Intense Thermal Radiation Research Articles

Rapid densification of nanocrystalline zirconia: Pressureless versus pressure-assisted spark plasma sintering

Spark plasma sintering (SPS) is the most straightforward way to rapidly sinter nanoceramics, but the applied pressure prevents sintering of additively manufactured ceramics. Therefore, fast firing techniques such as “pressureless” SPS and ultra-fast high-temperature sintering, based on intense thermal radiation, are gaining interest. Here we compare pressure/current-assisted and pressureless SPS techniques for the rapid heating (∼300 °C/min, 5 min) of nanocrystalline zirconia with high sintering activity. The applied pressure and current indeed contributed to the lowestr temperatures needed for full densification of nanocrystalline zirconia, retaining very fine grain size, but also induced tetragonal phase transformations in the final sintering stages. When the radiative heat transfer was “decoupled” (pressureless SPS), a pronounced temperature difference between graphite crucible wall and simulated specimen temperature along with non-steady-state conditions during dwell were observed. Nevertheless, high heating rates facilitated fine and dense microstructures even in the absence of pressure/current.

Measuring 3D shape and deformation in the presence of extremely strong ambient light and thermal radiation with a single time-gated camera.

Monochromatic light-illuminated active-imaging stereo-digital image correlation (stereo-DIC) has been extensively used for measuring the surface deformation of materials and structures at elevated temperatures. Despite the improvements in the image acquisition techniques or devices, it is still challenging to measure the 3D deformation of materials and structures in the presence of strong, time-varying ambient light and thermal radiation. In this study, we present what we believe to be a novel dual-filtering single-camera stereo-DIC technique for full-field 3D high-temperature deformation measurement, even in the case of extremely intense ambient light and thermal radiation. In contrast to conventional active-imaging stereo-DIC that only suppresses the thermal radiations in the spectral domain, the proposed technique utilized a dual-filtering strategy (i.e., narrow bandpass optical filtering and ultrashort exposing) to suppress the strong ambient light and thermal radiation in both time and spectral domains. Besides, a four-mirror adapter is adopted to realize 3D shape and deformation measurement using a compact single time-gated camera. Experimental verifications, including assessments with laboratory experiments and validations on real thermal deformation tests under transient aerodynamic heating and direct ohmic heating, convincingly demonstrated that the proposed single-camera dual-filtering stereo-DIC method can achieve accurate 3D shape, motion and deformation measurement, even with strong light and thermal radiation from the quartz lamps and the heated sample.

Thermal state of the body of workers exposed to extreme levels of infrared radiation and prevention overheating

Introduction. In an industrial environment, the thermal effect of a heating microclimate on a person through extreme levels of infrared radiation is a stressful factor that has a pronounced negative effect on the formation of the thermal state of the body, which requires the development of effective measures to prevent overheating. 
 The purpose of the study is to investigate the peculiarities of the formation of the thermal state of the body in the conditions of a production experiment under exposure to extreme levels of infrared radiation against the background of long-term heavy factory work and the justification of a set of effective measures to prevent overheating. 
 Materials and methods. The study of the thermal state of the body is conducted in the conditions of real blacksmithing production in accordance with the methodological instructions of MUK 4.3.1895–04 and the provisions of the standard GOST R ISO 9886–2008.
 Results. In modern forging and pressing production, one of the most unfavourable factors of the production environment is the intense thermal radiation from the metal heated to technological temperatures, which affects the total for 5–6 hours per shift against the background of high temperature from the heating furnaces themselves, which leads to the development of chronic overheating in workers. The main sources of thermal radiation include incandescent to a temperature of over 1200 °C with metal forgings of various lengths and various profile configurations, which largely determines the variability in the degree of radiation intensity of the radiant energy flow at the workplaces of blacksmiths and heaters. The formed thermal state of the workers of the studied occupational groups, dressed in standard cotton workwear, during the performance of the main work operations during the first half of the working shift in the cold and warm periods of the year, is estimated as the maximum permissible, requiring a limit of working time – no more than one hour per working shift. It is necessary to develop requirements for the working regime for prolonged heavy physical work in conditions of extreme exposure to a heating microclimate and the mandatory use of modern effective personal protective equipment (PPE) from infrared radiation.
 Limitations. The limitation of the study is the possibility of using the results obtained directly to a specific production, characterized by multifactorial effects against the background of extreme levels of the heating microclimate, rigidly determined by the technological process. The obtained indicators of the thermal condition of workers dressed in standard cotton workwear are estimated as the maximum permissible for a period of no more than one hour per work shift, which justifies the need to search for new effective personal protective equipment for the body of workers.
 Conclusion. It is necessary to develop requirements for the working regime during prolonged hard physical work in conditions of extreme exposure to a heating microclimate and the mandatory use of modern effective PPE from infrared radiation of extreme levels.

