Interior-collapsing mechanism by hydrothermal process of the MgAl2O4/MgO porous ceramic

Abstract

Ceramic core is a critical component in the super-alloy turbine blade casting. In our previous work, a novel multi-phase MgAl2O4/MgO porous ceramic was prepared for this purpose. The most important property was that it crumbled completely after hydrothermal treatment in just pure water, due to the hydration of MgO. In this work, the hydration process of the MgO embedded in the inert matrix was investigated in detail. The collapse behaved as an interior destruction without any bulk expansion of the sample. The hydration percentage was the only factor related to the water-collapsibility. The morphology of hydration product indicated that the reaction advanced in particular direction. Based on the finite element analysis for the expansion effect on the porous structure, the interior-collapsing mechanism was proposed. During the hydration process, the MgO grains exerted pressure to the surrounding matrix and induced the collapse in the adjacent structure. This process took place throughout the matrix. Finally, the sample crumbled completely to the powders. No bulk dilatation was detected before the powdering, indicating that the collapse process would not exert pressure outward. Thus the alloy blade would not be damaged during the removal of the ceramic core. It was also predicted that the decrease in the MgO grain size was beneficial to the water-collapsibility.

Cuttlefish-Bone-Structure-like Lamellar Porous Fiber-Based Ceramics with Enhanced Mechanical Performances

“…While using Al 2 O 3 as the binder, porous fibrous ceramics possess a relatively high compressive strength (2.78–3.40 MPa) and the highest bulk density (0.69–1.17 g·cm –3 ) simultaneously, whereas the bulk density also significantly increases. Hence, compared to porous fibrous ceramics bonded with different binders, − the synthesized CLPFCs bonded with mullite-SiO 2 possess a unique integration of low bulk density (0.48 g·cm –3 ) and excellent compressive strength (4.54 MPa). Furthermore, high-temperature compressive strength tests of porous fibrous ceramics are still lacking in most of the previously published studies, whereas the high-temperature compressive strength of CLPFCs in this work is investigated and has been enhanced up to 3.45 MPa at 1300 °C as illustrated in Figure .…”

“…On the other hand, the lamellas of the CLPFCs actually should be regarded as the binder with a specific structure that has significant influences on the microstructure and mechanical properties of the porous fibrous ceramic. Among diverse binders that have been utilized to fabricate porous fibrous ceramics, SiO 2 is one of the most common high-temperature binders and has been widely applied in porous fibrous ceramics. , The introduction of other binders like B 2 O 3 , and Al 2 O 3 ,, has been confirmed to be beneficial to reinforcing the porous fibrous ceramics. However, the low melting point of SiO 2 and B 2 O 3 tremendously limits their tolerance capacity and service life in the extremely high temperature environment.…”

Solid-phase sintering and vapor-liquid-solid growth of BP@MgO quantum dot crystals with a high piezoelectric response

“…Theoretically, this was because the Raman spectrum detects vibrations from nonpolar symmetric molecules [40,41], and the BP@MgO QD crystals are strongly polarized crystals with weak vibrations from symmetric molecules. In other words, different from MgO crystals [42,43], the lack of Raman signal just proved that the symmetry of the MgO QDs was broken, or even that it had no symmetry at all. In contrast, the FTIR spectrum showed ample information from polar molecules (Fig.…”

Hydrolysis‐induced simultaneous foaming and coagulation casting of secondary aluminum dross aqueous suspension

“…Porous ceramics possess low bulk density, large specific surface area, high specific strength, excellent permeability, stable physical and chemical properties, leading to the wide application in lightweight structural materials, thermal insulations, catalyst supports, filters, and so forth. 14,15 For ceramics forming, novel colloidal forming methods including gel-casting, direct coagulation casting method, and spontaneous coagulation casting have distinct advantages in the uniformity of green body with complex shape. 16,17 In addition, another colloidal forming approach, namely, the hydrolysis-assisted solidification (HAS) utilizes the easy hydrolysis of AlN to generate AlOOH in suspensions with high solid loading and little amount of AlN, commonly less than 5 wt.%.…”