MnO3 Powder Research Articles

SYNTHESIS OF ORTHORHOMBIC LiMnO2 BY HYDROTHERMAL PROCESS

This work synthesised layered structural orthorhombic LiMnO2 powder via a hydrothermal process. The influences of hydrothermal temperature (tr°), reaction time (tht), molar concentration of LiOH.H2O in aqueous solutions (CLH), and the ratio of Mn2O3 powder (xr/t) were investigated. A high-purity LiMnO2 powder was successfully synthesised using hydrothermal synthesis at CLH = 4M, tht = 8 h, tr° = 180 °C, and xr/t = 0.9. The synthesis LiMnO2 powders have layer structure, and the planar density calculations indicated that the (021) planes had a lower average planar density than those of (100) and (010) planes, which led to a faster crystal growth on (021) planes. Moreover, single crystals of LiMnO2 were pseudo-hexagonal also due to the lower average planar density of (221) planes compared to that of (021) planes, which made the crystal grow faster on (221) planes.

Lucky strike: testing the utility of manganese dioxide powder in Neandertal percussive fire making

Late Middle Palaeolithic Neandertals in France are known to have engaged in the collection and grinding of black minerals rich in manganese dioxide (MnO2), generally presumed for symbolic use as powdered pigments. However, lab-based experiments conducted by Heyes and colleagues (Sci Rep 6: 22159, 2016) have shown that the addition of powdered MnO2 to wood turnings both reduces the temperature required for combustion by ca. 80–180 °C and significantly increases the rate of combustion. This special pyrotechnic property of powdered MnO2 may have been observed and leveraged by Neandertals to aid in fire making—a technology known to Neandertals in this region by at least 50,000 years ago. To test this idea, a series of actualistic fire-making experiments were performed to determine the practical applicability of MnO2 as a tinder-enhancing additive. The flint-and-pyrite percussive fire-making method was employed to produce sparks that were directed onto eight different types of tinder common to temperate Northwest Europe to determine if and to what degree the addition of MnO2 powder improved their ability to capture sparks that then propagate into glowing embers. The results show that MnO2 does indeed considerably improve the ignition efficiency of tinder material over untreated tinder, both in terms of the point of first ignition and the total number of ignitions achieved. It was observed, however, that the incidental addition of pyrite dust onto a tinder over the course of an experiment also appeared to improve its ability to capture sparks. Supplemental experiments using tinder pre-mixed with powdered pyrite confirmed this hypothesis, suggesting pyrite powder similarly expedites fire production. While this finding may raise questions regarding the need for collecting MnO2 for this purpose, its potential utility may lie in (1) its relative softness compared to pyrite, making it much easier to grind or scrape into powder, and (2) the greater potential for MnO2-bearing deposits to yield larger quantities of usable raw material compared to pyrite-bearing outcrops, making it relatively more abundant in some areas. Thus, when available, it is clear that adding MnO2 to tinder would have noticeably reduced the time and energy required to produce fire, making it a potentially novel Neandertal innovation complementary to the fire-making process.

Phase evolution of nanocrystalline Mn-based oxides screened under different calcination temperatures using different precursors for proficient application in near infrared pigmentation

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 (MnCl2·4H2O, MnCO3, MnO2, and KMnO4). When MnCl2·4H2O was calcined at 800 and 1000 °C/3h, we obtained pure tetragonal Mn3O4 phase materials. Calcining MnCO3 at 600 and 1000 °C resulted in cubic Mn2O3 and tetragonal Mn3O4 phase materials, respectively. Heating commercial MnO2 powder at 600 and 800 °C transformed it into cubic Mn2O3 phase materials. At 400 °C, the tetragonal MnO2 phase remained, but at 1000 °C, mixed Mn3O4 and Mn2O3 phases formed. Calcining KMnO4 at 1000 °C/3h led to the formation of δ-MnO2 materials. The morphological features of Mn2O3 and Mn3O4 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 Mn3O4 phase indicates a reflectance of 68 % in the solar region and 91 % in the color pigment region.

