THERMODYNAMIC ANALYSIS OF THE CHEMICAL RESISTANCE OF CERAMIC MATERIALS IN THE RO- Al2O3-SiO2 SYSTEM

Abstract

Operational characteristics, properties of modern aircraft and aerospace devices and their technical characteristics owe a lot to the radio engineering systems that are installed on them. Therefore, their protection and the selection of the necessary ceramic material, which will ensure the protection of electronic devices from interaction with the external environment, is an important task of modern materials science.
 In order to substantiate the choice of a crystalline phase as the basis of a radio-transparent ceramic material that will be used in aggressive environments, it is advisable to conduct thermodynamic calculations, namely changes in the Gibbs free energy of chemical reactions of the interaction of the crystalline phase with an aggressive environment. To carry out thermodynamic calculations of chemical stability reactions, the three-component system RO- Al2O3-SiO2 (RО – SrО, BaО) was chosen and the crystalline phases that can exist within them were determined. When choosing experimental crystalline phases, a complex of physico-chemical and operational requirements for radio-transparent materials was taken into account. From the point of view of thermodynamics, the corrosion behavior of the selected crystalline phases: celsian BaO·Al2O3·2SiO2, slavsonite SrO·Al2O3·SiO2, SrO·SiO2, and 2SrO·SiO2 is considered.
 The paper presents the results of thermodynamic calculations of changes in enthalpy, entropy, and Gibbs free energy of reactions to determine acid resistance (HСl, H2SO4, HNO3) and alkali resistance (NaОН, Na2CO3) of these compounds under standard conditions. It was established that all considered compounds have a thermodynamic probability of corrosion resistance to the action of alkaline reagents. In relation to an acidic environment, under normal conditions, celsian and slavsonite show acid resistance to hydrochloric acid, and they are least prone to interaction with sulfuric acid, but are able to actively interact with HNO3. Regarding the investigated binary compounds SrO·SiO2 and 2SrO·SiO2, all calculated reactions are thermodynamically favorable, i.e. interaction with acidic reagents occurs.
 The obtained results are analyzed and the correlation of the calculations of the reaction of celsian and hydrochloric acid with experimental data is given. It was concluded that it is rational to plan the production of ceramic products based on celsian and slavsonite or their heterophase mixture with a minimum content of binary oxides of strontium and barium.