Next Article in Journal
In Situ DRIFTS Studies of NH3-SCR Mechanism over V2O5-CeO2/TiO2-ZrO2 Catalysts for Selective Catalytic Reduction of NOx
Next Article in Special Issue
Influence of the Preparation Method and Photo-Oxidation Treatment on the Thermal and Gas Transport Properties of Dense Films Based on a Poly(ether-block-amide) Copolymer
Previous Article in Journal
Recent Advances in Transmission Electron Microscopy for Materials Science at the EMAT Lab of the University of Antwerp
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Study on the Degradation of Optical Silicone Exposed to Harsh Environments

1
EEMCS Faculty, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherland
2
Department of Signify, High Tech Campus, 5600 JW, Eindhoven, The Netherlands
3
Dow Silicones Belgium sprl, Industrial zone C, 7180 Seneffe, Belgium
4
State Key Laboratory of Solid State Lighting, Changzhou 100083, China
*
Author to whom correspondence should be addressed.
Materials 2018, 11(8), 1305; https://doi.org/10.3390/ma11081305
Submission received: 16 July 2018 / Revised: 25 July 2018 / Accepted: 26 July 2018 / Published: 28 July 2018
(This article belongs to the Special Issue Durability and Life time of Polymers, Composites and Nanocomposites)

Abstract

:
Degradation mechanisms of silicone plates under harsh environment conditions are studied in this investigation. Environmental degradation of silicone free form, used as secondary optics in Light Emitting Diode LED lighting lamps and luminaires or any other applications requiring high quality optics being used, has negative implications for the optical performance. Degradation of silicone plates in harsh environment conditions was studied in salt bath and swimming water environments, using different light radiation and temperatures. Samples were exposed to harsh environment conditions for up to 4 months. Optical and chemical characteristics of exposed plates were studied using an Fourier transform infrared- attenuated total reflection FTIR-ATR spectrometer, an integrated sphere, and a Lambda 950 Ultraviolet-Visible UV-VIS spectrophotometer. Results show that 100 °C salt bath exposure had the most severe degrading effect on the optical characteristic of silicone plates. Increasing exposure time in the salt bath at that high temperature is associated with a significant deterioration of both optical (i.e., light transmission and relative radiant power value) and mechanical properties of silicone samples. On the contrary, silicone plates showed a great degree of stability against light exposure (UV at 360 nm and blue light at 450 nm).

1. Introduction

In order to control the light beam emitted from an Light Emitting Diode (LED) light source, a secondary optic, such as a free form lens, is used and aligned to the LEDs mounted on the printed circuit board (PCB). This secondary optic can be made of various optically transparent materials, such as glass, polymethylmethacrylate (PMMA), polycarbonate (PC), and silicone. The best material for a given application is highly dependent on technical requirements. Each of these materials has some advantages and disadvantages. Advantages of PMMA is its low cost, easy moldability into any shape, high light transmission, “green” material characteristics, and high UV transmittance. However, PMMA has the disadvantages of yellowing under prolonged UV exposure and higher water absorption. PC material has more benefits than PMMA. PC is harder, has a higher refractive index, is easily molded, has lower water absorption, and higher softening temperature than PMMA (130 °C). The main disadvantages of a PC sample are yellowing under prolonged UV exposure, PC is not eco-friendly, which is not suitable for several biomedical applications, and has a high price. Silicone material is a new kind of optical material that has some benefits over PC and PMMA like higher UV yellowing stability, higher temperature resistance up to 150 °C, low viscosity cure, high flexibility, as well as high impact resistance [1]. Because of its very low surface tension, silicone shows a strong resistance against moisture [1]. Therefore, there is a growing interest in replacing PMMA and PC with silicone in outdoor optical materials to protect components against damage [1,2]. This becomes even more critical in outdoor applications, especially in industrial applications. In our prior study, the photodegradation of polycarbonate under blue light radiation and its effect on optical properties have been described [3]. A limiting controlling factor in the performance and lifetime of lenses in LED-based products is degradation and aging of optical materials during service. This research aims at developing an understanding of the possible degradation of optical and mechanical properties of optical grade silicone plates in harsh environments that may be encountered in outdoor lighting applications. These aforementioned degradations and damages result in a colour shift and lumen decay, with both having serious negative implications for the quality and lifetime of LED lamps or luminaire. In harsh outdoor applications, interactions between temperature, moisture, radiation, and oxidation are inevitable. To our knowledge, there is no report dealing with degradation of silicone lenses in the presence of several degrading factors [4,5]. The information, obtained from the experiments, will be important when it comes to the development of products for harsh outdoor environment applications. Generally, lifetime estimation for LED-based products are typically based on the expected operating hours until light output (e.g., luminous flux) depreciates to 70% of initial levels. The term “lumen maintenance” (lm) is often used to describe the degradation in light output during operation. LM-80 standard is now widely used as an instruction for the luminous flux depreciation test [6]. With the test data provided by LM-80, Lumen degradation estimation method for LED light sources TM-21 standard presents a method for predicting the lumen maintenance of LED light sources beyond 6000 h [6]. A lot of research has been done to model the light output degradation of LED-based products and LED packages [7,8,9,10]. In addition to lumen maintenance, colour shift over service time is another concern for LED manufacturers [11,12,13,14,15,16,17,18]. Both colour shift and lumen depreciation normally take place with relatively slow kinetics. That is why accelerated lifetime testing, followed by extrapolation of data to real service conditions, is needed to estimate the lifetime of LED-based products. Accelerated lifetime testing is essentially based on the exposure of samples to higher levels of degrading factors, i.e., higher-than-normal light intensity, temperature, and humidity [19,20]. Extrapolation of accelerated ageing test results to real service conditions is difficult in case there is a change in the dominant degradation mechanism with changing temperature. Most of the previously done accelerated aging tests are in fact indoor aging tests [3,21,22,23,24,25,26], with temperature and light intensity being most widely used accelerating factors [24,25]. We showed in one of our previous studies that a highly accelerated test set-up (HAST), with 20 times faster kinetics of degradation, can be developed to study the reliability and degradation of LED-based products, using simultaneous temperature and light radiation [25]. Application of combined stresses to do accelerated degradation tests has been reported by Davis et al., in which they applied temperature and humidity at the same time to understand luminaire depreciation [27]. However, to our knowledge, there is no report on degradation and accelerated aging tests of silicone LED lenses in a harsh environment, in which there are other stresses other than temperature and light intensity. In harsh outdoor industrial environments or swimming pool conditions, the package is exposed to UV light, high levels of moisture, and ionic contaminations including exposure to Cl ions. This study is a step forward in making our understanding of the performance and degradation of silicone used as lens in LED-based products in harsh outdoor environments complete. Some examples of outdoor applications are depicted in Figure 1.

2. Experimental Procedures

In order to find out the degradation mechanisms of silicone plates under harsh environmental conditions, pure silicone samples of 3 mm thickness, and 3 cm diameter with a refractive index of 1.41 and hardness (Shore A) of 84 were aged under different conditions, given in Table 1:
In order to study the effect of blue light radiation, the high accelerated stress test (HAST, TU-Delft, Delft, The Netherlands) set-up was used to accelerate the aging test up to 10 times [25]. In order to analyze the effect of UV radiation, the UNICORN UV chamber (TU-Delft, Delft, The Netherlands) at room temperature was used. Sample series #4 and #5 were submerged under water boiling at 100 °C with 3 wt % salt, and for series #3, it was underwater in swimming pool water with 3 ppm chloride ions. Samples were exposed to the abovementioned conditions for up to four months. Maximum temperature for the aging of the silicone lens could not be over 120 °C. At temperatures higher than 120 °C, silicone becomes brittle and even fragile. A temperature of 100 °C is high enough to accelerate the ageing in a relatively short time with minimal effects on the mechanical properties of samples. Aging at temperatures lower than 100 °C have been done as well and it did not have any effect on radiation and thermal aging, which has to do with the slow kinetics of reactions at low temperature
Fourier transform infrared (FTIR, TU-Delft, Delft, The Netherlands) spectroscopy was used to study changes in the chemical structure of samples during degradation. Infrared spectra of aged specimens were also recorded using a Perkin–Elmer Spectrum 100 series spectrometer (TU-Delft, Delft, The Netherlands) in the attenuated total reflection (ATR) mode for 200 scans at a resolution of 4 cm−1. Infrared spectroscopy (IR) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum. The infrared spectrum of a sample is recorded by passing a beam of infrared light through the sample. When the frequency of the IR is the same as the vibrational frequency of a bond, absorption occurs. The ATR accessories with very small crystals, which is a diamond that is typically about 2 mm across. Diamond is used because it has the best durability and chemical inertness. An IR beam is directed onto an optically dense crystal with a high refractive index at a certain angle. This internal reflectance creates an evanescent wave that extends beyond the surface of the crystal into the sample held in contact with the crystal. In regions of the IR spectrum where the sample absorbs energy, the evanescent wave will be attenuated. The attenuated beam returns to the crystal, then exits the opposite end of the crystal and is directed to the detector in the IR spectrometer. The detector records the attenuated IR beam as an interferogram signal, which can then be used to generate an IR spectrum. A very decisive factor in the accuracy of results is flatness of samples. To obtain the best results with high repeatability, samples must be flat. All silicone samples are fortunately flat and will remain flat during exposure. Samples were first placed on top surface of the crystal. Then the gripper plate was placed on the sample. The pressure applied to the gripper plate was adjusted to ensure that consistent contact was achieved between the crystal and the sample. This was the same for all samples.
Examination of the transmitted light reveals how much energy was absorbed at each frequency (or wavelength).
Chemical analyses were combined with characterization of optical properties of the degraded samples. Integrated sphere and Lambda transmission spectroscopy (TU-Delft, Delft, The Netherlands) were used to study the optical properties of specimens. In order to study changes in the mechanical properties of degraded specimens, a shear punch test was performed on silicone plates, using a DMA Q800 machine (Dow Silicones Belgium, Seneffe, Belgium) with a punch diameter 3 mm.

3. Results and Discussion

Figure 2 shows the effects of blue/UV light radiations on the FTIR spectra of silicone samples. In general, the absorption peak at 1410 cm−1 was assigned to the rocking vibration of –CH2–. The ones at 1260 and 864 cm−1 were assigned to bending and rocking vibrations of Si–CH3. The absorption peak at 793 cm−1 was due to the coupling of stretching vibration of Si–C and rocking vibration of ACH3. The absorption peaks at 1080 cm−1 and 1010 cm−1 were attributed to the stretching vibration of Si–O–Si on the backbone of silicone rubbers. It was seen that neither UV nor blue light radiations affected transmission in the FTIR spectra. It appeared that silicone is a stable material under UV light and blue light radiations. As is shown in Figure 2a, there was a small change at 900 and 1680 cm−1, but because there was no difference in optical and mechanical properties of aged samples, the changes might have been because of instrument error.
Figure 3 shows the FTIR spectra of the silicone lens exposed to swimming pool water at 35 °C and to 100% RH environment at 100 °C (sample #4) for up to 3000 h. Again, none of these exposure conditions had any implication for the light transmission in the FTIR spectra.
Figure 4 shows the effects of exposure to a saline water environment (sample #5) on the FTIR spectra of silicone samples. Contrary to other exposure conditions, the decrease in the transmission of degraded samples with exposure time in this case is quite significant. This indicates that amongst different possible degrading factors in a harsh environment condition, Cl ions dissolved in water have the most negative contribution to the structural stability of silicone. Cl ions significantly accelerated the kinetics of degradation in silicone samples. Looking at the FTIR spectra, one can conclude that chemical degradation was associated with breaking Si–O–Si bonds and decomposition of methyl groups attached to silicone atoms. Many papers also reported similar results concerning hydrothermal stability of cross-linked silicone rubber [28,29,30,31].
Figure 5 shows the UV-visible light transmittance spectra of silicone samples aged under saline water exposure conditions. As expected, the transmission of light decreased in the visible light range with exposure time, which was an indication of deterioration of the quality of silicone plates.
Figure 6 shows the relative luminous intensity (%) versus wavelength (nm) in the spectral power distribution (SPD) spectra of as-received and saline water-exposed samples, showing that the maximum of peak at 450 nm was drastically reduced as a result of degradation. Figure 7 illustrates the effects of aging time on the normalized maximum light output at 450 nm. Interestingly, there was a linear reduction of maximum light output with exposure time.
Table 2 shows the chromaticity values of degraded samples, where these values are average values.
In order to study changes in the mechanical properties of the degraded specimens in a saline environment, a shear punch test was conducted on as-received and aged specimens with 3500 h of exposure to saline environment. Figure 8 compares force–displacement curves of these two samples, showing that exposure to a saline water environment was accompanied with embrittlement and a decrease in the ductility of specimens.

