Sol–gel derived Ba/SrTiO3–MgF2 solar control coating stack on glass for architectural and automobile applications

Fully dielectric solar control coatings based on alternating layers of Ba (or Sr) TiO3 and MgF2 were deposited on soda lime glass substrates. Three-layered stacks BaTiO3/MgF2/BaTiO3 and SrTiO3/MgF2/SrTiO3 were generated using BaTiO3, SrTiO3 and MgF2 sols deposited on glass using dip coating technique. The multi-layered coating stack was fired at 450oC with different heating rates using a conventional muffle furnace and a conveyorized belt furnace, by which two methods of heat treatment were investigated. Heat treatment after deposition of each layer and a consolidated firing of the three-layered stack with intermediate drying between the layers were carried out and optical properties of the coatings compared. The heat treated coatings were characterized for their UV–Vis–NIR transmittance, microstructure, phase purity, thickness and refractive indices. The coating stack based on BaTiO3 as the high refractive index material in conjunction with MgF2 exhibited better solar control properties than SrTiO3 as the high refractive index material. Moreover, a fast firing of the BaTiO3/MgF2/BaTiO3 stack in a conveyorized belt furnace yielded good NIR blocking and solar control properties, whereas slow firing in a muffle furnace exhibited ~ 80% visible light transmittance with an NIR transmittance of ~ 75%

Optical properties of multilayer BaTiO3/SiO2 film structures formed by the sol–gel method

Multi-layer film structures BaTiO3/SiO2 with a thickness of ~1 μm containing up to 14 pairs of layers were synthesized by the sol–gel method with sequential heat treatment. It is shown that the synthesized structures are X-ray amorphous. The formation of bands in the transmission and reflection spectra caused by interference effects is demonstrated. A more regular structure exhibits a photon band gap (opacity band) in the visible range with main minimum at 636 nm and corresponding maximum in the reflection spectra. Dispersion characteristics of barium titanate films with different concentrations of initial sols were studied and an increase in the refractive index with an increase in the concentration of sol was demonstrated. For a sol with a concentration of 60 mg/ml, the refractive index in the spectral range of 390–1600 nm is 1.88–1.81. The prospects of sol–gel technology for the formation of BaTiO3/SiO2 structures for nanophotonics and solar radiation converters are discussed

Оптические свойства многослойных пленочных структур BaTiO3/SiO2,сформированных золь–гель-методом

Золь–гель-методом с последовательной термообработкой синтезированы многослойные пленочные структуры BaTiO3/SiO2 толщиной _ 1 μm, содержащие до 14 пар слоев. Показано, что синтезированные структуры являются рентгеноаморфными. Продемонстрировано формирование в спектрах пропускания и отражения полос, обусловленных интерференционными эффектами. Для более регулярной структуры показано наличие фотонной запрещенной зоны (полосы непрозрачности) в видимом диапазоне с основным минимумом 636 nm с соответствием экстремумов в спектрах пропускания и отражения. Исследованы дисперсионные характеристики пленок титаната бария, различающихся концентрацией исходных золей и продемонстрировано увеличение показателя преломления с увеличением концентрации золя. Для золя с концентрацией 60mg/ml значение показателя преломления составляет 1.88−1.81 в спектральном диапазоне 390−1600 nm. Обсуждаются перспективы золь–гель-технологии формирования структур BaTiO3/SiO2 для нанофотоники и конверторов солнечного излучения

Upconversion emission from erbium doped sol-gel derived ВаТiOз powders and coatings

Upconversion is a process where light can be emitted with photon energies higher than those of the light generating the excitation (www.rp-photonics.com/upconversion). Diverse inorganic matrices doped with trivalent lanthanides - erbium and holmium exhibit upconversion, transferring infrared light into visible. Thus the effect attracts attention for detection and visualization of infrared radiation. Recently we reported that sol-gel derived barium titanate possessing refractive index about 1.9 in amorphous state can be used as component of optical interference filter in combination with low refractive index films as silica or magnesium fluoride. At the same time room-temperature luminescence of lanthanides in sol-gel derived barium titanate makes the material and method promising for light conversion. In this work we investigate erbium upconversion emission from sol-gel derived BaTiO3 films and powders

