Surface Crystallization Of Glass Research Articles

Crystallization of sodium calcium silicate glass for highly transparent glass-ceramics

Sodium-calcium-silicate glasses are the most widely used glasses in architectures, photovoltaics, etc. Development of highly transparent sodium-calcium-silicate glass-ceramics is important to extend the application areas. This work investigates the effect of glass composition on the crystallization and transmittance of sodium-calcium-silicate glasses containing ZrO2. It is found that concentration of Na2O in the glasses has large effect on the crystallization behaviors and transmittance of the glass-ceramics obtained. Higher concentration of Na2O in glasses leads to lower glass transition temperature and crystallization activation energy, facilitating the bulk crystallization. Lower concentration of Na2O in glasses results in the surface crystallization of glasses. Similarity in composition of crystalline grains and glass improves the transmittance of glass-ceramics up to above 75% in the visible region, even when the grain size is as large as ~150 μm. Results reported in this work are full of significance for the development of transparent sodium-calcium-silicate glass-ceramics.

Surface crystallization of glass based on blast furnace slags

Using differential thermal analysis, X-ray phase analysis, electron microscopy, and optical microscopy, surface nucleation of crystals in glass, obtained from metallurgical slags with the addition of SiO2, is studied. It is shown that the main phases, crystallized from the surface of the samples are melilite (solid solution of gehlenite 2СаО · Al2O3 · SiO2 in akermanite 2СаО · МgO · 2SiO2) and diopside (CaO · МgO · 2SiO2). The kinetics of the crystallization of glass is studied and the rates of the surface crystal growth are determined in the glass of nine compositions. The influence of the degree of dispersion of the particles of the original glass on the deposition order of the crystalline phases and the degree of crystallinity of the glass is studied.

Nano lamellae composed of yttrium aluminum garnet and yttrium silicate by surface crystallization of glass

Glasses with the mol% composition 17 Y2O3, 33 Al2O3, 40 SiO2, 2 AlF3, 3 CaO, 2 CeF3, 3 B2O3 were thermally annealed at 950 and 1000 °C for different periods of time. The crystallization kinetics as well as the mechanism of surface crystallization was clarified using X-ray diffraction, optical and electron microscopy as well as fluorescence microscopy. The surface nucleation led to a coupled growth of eutectic yttrium aluminum garnet (YAG). This surface layer consists of a lamellar structure composed by YAG and yttrium silicate. The nano lamellae originated from the surface and grew in an interpenetrating cell structure with an interspace of about 50 nm. The YAG surface layer is doped with cerium as seen from the intense broadband fluorescence.

Mutual Influence of Special Components in Baotou Steel Blast Furnace Slag on the Crystallization Behavior of Glass

In the process of glass-ceramics prepared with Baotou steel blast furnace slag, quartz sand, and other raw materials by melting method, the mutual influence of the special components such as CaF2, REXOY, TiO2, K2O, and Na2O in the blast furnace slag on the crystallization behavior of parent glass was investigated using differential thermal analysis (DTA) and X-ray diffraction (XRD). The results show that the special components in slag can reduce the crystallization temperature and promote crystallization of glass phase, which belongs to surface crystallization of glass, and they cannot play the role of the nucleating agent; the major crystal phase composed of diopside, diopside containing aluminum and anorthite, is slightly different from the expected main crystal phase of diopside. Therefore, the nucleating agents of proper species and quantity must be added into the raw materials in order to obtain glass-ceramics. The results have important theoretical guidance meaning for realizing industrial production of Baotou steel blast furnace slag glass-ceramics preparation.

