Addition Of Metal Oxides Research Articles

Phosphate-based geopolymer: Formation mechanism and thermal stability

Chemosynthetic phosphate-based geopolymer is a new type of low carbon and eco-friendly construction material. This article aims to investigate the formation mechanism and thermal stability of this new type of geopolymer. In this study, three mixes of the phosphate-based geopolymer were designed and synthesized at ambient temperature with different molar ratios of Si, Al and P, which were supplied by the raw materials of silica fume, metakaolin and monoaluminum phosphate. No accelerating setting condition (e.g., metal oxides addition or high temperature curing) was applied. The experimental results showed that the 28-day compressive strength of the hardened geopolymer paste arrived at about 31MPa when the Al/P molar ratio is equal to 1.0, which was ensured by the formation of an amorphous structure of SiO2·Al2O3·P2O5·nH2O and a crystalline phase, aluminum hydrogen phosphate (AlH3(PO4)2·3H2O). At elevated temperatures, a phase transition of the phosphate-based geopolymer was activated from aluminum hydrogen phosphate to berlinite (AlPO4) and the silicon-containing phase was rearranged.

Electrochemical Studies of Nano Metal Oxide Reinforced Nickel Hydroxide Materials for Energy Storage Applications

The electrode materials for secondary battery and supercapacitor applications have been synthesized by co-precipitation of nickel hydroxide in NiSO4 aqueous solution and subsequently reinforced with MgO, ZnO, TiO2 and CuO nanoparticles (NPs). These nickel hydroxide materials exhibit a typical β-phase when characterized by powder X-ray diffraction (PXRD). Further, addition of nanoparticles additives have shown a variation in the band gap of nickel hydroxide as noticed from diffuse reflectance spectral (DRS) analysis. The electrochemical characteristics have been investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV measurements indicate an increase in the reversibility of the electrode reaction whereas by reducing the EO-ER value, nano metal oxide reinforced β-Ni(OH)2 exhibits an improved capacitance by increasing the conductivity of an electrode as evident from EIS measurements. Galvanostatic charge-discharge tests for the β-Ni(OH)2 samples with nano metal oxide additives have shown excellent capacitance performance in battery and supercapacitor applications. These results may offer new pathways for the development of novel materials for energy storage applications in general and contribute to the development of this niche area at large.

Positron annihilation characteristics, water uptake and proton conductivity of composite Nafion membranes.

The free volumes and proton conductivities of Nafion membranes were investigated at different humidities by positron annihilation lifetime spectroscopy (PALS) and using an electrochemical workstation, respectively. The results showed that the variation in o-Ps lifetime τo-Ps was closely associated with the microstructure evolution and the development of hydrophilic ion clusters in Nafion membranes as a function of water uptake, regardless of metal oxide additives. In particular, with increasing relative humidity, the maximum value of τo-Ps in the Nafion membranes corresponded to the formation of numerous water channels for proton transportation. Numerous well-connected water channels in Nafion-TiO2 hybrid membranes could be formed at a much lower relative humidity (∼40% RH) than in the pristine one (∼75% RH), due to the better water retention ability of the Nafion-TiO2 membranes. Further, a percolation behavior of proton conductivity at high water uptake in Nafion membranes was observed, which showed that the percolation of ionic-water clusters occurred at the water uptake of ∼4.5 wt%, and ∼6 wt% was basically enough for the formation of a well-connected water channel network.

Impacts on combustion behavior of adding nanosized metal oxide to CH3N5-Sr(NO3)2 propellant

In firefighting area, the novel CH3N5-Sr(NO3)2 is of growing interest as solid propellant gas generating agent. However, undesirable reaction temperature and burning rate of CH3N5-Sr(NO3)2 limit their applications to fire-fighting systems, which forces fire researchers to find more fitting ingredient proportions or burning rate catalysts. This paper presents a detailed experimental study adding nanosized metal oxides (Fe2O3, CuO, and NiO) effects on CH3N5-Sr(NO3)2 burning behaviors, including thermal analysis, scanning electron microscopy, specific surface area measurement, and thermal conductivity test. Results show, the additions of transition metal oxides (TMOs) increase the burning rate of the CH3N5-Sr(NO3)2-based propellants and decrease reaction temperature. The modifying effects of TMOs on combustion behavior alter both the condensed phase and gas phase reactions in a synergistic manner. The novel propellant formulation has shown a superior property to promote CH3N5-Sr(NO3)2-based propellants’ application into fire-fighting area.

