Electrothermal Technique Research Articles

Analysis of the electrothermal technique for thermal property characterization of thin fibers

The transient electrothermal technique has been developed to measure the thermal conductivity and thermal diffusivity of electrically conductive or non-conductive nano-to-microscale fibers. In this work, a full theoretical model is developed in detail including the effects of radiation heat loss and non-constant heating as a result of sample temperature rise during measurement, and is compared to the more commonly used reduced model, which neglects these effects. Non-dimensional parameters are derived representing radiation heat loss and non-constant heating to identify the true parameter dependences on these effects. A numerical model is used to perform parametric analyses on the experimental setup providing results that were fitted with the full and reduced models to find thermal conductivity and thermal diffusivity. Additionally, the numerical model was used to investigate nonlinear radiation heat losses and spatially non-uniform heating effects resulting from uneven coating of the conductive layer on electrically non-conductive samples. As a result, these influences are shown to require careful consideration in the application of this technique. A clear linear relationship was found between the non-dimensional parameters and measurement error, which provides a measure for the proper estimation of systematic error induced by these effects. Using the reduced model for data reduction results in measurement percentage error equal to ten times the radiation and non-constant heating dimensionless parameters under the assumption of linear radiation heat losses (small sample temperature rise compared to ambient temperature).

Porous Graphitized Carbon for Adsorptive Removal of Benzene and the Electrothermal Regeneration

Graphitized carbons with mesoporous and macroporous structures were synthesized by a facile template-catalysis procedure using resorcinol and formaldehyde as carbon precursors and particulate hydrated metal oxides as both template and catalyst precursors. The materials were used as novel adsorbents for low-concentration benzene vapor. Furthermore, on the basis of the good electrical conductivities associated with the graphitized structures, an electrothermal desorption technique, which involved passing electric currents through the adsorbents to generate Joule heat, was employed to regenerate the saturated adsorbents and produce enriched benzene vapors. In comparison to microporous activated carbon, the porous graphitized carbons could afford a much quicker and more efficient regeneration by electrothermal desorption technique due to their enhanced conductivity and larger pore sizes. In addition, the concentration of the desorbed organics could be controlled by adjusting the applied voltages, which might be interesting for practical secondary treatment. It is promising that the joint utilization of porous graphitized carbon adsorbents and electrothermal desorption technique might develop effective and energy-saving processes for VOCs removal.

Characterization of thermal transport across single-point contact between micro-wires

A contact transient electrothermal technique (CTET) is developed to characterize the thermal transport between one-dimensional conductive and nonconductive microscale wires that are in point contact. This technique is a significant advance from the transient electrothermal method that is used to characterize the thermophysical properties of individual one-dimensional micro-wires. A steady-state analytical solution and a transient numerical solution are used to independently determine the value for the thermal contact resistance between the wires at the contact point. The CTET technique is applied to measurement of the thermal contact resistance between crossed Pt wires (25.4 μm diameter) and the thermal contact resistance between a glass fiber (8.9 μm diameter) in contact with a Pt wire (25.4 μm diameter). For Pt wire contact, the thermal contact resistance increases from 8.94×104 to 7.05×105 K/W when the heating current changes from 20 to 50 mA. For the Pt/glass fiber contact, the thermal contact resistance is much larger (2.83×106 K/W), mainly due to the smaller area at the contact point.

An Implantable Release-on-Demand CMOS Drug Delivery SoC Using Electrothermal Activation Technique

An implantable system-on-a-chip (SoC) integrating controller/actuation circuitry and 8 individually addressable drug reservoirs is proposed for on-demand drug delivery. It is implemented by standard 0.35- μ m CMOS technology and post-IC processing. The post-IC processing includes deposition of metallic membranes (200Å Pt/3000Å Ti/200Å Pt) to cap the drug reservoirs, deep dry etching to carve drug reservoirs in silicon as drug containers, and PDMS layer bonding to enlarge the drug storage. Based on electrothermal activation technique, drug releases can be precisely controlled by wireless signals. The wireless controller/actuation circuits including on-off keying (OOK) receiver, microcontroller unit, clock generator, power-on-reset circuit, and switch array are integrated on the same chip, providing patients the ability of remote drug activation and noninvasive therapy modification. Implanted by minimally invasive surgery, this SoC can be used for the precise drug dosing of localized treatment, such as the cancer therapy, or the immediate medication to some emergent diseases, such as heart attack. In vitro experimental results show that the reservoir content can be released successfully through the rupture of the membrane which is appointed by received wireless commands.

