High-speed Pyrometer Research Articles

Experimental investigation and CALPHAD modeling of the Mo-Nb-Zr system

To accelerate the design of novel nuclear fuel cladding materials for applications, the phase equilibria of the Mo-Nb-Zr system at 1223 K and 1773 K have been experimentally investigated by a combination of scanning electron microscopy, energy dispersive spectroscopy, electron probe microanalysis with wavelength dispersive spectrometer. In addition, the liquidus of the vertical sections at x(Mo) + x(Nb) = 0.67, x(Zr) + x(Nb) = 0.60 were also studied in this work utilizing an in-situ high-speed pyrometer. The thermodynamic assessment of the Mo-Nb-Zr system was carried out by the CALPHAD method based on the experimental data available in the present work and literature. A set of self-consistent thermodynamic parameters of the Mo-Nb-Zr system was obtained. The calculated liquidus projection of the Mo-Nb-Zr system over the whole composition was also presented.

Ni/Al multilayer reactions on nanostructured silicon substrates

Fast energy release, which is a fundamental property of reactive multilayer systems, can be used in a wide field of applications. For most applications, a self-propagating reaction and adhesion between the multilayers and substrate are necessary. In this work, a distinct approach for achieving self-propagating reactions and adhesion between deposited Ni/Al reactive multilayers and silicon substrate is demonstrated. The silicon surface consists of random structures, referred to as silicon grass, which were created by deep reactive ion etching. Using the etching process, structure units of heights between 8 and 13 µm and density between 0.5 and 3.5 structures per µm2 were formed. Ni and Al layers were alternatingly deposited in the stoichiometric ratio of 1:1 using sputtering, to achieve a total thickness of 5 µm. The analysis of the reaction and phase transformation was done with high-speed camera, high-speed pyrometer, and X-ray diffractometer. Cross-sectional analysis showed that the multilayers grew only on top of the silicon grass in the form of inversed cones, which enabled adhesion between the silicon grass and the reacted multilayers. A self-propagating reaction on silicon grass was achieved, due to the thermally isolating air pockets present around these multilayer cones. The velocity and temperature of the reaction varied according to the structure morphology. The reaction parameters decreased with increasing height and decreasing density of the structures. To analyze the exact influence of the morphology, further investigations are needed.

Phase equilibria in the TiO2–Nb2O5 system: New experiments and thermodynamic modeling

Phase equilibria in the TiO2–Nb2O5 system has been investigated by using the high-speed pyrometer, scanning electron microscopy and X-ray powder diffraction. The liquidus temperatures in the whole composition region are determined by cooling trace tests. Combining with the observation of solidification structure, liquidus at the TiO2-rich corner are clarified and the eutectic composition of Liquid→TiO2+TiNb2O7 is revised to be 62.3 mol % TiO2. TiNb2O7 has been measured to have some solid solubility, and the existence of Ti2Nb6O19 at high temperature is confirmed. It would probably form through the peritectic reaction of Liquid + TiNb2O7→Ti2Nb6O19. Moreover, congruent reactions of Liquid→TiNb2O7 and Liquid→TiNb5O14.5 are measured as 1491 °C and ∼1478 °C, respectively. Subsequently, thermodynamic assessment of TiO2–Nb2O5 system has been carried out by means of the CALPHAD method, and a set of self-consistent thermodynamic parameters is obtained. Calculated TiO2–Nb2O5 phase diagram can reasonably reproduce the available experimental data. The provided TiO2–Nb2O5 phase diagram and thermodynamic parameters may be useful to the development of titanium niobates and further multicomponent thermodynamic database.

Microstructure evolution in the self-propagating reaction in Al/Ru bilayers by phase-field simulations and experiments

The self-propagating reaction in binary Al/Ru multilayers with two different bilayer thicknesses (89 and 178 nm, respectively) forming single-phase AlRu intermetallic compound is investigated experimentally and by means of phase-field simulations. Experimentally, the time-temperature evolution in free-standing films was recorded with a high-speed pyrometer, and the resulting microstructure was determined from electron backscatter diffraction measurements. The phase-field model is constructed based on the minimization of the grand potentials for which the required thermodynamic data are taken from the Calphad database. The simulation of the reaction and subsequent AlRu grain growth starts from Al-rich and Ru-rich layer fillings. After the formation of the AlRu phase is complete, the grain growth during cooling is simulated based on the experimentally recorded time-temperature curves. Finally, the resulting grain sizes obtained from the simulation are found to be in good agreement with the experimental results. Furthermore, it is shown that the final grain sizes in both simulations and experiments depend on the initial bilayer thicknesses.

