Enamel Remineralization and Dentine Tubules Occlusion by Bioactive Formulations Based on Ion-Doped Nanohydroxyapatite and Precursor Nanoparticles.

Recent health care products are based on formulations claimed to provide enamel remineralization and dentinal tubules occlusion through calcium-phosphate bioactive nanocompounds ( ion-doped hydroxyapatite and precursor nanoparticles). This study aimed to test and characterize for the first time the structure and composition of a representative sample of remineralizing toothpastes and topical mousses available on the market. The enamel remineralization and dentinal tubules occlusion efficacy of tested formulations were investigated in vitro. Formulations were characterized in terms of water- and acid-insoluble fractions, and PXRD, FTIR, and EDS analyses were performed to determine their composition and investigate the presence of bioactive compounds and doping elements. All formulations containing Ca-P bioactive nanocompounds showed remineralizing ability, notably when hydroxyapatite and amorphous calcium phosphate compounds were doped with small amounts of CO3-, F, Mg, and Sr. Topical mousse formulations showed a higher tubules occlusion capability than toothpastes, independently from their composition. In conclusion, all tested formulations could express remineralizing potential both on enamel and dentin thanks to the presence of biomimetic Ca-P compounds. The presence of doping elements or CPP-ACP seems essential to allow such performances.

Corrosion Inhibition Mechanism of Steel Reinforcements in Mortar Using Soluble Phosphates: A Critical Review

The corrosion inhibition mechanism of soluble phosphates on steel reinforcement embedded in mortar fabricated with ordinary Portland cement (OPC) are reviewed. This review focuses soluble phosphate compounds, sodium monofluorophosphate (Na2PO3F) (MFP), disodium hydrogen phosphate (Na2HPO4) (DHP) and trisodium phosphate (Na3PO4) (TSP), embedded in mortar. Phosphate corrosion inhibitors have been deployed in two different ways, as migrating corrosion inhibitors (MCI), or as admixed corrosion inhibitors (ACI). The chemical stability of phosphate corrosion inhibitors depends on the pH of the solution, H2PO4− ions being stable in the pH range of 3–6, the HPO42− in the pH range of 8–12, while the PO43− ions are stable above pH 12. The formation of iron phosphate compounds is a thermodynamically favored spontaneous reaction. Phosphate ions promote ferrous phosphate precipitation due to the higher solubility of ferric phosphate, thus producing a protective barrier layer that hinders corrosion. Therefore, the MFP as well as the DHP and TSP compounds are considered anodic corrosion inhibitors. Both types of application (MCI and ACI) of phosphate corrosion inhibitors found MFP to present the higher inhibition efficiency in the following order MFP > DHP > TSP.

A Comparison in Metal Leachability Between Phosphoric Acid and Ascorbic Acid Stabilised Ferrochrome Slag

Ferrochrome (FeCr) slag was milled and stabilised with either ascorbic acid or phosphoric acid. The stabilised FeCr was then geopolymerised with 1 M KOH in order to obtain a monolith with at least an unconfined compressive strength of 1 MPa. The leachability of metals of the stabilised geopolymerised monoliths were then compared with the unstabilised geopolymerised monolith. Ascorbic acid stabilisation was only effective in Cr leaching reduction by 99.45% but was not effective on immobilisation of Fe, Zn, Ni and Mn. Ascorbic acid stabilisation was thought to proceed via the reduction of Cr(VI) species to insoluble Cr (III) species. Phosphate stabilisation reduced the leachability of Cr, Ni, Zn, Mn, Fe by 99.5%, 67.1%, 71.1%, 96.8% and 85.4% respectively. Phosphate stabilisation was thought to proceed via the formation of phosphate compounds of the metal ions in question. The phosphate stabilised FeCr slag leachability was within the allowable Toxicity Characteristic Leaching Procedure (TCLP) limits and its use is not detrimental to the environment.

Specificities of the study of physical and chemical treatment of wastewater with a significant content of synthetic phosphate-based detergents

The relevance of research. Despite the decrease in the total volume of sewage over the first decades of the 21st century in the territory of Ukraine, the nature of the contaminants that make up their composition has changed significantly. In particular, the content of phosphate compounds and ammonium nitrogen increased. The increase in the phosphate component of wastewater is caused by the widespread of synthetic phosphate-based detergents. Existing treatment facilities are not designed to remove significant volumes of phosphate compounds. That provokes the process of reservoirs eutrophication, their secondary contamination due to biological processes (catastrophic reproduction of cyanobacteria and rapid development of higher aquatic vegetation). Possible ways to solve this issue include: prohibition of the use of synthetic phosphate-based detergents; reconstruction of sewage treatment plants, which will enable effective retention of phosphate compounds; reconstruction of water treatment plants, which will enable to purify poor quality water from water sources and the combination of all these three ways, but not with the global prohibition of the use of synthetic phosphate-based detergents, but by increasing the extra charges for them to the level of phosphate-free detergents and subsidizing them for that. Research results. A number of physical and chemical methods based on the oxidation reactions of a model solution of synthetic detergent were investigated. In particular, such a promising area of new water purification technologies as the use of so-called advanced oxidation technologies (AOTs), in which strong oxidants are generated by electric discharges in the water-air environment or on the surface of a thin film of water. Ozonation was performed using an apparatus that combined cavitation treatment and ozonation. The results of organic component oxidation experimental studies of the model solution with the use of «Fenton» reagent, physical methods of purification (ozonation with cavitation, plasma treatment) and treatment with hydrogen peroxide are presented. Conclusions. The best oxidation effect of the organic component of the model solution was achieved with the use of «Fenton» reagent – 89.5 %. All physical methods (cavitation with ozonation and plasma treatment) achieved about 50 % reduction in COD content: ozonation - 58.3 %; plasma treatment - 51.3 %. The worst results were obtained when treating with hydrogen peroxide - 1.78 %. The experiments in this area need to be continued because all the methods that have been tested require further water purification. In our view, it may be advantageous to combine physical treatment methods with «Fenton» reagent or with additional adsorption of organic compounds residues or with additional biological treatment.