potassium fluoride in hydrogen fluoride Electrolysis; electrolysis in aq. HF (2.5 h, 4 V, room temp.), filtration, pptn. on addn. of concd. soln. of KF in HF; drying (KOH);

in water byproducts: NiO, KCl; hydrothermal method under pressure of 98 MPa at 600°C for 7 d;quenched in cold water; washed (water); powder XRD;

in neat (no solvent, solid phase) mixt. (3KF:2NiF2 ) annealed (700-800°C, 1-2 wk) in welded platinum ampules; XRD;