Metal oxide coated diatomite substrates

#The present invention relates to a process for coating particle substrates, the coated particle substrate and to applications and uses thereof. More particularly, the invention relates to coating particle substrates with a metal oxide-containing material, such material preferably being an electrically conductive and/or ferromagnetic oxide-containing material and such coated substrate.

#In many electronic and/or ferromagnetic applications it would be advantageous to have an electrically, electronically conductive; electro mechanical and/or ferromagnetic metal oxide coating which is substantially uniform, has high and/or designed electronic conductivity, and/or ferro magnetic properties and has good chemical properties, e.g., morphology, stability, etc.

#A number of techniques have been employed to provide certain metal oxide coatings on substrates. The CVD process is well known in the art for coating a single flat surface, which is maintained in a fixed position during the contacting step. The conventional CVD process is an example of a “line-of-sight” process or a “two dimensional” process in which the metal oxide is formed only on that portion of the substrate directly in the path of the metal source as metal oxide is formed on the substrate. Portions of the substrate, particularly internal surfaces, which are shielded from the metal oxide being formed, e.g., such as the opposite side and edges of the substrate, pores or channels which extend inwardly from the external surface and substrate layers which are internal or at least partially shielded from the depositing metal oxide source by one or more other layers or surfaces closer to the external substrate surface being coated, do not get uniformly coated, if at all, in a “line-of-sight” process. Such shielded substrate portions either are not being contacted by the metal source during line-of-sight processing or are being contacted, if at all, not uniformly by the metal source during line-of-sight processing. A particular problem with “line-of-sight” processes is the need to maintain a fixed distance between the source and the substrate. Otherwise, metal oxide can be deposited or formed off the substrate and lost, with a corresponding loss in process and reagent efficiency.

#A liquid slurry reaction mixture is formed from a silica platelet having an average particle size of about 50 microns, stannic chloride, antimony trichloride (15 mole %), water and methanol. The substrate is at a concentration of about 45 wt % basis the total weight of the reaction mixture. The tin and antimony chloride are soluble in the reaction mixture.

#The reaction mixture is fed into a reaction zone at elevated temperature. The elevated temperature is maintained by an RF induction plasma system operating at a power of about 30 kW at a frequency of 3 MHz. The central swirl gas is argon and the sheath gas, a mixture of argon and oxygen. The carrier gas is air. The reaction mixture is introduced into the reaction zone at a flow rate of 7.5 grams per minute. The gas velocities in the reaction zone are controlled to allow for an average particle residence time of about 15 milliseconds. The temperature within the reaction zone is controlled to allow for the structural solid maintenance of the substrate. The introduction of the reaction mixture is assisted by the air atomization of the reaction mixture. Tin oxide, antimony doped coated silica substrates are recovered in a collection zone. The collection zone uses a fabric bag filter to remove and recover the metal oxide coated substrates.

#Example 1 is repeated except that the alcohol is removed from the reaction mixture and hydroxide ion is slowly added to the solution to provide for precipitation of tin and antimony metal salts on the substrate. A tin oxide coated silica substrate is recovered in the collection chamber.