CATALYST AND THIN FILM FABRICATIONS FROM SOL-GEL

SOL-GEL What is sol-gel? One area of chemistry dealing with colloidal compounds of solid phase in liquid medium.

Sol-gel formation process Step 1: Sol formation Due to the existence of charges at the surface of colloidal particle, ions of opposite charge, i.e. counter-ions tend to cluster nearby, forming an electric double layer around the surface of the colloid.

Peptization: The dispersion of small sized particle in a polar solution by the addition of counter-ions, which then creates electric double layer around the surface of the colloid.

Step 2: Gel formation If the particles can grow to exceed the colloidal dimensions (gel point), the substance is then said to be a gel. Sol Aggregation Gel Aging

Application of the sol-gel compounds The application of sol-gel compounds depends on various shape of sol-gel. i.e. monolith, film and mono size powder.

S ome common examples sol-gel processing are listed below: 1. Sol-gel coating: for conversion filters, laser damage resistant coatings, absorptive layers and anti-reflective coatings. 2. Ceramics: are obtainable at lower processing temperatures.

3. Electro ceramics, e.g. Capacitors, ferroelectrics, piezoelectric and ferromagnetic crystals. 4. Catalysts which utilize the fact that gels always posses a high degree of porosity and thus have very high surface areas.

5. Composite materials, e.g. the production of fibre reinforced ceramics that increase the fracture toughness to levels that are acceptable for engineering purposes.

Advantages 1. The lower processing temperatures that are required especially in glass manufacturing. 2. The degree of thermal stability.

3. The degree of compositional and micro structural control that is obtainable (nanoparticle material). 4. The range of special shape available directly from the sol-gel state (e.g. Film, fibres and monoliths).

5. Excellent properties of mixed oxide catalysts - Greater control of catalyst stoichiometry and homogeneity - Greater thermal stability towards deleterious solid state processes such as sintering and phase separation

- More efficient and intimate particulate mixing at the nanometer level - Greater control of catalyst dispersion on inert supports. In contrast, co- precipitation gives poorly defined material usually accompanied by a range of particles sizes and of much higher density of lattice defects.

Disadvantages Possible disadvantages of the sol-gel method include: 1. The cost of the raw materials 2. Long processing times

3. Problems with cracking associated with the shrinkage that accompanies drying. 4. Toxicity (due to the use of solvent)

Head of the project: Assoc. Prof. Dr. Wan Azelee Wan Abu Bakar Member in the ECAT Group: Assoc. Prof. Dr. Yusuf Othman Dr. Nor Aziah Buang Mrs. Noor Khaida Wati Mr. Ahmad Jais Alimin Mr. Imran Syakir Mohamad Emission Catalyst Technology Group (ECAT) (Sub-Group of Catalyst Technology Group-Cat) Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, Johor Bahru, Johor.

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