Al2O3 Samples Research Articles

Digital Light Processing Followed by Pressureless Sintering of Metal-Reinforced Ceramics: Adjustment of Process Parameters and Correlation with Composites Properties

AbstractDigital light processing (DLP) belongs to additive manufacturing techniques and is frequently used in shaping ceramics. The paper concerns the adjustment of the DLP method to metal-reinforced ceramics, especially dispersions containing high concentrations of Al2O3 (45 vol%) and molybdenum or nickel particles (0.5 vol%). Different glycol acrylates, deflocculants (polyelectrolytes and diammonium hydrogen citrate), and photoinitiators (Omnirad group) were examined regarding their influence on the rheological properties of the dispersions and the cure depth under the external halide UV lamp and LED projector built into the 3D printer. In the examined systems, the cationic polyelectrolyte KD1 dissolved in 2-butanone allowed to obtain dispersions of the lowest viscosity. Printing parameters (light exposure time, single layer height) were matched, and the properties of the materials were examined. The Vickers hardness of the sintered bodies equalled 19.4 GPa, 14.5 GPa and 17.3 GPa for Al2O3, Al2O3-Ni and Al2O3-Mo samples, respectively. The microstructure was analyzed using SEM, followed by EDS and XRD. The addition of only 0.5 vol% of Ni has improved the fracture toughness of alumina by up to 36–40% (according to Niihara and Anstis equations). The exemplary objects in the form of cog wheels were printed and densified at 1550 °C in a reductive atmosphere of Ar/H2.

Sub-acute Inhalation Exposure to Aluminum Oxide Nanoparticles and its Effects on Wistar Rats as Opposed to the Micro-sized Chemical Analog.

Aluminum oxide nanoparticles (Al2O3 NPs) are widely used in various productions. Simultaneously, many research works report the toxic effects of this nanomaterial. Given that, there is a growing risk of negative effects produced by Al2O3 NPs on public health. This study aims to investigate the toxic effects of Al2O3 NPs as opposed to the micro-sized chemical analogue under sub-acute inhalation exposure. We identified the physical properties of Al2O3 NPs as opposed to the micro- sized chemical analogue, including size, specific surface area, and total pore volume. Inhalation exposure to Al2O3 NPs was simulated on Wistar rats in a chamber for whole-body. The animals were exposed for 4 hours each day for 28 days. NPs and MPs concentrations in the chamber were kept at ~ 1/4000 from LC50. Rats' behavior was examined prior to the exposure period and after it; after the last daily exposure, we examined biochemical and hematological blood indicators, NPs and MPs bioaccumulation, and pathomorphological changes in organ tissues. The tested Al2O3 sample is a nanomaterial according to its analyzed physical properties. Rats' behavior changed more apparently under exposure to NPs compared to MPs. Aluminum levels, which were 1.62-55.20 times higher than the control, were identified in the lungs, liver, brain, and blood under exposure to NPs. These levels were also 1.55-7.65 times higher than the control under exposure to MPs. Biochemical indicators of rats' blood also changed under exposure to NPs against the control. We identified more active ALT, AST, ALP, and LDH, elevated levels of GABA, MDA, and conjugated bilirubin, and a lower level of Glu. As opposed to exposure to MPs, ALT, AST, and ALP were more active; GABA and MDA levels were higher; Glu level was lower. Under exposure to NPs, the number of platelets grew, whereas no similar effect occurred under exposure to MPs. We established pathomorphological changes in tissues of the lungs, brain, heart, and liver under exposure to Al2O3 NPs; similar changes occurred only in the lungs under exposure to MPs. Exposure to NPs induced changes in tissue structures in a wider range of various organs, and these changes were more apparent than under exposure to MPs. Greater toxicity of Al2O3 NPs as opposed to MPs is evidenced by a wider range of organs where their bioaccumulation occurs, more apparent pathomorphological and pathological functional changes. Established peculiarities of toxic effects produced by the analyzed nanomaterial should be considered when developing hygienic recommendations aimed at preventing and mitigating adverse impacts of Al2O3 NPs on human health under inhalation exposure.

