The present invention concerns the field of solid state capacitors and in particular high performance capacitors for use in modern electronic devices. Specifically, the present invention relates to a method by which powders of valve-action material may be modified to make them suitable for use in the formation of capacitor anodes for solid state electrolytic capacitors. According to the present invention there is provided a method of modifying raw valve-action material powder into capacitor grade structured powder comprising: (i) providing a raw powder to be converted; (ii) compressing a portion of the powder to form a porous solid mass of powder (iii) heating the solid mass to a pre-determined sintering temperature and maintaining the temperature for a pre-determined time period to form a sintered body, (iv) pulverising the sintered body to form a processed powder and (v) optionally grading the powder particles within pre-determined size ranges so as to collect capacitor grade powder.