Thin amorphous alumina films were prepared on stainless steel, type AISI 304, by low pressure metal-organic chemical vapour deposition. The effect of thermal annealing in nitrogen (for 2, 4 and 17 h at 600, 700 and 800 °C) on the film properties, including the protection of the underlying substrate against high temperature corrosion and the chemical composition of the film, were investigated.\ud
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Corrosion experiments performed at 450 °C in a hydrogen sulphide-containing gas, showed that the thermal annealing process had a detrimental effect on the protective properties of the alumina films. From FTIR and Auger measurements, it was found that the amorphous alumina, containing boehmite, converted to ¿-alumina during the annealing process

Fransen, T.

Gellings, P.J.

Haanappel, V.A.C.

van Corbach, H.D.

van de Vendel, D.

Thin Solid Films

English

V.A.C. Haanappel

D. v.d. Vendel

H.D. van Corbach

T. Fransen

P.J. Gellings

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The effect of thermal annealing on the properties of thin alumina films prepared by low pressure metal-organic chemical vapour deposition

Thin amorphous alumina films were prepared on stainless steel, type AISI 304, by low pressure metal-organic chemical vapour deposition. The effect of thermal annealing in nitrogen (for 2, 4 and 17 h at 600, 700 and 800 °C) on the film properties, including the protection of the underlying substrate against high temperature corrosion and the chemical composition of the film, were investigated. Corrosion experiments performed at 450 °C in a hydrogen sulphide-containing gas, showed that the thermal annealing process had a detrimental effect on the protective properties of the alumina films. From FTIR and Auger measurements, it was found that the amorphous alumina, containing boehmite, converted to ¿-alumina during the annealing process

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The effect of thermal annealing on the properties of thin alumina films prepared by low pressure MOCVD

University of Twente Research Information

Thin Solid Films 256 (1995) 8-12 Letter The effect of thermal annealing on the properties of thin alumina films prepared by low pressure metal- organic chemical vapour deposition V.A.C. Haanappel, University of Twente, D. v.d. Vendel, H.D. van Corbach, T. Fransen, P.J. Gellings Department of Chemical Technology, P.O. Box 217, 7500 AE Enschede, Netherlands Received 15 September 1994; accepted 11 October 1994 Abstract Thin amorphous alumina films were prepared on stainless steel, type AISI 304, by low pressure metal-organic chemical vapour deposition. The effect of thermal annealing in nitrogen (for 2, 4 and 17 h at 600, 700 and 800 “C) on the film properties, including the protection of the underlying substrate against high temperature corrosion and the chemical composition of the film, were investigated. Corrosion experiments performed at 450 “C in a hydrogen sulphide-containing gas, showed that the thermal annealing process had a detrimental effect on the protective properties of the alumina films. From FTIR and Auger measurements, it was found that the amorphous alumina, containing boehmite, converted to y-alumina during the annealing process. Keywords: Aluminium oxide; Chemical vapour deposition; Coatings; Fourier transform infrared spectroscopy 1. Introduction Thin films of alumina have previously been prepared by metal-organic chemical vapour deposition (MOCVD) [l-8]. One of the advantages of MOCVD over conventional CVD, is the low process temperature which directly leads to a lowering of the energy con- sumption of the process. The low deposition tempera- ture is also of importance for the deposition of protective overlay coatings on substrates which could easily deteriorate at high temperatures [9]. Today, sev- eral metal-organic compounds have been used for the deposition of thin alumina films, such as, aluminium- acetyl-acetonate [lo- 141, aluminium-tri-ethoxide [7], aluminium-tri-iso-propoxide [ 2-4,151, aluminium-2- ethyl-hexanoate [ 161, and aluminium-tri-see-butoxide [ 17-201. Atmospheric as well as low pressure MOCVD has been used as a process for the deposition of thin alumina films. These films offer, in principle, great potential because of the large number of possible appli- cations, such as insulating layers, optical filters, wear resistant coatings and corrosion protective coatings. 0040-6090/95/$9.50 c 1995 - Elsevier Science S.A. All rights reserved SSDI 0040-6090(94)09473-X In this letter the effect of thermal annealing on the physical and chemical properties of thin alumina films, deposited on stainless steel AISI 304 by low pressure metal-organic chemical vapour deposition, is de- scribed. Sulphidation experiments were used to investi- gate the porosity and the film. Auger electron spectroscopy ( AES) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the ox- ide film. 2. Experimental Thin alumina coatings were produced by decomposi- tion of aluminium-tri-set-butoxide (ATSB, Janssen Chimica) at reduced pressure (0.167 kPa (1.25 Torr)). A stream of nitrogen gas was passed through the ATSB precursor. This saturated gas was diluted with pure nitrogen gas before entering the reactor. The gas line between the ATSB container and the reactor was heated to 150 “C to prevent condensation of the precur- sor. A full description of the low pressure MOCVD V. A. C. Haanappel et al. / Thin Solid Films 2.56 (1995) 4- 7 system is given elsewhere [21]. Standard conditions for the production of an alumina film with a thickness of 0.5 llrn were: deposition temperature, 280 “C; partial pressure of ATSB, 3.7 x 10 -4 kPa (ATSB saturation temperature, 134 ‘C); reactor pressure, 0.17 kPa; and gas flow, I I min ~ ‘. Depositions were performed on stainless steel, type AISI 304 ( 18% Cr, 8% Ni, 0.08% C, 1% Si, 2% Mn, 71% Fe). The AISI 304 samples (discs with a diameter of 20 mm and a thickness of 1 mm) were ground on SIC papel to a final size of 4000 grit followed by a polishing treatment with Al,O, (3 pm) and subsequently cleaned ultrasonically for 30 min in soap, hexane and ethanol. Finaliy, the samples were immersed in Streuer’s etching fluid i 5% solution of 3 M nitric acid in ethanol) for 15 min, washed with pure ethanol and dried in hot air. After the deposition process, the ATSB flow was stopped and the samples were exposed to a nitrogen atmosphere at temperatures ranging from 600 to 800 “C, and during 2, 4 and 17 h. After finishing the thermal annealing period, the temperature was lowered belom 200 C before the samples were removed from the furnace. Corrosion experiments were performed in order to investigate the protective capacity, i.e. the porosity, of the films against aggressive gas components such as oxyge? and sulphur at high temperatures and were carrielj out in a closed system at 450 -C for 70 h (gas mixtul’e: I% H,O, l’>i, H,S, 19% H,, bal. Ar). The morphology and the composition of the cor- roded specimens were investigated by means of optical and sc:anning electron microscopy (JEOL M 35 CF), the letter equipped with an EDX analysis system (Kevev Delta, class III). To characterize the chemical composition and the depth profile, the alumina films were analysed using a Perkir --Elmer PHI 600 scanning Auger multiprobe. Alternate sputtering and Auger analysis were used dur- ing in..depth analysis. The functional groups including hydrol;en-containing bonds within the films were mea- sured by Fourier I ransform infrared spectroscopy (FTIR), using a Nicolet 20 SX FTIR apparatus. Due to the non-transparency of the specimens, the spectrome- ter wzs equipped with a diffuse reflection cell. The microstructure of the films was investigated by X-ray diffracl.ion ( XRD), using a Philips PW 1710 X-ray diffractometer with monochromatic CuKx radiation. 3. Results and discussion The effect of temperature and exposure time of the post-deposition thermal treatment on the corrosion at- tack is shown in Fig. I. From this figure it is clear that the amount of corrosion products increases with in- creasing annealing temperature and/or time. The best “0° I r!j 1 m 2hr j_ 0.60 DC? EW m 0.40 .$ 0.20 0.00 no T.A 600 700 600 Annealing temperature [“Cl Fig. I. Bar diagram of the weight gain ,q of the specimens as a function of the thermal annealing time and temperature. protection against high temperature corrosion was ob- tained for the unannealed samples. SEM analysis showed the formation of mainly FeS, corresponding to the thermodynamically most stable phases [22]. Proba- bly. due to the anneal treatment. microcracks or mi- cropores were formed which act as fast diffusion paths for the aggressive gas compounds [ 191. The presence of cracks can be attributed to the formation of thermal stress and a lower adhesion strength between the sub- strate and the oxide film [22]. Fig. 2 shows the FTIR adsorption spectra of the annealed samples at 700 C. Two specific absorption bands were found at 900&950 cm ’ and 3000.-3700 cm ‘, indicative of the Al-0 and 0-H bonds. respec- tively. This figure shows that the O-H absorption band decreases in intensity at a given annealing temperature with increasing annealing time. The absorption band around 900-950 cm- ‘, increases in intensity. The max- imum of this Al-0 peak changed from 925 cm. ’ for the unannealed samples, to 950 cm ’ for samples an- nealed at 800 C, indicative of a lower internal stress in the alumina film [22]. From previous results [ 19,201. it is assumed that, due to the presence of OH groups, the as-deposited alumina film consists partly of boehmite (AlO(O According to Stumpf et al. [23], y-alumina was found as the crystalline phase after thermal annealing. If AlO were incorporated in the film, it will decompose to alumina and water at high temperatures: 2AlO( OH) PAT-m- -Al,O,$ 1 - .\‘) HZ0 i- .rH,O The transition of AIO(OH) to ;$-alumina was also found by Goton [24], Bugosh et al. [ 251 and Saalfeld [26]. Goton [24] found dehydroxylation of boehmite into AlzO, (with 0.1 mole H,O per mole of Al?O,). Bugosh et al. [25] and Saalfeld [26] found that heating of AlO results subsequently into ;‘-, (I- and r-alu- mina. The composition and the depth profile of the an- nealed alumina films were investigated by Auger elec- tron spectroscopy (AES) in combination with ion 10 V. A. C. Haanappel et al. 1 Thin Solid Films 2S6 (1995) 4-7 ll m t, I- m 0 P 3 0 m i? 3000 2500 2000 1500 1000 500 Wavenumber (cm-11 Fig. 2. FTIR reflectance spectra of alumina films annealed at 700 C for 0, 2, 4 and 17 h 2h 4h 17 h Al 0 , I 1 , 500 loo0 1500 2ooo Electmn Kinetic Energy (ev) Fig. 3. AES survey scan analysis of the alumina film on AISI 304, after thermal annealing for I7 h at 800 “C. V. A. C. Haanappel et al. 1 Thin Solid Film 256 (19951 4- 7 7 I I I I I _-_,’ /‘\\ 6- /“, ‘1 /’ ,-__.--“\ , \ ’ .__&‘/’ \/\\\ I’ ‘\,I’ ‘___ \ : \ \ S-1 \ \ \ : : ,/ . . . . . . . . ,, 0. .., . ..’ ;, .: 4- ‘. Sputter depth (MI) Fig. 4. AES depth profile analysis of the alumina film on AISI 304. after thermal annealing for 17 h at 800 C sputtering. From the steady state spectrum (survey scan). it is clear that next to Al and 0 a small amount of carbon was detected, even after annealing for 17 h at 800 ‘C ( Fig. 3). After one or more sputtering cycles (one cycle corresponds with one minute sputtering at a rate of 44 nm min - ‘) no carbon was found anymore. This mighi be explained by the adsorption of carbon contain- ing compounds, such as carbon dioxide and hydrocar bons on the outside of the alumina layer. Fig. 4 shows the AES depth profile analysis of the alumina film on ATSI 304 after 17 h at 800 “C. It was found that for the unannealed samples the interface was rather distinct. After longer annealing times and higher annealing tem- peratures, the interface became less distinct, due to penetration of alloying elements into the alumina film. Also small amounts of sulphur were detected at the interface. Due to the miscibility of chromium and alu- minium and the segregation of sulphur at the interface, the adhesion strength significantly decreased resulting in a higher susceptibility to crack formation [24]. XRD patterns did not reveal any transformation from amorphous to crystalline alumina, possibly owing to the slight thickness of the film. Earlier experiments [ 191 with alumina films deposited at atmospheric pres- sure showed a conversion from amorphous to y-alu- mina. 4. Conclusions From the corrosion experiments it was observed that the post-deposition thermal treatment did not exert any beneficial effect on the protectiveness of the alumina films against high temperature corrosion. This anneal- ing process resulted in a reduction of the amount of OH groups in the film, probably attributed to the presence of boehmite. During the annealing period the oxide-al- loy interface changes as a result of diffusion of alloying elements to or into the alumina matrix. Acknowledgments This research was supported by the Innovative Re- search Program on Technical Ceramics (IOP-TK) with financial aid of the Dutch Ministry of Economic Affairs. Thanks are due to L. Vrielink for the FTIR measure- ments, A.H.J. van den Berg (CMO) for the AES exper- iments, and J. Boeijsma for the XRD measurements. References [I] T. Maruyama and S. Arai, Appl. Phys. Left., 60(3) ( 1992) 322. [2] J.A. Aboaf, J. Electrochem. Sot.: Solid State Sb.. 114 ( 1967) 948. 12 V. A. C. Haanuppel et al. / Thin Solid Films 256 (1995) 4-~ 7 [3] M.T. Duffy, J.E. Carnes and D. Richman, Metallurgical Trans., [I61 T. Maruyama and T. Nakai, Appl. Phys. Lrtt., 58( 19) (1991) 2 (1971) 667. 2079. [4] C. Dhanavantri, R.N. Karekar and V.J. Rao, Thin Solid Films, 127 (1985) 85. [5] A.A. Barybin, V.I. Tomilin, V.A. Kempel and E.A. Makhotin, Pribory i Tekhnika Eksperimenta, 3 ( 1975) 238. [6] J. Saraie, J. Kwon and Y. Yodogawa, J. Electrochem. Sot., 132 ( 1985) 890. [17] K. Okuyama, Y. Kousaka, N. Tohge, S. Yamamoto, J.J. Wu, R.C. Flagan and J.H. Seinfeld. AIChE J.. 32 (1986) 2010. [7] M. Matsushita and Y. Koga, /. Electrochemical Sot.. I /5( 1968) 69C. [IS] Y.Y. Baryshnikov, I.L. Zakharov and G.I. Makin, Zhurnal Obshrhei Khimii, 60(6) ( 1990) 1350. [I91 V.A.C. Haanappel, Alumina Films on Metallic Substrates by MOCVD, PhD Thesis. University of Twente, Enschede. Nether- lands. 1994. [8] S.S. Yom, W.N. Kang, Y.S. Yoon, J.I. Lee, D.J. Choi, K.Y. Seo, P.H. Hur and F.Y. Kim, Thin Solid Films, 213 (1992) 72. [9] P.J. Gellings. British Corrosion J., 27(2) (1992) 105. [lo] O.B.A. Ajayi, M.S. Akanni, H.D. Burrow. J.N. Lambi, 0. Osasona and B.P. Podor, Thin Solid Films, 138 ( 1986) 91. [ll] O.B.A. Ajayi, M.S. Akanni, J.N. Lambi, C. Jeynes and J.F. Watts, Thin Solid Films, 185 ( 1990) 123. [12] V.M. Koleshko, V.V. Sviridov, V.P. Boldyrev, B.S. Reznikov. I.V. Nekaryukin, K.D. Yashin. N.N. Goroshko and A.A. Ko- valevskii, Neorganichoeskie Material),, 12 ( 1976) 1780. [ 131 V.P. Boldyrev. V.M. Koleshko. B.S. Resnikov, I.V. Nekaryukin, L.D. Buiko and K.D. Yashin, Neorganicheskie Materialy, 12 (1976) 2181. [20] V.A.C. Haanappel, H.D. van Corbach, T. Fransen and P.J. Gellings, Surjtice Coatings Technol., 63 ( 1994) 145. [21] H.D. van Corbach. V.A.C. Haanappel. T. Fransen and P.J. Gelhngs, Thin Solid Films, 239 ( 1994) 3 I, [22] V.A.C. Hadnappel, H.D. van Corbach, T. Fransen and P.J. Gellings. The effect of thermal annealing on the adherence of Al,O, films deposited by low pressure metal-organic chemical vapour deposition on AISI-304, submitted for publication in Oxidation qf‘ Metals. [23. H.C. Stumpf, A.S. Russell, J.W. Newsome and C.M. Tucker. lnd. Eng. Chem. 42 ( 1950) 1398. [24] R. Goton, PhD Thesis, no. 146. University of Lyon, France, 1955. [ 141 K. Kamata. European Patent Application EP 0 055 459 Al. [ 151 R.W.J. Morssinkhof, The Deposition of Thin Alumina Films on Steels by MOCVD, PhD Thesis, University of Twente, Nether- lands, 1991. [25] J. Bugosh, R.L. Brown, J.R. McWhorther, G.W. Sears and R.J. Sippel. Ind. Eng. Chem. Chem. Prod. Res. Develop., I( 3) (1962) 157. [26] H. Saalfeld, Neues. Jahrb. Mineral. Abh., 95 (1960) 1. 

1350. [I91 V.A.C. Haanappel, Alumina Films on Metallic Substrates by MOCVD, PhD Thesis.

Metallurgical Trans.,

Sot.: Solid State Sb..

The effect of thermal annealing on the adherence of Al,O, films deposited by low pressure metal-organic chemical vapour deposition on AISI-304, submitted for publication in Oxidation qf‘

Thin Solid Films,

http://purl.utwente.nl/publications/10062

The effect of thermal annealing on the properties of thin alumina films prepared by low pressure MOCVD

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