The influence of in-situ induced and MnO2 polymorph-dependent structural changes to the energy storage and mechanism of supercapacitors

Due to its economic, environmental, and theoretical advantages, manganese dioxide (MnO2) is a promising cathode material for supercapacitors. However, the commercial application of MnO2 still faces challenges such as low intrinsic conductivity, slow ion diffusion, and structural instability. In this study, four crystalline forms of MnO2 powder electrodes (α-, β-, γ-, and δ-MnO2) were prepared, and results showed that with a specific capacitance of 218.2 F∙g−1, δ-MnO2 exhibited the best electrochemical performance. This was primarily due to the fact that δ-MnO2 possesses a high specific surface area, rich oxygen vacancy, and fast electron-ion transfer speed. A self-supported electrode (δ-MnO2/NF) without binder addition was further prepared using an in-situ-induced technique. The results revealed that the specific capacitance of δ-MnO2/NF was as high as 809.4 F∙g−1 and that the capacity retention rate and coulombic efficiency after 5000 cycles were 92.8 % and 99.2 %, respectively, which were superior to those of δ-MnO2 (80.3 % and 93.5 %). In-situ induction not only amplifies the structural advantages of δ-MnO2 but also generates more electrochemical active sites due to the intense interaction between NF and δ-MnO2. In addition, ultrathin nanosheet arrays formed on the NF provide a three-dimensional conductive network for the transport of ions and electrons. Density functional theory calculations were performed to verify the excellent electronic conductivity and ion diffusivity of δ-MnO2 and showed that transferring electrons from metal Ni to δ-MnO2 is the basis for producing numerous oxygen vacancies in δ-MnO2/NF.

Comparison of separation of Mn(II), Co(II), and Ni(II) by oxidative precipitation between chloride and sulfate solutions

In hydrometallurgy, precipitation would be easier and simpler than solvent extraction as a separation operation. In this work, the separation performance of Co(II), Mn(II) and Ni(II) by oxidative precipitation was investigated. For this purpose, NaClO was employed as an oxidizing agent and the separation behavior of the three ions was compared between chloride and sulfate solutions by varying some factors such as the dosage of NaClO, solution pH and reaction temperature. By controlling the molar ratio of NaClO to Mn(II), manganese ions(II) were easily separated as MnO2 by oxidative precipitation from both chloride and sulfate solutions. At the same experimental conditions, precipitation percentage of Co(II) from chloride solution was higher than that from sulfate solution, which can be ascribed to the stronger tendency of Co(II) to form complexes with chloride ion than with sulfate ions. Addition of NaCl to sulfate solution and oxidative precipitation at high temperature enhanced the precipitation percentage of Co2O3 and thus separation degree between Co(II) and Ni(II) was improved. Under the optimum conditions, MnO2 and Co2O3 powders with 99.9% purity were completely recovered by oxidative precipitation from chloride solution. By contrast, the purities of the MnO2 and Co2O3 thus recovered from sulfate solution were only 76 and 91%, respectively. Our results indicated that chloride solution would be more effective than sulfate solution in separating Mn(II) and Co(II) by oxidative precipitation with NaClO. Therefore, the use of chloride-based leaching solutions such as HCl and FeCl3 might be better for the leaching medium of spent lithium-ion batteries.

