Role of chelating compounds towards thermal resistance property of industrial grade goethite

Abstract

Purpose The iron oxide-based goethite (FeOOH) is proven to be an alternative replacement for carcinogenic chrome-based pigments. Because of its low heat stability, it tends to lose water of hydration and turns red as temperature ascends beyond 240ºC. Thus, the purpose of this paper is to increase the heat stability temperature of industrial grade (IG) goethite pigment. For this, the IG goethite pigment was surface treated with sequestrant. The properties of untreated and treated IG goethite were compared. Design/methodology/approach Three different compounds (sodium hexametaphosphate, calcium disodium ethylene diamine tetra-acetate salt, sodium gluconate) were used into the IG goethite at different concentration level. The experiments were conducted by varying the temperature and exposure time of treated and untreated samples. The total colour difference value (DE) was compared for the treated and untreated samples. Findings The surface treatment of IG goethite showed significant enhancement in heat stability property. From X-ray diffraction results it was confirmed that with surface treatment, there was no phase change of IG goethite even at 300ºC. Fourier transform infrared analysis states that with surface treatment when there is gradual increase in temperature from 260ºC the % transmittance of the OH (hydroxyl) deformation region band is delayed due to sequestering effect. Also, based on the total colour DE, the colour tone of surface treated IG goethite was not perceptible by human eyes even at 280ºC. Research limitations/implications By increasing the heat stability of IG goethite, it will have increased spectrum of end usage in the high temperature coating segment. Coil coating is one of the biggest potential markets for this pigment. The increased heat stability will provide manufacturers with the option of an economical and non-toxic pigment in coil coatings and also in other sectors such as plastics, powder coatings and high temperature coatings. Practical implications The outcome of this study has been commercially implemented to produce heat stable goethite pigments in an industrial plant. The surface treated IG goethite pigments can be used in high-performance coil, powder and high temperature coatings. Originality/value The method for enhanced heat stability property of IG goethite by surface treatment with sequestrants is novel and could find numerous applications in high-performance coatings.

Surface Treatment of Industrial-Grade Magnetite Particles for Enhanced Thermal Stability and Mitigating Paint Contaminants

“…Therefore, with these results, we can interpret that sodium hexametaphosphate retards the oxidation of iron and has a strong affinity to bind with the magnetite surface, which acts as a passivating layer for inhibiting the growth of γ-Fe 2 O 3 (maghemite). The above-reported role of phosphate was also evident in the studies ofMohua et al (2020) [43], Jerina et al[44] andLesia et al (2000) [45].…”