The furnace built by Lenton for the Leeds IMR enables researchers to use both the Bridgman and the Czochralski growth techniques, currently the most common methods for growing artificial crystals
A special furnace from Lenton Thermal Designs is being used by the Institute for Materials Research (IMR) at the University of Leeds to develop new types of piezoelectric single crystals for high-temperature applications.
Single crystals provide considerably greater band widths, and therefore better image quality, than the ceramics generally used now for piezoelectric components in medical ultra-sound and sonar equipment.
However, their unsuitability for use at temperatures above 200C is a limitation, and researchers in Leeds are working on new crystal types that can perform well at up to 450C.
The furnace built by Lenton for the Leeds IMR enables researchers to use both the Bridgman and the Czochralski growth techniques, currently the most common methods for growing artificial crystals.
Both techniques involve growing crystals in a crucible at temperatures up to 1400C, using a small seed to initiate the process.
With the Bridgman technique the crucible is passed through separate heat zones with considerable temperature differences, while with the Czochralski technique the crucible is held at a constant temperature.
The Lenton furnace is a vertical split tube model with five heating zones, each with an advanced eight-segment set-point controller with RS422 and RS485 communication protocols.
The split-case design gives easy access to the inside.
The three central zones are heated by molybdenum disilicide elements and have a maximum temperature of 1500C, while the two outer zones have vacuum-formed wire elements and can be heated to 1200C maximum.
The different element types and the use of ceramic barriers between zones combine to provide the temperature gradient required for the Bridgman method.
The furnace bore is 75mm diameter in order to accommodate the crucible, which is raised, lowered and rotated on a turntable linked to the furnace control system, allowing sophisticated time/temperature programmes to be created.
A complete crystal-growth programme can last more than 200 hours.