Free‐standing δ‐MnO2 atomic sheets

Abstractδ‐Manganese dioxide (δ‐MnO2) is a 2D material which possesses distinct properties and features due to its unique atomic structure and has already been utilized in numerous disciplines recently, especially in the field of magnetism, energy storage, magnetic resonance imaging, biocatalysts, and fluorescence sensing. Keeping an eye on the huge potential of this 2D material, we report our recent discovery of single‐step synthesis of MnO2 nanosheets via bottom‐up laser crystallization (of aqueous KMnO4 solution) and top‐down sonochemical exfoliation of bulk MnO2 powder. The successful synthesis of δ‐MnO2 nanosheets has been proved through the observation of characteristic Raman peaks at 173 and 634 cm−1 and characteristic X‐ray diffraction peaks. The optical band gap was found to be 1.64 and 1.45 eV for both methods. We also demonstrated that 2D‐MnO2 is a prominent candidate material for ammonia sensing and strain sensing. δ‐MnO2 powder, when employed as cathode material in Li‐ion batteries, results in a stable voltage of ˜0.5 V and in contrast, gives ˜1 V when used in Li‐S batteries and the attained voltage is stable even for >5 h. New methods of synthesis of δ‐MnO2 and its hybrids with graphene will lead to future generation devices, it is expected.

A Kinetic Study on the Preparation of Al-Mn Alloys by Aluminothermic Reduction of Mn3O4 and MnO Powders

The study of aluminothermic reduction in manganese compounds is a complex challenge in preparing Al-Mn alloys. The primary objective of this study was to ascertain the activation energy values for the aluminothermic reduction of MnO and Mn3O4 oxides derived from alkaline batteries. The study melted aluminum found in beverage cans and utilized the technique of powder addition with mechanical agitation. The kinetics of the reaction were studied under the effects of temperature (750, 800, and 850 °C), degree of agitation (200, 250, and 300 rpm), and the initial concentration of magnesium in molten aluminum (1, 2, 3, and 4% by weight). Kinetic measurements for Mn3O4 particles suggest a reaction mechanism that occurs in stages, where manganese undergoes oxidation states [Mn+3] to [Mn+2] until it reaches the oxidation state Mn0, which allows it to dissolve in the molten aluminum, forming alloys with up to 1.5 wt.% of Mn. Therefore, the kinetic of the aluminothermic reduction of MnO is described by the geometric contraction model, while the mechanism of Mn3O4 reduction occurs in two stages: geometric contraction, followed by an additional stage involving the diffusion of chemical species to the boundary layer. In addition, this stage can be considered a competition between the formation of MnO and the chemical reaction itself.

Comparative study of electrochemical performance of 3D leaf-like MnO2 and Mn2O3 powder for supercapacitor application

Comparative study of electrochemical performance of 3D leaf-like MnO2 and Mn2O3 powder for supercapacitor application

Reacting Mn3O4 powders with quaternary ammonium hydroxides to form two-dimensional birnessite flakes

There is a current interest in synthesis of two-dimensional (2D) materials that would be cost-efficient to scale to industry production. In this study, we report on a bottom-up approach to convert a manganese oxide (Mn3O4) powder into crystalline, 2D layered birnessite flakes. The Mn3O4 precursor powder, is reacted with aqueous solutions of, tetramethyl-, tetraethyl- or tetrabutylammonium hydroxide in a shaker oven at 80 °C for 4 days. X-ray diffraction confirmed that in all cases, upon filtration of colloidal suspensions, well-stacked, crystalline, 2D MnO2 birnessite layers formed, that upon characterization were found to be quite similar. The major differences were the spacings between the flakes that depended on cation size. Selected area diffraction patterns in a transmission electron microscope confirmed both the structure and the polycrystallinity of the flakes. Raman spectroscopy confirmed the structure. The zeta-potentials of the 2D flakes were measured to be ≈−35 ± 2 mV. When UV–Vis spectra were converted to Tauc plots, direct and indirect band gap energies of ≈2.15 and ≈2.60 eV were obtained, respectively. Additionally, the oxygen evolution reactivity of our birnessite flakes significantly are better than those found for Pt/C, demonstrating a high degree of catalytic reversibility. The facile conversion of a relatively inexpensive, earth-abundant oxide, Mn3O4, into a highly value-added 2D birnessite using a one-pot, simple hugely scalable, protocol at near ambient temperatures and pressures with various quats can be considered a breakthrough in the production of these nanomaterials.

