Addition Of MnO2 Research Articles

Effects of basicity, MgO and MnO on mineralogical phases of CaO–FeOx–SiO2–P2O5 slag

The selective separation phosphorous rich phase from steel slag could be an effective way to utilise the steel slag. The mineralogical phase after cooling of steel slag is essential to selective separation of steel slag. In the present work, the mineralogical phases of CaO–FeOx–SiO2–P2O5 slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technique. It was found that the heat treatment at 1573 K would lead to the precipitation of Ca2SiO4–Ca3P2O8 (C2S-C3P) solid solution for all samples. The heat treatment at 1273 K would lead to the precipitation of C2S-C3P, CaSiO3 and Fe2O3. The increase of basicity would promote the crystallisation of CaO–FeOx–SiO2–P2O5 slag. The Effects of additions of MgO and MnO on phase formations of CaO–FeOx–SiO2–P2O5 slag were also studied. Fe2O3 gradually transformed into MgFe2O4 and MnFe2O4 in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe2O4 and MnFe2O4 crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe2O4 phase and MnFe2O4, respectively. The precipitation of crystals from slag during cooling was interpreted by the kinetic and thermodynamic factors. It was proposed that addition of MgO and MnO in slag would be beneficial to magnetic separation of steel slag.

Effect of MnO on Mineral Composition of CaO-SiO<sub>2</sub>-MgO-Al<sub>2</sub>O<sub>3</sub>-Cr<sub>2</sub>O<sub>3</sub> System

The chromium leaching from stainless steel slag highly depends on the occurrence of chromium. The effect of MnO on the mineral composition of stainless steel slag was investigated through CaO-SiO2-MgO-Al2O3-Cr2O3 synthetic slags. The experiments were performed in a conductive furnace, and the samples collected during tests were analyzed using X-ray Diffrac-tion (XRD) and Scanning Electron Microscope (SEM) equipped Energy Dispersive Spectroscopy (EDS). The results show that the addition of MnO significantly reduces the solidus temperature of oxide systems from 1204oC to 950oC, promotes the spinel precipitation and increases the size of spinel crystals. The fraction of chromium contained in non-spinel mineral phases decreases and the amount of larnite dissolved into spinel phase slightly reduces with the content of MnO increasing. In addition, the amorphous phase forms when the content of MnO is up to 6 wt%. Hence, the addition of MnO is beneficial to suppress chromium leaching from slag.

Unveiling the synergistic effect of polysulfide additive and MnO2 hollow spheres in evolving a stable cyclic performance in Li-S batteries.

Herein, we demonstrate a synergistic approach involving polar-based oxide and polysulfide additives for effectively suppressing polysulfide dissolution during cycling. The MnO2 hollow spheres not only provide physical confinement for the polysulfide species but also enable strong chemical interactions between polysulfide species and oxides, while the added polysulfide furnishes a mass buffering effect and compensates for the capacity losses due to partial cathode dissolution during discharge. The capacity retentions of S/KB, S/KB/LiPS, S/KB/MnO2, and S/KB/MnO2/LiPS composite cathodes are 31%, 45%, 59%, and 91% respectively. The remarkable capacity retention of the S/KB/LiPS/MnO2 composite electrode is mainly attributed to the synergistic effect between MnO2 and polysulfide additives.

Improvement of densification and mechanical properties of MgAl2O4–CaAl4O7–CaAl12O19 composite by addition of MnO

Composites containing spinel (MgAl2O4) and calcium hexaluminate (CaAl12O19) can excellently combine the properties of these two phases. However, their fabrication in dense composites for structural applications is limited on account of the poor sinterability. Considering this aspect, the effect of MnO addition on the sintering, microstructure and mechanical properties of MgAl2O4-CaAl4O7-CaAl12O19 composite was investigated by solid state reaction sintering at 1500–1600°C. The results showed that the grain growth of MA was significantly promoted due to the formation of Mg(Mn)Al2O4 by introducing MnO. The addition of MnO can also weaken the barrier effect of the elongated CA6 grains, indirectly promoting the development of MA and CA2 grains. Accordingly, highly uniform and dense microstructures were formed, with the apparent porosity decreased from 18.3% to 3.4% when adding 6wt% MnO at 1600°C. Significant improvements in the mechanical properties were also achieved for the MnO added composites sintered at this temperature. The optimum flexural strength was obtained by adding 6wt% MnO, achieving an increase from 186 to 308MPa, while the optimum fracture toughness was obtained by adding 4wt% MnO, with the value increased from 2.3 to 3.5MPam1/2.

