Aerosol Gel Research Articles

Hydroxyapatite coatings obtained by the thermal activation of polymeric sols

Hydroxyapatite (HAP) coatings have been developed to exploit the bioactive properties of this material which are related to its specific composition and crystalline structure. Carbonated HAP films were obtained on (100)/Silicon substrates by the thermal activation of a polymeric sol of selected stoichiometry utilising an aerosol–gel reactor. This technique provides several advantages in the control of the morphology and thickness of the coatings. Sintering temperatures reaching 1000°C were applied to enhance the crystallinity and purity of the films. The samples have been characterised by the use of FTIR, XRD and SEM. Measurements of the stoichiometry, crystallinity, microstructure and morphology of the coatings prove the formation of HAP films appropriate for several bioactive applications.

Mechanical and in vitro testing of aerosol–gel deposited titania coatings for biocompatible applications

The biocompatible properties of sol–gel titania have increased the interest in the mechanical properties of this material in the form of functional coatings for prosthetic applications. In the present work, titania coatings with thicknesses of 1 μm have been prepared using the aerosol–gel process. The main objective has been to evaluate the mechanical properties of the coatings and to prove their in-vitro biocompatibility. For this purpose, the hardness and Young's modulus of the coatings were measured by nanoindentation with loads in the 6–30 m n range. A continuous increase of these magnitudes was observed for the coatings treated at increasing sintering temperatures (150–800°C). The hardness and the Young's modulus ranged between 15.8–19.5 GPa and 142–186 GPa, respectively. This behaviour has been confirmed by measurements of the plastic energy of deformation in 10 m n full loading–unloading tests and by determination of the mean indentation creep under 30 m n loads. The films were additionally characterised by XRD, FTIR and ellipsometry to study the chemical and structural changes produced by sintering. Biocompatibility tests are very conclusive. Cells seeded on aerosol–gel titania coatings grow while adhered onto the surface. These coatings are thus of potential interest for the enhancement of the properties of prosthetic TiAlV alloys.

Optically active coatings deposited from an ultrasonically generated aerosol

Two deposition techniques, based on the ultrasonic pulverisation of a metal–organic liquid solution, have been developed and tailored for the preparation of optical oxide coatings. Both techniques are low-cost deposition processes, fully compatible with in-line technologies for mass production. The ultrasonic pulverisation leads to the formation of an aerosol that is deposited on a substrate surface either by pyrolysis in the vapour phase (Pyrosol process) or by sol–gel transformation of a liquid film deposited at room temperature (Aerosol–gel process). The preparation and properties of thin films deposited using these techniques for applications in integrated active optics are described.

Photoluminescence of terbium-organic complex in aerosol–gel-derived planar waveguides

This work deals with the low-temperature preparation of optically active silica-based materials. Tb3+-doped silica monolithic gels were elaborated at 40 °C. Tb3+–SSA-doped SiO2–TiO2 thin films were deposited by an original sol–gel approach, the aerosol–gel process, and heat-treated at 150 °C. Organic complexation of terbium ions was used to improve the active properties of doped silica gels and thin-film samples. Spectroscopic characterisations are reported for these samples. Photoluminescence increase by a factor two was observed for complexation by sulphosalicylic acid.

The effects of phosphorus on the crystallisation and photoluminescence behaviour of aerosol–gel deposited SiO 2–TiO 2–Er 2O 3–P 2O 5 thin films

Optically active films in the system, SiO 2–TiO 2–Er 2O 3–P 2O 5 have been prepared by aerosol–gel deposition. Crystallisation and morphology features that determine the preparation of transparent films are described and discussed in relation to the experimental conditions. The photoluminescence (PL) behaviour is then studied and discussed in relation to the films composition and to the nature of the crystallographic phases present in the films. It is concluded that concentration quenching and co-operative up-conversion mechanisms quench noticeably the PL. A 20Ti–0.5Er–10P composition is compatible with the preparation of transparent films together with an efficient prevention of these parasitic mechanisms.

