Development and evolution of a novel (Zr1-xSnx)O2 toughened alumina-mullite slip cast refractory: Effect of SnO2

Zr_1-xSn_xO₂ reinforced alumina-mullite refractory was manufactured by slip cast methods using SnO₂ as a sintering agent. SnO₂ had considerable influence in the enhanced reaction kinetics of zircon dissociation and subsequent reaction sintering of alumina and zircon. Presence of pro-eutectic transient Al₂O₃-SnO₂ liquid and SnO₂-SiO₂-ZrO₂ amorphous phases, enhanced densification and mullitisation through liquid phase sintering and, mitigated SnO₂ volatilisation by (Zr_1-xSn_x)O₂ solid-solution formation. Based on their morphology and aspect ratios, three types of mullite crystals, MI, MII and MIII, were evolved across the matrix microstructure. Characterization of the evolved microstructure revealed coalescence and grain growth of matrix alumina grains including the presence of an acicular tertiary MIII mullite which acts as both a reinforcement and bridging network of matrix to aggregate grains. SnO₂ had the effect of lowering the monoclinic – tetragonal phase transformation temperature. Hot flexural strength values remained nearly unchanged (±2%) compared with the AZS composition without SnO₂ doping.     

Synthesis of an innovative zirconia-mullite raw material sintered from andalusite and zircon precursors and an evaluation of its corrosion and thermal shock performance

This paper deals with the synthesis and the properties of an innovative zirconia-mullite raw material sintered from an andalusite/alumina/zircon mix. The microstructure of these composite grains consists of fine zirconia particles in a mullite matrix. This study highlights that the synthesis process (sintering from SiO₂.Al₂O₃, Al₂O₃ and ZrSiO₄ raw materials) plays an essential role in the improvement of both the corrosion resistance to alumina-lime slag and soda-lime glass and the thermal shock resistance of this refractory. The microstructural observations correlated with non-destructive characterizations, ultrasonic pulse echography and acoustic emission techniques, underline the repairing mechanism exhibited by this material after experiencing repeated thermal shock.     

Effect of ZrO2 additions on sintering of SnO2-based ceramics

The effect of zirconia additions on sintering of CoO doped tin dioxide has been investigated in the temperature range 1100–1250 °C. A first study showed that the substitution of tin by zirconium reduces significantly the volatilisation rate of SnO₂ for temperatures greater than 1400 °C. It appeared that the zirconium content increase inhibits the densification kinetics of SnO₂-based ceramics. Indeed, the relative density did not exceed 93% for a Zr content lower than 6 mol% in the Sn_(1–x)Zr_xO₂ solid solution. This negative effect can be imputed to the elastic distortions caused by the introduction of Zr in the tin dioxide lattice. So, the diffusion rate of point defects such as oxygen or cobalt ions is lowered.     

Experimental study of the SnO2–ZrO2 phase diagram

The study of the SnO₂–ZrO₂ phase diagram in the 1230–1750 °C temperature range has shown the existence of an immiscibility gap, leading to two (Zr_1−xSn_x)O₂ and (Sn_1−yZr_y)O₂ limited solid solutions. Four compositions were synthesised for each solid solution, leading to pure phases, which were characterised by room-temperature and high-temperature X-ray diffraction. The unit-cell parameters of tetragonal (Sn_1−yZr_y)O₂, monoclinic (Zr_1−xSn_x)O₂ and tetragonal (Zr_1−xSn_x)O₂ were determined and correlated with the content of the substituted atom. The monoclinic to tetragonal and reverse reactions for the (Zr_1−xSn_x)O₂ series were also characterised (transition temperatures) when varying the tin mole fraction.     

