MnO2 Content Research Articles

Effect of MnO2 content on the growth and electric properties of <110>c-oriented 0.85(Bi0.5Na0.5)TiO3-0.15BaTiO3 single crystals fabricated by solid-state crystal growth method

Effect of MnO2 content on the growth and electric properties of <110>c-oriented 0.85(Bi0.5Na0.5)TiO3-0.15BaTiO3 single crystals fabricated by solid-state crystal growth method

Phase and defect structures of MnO2‐doped 75BiFeO3–25BaTiO3 ceramics and their effects on electrical properties

AbstractBismuth ferrite (BiFeO3)‐based high‐temperature piezoelectric ceramics have high Curie temperatures and excellent thermal stability; however, their applications are limited by inadequate piezoelectric performance due to large coercive fields and high leakage conduction. This study investigates the impact of MnO2 doping on the phase transition, defect structure, domain morphology, as well as the dielectric, ferroelectric, and electrical conduction behaviors of 75BiFeO3–25BaTiO3 ceramics sintered under an oxygen atmosphere. A structural transformation from distorted rhombohedral to pseudo‐cubic symmetry was observed with increasing MnO2 content, accompanied by domain fragmentation. MnO2 doping at an appropriate level inhibited defects such as and . Regarding electrical properties, the reduction in rhombohedral distortion and enhancement in the pseudo‐cubic phase after MnO2 doping resulted in decreased remanent polarization and electrostrain, which could potentially hinder piezoelectric response. However, appropriate MnO2 doping effectively reduced leakage conduction, significantly enhancing the poling efficiency of the ceramics. The maximum d33 value of 107 pC/N and kp of 0.36 were achieved at an MnO2 doping content of 0.1 wt.%. Excessive MnO2 addition may generate defect dipoles, as indicated by increased coercive field (Ec) and dielectric loss. The observed increase in high‐temperature resistivity with MnO2 content is primarily attributed to reduced grain size and increased concentration of mobile defects. This study provides valuable insights for further research on the application of 75BiFeO3–25BaTiO3 systems in high‐temperature piezoelectric devices.

Beneficial role of manganese dioxide for reducing surface resistivity to increase surface flashover voltage of vacuum insulating ceramics

Electric vacuum insulated devices generate surface flashover and breakdown under instantaneous high voltage. Flashover voltage can be increased through coating without changing the structure of the ceramic device. Herein, multiphase coatings with different manganese dioxide contents are prepared on α-Al2O3 insulating ceramic surface by screen printing and solid-state sintering methods to yield an average film thickness of about 12.38 μm with good bonding strength. X-ray diffraction shows that the crystal phases of the coating are (Al0.9Cr0.1)2O3 and MnAl2O4. Scanning electron micrographs and atomic force microscopy reveal that greater surface height difference and deeper surface depth are more conducive to increasing the surface roughness and the formation of "pores", and decreasing the surface potential decay rate. When MnO2 content is 0.0069 mol, the deep trap center energy level on the material surface reaches its maximum, increasing from 1.506 eV to 1.550 eV, and the surface resistivity of ceramics decreases from 1016 Ω to 1013 Ω. The formation of deep trap centers on the surface makes it difficult for surface charges to detach, which reduces the charge mobility and surface potential decay rate, and leads to decrease in surface resistivity and increase in surface flashover voltage.

Microwave‐sintered mullite structural ceramics based on low‐grade bauxite applied for fracturing proppants

AbstractThis study aimed to assess the feasibility of manufacturing fracturing proppants by microwave sintering and using low‐grade bauxite as raw material. The effects of microwave hotspot SiC and sintering additive MnO2 content on the performance of the mullite‐based structural materials were studied, respectively. The optimum sintering condition was determined by single‐factor experiments. The sintering process and mechanism were explored based on the analysis of physicochemical properties, phase transitions, and microstructure. The results showed that (1) mullite ceramic composites could be successfully prepared only with SiC added and with poor interparticle bonding microstructure. (2) With the addition of MnO2 and CaO, the granular‐shaped mullite crystals transformed into rod‐like mullite crystals, forming a net structure. (3) As the input power increased, the overfast sintering rate would reduce proppants' mechanical properties, and it was also necessary to select a reasonable sintering time to avoid overburning. (4) When the mass ratio of MnO2:CaO:SiC:bauxite was 2:1.5:12:84.5 and under the sintering condition of 1000 W, 2 h, the performance (breakage ratio of 8.5% under 28 MPa closed pressure, apparent density of 2.58 g/cm3, turbidity of 52 FTU, and acid solubility of 6.77%) could meet the requirements of the Chinese Petroleum and Gas Industry Standard (SY/T 5108–2014). This study provides a powerful way for reducing the fracturing cost, which not only improves the low‐grade bauxite utilization scale within the ceramic industry, but also expands the application of microwave sintering technology in mullite structural materials for the petroleum and gas industry.

