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Transparent dispersions of hydrophobic SrF2 :Eu3+ nanoparticles in cyclohexane with up to 20% europium were obtained by fluorolytic sol-gel synthesis followed by Phase transfer into cyclohexane through capping with sodium dodecylbenzenesulfonate (SDBS). The particles were characterized by TEM, XRD and DLS as spherical objects with a diameter between 6 and 11 nm in dry state. 1H-13CP MAS NMR experiments revealed the binding of the anionic sulfonate head group to the particle surface. The particles show bright red luminescence upon excitation of the aromatic capping agents, acting as antennas for an Energy transfer from the benzenesulfonate unit to the Eu3+ centers in the particles. This synthesis method overcomes the current obstacle of the fluorolytic sol-gel synthesis that transparent dispersions can be obtained directly only in hydrophilic solvents. To demonstrate the potential of such hydrophobized alkaline-earth fluoride particles, transparent luminescent organic-inorganic composites with 10% SrF2 :Eu3+ embedded into polyTEGDMA, polyBMA, poly-BDDMA and polyD3MA, respectively, were prepared, endowing the polymers with the luminescence features of the nanoparticles.
This dissertation is devoted to explicitly investigate the suitability of titania and silica based precursors for wood modification.
Novel TiO2 / SiO2 wood inorganic composites were prepared by two-step process. In first step, freshly prepared precursor solutions of silicon and titanium alkoxides were vacuum impregnated (one or more cycles) to oven dried pine sapwood (Pinius sylvestris L.). Precursor solutions with nano-scaled species and particulates (TiO2 and SiO2) were soaked by the entire wood matrix during this step. In (second) subsequent curing step, these penetrating liquids transformed into respective gel layers and depositions therein by sol-gel processing (in-situ hydrolysis-condensation).
Sol-gel based depositions were evenly covered on the cell walls in the form of thin layers. These gel films were not crack-free however; very few cracks were visible in the gel coatings present within the wood matrix of composites prepared with precursors of low alkoxide content. In addition, the gels were randomly distributed, found to be mainly deposited in the wood cell lumen and also localized in the cell walls as ESEM-EDX mapping revealed.
The impregnated samples show an increase in mass and volume expressed as weight percent gain (WPG) and bulking (B). Both of the parameters are decisive for tailoring a number of physical properties of the resultant composites. In general, moisture and water sorption capacities were decreased by 43 to 50 % while anti-swelling efficiency (ASE) and bending strength (MOE) of the precursor-modified wood (composite) were increased up to 34 % and 41 % respectively, when compared to unmodified wood. These improvements are attributed mainly to gel depositions in the wood structure that physically interact with the wood matrix consequently narrowing the main flow passages there and reinforcing strengths of the fiber.
These materials show superior resistance against fire of different scenarios. In small scale fire, their flame was retarded markedly (up to 78 % in optimum case) in comparison to wood controls as studied by oxygen index test (LOI). Cone calorimetric investigations revealed their better fire retardancy in terms of time resolved heat release rates (HRR) in the developing fire scenario. A remarkable reduction of 40 % in the second peak of HRR was achieved through sol-gel treatment. Furthermore, fire hazards such as CO and total smoke production were considerably lowered for these materials. Beside these improvements, reductions in first peak HRR and in fire load (total heat evolved) were not worth considering in compliance to fire retardancy principles. In relation to the mechanism of protection, it can be concluded that stable gel layer (independence of material loading) inside the wood retards markedly the proceeding combustion processes (oxidation) after first pyrolysis by improving the overall protection properties of the fire residue.
These materials show excellent resistance against bio-deterioration. Almost full decay protection was achieved against wood destroying brown rot fungi (Coniophora puteana and Poria placenta) in 10 weeks laboratory trials only with 1 mass% loadings (WPG). Mass loss in prolonged test (16 weeks) was similar to 10 week lasted test indicating that protection is permanent. In addition, composites imparted moderate resistances against soft rot fungi and very minor one against surface blue stain. The lowering in moisture content that discourages fungal colonization, gel layer that provides better shielding against fungal exposure and un-hydrolyzed alkoxides (organics) that probably induce biocidal effects are the main reasons for protection against biological attack in these materials.
Composites are utmost leach resistant because of the insolubility of gel depositions in water as well as due to their fixture into the wood matrix. In addition to this intrinsic property, gel precipitates can also reduce substantially (70 to 80 %) the release of hazardous active agents (e.g. CuCl2) of wood preservatives into the environment. This anti-leaching effect is supposed to be due to the reduced ion mobility of active agents inside the wood by their encapsulations into the gel matrix, lowering of water penetration into the wood depths as well as due to the internal covering action of the gel layer.
In short, it can be assessed that TiO2 / SiO2 based sol-gel precursor treatment of wood has a possibility to be commercialize in near future due to easy handling and non-toxic nature of the precursor used. Resultant end products (composites) are also novel and promising multifunctional materials that can be used for multi-purposes in relation to use class 3 (outdoor but without ground contact according to EN 335 2006) environments.
Decay resistance of pine sapwood treated with titanium alkoxide solutions was tested against the brown-rot fungi Coniophora puteana and Poria placenta for exposure times of 10 and 16 wk. In practice, wood-specimens were vacuum-impregnated by alcoholic solutions of titanium alkoxide with concentrations in the range of 5–16 mass % (solid content in solution) and subsequently cured under different humidity conditions. Results reveal that treated wood degraded up to 5% in comparison to untreated one that deteriorated 38% and 50%, respectively against both wood-decay fungi. Even full protection (mass loss below 3%) was achieved against brown rot with titanium alkoxide solution containing solid content of around 5 mass% with a weight percentage gain (WPG) of 9 mass%. With increased concentration, fungal resistance decreased slightly which was associated with more cracks and imperfections formed in the deposited layers of titanium dioxide in the adjacent wood matrix. Thermal analysis verified that a considerable amount of precursor remained in the wood structure as un-hydrolyzed organic residues. These organics, being bioactive, had the tendency to induce similar fungicidal effects as those of conventional fungicides. The amount of organic residues is correlated with the decay resistance of the tested samples. In a prolonged decay test, mass losses of 16-wk incubated samples do not show behavior different from that of the wood samples incubated for 10 wk. This result implies that the decay protection is permanent and confirms further the fungicidal activity of titanium-alkoxide-treated wood.
The role of Fe3+ ions in the transformations from boehmites and pseudoboehmite xerogels via transition aluminas to corundum was studied here. Especially, the active iron species responsible for the decrease of the temperature of transformation to corundum were looked for. To enable the formation of various Fe3+
and Fe2+ species, samples were subjected to thermal treatments in different atmospheres as well as mechanically activated. Thermal analysis and ESR spectroscopy served to follow the processes and to characterise the resulting products. It was found that (i) isolated Fe3+ ions can indicate local structural changes but have (almost) no influence on the temperature of corundum formation, (ii) the temperature of corundum formation decreases in the result of action of small
α-Fe2O3 particles and (iii) during thermal treatments Fe3+ ions are distributed between different phases or precursors thereof: transition aluminas, corundum, Fe2O3, and a Fe3+ pool.