Potassium fluoride, KF

The Potassium fluoride, KF is produced by the interaction of hydrofluoric acid and potassium carbonate or hydroxide; by heating potassium silicofluoride or borofluoride with lime; and by the action of potassium on fluorine, hydrofluoric acid, or silicon fluoride or boride.

The anhydrous salt forms crystals belonging to the cubic system, melting at 789° C., 846° C., 859.9° C., or 867° C., and boiling at 1505° C. The vapour-pressure in atmospheres is given by the expression

log p = - 41900/4.57T + 5.138.

Its mean density is 2.481. It yields a deliquescent, crystalline dihydrate, KF,2H₂O, m.p. 41° C.; and a stable, transparent, crystalline tetrahydrate, KF,4H₂O, m.p. 19.3° C. The heat of formation is 110.6 Cal. The latent heat of fusion is 0.108 Cal. per gram. The molecular electric conductivity of potassium fluoride between 863.0° and 975° C. is given by the formula

μ_t = 101.8 + 0.3163(t - 900).

The heat of solution of the anhydrous salt at 20° C. is 3.6 Cal., and that of the dihydrate -1.0 Cal. The solubility of the dihydrate per 100 grams of water is 92.3 grams at 18° C., and 96.3 grams at 21° C., the solution being neutral. Electrolysis of the aqueous solution produces a considerable proportion of ozone.