Micro- and macro-cellular sintered glass-ceramics from wastes

Glass obtained from melting a mixture of industrial wastes (panel glass from dismantled cathode ray tubes, mining residues from feldspar excavation and lime from fume abatement systems of the glass industry) has been employed for manufacturing micro- and macro-cellular sintered glass-ceramics. Micro-cellular glass-ceramics, with a closed porosity, were prepared by the direct foaming of the glass mass, determined by viscous flow sintering of fine powders (<37 μm), due to addition of a SiC-based waste (from the polishing of glass articles). The surface crystallization of glass, upon sintering, limited the porosity (being about 50%), but imparted a remarkable crushing strength to the products (up to about 80 MPa), useful for construction applications. Micro- and macro-cellular glass-ceramics, with an open porosity and very low relative density (from 40 to less than 10%), were prepared by the sintering of fine glass powders mixed with sacrificial poly-methyl methacrylate microbeads or deposited on sacrificial poly-urethane sponges. The crystallization, besides imparting a good mechanical strength, allowed the maintenance of the open-celled morphology, useful for filtering applications.

Crystallization and Nonlinear Optical Properties of Potassium Niobium Silicate Glasses

The crystallization of the xK2O · xNb2O5· (1 – 2x)SiO2(x= 0.167–0.250) glasses and glasses close in composition to K2O · Nb2O5· 4SiO2at the ratio K2O : Nb2O5≠ 1 is investigated. In high-silica glasses, the metastable phase separation followed by the bulk multiphase crystallization are observed at temperatures close to the glass transition point Tg. The nanostructured transparent glasses that exhibit the optical second harmonic generation (SHG) effect are formed at the early stages of phase separation. The surface crystallization of glasses with the precipitation of the KNbSi2O7noncentrosymmetric phase occurs at higher temperatures.

Elastic stresses in surface crystallization of glasses: phase transformations at spike tips

Elastic energy, evolving in the crystallization of the tip of a spike located at a planar interface of a solid, is determined by finite element method calculations. The energy per volume of the newly evolving phase depends significantly on the geometry of the spike. In agreement with expectations expressed earlier, it tends to zero for thin needles. The results give additional support to the theoretical concept that differences in the degree of evolution of elastic strains in crystallization in the bulk and near interfaces may be the origin for the preferential surface crystallization of solids in general, and glasses as a special case. In particular, the results explain why sharp corners, edges etc. on the surface of the glass may act as catalysts for crystallization.

Preparation of polar oriented Sr2TiSi2O8 films by surface crystallization of glass and second harmonic generation

Abstract Sr 2 TiSi 2 O 8 films oriented in polar direction ( c -axis) were prepared by surface crystallization of a glass 33.3SrO · 16.7TiO 2 · 50SiO 2 (in mol%) promoted by ultrasonic surface treatment with aqueous suspensions of Sr 2 TiSi 2 O 8 and subsequent heat treatment with high heating rates. The effects of heating rates and suspension particles and media on the orientation were investigated. The thickness of the oriented films was controllable by the heating time and temperature. The resultant transparent films/glass was found to exhibit second harmonic generation, and the tensor components of the second order optical non-linearity were estimated.

Surface Crystallization Phenomena in MgO-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-SiO&lt;sub&gt;2&lt;/sub&gt; Glass

The surface crystallization of glass with a composition MgO(16.7), Al2O3(22.3), SiO2(61) (wt%) was investigated, using XRD, DTA and SEM. Aggregated particles of β-quartz precipitated from fire-polished surface of the glass. The aggregation of non-crystalline spherical particles of about 500-1000A was observed in the region cotiguous to the surface layer containing β-quartz. However, the number of spherical particles decreased with depth from the crystallized surface by the logarithmic function, with substantially the same particle size regardless of the depth. The precipitation of β-quartz, petallite and α-cordierite was observed for the sample with mechanically polished surface. The surface crystallization in this case developed into the glass with the dendrite structure. In the glass having a fire-polished surface, the amounts of β-quartz and petallite passed through maxima during isothermal treatment at 950°C, whereas the amount of α-cordierite increased monotonously with time. This suggests that α-cordierite was formed not only by the direct precipitation from the glass, but also by the transformation of β-quartz and petallite.