Effect of mercury and arsenic from industrial effluents on the drinking water and comparison of the water quality of polluted and non-polluted areas: a case study of Peshawar and Lower Dir

The purpose of the present study was to find out the sources of mercury and arsenic pollution of water in the industrial area of Peshawar, the capital of Khyber Pakhtunkhwa, Pakistan. Samples of effluents, mud, and water were collected from the target area (industrial area of Peshawar), the area of water supply source, and from the less polluted area, the Lower Dir district, as the control. Hg was determined by the cold vapor generation technique, while arsenic was determined using the electrothermal atomic absorption technique. Data of the water from the industrial area were compared with that of the source area, control area, as well as with the WHO and some international drinking water quality standards. The results show that some parameters, i.e., TDS, DO, pH, and hardness, were more than the permissible limits. Textile and glass industries were found to be the major sources of Hg and As pollution. Downstream dilution of these contaminants was also observed.

Nonlinear effects in transient electrothermal characterization of anatase TiO2 nanowires

As an effective transient thermal characterization technique, the transient electrothermal (TET) technique features a capability of measuring micro∕nanoscale samples of diverse electrical conducting natures. In this work, single anatase titanium dioxide (TiO(2)) nanowires fabricated using the electrospinning method are characterized using the TET technique. Time-dependent nonlinear effect is observed for both rise and fall stages in the voltage-time (U-t) response profile. The coated iridium film and soldered platinum pads possibly compromise the linear Ohmic effect and introduce undesired effects into the whole system. Two quantitative methods: generalized function analysis and direct capacitance derivation, are developed to suppress the nonlinear effect based on U-t profiles. Data processing is performed to determine the thermal diffusivity using global fitting under non-constant electrical heating. The effective thermal diffusivities from modified analysis processes stay in the range from 2 to 6 × 10(-6) m(2)/s. The results from both methods agree well with each other. The general function analysis method is also applicable for samples of short time thermal transport or for an experimental instrument that has relatively long rise time.

Use of Lichen and Moss in Assessment of Forest Contamination with Heavy Metals in Praded and Glacensis Euroregions (Poland and Czech Republic).

The concentrations of selected metals—Cr, Ni, Cu, Zn, Cd, and Pb—were determined in the samples of Hypogymnia physodes lichen and Pleurozium schreberi moss collected in Polish and Czech Euroregions Praded and Glacensis. More specifically, the samples were collected in Bory Stobrawskie, Bory Niemodlińskie, and Kotlina Kłodzka (Poland) and in Jeseniki (Czech Republic). The concentration of metals in the samples was measured using the atomic absorption spectrometry (flame AAS technique and electrothermal atomization AAS technique). The results were used to calculate the comparison factor (CF) that quantifies the difference in concentration of a given bioavailable analyte × accumulated in lichens and mosses: CF = 2 (c x,lichen − c x,moss) (c x,lichen + c x,moss)−1. The values of CF greater than 0.62 indicate the most probable location of heavy metals deposited in the considered area. In this work, the method was used to show a significant contribution of urban emissions to the deposition of heavy metals in the area of Bory Stobrawskie and in the vicinity of Kłodzko City.

Thermophysical properties of free-standing micrometer-thick Poly(3-hexylthiophene) films

The solution of Poly(3-hexylthiophene) (P3HT) in chloroform is generally adopted for fabricating P3HT thin films or nanofibers. In this work, 4 regular P3HT solution weight percentages, 2, 3, 5 and 7wt.%, are compounded to fabricate P3HT thin films by using spin-coating technique. Raman spectrum study suggests that the density of the P3HT thin films varies with different P3HT solution weight percentages while X-ray diffraction analysis reveals that the crystal structures are identical for all P3HT thin films. The transient electrothermal technique is employed to measure the thermal diffusivity of the P3HT thin films and an efficient temperature–resistance calibration is performed to cooperatively study the thermal conductivity. When the P3HT weight percentage changes from 2% to 7%, the thermal conductivity varies from 1.29W/m·K to 1.67W/m·K and the thermal diffusivity goes down from around 10−6m2/s to 5×10−7m2/s. The density of P3HT thin films is also determined from the experimental data. The relationship between the density and thermophysical properties clearly demonstrates that the thermal conductivity increases with density while the thermal diffusivity decreases.

