The carbon coatings on Nextel 550 and 720 were studied this investigation include the uniformity of the filament coating throughout the fabric or tow, adherence of the coating to the in batch (furnace) and continuous (solution fiber coating apparatus) modes, and in an inert atmosphere. Ashland filaments in the fabric or tow, and filament coating thickness. Aerocarb 240 pitch in toluene was used as the precursor material for carbon coating. The effect of processing vari-II. Experimental Procedure ables (i.e., pitch concentration, Nextel fiber sizing, and oxidative curing) was studied. Characterization was done by(1) Materials tactile, scanning electron microscopy (SEM), and thermalNextel 550 and 720 fabric and tow (3M Company, St. Paul, gravimetric-differential thermal analysis (TG-DTA). Coat-MN) was used for this coating work. A commercial toluene ing adherence, thickness, and uniformity were investigated.(Fisher Scientific, Fair Lawn, NJ) was used as the solvent for Applied carbon coatings adhered well onto the filaments; the pitch. Ashland Aerocarb 240 pitch (Ashland Petroleum however, the thickness and uniformity of the carbon coatCompany, Ashland, KY) was used to make the various pitchings were not good, mainly because of melting and wicking toluene solutions. of the pitch inside the tow prior to pyrolysis.(2) Thermal Analysis of Pitch TG-DTA analysis of the Ashland Aerocarb 240 petroleum I. Introduction pitch was performed with a Netzsch STA 409 Model thermal C HEMICAL vapor deposition (CVD) and chemical vapor analysis apparatus (Netzsch Inc., Exton, PA). The thermal analinfiltration (CVI) are the most widely used methods for ysis was conducted in a 10 sccm flowing argon atmosphere applying coatings to ceramic fibrous materials. Other methods from room temperature to 1100ЊC. Various heating rates of 10Њ, used to apply coatings to ceramic fibrous materials include 20Њ, and 40ЊC/min were used to accentuate any weak peaks. pyrolysis of hydrocarbons or preceramic precursors, slurry, sol-(3) Pitch-Toluene Preparation gel, and plasma spraying or thermal spraying. 1,2 The CVD or CVI coating routes have been reported to yield controllable and Ashland Aerocarb 240 pitch was mixed with toluene to make uniform coatings with required deposition temperatures on the 0.2, 2, 4, and 8 wt% pitch-toluene solutions. A 1-L stock order of Ն800ЊC. 3 Moreover, the CVD or CVI methods are solution was made for the nominal 2, 4, and 8 wt% pitchreported to offer more complete penetration and better property toluene solutions and a 300-mL stock solution for the 0.2 wt% control than liquid penetration methods. 4 Potential advantages pitch-toluene solution. The pitch-toluene solutions were placed of using a liquid penetration coating method (e.g., pyrolysis into a glass container and agitated for about 10 min. The of a pitch-solvent solution, coating solution, etc.) are lower absence of residue at the bottom of the glass container, after deposition temperatures (Յ1000ЊC), simplicity of coating pouring the solution into another container,...
