A gradient tube furnace is a split tube furnace with multiple heated zones, fitted with zone barriers. The zone barriers are pieces of insulation that fit between each heating element module, and help reduce the amount of heat transfer between heated zones.

Each heated zone is controlled by its own independent temperature controller, so it is possible to set different temperatures in each zone. The zone barriers reduce the amount of heat transfer between zones, increasing overall control and enabling the operator to create a temperature gradient across the heated length e.g., zone 1: 500°C, zone 2: 450°C, zone 3: 400°C.

There are many applications that require a gradient tube furnace, such as chemical vapour deposition (CVD), in which a substance is vaporised in the hottest zone, and transported along a work tube via a carrier gas, then condensed upon a substrate in the coolest zone. Gradient tube furnaces are ideal for this process, as each end of the furnace can operate at a different temperature, with a gradient of temperature between them.