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1.
Microsilica addition in Al2O3–MgO and Al2O3–spinel castables helps to improve their flowability and partially accommodate their residual expansion after firing. Nevertheless, there is a lack of conclusive statements in the literature regarding the effects of microsilica on one of the main requisites for steel ladle refractories: corrosion resistance. In the present work, the performance of alumina–magnesia and alumina–spinel with or without microsilica when in contact with a steel ladle slag was evaluated based on three aspects: the material's physical properties, its chemical composition and the microstructural features before the slag attack. According to the attained results, microsilica induced liquid formation and pore growth during sintering, favoring the physical slag infiltration. Moreover, due to this liquid, CA6 was formed in the matrix, mainly for the Al2O3–spinel composition, which also favored the castable dissolution into the molten slag. 相似文献
2.
Eight batches of low- and ultra-low cement castables were prepared from calcined Chinese bauxite and high alumina cement (HAC). The effect of alumina-cement replacement by SiC, graphite and aluminum metal on the sinterability and properties of these castables was investigated. Physical properties such as bulk density and apparent porosity of hydrated and sintered castables were studied. The sintered castables were also characterized for their solid phase compositions and microstructure using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. In the castables containing SiC, new phases such as mullite (3Al2O3·2SiO2), SiC, and quartz (SiO2) were formed at the expense of calcium aluminate phases (i.e. CA and CA2; the main cement phases). Generally, the bulk density of the control castable sample was the highest among all prepared samples, while the batches containing graphite showed the lowest bulk density. The presence of Al-metal reduced the oxidation of SiC and consequently increased the densification of the castables compared with castables containing graphite only. Cold crushing strength (CCS) of the hydrated specimens i.e. green castables, decreased as the additives contents increased at the expense of HAC which is responsible for the bonding at room temperature. The highest CCS value of the sintered castable was obtained for the sample containing 6 wt.% SiC, 3 wt.% CA and 0.5 wt.% Al-metal. 相似文献
3.
《Ceramics International》2019,45(15):18215-18221
Al2O3–Cr2O3 refractories are completely substitutional solid solutions and exhibit better corrosion and abrasion resistance. To enable the comprehensive utilization of it, the microstructure and properties of Al2O3–Cr2O3 samples with different corundum sources were investigated in this study. The starting sources of corundum sources included sintered tabular corundum, fused white corundum, or brown corundum with minor impurities of β-Al2O3 and TiO2. The results of mechanical test showed that the introduction of white corundum deteriorates the physical structure, while brown corundum acts in an opposite manner. The optimum bonding strength of the Al2O3–Cr2O3 brick was reached by combining white and brown corundum, whereby rapid neck growth occurred via surface diffusion during solid-phase sintering. 相似文献
4.
Rundong Fan Huizhong Zhao Han Zhang Pengda Zhao Jianwei Chen Xianghui Wang 《Ceramics International》2019,45(9):11204-11215
Alumina–chromium slag (ACS), a cheap and abundant refractory raw material comprising aluminum–chromium oxides and β-Al2O3, is a byproduct of ferrochrome smelting. For this reason, we investigated the relationships between composition and mechanical properties, abrasion resistance, oxidation resistance, and resistance to iron slag erosion for Al2O3–SiC–C trough castables in which ACS was substituted for alumina. Due to the presence of β-Al2O3 in ACS, the aluminum-chromium slag reacted with SiO2 to form a low-melting phase of albite and promoted the formation of mullite, which filled the pores at high temperatures and reduced the porosity, thereby promoting densification and strengthening of the sample. The cold mechanical properties of the sample and the normal temperature wear resistance were enhanced, but the high-temperature mechanical properties and the resistance to iron slag corrosion of the sample were impaired. According to the results of the anti-oxidation experiment, the presence of β-Al2O3 in the ACS reduced the porosity and made the sample more dense, which remarkably improved oxidation resistance of the sample. For industrial production requirements, ACS substitution should not exceed 48?wt% due to of thermomechanical properties and anti-slag corrosion performance in Al2O3–SiC–C trough castables. 相似文献
5.
The influence of oxide–oxide interaction on the catalytic properties of Co/Al2O3 in CO hydrogenation
The influence of oxide–oxide interaction on the catalytic properties of cobalt in CO hydrogenation is investigated on the example of a Co/Al2O3 catalyst. Oxide–oxide interaction was prevented by modification of the alumina surface with magnesia. It has been shown that oxide–oxide interaction affects catalytic activity and the amount of carbon deposited on the catalyst surface. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
The effects of fluorine content on the nucleation and crystallization behavior of SiO2–Al2O3–CaO glass ceramics system have been investigated. The crystalline phases were determined by X-ray diffraction (XRD). The crystallization kinetics was determined by differential thermal analysis (DTA). The microstructures were examined by using scanning electron microscope (SEM). Fourier transformed infrared spectra (FTIR) analysis was used to study the glass structure. The results showed that by increasing the fluorine content, both the crystallization peak temperature (Tp) and activation energy (E) decreased. Wollastonite, anorthite and gehlenite are the main crystalline phases that exist in the glass ceramics system. The study shows that fluorine promoted initial crystallization of glass and can be used as an effective nucleating agent in the SiO2–Al2O3–CaO system. 相似文献
7.
