• Ying Yuan

      Articles written in Bulletin of Materials Science

    • Microstructure and microwave dielectric properties of (Zn1–𝑥Mg𝑥)2SiO4 ceramics

      Bo Li Ying Yuan Shuren Zhang Hongmei Jiang

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      (ZnMg)2SiO4 powders was prepared by the sol–gel process, and the microstructure and dielectric properties of (Zn1–𝑥Mg𝑥)2SiO4 microwave materials were investigated systematically. TG-DSC and XRD analyzes for gels indicate that the (ZnMg)2SiO4 with pure willemite phase could be obtained at low temperature of 850°C. Further, XRD illustrates that just small amounts of Mg can be incorporated into Zn2SiO4 lattice, and the solid solution limit of Mg in Zn2SiO4 is about 𝑥 = 0.1. By appropriate Mg substitution for Zn, the sintering range is widened and the sintering temperature of Zn2SiO4 ceramics can be lowered effectively. SEM shows that Mg-substitution for Zn can promote the grain growth of Zn2SiO4. Moreover, the microwave dielectric properties strongly depended on the substitution content of Mg and sintering temperatures. (Zn0.8Mg0.2)2SiO4 dielectrics sintered at 1170°C show the condense microstructure with small uniform grains and best microwave properties: 𝜀r = 6.3, 𝑄 × 𝑓 = 189800 GHz and 𝜏f = –63 ppm/°C.

    • Biotransformation of ginsenoside using covalently immobilized snailase enzyme onto activated carrageenan gel beads


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      Ginsenoside transformation has received significant attention from scientists. The main objective of this study is to use immobilized enzymes in ginsenoside transformation. Factors affecting immobilization process were studied; carrageenan beads treated with polyethyleneimine and then activated using glutaraldehyde (GA) were used for snailase enzyme immobilization. The functionalized gel beads were characterized using Fourier transform infrared spectroscopy to verify the modification process. Furthermore, the optimum conditions for biotransformation of ginsenoside were also deliberatedand showed that optimum biotransformation pH is 4.5 and 5–5.5 and temperature 50 and 60$^{\circ}$C for free and immobilized snailase, respectively. Michaelis constants, $K_{\rm m}$ and $V_{\rm max}$, were also studied. The immobilized enzyme retains 96% of its initial activity after being used 10 consecutive times. The results clearly suggested that ginsenoside transformation was performed using immobilized snailase; this process can reduce the transformation cost as the enzyme can be reused many times.

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