Metal oxide sols

Bar, M. Muffler, H.-J. Fischer, Ch.-H. Lux-Steiner, M. C. 2001. ILGAR technology IV ILGAR thin film technology extended to metal oxides. Sol. Energy Mater. Sol. Cells 67 113-120. 

In a similar way, hydrogen and hydroxyl ions are potentialdetermining for hydrous metal oxide sols ... 

Sill. A sol is basically a stable dispersion of nanometer-sized particles and most of the voluminous research that has been conducted in this field is related to the formation of metal oxide sols. Metal oxide sols can be prepared by the following various techniques as summarized by Livage [1986] ... 

Matijevic, E. et al., Foimation and surface characteristics of hydrous metal oxide sols, J. Electrochem. Soc.. 120, 893. 1973. 

The sol-gel method is widely used to obtain oxide layers on the walls of microchannels. This method is advantageous because a large variety of compositions can be produced, and porosity and surface texture can be tailored. The sol-gel method is also used for the preparation of particulate porous catalytic supports [155,201,202], The colloidal metal oxide sols can be prepared by various methods such as reactions of metal salts with water or by hydrolysis and polycondensation of metal alkoxides. The latter is the most versatile procedure and has been investigated extensively. Often the sol contains varying concentrations of solid particles, and the procedure is no longer a sol-gel but rather a hybrid method, with the coating medium being a mixture between a sol and a suspension (Table 3). 

By controlling the carbon-to-metal ratio in the precursor mixed sols, a broad range of compositions can be prepared. Materials such as carbides, nitrides, solid solutions of carbonitrides, and multiple-phase systems with excess carbon were obtained. By using heavy metal oxide sols of very small micelle size and high surface reactivity, it was possible to produce some of the most refractory solids known at relatively low temperatures. Carbides, nitrides, and carbonitrides of U, Th, Zr, Hf, Y, the lanthanides, and so forth were prepared. 

Many of the different pillaring agents reported in the literature (organic compounds, metal trischelates, organometallic complexes, metal cluster cations, metal oxide sols, polyoxocations, etc.) have drawbacks such as low reactivity or lack of thermal stability, and polyoxocations are by far the most widely employed. Many different polyoxocations (Al, Ni, Zr, Fe, Cr, Mg, Si, Bi, Be, B, Nb, Ta, Mo, Ti, and, more recently, Cu, Ga, and Ce) have been reported in the open and patent literature and clays with multielement or doped pillars also have been claimed [2,8,9,19,20,68-70,73-75]. However, the chemical composition, structure and charge are at present well defined only for the Al-polyoxocation, in which the Keggin ion [Al,304(0H)24(H20)i2] is identified. 

The intercalation of imogolite monolayers in smectite cogently demonstrates the concept of forming regular, supergallery pillared products by direct intercalation on metal oxide sol particles of regular size and shape. 

Epifani M, Comini E, Arbiol J, Sicdiano P, SbervegUeri G, Joan RM. Oxide nanopowders from the low-temperature processing of metal oxide sols and their application as gas-sensing materials. Sens Actuators B 2006 118(l/2) 105-9. 

In polymerization-induced colloidal aggregation (PICA) processes, a reactive monomer, generally urea formaldehyde, is mixed with a stable, submicrometer diameter metal oxide sol and undergoes an acid-catalyzed polymerization that results in porous, uniformly sized polymer-oxide composite microspheres [24,25], PICA has been applied to a variety of metal oxide systems, primarily silica, but also alumina, titania, zirconia, ferric oxide, and antimony pentoxide [24,25]. The process is affected strongly by solution acidity [26]. At lower pH, polymerization is more rapid and a more porous but mechanically weaker particle is formed. 

---