Система защиты воздушной среды участка сварочных работ с применением восстановительной вентиляции

The technology is considered related to the protection of the air environment of electric welding areas with the use of restorative ventilation and showering. With the help of it, polluted air is removed from the working area and the conditioned air is supplied instead for meeting the requirements of sanitary norms for the microclimate parameters of working premises and the content of harmful substances in them. The traditional technology of air purification from welding smoke has fundamental disadvantages, the main of which is the inability to clean the air from carbon monoxide and nitrogen dioxide impurities. To normalize the microclimate of working areas, the volumetric air conditioning is used, which requires enormous energy costs. At the same time, the distribution of supply air does not provide for the protection of the welder from intense thermal radiation. The system of harmful substances suction from the welding station limits the freedom of the welder action. Therefore, in some cases, he is forced to raise the suction funnel above his head, as a result of what the welding smoke enters the room. It is proposed to avoid the above shortcomings by improving the system of complex protection of the air environment, containing an exhaust panel, an apparatus for cleaning and heat-moisture treatment of air with its cooling and subsequent return to the welder working area. It is advisable to use an apparatus for wet air treatment made according to the type of a packed scrubber-absorber using water with active additives of permanganate and sodium bicarbonate dissolved in it, which contribute to the dissolution and retention of toxic gases of the welding smoke in water. To increase the efficiency of air purification in this apparatus, it is proposed to use a special irrigated nozzle made of porous plastic plates, in which artificial turbulence of the air flow is carried out, which ensures its intense heat and mass transfer and temperature reduction. The use of such a device allows to implement an energy-saving technology by reducing the performance of the supply units to the minimum required level of outdoor air supply.

Compatible and energy conserving multi-material arbitrary Lagrangian Eulerian scheme for multi-group radiation hydrodynamics simulations

A compatible, bounds preserving and energy conserving multi-material arbitrary Lagrangian Eulerian (ALE) scheme suitable for an unstructured mesh is developed for multi-group radiation hydrodynamics (RHD) simulation of various high energy density physics (HEDP) phenomena involving large material deformations, such as intense thermal radiation or high-power laser driven systems. In order to study very short time scale HEDP phenomena, the electron and ion energy equations (with the effect of electron-ion energy relaxation) are solved separately with an assumption of single macroscopic fluid velocity for each species (two-temperature hydrodynamics model). The governing multi-material hydrodynamics equations are solved by using a higher-order cell-centered hydrodynamics (CCH) scheme. In multi-material flows, the remapping step introduces mixed computational cells in which multiple materials exist in a single cell. Therefore, material interfaces in mixed cells are required to be reconstructed and tracked. In our implementation, this is achieved by using moment-of-fluid (MOF) method. The information of these interfaces is further used to formulate an interface aware sub-scale dynamics (IASSD) scheme for multi-material closure in mixed computational cells. The IASSD scheme is generalized for the two-temperature hydrodynamics model in which separate equations are used to update the electron and ion energies. The multi-group radiation transport on an unstructured mesh is computed using a cell-centered, monotonic, nonlinear finite volume (NLFV) scheme. The flux-limited diffusion (FLD) approximation is used to recover the free-streaming limit of the radiation propagation in optically thin regions. In the ALE step, the electron, ion and radiation energies due to MG-RHD model are conservatively remapped using a center-of-mass (CM) reconstruction of the fields and a compatible and energy conserving remapping scheme. An exact integration based on the intersection between the new (rezoned) and old meshes is used in the remap step. Similar procedure is followed for the remap of cell mass and cell-centered momentum components. In this paper, the details of a compatible, bounds preserving and conservative ALE scheme developed for MG-RHD are described. The remapping of relevant physical quantities due to multi-physics models implemented in the code such as non-local electron energy transport are also discussed. Several validation test problems including laser driven shock propagation in multi-material geometries are provided to demonstrate the accuracy and performance of the ALE scheme implemented.