《Journal of the European Ceramic Society》2023,43(6):2675-2689
The beneficial effects of adding nanostructured expandable graphite (EG) hybridized yttrium aluminium garnet (EG\YAG) powder as a composite reinforcement in improving the oxidation resistance, hot-strength, and microstructure development in Al2O3–MgO–C refractories were studied. The refractory components reinforced with EG\YAG exhibited more than 60% of oxidation resistance enhancement and as high as 200% increase in hot-strength performance over the standard refractories, formulated without EG\YAG. Correlating the damage parameter (DE) calculations based on ultrasonic measurements with residual strength data (Rc, Rb) showed that there was a progressive increase in Rc and Rb values with consistent reduction in the oxidative damage of EG\YAG reinforced refractories. Analysis indicated that these beneficial features were majorly ascribed to the in-situ development of bimodal microstructure with EG\YAG sintered framework throughout the refractory interior in these new class of reinforced systems. Additionally, the mechanism of toughening and implications of these results to materials design are discussed. 相似文献
8.
Justyna Zygmuntowicz Paweł Falkowski Marcin Wachowski Konrad Cymerman Paulina Piotrkiewicz Waldemar Kaszuwara 《International Journal of Applied Ceramic Technology》2020,17(4):1731-1741
In the present research, the influence of sintering temperature on the microstructure and properties of Al2O3–Cu–Ni hybrid composites prepared by the Pulse Plasma Sintering (PPS) technique were described. In this research, three temperatures have been selected: 1250°C, 1300°C, and 1350°C. SEM observations were carried out to determine the distribution of the metallic phase in the composite depending on the sintering temperature. The conducted experiments and microscopic observations enabled a better understanding of the phenomena occurring between the ceramic matrix and metallic phase in the obtained materials. The mechanical properties like a hardness and fracture toughness were measured. The technology applied allowed us to obtain ceramic-metal composites with a homogeneous microstructure. It was found that the sintering temperature influences the selected physical and mechanical properties of the composites produced. It was found that samples produced at 1300°C are characterized by the highest relative density and the mechanical properties. 相似文献
9.
《Applied catalysis. B, Environmental》2009,85(3-4):552-562
The effect of La2O3 content on the structural properties and catalytic behavior of Pt/xLa2O3–Al2O3 catalysts in steam reforming of methane and partial oxidation of methane was investigated. There was a decrease in the density of Pt sites with the increase of La2O3 loadings according to Fourier transform infrared spectroscopy of adsorbed CO and to dehydrogenation of cyclohexane results. However, transmission electron microscopy data indicates an opposite trend. This apparent disagreement could be due to the partial coverage of Pt sites by LaOx species. CH4 turnover rates and specific rates of steam reforming of methane increased for higher La2O3 loadings. The Pt/Al2O3 catalyst was strongly deactivated during partial oxidation of methane, while La2O3-containing catalysts exhibited higher stability. The increase of activity observed during the reactions was ascribed to the ability of the [LaPtxO]Pt0-like species to promote the gasification of coke. This cleaning mechanism led to higher accessibility of the active sites to CH4. 相似文献
10.
《Ceramics International》2022,48(4):5174-5186
The CaCO3 coated corundum aggregates were prepared by impregnating tabular corundum aggregates with sizes of 1–5 mm in calcium hydrogen citrate solution and heat treatment at 430 °C, which were also used in Al2O3–MgO castables. The effects of Ca2+/Cit3? mole ratio in precursor solution on coating characteristics of CaCO3 coated corundum aggregates as well as the effects of CaCO3 coatings on properties and microstructure of castables were investigated. It is found that the thickness and continuity of CaCO3 coating is increased and the size of CaCO3 particles in coatings decreases first and then increases as Ca2+/Cit3? mole ratio is decreased. High-temperature properties of castables are improved by in-situ formation of calcium hexaaluminate (CA6) layer at aggregate/matrix interface after sintering at 1600 °C. The Al2O3–MgO castables exhibit the best thermal shock resistance when Ca2+/Cit3? mole ratio is 1/3. It is contributed by deflections of cracks and consumptions of fracture energy in a continuous platelet CA6 layer with thickness of 10 μm, which is in-situ formed through reaction between Al2O3 and CaO derived from CaCO3 coatings. The present investigation provides a novel approach to enhance thermal shock resistance of the Al2O3–MgO castables. 相似文献
11.
