Silicate Formation Research Articles

Study on the thermal stability of Ce0.8Gd0.2O1.9 nanocubes on Al2O3 and SiO2 supports

The structural evolution of the Ce0.8Gd0.2O1.9 nanocubes supported on Al2O3 and SiO2 was investigated in oxidizing and reducing atmosphere over a temperature range up to 1100°C by XRD, TEM and SEM–EDS methods. The supported Ce0.8Gd0.2O1.9 particles preserved perfect cubic shape to 900°C in oxidizing atmosphere and to 750°C in a hydrogen atmosphere. No evidence of crystalline aluminate or silicate formation was observed for both supports during heating in oxidizing atmosphere up to 1100°C. However, for Ce0.8Gd0.2O1.9/SiO2 segregation of Gd3+ from the mixed oxide and its spreading over the silica surface was noticed at 1000°C–1100°C. Crystalline aluminate/silicate occurred in a hydrogen atmosphere already at 900°C. Apatite type (Ce,Gd)4.67(SiO4)3O mixed silicate was formed after reaction with SiO2 substrate, while monoclinic (Gd,Ce)4Al2O9 and tetragonal (Ce,Gd)AlO3 were formed on Al2O3. The (Gd,Ce)4Al2O9 phase became unstable at 950°C and transformed into (Ce,Gd)AlO3 aluminate, which was stable up to 1100°C. Various mechanisms of the solid-state reaction of mixed ceria with Al2O3 and SiO2 supports operate depending on the size of ceria nanocubes. Small particles (10–30nm) reacted as a whole with the support forming single crystal silicate or aluminate; at the same time, for bigger particles (30–80nm) reactions happen only near the boundary between the particle and the support.

Efficiency and mechanism of stabilization/solidification of Pb(II), Cd(II), Cu(II), Th(IV) and U(VI) in metakaolin based geopolymers

This work deals with stabilization/solidification of Pb(II), Cd(II), Cu(II), Th(IV) and U(VI) in metakaolin (MK) based geopolymer (GP) prepared using one activator (sodium silicate) or two activators (sodium silicate and sodium hydroxide). Different leaching solutions with varying pH and ionic strength were used: deionized water, 0.1M HCl, 0.1M NaCl, 1.0M NaCl and 0.1M NaOH to evaluate the efficiency of stabilization. Effective stabilization was achieved regardless of using one or two activators. The efficiency of stabilization was found to increase with increasing the ionic size of heavy metal which was explained by ion-pair theory. The leaching of total ions from the GP matrix was studied by conductivity measurements which indicated that heavy metal ions in the GP matrix resulted in reduction of the leaching of the alkali ions. This excluded the mechanism that heavy metal ions can be exchanged with the alkali ions balancing the negatively charged Al tetrahedral in GP. Heavy metals were proposed to form coordination bonds between the nonbridging SiO− and AlO− of GP framework (crosslinkers) leading to more effective stabilization of total ions in the GP matrix. The FTIR study suggested formation of heavy metal hydrates, carbonates and silicates. The XRD patterns revealed an amorphous structure, and the SEM analysis indicated almost condensed homogenous surface of GP.

Steam Gasification of Low-Rank Coals with Ion-Exchanged Sodium Catalysts Prepared Using Natural Soda Ash

Ion-exchange reactions of brown and sub-bituminous coals with natural soda ash, composed of >99% Na2CO3, have been studied at 20–40 °C without any pH-adjusting reagents, and the pyrolysis and subsequent steam gasification of the resulting Na+-exchanged coals have been conducted using a fixed-bed quartz reactor at 700 °C. When the Na+ concentration and pH of an aqueous mixture of coal and soda ash are monitored during the ion-exchange process, both values decrease at a greater rate with brown coal with a higher content of COOH groups, indicating that ion exchange of Na+ with H+ of the COOH group is the predominant process. About 65% of COOH can be exchanged with Na+ ions under optimal conditions, irrespective of the coal type. The reactivity of these raw coals in steam at 700 °C is similar, with char conversions of less than 20 mass %, even after 2 h of reaction. Exchanged Na promoted the gasification of both coals at this temperature, but the rate profiles were different: conversion of brown coal increased linearly with time and reached nearly 100% at 1 h, whereas sub-bituminous coal needed approximately 2 h to be gasified completely. The temperature dependence of the conversion with this coal revealed that the use of a Na catalyst can lower the reaction temperature by about 120 °C, and the apparent activation energies were estimated to be 190 and 120 kJ/mol without and with the catalyst, respectively, from Arrhenius plots of the initial specific rate. The scanning electron microscopy–electron probe microanalysis and X-ray diffraction analysis of Na-containing chars recovered after pyrolysis and gasification suggested that the Na catalysts were finely dispersed at the initial stage of the reaction but that they may be deactivated by the formation of sodium silicates at high char conversions at temperatures higher than 90%, even at the low temperature of 700 °C.

