Al2O3 SiC Research Articles

Transfer of Heteroepitaxial Grown 3C-SiC Layers for Application in Optical Frequency Combs

We developed a process for the fabrication of SiCOI stacks which are a suitable platform for optical devices. Starting from 3C‑on‑Si samples the silicon substrate was removed by wet chemical etching and the remaining 3C‑SiC layers were bonded to two different low refractive substrates (Al2O3 and polycrystalline SiC with a 3 µm thick SiO2 layer on top deposited by PECVD). We found that also bonding onto Al2O3 was possible, the stability of the resulting stack wasn´t strong enough for further processing. In contrast mechanical stable SiCOI stacks could be realized using the oxide coated polycrystalline SiC as substrate. Besides the substrate materials three different bonding approaches (hydrophilic, hydrophobic and adhesive bonding using an HSQ resist) as well as multiple process parameters were analyzed with regard to the bonding performance. The best results could be achieved using the adhesive bonding approach with a bonding temperature ≥ 400°C, a process time ≥ 4 h and a bonding pressure of 96 N/cm2.

Microstructure and enhanced slag resistance of Al2O3–SiC–C refractory castables with addition of ammonium metatungstate

The present study aims to clarify the influence of ammonium metatungstate (AMT) on composition, microstructural evolution and properties of Al2O3–SiC–C (ASC) refractory castables. Castables with different AMT contents were prepared using brown corundum, white corundum, silicon carbide, calcium aluminate cement, and AMT as major raw materials. The results show that hot modulus of rupture, thermal shock resistance and slag resistance were significantly improved for castables with addition of AMT (lower than 1.0 wt%), due to the optimized microstructure from the formation and development of mullite and SiC whiskers in castables. Along with the in-situ formed whiskers in pores, formation of Fe7W6 from the reaction between W ions in castables and Fe ions in the penetrated molten slag led to the enhanced slag viscosity and inhibited continuous penetration (penetration index decreased from 30.5% to 20.2%) for castables with AMT ranging from 0 to 0.5 wt%. The research of this work provides a new insight into microstructure and high-temperature properties enhancement of ASC refractory castables.

Investigation of the effect of silicon carbide nanoadditives on the structure and properties of microfine corundum during electroconsolidation

The effect of nanodisperse powders on the microstructure and properties of corundum was studied. The microstructures of composites under different modes of electroconsolidation are considered. The phase composition and some mechanical properties of the composite materials obtained by the electrosintering method were determined. A comparative assessment of the properties is provided and recommendations are formulated for further improvement of the physical and mechanical properties of Al2O3–SiC composites, where silicon carbide nanopowders are used as additives.

A novel iterative algorithm to improve segmentations with deep convolutional neural networks trained with synthetic X-ray computed tomography data (i.S.Sy.Da.T.A)

We propose a novel iterative segmentation algorithm (i.S.Sy.Da.T.A: Iterative Segmentation Synthetic Data Training Algorithm) employing Deep Convolutional Neural Networks and synthetic training data for X-ray tomographic reconstructions of complex microstructures. In our method, we reinforce the synthetic training data with experimental XCT datasets that were automatically segmented in the previous iteration. This strategy produces better segmentations in successive iterations. We test our algorithm with experimental XCT reconstructions of a 6-phase Al-Si Matrix Composite reinforced with ceramic fibers and particles. We perform the analysis in 3D with a special network architecture that demonstrates good generalization with synthetic training data. We show that our iterative algorithm returns better segmentations compared to the standard single training approach. More specifically, phases possessing similar attenuation coefficients can be better segmented: for Al2O3 fibers, SiC particles, and Intermetallics, we see an increase of the Dice score with respect to the classic approach: from 0.49 to 0.54, from 0.66 to 0.72, and from 0.55 to 0.66 respectively. Furthermore, the overall Dice score increases from 0.77 to 0.79. The methods presented in this work are also applicable to other materials and imaging techniques.

Study of the performance of a coolant mixed with an Al2O3/SiC nanomaterial in an engine radiator

One of the important components of a car to control the temperature of a car's engine is the radiator. To increase the heat absorption capacity of the coolant/fluid used in the radiator with minimum pumping power, innovative fluids called nanofluids have become the main area of research these days. Therefore, with the development of new technologies in the field of “nano-materials” and “nano-fluids,” the physical and chemical properties of coolant/fluid can be improved which in turn improves the radiator and engine efficiency, and reduces radiator weight and size. In this article, the heat transfer by forced convection in nanofluids based on Al2O3 and SiC was studied experimentally and compared to that of base fluid in an automotive radiator. The nanofluid is mixed with ethylene glycol and the fluid is prepared by the sonication method. The nanofluids were prepared by varying the nanomaterials and the amounts of nanomaterials in the base fluid and their heat transfer performance in the radiator was analyzed using ANSYS FLUENT software. Approximately 15% and 12% increase in radiator efficiency by using Al2O3 mixed nanofluid and SiC mixed nanofluid, respectively.

