Effects of Heat Treatment of ZnS Nanoparticles Prepared by Hydrothermal Synthesis on Microstructure and Optical Properties in Spark Plasma Sintering (SPS)

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Zinc sulfide (ZnS) is one of the most widely used infrared transmitting window and lens materials for systems operating in the long wave range (8~12 ㎛). ZnS nanoparticles have been intensively studied because of their unique electrical and optical properties and potential applications (optical sensor, solid state solar window layers, photoconductors, phosphors, and catalysts). Therefore various synthetic methods to prepare ZnS nanocrystals in order to obtain desired physical and chemical properties have been developed such as sol-gel, electrochemical deposition, sonochemical, solvothermal, hydrothermal technique and so on. Chemical-vapor-deposited ZnS (CVD-ZnS) has less optical absorption from impurities and can be made in larger sizes with greater homogeneity than hot-pressing (HP) or spark plasma sintering (SPS) of ZnS. There have been many attempts to produce ZnS directly with more or less success for reducing the cost. Since ZnS nanoparticles are prepared by various synthesis methods, the final sintering properties are different. In addition, the optical properties of the sintered body vary depending on the heat treatment of the raw powders. In this study we have investigated the effects of heat treatment of ZnS nanoparticles prepared by hydrothermal synthesis and commercial CVD method for comparison on microstructure and optical properties of spark plasma sintered (SPS) ZnS. The heat treatments of ZnS nanoparticles were carried out at 550℃ for several hours in a vacuum. To observe the change of crystal phases, morphologies and optical characteristics of heat-treated nanoparticles was conducted using XRD analysis, FE-SEM, and FT-IR spectroscopy. As a result of the heat treatment, the reactivity of ZnS nanoparticle surface decreased and pyrolysis phenomenon appeared, which were tentatively considered to affect the infrared transmittance of SPS sintered body. Also wurtzite phase may causes birefringence due to the optical anisotropy began to be produced in more than 950℃. Good optical properties of ZnS ceramics were shown in 950℃ by SPS. When sintering with SPS method, it could be deteriorated in the optical properties by light scattering caused by the refractive index difference among ZnS, impurities, defects, and pores.

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Journal: TechConnect Briefs
Volume: 4, Informatics, Electronics and Microsystems: TechConnect Briefs 2018
Published: May 13, 2018
Pages: 193 - 196
Industry sector: Sensors, MEMS, Electronics
Topic: Photonic Materials & Devices
ISBN: 978-0-9988782-1-8