Patent ID: 6899858

Claim:
A method of preparing a hafnium nitrate thin film comprising: placing phosphorus pentoxide in a first vessel; connecting the first vessel to a second vessel containing hafnium tetrachloride; cooling the second vessel with liquid nitrogen; dropping fuming nitric acid into the first vessel producing N 2 O 5 gas to produce the following reaction: P 2 O 5 +2HNO 3 →N 2 O 5 +2HPO 3 ; allowing the N 2 O 5 gas to enter the second vessel to produce the following reaction: 4N 2 O 5 +HFCl 4 →HF(HNO 3 ) 4 →4NO 2 Cl; heating the first vessel until the reaction is substantially complete; disconnecting the two vessels; removing the second vessel from the liquid nitrogen bath; heating the second vessel; refluxing the contents of the second vessel; drying the compound in the second vessel by dynamic pumping; and purifying the compound in the second vessel by sublimation to produce Hf(NO 3 ) 4 .