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This paper makes an investigation on the synthesis of tantalum carbide (TaCx) based chromel composites and their tribological behaviour using pin on disc under various load conditions. The reinforced chromel alloy with TaCx was prepared at the rate of 0, 3 and 6 wt.% of TaC using stir casting route. The wear resistance of composites was found to improve with the increase in weight percentage of TaC. The wear properties of Chromel-TaCx composite were enhanced due to the presence of 6% TaC. The wear worn out surface of chromel composite was studied through microstructures. The optimal process factors and their effect on responses have been analyzed through Response Surface Methodology (RSM) and Analysis of Variance (ANOVA). more...

We developed thermocouple probes consisting of constantan and chromel segments with nanoscale sharpness. The ends of wires made of these alloys were polished utilizing a single step drop-off electrochemical procedure in a H3PO4 solution. The macroscopic shapes of the etched wires were designed to detect ultra-small heat inputs with high sensitivity after assembling a thermocouple. After electrochemical treatment, ultimately smooth, mirror-polished wire surfaces were observed. The etched wires were then assembled in a transmission electron microscope (TEM) to create a miniature thermocouple by using which we successfully detected a small temperature increase induced by focused TEM electron beam irradiation. Judging from high- resolution TEM imaging, a thermocouple with the tip-end of only ~5 nm in diameter was fabricated. more...

International audience; An experimental setup for 3 method with a constant current source and two differential amplifiers was built to measure the thermal conductivity and the volumetric heat capacity of single polyacrylonitrile (PAN)-based carbon fiber. In complement to a well known analytical thermal model, a numerical one was developed that can check the validity of the analytical one and can also take into account the effect of convective heat loss on the measurements. A detailed sensitivity analysis of the unknown parameters was presented that would finally help in the better design of the setup for 3 method. The tests were performed under vacuum and atmospheric pressure for chromel wire as a reference sample and under vacuum for two types of polyacrylonitrile-based carbon fiber. Detailed measurements were performed displaying the influence of convective loss and the thermal contact resistance between fiber and copper electrodes on the estimation of thermal properties of carbon fiber. more...

Coaxial thermocouples have the advantages of fast response and good durability. They are widely used for heat transfer measurements in transient facilities, and researchers have also considered their use for long-duration heat transfer measurements. However, the model thickness, transverse heat transfer, and changes in the physical parameters of the materials with increasing temperature influence the accuracy of heat transfer measurements. A numerical analysis of coaxial thermocouples is conducted to determine the above influences on the measurement deviation. The minimum deviation is obtained if the thermal effusivity of chromel that changes with the surface temperature is used to derive the heat flux from the surface temperature. The deviation of the heat flux is less than 5.5% when the Fourier number is smaller than 0.255 and 10% when the Fourier number is smaller than 0.520. The results provide guidance for the design of test models and coaxial thermocouples in long-duration heat transfer measurements. The numerical calculation results are verified by a laser radiation heating experiment, and heat transfer measurements using coaxial thermocouples in an arc tunnel with a test time of several seconds are performed. more...

The magnitude of surface heat flux and its accurate estimation are very crucial owing to their applicability in impulsive thermal loads for high-speed flights. The correctness of such heat flux is associated with the implications from highly responsive thermal sensors in ground-based aerodynamic studies. In the present study, the performance effectiveness of an indigenous, in-house-made coaxial thermal probe (CTP) is validated against a standard silver thin film gauge (TFG) counterpart. The thermal probe has been fabricated in-house from two metal alloys; chromel (3.25 mm diameter and 10 mm length) and constantan (0.91 mm diameter and 15 mm length), by disposing one in the annulus of another coaxially, subsequently clubbed by a thin layer of epoxy in between them. Similarly, the thin film gauge is fabricated by putting silver paste (~1 µm thickness) on the pyrex substrate (3.25 mm diameter, 10 mm length). The fabrication process is followed by different calibration activities to determine the characteristics constants for sensors (sensitivity, thermal product value for CTP, and temperature coefficient of resistance for TFG). Both the probes are tested in a highly transient environment in a shock tube that generates high density, high pressure, and high enthalpy flows. The response time of the CTP and TFG are found to be 265 µs and 240 µs, respectively. The heat flux values estimated through temperature responses are having a nice match for CTP as well as TFG with a deviation in peak heat flux value within a range of ±2%. A similar trend and magnitude are also re-assured through numerical simulation within an uncertainty band of ±1.5%. The exhaustive study carried out in a shock tube has assured the performance and reliability of a CTP. Hence, it is recommended as an effective heat flux sensor for routine measurements in impulsive heat loadings. more...

