A range of titanium dioxide (titania) samples provided by Huntsman Pigments and Additives were investigated for their suitability for use in various optoelectronic devices, specifically dye-sensitized solar cells (DSSCs). Five of the titania samples are 1-20 micrometre size spherical 3D porous beads made up of titania nanoparticles and a further six samples are porous titania nanoparticle clusters of no specific shape, all of which possess high surface areas from 85 to 276 m2g-1. The samples were compared to commercially available nanocrystalline TiO2 powders and paste. All of the samples were initially assessed for suitability in DSSC devices by investigating various properties such as crystal phase, particle size, band gap, morphology and N719 dye adsorption, both as a powder sample and as a sintered film, employing techniques such as powder x-ray diffraction, UV/Vis spectroscopy and scanning electron microscopy. Different methods of formulating the samples into pastes for application to a substrate were attempted and electrochemical properties of a selection of films were also compared. The more promising titania samples were formulated into dye-sensitized solar cells and cell efficiencies calculated. DSSC devices were also fabricated with low temperature (125oC) sintering of the titania layer to assess the suitability of the samples for use in devices with flexible substrates. Initial devices incorporating the Huntsman TiO2 samples provided low efficiencies (< 0.1%). The samples were then modified with pre-sintering treatment prior to paste formulation to optimize crystallinity, particle size, porosity and surface area. The modified titania bead samples showed great promise in low temperature sintered devices, providing device efficiencies of 2.8%, more than double that of those incorporating the standard P25 TiO2 (1.3%). After sample modification a superior solar cell performance (3.2%) was also observed in 510oC sintered devices when compared to the standard P25 TiO2 devices (2.9%), with higher photocurrent and open circuit voltage than devices fabricated from commercially optimized TiO2 paste. Devices were also fabricated using pre-sensitized titania in an attempt to reduce device manufacturing time. The modified samples again showed good performance, providing working devices with efficiencies comparable to the equivalent pre-sensitized P25 devices.

The current interest in energy saving asphalt production techniques is great and several new processes have been developed to reduce the mixing and compaction temperatures for hot mix asphalt. In particular, mastic asphalt products (Gussasphalt) require high working temperatures, and harder requirements concerning bitumen fumes and carbon dioxide emissions have been introduced for such products. Consequently, the need of a new means of producing and placing mastic asphalt at lower temperatures is particularly large. One way of reducing asphalt mixture temperature is by using special flow improving additives like wax. This technique has successively been tried in several studies for polymer modified mastic asphalt used for bridge decks and parking areas in Sweden. However, there still are uncertainties about possible negative impact on crack susceptibility at lower temperatures due to the addition of wax. In this study, 4% montan wax (Asphaltan A) was used for one particular polymer modified mastic asphalt product. Type and amount of wax additive was selected based on results from earlier studies. The impact on binder, binder/filler mixtures and mastic asphalt from production was tested in the laboratory, focusing on low temperature performance. The bending beam rheometer (BBR) was used for determining low temperature creep compliance and the tensile stress restrained specimen test (TSRST) for determining fracture temperatures. Binder properties were determined using dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR) spectroscopy and conventional tests (softening point, penetration, elastic recovery, Fraass breaking point, viscosity and storage stability). Aging was performed using the rolling thin film oven test (RTFOT) at 200°C. As expected, the addition of wax to the polymer modified binder showed a viscosity reduction at higher temperatures, corresponding to a similar positive effect of more than 10°C on production and laying temperature for the mastic asphalt. DMA and BBR results showed some increase in stiffness and a more elastic response of the wax modified binder at medium and low temperatures. The TSRST fracture temperature was 5 °C higher for the mastic asphalt containing 4% wax, indicating however no dramatic negative impact on crack susceptibility.

This doctoral thesis consists of a literature review, presented in two papers, and another six papers describing experimental studies of the influence of different kinds of wax and polyphosporic acid on bitumen and asphalt concrete mixture properties. The literature review should give an extensive description of the field of knowledge concerning wax in bitumen. Effects of wax in crude oil, bitumen and asphalt concrete as well as test methods for studying these effects are described. Theories behind possible mechanisms are also discussed, and commercial wax as additive to bitumen for different purposes included. The experimental parts comprise laboratory studies involving totally five 160/220 penetration base bitumens from different sources, two isolated bitumen waxes, five commercial waxes and one polyphosphoric acid. Asphalt concrete slabs, containing base or modified bitumen were prepared and tested. Binder properties were evaluated using different types of laboratory equipment, such as dynamic shear rheometer (DSR), bending beam rheometer (BBR), differential scanning calorimeter (DSC), force ductilometer, as well as equipment for determining conventional parameters like penetration, softening point, viscosity, and Fraass breaking point. Fourier Transform Infrared (FTIR) spectroscopy and Thin Layer Chromatography (TLC-FID) were used for chemical characterization. The binders were aged by means of the rolling thin film oven test (RTFOT) and pressure ageing vessel (PAV) in combination. Asphalt concrete properties were evaluated at low temperatures using the tensile strain restrained specimen test (TSRST) and creep test at -25°C. Dynamic creep testing was performed at 40°C, as well as complex modulus tests between 0 and 20°C. Binder test results indicated that the magnitude and type of effect on bitumen rheology depend on the bitumen itself, type of crystallizing fraction in the bitumen and/or type and amount of additive used. Bitumen composition was found to be of decisive importance. Adding polyethylene wax or polyphosphoric acid, especially to a non-waxy 160/220 penetration grade bitumen, showed no or positive effects on the rheological behaviour at low temperatures (decrease in stiffness) as well as medium and high temperatures (increase in complex modulus and decrease in phase angle). However, the corresponding positive effects could not be shown in dynamic creep testing (at 40°C) of asphalt concrete mixtures containing these modified binders. Adding FT-paraffin decreased the physical hardening index for all bitumens. Also polyethylene wax and montan wax showed this effect for some bitumens. Slack wax showed a large increasing effect on physical hardening, and polyphosphoric acid none or a minor negative effect. No correlation between physical hardening index (PHI) and wax content by DSC was found in this study, involving both natural bitumen wax and commercial wax. Addition of the commercial waxes used showed no or marginally positive influence on bitumen ageing properties for the bitumens and test conditions used. Comparing asphalt mixture test results to the corresponding binder test results, the effects on asphalt mixtures from adding commercial wax or polyphosphoric acid were less evident. Significant binder physical hardening by BBR could not be confirmed by TSRST. / QC 20101006