Calcination-free production of calcium hydroxide at sub-boiling temperatures.

Calcium hydroxide (Ca(OH)2), a commodity chemical, finds use in diverse industries ranging from food, to environmental remediation and construction. However, the current thermal process of Ca(OH)2 production via limestone calcination is energy- and CO2-intensive. Herein, we demonstrate a novel aqueous-phase calcination-free process to precipitate Ca(OH)2 from saturated solutions at sub-boiling temperatures in three steps. First, calcium was extracted from an archetypal alkaline industrial waste, a steel slag, to produce an alkaline leachate. Second, the leachate was concentrated using reverse osmosis (RO) processing. This elevated the Ca-abundance in the leachate to a level approaching Ca(OH)2 saturation at ambient temperature. Thereafter, Ca(OH)2 was precipitated from the concentrated leachate by forcing a temperature excursion in excess of 65 °C while exploiting the retrograde solubility of Ca(OH)2. This nature of temperature swing can be forced using low-grade waste heat (≤100 °C) as is often available at power generation, and industrial facilities, or using solar thermal heat. Based on a detailed accounting of the mass and energy balances, this new process offers at least ≈65% lower CO2 emissions than incumbent methods of Ca(OH)2, and potentially, cement production.

Elucidating the corrosion-related degradation mechanisms of a Ti-6Al-4V dental implant.

OBJECTIVE: The Ti-6Al-4V (TAV) alloy is commercially used as a dental implant material. This work seeks to elucidates the origins of degradation of Ti-6Al-4V (TAV) implant alloys that result in peri-implant bone loss. 
Methods: In this work, a combination of microstructure, surface, and solution analyses was utilized to study the corrosion mechanism of the TAV alloy in oral environments. The corrosion of TAV alloys in the F--enriched environment of a crevice was evaluated through nanoscale surface analysis. And, the findings were further rationalized via electrochemical means. 
 RESULTS: Our results suggest the bone loss was caused by crevice corrosion and the consequential release of by-products, and the crevice corrosion was potentially induced by the buildup of corrosive species such as fluorides, which are common additives in dental products. In turn, the corrosion properties of the TAV alloy were evaluated in fluoride enriched environments. Nanoscale analysis of corroded surfaces, carried out using vertical scanning interferometry (VSI) showed that the corrosion susceptibility of the constituent phases dictates the corrosion product species. In specific, the aluminum-rich α phase preferentially dissolves under potential-free conditions and promotes the formation of insoluble Al-Ti oxides. Notably, under conditions of applied potential, oxidative dissolution of the vanadium-rich ß phase is favored, and the vanadium release is promoted. 
 SIGNIFICANCE: These findings elucidate the origins of degradation of TAV-implants that result in the release of corrosion by-products into the local biological environment. More important, they offer guidelines for materials design and improvement to prevent this nature of degradation of dental implants.