Untitled in english

Author(s)

Paulo Jorge Brazão Marcos

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2001-09-12

Examining board members

Douglas Gouvêa; Eliana Navarro dos Santos Muccillo; Samuel Marcio Toffoli

• Advisor: Douglas Gouvêa

Abstract

The interest for alternative materials cast methods that favors the economical, productive and environmental aspects has remarkably increased during the last years. The cast by electrophoretic deposition (EPD) in aqueous media shows, as main problem, the electrolysis of water, which results in the formation of gaseous oxygen and hydrogen upon the cathode and the anode, respectively, prejudicing the formation of a homogeneous material. Such problem can be avoided by using organic solvents as suspension media. The cast of the magnesia partially stabilized ZrO2 by the electrophoretic deposition technique is proposed in this work. This material was prepared in the capillaries shape. This small \"hollow fibers\" show an important length/diameter relationship and where other cast methods are less adapted. The essential prerequisite for a successful electrophoretic deposition is the electric charging of the solid particles that constitute the ceramic suspension. According to DLVO theory, the particles of a suspended ceramic material can be electrokineticly stabilized by the development of surface electric charges or by adsorbing surfactant substances (active at surface), which results in a repulsion between them. This charging development leads to the formation of an electric double-layer around each particle, being responsible for its electrokinetic stabilization and movement in an electric field as well as the rheologic behavior resultant from the interaction ofsolid particles with the solvent. Thus, the stability and homogeneity study of ZrO2-MgO dispersions in ethanol and water by changing the surface electric charges as a function of the pH and the presence of dispersants are important for the physical-chemical phenomena comprehension related to the particles behavior in this media and consequently, for the optimization of the electrophoretic cast process. (AU)