Abstract
Phosphate glasses have potentially interesting properties that can be used in various applications. Recently, different studies are focusing on their dissolution behaviours that can be modified to suit some environmental applications, such as controlled-release fertilisers. In this work, magnesium had been suggested to improve the glass durability of 3P2O5-2K2O-(1 − x)CaO-xMgO glasses (0 ≤ x ≤ 1). Indeed, its effect on glass structure, thermal properties and most important dissolution behaviours were studied, in order to evaluate their suitability of being used as controlled-release fertilisers. Various compositions in which calcium was partially replaced by magnesium were prepared by melting at 800 °C. The samples were characterised by differential scanning calorimetry, density measurements, X-Ray diffraction, FTIR spectroscopy and Raman spectroscopy. The dissolution behaviours were investigated using inductively coupled plasma optical emission spectrometry ICP-OES, pH measurements and SEM. Substitution of calcium by magnesium reduced the glass density, owing to the lower atomic weight of magnesium compared to calcium, and caused an increase in glass transition and crystallisation temperatures. Magnesium substitution significantly improved the chemical durability of the glasses due to more covalent Mg–O bond than the Ca–O bond. This study demonstrated that 3P2O5-2K2O-0.3CaO-0.7MgO (x = 0.7) had a dissolution profile adequate to the criteria of controlled-release fertilisers and could be used to nourish the plants with phosphorus, potassium, calcium and magnesium.
Highlights
Glasses are a unique and extremely flexible material that can be designed to exhibit particular properties
Phosphate glasses are known by their poor chemical durability; they offer the possibility of being completely degradable in an aqueous environment [9]; this solubility can be controlled via their composition [10], which makes them of interest for use as controlled-release fertilisers [11,12]
This work aimed to study the effect of calcium substitution by magnesium on physical properties, glass structure and, most importantly, the chemical durability of 3P2 O5 -2K2 O-(1 − x)CaO-xMgO glasses for 0 ≤ x ≤ 1, to evaluate their suitability of being used as controlled-release fertilisers that nourish the plants with phosphorus, potassium, calcium and magnesium
Summary
Glasses are a unique and extremely flexible material that can be designed to exhibit particular properties. The most familiar and, historically, the oldest types of glass are “silicate glasses” based on the chemical compound silica. The production of other types of glass, especially those based on phosphate, is limited until today [1]. Phosphate glasses have potentially interesting properties that can be used in various applications. Their thermo-optical characteristics as a laser host matrix for eye protection [2,3] and Materials 2020, 13, 2637; doi:10.3390/ma13112637 www.mdpi.com/journal/materials. Phosphate glasses are known by their poor chemical durability; they offer the possibility of being completely degradable in an aqueous environment [9]; this solubility can be controlled via their composition [10], which makes them of interest for use as controlled-release fertilisers [11,12]
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