Unidirectional thermal expansion in KZnB3O6: role of alkali metals.

Unidirectional thermal expansion in edge-sharing BO4 tetrahedra contained KZnB3O6

Borates are among a class of compounds that exhibit rich structural diversity and find wide applications. The formation of edge-sharing (es-) BO4 tetrahedra is extremely unfavored according to Pauling's third and fourth rules. However, as the first and the only es-borate obtained under ambient pressure, es-KZnB3O6 shows an unexpected high thermal stability up to its melting point. The origin of...

Ion exchanged vermiculites with lower expansion onset temperatures

South African Palabora vermiculite was modified by ion exchange with ammonium and selected alkali metal and alkaline earth metal ions. In the exchanged vermiculite with ammonium ions, it was found that ammonia and water were the blowing agents and they were simultaneously released during thermal degradation. In the increasing ionic potential series: Na, Ba, Ca and Mg, it was found that the onse...

Comparison of Catalytic Effect of Alkali and Alkaline Earth Metals Hydrogen Sulfate: As the Promoter for an Efficient Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones under Solvent-Free Conditions

Alkali and alkaline earth metals hydrogen sulfate catalyzed the one-pot three component condensation reactions of aldehydes, 1,3-dicarbonyl compounds and urea or thiourea under solvent-free conditions leading to 3,4-dihydropyrimidin-2(1H)-ones in high yields at 80 °C. Our results showed that Biginelli reaction not only is pH dependent, but the cation of catalyst plays an importan...

The Crystal Structures and Thermal Behavior of Hydrogen Monofluorophosphates and Basic Monofluorophosphates with Alkali Metal and N-containing Cations

Thermal desorption of Na in meteoroids Dependence on perihelion distance of meteor showers

Context. The observed sodium abundance of meteoroids in meteor showers might differ from the original abundance because of processing in interplanetary space after ejections from their parent bodies. Among various processes, thermal alteration of alkali silicate is most likely the major process of Na depletion. Aims. We clarify at which perihelion distances the thermal desorption alters the Na ...