The development of advanced nuclear fuels requires detailed understanding of their transmutation and micro-structural evolution. Alloy fuels have the advantage of high thermal conductivity and improved characteristics in fuel-cladding chemical reaction. However, information on thermodynamic and thermophysical properties is limited. The objective of this work was to develop an experimental system, integrated with thermal conductivity measurement capability to measure the thermodynamic properties of solid materials, from which an understanding of their phase change(s) can be determined. With the coupled system, both thermal conductivity and electromotive force (EMF) may be measured. In order to validate the system, the apparatus was employed to measure the EMF of several materials. As an initial calibration test, the EMF of Chromel was measured from 100 °C to 800 °C and compared with theoretical values. Subsequent EMF measurements were made for pure iron, iron-nickel alloy, and ANSI 1018 carbon steel rods. The measured phase transition temperatures were compared with the corresponding alloy equilibrium phase diagrams. The results indicate that the system is able to determine material phase change based on EMF measurement. In the future, this prototype system is to be adapted for hot-cell use on irradiated samples. more...

Understanding the cell temperature distribution of solid oxide fuel cell (SOFC) stacks during normal operation has multifaceted advantages in performance and degradation studies. Present efforts on measuring temperature from operating SOFCs measure only the gas channel temperature and do not reveal the cell level temperature distribution, which is more important for understanding a cell's performance and its temperature-related degradation. The authors propose a cell-integrated, multi-junction thermocouple array for in-situ cell surface temperature monitoring of an operational SOFC. The proposed thermocouple array requires far fewer numbers of thermoelements than that required by sets of thermocouples for the same number of temperature sensing points. Hence, the proposed array causes lower disturbance to cell performance than thermocouples. The thermoelement array was sputter deposited on the cathode of a commercial SOFC using alumel (Ni:Al:Mn:Si – 95:2:2:1 by wt.) and chromel (Ni:Cr – 90:10 by wt.). The thermocouple array was tested in a furnace over the entire operating temperature range of a typical SOFC. The individual sensing points of the array were shown to measure temperature independently from each other with equivalent accuracy to a thermocouple. Thus, the concept of multi-junction thermocouples is experimentally validated and its stability on a porous SOFC cathode is confirmed. more...

A transition boiling on a high temperature solid beyond the Leidenfrost temperature is characterized by a strong unstable heat transfer. This unstable one brings a rapid temperature change beneath the surface in the solid and causes a repetition in time as well as a space of wet and dry on the surface. Therefore, the development of a fast temperature measurement technique is indispensable to understand this transition phenomenon. The developed temperature sensor has a junction of the end face of chromel fine wire of ϕ0.32 mm diameter, whose position is 3 μm away from the surface of nickel disk of 5 mm thickness and can follow a rapid temperature change within 100 kHz. The heat transfer can be calculated from the measured temperature by using an inverse problem analysis for one-dimensional unsteady heat conduction. Besides, the calculated heat flux is also confirmed to be sufficient to capture the characteristics of unsteady boiling heat transfer in the experiment that a sessile ethanol droplet impacts onto the hot surface. more...

International audience; The purpose of this paper is to investigate a steady-state method enabling the measurement of the thermal conductivity of an electric conducting wire. Instead of varying the pulsation of a periodic current as done in the 3ω method, the proposed method is based on steady-state measurements realized for different lengths of the same wire. The model developed takes into account an external heat transfer coefficient (conduction + radiation) often neglected in previous works. A sensitivity analysis shows the possibility of estimating simultaneously the wire thermal conductivity and the external heat transfer coefficient. The experimental results obtained with Chromel and Copper wires are in good agreement with references values (less than 5% deviation). more...