Gradient composites Al2O3-Ni obtained via the CSC technique in a magnetic field - microstructure and mechanical properties

This article presents the formation of composite microstructures by combining two established concepts: centrifugal slip casting and the utilization of a magnetic field to control the distribution of magnetic particles. The integration of these methodologies offers the potential to create zones within the composite with distinct hardness values. The study introduces a novel method for fabricating ceramic-metal composites, with a key focus on determining the feasibility of manipulating the location of the metallic phase using a magnetic field. Through this innovative approach, the research aims to produce composite hollow cylinders with a gradient distribution of metallic particles. The relative density of the composites was 97 %. The hardness values for the samples range from 970 HV to 2700 HV, displaying variability based on the metallic phase content within the material. The compressive strength for Al2O3-Ni samples was equal to 128.92 MPa. The Al2O3 grains in zone III after the sintering process have an average size of 1.27 ± 0.68 µm. The Al2O3-Ni composites indicate a smaller heat capacity of the material compared to pure Al2O3 samples.

Preparation and characterization of ion-exchanged Ni-Na-β”-Al2O3 and Fe-Na-β”-Al2O3 solid electrolytes for applications in liquid metals

Accurate determinations of the thermochemical properties for the steel alloying elements (Fe, Cr, Ni, Co and Mn) dissolved as corrosion product impurities in Pb and Pb–Bi alloy (LBE) are relevant for the development of Lead-Cooled Fast Nuclear Reactors (LFRs). Ion-selective solid electrolytes are suitable for an electrochemical characterization of the dissolved impurities. Among these, ion-exchanged Ni-β”-Al2O3 and Fe-β”-Al2O3 are promising solid electrolytes for the selective detection of Ni and Fe dissolved in HLMs. In the present works we proposed a preliminary test of liquid and vapor ion-exchanges on commercial polycrystalline Na-β”-Al2O3 tubes at different conditions of temperature and reaction time with NiCl2 and FeCl2 salts, characterizing the effects on the material microstructure. The resulting Ni-Na-β”-Al2O3 and Fe-Na-β”-Al2O3 samples were only partially replaced by nickel or iron, extremely porous, damaged by molten salt corrosion, and contaminated by residual chlorides. When tested as selective sensors in molten LBE, they failed in detecting dissolved nickel or iron. Thus, ion-exchange procedure on polycrystalline Na-β”-Al2O3 substrates still needs to be improved by properly combining the liquid and vapor ion-exchange with optimized reaction conditions in order to increase the sodium replacement yield. Alternatively, efforts may be focused on the preparation and application of other different nickel and iron solid electrolytes.

The role of Ga and Y on binary Al2O3-Y2O3 and Al2O3-Ga2O3 mixed oxides nanoparticles towards potential Ni water-gas shift catalysts

This work focuses on the study of binary Al2O3-Y2O3-x and Al2O3-Ga2O3-x mixed oxides with varying Y2O3 or Ga2O3 nominal loading (x=25, 50) prepared by hydrothermal synthesis assisted by Triton X-100. The mixed oxides were used to prepare Ni-based (5 wt%) catalysts for the Water Gas Shift Reaction. The Al2O3 sample presented urchin-like hollow nanosphere morphology, which evolved to solid nanospheres with Y2O3 or Ga2O3 in the mixed oxides. The physicochemical characterization indicated good integration of the mixed oxides, especially on the low-content additive oxides. The theoretical results confirmed that Ga goes deeper into the alumina matrix than Y, partially explaining the XPS and HRTEM results in which the Ni dispersion was better in the Ni/AlGa-x samples. The FTIR in-situ measurements of the reaction allowed us to propose that the reaction occurs minimally through the carbonyl mechanism at low temperatures (<300 °C) and the formate mechanism at high temperatures (>300 °C).

