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.     

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).     

Effects of Composition and Thermal Cycle on Transformation Behaviors, Thermal Stability and Mechanical Properties of CuAlAg Alloy

The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6Al-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.     

Selective Laser Melting of an Al–Fe–V–Si Alloy: Microstructural Evolution and Thermal Stability

Selective laser melting was used to produce an aluminum alloy Al-8.5Fe-1.3V-1.7Si(wt%). The effects of heat treatment on microstructure evolution and phase stability during long-term thermal exposure of the deposits were investigated. Results show that the microquasi-crystalline phase, Al12(Fe,V)3Si and AlmF e metastable phases coexisted with α-Al in the as-produced alloy. Annealing at 400 °C resulted in decomposition of microquasi-crystalline phase and supersaturated α-Al into Al12(Fe, V)3Si phase in the fusion zone, accompanied by the decrease in alloy hardness. The activation energy of this decomposition process was 115 k J/mol. A more homogenous microstructure was obtained after annealing at 400 °C for 60 min,which was resistant to coarsening exposed at 425 °C up to 500 h. The Al12(Fe,V)3Si and AlmF e phases were coarsened at 475 and 525 °C with increasing the exposure time. Coarsening of Al12(Fe,V)3Si phase was attributed to a combination of volume diffusion and grain boundary diffusion mechanism of Fe. Heat treatment at 600 °C resulted in accelerated microstructure coarsening and formation of large-sized equilibrium phases, which signi?cantly degraded the room temperature microhardness.     

Controlled Growth of Pt–Au Alloy Nanowires and Their Performance for Formic Acid Electrooxidation

Pt–Au alloy nanowires have been controllably electrodeposited on microelectrodes by applying an alternating current and were used as the electrocatalyst for formic acid oxidation. The frequency and voltage of the alternating current and the electrolyte composition were adjusted to precisely control the morphologies, alloying structures and composition. The characteristics of Pt–Au alloy nanowires were analyzed by scanning electron microscopy, X-ray diffraction and transmission electron spectroscopy. Electrocatalytic performance of formic acid oxidation at Pt–Au alloy nanowires electrode was investigated by cyclic voltammetry and chronoamperometry. The results showed that the Pt–Au alloy nanowires possessed highlycrystalline morphologies, the controllable bimetallic composition and single-phase alloy structures, which mainly grow in the 111 crystal orientation. The electrocatalytic activity of formic acid oxidation strongly depended on the bimetallic Pt/Au composition. The Pt35Au65 alloy nanowires displayed superior electrocatalytic performance and high stability toward the electrooxidation of formic acid in acidic solution, owing to the ensemble effect of the Pt and Au components. These ?ndings provided insights into the design of the Pt–Au bimetallic nanomaterials as electrocatalysts for formic acid oxidation.     

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.     

Effects of the Composition of Electrodeposited Fe-Ni-P Alloy on the Thermostability and Magnetic Properties

The magnetic properties, structure defects of electrodeposited Fe-Ni-P alloys with various compositions and the thermostability at amorphous state have been studied by DSC, positron annihilation and electronic integrating instrument methods. The results show that the thermostability of amorphous Fe-Ni-P alloys increases with Fe content. Emergence and recrystallization of stable phases defer as the P content of the coating increases. The minimum Hc, Br and Ph occur at 9.4 P (wt pct) content. Maximum Hc, Br and Ph occur at the weight ratio of Fe to Ni equaling to 1/9.     

Influence of a Phosphate–Nitrate Composition on the Corrosion of Mechanically Activated Aluminum Alloy

Materials Science - We study the protective properties of a phosphate–nitrate composition on aluminum alloy in a medium of synthetic acid rain. The proposed composition has high anticorrosion...     

Equilibrium Phase Constituents and Discontinuous Precipitation Behavior of Al-Zn-Cu Alloy with Symmetrical Composition

Through microstructure observation and X-ray diffraction analysis, the equilibrium phase constituents of Al-Zn alloy that contains 2 at. pct Cu at room temperature have been determined as AI-based solid solution (α), Zn-based solid solution and AlCu3Zn phase (T′-phase), which are different from α phase, Zn phase and CuZn4 phase originally believed. It is determined that the products of discontinuous precipitation transformation below 277℃ are not the equilibrium phase constituents, but the metastable phases made up of α phase, Zn phase and CuZn4 phase. The phase constituents after discontinuous precipitation of AlZn-2Cu alloy would transform to the ones in equilibrium status: Al-based solid solution (α) in fcc structure, Zn-based solid solution in hcp structure and Al4Cu3Zn phase (T′-phase) ultimately through plastic deformation at room temperature and re-heating treatment below 277℃.     

Measurement of the Inhomogeneity in Type B and Land–Jewell Noble-Metal Thermocouples

Inhomogeneity is the largest contributor to uncertainty in temperature measurements made with thermocouples, and the knowledge of inhomogeneity is essential if low-uncertainty measurements are required. Inhomogeneity is a particular problem for long-term applications at temperatures near or above 1500 \(^{\circ }\hbox {C}\), where pairs of alloyed noble-metal thermocouples must be used and the alloy components and potential contaminants become very mobile and cause large deviations in the Seebeck coefficient. While changes in inhomogeneity are a known and well-studied problem in noble-metal alloys at temperatures below 1100 \(^{\circ }\hbox {C}\), the effects are not well quantified at higher temperatures. This paper reports the first detailed measurements of inhomogeneity in a number of Type B and Land–Jewell thermocouples exposed to either short-term calibration up to 1600 \(^{\circ }\hbox {C}\) or long-term in situ measurements for a period of approximately 3000 h at 1600 \(^{\circ }\hbox {C}\). The inhomogeneity is measured in a high-resolution scanner operating over the range from 600 \(^{\circ }\hbox {C}\) to 900 \(^{\circ }\hbox {C}\). The results show that drifts of between 0.2 % and 0.6 % can be expected for reversible crystallographic and oxidation effects, whereas drift caused by irreversible contamination effects can be expected to be between 0.6 % and 1.1 %. It is also shown that the deviations in emfs caused by irreversible homogeneities in these thermocouples scale approximately linearly with temperature. This scalability allows uncertainties assessed at one temperature, to be extrapolated to other temperatures. Additionally it is shown that a preconditioning anneal at 1100 \(^{\circ }\hbox {C}\) should be applied both before and after calibration to remove undesirable crystallographic and rhodium-oxidation effects.     

Microstructural Characteristics and Stability in a RapidlySolidified Al-Fe-Nb-Si Alloy

The microstructure and stability in a rapidly solidified Al-Fe-Nb-Si alloy were studied by using transmission electron microscopy (TEM) with energy dispersive X-ray spectrometry (EDXS) and X-ray difFraction technique. It is shown that the addition of Nb to Al-Fe-Si alloy may increase undercooling of melt, and form the featureless zone structure, the size of the intercellular phases and the distance betWeen intercellulars of Al-Fe-Nb-Si alloy are two times smaller than that of Al-Fe-V-Si alloy under the same conditions. Further, the microstructure of the featureIess zone has the better thermal stability after annealing at 623 K for 24 h.     

Selection of the Composition of a Multicomponent Alloy of the Nb–Ti–Al–X System with High-Temperature Strength,Heat Resistance,and Technological Efficiency

Materials Science - We establish the physicochemical conditions required for the creation of multicomponent Nb–Ti–Al–X (X – Cr, Zr, Mo, Sr) niobium alloys with improved...     

Effect of Precipitating Phases on Tensile Strength and Microstructural Stability of a Spray-Deposited Al-Si-Fe-Mn-Cu-Mg Alloy

Spray deposition is a novel process which is used to manufacture rapidly solidified bulk and near-net-shape preforms. In this study, AI-20Si-5Fe-3Mn-3Cu-1Mg alloy was synthesized by spray deposition technique. The aging process of the alloy was investigated by differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM). The results show that two kinds of phases, i.e. S(Al2CuMg) and σ(Al5Cu6Mg2), precipitate from matrix and improve the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300℃). In addition, the σ-Al5Cu6Mg2 is a relatively stable phase which improves microstructural stability of the alloy.     