Impurity and silicate formation dependence on O3 pulse time and the growth temperature in atomic-layer-deposited La2O3 thin films.

Atomic-layer-deposited La2O3 films were grown on Si with different O3 pulse times and growth temperatures. The interfacial reactions and impurity behaviors were observed using in situ X-ray photoelectron spectroscopy. Longer pulse time of O3 formed the solid SiO2 interfacial barrier layer, which suppressed La-silicate formation. Meanwhile, the carboxyl compound acting as an impurity phase was replaced with LaCO3 on increasing the O3 pulse time due to further oxidation and reaction of La. Higher growth temperatures enhanced La-silicate formation by mixed diffusion of Si and La2O3, during which most of the La2O3 phase was consumed at 400 °C. C and N impurities decreased with increasing growth temperature and completely disappear at 400 °C.

Deformation-aided segregation of Fe-S liquid from olivine under deep Earth conditions: Implications for core formation in the early solar system

The planets and larger rocky bodies of the inner solar system are differentiated, and consist of metallic, iron-rich cores surrounded by thick shells of silicate. Core formation in these bodies, i.e. the segregation of metal from silicate, was a key process in the early solar system, and one which left a lasting geochemical signature. It is commonly assumed that extensive silicate melting and formation of deep magma oceans was required to initiate core formation, due to the inability of iron-rich melts to segregate from a solid silicate matrix. Here we assess the role of deformation in aiding segregation of core-forming melts from solid silicate under conditions of planetary deep interiors. Low-strain rate, high-pressure/temperature deformation experiments and high-resolution 2-D and 3-D textural analysis demonstrate that deformation fundamentally alters iron-rich melt geometry, promoting wetting of silicate grain boundaries and formation of extensive micron to sub-micron width Fe-rich melt bands. Deformation-aided Fe-S melt networks noted here contrast those observed in higher finite strain experiments conducted at lower pressure, and may reveal either an alternative mechanism for melt segregation at higher pressures, or an early stage process of melt segregation. Results suggest, however, that core-mantle chemical equilibration cannot be assumed in models of planetary formation, and that instead, the chemistry of rocky planets may record a complex, multi-stage process of core formation.

Determination of the initial ash sintering temperature by cold compression strength tests with regard to mineral transitions

Ash deposition, fouling, and slagging are commonly undesirable occurrences in coal utility boilers and gasifiers. Ash deposit formation is usually initiated by sintering of the particles. The sintering characteristics of the ash have to be evaluated to understand the process of deposit formation. Cold compression strength (CCS) tests on heat treated ash pellets produced under defined conditions can be applied for the determination of the initial sintering temperature (IST). Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDX), high temperature X-ray diffraction analysis (HT-XRD), and thermogravimetric differential scanning calorimetry (TG-DSC) are analytical methods to characterize the mineral transitions responsible for sintering.CCS tests were done on ashes of three different coals to determine their IST. For this purpose ash pellets were pretreated at different temperatures. The influence of oxidizing, inert, and reducing conditions at ambient pressure was investigated. The IST were compared with the characteristic temperatures from ash fusibility tests (AFT). HT-XRD, TG-DSC, and SEM/EDX were applied for a more detailed characterization of sintering.The IST determined by CCS tests are considerably lower than the respective initial deformation temperature (IDT) obtained by AFT. Thus, the AFT is not suitable to detect IST. Major mineral transitions were found which are responsible for initial sintering in the case of the investigated ashes. The formation of silicates or the crystallization of iron-aluminum-oxides were found to induce sintering at oxidizing and inert conditions. Sintering at reducing conditions was initiated by carbonation of calcium compounds, silicate formation, or melting of iron sulfide. These phases can be understood as the relevant phases for initial strengthening of fouling deposits in coal utility boilers and gasifiers in the case of the investigated ashes.

