The Rate of Oxidation of Copper at Room Temperature

Abstract

Electron diffraction was used to measure the rate of the reaction between copper and pure dry oxygen at room temperature and 20 mm. pressure. The experimental technic is described in detail. The empirical rate of reaction is found to be inversely proportional to ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML1" overflow="scroll"> <mml:mi>t</mml:mi> <mml:mo>+</mml:mo> <mml:mi>c</mml:mi> </mml:math> ) for the time <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML2" overflow="scroll"> <mml:mi>t</mml:mi> </mml:math> greater than two minutes; the constant <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML3" overflow="scroll"> <mml:mi>c</mml:mi> </mml:math> is experimentally indistinguishable from zero but must be finite. It is estimated that the local thickness, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML4" overflow="scroll"> <mml:mi>x</mml:mi> </mml:math> , in Ångstrom units of the oxide film increases according to the equation: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML5" overflow="scroll"> <mml:mi>x</mml:mi> <mml:mo>=</mml:mo> <mml:mn>4</mml:mn> <mml:mo>+</mml:mo> <mml:mn>6.5</mml:mn> <mml:mo> </mml:mo> <mml:msub> <mml:mo>log</mml:mo> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo> </mml:mo> <mml:mi>t</mml:mi> </mml:math> where <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML6" overflow="scroll"> <mml:mi>t</mml:mi> </mml:math> is measured in minutes and is greater than 2 min. A limiting film thickness of about 50 Å is predicted by this equation.