(73b) Synthesis and Applications of Nanocoatings

The production of cell phones and emergence of solar power plants has lead to the preparation of nanocoatings. Flake production, functionalization, particulation, sacrificial coating, specifications are critical in order to prepare lubricous, high performance, nanocoatings.  Questek developed a steel grade made of nanophase precipitated dispersion. The three phases during the development of nanocoating are; (i) conception, production in bench scale, scale-up to pilot an plant; (ii) obtaining license, purpose of development of product and; (iii) marketing. Coating is the interface between product and environment.

    GMR, giant magneto resistive thin film heads used in hard drives of desktop computers comprises of seven layers. The seven layers are silicon substrate, tantalum buffer layer, nickel-iron free layer, copper spacer, germanium pinned layer, iron-manganese pinning layer and tantalum gap layer. In addition to GMR, nanocoatings are also used as thermal barrier coatings. Magnesium oxychloride sorrel cement coatings are used, for example. Ceramic coatings can be used to prevent corrosion and oxidation of blades.  Electron beam physical deposition process is used to obtain nanocoating.  SSA, specific surface area can be used to characterize nanocoating such as the degree of nanostructuring.  TBC comprises of oxide layer, bond coat layer, insulating layer, mixed oxide particles with particle size in the range of 10-100 nm. Aluminum projections with width of 1-5 nm and lateral grains with radius of curvature less than 1 A and length 5-8 nm are other nanofeatures.  TBC can be used to prevent fire spread.  Transient temperature in TBC was modelled including the effects of damped wave conduction and relaxation. There is a critical thickness of coating below which subcritical damped oscillations in temperature can be expected. For materials with relaxation times greater than R²/15.33a_nr the temperature in the naval warhead can be expected to undergo subcritical damped oscillations.

            X-ray lithography and electroplating techniques were used in order to create a zone plate of thickness of 500 nm with zone dimensions less than 50 nm.  PU coating can be grafted with nano-alumina in order to improve the performance of the coating by increasing the adhesion between nanoalumina and organic substrate.  Coating machines and rollers can be used to manufacture solar cells at lower cost. Flexible film are laminated on top of cell phones.  A PV, photovoltaic device was created by casting a solution of conducting polymer and fullerenes into a thin film.  Nanocoatings has been shown to improve the light to electricity conversion efficiency in solar cells.

            Nanostructured alumina/titania powders can be used to improve abrasive wear resistance of ceramic coatings by 400%. Process comprises of dispersion of nanopowders into a colloid, binded and granules spray dried using a Metro 9 MB plasma gun. Thermal spray robots are used to obtain nanocoating.  Nanostructures can result from control of morphology of phase separated polymer blends. Kinetics and thermodynamics of phase separation can be modeled. Polymer morphology with a single characteristic length scale can be made by quenching partially miscible polymer blend below the critical temperature of demixing. Spinodal patterns are formed that evolve with passage of time.  Nanostructuring can be controlled during preparation of metal chalcogenide nanostructured films by electrodeposition. These films can be formed within mesopores of silica.

            Cost of solar cells cen be reduced by use of graphene layers as AR coatings. Light to electricity conversion was found to increase to 14.6%.  Graphene sheets with less than 24,000 atoms/25 nm are metastable.  This can result when Gibbs free energy of mixing is negative and the phase stability criterion is not met.  Large single layer graphene sheets that are made by roll transfer are stable. Annular Plug Flow Reactor is used to decompose acetylene autocatalytic decomposition and carbon is grown by deposition on rolls. 

            Nanocoatings are used in the design and application of nanorobots for drug delivery. Principles of photodynamic therapy, fullerene chemistry, nanostructuring, x-rays, computers, pharmacokinetic and robotics are applied to design a nanorobot in order to treat Alzheimer’s disease.  Drug is inactive in caged form and activiated by breakage of fullerenes by irradiation at desired site.

Protein folding, secondary structure of proteins,  nucleic acid structure,  ribosomes, chromosomes and phospholipid membranes are examples where self-assembly is critical. 

Graphene is a interesting material of choice in Naval applications in order to demonstrate an infrared-transparent, electromagnetic shielding coating that can be applied to electrooptic sensor windows and domes.  Transmission greater than 90% in the 3-5 micron wavelength region can be achieved

Fluidized bed can be used to obtain the nanocoating.  The precursor material is calcined in ammonia at 1000 ⁰C for 48 hours in a fluidized bed reactor.  A red tri-tantallumpenta nitride, Ta₃N₅ coated mica pigment is produced. Bubbles and slugs and other instabilities formed during the operation of the fluidized bed  are reduced by use of vibrators/agitators.  The substrate particle size range is between 1 – 500 mm.After the pigments of the desired thinness is obtained a surface treatment step can be used to increase the weather stability and chemical stability of the pigment