Assessment of Fe(III) and Eu(III) complexation by silicate in aqueous solutions

Prior investigations of Eu3+ complexation by silicate have led to predictions that rare earth silicate complexes (REESiO(OH)32+) are the dominant species of REEs in deep waters of the Atlantic and Pacific Oceans. The proposed importance of REE–silicate complexes has been used as a foundation to explain oceanic REE profiles. In the present work, we examine the significance of rare earth element complexation by silicate ions. As one fundamental means of assessing prior depictions of REE–silicate formation constant behavior, our work examines the comparative stability constant behavior of Eu(III) and Fe(III). Plots of Eu(III) complexation constants against Fe(III) formation constants, in conjunction with experimental determinations of FeSiO(OH)32+ formation constants, indicate that previously published EuSiO(OH)32+ formation constants are substantially overestimated. Assessment of prior EuSiO(OH)32+ formation constant determinations reveals that results obtained in the presence and absence of silicic acid polymerization are inconsistent. Much larger EuSiO(OH)32+ formation constants are obtained in the presence of polymeric silica. Reanalysis of complexation results obtained under conditions of minimal silicate polymerization leads to a EuSiO(OH)32+ formation constant that is smaller than previously published estimates by as much as a factor of ∼25. The dramatically reduced magnitude of Siβ1(Eu) relative to previously published results indicates that the role of silicate complexation in oceanic REE cycling is much less significant than previously proposed. The spectrophotometric investigations of FeSiO(OH)32+ formation in the present study yield the first characterization of FeSiO(OH)32+ formation constant behavior as a function of ionic strength: logsi*β1(Fe)=(-0.121±0.043)-2.036*I1/2/(1+1.5*I1/2)+(0.568±0.098)I where Si∗β1(Fe)=[FeSiO(OH)32+] [H+]/[Fe3+] [Si(OH)40]. This result can be used to show that ferric silicate complexes in seawater are present at much lower concentrations than ferric hydroxide complexes. The Siβ1(Eu) formation constant obtained in our reanalysis of prior work is given as Siβ1(Eu)=[EuSiO(OH)32+]/([Eu3+][SiO(OH)3-)]=106.03±0.16 (25°C and ∼0.7 molal ionic strength). This result indicates that europium silicate complexes in seawater are present at concentrations much lower than europium carbonate complexes.

Chemical Mechanical Polishing and Planarization of Mn-Based Barrier/Ru Liner Films in Cu Interconnects for Advanced Metallization Nodes

Mn-based (referred to simply as Mn in the following) barrier/Ru liner stack has been proposed to replace TaN/Ta barrier-liner in Cu interconnects for 7 nm and 5 nm technology nodes. During chemical mechanical planarization (CMP) of the associated Cu/Ru/Mn/SiCOH pattern structures, the usual galvanic corrosion and removal rate selectivity issues need to be resolved. In this study, we investigated the polishing and electrochemical behavior of Cu, Mn, Ru and SiCOH films on the relevant substrates in the alkaline region using silica dispersions containing potassium permanganate (KMnO4), guanidine carbonate (GC) and benzotriazole (BTA) and identified compositions that address these challenges. An XPS study of the as-deposited and annealed Mn films confirmed the formation of amorphous manganese silicate (MnSixOy), a self-forming dielectric layer, at the Mn/SiCOH interface. A cross-sectional TEM analysis of the polished Cu/Ru/Mn/SiCOH patterned wafers (32 nm half pitch Cu lines) with our candidate slurry showed excellent post-polish performance with no corrosion and no post-CMP loss of either Cu or the Mn barrier/Ru liner film.

Methods for Calculating and Matching Thermodynamic Properties of Silicate and Borate Compounds

New methods for processing the experimental and calculated thermodynamic data have been elaborated and the existing ones have been improved. The developed approaches provide a physically reasonable description of the first-order phase transitions, which makes it possible to compare and correct the values of their thermodynamic properties, as well as to calculate the thermodynamic parameters of unstudied compounds. Regression equations have been proposed for calculating the standard entropy and enthalpy of formation of lithium, sodium, and potassium silicates and borates. The resulting entropy and enthalpy values for 14 alkali metal silicates and 12 alkali metal borates can be used to optimize the technological processes for manufacturing glass, ceramics, and coatings.

