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Materials 2018, 11(9), 1693; https://doi.org/10.3390/ma11091693

Synthesis and Irreversible Thermochromic Sensor Applications of Manganese Violet

1
Department of Civil Engineering, Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Korea
2
Sustainable Management of Natural Resources and Environment Research Group, Faculty of Environment and Labour Safety, Ton Duc Thang University, Ho Chi Minh City, Vietnam
3
Department of Civil Engineering, Daegu University, 201, Daegudae-ro, Gyeongsan, Gyeongbuk 38453, Korea
*
Author to whom correspondence should be addressed.
Received: 10 July 2018 / Revised: 7 September 2018 / Accepted: 10 September 2018 / Published: 12 September 2018
(This article belongs to the Section Smart Materials)
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Abstract

An irreversible thermochromic material based on manganese violet (MnNH4P2O7) is synthesized. The crystal phase, chemical composition, and morphology of the synthesized material are analyzed using X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and Fourier-transform infrared spectroscopy. The absorption spectra of the synthesized material are obtained using a UV-Vis spectrometer, and the thermochromism exhibited by the powdered samples at high temperatures is also investigated. The as-synthesized manganese violet pigment consists of pure α-MnNH4P2O7 phase. In addition, the synthesized pigment largely consists of hexagonal crystals with a diameter of hundreds of nanometers. On heating, the pigment simultaneously loses H2O and NH3 in two successive steps at approximately 330–434.4 °C and 434.4–527 °C, which correspond to the formation of an intermediate phase and of Mn2P4O12, respectively. An overall mass loss of 14.22% is observed, which is consistent with the expected 13.79%. An irreversible color change from violet to white is observed after exposure of the synthesized manganese violet pigment at 400 °C for 30 min. This is attributed to the oxidation of ammonia to hydroxylamine, which then decomposes to nitrogen and water, or alternatively to the direct oxidation of ammonia to nitrogen. Furthermore, we demonstrate the potential application of synthesized manganese violet in the production of irreversible thermochromic paint by mixing with potassium silicate solution as a binder and deionized water as a solvent at a specific ratio. The thermochromic paint is then applied in fabrication of irreversible thermochromic sensors by coating it onto a steel plate surface. Finally, we show that manganese violet-based irreversible thermochromic sensors are able to detect temperatures around 400 °C by changing color from violet to white/milky. View Full-Text
Keywords: irreversible thermochromic sensors; manganese violet; thermochromic materials; irreversible thermochromic paint; MnNH4P2O7 irreversible thermochromic sensors; manganese violet; thermochromic materials; irreversible thermochromic paint; MnNH4P2O7
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Nguyen, D.K.; Bach, Q.-V.; Lee, J.-H.; Kim, I.-T. Synthesis and Irreversible Thermochromic Sensor Applications of Manganese Violet. Materials 2018, 11, 1693.

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