Nanocomposites and nanomaterials

Electrochemical behavior of titanium compounds in acidic solutions
Malyshev V.V., Shakhin D.B., Lukashenko T.F., Rybalka O.V.
University”Ukraine”, 23 Lvivska St., Kyiv-03115, Ukraine. 
E-mail: viktor.malyshev.igic@gmail.com

A comparative study of the corrosion resistance and anode behavior of products from sintered nanopowders of carbide, titanium nitride and diboride in solutions of sulfuric and phosphoric acids in a wide range of concentrations and temperatures was carried out. For comparison, data on titanium (VT1-0) are given. Anodic potentiodynamic curves were taken from the stationary potential during separation of the cathode and anode spaces. Corrosion was determined by the amount of titanium transferred to the solution spectrophotometrically.
Titanium diboride differs significantly in corrosion resistance from titanium carbide and nitride and has practically no advantages over titanium. In some cases, it exhibits lower resistance than titanium. The corrosion resistance of titanium carbide and nitride is 2-3 orders of magnitude higher than that of titanium. Titanium nitride and carbide are very close to each other in corrosion resistance, both in sulfuric and in phosphoric acids.
For all investigated materials, an increase in the corrosion rate with increasing temperature and acid concentration is noted.
All investigated refractory compounds dissolve in a passive state at a significantly higher rate than titanium metal. This, apparently, is associated with a higher defectiveness of the oxide layers on them. Defectiveness is caused by both microdefects in the form of nonmetallic atoms in the lattice of titanium oxide and microdefects on the surface of the material. The high corrosion resistance of titanium nitride and carbide is mainly due to their increased thermodynamic stability - the high strength of Ti-N and Ti-C bonds. In titanium diboride, B-B bonds seem to play a decisive role. In addition, boron is unstable with the corrosion potential of titanium, unlike carbon and nitrogen. Therefore, with the potential for corrosion, titanium diboride is intensively dissolved.
Due to the high hardness and brittleness of titanium carbide and nitride, the manufacture of parts and products from them is technologically problematic. The most promising is their use as corrosion-resistant and wear-resistant coatings on titanium, which are used in aggressive environments under abrasive action.