Aluminium Oxide Flame Test

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The aluminium oxide flame test is a quick and simple way to identify certain metal ions in a compound. However, it is only good for Group 1 compounds, and the colour produced depends on the contaminant and the type of fuel used (for example, sodium may mask other colours). The method involves placing the metal sample into a non-luminous flame and observing its colour. The colour is produced by the emission of photons from the electrons in the sample in the hot flame. This is known as thermophoresis.

The aluminum particles in the solution oxidize and form a stoichiometric oxide film on their surface. Then the particle combusts in water vapor, burning it five times more quickly than in air. The water vapor releases hydrogen which helps destroy the oxide film and releases pure aluminium droplets.

The stoichiometric oxide film prevents the aluminium particles from reacting with oxygen. This limits the reaction to only one of two possible pathways, stoichiometric oxidation or oxide lobe formation. The oxide lobe mechanism is unclear and requires further study. However, the results of inhalation studies using tagged gamma alumina suggest that the lobes act as insoluble dust and are mechanically cleared from the lung. This would help explain the observations that long-term exposure to alumina in aluminum refineries does not lead to pulmonary fibrosis or pneumoconiosis but rather to non-specific chronic industrial bronchitis. (Source: American Conference of Governmental Industrial Hygienists).

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