Photoacoustic thermal characterization of kaolinite clays

Abstract

The usefulness of photoacoustic techniques in characterizing the thermal properties of kaolinite clays, which are a very abundant mineral in some regions of Brazil, was investigated. Different behavioural patterns are observed below and above a heating temperature of 950 °C and can be attributed to the change from metakaolinite to an amorphous three-dimensional mineral which crystallises to mullite and crystobalite above 1200 °C. The implications of the results in the manufacture of clay bricks are briefly considered. This is important in tropical regions where a knowledge of the thermal properties of materials used in the building construction industry is highly desirable.

Thermal characterisation of dye-intercalated K-10 montmorillonite ceramics using photoacoustic technique

“…The measured TD values of the samples under investigation are shown in Tables 1 and 2. Clay and soil samples possess TD values of the order of 10 À7 to 10 À4 m 2 s À1 [8,14,[45][46][47]. However, TD is a transient thermo-physical parameter that measures how effectively phonons carry heat through the sample.…”

“…This non-radiative relaxation produces temperature fluctuations in the sample. These temperature fluctuations facilitate an indirect measurement of the thermal and optical properties of the sample [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. In photoacoustics (PA), the pressure variations produced within the cell are detected using a sensitive microphone.…”

Photothermal techniques applied to thermophysical properties measurements (plenary)

“…3 we show a typical application of the OPC method for the characterization of kaolinite clays. 25 The overall behavior of the thermal diffusivity of the heat-treated clay samples was explained by these authors with the help of both crystallinity and porosity measurements. The sharp increase in the thermal diffusivity between 800 and 950°C was attributed to the observed sharp increase in the sample crystallinity in this temperature range.…”

“…The use of a minimal gas chamber ensures an enhanced signal-to-noise ratio, and, consequently, higher accuracy in the value of ␣, and offers greater adaptability to practical restrictions imposed by experimental system requirements, especially when minimal preparation is required. The OPC technique is widely used for several applications aiming at the thermal characterization of a great variety of samples such as instant corn dry masa flour, 16 wood, 17 twolayer systems, 18 semiconductors, [19][20][21] food products, 22 polymers, 23,24 clays, 25 and so on. In Fig.…”

On the Use of Photothermal Techniques as a Tool to Characterize Ceramic-Metal Materials

“…al., 1997), polymers (Cella et. al., 1989), clays (Alexandre et. al., 1999, Mota et al, 2008, coating materials and so on.…”