Influence of extrinsic induced tensile stress on the self-propagating high-temperature synthesis of nanosized Al/Ni multilayers

Reactive multilayer systems consisting of alternating nanoscale Al and Ni layers are applicable in joining, various pyrotechnic applications and thermal batteries. Since diffusion based high-temperature synthesis occurs without the presence of air, efforts have focused on investigating the understanding of the fundamental reaction processes and characteristics. The aim of this study is to expose the reactive multilayers to extrinsic induced tensile stress so that the self-propagating synthesis can proceed under these conditions. Further, the properties during and after the reaction will be investigated. Multilayers deposited by sputtering on Kapton® substrates with different bilayer– and total thicknesses as well as commercial Nanofoils® with thicknesses of 40 µm and 60 µm were used as samples. The investigations focused on the propagation velocity measured with a high-speed camera, the temperature regime determined with a high-speed pyrometer, and the formed phases after the synthesis examined via X-ray diffraction. The gained results of this study reveal important insights for the application of the reactive Al/Ni multilayer system in terms of stability or reliability related to propagation front velocity, maximum temperature and formed phases under induced external tensile stresses.Graphical abstract

A study on the phase diagram of Re-Zr refractory system

The different volume of Rhenium (Re) and zirconium (Zr) will affect the phase composition and thus change the mechanical properties of the core critical hot end components of gas turbines and aero engines. In this work, the Re-Zr system was studied experimentally by electron probe microanalyses (EPMA) with wavelength dispersive spectrometer (WDS), scanning electron microscopy (SEM) and X-ray diffraction (XRD), and then was measured the phase-transition temperature with the high-speed pyrometer. The phase Re25Zr21 was confirmed to be stable in this system. Besides, the eutectic point of the eutectic reaction Liquid → bcc (Zr) + Re25Zr21 was determined as 14.4% Re by WDS. The present phase transitions (melting point, solidus, and liquidus) measurements indicate that the Re-Zr system is different from the existing Re-Zr phase diagram. Then, the current obtained results, combined with a critical review of the previous publication data, were used to develop the thermodynamic description of the Re-Zr system by utilizing the CALPHAD (CALculation of PHAse Diagram) method. A set of self-consistent thermodynamic parameters was obtained.

Investigation of the surface temperature in contact with plasma by two-color pyrometry

A high-speed two-color pyrometer has been developed that allows measuring the intensity of thermal radiation in temperature range of 100-3500oC with 2 μs time resolution. The analysis of the main factors affecting the measurement of surface temperature in the conditions of its interaction with plasma is carried out. It is shown that at plasma temperature of more than 10 eV and moderate concentration of particles, the wall plasma can be considered transparent to thermal radiation. Experimental studies on non-contact measurement of temperature of surface interacting with plasma on Globus-M2 tokamak and plasma gun test bench have been carried out. Sawtooth temperature fluctuations were detected on the wall of tokamak chamber near the exit of outer separatrix branch. The period of these flashes was 3-4 ms, and duration was 2 ms. The maximum wall temperature measured by a high-speed pyrometer exceeded the temperature measured by infrared camera. Measurements of temperature of the front surface of W-Li sample were carried out at plasma gun test bench under conditions of deuterium plasma jet cyclic action under loads simulating regimes of plasma current disruption in tokamak. The sample temperature reached more than 3000^oC during <1 ms. The thermal conductivity of the sample degraded with an increase in number of plasma exposure cycles, which was expressed in progressive decrease in target cooling rate after the pulse. Using a high-speed pyrometer, it is proposed to control the formation of heat-insulating foils on surface interacting with plasma Keywords: two-color pyrometer, thermal radiation, surface temperature, materials irradiation.

