Changes in compositional fluctuation during sintering of PZT ceramics were studied both for ordinary sintering and for the spark plasma sintering (SPS) method. Generally, sintering is established by diffusion at high temperatures. In ordinary sintering, compositional fluctuation decreased with increasing bulk density. In contrast, compositional fluctuation changed little with increasing bulk density during SPS.
The restoration of ancient ceramics has attracted widespread attention as it can reveal the overall appearance of ancient ceramics as well as the original information and artistic charm of cultural relics. However, traditional manual restoration is constrained due to its time-consuming nature and susceptibility to damaging ancient ceramics. Herein, a three-dimensional (3D) printing technique was employed to accurately restore Chinese Yuan Dynasty Longquan celadon using hollow Al2O3 microsphere-modified 3D printing paste. The results show that the hollow Al2O3 microsphere content plays a vital role in the printability, physical properties, and firing performance of the modified 3D printing paste. The printed green bodies show no noticeable spacing or voids under moderate rheological conditions. The as-prepared ceramic body modified with 6 wt.% hollow Al2O3 microspheres and fired at 1280 °C exhibits optimal bending strength of 56.66 MPa and a relatively low density of 2.16 g∙cm−3, as well as a relatively uniform longitudinal elastic modulus and hardness along the interlayer. This 3D printing technique based on hollow Al2O3 microsphere-modified paste presents a promising pathway for achieving non-contact and damage-free restoration of cultural relics.
The modeling of ceramics with complex geometric structures currently depends on the handcrafted mode, with long cycles, high costs, and low efficiency; additive manufacturing (AM) technology can solve this problem well. Herein, the porcelain clay paste was successfully prepared for the direct ink writing (DIW) 3D printing process of ceramics with complex geometric structures, and the effects of sodium citrate (SC) content on the rheological properties and DIW 3D printability of the porcelain clay paste were investigated in detail. The SC has a vital role in the rheological behavior of porcelain clay paste. Adding SC increases the absolute zeta potential and decreases the viscosity of the paste, while a high SC content will lead to a low storage modulus of the paste. The porcelain clay paste with an SC content of 0.05% and a paste solid content of 75% possesses suitable rheological properties and a storage modulus for DIW 3D printing. The as-prepared porcelain clay paste has high DIW 3D printability at a pressure of 0.5 MPa, and a 3D-printed green body with a well-densified structure can be achieved. After being sintered, the 3D-printed ceramic exhibits high densification and mechanical properties. A green body with complex geometric structures is quickly and precisely modeled by the DIW 3D printing process with the resultant porcelain clay paste as the raw material. This work provides a practical approach to rapidly fabricating ceramics with complex geometrical structures.
AbstractBa1−xSrxTiO3 (x = 0·3, 0·35) ceramics are fabricated by spark plasma sintering (SPS) technique and conventional sintering (CS) route. Their microstructures are determined together with the dielectric and ferroelectric properties. The grain sizes of SPS samples are smaller than those of CS. The differential scanning calorimetry data show that almost no latent heat associated with phase transition can be detected in the SPS sintered ceramics. Raman spectroscopy analysis suggests that the tetragonal phase increases with increasing the grain size, and the higher content of tetragonal phase leads the superior dielectric properties in CS sintered samples. Transmission electron microscopy analysis indicates that domain structure heavily relies on the grain size of ceramics. The poor ferroelectric properties of SPS ceramics are originated from the incomplete development of the tetragonal structure.
The Guangyuan kiln, located in the Sichuan Province, Southwest China during the Song Dynasty (960–1279 A.D.), is renowned for its high-temperature iron-series glazed wares, including pure black glazed ware, hare’s fur glazed ware, glossy brown glazed ware, and matte brown glazed ware. To elucidate the raw materials, processing techniques, and coloration mechanisms of these wares, multiple analytical experiments were employed to investigate chemical composition, microstructure, and the phase of Fe-bearing minerals. We found that glossy brown glazed ware has the highest Fe2O3 content in the glaze (7.67 wt% on average), while pure black glazed ware exhibits the lowest (4.84 wt% on average). Higher Fe2O3 content leads to more iron for Fe-bearing mineral crystallization and larger ε-Fe2O3 precipitation. Based on microscopic observations, pure black glazed ware has numerous 100–250 nm crystalline grains, while hare’s fur glaze ware features dendritic crystal flowers (200–400 nm), which exhibited liquid-liquid phase separation within the glaze, suggesting localized phase separation inducing iron oxide crystallization. Glossy brown glazed ware contains well-developed ε-Fe2O3 crystals (25 µm), and matte brown glazed ware, with the highest CaO and total flux, has acicular anorthite crystals alongside ε-Fe2O3 crystals. In summary, the decorative effect of four different types of iron-series glazed wares is determined by their chemical composition, phase composition, and microscopic structure. The findings offer valuable insights for the study of ancient iron-glazed ware.
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