Thermal Expansion of Sintered Glass Ceramics in the System BaO-SrO-ZnO-SiO2 and Its Dependence on Particle Size.

The thermal expansion behavior of sintered glass-ceramics containing high concentrations of Ba1-xSrxZn2Si2O7, a phase with very low and highly anisotropic thermal expansion behavior, was investigated. The observed phase has the crystal structure of the high-temperature phase of BaZn2Si2O7, which can be stabilized by the introduction of Sr(2+) into this phase. The high anisotropy leads to microcracking within the volume of the samples, which strongly affects the dilatometric thermal expansion. However, these cracks also have an influence on the nominal thermal expansion of the as-mentioned phase, which decreases if the cracks appear. Below a grain size of approximately 80 µm, the sintered glass-ceramics have almost no cracks and show positive thermal expansion. Hence, coefficients of thermal expansion between -5.6 and 6.5 × 10(-6) K(-1) were measured. In addition to dilatometric studies, the effect of the microstructure on the thermal expansion was also measured using in situ X-ray diffraction at temperatures up to 1000 °C.

Broadband near-IR emission from cubic perovskite KZnF(3):Ni(2+) nanocrystals embedded glass-ceramics.

Transparent KF-ZnF(2)-SiO(2) glass-ceramics were prepared with the precipitation of KZnF(3)Ni(2+) nanocrystals. During excitation with a wavelength of 405 nm at room temperature, a broadband near-IR emission centered at 1695 nm with the FWHM of more than 350 nm was observed, which is originated from the T(2g)3(F3)→A(2g)3(F3) transition of octahedral Ni(2+) incorporated in the KZnF(3) crystalline phase. In comparison to oxide glass-ceramics, a redshift of the luminescence is observed, which is due to the low crystal field of these octahedral Ni(2+). The shift and extension of near-IR emission in the KZnF(3):Ni(2+) nanocrystals embedded in a glassy matrix do not only complete the broadband emission in the whole near-IR region for the Ni(2+) ions-based photonics, but also open an easy way to approach the broadband optical amplifier and tunable lasers operating in the wavelength region near 1800 nm, which was up to now achieved by codoping of several types of active ions.

Nanocrystallization in Oxyfluoride Glasses Controlled by Amorphous Phase Separation.

Transparent bulk glass-ceramics containing ZnF2, K2SiF6, and KZnF3 nanocrystals are successfully obtained from xKF-xZnF2-(100 - 2x)SiO2 oxyfluoride glasses for the first time to the best of our knowledge. The glass transition temperatures of heat-treated samples increase with time and approach values that resemble the temperatures chosen for thermal treatment. During nucleation and crystal growth, the residual glass around the crystals is depleted in fluoride which as glass component usually leads to a decrease in viscosity. The crystallization behavior notably depends on the glass composition and changes within a small range from x = 20 to 22.5 mol %. The occurrence of liquid/liquid phase separation in dependence of the composition is responsible for the physicochemical changes. Two different microstructures of droplet and interpenetrating phase separation and their compositional evolution are observed by replica transmission electron microscopy technique in the multicomponent glassy system. This study suggests that the size and crystal phase of precipitated crystallites can be controlled by the initial phase separation.

Replica extraction method on nanostructured gold coatings and orientation determination combining SEM and TEM techniques.

In the field of electron microscopy the replica technique is known as an indirect method and also as an extraction method that is usually applied on metallurgical samples. This contribution describes a fast and simple transmission electron microscopic (TEM) sample preparation by complete removal of nanoparticles from a substrate surface that allows the study of growth mechanisms of nanostructured coatings. The comparison and combination of advanced diffraction techniques in the TEM and scanning electron microscopy (SEM) provide possibilities for operators with access to both facilities. The analysis of TEM-derived diffraction patterns (convergent beam electron diffraction) in the SEM/electron backscatter diffraction software simplifies the application, especially when the patterns are not aligned along a distinct zone axis. The study of the TEM sample directly by SEM and transmission Kikuchi diffraction allows cross-correlation with the TEM results.

Treatment optimization of aortocoronary dissection as a complication after heart catheterization using coronary computerized tomographic angiography.

We present the case of a 71-year-old patient with a chronic total occlusion of the right coronary artery (RCA) resulting in a retrograde aortic dissection as a complication of coronary intervention. Acute therapy consisted of coronary stent implantation into the proximal RCA to cover the dissection's entry. One day after, computed tomography-guided angiography revealed a progression of the intramural aortic hematoma with a residual dissection at the RCA ostium. Recurrent coronary angiography was performed to implant another stent covering the entry. Imaging at follow-up demonstrated complete coverage of the Dunning dissection and regression of the intramural aortic hematoma.

In situ crystallization of barium zinc silicate in glass-ceramics studied by hot stage scanning electron microscopy.

Glasses with the mol% composition 30ZnO, 10Na(2)O, 10BaO and 50SiO(2) were annealed at 700°C and 760°C ex situ as well as in situ using a hot stage scanning electron microscope (SEM). The formed crystal phase (BaZn(2)Si(2)O(7)) was proved ex situ by X-ray diffraction. Annealing the glass samples in the SEM resulted in a strong surface crystallization, which was monitored for 1 h and 21 min and 2 h and 2 min at the temperatures 700°C and 760°C, respectively. The crystal growth velocities for these two temperatures were determined from a series of micrographs. It is experimentally shown that during the course of the crystallization in this non-isochemical system, the residual glassy phase changes its composition, and hence, the crystal growth velocity depends on time. Furthermore, it is shown that the electron beam irradiation directly affects the nucleation and crystal growth velocities.

Experimental evidence of self-limited growth of nanocrystals in glass.

Growth of nanocrystals precipitated in glasses with specific compositions can be effectively limited by diffusion barriers forming around crystallites. For the first time, we do experimentally prove this concept of self-limited growth on the nanoscale for a SiO(2)/Al(2)O(3)/Na(2)O/K(2)O/BaF(2) glass in which BaF(2) nanocrystals are formed. As shown by advanced analytical transmission electron microscopy techniques, the growth of these BaF(2) crystals, having great potential for photonic applications, is inherently limited by the formation of a ca. 1 nm wide SiO(2) shell.