4. Conclusions

The degradation of silicone used in secondary optical designs combined with an LED package under harsh environment conditions was investigated. The effects of UV 360 nm exposure or blue 450 nm light exposure, combined with high temperature (100 °C), water environment (35 and 100 °C), and saline 100 °C water environment on the color shift, transmission, and radiant power intensities of silicone samples were studied. The following conclusions can be drawn:
(1)
Silicone samples showed a great degree of stability against light exposures (both UV and blue light). A total of 3500 h of radiation at 100 °C did not result in any change in the optical characteristics of silicone samples.
(2)
Exposure to saline and high-temperature environmental conditions had major negative implications for the optical characteristics of the samples. Saline water exposure at 100 °C resulted in a significant reduction in the transmission of samples in the visible light range, reduction in the maximum radiant power at 450 nm, and a change in the color chromaticity values.
(3)
Saline water exposure at 100 °C changed the mechanical properties of silicone plates by making them more brittle.

Author Contributions

Conceptualization, M.Y.M. and W.v.D.; Methodology, M.Y.M.; W.v.D. and F.D.B.; Formal Analysis, M.Y.M.; Investigation, M.Y.M.; Writing-Original Draft Preparation, M.Y.M.; Writing-Review & Editing, W.v.D., F.D.B.; Supervision, K.Z.; Funding Acquisition, HTSM, STW.