A.V. Benedetti P.L. Cabot J.A. Garrido A.H. Moreira 《Journal of Applied Electrochemistry》2001,31(3):293-300
The effect of Fe addition on the microstructural properties and the corrosion resistance of Al–Zn–Mg alloys submitted to different heat treatments (cast, annealed and aged), has been studied in chloride solutions using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), cyclic polarization (CP) and open circuit potential (o.c.p.) measurements. The presence of 0.3% Fe in the alloy limited the growth of the MgZn2 precipitates, both in the annealed and in the quenched specimens. No effect of Cr on the grain size in the presence of Fe was found because of the accumulation of Cr in the Fe-rich particles. Fe in the Al–Zn–Mg alloys also made them more susceptible to pitting. Pitting occurred mainly near the Fe-rich particles both, under o.c.p. conditions in O2-saturated solutions and during the CP. 相似文献
12.
《Ceramics International》2017,43(8):5856-5861
High density and low electrical resistivity ITO targets were prepared by normal pressure sintering in oxygen with Bi2O3–Nb2O5 addition. The relative density, microstructure and electrical properties of the ITO targets can be adjusted by changing the sintering temperature (1350 °C~1550 °C) and the content of Bi2O3–Nb2O5. The results show that the sintering temperature of ITO targets with Bi2O3–Nb2O5 decreased from 1550 °C to 1450 °C, and the maximum relative density (99.6%) and the lowest electrical resistivity (1.78×10−4 Ω cm) were reached when the sintering temperature was 1450 °C with 5 wt% Bi2O3–Nb2O5. The carrier concentration increased as the increase of the contents of Bi2O3–Nb2O5 and sintering temperature. The mobility first increased, and then decreased above 1450 °C as the sintering temperature increased. 相似文献
13.
C.-W. Nahm 《Ceramics International》2009,35(2):541-546
The microstructure and electrical properties of ternary system ZnO–0.5 mol% V2O5–MnO2 ceramics sintered were investigated in accordance with MnO2 content by sintering at 900 °C. For all samples, the microstructure of the ternary system ZnO–V2O5–MnO2 ceramics consisted of mainly ZnO grain and secondary phase Zn3(VO4)2. The incorporation of MnO2 to the binary system ZnO–V2O5 ceramics was found to restrict the abnormal grain growth of ZnO. The breakdown field in the E–J characteristics increased from 175 to 992 V/cm with the increase of MnO2 content. The incorporation of MnO2 improved non-ohmic properties by increasing non-ohmic coefficient. The highest non-ohmic coefficient (27.2) in the ternary system ZnO–0.5 mol% V2O5–MnO2 was obtained for MnO2 content of 2.0 mol%. 相似文献
14.
《Ceramics International》2023,49(20):33188-33196
Nowadays, Y2O3–Al2O3–SiO2 (YAS) glass joining is considered to be a promising scheme for nuclear-grade continuous silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC). CaO has great potential for nuclear applications since it has low reactivity and low decay rate under nuclear irradiation. In this paper, the effect of CaO doping on the structure, thermophysical properties, and crystallization behavior of YAS glass was systematically studied. As the CaO doping content increased, the number of bridge oxygens and the viscosity at high temperatures reduced gradually. After heat treatment at 1400 °C, the main phases in YAS glass were β-Y2Si2O7, mullite, and SiO2 (coexistence of crystalline and glass phases), while that with 3.0% CaO doping turned into a single glassy phase under the same treatment conditions. Moreover, a structural model and the modification mechanism were proposed, which provided a theoretical basis for the subsequent component design and optimization. 相似文献
15.
《Ceramics International》2015,41(8):9947-9956
This work addresses the main aspects related to the use of alternative binders [hydratable (HA) or colloidal alumina (ColAlu)] in castables containing different spinel sources (pre-formed or in situ generated), in order to point out: (i) the features that control the corrosion behavior of these materials, and (ii) the key factors to better select a refractory composition. Thermodynamic calculations, corrosion cup-test and SEM analyses were carried out in order to evaluate the slag attack of the designed refractory compositions. According to the attained results, the alumina-based binders (HA or ColAlu) induced a more effective sintering process due to their high specific surface area, improving the physical properties and the binding level of the generated microstructure. The spinel grain size also played an important role in the corrosion behavior of these refractories, as the finer the particles, the greater their dissolution was into the molten liquid, leading to further precipitation of spinel in the solid–liquid interface as a continuous and thick layer. Among the evaluated compositions and considering the presence of silica fume, the most suitable formulation with optimized corrosion resistance was the one with in situ spinel generation and HA as a binder. 相似文献
16.
