The Effect of Impurities on the Evolution of the Melting Front Analyzed in a Two-Dimensional Representation for the Eutectic Pt–C

The paper discusses the effect of two-front melting on the liquidus temperature of the eutectic Pt–C and the eutectic temperature of the system in its pure state. This influence factor has not been considered thus far in the uncertainty budget associated with the assignment of thermodynamic temperatures to the eutectics Co–C (1597.15 K), Pt–C (2011.05 K), and Re–C (2747.35 K), selected in the European Metrology Research Programme project Implementing the New Kelvin. For Pt–C, simulation of the effect of two-front melting on the melting process has been done before in a 1D analytical model, and this formed the starting point to the present study. In this study the melting process is analyzed by means of a 2D axisymmetrical finite-volume model. In the model, freezing and melting are considered for an impure ingot and for a pure ingot. As to the impure ingot, the impurity concentrations are the concentrations met in current practice of the realization of the high-temperature reference fixed point, but formulated in terms of an effective concentration and associated effective distribution coefficient \(k< 1\) , related to a Scheil fit to the melting curve at given melting conditions as measured for the eutectic Pt–C. Heat injection rates for melting varied from 15 000 W \({\cdot }\) m \(^{-2}\) down to 3000 W \({\cdot }\)  m \(^{-2}\) . In any case for the impure system, two melting fronts are showing up. For the pure system, only one melting front is generated, traveling from the outside of the ingot toward its inside.     

On the Freezing and Melting Behavior of the Eutectic Pt?CC

The feasibility of referring to freezing as an alternative to melting for defining the eutectic transition temperature has been studied using two Pt?CC cells constructed at NIM, one of a sleeve type, and the other of a hybrid type, including support. Freezing and melting experiments have been done by varying the offset of the furnace temperature T _furn with respect to the nominal eutectic temperature T _E used to freeze the fixed point with offsets (T _furn?T _E)_freeze from ?5 K to ?40 K, followed by melting at a fixed offset (T _furn?T _E)_melt =?+?20 K. Plotting the liquidus temperatures T _liq,freeze and T _liq,melt obtained for freezing and melting against ${(T_{\rm E}-T_{\rm furn})^{1/2}_{\rm freeze}}$ resulted in linear relations for both cells, allowing extrapolation toward T _liq,freeze(0) and T _{liq, melt}(0). For the cells Pt?CC5# and Pt?CC6# under study: T _liq,melt(0)?T _liq,freeze(0) =?10 mK and 20 mK, respectively, with a standard uncertainty of 30 mK for both T _liq,melt(0) and T _liq,freeze(0). The coherence of the results obtained for melting and freezing indicates that freezing can be used, as an alternative to melting, to define the liquidus temperature T _liq(0) of the eutectic Pt?CC.     

The Effect of the Rear Cavity Wall Ingot Shape on the Evolution of the Liquid–Solid Interface During Melting for the Eutectic Pt-C

When characterizing high-temperature fixed points, the fraction of the melting time of the regular part of the plateau with respect to the total melting time, is critical. Maximizing the melting duration minimizes the uncertainty associated with the determination of the fixed-point temperature. One factor that affects this quality is the effect of the thermal bridging between the external and internal surfaces of the ingot enclosed by the cell. This paper presents the results of simulations for the eutectic Pt-C, investigating the effects of different ingot shapes on the duration of the melt plateau. It was found that the formation of a thermal bridge from the rear of the blackbody cavity toward the outer surface of the ingot was critical and that its formation could be delayed or suppressed through a proper choice of the ingot shape. The shapes considered included, firstly, the shape of the rear of the cavity, in contact with the ingot, either cone-shaped or dome-shaped, and secondly, the inside rear surface of the cell, in contact with the ingot, being a cone, a convex dome, or flat. The presence of impurities in the alloy was taken into consideration, and its influence in the evolution of the liquid–solid interface compared with that for the pure alloy. The effect of changing the thermal isolation of the cell, at its front side, was also considered. A dome-shaped surface for the rear of the cavity was found to be more favorable for the development of a regular melting front, in conjunction with the segregation of impurities during melting. At the rear of the cell, a flat surface ensures the back wall is the last to experience thermal bridging, resulting in more extended melting plateaus.     