Aerosol–gel preparation of optically active layers in the system Er/SiO 2–TiO 2

Er-doped silica–titania multilayer coatings have been successfully deposited using an original sol–gel deposition technique: the Aerosol–gel process. This study is the first step toward Aerosol–gel preparation of active planar wave guides. In this paper, we report on the physical, chemical, optical, microstructural and spectroscopic properties of the multilayer coatings. A new optically active crystalline phase, Er 2Ti 2O 7 (ETO), has been identified. This study shows that, depending on the experimental conditions (titanium and erbium content, heat treatment temperature), ETO can be obtained in the form of nanocrystallites dispersed in a transparent amorphous matrix.

Aerosol–gel deposition of doped titania thin films

The morphology, microstructure and chemical composition of pure as well as Ca and P doped TiO2 films have been studied. The films were deposited using the aerosol–gel technique. After deposition as a liquid coating, subsequent evaporation of the solvent induces the polycondensation in the film. The final film densification was performed by heat-treatment at 80–500°C. The thickness of the titanium oxide layers was adjusted to be in the range of 10 to 100 nm by varying the deposition time. Thicker films were prepared using a multi-layer deposition procedure. The films were characterized using Fourier transform infrared (FTIR) spectroscopy, ellipsometry, X-ray diffraction (XRD) and atomic force microscopy (AFM). Addition of dopants resulted in a pronounced densification of the films during the heat treatment due to loss of film crystallinity.

Aero-sol-gel reactor for nano-powder synthesis

This paper discusses a new approach to the synthesis of nano-structured oxides where sol-gel reactions are carried out in aerosol droplets. This aero-sol-gel (ASG) reactor allows for manipulation of the structure, chemical composition and surface area of silica powders through variation of process parameters. ASG powders differ in nanostructure from other continuous process powders such as pyrolytic and solution-route powders. ASG powders contain mesopores (>2-nm) and micropores (<2-nm), the mesopores being responsible for high surface areas measured by nitrogen adsorption using BET theory. Primary particles of close to molecular scale are believed to lead to exceedingly large specific surface areas on the order of 600-m2/g. These primary particles aggregate into nanometer scale mass-fractal aggregates that cluster in micron scale agglomerates. Under controlled reaction conditions the powder structure is reproducible as measured by small-angle X-ray scattering, SAXS, analysis. The ASG reactor displays transport effects similar to those previously seen in laminar flame reactors as evidenced by the effect of reactor geometry and reactant concentration on product structure.

Some aspects of the aerosol–gel process

Aerosol–gel process is a thin film deposition process based on the sol–gel polymerization of a liquid film deposited from an ultrasonically sprayed aerosol. This process offers an attractive alternative for the deposition of sol–gel thin films. The effects of the aerosol deposition route on the film characteristics were investigated with regard to sol–gel chemistry. TEOS solutions were studied by viscosimetry and FTIR spectroscopy using an ATR device. Silica xerogel coatings were studied by transmission FTIR and optical microscopy. We observed that film morphology and uniformity depend closely on the aerosol deposition conditions. The film growth mechanism was studied and some general rules for the deposition of good quality thin films were set up.

Performance of abamectin bait formulations against German cockroaches (Dictyoptera: Blattellidae).

Commercial and experimental formulations of abamectin-based baits were evaluated in laboratory and field studies against the German cockroach, Blattella germanica (L.). In continuous exposure tests with adult males, toxicity and presumably bait consumption varied with the design of the bioassay. LT50s ranged from approximately 0.9 to > 41 d for an aerosol gel formulation for males deprived of water for 72 h before the test and for undeprived males tested with alternative food and water, respectively. Dry formulations had lower LT50s than water containing formulations for nondeprived males. There was no difference in bait toxicity between males deprived of food or water, but in arena tests, moist formulations were preferred by mixed-stage populations of cockroaches. Powder formulations were more repellent (approximately 14.9%) than moist formulations (approximately 6.4%) in Ebeling choice boxes assays, but all abamectin formulations had positive performance indices. A powder formulation reduced cockroach trap catch in infested apartments more rapidly when applied to 50, rather than 12 sites, even when the same amount of bait was applied per apartment. When applied at approximately 50 sites as a series of thin smears, an aerosol formulation provided nearly an 80% reduction in trap catch. Other abamectin formulations provided substantial, but smaller reductions in trap catch. Abamectin-based baits can reduce German cockroach populations when properly applied.