Effect of Transition Metal Oxides Addition on Yttria - stabilized Zirconia for improving Physical and Mechanical Properties

Mechanical properties of Y2O3-containing tetragonal ZrO2 polycrystals(Y-TZP) were investigated. Several additives were used to modify the hardness and fracture toughness of Y-TZP. The effects of these individual additives were discussed and their interactions were also analysed. Each additive, such as CoO, Fe2O3, MnO2 was found to deteriorate the mechanical properties of Y-TZP when it was used singly. But the fracture toughness of Y-TZP was significantly improved when these additives and Al2O3 were added in combination at a certain ratio. The addition of CoO, Fe2O3 and MnO2 into Y-TZP resulted in the more complex behavior of fracture toughness and hardness. The specimen with 1.5 wt%-Fe2O3, 3.0 wt% -Al2O3 and 1.5 wt%-CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of <TEX>$10.8MPa{\cdot}m1/2$</TEX> with Vickers hardness of 1201 kgf/mm2. However, the toughness decreased as the ratio increased and macrocracks developed beyond the ratio of 25%. Sample No. 16 is improved high Physical and Mechanical Properties.

Thermal and fragility aspects of microwave synthesized glasses containing transition metal ions and heavy metal ions

A simple, clean and energy efficient microwave heating route is used to prepare glasses in the systems xMnO-33(0.09PbCl2:0.91PbO)-(67-x) NaPO3 and xPbCl2-33PbO-(67-x) NaPO3 where 0.1 ≤ x ≤ 4 (mol%). Thermal data extracted from differential scanning calorimetry (DSC) thermograms are used to study the composition dependence of glass transition temperature (Tg), heat capacity, thermal stability and fragility. The decrease in glass transition temperature with modifier oxide (Na2O + MnO) content can be ascribed to network degradation and the volume increasing effect caused by PbCl2. The change in heat capacity of MnPb glass being greater than that of PbNP glass, suggests that MnPb glasses are more covalent than PbNP glasses. DSC thermograms taken at different heating rates (φ) reveal the dependence of Tg on φ, and the thermal stability of the glass increases due to MnO addition. Fragility aspects have also been studied by calculating the fragility functions \(\left( {\frac{{\Delta {\text{C}}_{\text{p}} }}{{{\text{C}}_{\text{pl}} }}\;{\text{and}}\;\frac{{\left[ {\text{NBO}} \right]}}{{{\text{V}}_{\text{m}}^{3} {\text{T}}_{\text{g}} }}} \right)\). Results obtained from both the fragility functions compare well and reveal the dependence of fragility functions on modifier content and PbCl2 mol%. Further, the decrease in Tg and Hv are suggested to be due to the increase in the number of non-bridging oxygens, which results in the lowering of stiffness and rigidity of the glass network. Analysis of the infrared spectra confirms that the glassy matrix is composed of P–O–P, P–O–Pb, P=O and P–O− bonding.

Further Enhancing Piezoelectric Properties by Adding MnO2 in AgSbO3‐Modified (Li,K,Na)(Nb,Ta)O3 Lead‐Free Piezoceramics

This work investigated the effect of MnO2 addition on the phase structure, microstructure, and electrical properties of AgSbO3‐modified (Li,K,Na)(Nb,Ta)O3 (abbreviated as LKNNT‐AS) lead‐free piezoelectric ceramics with an optimized composition endowed with a state of two‐phase coexistence. A small amount (0.1 wt%) of MnO2 can significantly further enhance the piezoelectric property of LKNNT‐AS ceramics, whose piezoelectric constant d33 and converse piezoelectric coefficient d33* as well as planar electromechanical coupling factor kp reach 363 pC/N, 543 pm/V, and 0.49, respectively. The temperature stability of piezoelectricity in MnO2‐modified LKNNT‐AS samples also improved, which is associated with the more uniform and better thermally stable ferroelectric domains that were revealed by piezoresponse force microscopy.

