Electrochemical Properties of Li<sub>3</sub> N  Dissolved in Molten LiCl at 900 K (2001)

Thermodynamic properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML1" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>N</mml:mo> </mml:math> dissolved in the molten LiCl salt at 900 K were explored using electrochemical methods. It was difficult to determine precisely the decomposition voltage of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML2" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>N</mml:mo> </mml:math> dissolved in the molten salt by cyclic voltammetry. The oxidation wave of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML3" overflow="scroll"> <mml:msup> <mml:mo>N</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> </mml:math> ion could not be located with high accuracy. However, the lithium activity of the Pb-Li alloy in equilibrium with the molten salt containing dissolved <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML4" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>N</mml:mo> </mml:math> under nitrogen atmosphere could be measured electrochemically with high accuracy using the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML5" overflow="scroll"> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mo>/</mml:mo> <mml:msup> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> </mml:math> reference electrode. Under the conditions used in this study, the potential of the Li-Pb electrode is equal to the decomposition voltage of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML6" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>N</mml:mo> <mml:mo>.</mml:mo> </mml:math> The activity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML7" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>N</mml:mo> </mml:math> in molten LiCl was determined for anionic fractions of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML8" overflow="scroll"> <mml:msup> <mml:mo>N</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> </mml:math> ranging from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML9" overflow="scroll"> <mml:msub> <mml:mi>x</mml:mi> <mml:mrow> <mml:msup> <mml:mo>N</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:math> to 0.028. The nitride ion concentration in the salt was determined by chemical titration. The activity coefficient of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML10" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Li</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>N</mml:mo> </mml:math> at high dilution was found to be very low, around <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML11" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mo>.</mml:mo> </mml:math> The activity coefficient increases sharply with composition and has a value of 0.25 at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML12" overflow="scroll"> <mml:msub> <mml:mi>x</mml:mi> <mml:mrow> <mml:msup> <mml:mo>N</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.028</mml:mn> <mml:mo>.</mml: