Readily available temperature sensing in boilers is necessary to improve efficiencies, minimize downtime, and reduce toxic emissions for a power plant. The current techniques are typically deployed as a single-point measurement and are primarily used for detection and prevention of catastrophic events due to the harsh environment. In this work, a multi-point temperature sensor based on wavelength-multiplexed sapphire fiber Bragg gratings (SFBGs) were fabricated via the point-by-point method with a femtosecond laser. The sensor was packaged and calibrated in the lab, including thermally equilibrating at 1200 °C, followed by a 110-h, 1000 °C stability test. After laboratory testing, the sensor system was deployed in both a commercial coal-fired and a gas-fired boiler for 42 days and 48 days, respectively. The performance of the sensor was consistent during the entire test duration, over the course of which it measured temperatures up to 950 °C (with some excursions over 1000 °C), showing the survivability of the sensor in a field environment. The sensor has a demonstrated measurement range from room temperature to 1200 °C, but the maximum temperature limit is expected to be up to 1900 °C, based on previous work with other sapphire based temperature sensors.

In this paper we report the fabrication of glass-clad BaO-TiO₂-SiO₂ (BTS) glass–ceramic fibers by powder-in-tube reactive molten-core drawing and successive isothermal heat treatment. Upon drawing, the inserted raw powder materials in the fused silica tubing melt and react with the fused silica tubing (housing tubing) via dissolution and diffusion interactions. During the drawing process, the fused silica tubing not only serves as a reactive crucible, but also as a fiber cladding layer. The formation of the BTS glass–ceramic structure in the core was verified by micro-Raman spectroscopy after the successive isothermal heat treatment. Second-harmonic generation and blue-white photoluminescence were observed in the fiber using 1064 nm and 266 nm picosecond laser irradiation, respectively. Therefore, the BTS glass–ceramic fiber is a promising candidate for all fiber based second-order nonlinear and photoluminescence applications. Moreover, the powder-in-tube reactive molten core method offers a more efficient and intrinsic contamination-free approach to fabricate glass–ceramic fibers.

This work presents a thorough identification and analysis of the dissolution and diffusion-based reaction processes that occur during the drawing of YBa₂Cu₃O_7−x (YBCO) glass-clad fibers, using the molten-core approach, on a fiber draw tower in vacuum and in oxygen atmospheres. The results identify the dissolution of the fused silica cladding and the subsequent diffusion of silicon and oxygen into the molten YBCO core. This leads to a phase separation due to a miscibility gap which occurs in the YBCO–SiO₂ system. Due to this phase separation, silica-rich precipitations form upon quenching. XRD analyses reveal that the core of the vacuum as-drawn YBCO fiber is amorphous. Heat-treatments of the vacuum as-drawn fibers in the 800–1200 °C range show that cuprite crystallizes out of the amorphous matrix by 800 °C, followed by cristobalite by 900 °C. Heat-treatments at 1100 °C and 1200 °C lead to the formation of barium copper and yttrium barium silicates. These results provide a fundamental understanding of phase relations in the YBCO–SiO₂ glass-clad system as well as indispensable insights covering general glass-clad fibers drawn using the molten-core approach.

Abradable coating systems in aircraft gas turbines minimize the clearance between rotating blade tips and stationary liners, acting as sealants that improve engine efficiency. In this work, abradable liners made of a nickel‐based superalloy substrate are coated with a CoNiCrAlY bondcoat, an intermediate Y ₂ O ₃ ‐stabilized ZrO ₂ (YSZ) layer, and a MgAl ₂ O ₄ abradable top layer. The coated systems are evaluated using both thermal gradient cycling and incursion tests designed to replicate real operating conditions. To enhance bonding strength for thicker abradable coatings, laser ablation is applied to the bondcoat and YSZ layer to increase mechanical interlocking between layers. Furthermore, a combined dense and porous microstructure is introduced in the thick MgAl ₂ O ₄ coating to lower the overall energy release rate while improving toughness near the interface. Three coating configurations are tested: (i) a standard high velocity oxygen fuel (HVOF) sprayed bondcoat with a standard atmospherically plasma sprayed (APS) YSZ/MgAl ₂ O ₄ double‐layer used as a reference, (ii) a laser‐ablated HVOF bondcoat with a laser‐ablated APS YSZ layer and a standard MgAl ₂ O ₄ layer, and (iii) a laser‐ablated HVOF bondcoat with a standard APS YSZ layer and a dense/porous MgAl ₂ O ₄ layer. Both modified liners showed superior incursion performance and no failure after 1500 thermal cycles (125 h at 1390°C).