Effect of zirconia addition on crystallinity,hardness, and microstructure of gel-derived barium aluminosilicate,BaAl2Si2O8

The effect of zirconia (ZrO₂) additions, in amounts equivalent to 5, 10, 20 and 40 mol%, to barium aluminosilicate, BaAl₂Si₂O₈, was studied by examination of the phase assemblage of the mixtures after crystallization heat treatments at ∼ 1050°C or more using X-ray diffraction (XRD). In all cases, BaAl₂Si₂O₈ gel crystallized into the hexacelsian polymorph. XRD results also indicated solid solubility of 10mol% or more ZrO₂ in hexacelsian material. Precipitation of an additional phase, tetragonal ZrO₂, occurred in the BaAl₂Si₂O₈ material containing 20 mol% ZrO₂. Also, 95% and 99% dense celsian ceramics were fabricated at 1450 and 1580°C sintering temperatures, respectively, using cold isostatically pressed pellets produced from powder mixtures containing 20 and 40 mol% ZrO₂. These pellets also contained 20 wt% gel-derived lithia-doped celsian “seed” powder to promote hexacelsian to celsian transformation during sintering. Indentation hardness values for the 99% dense celsian ceramic without and with 20 mol% ZrO₂ were 8.04 and 10.80 GPa, respectively. Scanning electron microscopy was used to examine the microstructures of these samples.     

Oxides reactions with a High-chrome sesquioxide refractory

In slagging coal-gasifier systems, the combination of oxides present as impurities in coal and combustion temperatures that can exceed 1650°C restrict the use of liner materials in the coal combustion chambers to refractories. In this study, the slag-refractory interactions of a new high chrome sesquioxide refractory was characterized. High-temperature cup tests showed that the molten oxides infused into the refractory and that the sesquioxide refractory reacts with the oxides in a manner similar to spinel phase refractories. Studies of the coal slag's individual oxide components showed CaO reacts with the chrome refractory to form a low melting Ca(CrO₂)₂. FeO reacts with the sesquioxide to form a interface layer of (Cr,Fe)₃O₄ spinel phase. Results of this study now make it possible to design studies for improving corrosion resistance to increase refractory life.     

Effect of interfacial interaction on morphology and mechanical properties of PP/POE/BaSO4 ternary composites

Ternary composites of Polypropylene (PP)/ethylene-octene copolymer (POE)/Barium Sulfate (BaSO₄)(PP/POE/BaSO₄) were prepared through a two-step process: BaSO₄ master-batches were first prepared through blending of BaSO₄ and POE, then blending with PP. Two families of phase structure were confirmed through SEM and DSC, depending on their interfacial interaction. Separation of POE and BaSO₄ filler was found when untreated or titanate coupling agent treated BaSO₄ filler were used. Encapsulation of BaSO₄ particles by POE elastomer was achieved by using BaSO₄ master-batch prepared through reactive blending of BaSO₄ with POE in the presence of maleic anhydride (MAH) and dicumyl peroxide (DCP). The mechanical properties of the composites greatly rely on the morphology. The yield strength and the impact toughness of a composite with core-shell morphology are higher than those of composites with separated morphologies, but the former has lower flexural modulus and elongation at break than the latter. The interfacial interaction was evaluated by semi-empirical equations developed previously. The deformation and toughening mechanisms of the composites were also investigated.     

Effect of Sc,Zr, and Ti on the interfacial reactions of the B<Subscript>4</Subscript>C/Al system

B₄C plates were immersed in liquid aluminum alloyed with Sc, Zr, and Ti to investigate the interfacial reactions between B₄C and liquid aluminum at 730 °C. The influences of alloying elements on the interfacial microstructure and reaction products in terms of individual and combined additions were examined using a scanning electron microscopy (SEM) and a transmission electron microscopy (TEM). Results reveal that all three elements react with B₄C and form interfacial layers that act as a diffusion barrier to limit the decomposition of B₄C in liquid aluminum. The interfacial reactions and the reaction products in each system are outlined. Moreover, by the combined addition of Sc, Zr, and Ti, most of the Ti is enriched at the interface, which not only offers appropriate protection of the B₄C but also reduces the consumption of Sc and Zr at the interface.     