Исследование температуры поверхности, контактирующей с плазмой, методом двухцветной пирометрии

A high-speed two-color pyrometer has been developed that allows measuring the intensity of thermal radiation in temperature range of 100-3500 0C with 2 µs time resolution. The analysis of the main factors affecting the measurement of surface temperature in the conditions of its interaction with plasma is carried out. It is shown that at plasma temperature of more than 10 eV and moderate concentration of particles, the wall plasma can be considered transparent to thermal radiation. Experimental studies on non-contact measurement of temperature of surface interacting with plasma on Globus-M2 tokamak and plasma gun test bench have been carried out. Sawtooth temperature fluctuations were detected on the wall of tokamak chamber near the exit of outer separatrix branch. The period of these flashes was 3-4 ms, and duration was 2 ms. The maximum wall temperature measured by a high-speed pyrometer exceeded the temperature measured by infrared camera. Measurements of temperature of the front surface of W-Li sample were carried out at plasma gun test bench under conditions of deuterium plasma jet cyclic action under loads simulating regimes of plasma current disruption in tokamak. The sample temperature reached more than 3000 0C during < 1 ms. The thermal conductivity of the sample degraded with an increase in number of plasma exposure cycles, which was expressed in progressive decrease in target cooling rate after the pulse. Using a high-speed pyrometer, it is proposed to control the formation of heat-insulating foils on surface interacting with plasma.

Phase equilibria in the Y2O3-Nb2O5 system up to 2500 ℃: New high-temperature experiments and thermodynamic modeling

The high-temperature phase transformation of the Y2O3-Nb2O5 system in the whole composition range was investigated up to 2500 ℃, based on the cooling trace tests using a combination of CO2 laser heater and high-speed pyrometer. Solidification characteristics of the as-cast oxides were clarified by using X-ray diffractometer and scanning electron microscopy. Three eutectic reactions were detected in this work: Liquid→Y3NbO7 +Y2O3, Liquid→Y3NbO7 +YNbO4 and Liquid→YNbO4 +Nb2O5. The Y3NbO7 and YNbO4 compounds were determined to form through the congruent reactions of Liquid→Y3NbO7 at 2487 ℃ and Liquid→YNbO4 at 2070 ℃, respectively. After that, thermodynamic optimization of the Y2O3-Nb2O5 system was performed by means of CALPHAD method based on the new experimental results and a systematic review of the literature. The ionic two-sublattice model was used to describe the liquid phase, and the fluorite-type Y3NbO7 compound was expressed by the formula (Y+3, Nb+5)1(O−2,Va)2 in order to explain its crystal structure. The comparisons between the calculated phase diagram and the new experimental data exhibit that our thermodynamic parameters are reasonable and self-consistent. The results emerging in this work can aid in future efforts for the development of yttrium niobates and further researches of phase equilbria and thermodynamic database of the related multicomponent systems.

A High-Speed Spectral Pyrometer Based on a Kolibri-2 Spectrometer

The operating speed of commercially available spectral-ratio pyrometers and brightness pyrometers often appears insufficient for control of a fast-changing temperature (e.g., in a graphite cell of an AAS electrothermal atomizer, whose temperature increases at a rate of 104 °C/s). An advantage of spectral pyrometers is high speed and ability to measure the temperature of objects with unknown emissivity. The goal of this work is to develop a high-speed spectral pyrometer based on a Kolibri-2 spectrometer with a BLPP-2000 photodetector array that provides a working wavelength range of 400–1050 nm and a minimum basic exposure time of 0.4 ms. The temperature was calculated by plotting the emission spectrum of the object in Wien coordinates (with allowance for calibration of the spectral pyrometer using a radiation source of known temperature) and by measuring the slope angle of the obtained graph. The relative error of temperature measurements with a spectral pyrometer estimated by comparing the measurement results and the data obtained with a calibrated Termokont-TN5S1M single-channel pyrometer (Termokont company) was no more than 1.5% in a temperature range of 1000–2400°C and higher and the operating speed was up to 2500 measurements/s. The results of measuring the temperature of the graphite cell in the electrothermal atomizer using a spectral pyrometer during sample atomization at a rate of the temperature increase up to 10 000°C/s are presented.

Measurements of the melting points, liquidus, and solidus of the Mo, Ta, and Mo[sbnd]Ta binary alloys using a novel high-speed pyrometric technique

The measurement of high phase-transition temperature is equally challenging and useful for developing high-temperature materials for critical applications. Pyrometer is a suitable option to measure the phase-transition temperature above 2300 K. In this work, Mo, Ta, and their isomorphous binary alloys are selected as the target system for high-speed pyrometer temperature measurements in the arc-melting setup. The present phase transitions (melting point, solidus, and liquidus) measurements indicate that the MoTa is an isomorphous system with a narrow freezing range (i.e., an average value < 35 K). The results from this present work would change the existing MoTa phase diagram. The Gibbs energy modeling for liquid (L) and BCC_A2 (α) phases of the MoTa system are then performed, including the latest experimental results from this work. The applications of the current experimental methodology could be extended to measure the high phase-transition temperatures in superalloys with significant commercial values.

