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The mechanical and thermal behaviors of porous silica-based ceramic cores for preformation of internal cooling passages ingas turbine blades were studied. The silica-based ceramic cores are composed of fused silica and zircon powders, and siliconcarbide powder (SiC) was added to improve the mechanical and thermal properties of the silica-based ceramic cores. Cristobalite, which was formed by crystallization of amorphous silica on SiC surface, improved the flexural strength, bulkdensity and thermal conductivity of silica-based ceramic cores up to an addition of 10 wt% SiC. The SiC on the silica-basedceramic cores enhanced the thermal conductivity, because SiC has higher thermal conductivity compared with matrixmaterials of ceramic cores (fused silica and zircon). However, in case of 20 wt% SiC on ceramic core, the crystallization offused silica was accelerated due to SiC addition which acts as a seed of crystallization, therefore, many microcracks weregenerated by phase transformation (β→α) of cristobalite. As a result, the flexural strength, relative density and thermalconductivity of the ceramic core with 20 wt% SiC were reduced.
The Na2O-CaO-SiO2-MgO-Al2O3-TiO2 (NCSMAT) glass-ceramic having the composition of 49 Na2O, 19 CaO, 31 SiO2,0.25 MgO, 0.50 Al2O3 and 0.25 TiO2 (wt.%) was prepared by conventional method. The crystal structure, phase composition,microstructural, chemical, thermal and dielectric properties of the glass-ceramic were investigated. Using the X-ray diffraction(XRD) results, biphasic structure of the glass-ceramic sample was detected, the crystallite size was found to be 13.21 nm forNa4CaSi3O9 phase and 11.02 nm for Na8Al4Si4O18 phase, and the crystallinity percent was calculated to be 86.74 %. Scanningelectron microscope (SEM) observations show that the NCSMAT glass-ceramic has the fine-grained particle distribution withthe smaller particles than 1 µm. The stretching modes of Si-O-Si bound were detected from Fourier transform infrared (FTIR)spectrum. The NCSMAT glass-ceramic is thermally stable from room temperature to 1173 K and the mass loss of the samplein this range is 1.05%. The density was calculated to be 2,751 kg m−3. The relative permittivity at 1 kHz was found to be 85.35. The alternating current conductivity increases with increasing frequency and obeys the universal power law.
Experimental research on carbon ceramic composites fabricated from carbon and organoclay had been conducted. Electrical conductivity, specific wear rate, density and porosity, morphology, SEM EDX, and XRD were studied. The higher the content of carbon powder, the higher the electrical conductivity produced. Likewise, the higher the sintering temperature of composite increases the electrical conductivity of carbon ceramic composite. The higher the carbon powder content reduces the composite wear rate. Carbon content can increase the hardness of carbon ceramic composites. Composite density tends to be relatively stable with increasing sintering temperature. Increasing the content of carbon powder has shown to reduce composite density. The composite is getting lighter. The higher the carbon content in the composite increases the percentage of porosity of carbon ceramic composites, but it can still increase the electrical conductivity. Generally, carbon ceramic composites contain macroporous.
Cochlodinium red tides occur over a wide area in South Korea, from the south coast to the east coast, and last from Augustuntil October. The damage to fisheries caused by these red tides amounts to tens of billions per year. Chemical spray,sedimentation, and red clay spray methods can prevent red tides, but the most practical method, the red clay spray method,also has a negative effect on marine ecosystems. Therefore, to protect marine life from a Cochlodinium red tide withoutaffecting the marine ecosystem, six ceramic absorbers were applied to a pontoon system, a type of cage fish farm, to comparetheir absorbing capacity for red tide algae that is dependent on the porosity of the ceramic absorber. This experiment wasperformed to determine which ceramic absorber can effectively prevent red tide penetration. Previous studies have shown thatmost fish die when exposed to 8.0 × 103 cells/mL of Cochlodinium polykrikoides for 8 hrs. From the results of this experiment,the concentration of red tide algae that passed through ceramic absorber D (average porosity 60.3%), was 0.14 × 103 cells/mL. For ceramic absorber L (average porosity of 57.3%) it was 0.18 × 103 cells/mL. These two values were the highest red tideabsorption rates recorded in this study. Even when the average porosity was as low as 34.6%, such as in ceramic absorberK that had a small particle size, a high absorption efficiency of 0.18 × 103 cells/mL was observed.