A study on the effect of metal skeleton auxiliary heating device on microwave heating efficiency of batch Al2O3 ceramics

In order to improve the microwave heating efficiency of the batch Al2O3 ceramics, according to generalized transmission line theory in this paper, the relationship between the amplitude and phase of the electromagnetic field in the microwave resonant cavity was deduced by using the distribution relationship of voltage and current on the transmission line. SiC auxiliary heating plate was used as the auxiliary heating device. Based on the reflection principle of metal material to electromagnetic wave, the metal skeleton was added to SiC auxiliary heating plate. The COMSOL multi-physics field simulation software was used for simulation. The results showed that the addition of metal materials could change the intensity and distribution of the electromagnetic field on SiC auxiliary heating plate and Al2O3 ceramic blocks, so as to affect the microwave energy utilization rate of heating area and the heating efficiency of Al2O3 ceramic blocks. The numerical simulation results showed that the microwave energy utilization rate of the heating area could be improved by adding the metal skeleton in the SiC auxiliary heating plate and employing a reasonable design, so as to improve the overall heating efficiency of the Al2O3 ceramic blocks. Compared with the traditional SiC auxiliary heating device, the heating efficiency of Al2O3 ceramic blocks was improved by 26.4%, and the overall temperature uniformity was improved by 12.5%.

In situ synthesis of Al2O3–SiC powders via molten-salt-assisted aluminum/carbothermal reduction method

Al 2 O 3 –SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al 2 O 3 –SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures.

Enhanced performance of Al2O3–SiC–C castables via in-situ formation of multi-reinforced phases by introducing surface treated composite metal powders

Al2O3–SiC–C (ASC) castables were prepared with bauxite and silicon carbide as major raw materials and introducing large amount of surface treated composite metal powders (STCMPs) as antioxidant. Their comprehensive properties were greatly improved attributed to the in situ formation of multi-reinforced phases including carbide silicon whiskers and mullite fibers in the matrix. Compared with the corresponding samples without STCMPs, the high temperature modulus of rupture of those with 6 wt% STCMPs calcined in air increased by 47.3% and with 8 wt% STCMPs calcined in reducing atmosphere increased by 220%. The retained CMOR ratio of the sample with 6 wt% STCMPs calcined in reducing atmosphere was high up to 50% after 5 cycles thermal shocks. Moreover, the oxidation index and slag erosion index of samples with 6 wt% STCMPs were decreased by 45% and 74%. This work provides a new perspective for the preparation of ASC castables with excellent high-temperature performance.

Enhancing surface insulation of epoxy composite by constructing nanofiller‐skeleton charge channel

AbstractWith the increase of voltage level, the surface flashover of epoxy composite insulation material becomes an important issue, which restricts the development of UHV (Ultra High Voltage) transmission technology. In this article, a method of using SiC skeleton to construct charge channel was proposed, which can enhance the surface insulation performance of epoxy composite. In addition, we investigated the influence of SiC skeleton structure on charge dissipation and flashover voltage. At the same time, we explored the synergistic influence mechanism of SiC and Al2O3 nanofillers and SiC skeleton on the surface flashover characteristics of epoxy resin. The results showed that the SiC skeleton effectively enhances the surface insulation performance of epoxy resin. When Al2O3 nanofiller and SiC skeleton act simultaneously, the flashover voltage enhancement reached 13.65%. Combining with finite element simulation, the flashover voltage enhancement mechanism of epoxy resin after modified by nanofiller‐skeleton method was analyzed. It showed that the internal charge channel formed by the SiC skeleton plays an important role in suppressing the local field distortion. The results of the study provided a new idea for modifying epoxy composite to improve the flashover voltage.

Spark Plasma Sintering of Al2O3–SiC Ceramics. Study of the Microstructure and Properties

Spark Plasma Sintering of Al2O3–SiC Ceramics. Study of the Microstructure and Properties

Study on machining characteristics of SiC–Al2O3 reinforced aluminum hybrid nanocomposite in conventional and laser-assisted turning

In the present paper, the laser-assisted machining (LAM) of aluminum nanocomposite reinforced with SiC–Al2O3 nanoparticles was carried out using turning process. The laser power, depth of cut and cutting speed were considered as control factors. The optimization of factors was performed using Taguchi method by seeking the smallest surface roughness and cutting force. The results were compared with conventional machining (CM) process. According to the results, depth of cut had maximum influence on the cutting force in the LAM and CM processes. However, for surface roughness, the cutting speed and feed exhibited the major effect in LAM and CM processes, respectively. Moreover, the LAM had a reduction of 26% in the cutting force in comparison with CM process at optimal conditions. The lower cutting force resulted in a reduction of 51% in the surface roughness during LAM in comparison with CM process.

