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).     

Relating Composition and Thermoelectric Stability of Pt–Rh Alloy Thermocouples

A simple model is presented which relates the electromotive force drift rate of Pt–Rh thermoelements to dS/dc, the sensitivity of the Seebeck coefficient, S, to rhodium mass fraction, c. The model has been tested by repeated measurements of a Pt–Rh thermocouple assembly consisting of five thermoelements, using a Co-C high-temperature fixed point (\(1324{\,}^{\circ }{\mathrm{C}}\)) for a total duration of 500 h. By considering various thermocouples from the assembly, it is demonstrated that in this case, remarkably, there is a linear relationship between the measured drift rate and the combined dS/dc, where the combination is determined by addition of the individual values for each wire. Particular emphasis is placed on evaluation of the uncertainties associated with the calculations. This result supports previous findings that the thermoelectric stability of Pt–Rh thermoelements improves as the rhodium mass fraction increases. Within this paradigm, it is shown that for a selected Pt–Rh thermoelement of any given composition, there exists a second thermoelement having a composition that yields a minimum drift when combined with the first to form a thermocouple.     

Properties of Phases and Alloys of the Mo–Ni–B System in the Ni–MoNi–Mo2NiB2–Ni2B Region

Materials Science - For alloys of the Mo–Ni–B system annealed at subsolidus temperatures (and some as-cast alloys) in the Ni–MoNi–Mo2NiB2–Ni2B region, we study the...     

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.     

Comparative Study of Pt/Pd and Pt–Rh/Pt Thermocouples

The Pt/Pd thermocouple has demonstrated superior thermoelectric drift and homogeneity performance over conventional Pt–Rh/Pt thermocouples. Here, we present a systematic comparison of the drift and homogeneity performance of Pt/Pd and Type R thermocouples by ageing the thermocouples at 1350 °C for a total of 500 h and measuring the performance at regular intervals during this time. The thermocouples studied were one Pt/Pd thermocouple, one Type R thermocouple and one ‘special’ Type R thermocouple which was given the same preparatory annealing treatment as the Pt/Pd thermocouple prior to use. The thermoelectric stability of each thermocouple was measured at the freezing point of Ag (961.78 °C) and the melting point of Co–C eutectic (1324.29 °C). The thermoelectric homogeneity of the thermocouples was also measured. Two difference methods were used by withdrawing the thermocouple from the Ag cell and by moving a localized heat source along the thermocouple. The long-term drift of the Pt/Pd thermocouple was around 50 mK (Ag) and 65 mK (Co–C) after the first 100 h ageing at 1350 °C, followed by a further 25 mK (Ag) and 35 mK (Co–C) over the subsequent 400 h ageing. This drift performance and inhomogeneity were an order of magnitude lower than for the two Type R thermocouples. The Type R thermocouple which was given the ‘special’ preparatory treatment was about 50 % more stable than the conventional Type R thermocouple.     

Special features of the diamond crystallization in the Mg–Zn–B–C system

The diamond crystallization in the Mg–Zn–B–C system occurring in the diamond thermal stability region have been considered. The phase transformations, which take place during the preparation of the alloy–solvent for carbon and its structure, the diamond crystallization and properties of the resultant diamond crystals have been studied. The formation of the acceptor centers and inclusions in diamond crystals caused by the addition of boron into the growth system have been considered. It has been found that the use of the diamond powder produced in this system for abrasive machining surfaces of sapphire parts makes it possible to increase the machining efficiency and quality as compared with that of the powder produced in the Ni–Mn–C system.     