Matevosyan A. B. Gasparyan L. A. Knyazyan N. B. 《Theoretical Foundations of Chemical Engineering》2017,51(5):781-785
Theoretical Foundations of Chemical Engineering - The glass-forming region of the LiF–Al2O3–B2O3 system and the phase diagram of this region have been studied. Properties of glasses and... 相似文献
17.
《Ceramics International》2022,48(18):25933-25939
In order to gain more insights into the influence of rare earth elements on the melt structure of SiO2–CaO–Al2O3–MgO glass ceramics, Raman and X-ray photoelectron spectroscopy techniques were used to study the influence of La2O3 on the Si–O/Al–O tetrahedron structure within SiO2–CaO–Al2O3–MgO–quenched glass samples in this study. Results showed that some Raman peak shapes at low frequencies (200–840 cm?1) changed significantly after the addition of La2O3, compared to the high frequency (840–1200 cm?1) region that corresponds to the [SiO4] structure, suggesting that the depolymerization of the low-frequency T–O–T (T=Si or Al) structure was more prevalent with La3+ addition. Besides, the depolymerization extent of the Si–O/Al–O tetrahedral network varied when the melt composition altered. Most notably, depolymerization is the most significant at a low CaO/SiO2 ratio (0.25) and a high Al2O3 content (8%). Meanwhile, La3+ can promote the transformation of Si–O–Si and Al–O–Al bonds to the Si–O–Al ones, thereby forming a complex ionic cluster network interwoven with Si–O and Al–O tetrahedrons. 相似文献
18.
We have recently reported the production of Al2O3-matrix nanocomposites via solid state precipitation of nanosized FeAl2O4 particles within the matrix grains during aging of Al2O3–10 wt.% Fe2O3 solid solutions in a reducing atmosphere (N2 + 4% H2). In addition to these nanoparticles, however, coarse micron-sized FeAl2O4 particles were present along the matrix grain boundaries. In the present work, we show that the addition of ~250 ppm yttria to the solid solutions suppressed the development of these intergranular particles, reducing their size by a factor of ~2 with optimum aging. A fracture toughness improvement by 45% and flexural strength improvement by 50% with respect to monolithic Al2O3 were recorded with the yttria-containing nanocomposite developed by aging for 20 h at 1450 °C. Aging also improved the hardness with respect to the solid solution. The change in fracture mode in the presence of the nanosized intragranular particles was believed to be the major contributing factor towards the improvement in toughness and therefore the strength. The higher strengths obtainable in the presence of yttria were attributed to the reduction of intergranular precipitate size relative to yttria-free nanocomposites. 相似文献
19.
Low wettability between reinforcements and matrix is a key challenge in the production of metal matrix nanocomposites with improved properties. In this paper, we employed electroplating technology to coat Al2O3 and Graphene Nano sheets (GNs) with Ag nanoparticles to improve their wettability with Al matrix. After coating, we used mechanical milling and sintering to manufacture Al–10%Al2O3/GNs hybrid nanocomposites with different GNs content. For all the manufactured composites, we evaluated the structural, mechanical and wear behaviors. The results revealed the efficiency of electroplating process for improving wettability between composite components resulting in very dense samples even for samples with relatively high GNs content. This improved wettability enable the production of hybrid composite with 2 times larger hardness and reduced wear rates due to the improved surface characteristics of Al2O3 and GNs nanoparticles caused by Ag plating over their surfaces. In comparison with available techniques and results in the literature, we achieved hybrid nanocomposite with 1.85 times larger hardness than the available Al-GNs nanocomposite and 1.75 times larger hardness than the available Al–Al2O3/GNs nanocomposites. 相似文献
20.
《Ceramics International》2017,43(4):3465-3474
This study investigated the effect of elemental crystal Ge or/and GeO2 doping on the microstructure and varistor properties of TiO2–Ta2O5–CaCO3 varistor ceramics, which were prepared via the traditional ball milling–molding–sintering process. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy demonstrated that co-doping with Ge and GeO2 changed the microstructure of TiO2–Ta2O5–CaCO3 ceramics, thereby increasing the nonlinear coefficient and decreasing the breakdown voltage. The optimum doping concentrations of Ta2O5, CaCO3, Ge, and GeO2 exhibited the highest nonlinear coefficient (α=14.6), a lower breakdown voltage (EB=18.7 V mm−1), the least leakage current (JL=10.5 μA cm−2), and the highest grain boundary barrier (ΦB=1.05 eV). In addition, Ge and GeO2 function as sintering aids, which reduce the sintering temperature because of their low melting points. 相似文献