Electro-spark coatings for enhanced performance of twist drills

Surface engineering approaches are being increasingly employed for enhancing the effective life of twist drills with a view to reduce machining costs. The electro-spark coating (ESC) technique provides a promising means of depositing wear resistant coatings that can potentially enhance the performance of these tools. However, it is often necessary to also optimize the machining conditions for coated tools to achieve an enhanced tool life. In the present investigation, varying spindle speeds were employed at a fixed vertical feed to evaluate the performance of WC-8Co ESC coated HSS drills in comparison to bare HSS drills. The number of holes drilled before reaching a preset average flank wear (0.5 mm), or catastrophic failure of the drill, was taken as the measure of tool life. The drill flank wear, monitored at regular intervals, as well as the cutting torque and thrust measured for all holes, were considered to be the key criteria for optimizing the cutting conditions. Results indicate that the WC-8Co coated drill tool life can be increased by a factor of more than 5, depending on the machining conditions selected. Furthermore, flank wear of the drill was found to increase rapidly at the end of drill life. Cutting torque data was also found to provide a useful indicator for predicting the end of tool life

Sol-gel synthesis and transmission of BaTiO3/SiO2 multilayer coatings

В работе изложены результаты формирования золь-гель методом многослойных покрытий, отличающихся показателем преломления BaTiO3/SiO2, на кварцевых и кремниевых подложках. Показано, что многослойные покрытия после термообработки при температуре 450 єС формируют полосу непрозрачности на спектре пропускания с минимумом 693 нм для 14 пар слоев BaTiO3/SiO2, уменьшая пропускание до 35 %, при этом пропускание в ИК-диапазоне 1000–2000 нм ослабляется до 70–75 %. Пленки являются рентгеноаморфными после термообработки при температурах 450 и 600 єС. Обсуждается перспектива применения разрабатываемых фильтров для оптики и нанофотоники. The paper presents a method for the formation of multilayer coatings differing in the refractive index of BaTiO3 / SiO2 on quartz and silicon substrates. It is shown that multilayer coatings after heat treatment at 450oC create a dip in the optical transmission spectrum at 693 nm for 14 pairs of BaTiO3 / SiO2 layers, reducing the transmission to 35 %, while the transmission in the IR range of 1000–2000 nm is attenuated to 70–75 %. The films are amorphous for X-ray diffraction analysis after heat treatment at 450 and 600 °C. The prospects of using the developed filters for optics and nanophotonics are discussed

Evaluation of prognostic risk models for postoperative pulmonary complications in adult patients undergoing major abdominal surgery: a systematic review and international external validation cohort study

Background Stratifying risk of postoperative pulmonary complications after major abdominal surgery allows clinicians to modify risk through targeted interventions and enhanced monitoring. In this study, we aimed to identify and validate prognostic models against a new consensus definition of postoperative pulmonary complications. Methods We did a systematic review and international external validation cohort study. The systematic review was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched MEDLINE and Embase on March 1, 2020, for articles published in English that reported on risk prediction models for postoperative pulmonary complications following abdominal surgery. External validation of existing models was done within a prospective international cohort study of adult patients (≥18 years) undergoing major abdominal surgery. Data were collected between Jan 1, 2019, and April 30, 2019, in the UK, Ireland, and Australia. Discriminative ability and prognostic accuracy summary statistics were compared between models for the 30-day postoperative pulmonary complication rate as defined by the Standardised Endpoints in Perioperative Medicine Core Outcome Measures in Perioperative and Anaesthetic Care (StEP-COMPAC). Model performance was compared using the area under the receiver operating characteristic curve (AUROCC). Findings In total, we identified 2903 records from our literature search; of which, 2514 (86·6%) unique records were screened, 121 (4·8%) of 2514 full texts were assessed for eligibility, and 29 unique prognostic models were identified. Nine (31·0%) of 29 models had score development reported only, 19 (65·5%) had undergone internal validation, and only four (13·8%) had been externally validated. Data to validate six eligible models were collected in the international external validation cohort study. Data from 11 591 patients were available, with an overall postoperative pulmonary complication rate of 7·8% (n=903). None of the six models showed good discrimination (defined as AUROCC ≥0·70) for identifying postoperative pulmonary complications, with the Assess Respiratory Risk in Surgical Patients in Catalonia score showing the best discrimination (AUROCC 0·700 [95% CI 0·683–0·717]). Interpretation In the pre-COVID-19 pandemic data, variability in the risk of pulmonary complications (StEP-COMPAC definition) following major abdominal surgery was poorly described by existing prognostication tools. To improve surgical safety during the COVID-19 pandemic recovery and beyond, novel risk stratification tools are required. Funding British Journal of Surgery Society