Effect of functionalized metal oxides addition on the mechanical, thermal and swelling behaviour of polyester/jute composites

The unsaturated polyester composites were fabricated in hand lay-up method by reinforcing with jute fibre along with alumina or zirconia particles in different filler loading viz. 5, 10, 15 and 20wt%. It was observed that with incorporation of fillers, the microhardness value of the resulting composites increases and reaches its maximum at 20wt% filler content. Characterizations were performed on the composites fabricated with overall 20wt% filler content (18wt% fibre and 2wt% metal oxide particles). Various characterizations like Vicker’s microhardness testing, scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), limiting oxygen index (LOI) testing and water absorption test were performed. Tensile, Flexural testing were also performed on the normal and water absorbed samples. SEM analysis ensured good dispersion of filler within the polymer matrix. EDS and XRD were performed to identify the filler in the composites. FITR spectroscopy revealed the bonding of fillers with the matrix. TG analysis showed that thermal stability, degradation temperature of jute-ZrO2 composites were best over the others. LOI testing also shows similar trend, showing better fire resistant property of jute-ZrO2 composites than the Al2O3 dispersed. Water absorption test indicates the stability of different composite in various atmospheres (normal, boiling, simulated marine, alkali and acid water).

Effect of metal oxide additions to quality on Ge/GeO2 interfaces

Alloying amorphous GeO2 with Y2O3 or related group IIIA oxides is known experimentally to improve its properties as a gate dielectric in field effect transistors. The mechanism of this is studied here by density functional calculations. The metal site coordination is found to be 6–7, by increasing the oxygen coordination to 3 or higher. The alloying is found to increase the bulk modulus. Alloying also increases the diffusion energy of the oxygen vacancies in GeO2 next to the metal and also increases the vacancy formation energy of oxygens that are second neighbors of the metal sites. In this way, a relatively small metal concentration can reduce the O vacancy diffusion rate and thereby the GeO evolution rate. Oxygen vacancies at the Ge/GeO2 interface next to a metal site are found to divide into two types, those which rebond across the vacancy (La, Hf) and those without rebonding (Y, Sc, Al), the latter being preferable as they do not give rise to interfacial gap states.

VOx-Pt/Al2O3 catalysts for hydrogen production

Platinum supported catalysts are promising systems to a wide range of catalytic reactions involved in the hydrogen production chain. The performance of these catalysts can be enhanced by designing properly their nature, composition and structure. In this context, the addition of a second metal oxide on a catalyst composed of a well dispersed Pt phase over a high surface area support may be a powerful strategy. In this work we impregnated VOx species over Pt/Al2O3 and evaluated the catalysts performance for water-gas shift (WGS) and glycerol steam reforming (GSR) reactions. The catalysts characterization showed that VOx species formed over the Pt/Al2O3 surface were not deeply affected by the loading in the range of 0.5–2.0V atoms per nm2 and were reduced at mild temperatures. In situ measurements during catalysts activation and WGS reaction showed that VOx species presented mixed valence (V3+/V4+) while Pt was in metallic state. The addition of vanadium increased Pt/Al2O3 WGS activity; however, the improvement did not linearly correlate with the loading. Under GSR, the results indicated that the WGS step was favored by the presence of vanadium but the selectivity to H2 decreased, which could be attributed to the parallel reactions enhanced by the acidic nature of the VOx sites.

Photocatalytic activity of binary metal oxide nanocomposites of CeO2/CdO nanospheres: Investigation of optical and antimicrobial activity

We report the synthesis of high quality CeO2-CdO binary metal oxide nanocomposites were synthesized by a simple chemical precipitation and hydrothermal method. Cerium nitrate and cadmium nitrate were used as precursors. Composition, structure and morphology of the nanocomposites were analyzed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). XRD pattern proves that the final product has cubic phase and the particle size diameter of the nanocomposites are 27nm, XRD results also indicated that the crystalline properties of the nanocomposite were improved without affecting the parent lattice, FESEM analysis indicates that the product is composed of spherical particles in clusters. The morphological and optical properties of CeO2-CdO nanosamples were characterized by HRTEM and DRS spectroscopy. The IR results showed high purity of products and indicated that the nanocomposites are made up of CeO2 and CdO bonds. Absorption spectra exhibited an upward shift in characteristic peaks caused by the addition of transition metal oxide, suggesting that crystallinity of both the metal oxide is improved due to specific doping level. TGA plots further confirmed the purity and stability of nanomaterials prepared. Hence the nanocomposite has cubic crystal lattice and form a homogeneous solid structure. From the result, Cd2+ ions are embedded in the cubic crystal lattice of ceria. The growth rate increases which are ascribed to the cationic doping with a lower valence cation. Ce-Cd binary metal oxide nanocomposites showed antibacterial activity, it showed the better growth inhibition towards p.aeruginosa. Exploit of photodegradation and photocatalytic activity of large scale synthesis of CeO2-CdO binary metal oxide nanocomposites was reported.