Thermo-physical properties of thin films composed of anatase TiO 2 nanofibers

In this paper, anatase titanium dioxide (TiO 2) thin films ∼60 μm thick are fabricated using the electrospinning technique. The prepared thin films are composed of interconnected anatase TiO 2 nanofibers. The transient electro-thermal technique, combined with a temperature–resistance calibration procedure, provides a full spectrum study which examines the relationship between the film’s thermal diffusivity, density and thermal conductivity. It is found that the annealing process significantly reduces the thermal diffusivity of the sample from 3.73 × 10 –5 m 2 s −1 to the order of 10 –6 m 2 s −1. The effective thermal diffusivity, conductivity and density of the films are 1.35–3.52 × 10 –6 m 2 s −1, 0.06–0.36 W m −1 K −1 and 25.8–373 kg m −3, respectively. These values are about one order of magnitude or more lower than the bulk property values. This difference is attributed to the loose interior structure and large concentration of vacancies. A microscale physical model is designed to explore the intrinsic thermal conductivity of the discrete TiO 2 nanofibers that compose the films. The calculated intrinsic thermal conductivity of the TiO 2 nanofibers varies from 4.67 to 12.2 W m −1 K −1, which is comparable with the bulk thermal conductivity of 8.5 W m −1 K −1. The phonon mean free path calculation demonstrates that the nanofiber size has a negligible impact on the phonon transport. The major restriction on the heat transfer originates from the crystalline structure defect.

Thermophysical properties of multi-wall carbon nanotube bundles at elevated temperatures up to 830 K

Thermal transport measurements in multi-wall carbon nanotube (MWCNT) bundles at elevated temperatures up to 830 K are reported using a novel generalized electrothermal technique. Compared with individual CNTs, the thermal conductivity ( k) of MWCNT bundles is two to three orders of magnitude lower, suggesting the thermal transport in MWCNT bundles is dominated by the tube-to-tube thermal contact resistance. The effective density for the two MWCNT bundles, which is difficult to measure using other techniques, is determined at 116 kg/m 3 and 234 kg/m 3. The thermal diffusivity slightly decreases with temperature while k exhibits a small increase with temperature up to 500 K and then decreases. For the first time, the behavior of specific heat for MWCNTs above room temperature is determined. The specific heat is close to graphite at 300–400 K but is lower than that for graphite above 400 K, indicating that the behavior of phonons in MWCNT bundles is dominated by boundary scattering rather than by the three-phonon Umklapp process. The analysis of the radiation heat loss suggests that it needs to be considered when measuring the thermophysical properties of micro/nano wires of high aspect ratios at elevated temperatures, especially for individual MWCNTs due to their extremely small diameters.

Simultaneous measurements of the specific heat and thermal conductivity of suspended thin samples by transient electrothermal method

The electrothermal technique is developed to simultaneously measure the specific heat and thermal conductivity of individual thin samples suspended across two heat sinks, resorting to pulsed direct currents with or without a dc offset. The temperature evolution due to Joule self-heating is recorded and compared with the numerical solutions of transient heat conduction equations using the finite volume method. The thermal conductivity is determined by the steady temperature level and the specific heat by the transient temperature rise or relaxation. This technique is applied to a 10 microm thick platinum wire and the thermal conductivity and specific heat are in good agreement with the literature values. In addition, the influences of thermal radiation and thermal boundary resistance between the sample and heat sinks on the experimental results are discussed.