Point defect engineering of high temperature piezoelectric BiScO3–PbTiO3 for high power operation

BiScO3–PbTiO3 is used as a model system of BiMO3–PbTiO3 perovskite solid solutions with enhanced electromechanical response at ferroelectric morphotropic phase boundaries, and high Curie temperature to demonstrate specific point defect engineering for high power operation. The objective is to obtain a range of piezoelectric ceramics comparable to hard Pb(Zr,Ti)O3 materials, optimized for the different applications. In this work, a comprehensive study of Mn substitution for Sc is provided. Care is taken to isolate the effects of the point defects from those of concomitant structural and microstructural changes that have been previously described after MnO2 addition. Results strongly suggest that Mn substitution results in the formation of (MnSc′-VO) dipolar complexes that effectively clamp domain walls. This is the same mechanism responsible of hardening in Pb(Zr,Ti)O3. Indeed, Bi0.36Pb0.64Sc0.36-x MnxTi0.64O3 with x=0.02 is shown to be a high sensitivity piezoelectric with strongly reduced losses, suitable for high power operation between 200 and 400°C.

Aluminum Deoxidation Equilibria in Liquid Iron: Part III—Experiments and Thermodynamic Modeling of the Fe-Mn-Al-O System

Deoxidation equilibria in high-Mn- and high-Al-alloyed liquid steels were studied over the entire Fe-Mn-Al composition range by both experiments and thermodynamic modeling. Effect of Mn on the Al deoxidation equilibria in liquid iron was measured by the different experimental techniques depending on the Al content. In order to confirm the reproducibility of the experimental results, the deoxidation experiments were carried out reversibly from high oxygen state by addition of Al as a deoxidizer, and from low oxygen state by addition of Fe2O3 or MnO as an oxygen source. For the Al-rich side, CaO flux was added on top of liquid iron in order to remove suspended Al2O3 inclusions in the melt. Based on the present experimental result and available critically evaluated literature data, the Al deoxidation equilibria in Fe-Mn-Al-O liquid alloy were thermodynamically modeled. The Modified Quasichemical Model was used in order to take into account a strong short-range ordering of atoms in molten state. Deoxidation equilibria and inclusion stability diagram for entire Fe-Mn-Al melt were successfully reproduced by the present model.

Effect of MnO2 on properties of SiC-mullite composite ceramics for solar sensible thermal storage

For improving the properties of SiC-mullite composite ceramics used for solar sensible thermal storage, MnO2 was introduced as sintering additive when preparing. The composite ceramics were synthesized by using SiC, andalusite, α-Al2O3 as the starting materials with non-contact graphite-buried sintering method. Phase composition and microstructure of the composites were investigated by XRD and SEM, and the effect of MnO2 on the properties of SiC composites was studied. Results indicated that samples SM1 with 0.2 wt% MnO2 addition achieved the optimum properties: bending strength of 70.96 MPa, heat capacity of 1.02 J·(g·K)-1, thermal conductivity of 9.05 W·(m·K)-1. Proper addition of MnO2 was found to weaken the volume effect of the composites and improve the thermal shock resistance with an increased rate of 27.84% for bending strength after 30 cycles of thermal shock (air cooling from 1 100 °C to RT).

