Synthesis and Properties of Porous Hybrid Materials containing Metallic Nanoparticles

Abstract

The pyrolysis of preceramic polymers like polysiloxanes provides the possibility of manufacturing ceramics at lower temperatures (500-1500°C) compared to the powder sintering route and of using versatile polymer shaping routes, what has attracted a growing attention in the last decade. [1] Ceramic products with different structures and functions (e.g. bulk materials, [2] composites, [3] coatings [4] and foams [5] ) were manufactured by this route and their properties (e.g. oxidation and thermal resistance, [6] electrical conductivity [7] ) can be altered by tailoring the molecular structure of the precursor and by loading the polymer with filler particles. [8] The transformation of polysiloxanes [RSiO 3/2 ] carrying hydrocarbon groups (R = methyl, phenyl, vinyl) in an inert atmosphere is well investigated and results in the formation of an amorphous silicon oxycarbide (SiOC, 800-1000°C), which decomposes to a ceramic consisting of SiC, SiO 2 and graphite at higher temperatures (1400-1500°C). [9][10][11][12] There are many examples, where a combination of a polysiloxane with a metal or a metal salt was used to prevent shrinkage, crack and pore formation of the resulting dense ceramic following the active filler controlled polymer pyrolysis concept (AFCOP). [2,13,14] Other groups used metal salts to introduce electrical conductivity or magnetic properties to SiOC materials [15] or investigated the Ni catalysed formation of carbon nanotubes in the resulting ceramics, which was observed applying temperatures beyond 800°C. [16] The size of Ni nanoparticles (< 1 wt.%) formed during pyrolysis from methylphenyl polysiloxanenickel acetate precursor came up with average diameters of 40-60 nm.A partial conversion of polysiloxane precursors below 800°C yields novel hybrid materials, which often exhibit high porosities and are therefore considered to be potential materials for adsorption and for catalyst supports. However, an adjusted design or functional testing of these hybrid materials in terms of sorption behaviour or catalytic activity has only been performed in far cases. [17] The current study focuses on the use of Ni and Pt containing polysiloxanes for preparation of highly porous hybrid materials (so called "ceramers") by inert gas pyrolysis (400-600°C) for use as adsorbent and as catalyst. In order to realize a homogeneous distribution of metallic particles at high metal contents 3-aminopropyltriethoxysilane was used for complexation of metal ions also in the combination with varying amounts of phenyltriethoxysilane. At the same time it was of interest how the different polarity of the siloxanes used for precursor preparation influenced the surface characteristic (hydrophilic/hydrophobic) of the resulting ceramers. These surface characteristics were examined in sorption experiments and first catalytic measurements revealed the catalytic activity of these ceramers. Experimental Synthesis of Polysiloxane Precursors and Processing of CeramersFor the synthesis of metal containing polysiloxane precursors 3-aminopropyltr...

Effect of titania addition on the properties of freeze-cast alumina samples

“…Subsequently, they were deconvoluted using the Peakfit software and keeping the correlation coefficient (r 2 ) above 0.995. SEM was 6 carried out using JEOL JSM-6360 LV and FEI Quanta 200F microscopes using accelerating voltages from 15 to 20 kV. The samples used in these tests were embedded in epoxy resin, ground, and polished with diamond paste.…”

“…These include, among others, the replication of polymer foams by impregnation [1,2], foaming of aqueous powder suspensions [3,4], pyrolysis of pre-ceramic precursors [5,6], and heating of powder compacts with pore-forming sacrificial templates [7,8]. However, these methods cannot completely satisfy a controlled level of interconnected porosity combined with an outstanding mechanical strength.…”

Use of polysiloxane resins in friction materials

“…In both resins, the first weight loss occurs between 200 and 300uC. Such loss is related to a cross-linking reaction leading to the loss of either H 2 O or alcohols 6 and possibly to some extent of polymer sublimation. 5 Methyl functionalised resin MK shows a weight loss that is twice the loss of the methyl phenyl one, probably due to a more significant sublimation of the material as compared to the H44 one.…”

Surfactant assisted syntheses of monolithic hybrid ceramics with hierarchical porosity

“…As already mentioned in the SEM part, the macroscopic morphology of the not pyrolyzed samples and the pyrolyzed samples are identical. In general it can be observed that the MEBC pyrolyzed at 600 • C generates higher SSA than the samples pyrolyzed at 500 • C. The explanation for that is the higher decomposition degree at 600 • C which results in more micropores and in this way in higher SSA [7][8][9]26,27]. Fig.…”

“…The explanation for that is quite simple. MK and H44 show a higher decomposition degree at 500 • C compared to 600 • C, which results in a higher amount of micropores and by this in higher SSA [7][8][9]26,27].…”