The Guarded Longitudinal Bar Cryostat uses a steady-state technique to directly measure thermal conductivity. The instrument is designed to operate from cryogenic temperatures up to 200^oC under high vacuum. The bar-shaped test specimen is mounted to a temperature controlled heat sink. A small heater is applied to the opposite end of the specimen and produces a temperature gradient along the specimen. This temperature gradient is measured by two differential thermocouples. To minimize radiation heat loss from the test specimen, it is surrounded by a guard with a matching temperature gradient. Thermal conductivity is calculated from a knowledge of the temperature gradient of the specimen, the cross-sectional area of the specimen, and the power dissipated in the specimen heater. The vacuum system, temperature control and sequencing, and data acquisition and analysis are fully automated and controlled by menu-driven software. The cryostat can simultaneously measure electrical resistivity of metal specimens over the entire temperature range.

Features:

• Measures thermal conductivity from cryogenic temperatures up to 200^oC
• Requires relatively small bar- or rod-shaped specimens (typically flexure strength bars) are used
• Measures thin, high thermal conductivity specimens
• Automatic temperature sequencing and control
• Complete computer control of vacuum operations and data acquisition
• Easy-to-learn menu-driven software
• Option for measuring electrical resistivity

Applications:

Low-temperature thermal conductivity measurements have been used extensively in the study of factors affecting the properties of materials, such as processing conditions, composition, heat treatments, sintering aids and dopants, composite structure, grain size, chemical impurities, lattice defects, and porosity. The technique can be applied to a wide range of materials including metals, ceramics, composites, and diamond films.