The objective of the current investigation is to find out temperature distribution regimes in a horizontal pipe when condensation process is happened. The research was conducted at Pusat Studi Ilmu Teknik Universitas Gadjah Mada. The experiment apparatus consists of an inner annulus pipe made from copper (din = 17.2 mm, do = 19 mm) with the length of 1.8 m. The outer annulus pipe is a galvanized iron pipe (din = 108.3 mm, do = 114.3 mm) with the length of 1.6 m. Thermocouples type K 36 TT OMEGA with chromel (+) and alumel (-) materials were used as temperature sensors, to detect the spread of temperature in radial or axial direction along the pipe. The measurement ranged from -50 to 260 oC, with an accuracy of 0.01 °C. A data logger of RX 40 serial (OMRON, 20 Channels) was used to read and record temperature data with the sampling rate of 5 Hz. In the experiment, the water (H2O)was heated using a boiler to generate steam which was then flowed and condensed inside the annulus pipe to form a steam-condensate two-phase flow in horizontal pipe. On the other hand, the water was used as a coolant in the outer of annulus pipe. The results indicated that the temperature distribution regimes are influenced by axial posisition.The farther distances from the inlet the lower the temperatures being recorded which indicate the increase of film condensate thickness. Such phenomena can affect slugging in the location. more...

Novel multi-junction thermocouple architecture was developed and simulated to in-situ monitor the temperature distribution over a Solid Oxide Fuel Cell (SOFC). This thermocouple architecture requires only {N+1} number of wires for N number of independent temperature measuring points. Therefore, N+1 architecture can independently measure temperature at multiple points simultaneously with much less number of wires than a set of thermocouples require for the same number of independent temperature measurements. Requiring less number of external wires is a distinct advantage, particularly, in constrained environments such as those within SOFC stacks. A thermocouple array having 4 independent temperature measuring points with 5 thermo-elements was simulated in MATLAB. Alumel (Ni:Al:Mn:Si – 95:2:2:1 wt) and Chromel (Ni:Cr – 90:10 wt) were chosen as thermo-element materials because of their wide applicability in the industry as K-type thermocouples. The junctions were considered to be spot welded. Three sets of simulations were performed to investigate two aspects: validation of the multi-junction thermocouple concept and investigation of the effect of the heat affected zone created in spot welding to the temperature measurement. Simulation code generates random temperature values for each junction within a pre-defined range. Temperatures at the boundaries of heat affected zones were also generated randomly according to a pre-defined criterion. The change of Seebeck coefficients within the heat affected zone was set as a percentage change of their corresponding materials Seebeck coefficient. The temperature gradient induced emf values for each sensing point were calculated from Seebeck coefficients. The calculated emf was then mapped back to temperature using ASTM approved inverse conversion function. These mapped temperatures were then compared with the set temperatures for each junction and they were in very good agreement. more...

International audience; This paper presents a dynamic characterization setup to calibrate transient surface temperature sensor in radiative conditions. The temperature sensor is a K type (Chromel/Alumel) wire microthermocouple which hot junction is obtained from a layer deposition by PVD process. Three different metallic layers are used (Tungsten, gold and chromium) with two thin film thicknesses (0.4 μm and 0.8 μm). The aim of this work is to develop a dynamic characterization with a radiation source from a laser focused onto the thermocouple's hot junction. The dynamic performance of the sensor is obtained by measuring its unit-impulse response function (Yag laser) and its periodic response under a chopped continuous laser beam (Argon laser). Experiments are realized at atmospheric pressure. The best results are obtained with deposited probes with gold junction of 0.4 μm thickness. The rise-time and decrease-time are equal to 10 μs and 80 μs respectively (Yag laser). more...

In this study, we fabricated a thermoelectric module made of Ni-based alloy as standard reference for use in cross-checking the power generation characteristics of module testing systems. The module was fabricated with eight pairs of legs made from mechanically durable p-type Ni90Cr10 (chromel) and n-type Cu55Ni45 (constantan). To increase thermal resistance of the module, holes were made in the p- and n-type Ni-based alloys, thereby reducing the effective density of the legs by ~57.1%. As a result, a thermal resistance of 6.16 K W−1 was obtained at a hot-side temperature (Th) of 773 K and cold-side temperature (Tc) of 323 K. A maximum electrical power (Pmax) of ~0.39 W and maximum conversion efficiency (ηmax) of ~0.53% were obtained for the module with holes at Th of 773 K and Tc of 323 K. We confirmed the reproducibility of power generation characteristics, including the open circuit voltage (Voc), internal resistance (Rin), Pmax, output heat flow (Qout), and ηmax of the module, through 12 repeated tests and ~120 h of continuous tests at Th of 773 K and Tc of 323 K. The variation of Voc, Rin, Pmax, Qout, and ηmax is with standard deviation less than 1% from their mean values. more...

