ИСТИНА

Synthesis and stabilization of nanoparticles of different nature are the actual problems of modern science. The composite materials containing iron nanoparticles are very interesting for the realization of the high-density magnetic recording. The new approach of the iron-polymer composite production is to carry out in situ the reaction of chemical reduction between iron salt and a reducer in the porous polymer matrices obtained via solvent crazing. Crazing is accompanied by the development of a system of interpenetrating pores in a polymer, which can be used as microreactors for various chemical processes. In this work, synthesis of iron nanoparticles is carried out in porous matrices of high-density polyethylene and polypropylene. Porous polymer matrices were obtained via solvent crazing, i.e. via uniaxial stretching in the presence of isopropyl alcohol. The value of an effective volume porosity of these matrices is 40 vol.%, the average diameter of pores is 6-8 nm. Introduction of the initial reagents (Fe(II) or Fe(III) salts and sodium boronhydride) in porous structure is carried out during the pores’ formation (method I) and via the counter-current diffusion (method II). The structure and the phase content of the composites produced are studied by Mössbauer spectroscopy as well as X-ray analysis and SEM. The content of iron in the composite is varied from 2 to 40 wt.%. X-ray investigation of samples obtained shows that they contain metallic iron. The average diameter of iron crystallites is 5-40 nm for different preparation conditions. SEM investigation shows that iron particles with a diameter of 0.1-0.4 mcm in polymers can be uniformly distributed (method I) or can be concentrated as a layer with a thickness of 4-6 mcm (method II). These particles are the complicated aggregates consisting of the initial iron crystallites with a diameter of 10-40 nm, compounds of Fe (III) and the polymer fibrils. Mössbauer spectrum of a sample received via method I is a sextet of a-Fe and a doublet related to Fe(III) compounds. The content of -Fe depends on the type of iron salt used and varies from 20 to 60 wt.%. Mössbauer absorption spectrum of the iron-polymer sample obtained by method II can be presented as a superposition of two doublets with isomer shifts delta1 =0.33(1) mm s-1 and delta2 =0.24(1) mm s-1 and quadrupole splitting values delta1 = 0.79(1) mm s-1 and delta2 = 0.29(1) mm s-1. These Mössbauer parameters correspond to oxo-compounds of Fe(III) with octahedral and tetrahedral coordination of the metal, respectively. There are no a-Fe lines in the spectrum that can be explained by rapid oxidation of highly dispersed iron particles, discretely distributed within the porous polymer matrix, by water and alcohol.