Characterization of UME-Made Co–C Eutectic Fixed-Point Blackbody Cells

Eutectic phase transitions are commonly considered for use as fixed points in future 20XX temperature scales. Despite their potential as possible interpolation points in a high-temperature radiation thermometry scale (1000 °C and above), more studies on the reproducibility of the plateau temperature values are required. Various ongoing research projects on the long-term stability and reproducibility of the eutectic fixed points will likely improve the uncertainties enough to allow for their use as reference (or secondary) temperature points. In this article, the long-term reproducibility results of Co–C eutectic plateau realizations performed in the UME Radiation Thermometry Laboratory over four years, along with studies of the dependence on furnace heating/cooling rate and the short-term (1 day) repeatability, are presented. These measurements were performed with a monochromatic radiation thermometer calibrated according to ITS-90.     

On the Use of the Co–C Fixed Point for Calibration of Pt/Pd Thermocouples

At INRIM, different Co–C fixed-point cells have been constructed and investigated. Two cells of different design and volume and filled with highly pure cobalt (99.998%) were used to extend the fixed-point calibration of five Pt/Pd thermocouples that had been previously calibrated at the triple point of water and at the fixed points of In, Sn, Zn, Al, and Ag. The calibration at the Cu point was also added during this exercise. Because a previous calibration from 962 °C up to 1,500°C against the local standard radiation thermometer was available, a comparison was possible with the Co–C fixed-point calibration. Agreement within 0.10 °C was found when the value of 1,324.0 °C, the same value proposed for the Co–C point to be included as a secondary reference point of the ITS-90, was assumed.     

Co–C and Pd–C Eutectic Fixed Points for Radiation Thermometry and Thermocouple Thermometry

Two Co–C and Pd–C eutectic fixed point cells for both radiation thermometry and thermocouple thermometry were constructed at NMC. This paper describes details of the cell design, materials used, and fabrication of the cells. The melting curves of the Co–C and Pd–C cells were measured with a reference radiation thermometer realized in both a single-zone furnace and a three-zone furnace in order to investigate furnace effect. The transition temperatures in terms of ITS-90 were determined to be \(1324.18\,{^{\circ }}\hbox {C}\) and \(1491.61\,{^{\circ }}\hbox {C}\) with the corresponding combined standard uncertainty of \(0.44\,{^{\circ }}\hbox {C}\) and \(0.31\,{^{\circ }}\hbox {C}\) for Co–C and Pd–C, respectively, taking into account of the differences of two different types of furnaces used. The determined ITS-90 temperatures are also compared with that of INRIM cells obtained using the same reference radiation thermometer and the same furnaces with the same settings during a previous bilateral comparison exercise (Battuello et al. in Int J Thermophys 35:535–546, 2014). The agreements are within \(k=1\) uncertainty for Co–C cell and \(k = 2\) uncertainty for Pd–C cell. Shapes of the plateaus of NMC cells and INRIM cells are compared too and furnace effects are analyzed as well. The melting curves of the Co–C and Pd–C cells realized in the single-zone furnace are also measured by a Pt/Pd thermocouple, and the preliminary results are presented as well.     

Thermal Calculation of the Furnace Chamber of a Fire‐Tube Boiler With a Dead‐End Furnace

An engineering procedure for calculating the thermal regime of the furnace chambers of firetube boilers with a deadend furnace is given. The procedure proposed is devoid of many drawbacks that are inherent in the standard method for calculating boiler units and permits more accurate allowance for the special features of combined energy exchange in furnace chambers of boilers that differ significantly in type and size from traditional ones.     