Profitable approach for the synthesis of Mn3O4 phase materials and its interesting pigmentation applications

A simple precipitation synthesis of Mn3O4 phase with average crystalline size of 27.8 nm in the form of as-precipitated product crystallized in tetragonal symmetry, space group, I41/amd (141) 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 (Eg) 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 Mn3O4 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 A1g, Eg, and T2g Raman active modes of tetragonal Mn3O4 phase materials.

Photocatalytic Decomposition of Methylene Blue over Nanosized Ca2+ Doped LaMnO3 under Visible Light Irradiation

The Photocatalytic performance of the Calcium doped lanthanum manganite nanocomposite for photodegradation of Methylene Blue(MB) dye as an Organic water pollutant,was evaluated over visible light irradiation, at a pH of 4, at constant dose for several hours. The result showed La0.75Ca0.25MnO3 having Perovskite structure shows high degree of catalytic efficiency of 69% within 100 min illumination time, for the removal of Methylene Blue organic dye from its aqueous solution. The sample powder(LCMO) was prepared through sol-gel technique and was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Inductively coupled plasma- atomic emission spectroscopy (ICP-AES), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX) and UV-Vis spectroscopy (UV-Vis). The XRD data revealed the formation of single phase crystallinity.SEM images shows that the micro sized La0.75Ca0.25MnO3 powder has nanocrystalline structure with average diameter of 1-3 µm. The ICP-AES data confirmed formation of required stoichiometric La1-xCaxMnO3 Oxide. The rates of photodegradation linearly increase as a function of time of irradiation, which was confirmed from study of the optical properties of the resulting aqueous solutions. These findings shows convincingly that La0.75Ca0.25MnO3 photocatalyst possess great promise for visible light driven photodegadation of Methylene Blue dye.

Surface Morphology and Properties of Diamond Etched by MnO2 Powder

Surface Morphology and Properties of Diamond Etched by MnO2 Powder

Correlation analysis with measurement conditions and peak structures in XPS spectral round-robin tests on MnO powder sample

Spectral measurements provide valuable information on the electronic states and crystal structures of materials. In particular, X-ray photoelectron spectroscopy (XPS) can facilitate the analysis of the chemical-bond states of the surfaces of materials. In the analysis of XPS spectra, the spectrum to be measured is typically compared to a reference spectrum measured from a known single-phase sample. Therefore, establishing a reference spectral database is imperative. In this study, round-robin tests (RRT) of XPS spectra are performed to obtain recommended XPS reference spectra and develop appropriate measurement conditions, including preprocessing procedures. Determining the variations in peak structures between equipment- and sample-derived spectral shapes and quantitatively discussing them through RRT of XPS spectra are challenging. Therefore, an analysis method that automatically determines the above-mentioned variations and extracts the sample-derived common spectral structures is developed in this study. This paper presents a new approach to the quantitative analysis of round-robin XPS spectral tests. The required common peak structure, a new definition of the XPS reference spectrum, is obtained. Further, a correlation between the variability of deviations in the spectral data of the RRT and the measurement condition and XPS measurement equipment used is determined. Such a framework is essential for standardizing XPS spectra and expanding the XPS reference spectral database.

Options to recover high-purity MnO2 from leach liquors of manganese dust containing Mn3O4 and iron and zinc oxide as minor impurities

Manganese dust, predominantly made up of manganese oxides is produced during the manufacturing of ferromanganese alloys at high temperatures. Pure Mn compounds can be recovered from manganese dust. In this study, a hydrometallurgical process was developed to recover pure MnO2 from manganese dust containing iron and zinc oxides. The oxide species Mn3O4 in manganese dust was first completely dissolved using a mixture of sulfuric and oxalic acids at room temperature. Small amounts of iron and zinc oxides were also dissolved during manganese leaching. Iron(III) in the clarified leach liquor was then completely separated by solvent extraction using D2EHPA. Zinc(II) in the Fe(III) free raffinate was separated by either solvent extraction with Cyanex 272 or by ZnS precipitation through the addition of Na2S. Addition of Mn powder to the leach liquor separated Zn(II) by cementation and increased the solution pH and hence Fe(III) was separated by precipitation. The MnO2 powder with a purity of 99.995% was recovered from real leach liquor of manganese dust after consecutive solvent extractions of Fe(III) and Zn(II) by D2EHPA and Cyanex 272, respectively and oxidative precipitation of MnO2 from the purified solution (raffinate) using NaClO at room temperature.