Assessment of mechanical performance of Al2O3 ceramic honeycomb sandwich structures produced with SLA 3D-printing regarding unpolymerized slurry removal strategy

Al2O3 ceramic honeycomb sandwich bars with a hexagonal core were manufactured through SLA 3D-printing to analyze the impact of hole placement, designed for the removal of uncured slurry, on the bending strength of the samples. Several holes were placed specifically on the samples in the design in two different ways. In the initial design, the holes were placed on the honeycomb sandwich structure’s upper and lower face-sheets. In the second design, the holes were positioned in the direction of the sample thickness, in the lateral walls. The moment of inertia values for the honeycomb structures were calculated with the help of experimental elastic modulus results, and true bending strength was determined according to these results. Nominal strength values were found using the common three-point bending formula. The true bending strength value of Al2O3 with lateral holes was 73% higher than Al2O3 with holes on face-sheets, while the nominal bending strength was 79% higher. Al2O3 samples with holes on face-sheets exhibited a significantly higher failure index compared with both the bulk samples and the Al2O3 samples with lateral holes. The holes on the face-sheets reduced the cross-sectional area of the tensile surface and contributed to an increase in stresses due to the stress concentration effect. The Al2O3 samples with lateral holes provided a great advantage of specific strength, reaching an average value of 65% above the specific strength of the bulk samples.

Electrothermal Simulation of the Production of Alumina by Spark Plasma Sintering

Although the spark plasma sintering (SPS) method is a very advantageous technque in many aspects, the inability to clearly read the temperature formed on the material during sintering and heterogeneous temperature distributions are the biggest problems of this process. Therefore, it is a common situation that samples taken from different regions of the produced material have different densities and mechanical properties. In this study, the temperature distributions, current density and joule heating effect of the entire setup consisting of the alumina (Al2O3) sample to be sintered, inconel electrodes, graphite dies, punches and spacers, as well as the critical regions in this setup, are modeled by using finite element software. According to the results, the temperature is maximum at the centre of the Al2O3 sample and the temperature gradient along its radius is 22.4°C. The temperature difference between the inner wall of the hole which is opened in the graphite mold to measure the sintering temperature and the centre of the Al2O3 sample is around 40°C. In addition, during the SPS process, Al2O3 is not heated directly by the joule effect and the temperature gradient in the sample occurs due to mold surface radiation.

Facile Al2O3 coating suppress dissolution of Mn2+ in Mn-substituted Na3V2(PO4)3 with outstanding electrochemical performance for full sodium ion batteries

Na3V2(PO4)3 (NVP) encounters significant obstacles, including limited intrinsic electronic and ionic conductivities, which hinder its potential for commercial feasibility. Currently, the substitution of V3+ with Mn2+ is proposed to introduce favorable carriers, enhancing the electronic conductivity of the NVP system while providing structural support and stabilizing the NASICON framework. This substitution also widens the Na+ migration pathways, accelerating ion transport. Furthermore, to bolster stability, Al2O3 coating is applied to suppress the dissolution of transition metal Mn in the electrolyte. Notably, the Al2O3 coating serves a triple role in reducing HClO4 concentration in the electrolyte, inhibiting Mn dissolution, and functioning as the ion-conducting phase. Likewise, carbon nanotubes (CNTs) effectively hinder the agglomeration of active particles during high-temperature sintering, thereby optimizing the conductivity of NVP system. In addition, the excellent structural stability is investigated by in situ XRD measurement, effectively improving the volume collapse during Na+ de-embedding. Moreover, the Na3V5.92/3Mn0.04(PO4)3/C@CNTs@1wt.%Al2O3 (NVMP@CNTs@1wt.%Al2O3) possesses unique porous structure, promoting rapid Na+ transport and increasing the interface area between the electrolyte and the cathode material. Comprehensively, the NVMP@CNTs@1wt.%Al2O3 sample demonstrates a remarkable reversible specific capacity of 122.6 mAh/g at 0.1 C. Moreover, it maintains a capacity of 115.9 mAh/g at 1 C with a capacity retention of 90.2 mAh/g after 1000 cycles. Even at 30 C, it achieves a capacity of 87.9 mAh/g, with a capacity retention rate of 84.87 % after 6000 cycles. Moreover, the NVMP@CNTs@1wt.%Al2O3//CHC full cell can deliver a high reversible capacity of 205.5 mAh/g at 0.1 C, further indicating the superior application potential in commercial utilization.

