Effect of Chopped ZrO2 Fiber Content on the Microstructure and Properties of CaO-Based Integral Ceramic Mold

A chopped ZrO2 fiber (ZrO2(f)) reinforced CaO-based integral ceramic mold was successfully fabricated by stereolithography (SLA) and tert-butyl alcohol (TBA)-based gel-casting, and the effect of chopped ZrO2(f) content on properties of the ceramic mold was investigated. The results show that the ZrO2(f) content had a significant effect on the viscosity of CaO-based ceramic slurry, which directly affects the filling ability of slurry in complex structures of the integral mold. The tiny structures of the ceramic mold cannot be filled completely with a ZrO2(f) content exceeding 3 vol %. The sample fabricated with 3 vol % fiber content showed a harmonious microstructure and exhibited an excellent comprehensive performance with 25 °C bending strength of 22.88 MPa, an 1200 °C bending strength of 15.74 MPa, a 1200 °C deflection of 0.86 mm, and a sintering shrinkage of 0.40%, which can meet the requirements of casting very well.

Effect of chopped ZrO2 fiber content on the microstructure and properties of CaO-based integral ceramic mold

A chopped ZrO2 fiber (ZrO2 (f)) reinforced CaO-based integral ceramic mold was successfully fabricated by stereolithography (SLA) and tert-butyl alcohol (TBA)-based gel-casting, and the effect of chopped ZrO2 (f) content on properties of the ceramic mold was investigated. The results show that the ZrO2 (f) content had a significant effect on the viscosity of CaO-based ceramic slurry, which directly affects the filling ability of the ceramic slurry in complex structures of the integral mold. The tiny structures of the ceramic mold cannot be filled completely with a ZrO2 (f) content exceed 3 vol%. When the content of ZrO2 (f) was 3 vol%, the ceramic slurry could meet the requirement of gel-casting with a viscosity of 0.84 Pa·s. The ZrO2 (f) content played an important role in tailoring properties of the ceramic mold, the sample fabricated with 3 vol% fiber content showed a harmonious microstructure and exhibited an excellent comprehensive performance with a room temperature (25 ºC) bending strength of 22.88 MPa, the elevated temperature bending strength (1200 ºC) of 15.74 MPa, the elevated temperature (1200 ºC) deflection of 0.86 mm and the sintering shrinkage of 0.40%, which can meet the requirements of casting very well.

Sealing Performance and Mechanism of a High-Temperature Near-Neutral Sealing Adhesive in the Ternary System of ZrO2-Al2O3-SiO2

A high-temperature sealing adhesive was prepared using kyanite, andalusite, and magnesia fully stabilized zirconia (Mg-FSZ) as raw materials and nanozirconia (ZrO2) sol as binder. The adhesive is chemically near-neutral and suitable for bonding acid, neutral, or alkaline materials at 1560 °C. The mineral composition, volume expansion, and air permeability of multiple thermal cycles were analyzed. Results showed that the volume expansion caused by the mullitization of kyanite and andalusite can compensate for the sintering shrinkage high temperature. MgO could gradually desolvatize from the Mg-FSZ particles and react with SiO2 and Al2O3 to produce a stable forsterite and magnesium aluminate spinel. Hence, Mg-FSZ became unstable, and cubic ZrO2 transformed into monoclinic ZrO2 when cooled, leading to a volume expansion of the adhesive, which ensured the sealing effect. A larger critical particle size of Mg-FSZ can provide the adhesive with a more persistent volume expansion during thermal cycles due to the more durable desolvatization of MgO. The nanoZrO2 sol binder can improve the sintering of the adhesive and bonding of the joint, resulting in a low gas permeability.

Effect of Urchin-Like Mullite Whiskers on the High-Temperature Performance of Porous SiO2-Based Ceramic Molds

Urchin-like mullite whiskers synthesized by the vapor–liquid–solid growth method were used to improve the high-temperature performance of porous gelcast SiO2-based ceramic molds. Aluminum was used to facilitate the synthesis of polycrystal urchin-like mullite whiskers which acted as bridges between particles. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the microstructures and phase compositions of the sintered ceramic samples, respectively. Urchin-like mullite whiskers with diameters of 0.2~1.0 µm and lengths of 1.0~8.0 µm were successfully synthesized in SiO2-based ceramic. When 15 vol% Al was added, the high-temperature strength at 1200 °C was improved from 8.5 to 27.5 MPa, and the creep deformation was decreased to 0.56 mm. Meanwhile, a sintering shrinkage below 0.3% was obtained, and the de-coring rate was accelerated by 67% compared to that of the pure SiO2-based ceramic. This method showed excellent high-temperature strength and high precision, having remarkable potential in the fabrication of hollow turbine blades.

The effect of CaO/SiO2 and B2O3 on the sintering contraction behaviors of CaO-B2O3-SiO2 glass-ceramics

We investigate the effect of CaO/SiO2 (molar ratio) and B2O3 content on the structure and sintering contraction behaviors of Calcium borosilicate (CaO–B2O3–SiO2, CBS) glass-ceramic through the dilatometer and the Fourier transform infrared (FTIR) spectroscopy. The results show that the sintering-shrinkage of CBS glass-ceramics is promoted dramatically with the increase of CaO/SiO2 to 1.14, and then keeps nearly constant as the CaO/SiO2 further increases. This phenomenon is correlated with the degree of polymerization (DOP) of the Si–O network structure modulated by the CaO/SiO2, additionally, two sintering shrinkage peaks, corresponding to two-step depolymerization, are detected in the sintering-shrinkage curves of the CBS glass-ceramic as the B2O3 content is elevated to 13.6 mol%. Meanwhile, the shrinking rate of CBS glass-ceramics is increased from 8 × 10[Formula: see text] to 37 × 10[Formula: see text] min[Formula: see text] and the softening point is decreased from 736[Formula: see text]C to 691[Formula: see text]C with the increase of B2O3 content from 6.8 to 20.8 mol⋅%. This is due to the introduction of BO3 trihedral into Si–O–Si three-dimensional structure, which greatly reduces the uniformity and symmetry of the networks, inducing the decrease of the strength for the whole Si–O–Si network structures. The results obtained in this paper reveal the relationship between the glass structure and sintering behavior of the CBS glass-ceramic, which gives an avenue to improve its physical properties.