Funding

This research was funded by HTSM grant number 15350.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Zhang, G.Q.; van Roosmalen, A.J. Reliability challenges in the nanoelectronics era. J. Microelectron. Reliab. 2006, 46, 1403–1414. [Google Scholar]
  2. Van Driel, W.D.; Fan, X.J. Solid State Lighting Reliability: Components to Systems; Springer: New York, NY, USA, 2012. [Google Scholar]
  3. Yazdan Mehr, M.; van Driel, W.D.; Jansen, K.M.B.; Deeben, P.; Boutelje, M.; Zhang, G.Q. Photodegradation of bisphenol A polycarbonate under blue light radiation and its effect on optical properties. Opt. Mater. 2013, 35, 504–508. [Google Scholar] [CrossRef]
  4. De Buyl, F.; Beukema, M.; Van Tiggelen, K.; Rong, K.W.; Rankey, N.L.; Steinbrecher, J. Dow Corning Moldable Silicone Leading Innovation in LED Light Fixtures. J. Soc. Silicone Chem. Japan 2014, 31, 23–38. [Google Scholar]
  5. De Buyl, F.; Beukema, M.; Van Tiggelen, K. How Silicones are Evolving to Meet the Growing Needs of LED Lighting Industry. LED Prof. 2013, 36, 40–44. [Google Scholar]
  6. Approved Method for Lumen Maintenance Testing of LED Light Source (IES-LM-80-08); Illuminating Engineering Society: San Jose, CA, USA, 2008.
  7. Projecting Long Term Lumen Maintenance of LED Light Sources (IES-TM-21-11); Illuminating Engineering Society: San Jose, CA, USA, 2011.
  8. Fan, J.J.; Yung, K.C.; Pecht, M. Lifetime estimation of high-power white LED using degradation-data-driven method. Trans. Device Mater. Reliab. 2012, 12, 470–477. [Google Scholar] [CrossRef]
  9. Wang, F.K.; Lu, Y.C. Useful lifetime analysis for high-power white LEDs. Microelectron. Reliab. 2014, 54, 1307–1315. [Google Scholar] [CrossRef]
  10. Fan, J.J.; Yung, K.C.; Pecht, M. Prognostics of lumen maintenance for high power white light emitting diodes using a nonlinear filter-based approach. Reliab. Eng. Syst. Saf. 2014, 123, 63–72. [Google Scholar] [CrossRef]
  11. Wang, X.; Balakrishnan, N.; Guo, B. Residual life estimation based on a generalized Wiener degradation process. Reliab. Eng. Syst. Saf. 2014, 124, 13–23. [Google Scholar] [CrossRef]
  12. Huang, J.L.; Golubović, D.S.; Koh, S.; Yang, D.G.; Li, X.P.; Fan, X.J.; Zhang, G.Q. Degradation modelling of mid-power white-light LEDs by using Wiener process. Opt. Express 2015, 23, A966–A978. [Google Scholar] [CrossRef] [PubMed]
  13. Tseng, S.T.; Peng, C.Y. Stochastic diffusion modeling of degradation data. J. Data. Sci. 2007, 5, 315–333. [Google Scholar]
  14. Yazdan Mehr, M.; van Driel, W.D.; Zhang, G.Q. Reliability and life time prediction of remote phosphor plates in solid state lighting applications using accelerated degradation testing. J. Electr. Mater. 2016, 45, 444–452. [Google Scholar] [CrossRef]
  15. Lu, G.; van Driel, W.D.; Fan, X.; Yazdan Mehr, M.; Fan, J.; Jansen, K.M.B.; Zhang, G.Q. Degradation of microcellular PET reflective materials used in LED-based products. Opt. Mater. 2015, 49, 79–84. [Google Scholar] [CrossRef]
  16. Lu, G.; Yazdan Mehr, M.; Fan, X.; Fan, J.; Jansen, K.M.B.; Zhang, G.Q. Color shift investigations for LED secondary Optical designs: Comparison between BPA-PC and PMMA. Opt. Mater. 2015, 45, 37–41. [Google Scholar] [CrossRef]
  17. Yazdan Mehr, M.; van Driel, W.D.; Jansen, K.M.B.; Deeben, P.; Zhang, G.Q. Lifetime Assessment of Bisphenol-A polycarbonate (BPA-PC) Plastic Lens, used in LED-based Products. Microelectron. Reliab. 2014, 54, 138–142. [Google Scholar] [CrossRef]
  18. Van Driel, W.D.; Fan, X.J. Solid State Lighting Reliability: Components to Systems; Springer: Basel, Switzerland, 2012; ISBN 978-1-4614-3066-7. [Google Scholar]
  19. Yazdan Mehr, M.; van Driel, W.D.; Zhang, G.Q. Reliability and Accelerated Tests of Plastic Materials in LED-Based Products. In Proceedings of the 16th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystem, Budapet, Haungry, 22 April 2015. [Google Scholar]
  20. Van Driel, W.D.; Yazdan Mehr, M.; Zhang, G.Q. Reliability of LED based Products is a Matter of Balancing Temperatures. In Proceedings of the Therminic Conference, London, UK, 20–24 September 2014. [Google Scholar]
  21. Han, D. Time and cost constrained optimal designs of constant-stress and stepstress accelerated life tests. Reliab. Eng. Syst. Saf. 2015, 140, 1–14. [Google Scholar] [CrossRef]
  22. Oh, H.; Choi, S.; Kim, K.; Youn, B.D.; Pecht, M. An empirical model to describe performance degradation for warranty abuse detection in portable electronics. Reliab. Eng. Syst. Saf. 2015, 142, 92–99. [Google Scholar] [CrossRef]
  23. Yazdan Mehr, M.; van Driel, W.D.; Koh, S.; Zhang, G.Q. Reliability and optical properties of LED lens plates under high temperature stress. Microelectron. Reliab. 2014, 54, 2440–2447. [Google Scholar] [CrossRef]
  24. Yazdan Mehr, M.; van Driel, W.D.; Zhang, G.Q. Progress in Understanding Color Maintenance in Solid-State Lighting Systems. Engineering 2015, 1, 170–178. [Google Scholar] [CrossRef]