Correlation between the structure and modified microwave dielectric characteristics of Zr4+ substituted Ni0.4Zn0.6Ti(1-x)ZrxNb2O8 ceramics

Microwave ceramics are an important classes of materials that are used in microwave communication systems, especially in the area of 5G wireless communication and the internet of things. In this work, to improve the Q×f values and enhance the temperature stability of Ni_0.4Zn_0.6TiNb₂O₈ ceramics, the influence of the substitution of Zr⁴⁺ ions at the Ti site in Ni_0.4Zn_0.6Ti_(1-x)Zr_xNb₂O₈ ceramics was investigated. The Q×f value increases from 32114 GHz to 45733 GHz and the τ_f value changes from 38.1 ppm/°C to 3 ppm/°C with a slight Zr⁴⁺ ion substitution (x = 0.1). Meanwhile, the sample with the Zr⁴⁺ ion substitution (x = 0.3) that was sintered at 1120 °C shows a very high Q×f value of 92078 GHz. Furthermore, the XRD results reveal that the phase and structure of the Ni_0.4Zn_0.6Ti_(1-x)Zr_xNb₂O₈ ceramics change with the different Zr⁴⁺ ion contents. The substitution of the Zr⁴⁺ ion can promote the sintering process for the Ni_0.4Zn_0.6Ti_(1-x)Zr_xNb₂O₈ ceramics and restrain the Ni_0.5Ti_0.5NbO₄ phase formation. The results obtained from Ni_0.4Zn_0.6Ti_(1-x)Zr_xNb₂O₈ ceramics can offer useful information for the study and application of high-frequency microwaves.     

Enhancement of reaction-sintering of alumina-excess magnesium aluminate spinel in presence of titania

Alumina-excess magnesium aluminate spinel finds use in different high temperature applications including steel ladles. Alumina-excess spinel was prepared by solid oxide reaction using magnesia (MgO=10?wt%) and calcined alumina (Al₂O₃ = 90?wt%), in the sintering temperature range of 1500–1700?°C. The role of titania on the densification, spinelisation, evolution of microstructure and phase assemblage was investigated in this MgO-Al₂O₃ system. Titania addition increased the rate of densification 20x compared to undoped composition at 1500?°C under dynamic heating condition. However, under static firing, the beneficial effect of titania on densification could only be discerned at lower temperatures. The microstructure of titania doped sintered alumina-excess spinel compacts contain magnesium aluminium titanate phase in the grain boundary of corundum and spinel grains. The beneficial effect of titania on densification is attributed to magnesium aluminium titanate phase (Mg_xAl_2(1-x)Ti_(1+x)O₅) development and also by incorporation of Ti⁴⁺ into the spinel structure.     

Phase composition,microstructure and thermophysical properties of the Srx(Zr0.9Y0.05Yb0.05)O1.95+x ceramics

Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8, 0.7) ceramics were prepared by solid state reaction sintering. The sintered Sr_1.0(Zr_0.9Y_0.05Yb_0.05)O_2.95 is a single-phase solid solution while the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9?0.7) are composites, and a significant grain growth inhibition is observed in the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9). Rare-earth elements distribution in the bulk materials indicates that Yb and Y preferentially substitute Zr-sites in SrZrO₃, and the highest solubility of RE₂O₃ in pure SrZrO₃ is ～0.8 mol%. The sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x have high thermal expansion coefficients up to ～11.0×10^?6 K^-1 (1200°C). Sr_0.8(Zr_0.9Y_0.05Yb_0.05)O_2.75 has the lowest thermal conductivity of 1.38 W·m^-1·K^-1 at 800°C. Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) show no phase transition from 600 to 1400°C, whereas Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9, 0.8) have excellent high-temperature phase stability over the whole investigated temperature range. Therefore, Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) are considered as promising TBCs materials that might be operated at higher temperatures compared to YSZ.     

Low Thermal Conductivity of Rare‐Earth Zirconate‐Stannate Solid Solutions (Yb2Zr2O7)1−x(Ln2Sn2O7)x (Ln = Nd,Sm)

