Formation of a unique glass by spark plasma sintering of a zeolite
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Zhijian Shenb) Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden (Received 2 April 2009; accepted 29 June 2009)
A simple approach, order–disorder transition (ODT), has been developed to synthesize a novel glass using ZSM-5 as starting materials. In this process, the ZSM-5 powders were pressed uniaxially in a graphite die and rapidly sintered using spark plasma sintering (SPS). High-resolution transmission electron microscopic images revealed that a few crystalline zeolite fragments were still preserved locally inside the SPS consolidated sample. Vickers microhardness and fracture toughness of this as-prepared transparent glass sample at room temperature reaches 7.3 0.2 GPa and 2.0 0.3MPam1/2, respectively. It is very interesting that these novel bulk transparent glasses exhibit ultraviolet photoluminescence (PL) properties at about 360 nm.
Glass materials normally are synthesized by mixing oxide precursors and melting them at high temperature for extended durations of time followed by quenching the melt. This traditional process is characterized by the high temperature (2273–2573 K), because SiO2 glass has a high softening point (1873 K). Attempts have been made to fabricate glasses at lower temperature, e.g., by sol-gel processing, which has the advantage that the high-purity glass can be prepared at low sintering temperature. Although much progress has been made to fabricate glass by the sol-gel method, it is still a challenge to seek a strategy to obtain a large-size bulk glass.1–6 Still another potential way of fabricating glasses is to consolidate amorphous powders by spontaneous heating and pressurization, e.g., by spark plasma sintering (SPS).7 This technique comprises a combination of a pulsed electrical current and a uniaxial pressure applied to compacted powder bodies. SPS has been used to prepare bulk ceramics, such as biomaterials, composites, dielectrics, superconductors, and transparent ceramics.8–12 Zeolites are microporous crystalline aluminosilicates that possess three-dimensional frameworks composed of tetrahedral units (TO4, where T = Si or Al) linked through oxygen atoms.13 The framework structures are characterized by submicroscopic channels that let zeolites act as molecular sieves.13 Several well-known cases exist where superior performance has been attributed to Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2009.0385 J. Mater. Res., Vol. 24, No. 10, Oct 2009
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crystal size and shape characteristics, which have been widely used in industry such as shape-selective catalysts, ion exchangers, and adsorbents.13 The microporous zeolite has long-range order of crystalline structure, which will collapse and transform to an amorphous phase on heating or pressurization because amorphous materials possess lower free energy.14–16 This behavior is known as amorphization, and it occurs without the system ever
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