Effect of the Electron–Phonon Coupling on the Effective Thermal Conductivity of Metallic Bilayers

Systems consisting of metallic layers are commonly used in many applications for microelectronics, data storage, protection coatings, and microelectro-mechanical systems. The physical properties of such systems are strongly determined by the flow of the electron and phonon gases and their interactions. In this study, the effective thermal conductivity of a metal–metal bilayer system is studied using the two-temperature model of heat conduction. By defining the total interfacial thermal resistance, it is shown that the thermal conductivity of the bilayer system depends on the ratio between the thicknesses of the metallic layers and their intrinsic coupling length and it has a simple interpretation as the sum of thermal resistances in series. It is demonstrated that the total interfacial thermal resistance can be minimized by choosing appropriately the thermal and geometrical properties of the component layers. The proposed approach could be useful for thermally characterizing and guiding the design of novel metal–metal-layered systems involved in diverse technological applications.     

Stability Evaluation and Calibration of Type C Thermocouples at the Pt–C Eutectic Fixed Point

Tungsten–rhenium thermocouples (type C thermocouples) are used to measure temperatures higher than 1500 \({^{\circ }}\)C under protective, inert, or vacuum conditions in a wide range of industries, such as metallurgy, power generation, and aerospace. Generally, the measurement uncertainty of a new tungsten–rhenium thermocouple is about 1 % (20 \({^{\circ }}\)C at 2000 \({^{\circ }}\)C), and a significant drift is always observed above 1200 \({^{\circ }}\)C. Recently, the National Institute of Metrology, China, has spent great efforts to calibrate tungsten–rhenium thermocouples with high-temperature fixed points of up to 2000 \({^{\circ }}\)C. In the present work, three tungsten–rhenium thermocouples made by two manufacturers were calibrated at the Pt–C eutectic fixed point (1738 \({^{\circ }}\)C) and their stability was investigated. A linear fitting and extrapolation method was developed to determine the melting and freezing temperatures of the Pt–C eutectic fixed point for avoiding the effect of thermal resistance caused by the sheath and protection tube. The results show that the repeatability of the calibration is better than 0.9 \({^{\circ }}\)C from the melting curve of the Pt–C fixed point and better than 1.2 \({^{\circ }}\)C from the freezing curve of the Pt–C fixed point, and a good agreement was obtained for the calibration with the melting and freezing temperature plateau through the linear fitting and extrapolation method. The calibration uncertainty of the thermocouples at the Pt–C eutectic fixed point was 3.1 \({^{\circ }}\)C (k \(=\) 2).     

Effect of the Eutectic Phase on the Microstructure and Tensile Strength of an Al–Zn–Ni–Mg–Cu Casting Aluminum Alloy

Strength of Materials - The effect of composition, casting, and heat treatment on the eutectic phase morphology of an Al–Zn–Ni–Mg–Cu casting aluminum alloy was studied. The...     

Manipulating the Melting Behavior of Metal–Metal Eutectics

Experiments were carried out in order to determine why a given eutectic sample approaches its state of equilibrium either rapidly or slowly during melting-curve determinations. The results of these experiments suggest that, when eutectic liquids are frozen, nonequilibrium solids normally form. The experimental results also suggest that the melting temperatures increase and the reproducibility of the melting curves improves considerably if the nonequilibrium solid is converted into the equilibrium eutectic solid lattice. As specific examples, Al–Cu and Al–Ag eutectic samples were studied.     