AlN particles coated with nano-BN were synthesized. The AlN/BN ceramic composites were sintered by Plasma Active Sintering (PAS). Because the nano-BN crystals were homogeneously dispersed around the AlN grains of the matrix, the chemical corrosion resistance of AlN/nano-sized h-BN ceramic composites was higher than that of AlN/micro-sized h-BN ceramic composites and monolithic AlN ceramics. Due to the better hydrophobic property of h-BN, the AlN/BN composites had a better hydrophobic property than the monolithic AlN ceramic, at the same time, because of the homogeneous dispersion of the nano-BN, the creepage discharze voltage of AlN/nano-sized BN composites was the highest. AlN particles coated with nano-BN were synthesized. The AlN/BN ceramic composites were sintered by Plasma Active Sintering (PAS). Because the nano-BN crystals were homogeneously dispersed around the AlN grains of the matrix, the chemical corrosion resistance of AlN/nano-sized h-BN ceramic composites was higher than that of AlN/micro-sized h-BN ceramic composites and monolithic AlN ceramics. Due to the better hydrophobic property of h-BN, the AlN/BN composites had a better hydrophobic property than the monolithic AlN ceramic, at the same time, because of the homogeneous dispersion of the nano-BN, the creepage discharze voltage of AlN/nano-sized BN composites was the highest.
Ceramic proppants is crucial in hydraulic fracturing for increasing oil and gas reservoirs. In this study, the ceramic particlesand resin-impregnated ceramic particles were prepared with fly ash, and then ultra-lightweight ceramic particles (proppants)were obtained by double resin-coating process. Crystalline phase and microstructure of the ceramic particles were investigatedby X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Effects of silicon carbide and epoxy resinconcentrations on the phase, apparent density, and breakage ratio of the ceramic particles were all studied systematically. Withincreasing silicon carbide contents, the corundum phase transform to mullite phase, decreasing the apparent density andincreasing the breakage ratios. The double resin-coated ceramic proppants featured smoother surface and less pores than theresin-impregnated samples, accompanying low apparent density (1.94 g/cm-3) and high strength (breakage ratio under 52 MPa,1.69%) when silicon carbide was 3.0 wt.% and epoxy resin concentrations was 55 wt.%. The results suggest the particles bythe effective double resin-coating process possess promising candidates for fracturing proppants in practical applications.
This research investigated the relationship between the quantitative phase crystal structure and mechanical properties of ZrO2ceramic addition of Y2O3, MgO and BaCO3 at 0.0, 2.0, 4.0 and 6.0 mol%. Ceramic samples were prepared using mixed oxidemethod under normal sintering at 1,600 oC with dwell time for 120 min . ZrO2-Y2O3 and ZrO2-MgO ceramics were obtainedwith bulk densities values between 5.324-5.722 g/cm3 while ZrO2-BaCO3 ceramic showed densification values about 4.412-4.827 g/cm3. It was found that ZrO2-Y2O3 and ZrO2-MgO ceramic showed higher fracture toughness values than ZrO2-BaCO3ceramics. Refinement of lattice parameter using Rietveld analysis in ceramic samples revealed the percentage of fraction phaseratios of m-ZrO2, t-ZrO2 and c-ZrO2. The refinement parameters result in sample ceramic which are Y2O3 addition between4-6 mol% obtained a high ratio of t-ZrO2 phase and the result supported optimal mechanical properties. ZrO2-Y2O3 ceramicshowed a higher lattice stain value compared with the additions of other ZrO2 oxides and it was found that lattice strainincrease with high ratio of t-ZrO2 phase. Sample ceramics had crystallite size values between 56.65-82.30 nm. SEMmicrographs revealed morphology and average grain sizes. All samples grains were spherical in shape combined with irregularshape and were gray in color and were obtained with an average grain size between 0.63 -2.18 μm. It was found that the ZrO2-Y2O3 ceramic showed small crystallize size and size of grains. The optimal condition for addition of oxide were found inceramics of ZrO2-Y2O3 and ZrO2-MgO and confirmed that good mechanical properties were obtained from a high ratio of t-ZrO2 phase and fine grain size.