Research on High-Temperature Corrosion-Resistance Performance of Exhaust Pipe of Heavy Duty Vehicle

The exhaust pipe of a heavy duty vehicle, due to its harsh operating environment, is subject to corrosion caused by high temperature oxidization, chlorination and sulfuration, therefore, corrosion occurs very easily, which affects normal operation of the engine. The exhaust pipe of the engine can be protected by means of electro-thermal explosion spray-coating technique. The corrosion-resistant ability of coating in high temperature environment is surveyed respectively. The micro organizational structure of coating is studied in combination with SEM, EDS and other tests to search for corrosion-resistant principle of the coating in an attempt to improve the corrosion-resistance of the exhaust pipe of the engine.

Transient thermal characterization of micro/submicroscale polyacrylonitrile wires

In this work, the thermal diffusivity of single polyacrylonitrile (PAN) wires with diameters from 4.62 μm down to 324 nm is measured by using our recently developed transient electro-thermal technique. The wires span from 23 μm to 126.2 μm in our measurement. Since PAN wires are dielectric, a thin Au film is coated on the surface of the wires to make them conductive. In the experiment, a step current (with ∼2 μs rising time) is fed to the sample. The sample is heated and takes a certain time to reach its steady thermal state. The temperature rising response of the sample is sensed by measuring the resistance change of the thin Au coating. From the average temperature evolution of the sample, the thermal diffusivity can be extracted. Three PAN wires with different diameters are synthesized using the electro-spinning technique and are measured to obtain their thermal diffusivities (around 1.53×10-7 m2/s), which are slightly smaller than the bulk value.

Magnetron Sputtering of Aluminium Nitride Thin Films for Thermal Management

Well-crystallized aluminium nitride (AlN) thin films were synthesized on silicon substrates at room temperature using magnetron sputtering. Physicochemical properties of the film were investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectrometry and Raman spectrometry. The thermal conductivity of the AlN films was characterized using an original electro-thermal technique. Thanks to an optimization of deposition parameters and target preparation, the different hexagonal crystalline orientations of AlN, i.e. (002), (100), (101) were isolated. It appears that AlN thin films deposited by DC magnetron sputtering exhibit a wide range of thermal conductivity, from 2 to 50 W · K−1 · m−1.

Thermal characterization of microscale conductive and nonconductive wires using transient electrothermal technique

In this paper, a transient technique is developed to characterize the thermophysical properties of one-dimensional conductive and nonconductive microscale wires. In this technique, the to-be-measured thin wire is suspended between two electrodes. When feeding a step dc to the sample, its temperature will increase and take a certain time to reach the steady state. This temperature evolution is probed by measuring the variation of voltage over the wire, which is directly related to resistance∕temperature change. The temperature evolution history of the sample can be used to determine its thermal diffusivity. A 25.4μm thick platinum wire is used as the reference sample to verify this technique. Sound agreement is obtained between the measured thermal diffusivity and the reference value. Applying this transient electrothermal technique, the thermal diffusivities of single-wall carbon nanotube bundles and polyester fibers are measured.

Concentrations of selected toxic elements (cadmium, lead, mercury and arsenic) in ewe milk in dependence on lactation stage

Biological investigations on ewes of Merinolandschaf breed (n = 10) were conducted by the 60<sup>th</sup> lactation day during the summer on pasture. Ewe milk sampling was carried out on the 2<sup>nd</sup>; 10<sup>th</sup>; 30<sup>th</sup> and 60<sup>th</sup> lactation day. An electrothermal technique was used to determine Cd and Pb concentrations in food and milk whereas As and Hg concentrations in food and milk were determined by a hydrid technique on an atomic absorption spectrophotometer. The investigation results indicate that concentrations of selected toxic elements in ewe milk varied in dependence on lactation stage. In colostrum (2<sup>nd</sup> lactation day) Cd and Pb (0.011 and 0.035 mg/kg)concentrations were significantly higher (P < 0.01) whereas As (0.011 mg/kg) concentrations were lower in comparison with milk on the 10<sup>th</sup> (Cd: 0.004; Pb: 0.022; As: 0.025 mg/kg), 30<sup>th</sup> (Cd: 0.005; Pb: 0.024; As: 0.028 mg/kg) and 60<sup>th</sup> (Cd: 0.006; Pb: 0.026; As: 0.029 mg/kg) lactation day. However, no significant differences (P > 0.05) were found in milk Hg concentration in relation to lactation stage (from 0.021 to 0.026 mg/kg). The selected toxic elements appeared to be present in ewe milk in very low concentrations.    

