The fundamental free hydroxyl group vibration of silica gel has been studied using high-resolution Fouriertransform infrared photo-acoustic spectroscopy (FTIR-PAS). The position of the absorption maximum shifts according to the pretreatment temperature of the silica gel. The hydroxylic environment of the free hydroxyl group probably influences the peak position. This was modelled to estimate the relative surface coverages of the free and bridged hydroxyl groups.Silica gel is a polycondensation product of silicic acid, Si(OH), . Inefficient polymerisation of the primary silica sols results in a random distribution of hydroxyl groups over the surface. The structure of silica gel, therefore, is highly porous and amorphous.' Two types of hydroxyl group exist on the surface: free and bridged hydrogen-bonded hydroxyl group^.^,^ These surface hydroxyl groups induce hydrophilic proper tie^.^ The silica gel surface is covered with adsorbed water at ambient temperature. Progressive thermal treatment dehydrates and dehydroxylates the silica gel surface. Dehydration and dehydroxylation operate in a different temperature range, although the processes are not fully separated. It is believed that the silica gel is dehydrated at 200°C under atmospheric conditions and even at lower temperatures in vacuum.' Infrared spectroscopy has been widely applied for the characterisation of hydroxyl groups on silica gel, especially in their fundamental absorption region 3800-3200 cm-'. A characteristic infrared feature in that region is the presence of only one sharp band (CQ. 3745 cm-') of free hydroxyl groups. At low and moderate pretreatment temperature, the infrared spectra also reveal a broad band (3650-3300 cm-') due to the absorption of bridged hydroxyl

The timely identification of vehicles involved in an accident, such as a hit-and-run situation, bears great importance in forensics. To this end, procedures have been defined for analyzing car paint samples that combine techniques such as visual analysis and Fourier transform infrared spectroscopy. This work proposes a new methodology in order to automate the visual analysis using image retrieval. Specifically, color and texture information is extracted from a microscopic image of a recovered paint sample, and this information is then compared with the same features for a database of paint types, resulting in a shortlist of candidate paints. In order to demonstrate the operation of the methodology, a test database has been set up and two retrieval experiments have been performed. The first experiment quantifies the performance of the procedure for retrieving exact matches, while the second experiment emulates the real-life situation of paint samples that experience changes in color and texture over time.

The infrared spectra of U.I.C.C. standard asbestos have been investigated in relation to their mineral structure. A quantitative account is given of the surface hydroxy species. The effect on the spectra of pretreatments in dilute acid and basic solutions have been studied with reference to the carcinogenic activity of asbestos minerals.

Three natural allophane samples from New Zealand, the Egmont, Waxy-Pan and iron-rich Ruapehu, were investigated by infrared spectroscopy, X-ray diffraction and Mossbauer spectroscopy. The specific surface area and the pore sizes of these samples increase as the pretreatment temperature is raised, up to a temperature where a decrease of the surface area and a narrowing of the pores is observed. This can be explained by two competing phenomena : the release of water from the pores and the collapse of other pores. In comparison with the Egmont and Waxy-Pan allophanes, the iron-rich Ruapehu sample contains considerably less pores of sufficient size to accommodate water.Its exceptional chemical composition and the infrared spectra, X-ray diffraction patterns and Mossbauer spectra suggest the presence of a separate, amorphous iron (111) oxide phase in the pores of this allophane.

The chemisorption of diborane on silica gel strongly influences the porosity of the structure. A method, based on a cylindrical pore model, is proposed to probe the pore-narrowing as well as the pore-blocking of a mesoporous silica gel. It was observed that pore-narrowing increases linearly with the averge pore diameter, while poreblocking decreases with an increasing pore diameter. The proposed method proved to be suitable for semiquantitative ap pl ication.