Mechanical and optical properties of porous black Al2O3: Experimental, DFT, and wave optics investigation

Porous black Al2O3 was fabricated by gel casting and pressureless sintering (PS). MnO2 and Fe2O3 incorporated in Al2O3 led to the formation of MnAl2O4 and FeAl2O4 at ≥1200 °C, enhancing its opacity. The influence of various MnO2 content and sintering temperature on the mechanical and optical properties of porous black Al2O3 was investigated. The results showed that as MnO2 content and sintering temperature increased, porosity decreased, bulk density increased, compressive strength increased, and opacity increased. Using density functional theory (DFT), the intrinsic properties of MnAl2O4 and FeAl2O4 were investigated, including band structure (BS), electron distribution, partial density of states (PDOS), and optical properties such as refractivity, absorption, dielectric constant, conductivity, and dissipation factor across various wavelengths. These DFT calculations were incorporated into the wave optics model to assess the response and impedance matching of porous black Al2O3 to transverse electric (TE) and transverse magnetic (TM) waves with various MnAl2O4 content.

Manganese dioxide-coated biocarbon for integrated adsorption-photocatalytic degradation of formaldehyde in indoor conditions

Formaldehyde is a common indoor air pollutant with hazardous effects on human health. This study investigated the efficiency of biocarbon (BC) functionalized with variable contents of MnO2 for formaldehyde removal in ambient conditions via integrated adsorption-photocatalytic degradation technology. The sample with the highest formaldehyde removal potential was used to prepare a functional coating made of acrylic binder mixed with 20 wt% of the particles and applied on beech (Fagus sylvatica L) substrate. SEM images showed that MnO2 was deposited around and inside the pores of the BC. EDX spectra indicated the presence of Mn peaks and increased content of oxygen in the doped BC compared to pure BC, which indicated the successful formation of MnO2. Raman spectra revealed that the disorder in the BC's structure increased with increasing MnO2 loadings. FTIR spectra of BC–MnO2 samples displayed additional peaks compared to the BC spectrum, which were attributed to MnO vibrations. Moreover, the deposition of increased MnO2 loadings decreased the porosity of the BC due to pores blockage. The BC sample containing 8 % Mn exhibited the highest formaldehyde removal efficiency in 8 h, which was 91 %. A synergetic effect between BC and MnO2 was observed. The formaldehyde removal efficiency and capacity of the coating reached 43 % and 6.1 mg/m2, respectively, suggesting that the developed coating can be potentially used to improve air quality in the built environment.

Fabrication of MnO2@Porous Carbons with High Energy and Power Density and Their Application in Supercapacitors

MnO2@PCs (porous carbons) exhibiting high energy and power density are utilized as supercapacitor electrodes and prepared by impregnating porous carbons (PCs) derived from coal tar pitch (CTP) with KMnO4 as the manganese source. This study systematically investigates the impact of MnO2 loading on the microstructure and electrochemical performance in sample. It is found that the specific surface areas (SSA) of all MnO2@PCs significantly reduced compared to that of the PCs 2789 m2 g−1. The suggested mechanism might be a combination of the energy storage mechanism of dual layer capacitors with pseudo‐capacitance due to redox reactions of MnO2. Notably, MnO2@PCs‐0.0075 exhibits a maximum SSA of 1454.62 m2 g−1. Its specific capacitance reached 561 F g−1 at 0.5 A g−1, while the capacitance of the PCs increased by 81.5% to 309 F g−1. Remarkably, the Coulombic efficiency remained at 100%. The power density and energy density are determined in a two‐electrode test system to be 0.5 kW kg−1 and 58.01 Wh kg−1, respectively, at 0.5 A g−1. Concluding from these results and related literature, the MnO2 content significantly influences the electrochemical performance, suggesting that MnO2@PCs‐0.0075 could be a promising supercapacitor (SC) electrode material, provided its capacitance retention is enhanced.