Enhancement of mechanical properties of ramie and jute fibres reinforced epoxy hybrid composites: Influencing of SiC and Al2O3

Due to rising environmental awareness and dwindling oil supplies, many efforts have been made to replace synthetic fibres with plant fibre reinforced composites (PFRC). The need to eliminate plastics from everyday life has resulted in the development of a diverse range of eco-friendly natural-based composites for the automotive, chemical, and food packaging industries. PFRC plays an important role in the production of lightweight and cost-effective products. The current study looked at how different proportions of SiC/Al2O3 filler affected the mechanical properties of a plant fibre-based ramie/jute epoxy hybrid composite. By reinforcing a constant ramie (20 wt.%) and jute (10 wt.%) fibre with different proportions of SiC (2 –10 wt.%) and Al2O3 (0 –8 wt.%), hybrid composites were created using traditional stirring and compression moulding methods. The hybrid composite with 8% SiC and 2% Al2O3 (sample D) has higher tensile, flexural, hardness, impact, and interlaminar shear strength than the other combinations. The functional group of a nanoparticle-filled hybrid composite was evaluated using Fourier Transfer infrared Spectroscopy. Furthermore, SEM confirmed the excellent bonding of the viable hybrid composite combination’s filler, fibre, and matrix. According to the findings, a nano filler content of 8% SiC and 2% Al2O3 can improve mechanical properties and serve as a viable reinforcement in hybrid polymer composites for major engineering applications.

Mechanical properties of Al2O3–LaPO4 composites with eutectic microstructure produced by flash sintering

AbstractThe mechanical properties of Al2O3–LaPO4 composites with varying microstructures produced by flash sintering and conventional sintering are evaluated. Specifically, Vickers and Knoop hardness values were measured and calculated for different resultant microstructures, including eutectic microstructures with varying layer thickness, polycrystalline (noneutectic) microstructures, and single‐phase samples of Al2O3, LaPO4, and 8YSZ. The findings indicate that eutectic microstructures exhibited higher hardness values than polycrystalline counterparts on the flash‐sintered sample. However, the hardness values of eutectic microstructures with varying layer thicknesses show no significant or systematic variation. The grain size, indentation size, eutectic colony size, indentation shape (elastic recovery in Knoop indentations), and crack propagation pathways in the indented samples are also discussed. Overall, the results suggest that Al2O3–LaPO4 eutectic composites have higher hardness than their polycrystalline counterparts and have great potential as abradable coatings with high machinability and durability.

Preparation, Characterization, and Photocatalytic Activity of Ni-Cd/Al2O3 Composite Catalyst

This study was conducted to determine the effect of the radiation source and radiation time on the methylene blue (MB) solution by adding Ni-Cd/Al2O3 to the percent degradation of MB. To investigate similar purposes, the pH of the MB solution varied as well. The preparation, characterization, and photocatalytic activity of Ni-Cd/Al2O3 are three steps in this research. The Ni-Cd was prepared by mixing Ni(NO3)2.6H2O and Cd(NO3)2.4H2O. Various concentrations of Ni-Cd were mixed with Al2O3, then heated, stirred, dried, and calcined to form Ni-Cd/Al2O3 powder. The dried powder catalysts were characterized using Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDS), Brunauer-emmett-teller (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Diffused reflectance spectrometer spectra (DR-UV-Vis). Higher degradation was observed at pH 11, when MB was degraded by 68% and 76% using the 5Ni-2Cd/Al2O3 and 6Ni-1Cd/Al2O3 catalysts, respectively. The 6Ni-1Cd/Al2O3 sample has higher absorption, less surface area, and less band gap; therefore, it has higher performance against degraded MB in the solution. In summary, 6Ni-1Cd/Al2O3 is capable of degrading MB and can be utilized in MB dye waste. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Carbon dioxide reforming of methane over modified iron-cobalt alumina catalyst: Role of promoter

BackgroundCobalt-based catalysts are widely employed in methane dry reforming but tend to deactivate quickly due to coke deposits and metal sintering. To enhance the performance, iron, a cost-effective promoter, is added, improving cobalt's metal dispersibility, reducibility, and basicity on the support. This addition accelerates carbon gasification, effectively inhibiting coke deposition. MethodsA series of iron-doped cobalt alumina MFe-5Co/Al2O3 (M= 0, 0.4, 0.8, 1, 2 wt.%) were prepared via simple incipient-wetness impregnation. The catalysts were thoroughly characterized via modern techniques including BET, XRD, H2-TPR, CO2-TPD. Significant findingsThe addition of iron had a minimal impact on the properties of γ-Al2O3, but it significantly affected the dispersibility of cobalt. At an optimal dosage of 0.8 wt.%, there was a notable decrease of 29.44% in Co3O4 particle size. However, excessive iron loading induced agglomeration of Co3O4, which was reversible. The presence of iron also resulted in a decrease in the reduction temperature of Co3O4. The material's basicity was primarily influenced by the loading of iron, reaching its highest value of 705.7 μmol CO2 g−1 in the 2Fe-5Co/Al2O3. The correlation between catalytic activity and the physicochemical properties of the material was established. The 0.8Fe-5Co/Al2O3 sample exhibited excellent performance due to the favorable dispersibility of cobalt, its reducibility, and its affordable basicity.

Effect of TiO2 addition on the microstructure and electrical properties of Al2O3 ceramics

The resistivity of the dielectric layer material of a Johnsen–Rahbek (J–R) electrostatic chuck is generally between E8 and E12 Ω⋅cm, while that of pure alumina ceramic is more than E15 Ω⋅cm. Therefore, it is necessary to regulate the resistivity of the alumina ceramic for use as a dielectric layer material for a J–R-type electrostatic chuck. An electrostatic chuck requires a uniform and controllable surface temperature on the silicon wafer. Therefore, there is a certain requirement for the thermal conductivity of the dielectric layer.In this experiment, Al2O3 ceramics with different TiO2 contents (ranging from 0.08 to 3.6 wt%) were used as the research system and sintered at 1550 °C in a reducing sintering atmosphere. The obtained samples showed electrical resistivity from E9 to E14 Ω⋅cm and thermal conductivity from 26 to 37 W/m·K. The effects of Al2O3 ceramics with TiO2 on the phase composition, microstructure, relative density, electrical conductivity, and thermal conductivity were systematically studied, along with the relationship between the temperature and electrostatic adsorption force J–R and the resistivity of the sample. The addition of 1.2 wt% TiO2 gave the Al2O3 sample better overall performance; its relative density was up to 97.88 %, resistivity was reduced to 7.09 × 109 Ω cm, thermal conductivity was 27.211 W/m·K, and the electrostatic adsorption forces at 300 and 500 V/mm were up to 119 and 331 gf/cm2, respectively. The samples were primarily used as dielectric layers of the electrostatic chuck. By simulating the electrostatic adsorption between the dielectric layer and silicon wafer under an external voltage, the J–R force of stable adsorption between the electrostatic chuck and the silicon wafer was realised.

Investigation of phase and structural states in nanocrystalline powders based on zirconium dioxide

The behavior of a polycrystalline body during sintering ZrO2 is determined not so much by the properties of individual particles but by the properties of aggregates, and the strength of the bonds between powder particles significantly affects the sintering process and the final properties of the ceramic composite materials. An increase in density and a uniform porosity distribution is achieved at such a pressure and sintering temperature when the process of intensive recrystallisation has not yet begun. Conventional sintering at a temperature of 1500 °C with a holding time of 1 h of ZrO2 and ZrO2–20 wt. % Al2O3 samples with an initial particle size of 120 nm and 40 nm, respectively, allowed us to obtain a material with a relative density of 81% (ZrO2) and 86% (ZrO2–20 wt. % Al2O3). The method of electroconsolidation was used to produce bulk samples of submicron ceramics of ZrO2–n wt. % Al2O3 (n = 10; 20; 30) compositions with a density of up to 99% of the theoretical one and a microstructure scale of about 270 nm. It was established that the addition of metastable Al2O3 nanopowders causes a shift in the onset of shrinkage of tetragonal YSZ to high temperatures and affects the reduction of the grain size of tetragonal YSZ to 170–200 nm.

