This study describes an oxidation and corrosion resistant environmental barrier coating (EBC) applied to an AISI 441 stainless steel substrate. For this purpose, four polymer-derived ceramic (PDC) coating systems were developed. These coating systems consisted of a bond coat applied by dip coating, and a top-coat that was loaded with passive fillers and deposited by spray coating. The microstructures of the coatings were investigated using optical microscopy and scanning electron microscopy, including energy dispersive spectroscopy (EDS). X-ray powder diffraction (XRD) was used to investigate the phase composition of the coatings. The optimized composite top coatings were prepared from the preceramic polymer HTT1800, filled with yttria-stabilized zirconia and a specially tailored Al 2 O 3 -Y 2 O 3 -ZrO 2 (AYZ) passive filler, and commercial barium silicate glasses were used as sealing agents. After thermal treatment in air at 750°C, uniform and crack-free composite coatings on stainless steel substrates were developed, with thicknesses of up to 93 μm. Oxidation tests, which were performed at 850°C in synthetic air, showed that every tested coating system remained undamaged by oxidation and showed good bonding to the metal substrate. K E Y W O R D Senvironmental barrier coating, high-temperature oxidation, passive filler, polymer-derived ceramics

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The efficacy of catalytic distillation (CD) and the economic merits that it would bring into the biodiesel production process is studied. Process flow sheets depicting conventional and CD technology are modeled in Aspen Plus, and detailed operating conditions and equipment designs are provided for each process. The feedstock considered is soybean oil, and the transesterification reaction for the triglyceride is considered for biodiesel production. After optimal design of both process flow sheets to produce 10 million gallons of biodiesel per year, adhering to ASTM purity standards, a detailed cost analysis is carried out using the Aspen economic analyzer tool to predict capital, operating, and utility costs and to calculate the cost of production per gallon of biodiesel. Results depict CD to be a promising candidate to replicate the conversion and product purity of conventional biodiesel processes while having significant savings in capital (41.42% cheaper than the conventional process) and utility (18.12% less than the conventional process) costs, thereby making it a very competitive alternative. The total operating costs and price of production per gallon of biodiesel are only meagerly cheaper for a CD process because the most significant factor to the biodiesel production process is the raw material cost. For both processes, the price of production per gallon of biodiesel after accounting for revenue generated from glycerol product is predicted to be around 1.7 dollars/gallon. The Aspen model is flexible to accommodate higher flow rates for scale-up of operations, add or remove stages of operation into the biodiesel process, modify feedstock and stream prices, and predict associated capital and production costs.

This article features the oxidation behavior of ferritic stainless steel grade AISI 441 coated with protective polymer‐derived ceramics (PDC). Two PDC compositions are studied with respect to their oxidation resistance in a flow‐through atmosphere of synthetic air at temperatures of up to 1000°C. The coatings contain a combination of six passive fillers: Y‐containing ZrO2, glass microspheres, alumina‐yttria‐zirconia (AYZ) powder, and three commercial glasses. They are pyrolyzed in air for 1 hour at 800°C with heating and cooling rates of 3 K/min. Detailed microstructural examination of the oxide products formed at the surface of samples after exposure to air at 900°C, 950°C, and 1000°C for 1‐48 hours is analyzed. Both uncoated steel and steel coated with two of the protective systems described in part 1 of this article are investigated. Fe, Cr2O3, TiO2, and a spinel of the composition (Mn,Cr)3O4 are identified at the oxidized surface of the steel substrate using X‐ray diffraction. A significant weight gain of the unprotected steel is measured after all experiments, while oxidation tests of the coated steel show a negligible weight gain after 900°C and 950°C. During the early stages of coating oxidation, the monoclinic‐to‐tetragonal ratio in the zirconia filler is shifted toward the monoclinic modification. Longer exposures and higher temperatures lead to the formation of yttrium aluminum garnet (YAG) due to glass microsphere crystallization and solid state reactions in the AYZ powder. The crystallization of the three commercial glasses functioning as sealants leads to the formation of Ba(AlSiO4)2 also known as hexacelsian, which subsequently transforms to celsian. YZr8O14 is also formed. The protective effect of the PDC coatings applied to the stainless steel is demonstrated up to 950°C.

The present study deals with the synthesis of Mg 2 SiO 4 (Forsterite) applying the route of polymer derived ceramics (PDCs). The liquid, inorganic perhydropolysilazane (PHPS) was used because it is very reactive during pyrolysis in air and forms amorphous SiNO ceramic containing a tremendous amount of SiO 2 . Both facts are crucial for the reaction with MgO in order to synthesize Mg-silicates. The results of this study demonstrate, that the Mg-orthosilicate phase is formed at the MgO/SiNO interface via solid state reaction at comparably low temperatures of 1100°C during pyrolysis in air for 2 h. Furthermore the high reactivity of the polysilazane leads to an almost full conversion of the MgO to Mg 2 SiO 4 under the used conditions.