Mixed Flowing Gas Testing of Silver Mirror Coatings

Chu, C.-T.; Chaffee, Paul; Panetta, Christopher J.; Fuqua, Peter D.; Barrie, James D.

doi:10.1364/oic.2007.tuepdp5

Cited by 7 publications

(4 citation statements)

References 2 publications

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“…Most of the degradation 4 studies performed on space silver-based mirrors addressed the efficiency of the protection layer and the effect of aging on the optical properties. 25,29,[34][35][36][37] Few studies were found to discuss their degradation mechanisms. [38][39][40] Here we bring new physical insight on the local tarnishing mechanisms of model stack samples of space mirrors grown by cathodic magnetron sputtering and consisting of thin silver layers protected by SiO2 layers and deposited on SiC, a substrate already in use in all SiC space telescopes assigned to scientific missions and earth observation missions.…”

Section: Introductionmentioning

confidence: 99%

“…Dielectric layers consisting of SiO 2 , Al 2 O 3 , , Si 3 N 4 , , or SiN x , − have been used as overcoats for confinement of the silver layer and protection from environmental degradation by tarnishing. Most of the degradation studies performed on space silver-based mirrors addressed the efficiency of the protection layer and the effect of aging on the optical properties. ,,− Few studies were found to discuss their degradation mechanisms. − …”

Section: Introductionmentioning

confidence: 99%

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Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis

et al. 2017

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In this work, we addressed the local degradation mechanisms limiting the prelaunch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on lightweight SiC substrates and protected by thin SiO overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous HS. The results show that tarnishing is locally initiated by the formation of AgS columns erupting above the stack surface. AgS growth is promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result of an imperfect protection by the SiO overcoat. Channels most likely connect the silver layer to its environment through the protection layer, which enables local HS entry and AgS growth. The silver sulfide columns grow in number and size eventually leading to coalescence with increasing HS exposure. In more advanced stages, tarnishing slows down owing to saturation of all pre-existing imperfectly protected sites of preferential sulfidation. However, it progresses radially at the basis of the AgS columns underneath the protection layer, consuming the metallic silver layer and deteriorating the protecting overcoat.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis

et al. 2017

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“…It has been shown that a H2S concentration as low as 0.2 ppb is sufficient to initiate silver sulfidation [28]. Degradation studies performed on space silver mirrors mostly addressed the efficiency of the protection layer and the effect of environmental aging on the optical properties [10,15,25,[29][30][31], and more seldom their tarnishing mechanism [32][33][34][35].…”

Section: Introductionmentioning

confidence: 99%

Role of SiC substrate surface on local tarnishing of deposited silver mirror stacks

Limam

Maurice

Seyeux

et al. 2018

Applied Surface Science

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The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H2S entry and Ag2S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H2S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO2 layer.

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“…The test achieves realistic simulation of natural environments through the synergistic effects of temperature, humidity, and relevant air pollutants in low concentrations. As part of our effort in studying long-term stability of front surface metal mirrors, we previously looked into the effects of MFG exposure to several different silver mirror coatings 15 . In this study, we investigated the corrosion behavior and optical performance of electroplated gold mirror coatings with the accelerated MFG test.…”

Section: Introductionmentioning

confidence: 99%

Accelerated atmospheric corrosion testing of electroplated gold mirror coatings

2010

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Gold-coated mirrors are widely used in infrared optics for industrial, space, and military applications. These mirrors are often made of aluminum or beryllium substrates with polished nickel plating. Gold is deposited on the nickel layer by either electroplating or vacuum deposition processes. Atmospheric corrosion of gold-coated electrical connectors and contacts was a well-known problem in the electronic industry and studied extensively. However, there is limited literature data that correlates atmospheric corrosion to the optical properties of gold mirror coatings. In this paper, the atmospheric corrosion of different electroplated gold mirror coatings were investigated with an accelerated mixed flowing gas (MFG) test for up to 50 days. The MFG test utilizes a combination of low-level air pollutants, humidity, and temperatures to achieve a simulated indoor environment. Depending on the gold coating thickness, pore corrosion started to appear on samples after about 10 days of the MFG exposure. The corrosion behavior of the gold mirror coatings demonstrated the porous nature of the electroplated gold coatings as well as the variation of porosity to the coating thickness. The changes of optical properties of the gold mirrors were correlated to the morphology of corrosion features on the mirror surface.

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Mixed Flowing Gas Testing of Silver Mirror Coatings

Cited by 7 publications

References 2 publications

Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis

Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis

Role of SiC substrate surface on local tarnishing of deposited silver mirror stacks

Accelerated atmospheric corrosion testing of electroplated gold mirror coatings

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