Development of silica based coatings on zinc particles for improved oxidation behavior in battery applications

ZnO and Zn(OH)2 layers formed on zinc metal upon contact with aqueous media, like 6M KOH electrolyte used in zinc air batteries, do not provide sufficient protection against further zinc oxidation leading to hydrogen evolution as well as self-discharge of the battery itself. In this work, the syntheses of artificial coatings based on silica, SiO2, were investigated, which should improve zinc metal oxidation stability to reduce aqueous corrosion of battery grade zinc particles. For synthesis of silica coatings the precursor tetraethyl orthosilicate (TEOS) was used. Chemical vapor deposition (CVD) in synthetic air and chemical solution deposition (CSD) under argon in polyol media were used for synthesis of these coatings on zinc under different thermal conditions. Zinc silicate formation was observed upon CVD while silica was formed upon CSD. The capability of the silicate based coatings to enhance oxidation resistance of zinc was analyzed via volumetric measurement of hydrogen evolution upon wet corrosion in 6M KOH. Thermodynamic calculations were used to analyze the composition of the synthesized coatings and their compositional changes in concentrated KOH. As a result, silicate based coatings are able to reduce zinc corrosion by almost 40% by formation of protective layers in 6M KOH. These results were confirmed by hot air corrosion tests.

The genesis of supported cobalt catalysts

The general objectives of this research were to investigate the effect of the support and the gas atmosphere on the decomposition and reduction of cobalt nitrate hexahydrate supported on silica and alumina to gain a greater understanding of the calcination and reduction procedures used in catalyst manufacturing processes. The decomposition was followed by TGA-DSC-MS. The observed breakdown on the unsupported complex is similar but not identical to previous reports with NO detected as an evolved gas. In an oxygen/argon atmosphere the decomposition is generally simplified for the supported samples with a fewer number of weight loss events. When supported on alumina, cobalt nitrate is stabilised with decomposition events shifting to higher temperatures, whereas when supported on silica, cobalt nitrate is destabilised with only one significant decomposition event, which occurs at a lower temperature than that of the unsupported complex. In a hydrogen/nitrogen atmosphere partial decomposition of cobalt nitrate occurs before reduction is initiated with both supported samples. When supported on alumina, cobalt nitrate reduction is catalysed with the two events that occur below 350 °C happening at lower temperatures, while reduction above 350 °C is moved to higher temperatures. The silica-supported complex in contrast exhibits reduction events that are all reduced in temperature relative to the unsupported salt. However, there is evidence of the formation of cobalt silicate with a high temperature reduction. The study has shown that the calcination and direct reduction of supported cobalt nitrate is significantly affected by the support and that different conditions are required to achieve the same state.

Diversity of the initial rocky planetary building materials at the edge of the solar system

AbstractAsteroids and comets are surviving members of the vast planetesimal population that was distributed across the early solar system. They appear to be a diverse set of bodies but we present evidence from comet samples that the body‐to‐body diversity of the initial rocky component mix in planetesimals may have declined with distance from the Sun. Laboratory measurements of the minor element Mn in olivine collected from Comet Wild 2 suggests that the micron‐sized rocky crystalline contents of this comet formed in numerous inner solar system environments. The results are consistent with a scenario where silicates such as olivine form at incandescent temperatures in multiple environments and then mix as they are transported to distant cold regions where silicates could accrete with ice and organics to form comets. Accreting far from silicate formation regions, many ice‐rich planetesimals are likely to have started with similar complex mixtures of diverse rocky components formed in various high‐temperature environments. This contrasts with asteroidal meteorite parent bodies whose silicates retain regional properties that give different chondrite classes their distinctive properties.

Modes of Deposit-Induced Accelerated Attack of MCrAlY Systems at 1100 °C

The reaction of cast NiCoCrAlY alloys with oxide–sulfate deposits in CO2–H2O–O2 was studied at 1100 °C. The minimum Al concentration needed to form an external Al2O3 scale was increased compared with deposit-free exposures, as Al2O3-forming compositions transitioned to internal Al2O3 and external Cr2O3 growth in the presence of certain deposits. Model deposits were used to investigate the role of each constituent in the complex reaction morphology observed with an industrial fly-ash. Two main modes of degradation were identified, which involved Al2O3 dissolution in molten Na silicate and solid-state Al2O3 reaction with CaO. Both led to enhanced Al consumption and promoted non-selective oxidation. Additions of Al2O3 or SiO2 decreased the CaO reactivity due to the formation of aluminates or silicates, while Na2SO4, on the contrary, enhanced the degradation by providing rapid mass transport in the molten state, and reduced alloy/scale adherence. A systematic study of the role of phase fractions and phase compositions in the γ-(Ni,Co) + β-(Ni,Co)Al metal system is reported, with the aim of providing guidance in coating design. In particular, high γ fractions and Cr concentrations, which offer optimal hot corrosion resistance, were most susceptible to degradation by oxide–sulfate deposits.

