On the hafnium state in sulfuric-acid solutions

The state of hafnium in concentrated sulphuric acid solutions has been studied by viscosity measurements at 25 deg C over the concentration ranges 0.5-24% HfO2 and 0.3-34% SO3. Changes in viscosity and density are indicated in the solubility diagram of the HfO2-SO3-H2O system. The area of negative viscosity is determined and hafnium is shown to be primarily responsible for its formation. The different viscosity changes in the area where basic sulphates and the disulphate exist indicates that polymers of different types are formed. In the area where hafnium solubility is high the existence of mixed polymers containing both the hydroxylic and the sulphate bridges is assumed. Being mixed, the polymers show high disorder and thus may give rise to very concentrated hafnium solutions