The Influence of Cu2+ and Mn2+ Ions on the Structure and Crystallization of Diopside–Calcium Pyrophosphate Bioglasses

The influence of two divalent cations, Cu2+ and Mn2+, on the structure, sintering, and crystallization of glasses and glass‐ceramics in the diopside–calcium pyrophosphate system (90 wt.% diopside (CaMgSi2O6), 10 wt.% calcium pyrophosphate (Ca2P2O7)) was investigated. Glasses with 1, 3, and 5 wt% MnO or CuO additives were prepared by melt‐quenching and characterized by XRD, 29Si and 31P NMR, DTA, and FTIR This revealed that the silicate network is predominantly coordinated in Q2 (Si) units for all glasses, while phosphorus tends to inhabit an orthophosphate (Q0) environment. All glasses had a high rate of bioactivity after immersion in simulated body fluid. A slight depolymerization was observed in the doped glasses leading to lower Tg values in comparison with the parent glass. All glass‐ceramics exhibited the formation of diopside as the primary crystalline phase after sintering at 850°C/1 h. In comparison with the parent glass, the doped glasses featured significantly larger processing windows (∆T = Tc–Tg), ensuring good sinterability. Further, with increasing doping levels, the glasses exhibited a gradual decrease in Tp and ∆T, suggesting an increased tendency toward devitrification. All Cu‐ and Mn‐containing glasses exhibited the formation of hydroxyapatite, making them good candidates for biomedical applications and tissue engineering.

Effect of MnO2 Addition on Microstructure and Piezoelectric Properties of 0.95(Na0.5K0.5)NbO3-0.05CaTiO3 Piezoelectric Ceramics

MnO₂ was added to the 0.95(Na 0.5 K 0.5 )NbO₃-0.05CaTiO₃ (NKN-CT) ceramics in order to promote the densification and improve the poling efficiency by increasing the resistance of the specimens. Densification and abnormal grain growth occurred in the MnO₂-added NKN-CT ceramics sintered at 1020°C, indicating that MnO₂ assisted the liquid-phase sintering of these materials. Mn 3+ ions were considered to enter the A-site of the matrix, thereby producing the free electrons, which interacted with the holes resulting from the evaporation of alkali ions. This interaction results in an increase in the resistance of the specimens. The increased resistance improved the poling efficiency and, hence, the dielectric and piezoelectric properties of the NKN-CT ceramics. A few of the Mn 3+ ions that entered the B-site of the NKN-CT matrix led to a slight increase in the mechanical quality factor.

Effect of carbon black to facilitate galvanic leaching of copper from chalcopyrite in the presence of manganese(IV) oxide

It is well known that galvanic interactions between sphalerite or pyrite and manganese (IV) oxide(MnO2) accelerate the leaching of these minerals. Because MnO2 is nobler than chalcopyrite, chalcopyrite acts as cathode to be oxidized in contact with MnO2. We investigated the feasibility of galvanic leaching of chalcopyrite concentrate using chemical reagent MnO2. Leaching experiments were performed in an erlenmeyer flask containing a sulfuric medium agitated on a magnetic stirrer at room temperature. Although the addition of MnO2 improved the leaching rate of chalcopyrite, its effect was limited. Adding carbon black significantly accelerated the kinetics of chalcopyrite leaching in the presence of MnO2, and the Cu extraction yield was 81% at MnO2/carbon black/chalcopyrite ratios of 4:1:1 in 29h. In the absence of carbon black, the extraction was 7%. The extraction rate of Mn from MnO2 also increased. Carbon black did not affect the sulfuric acid or ferric sulfate leaching of chalcopyrite without MnO2, indicating that it could play an important role in the galvanic interaction between chalcopyrite and MnO2. The effects of several variables such as pH, dosage of MnO2 and carbon black, and temperature on the kinetics of chalcopyrite leaching were examined.

Low-temperature sintering of bauxite-based fracturing proppants containing CaO and MnO2 additives

Bauxite-based fracturing proppants with high strengths were prepared at sintering temperatures below 1200°C via the addition of CaO and MnO2. The effects of CaO and MnO2 addition on the sintering behavior and the crush resistance of the bauxite-based proppants were investigated. The addition of CaO and MnO2 promoted the formation of a low-temperature liquid phase, allowing a decrease in the sintering temperature. When the MnO2 content was increased in the additive, the proppants displayed enhanced crystallinities and denser microstructures, and proppants doped with 2wt% CaO and 2wt% MnO2 exhibited the lowest breakage ratio, because of their higher density and greater reinforcement with mullite whiskers.

