Yidong Hu,Fan Yang,Guoliang Ren,Jianguo Li,Qiaodan Hu
Preparation of dense Bi 2 Ti 2 O 7 ceramics with single-phase pyrochlore structure is challenging using the conventional sintering method due to its thermal instability at ≥ 650 °C. Here we synthesized dense and phase-pure Bi 2 Ti 2 O 7 ceramics from a mixture of Bi 2 O 3 and TiO 2 by a novel deep undercooling rapid solidification method using the aerodynamic levitation technique. We reported a surprising discovery that the pyrochlore phase can exist with Bi/Ti ratio varying between 0.9 and 1.1. By a comprehensive investigation on the phase purity, crystal structure, oxidation states and electrical properties, we revealed that the pyrochlore structure is primarily stabilized by the solidification process rather than presence of a large amount of Ti 3+ . With the advantages of being containerless, one-step and fast processing, deep undercooling rapid solidification is an effective and efficient approach to prepare dense Bi 2 Ti 2 O 7 pyrochlores, and can be expanded to other thermally unstable compounds to obtain bulk materials.
An-Nan Chen,Jia-Min Wu,Meng-Yue Liu,Li-Jin Cheng,Jing-Yan Chen,Huan Xiao,Xiao-Yan Zhang,Chen-Hui Li,Yu-Sheng Shi
Rapid in-situ solidification of SiO 2 suspension under the joint action of releasing calcium ions and shifting pH has been proposed. When the suspension was heated up to 60 ℃, decomposition of calcium iodate which released calcium ions , as well as hydrolysis of diacetate (GDA) which shifted the pH toward the isoelectric point, both contributed to the solidification of suspension. The controlled coagulation of SiO 2 suspension could be realized via controlled release of high valence counter ions and pH shift at 60 ℃ within 30 min, which could considerably shorten the coagulation time compared with present reported results (1–3 h). Green body prepared by heating the SiO 2 suspension with 6.5 g L −1 calcium iodate and 2.0 vol% GDA at 60 ℃ for 30 min shows uniform microstructure with compressive strength of close to 0.3 MPa. SiO 2 ceramics sintered at 1275 ℃ for 3 h possess homogeneous microstructure with bulk density of 2.06 g cm −3 and flexural strength of 40.3 MPa.
Cementitious solidification is an effective but time-consuming method for waste disposal, and the incorporation of polyacrylamide hydrogel in Portland cement paste is a simple way to enhance the time-efficiency of cementitious solidification. In this study, a series of Portland cement/polyacrylamide hydrogel (PC/PAM) composites suitable for the wastewater treatment were prepared by a one-pot method and their time-dependent reaction processes, mechanical properties and microstructures were tested. Based on the gelation time method, PC/PAM composites showed great solidification efficiency when treating simulated radioactive liquids, organic dye waste and solutions with strong alkalinity and acidity. At temperatures ranging from 5 °C to 40 °C, it took only a few minutes for these composites to solidify wastes. Also, PC/PAM composites containing wastes had a compressive strength that is more than 2 MPa after reacting for 3 days and were suitable for landfill or secondary treatments. The rapid gelation and sufficient strength development demonstrated that PC/PAM composites have great potential for application in solidifying multi-component wastes, especially in some emergency circumstances.
Lithium lanthanum titanate (LLTO) is a promising solid electrolyte for all-solid-state lithium-ion batteries (ASSLIBs), and its total conductivity is dramatically influenced by the ceramic microstructure. Here we report a novel aerodynamic levitation rapid solidification method to prepare dense LLTO ceramics with a dendrite-like microstructure, which can be hardly obtained by conventional sintering. At optimal nominal lithium content and cooling rate, the solidified LLTO ceramic achieved a high total conductivity of 2.5 × 10−4S·cm−1at room temperature, along with excellent mechanical properties such as a high Young’s modulus of 240 GPa and a high hardness of 16.7 GPa. Results from this work suggest that aerodynamic levitation rapid solidification is an effective processing method to manipulate the microstructure of LLTO ceramics to minimize the GBs’ contribution to the total conductivity, which may be expanded to prepare other oxide-type lithium electrolytes.
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