Al2O3f/Al2O3 composites with high bending strength prepared via a MnO2 modified slurry impregnation method

The limitations of oxide/oxide ceramic matrix composites lie in the need to improve their mechanical properties. It is challenging to reconcile the conflict between matrix densification at high temperature and the potential thermal damage to fibers. The concept of using element doping to control the sintering behavior of matrix was initially applied to prepare alumina-based ceramic matrix composites (CMCs). To lower the sintering temperature of the Al2O3 matrix, MnO2 dopant was used as a sintering aid. As a result, the thermal damage to alumina fibers was decreased, and the mechanical properties of the composite were significantly enhanced. The effect of MnO2 content on the bending strength and micro-morphology of the composite was investigated. The composite exhibits optimal mechanical properties with a 0.01 wt% MnO2 doping, and its bending strength is approximately 405 MPa. The investigation aimed to determine the mechanism by which the fluctuation in micro-mechanical properties of the composites with different MnO2 contents. After the thermal aging at 1000℃ for 500 h, the bending strength of the N610/Al2O3-0.01 composite decreases to 297 MPa. The evolution and mechanism of thermal aging damage have been studied.

Effect of manganese on the structure of CMAS slag glass–ceramics

With the acceleration of industrialization, environmental issues have received great attention from governments and societies around the world. Utilizing solid wastes containing valuable heavy metals and exploring their role and application in materials is one of the focal issues of environmental protection in recent years. In this paper, in order to explore the effect of Mn content on the crystallization of CaO-MgO-Al2O3-SiO2 glass–ceramics, glass–ceramics with different content of MnO2 were prepared by sintering method and the effect of MnO2 doping on the crystalline properties, glass stability and heavy metal fixation properties of the stainless steel slag glass–ceramics was investigated by differential scanning calorimetry (DSC), Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM). The analysis using crystallization kinetics showed that surface crystallization dominated the whole crystallization process in the range of 0% to 10% MnO2 content. The peak glass crystallization and depolymerisation temperatures of the glass–ceramics increased gradually with increasing MnO2 content, and the main crystallization mode of the samples was one-dimensional crystallization. The main crystalline phase of the resulting glass–ceramics was transformed from diopside to spinel, with a crystallization temperature of 860℃. Heavy metals solidified in the spinel phase. This study shows that heavy metals can be effectively immobilized in glass–ceramics. In summary, the use of solid waste to prepare final products with good environmental performance provides a feasible way to utilize solid waste resources.

Enhancing sintering behavior and conductivity of YSZ electrolyte by co-doping of ZnO and MnO2

This study aimed to enhance the sinterability and conductivity of yttria fully stabilized zirconia electrolyte through co-doping by 2 mol% of ZnO and different contents of MnO2 (0, 0.5, 1, 1.5 mol%) at two sintering temperatures of 1300 and 1400 °C. Phase composition identification, density, microstructure, and conductivity of the samples were evaluated using X-ray diffraction (XRD), Archimedes' method, field emission scanning electron microscopy (FESEM), and electrochemical impedance spectroscopy (EIS), respectively. The XRD results revealed that ZnO and MnO2 are successfully doped in the fluorite structure of YSZ sintered at 1400 °C, and the cubic structure is completely preserved. However, at a sintering temperature of 1300 °C, the (111) peaks of doped samples were slightly split, which implied a slight phase transformation of YSZ from cubic to a tetragonal structure. The co-doped samples, at both sintering temperatures, showed higher relative density and grain size compared with pure YSZ. The addition of 2 mol% of ZnO and 0.5 mol% of MnO2 at 1400 °C increased the relative density of YSZ from 81.6% to 95.1%. The increase in relative density and grain size, while maintaining the cubic structure, caused an increase in the conductivity of the mentioned sample. Compared with pure YSZ, the sample's total conductivity increased from 7.37 to 10.03 S m−1 at 800 °C. The proposed composition showed better sintering behavior, lower activation energy of grain conductivity, and higher conductivity than pure YSZ. This behavior is thought to be due to the facilitating rearrangement of atoms during sintering and an increase in oxygen ion vacancy concentration due to co-doping with the appropriate amount of ZnO and MnO2.