A ceramic layer was produced on a steel pipe inner surface by a centrifugal thermite process. A powdery mixture of ferric oxide and aluminum was used with the glass whose major compositions were SiO2, Na2O, CaO, and MgO. The ceramic layer consisted of the crystalline structures of corundum (α-Al2O3) and hercynite (FeAl2O4). The amorphous phases of Ca3Al2(SiO4)3, MgFeAlO4 and NaAlSiO4 in the ceramic layer were found to be responsible for a significant improvement of the dense structure. The glass addition increased the density of the ceramic layer from 2.9 g/cm3 to 3.6 g/cm3 and the hardness from 1,450 to 1,800 Hv. A ceramic layer was produced on a steel pipe inner surface by a centrifugal thermite process. A powdery mixture of ferric oxide and aluminum was used with the glass whose major compositions were SiO2, Na2O, CaO, and MgO. The ceramic layer consisted of the crystalline structures of corundum (α-Al2O3) and hercynite (FeAl2O4). The amorphous phases of Ca3Al2(SiO4)3, MgFeAlO4 and NaAlSiO4 in the ceramic layer were found to be responsible for a significant improvement of the dense structure. The glass addition increased the density of the ceramic layer from 2.9 g/cm3 to 3.6 g/cm3 and the hardness from 1,450 to 1,800 Hv.
A wide range of possible hazards existing in thermal batteries are mainly caused by thermal runaway, which results in overheating or explosion in extreme case. Battery separators ensure the separation between two electrodes and the retention of ion-conductive electrolytes. Thermal runaways in thermal batteries can be significantly reduced by the adoption of these separators. The high operating temperature and the violent reactivity in thermal batteries, however, have limited the introduction of conventional separators. As a substitute for separators, MgO powders have been mostly used as a binder to hold molten salt electrolyte. During recent decades the fabrication technology of ceramic fiber, which has excellent mechanical strength and chemical stability, has undergone significant improvement. In this study we adopted wet-laid nonwoven paper making method instead of the electrospinning method which is costly and troublesome to produce in volume. Polymeric precursor can readily be coated on the surface of wet-laid ceramic paper, and be formed into ceramic film after heat treatment. The mechanical strength and the thermo-chemical stability as well as the wetting behaviors of ceramic separators with various molten salts were investigated to be applicable to thermal batteries. Due to their excellent chemical, mechanical, and electrical properties, wet-laid nonwoven separators made from ceramic fibers have revealed positive possibility as new separators for thermal batteries which operate at high temperature with no conspicuous sign of a short circuit and corrosion.
Aneis Maasyirah Hamzah,Siti Koriah Zakaria,Siti Zuliana Salleh,Abdul Hafidz Yusoff,Arlina Ali,Mardawani Mohamad,Mohamad Najmi Masri,Sharizal Ahmad Sobri,Mustaffa Ali Azhar Taib,Faisal Budiman,Pao Ter 한양대학교 세라믹연구소 2021 Journal of Ceramic Processing Research Vol.22 No.2
In this work, the effect of various weight percentage of rice husk ash (RHA) in ceramic brick production was investigated interms of mineralogical, physical, chemical and morphological properties. The evaluation of the use of RHA as a raw materialfor ceramic products is tested to determine the linear shrinkage, volumetric shrinkage, water absorption, apparent density andbulk density. These physical results suggested that the addition of RHA can improve the physical properties of ceramic brick. Scanning electron microscopy images confirmed the increased of ceramic strength with the addition of RHA and firingtemperature. In addition, quantitative and qualitative chemical analysis supported the results obtained. Overall, the resultsdemonstrated the high potential of RHA in green technology for ceramic production.