Measurement of interdiffusion coefficients in Co–AI and Ni–AI systems between 1000 and 1200°C

Abstract

Interdiffusion coefficients between 1000 and 1200°C have been measured in the Co-Al and Ni-Al solid-solution phases using a modified form of the Boltzmann- Matano method. Interdiffusion in the Co-Al phase is at least half an order of magnitude lower than in the corresponding Ni-Al phase. Established equations using these coefficients were used to determine theoretical critical mole fractions of aluminium necessary to form protective Al₂O₃ scales during oxidation. While these equations are reasonably accurate in predicting the amounts of chromium necessary to form Cr₂O₃ scales, they give inaccurate predictions of the amounts of aluminium necessary to form Al₂O₃ scales because the kinetics of the early stages of oxidation are not taken into account.

MST/144     

Life Expectancy Study of Small Diameter Type E, K, and N Mineral-Insulated Thermocouples Above 1000???C in Air

Very little if any current data is available for the life expectancy of very small diameter thermocouples operating at high temperatures, greater than 1000???C. Over the past 10?years significant changes in the supply stream of the materials used to manufacture base metal thermocouples have occurred. In many industrial applications, small diameter thermocouples are the only solution for high-temperature measurements. This study has been undertaken to assess the performance of small diameter magnesium oxide insulated metal sheathed thermocouple sensors at or above 1000???C. Three different American Society of Testing and Materials (ASTM) standard letter designation thermocouple types have been included in this study, Types E, K, and N. Inconel 600 and 316 stainless, for three different sizes, 0.5?mm, 1.0?mm, and 1.5?mm, have been tested for different thermocouple types. Each group of sensors was placed in an equalization block in air for a maximum of 500?h or until failure. The performance of 0.5?mm diameter thermocouples varies widely depending on the thermocouple type, sheath material, and test temperature. Larger diameter Type K and N thermocouples show very little drift up to 500?h at 1100???C. The data for each test was collected at 10?s intervals for the entire duration of the test. Data for the sensor drift and subsequent failure are presented.     

Influence of Overheating and Cooling Rate on the Structures and Properties of Alloys of the Fe–B System

Materials Science - It is shown that the overheating of a melt by 150°K over the liquidus curve and a cooling rate of 102?104 °K/sec favor the formation of a homogeneous finely...     

Measurement of the monochromatic emissivity of coatings at 100–400°C

Results of measurement of the normal emissivities of certain coatings by a two-beam method in the 2–25 range are reported.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 27, No. 2, pp. 203–207, August, 1974.     

Corrosion Resistance of Alloys of the Al–Cu–Fe–(Si,B) System in Mineralized Saline and Acid Solutions

Materials Science - We study the influence of alloying with 4–7 at.% Si and/or 1–3 at.% B on the corrosion behavior of Al– Cu–Fe quasicrystalline alloys in the solutions of...     

Numerical and experimental evaluation of the influence of the filler–bitumen interface in mastics

The successful use of additives in modified asphalt mixtures, such as warm mix asphalt, depends largely on the effect such modification has on the mastic. Previous research indicated that such modifiers do not simply change the bitumen properties, but can also change the interaction between the filler and the bitumen matrix. Understanding the effect of the properties of the fillers, the bitumen and their interaction is thus important for future asphalt mix design. In order to investigate this and to define the dominant relationships, this paper combines a numerical and experimental approach. In the experiments, the viscosities of modified and unmodified mastics with different filler concentrations and types were systematically investigated utilizing a novel testing protocol. In the numerical analyses, the Finite Element Method was utilized for a micro-mechanical analysis, in which the shape and size of the filler particles were varied in the bitumen matrix. Combining the experimental and numerical results allowed for a detailed investigation of the effect of the interface properties, with and without modifiers. The research further indicated that the effect of the shape and size of the fillers varied, depending on the interface properties. From the research relationships were established between the overall mastic viscosity and the influence of the filler–bitumen interface, considering shape and size. The conclusion of this paper can thus be useful for the effective development of modified asphalt mixtures and gives strong indications towards future research directions.     

Measurement and Correlation of Electrical Conductivity of β-Cyclodextrin in Water Solution

The electrical conductivity of 4% β-cyclodextrin in water solution had been measured by electrode method from（323.65~353.65） K at atmospheric pressure. The expe...