Anderson Materials Evaluation, Inc. provides silicone contamination collection kits so that silicone and fluorocarbons can be detected and identified as contaminants in facilities and ovens, in addition to our long-time service of directly analyzing parts or other samples for contamination. We provide our own qualified as silicone-free collection kits for the ultra-sensitive measurement of silicone contamination in your facility by means of an XPS analysis detection method when the collection kits are returned to our laboratory for analysis. This test method allows the determination of the silicone concentration relative to known concentrations causing significant adhesive bonding degradation or other surface wetting and sealing problems. Silicone contamination also causes problems in some devices when exposed to ultraviolet and blue light, which can decompose the silicone materials and cause the deposition of silica-like particulate materials on optical elements or other parts of a system.
The XPS analysis of the kit test surface usually distinguishes sources of the element silicon as those due to each of the following:
- Silica or glass
- Silicates
- Diphenyl siloxane
- Long chain length dimethyl siloxane (such as in sealants or electronics encapsulants)
- Medium chain length dimethyl siloxane (such as in pressure-sensitive adhesives)
- Short chain length dimethyl siloxane (such as in lubricants or mold release agents)
- Very short chain length dimethyl siloxane (such as in lubricants or mold release agents)
- Extremely short chain length dimethyl siloxane or small molecule silicones
- Silane coupling agents
The most common silicone contaminant is polydimethyl siloxane (PDMS). The various short chain dimethyl siloxanes are usually the cause of airborne silicone contamination and are usually more harmful to adhesive bond strength when they contaminate an adhesive bondline because a given concentration of contaminant commonly covers more surface area and prevents adherend surface wetting by adhesives, sealants, and coatings. The shorter the chain length of dimethyl siloxane, the further the airborne contaminant is likely to spread in a facility. Longer chain length silicones may become airborne when heated. Also, some silicones have a wide range of chain lengths in them and the shorter chain lengths in the distribution will be preferentially inclined to become airborne.
The determination of the chain length of the PDMS is very useful in discovering the source of the silicone contamination and in taking preventive measures to prevent the recurrence of contamination. Silicone contamination often causes product failures and is commonly very time-consuming and expensive to clean up. It can have catastrophic consequences.
We provide specialized silicone contamination testing kits for the following purposes:
- Facility airborne contaminants, suitable for temperatures below 60°C, P/N SILTK-AA3
- Airborne contaminants in ovens, autoclaves, or other heated environments for temperatures above 60°C, P/N SILTK-HT2
- Contaminants on surfaces, such as walls, floors, and production equipment by means of transfer to an adhesive tape surface, P/N SILTK-TT2
Each of these silicone contamination test kits is optimized for the detection of silicone contamination and the materials in the kit are tested and validated as free of silicone contamination. XPS surface analysis is used to measure the silicon concentration as an atomic percentage on the test surface. The practical detection limit for silicon on most surfaces is about 0.2 atomic percent (at.%), though we can detect it down to about 0.1 at.% using the ambient airborne collection kits because of the unusually low spectral background of that test surface. Silicon at 0.2 at.% in the form of polydimethyl siloxane on the test surface of these kit materials is about 0.007 mg/sq.ft. or about 0.08 mg per square meter. Significant adhesive bond strength loss for virtually all combinations of adhesives and adherends usually occurs at about 3 at.% silicon in the form of a dimethyl siloxane, or about 15 times the concentration at the detection limit for our ambient airborne and tape transfer collection kits of 0.2 at.% Si. 3 at.% Si as PDMS is about 0.11 mg/sq.ft. or about 1.2 mg per square meter. These collection kits can also be used to measure fluorocarbon contamination of surfaces or airborne fluorocarbon contamination. Tests for nitrogen organic contaminants are also possible with these test kits.
The collection kits of silicone-free and fluorocarbon-free materials protect the exposure surface from exposure to contaminants during shipment to your facility and back to our laboratory. They also prevent the exposure surface from being compromised by rubbing against the shipping materials, which would be deleterious to the quantitative analysis of the contaminants picked up by the exposed surface in your facility.
Should you require silicone contamination testing instead by a Soxhlet method such as those procedures often based on Rohr testing methods, we can also provide that with some improvements to make the method somewhat more quantitative. Nonetheless, the method is usually poor for detecting the small concentrations of silicones often responsible for airborne silicone contamination and it offers little identification of the silicone in comparison to our XPS silicone contamination test method. Furthermore, it does not always have the sensitivity to detect silicones at concentrations sufficient to cause major adhesive bonding degradation or surface wetting problems.
For assistance with your possible silicone contamination needs, contact Charles R. Anderson, Ph.D. at canderson@andersonmaterials.com or complete a form on our “Contact Us” page.
