Limiting Catalytic Coke Formation by the Application of Adherent SiC Coatings via Pulsed Laser Deposition to the Inner D
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Limiting Catalytic Coke Formation by the Application of Adherent SiC Coatings via Pulsed Laser Deposition to the Inner Diameter of Tube Material Traditionally Used for Ethylene Pyrolysis Service Alok Chauhan 1, Wilton Moran 1, Elizabeth Casey 2, Weidong Si 3, Henry White 1,* 1. Dept. of Materials Science, Stony Brook University, Stony Brook, New York 11794-2275 2. Comsewogue High School, Port Jefferson Station, New York, 11776 3. Physics Department, Brookhaven National Laboratory, Upton, New York 11973-5000 Abstract Pulsed laser deposited coatings can be used to enhance the corrosion resistant of materials traditionally used for industrial applications. In this paper, we describe our initial results on coating HK40 (a material used for ethylene heater tubing) with silicon carbide (a carburization resistant coating) to increase tube life. A 1 um thick film of silicon carbide was successfully deposited onto a heated HK40 substrate. An array of characterization techniques (scanning electron microscopy, atomic force microscopy, and scratch tests) demonstrated that the processing conditions were suitable for good coverage and promising adhesion behavior. Introduction Iron based alloys such as HK40 have been used for ethylene heater tubing with operating temperatures near 1000 C [1,2]. In service carburization has reduced tube life from 100,000 to ~ 50,000 hours [3]. Nickel based materials have been suggested for higher operating temperatures with only marginal improvement in carburization resistance [1,2]. In this paper, we report on our initial efforts to utilize pulsed laser deposited (PLD) coatings to reduce carburization and increase tube life. A thin (~ 1 um) silicon carbide (SiC) layer, a candidate material for this application, was deposited on as machined and shot peened HK40 substrates. Hou et al. [4] deposited SiC on Ni-Cr surfaces and found that adhesion improved when composition graded intermediate layers were employed. Surface preparation, which is an essential variable for good adhesion, was not reported in this work. Pulsed laser deposition has been previously used to deposit SiC on smooth semi-conductive surfaces [5-7]. To our knowledge, this paper represents the first study of the effect of surface preparation on the adhesion behavior of PLD films.
Experimental Procedure Centrifugally Cast A609 Grade HK40 [19.0-22.0% Ni, 23.0 –27.0%Cr, 0.35-0.45% C, 0.05 – 2.0% Si, 1.5% max. Mn] was obtained from Ultra-cast Inc. The target material, SiC [0.009% Al, 0.020% B, 0.031% Fe, 0.015% O and 0.017% Mn, traces of Ni and Ti], was supplied by Kurt J. Lesker Company. A KrF Excimer Laser (λ = 248 nm) was used to ablate and deposit SiC on as machined and shot peened (170/ 325 mesh glass beads) HK40 substrates. The films were deposited inside a stainless steel vacuum system pumped to a base pressure in the range of 10-4 to 10-5 torr. The KrF laser was focused to a rectangular spot 0.125 cm x 0.078 cm onto the rotating (10 - 20 rpms) 2.54 cm in diameter SiC target. The pulse energy and frequency of the laser was
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