Formation of Alumina on Kanthal A-1

[ValHeli]

I always see on the forums that aluminum oxide aka Alumina is formed by torching Kanthal A-1. I've been searching the net for the past couple of days and I could not find any reference to support this. I have seen a paper on the growth structure of Alumina on FeCrAl alloys but in the study, it took hours to form alumina at a minimum of 800 deg C (1472 F ). This is obviously much longer than the quick torch to orange we do on Kanthal A-1 and I highly doubt the time is sufficient to form beneficial Alumina.

My line of thought is that since Alumina serves as an electrical insulator, then a tightly wound micro coil should light up evenly and the geometry of the wire should not affect the resistance flow. ( lighting from the middle out ). A coil with a coating of alumina should light up the same as straight wire connected to the + / - poles which should be quick and even due to its electrical insulating properties.

No offense meant to anyone but please back up your responses with links to references. I thank you all in advance for your help

 

[TomCatt]

I can answer this question from personal experience. Not for Kanthal wire; but for FeCrAl foil. It does indeed take hours at 800 - 1000 C to form aluminum oxide on the surface.

Here's some links to articles about this (none of the work I participated in):

http://www.sciencedirect.com/science/article/pii/016943329190069V

Quantification of Aluminum Outward Diffusion During Oxidation of FeCrAl Alloys - Springer

http://onlinelibrary.wiley.com/doi/10.1002/maco.200403851/abstract
Abstract
Industrial FeCrAl foils were isothermally oxidized during 5 hours between 850 and 1000°C in atmosphere of pure oxygen. Characterization of transition and α-alumina phases was performed by XRD and XPS, using reference spectra obtained by various air annealing treatments of pure γ-Al2O3. An original model was proposed to deconvolute XPS spectra to obtain quantification of transition alumina formation and transformation. At 850°C, oxide scales on FeCrAl consisted of transition alumina, whereas higher temperature treatments resulted in decreased amounts of transition aluminas and in increasing α-alumina formation. At 1000°C, the highest temperature studied, the scale could be described by XPS and XRD as pure alpha.