Study of gamma radiation shielding on tellurite glass containing TiO2 and Al2O3 nanoparticles

Radiation shielding incorporates material between the radioactive source and environment to decrease exposure to hazardous radiation. It remains to be seen whether the addition of nanoparticles effectively increases the protection of tellurite glass system from further degradation under irradiation conditions. This study revealed the gamma radiation effects on tellurite glass. The tellurite glass samples were irradiated with 50 kGy and 100 kGy gamma ray, and subsequently analysed using X-ray diffractometer (XRD), atomic force microscopy (AFM), and ultraviolet–visible spectroscopy (UV–Vis). Gamma radiation increased the creation of non-bridging oxygen (NBO) and caused colour change on TZNETi and TZNETiAl glasses. Consequently, the addition of aluminium oxides (Al2O3) was found to lower the density of glass systems. The glass samples surface roughness increased, while the optical transmission spectra decreased after 50 kGy of gamma ray irradiation. Nevertheless, the glass system maintained its transparency even after irradiation. The mass attenuation coefficient (MAC) values represented the shielding effectiveness demonstrated by the investigated glass with the addition of Al2O3. The physical, structural, optical, and radiation shielding properties showed that 69.1TeO2–20ZnO–9Na2O–1Er2O3–0.3TiO2–0.6Al2O3 (TZNETiAl) sample exhibited strong shielding properties amongst the fabricated tellurite samples.

Neutron irradiation impact on structural and electrical properties of polycrystalline Al2O3

High energy neutron irradiations impact on structural and electrical properties of alumina are studied with particular emphasis on real time in-situ radiation induced conductivity measurement in low flux region. Polycrystalline Al2O3 samples are subjected to high energy neutrons produced from D-T neutron generator and Am–Be neutron source. 14 MeV neutrons from D-T generator are chosen to study the role of fast neutron irradiation in the structural modification of samples. Real time in-situ electrical measurement is performed to investigate the change in insulation resistance of Al2O3 due to radiation induced conductivity at low flux regime. During neutron irradiation, a significant transient decrease in insulation resistance is observed which recovers relative higher value just after neutron exposure is switched off. XRD results of 14 MeV neutron irradiated samples suggest annealing effect. Impact of relatively low energy neutrons on the structural properties is also studied using Am–Be neutrons. In this case, clustering is observed on the sample surface after prolonged neutron exposure. The structural characterizations of pristine and irradiated Al2O3 samples are performed using XRD, SEM, and EDX. The results from these characterizations are analysed and interpreted in the manuscript.

Design and fabrication of the alumina nanofibers decorated with isolated ZSM-5 using electrospinning method: A novel catalyst for methanol conversion to light olefins

ZSM-5 nanoparticles are widely used as the catalyst in the methanol conversion to olefins (MTO) process due to their high surface area and short diffusion path length. However, agglomerate formation is a challenge for this catalyst. To address this issue, in this study, electrospinning was used for the first time to synthesize fibrous catalysts comprised of ZSM-5 nanoparticles embedded in the alumina nanofibers. The catalysts were characterized using XRD, FTIR, SEM, TEM, EDX-map, BET, and NH3-TPD analyses. In the synthesized samples, ZSM-5 nanoparticles with an average particle size of 683 nm are uniformly and homogeneously dispersed over alumina nanofibers with a 300 nm diameter. These composites form core-shell structures and have a reactor porosity of 0.85, which is higher than that of parent ZSM-5. In the MTO process, electrospun catalysts demonstrate superior catalytic activity and a longer lifespan than powder catalysts. 80 wt% ZSM-5- 20 wt% Al2O3 with 47.76 % light olefin selectivity and complete methanol conversion after 321min on stream performed better than 50 wt% ZSM-5-50 wt% Al2O3. Moreover, a lower coke formation of about 3.28 % was achieved for the 80 wt% ZSM-5- 20 wt% Al2O3 sample. The reduced bulk density of the electrospun samples increases the probability of reactant and catalyst contact. Additionally, electrospinning is an effective method for reducing particle aggregation and improving catalytic process efficiency.