S-wave velocity characteristics and mineralization of the southern tibet detachment system-yalaxiangbo dome

A series of extensional structures, including the southern Tibet detachment system (STDS), the north-south trending rifts (NSTR), and the northern Himalayan gneiss dome (NHGD), developed from the collision and compression between the Indian and Eurasian plates. These tectonic movements were accompanied by magmatism and polymetallic mineralization. Cuona Rift (CR) is located on the STDS next to the Yalaxiangbo Dome (YD) and passes through the Zhegucuo-longzi fault (ZLF), the Lhozhag fault (LZF), the Rongbu-Gudui fault (RGF), the Cuonadong dome (CD), and the YD. The study area contains numerous metal deposits, such as rare metal ore, lead zinc ore, gold deposits, and two geothermal fields, i.e., the Cuona geothermal field (CGF) and the Gudui geothermal field (GGF). Current research on the geological structures from the STDS to the YD is mainly based on magnetotelluric and natural seismic imaging. These surveys have a low resolution, making it impossible to image the shallow crust in detail. This study obtained about a 112 km S-wave velocity profile from the STDS to the YD using the multichannel surface wave imaging method. The profile results indicated that the average thickness of the sedimentary layer from the STDS to the YD is 400–500 m, while it is more than 800 m at certain fault zones. The CD is connected to the high-velocity body below the Zhaxikang ore concentration area (ZOCA) and may have the same provenance. The thermal conductivity reveals that the CGF, the GGF, and the ZOCA have high values and a more intense thermal radiation capacity. This drives the migration and circulation of the thermal fluids in the CGF and the GGF, causing them to continuously transmit heat to the shallow surface along the fault system. The migration of the thermal fluids extracts useful elements from the geological bodies through which it flows. When these elements mix with the atmospheric infiltration water, it precipitates to form the Zhaxikang hydrothermal superimposed transformation type lead-zinc polymetallic deposit.

Thermal Protection by Integration of Vacuum Insulation Panel in Liquid-Cooled Active Thermal Management for Electronics Package Exposed to Thermal Radiation

Abstract Thermal management systems (TMSs) working for electronics packages under harsh environments like intense thermal radiation are challenging due to external thermal interactions. Thermal insulation protection for TMS is very critical in these harsh conditions. An experimental setup was developed to analyze the effect of insulation protection against thermal irradiation over a pumped liquid-cooling active thermal management system (ATMS) with varying heat dissipation rate (0–4.2 kW/m2), thermal irradiation (0.85–3.80 kW/m2), and coolant temperature (15–25 °C). Three configurations of ATMS are considered in the experimental study: ATMS without thermal insulation protection, ATMSs integrated with Cellulose Fibre Insulation (CFI), and Vacuum Insulation Panel (VIP). The effect of insulation on each parameter in all three ATMS configurations over the temperature of the electronics component, cooling load, and nature of heat flow in ATMS was analyzed. VIP outperformed CFI on achieving a significant reduction in the temperature of electronics systems (35.67%) and cooling load (45.64%) experienced by the ATMS. VIP effectively reduced the impact of temperature and cooling load change in ATMS against change in thermal irradiation. The study concluded that thermal insulation protection was most effective at high thermal irradiation and low heat dissipation rate. Heat Flow Direction Index (HFDI) concept was developed to find the nature of heat transfer direction in ATMS without temperature distribution trend. Heat generation rate and irradiation possess significant influence over the nature of heat flow direction.

