Lamp black and hematite contribution to laser yellowing: A study on technical gypsum samples

Oliveira, Cécile de; Vergès‐Belmin, Véronique; Demaille, Dominique; Bromblet, Philippe

doi:10.1179/2047058415y.0000000003

Cited by 12 publications

(20 citation statements)

References 9 publications

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“…This color shift can be correlated with morphology changes observed by SEM on the laser ablated particles: gypsum crystals from the reference plate show a smooth surface, while those coming from the synthetic black crust are, after irradiation, covered by spherical nanoparticles and a rough nano-layer. These observations are very similar to those already made on laser irradiated model crust samples [3,8,9]. Actually, the first studies on the interactions between the laser beam and black crust have begun with simplified model crust samples as natural black crusts were considered as too heterogeneous and complex.…”

Section: Discussionsupporting

confidence: 75%

“…In their study on laser yellowing, Klein et al [3] detected spherical nanoparticles after laser irradiation at the surface of a ternary model crust containing hematite α-Fe 2 O 3 , graphite and gypsum. More recent studies focused on binary model crusts containing only hematite α-Fe 2 O 3 and gypsum have put in evidence that both the model crusts substrate and the laser ablated material were covered, after irradiation, by spherical nanoparticles and by a rough nano-layer [8,9]. The laser irradiation thus appears to have an analogous effect on the morphologya nano-structuration of the gypsum crystals surface -whether the crystals come from a model or from a natural crust.…”

Section: Discussionmentioning

confidence: 99%

“…Synthetic crusts are elaborated following the same procedure as the one described in De Oliveira et al [8] but using a natural black crust collected at the Saint-Denis Basilica instead of hematite. The natural crust is a coherent, black, 5 -10 mm thick material.…”

Section: Methodsmentioning

confidence: 99%

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Laser yellowing effect: study of the nanophases created by laser irradiation of synthetic black crusts using transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) spectroscopy

Godet¹,

Vergès‐Belmin²,

Saheb³

et al. 2017

Proceedings of the International Conference LACONA XI

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Nd:YAG Q-Switched laser cleaning at 1064 nm can sometimes lead to a more yellow appearance of the stone surface in comparison with other cleaning techniques. The yellow hue can originate from different contributions among which the presence of nano-sized residues generated by the laser interaction with the surface materials to be eliminated. In this study, the nature of such residues has been investigated. The analyzed materials are (i) particles collected from a pure gypsum reference plate; (ii) a synthetic crust, composed of 80 wt % natural black crust and 20 wt % synthetic gypsum; (iii) particles ejected from the synthetic crust during laser irradiation. Optical, scanning electron and transmission electron microscopies were used to link color changes at the macro-scale to morphology changes at the submicron-and nano-scales. Chemical composition was also obtained at the nano-scale using TEM coupled with energy dispersive X-ray (EDX) spectroscopy. This multi-scale approach was combined with electron paramagnetic resonance spectroscopy (EPR) analysis at low and room temperatures to examine the possible presence of iron-containing species presenting particular magnetic properties in the sample before and after irradiation. Under laser irradiation, both the crust sample and the ejected gypsum particles take a yellow color. This color shift can be linked with morphology changes occurring at the nano-scale: gypsum crystals from the reference plate show a smooth surface, while those coming from the synthetic black crust are, after irradiation, covered by many spherical nanoparticles and a rough nano-layer ranging from less than 20 nm to more than 100 64Marie Godet et al.nm. TEM-EDX analysis reveals that the two types of nanostructures have a chemical composition very similar to that of iron-rich coal fly-ashes called magnetospheres or ferrospheres. It is suggested that laser irradiation induces a transformation of micrometric size fly-ashes present in the black crust into different types of nanostructures having a chemical composition similar to the one of ferrospheres. EPR analysis demonstrates the presence of ferri-ferro-superparamagnetic species both before and after irradiation, thus indicating that nanosized magnetic iron compounds probably corresponding to magnetite or maghemite oxides are present in the black crust, most probably crystallized on the surface or within the fly-ashes microparticles. This study brings to light the contribution of fly-ashes to the laser induced yellowing process.

