Enhanced CO2 Chemisorption Properties of Li4SO4, Using a Water Hydration–Calcination Technique

High-temperature CO2 sorption over Li4SiO4 synthesized from diatomite: study of sorption heat and isotherm modeling

The Li4SiO4 seems to be an excellent sorbent for CO2 capture at post-combustion. Our work contributes to understanding the effect of the natural Algerian diatomite as a source of SiO2 in the synthesis of Li4SiO4 for CO2 capture at high temperature. For this purpose, we use various molar % (stoichiometric and excess) of calcined natural diatomite and pure SiO2. To select the best composition, CO2 sorption isotherms at 500 °C on the prepared Li4SiO4 are obtained using TGA measurements under various flows of CO2 in N2. The sorbent having 10% molar SiO2 in diatomite (10%ND-LS) exhibits the best CO2 uptake, probably due to various factors such as the content of the different secondary phases. A comparative study was performed at 400 to 500 °C on this selected 10%ND-LS and those with stoichiometric composition obtained with diatomite and pure SiO2. The obtained isotherms show the endothermic character of CO2 sorption. In addition, the evolution of isosteric heat highlights the nature of the involved CO2/Li4SiO4 interactions, by considering the double-shell mechanism. Finally, the experimental sorption isotherms are confronted with some well-known adsorption models to explain the phenomenon occurring over our prepared sorbents. Freundlich and Jensen-Seaton models present a better correlation with the experimental results.

Performance of Li₄SiO₄ Material for CO₂ Capture: A Review

Lithium silicate (Li₄SiO₄) material can be applied for CO₂ capture in energy production processes, such as hydrogen plants, based on sorption-enhanced reforming and fossil fuel-fired power plants, which has attracted research interests of many researchers. However, CO₂ absorption performance of Li₄SiO₄ material prepared by the traditional solid-state reaction method is unsatisfactory during the absorption/regeneration cycles. Improving CO₂ absorption capacity and cyclic stability of Li₄SiO₄ material is a research highlight during the energy production processes. The state-of-the-art kinetic and quantum mechanical studies on the preparation and CO₂ absorption process of Li₄SiO₄ material are summarized, and the recent studies on the effects of preparation methods, dopants, and operating conditions on CO₂ absorption performance of Li₄SiO₄ material are reviewed. Additionally, potential research thoughts and trends are also suggested.

Color stability of lithium disilicate ceramics after aging and immersion in common beverages

STATEMENT OF PROBLEM

The color of an esthetic restoration and its color stability are important for long-term success. However, the impact of common beverages on lithium disilicate ceramic is not well known.

PURPOSE

The purpose of this in vitro study was to investigate color variations of lithium disilicate ceramics after thermocycling (TC) and immersion in commonly consumed beverages.

MATERIAL AND METHODS

A total of 288 specimens (1×10×10 mm) were fabricated from IPS e-max computer-aided design (CAD) (n=72), IPS e-max CERAM ([CER] n=72), IPS e-max Press with glazing ([PG] n=72), and IPS e-max Press without glazing ([PNG] n=72) according to the manufacturer's instructions. Each group was divided into 4 subgroups (n=18): TC, coffee, black tea, and red wine. Thermocycling was performed at 21 900 cycles at 5°C, 37°C, 55°C, and 37°C (3 years' clinical simulation), whereas the specimens were soaked in the staining solutions for up to 54 hours (3 years' clinical simulation). Color parameters L*, a*, and b* were assessed with an ultraviolet-visible spectroscopy recording spectrophotometer. Color difference (ΔE) was calculated using the equation [ΔΕ= [(ΔL*)² + (Δa*)² + (Δb*)²]½]. Intraexaminer reliability was assessed by using the intraclass correlation coefficient. Two-way analysis of variance was used for the analysis of ΔΕ, and the parameters L*, a*, and b* were analyzed with linear mixed models for repeated measurements and the Bonferroni pair-wise comparison test (α=.05).

RESULTS

Parameters ΔΕ, L*, a*, and b* were significantly affected by the interaction between material and treatment (P<.001). A ΔΕ >1 was recorded for PG with tea, wine, and coffee, PG after TC and CER after TC. For L*, greater reduction was observed for PNG with tea and CER after TC, whereas for a* significant changes were positive (to red shades), except for PNG with TC, where PNG with wine showed the greatest positive change. For b*, significant changes were negative (to blue shades) except for PNG with tea and coffee and CAD with tea.

CONCLUSIONS

All groups demonstrated color changes below the clinically perceptible level (ΔΕ<3.7), except PNG in tea which showed statistically significant color differences (ΔΕ>4). CAD presented higher color stability compared with the nonglazed Press specimens.