Constructing mesoporous FeAlOx based catalysts through framework-confined strategy with superior performance for the oxidative dehydrogenation of 1-butene with CO2

The activation of oxygen species is always a challenging problem in the oxidative dehydrogenation (ODH) of 1-butene with CO2. The oxygen species play an important role in improving the conversion, yield, selectivity, and stability of FeAlOx-based catalysts. In this paper, the framework-confined (FC) strategy was used to active the oxygen species. The changed crystalline phase from Fe2O3 to FeAlO4 illustrated the introduction of Fe species destroyed the Al2O3 lattice and more active oxygen species were released. Compared with the WI-Fe2O3/Al2O3 samples, the ratio of active lattice oxygen was increased from 0.03 to 0.1 and the ratio of Fe3+ was also increased from 0.63 to 0.76 in the FC-FeAlOx samples. After doping with other metal species, the ratio of active lattice oxygen was further increased. The 1-butene conversion could reach 80 % and the 1, 3-Butadiene selectivity could reach 33 % over the FC-FeCrAlOx samples. Besides this, the FC-FeCrAlOx samples showed an outstanding thermal stability, which might be caused that Cr species could reduce the coke formation. The FC-FeCaAlOx samples had a higher utilization rate of CO2, which might be caused that Ca species could improve the basicity of the catalyst.

Sintering, microstructure, and mechanical properties of ZrO2-doped Al2O3

ABSTRACT In the present work, the effect of Zr-doping on the sintering, microstructure development, and mechanical properties of polycrystalline Al2O3 was studied. Dopant concentrations of 830 and 2070ppm cationic ratio of Zr in Al2O3 corresponding to 2000 and 5000 wt. ppm of ZrO2 in Al2O3, respectively, were used. The sintering schedule of undoped as well as Zr-doped Al2O3 samples was optimised following a series of precoarsening experiments. The Zr-doped Al2O3 ceramics exhibited controlled grain size and improved density. Upon increasing the Zr-dopant concentration from 830 cat. ppm to 2070 cat. ppm. Zr-doped Al2O3 ceramics having a refined microstructure with a homogeneous distribution of controllably grown ZrO2 in Al2O3 matrix was obtained. Microhardness of the Zr-doped samples showed negligible dependence with Zr-doping, whereas mechanical strength was found to improve with it. The improvement in strength was attributed to the combined effect of improved sinter density, microstructural refinement, and grain-boundary strengthening.

Influence of sintering aids on properties of dense Si2N2O ceramic developed by spark plasma sintering

Through reactive liquid phase sintering, dense and homogenous pellets with a diameter of 40 mm were successfully achieved after 50 min. These samples contain at least 95 vol% of Si2N2O. The microstructure, fracture toughness, coefficient of thermal expansion (673–1673 K), dielectric properties and high-temperature oxidation resistance were investigated to determine the influence of sintering aids such as lanthanide oxides (Sm2O3 and Y2O3) and metal oxide (Al2O3). The nano-sized grains generated have a uniform distribution. The composition of the sintering aid has no influence on the coefficient of thermal expansion or the dielectric properties. The crack propagation mode shifts from transgranular to intergranular in Al2O3 samples, which increases the fracture toughness. The lanthanide oxide samples, on the other hand, outperform the Al2O3 samples in terms of oxidation resistance, as a protective SiO2 and Ln2Si2O7 layer forms on the surface of the oxidized samples.