This research demonstrates femtosecond (FS) laser-written distributed fiber Bragg gratings (FBGs) sensors within sapphire crystalline fiber, tailored for steelmaking applications. The study precisely assesses sensor stability during a 72-hour exposure to severe conditions, including temperatures reaching 1600°C. The FBGs exhibit excellent signal strength and a maintained high signal-to-noise ratio (SNR) by averting external surface reactions with the sapphire fiber. Extensive annealing at 1600°C purifies the sheathing material. By utilizing an extended 1-meter sapphire fiber, this work surmounts the challenges of cascading FBGs in highly multimode waveguides, enabling FBG signal capture in demanding applications. This research enhances our comprehension of FBG performance in high-temperature environments and paves the way for robust optical fiber systems in steelmaking applications, including tundish probes and submerge entry nozzles (SEN) for molten metal casting. Additionally, the exceptional efficiency and precision of sapphire FBG sensors, in contrast to conventional thermocouples, offer the potential to boost productivity, lower energy consumption, and reduce the carbon footprint in the steel industry.
This study presents a pioneering technique for fabricating highly cascaded first-order fiber Bragg gratings (FBGs) using a femtosecond laser-assisted point-by-point inscription method in highly multimode optical fibers, specifically Sapphire crystalline fiber, and pure silica coreless fiber. Notably, it marks the first successful demonstration of a distributed array comprising 10 FBGs within highly multimode fibers. This achievement is facilitated by a high-power laser technique that yields larger reflectors characterized by a Gaussian intensity profile. These first-order FBGs offer various advantages, including enhanced reflectivity, reduced fabrication time, and simplified spectral characteristics, enhancing their accessibility for interpretation when contrasted with higher-order FBGs. In addition to that it encompasses a comprehensive analysis of the robustness and efficacy of these FBGs, with particular emphasis on their ability to endure extreme temperatures. These FBGs demonstrate an advantageous capability for localized multi-point temperature monitoring, reaching temperatures up to 1500°C with sapphire crystalline fiber and 1100°C with pure silica coreless fiber. This resilience makes them suitable for deployment in harsh environmental conditions. This innovative approach substantially broadens the potential applications of highly multimode optical fibers, particularly in the arena of sensing and communication, where challenges related to thermal gradients and harsh environments prevail. These groundbreaking first-order FBGs signify a substantial advancement in the realm of distributed temperature sensing, offering supreme capabilities for temperature monitoring and signal stability. As such, our work holds the promise of a substantial impact on industries and applications that demand unwavering reliability under extreme conditions.
This study presents an advancement in high-temperature Raman spectroscopy, specifically for analyzing molten materials. It introduces an approach by integrating a fiber-optic Raman probe with a copper block protection system designed to endure extreme thermal conditions. The copper block features an open port designed to accommodate an external telescope with a 3cm focal length, enabling Raman spectra collection in challenging high-temperature environments. A built-in gas channel ensures a continuous flow of argon gas to prevent flux intrusion. The robust copper block acts as a reliable shield, safeguarding the fiber-optic Raman probe within molten materials. This enhancement maintains the probe's integrity and significantly improves its resilience, making it ideal for rigorous investigations of molten substances. This advancement is particularly relevant in metallurgy, where flux materials impact production quality and efficiency. The ability to acquire Raman signals under elevated thermal conditions offers opportunities for studying molecular dynamics, compositional changes, and chemical interactions within molten substances. This introduced direct immersion probing technique has implications, benefiting both scientific and industrial fields. It holds promise for advancing research and exploration in various contexts, from fundamental scientific inquiries to practical applications in metallurgical processes, where flux materials are critical for optimizing production quality and efficiency. This approach enhances the capabilities of high-temperature Raman spectroscopy, making it a valuable tool for investigating molten materials and their properties in diverse settings.
This study presents a novel in situ high-temperature fiber optic Raman probe that enables the study of the physical properties and structure of molten samples at temperatures up to 1400 °C. To demonstrate the functionality of the high-temperature fiber optic Raman probe, different composition mold fluxes were evaluated in this report. The Raman spectra at flux molten temperature were successfully collected and analyzed. A deconvolution algorithm was employed to identify peaks in the spectra associated with the molecular structure of the components in each sample. The experimental results demonstrate that the composition-dependent Raman signal shift can be detected at high temperatures, indicating that molten materials analysis using a high-temperature Raman system shows significant promise. This flexible and reliable high-temperature Raman measurement method has great potential for various applications, such as materials development, composition and structure monitoring during high-temperature processing, chemical identification, and process monitoring in industrial production.
The continuous casting process for steel production utilizes specially designed oxyfluoride glasses (mold fluxes) to lubricate the mold and control the steel solidification process. The composition of the flux controls important properties, such as viscosity, basicity, and crystallization rate, which in turn influences the quality of the as-cast product. However, these fluxes also interact with the steel during casting, causing chemistry shifts that must be anticipated in the design of the flux.
Today, the in-service chemistry of the flux must be determined by taking flux samples from the mold during casting and then processing the samples off-line to determine chemistry and other physical properties, such as viscosity. Raman spectroscopy provides an alternative method for flux analysis, with the possibility of performing direct on-line analysis during casting. Raman spectroscopy has the unique ability to identify specific molecules through well-resolved vibrational bands that provide fingerprint signatures of the structure of the molecules. Specific peaks in the Raman spectra can be correlated with flux chemistry and viscosity.
The work reported here aims to assess the structure and chemical composition of flux samples at high temperatures using fiber-optic Raman spectroscopy. Results from Raman spectral analyses captured the 1300 °C for a range of flux chemistries are presented. The experimental results demonstrate that the composition-dependent Raman signal shift can be detected at high temperatures and that on-line flux analysis using a high-temperature Raman system shows significant promise.
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