Effect of vacuum insulation panel on active thermal management for electronics system exposed to thermal radiation

The electronics package exposed to harsh environments like intense thermal radiation is challenging to the Thermal Management System (TMS) designers. An experimental setup has been developed to analyse the thermal response of insulation integrated pumped liquid-cooling Active Thermal Management System (ATMS) for an electronic package exposed to intense thermal radiation. Cellulose Fibre Insulation (CFI) and Vacuum Insulation Panel (VIP) of the same thickness were tested in ATMS at a heat dissipation rate of 0–20 W. This was compared with ATMS exposed to thermal radiation without insulation to analyse the impact of insulation integration. VIP integrated ATMS recorded the lowest electronic package temperature with an average temperature and cooling load reduction of 51.52 % and 65.18 %. Heat Flow Direction Index (HFDI) concept was introduced to determine the heat flow direction in ATMS. The experimental study reveals that the integration of VIP was effective in reducing the temperature and cooling load in ATMS. VIP outperformed CFI in maintaining the lowest temperature and cooling load over different power levels in ATMS. VIP possessed thermal conductivity of 5.95 mW/m-K and 73.87 % average surface reflectivity dominates over CFI shows its potential as an insulation in ATMS against thermal irradiation.

Photonic response and temperature evolution of SiO2/TiO2 multilayers

The microstructural and optical reflectivity response of photonic SiO2/TiO2 nanomultilayers have been investigated as a function of temperature and up to the material system’s melting point. The nanomultilayers exhibit high, broadband reflectivities up to 1350 °C with values that exceed 75% for a 1 μm broad wavelength range (600–1600 nm). The optimized nanometer sized, dielectric multilayers undergo phase transformations from anatase TiO2 and amorphous SiO2 to the thermodynamically stable phases, rutile and cristobalite, respectively, that alter their structural morphology from the initial multilayers to that of a scatterer. Nonetheless, they retain their photonic characteristics, when characterized on top of selected substrate foils. The thermal behavior of the nanometer sized multilayers has been investigated by differential thermal analysis (DTA) and compared to that of commercially available, mm-sized, annealed powders. The same melting reactions were observed, but the temperatures were lower for the nm-sized samples. The samples were characterized using X-ray powder diffraction before DTA and after annealing at temperatures of 1350 and 1700 °C. The microstructural evolution and phase compositions were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements. The limited mutual solubility of one material to another, in combination with the preservation of their optical reflectivity response even after annealing, makes them an interesting material system for high-temperature, photonic coatings, such as photovoltaics, aerospace re-entry and gas turbines, where ultra-high temperatures and intense thermal radiation are present.

In-Process Height Displacement Measurement Using Crossed Line Beams for Process Control of Laser Wire Deposition

We propose the use of the line section method with crossed line beams for the process control of laser wire deposition. This method could be used to measure the height displacement in front of a laser spot when the processing direction changes. In laser processing, especially laser deposition of metal additive manufacturing, the laser process control technique that controls the processing parameters based on the measured height displacement in front of a laser processing spot is indispensable for high-accuracy processing. However, it was impossible to measure the height displacement in front of a processing laser spot in a processing route in which the processing direction changes as the measurement direction of the conventional light-section method comprising the use of a straight-line beam is restricted although the configuration is simple. In this paper, we present an in-process height displacement measurement system of the light-section method using two crossed line beams. This method could be used to measure the height displacement in a ±90° direction by projecting two crossed line beams from the side of a laser processing head with a simple configuration comprising the addition of one line laser to the conventional light-section method. The height displacement can be calculated from the projected position shift of the line beams irrespective of the measurement direction by changing the longitudinal position on the crossed line beams according to the measurement direction. In addition, the configuration of our proposed system is compact because the imaging system is integrated into the processing head. We could measure the height displacement at 2.8–4 mm in front of a laser processing spot according to the measurement direction by reducing the influence of intense thermal radiation. Moreover, we experimentally evaluated the height displacement measurement accuracy for various measurement directions. Finally, we evaluated continuous deposition in an “L” shape wherein the deposition direction was changed while using a laser wire direct energy deposition machine for the laser process control based on the in-process height displacement measurement result. We achieved highly accurate continuous deposition at the position wherein the processing direction changes despite the acceleration and deceleration of the stage by laser process control.