  25. Mehr, M.Y.; Volgbert, S.; van Driel, W.D.; Zhang, G.Q. Effects of Graphene Monolayer Coating on the Optical Performance of Remote Phosphors. J. Electr. Mater. 2017, 46, 5866–5872. [Google Scholar] [CrossRef] [Green Version]
  26. Yazdan Mehr, M.; van Driel, W.D.; Udono, H.; Zhang, G.Q. Surface aspects of discolouration in Bisphenol A Polycarbonate (BPA-PC), used as lens in LED-based products. Opt. Mater. 2014, 37, 155–159. [Google Scholar] [CrossRef]
  27. Davis, J.L.; Lamvik, M.; Bittle, J.; Shepherd, S.; Yaga, R.; Baldasaro, N.; Solano, E.; Bobashev, G. Insights into accelerated aging of SSL luminaires. In Proceedings of the SPIE 8835, LED-based Illumination Systems, 88350L, Bellingham, DC, USA, 30 September 2013. [Google Scholar] [CrossRef]
  28. Ghanbari-Siahkali, A.; Mitra, S.; Kingshott, P.; Almdal, K.; Bloch, C.; Rehmeie, H.K. Investigation of the hydrothermal stability of cross-linked liquid silicone rubber (LSR). Polym Degrad. Stab. 2005, 90, 471–480. [Google Scholar] [CrossRef]
  29. Wu, X.; Li, X.; Hao, L.; Wen, X.; Lan, L.; Yuan, X.; Zhang, Q. Effect of vulcanization temperature and humidity on the properties of RTV silicone rubber. IOP Conf. Ser. Mater. Sci. Eng. 2017, 207, 012011. [Google Scholar] [CrossRef] [Green Version]
  30. Qin, Y.; Fu, J.; Yu, L.; Yang, Z.; Guo, W. Comparative Research on Aging Properties of HTV Silicone Rubber via Outdoor Electric Aging and Ultraviolet Accelerated Aging. Adv. Mater. Res. 2013, 641–642, 333–337. [Google Scholar] [CrossRef]
  31. Thong-Om, S.; Payakcho, W.; Grasasom, J.; Marungsri, B. Comparison of Ageing Deterioration of Silicone Rubber Housing Material for Outdoor Polymer Insulators. Int. J. Mater. Metall. Eng. 2011, 80, 533–539. [Google Scholar]
Figure 1. Outdoor applications: street lighting (a); outdoor luminaire (b); and lens optics (c).
Figure 1. Outdoor applications: street lighting (a); outdoor luminaire (b); and lens optics (c).
Materials 11 01305 g001
Figure 2. FTIR-ATR spectra of (a) UV at 35 °C, and (b) blue-light exposed at 100 °C.
Figure 2. FTIR-ATR spectra of (a) UV at 35 °C, and (b) blue-light exposed at 100 °C.
Materials 11 01305 g002aMaterials 11 01305 g002b
Figure 3. FTIR-ATR spectra of samples exposed to (a) swimming pool environment at 100 °C; and (b) 100% RH environment at 100 °C.
Figure 3. FTIR-ATR spectra of samples exposed to (a) swimming pool environment at 100 °C; and (b) 100% RH environment at 100 °C.
Materials 11 01305 g003
Figure 4. FTIR-ATR spectra of aged Si in a salt batch at 100 °C.
Figure 4. FTIR-ATR spectra of aged Si in a salt batch at 100 °C.
Materials 11 01305 g004
Figure 5. Lambda spectra of 3 mm silicone plates exposed to saline underwater at 100 °C.
Figure 5. Lambda spectra of 3 mm silicone plates exposed to saline underwater at 100 °C.
Materials 11 01305 g005
Figure 6. SPD of the saline water-exposed specimen at 100 °C for 3500 h, compared to that of the as-received sample.
Figure 6. SPD of the saline water-exposed specimen at 100 °C for 3500 h, compared to that of the as-received sample.
Materials 11 01305 g006
Figure 7. Variation of maximum power intensity at 450 nm with exposure time under a saline water environment condition at 100 °C.
Figure 7. Variation of maximum power intensity at 450 nm with exposure time under a saline water environment condition at 100 °C.
Materials 11 01305 g007
Figure 8. Force displacement curve for aged silicone in a salt bath at 100 ºC.
Figure 8. Force displacement curve for aged silicone in a salt bath at 100 ºC.
Materials 11 01305 g008
Table 1. Experimental exposure conditions.
Table 1. Experimental exposure conditions.
Sample/VariablesTemperature (°C)UV LightBlue LightEnvironment
#135360 nm-Air
#2100-450 nmAir
#335--Water (standard swimming pool water)
#4100--Water (100% RH)
#5100--Water (100% RH, 3 wt % Salt)
Table 2. Variation of chromaticity values with exposure time in saline water-exposed specimens.
Table 2. Variation of chromaticity values with exposure time in saline water-exposed specimens.
Samplesxyz
As-received0.2360.1450.619
770 h0.2410.1510.610
1440 h0.2460.1610.573
3500 h0.2510.1670.582

Share and Cite

MDPI and ACS Style

Yazdan Mehr, M.; Van Driel, W.; De Buyl, F.; Zhang, K. Study on the Degradation of Optical Silicone Exposed to Harsh Environments. Materials 2018, 11, 1305. https://doi.org/10.3390/ma11081305

AMA Style

Yazdan Mehr M, Van Driel W, De Buyl F, Zhang K. Study on the Degradation of Optical Silicone Exposed to Harsh Environments. Materials. 2018; 11(8):1305. https://doi.org/10.3390/ma11081305

Chicago/Turabian Style

Yazdan Mehr, Maryam, Willem Van Driel, Francois De Buyl, and Kouchi Zhang. 2018. "Study on the Degradation of Optical Silicone Exposed to Harsh Environments" Materials 11, no. 8: 1305. https://doi.org/10.3390/ma11081305

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop