Ashing is also referred to as charring; this is the step in a graphite furnace AA program that is designed to remove matrix constituents that might interfere with the measurement of the analyte. Ashing temperatures vary from 200º to 1800° C, depending on the matrix and analyte element.
Box furnaces are convenient furnaces to use. As the name implies, the furnace has a box shape and a box-shaped interior. The interior dimensions (10 to 50 cm per side) are much larger than a tube furnace, but the unit is often compact enough to sit on a benchtop. A door on the side permits quick and easy access to the interior. Several examples of box furnaces and their controllers are shown below.
A tube furnace is designed to heat a tube that is usually 50 to 100 cm in length and from 25 to 100 mm in diameter. Samples are placed inside the tube in ceramic or metal boats using a long push rod. The tube is surrounded by heating elements, which may also incorporate a thermocouple (a thermocouple can also be inserted down the tube if desired).
Other unlisted, specialized, or proprietary configuration.
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Maximum temperature at which the unit may operate and still maintain rated performances.
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A three zone or multi-zone furnace has the ability to ramp up to a specified temperature and maintain that temperature for a set time and then ramp up to a secondary higher temperature and maintain that temperature for a set time.
These types of furnaces contain a rotating refractory cylinder to rotate the product under test in a cylindrical container enabling thorough mixing with air.
A specialized tube furnace that normally has a modified control system with a special readout, frequently uses components calibrated to national standards, and often incorporates a centralized equaling block and end plugs to accommodate the thermocouples.
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Normally when the word vacuum is used it refers to any absolute pressure below that of normal atmospheric pressure. Atmospheric pressure is defined as 14.6 psia or 760 torr, any pressure less than this is considered a vacuum. In a vacuum furnace, the heat-treating process takes place inside a vessel that is airtight. This allows a vacuum to be drawn inside the vessel. The entire heat-treating process can take place under vacuum or precisely controlled atmospheres can be introduced. Heat treating under vacuum can: prevent surface reactions, such as oxidation or decarburization; remove surface contaminants such as oxide films and residual traces of lubricants; add a substance to the surface layers of the work; remove dissolved contaminating substances from metals by means of degassing.
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Furnace may be programmed to reach different temperatures at different time intervals.
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