INVESTIGADORES
MARTINEZ Oscar Eduardo
artículos
Título:
Photoacoustic detection of phase transitions sensitive to small volume changes using a resonant piezoelectric scheme
Autor/es:
O.E.MARTÍNEZ; Y.CESA; N.MINGOLO; R. ROMERO
Revista:
APPLIED PHYSICS B - LASERS AND OPTICS
Editorial:
Springer Verlag
Referencias:
Lugar: Berlin; Año: 2005 vol. 80 p. 365 - 371
ISSN:
0946-2171
Resumen:
ABSTRACT Resonant piezoelectric photoacoustic detection is
demonstrated to be a sensitive tool for the determination of
phase transitions. A model is presented that describes the
changes in the signal expected during phase transitions when
resonant detection is used. The technique is applied to the
study of first-order martensitic diffusionless transformations
in copper-based shape-memory alloys. The model takes into
account the signal changes arising from two sources. One
behaves like an effective change in the heat capacity, and
arises due to the enthalpy of the reaction, and the other can
be described as an effective change in the thermal expansion
coefficient, and arises from the volume change during
the transformation. Due to the relative high frequency used
(around 20 kHz), the transformation lags behind the temperature
oscillations, yielding a phase shift in the acoustic signal as
the transformation temperature is passed. The relative sign of
the phase angle and amplitude as the transformation proceeds
is an indication as to whether the signal arises from volume
changes or heat exchange (enthalpy). Huge signals from very
small volume changes (smaller than 0.5%) were observed.
PACS 78.20.Nv; 64.70.Kb; 81.30.Kf