Proposals for maintaining temperature condition in the undersuit space of the rescuer

The elimination of fires and the consequences of emergencies is carried out in conditions of high temperatures, abnormal humidity of the environment, smoke screening, and is often accompanied by intense physical exertion, nervous tension, that is, it is carried out under high ergothermic and psycho-emotional stresses of the rescuer. The purpose of this work is to develop proposals to improve the temperature regime in the undersuit space of the rescuer during operations at low ambient temperatures by substantiating the parameters of the water cooling system of the heat-proof suit. The article discusses the urgent issue of maintaining a comfortable temperature in the undersuit space of the rescuer during the elimination of fires. The most effective way to protect rescuers from the negative effects of fires is to use a flow-through cooling scheme with either water or a foaming solution as a refrigerant. The disadvantage of this method is the effect of contrasting temperatures on the human body, which creates a danger of hypothermia. To prevent the effects of low temperatures in the cold season, it is proposed to use a heater manifold made of elastic heat-conducting material. The heater manifold with thermostat performs a dual function, namely the heating of the refrigerant, as well as shielding the outer shell of the thermal suit from the direct action of heat rays and convection gas flows. The scientific significance of the article is that for the first time it has been proposed to use the radiation energy of a combustion source to heat a low-temperature refrigerant in the cooling systems of rescuers. The practical significance of the results obtained in the article is that the proposed technical solution will make it possible to improve the temperature regime in the undersuit space of the rescuer while conducting operative actions in the conditions of intense thermal radiation and low ambient temperatures

A Hardware Complex Using a Scheme for Simultaneously Obtaining the Image of a Rapid Process in Reflected and Passing Light

This paper describes the results of the development and the main technical characteristics of an optical-photoelectronic complex, which is designed to simultaneously obtain images of rapid processes in reflected and transmitted light. It consists of two devices for high-speed registration of domestic production, a pulsed light source with a gas-discharge point emitter, and a translucent diffuse-scattering screen. Examples of the practical application of the complex for obtaining information in aeroballistic and gas-dynamic experiments, including those accompanied by intense background thermal radiation, are given.

Effect of thermal radiation on conjugate natural convection flow of a micropolar fluid along a vertical surface

This article investigates the behavior of conjugate natural convection over a finite vertical surface immersed in a micropolar fluid in the presence of intense thermal radiation. The governing boundary layer equations are made dimensionless and then transformed into suitable form by introducing the non-similarity transformations. The reduced system of parabolic partial differential equations is integrated numerically along the vertical plate by using an implicit finite difference Keller-box method. The features of fluid flow and heat transfer characteristics for various values of micropolar or material parameter, K, conjugate parameter, B, and thermal radiation parameter, Rd, are analyzed and presented graphically. Results are presented for the local skin friction coefficient, heat transfer rate and couple stress coefficient for high Prandtl number. It is found that skin friction coefficient and couple stress coefficient reduces whereas heat transfer rate enhances when the micro-inertia parameter increases. All the physical quantities get augmented with thermal radiation.

Optical in-process height measurement system for process control of laser metal-wire deposition

We propose an in-process height measurement system for a weld bead and feedback control system for wire-feeding speed for high-quality laser deposition. Metal additive manufacturing, especially laser metal-wire deposition, is effective for complex shape fabrication and repair processing. However, we must control the gap between a weld bead and a feed wire in an optimal range for high-quality deposition. Conventionally, the Z-stage pitch for multi-layer deposition must be precisely adjusted by each deposition shape. In this paper, we design an in-process height measurement system that is integrated in a laser processing head, which measures the weld bead height by a line section method. We decreased the influence of the intense thermal radiation generated from a melt pool by inserting the band-pass filter of the line beam's wavelength in the imaging system and optimizing its line laser power. Consequently, our system can measure the weld bead height near the melt pool, which is 4 mm in front of it. Next we show that our proposed system can measure the weld bead height during wire-laser metal deposition with 50-μm accuracy by comparing its value to the true value. Finally, we achieved a cylinder shape deposition of 50-mm height, regardless of the Z-stage pitch and the cylinder diameter of the multi-layer deposition, by controlling the wire-feeding speed based on the measured weld bead height.