EFFECT OF MNO2 DOPING ON NONLINEAR COEFFICEINT OF ZN-BI-TI-O VARISTOR CERAMICS

The work aims the improvement of nonlinear coefficient ( ) can achieve by the addition of MnO2. The investigation regarding to the variation of MnO2 doping on ZnO-Bi2O3-TiO2 system is discussed. The crystalline phases were identified by an XRD (PANalytical (Philips) X’Pert Pro PW3040/60) with CuK radiation and the data were analyzed by using X’Pert High Score software. The density of varistor ceramics was measured by the geometrical method. The current-voltage characteristics of the varistor ceramics were evaluated. The average grain size ( ) was determined by lineal intercept method. The of ZnO doped with 0.5 mol% of Bi2O3, 0.5 mol% of TiO2 and x mol% of MnO2 was calculated from data analysis of current-voltage characteristics obtained through a Source Measure Unit (Keithley 236). The calculation of is done by using Origin Pro8.0 software which at low concentration at 1170 oC has the value 10.36 and 9.21 at 45 and 90 min sintering time, respectively, and then decreases to 5.63 and 5.27 at 0.8 mol% MnO2 concentrations. The addition of MnO2 dopant in Zn-Bi-Ti oxide ceramics sintered at 45 minutes cause the value of to increase up to 0.4 mol% and decrease after further addition.

The change of the local environment of MnO incorporated in the lead-germanate glassy network

InfraRed, UltraViolet–visible and Electron Paramagnetic Resonance Spectroscopies were employed to investigate the xMnO∙(100−x)[7GeO2∙3PbO2] vitreous system, where x=0–50mol% MnO, in order to obtain valuable information about the competitive role played by the manganese ions in manganese-lead-germanate network formation.Our results evidenced that the local environment of the manganese ions was modified depending on the MnO content of samples. As a result of this fact, the presence of manganese cations in these samples increases the structural disorder by breaking some of the Ge–O bonds and formation of non-bridging oxygen ions. Variations in optical gap energy and resonance EPR lines are also attributed to the structural modifications of the local environment of the manganese ions. This compositional evolution can be explained considering that the addition of MnO to the host matrix causes a progressive conversion of lead-germanate glassy network leading to the formation of non-bridging oxygen ions and further, to the decrease of the strength of the glass structure by the interconnection of the new structural units.

Li2O[sbnd]LiF[sbnd]ZnF2[sbnd]B2O3[sbnd]P2O5: MnO glasses – Thermal, structural, optical and luminescence characteristics

Here, we present results pertaining to thermal, structural, optical and photoluminescence properties of Li2OLiFZnF2B2O3P2O5: (0.1–1.5mol.%) MnO glasses. DTA profiles revealed a change in glass transition temperature with the addition of MnO suggesting an increase in glass stability. The modifications in structural units are interpreted from FTIR and Raman spectral profiles, which confirm the formation of stable POB bonds. The host Li2OLiFZnF2B2O3P2O5 (labelled as LZBP) glass exhibits emission in the blue region on excitation with 361nm. The red shift in optical absorption edge and decrease in energy of band gap as a function of MnO concentration is analysed from Tauc’s plot. The nature of local symmetry around manganese ions in LZBP matrix has been understood by evaluating the crystal field strength (Dq) and Racah inter-electronic repulsion parameters (B &C) from absorption spectrum and electron-lattice interaction energy (Sħω) factor from emission spectrum. The emission spectra of (0.1–1.5mol.%) Mn2+: LZPB glasses have shown broad band at 613nm assigned to electronic transition 4T1g(G)→6A1g(S) displaying orange-red emission upon excitation at 413nm. Octahedral coordination of Mn2+ ions has been estimated from the position of emission in luminescence spectra. The effect of Mn2+ concentration on emission properties has been discussed from lifetime curves and energy level scheme.

