Glass Formation in Carbonate Systems

Abstract

YNTHESIS of a glass from the composition K2C02-MgCO3 was reported by Eitel and Skaliks' and since then no systematic S attempts to form carbonate glasses have been reported.The highly symmetrical co3 group is not expected to be easily distorted and consequently should not lend itself readily to glass formation. Limited areas of glass formation, however, have been found with certain carbonate compositions and with other selected compositions where volatile compounds must take part in network formation.at 1 kilobar pressure in most instances, using samples contained in sealed noble metal capsules. After heat treatment and quenching, refractive indices of glasses were measured and infrared absorption spectra were obtained where desired. Relatively stable glasses were formed from 40, 50, and 60 mole % MgC03 compositions in the binary system KzC03-MgCOa. Refractive indices of these glasses are plotted in Fig. 1, with circles indicating stable glasses and crosses indicating partly devitrified samples. The indices are 4 to 5% lower than the mean value of the crystalline carbonates. Infrared spectra were also obtained and the spectrum of the K~C03.MgC03 glass (in the 2 to 13p region) was very similar to that of crystalline K2C03-MgC03 showing typical COS frequencies. The spectrum of the glass differs in having broader absorption maxima correspondingly shifted to slightly lower frequencies. No major change in coordination number of the C (e.g., 3 to 4) is, however, suggested foi the glass structure. The lowa refractive index and density of the glasses compared to the crystalline phases may, therefore, be a result of decrease in averape Mg coordination.3 Some samples containing small amounts of hydroxyl were found to devitrify, apparently through the formation of discrete hydroxyl complexes which interrupt the carbonate polymerization.The necessity of ions such as Mg2+, which may assume small coordination numbers, for stabilizing carbonate glasses seems to be further borne out by the limited conditions of glass formation observed with ternary compositions and with other binary mixtures. Glasses were produced on quenching the following compositions from 900" and 1 kilobar: 5 mole yo of either Mn-C 0 3 , PbCOa, or CaC03 added to 95 mole ' % KzCOs.MgCO3.Substitutions of 10% or greater in each instance, however, caused devitrification on quenching. A number of other binary systems were explored but crystallization took place during quenching. BaC03. Li2C03 gave very slightly devitrified glasses; the Li in this case may have a role similar to that of Mg, but is not as effective because of its lower charge. The BaC03-Li2COa mixtures, however, might be expected to form glasses when mixed with additional components. Some more complex systems of volatile constituents were investigated using component binary systems in which no glass formation was observed. The system CaFz-Ca(OH)z-CaCOs-BaS04 rather surprisingly contains a series of glass-forming compositions The reason for glass formation in this instance is not clear; the most obv...

Strategies and new developments in the field of molten carbonates and high-temperature fuel cells in the carbon cycle

“…-Synthesis of carbon nanoparticles in molten alkali carbonates for application in lithium-ion batteries [38]. -Use of some specific carbonate systems, such as K 2 CO 3 eMgCO 3 , where melts can be quenched to glasses [39]. -Role and properties of molten carbonate in geological applications [40].…”

CO3+1 network formation in ultra-high pressure carbonate liquids

“…The formation of a glass in the system K 2 CO 3 -MgCO 3 was, however, reported by Eitel and Skaliks as long ago as 1929 29 as a passing observation and has, with a few exceptions 30,31 received little attention. Glass in this system can be formed in a deep eutectic region at pressures of ~50 MPa 32,33 . The elevated pressure is believed to prevent the carbonate decomposing.…”

Ultralow viscosity of carbonate melts at high pressures

“…3). K 2 Mg(CO 3 ) 2 is unique among all carbonates in forming glass upon quenching 28 , which may explain the discrepancy in viscosity between K 2 Mg(CO 3 ) 2 and K 2 Ca(CO 3 ) 2 carbonate melts. Figure 5a shows a comparison of viscosities of carbonates (calcite and dolomite) melts determined in this study and those of basalt melts reported in a previous study 20 at high pressures.…”

“…27. However, because K 2 Mg(CO 3 ) 2 has a structure distinct from other carbonate melts as evidenced by glass formation on quenching 28 , it likely does not represent typical carbonate melts. In addition, the frame rate employed for capturing images of the falling sphere during these experiments was insufficient to accurately define the terminal velocity, which is the basis for viscosity determination.…”