Ionic transport modification in proton conducting BaCe0.6Zr0.3Y0.1O3−δ with transition metal oxide dopants

Proton conducting BaCe0.6Zr0.3Y0.1O3−δ (BCZY63) pellets were fabricated by the solid-state reactive sintering method whereby a small extra amount of a metal oxide additive (5mol%) was included in the precursor mixture before sintering. The effect of the addition of six different metal oxide additives (CuO, ZnO, Fe2O3, MnO2, PdO, and Cr2O3) on the transport properties of BCZY63 was investigated. Although most additives (e.g. ZnO, Fe2O3, MnO2, Cr2O3) led to a decrease (sometimes minor) in conductivity, CuO and PdO dopants yielded an increase in total conductivity compared to the BCZY63 control. The enhancement in the total conductivity is found to be related to two factors: 1) the additive can act as a sintering aid to produce larger grain size; 2) the presence of the metal ions from additives in the structure can lead to increased bulk proton concentration. Due to its excellent sinterability and moderately improved proton conductivity, CuO-doped BCZY63 was subsequently applied as the dense electrolyte layer in protonic ceramic fuel cells utilizing a recently developed single firing step fabrication technique to produce high quality single cells that showed exceptional performance and long-term stability.

Preparation of Nano-composite Gel Electrolytes with Metal Oxide Additives for Dye-sensitized Solar Cells

The dye-sensitized solar cell (DSSC) has been widely studied due to the low-cost and interesting efficiencies. The solar-to-electricity conversion efficiency (η) is an important factor governing the performance of DSSC, so is the long-term stability. In this study, three kinds of inorganic nanoparticles, i.e., SiO2, TiO2, and ZnO, are employed to solidify an acetonitrile-based liquid electrolyte for quasi-solid-state DSSCs based on ZnO photoanodes. The concentrations of I2 and LiI in the liquid electrolyte are first optimized with respect to the diffusion-limited current density of I3− ions and the photovoltaic performance of DSSC. Different amounts of the inorganic nanoparticles are then introduced into the optimized liquid electrolyte to accomplish gelation for quasi-solid-state DSSCs. All the nanoparticles tested can accomplish gelation while achieving a η higher than the reference liquid-state cell. The highest η of 4.17% was recorded for quasi-solid-state DSSCs under simulated full sunlight (AM1.5G, 100mW/cm2) with 35.0wt% ZnO nanoparticles as the gelator. This is due to an enhancement in short-circuit current density and open-circuit voltage as a result of efficient charge transfer channels and improved electron lifetime generated by the gelling nanoparticles. The electrochemical impedance spectroscopy was also applied to analyze the interfacial resistances in the devices. The optimized quasi-solid-state DSSC also shows excellent at-rest stability exhibiting 95% retention of the η value after 150days of storage.

Synthesis and properties of solid electrolyte Ce0.9Gd0.1O2–δ with Co, Cu, Mn, Zn doping

The influence of small additions (1, 3, 5 mol %) of transition metal (Co, Cu, Mn, Zn) oxides on the properties of solid electrolyte Ce0.9Gd0.1O2–δ (GDC) have been investigated. It has been shown that the addition of dopants results in intensification of GDC sintering and reduction of the shrinkage end temperature by 300–400°C, which decreases in the sequence Zn–Mn–Co–Cu. The ultimate dopant concentration above which the further activation of GDC sintering does not occur is about 3 mol % for Co, Cu, and Mn and about 1 mol % for Zn. It has been shown that Co and Cu increase the total conductivity of GDC, while Mn and Zn decrease it.

Melt Protection of Mg-Al Based Alloys

This paper reports the current status of Mg melt protection in view to identify near-future challenges, but also opportunities, for Mg melt protection of Mg-Al based alloys. The goal is to design and manufacture sustainable Mg alloys for resource efficiency, recycling and minimising waste. Among alternative cover gas technologies for Mg melt protection other than SF6: commercially available technologies containing―HFC-134a, fluorinated ketone and dilute SO2―and developed technologies containing solid CO2, BF3 and SO2F2, can potentially produce toxic and/or corrosive by-products. On the other hand, additions of alkaline earth metal oxides to Mg and its alloys have developed a strong comparative advantage in the field of Mg melt protection. The near-future challenges and opportunities for Mg-Al based alloys include optimising and using CO2 gas as feedstock for both melt protection and grain refinement and TiO2 additions for melt protection.

