Alejandro Leopoldo Cabrera

Preparation of carbon molecular sieves, I. Two-step hydrocarbon deposition with a single hydrocarbon

Abstract A process is described for preparing a carbon molecular sieve that is suitable for the kinetic separation of gases, such as oxygen from nitrogen. The process involves modifying a carbon support, having a majority of micropores with an effective pore size of about 4.5 to 20 A, using a two-step process in which the sieve is contacted with two different concentrations of a volatile carbon-containing organic compound. The concentration of the carbon-containing compound used in the first step is larger than that in the second step, so that the pore openings of the micropores of the support are narrowed successively in two distinct steps without excessively filling the micropores themselves.

Oxidation protection for a variety of transition metals and copper via surface silicides formed with silane containing atmospheres

The reaction of SiH 4 /H 2 mixtures with iron, cobalt, nickel, copper, chromium, molybdenum, and tungsten, at temperatures between 350 and 800 °C and 1 atm of total pressure, was studied. When the amount of water vapor in the gas mixture is carefully controlled, a metal silicide diffusion coating forms at the appropriate treatment temperature. Cu silicide coatings form at temperatures as low as 350 °C. Metal silicide coatings for Fe, Ni, Co, and Cr form at intermediate temperatures (500–700 °C), and higher temperatures (above 700 °C) are required for W and Mo. Composition and structure of the metal silicide coatings were determined by Auger depth profiling and x-ray diffraction. Kinetics of the surface reaction between SiH 4 and the metal substrate as well as the behavior of these coatings in oxidizing environments at high temperatures were studied by a microgravimetric technique. The metal silicide coatings provide oxidation protection for Fe, Ni, and Cr in pure O 2 up to 1000 °C, for W and Mo in air up to 900 °C, and for Cu exposed to air up to 700 °C.

Si diffusion coating on steels by SiH 4 /H 2 treatment for high temperature oxidation protection

The reaction of SiH{sub 4}/H{sub 2} mixtures with iron and steels was studied at a total pressure of 1 atm and temperatures above 500 {degree}C. When the amount of water vapor in the gas mixture is carefully controlled, a metal silicide diffusion coating forms at low temperatures (below 900 {degree}C). Composition and structure of the Si diffusion coatings were determined with Auger depth profiling and x-ray diffraction. Kinetics of the surface reaction between SiH{sub 4} and the metal substrate as well as the behavior of these films in severe environments at high temperatures were studied by a microgravimetric technique. Characterization of these Si coatings on iron, low carbon steel (1010), 9% Cr/1% Mo steel (alloy A182F9), and stainless steels (310) and their applications to reduce oxidation, nitriding, or coking at high temperatures or corrosion in mineral acids are described.

Thermodynamic control of H2-N2 bright annealing atmospheres to inhibit nitrogen uptake by stainless steel

Passive SiO2 films that inhibit undesirable nitrogen uptake form on the surface of stainless steel during bright annealing in H2-N2 atmospheres. The SiO2 films can form at H2O/H2 ratios that are reducing to Cr in the alloy. Algebraic expressions were thermodynamically derived to predict the minimum H2O/H2 ratios required for forming SiO2 (to inhibit nitriding) and the maximum H2O/H2 ratios allowed for preventing formation of Cr2O3 (to prevent surface dulling), as functions of annealing temperature and concentrations of the elements in stainless steels. Predicted results agreed well with observed laboratory and field test data obtained over a range of annealing temperatures and H2O/H2 ratios for stainless steels with varying Si levels. This understanding of the surface chemistry can be used to improve control of H2-N2 annealing atmospheres to inhibit nitriding and prevent surface dulling. In addition, the literature suggests that SiO2 films that inhibit nitrogen uptake during annealing will also improve subsequent corrosion resistance of annealed parts.