Angel Sanjurjo

Corrosion-resistant metallic coatings for applications in highly aggressive environments

Surface modification to improve the corrosion resistance of low-cost alloys is an economically attractive alternative to the use of expensive corrosion-resistant alloys. A low-grade steel surface modified by a suitable metallic diffusion coating can provide excellent corrosion resistance similar to that obtained with an expensive super alloy. We have used the fluidized bed reactor chemical vapor deposition (FBR-CVD) technique for the preparation of diffusion coatings containing Cr, Ni, Si and Ti on carbon and low-grade stainless steels. Several formulations of diffusion coatings on 409 SS have shown corrosion resistance similar to that of alloys AL6XN® or AL29-4C® in chemical heat pump applications. In this paper, we describe the preparation, characterization, and performance evaluation of a number of corrosion-resistant metallic diffusion coatings.

Electrocatalytic reduction of NOx on La1−xAxB1−yB′yO3−δ: evidence of electrically enhanced activity

Abstract Solid-state electrochemical cells can be used to sense and reduce NO x from combustion exhaust gases. In the reduction process the products are N 2 and O 2 . For these cells to be effective in fuel-lean combustion exhaust, cathode materials with high selectivity for NO vs. O 2 are necessary. Numerous compositions of La 1− x A x B 1− y B′ y O 3− δ (where A is Sr or Ba; and B and B′ are transition metals) were investigated for heterogeneous catalytic activity and selectivity for NO reduction using temperature programmed reaction (TPR). Ceramic cells using these materials as cathodes were fabricated and used to electrocatalytically reduce NO in NO/He and simulated exhaust atmospheres. An enhanced electrocatalytic three-way activity for NO x reduction was demonstrated that increases the window of operation into fuel-lean conditions.

Silicon by Sodium Reduction of Silicon Tetrafluoride

High purity silicon can be prepared from the reaction of Na with SiF4 to form Si and NaF. The SiF4 is obtained from inexpensive H2SiF6 by precipitation and decomposition of Na2SiF6. Concentrations of B and P are each in the 0.1 ppm wt range in the product Si, separated from NaF by aqueous leaching.

Microwave-assisted NO reduction by methane over Co-ZSM-5 zeolites

The microwave-assisted reduction of NO by methane in the presence of oxygen over Co-NaZSM-5, and H-ZSM-5 catalysts was studied. We demonstrated that microwave radiation at 2.45 GHz significantly enhances the catalytic conversion of NO to N2. High conversions (>70%) of NO were achieved over both Co-NaZSM-5 and Co-HZSM-5 zeolite catalysts at temperatures 250–400 ºC. Under similar conditions, thermal runs failed to show significant conversion of either NO or methane.

Coating particles by chemical vapor deposition in fluidized bed reactors

Abstract A technique to deposit a thin, adherent, uniformly dispersed coating onto the individual particles in a batch of granular or powdered material is described. We have been able to apply successfully a number of coatings to a variety of particulate materials using a fluidized-bed chemical vapor deposition (CVD) technique. By means of this technique we used tri-isobutylaluminum to apply adherent coatings of aluminum on powdered mica and powdered nickel. The powdered mica was also coated with titanium in a fluidized bed reactor in which titanium precursors were generated in situ by the reaction between HCl and metallic titanium. Post treatment of the titanium coated mica with ammonia produced agglomerates coated with TiN. These systems demonstrate the potential utility of the fluidized bed reactor for depositing a variety of coatings onto metallic and non-metallic dispersed materials. Preparation of such coated powders is likely to be valuable in a variety of industrial applications, such as the manufacture of composite structures.

Chemical vapor deposition coatings in fluidized bed reactors

Summary A coating technique based on chemical vapor deposition (CVD) in a fluidized bed reactor (FBR) is described. To coat an article, we load the coating material as a powder in an FBR and fluidize it using an inert gas. The system is heated to operating temperature, and vapors of HBr are mixed with the fluidizing gas. The sample to be coated is suspended on top of the bed or immersed into the bed. The reaction of the HBr with the powder in the bed produces halide species of the coating material that can deposit a coating on the substrate by a disproportionation or reduction reaction. Using this technique, we deposited titanium, silicon, zinc, TiN and Si 3 N 4 coatings on substrates such as copper, steel, silica and graphite.

Aluminum and alumina coatings on copper by chemical vapor deposition in fluidized bed reactors

Abstract High temperature Knudsen cell mass spectrometry was used to study the reactions of Al(c) with HCI(g) and with HCl(g) + 0 2 (g) over the range 127–627°C (400–900 K) to gain information pertinent to the chemical modeling of aluminum coating on copper by chemical vapor deposition in a fluidized bed reactor (CVD-FBR). In the Al−H−Cl system the measured pressures of AlCl 3 and AlCl were in remarkably good agreement with the values predicted by thermochemical calculations when the system is at equilibrium in the temperature range 377–623°C (650–900 K). Neither AlH x Cl3 − x ( x =1–3) nor AlCl 2 species were observed within the entire investigated temperature range. An upper limit of about − 218 ± 20 kJ mol −1 was estimated for the enthalpy of formation of AlCl 2 required to bring the observed and predicted pressures into agreement. The revised database was used to model aluminum coating on copper from a halide system by CVD-FBR. All the experimental results arid thermochemical calculations show that AlCl gas is an important reactive precursor in the aluminium-coating process. Using the most favorable conditions determined from these experiments and the thermodynamic calculations, a thin aluminum coating was deposited on a copper wire immersed for 30 min in a fluidized bed of aluminium particles at 487°C (760 K), using argon containing 0.12% HCl and 7% H 2 as the fluidizing gas. This coating significantly improves the corrosion resistance of copper exposed to air.

Titanium-based coatings on copper by chemical vapor deposition in fluidized bed reactors

Abstract Titanium, TiN and TiOx coatings were deposited on copper and Cu-Ni alloys by chemical vapor deposition in fluidized bed reactors. These coatings provide the copper with a tenfold increase in corrosion resistance in chloride aqueous environments, as determined by a.c. impedance studies.

Silicon coatings on copper by chemical vapor deposition in fluidized bed reactors

Abstract A coating technique based on (a) chemical vapor deposition, (b) fluidized bed technology and (c) subhalide chemistry was used to siliconize copper. Copper samples were siliconized in silicon beds kept at temperatures in the range 350–550 °C. Alternating current (a.c.) impedance measurements indicate that the corrosion resistance of the coated samples is significantly better than that of uncoated copper.

Corrosion-resistant metallic coatings on low carbon steel

Abstract Corrosion resistant coatings of various metals and alloys such as Si, Ti, Ni, and TiNi were formed on steel rebars by fluidized bed chemical vapor deposition (FBR-CVD), paint-and-heat or FBR-plasma spray techniques. The paint-and-heat metallization and FBR-plasma spray are powder coating techniques that can be applied easily and economically on new components as well as on existing steel structures, such as bridges. These metallic powder coatings provide non-sacrificial, superior corrosion protection for a long time. TiNi (70:30 wt. %) coatings on steel rebars provided a 20 fold increase in corrosion resistance over uncoated steel. These metallic coatings can be used to prevent corrosion in many industrial applications.