Enable high reversibility of Fe/Cu based fluoride conversion batteries via interfacial gas release and detergency of garnet electrolytes

Garnet-type Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) electrolyte suffers from unstable chemical passivation under air exposure, responsible for the poor interfacial wettability and conductivity with Li metal. Instead of conventional methods to remove surface contaminants by mechanical polishing, acid etching and high temperature reduction, herein we propose a simple strategy of interfacial gas release and detergency to smartly convert Li₂CO₃ passivation layer into ion-conductive Li₃PO₄ domains at mild temperature (∼200 ℃). The in-situ formation of PH₃ vapor and its phosphorization enables a dramatic decrease of Li/garnet interfacial resistance down to 2 Ω cm² at room temperature (RT). The improved interfacial wettability and conductivity endow the symmetric cells with ultra-stable galvanostatic cycling over 1500 h and high critical current density of 2.6 mA/cm². The high coulombic efficiency of Li plating enables a high reversibility of solid-state NCM811/Li cells even under a low N/P ratio (∼4) and high cut-off voltage of 4.5 V at RT. The prototype of fluoride-garnet solid-state batteries are successfully driven as rechargeable system (rather than widely known primary battery) with high conversion capacity (400 ∼ 500 mAh/g) and high-rate performance (251.2 mAh/g at 3 C). This interface infiltration-detergency approach provides a practical solution to the achievement of high-energy solid-state Li metal batteries.     

Interfacial microstructures and properties of aluminum alloys/galvanized low-carbon steel under high-pressure torsion

A new composite processing technology characterized by hot-dip Zn–Al alloy process was developed to achieve a sound metallurgical bonding between Al–7 wt% Si alloy (or pure Al) castings and low-carbon steel inserts, and the variations of microstructure and property of the bonding zone were investigated under high-pressure torsion (HPT). During hot-dipping in a Zn–2.2 wt% Al alloy bath, a thick Al₅Fe₂Zn_x phase layer was formed on the steel surface and retarded the formation of Fe–Zn compound layers, resulting in the formation of a dispersed Al₃FeZn_x phase in zinc coating. During the composite casting process, complex interface reactions were observed for the Al–Fe–Si–Zn (or Al–Fe–Zn) phases formation in the interfacial bonding zone of Al–Si alloy (or Al)/galvanized steel reaction couple. In addition, the results show that the HPT process generates a number of cracks in the Al–Fe phase layers (consisting of Al₅Fe₂ and Al₃Fe phases) of the Al/aluminized steel interface. Unexpectedly, the Al/galvanized steel interface zone shows a good plastic property. Beside the Al/galvanized steel interface zone, the microhardnesses of both the interface zone and substrates increased after the HPT process.     

An analysis of the electrical conductivity in BaSO4-added Ag2SO4 solid electrolyte system

The compositions (1 −x)Ag₂SO₄−(x)BaSO₄, wherex=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba²⁺ in Ag₂SO₄ was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained using a detailed impedance analysis. The partial substitution of Ba²⁺ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model based on lattice distortion (expansion) due to partial substitution of Ag⁺ by the bigger Ba²⁺ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO₄-dispersed Ag₂SO₄ conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO₄ dispersed Ag₂SO₄ is due to percolation threshold.     

Molten salt synthesis of barium molybdate and tungstate microcrystals

Pure microcrystalline barium molybdate BaMoO₄ and barium tungstate BaWO₄ materials were prepared by molten flux reaction using alkali metal nitrates as reaction media. The obtained crystals have rhombic shape and expose mostly (111) crystallographic planes. Their mean size depends on the flux temperature and the nature of the alkali metal cation. Monomeric molybdate and tungstate used as precursors yield target products already at 673 K whereas if polymerized ammonium oxosalts were used, then higher temperatures were necessary to obtain barium salts. The optimal temperature for the preparation of pure crystals with well defined shape was found to be near 773 K. UV–visible spectra have been measured to precise energy gaps in these important d⁰ transition metal compounds. The values of Eg for these two mixed oxides are 4.3 eV for BaMoO₄ and 3.8 eV for BaWO₄. Such values contradict to what can be expected from the known data on their structure and the relative electronegativity of W and Mo ions. The possible explanations of this observation are commented.     

