Ultra-High-Temperature Differential Thermal Analyzer

What is the Ultra-High-Temperature Differential Thermal Analyzer?

An ultra-high-temperature differential thermal analyzer uses a graphite furnace and tungsten-rhenium thermocouples or optical pyrometry to reach 2000 to 2400 degrees Celsius. It supports slags, refractory oxides, alloys and nuclear or metallurgical materials research.

Overview

At these temperatures only graphite, tungsten and certain ceramics remain usable, so the furnace is a graphite resistance or induction heated cell operated under argon or helium, with oxygen controlled to very low levels to protect the elements. Temperature is measured with tungsten-rhenium thermocouples up to about 2300 degrees Celsius, and optical pyrometry or a black-body cavity is used above that, with the measurement point calibrated against certified melting standards such as gold, palladium and alumina. Samples are held in graphite, tungsten or zirconia crucibles and are typically 100 to 500 milligrams because reaction heats are often small relative to the large heat capacity of the cell. Typical performance includes heating rates of 2 to 30 degrees Celsius per minute, temperature accuracy of 5 to 10 degrees Celsius at the upper limit and a controlled cooling program. Applications include melting and solidification of slags, dissolution of alumina in cryolite, alloy phase diagrams and nuclear fuel behaviour studies.

How does it work?

The sample and a thermally inert reference, usually calcined alumina, sit in the same furnace and are heated on the same program. A differential thermocouple or two matched thermocouples measure the temperature difference between them, recorded as microvolts against temperature or time, alongside the sample temperature. When the sample undergoes a transition that absorbs heat, its temperature lags the reference and produces an endothermic peak; exothermic reactions such as crystallization or oxidation give a peak in the opposite direction. The peak position identifies the transition temperature and the peak area is roughly proportional to the enthalpy change, although DTA is less quantitative than DSC because the heat path is not calibrated in absolute terms. Sensitivity depends on sample mass, packing density, thermocouple position and atmosphere. Typical samples are 10 to 100 milligrams, and inert, oxidising, reducing or vacuum atmospheres are selectable.

What are the key features?

• Graphite resistance or induction furnace to 2000–2400 °C
• Tungsten-rhenium thermocouples with optical pyrometry above 2300 °C
• Argon or helium atmosphere with oxygen control below 10 ppm
• Graphite, tungsten or zirconia crucibles for reactive melts
• Temperature calibration against certified high-purity melting standards
• Controlled cooling programs for solidification studies

What are the technical specifications?

A typical ultra-high-temperature differential thermal analyzer configuration offers temperature range of Ambient–2400 °C, heating rate of 2–30 °C/min, temperature accuracy of ±5–10 °C at 2000 °C, temperature sensing of W-Re thermocouple and optical pyrometer, atmosphere of Argon or helium, < 10 ppm O₂ and sample mass of 100–500 mg. 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 Ultra-High-Temperature Differential Thermal Analyzer is used in slag melting and solidification studies, refractory oxide phase behaviour, alloy and intermetallic phase diagrams, nuclear and metallurgical materials research and cryolite and molten salt investigations. Across the wider DTA class, laboratories also deploy it for clay and mineral phase identification, cement and gypsum dehydration studies and ceramic and refractory development.

Which standards and certifications apply?

Relevant standards and methods include ASTM E967, ASTM E794, ASTM D3418, ISO 11357-1, IEC 61010-1 and GB/T 13464. 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.

Package the sample uniformly and keep mass and packing the same as the reference to avoid baseline distortion, and dilute reactive samples with alumina when necessary. Select crucible and thermocouple materials that do not react with the sample at the working temperature, and use a platinum or alumina holder for oxidising conditions. Purge the furnace with the intended gas at a stable flow, and verify the thermocouple pair against melting point standards such as indium, tin, aluminium, silver or gold depending on range. Record the crucible type, sample mass, gas, flow rate and heating rate with every curve. Thermal analysis of minerals often shows overlapping peaks that require a consistent, documented heating rate and reference material to be compared between laboratories, so method details should be exchanged with results.

How do I select the right Ultra-High-Temperature Differential Thermal Analyzer?

Specify an ultra-high-temperature instrument only when reactions occur above about 1600 degrees Celsius, since the furnace requires strict atmosphere control, graphite consumables and slower cycles. For work up to 1600 degrees Celsius, a standard high-temperature DTA is cheaper and simpler to operate.

How does it compare with other DTA variants?

The decisive parameter is the temperature range, because DTA is chosen mainly when transitions lie above the working range of a DSC: minerals, clays, cements, refractories and glasses often require 1500 to 1600 degrees Celsius, and some slags and alloys need graphite furnaces above 2000 degrees Celsius. Below 700 degrees Celsius a DSC is usually a better choice because it also gives enthalpies. After range, consider the thermocouple type and hence the maximum temperature, the crucible and thermocouple materials compatible with the sample, atmosphere and vacuum control, sensitivity to small transitions, and whether automation is required. Peak resolution depends on the heat path, so sample packing and mass must be matched between runs. For routine quality control, an automated instrument with a sample changer reduces operator time, and calibration with melting point and phase transition references should be part of the method.