Laboratory furnaces provide continuous heating to process samples and materials. They are generally built from high temperature (refractory) materials so that they can maintain high temperatures without breaking down. Often, laboratory furnaces are set to function for months at a time to complete a processing set. Configuration, general specifications, tube furnace features, and atmosphere and control are all important to consider when searching for laboratory furnaces.
Choices for configuration for laboratory furnaces include ashing, box or muffle, bottom loading, top loading, and tube. 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 interference with the measurement of the analyte. Box furnaces are convenient furnaces to use. As the name implies, the furnace has a box shape and a box-shaped interior. Bottom loading furnaces load the sample or product to be treated through the bottom of the chamber via a platform elevator. In top loading laboratory furnaces the product to be processed is loaded through the top. Tube furnaces are 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).
Important specifications to consider when searching for laboratory furnaces include process temperature, width or tube outer diameter, length of the chamber or tube, and height. The process temperature is the maximum temperature at which the unit may operate and still maintain rated performances. The width refers to the internal width dimension of the unit, or for tube furnaces, the outer diameter of the tube. The length is the length dimension of the unit, or on tube furnaces, the heated length. The height refers to the internal height dimension of the unit.
Common atmospheres for laboratory furnaces include air or oxidizing, inert, reducing, salt bath, and vacuum. Laboratory furnaces are generally designed in one of two heating modes - single set point or programmable controller - to adjust temperature and temperature stability. Choices for heat source include arc, combustion, electrical or resistance, indirect or contact or conduction, induction, infrared or radiant, natural gas, propane, oil, other fuel, RF or microwave or dielectric, and steam. Other features for laboratory furnaces include overtemperature protection, computer interface, and application software.
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Vacuum furnaces are heat-treating furnaces that use a low atmospheric pressure instead of a protective gas atmosphere. This helps to alleviate surface reactions.