1 Crack formation during post-treatment of nano- and microfibres prepared by sol-gel technique T. Tätte 1) , A.L. Kolesnikova 2) , M. Hussainov 1) , R. Talviste 1) , R. Lõhmus 1) , A.E. Romanov *1, 3) , I. Hussainova 4) , M. Part 1) , A. Lõhmus 1) 1) Institute of Physics, University of Tartu, Tartu, Estonia 2) Institute of Problems of Mechanical Engineering, St.-Petersburg, Russia 3) Ioffe Physico-Technical Institute, St.-Petersburg, Russia 4) Tallinn University of Technology, Tallinn, Estonia Date of Submission: Date of Acceptance: Email Address: aer@mail.ioffe.ru Abstract We report on the method of TiO 2 nano- and microfibres preparation and their cracking during processing and post-treatment. Nano- and microfibres were fabricated by drawing from viscous alkoxide based oligomeric concentrate precursors with the following exposure into an atmosphere of 30-50% humidity. The fibres microstructure was analyzed with TEM, solid state NMR, X-ray diffraction tools, and AFM. Experiments on crack formation in TiO 2 microfibres proved that fibres with diameter larger than 10 micron are fractured for chosen post-treatment regimes. In theoretical considerations sol-gel produced and thermally treated microfibres are modeled as core/shell structures. It is suggested that the formation of fibres starts via solidification of liquid jet through the appearance of a rigid solid shell, which reveals tensile mechanical stresses because of material shrinkage. The effect of post-treatment is taken into account by additional densification of the fibre surface layer. The stress intensity factor K I is calculated for the model core/shell structures and the dependence of K I on the fibre diameter is demonstrated. The results of modeling qualitatively confirm experimental data of microfibre cracking above a certain threshold diameter. Key words: sol-gel technique, nano- and microfibres, shrinkage, cracking PACS: 62.20mt; 62.23.Hj * Address for correspondence: A. E. Romanov, Ioffe Physico-Technical Institute, RAS, Polytechnicheskaya 26, 194021, St. Petersburg, Russia. Phone: +812-292-73-04. Fax: +812-294-10-17. Email: aer@mail.ioffe.ru