Abstract
The effect of the ultrasound on electrochemical processes has been investigated employing a microelectrode within the cavitating media. Transient mass transport was strongly enhanced in the presence of ultrasound. High rates of mass transfer of up to 1.5 cm s-1 were observed. These high rates of mass transfer were attributed to two cavitation processes. First, bubble collapse at or near the solid-liquid interface with the consequent formation of a high speed liquid microjet directed at the electrode surface. Second, bubble motion near or within the diffusion layer or the electrode. Single current transients were also recorded at high time resolution. These single current transients were attributed to the short-time perturbation of the diffusion field of the microelectrode due to impacts of cavitation bubble collapse followed by a long time relaxation of the diffusion field back to the steady state. The influence of the ultrasonic source to electrode separation, temperature of the bulk solution, electrode potential and electrode size on the magnitude of current transients was also studied. All of these parameters affected markedly the magnitude of the current transients recorded at microelectrode in the presence of ultrasound. An alternative approach is presented to characterise fast heterogeneous electron transfer reactions employing
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Citation Formats
Silva Martinez, Susana.
Applications of ultrasound in electrochemistry.
Mexico: N. p.,
1997.
Web.
Silva Martinez, Susana.
Applications of ultrasound in electrochemistry.
Mexico.
Silva Martinez, Susana.
1997.
"Applications of ultrasound in electrochemistry."
Mexico.
@misc{etde_693219,
title = {Applications of ultrasound in electrochemistry}
author = {Silva Martinez, Susana}
abstractNote = {The effect of the ultrasound on electrochemical processes has been investigated employing a microelectrode within the cavitating media. Transient mass transport was strongly enhanced in the presence of ultrasound. High rates of mass transfer of up to 1.5 cm s-1 were observed. These high rates of mass transfer were attributed to two cavitation processes. First, bubble collapse at or near the solid-liquid interface with the consequent formation of a high speed liquid microjet directed at the electrode surface. Second, bubble motion near or within the diffusion layer or the electrode. Single current transients were also recorded at high time resolution. These single current transients were attributed to the short-time perturbation of the diffusion field of the microelectrode due to impacts of cavitation bubble collapse followed by a long time relaxation of the diffusion field back to the steady state. The influence of the ultrasonic source to electrode separation, temperature of the bulk solution, electrode potential and electrode size on the magnitude of current transients was also studied. All of these parameters affected markedly the magnitude of the current transients recorded at microelectrode in the presence of ultrasound. An alternative approach is presented to characterise fast heterogeneous electron transfer reactions employing ultrasound as a mass transport enhancement tool. Two innovative techniques, sampled-current voltammetry and sampled-mean current voltammetry, were developed during the course of this thesis. The technique of sample-current voltammetry reported values of the standard rate constant of heterogeneous electron transfer of up to 1.2 cm s-1 in the presence of ultrasound. This technique focuses on the electrochemical phenomena under investigation at the point of impact of the ultrasonic event, produced by asymmetric cavitation bubble collapse near the electrode surface. Bubble dynamics were also examined under the experimental conditions employed in the present study. The bubble behaviour was observed from the numerical solution of the RPNNP equation that describes the motion of a gas filled bubble in a homogeneous phase. This equation was solved numerically employing the Fourorder Runge-Kutta method. Finally, a preliminary study of surface process in the presence of ultrasound is presented. Erosion current events were recorded at high time solution. These current events were attributed to the reoxidation of the exposed metal as a result of cavitation events. This study shows that surface erosion can be electrochemically investigated in-situ withing a cavitating media. [Espanol] El efecto del