Thick silica foam films through combined catalytic decomposition of H 2 O 2 and sol–gel processes Martin Timusk a,b, ⁎, Agnes Kuus b , Kathriin Utt b , Triin Kangur b , Andris Šutka b,c , Martin Järvekülg b,d , Maris Knite a a Institute of Technical Physics, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Paula Valdena 3/7, Riga, LV 1048, Latvia b Institute of Physics, University of Tartu, W. Ostwaldi Str. 1, 50411 Tartu, Estonia c Institute of Silicate Materials, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Paula Valdena 3/7, Riga, LV 1048, Latvia d Biomaterials Research Laboratory, Riga Technical University, Paula Valdena 3/7, Riga, LV 1048, Latvia HIGHLIGHTS • Low-density silica foams with a previ- ously unreported closed-cell morpholo- gy were prepared in a novel fashion. • H 2 O 2 -containing silica sol was spray- coated onto MnO 2 -coated substrates, leading to foam formation. • Gelation of the sol occurs concurrently with the foam formation, “freezing” the formed structure. • This work is a step towards a simple route to aerogel-like silica materials without the supercritical drying of wet gels. GRAPHICAL ABSTRACT abstract article info Article history: Received 21 April 2016 Received in revised form 30 August 2016 Accepted 31 August 2016 Available online 1 September 2016 A novel method for the preparation of thick silica foam films is reported that combines an alkoxide-based hydro- lytic sol–gel process and in situ catalytic decomposition of hydrogen peroxide on a catalyst-coated support. A hy- drogen peroxide/nitric acid aqueous solution was used to carry out acid-catalysed hydrolysis of tetramethoxysilane. Complete stability of H 2 O 2 in the resulting silica sols over extended periods (N 120 min) was demonstrated by in situ Raman spectroscopy. The H 2 O 2 -loaded sols were sprayed on MnO 2 -coated sub- strates, resulting in heterogeneous catalytic decomposition of H 2 O 2 and effective foaming and simultaneous gel formation due to oxygen gas and water formation. Silica foam films with a well-defined closed-cell porosity were annealed at 600 °C without any damage to the closed-cell porous film morphology. Up to 530 μm thick films were prepared with macropore sizes in the range of 29–47 μm, exceptionally thin macropore wall thicknesses of 16–50 nm and a bulk density as low as 64 kg/m 3 , comparable to that of the aerogels. The lowest measured ther- mal conductivity of the prepared foams was 0.018 ± 0.001 W/(m* K), which is also similar to silica aerogels, en- abling the prepared foams to be used as efficient thermal insulation materials. © 2016 Elsevier Ltd. All rights reserved. Keywords: Silica foam Low-density material Closed-cell porosity Sol–gel Hydrogen peroxide Manganese dioxide 1. Introduction Sol–gel chemistry is one of the cornerstones of material science and nanotechnology, enabling the preparation of materials with a wide Materials and Design 111 (2016) 80–87 ⁎ Corresponding author at: Institute of Technical Physics, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Paula Valdena 3/7, Riga, LV 1048, Latvia. E-mail address: martin.timusk@ut.ee (M. Timusk). http://dx.doi.org/10.1016/j.matdes.2016.08.092 0264-1275/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes