Phosphating is the process of depositing, by conversion, a layer of insoluble phosphate compounds, on the metal’s surface. Although phosphate coatings have been studied since the early nineteenth century, they are not only still being studied, but are an area of interest due to their many applications. The advantages of these types of coatings are well known, such as the low cost of the deposition process, the improvement of corrosion resistance properties, and the improvement of wear resistance and adhesion of further deposited layers such as paint. All this, leads to studies on the constant improvement of the properties of the phosphate coating, by modifying the parameters of the phosphating process, as well as by modifying/replacing the substances used in the phosphating solutions with “environmentally friendly” solutions. Also due to these advantages, several researchers are studying the possibility of using phosphate coatings in fields such as civil engineering or medicine (biomaterials coatings). This paper aims to present some essential aspects of phosphating and to bring to the fore the latest research on “eco-friendly” phosphating solutions and the possibility of using the phosphating process in other fields, such as the medical field. Also, the paper aims to discuss the possibility of eliminating/reducing the harmful effect that the use of phosphating has on the environment.

An alternative for Ordinary Portland cement (OPC) consumption is the production and integration of green cement. In other words, the clinker consumption has to be replaced with new low-carbon binders. A possible solution was introduced by the geopolymerisation technology. However, the alkaline activation of geopolymers offers the possibility of obtaining greener materials with high properties, superior to OPC, but due to the high price of sodium silicate, their industrial use is limited. In the past few years, a new activator has been discovered, namely phosphoric acid. This study approaches the obtaining of coal ash-based geopolymers activated with acid solution cured at room temperature. Accordingly, phosphoric acid, 85% by mass, was diluted in distilled water to obtain a corresponding activation solution for H3PO4/Al2O3 ratio of 1.0 and two types of geopolymers were ambient cured (22°C ±2°C). Moreover, to evaluate the geopolymerisation potential of this system (coal ash – phosphoric acid), SEM and EDS analysis was performed to investigate their morphologic characteristics.

Currently, one of the main challenges of civil engineering and science materials engineers is to develop a sustainable substitute for Ordinary Portland Cement. While the most promising solution is provided by the geopolymerisation technology, most of the studied geopolymers are based on natural raw materials (kaolin). The metakaolin is mainly preferred because of its rapid rate of dissolution in the activator solution, easy control of the Si/Al ratio, and white color. However, its high cost prevents it from being widely used in geopolymer composites or other materials that can become an industrial alternative for Ordinary Portland Cement. Several studies have shown that geopolymers with good performance can also be obtained from secondary raw materials (industrial wastes such as coal ash or slag). This explains why countries with rapidly developing economies are so interested in this technology. These countries have significant amounts of industrial waste and lack a well-developed recycling infrastructure. Therefore, the use of these by-products for geopolymers manufacturing could solve a waste problem while simultaneously lowering virgin raw material consumption. This study evaluates the effect of replacing different amounts of coal ash with sand on the microstructure of sintered geopolymers. Accordingly, scanning electron microscopy and energy dispersive X-ray analysis were involved to highlight the morphological particularities of room-cured and sintered geopolymers.

Quenching technology requires the use of media with different cooling intensities and various shapes of cooling curves that show different particularities compared to that of conventional media such as water, oil, or emulsions. The use of synthetic quenching media is relatively new and also has multiple advantages such as non-flammability, safety in use and low cost. In this study, the cooling media tested was obtained by mixing 2 wt% carboxymethyl cellulose with 2 wt% NaOH in one litter of water. Moreover, three different temperatures (20°C, 40°C and 60°C) of the quenching media were evaluated. By dissolution in water, a synthetic solution with low viscosity, surfactant and lubricant was obtained. Because carboxymethyl cellulose is a biodegradable organic material, that is obtained as a by-product in the manufacture of paper, a basic substance with a preservative effect was added. According to this study, both the variation diagram of the heat transfer coefficient and the diagram of the cooling rates, during the cooling stages give important indications regarding the use of a liquid cooling medium for quenching.