Au/TiO2 catalysts promoted with Fe and Mg for n-octanol oxidation under mild conditions

This work aims to further the understanding of gold-based catalytic oxidation of n-octanol in liquid phase. Modification of catalysts with metal oxides additives (Fe or Mg) was used as a tool for transforming and stabilizing gold species. Structural, electronic and catalytic properties of gold catalysts were systematically investigated by means of DRS, H2, CO FTIR, SBET, EDS and SEM, HRTEM, SR-XRD, XANES, XPS and liquid phase n-octanol oxidation. Addition of modifiers affects Au electronic properties, but not the structural ones. Characterization results allow excluding Au3+ ions as candidates for active sites in n-octanol oxidation. In Au/Mg/TiO2, gold exhibited more reduced states while in Au/Fe/TiO2 gold was more oxidized; Au/TiO2 for intermediate oxidized states was found. The proper balance of oxidation states in the gold surface of Au/Mg/TiO2 can be responsible for its higher activity compared with Au/Fe/TiO2 and Au/TiO2 towards n-octanol oxidation. Finally our approach shed light on the nature of active sites for n-octanol oxidation on gold and furthers the development of green base-free catalytic oxidation of alcohols.

A computational study of the addition of ReO3L (L=Cl(-), CH3, OCH3 and Cp) to ethenone.

The periselectivity and chemoselectivity of the addition of transition metal oxides of the type ReO3L (L = Cl, CH3, OCH3 and Cp) to ethenone have been explored at the MO6 and B3LYP/LACVP* levels of theory. The activation barriers and reaction energies for the stepwise and concerted addition pathways involving multiple spin states have been computed. In the reaction of ReO3L (L = Cl−, OCH3, CH3 and Cp) with ethenone, the concerted [2 + 2] addition of the metal oxide across the C=C and C=O double bond to form either metalla-2-oxetane-3-one or metalla-2,4-dioxolane is the most kinetically favored over the formation of metalla-2,5-dioxolane-3-one from the direct [3 + 2] addition pathway. The trends in activation and reaction energies for the formation of metalla-2-oxetane-3-one and metalla-2,4-dioxolane are Cp < Cl− < OCH3 < CH3 and Cp < OCH3 < CH3 < Cl− and for the reaction energies are Cp < OCH3 < Cl− < CH3 and Cp < CH3 < OCH3 < Cl CH3. The concerted [3 + 2] addition of the metal oxide across the C=C double of the ethenone to form species metalla-2,5-dioxolane-3-one is thermodynamically the most favored for the ligand L = Cp. The direct [2 + 2] addition pathways leading to the formations of metalla-2-oxetane-3-one and metalla-2,4-dioxolane is thermodynamically the most favored for the ligands L = OCH3 and Cl−. The difference between the calculated [2 + 2] activation barriers for the addition of the metal oxide LReO3 across the C=C and C=O functionalities of ethenone are small except for the case of L = Cl− and OCH3. The rearrangement of the metalla-2-oxetane-3-one–metalla-2,5-dioxolane-3-one even though feasible, are unfavorable due to high activation energies of their rate-determining steps. For the rearrangement of the metalla-2-oxetane-3-one to metalla-2,5-dioxolane-3-one, the trends in activation barriers is found to follow the order OCH3 < Cl− < CH3 < Cp. The trends in the activation energies for the most favorable [2 + 2] addition pathways for the LReO3–ethenone system is CH3 > CH3O− > Cl− > Cp. For the analogous ethylene–LReO3 system, the trends in activation and reaction energies for the most favorable [3 + 2] addition pathway is CH3 > CH3O− > Cl− > Cp [10]. Even though the most favored pathway in the ethylene-LReO3 system is the [3 + 2] addition pathway and that on the LReO3–ethenone is the [2 + 2] addition pathway, the trends in the activation energies for both pathways are the same, i.e. CH3 > CH3O− > Cl− > Cp. However, the trends in reaction energies are quite different due to different product stabilities. The formation of the acetic acid precursor through the direct addition pathways was unsuccessful for all the ligands studied. The formation of the acetic acid precursor through the cyclization of the metalla-2-oxetane-3-one is only possible for the ligands L = Cl−, CH3 whiles for the cyclization of metalla-2-oxetane-4-one to the acetic acid precursor is only possible for the ligand L = CH3. Although there are spin-crossover reaction observed for the ligands L = Cl−, CH3 and CH3O−, the reactions occurring on the single surfaces have been found to occur with lower energies than their spin-crossover counterparts.

