Low-Temperature Differential Scanning Calorimeter

What is the Low-Temperature Differential Scanning Calorimeter?

A low-temperature DSC uses liquid nitrogen or a cascade cooler to reach as low as minus 180 degrees Celsius, making it suitable for frozen foods, elastomers, biologics and any material whose transitions lie well below ambient temperature.

Overview

Sub-ambient operation is achieved by a liquid nitrogen cooling accessory with automatic level control, or by a cascade refrigeration system that avoids consumable nitrogen. Mechanical cooling suits laboratories without nitrogen supply and gives reproducible cooling rates up to about 30 degrees Celsius per minute, while liquid nitrogen reaches lower temperatures and faster quench rates. Typical ranges are minus 90 to 600 degrees Celsius with single-stage cooling and minus 180 to 600 degrees Celsius with liquid nitrogen. Ice formation must be controlled: the cell is purged with dry gas and the enclosure kept above the dew point with a dry-box or positive-pressure cover. Applications include glass transitions of elastomers and adhesives, crystallization of fats and frozen foods, water and ice behaviour, and protein or cryoprotectant studies. Sub-ambient calibration uses cyclohexane or water transitions in addition to indium, because the sensor response changes with temperature.

How does it work?

The sample and an empty reference pan sit on a sensor in a furnace whose temperature follows a program. In heat-flux instruments a single furnace heats both positions and thermocouples measure the small temperature difference that develops when the sample absorbs or releases heat; the difference is converted to heat flow using a calibration factor. Power-compensation instruments place the sample and reference in separate small furnaces and vary the heating power needed to keep both at the same temperature, recording power difference directly. Either way the result is a curve of heat flow against temperature or time, with the area under a peak giving transition enthalpy in joules per gram. A purge gas, usually nitrogen, prevents oxidation and removes volatiles, and cooling may use liquid nitrogen, a mechanical cooler or an air vortex. Temperature and enthalpy calibration use indium, zinc and other reference materials of known melting point and enthalpy.

What are the key features?

• Liquid nitrogen or cascade cooling to −180 °C
• Automatic coolant level control for reproducible cooling rates
• Dry-gas purge and anti-icing enclosure to prevent frost
• Sub-ambient calibration with cyclohexane and water standards
• Cooling rates up to 30 °C/min with mechanical refrigeration
• Software for slow-rate and step-cooling sequences

What are the technical specifications?

A typical low-temperature differential scanning calorimeter configuration offers temperature range of −180–600 °C (liquid nitrogen), mechanical cooling range of −90–600 °C, heating rate of 0.1–50 °C/min, cooling rate of up to 30 °C/min (mechanical), temperature accuracy of ±0.1 °C and temperature precision of ±0.02 °C. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Low-Temperature Differential Scanning Calorimeter is used in elastomer and adhesive glass transitions, frozen food and ice behaviour, fat crystallization studies, biologic and cryoprotectant characterisation and battery electrolyte low-temperature behaviour. Across the wider DSC class, laboratories also deploy it for polymer melting and crystallinity testing, pharmaceutical polymorph and purity screening and food starch and fat behaviour studies.

Which standards and certifications apply?

Relevant standards and methods include ASTM E967, ASTM E968, ASTM E1356, ASTM E1269, ISO 11357-1, ISO 11357-2 and USP <891>. Certification candidates for this model are CE, IEC 61010-1 safety and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Calibrate temperature and enthalpy before a measurement campaign, and verify at least one check standard afterwards. Choose the pan material and type for the temperature and chemistry involved: sealed or hermetic pans for volatile samples, high-pressure crucibles for pressure work and open pans for evolved gases. Keep sample mass similar between runs, because thermal lag grows with mass and shifts peaks to higher temperature. Use a defined purge gas flow, dry the cell if moisture condenses, and run an empty baseline periodically. Consumables such as pans, lids and seals are single-use, and crucibles used for pressure work must be inspected for deformation. Follow ASTM E967, E968 or ISO 11357 for calibration and reporting, and record pan type, gas, rate and mass with each curve.

How do I select the right Low-Temperature Differential Scanning Calorimeter?

Choose a low-temperature instrument when transitions lie below room temperature. If minus 70 degrees Celsius is sufficient, mechanical cooling avoids nitrogen logistics; for lower temperatures or fast quenching, liquid nitrogen is needed. In an RFQ, specify the lowest temperature, cooling rate, coolant supply available and calibration standards.

How does it compare with other DSC variants?

Start with the temperature range you need, because it decides the cooling system: studies above room temperature need only an air or mechanical cooler, while glass transitions well below zero require liquid nitrogen. Then choose the measuring principle. Heat-flux instruments are robust, accept larger samples and cover most materials work; power-compensation instruments give sharper peaks and better resolution for small transitions and fast heating rates; temperature-modulated instruments separate reversing from non-reversing events; high-pressure cells are needed for oxidation stability and reactions under pressure. Check calorimetric accuracy and repeatability, resolution of weak transitions, sample pan options including sealed and hermetic pans, purge gas control, autosampler availability and the calibration standards supplied. Specify the heating rates, sample mass and the standards the method must follow.