Iranian Journal of Materials Science and Engineering

In this research, Germanium-carbon coatings were deposited on ZnS substrates by plasma enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ precursors. Optical parameters of the Ge_1-xC_x coating such as refractive index, Absorption coefficient, extinction coefficient and band gap were measured by the Swanepoel method based on the transmittance spectrum. The results showed that the refractive index of the Ge_1−xC_x coatings at the band of 2 to 2.2 µm decreased from 3.767 to 3.715 and the optical gap increased from 0.66 to 0.72 eV as CH₄:GeH₄ increases from 10:1 to 20:1.

Various analysis techniques were used to investigate the effects of P₂O₅ on the crystallization, mechanical features, and chemical resistance of canasite-based glass-ceramics. The results showed that canasite-type crystals were the primary crystalline phase in the examined glass-ceramics subjected to the two-step heat treatment, while fluorapatite was the secondary crystalline phase in some specimens. The microstructural observations by field emission electron microscope indicated that the randomly oriented interlocked blade-like canasite crystals decreased with an increase in the P₂O₅ content of the parent glasses. Among the examined glass-ceramics, the Base-P2 composition (containing 2 weight ratios of P₂O₅ in the glass) showed the most promising mechanical features (flexural strength of 176 MPa and fracture toughness of 2.9 MPa.m^1/2) and chemical resistance (solubility of 2568 µg/cm²). This glass-ceramic could be further considered as a core material for dental restorations.

 

This study investigates the crystallization behavior and microstructural evolution of lithium metasilicate (Li₂SiO₃) glass subjected to thermal histories designed to emulate the cooling stage of zirconia infiltration in dental restorations. Three thermal routes were examined: (i) a non-isothermal schedule to identify crystallization and melting events, (ii) a controlled isothermal schedule to obtain homogeneous glass–ceramic microstructures, and (iii) a quasi-isothermal natural cooling schedule from the molten state to mimic the thermal profile during infiltration without reproducing actual capillary flow or interfacial reactions. Phase identification and quantitative analysis were performed by X-ray diffraction with Rietveld refinement, and the resulting microstructures were characterized by field-emission scanning electron microscopy. Under isothermal conditions, lithium metasilicate (Li₂SiO₃), lithium disilicate (Li₂Si₂O₅), γ-spodumene (γ-LiAlSi₂O₆), β-lithium phosphate (β-Li₃PO₄), and quartz crystallized with an overall crystallized fraction of approximately 62±0.9 wt.%. In contrast, quasi-isothermal cooling produced a crystallized fraction exceeding 87±1 wt.%, dominated by lithium metasilicate (Li₂SiO₃), β-lithium phosphate, quartz, and cristobalite, with neither lithium disilicate (Li₂Si₂O₅) nor γ-spodumene (γ-LiAlSi₂O₆) detected under the present XRD conditions. The quasi-isothermal route also generated significantly coarser morphologies: average crystal length and thickness were roughly 10-fold and 31-fold larger, respectively, than those in the isothermally treated sample. These results demonstrate that the thermal path strongly governs phase assemblage, crystallized volume fraction, and crystal morphology in lithium silicate glass–ceramics. By clarifying how controlled versus quasi-isothermal cooling histories shape the final microstructure, this work provides a structural basis for optimizing lithium silicate glasses used in zirconia infiltration technology and for guiding future studies on the mechanical and functional performance of these materials.