Corrosion resistance of phosphorus-clad iron powders in biological and inorganic media

The production and use of clad iron-based powder materials is a promising area of powder metallurgy that allows variation in their process and magnetic properties in wide ranges. The corrosion properties of phosphorus-clad iron powders and their interaction with biological media of the living organisms are studied. The PZhRV 3.200.26 (Ukraine), AHC 100.29 (Sweden), and PZhV 200 (Russia) iron powders with different particle sizes are clad with phosphorous by the method of thermochemical decomposition of phosphorous compounds and by the method of thermochemical synthesis in a vibrating bed. Corrosion tests of the iron powders clad with phosphorous are performed in a 3% NaCl solution. Calculations of the corrosion depth index show that the clad powders are much more resistant to corrosion in aggressive media (3–4 points according to the ISO 11130:2010 standard) than the starting powders (1 point). The low values of the corrosion depth index of phosphorus-clad powders testify that surface corrosion proceeds on powder particles. It is shown that the interaction of the starting PZhRV 3.342.28 and AHC 100.29 iron powders with human blood plasma is 5.8 and 7.2 times more intensive, respectively, than that for PZhRV 3.342.28 and AHC 100.29 powders clad with phosphorous. On the surface of iron powders, phosphorus interacts with blood plasma proteins to form a protective colloidal biocomplex, which increases substantially the resistance of clad powders in blood plasma. Thus, the cladding of iron powders with phosphorus enhances significantly their chemical stability both in human blood plasma and in air.