A model for the mechanism of nickel fluoride cold sealing of anodized aluminium

Kalantary, M. R.; Gabe, D. R.; Ross, Don

doi:10.1007/bf01030188

Cited by 38 publications

(30 citation statements)

References 6 publications

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“…Better results were obtained for cold nickel acetate sealing which is in agreement with the results reported by Kalantary et al [18,19], who suggest that nickel hydrolysis is more rapid at room temperature. A top view of the oxide film formed on Al/SiC composite obtained with the SEM demonstrates that the ''mud-cracked'' structure was repaired probably by Ni(OH) 2 /Al(OH) 3 hydrates.…”

Section: Film Growth On Al7075-t6 Alloy and Al/sic Composite By Anodisupporting

confidence: 82%

“…Industrially, this has traditionally been done by immersion in boiling deionized water, a method known as hot water sealing (HWS) [14]. This method becomes uneconomical due to the high temperature that uses substantial amounts of energy and is subject to health problems when chromates (Cr þ6 ) are involved [18,19]. In aggressive corrosive environments the anodized surface layer sealed in conventional hot solutions can be penetrated by aggressive anions such as Cl À and pitting or other types of corrosion can occur [20].…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of different sealing methods for anodized aluminum‐silicon carbide (Al/SiC) composites using EIS and SEM techniques

Herrera-Hernández

Vargas-Garcı́a

Hallen-López

et al. 2007

Materials & Corrosion

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Electrochemical impedance spectroscopy (EIS) and the scanning electron microscope (SEM) have been used in an investigation of the effectiveness of various sealing methods that can be used to improve the corrosion resistance of an anodized aluminum-silicon carbide (Al/SiC) composite. Anodic oxide films were grown on Al7075-T6 and the Al/SiC composite by sulfuric acid anodizing and sealing in a cold saturated solution of nickel acetate. Other samples were sealed using the traditional method of boiling water or hot nickel acetate for comparison. The results revealed a uniform anodized layer on Al7075-T6 that resisted pitting corrosion for more than 2 weeks exposure to NaCl, whereas a cracked oxide film with variations in thickness was observed on the composite material. Pit initiation occurred in less than 5 days on the anodized Al/SiC that was sealed in the hot solutions. This study suggests that the traditional hot sealing methods did not provide sufficient corrosion protection for aluminum metal-matrix composites (MMCs) because the reinforcing SiC particles deteriorated the surface film structure. However, this defective film can be repaired by nickel hydrate precipitation during cold sealing or by applying a thick polyurethane coating.

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Section: Film Growth On Al7075-t6 Alloy and Al/sic Composite By Anodisupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Evaluation of different sealing methods for anodized aluminum‐silicon carbide (Al/SiC) composites using EIS and SEM techniques

Herrera-Hernández

Vargas-Garcı́a

Hallen-López

et al. 2007

Materials & Corrosion

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“…Estos inconvenientes explican el gran interés que han suscitado en los últimos años los procedimientos alternativos de sellado a bajas temperaturas (3)(4)(5)(6)(7)(8)(9). También se han investigado y llegado a apUcar industrialmente aditivos aceleradores del proceso de sellado como las sales de níquel (2 y 9), los acetatos (3, 10 y 11) o la trietanolamina (TEA) (3).…”

Section: Fig 1-schematic Representation Of the Structure Ofporous Aunclassified

Envejecimiento del aluminio anodizado insuficientemente sellado

López¹,

Bautista²,

Otero³

et al. 1996

REVMETAL

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Resumen En este trabajo se estudiaron los diferentes grados de sellado de recubrimientos anódicos de aluminio obtenidos por inmersión en agua desionizada y en disoluciones de acetato y trietanolamina a 50 °C (temperatura muy inferior a la empleada en el sellado hidrotérmico tradicional). Para ello se emplearon los ensayos normalizados de absorción de la gota de colorante, inercia a la disolución acida y medida de la admitancia a 1 kHz y se realizaron medidas de espectroscopia de impedancia electroquímica (EIE). Se estudió, además, el efecto del envejecimiento en la atmósfera sobre los recubrimientos sellados en estas condiciones y el aumento de su grado de sellado que tiene lugar espontáneamente.Palabras clave: Sellado. Aluminio anodizado. Envejecimiento. Atmósfera. Aditivos. Ageing of anodized aluminium insuffíciently sealedAbstract In this paper, the different qualities of sealing of aluminium anodic films obtained in de-ionized and in acétate and triethanolamine solutions at 50 °C (temperature much lower than the one used in the traditional hydrothermal sealing) are studied. The standarized dye absortion, acid disolution and admitance at 1 kHz tests have been employed, and mesurements of electrochemical impedance spectroscopy have been carried out. The effect of the ageing in the atmosphere on the films sealed in these conditions and the increase of their degree of sealing which spontaneously takes place, are also studied.Keywords: Sealing. Anodized aluminium. Ageing. Atmosphere. Aditives. INTRODUCCIÓNLa anodización del aluminio es un proceso industrial mediante el cual se aumenta el espesor de la capa natural de alúmina (AI2O3) con el objeto de conseguir un material de mayor resistencia a la corrosión y a la abrasión. Estos recubrimientos protectores, cuando se generan con fines arquitectóni-cos o decorativos, son porosos, tienen un espesor de 3-35 ¡xm y están formados por dos capas ( Fig. 1): la capa barrera y la porosa. La capa barrera es la más interna, se halla en contacto directo con el metal y representa sólo entre un 0,1 y un 2,0 % del espesor total del recubrimiento de óxido, es compacta y posee una elevada constante dieléctrica. La capa porosa es la más externa, comprende todo el volumen de óxido atravesado por los poros y no tiene propiedades aislantes. La estructura de la capa porosa fue descrita por primera vez por Keller (1) en 1953, y está formada por celdas hexagonales con un poro central que atraviesa el óxido perpendicularmente a la superficie. El carácter poroso de los recubrimientos de aluminio obtenidos anódicamente hace que tengan propiedades absorbentes y posibilita su coloración. Estas mismas propiedades absorbentes, sin embargo, son la causa de la gran capacidad para absorber suciedad del aluminio anodizado, y hacen que necesite un proceso posterior de sellado. El sellado transforma la superficie de los recubrimientos mediante la eliminación o la disminución drástica de su porosidad. Con el sellado se consigue conservar el aspecto de las piezas, aumentar su resistencia a la corrosión ...

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“…In our previous studies [6,7] the effects of anodizing temperature, heating temperature and heating/cooling ratio on the cracking behavior of anodic films on cast aluminum alloy were reported. The properties of sealed layer were different due to different sealing mechanisms [9][10][11]. For anodic films sealed in boiling water, there were boehmite, aluminum hydroxide gel and pseudoboehmite in the sealed layer, of which only boehmite was stable and the other two sealing products may lose water to form boehmite [12].…”

Section: Introductionmentioning

confidence: 98%