Dense monoliths of rare‐earth zirconate‐stannate solid solutions (Yb₂Zr₂O₇)_1?x(Ln₂Sn₂O₇)_x (Ln = Nd, Sm) were prepared by solid‐state reaction. Characterized by XRD, Raman, SEM, and TEM, a double‐phase structure of Yb₂Zr₂O₇‐rich fluorite and Nd₂Sn₂O₇‐rich pyrochlore was observed in the specimens of x = 0.4 and 0.5 of (Yb₂Zr₂O₇)_1?x(Nd₂Sn₂O₇)_x series while complete solid solutions were formed within the whole composition range of (Yb₂Zr₂O₇)_1?x(Sm₂Sn₂O₇)_x series. Except for the defect phonon scattering, lattice softening caused by order–disorder phase transformation between pyrochlore and fluorite structures also plays an important role in minimizing the thermal conductivity. Low thermal conductivity with positive temperature dependence is achieved in both the series. Considering the structure stability and low thermal conductivity, rare‐earth zirconate‐stannate solid solutions may be promising materials for thermal insulating applications, such as thermal barrier coatings.     

Effects of SnO2 layer coated on carbon nanofiber for the methanol oxidation reaction

Carbon nanofibers (CNFs) are used as active materials for electrodes in various energy devices, such as lithium ion secondary batteries, supercapacitors, and fuel cells. Recent studies have shown that nanoscale coatings on carbon nanotubes increase the output and lifespan of these devices owing to the improvement of their mechanical and chemical properties. Among various coating methods, atomic layer deposition (ALD) can adjust the thickness of the coating layer conformally without any directional growth. Therefore, ALD can coat particles with high aspect ratios, such as CNFs, even at nanometer levels of thickness.In this work, we grew two different morphologies of a SnO₂ layer on CNF. We used two types of ALD equipment: flow-type ALD (static ALD), and fluidized bed reactor-type ALD (dynamic ALD). Static ALD could form a discontinuous SnO₂, while a uniform SnO₂ layer was formed by pre-inserting a layer of Al₂O₃. On the other hand, dynamic ALD formed a uniform SnO₂ layer without pre-insertion of an Al₂O₃ layer. X-ray photoelectron spectroscopy analysis revealed that both Sn⁴⁺ and Sn²⁺ were present in SnO₂ on the CNF deposited by static ALD, probably due to the formation of an interfacial layer between the SnO₂ and CNF. When the dynamic ALD method was used, only Sn⁴⁺ was present in the SnO₂ on CNF. Cyclic voltammetry analysis was performed to characterize the electrochemical properties of the SnO₂-coated CNF as an electrode on a direct methanol fuel cell. It was revealed that the discontinuous SnO₂ on CNF deposited by static ALD showed the highest current efficiency as well as enhanced electrocatalytic stability.     

Structure Characteristics and NO Selective Catalytic Reduction Property of Sn x Zr1-x O2 Solid Solution Catalysts

Novel catalysts, Sn_xZr_1-xO₂ solid solutions, for NO selective catalytic reduction:NO SCR) are reported. They have much higher activity and selectivity than SnO₂ and ZrO₂. Sn⁴⁺ is the main reductive sites as proved by TPR. The dilution of Sn sites by the coexisting Zr causes a suppression of propene combustion and consequently promoted the selective reduction of NO. The rutile structure might be beneficial to NO SCR.     

Effect of phosphoric acid concentration on some properties of finely milled refractory materials

Conclusions The concentration of phosphoric acid seriously affects the setting, weakening, and sintering of the finely milled refractory materials.Increasing the acid concentration boosts the setting rate of alumina, MgO·Al₂O₃, chromite, electrocorundum, dunite, and dinas, but hardly affects the setting of MgO, Cr₂O₃, magnesite, zircon, and quartzite.The materials that were studied are almost unaffected at 800°C. Increasing the concentration of H₃PO₄ improves the sintering of alumina, MgO·Al₂O₃, chromite, zircon, and dinas, but impairs the sintering of MgO, Cr₂O₃, magnesite, electrocorundum, dunite, and quartzite.Translated from Ogneupory, No.3, pp. 40–43, March, 1968.     

Modelling of the grain growth and the densification of SnO2-based ceramics

This work consisted in the kinetic study of grain growth and densification processes for SnO₂ and Sn_0.94Zr_0.06O₂ ceramics between 1100 and 1200 °C.     