ANALYSIS OF HARMFUL AND DANGEROUS PRODUCTIVE FACTORS OF ELECTROMETALLURGY PRODUCTION

The health of the working population is shaped by a whole range of factors, including working conditions, economic conditions, the way and quality of life are leading, determining the level of health of the population and labor potential of any country.An important place in the structure of factors that shape the health of workers belongs to working conditions. One of the most numerous contingents that are subject to increased professional risk is workers in metallurgical production, 75% of whom work in conditions that do not meet hygienic standards. At the present stage of development of electrometallurgy production, the replacement of old technological equipment and the introduction of new technologies are extremely slow. This gives rise to a number of acute hygienic problems and the significant influence of dangerous and harmful factors of the production environment of electrometallurgy production on the health of workers remains.Dangerous and harmful production factors are the main causes of real potential hazards in the enterprise. Working conditions in electrometallurgy production are characterized by a harmful microclimate, intense thermal radiation, sharp temperature changes, high concentrations of dust and intense noise. The working conditions and the labor process in electrometallurgy production belong to III to the class 3 degrees. The workplace of the steelmaker electric furnace has 2 factors of I degree, 2 factors of II degree and 5 factors of III degree. According to the indicators, the workplace should be considered with especially harmful and especially difficult working conditions.The complete exception of dangerous and harmful productive factors in the conditions of production is impossible, but the decline of their negative influence is quite needed attainable task that it is necessary to decide by development and application of corresponding measures and facilities.

Dense and strong ZrO2 ceramics fully densified in

ABSTRACTCrack-free zirconia ceramics were consolidated via sintering by intense thermal radiation (SITR) approach at 1600–1700°C for 3–5 min. The resulted ceramic bulks can achieve a relative density up to 99.6% with a grain size of 300–1200 nm. Their bending strength, Vickers hardness and indentation toughness values are up to 1244 ± 139 MPa, 13.3 ± 0.3 GPa and 5.5 ± 0.1 MPa m1/2, respectively. Quantitative Raman and XRD analysis show the presence of minor m phase on the natural surface (<7%), fracture surface (<10%) and indentation areas (<15%). It reveals that the SITR method is efficient for rapidly manufacturing zirconia ceramics with desired density, fine grained microstructure and good mechanical properties that are strongly demanded in dental applications.

Experience in application of SOGDA thermal-protection shields at fire and explosion hazardous facilities in Uzbekistan

Goal. The aim and objective of the study is to summarize the long-term experience of the State Fire Safety Service of the Republic of Uzbekistan in equipping the industrial enterprises of the oil and gas and chemical industries with various models of thermal-protection shields, their optimal location, methods of their application and delivery, training of firefighters and members of the Voluntary Fire Brigade (VFB) in the application of this innovative equipment, as well as the experience in application of special types of shields in the elimination of accidents at oil and gas gushers. Review of experience in application of the shields. Outputs. The experience of using SOGDA thermal-protection shields at fire hazardous facilities in Uzbekistan, as evidenced by the example of the Bukhara Oil Refinery Plant, shows that they increase the operational readiness of the force and VFB members of the facility in the event of an emergency, protect their life and health during the elimination of accidents, which will obviously improve fire-fighting efficiency. Thermal-protection shields SOGDA are adopted by such large facilities in theRepublicofUzbekistanas the Bukhara Oil Refinery Plant (refinery), theFerganarefinery, etc. Conclusions. In more than 15 years of using different types of thermal-protection shields by the companies in the oil and gas chemical industry, their most rational modifications have been developed separately for each of the fire and explosion hazardous sites of the facilities, depending on their risk degree. For example, tank batteries, truck and rail loading and unloading racks, barrel storage warehouses for oil products, gas stations, as well as fire-fighting stations at highly important facilities are recommended to be equipped with mobile thermal-protection shields, and for fixed fire-fighting monitors a stationary thermal-protection shield, which protects the operator of the monitor against high intensity thermal radiation, is recommended. Further research showed that the scientific idea of “attenuation of heat flow” represents a breakthrough innovative technology not only in the field of fire safety, but also in wider areas ensuring safety of human activities. The implementation of research based on this scientific idea will open wide opportunities for creating hundreds of devices implementing this technology.