Effect of MnO2 addition on structure, electrical and optical properties of Ba(Fe0.5Nb0.5)O3 ceramics

Admixture of Ba(Fe0.5Nb0.5)O3 (BFN) ceramics with different content of MnO2 (0, 0.5, 1.0, 1.5 and 2.0 wt.%) powder were processed through conventional solid-state reaction route. The XRD characterization of all sintered samples confirmed the formation of a single cubic perovskite structure.MnO2 acts as sintering aid, which significantly enhances grain size of the BFN ceramics. The room temperature dielectric constant and conductivity of the MnO2 modified BFN ceramics were suppressed compared to the pure BFN ceramics. However, the dielectric constant increases with the increase in temperature above 250 ?C. The relaxation activation energy (>0.6 eV) and high dielectric constant (?104 at temperature above 250 ?C) of the MnO2 modified BFN ceramics were explained on the basis of ionization of oxygen vacancies, mobile oxygen vacancies and polaron hopping between multiple oxidation states of manganese (Mn2+ and Mn3+). A narrow band gap of 1.45 eV was observed in the 1.5 wt.% MnO2 modified BFN ceramics.

Na-Enriched Titanite in Apoquartzite Fenites From Azov Area (Ukraine)

The Na-enriched titanite (up to 3.53 % Na2O) was found in the apoquartzite fenites of the Tunikova gully (Eastern part of the Azov megablock, Ukrainian Shield). It is observed in association with alkaline amphiboles, aegirine, low-Al and high-F phlogopites, rutile, bastnaesite-(Ce), monazite-(Ce), albite, and Ba-enriched potassium feldspar. This mineral association, as well as the agpaitic specificity of apoquartzite fenites (peralkaline index >2), is the result of the influence of undiscovered intrusion of alkaline igneous rocks (silicate or carbonatite) that were the source of alkaline fluids. In general, the Na-enriched titanite contains (wt. %): Y2O3 (up to 3.48), Ce2O3 (up to 0.98), Nd2O3 (up to 1.13), increased F (up to 1.94), but moderate Nb2O5 (0.2-2.8) and negligible content of FeO and MnO, in the almost complete absence of Al2O3. It is assumed that the Na-enriched titanite substitutes the primary rutile of quartzites and reflect high concentration of Na2O, CaO, REE, Y, F introduced by alkaline fluids. The Na → Ca isomorphism was accompanied by parallel substitution Y, REE → Ca, and partially O → F. Other schemes of substitution intrinsic for titanites of alkaline rocks, such as Na+Nb → Ca+Ti or Nb+Fe(Al) → 2Ti, are practically not manifested that obviously due to the low Nb content in the primary rutile and introduced alkaline fluids, as well as the depletion of quartzite in alumina and iron.

Impacts of Mn Content and Mass Loading on the Performance of Flexible Asymmetric Solid-State Supercapacitors Using Mixed-Phase MnO2/N-Containing Graphene Composites as Cathode Materials

MnO2/nitrogen-containing graphene (x-NGM) composites with varying contents of Mn were used as the electrode materials for flexible asymmetric solid-state supercapacitors. The MnO2 was a two-phase mixture of γ- and α-MnO2. The combination of nitrogen-containing graphene and MnO2 improved reversible Faraday reactions and charge transfer. However, excessive MnO2 reduced conductivity, hindering ion diffusion and charge transfer. Overloading the electrode with active materials also negatively affected conductivity. Both the mass loading and MnO2 content were crucial to electrochemical performance. x-NGM composites served as cathode materials, while graphene acted as the anode material. Operating by two charge storage mechanisms enabled a synergistic effect, resulting in better charge storage purposes. Among the supercapacitors, the 3-NGM1//G1 exhibited the highest conductivity, efficient charge transfer, and superior capacitive characteristics. It showed a superior specific capacitance of 579 F·g−1, leading to high energy density and power density. Flexible solid-state supercapacitors using x-NGM composites demonstrated good cycle stability, with a high capacitance retention rate of 86.7% after 2000 bending cycles.