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Section: Discussionsupporting

confidence: 75%

Section: Discussionmentioning

confidence: 99%

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Laser yellowing effect: study of the nanophases created by laser irradiation of synthetic black crusts using transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) spectroscopy

Godet¹,

Vergès‐Belmin²,

Saheb³

et al. 2017

Proceedings of the International Conference LACONA XI

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“…This was informally supported by cleaning an additional area at medium fluence with 1064 nm to generate the red stain, and then removing the red stain by passing over the same area at comparable fluence with 532 nm pulses. Similar behavior has been observed for removal of carbonaceous deposits on gypsum by 1064 nm Nd:YAG pulses [14,15]. These experiments showed that nanoparticles of remnant soot-derived material are present in colored areas, and that the presence of other organic compounds can enhance the development of colored deposits.…”

Section: Reference Materials Studysupporting

confidence: 64%

Laser Cleaning of a First Phase Navajo Wool Chief’s Blanket by Nd:YAG

Londero¹,

Corda²,

Ciofini³

et al. 2017

Proceedings of the International Conference LACONA XI

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A case study was performed for laser cleaning of a soiled First Phase Navajo chief 's blanket using the first and second harmonics of a Nd:YAG laser. A cleaning protocol was developed by mapping the impact of wavelength, fluence, pulse number, and surface pre-wetting on churro wool reference samples. Afterward, an approach for applying the protocol to the Navajo blanket was developed, including a number of custom jigs for mounting the object under controlled tension. The most effective laser cleaning parameters were determined to be a wavelength of 532 nm, a fluence of 350mJ/cm 2 , approximately 100 pulses per cross-sectional area of the laser beam, and no pre-wetting. Good results with no observable damage were obtained with ~280 hours of laser cleaning for the entire blanket, which measured 138 cm by 208 cm.

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“…Physicochemical analyses and evaluation of the treated surfaces and/or the material removed [7,12,15,19] were also employed to further investigate the yellowing issue.…”

Section: The Yellowing Effectmentioning

confidence: 99%

Towards the understanding of the two wavelength laser cleaning in avoiding yellowing on stonework: a micro-Raman and LIBS study

Παπανικολάου¹,

Siozos²,

Philippidis³

et al. 2017

Proceedings of the International Conference LACONA XI

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The synchronous use of Infrared (IR at 1064nm) and Ultraviolet (UV at 355nm) wavelengths of a Q-Switched Nd:YAG laser has been shown to efficiently confront the issue of discoloration, which may be observed upon laser ablation of environmental encrustation from marble surfaces, and thus this methodology is effectively employed in various laser cleaning applications. In order to further investigate the mechanisms that influence this result, a series of tests were undertaken on fragments of marble with environmental homogeneous compact crust. Through a number of irradiation tests applying a variety of laser parameters (individual use of IR and UV beams, as well as, their synchronous use) the different ablative processes have been investigated. In this paper, micro-Raman and Laser Induced Breakdown Spectroscopy (LIBS) were employed in order to examine the role of each laser beam, as well as their combination, and so to approach the reasons that induce yellow discoloration. The results of the above studies will be presented with the aim to further describe the two wavelength laser cleaning methodology and its principle, thus elucidating its effectiveness.

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Lamp black and hematite contribution to laser yellowing: A study on technical gypsum samples

Cited by 12 publications

References 9 publications

Laser yellowing effect: study of the nanophases created by laser irradiation of synthetic black crusts using transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) spectroscopy

Laser yellowing effect: study of the nanophases created by laser irradiation of synthetic black crusts using transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) spectroscopy

Laser Cleaning of a First Phase Navajo Wool Chief’s Blanket by Nd:YAG

Towards the understanding of the two wavelength laser cleaning in avoiding yellowing on stonework: a micro-Raman and LIBS study

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