Fabrication of fiber-reinforced celsian matrix composites

A method has been developed for the fabrication of small diameter, multifilament tow, fiber-reinforced ceramic matrix composites. Its application has been successfully demonstrated for the Hi-Nicalon/celsian system. Strong and tough celsian matrix composites, reinforced with BN/SiC-coated Hi-Nicalon fibers, have been fabricated by infiltrating the fiber tows with the matrix slurry, winding the tows on a drum, cutting and stacking of the prepreg tapes in the desired orientation, and hot pressing. The monoclinic celsian phase in the matrix was produced in situ, during hot pressing, from the 0.75BaO–0.25SrO–Al₂O₃–2SiO₂ mixed precursor synthesized by solid state reaction from metal oxides. Hot pressing resulted in almost fully dense fiber-reinforced composites. The unidirectional composites having ∼42 vol.% of fibers exhibited graceful failure with extensive fiber pullout in three-point bend tests at room temperature. Values of yield stress and strain were 435±35 MPa and 0.27±0.01%, respectively, and ultimate strengths of 900±60 MPa were observed. Young's modulus of the composites was measured to be 165±5 GPa.     

Characterization of BaO-Al2O3-SiO2 (BAS) gels during heat treatment

Gels in the system BaO-Al₂O₃-SiO₂ have been prepared from metal alkoxides and barium acetate. The processes during calcination and crystallization as a function of composition have been followed by means of DTA, TGA, IR and XRD. Three major regions of accelerated weight loss have been observed which correspond to the evaporation of physically adsorbed species, the oxidation of-Al(OOCCH₃) and the oxidation of Ba(OOCCH₃)₂. The latter reactions are accompanied by strong exothermic DTA signals. The oxidation products of barium acetate tend to foam and to block the paths and channels for the oxygen supply and the removal of the volatile oxidation products, inhibiting a complete oxidation. Thus, the combustion of Ba(OOCCH₃)₂ is strongly dependent on the concentration, the sample volume and the heating conditions. IR shows that the gels heated up to 800 °C are structurally similar to glasses of the same composition. In all gels the metastable crystallization of hexacelsian is strongly preferred to the stable monoclinic celsian. DTA crystallization peaks appear between 960 and 1080 °C, depending on composition. In most samples hexacelsian is the only phase present, even after 5 h isothermal heat treatment.     

Interfacial reactions in Sn–20In–2.8Ag/Cu couples

Interfacial reactions between Sn–20 wt.%In–2.8 wt.%Ag (Sn–20In–2.8Ag) Pb-free solder and Cu substrate at 250, 150, and 100 °C were investigated. A scallop-type η-Cu₆Sn₅ phase layer and a planar ε-Cu₃Sn phase layer formed at the interface at 250 °C. The indium content in the molten solder near the interface was increased with the formation of the η-Cu₆Sn₅ phase; and the η-Cu₆Sn₅, Ag₂In, Cu₂In₃Sn, and γ-InSn₄ phases formed from the solidification of the remaining solder. At 100 and 150 °C, only the η-Cu₆Sn₅ phase was found at the interface. However, unusual liquid/solid reaction-like interfacial morphologies, such as irregular elongated intermetallic layers and isolated intermetallic grains, were observed in the solid-state reactions. These η phase layers had less Sn content than the Sn–20In–2.8Ag alloy, resulting in an excess Sn-rich γ-InSn₄ phase accumulating at the interface and forming porous η layers on top of the initially formed dense η layers at 150 °C. At 100 °C, large elongated η grains were formed, whereas the interfacial layers remained almost unchanged after prolonged reaction. Based on the experimental evidence, the growth of the η phase was proposed to follow a diffusion-controlled mechanism at 250, 150 and 100 °C, while that of the ε phase was probably controlled by the reaction.     