A setup is designed for measuring the Seebeck coefficient (S) of materials in form of thin film, bar and wire. The main feature of this setup is control in heating and cooling cycles. In this setup heat pulse is used to generate the temperature gradient. To demonstrate the capabilities of this setup, S vs T of standard wire samples such as Au-Fe (0.07 \%), chromel, Pt and thin films of Pt and F doped SnO$_2$ are presented. The standard uncertainty of the repeatability in S measurement is found to be $\sim$ $\pm 0.056~\mu V/K$ while temperature stability is $\sim$ $\pm 10~mK$ (at 320 K), estimated for a chromel wire sample. We have tested the setup in temperature range 100 K to 320 K, while it does not have any intrinsic limitation in going down to liquid He temperatures. For temperatures above 320 K limitation is due to gluing material like varnish., Comment: 5 pages, 4 figures more...

A Seebeck coefficient measurement apparatus has been designed and developed, which is very effective for accurate characterization of different type of samples in a wide temperature range (80 - 650K) simultaneously covering low as well as the high-temperature regime. Reducing the complexity of the technical design of sample holder and data collections has always been challenging to implement in a single instrument when samples are in different geometrical shape and electronic structure. Our unique design of sample holder with pressure probes covers measurements of different samples shapes (wires, thin films and pellets) as well as different resistivity ranges (metals, semiconductors and insulators). It is suitable for characterization of different samples sizes (3-12 mm). A double heater configuration powered by a dual channel source meter is employed for maintaining a desired constant temperature difference across the sample for the whole temperature range. Two K-type thermocouples are used for simultaneously reading of temperatures and Seebeck voltages by utilizing different channels of a multichannel digital multimeter. Calibration of the system has been carried out using constantan, chromel and alumel materials and recorded data is found to be very accurate and consistent with earlier reports. The Seebeck coefficients of standard samples of constantan (wire) and GaN (thin film) have been reported, which shows the measurement capability of designed setup with versatile samples., Comment: 16 PAGES, 5 FIGURES more...

This article presents the results of research on sputtering of thermoelectric alloys chromel and kopel. Sputtering was performed in argon atmosphere with magnetron sputtering system. Results of this work can be used in creation of thin-film thermoelectric generators. more...

Heat exchange of a blunt cylinder in a hypersonic (M = 6) air flow are studied numerically. Calculations are carried out in ANSYS Fluent, taking into account the conjugate heat transfer between the external flow and the solid model under steady and transient incoming flow conditions. As a result of the calculations, the fields of temperature and other external flow parameters were obtained. The heating regimes are defined for the steel model and the heat transfer sensor installed in the frontal part of the model. Results of the analysis of gas temperature measurement are presented at change of the temperature from 1400 K to 2000 K in an impulse wind tunnel with operation time up to 160 ms. The total temperature was measured by chromel -alumel thermocouples with the junction sizes of 0.05, 0.1 and 0.2 mm. Deconvolution method was used for the solution of convolution integral equation. Thermocouples calibration was done by measurements of temperature step-function. Deconvolution method allows obtaining dist... more...

This paper investigates the corrosion behaviour of type K thermoelements and their thin films, and compares the performance of chromel–alumel thin film thermocouple with its wire counterpart before and after exposure to 5% NaCl medium. Potentiodynamic polarisation tests reveal that chromel and alumel films are more “noble” than their respective wires. Alumel corrodes faster when coupled with chromel in films than as wires. Secondary electron micrographs and electrochemical impedance spectroscopy measurements suggest that chromel shows localised corrosion while alumel undergoes uniform corrosion. Corrosion adversely affects the thermocouple output and introduces an uncertainty in the measurement. more...

This article deals with an experimental investigation into the different cutting factors which influence the machinability factors such as cutting force, cutting temperature, and tool life during high speed turning of superalloy Inconel 718. Also the article aims to study the relationship of cutting parameters with respect to the tool-chip contact length and chip microstructure. A standard K-type (alumel/chromel) thermocouple was embedded in to the top shim of the tool holder to measure temperature during turning. The test results show that there exist a close relationship between the cutting parameters and tool-chip contact length, thermal loading equivalent, and chip microstructure. In particular, it was observed that by the proper selection of cutting parameters the cutting force, cutting temperature and tool life can be controlled to the great extent. Also by selecting the proper cutting parameters, the tool-chip contact length can be controlled effectively so as to reduce the temperature which is responsible for rapid tool wear (flank wear) and plastic deformation of the cutting edge. The cutting parameters greatly affect the microstructure grain orientation of the chip. more...

