Search

[Display omitted] • Mn-based oxides were acquired by calcining the precursors of MnCl 2.4H 2 O, MnCO 3 , MnO 2 , and KMnO 4. • The phase formation was influenced by the temperatures (400–1000 °C) and precursors. • The obtained phases were analyzed for their thermal and spectroscopic properties. • The nanostone was seen in the form of Mn 3 O 4 , while the nanorod-like shape was observed in Mn 2 O 3. • The Mn 3 O 4 phase exhibited a high NIR reflectance of 68 % in the solar region and 91 % in the color region. We examined how different calcination temperatures and precursors affect the formation of Mn-based oxides. The formation of these oxides was influenced by both the temperature (400–––1000 °C) and the type of precursors used (MnCl 2 ·4H 2 O, MnCO 3 , MnO 2 , and KMnO 4). When MnCl 2 ·4H 2 O was calcined at 800 and 1000 °C/3h, we obtained pure tetragonal Mn 3 O 4 phase materials. Calcining MnCO 3 at 600 and 1000 °C resulted in cubic Mn 2 O 3 and tetragonal Mn 3 O 4 phase materials, respectively. Heating commercial MnO 2 powder at 600 and 800 °C transformed it into cubic Mn 2 O 3 phase materials. At 400 °C, the tetragonal MnO 2 phase remained, but at 1000 °C, mixed Mn 3 O 4 and Mn 2 O 3 phases formed. Calcining KMnO 4 at 1000 °C/3h led to the formation of δ-MnO 2 materials. The morphological features of Mn 2 O 3 and Mn 3 O 4 materials exhibited different sizes and shapes, including nanostone-like, nanorod-like, and nanoflakes morphologies. The thermal analysis revealed significant differences in weight loss and thermal events, including exo and endothermic peaks. The Raman spectra and UV–Vis DRS measurements data support the formation of Mn-based oxides. The highest NIR reflectance for the various synthesized materials of Mn 3 O 4 phase indicates a reflectance of 68 % in the solar region and 91 % in the color pigment region. [ABSTRACT FROM AUTHOR]

The as-precipitated product of the Mn 3 O 4 phase with spherical-shaped aggregates with rod-shaped morphology crystallized in tetragonal symmetry with space group, I 4 1 / amd (141): Phase formation (left), Morphology (centre), and NIR pigmentation (right). [Display omitted] A simple precipitation synthesis of Mn 3 O 4 phase with average crystalline size of 27.8 nm in the form of as-precipitated product crystallized in tetragonal symmetry, space group, I 4 1 / amd (1 4 1) with the lattice parameters of a = 0.5761(3) nm and c = 0.9451(6) nm. The rod-shaped (diameter of ∼ 400 nm) morphology with a spherical particle size of ∼ 50 nm is observed for the as-precipitated product. A weight loss of ∼ 4% is noted for the as-precipitated product powder up to 1000 °C with neither exothermic nor endothermic peaks in the thermal profiles. The UV–Vis absorbance spectrum reveals an absorption edge at 550 nm, which is due to optical band gap absorption with a calculated band gap (E g) of 1.95 eV from the Tauc plot. The NIR (750 – 2500 nm) spectrum shows the NIR reflectance of 27–66 % and 50–69 % in the solar and color pigment regions, respectively. As a result, the present obtained Mn 3 O 4 powder can be used in the color pigmentation industry. The Raman reveals a dominant peak at ∼ 652 cm−1 and two minor peaks at 315 and 369 cm−1 are due to A 1g , E g , and T 2g Raman active modes of tetragonal Mn 3 O 4 phase materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • To identify the CaWO 4 phase, several attempts were taken through solid-state reaction and ball milling method under wet and dry conditions. • Upon ball-milling of the reaction mixtures under wet conditions (ethanol and/or water as solvent) showed no indication of CaWO 4 phase, whereas different quantities of reaction mixtures ball milled under dry conditions revealed the CaWO 4 phase. • Subsequent annealing of the wet conditions ball-milled powder at 850 °C yielded mixed phases of CaWO 4 and WO 3 in contrast to solid-state reaction method which yielded CaWO 4 phase at 850 °C. • Agglomeration of spherical-shaped morphologies is seen in the CaWO 4 phase materials obtained via ball milling method, whereas solid-state reaction method obtained CaWO 4 materials revealed dense microstructures. • The higher (∼90%) NIR reflectance of CaWO 4 materials obtained by solid-state reaction method guarantying it for solar reflecting roof and color pigmentation applications. We have attempted to synthesize the CaWO 4 phase materials under varied conditions and report their experimental findings related to phase identification and its different properties. While the solid state reaction requires a high temperature of 850 °C to form CaWO 4 phase, ball milling of the reaction mixture under different processing conditions yields different results that are quite interesting and debatable. The different quantities of reaction mixtures ball milled under the dry condition exhibit CaWO 4 phase. On the other hand, ball milling of the reaction mixtures under wet conditions using ethanol and/or water as solvent show WO 3 as the main phase with broader XRD reflections. Subsequent annealing of the ball-milled powder at 850 °C yields major CaWO 4 phase and WO 3 as secondary phase in contrast to the solid state reaction. The optical properties of pure CaWO 4 phase materials were examined by different spectroscopic techniques. The stress developed by ball milling of the reaction mixture remarkably reduces the NIR features of the as-milled CaWO 4 phase powder. The higher (∼90%) NIR reflectance of CaWO 4 phase materials obtained by SSR method guarantying it for solar reflecting roof and color pigmentation applications. An agglomeration of spherical-shaped fine particles (ball milling method) is different from solid state reaction method formed CaWO 4 phase having dense microstructures. [ABSTRACT FROM AUTHOR]