling