The Chemical Vapor Deposition of Zirconium Carbide onto Ceramic Substrates
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Barber-Coleman digital temperature controller and a custom-built power supply. The gas delivery system separately feeds hydrogen/methane and zirconium tetrachloride/argon flows to the hot substrate. MKS mass flow controllers were used to control the flows of all gases. After zirconium carbide deposition onto the hot substrate, reaction byproducts are feed into an exhaust system for titration and/or decomposition by bubbling the exhaust gas through a sodium hydroxide aqueous solution. A natural gas bum-off is used to combust excess Loading/Unloading Chamber Methane - CH. (g) /Titrations Hydrogen - H, (g)
/ Exhaust 4-1009 -
2000'C
ZrO, Based Substrate Argon -
'
r
ZrCl4 (g) + CH4 (g) -* ZrC(s) + 4HCI(g) Ar(g)/H 2(g)
250 - 3310C
Heated Gas Lines 250 - 6400C Argon - Ar (g)
Figure 1.
Atmospheric Pressure High Temperature Chemical Vapor Deposition System.
hydrogen and methane. Once the substrate is cooled back to room temperature, it was removed from the chamber via the inert atmosphere chamber for further analysis. Heating of the zirconium tetrachloride was necessary in order to generate sufficient flow of zirconium tetrachloride into the argon gas flowing through the vaporizer. Heated gas lines were used to maintain the zirconium tetrachloride vapor stream and prevent clogging of the gas lines via zirconium tetrachloride condensation. Analysis of the zirconium carbide films involved film thickness determination, morphology, density, chlorine content, and stoichiometry. Scanning Electron Microscopy (SEM) samples were prepared by cross sectioning the samples and mounting them onto double-sided carbon tape. Samples were then analyzed on a R.J. Lee Personal SEM at l5keV. Density determinations were completed using mercury porosimetry (Stem Penetrometer Aminco #JS-7113). Chlorine content was determined by dissolving in water and titrating using mercury nitrate and bromophenol blue. The film stoichiometry was determined using three different methods. In the first method, a comparison was made between the sample X-ray lattice parameter and both literature and standards lattice parameters. The diffraction data used to determine the zirconium carbide lattice parameter were obtained using a Scintag PAD-V x-ray diffratometer by measuring the intensity of diffracted copper Koa radiation over a range of 5°_•20• 148' in steps of 0.03' at a rate of 15 steps/minute.
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The second method used to determine film stoichiometry was Auger Electron Spectroscopy (AES). The AES data was collected on a Physical Electronics 595 spectrometer using 10 kV electrons and a 4 kV argon ion beam for sputtering. Relative sensitivity factors were determined from ZrC 0.83 and ZrC 0.97 zirconium carbide standards provided by Aptech, Inc. The third method used to determine film stoichiometry involved the direct determination of carbon content by measuring weight percent of carbon in the film using a LECO® IR-412 carbon determinator. RESULTS AND DISCUSSION Zirconium carbide films (10 - 39 jim) of superstoichiometric, stoichiometric and substoic
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