Optical Properties of Liquid Aluminum and Al–Ce Alloy

The Beattie ellipsometric method is used to investigate the index of refraction and the absorption coefficient of liquid aluminum and Al–3 at. % Ce alloy in the wavelength range from 0.44 to 2.3 m at a temperature of 1173 K. The experimental results are used to calculate the dispersion dependences of light conductance, reflectivity, and functions of characteristic loss of electron energy. The results of measurements in the infrared (IR) spectrum are used to determine the concentration of conduction electrons, plasma frequency, relaxation frequency, and the limiting light conductance. It turns out that an addition of 3 at. % Ce to aluminum causes almost no change in the concentration of charge carriers, whereas the relaxation frequency increases, which leads to a decrease in the electrical conductivity of the liquid alloy.     

Composition and lattice parameters of silicide and matrix in cast Ti–Si–Al–Zr alloys

Abstract

The silicide chemistry, i.e. the type, composition, and lattice parameters of the silicide in as cast titanium based Ti–Si–Al–Zr alloys, has been studied. It has been shown that the stoichiometry of the silicide in the alloys can be expressed as (Ti_1?x , Zr_x)₅(Si_l?y, Al_y) _2·76?3·04(0≤X< 0·2, 0≤y<0·1). The presence of Al and Zr in the silicide increases its lattice parameters. Addition of Al coarsens the eutectic silicide and slows the formation of secondary silicide precipitates by solid state reaction. Addition of zirconium refines the eutectic silicide and promotes secondary silicide precipitation. The silirides are low in Al and rich in Zr, whereas the Ti matrix is rich in Al and low in Zr. The lattice parameters of the Ti matrix are decreased by Al and increased by Zr.

MST/1427     

Deformation of the Shape Memory and Surface Microrelief of Ni–Fe–Ga–Co and Cu–Al–Ni Alloy Single Crystals

Technical Physics Letters - We present the results of experimental studies of the return of Ni–Fe–Ga–Co and Cu–Al–Ni single crystals to the initial form at the macro-...     

Composition and properties of silver-containing calcium carbonate–calcium phosphate bone cement

The introduction of silver, either in the liquid phase (as silver nitrate solution: Ag(L)) or in the solid phase (as silver phosphate salt: Ag(S)) of calcium carbonate–calcium phosphate (CaCO₃–CaP) bone cement, its influence on the composition of the set cement (C-Ag(L) and C-Ag(S) cements with a Ca/Ag atomic ratio equal to 10.3) and its biological properties were investigated. The fine characterisation of the chemical setting of silver-doped and reference cements was performed using FTIR spectroscopy. We showed that the formation of apatite was enhanced from the first hours of maturation of C-Ag(L) cement in comparison with the reference cement, whereas a longer period of maturation (about 10 h) was required to observe this increase for C-Ag(S) cement, although in both cases, silver was present in the set cements mainly as silver phosphate. The role of silver nitrate on the setting chemical reaction is discussed and a chemical scheme is proposed. Antibacterial activity tests (S. aureus and S. epidermidis) and in vitro cytotoxicity tests (human bone marrow stromal cells (HBMSC)) showed that silver-loaded CaCO₃–CaP cements had antibacterial properties (anti-adhesion and anti-biofilm formation) without a toxic effect on HBMSC cells, making C-Ag(S) cement a promising candidate for the prevention of bone implant-associated infections.     

Influence of Cerium on Microstructure and Solidification of Eutectic Al–Si Piston Alloy

Thermal analysis has become very important in foundry because it aids in studying the effect of additives on eutectic growth temperature and assessing the quality of modifications. This research was performed to investigate the influence of the addition of Ce (0.1–1.0 wt.%) on the eutectic Al–Si–Cu–Mg alloy characteristics of solidification. Field emission scanning electron microscopy (FESEM) and optical microscopy were employed to characterize the alloy microstructure. The main phases studied were the Al–Cu (Al₂Cu) and Al–Si phases. The addition of Ce decreased the nucleation and growth temperatures and acted as a refiner for the alloy. The larger amounts of Ce significantly impacted the Si structure: the average Si particle size decreased as the Ce concentration was increased, which led to a finer grain structure. The Ce formed intermetallic compounds with the alloyed elements that had plate- or needle-like structures and that interrupted the modification of Si. The solidification parameters, including the growth and nucleation temperatures, increased with increasing change in the morphology of the Al–Cu phase that were caused by Ce addition.