ultrasonido en procesos electroquimicos ha sido investigado empleando un micro-electrodo dentro de un medio cavitante. El transporte de masa transitorio fue realzado fuertemente en la presencia de ultrasonido. Altos indices de la transferencia de masa de hasta 1.5 cm s-1 fueron observados. Estos altos indices de la transferencia de masa fueron atribuidos a dos procesos de la cavitacion. Primero, el colapso de la burbuja en/o cerca de la interfase solido-liquido con la formacion consiguiente de un microjet liquido de alta velocidad dirigido hacia la superficie del electrodo. En segundo lugar, movimiento de la burbuja cerca o dentro de la capa de difusion o del electrodo. Tambien se registraron los simples transitorios de corriente a una alta resolucion de tiempo. Estos transitorios simples de corriente fueron atribuidos a la perturbacion a corto plazo del campo de difusion del micro-electrodo debido a los impactos de cavitacion del colapso de la burbuja seguido por una relajacion de largo tiempo del campo de la difusion de nuevo al estado estable. La influencia de la fuente ultrasonica a la separacion del electrodo, la temperatura total de la solucion, el potencial del electrodo y el tamano del electrodo sobre la magnitud de transitorios de corriente tambien fue estudiada. Todos estos parametros afectaron marcadamente la magnitud de los transitorios de corriente registrados en el micro-electrodo en presencia del ultrasonido. Se presenta una opcion alternativa para caracterizar reacciones heterogeneas rapidas de transferencia del electron que empleando el ultrasonido como herramienta, de realce del transporte de masa. Dos tecnicas innovadoras, la voltametria corriente muestreada y la voltametria corriente-media muestreada, se desarrollaron durante el curso de esta tesis. La tecnica del voltammetria corriente de muestra senalo los valores del regimen estandar constante de la transferencia heterogenea del electron de hasta 1.2 centimetros s-1 en la presencia del ultrasonido. Esta tecnica se centra en los fenomenos electroquimicos bajo investigacion en el punto de impacto del acontecimiento ultrasonico, producido por colapso asimetrico de la burbuja de cavitacion cerca de la superficie del electrodo. Las dinamicas de la burbuja tambien fueron examinadas bajo las condiciones experimentales empleadas en el presente estudio. El comportamiento de la burbuja fue observado desde la solucion numerica de la ecuacion de RPNNP que describe el movimiento de una burbuja llena gas en una fase homogenea. Esta ecuacion fue resuelta numericamente empleando el metodo de cuarto orden de Runge-Kutta. Finalmente se presenta un estudio preliminar del proceso superficial en presencia del ultrasonido. Los eventos de erosion por corriente fueron registrados a una alta resolucion de tiempo. Estos eventos de corriente fueron atribuidos a la re-oxidacion del metal expuesto como resultado de eventos de cavitacion. Este estudio muestra que la erosion superficial puede ser investigada electroquimicamente in situ dentro del medio de cavitacion.}
place = {Mexico}
year = {1997}
month = {Oct}
}
title = {Applications of ultrasound in electrochemistry}
author = {Silva Martinez, Susana}
abstractNote = {The effect of the ultrasound on electrochemical processes has been investigated employing a microelectrode within the cavitating media. Transient mass transport was strongly enhanced in the presence of ultrasound. High rates of mass transfer of up to 1.5 cm s-1 were observed. These high rates of mass transfer were attributed to two cavitation processes. First, bubble collapse at or near the solid-liquid interface with the consequent formation of a high speed liquid microjet directed at the electrode surface. Second, bubble motion near or within the diffusion layer or the electrode. Single current transients were also recorded at high time resolution. These single current transients were attributed to the short-time perturbation of the diffusion field of the microelectrode due to impacts of cavitation bubble collapse followed by a long time relaxation of the diffusion field back to the steady state. The influence of the ultrasonic source to electrode separation, temperature of the bulk solution, electrode potential and electrode size on the magnitude of current transients was also studied. All of these parameters affected markedly the magnitude of the current transients recorded at microelectrode in the presence of ultrasound. An alternative approach is presented