Solid state sintering of nano-crystalline indium tin oxide

The sintering of single phase nano-crystalline In₂O₃ and ITO (In_1.9Sn_0.1O_3.05) powders is reported and discussed with particular focus on the underlying mass transport mechanisms. The mass transport in the initial stage of sintering was surface diffusion, resulting in necking and coarsening, and grain boundary diffusion, accompanied by grain growth. Lattice diffusion caused significant densification at higher temperatures, leading to densities higher than 95%. The onset of densification and the maximum densification rate were shifted significantly to higher temperatures for ITO compared to In₂O₃. The reduced sintering rate of ITO was related to the higher valence state of Sn⁴⁺ relative to In³⁺, and due to precipitation of SnO₂(s). The volatile sub-oxides In₂O(g) and SnO(g) caused significant weight losses at high temperatures, particularly in the case of ITO and inert conditions. The sintering at intermediate temperatures is discussed with focus on heat treatment of ITO thin films.     

Improved resistance of lanthanum zirconate coatings to calcium-magnesium-alumina-silicate corrosion through composition tailoring

Calcium–magnesium–alumina–silicate (CMAS) corrosion resistance is an important issue on the design of next-generation thermal battier coatings. As one of the promising thermal battier coatings, the lanthanum zirconate coating has attracted continuous attention. In this work, three lanthanum zirconate coatings with different La/Zr composition, i.e., La_1.8Zr_2.2O_7.1, La₂Zr₂O₇, and La_2.5Zr_1.5O_6.75, are fabricated by laser-enhanced chemical vapour deposition, and their resistance to CMAS corrosion at 1250?°C is investigated. Among them, La_2.5Zr_1.5O_6.75 shows the best CMAS corrosion resistance because increased La content is beneficial to the formation of a dense and continuous apatite Ca₂La₈(SiO₄)₆O₂ layer, which effectively slows down the subsequent molten CMAS penetration. This study clarifies the significant role of rare earth on CMAS corrosion resistance and is expected to guide the future design of rare-earth-based thermal battier coatings through composition tailoring.     

Microstructure stabilization of a novel glass/YSZ composite coating material by adding alumina particles

Glass-based composite coating materials incorporating particles of alumina or YSZ were prepared by reaction sintering. It was revealed that phase evolution played a key role on thermal expansion behavior of the composite coating materials. Both precipitating of t-ZrO₂ crystals and adding YSZ inclusions could raise CTEs of the glass-based matrix, while the formation of zircon produced the reverse effect. Especially, alumina additives retarded the crystallization of the base glass and reduced reaction rates between YSZ and the glass matrix remarkably. Thus, the Al₂O₃/YSZ/glass tri-composites could serve as an environmental barrier coating for intermetallics and superalloys because of the stabilized microstructure.     

Semiconducting densified SnO2-ceramics obtained by a novel sintering technique

Dense and electroconductive SnO₂ ceramics, important for special electrodes applications, with the Sn_0.75Cu_0.083Sb_0.167O₂ final composition were densified by applying the Field Activated Sintering Technique (FAST). The same composition, obtained starting both from the initial oxides (i. e. SnO₂, Sb₂O₃ and CuO) and from SnO₂ and the CuSb₂O₆, was conventionally sintered by thermal treatment at 1100 °C–3 h. High relative density values (i.e. 99%) and a consolidated microstructure (grain size below 1 μm) were obtained only by applying FAST. The resulting SnO₂-based solid solutions, presented a semimetallic behaviour sustained by the conductivity vs. temperature dependence and the obtained negative values for the Seebeck coefficients, with electrons as major charge carriers. For the conventional sintered specimens, the poor sintering capabilities evidenced by density and porosity measurements limited the electrical applications of the obtained materials as densified ceramics.     