Improvement of Structures and Properties of Al2O3 Coating Prepared by Cathode Plasma Electrolytic Deposition by Incorporating SiC Nanoparticles

A serious issue in the preparation of Al2O3 coatings by cathode plasma electrolytic deposition (CPED) is that the coatings have a porous structure, which is detrimental to their protective performance. Therefore, to address this problem, SiC nanoparticles are incorporated into the Al2O3 coating in this study. A series of Al2O3–SiC composite coatings are efficaciously prepared on the surface of 316L stainless steel by CPED. The microstructures, compositions and phase components of the composite coatings are characterized; the electrochemical corrosion resistance and tribological behavior are evaluated; and the mechanism of SiC nanoparticles in the coating formation process is discussed in detail. The results indicate that the Al2O3 coating prepared by CPED consists of α-Al2O3 and γ-Al2O3, and the former is the main crystalline phase. With the incorporation of SiC nanoparticles in the coating, the content of α-Al2O3 gradually decreases, almost disappearing, accompanied by an increase in γ-Al2O3 as the main crystalline phase. The incorporation of SiC nanoparticles significantly reduces the surface irregularity and roughness of Al2O3 coatings and remarkably improves the corrosion resistance and wear resistance of the Al2O3 coatings. The improvement in corrosion resistance and anti-wear properties can be explained by the fact that the SiC nanoparticles effectively weaken electrical breakdown and increase the compactness of the coatings.

Effect of modified coal tar pitch addition on the microstructure and properties of Al2O3–SiC–C castables for solid waste incinerators

Al2O3–SiC–C (ASC) castables were performed using brown alumina, SiC, ultrafine α-Al2O3, microsilica, Si powder, calcium aluminate cement and modified coal tar pitch (CP) as starting materials. Effect of CP content and firing atmosphere on the microstructure and properties of ASC castables were investigated. The results show that cold strength, hot strength, thermal shock resistance and slag resistance of ASC castables were slightly improved with increasing of CP content. As an example of castables containing 2 wt% CP, it can be found that the cold strength and hot strength of the sample after firing in oxidizing atmosphere and reducing atmosphere were higher than that of in weak oxidizing atmosphere, and the sample after firing in reducing atmosphere possess overall properties including higher strength, good thermal shock resistance and slag resistance. The differences in properties of ASC castables with different CP addition were closely related to their phase compositions, microstructure including pore size distribution, and the amount of in-situ formed SiC whiskers.

Analysis of Parametric Influences and Tribological Behaviour of Al 6063–SiC–Al2O3

Analysis of Parametric Influences and Tribological Behaviour of Al 6063–SiC–Al2O3

Superlubricity and running-in wear maps of water-lubricated dissimilar ceramics

Water-lubricated ceramic sliding tribosystems, when operating under superlubricity conditions, reduce frictional energy losses in many applications. Aqueous superlubricity of 5 dissimilar ceramic tribopairs (Si3N4–Al2O3, Si3N4-ZTA, Si3N4–SiC, Al2O3–SiC, ZrO2–SiC) was thus studied in a series of ball-on-disk tests, with the identification of wear mechanisms and lubrication regimes, while introducing a running-in wear map approach to elucidate transient tribological phenomena. All pairs presented superlubricity for certain combinations of normal load and sliding speed, after a running-in period where mechanical and thermal severities of contact remained mostly below their respective threshold values, promoting mild wear regimes. Load-carrying capacity of ZrO2–SiC was the highest due to high homogeneity and low roughness of the tribofilm on SiC disk’s wear track.

Dependence of composition of SiC–Al2O3 composite absorbers on microwave heating characteristics

Spark plasma sintering technology was used to prepare SiC–Al2O3 composite absorbers with a range of compositions. Scanning electron microscopy showed that of the components was uniform in all compositions. The influences of composition, heating time, and microwave power of the composite absorbers on their heating characteristics were analyzed. As the microwave power was increased from 500 W to 1000 W, the temperature achieved by the absorber increased. After being heated for 24 min at a microwave power of 1000 W, all samples maintained a constant temperature. The absorber with 40mass% Al2O3 content reached the highest temperature (952 °C); the absorber with 95 mass%Al2O3 content achieved the lowest temperature (313 °C). These findings have importance as a reference for precise temperature control in microwave heating of composite absorber.

