Beschreibung:
<jats:p>A revised equilibrium diagram is presented for the system NaF–BeF<jats:sub>2</jats:sub>, a weakened model of the system CaO–SiO<jats:sub>2</jats:sub>. The compound Na<jats:sub>2</jats:sub>BeF<jats:sub>4</jats:sub> has four structural modifications corresponding to the γ, β, α', and α forms of Ca<jats:sub>2</jats:sub>SiO<jats:sub>4</jats:sub>. Inversion temperatures were found to be as follows: α→α’= 320°C., γ→α’= 225°C., α’→β (metastable) = 115°C. The quartz form of BeF<jats:sub>2</jats:sub> was found to have a high‐low inversion at 220°C. The high‐quartz form exists in equilibrium with liquid in binary fluoride systems up to the melting temperature of BeF<jats:sub>2</jats:sub>, as closely as can be determined. The cristobalite form appears to have only a metastable existence, and a tridymite form has not been found. The compound NaBeF<jats:sub>3</jats:sub> has a structure similar to β‐CaSiO<jats:sub>3</jats:sub> below 343°C., with a different structure (not that of α‐CaSiO<jats:sub>3</jats:sub>) above this temperature.</jats:p>