MnFe2O4-based spinels by mechanochemical and thermochemical reaction of siderite and MnO2 powder mixtures

The manganese ferrite has been processed by mechanosynthesis, using reactive siderite and MnO2 powder mixtures, with and without subsequent heat treatment. Taguchi planning was used to assess the impact of milling conditions (rotational speed and time) and subsequent calcination temperature on conversion of precursors, based on integrated intensities of the main XRD peaks of precursor phases FeCO3 (104) and MnO2 (110), and spinel phase (311), using Ni as internal pattern. Thermogravimetry provided additional information on the residual contents of reactants in the as-milled samples. The best conditions for complete conversion to spinel phase of as-milled samples were obtained by milling at 650 rpm, for 6 h (I311,sp/I111,Ni=2.41), and for calcined samples were obtained after milling at 650 rpm, for 3 h, and calcination at 650 °C (I311,sp/I111,Ni=2.35). The impact of processing conditions on structural features of the spinel phase was accounted by the contributions to variance of intensity of its (311) reflection, which were 90% ascribed to rotational speed and only 4% ascribed to milling time, for as-milled samples, or 58%, 15% and 16% ascribed to rotational speed, milling time and calcination temperature, for calcined samples. Readier conversion of FeCO3 relative to MnO2 occurred during the milling stage, at low or intermediate rotational speed, with impact on Mn:Fe ratio in the spinel phase, as revealed by changes in lattice parameter of as-milled samples, in the range of 0.8424–0.8464 nm. Subsequent calcination minimized or eliminated traces of secondary phases. The incorporation of magnesium oxide and possibly other secondary components of the siderite precursor also induced structural changes in the resulting spinel phase, mainly in calcined samples (ao = 0.8370–0.8434 nm). Partial oxidation also contributed to structural changes in calcined samples, as revealed by differences between samples calcined in inert and oxidising atmospheres.

The Distorted Octahedral and Magnetocrystalline Anisotropy of FeMnO<sub>3</sub> by Stoner-Wohlfarth Model

Among magnetic materials, ferrites have significant attention due to their potential application, such as magnetic recording, sensors, radar-absorbent materials, catalysts, and energy-storage devices. One of the ferrites family, FeMnO3, has been synthesized by solid-state reaction using Fe2O3 powder with an excess of 0.02% MnO2 powder in the stoichiometric composition. The structural and morphological properties have been performed using XRD and SEM at room temperature. The diffraction peaks in the pattern were indexed as FeMnO3 with a cubic (bixbite, Ia3) crystal structure. It showed no additional peaks due to impurities. The SEM image reveals the grains nucleate in a cube-like shape. Some of the particles also seem to agglomerate into larger particles. The magnetic characterization was carried out using VSM at room temperature. The magnetic hysteresis loop (M-H curves) notices the ferrimagnetic behavior. The results show remnant magnetization (Mr), coercive field (Hc), magnetic moment (µB), and anisotropy constant of FeMnO3 are 0.296 emu/g, 299 Oe, 0.046 emu/mol, and 0.1 when the external field is 70˚-80˚ from the easy axis, respectively.

Classification of Ultrafine Particles Using a Novel 3D-Printed Hydrocyclone with an Arc Inlet: Experiment and CFD Modeling.

Ultrafine particle classification can be realized using hydrocyclones with novel structures to overcome the limitations of conventional hydrocyclones with tangential inlets or cone structures. Herein, the hydrocyclones with different inlet structures and cone angles were investigated for classifying ultrafine particles. Computational fluid dynamics (CFD) simulations were performed using the Eulerian-Eulerian method, and ultrafine MnO2 powder was used as a case study. The simulation results show a fine particle (≤5 μm) removal efficiency of 0.89 and coarse particle (>5 μm) recovery efficiency of 0.99 for a hydrocyclone design combining an arc inlet and a 30° cone angle under a solid concentration of 2.5 wt %. Dynamic analysis indicated that the novel arc inlet provided a preclassification effect to reduce the misplacement of fine/coarse particles, which cannot be provided by conventional tangential or involute inlets. Furthermore, the proposed design afforded comprehensive improvement in the flow field by regulating the residence time and radial acceleration. Subsequently, a novel hydrocyclone with an arc inlet and 30° cone angle was manufactured using the three-dimensional (3D) printing technology. Experiments were conducted for classifying ultrafine MnO2 particles using the novel 3D-printed hydrocyclone and conventional hydrocyclone. The results demonstrate that the classification performance of the 3D-printed hydrocyclone was superior to that of the conventional one, in particular, the removal efficiency of fine particles from 0.719 to 0.930 using a 10 wt % feed slurry.

Synthesis of galaxite by sintering at various temperatures and atmospheres

Galaxite has broad application prospects in the field of cement rotary kiln burning zones owing to its excellent properties (high melting point and corrosion resistance). In this study, MnO and α-Al2O3 powders were used as raw materials to synthesize galaxite in air, coke bed, or nitrogen at 1500–1600 °C. Their phase compositions and microstructure changes were investigated by XRD and SEM-EDS. The results show that MnII(Al, MnIII)2O4 composite spinel were formed in the air at 1500–1600 °C and increased with increasing temperature, whereas only MnAl2O4 was formed in the coke bed and nitrogen at 1550 °C. Therefore, the specimens treated at 1600 °C in air exhibited a high density of 3.88 g/cm3, which was similar to those of the specimens sintered in the coke bed and nitrogen at 1550 °C, demonstrating good sintering properties. Furthermore, the number and size of pores gradually decreased, and the bulk density increased as the temperature increased from 1500 °C to 1600 °C in the air.

Hierarchically MnO2/SiO2 nanocomposites with high solar light-driven photo-thermo catalysis activity for efficient toluene removal

Catalytic oxidation of toluene by employing manganese dioxide (MnO2) as catalysts has shown great potential, however, the huge energy demands during the MnO2 catalytic process limits its application. Herein, a new type of MnO2/SiO2 nanocomposites with outstanding solar light-driven photo-thermo catalysis activity was successfully fabricated. The MnO2 nanoparticles in homogeneous dispersion state were decorated on the surface of SiO2 nanofiber. The abundant hydroxyl groups on the surface of SiO2 nanofiber facilitated toluene enrichment. Moreover, abundant oxygen vacancies were generated through the substitution between the Mn4+ and Si4+, which improved the concentration and mobility of active oxygen. An excellent photo-thermo catalytic activity of MnO2/SiO2 nanocomposites on toluene degradation was observed with a significant CO2 yield (100 %) and high value of CO2 production rate under simulated sunlight, which was much superior to that of P25 and MnO2 powders. The mechanism of the enhanced catalytic performance of MnO2/SiO2 nanocomposite is ascribed to the synergism of photo-activation and solar light-driven thermo-catalytic oxidation. This work demonstrates a new route to develop MnO2-based photo-thermo catalyst and provides an energy-saving way for toluene removal on overall utilization of solar energy.

Solution combustion synthesis of nano crystalline La0.67 (Sr0.25Ca0.75)0.33MnO3 powder and its characterizations

Solution combustion synthesis of nano crystalline La0.67 (Sr0.25Ca0.75)0.33MnO3 powder and its characterizations