返回Google圖書搜尋

Phosphate-doped Borosilicate Enamel Coating Used to Protect Reinforcing Steel from Corrosion

出版	Missouri University of Science and Technology, 2014
URL	http://books.google.com.hk/books?id=BsZ-rgEACAAJ&hl=&source=gbs_api

註釋"Phosphate-doped sodium borosilicate glasses were developed for enamel coatings to provide corrosion protection for reinforcing steel in concrete. Phosphates have low solubilities in borosilicate glasses, generally less than about 4 mol%, and are incorporated mainly as isolated PO43− and P2O--4− anions, along with some borophosphate bonds. With the addition of P2O5, the silicate network is repolymerized and tetrahedral borates are converted to trigonal borates, because the phosphate anions scavenge sodium ions from the borosilicate network. The addition of Al2O3 significantly increases the solubility of P2O5 due to the formation of aluminophosphate species that increases the connectivity of phosphate sites to the borosilicate glass network. The addition of P2O5 has an insignificant effect on thermal properties like T[subscript g], T[subscript s] and CTE, and chemical durability in alkaline environments can be improved, particularly for glasses co-doped with alumina. When the solubility limit is reached, a phase-separated microstructure forms, degrading the chemical durability of the glass because of the dissolution of a less durable alkali borate phase. The dissolution rates of glasses in a simulated cement pore water solution are orders of magnitude slower than in Ca-free solutions with similar pH. In Ca-saturated solutions, a passivating layer of calcium silicate hydrate (C-S-H) forms on the glass surface. Phosphate-rich glasses react with the simulated cement pore water to form crystalline hydroxyapatite (HAp) on the glass surface. Electrochemical tests reveal that the HAp precipitates that form on the surfaces of intentionally-damaged phosphate-doped enamel coatings on reinforcing steel suppress corrosion. The enhanced corrosion protection is retained in chloride-containing pore water, where the development of hydroxyl-chlorapatites immobilizes the free chloride ions in solution"--Abstract, page iv.