Photoacoustic Measurement of Thermal Properties of Co–Ni–Li Ferrite Nanoparticles

A simple home-made open photoacoustic cell is used for measuring some of the thermal properties of nanoparticles of $\mathrm{{Co}}_{0.5}\mathrm{{Ni}}_{0.5\text{-- }2{x}}\mathrm{{Li}}_x\text{ Fe }_{2+{x}}\mathrm{{O}}_{4}$ Co 0.5 Ni 0.5 -- 2 x Li x Fe 2 + x O 4 (with $x$ x ranging from 0.00 to 0.25 in steps of 0.05) prepared by the citrate precursor method. The influence of sintering temperatures on the thermal properties of a selected sample for $x=0.25$ x = 0.25 was also investigated. The thermal-diffusivity and thermal-effusivity measurements of the investigated samples are obtained by measuring the photoacoustic signal as a function of the modulated frequency depending on the existence of a reference sample. The thermal diffusivity of the as-prepared samples decreases as the $\mathrm{{Li}}^{1+}$ Li 1 + content increases except for the samples for $x=0.15$ x = 0.15 and $x=0.20$ x = 0.20 . These exceptions may be due to a better magnetic ordering in these samples leading to reduced phonon scattering and a higher thermal diffusivity. Finally, the thermal diffusivity of the sintered samples increases as the sintering temperature increases due to the increase in grain size.     

Investigation of TiC–C Eutectic and WC–C Peritectic High-Temperature Fixed Points

TiC–C eutectic (2,761°C) and WC–C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC–C and three WC–C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC–C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC–C peritectic within 1 day was 17 mK with a melting range of ∼70 mK. The repeatability of the freezing temperature of the WC–C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC–C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC–C cells were easily constructed, like metal–carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC–C peritectic has more potential than the TiC–C eutectic as a high-temperature reference point. The investigation of the purification of the TiC–C cell during filling and the plateau observation are also reported.     

A Study on the Effect of Thermal Ageing on the Specific-Heat Characteristics of 9Cr–1Mo–0.1C (mass%) Steel

The effect of thermal ageing on the heat-capacity behavior of 9Cr–1Mo–0.1C (mass%) ferritic/martensitic steel has been studied using differential scanning calorimetry (DSC) in the temperature range from 473 K to 1,273 K. The DSC results in the case of slow cooled, normalized and tempered, and subsequently thermally aged samples (500 h to 5,000 h at 823 K (550 °C) and 923 K (650 °C), clearly marked the presence of both magnetic and α-ferrite + carbide → γ-austenite phase transformations that take place successively upon heating. Furthermore, for the case of fully martensitic microstructure, an additional exothermic transformation at about 920 K(647 °C), arising from carbide precipitation is noticed. This event is characterized by a sharp drop in C _P . It is found that the α-ferrite + carbide → γ-austenite phase transformation temperature is only mildly sensitive to microstructural details, but the enthalpy change associated with this phase transformation, and especially the change in specific heat around the transformation regime, are found to be dependent on the starting microstructure generated by thermal ageing treatment. Prolonged ageing for about 500 h to 5,000 h in the temperature range from 823 K to 923 K (550 °C to 650 °C) contributed to a decrease in heat capacity, as compared to the normalized and tempered sample. This is due to the increase in carbide volume fraction. The martensitic microstructure is found to possess the lowest room-temperature C _P among different microstructures.     

On the Nature of the Effect of Interfaces between Constituents on the Strength of Fibrous Copper–Niobium–Titanium Composite

This paper describes the regularities of the variation of the mechanical characteristics of fibrous copper- and copper-alloy-based composites reinforced by niobium–titanium alloy fibers as a function of the state of the interfaces between its constituents under different conditions of deformation and thermal treatment.     

Prediction of the Inversion Curve and the Maximum Value of μJ–T for Some Refrigerants

In the present work, the thermodynamic states of the inversion curve have been obtained using only p–v–T data. We have also shown a linear relationship between compressibility factor and pressure for each branch of the inversion curve. These lines can be used to find the maximum inversion pressure, P _in ^M . Finally, we have predicted the temperature at which the Joule–Thomson coefficient, _J–T, has its maximum value for each isobar, by using the specific heat capacity, isobaric expansivity, or compressibility factor.