Fining Behavior in Alkaline Earth Aluminoborosilicate Melts Doped with As2O5 and SnO2

In this work the gas evolution behavior and the fining ability of the alkali‐free alkaline earth aluminoborosilicate glass batches doped with As₂O₅ or SnO₂ were examined, and the redox behavior of As and Sn ion in the corresponding fined melts was investigated by square wave voltammetry. The evolved gas analysis showed a distinct difference at begin temperature of O₂ emission and in evolved O₂ volume between glass batches doped with As₂O₅ and SnO₂. One peak due to reduction of As⁵⁺ to As³⁺ or Sn⁴⁺ to Sn²⁺ was shown in the voltammograms. Glass batch doped with SnO₂ showed better fining in the first fining zone, but batch doped with As₂O₅ is more excellent in the overall fining inclusive of the second fining. This difference in fining behavior was discussed by combination of O₂ evolution from batches and redox ratio in melts. Finally, it was suggested that the earlier oxidation of As ion in the second fining zone contributed to the excellent fining of melts.     

Combustion of Methane at Low Temperature over Pd and Pt Catalysts Supported on Al2O3, SnO2 and Al2O3-Grafted SnO2

Pd and Pt catalysts supported on alumina, tin(IV) oxide and tin(IV) oxide grafted on alumina were prepared, characterised and tested with respect to the low-temperature combustion of methane after reduction in H₂ and ageing under reactants at 600°C. In the case of Pd, the use of SnO₂ or SnO₂-based supports led to catalysts slightly less active than Pd/Al₂O₃. In contrast, SnO₂ was found to strongly promote the oxidation of methane over Pt catalysts with respect to Pt/Al₂O₃, even after ageing under reactants. When Pt was supported on SnO₂ grafted on Al₂O₃, the activity was found at most similar to or, after ageing, lower than Pt/Al₂O₃. This negative effect was discussed, being partly related to the sintering of SnO₂ under reactants observed by FTIR and XRD.     

The effect of non-equimolar doping on the preparation and electrical conductivity of Sr(Ti,Zr,Zn,Sn,Hf)O3-σ high entropy perovskite oxide

A series of high entropy oxides (HEOSs) with non-isomolar ratios of perovskite structures were prepared by ball milling a mixture of SrO, TiO₂, ZrO₂, ZnO, SnO₂ and HfO₂ followed by sintering using a high-temperature solid-phase method. Both XRD and TG-DSC results indicate that single-phase Sr(Ti_0.2Zr_0.2Zn_0.2Sn_0.2Hf_0.2)O_3-σ is formed at 1500 °C. According to the SEM-EDS pictures, the elements in the oxide are uniformly distributed with no significant segregation or accumulation. The TEM results show that the polycrystalline ceramic powders can be classified as orthogonal Pbnm perovskite structure. The electrical conductivity (σ) was measured by the EIS technique and the activation energy (Ea) of HEOSs is calculated. In the temperature range of 300–750 °C, Sr(Ti_0.28Zr_0.18Zn_0.18 Sn_0.18 Hf_0.18)O_3-σ exhibits the highest conductivity (2.41 × 10⁻³ S/cm) and the lowest activation energy (Ea = 0.57 eV) due to lattice distortion and oxygen vacancy concentration.     

Microstructure evolution,mechanical and tribological properties of Ti3(Al,Sn)C2/Al2O3 composites

In this paper, in situ formed Ti₃(Al,Sn)C₂/Al₂O₃ composites were fabricated by sintering the mixture of Ti₃AlC₂ and SnO₂. The Al atoms could diffuse out of the Ti₃AlC₂ layered structure to react with SnO₂, resulting in the formation of Ti₃(Al,Sn)C₂ solid solution and Al₂O₃. When the SnO₂ content was 20?wt.%, the sintered Ti₃(Al,Sn)C₂/Al₂O₃ composite exhibited the best overall mechanical properties, because of the optimized cooperative strengthening effect of solution strengthening and Al₂O₃ enhancement. When the SnO₂ content increased up to 30?wt.%, the flexural strength and fracture toughness of Ti₃(Al,Sn)C₂/Al₂O₃ composite dramatically decreased on account of the large accumulation of generated Al₂O₃. Moreover, according to the SiC ball-on-flat wear tests, it was found that the wear resistance of Ti₃(Al,Sn)C₂/Al₂O₃ composites was significantly improved as the SnO₂ content increased.