“…This is because that the mullite fibers provide grain seeds for the transformation of fused silica to cristobalite, and accelerate the formation of cristobalite. However, the specific surface area of mullite fibers is small due to the large aspect ratio, and the promotion effect of mullite fibers on heterogeneous nucleation is limited according to the previous research 18,19 …”
Section: Resultsmentioning
confidence: 99%
“…However, the specific surface area of mullite fibers is small due to the large aspect ratio, and the promotion effect of mullite fibers on heterogeneous nucleation is limited according to the previous research. 18,19 Figure 3 illustrates the evolution of linear shrinkage of the specimens after sintering at 1200 • C with various contents of mullite fibers. The linear shrinkage decreases with the increase of mullite fibers, from 0 wt.%, 1.57% to 3 wt.%, .51%.…”
Section: Phase Composition and Microstructurementioning
Mullite fibers composite silica-based ceramic cores were successfully prepared by injection molding. The effects of mullite fibers on the mechanical and thermal properties of ceramic cores were investigated. The results indicated that the linear shrinkage was significantly decreased and the porosity was gradually increased with the increase of mullite fibers. In addition, the flexural strength for the room temperature and the simulated casting temperature of 1500 • C was increased to a maximum value when the content of mullite fibers was about 1 wt.%, and then decreased with the increase of mullite fibers. The mullite fibers of 1 wt.% presented excellent mechanical properties with a linear shrinkage of .65%, a porosity of 6.96%, and a flexural strength of 17 MPa at room temperature and 34.83 MPa at the simulated casting temperature of 1500 • C. Besides, the change in microstructure and properties in various contents of mullite fibers were analyzed.
“…This is because that the mullite fibers provide grain seeds for the transformation of fused silica to cristobalite, and accelerate the formation of cristobalite. However, the specific surface area of mullite fibers is small due to the large aspect ratio, and the promotion effect of mullite fibers on heterogeneous nucleation is limited according to the previous research 18,19 …”
Section: Resultsmentioning
confidence: 99%
“…However, the specific surface area of mullite fibers is small due to the large aspect ratio, and the promotion effect of mullite fibers on heterogeneous nucleation is limited according to the previous research. 18,19 Figure 3 illustrates the evolution of linear shrinkage of the specimens after sintering at 1200 • C with various contents of mullite fibers. The linear shrinkage decreases with the increase of mullite fibers, from 0 wt.%, 1.57% to 3 wt.%, .51%.…”
Section: Phase Composition and Microstructurementioning
Mullite fibers composite silica-based ceramic cores were successfully prepared by injection molding. The effects of mullite fibers on the mechanical and thermal properties of ceramic cores were investigated. The results indicated that the linear shrinkage was significantly decreased and the porosity was gradually increased with the increase of mullite fibers. In addition, the flexural strength for the room temperature and the simulated casting temperature of 1500 • C was increased to a maximum value when the content of mullite fibers was about 1 wt.%, and then decreased with the increase of mullite fibers. The mullite fibers of 1 wt.% presented excellent mechanical properties with a linear shrinkage of .65%, a porosity of 6.96%, and a flexural strength of 17 MPa at room temperature and 34.83 MPa at the simulated casting temperature of 1500 • C. Besides, the change in microstructure and properties in various contents of mullite fibers were analyzed.
“…As the particle size of cristobalite seeds in was further decreased, further crystallisation of cristobalite took place in the sintered ceramic cores, and the volume fractions of cristobalite were calculated to be 35%, and 48% when the D(50) values were 5, and 3 μm, respectively. It can be inferred that, the pre-added cristobalite worked as crystal seeds inducing the transformation of fused silica to cristobalite at high temperature; the larger surface area of cristobalite powders caused by the smaller particle size is beneficial to the inhomogeneous nucleation and crystal growth on the surface of cristobalite seeds [25], and therefore promotes the phase transformation from fused silica to cristobalite, which can probably have strong effect on the properties of sintered ceramic cores [26,27]. Figure 2 (a) XRD patterns recorded from the sintered samples with various particle size of cristobalite seeds; (b) the content of cristobalite in the sintered samples based on K method.…”
In this work, cristobalite seeds were doped in silica-based ceramic cores, and the effect of particle size on the properties of ceramic cores was investigated. With decreasing particle size of the cristobalite seeds, the content of crystallised cristobalite in the sintered ceramic cores increased gradually due to the elevated surface area; the linear shrinkage, bulk density and leachability exhibited drastic increase after gradual decrease, and the flexural strength displayed an opposite tendency. When the mean particle size of cristobalite seeds is 5 μm, the ceramic cores showed optimal comprehensive properties, including linear shrinkage of 0.35%, apparent porosity of 31.2%, leachability of 0.31 g min −1 , creep deformation of 0.12 mm, and flexural strength of 23.5 MPa at home temperature and 26.0 MPa at 1550°C, which well meets the need of ceramic cores for hollow turbine blades. This work may provide new guidance for enhanced properties of silica-based ceramic cores.
In the current study, the ceramifiable-silicone-rubber-composites (CSRs) containing allyl-functionalized cyclophosphazene (CP-Allyl) were prepared for studying as novel fire-resistant insulating materials. Electron-beam (EB) irradiation was applied to obtain the cross-linked networks, and the gel content of 98.8% could be achieved at an irradiation dose of 120 kGy. The thermal, mechanical, flame retardancy and insulation properties were well investigated, and it was found that the involvement of CP-Allyl could have a great influence on the properties. The tensile stress of the EB-irradiated CP-Allyl containing composite reached 5.2 MPa, and its limiting oxygen index was up to 32.4%. After ablation at 700-1000 C, it was observed that the shapes of the CSR samples could be well maintained, and the hard and integrated ceramic phases were formed. All the studies indicate that these CSRs may be the promising insulating materials for wires and cables.
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