Effect of carbon black on corrosion resistance of Al2O3–SiC–C castables to SiO2–MgO slag

Metallurgical solid waste recycling is the shape of things to come in green development of Chinese iron and steel industry. Utilization of ironworks slag for producing mineral wool at high temperature is an important approach. However, refractory lining is seriously corroded by the SiO2–MgO based slag at 1600 °C during the production process. Different production steps need different atmospheres, the changeable service atmospheres (air and reducing atmosphere) put forward high requirements for slag resistance. The Al2O3–SiC–C castables containing carbon black are usually used in iron runner, which faces high-temperature service condition of 1450 °C–1500 °C. Nevertheless, the function of carbon black in the Al2O3–SiC–C castables at 1600 °C is till essentially unknown. In the current study, the carbon black was introduced to tabular alumina based Al2O3–SiC–C castables to improve corrosion resistance to SiO2–MgO based slag at 1600 °C. The result showed that 0.4 wt% carbon black was suitable for the castables, which the slag resistance of castables was significantly improved. The carbon black had contributed to block slag by wettability resistance. By comparison with the castables without carbon black, the corrosion index and penetration index had been reduced by 20.2% and 28.0%, respectively, under air atmosphere. And there were little corrosion or penetration under reducing atmosphere for castables with 0.4 wt% carbon black. For the mechanical properties, the Al2O3–SiC–C castables with 0.4 wt% carbon black could serve production process although the carbon black impaired the physical properties.

The critical role of aggregate microstructure in thermal shock resistance and slag resistance of Al2O3–SiC–C castable

In this study, four types of commercial tabular corundum were selected as aggregates, and four Al2O3–SiC–C castables were prepared under same conditions. The microstructure characteristics of the aggregates were observed. The thermal shock resistance and slag resistance mechanism were evaluated. Dendritic pores were proven to be beneficial for relieving and guiding thermal stress. According to the Lobe method, the dendritic pores provided the aggregates with a higher thermal conductivity and better thermal stability than the circular pores. The role of the aggregate microstructure in resisting slag erosion was discussed through thermodynamic and kinetic analyses. The presence of dendritic pores and a small neck size led to a faster dissolution rate during the slag erosion process. At the same time, the dissolution rate and dissolution amount increased, resulting in the faster supersaturation of the slag. Based on Ostwald's supersaturation theory, a thicker spinel isolation layer would be precipitated on the inner walls of the slag erosion path, thereby preventing the further erosion of the slag.

Effects of different carbon-containing calcium aluminate cements on the microstructure and properties of Al2O3–SiC–C castables

The microstructure and properties of Al2O3–SiC–C castables with spherical asphalt, high-content carbon-containing calcium aluminate cement (HCCAC), and carbon nanotube/calcium aluminate cement (CNTs/CAC) as carbon sources, respectively, were investigated. The microstructure of castables was characterized by scanning electron microscopy and transmission electron microscopy. The results showed that three kinds of SiC whisker structures were formed in the castable matrix with these carbon sources: “independent cluster structure” (SC specimen), “discontinuous network structure” (HC specimen), and “continuous network structure” (CC specimen), respectively. By comparison with the SC and HC specimens, the residual strength ratio of the CC specimen after thermal shock reached 39.59%, which is 35% and 33% higher, and the corrosion index reached 9.58%, which reduced by 57% and 50%, respectively. The continuous network SiC whiskers formed in Al2O3–SiC–C castables with CNTs/CAC improved significantly the thermal shock resistance and slag corrosion resistance of castables due to their effective crack deflection and better non-wettability with slag.

The Modeling of the Fracture of Three-Phase Ceramic Composite

In the present study, elastic and strength properties of three-phase Al2O3–ZrB2–SiC composite are investigated based on numerical modeling. Representative volume element (RVE) consisting of Al2O3 matrix, pores, and ZrB2 and SiC inclusions is built based on the experimental data. The uniaxial tension loading of the RVE model under plane strain conditions is considered. The relations of an isotropic elastic-plastic medium with the Drucker–Prager yield criterion are used as constitutive equations. The determination of the effective mechanical properties of the composite is based on the analysis of numerical averaged stress-strain curves. The simulation results demonstrate that the cracks nucleate in the regions of high stress concentration caused by the pore shape. The alumina matrix fractures due to the criterion based on the tensile pressure, while the fracture of inclusions occurs when the criterion based on the accumulated inelastic strain is fulfilled. The influence of the fraction of SiC inclusions on the effective elastic properties of the composite material was studied. It was shown that the elastic moduli weakly depend on the increase of SiC volume fraction in the considered range from 0 % to 34 %.