to characterise fast heterogeneous electron transfer reactions employing ultrasound as a mass transport enhancement tool. Two innovative techniques, sampled-current voltammetry and sampled-mean current voltammetry, were developed during the course of this thesis. The technique of sample-current voltammetry reported values of the standard rate constant of heterogeneous electron transfer of up to 1.2 cm s-1 in the presence of ultrasound. This technique focuses on the electrochemical phenomena under investigation at the point of impact of the ultrasonic event, produced by asymmetric cavitation bubble collapse near the electrode surface. Bubble dynamics were also examined under the experimental conditions employed in the present study. The bubble behaviour was observed from the numerical solution of the RPNNP equation that describes the motion of a gas filled bubble in a homogeneous phase. This equation was solved numerically employing the Fourorder Runge-Kutta method. Finally, a preliminary study of surface process in the presence of ultrasound is presented. Erosion current events were recorded at high time solution. These current events were attributed to the reoxidation of the exposed metal as a result of cavitation events. This study shows that surface erosion can be electrochemically investigated in-situ withing a cavitating media. [Espanol] El efecto del ultrasonido en procesos electroquimicos ha sido investigado empleando un micro-electrodo dentro de un medio cavitante. El transporte de masa transitorio fue realzado fuertemente en la presencia de ultrasonido. Altos indices de la transferencia de masa de hasta 1.5 cm s-1 fueron observados. Estos altos indices de la transferencia de masa fueron atribuidos a dos procesos de la cavitacion. Primero, el colapso de la burbuja en/o cerca de la interfase solido-liquido con la formacion consiguiente de un microjet liquido de alta velocidad dirigido hacia la superficie del electrodo. En segundo lugar, movimiento de la burbuja cerca o dentro de la capa de difusion o del electrodo. Tambien se registraron los simples transitorios de corriente a una alta resolucion de tiempo. Estos transitorios simples de corriente fueron atribuidos a la perturbacion a corto plazo del campo de difusion del micro-electrodo debido a los impactos de cavitacion del colapso de la burbuja seguido por una relajacion de largo tiempo del campo de la difusion de nuevo al estado estable. La influencia de la fuente ultrasonica a la separacion del electrodo, la temperatura total de la solucion, el potencial del electrodo y el tamano del electrodo sobre la magnitud de transitorios de corriente tambien fue estudiada. Todos estos parametros afectaron marcadamente la magnitud de los transitorios de corriente registrados en el micro-electrodo en presencia del ultrasonido. Se presenta una opcion alternativa para caracterizar reacciones heterogeneas rapidas de transferencia del electron que empleando el ultrasonido como herramienta, de realce del transporte de masa. Dos tecnicas innovadoras, la voltametria corriente muestreada y la voltametria corriente-media muestreada, se desarrollaron durante el curso de esta tesis. La tecnica del voltammetria corriente de muestra senalo los valores del regimen estandar constante de la transferencia heterogenea del electron de hasta 1.2 centimetros s-1 en la presencia del ultrasonido. Esta tecnica se centra en los fenomenos electroquimicos bajo investigacion en el punto de impacto del acontecimiento ultrasonico, producido por colapso asimetrico de la burbuja de cavitacion cerca de la superficie del electrodo. Las dinamicas de la burbuja tambien fueron examinadas bajo las condiciones experimentales empleadas en el presente estudio. El comportamiento de la burbuja fue observado desde la solucion numerica de la ecuacion de RPNNP que describe el movimiento de una burbuja llena gas en una fase homogenea. Esta ecuacion fue resuelta numericamente empleando el metodo de cuarto orden de Runge-Kutta. Finalmente se presenta un estudio preliminar del proceso superficial en presencia del ultrasonido. Los eventos de erosion por corriente fueron registrados a una alta resolucion de tiempo. Estos eventos de corriente fueron atribuidos a la re-oxidacion del metal expuesto como resultado de eventos de cavitacion. Este estudio muestra que la erosion superficial puede ser investigada electroquimicamente in situ dentro del medio de cavitacion.}
place = {Mexico}
year = {1997}
month = {Oct}
}