FEATURE MATERIALS IN DESIGN & PROTOTYPING
How reflector technologies can help improve performance
Ever since Isaac Newton built his first reflecting telescope in 1668, using an alloy of tin and copper for the objective mirror, engineers have been exploring the potential of reflective technologies. Here Dr. Stefan Ziegler, head of research & development at Alanod, discusses how the latest reflector technologies are being designed to deliver increased performance, durability and ease of use
T
he power of UV light has long been recognised for its ability to rapidly cure
coatings and to manage bacteria and viruses, with UV’s photons being used to break DNA and RNA bonds, rapidly inactivating the microbes. When it comes to the design process and the specification of components and materials for equipment used in UV applications, the performance and durability of products can be significantly improved by incorporating the latest in reflector technology innovations.
INCREASED PERFORMANCE The aim of any product that features UV technology is to ensure that it is as effective as possible – and the key to this lies in the efficacy of the reflector’s surface. Many materials that are highly efficient reflectors of visible light perform poorly at UV wavelengths. For example, polished stainless steel reflects only approximately 25% of incident UV-C radiation, whereas a conventional anodised aluminium surface will reflect more than 80% of incident light at UV wavelengths. Although that’s a three-fold improvement over stainless steel, with the latest in surface innovation even better reflection rates are possible. This has been achieved by turning a limitation
of standard aluminium reflectors into a strength. The UV reflectivity of anodised aluminium varies by as much as 10% depending on the exact wavelength of the incident light. That phenomenon is the result of interference effects. When UV light hits an anodised surface, part of the light is reflected from the material’s oxide layer and part is reflected from the pure aluminium beneath the anodised surface. Those two reflections interact, effectively boosting reflectivity at some wavelengths and reducing it at others. Using conventional surface
treatment techniques, this interference effect is impossible to control as the oxide layer on an anodised surface varies in thickness, and it grows over time as the material reacts with
36 MARCH 2021 | DESIGN SOLUTIONS
oxygen in the environment. To overcome this, a new way to add a protective surface to pure aluminium was needed.
A NEW APPROACH Alanod has adopted a new approach called plasma-enhanced chemical vapour deposition (PECVD). This technique uses an energetic plasma to deposit material onto a surface at lower temperatures than conventional physical vapor deposition methods. Because the new process gives much greater control over the thickness of the surface layer, the performance of materials can be finetuned to specific UV wavelengths. The result is that Alanod’s MIRO UV A/B offers UV reflectivity of more than 90% at wavelengths of 300 to 350nm, making it the ideal reflector material for a wide range of applications such as UV curing, while MIRO UV C has been designed to deliver a peak of well over 90% at the 250nm wavelength, enabling the creation of materials most commonly used in disinfection and sterilisation product applications. Another benefit of the new PECVD process
is that it also greatly enhances the durability of a material’s surface. This is essential, as the intensity of UV light creates demanding conditions for any surface coating. UV light generates large numbers of charged particles that can greatly accelerate normal oxidation processes, significantly reducing material longevity. However, the low-porosity silicon surface of MIRO UV materials creates an effective barrier against oxygen ions and in intensive tests in a high temperature, high humidity environment, MIRO UV has exhibited a change in reflectivity
of less than 1% after 1000 hours.
EASE OF USE It isn’t just the PECVD surface coating that delivers high performance. Although the reflection layer consists of a 99.99% pure aluminium layer, which provides the maximum reflectivity, the base material under this layer is anodised aluminium, which has an anodic coating that is optically inactive so that it can provide a high surface strength yet allow for ease of handling and cleaning. As the substrate is aluminium it can also be easily recycled when replaced. Equipment used in UV applications needs to
be effective and long-lasting. With the help of the latest in reflector technologies, it is now possible for specifiers and designers to choose reflective surfaces that will deliver exactly what is needed, in terms of performance, reliability and longevity.
Alanod
www.alanod.co.uk
“Because the new process gives much greater control over the thickness of the surface layer,
Dr. Stefan Ziegler
the performance of materials can be finetuned to specific UV wavelengths”
/ DESIGNSOLUTIONS
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