NIST Accelerated Weathering Laboratory: Metrology and Operations Project

Objective - To maintain, improve and expand capabilities at the NIST Accelerated Weathering Laboratory (AWL) and to use the facility to conduct safe, accurate and traceable aging experiments. Enable the technology transfer of the SPHERE technology to industrial stakeholders.

What is the new technical idea? The new technical idea is to deliver the best in the world, NIST traceable weathering measurement technology to stakeholders through the development of the NIST AWL. The current technology for accelerated weathering includes design and engineering innovations to improve irradiance light exposure uniformity, airflow, temperature and relative humidity control.[1-4] Commercial weathering devices are dominated by xenon arc lamp systems and traditional mercury lamps.[3,4] However, the integrating sphere technology used in the NIST weathering devices provides the highest uniformity and intensity of UV irradiation and the electrode less microwave-energized mercury arc lamp provides more stability.[5] Furthermore, the NIST environmental chambers have precise control of temperature and relative humidity that operate at ambient temperatures without the use of chillers.

The AWL will be used to conduct accelerated weathering experiments on polymeric materials, support advances in weathering metrology capabilities, facilitate the transfer of UV integrating sphere exposure technology, enable service life prediction model validation and promote advances in standards and codes. The AWL is composed of the NIST 2m SPHERE and the hygrothermal test chambers (no UV component). In order to meet the needs of the researchers that use the AWL (both NIST staff and external collaborators), a focus is placed on improving the operational capabilities of these accelerated weathering devices. New data acquisition methods will be developed to improve the measurement and safety systems in the expanded AWL. Extensive SPHERE irradiance calibration using a specialized spectral radiometer will be completed to maintain accurate irradiance values for the weathering devices. Statistical methods for uncertainty analysis and computational modeling will be used to systematically examine and improve the accuracy and control of all of the devices. The current methodologies that have been used for generating weathering data will be developed into standardized test methods and utilized to provide publically available reference data for weathering experiments. Technology transfer will be supported in two new directions. The 6-port MUUSIC (Multi-port Uniform Ultraviolet Solar Irradiance Chamber) system and the NIST strain SPHERE will be installed. Both systems represent design improvements in SPHERE technology which will facilitate transfer of technology to stakeholders and, in out years, support round robin testing. After installation of the MUUSIC system, the project will focus on developing the validation protocols to confirm its performance against the current 2m SPHERE.

What is the research plan?  

The research plan is divided in three goals:

1. Maintain and improve operation of the NIST 2m SPHERE to support current research and achieve 90 % operation time in the temperature and relative humidity range of 85 °C and 60% RH
2. Attain full operation of the 6-port MUUSIC system complete with functioning environmental chambers
3. Attain full operation of NIST Strain SPHERE  

The AWL will continue to improve operations by upgrading control systems and developing a maintenance logging program in the legacy NIST 2m SPHERE and hygrothermal chambers. In addition, the AWL staff will provide metrology and technical support for the commissioning of the new capabilities; 6-port MUUSIC system and the NIST strain SPHERE. New instrumentation, data acquisition systems, and test fixtures will be developed and maintained, including installation and functional testing of the weathering devices and safety systems. The validation of the 6-port MUUSIC system by comparing reciprocity data with NIST 2m SPHERE at room temperature and dry conditions will also be completed. Furthermore, a management system for capture and sharing of environmental (temperature and relative humidity) and irradiance data will be developed.

The AWL staff will develop and procure a validated safety system for NIST 2m SPHERE location, manufacture and validate environmental chambers for 6-port MUUSIC system and identify database software for environmental (temperature, relative humidity and ultraviolet) data. The safety system is a series of electronic interlocks to protect the facilities, samples, and users from over-temperature, chamber water overflow, and loss of experimental control. The validation of the strain SPHERE will also be completed by comparing reciprocity data with NIST 2m SPHERE at room temperature and dry conditions.

Finally, the database package for environmental (temperature, relative humidity and ultraviolet) data will be completed. In addition, a program for real-time sample irradiance data using the environmental database will be developed. An ASTM Round Robin program for the MUUSIC systems will also be developed.

Reference Documents:

1. Buyers Guide: Accelerated Weathering." Coatings World Magazine. Online. Accessed May 15, 2014;  http://www.coatingsworld.com/buyersguide/laboratory-equipment/accelerated-weathering.
2. "Laboratory Apparatus and Testing Equipment." JCT Coatings Tech., November-December 2013.
3. Atlas Material Testing Technology LLC (Chicago, Illinois)
4. Q-Lab Corporation (Westlake, OH)4.
5. "Ultraviolet Chambers Based on Integrating Spheres for Use in Artificial Weathering" J. W. Chin, E. Byrd, N.Embree, J.Martin, J.D. Tate, J. Coatings Tech., 2002, 74(929), 39.