Oscillatory behaviour during methane oxidation over a cobalt foil has been studied using on-line mass-spectrometry and video recording of the colour of the catalyst surface. It was demonstrated that during oscillatory behaviour, periodic transitions of the catalyst surface from an oxidised state (dark colour) to a reduced state (light colour) occurred together with the variation of the catalyst temperature. Oscillations over the cobalt foil appeared at higher temperatures (860–950 °C), and had longer periods, in comparison with oscillatory behaviour which was observed earlier over a nickel foil. The application of TGA in combination with TPR experiments revealed the differences in nickel and cobalt redox properties which are responsible for the variation in the properties of the oscillations. Forced oscillations could be obtained in a low temperature region (700–860 °C), if bare chromel and alumel wires were spot-welded separately to the cobalt foil. It was shown that in this case the chromel wire induced oscillatory behaviour of the whole cobalt foil. Complicated mixed mode oscillations detected at higher temperatures were shown to be the result of the coupling of high frequency oscillations produced by the unshielded chromel–alumel thermocouple and low frequency oscillations appearing over the cobalt foil. more...

Metallic coils (in most cases Cu coils) are often used in high-pressure experiments to protect thermocouple wires. In this paper we show that these coils have important influences on thermocouple EMF and therefore on the temperature measurements. We tested this effect by measuring EMF from Cu coiled single wires of chromel and alumel, and, further, we conducted experiments to compare the EMF from W5Re-W26Re thermocouples with and without Cu coils attached to them. The results show systematic differences in thermocouple readings; the EMFs from W-Re thermocouples with Cu coils give systematically lower values than EMFs from thermocouples without Cu coils. The results were analyzed using a simple model. The difference in thermocouple EMFs between thermocouples with and without protection coils is given by \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[{\Delta}\mathit{E}\_{TC}\ =\ \frac{\mathit{E}\_{2}\ {-}\ \mathit{E}\_{1+}}{1\ +\ \frac{\mathit{R}\_{2}}{\mathit{R}\_{1+}}}\ {-}\ \frac{\mathit{E}\_{2}\ {-}\ \mathit{E}\_{1{-}}}{1\ +\ \frac{\mathit{R}\_{2}}{\mathit{R}_{1{-}}}}\] \end{document} where E i and R i are the EMF and the electrical resistance of metal i in the portion of the Cu coil, and the subscripts 1+, 1–, and 2 indicate positive thermocouple metal, negative thermocouple metal, and coil metal, respectively. The addition of a coil with different metal has a large effect — the Δ E TC will be close to –( E 1+ – E 1–) > R 2 and therefore thermocouple readings with a Cu coil will lead to underestimation of the real temperature. Under common experimental conditions with a multi-anvil apparatus, the error in the temperature estimate caused by Cu protection coils is ~100–150 K for a peak temperature of 1600–2000 K. more...

Nickel-based alloys – Ni 0.98 Ti 0.02 , Ni 0.4 Cu 0.6 (constantan) and Ni 0.9 Cr 0.1 (chromel) have been saturated with hydrogen at ca. 1 GPa at room temperature. The electrical resistance and thermoelectric power of the hydrogenated samples have been simultaneously measured in the temperature range between 80 and 300 K. The electrical resistance of Ni–Ti/H and Ni–Cu/H alloys exhibits an anomalous behavior. The temperature dependent component of the resistance of the Ni 0.98 Ti 0.02 alloy increases upon hydrogenation and continues its increase when hydrogen is desorbed in a stepwise manner. The hydrogenation of Ni 0.4 Cu 0.6 results in a decrease of electrical resistance while the opposite effect is usually observed in other hydrogenated Pd- and Ni-based alloys. more...

