Modulated IR radiometry as a tool for the thickness control of coatings

The thickness of coatings can be determined using the data measured by Modulated IR Radiometry for sets of coatings, produced under specific controlled conditions: – Keeping constant all deposition parameters except the deposition time, coatings of approximately constant thermal transport properties, but different thickness are produced. The modulated IR phase lag signals measured for the coatings are calibrated with the help of signals obtained for homogeneous opaque reference samples of smooth surface. Quantitative results for the thermal transport properties are obtained using the inverse solution of the 2-layer thermal wave problem by which direct relations are established between the relative extrema of the inverse calibrated thermal wave phase signals measured as a function of the heating modulation frequency and the thermal coating parameters, the ratio of the effusivities coating-to-substrate, the coating's thermal diffusion time, and the coating thickness. The coating thickness values obtained by Modulated IR Radiometry are compared with the values measured by standard microscopic methods, and relative errors of 3 – 4% have been found for the coating thickness of a set of TiCO coatings on steel, presented here as an example.(undefined

THERMAL-WAVE MEASUREMENTS OF MULTI-LAYER SUPERINSULATION FOILS

Abstract Thermal wave measurements rely on modulated laser heating and IR detection of the thermal response, using a MCT detector with IR optics and lock-in amplifier. Both, the amplitude and the phase retardation of the thermal wave response with respect to the heating modu-lation, provide information on the effective thermal transport properties of the measured samples. Here we apply this method to determine the shielding properties of multilayer superinsulation foils, used for the thermal insulation of superconducting magnetic coils in particle accelerators, e.g. in LHC at CERN. The measurements, performed at ambient temperature and ambient and reduced pressure, have been interpreted using a theoreti-cal model, including both conductive and radiative heat transport. The results show that the radiative heat transport can be well identified, although the conductive heat transport is dominant across multi-layer samples. At reduced pressures, the conductive heat transport decrea-ses considerably and, depending on the number of spacer layers, the radiative heat transport can become dominant. Applying this new photothermal technique, the shielding efficiencies of multi-layer superinsulation foils have been compared in this work for the first time

Thin films composed of Ag nanoclusters dispersed in TiO2: Influence of composition and thermal annealing on the microstructure and physical responses

Noble metal powders containing gold and silver have been used for many centuries, providing different colours in the windows of the medieval cathedrals and in ancient Roman glasses. Nowadays, the interest in nanocomposite materials containing noble nanoparticles embedded in dielectric matrices is related with their potential use for a wide range of advanced technological applications. They have been proposed for environmental and biological sensing, tailoring colour of functional coatings, or for surface enhanced Raman spectroscopy. Most of these applications rely on the so-called localised surface plasmon resonance absorption, which is governed by the type of the noble metal nanoparticles, their distribution, size and shape and as well as of the dielectric characteristics of the host matrix. The aim of this work is to study the influence of the composition and thermal annealing on the morphological and structural changes of thin films composed of Ag metal clusters embedded in a dielectric TiO2 matrix. Since changes in size, shape and distribution of the clusters are fundamental parameters for tailoring the properties of plasmonic materials, a set of films with different Ag concentrations was prepared. The optical properties and the thermal behaviour of the films were correlated with the structural and morphological changes promoted by annealing. The films were deposited by DC magnetron sputtering and in order to promote the clustering of the Ag nanoparticles the as-deposited samples were subjected to an in-air annealing protocol. It was demonstrated that the clustering of metallic Ag affects the optical response spectrum and the thermal behaviour of the films.This research was sponsored by FEDER funds through the COMPETE program (Programa Operacional Factores de Competitividade) and by FCT (Fundação para a Ciência e a Tecnologia), under the projects PEST-C/FIS/UI607/2013 and PEst-C/EME/UI0285/2013. The authors also acknowledge the financial support by the project Nano4color – Design and develop a new generation of color PVD coatings for decorative applications (FP7 EC R4SME Project No. 315286). J. Borges also acknowledges the support by the European social fund within the framework of realising the project “Support of inter-sectoral mobility and quality enhancement of research teams at Czech Technical University in Prague”, CZ.1.07/2.3.00/30.0034. C. Lopes acknowledges FCT for the PhD grant SFRH/BD/103373/2014. F.M. Couto acknowledges CAPES – Foundation, Ministry of Education of Brazil, Brasília – DF 70040-20, Brazil, funding by stage sandwich doctorate, through PDSE – Doctoral Program Sandwich

Emissivity measurements by means of combined photoacoustics and modulated IR radiometry

A new method for the determination of the emissivity $\epsilon$ is presented, which relies on thermal wave excitation by intensity-modulated heating in the visible spectrum and on simultaneous detection of the response in the transmission configuration of thermal waves by means of IR radiometry and photoacoustics (PA)

Effect of moisture take-up on the effusivity and ignition of dry fibrous carbon-based materials

The moisture take-up from the humid atmosphere and its effect on the effective thermal properties of dry fibrous carbon-based material have been measured with the help of modulated IR radiometry. For the measured samples, black graphitized paper, the results are independent of the emissivity, and the observed changes mainly refer to the effective thermal properties. The effects of moisture take-up are analyzed with respect to thermal effusivity, thermal diffusivity, and two specific thermal parameters (surface area heat capacity, thermal conductivity per sample thickness), which are relevant in surface heating processes in cylindrical geometry

Position modulated tangential photopyroelectric (PPE) spectrometry for low absorptions in liquids

A novel tangential photopyroelectric (PPE) cell for liquids is described in which the excitation laser beam is position-modulated. As a result, only the thermal wave is modulated and the background signal due to scattered light is suppressed by more than 50 times. The application for water pollution monitoring shows a detection limit of 1 mmol/m3 ammonium ion in water

Thermal characterization of micro-structured NiTi samples by 3ω scanning thermal microscopy

The lateral modification of the thermal conductivity of a NiTi sample have been measured by scanning thermal microscope using the 3ω-technique. Squares of lateral length in the micrometer range had been drawn in a polycrystalline NiTi sample by a focussed ion beam of Ga. Amplitude and phase of the 3ω-signal have been recorded at some selected positions as a function of frequency between 10 Hz and 10 KHz and as a function of position at selected modulation frequencies. The 3ω-signals are modified inside the squares as well as the border lines and also change when the temperature is increased above the martensite-austenite transition temperature