Photon diffusion in microscale solids

This paper presents a theoretical and experimental investigation of photon diffusion in highly absorbing microscale graphite. A Nd:YAG continuous wave laser is used to heat the graphite samples with thicknesses of 40 μm and 100 μm. Optical intensities of 10 kW cm−2 and 20 kW cm−2 are used in the laser heating. The graphite samples are heated to temperatures of thousands of kelvins within milliseconds, which are recorded by a 2-color, high speed pyrometer. To compare the observed temperatures, differential equation of heat conduction is solved across the samples with proper initial and boundary conditions. In addition to lattice vibrations, photon diffusion is incorporated in the analytical model of thermal conductivity for solving the heat equation. The numerical simulations showed close matching between experiment and theory only when including the photon diffusion equations and existing material properties data found in the previously published works with no fitting constants. The results indicate that the commonly-overlooked mechanism of photon diffusion dominates the heat transfer of many microscale structures near their evaporation temperatures. In addition, the treatment explains the discrepancies between thermal conductivity measurements and theory that were previously described in the scientific literature.

High-speed spectral pyrometer based on a «Kolibri-2» spectrometer

The operation speed of commercially available spectral-ratio pyrometers and brightness pyrometers often appears insufficient for control of fast-changing temperature (e.g., in a graphite cell of an AES electrothermal atomizer, the rate temperature change is 104°C/sec). An advantage of spectral pyrometers is high speed and ability to measure the temperature of objects with unknown emissivity. The goal of this study is to develop a high-speed spectral pyrometer based on a «Kolibri-2» spectrometer with BLPP-2000 photodetector array that provides a wide working wavelength range 400 – 1050 nm, and minimum basic exposure time of 0.4 msec. The temperature was calculated by plotting the emission spectrum of the object in Wien coordinates (with allowance for calibration of the spectral pyrometer using radiation source of the known temperature) and measuring slope of the obtained graph. The relative error of temperature measurements on a spectral pyrometer estimated by comparing measurement results and data obtained with a calibrated Termokont-TN5S1M (Termokont company) single-channel pyrometer was not more than 1.5% in a temperature range of 1000 — 2400°C and higher, and rapidity up to 2500 measurements/sec. The results of measuring temperature of the graphite cell of the electrothermal atomizer using a spectral pyrometer during sample atomization at a rate of temperature change up to 10 000°C/sec are presented.

Electrical Resistance of the Most Refractory Carbide Ta0.8Hf0.2C in the Solid and Liquid States (2000–5000 K)

Carbide Ta0.8Hf0.2C in the form of a thin magnetron sputtering layer (~1 μm) was studied under rapid heating (5 μs) by an electric current pulse. The resistivity of this carbide (referred to initial dimensions) and temperature coefficient of resistance were obtained up to 5000 K for the first time. The temperature was measured by surface radiation with the help of high-speed pyrometer calibrated by a temperature tungsten lamp. The sharp rise of temperature coefficient of resistance before melting indicates an increase in the concentration of defects before melting. This confirms the assumption of the appearance of non-stationary paired Frenkel defects in the lattice of rapidly heated solids, which does not have time to establish the equilibrium concentration of vacancies in the lattice.

Study of Selective Laser Melting of intermetallic TiAl powder using integral analysis

Abstract Selective laser melting (SLM) of intermetallic Ti–48Al–2Cr–2Nb powder is studied using different and complementary methods: (a) experimental parametric analysis (variation of laser power, beam scanning velocity, etc.); (b) metallography including X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM); (c) optical monitoring by infra-red (IR) camera, high speed pyrometer and (d) mathematical modelling. The advantage of the present approach is based on parallel application of diverse methods of analysis using the same SLM set-up and feedstock powder. Also the novelty is related to the preheating of the entire manufacturing module up to 450 °C which is applied before and during the manufacturing of the samples. XRD analysis shows domination of the α2-Ti3Al phase in the initial powder, heat treated powder before SLM and in the developed samples. Some minor peaks of γ-TiAl are identified in SLM parts. EDS analysis confirms the effect of Al evaporation, which intensifies with laser energy input. IR-camera is used for optical monitoring of a single track formation. The geometry of the thermal emission field for different processing parameters is compared with the track geometry. The intensification of hydrodynamic instabilities accompanied by material rejection from the zone of powder consolidation with beam scanning velocity is found. For the first time the evaporation of Al for elevated laser energy input is clearly detected by the IR-camera. Mathematical modelling shows that the same elementary volume of SLM sample can be remelted several times during its fabrication depending on the SLM processing parameters and beam scanning strategy. The maximum values of calculated cooling rates are in the order of 106 °C/s. For the first time the thermo-cycling during SLM parts fabrication is confirmed experimentally by pyrometer measurements.