Insights into the promotional roles of palladium in structure and performance of cobalt-based zeolite capsule catalyst for direct synthesis of C5–C11 iso-paraffins from syngas

Pd-promoted zeolite capsule catalyst (Co/Pd/SiO2-HZSM5) was developed by coating H-ZSM-5 zeolite shell over Pd-modified core catalyst (Co/Pd/SiO2), and employed for direct synthesis of C5–C11 iso-paraffins from syngas via Fischer-Tropsch synthesis (FTS). The roles of Pd promotion in structure and performance of the capsule catalyst for C5–C11 iso-paraffins synthesis were deeply studied. Structure characterizations (XRD, FTIR, TPR, and XPS) indicated that the main cobalt species in Pd-promoted capsule catalyst was cobalt silicate, while Co3O4 was the predominant cobalt species in un-promoted capsule catalyst (Co/SiO2-HZSM5). Evolution of cobalt species in the synthesis of Pd-promoted capsule catalyst revealed that Pd improved the formation of cobalt silicate in strong basic TPAOH solution during the hydrothermal synthesis of H-ZSM-5 zeolite shell. It was found that Pd not only promoted the reduction in cobalt oxides, but also improved the reduction in cobalt silicate, which could not be reduced under traditional reduction condition for cobalt-based FTS catalysts. Catalytic tests indicated that Pd-promoted capsule catalyst exhibited highly enhanced performance for C5–C11 iso-paraffins synthesis with molar ratio of iso-paraffins to n-paraffins up to 1.03. Long-chain hydrocarbons were completely eliminated in the capsule catalyst as a consequence of spatial confinement effect of the H-ZSM-5 zeolite shell. The hydrogenation of olefins to paraffins, which was enhanced by Pd promotion, together with the hydrocracking and isomerization of primary hydrocarbons, contributed to the high selectivity of C5–C11 iso-paraffins in Pd-promoted capsule catalyst.

Influence of the substrate on the structure stability LaLuO3 thin films deposited by PLD method

LaLuO3 amorphous thin films were elaborated by pulsed laser deposition technique on different support: Si (100), Si(100) with buffer layer CeO2, MgO(111) and Al2O3 (1101). For obtained the crystallizes phase the thin films were annealed in temperature 1100 °C in air during 2 h. TEM analysis clearly showed the reaction between Si support and LaLuO3 thin films and their polycrystalline structure. The spectroscopy investigations indicate the reaction between Si support and LaLuO3 thin films and formation of silicates. The CeO2 thin buffer layers on Si support limited the reaction between support and thin films. No reactions were observed between the surface Al2O3 and MgO and thin films.

Structure stabilization by zirconia pinning effect of Y 2 Si 2 O 7 environmental barrier coatings synthesized by solution precursor plasma spraying process

Abstract Y2Si2O7-xZrO2 coatings have been synthesized by solution precursor plasma spraying (SPPS) process. Their nanostructure is temperature-sensitive and is prone to sintering. This study explores the effect of zirconia introduction as a non-miscible secondary phase in the coating in order to take advantage of the Zener pinning effect and ensure a stabilization of the structure at high temperature. Short-time heat treatments and XRD analysis allowed to observe the yttrium silicate formation in the presence of zirconia. Then, after a 7-hour heat treatment at 1500 °C, the grain size distribution has been measured by image analysis on coating cross sections. The zirconia addition induced a stabilization effect of the grain boundary structure. Y2Si2O7 coatings are composed of grains with equivalent disc diameters (EDD) from 50 to 1500 nm. Y2Si2O7-0.25ZrO2 coatings have a bi-modal distribution with zirconia grains located at grain boundaries with mean EDD of 200 nm, and yttrium silicate grains with EDD between 500 and 1500 nm. Grains (with EDD > 500 nm) of Y2Si2O7-0.25ZrO2 coatings have a 10% higher circularity than those of Y2Si2O7 coatings resulting from Zener pinning effect.

Dynamic atmospheres and winds of cool luminous giants

High spatial resolution techniques have given valuable insights into the mass loss mechanism of AGB stars, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust. Observations indicate that Al$_2$O$_3$ condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al$_2$O$_3$ grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. We have constructed a new generation of Dynamic Atmosphere & Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth & evaporation for both Al$_2$O$_3$ and Fe-free silicates (Mg$_2$SiO$_4$). The equations describing these dust species are solved in the framework of a frequency-dependent radiation-hydrodynamical model for the atmosphere & wind structure, taking pulsation-induced shock waves and periodic luminosity variations into account. Condensation of Al$_2$O$_3$ at the close distances and in the high concentrations implied by observations requires high transparency of the grains in the visual and near-IR region to avoid destruction by radiative heating. For solar abundances, radiation pressure due to Al$_2$O$_3$ is too low to drive a wind. Nevertheless, this dust species may have indirect effects on mass loss. The formation of composite grains with an Al$_2$O$_3$ core and a silicate mantle can give grain growth a head start, increasing both mass loss rates and wind velocities. Furthermore, our experimental core-mantle grain models lead to variations of visual and near-IR colors during a pulsation cycle which are in excellent agreement with observations.