Self-generated clouds of micron-sized particles as a promising way of a Solar Probe shielding from intense thermal radiation of the Sun

An effect of shielding of an intense solar radiation towards a solar probe with the use of micron-sized SiC particles generated during ablation of a composite thermal protection material is estimated on a basis of numerical solution to a combined radiative and heat transfer problem. The radiative properties of particles are calculated using the Mie theory, and the spectral two-flux model is employed in radiative transfer calculations for non-uniform particle clouds. A computational model for generation and evolution of the cloud is based on a conjugated heat transfer problem taking into account heating and thermal destruction of the matrix of thermal protection material and sublimation of SiC particles in the generated cloud. The effect of light pressure, which is especially important for small particles, is also taken into account. The computational data for mass loss due to the particle cloud sublimation showed the low value about 1kg/m2 per hour at the distance between the vehicle and the Sun surface of about four radii of the Sun. This indicates that embedding of silicon carbide or other particles into a thermal protection layer and the resulting generation of a particle cloud can be considered as a promising way to improve the possibilities of space missions due to a significant decrease in the vehicle working distance from the solar photosphere.

Evaluation of the in-depth temperature sensing performance of Eu- and Dy-doped YSZ in air plasma sprayed thermal barrier coatings

In-depth temperature sensing in air plasma sprayed (APS) thermal barrier coatings (TBCs) has been achieved with europium (Eu) and dysprosium (Dy) doped yttria stabilized zirconia (YSZ) sensor coatings. The luminescence properties of YSZ:Eu and YSZ:Dy, including spectrum, intensity and lifetime, were evaluated and their temperature sensing performances were compared using a lifetime-based measurement system. Both sensor TBCs display excellent temperature sensitivity in high temperature environment (400–800°C for YSZ:Eu, 500–900°C for YSZ:Dy) with a topcoat thickness up to 300μm. It was found that the upper limit of temperature sensing was determined by the ratio between luminescence intensity and background thermal radiation (signal-background-ratio). YSZ:Dy showed higher luminescent intensity than YSZ:Eu at elevated temperatures, and therefore displayed better temperature sensing performance with an increased limit. The effect of topcoat thickness on the temperature sensing performance was also evaluated, showing that the attenuation factor of YSZ increased significantly with topcoat thickness. Interestingly, it was found that the topcoat attenuation factor gradually decreased as temperature increased, which improved the temperature sensing performance of sensor TBCs at elevated temperature. The findings in the temperature sensing of APS TBCs provide basis for the future development of on-line APS TBCs temperature monitoring technology.

Reduced radiative conductivity of low spin FeO6-octahedra in FeCO3 at high pressure and temperature

The ability of Earth's mantle to conduct heat by radiation is determined by optical properties of mantle phases. Optical properties of mantle minerals at high pressure are accessible through diamond anvil cell experiments, but because of the intense thermal radiation at T>1000 K such studies are limited to lower temperatures. Accordingly, radiative thermal conductivity at mantle conditions has been evaluated with the assumption of the temperature-independent optical properties. Particularly uncertain is the temperature-dependence of optical properties of lower mantle minerals across the spin transition, as the spin state itself is a strong function of temperature. Here we use laser-heated diamond anvil cells combined with a pulsed ultra-bright supercontinuum laser probe and a synchronized time-gated detector to examine optical properties of high and low spin ferrous iron at 45–73 GPa up to 1600 K in an octahedral crystallographic unit (FeO6), one of the most abundant building blocks in the mantle. Siderite (FeCO3) is used as a model for FeO6-octahedra as it contains no ferric iron and exhibits a sharp optically apparent pressure-induced spin transition at 44 GPa, simplifying data interpretation. We find that the optical absorbance of low spin FeO6 increases with temperature due to the partially lifted Laporte selection rule. The temperature-induced low-to-high spin transition, however, results in a dramatic drop in absorbance of the FeO6 unit in siderite. The absorption edge (Fe–O charge transfer) red-shifts (∼1 cm−1/K) with increasing temperature and at T>1600 K and P>70 GPa becomes the dominant absorption mechanism in the visible range, suggesting its superior role in reducing the ability of mantle minerals to conduct heat by radiation. This implies that the radiative thermal conductivity of analogous FeO6-bearing minerals such as ferropericlase, the second most abundant mineral in the Earth's lower mantle, is substantially reduced approaching the core–mantle boundary conditions.