NIR reflective, anticorrosive magenta pigment for energy saving sustainable building coatings

• Published in: Solar energy 2021-07, Vol.222, p.103-114
• Main Authors: Thejus, P.K., Krishnapriya, K.V., Nishanth, K.G.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Anticorrosivity; Carbon dioxide; Charge transfer; Chromophores; Coatings; Cobalt; Cobalt aluminate; Color; Corrosion mechanisms; Corrosion prevention; Corrosion resistance; Corrosion resistant steels; Energy conservation; Energy efficiency; Green buildings; Magenta pigment; NIR reflectance; Octahedral geometry; Pigments; Polymer colouration; Polymethylmethacrylate; Reflectance; Roofing; Shielding; Solar energy
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2021.05.017

•Solid-state synthesized, Co doped LiMgPO4 pigment, exhibited excellent magenta colour.•LiMg0.8Co0.2PO4 composition shown high NIR reflectance of 67%.•Temperature shielding analysis offered 7 °C reduction in interior temperature than CoAl2O4.•Pigment loaded epoxy coating delivered substantial corrosion resistance on steel.•Multifunctional magenta pigment with NIR reflectance and corrosion resistance properties. A series of inorganic pigments LiMg1-xCoxPO4 have synthesized by conventional solid-state method. Optical features of the phase pure compounds have investigated, the characteristic absorption spectra confirmed the octahedral geometry of Co2+ chromophore. The spin allowed d-d transition in the visible region attributed to the excellent magenta hue of the pigment series. The best composition LiMg0.8Co0.2PO4 exhibited colour a* = 26.45, b* = −26.83 and NIR reflectance 67% and total solar reflectance (TSR) 55%. Acrylic coatings of LiMg0.8Co0.2PO4 on concrete and Al roofing sheet have successfully retained the pigment properties. Subsequent temperature shielding experiment and thermal images of coatings revealed 7 °C reduction in interior temperature for the magenta coatings compared to commercial CoAl2O4. The pigment LiMg0.8Co0.2PO4 shown excellent corrosion resistance on steel epoxy coatigs, because of the active phosphatization mechanism. The charge transfer resistance Rct = 9.3 × 109 Ωcm2, of the coatings are 4 order higher than that of bare and CoAl2O4 loaded epoxy coatings. In addition, 10 wt% of the pigment shown an intense colour in transparent PMMA matrix, substantiated the colour deliverability of the material. Eventually, the studies concluded that LiMg0.8Co0.2PO4 could be a potential inorganic pigment for developing an anticorrosive ‘cool’ paint for energy efficient buildings.