Electrical properties of silica-doped 3\xa0mol% yttria-stabilized tetragonal zirconia

Inconsistent opinions in the literature on the impact of silica on the conductivity of Y2O3–ZrO2 system become a motivating reason to reinvestigate this matter. Too low a value of the grain boundaries’ conductivity in the case of 3YSZ (3 mol% yttria-stabilized zirconia) is a fundamental barrier to using this material in the solid oxide fuel cell technology. The presence of silica is considered as the main cause of blocking effect on grain boundaries. The main purpose of this study involved the synthesis of nanomaterials, 3YSZ, with the addition of restricted amounts of silica. Two series of samples were prepared and sintered at the temperatures of 1073 and 1473 K. Then the obtained materials were tested for their phase composition, microstructure and electrical properties (based on analysis of the impedance spectra). The SEM microphotograph analysis indicated the decrease in the grain sizes of zirconia with the addition of SiO2. Moreover, X-ray diffraction measurements showed the beginning of formation of zirconium silicate at 1473 K. The detailed investigation of microstructures and electrical properties shows that the two factors reported in the literature have an influence on grain boundary conductivity—grains sizes and the amount of introduced silica. Presented studies shows that up to temperature in which silica reacts with zirconia to form zircon (ZrSiO4), its presence actually improves the grain boundaries conductivity due to decrease in particle size of YSZ (pinning effect). The blocking effect of silica at the grain boundaries begins to play a greater role causing the formation of glassy layers at a higher temperature.

Influence of sodium-based materials on the slagging characteristics of Zhundong coal

Zhundong coal from the Zhundong coalfield in in Xinjiang, China, is charactered by high content of Na. Na-related slagging of Zhundong coal is unclear. The aim of this study is to determine the influence of Na-based materials on the slagging characteristics of the coal. The raw coal was prepared by first removing Na by chemical extraction and subsequently impregnating it with the Na-based materials, such as NaCl, Na2SO4 and NaAc. Laboratory slagging experiments in a muffle furnace were conducted using the mixtures of prepared Zhundong coal and quartz sand. It was found that the Na-based materials affected the slagging behavior of the coal in the order NaAc/Na2SO4 > NaCl. For the mixtures with the NaCl additive, fusion was most noticeable at 900 °C. However, for the mixtures soaked with Na2SO4 and NaAc, a monotonically increasing relationship was indicated between the degree of slagging and the temperature. Adding the Na-based materials to the coal resulted in increased Na content in the residual ash, especially in the instances with Na2SO4 and NaAc additives. The formation of silicates, which were ascribed to the reactions between the Na-based materials and the SiO2, was the primary cause of slagging. Various mineral elements, especially Fe, were captured by Na2O, derived from the decomposition of Na2SO4 or the combustion of NaAc, to exist in the form of a low-melting temperature eutectic. Additionally, the presence of Fe, Ca, K, and Mg in the ash aggravated slagging under the influence of Na2O.

Aqueous chemical solution deposition of ultra high-k LuFeO3 thin films

Thin orthorhombic ultra high-k LuFeO3 (LFO) films on Si3N4/SiO2/Si substrates were obtained by means of aqueous chemical solution deposition (CSD). Prior to thin film deposition, the precursor synthesis, thermal decomposition and crystallization behavior of the bulk material were studied. It was shown that phase-pure hexagonal LFO powder could be formed at 650°C while a higher temperature of 900°C was required to obtain the orthorhombic phase. Deposition on SiO2/Si resulted in the development of silicates in this temperature range, thus preventing the formation of the orthorhombic LuFeO3 phase. The use of Si3N4/SiO2/Si as the substrate shifted the silicate formation to higher temperature, allowing the synthesis of phase-pure orthorhombic LuFeO3 as a thin film at 1000°C. Impedance spectroscopy analyses confirmed its associated ultra high dielectric constant (>10,000) at room temperature for frequencies lower than or equal to 1kHz.