A thin-film multijunction thermal converter was fabricated through the process using 6 inch silicon wafer semiconductor process and bulk micromachining. Evanohm R alloy and chromel-constantan were used as a heater and thermocouple materials, respectively. The temperature coefficient of resistance of Evanohm R heater was about 75.12 ppm/ and the voltage sensitivity of the thermal converter indicated about 5.75 mV/mW in air. The transfer differences, measured by FRDC-DC method in the frequency range from 20 Hz to 10 kHz, showed the value under about 1.36 ppm, 0.83 ppm for the film thickness of 500, 200 nm, respectively. And in case of a 200 nm-thick thermal converter, the AC-DC transfer differences seems to be stabilized below the value of 1 ppm in the frequency range from 1 kHz to 500 kHz. more...

An isothermal section of the phase diagram of the system Fe–Sb–O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. Two ternary oxides namely FeSb2O4 and FeSbO4 were identified. Making use of the phase diagram, the oxygen potentials of the ternary phases were measured by employing the following solid electrolyte based galvanic cells: (I) Chromel, Mo, Sb, Fe 3 O 4 , FeSb 2 O 4 ∣15 CSZ∣NiO, Ni, Mo, Chromel (II) Pt, Fe 3 O 4 , FeSb 2 O 4 , FeSbO 4 ∣15 CSZ∣air (P O 2 =0.21 atm), Pt (III) Pt, FeSb 2 O 4 , FeSbO 4 , Sb 2 O 3 ∣15 CSZ∣air (P O 2 =0.21 atm), Pt where 15 CSZ stands for ZrO2 stabilized by 15 mol% CaO. The least-squares regression analyses of the emfs of the galvanic cells I, II and III (split into two ranges) measured over the temperature ranges 771–911, 771–921 and 787–981 K, respectively, can be represented by the expressions E I ±0.39 (mV)=152.8–0.04728 T ( K ) E II ±0.22 (mV)=1010.0–0.4172 T ( K) E IIIA ±0.46 (mV)=870.1–0.3665 T ( K ) E IIIB ±0.31 (mV)=809.3–0.2992 T ( K ) These emf expressions were used to derive the standard Gibbs’ energies of formation of FeSb2O4 and FeSbO4 and are given by Δ G f o (FeSb 2 O 4 )±3.5 (kJ mol −1 )=−1068.7+0.3561 T ( K ) Δ G f o (FeSbO 4 )±5.5 (kJ mol −1 )=−976.9+0.3289 T ( K ) The emf of the cell III exhibited a break corresponding to the liquidus temperature of Sb2O3. The cell III was used to assess the internal consistency of ΔGfo (FeSbO4) derived from cell II. The consistency of ΔGfo data for these two interoxides with the relevant tie-lines in Fe–Sb–O system is highlighted. Comparison of iron interoxide stabilities with those of six other interoxides in the systems M–Sb–O where M is Cr, Co or Ni reported earlier in the literature revealed FeSb2O4 to be the most stable interoxide with respect to the equilibrium oxygen dissociation pressure in the corresponding set of coexisting phases. Hence, this interoxide is proposed to substitute Sb2O3 in the auxiliary neutron source of liquid metal cooled fast breeder reactors subject to meeting other physics requirements. more...

A chromel-alumel thermoelectric flow sensor using thermal isolation membrane was fabricated. Temperature coefficient of resistance of thin film Pt-heater was about , and Seebeck coefficient of chromel-alumel thermocouple was about . The sensor showed that thermoelectric voltage decreased as thermal conductivity of gas increased, and -flow sensitivity increased as heater voltage increased or the distance between heater and thermocouple decreased. When heater voltage was about 2.5 V, -flow sensitivity and thermal response time of the sensor were about and 0.18 sec., respectively. Linear range in flow sensitivity of the flow sensor was wider than that of Bi-Sb flow sensor. more...

Surface junction thermocouples are used extensively for transient heat flux measurements, but their accuracy is dependent on the effective thermal product (TP) of the gauge and this can be a function of the time scale of interest. In the present work the response of surface junction k-type thermocouples was investigated experimentally using a water droplet calibration technique (for millisecond times scales) and a small shock tube (for microsecond time scales). Different junctions formed by scalpel blade scratches and abrasive paper were investigated. When scratches from scalpel blades were used to form the junction, the TP identified from the water droplet calibrations consistently differs by approximately 20% depending on whether the junction was made on the chromel or alumel substrate, in accord with existing thermal properties data. However, the shock tube calibrations indicate that for scalpel-scratched junctions there is considerable variability in thermocouple response time due to effective junction depth variations produced during construction. In contrast, junctions formed with abrasive paper produced rise times consistently less than 1s, but the water droplet and shock tube experiments both indicated significant variability in the effective TP for these gauges. The consistency in TP for scalpel-scratched junctions for millisecond time scales and the variability for junctions created with abrasive grit for both the millisecond and microsecond time scales is attributed to the differences in the effective proximity of the junction to the insulation between chromel and alumel substrates. For junctions created with abrasive grit, the effective TP is approximately 30% smaller for microsecond time scales than it is for millisecond time scales. more...