Interfacial reactions in the liquid diffusion couples of Mg/Ni,Al/Ni and Al/(Ni)-Al2O3 systems

The interfacial reactions between various molten metals and solid plates were investigated in this diffusion couple study. The molten metals were pure magnesium, pure aluminium, aluminium-rich Al-Mg alloy, and aluminium-rich Al-Cu alloys, and the solid plates were pure nickel plate, alumina plate, and nickel-plated alumina plate. The interfacial reactions in the diffusion couples were determined by using optical microscopy, scanning electron microscopy and electron probe microanalysis in regard to the formation of intermetallic phases, the dissolution rates of the nickel plates, and the morphology of the interfaces. Mg₂Ni phase was found in the pure Mg/Ni plate diffusion couples, and the Al₃Ni and Al₃Ni₂ phases were observed in the pure Al/Ni plate and Al-alloys/Ni plate diffusion couples. In the Al-Cu alloy/Ni-plated alumina plate diffusion couple, Al₂O₃ formed at the interface, while spinel particles were found in the diffusion couples of Al-7.4wt% Mg alloy/Ni-plated alumina plate. Experimental difficulty was encountered in preparing the diffusion couples with alumina plate, and a gap existing at the interface prohibited reactions between the molten metal with alumina plate.     

Effect of Bi content on spalling behavior of Sn–Bi–Zn–Ag/Cu interface

The effect of the Bi content on the formation of intermetallic compounds (IMCs) layers between the Sn-xBi-0.9Zn-0.3Ag lead-free solder (with x = 1, 2, 3 and 4, in weight percent, hereafter) and Cu substrate was investigated. The structure of the IMC layer in the soldered interface varies apparently with increasing the Bi content. When the Bi content is 1 wt%, the interface soldered is consisted of CuZn and Cu₆Sn₅ IMC layers, which are separated by an intermediate solder layer. As the Bi content increases, the spalling phenomenon tends to disappear. Moreover, the layer between the Sn-2Bi-0.9Zn-0.3Ag solder and Cu substrate is thicker than others. The evolution of the soldered interfacial structure could be attributed to the existence of Bi.     

New Approach for the Application of Functional Ceramic Material in Carbon Bonded Doloma Refractories to Reduce Emissions

Doloma carbon bricks with graphite contents of approximately 2 wt% are widely used in the production of stainless steels in argon oxygen decarburisation (AOD) or in vacuum oxygen decarburisation (VOD) vessels as lining material. The application of doloma refractories is connected with metallurgical benefits such as high oxidic stability of its oxides, and the ability to bond sulphur from the hot metal. The production and application of carbon bonded refractories is linked with environmental harmful emissions in the broadest sense. Amongst the aspect of environmental friendly refractory systems this work has observed and shown the interaction of functional ceramic material TiO₂ with the organic binder system. In the centre of this work is the aspect of increased residual carbon content of the binder resin due to TiO₂ addition. The increased residual carbon content of the binder resin connected with improved mechanical, physical and thermomechanical properties due to sub‐micro scaled TiO₂ addition offers the feasibility to reduce the total carbon content without downgrading the brick properties. This aspect has not been observed yet and is of high interest with respect to reduced emissions and environmental friendly refractories. Previous works have investigated the influence of TiO₂ on other carbon bonded refractory systems such as alumina carbon and magnesia carbon. As illustrated in this work and previous work, TiO₂ is working completely different in the Doloma Carbon system from other systems.     

A TEM study of the interfaces and matrices of SiC-coated carbon fibre/aluminium composites made by the K2ZrF6 process

Carbon fibre-reinforced aluminium composites were pressurelessly cast by using K₂ZrF₆ as the wetting promotion agent. Transmission electron microscopy (TEM) and energy dispersed analysis of X-rays, (EDAX) were used. The results showed that interfacial reactions were very active after K₂ZrF₆ treatment. This was caused by the diffusion and reaction of zirconium in the surface of carbon fibres or in the SiC coating. Silicon alloying of aluminium could suppress the interfacial reactions by decreasing the activity of zirconium and changing intermetallic Al₃Zr to Zr₃Al₄Si₅, and building up the phase equilibrium between SiC, aluminium and silicon. The requested silicon content was higher than the equilibrium content of Al-Si-SiC system to suppress the SiC/Al interfacial reaction. A perfect interface was achieved in SiC-coated carbon fibre Al-12 wt% Si composite.     

