Jocelyn Veilleux

A total internal reflection fluorescence microscopy study of mass diffusion enhancement in water-based alumina nanofluids

Mass diffusion of rhodamine 6G (R6G) in water-based alumina nanofluids is studied by means of total internal reflection fluorescence (TIRF) microscopy. We report a mass diffusivity enhancement that reaches an order of magnitude in a 2 vol % nanofluid when compared to the value in deionized water. Since experiments were performed with positively charged R6G, interfacial complexation between the dye and the nanoparticles was not observed. The effect of local density variations on mass diffusivity measurements is also addressed. An explanation for the enhancement of mass diffusion is presented using arguments based on dispersion, and it is shown that it correctly describes the order of magnitude differences between the thermal conductivity and mass diffusivity enhancements reported in the literature.

Particle size measurement in glass powder beds using optical coherence tomography

Optical coherence tomography was used to collect cross- sectional images of glass powder beds consisting of microspheres with diameters ranging from 8 to 175 m. Images were formed by a collection of individual interferogram envelopes that give the backscattered light amplitude as a function of the optical path in the glass powder bed. The diameter distribution, for microspheres located near the surface of the beds, is obtained by appropriate peak distance measurements on threshold-selected envelopes after having performed the surface profilo- metry. The measured distributions are in good agreement with those obtained by laser diffraction. When considering the whole powder vol- ume, the evaluation of the mean light penetration depth inside the pow- der beds proves to be a useful approach to evaluate the mean particle diameter, although no information is obtained on the actual particle size distribution in this case. Two simplified models are introduced to under- stand the linear relationship observed between the penetration depth and the mean particle size.

Multi-element, high-temperature integrated ultrasonic transducers for structural health monitoring

This paper reports recent developments on high-temperature, multi-element integrated ultrasonic transducers (IUTs). The multi-element IUTs are fabricated from a sol-gel route, where piezoelectric films are deposited, poled and machined into an array of 16 elements. Electrical wiring and insulation are also integrated into a practical, simple high-temperature assembly. These multi-element IUTs show a high potential for structural health monitoring at high temperatures (in the 200-500°C range): they can withstand thermal cycling and shocks, they can be integrated to complex geometries, and they have broadband and suitable operating frequency characteristics with a minimal footprint (no backing needed). The specifics of multi-element transducers, including the phased array approach, for structural health monitoring are discussed.

Optical Coherence Tomography for Inspection of Highly Scattering Ceramic Media: Glass Powders and Plasma‐Sprayed Coatings

Optical coherence tomography (OCT) is used to collect images of spherical glass powders with mean diameter ranging from 10 to 150 microns. Appropriate peak distance measurements on image interferograms provide a good approximation of particle size distribution. The relationship between the light penetration depth inside powders and the particle diameter is also discussed based on Mie theory. Thereafter, OCT images of plasma‐sprayed ceramic coatings are presented as well as an approach for establishing light penetration depth inside zirconia coatings.

Characterization of the Phase Composition of Nanosized Lithium Titanates Synthesized by Inductive Thermal Plasma

The properties of lithium titanates anodes in Li-ion batteries are highly dependent on their secondary constituents. While their main phase is usually constituted of Li4Ti5O12, significant quantity of lithium titanates compounds of various stoichiometry are often present, due to either the processing, usage or aging of the material. These may go underreported, as many of these spectrums overlap or display low signal in X-ray diffraction (XRD). Samples of nanosized lithium titanates synthetized by inductive plasma were characterized by XRD and scanning electron microscopy (SEM), as they provide a regular yet typical crystallite size and shape including multiple phases. A Rietveld refinement was developed to extract the composition of these samples. Mass balance through further annealing and differential scanning calorimetry (DSC) enthalpy measurements from phase transformations were also used as identification and validation techniques.