What is Negative Thermal Expansion?
Create Athermal Optics
Temperature changes can detrimentally affect an optic’s performance due to the lens elements’ changes in radius of curvature, thickness, and index of refraction. For infrared lens materials, combinations of these changes often produce a decrease in focus with increasing temperature.
Passive athermalization is a a common solution to passively compensate for the thermal focus shift problem. Dissimilar materials in the optic housing are paired to a specific coefficient of thermal defocus of the particular optic design. This poses a problem for infrared lens materials as the thermal defocus values are usually negative.
ALLVAR Alloy 30 can decrease the overall length of a re-entrant system up to 38% by replacing Aluminum in the commonly used Aluminum and Acetal re-entrant design. Using ALLVAR Alloy 30 in Infrared optics systems provides advantages for improved size, weight, image stability, and focus under widely varying temperature conditions. Applications include augmented and virtual reality (AR/VR), head mounted systems, and military and aerospace refractive optics.
Athermalize Telescopes, Satellites and Spacecraft
ALLVAR Alloys has a long history of working with NASA through a series of SBIR Grants to develop Ultra-Stable Telescope Structures. These instruments require precise stability – down to a picometer – over several hours, regardless of thermal effects in the space craft. Currently available materials are brittle or exhibit too much expansion to be considered for telescope thermalization.
ALLVAR has developed structures that are paired with a base alloy with known thermal expansion rates. The ALLVAR Alloy-30 is created to a length that, through negative thermal expansion, nearly negates any change from the base alloy for a near zero thermal expansion regardless of thermal conditions. Similarly, sensitive optical or photonic detection systems mounted on rails or rods can be created in much the same way for nearly flawless alignment regardless of thermal conditions encountered in space exploration.
Tackle CTE Mismatch in Extreme Environments
Weather stations, remote research stations and even cargo transport ships can experience large temperature swings throughout the course of the day, or endure extreme cold or heat for months on end. The thermal expansion or contraction of critical elements can erode their reliability over time.
Thermal stress caused by the different expansion and contraction of dissimilar materials can lead to failure. Bolted joints can lose their pre-load as temperature shift, reducing reliability, and effecting performance of assemblies. For example, within cryostats and cryocoolers, fastened items may lose their force load and become unfastened, losing alignment or positioning of valuable equipment or seals. Can a simple washer help? One that exhibits negative thermal expansion can counteract the temperature extremes.
Increase Reliability of Components in Energy and Petrochemical Industries
The Energy and Petrochemical industries are constantly battling the effects thermal cycling has on valves and pumps in a variety of applications. Harsh environments, high pressures, and drastic temperature cycles are challenges when trying to keep a line sealed and safe. What if there was a simple washer or seal ring that could help?
Yes. ALLVAR Alloys offers a wide range of spacers, seal rings or washers that expand when everything else is contracting, and contract when everything else is expanding. Stop those leaks with ALLVAR.
Maintain Optical and Laser Alignment in Extreme Temperatures
Free space optics systems rely on precise alignment and focus of both the transmitter and receiver. Many of these communication systems are located outdoors in harsh environments with extreme heat or cryogenic chambers. Precise alignment is key while performing room temperature adjustments and at the extreme operating temperature.
ALLVAR Alloys offers a range of products that maintain precise alignment. Whether your system is rail mounted or screwed down, ALLVAR can provide you with athermal components that will virtually eliminate any slip of alignment due to excess heat or cold, and maintain your laser’s tight alignment.
Maintain Constant Force load in Industrial Seals and Pre-Loaded Bolts
If your factory or workplace relies on high temperature or cryogenic transport of gas or liquids, chances are you’re doing a lot of maintenance on these systems. Thermal mismatches between stainless steel housings and the bolts that hold them tight can cause rapid deterioration around the connector and the seal.
A simple negative thermal expansion washer from ALLVAR can help. These washers expand when cold, and contract when hot, countering the thermal actions of the joint to bring the net thermal change to nearly zero. This added safety is essential for facilities operating at capacity to avoid unintended downtime.
Improve Reconaissance Optics
Reconnaissance missions take place with high quality optics with long range lenses at extremely high altitude to avoid detection and missile strikes.
The extreme cold of the upper atmosphere compared to the heat of the earth’s surface causes a rapid temperature change upon take off and landing. Optics that were solid and well focused on the ground can lose that focus when cold air causes the housing and mounting to contract.
ALLVAR’s unique negative thermal expansion alloys are designed to counter extreme and rapid temperature changes to maintain proper alignment and focus – and in many cases it can provide solutions that offer a smaller housing size and lighter weight. Ask us how.
Tackle Thermal Mismatch in Liquid Natural Gas Transport
Natural gas is liquified for efficient transport and transfer to storage facilities. Liquid gas must be cooled to a temperature of -160°C and requires an extensive insulation system making LNG pipes significantly more expensive than gas pipes.
The extreme contrast between liquid temperature and environment can cause critical bolts or rings to fail due to excessive thermal expansion mismatch. ALLVAR Alloys manufactures Negative CTE washers and spacers to mitigate any extreme expansion or contraction caused by temperature differences between the pipes and any ambient temperature. Keep your cargo and crew safe by reducing the chances of a leak with ALLVAR Alloys.