Determination of platinum, palladium and rhodium in biological and environmental samples by low temperature electrothermal vaporization inductively coupled plasma atomic emission spectrometry with diethyldithiocarbamate as chemical modifier

A novel method for inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of trace amounts of Pt(II), Pd(II) and Rh(III), based on gaseous compounds introduction into the plasma as their diethyldithiocarbamate complexes by electrothermal vaporization (ETV), was developed. At the temperature of 1100 °C, the trace amounts of Pt, Pd and Rh were vaporized into plasma. The factors affecting the formation of the chelates and their vaporization behaviors, such as ashing temperature and time, vaporization temperature and time, pH and the concentration of chelating reagents were studied in detail. Under the optimized conditions, the limits of detection (LODs) (3 σ) of Pt, Pd and Rh for tested solutions were 5.4, 1.4 and 0.8 ng ml −1, and for actual sample (auto-catalyst NIST SRM 2557) were 0.27, 0.07 and 0.04 μg g −1, respectively. The relative standard deviations (RSDs) for Pt, Pd and Rh were 1.4, 2.6 and 2.4% ( C Pt=0.5 μg ml −1, C Pd,Rh=0.25 μg ml −1, n=7), respectively. The linear ranges of calibration graphs for Pt, Pd and Rh cover three orders of magnitude. Compared with conventional electrothermal vaporization technique, using the reagent of diethyldithiocarbamate as chemical modifier could not only enhance the analytical sensitivities, but also reduce the vaporization temperature. By combination with a separation/preconcentration step, the proposed method had been successfully applied to the analysis of the artificial seawater, tap water and urine with recoveries ranging from 91 to 106%. The two certified reference material meager platinpalladium ore GBW 07293 and auto-catalyst NIST SRM 2557 was also analyzed for validation, and the determined values obtained were in good agreement with the certified values.

Determination of Bismuth in Nonferrous Alloys by Inductively Coupled Plasma Mass Spectrometry Combined with Use of Solid-Phase Methylation and Electrothermal Vaporization Technique

Determination of Bismuth in Nonferrous Alloys by Inductively Coupled Plasma Mass Spectrometry Combined with Use of Solid-Phase Methylation and Electrothermal Vaporization Technique

Simultaneous measurements of electric and thermal fields utilizing an electrooptic semiconductor probe

A method to simultaneously measure electric and thermal fields with a single probe is presented in this paper. The Pockels effect is employed within a gallium-arsenide probe to measure electric fields, and the effect of photon absorption due to bandtail states in the semiconductor is used to determine temperature. The measured optical power is found to be inversely related to temperature, in agreement with theory, and experimental results demonstrate a temperature sensitivity of 0.31 /spl mu/W//spl deg/C at 25/spl deg/C and an accuracy of /spl plusmn/0.5/spl deg/C between 20/spl deg/C-60/spl deg/C. The minimum detectable electric field is 1.24/spl plusmn/0.06 V/m using a 300-ms electrical bandwidth. Temporal phase stability of /spl plusmn/3/spl deg//h is achieved through the implementation of a system phase reference channel. The invasiveness of the probe is quantified by examining the change in the characteristic impedance and capacitance per unit length of a planar transmission line. Measured and simulated data show that the effect is equivalent to a lumped shunt capacitance on the order of a few femtofarads. The examination of a monolithic microwave integrated circuit in an X-band quasi-optical power-combining array and the calibration of electric-field data that was corrupted by temperature-dependent effects inherent to the electrooptic probe demonstrate the capability of this combined electrothermal measurement technique.

In-situ profiling of dipole polarization distributions in poled nonlinear optical polymers with electrothermal and optical techniques

Poling is an essential process step in the preparation of dipolar chromophore-based second-order nonlinear optical polymers. In single- and multilayer film structures, poling often yields a spatially nonuniform orientation of the chromophores across the film thickness. An electrothermal technique, based on the measurement of electrical transients after pulsed thermal excitation, as well as an optical second-harmonic generation technique have been developed for the depth profiling of the dipole polarization with a high spatial resolution around 100 nm.