Synthesis and properties of foam glass-ceramics from granite tailings by using SiC and MnO2 as the mixed foaming agent

Foam glass-ceramics were successfully prepared with the powder sintering method using granite tailings as the main raw material, and silicon carbide (SiC), and manganese dioxide (MnO2) as the mixed foaming agent. The effects of the mixed foaming agent and sintering temperature on the crystalline phase, pore-wall structure, and the properties of the prepared foam glass-ceramics were systematically studied. Moreover, the foaming mechanism of the foam glass-ceramics prepared by using the mixed foaming agent was revealed. The results showed that, with a decrease of SiC content, the thermal conductivity and compressive strength decreased, and with an increase of MnO2 content, a special connected pore structure formed in the pore wall of the sample. The optimum mass ratio of MnO2: SiC in the mixed foaming agent was 1: x (x = 3‒7). Foam glass-ceramics with good thermal insulation performance, a bulk density of 0.35–0.50 g/cm3, a porosity of 85.05–88.12%, a thermal conductivity of 0.037–0.046 W/(m·K), and high compressive strength (0.46–3.11 MPa) were obtained at the sintering temperature of 880 °C.

Hydrothermal Synthesis and Magnetic Properties of Zn/Mn Oxides Nano Particles

The aim of this study was to investigate the magnetic properties of mixed nanocrystalline Zn/manganese oxide compounds synthesized by a hydrothermal method. These compounds are designed as (ZnO)1−n(MnO)n, where index n ranges from 0.05 to 0.60. The results of magnetic measurements, including AC magnetic susceptibility as a function of temperature (up to 160 K) and frequency (from 7 Hz up to 9970 Hz), as well as DC magnetization in magnetic fields up to 9 T and temperature up to 50 K, are reported. We observed various types of magnetic behavior depending on the nominal weight content of MnO. Samples with a low nominal content (up to n = 0.10) of MnO exhibited Curie–Weiss behavior at higher temperatures. For samples with high nominal weight contribution (from n = 0.30 to 0.60), spin-glass-like or/and weak ferromagnetic behavior is observed.

Assessing synchronous removal of nutrients and SMX based on novel Mn-C composites: Impact of different proportion of manganese dioxide

In this study, Mn-C composites using different MnO2 contents and solid carbon material were prepared to explore the synchronous removal performance of nutrients and SMX. Higher nitrate removal performance (97–98 %) with quickest nitrate removal rate (4.97 mg N L-1h−1) was obtained in Mn_20 systems. The increased Mn content and Mn-P compound were observed via surface characteristics, indicating the involvement of MnOx in pollutants removal, particularly for higher phosphorus removal (84–89 %) via Mn-P precipitation and BioMnOx adsorption. Nevertheless, compared to systems based on Mn_0 composites (74 %), systems with Mn-C composites presented lower SMX reduction efficiency (34–51 %), which might be attributed to the large Mn(II) accumulation, impairing certain microbes and lower the MnOx function. Higher abundance of genera affiliated to Bacteroidetes_vadinHA17 and Rhodocyclaceae was observed in the Mn-C composites, as well as the gathering of Geobacter and Desulfovibrio as keystone taxa, responsible for the removal of nitrate and SMX and microbial interactions. Besides, the increase of sulfonamide ARGs was closely related to the predominant microbes in the Mn-C composites, which acted as the hosts of ARGs. This study broadens the knowledge of Mn-C composites in synergetic removal of nutrients and organics, and supports the potential application of manganese oxide in wastewater treatment.

