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.

Production of Colored Phosphate Coatings on Steel

Phosphating has long been successfully used as a method of protecting metal products and structures from corrosion. The possibility of obtaining non-ferrous phosphate coatings on steel by cold method was investigated. Compositions of cold phosphating solutions for the deposition of colored phosphate coatings of green and blue colors are proposed. To obtain green phosphate films, chromium salts and procyon olive green dye were introduced into the compositions of cold phosphating solutions. To obtain phosphate films of orange color, cobalt salts were introduced into the compositions of cold phosphating solutions. To obtain blue phosphate films, methylene blue and Prussian blue were introduced into the compositions of cold phosphating solutions. It was found that colored phosphate films are worse at preventing metal corrosion. Colored phosphate coatings have a higher porosity and are less uniform compared to modified phosphate films.

Fire Characteristics of Selected Tropical Woods without and with Fire Retardant

The flammability of tropical woods and the effect of a selected fire protection coating were evaluated using a cone calorimeter at a cone radiancy of 35 kW/m2. Three samples were from the South American continent (Cumaru, Garapa, Ipe), and two were from the Asian continent (Kempas and Merbau). Samples were treated with commercial fire retardant (FR) containing ferrous phosphate as an essential component. The untreated samples were used as reference materials that were of particular interest concerning their flammability. It was shown that there is unambiguous correlation between the effective heat of combustion (EHC) and total oxygen consumed (TOC) related to mass lost during burning for both the untreated and treated samples. In the case of Cumaru and Garapa, there exists an inverse relation between the amount of smoke and carbon residue. The decisive effect on the time of ignition was performed by the initial mass of the sample. This is valid for the spruce and the Cumaru, Ipe, and Kempas, both treated and untreated with retardant, while Garapa and Merbau were found to decline. According to the lower maximum average rate of heat emission (MARHE) parameter, a lower flammability was observed for the treated samples of wood, except for Garapa wood. Fire-retardant treated Garapa and Merbau also have a significantly lower time to ignition than untreated ones.

Competitive divalent cation incorporation in the ferrous phosphate mineral vivianite

<p>Phosphorus (P) is often a limiting nutrient in soils and aquatic systems, but excessive concentrations can lead to eutrophication. The chemical forms in which P is retained in soils and sediments determine its bioavailability. Under reducing conditions, the ferrous phosphate mineral vivianite has been shown to be a major P burial phase in various environments such as coastal sediments. Depending on the local environmental geochemistry, ferrous iron (Fe<sup>2+</sup>) can be substituted by other divalent cations such as magnesium (Mg<sup>2+</sup>) and manganese (Mn<sup>2+</sup>). The substitution of Fe<sup>2+</sup> could alter mineralogical characteristics of vivianite, which influences its further reactivity and thus the P and iron (Fe) cycle. Despite the importance of divalent cation substitution in vivianite in the environment, questions remain if certain divalent cations are preferentially incorporated and how they compete for substitution.</p><p>Here, we assessed the competitive incorporation of Mn<sup>2+</sup> and Mg<sup>2+</sup> into vivianite by carrying out vivianite precipitation experiments in anoxic aqueous solutions at pH 7. Additionally, we explored how varying salinity simulating an estuarine gradient influences the incorporation of Mn<sup>2+</sup> and Mg<sup>2+</sup>. Changes in mineralogy with different degrees of Mn<sup>2+</sup>/ Mg<sup>2+</sup> substitution were studied with X-ray powder diffraction, Raman spectroscopy, total elemental dissolution and other techniques.</p><p>Based on 19 different vivianites, our results demonstrate that Fe<sup>2+</sup> is replaced by up to 50% by Mn<sup>2+</sup>/ Mg<sup>2+</sup> in the vivianite structure, with preferential incorporation of Mn<sup>2+</sup> over Mg<sup>2+</sup>. Increases in salinity seem to slightly enhance divalent cation incorporation. Following from our results, we will discuss the factors influencing divalent cation incorporation into vivianite, and how divalent cation substitution alters mineralogical characteristics. Finally, we will highlight how the substitution of Fe<sup>2+</sup> by other divalent cations potentially enhances P fixation in form of vivianite under Fe-limiting conditions.</p>

Phosphorus recovery as ferrous phosphate (vivianite) from wastewater produced in manufacture of thin film transistor-liquid crystal displays (TFT-LCD) by a fluidized bed crystallizer (FBC)

In this investigation, fluidized bed crystallization (FBC) is utilized to treat phosphorus wastewater that is produced by the manufacture of thin film transistor-liquid crystal displays (TFT-LCD).

Remediation of Cd(ii)-contaminated soil by three kinds of ferrous phosphate nanoparticles

Three kinds of iron phosphate nanoparticles were synthesized and they could reduce leachability and bioaccessibility of Cd effectively.