Growth mechanism and enhanced electrical properties of K0.5Na0.5NbO3-based lead-free piezoelectric single crystals grown by a solid-state crystal growth method

(K0.45Na0.55)0.94Li0.06NbO3 (KNLN) single crystals were grown by a solid-state crystal growth (SSCG) method. The effects of MnO2 and crystal orientation of the seeds on the KNLN single crystal growth were investigated. It is found that liquid phase and interfacial reaction mechanisms affect the crystal growth for the SSCG. Using the <110>-oriented KTaO3 crystal as seeds, prism-shaped KNLN-100xMnO2 (x=0–0.02) single crystals with a dimension of ∼10mm×10mm were successfully obtained. The electrical properties of such single crystals were affected with MnO2 addition. The resultant <100>-oriented KNLN single crystals exhibit excellent piezoelectric performances: Smax=0.38% and d33*=995pm/V at Emax=38kV/cm, TC=460°C, superior to other KNN-based piezoceramics even exceed lead-based ceramics. This work indicates that the SSCG is a practicable approach to prepare high-performance KNLN lead-free piezoelectric single crystals.

Hydrogen dissolution and structural analysis in high temperature TiOx–MnO–SiO2 oxide melts

The effects of the composition and temperature on the hydrogen solubility and melt structure in the TiOx–MnO–SiO2 welding flux system were investigated. The redox reaction between Ti3+ and Ti4+ was distinguished within TiOx based on the substitutional effects of TiOx in SiO2. A higher TiOx content compared with SiO2 decreased the hydrogen solubility because the dominant hydrogen dissolution mechanism changed from an incorporated hydroxyl to a mixed region that included both the incorporated and free hydroxyl mechanisms. The Ti3+/Ti4+ trend and the decrease in the absolute amount of SiO2 appear to cause this mechanistic change. Based on the effects of the basic and acidic components on the hydrogen solubility in the melt, the effect of the extended basicity ((Ti2O3+MnO)/(TiO2+SiO2)) was also analyzed and exhibited a parabolic behavior. Three regions were observed from low to high extended basicity, which correspond to the incorporated to free hydroxyl modification with a mixed region. FTIR analysis of the as-quenched melts provided insight into the changes in the Si–O tetrahedral stretching bands and Si–OH bending, which were more pronounced as the SiO2 content increased. The FTIR and XPS results obtained for the melts quenched from 1773 to 1823 K were compared to identify the effect of temperature on the unit structures, and these results indicated that Si–OH was more pronounced at low TiOx/SiO2 and less pronounced at high TiOx/SiO2 at higher temperatures. The changes in the structural units as a function of the composition and temperature correlated well with the hydrogen solubility. Basic oxides of MnO additions can depolymerize the melt by providing O2−, which can increase or decrease the hydrogen solubility depending on the dominant hydrogen dissolution mechanism.

Promotion effect of manganese oxide on the electrocatalytic activity of Pt/C for methanol oxidation in acid medium

The modification of Pt/C by incorporating metal oxides for electrocatalytic oxidation of methanol has gained major attention because of the efficiency loss during the course of long-time operation. This work describes the preparation of Pt–MnO2/C electrocatalysts through a chemical route using ethylene glycol or a mixture of ethylene glycol and sodium borohydride as a reducing agent. The crystallite structure and particle size of synthesized electrocatalysts are determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The addition of MnO2 improves the dispersion of Pt nanoparticles. The electrocatalytic activity of Pt–MnO2/C towards methanol oxidation in H2SO4 solution is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The onset potential value of methanol oxidation peak is negatively shifted by 169mV when MnO2 is introduced to Pt/C. Moreover, the charge transfer resistance value at Pt–MnO2/C is about 10 times as low as that at Pt/C. Chronoamperometry and chronopotentiometry show that CO tolerance is greatly improved at Pt–MnO2/C. The increased electrocatalytic activity and enhanced ability to clean platinum surface elect manganese oxide as a suitable promoter for the anode performance in direct methanol fuel cells (DMFCs).