Thermophysical properties of graphite HOPG and HAPG in the solid state and under melting (from 2000 K up to 5000 K)

Experiments with HOPG graphite grade showed that the melting temperature of graphite equals 4800-4900 K and that the melting of graphite is possible only at elevated pressures. The data were obtained for resistivity, specific heat and input (Joule) energy up to 5000 K. HAPG (Highly Annealing Pyrolytic Graphite) is a form of highly oriented pyrolytic graphite. HAPG specimens in the form of strips (thickness 30 microns) were placed in a cell (between two plates of glass-sapphire). The specimen temperature was measured by a high speed pyrometer. The heat of fusion for both graphite grades (heated in a confined volume) was less (and specific heat – higher) than for the case with nearly free expansion. A possible reason for the observed effects is discussed in the report.

A high-speed, eight-wavelength visible light-infrared pyrometer for shock physics experiments

An eight-channel, high speed pyrometer for precise temperature measurement is designed and realized in this work. The addition of longer-wavelength channels sensitive at lower temperatures highly expands the measured temperature range, which covers the temperature of interest in shock physics from 1500K-10000K. The working wavelength range is 400-1700nm from visible light to near-infrared (NIR). Semiconductor detectors of Si and InGaAs are used as photoelectric devices, whose bandwidths are 50MHz and 150MHz respectively. Benefitting from the high responsivity and high speed of detectors, the time resolution of the pyrometer can be smaller than 10ns. By combining the high-transmittance beam-splitters and narrow-bandwidth filters, the peak spectrum transmissivity of each channel can be higher than 60%. The gray-body temperatures of NaI crystal under shock-loading are successfully measured by this pyrometer.

Minimal required boundary conditions for the thermal spallation process of granitic rocks

The spallation process is based on the effect, that hard rocks with a high quartz content disintegrate into small disc-like fragments, if the rock surface is rapidly exposed to high thermal loads. Spallation is pursued as a contact-free drilling technology for various applications. In view of increasing the knowledge about the process and for determining the limitations of the applicable operating range, a profound knowledge of the minimal required boundary conditions are of significant importance. These conditions are characterized by the lowest surface temperature and heat transfer coefficient at which spallation can be successfully initiated. In order to determine the minimal required boundary conditions, spallation experiments were conducted in which granitic rock samples were rapidly heated by a methane–air burner. A novel measuring concept is proposed to measure the surface temperature, using high-speed pyrometers to temporally resolve the detachment of single spalls. The heat transfer coefficient of the impinging flame was determined by measuring the heat flux in the stagnation point of the jet using an industrial heat flux sensor. The reported data of the boundary conditions show good accordance with data published by other researches and supports their proposed characteristic for the specific heating process.

Determination procedure of the heat resistance of ceramics using radiant heating

A procedure for the comparative assessment of the heat resistance of ceramics using radiant heating in an URAN-1 optical furnace has been developed. To measure the specimen surface temperature, an IGA-100 high-speed high-precision pyrometer in combination with a shutter device was used. The procedure was evaluated by comparing the resistance of a multilayer ceramic material of two types. The material of type 1 was thin ZrO2 shuts + knitted Kh18N9T steel net, and the material of type 2 was the same layered ceramic but, without a metallic net. Heat resistance was assessed by the number of cycles to fracture: heating to 1000°C for 2 min + cooling to 300°C. The use of the procedure developed shows a considerable advantage of net-reinforced material.

Evaluation of a Pyrometric-based Temperature Measuring Process for the Laser Transmission Welding

Abstract An on-axis pyrometric-based temperature measurement method suitable for different laser transmission welding techniques is presented. A temperature detection during contour and quasi-simultaneous welding is demonstrated to fit the requirements of laser transmission welding with part adapted temperature fields. For the experiments a pyrometer is connected to a scanner optic with a non-color-corrected lens. The experiments are performed with a high-speed pyrometer detecting in spectral range of 1.65 - 2.1 μm. Potential errors caused by the measurement method are evaluated and its limits depend on the welding technique performed are examined by creating different defects in the weld seam.