Solid-State Electrolyte Design for Lithium Dendrite Suppression

All-solid-state Li metal batteries have attracted extensive attention due to their high safety and high energy density. However, Li dendrite growth in solid-state electrolytes (SSEs) still hinders their application. Current efforts mainly aim to reduce the interfacial resistance, neglecting the intrinsic dendrite-suppression capability of SSEs. Herein, the mechanism for the formation of Li dendrites is investigated, and Li-dendrite-free SSE criteria are reported. To achieve a high dendrite-suppression capability, SSEs should be thermodynamically stable with a high interface energy against Li, and they should have a low electronic conductivity and a high ionic conductivity. A cold-pressed Li₃N–LiF composite is used to validate the Li-dendrite-free design criteria, where the highly ionic conductive Li₃N reduces the Li plating/stripping overpotential, and LiF with high interface energy suppresses dendrites by enhancing the nucleation energy and suppressing the Li penetration into the SSEs. The Li₃N–LiF layer coating on Li₃PS₄ SSE achieves a record-high critical current of >6 mA cm⁻² even at a high capacity of 6.0 mAh cm⁻². The Coulombic efficiency also reaches a record 99% in 150 cycles. The Li₃N–LiF/Li₃PS₄ SSE enables LiCoO₂ cathodes to achieve 101.6 mAh g⁻¹ for 50 cycles. The design principle opens a new opportunity to develop high-energy all-solid-state Li metal batteries.     

Effect of holding time on microstructure and mechanical properties of Si3N4/Si3N4 joints brazed with Au58.7Ni36.5V4.8 filler alloy

Si₃N₄ ceramics were brazed using Au–Ni–V metal foils at 1423 K for different holding times. Effect of holding time on microstructure and mechanical properties of the joints was investigated. The results indicate that a reaction layer of VN exists at the interface between Si₃N₄ ceramic and filler alloy. With increasing holding time from 0 to 90 min, thickness of the VN reaction layer increases from 0.4 to 2.8 μm, obeying a linear relation. Mechanism of the interfacial reaction was discussed by calculating the formation of free energy of VN. No specific orientation relationship exists between VN reaction layer and Si₃N₄ ceramic. In addition, Ni₃Si intermetallic compound appears in the joint when the holding time increases to 90 min, resulting in the deterioration of the joint strength.     

Molten salt synthesis of Cr3C2-coated flake graphite and its effect on the physical properties of low-carbon MgO–C refractories

To improve the performance of low-carbon MgO–C refractories, the Cr₃C₂-coated flake graphite was synthesized by molten salt method, then the Cr₃C₂-coated flake graphite was added to low-carbon MgO–C refractories. In this work, the effects of reaction temperature, Cr/C mole ratio, and holding time on the synthesis of Cr₃C₂-coated flake graphite were studied. Furthermore, the effect of Cr₃C₂-coated flake graphite on the physical properties of low-carbon MgO–C refractories was evaluated. The results indicated that when the reaction temperature was 950 °C, Cr/C molar ratio was 1/2 and holding time was 3 h, the synthesized Cr₃C₂-coated flake graphite had fewer surface micropores and the crystallinity of Cr₃C₂ grains was high. In addition, the Cr₃C₂-coated flake graphite exhibited excellent oxidation resistance. MgO–C refractories containing 2 wt% Cr₃C₂-coated flake graphite exhibited more excellent physical properties. The results of nano CT detection system showed that the addition of Cr₃C₂-coated flake graphite promoted the densification of MgO–C refractories.     

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al₄C₃ and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl₂O₄ in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution.     

Improving interfacial properties of a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications

Dissimilar welds of aluminium alloy AA6056 and titanium alloy Ti6Al4V were produced by a novel technique. AA6056 sheet was machined at one end to a U-slot shape, enabling the intake of the Ti6Al4V sheet. The Al-alloy U-slot was then butt welded by split laser beam without using a filling wire, thus making a weld by melting only the Al-alloy. Thereby the intermetallic brittle phase TiAl₃ formed at the weld interface and affected mechanical properties. As a continuation of the previous work, the joint design was modified by chamfering Ti6Al4V to reduce the formation of interfacial TiAl₃. It is shown in this work how this seemingly insignificant joint modification has refined microstructure and increased hardness and strength. The most impressive feature was the improved resistance to fatigue crack propagation whereby the fracture type in the fusion zone of AA6056 adjacent to the weld interface changed from partially intercrystalline to completely transcrystalline. Possible metallurgical processes leading to the property improvements are discussed.