Effect of MO2 (M = Ce, Mo, Ti) layer on activity and stability of PtCo/C catalysts during an oxygen reduction reaction

The performance of PtCo/C catalysts in the presence of a metal oxides layer for an oxygen reduction reaction (ORR) was investigated. Different types of metal oxides (CeO2, MoO2 and TiO2) and metal loadings (0.03–0.45mg/cm2) were incorporated on the PtCo/C catalyst layer. Their activity was analyzed in acid solution and proton exchange membrane (PEM) fuel cell under a H2/O2 environment at 60°C and ambient pressure, while the stability was tested in an N2-saturated H2SO4 solution using repetitive potential cycling. It was found that the addition of metal oxides on a catalyst layer had no influence for PtCo/C morphology. However, they significantly affected the electrochemical surface area (ESA), internal contact resistance (ICR) and hydrophilic/hydrophobic properties of the catalysts layer. Furthermore, they significantly affected the ORR activity and stability in acid solution and PEM fuel cell operation. Among all studied metal oxides, the TiO2 exhibited the best property for use as the catalyst interlayer in PEM fuel cell for both activity and stability enhancement.

Aesthetic Value Addition and Surface Study of Odisha Ruby Stones by Heat Treatment with Different Metal Oxide Additives

Aesthetic Value Addition and Surface Study of Odisha Ruby Stones by Heat Treatment with Different Metal Oxide Additives

Enhancing ethanol oxidation rate at PtRu electro-catalysts using metal-oxide additives

Metal oxides are investigated, as additives of a PtRu/C catalyst, for enhancing the electro-oxidation of ethanol in acidic solution. High surface area TiO2 and SnO2 additives are synthesized and physico-chemically characterized. These oxides are added to PtRu/C during the catalytic ink preparation to obtain tri-metallic composite electrodes. These composite electro-catalysts are investigated for the ethanol electro-oxidation in half-cell configuration in comparison with additive-free PtRu/C and Pt/C catalysts. The PtRu-based composite catalyst containing SnO2 promoter shows a lower onset potential and larger current density for ethanol oxidation than the additive-free catalyst and that containing TiO2 promoter. The composite catalysts (PtRu/C+metal oxide) are also used in a direct ethanol fuel cell under practical operating conditions and assessed against the benchmark PtRu catalyst. An increase in performance is recorded with the composite tri-metallic electrodes. The analysis of electro-catalytic activity towards ethanol oxidation reaction and ethanolic residues coverage indicates an enhanced capability to activate ethanol chemisorption or a larger electroactive surface area, together with a faster intrinsic activity at lower overpotential, as the reasons for the improved performance with the use of metal oxide additives.

Effect of Addition of Transition Metal Oxides on the Optical and Structural Properties of Phosphate Glasses

Effect of Addition of Transition Metal Oxides on the Optical and Structural Properties of Phosphate Glasses

Effect of MnO2 on structural and electrical characteristics of Ba0.5Sr0.5TiO3

As the variable dielectric constant, loss and some electric characteristics over the frequency and temperature band of operation make a material unsuitable for some devices, an attempt has been made through this work to obtain frequency–temperature independence of said parameters by suitable addition of metal oxide (MnO2) in lead-free ferroelectric (BaSr) TiO3 in the band of interest. The doping concentration of the oxide in Ba0.5Sr0.5TiO3 has been optimized for the purpose. The doping of manganese oxide reduces the loss by compensating the oxygen vacancies and the structural defects. With variable doping concentration of MnO2 dielectric loss is brought down to an acceptable limit (<10−3). Impedance and modulus spectroscopy of the prepared materials provide an insight into the electrical processes involved in it. The AC/DC conductivity analysis provides loss-conductivity spectrum for device utilization.

Nanostructures constituted by unusually small silica nanoparticles modified with metal oxides as support for ultra-small gold nanoparticles

Abstract Mesoporous silica composed by small nanoparticles has been synthesized by a modified neutral S 0 I 0 templating route method (S 0 , neutral primary amine surfactant; I 0 , neutral inorganic precursor). Decreasing the polarity of the medium and tuning the composition of the S 0 I 0 pair allow the formation of silica nanoparticles that are agglomerated into silica fractal or sponge-like structures. Those nanoparticles conform the building blocks of the neutral S 0 I 0 method. In this work for the first time they are observed isolated by HRTEM. On the other hand, the addition of metal oxides triggers the formation of aggregates containing unusually small silica nanoparticles, i.e. smaller building blocks that in bare silica, in the range of 2–4 nm. Further, through the impregnation of a gold precursor post-synthesis, ultra small gold nanoparticles (1 nm) were embedded in the final silica nanostructures upon calcination of the organic precursors. FTIR and UV–vis spectroscopies, TEM and SEM, XRD and N 2 absorption were used to characterize the resultant materials.