This paper describes micromachined scanning thermocouple probes that exploit the low thermal conductivity and the high mechanical flexibility of polyimide as a structural material. They are surface micromachined using a low-temperature six-mask process suitable for appending to a CMOS fabrication sequence. The probes are 200-1000-/spl mu/m long, 40-120-/spl mu/m wide, and of varying thickness. They are assembled by a flip-over approach that eliminates the need for dissolving the substrate wafer or removing the probe from it. Temperature sensing is provided by thin-film Ni/W or chromel/alumel thermopiles embedded in the polyimide, which provide Seebeck coefficients of 22.5 and 37.5 /spl mu/V/K per junction, respectively. Modeling results indicate that the low thermal conductivity of polyimide causes the temperature drop along the probe length to be much higher than with other candidate materials such as Si or SiO/sub 2/, which contributes to improved thermal isolation of the sample and higher temperature sensitivity of the probe. However, the response time of the probe is compromised, and the measured -3 dB bandwidth of the probes is /spl ap/500 Hz. A sample scan is presented. more...

Semisolid processing using laser irradiation was proposed to fabricate porous media. This processing is based on semisolid processing and rapid prototyping technology. In the processing, laser irradiation is used to produce the semisolid state in objective particles. The particles can remain their spherical shape due to high viscosity of the semisolid state. The liquid phase in the semisolid particles locally flows into gap between the particles and consequently the particles are joined to each other. Porous media were experimentally fabricated for constantan, chromel, pure copper and Cu–5 mol%Ag alloy by using the proposed processing. The range of laser power and irradiation time to fabricate porous media became wider as the temperature range in which the semisolid state was obtained was larger. Preheating the green particles also increased the fabrication range. The large latent heat of metallic alloys contributed to the fabricability of porous media. The proposed semisolid processing using laser irradiation can fabricate porous media of metallic alloys with three-dimensional shape. more...

A chromel–alumel thermocouple has been found to catalyse the methane/oxygen reaction, the main products being CO, H2 with some CO2 and H2O. Regular oscillations in both reactants, products and temperature have been observed at temperatures around 700thinspcirC. Similar behaviour has been obtained using nickel wires. more...

An isothermal section of the phase diagram of the system Ni–Sb–O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. Two ternary oxides, namely NiSb2O4 with Sb in trivalent and NiSb2O6 with Sb in pentavalent state, were identified. Making use of coexistence of NiSb2O4 with NiO and Sb, as well as NiSb2O6 with NiO and NiSb2O4, the following galvanic cells were designed to measure the Gibbs energies of formation of the ternary oxides: I Chromel, Mo, Sb, NiO, NiSb 2 O 4 ∣15 CSZ∣NiO, Ni, Mo, Chromel II Pt, NiO, NiSb 2 O 4 , NiSb 2 O 6 ∣15 CSZ∣air ( P O 2 =0.21 atm), Pt where 15 CSZ stands for ZrO2 stabilized by 15 mol% CaO The reversible emfs of the cells were measured over the temperature ranges 769–931 K and 894–1138 K respectively. The results could be represented by the following expressions: E±0.3 ( mV )=88.3–0.1043 T ( K ) E±0.3 ( mV )=1053.5–0.5544 T ( K ) The standard Gibbs energies of formation of NiSb2O4 and NiSb2O6 were computed from the emfs: Δ G° f (NiSb 2 O 4 )±4.2 (kJ mol −1 )=−988.3+0.3472 T (K) (769–931 K) Δ G° f (NiSb 2 O 6 )±4.3 (kJ mol −1 )=−1394.9+0.5472 T (K) (894–1138 K) The reasonability of the above data were assessed by computing the entropy change for the solid–solid reactions leading to the formation of ternary oxides from the respective pairs of constituent binary oxides. It was found that NiO forms a much more stable compound with Sb2O5 than with Sb2O3. more...