Addition of V2O5-MnO2/USY-zeolite catalyst in PTFE fiber for bag filter and its catalytic activity tests for NH3-SCR at low-temperature

This study investigated the catalytic activity of vanadium-manganese supported on USY-zeolite as a catalyst for low-temperature NO removal, and embedded the powder catalyst in PTFE filter of bag filter. The V2O5-MnO2/USY-zeolite catalyst was prepared using the co-impregnation method, and the V2O5/MnO2 ratio was 0/10, 2.5/7.5, 5/5, 7.5/2.5, or 10/0. The catalytic activity test for NH3-SCR(selective catalytic reduction) of NO was performed at 150–230 °C. An enhanced NO conversion above 60% was exhibited in the low-temperature region below 230 °C, and the NO removal efficiency increased as the MnO2 content increased. The NH3-TPD and NO-TPD(Temperature Programmed Desorption) analysis confirmed that the NH3 adsorption of the catalyst more significantly influences the NO removal performance than the NO adsorption. As the MnO2 content on the catalysts increased, the strength and amount of adsorbed NH3 increased, resulting in enhanced NO conversion. The catalyst-embedded PTFE (polytetrafluoroethylene) fiber was prepared by extruding physically mixed PTFE and catalyst powder. Scanning electron microscopy/energy dispersive X-ray spectroscopy confirmed that the catalyst was well dispersed on the surface and inside the PTFE fiber. The NO removal performance of the catalyst included PTFE fiber increased as the amount of the catalysts added was increased.

Dating rare earth element enrichment in deep-sea sediments using U-Pb geochronology of bioapatite

Abstract Deep-sea sediments rich in rare earth elements and yttrium (REY) are promising mineral resources that are believed to be associated with the burial of fish debris. However, the nature of the REY enrichment is poorly understood, in part due to a lack of robust age constraints. We report bioapatite U-Pb ages from an Ocean Drilling Program (Leg 199, Hole 1218A) core and a REY-rich sedimentary core from the Pacific Ocean, which yielded U-Pb ages ranging from 22.8 to 18.2 Ma and 6.5 to 2.2 Ma, respectively. The U-Pb fish teeth ages from the 1218A core are consistent with biostratigraphic constraints, shed light on the application of the U-Pb bioapatite chronometer, and yield an absolute time scale for stratigraphy, especially for sequences deposited below the calcite compensation depth (CCD), where there is an absence of fossil carbonate. The successful measurement of U-Pb ages from REY-enriched fish teeth in the REY-rich sediment core suggests the mineralization occurred no later than the Miocene in the western Pacific Ocean. Uranium is positively correlated with REY, suggesting that the U and REY were incorporated into the fish teeth lattice simultaneously, making the bioapatite U-Pb chronometer suitable for constraining the timing of REY mineralization. When combined with published data, our study suggests that the Miocene REY accumulation event in the western Pacific Ocean was influenced by high P2O5 and MnO2 contents correlated with oxic bottom water.

Natrium Diacid Phosphate-Manganese-Lead Vitroceramics Obtained from Spent Electrodes

NaH2PO4-MnO2-PbO2-Pb vitroceramics were studied usinginfrared (IR), ultraviolet-visible (UV-Vis) and electron paramagnetic resonance (EPR) spectroscopies to understand the structural modifications as potential candidates for electrode materials. The electrochemical performances of the NaH2PO4-MnO2-PbO2-Pb materials were investigated through measurements of cyclic voltammetry. Analysis of the results indicates that doping with a suitable content of MnO2 and NaH2PO4 removes hydrogen evolution reactions and produces a partial desulphatization of the anodic and cathodic plates of the spent lead acid battery.

Effect of pH on Microstructure and Catalytic Oxidation of Formaldehyde in MnO2 Catalyst

Layered δ-MnO2 catalysts were prepared using the one-step redox method in precursor solutions with five different pH values (pH = 7, 9, 11, 13, and 14). The effects of pH on the physical properties and catalytic activity of the catalyst were investigated through XRD, SEM, TEM, BET, XPS, H2-TPR, and HCHO degradation tests at room temperature. The results showed that the layer spacing, manganese vacancy content, Mn4+/Mn3+ ratio, and surface-reactive oxygen species content of MnO2 increased with the increase in pH value in the alkaline range. When the catalyst was prepared at pH = 13, the above characteristics of the catalyst reached the optimal value which contributed to the high catalytic activity. Combined with the related characterization results, it was proved that changing the pH can affect the degree of oxidation in the catalyst synthesis process, increase the number of active oxygen and the oxygen mobility of the catalyst, and effectively improve the catalytic activity of the manganese dioxide catalyst for HCHO. This work represents a giant step toward the preparation of an effective catalyst for practical applications of HCHO removal at room temperature at a low concentration and high velocity.