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Title: The Effect of HF/NH4F Etching on the Morphology of Surface Fractures on Fused Silica

Abstract

The effects of HF/NH{sub 4}F, wet chemical etching on the morphology of individual surface fractures (indentations, scratches) and of an ensemble of surface fractures (ground surfaces) on fused silica glass has been characterized. For the individual surface fractures, a series of static or dynamic (sliding) Vickers and Brinnell indenters were used to create radial, lateral, Hertzian cone and trailing indentation fractures on a set of polished fused silica substrates which were subsequently etched. After short etch times, the visibility of both surface and subsurface cracks is significantly enhanced when observed by optical microscopy. This is attributed to the removal of the polishing-induced Bielby layer and the increased width of the cracks following etching allowing for greater optical scatter at the fracture interface. The removal of material during etching was found to be isotropic except in areas where the etchant has difficulty penetrating or in areas that exhibit significant plastic deformation/densification. Isolated fractures continue to etch, but will never be completely removed since the bottom and top of the crack both etch at the same rate. The etching behavior of ensembles of closely spaced cracks, such as those produced during grinding, has also been characterized. This was done using a secondmore » set of fused silica samples that were ground using either fixed or loose abrasives. The resulting samples were etched and both the etch rate and the morphology of the surfaces were monitored as a function of time. Etching results in the formation of a series of open cracks or cusps, each corresponding to the individual fractures originally on the surface of the substrate. During extended etching, the individual cusps coalesce with one another, providing a means of reducing the depth of subsurface damage and the peak-to-valley roughness. In addition, the material removal rate of the ground surfaces was found to scale with the surface area of the cracks as a function of etch time. The initial removal rate for the ground surface was typically 3.5 x the bulk etch rate. The evolving morphology of ground surfaces during etching was simulated using an isotropic finite difference model. This model illustrates the importance that the initial distributions of fracture sizes and spatial locations have on the evolution of roughness and the rate at which material is removed during the etching process. The etching of ground surfaces can be used during optical fabrication to convert subsurface damage into surface roughness thereby reducing the time required to produce polished surfaces that are free of subsurface damage.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
962799
Report Number(s):
LLNL-JRNL-402939
Journal ID: ISSN 0022-3093; JNCSBJ; TRN: US200916%%380
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Journal of Non-Crystalline Solids
Additional Journal Information:
Journal Volume: 355; Journal Issue: 13; Journal ID: ISSN 0022-3093
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; ABRASIVES; CONES; ETCHING; FABRICATION; FRACTURES; GLASS; GRINDING; MORPHOLOGY; OPTICAL MICROSCOPY; PLASTICS; REMOVAL; ROUGHNESS; SILICA; SUBSTRATES; SURFACE AREA; VISIBILITY

Citation Formats

Wong, L, Suratwala, T, Feit, M D, Miller, P E, and Steele, R A. The Effect of HF/NH4F Etching on the Morphology of Surface Fractures on Fused Silica. United States: N. p., 2008. Web.
Wong, L, Suratwala, T, Feit, M D, Miller, P E, & Steele, R A. The Effect of HF/NH4F Etching on the Morphology of Surface Fractures on Fused Silica. United States.
Wong, L, Suratwala, T, Feit, M D, Miller, P E, and Steele, R A. 2008. "The Effect of HF/NH4F Etching on the Morphology of Surface Fractures on Fused Silica". United States. https://www.osti.gov/servlets/purl/962799.
@article{osti_962799,
title = {The Effect of HF/NH4F Etching on the Morphology of Surface Fractures on Fused Silica},
author = {Wong, L and Suratwala, T and Feit, M D and Miller, P E and Steele, R A},
abstractNote = {The effects of HF/NH{sub 4}F, wet chemical etching on the morphology of individual surface fractures (indentations, scratches) and of an ensemble of surface fractures (ground surfaces) on fused silica glass has been characterized. For the individual surface fractures, a series of static or dynamic (sliding) Vickers and Brinnell indenters were used to create radial, lateral, Hertzian cone and trailing indentation fractures on a set of polished fused silica substrates which were subsequently etched. After short etch times, the visibility of both surface and subsurface cracks is significantly enhanced when observed by optical microscopy. This is attributed to the removal of the polishing-induced Bielby layer and the increased width of the cracks following etching allowing for greater optical scatter at the fracture interface. The removal of material during etching was found to be isotropic except in areas where the etchant has difficulty penetrating or in areas that exhibit significant plastic deformation/densification. Isolated fractures continue to etch, but will never be completely removed since the bottom and top of the crack both etch at the same rate. The etching behavior of ensembles of closely spaced cracks, such as those produced during grinding, has also been characterized. This was done using a second set of fused silica samples that were ground using either fixed or loose abrasives. The resulting samples were etched and both the etch rate and the morphology of the surfaces were monitored as a function of time. Etching results in the formation of a series of open cracks or cusps, each corresponding to the individual fractures originally on the surface of the substrate. During extended etching, the individual cusps coalesce with one another, providing a means of reducing the depth of subsurface damage and the peak-to-valley roughness. In addition, the material removal rate of the ground surfaces was found to scale with the surface area of the cracks as a function of etch time. The initial removal rate for the ground surface was typically 3.5 x the bulk etch rate. The evolving morphology of ground surfaces during etching was simulated using an isotropic finite difference model. This model illustrates the importance that the initial distributions of fracture sizes and spatial locations have on the evolution of roughness and the rate at which material is removed during the etching process. The etching of ground surfaces can be used during optical fabrication to convert subsurface damage into surface roughness thereby reducing the time required to produce polished surfaces that are free of subsurface damage.},
doi = {},
url = {https://www.osti.gov/biblio/962799}, journal = {Journal of Non-Crystalline Solids},
issn = {0022-3093},
number = 13,
volume = 355,
place = {United States},
year = {Thu Apr 03 00:00:00 EDT 2008},
month = {Thu Apr 03 00:00:00 EDT 2008}
}