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Abstract

In nature extreme PT-conditions result in numerous glass-like solids, the study of which allows specifying various structural and chemical features of extreme materials, which have a great application potential in various fields of technology. We studied features of nanostructure of natural impact glasses, including recently discovered ultrahigh-pressure high-temperature impact glasses, compared to low-pressure natural and synthetic standard silica glasses. In this paper we presented complex data of atomic force microscopy, X-ray diffraction, X-ray energy-dispersive spectrometry, infrared and Raman spectroscopy. We described nanostructural characteristics of impact glasses and showed influence of chemical composition on the features of their structure. We discovered that the elemental composition was the most important factor determining the glasses nano-heterogeneity. We noted an essential role of influence of Na impurity on glass nanostructure. The impact glasses with pure SiO2 composition have the smallest sizes of nanostructural elements.

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... However, the structure and features of phase composition of glasses remain not quite clear, in spite of actively provided studies in materials science. The behaviour of the disordered systems under strong compression attracts a special interest for fundamental understanding and application needs [1][2][3][4]. To the date, numerous studies have been carried out mostly at room temperature in microvolume output within diamond anvil cells under pressure of up to 100 GPa. ...
... The impact glasses have specific structural composition and physical features [3,4]. However, so far the essential attention to natural impact glasses as to a possible new type of high pressure materials is not fully studied. ...
... The technique of sizes measure was described in detail in Refs. [4,7]. ...
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Newly found impact vein-bodied ultrahigh pressure high temperature (UHPHT) glasses from Kara astrobleme (Russia) and impact drop-shaped glasses from Ries crater suevites (Germany) have been investigated. The nanostructure of the glasses has been analysed using atomic force microscopy (AFM) supported by a complex of optical microscopy, scanning electron microscopy (SEM) combined with EDS analysis, and Raman spectroscopy. The received data demonstrate the different levels of impact melt differentiation through partial crystallization and polymerization; the amorphous substance is presented by similar 60-80 nm globular nanostructural composition.
... The atomic force and scanning electron microscopies have shown that amorphous diamond-like carbon of geological origin has a more homogeneous structure at the nanoscale, in contrast to natural and synthetic glasses and glassy carbon [16]. ...
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The paper presents the results of study of the carbon-containing phase discovered in the impact glass of the Kara astrobleme. We used the following research methods: optical, scanning electron, and atomic force microscopies, as well as Raman spectroscopy. This phase represents carbon-containing inclusions up to several tens of micrometres in size with an amorphous diamond-like structure. At the nanoscale, the studied phase is characterized mainly by a homogeneous structure.
... The microstructures of natural high-pressure glasses have only been slightly discussed 11,[22][23][24] , and the comprehensive study of the structure and properties of natural high-pressure glasses remains practically unexplored. ...
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High-pressure glass has attracted interest in terms of both its fundamental state under extreme conditions and its possible applications as an advanced material. In this context, natural impact glasses are of considerable interest because they are formed under ultrahigh-pressure and high-temperature (UHPHT) conditions in larger volumes than laboratory fabrication can produce. Studying the UHPHT glasses of the unique giant Kara astrobleme (Russia), we found that the specific geological position of the UHPHT melt glass veins points to an origin from a secondary ultrahigh-pressure (UHP) melt according to the characteristics of the host suevites, which suggest later bottom flow. Here, we propose a fundamentally novel model involving an upward-injected UHP melt complex with complicated multi-level and multi-process differentiation based on observations of the UHP silica glass, single-crystal coesite and related UHP smectite that crystallized from an impact-generated hydrous melt. This model proposes a secondary UHP crisis during the modification stage of the Kara crater formation. The results are very important for addressing fundamental problems in fields as diverse as condensed matter states under extreme pressure and temperature (PT) conditions, material and geological reconstructions of impact structures, water conditions in mineral substances under UHP conditions in the deep Earth, and the duration and magnitude of the catastrophic effects of large asteroid impacts.
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Atomic force microscopy (AFM) is routinely used with indentation techniques to characterize the plastic deformation of materials. The accurate quantification of the features associated with the indent, which is used to quantify the hardness and indentation deformation mechanisms, depends on the sharpness of the AFM tip used for imaging. However, identifying the tip-sharpness of an atomic force microscope requires non-trivial measurements. Here, using machine learning, we develop a model to predict the tip sharpness of the AFM cantilever directly from the indent images. Further, we employ explainable machine learning models, such as integrated gradients and gradient shap, to interpret the features learned by the model. Altogether, we show that machine learning approaches can accelerate experiments by providing non-trivial information about the instrument performance, thereby enabling researchers to perform better quality experiments.
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Ultra-high-pressure high-temperature (UHPHT) glass from astroblems is a very promising natural material from the point of view of the fundamental problem of the structure and properties of a substance formed under extreme PT-conditions. Such glasses consist of disordered aluminosilicate and silicate micro-sized phases with a heterogeneous structure with domain from units to tens of nanometers in size. We used AFM to evaluation the mechanical properties distribution at nanoscale in UHPHT glasses from the Kara astrobleme. The results of AFM were supplemented with optical and electron microscopy data. It is shown in the work that the nanomechanical properties of glasses measured using by PeakForce QNM generally correspond to the macroscopic properties of a bulk sample. We measured the Young's modulus for the first time for aluminosilicate and silicate phases of UHPHT glasses. AFM can be an effective tool for studying at the micro- and nanoscale mechanical properties of such rigid materials.
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UHPHT natural glasses are interesting not only to geologists and mineralogists, but also to physicists, chemists, and materials scientists from the point of view of the fundamental problem of the existence of matter under extreme PT-conditions. The specificity of the structure of such materials requires complex study. In this work we used optical, electron and atomic force microscopy, as well as Raman spectroscopy to assess the phase separation in UHPHT glasses of the Kara astrobleme. Their microscopic images show the separation of disordered aluminosilicate and silicate phases, their heterogeneous and partially heterogeneous structure with domain sizes of several tens of nanometers. The revealed highest structural homogeneity at the nanoscale level of UHPHT vein silica impact glasses, compared to high-pressure and low-pressure silica-rich glasses, confirms the specificity of the formation of UHPHT glasses and indicates promising further physical studies of this natural material to analyze the matter at ultra-high pressure conditions.
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Liquation structures were described in ultrahigh-pressure impact glasses of the Kara astrobleme (Pay-Khoy) with differentiation into the bisilica, aluminosilicate, and ore components for the first time. The sequence of differentiation of mineral phases upon solidification of an ultrahigh-pressure impact melt was established: coesite, silicate glass, augite, aluminosilicate glass of albite composition, and pyrite. The discovered impact glasses are highly resistant to postimpact alterations.
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The state of substances under ultrahigh pressures and temperatures (UHPHT) now raises a special interest as a matter existing under extreme conditions and as potential new material. Under laboratory conditions only small amounts of micrometer-sized matter are produced at a pressure up to 100 GPa and at room temperature. Simultaneous combination of ultrahigh pressures and temperatures in a lab still requires serious technological effort. Here we describe the composition and structure of the UHPHT vein-like impact glass discovered by us in 2015 on the territory of the Kara astrobleme (Russia) and compare its properties with impact glass from the Ries crater (Germany). A complex of structural and spectroscopic methods presents unusual high pressure marks of structural elements in 8-fold co-ordination that had been described earlier neither in synthetic nor natural glasses. The Kara natural UHPHT glasses being about 70 Ma old have well preserved initial structure, presenting some heterogeneity as a result of partial liquation and crystallization differentiation where an amorphous component is proposed to originate from low level polymerization. Homogeneous parts of the UHPHT glasses can be used to deepened fundamental investigation of a substance under extreme PT conditions and to technological studies for novel material creations. The full paper text is available by the link https://rdcu.be/Nbgr
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We have studied different mineralogical objects: natural glasses of impact (tektites, impactites) and volcanic (obsidians) origin, using atomic force microscopy, X-ray microanalysis, infrared and Raman spectroscopy. The spectroscopy showed the difference in the structure and chemical composition of the glasses of different origin. The analysis of the dependence of nanoscale heterogeneity of the glasses, revealed by the atomic force microscopy, on their structural and chemical features was carried out.
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An original setup combining a very stable loading stage, an atomic force microscope and an environmental chamber, allows to obtain very stable sub-critical fracture propagation in oxide glasses under controlled environment, and subsequently to finely characterize the nanometric roughness properties of the crack surfaces. The analysis of the surface roughness is conducted both in terms of the classical root mean square roughness to compare with the literature, and in terms of more physically adequate indicators related to the self-affine nature of the fracture surfaces. Due to the comparable nanometric scale of the surface roughness, the AFM tip size and the instrumental noise, a special care is devoted to the statistical evaluation of the metrologic properties. The roughness amplitude of several oxide glasses was shown to decrease as a function of the stress intensity factor, to be quite insensitive to the relative humidity and to increase with the degree of heterogeneity of the glass. The results are discussed in terms of several modeling arguments concerning the coupling between crack propagation, material's heterogeneity, crack tip plastic deformation and water diffusion at the crack tip. A synthetic new model is presented combining the predictions of a model by Wiederhorn et al. [1] on the effect of the material's heterogeneity on the crack tip stresses with the self-affine nature of the fracture surfaces. This article is protected by copyright. All rights reserved.
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uaitz as a ubiquitous inineral constituent of the Earth's crust, displays the greatest variety of residual shock effects among all rock-forming minerals. It represents an important and most reliable shock barometer and thermometer for terrertrial impact formations. In this paper, the current status of knowledge about the nature, origin, and experimental preasure-tenererature calibration of shock-induced deformations and phase transformations is reviewed for natural and experimental shock conditions.
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Moldavites from southern Bohemia, from western Moravia, from the Cheb Basin, from Lusatia (Germany), and from Waldviertel (Austria) are the only known European tektites. In the present paper, we briefly sum up the existing knowledge about their strewn fields and geology, about their properties, and their origin. The present survey should enable a detailed comparison with other groups of tektites and separation of primary differences from differences caused by earth history. The extent of moldavite occurrences is a result of intensive denudation and redeposition of the initial strewn field. All regions of moldavite occurrences are spatially associated with regional basins and depressions. The oldest moldavite-bearing sediments with very short-transported material are unsorted colluvio-fluvial gravelly sands and clays of Middle to Upper Miocene age. Fluvial transport of moldavites to more distant places determined their present distribution and led to a substantial lowering of their content in the sediments. Roughly 106 metric tons of moldavite matter (macrotektites) formed initially. Only about 1% of this mass has been preserved till the present. Most moldavites are splash-form moldavites. No ablation features were found on their surface. Muong Nong type moldavites occur sporadically but their amount could be much higher at the time of their formation. Micromoldavites were not found. Their preservation in the conditions of continental sediments over a time period of about 15 m.y. is not probable. It is, however, a question whether they were formed or not. Moldavites represent the most acid group of tektites with silica content of around 80 wt%. They are relatively rich in K2O, too. On the other hand, they are characterized by low average contents of Al2O3, TiO2, FeO and Na2O. These low contents of TiO2 and FeO lead to their higher translucency, similarly as in georgianites. In the same way as with other tektites, moldavites originated by fusion and ejection of porous target rocks during an oblique impact of a large meteorite. The impacting body - in the case of moldavites - was probably a chondrite 500-1000 m in diameter. Its impact also created the Ries crater at approximately 14.4-15.1 Ma.
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Atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), and solution analysis by inductively coupled plasma mass spectrometry (ICP‐MS) were used to investigate the molecular scale processes responsible for the roughening of glass surfaces due to aqueous corrosion. The study of atomically smooth fiber and melt surfaces allowed direct investigation of the atomic and molecular scale effects of dissolution on surface roughness. The combined use of these analytical techniques clearly showed that the change in RMS roughness with aqueous corrosion could be directly related to the concentration of silica released to solution from the glass; cation leaching alone did not generate detectable roughening. It is well known that nano‐/microscale surface roughness can influence strength, optical response, adsorptivity, and other surface properties of glass. It is shown here that the roughening of silicate glass surfaces can be expected based on the amount of silica released from the glass and does not show a dependence on the extent of modifier ion leaching. It is also suggested that the glass composition dependence of this roughening may be a measure of the nanoscale heterogeneity of the glass network structure.
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The determination of the atomic structure of amorphous materials with conventional diffraction techniques is hindered by the missing periodicity of the samples. Consequently, a deeper insight into the structural properties of glasses can only be obtained in real space. In this work AFM investigations of silicate glass surfaces, namely fresh barium silicate and silica glass fracture surfaces, are described. The observed atomic-scale features and arrangements are compared with each other as well as with results from other methods and discussed in the context of classical glass structure theories. The results clearly demonstrate that AFM is able to provide atomically resolved surface structures of amorphous glass surfaces.
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This paper reports that sodium aluminosilicate (NAS) glass surfaces with compositions containing approximately 63% SiO[sub 2] and Al/Na ratios, R, of 0.25 [le] R [le] 2.0 were simulated using the molecular dynamics technique with a multibody interaction potential. There were changes to the surface structure and composition in comparison to bulk NAS glasses. The changes included an increased concentration of sodium and oxygen and the formation of nonbridging oxygen at the outermost surfaces, although the increases were smaller with increased Al concentration. In addition, the formation of small-membered rings and three-coordinated aluminum occurred in the subsurface regions. These changes were accompanied by a change in the ratio of Al/Na in the region extending to 4 [Angstrom] below the surface.
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Addition of alumina to sodium silicate glasses considerably improves the mechanical properties and chemical durability and changes other properties such as ionic conductivity and melt viscosity. As a result, aluminosilicate glasses find wide industrial and technological applications including the recent Corning(®) Gorilla(®) Glass. In this paper, the structures of sodium aluminosilicate glasses with a wide range of Al∕Na ratios (from 1.5 to 0.6) have been studied using classical molecular dynamics simulations in a system containing around 3000 atoms, with the aim to understand the structural role of aluminum as a function of chemical composition in these glasses. The short- and medium-range structures such as aluminum coordination, bond angle distribution around cations, Q(n) distribution (n bridging oxygen per network forming tetrahedron), and ring size distribution have been systematically studied. In addition, the mechanical properties including bulk, shear, and Young's moduli have been calculated and compared with experimental data. It is found that aluminum ions are mainly four-fold coordinated in peralkaline compositions (Al∕Na < 1) and form an integral part of the rigid silicon-oxygen glass network. In peraluminous compositions (Al∕Na > 1), small amounts of five-fold coordinated aluminum ions are present while the concentration of six-fold coordinated aluminum is negligible. Oxygen triclusters are also found to be present in peraluminous compositions, and their concentration increases with increasing Al∕Na ratio. The calculated bulk, shear, and Young's moduli were found to increase with increasing Al∕Na ratio, in good agreement with experimental data.
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A variety of fulgurites from diverse locations have been studied. Morphological features were measured and physical properties documented, and a classification scheme was developed. Three major types are introduced and described: Type I, Type II, and Type III, along with two minor types: Type IV and Melt Droplets. Fulgurites representative of each major taxonomic type were investigated using electron microprobe point analyses and x-ray mapping. A range of compositions were found, including nearly pure glass, detrital zircons with baddeleyite rims, Fe-metal with P-rich rims, and unusual Fe-Si metals. The fulgurite formation process is considered within the planetary context through a discussion of lightning detection and potential for formation on other terrestrial bodies. Finally, suggestions for future investigations are presented and discussed.
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As microstructured glass becomes increasingly important for microsystems technology, the main application fields include micro-fluidic systems, micro-analysis systems, sensors, micro-actuators and implants. And, because glass has quite distinct properties from silicon, PMMA and metals, applications exist where only glass devices meet the requirements. The main advantages of glass derive from its amorphous nature, the precondition for its - theoretically - direction-independent geometric structurability. Microstructuring of Glasses deals with the amorphous state, various glass compositions and their properties, the interactions between glasses and the electromagnetic waves used to modify it. Also treated in detail are methods for influencing the geometrical microstructure of glasses by mechanical, chemical, thermal, optical, and electrical treatment, and the methods and equipment required to produce actual microdevices. Keywords » Laser treatment - Microstructural glass devices - Microstructuring of glasses - Microsystems technology - Photoform process Table of Content: Fundamentals of Inorganic Nonmetallic Glasses and Glass Processing.- Silicate Glasses: A Class of Amorphous Materials.- Thermodynamic Phenomena in Glass.- Melting and Forming Glass Half Products for Microstructuring.- Geometrical Microstructuring of Glasses and Applications.- to Geometrical Microstructuring.- Mechanical Structuring Processes.- Chemical and Complex Structuring Processes.- Thermal and Thermomechanical Structuring Processes.- Microstructuring Glasses Using Lasers.- Geometrical Photostructuring.- Joining Methods for Glass Based Microdevices.- Properties and Selected Applications of Microstructured Glass Devices.
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Fractal analysis has been used as a method to study fracture surfaces of brittle materials. However, it has not been determined if the fractal characteristics of brittle materials is consistent throughout the fracture surface. Therefore, the fractal dimensional increment of the mirror, mist, and hackle regions of the fracture surface of silica glass was determined using atomic force microscopy. The fractal dimensional increment of the mirror region (0.17–0.26) was determined to be statistically greater than that for the mist (0.08–0.12) and hackle (0.08–0.13) regions. It is thought that the increase in the fractal dimensional increment is caused by a greater tortuosity in the mirror region due to, most likely, the slower crack velocity of the propagating crack in that region and that there is a point between the mirror and mist region at which the fractal dimension decreases and becomes constant.
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Vitreous materials are quite routinely found in natural settings. Most of them are aluminosilicates, which often occur in large deposits. Considering the geological formations in which naturally occurring vitreous aluminosilicates are found, they have generally remained stable for more than 1 Ma on the earth's surface, even in different geological and climatic environments. These non-crystalline solids played a very important role in the development of ancient human civilizations, long before the introduction of metallic tools. Today, however, the properties of natural glasses are of interest to mankind for completely different reasons. For example, industrial glasses are used today for encapsulating toxic wastes, especially radioactive waste, which remains active for centuries or more, in order to prevent the unwanted transfer of harmful materials to the environment. The chemical compositions of industrially produced glasses are in large part different from the compositions of natural glasses. Little is quantitatively known about the stability of industrial glasses over very long periods of time (>10,000 years). However, the physical and chemical stability of natural aluminosilicate glasses is known to extend over very long periods of time.
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Natural-silica-rich glasses (impaetites, tektites and obsidians) have been investigated with infrared (IR), Raman and optical spectroscopy. Comparison with artificial glasses with silica-rich and alkali-rich compositions is made. The vibrational data of these compounds are discussed in relationship with their structures, particularly with respect to (i) Si-O-Si bonding differences, (ii) SiO4-ring arrangements, (iii) lattice disorder. IR spectra are strongly dependent on silica content: frequencies of the v3 and vD bands increase with the silica content. A general finding in the Raman spectra of tektites, is the relationship between silica, alumina, sodium contents and the presence of vibrational bands peaked at very specific energies. Raman spectra of Lybian desert glass (LOG), Darwin glass (DG) and vitreous silica are almost identical with the typical doublet at 440-490 cm-1 whereas in tektites the band at 440 cm-1 has relatively less pronounced doublet structure. A common character of Raman spectra of tektites and obsidians is the appearance of broad bands centered around 1000 and 1600 cm-1 due to substitutions of silicon by metals. Tektites have a strong absorption band at 1100 nm which originates from Fe2+ ions. In the other glasses, this absorption is slightly shifted towards 1110-1130 nm. Additional sharp features of impaetites and obsidians at 1380, 2210-2250 nm are completely absent in the absorption spectra of tektites. These bands are the signature of molecular water trapped inside the structure.
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Much progress has been made in elucidating the complex structures of silicate glasses and melts. X-ray and neutron scattering, spectroscopy, and theoretical calculations now provide a reasonable clear picture of many aspects of the short-range structure of glasses (which approximates the melt structure at the glass transition temperature). Critical effects of redox conditions and volatiles on structure have been clarified. Qualitatively, links between structure and properties such as molar volume, entropy, cation partitioning, and viscosity have been established, but quantitative connections remain challenging. Effects of temperature and pressure on structure have been the subject of much recent work.
Article
The application of vibrational spectroscopy to the study of silicate liquids and glasses is described, and new Raman data for K2Si2O5 and K2Si4O9 compositions are presented. The timescale of the vibrational spectroscopic experiments relative to relaxation timescales in the melts is discussed. Silicate systems are usually described as “liquid” or “glassy” based on experimental measurements of viscosity or heat capacity. These have a much longer characteristic measurement timescale than the vibrational spectroscopic experiments. Because of the long structural relaxation times for silicate frameworks over the normal laboratory temperature range, silicate “glasses” and “liquids” always show the same, unrelaxed response to the vibrational spectroscopic experiment. This is one reason for the observed close similarity between “glass” and “melt” spectra. Vibrational spectroscopy can readily be used to investigate structural changes which occur within supercooled silicate liquids due to structural relaxation on the laboratory timescale, above the glass transition temperature, Tg. The vibrational spectroscopies are complementary to other spectroscopic methods, including nuclear magnetic resonance, for this type of study. Our new Raman spectroscopic results on K-disilicate and -tetrasilicate glasses and liquids show effects due to structural relaxation above Tg. The spectra for K2Si2O5 show evidence for an increase in the concentration of Q2 silicate species with increasing temperature. We have determined the enthalpy change for the 2Q3  Q2 + Q4 speciation reaction in K2Si2O5 to be ∼ 20 kJ mol−1, of the same order of magnitude as those obtained for liquids near Na2Si2O5 composition by previous workers. For K2Si4O9 glass, the Raman data show evidence for a different type of structural relaxation. The intensity of a peak near 590 cm−1 increases with increasing temperature above Tg, which is interpreted as an increase in the proportion of three-membered siloxane rings in the liquid. The enthalpy change for formation of these three-membered rings is also 20 kJ mol−1, consistent with the results of a previous study on SiO2 glass.
Article
Fracture surfaces of Suprasil 2, Herasil 2, AR glass and Duran glass rods have been studied by an atomic force microscope (AFM) in the contact mode. They could be characterized in the fracture mirror, the mist and the hackle zones. The RMS (root mean square) roughness in the fracture mirror of all glasses investigated increased with growing distance from the origin of the fracture. On several fracture surfaces of different glasses steps have been observed, due to fracture in shear mode. Furthermore changes in the fracture surfaces during scanning have also been observed. They are thought to stem from reactions of the freshly broken glass surface with the surrounding atmosphere and forces between the scanning tip and the soft surface.
Article
Glass forming melts frequently exhibit liquid–liquid immiscibility resulting in phase separation. The chemical and spatial variation of phase separated morphologies in glasses can range from a few angstroms to microns, often requiring very high magnification for detection. Historically, phase separated glasses have been characterized by transmission electron microscopy (TEM). This technique is very time consuming and costly, requiring specialized equipment and training. Atomic force microscopy (AFM) provides an inexpensive alternative to TEM and has proven to be a powerful tool in the characterization of phase separation in glasses. AFM provides rapid and accurate evaluation of the type, degree and scale of phase separation in glasses down to the nanometer level. Using a combination of topographical and phase imaging AFM we were able to quantitatively determine the microstructures of phase separated glasses with a resolution down to 50nm. Additionally we were able to quantitatively confirm the time dependence of the chemical segregation and growth processes for phase separation in glass by spinodal decomposition. This paper will present sample preparation techniques and results for evaluation of phase separation in alkali borosilicate and sodium silicate glass systems.
Article
This paper presents a study on the roughness of glass fracture surfaces formed as a consequence of sub-critical crack growth. Double-cantilever-beam specimens were used in these studies to form fracture surfaces with areas under well-defined crack velocities and stress intensity factors. Roughness depends on crack velocity: the slower the velocity, the rougher the surface. Ranging from approximately 1×10−10m/s to approximately 10m/s, the velocities were typical of those responsible for the formation of fracture mirrors in glass. Roughness measurements were made using atomic force microscopy on two glass compositions: silica glass and soda lime silica glass. For silica glass, the RMS roughness, Rq, decreased from about 0.5nm at a velocity of 1×10−10m/s to about 0.35nm at a velocity of 10m/s. For soda lime silica glass, the roughness decreased from about 2nm to about 0.7nm in a highly non-linear fashion over the same velocity range. We attributed the roughness and the change in roughness to microscopic stresses associated with nanometer scale compositional and structural variations within the glass microstructure. A theory developed to explain these results is in agreement with the data collected in the current paper. The RMS roughness of glass also depends on the area used to measure the roughness. As noted in other studies, fracture surfaces in glass exhibit a self-affine behavior. Over the velocities studied, the roughness exponent, ζ, was approximately 0.3 for silica glass and varied from 0.18 to 0.28 for soda lime silica glass. The area used for these measurements ranged from (0.5μm)2 to (5.0μm)2. These values of the roughness exponent are consistent with values obtained when the scale of the measurement tool exceeds a critical size, as reported earlier in the literature.
Article
Using wide-angle X-ray diffraction measurements, atomic force microscopy and several physical properties of natural non-crystalline silicates, a structural classification can be derived. Qualitative differences in the intermediate range structure between tektites and relaxed tektites are found, but strength changes with water content.
Article
In this research we compare chemical and plasma treatment methods for surface of SiO2 glass. For chemical treatment of surface tequila and alcohol were used but for plasma treatment - Ar+As and Ar+Se plasmas. Surface topography was analyzed using atomic force microscope. Comparison of chemical and plasma treatment methods shows that surface treated with plasma is smoother. Because of their various chemical compositions tequila and alcohol show different results.
Article
Differently prepared SiO2, Na2O–SiO2, and Duran borosilicate glass surfaces were imaged by atomic force microscopy (AFM), both with an air-AFM and an ultra-high vacuum-AFM. The images of both microscopes display a nanostructure of SiO2 glass with a ripple pattern and a domain pattern, respectively, with coinciding sizes of several 10nm. These domains show clusters of ⩾1nm in diameter, in accordance with Brückner’s SiO2 glass model of preordered regions. Inspecting glass fracture surfaces, prepared and imaged under ultra-high vacuum conditions, reveals structural features like interatomic distances, groupings of atoms, network holes, distribution of atomic distances, percolation paths, and topological connectivities of the glass structures.
Article
Impact glass samples collected during expeditions to the Zhamashin and Lonar craters were subjected to a morphology survey and compared to Wabar, Henbury and Darwin impact glasses to reveal that the accretion of fibres and spherules is not exclusive for irghizites but occurs in other splash form glasses over the world. WDS EPMA and LA-ICP-MS assays of Zhamanshin and Lonar glasses enabled the definition of akmurynites as Zhamanshin glass of specific morphology, chemistry and absence of extraterrestrial contamination. However, extraterrestrial contamination in irghizites was verified and further WDS EPMA analyses led to the conclusion that the Zhamanshin crater had been formed by the impact of a primitive achondrite of Lodran chemistry.
Article
Obsidian artefacts used by prehistoric people could be dated by the SIMS-SS method. However, the method contains some limitations regarding the degree of smoothness of the surface. The presence of wells, cracks, pits, crystals and/or crests induce errors in the dating. Here, we briefly introduce the SIMS-SS method and provide first images of the atomic force microscopy (AFM) of obsidian surfaces and discuss the impact of AFM results on the SIMS-SS dating. The presented dating is straightforward for flat regular surfaces and problematic for irregular surfaces. Copyright © 2008 John Wiley & Sons, Ltd.
Article
In this work, features of research of the supermolecular structures of native metacolloids by STM and AFM are presented. The features associated with metastable structures and the polyphasal nature of colloidal products of geological processes are considered. As a result of the researches carried out local and global of characteristics of their supermolecular structures are established. We show qualitative and quantitative superstructural data obtained using a combination of microscopic researches with diffractional and the structural-morphological analysis of received images. From the structural-transformation row of dependence of superstructural features obtained from findings of geological conditions, PT-parameters of processes of formation were established. The multilevel structure of shungite carbon (where supermolecular structure is formed by multilayered fullerene-like globules) is considered. Both chains and compact aggregates were determined in shungites. Possible mechanisms of aggregations of shungites globules were analyzed.
Article
Abstract— We studied the infrared reflectance (IR), Raman, and cathodoluminescence (CL) spectroscopic signatures and scanning electron microscope-cathodoluminescence (SEM-CL) images of three different types of impact glasses: Aouelloul impact glass, a Muong Nong-type tektite, and Libyan desert glass. Both backscattered electron (BSE) and CL images of the Muong Nong-type tektite are featureless; the BSE image of the Libyan desert glass shows only weak brightness contrasts. For the Aouelloul glass, both BSE and CL images show distinct brightness contrast, and the CL images for the Libyan desert glass show spectacular flow textures that are not visible in any other microscopic method. Compositional data show that the SiO2 composition is relatively higher and the Al2O3 content is lower in the CL-bright areas than in the CL-dark regions. The different appearance of the three glass types in the CL images indicates different peak temperatures during glass formation: the tektite was subjected to the highest temperature, and the Aouelloul impact glass experienced a relatively low formation temperature, while the Libyan desert glass preserves a flow texture that is only visible in the CL images, indicating a medium temperature. All IR reflectance spectra show a major band at around 1040 to 1110 cm−1 (antisymmetric stretching of SiO4 tetrahedra), with minor peaks between 745 and 769 cm−1 (Si-O-Si angle deformation). Broad bands at 491 and 821 cm−1 in the Raman spectra in all samples are most likely related to diaplectic glass remnants, indicating early shock amorphization followed by thermal amorphization. The combination of these spectroscopic methods allows us to deduce information about the peak formation temperature of the glass, and the CL images, in particular, show glass flow textures that are not preserved in other more conventional petrographic images.
Article
Abstract— Libyan Desert Glass (LDG) is an enigmatic type of glass that occurs in western Egypt in the Libyan Desert. Fairly convincing evidence exists to show that it formed by impact, although the source crater is currently unknown. Some rare samples present dark-colored streaks with variable amounts of Fe, and they are supposed to contain a meteoritic component.We have studied the iron local environment in an LDG sample by means of Fe K-edge highresolution X-ray absorption near edge structure (XANES) spectroscopy to obtain quantitative data on the Fe oxidation state and coordination number in both the Fe-poor matrix and Fe-rich layers. The pre-edge peak of the high-resolution XANES spectra of the sample studied displays small but reproducible variations between Fe-poor matrix and Fe-rich layers, which is indicative of significant changes in the Fe oxidation state and coordination number. Comparison with previously obtained data for a very low-Fe sample shows that, while iron is virtually all trivalent and in tetrahedral coordination ([4]Fe3+) in the low-Fe sample, the sample containing the Fe-rich layers display a mixture of tetra-coordinated trivalent iron ([4]Fe3+) and penta-coordinated divalent iron ([5]Fe2+), with the Fe in the Fe-rich layer being more reduced than the matrix. From these data, we conclude the following: a) the significant differences in the Fe oxidation state between LDG and tektites, together with the wide intra-sample variations in the Fe-oxidation state, confirm that LDG is an impact glass and not a tektite-like glass; b) the higher Fe content, coupled with the more reduced state of the Fe, in the Fe-rich layers suggests that some or most of the Fe in these layers may be directly derived from the meteoritic projectile and that it is not of terrestrial origin.
Article
Shock-recovery experiments for obsidian and its fused glass have been carried out with pressure up to 35 GPa. Structural evolution accompanying the shock compression was investigated using X-ray diffraction technique, Raman and infrared spectroscopy. The densities of obsidian and its fused glass increased with applied shock pressure up to 25 GPa. Densification reached a maximum of 4.7 and 3.6% for obsidian and its fused glass, respectively. The densification mechanism is attributed to reduction of the T–O–T angle, and changes in ring statistics in the structure. Density reduction observed at greater than 25 GPa of applied shock pressure is due to partial annealing of the high-density glass structures brought by high post-shock residual temperature. The density of fused glass is almost equal to its original value at 35 GPa while the shocked obsidian has a slightly lower value than its original value. Amorphization of crystallites present in the obsidian due to shock compression is probably the cause of the density decrease. The structural evolution observed in shock-compressed obsidian and its fused glass can be explained by densification resulting from average T–O–T angle reduction and increase of small rings, and subsequent structural relaxation by high post-shock temperature at applied shock compression above 25 GPa.
Article
In this work the investigation of an amorphous barium silicate surface with the atomic force microscope (AFM) under ultrahigh vacuum conditions is described. We show atomically resolved images of a disordered surface. Using the atomic positions it is possible to calculate radial distribution functions, which can be compared with data from neutron diffraction measurements. The analysis of the interatomic distances supports the view, that the glass consists of a network of SiO4 tetrahedra and terminates with oxygen atoms at the surface. In the range 0.3 nm-1 nm characteristic distances are found, which points to the existence of some medium-range order. The results provide an unique insight into the structure of glasses and may lead to a deeper understanding of the interactions present in such amorphous solids.
Article
A thorough understanding of the properties of glasses in sufficient detail to offer predictions requires adequate knowledge of the atomic structure. This is common ground among those researching in this field. What is less clear is just what constitutes adequate knowledge of the structure of glasses — in order to adequately understand their properties? How far do we need to go? Is there any alternative to fully characterised and verified computer-generated atomic models with accurate interatomic potentials? For every major type of glass? We address these questions and review the different classes of physical and chemical properties in relation to the structural data available from experiment and simulation. The conclusion is that much can be done, as has already been demonstrated, to understand those properties that depend on the local or the long-range structure of the glass — optical properties and ionic diffusion in mesoscopic structures are examples. Investigation of medium-range structure is more hazardous. The difficulty of obtaining good structural data is matched by the limited usefulness of those data in predicting and controlling properties — unless the questions are very carefully chosen. When questions are properly posed, then results can give very valuable insights. Moreover, solutions to this part of the structural puzzle could lead to spectacular changes in fundamental concepts of the nature of glasses, amorphous solids and even liquids.
Article
Study by transmission electron microscopy of samples from the Cretaceous–Tertiary (K–T) boundary clay at Flaxbourne River and Woodside Creek, New Zealand, has revealed the occurrence of nanometer-sized meteorite impact-derived glass. The average glass composition is exceptionally Ca-rich and is distinct from other glass found on Earth, apart from glass inferred to be of impact origin at Mexican and Haitian K–T sites. The glass shards are partially altered to montmorillonite-like smectite, with the dominant interlayer cation, Ca, reflecting the composition of the parent glass. The data imply a heterogeneous global distribution in composition of K–T boundary impact glass: Si-rich and Ca-rich in Mexico and Haiti, Si-rich in Denmark, and Ca-rich in New Zealand. This heterogeneous distribution may relate to dispersal processes similar to those used to account for the asymmetric distribution of clastic debris from the Chicxulub impact site. However, recent discovery of an impact crater of K–T boundary age in Ukraine raises the possibility of impact clusters which produce material of heterogeneous composition.
Article
Natural glass can be formed by volcanic processes, lightning (fulgarites) burning coal, and by meteorite impact. By far the most common process is volcanic - basically the glass is rapidly chilled molten rock.All natural glasses are thermodynamically unstable and tend to alter chemically or to crystallize. The rate of these processes is determined by the chemical composition of the magma. The hot and fluid basaltic melts have a structure that allows for rapid crystal growth, and seldom forms glass selvages greater than a few centimeters thick, even when the melt is rapidly cooled by extrusion in the deep sea. In contrast the cooler and very viscous rhyolitic magmas can yield bodies of glass that are tens of meters thick. These highly polymerized magmas have a high silica content - often 71–77% SiO2. Their high viscosity inhibits diffusive crystal growth.Basalt glass in sea water forms an alteration zone called palagonite whose thickness increases linearly with time. The rate of diffusion of water into rhyolitic glass, which follows the relationship - thickness = , has been determined as a function of the glass composition and temperature. Increased SiO2 increases the rate, whereas increased CaO, MgO and H2O decrease the rate. The activation energy of water diffusion varies from about 19 to 22 kcal/mol. for the glasses studied. The diffusion of alkali out of rhyolite glass occurs simultaneously with water diffusion into the glass. The rate of devitrification of rhyolitic glass is a function of the glass viscosity, which in turn is a function of water content and temperature.Although all of the aforementioned processes tend to destroy natural glasses, the slow rates of these processes, particularly for rhyolitic glass, has allowed samples of glass to persist for 60 million years.
Article
The fracture minor surface of a silica glass, prepared at 1×10−11 mbar in the chamber of an ultra-high-vaccum-atomic-force microscope (UHV–AFM), was imaged at 1×10−8 mbar with high spatial resolution. The features directly seen were interatomic distances, e.g., O–O and Si–O, groupings of atoms, e.g., SiO4 tetrahedra and rings of tetrahedra, and network holes. A comparison with a structure calculated by a molecular dynamics simulation gave good coincidence. This direct view of the silica glass surface supports Zachariasen's network structure model of glass.
Article
Atomic force microscopy (AFM) provides high resolution images of surfaces even if they are non-conducting. Thus, glass can be investigated without conductive preparation or other complicated preparation techniques. So far, the great advantage of this microscopy in ambient atmosphere impeded atomic resolution on vitreous surfaces. However, AFM proved to be an appropriate tool for imaging the structure on a nanometre scale, of glasses, glass ceramics and coatings on glass. AFM serves to detect surface defects and changes in the overall surface topology after different treatments, such as polishing, cleaning, aging and corroding. With the help of suitable preparation, volume properties can also be investigated with a spatial resolution in the nanometre range. AFM contributions to glass research fields like fracture mechanics, crystallization, interfaces and gel consolidation are reviewed in this paper.
Article
A quantitative assessment is presented of the structural information derived from X-ray and neutron diffraction and small angle scattering investigations of vitreous silica, starting from the classic studies of Warren and co-workers in the 1930s. Particular points that are addressed include the regularity of the SiO4 tetrahedral structural units, the SiOSi angle distribution, the interpretation of the first peak in the diffraction pattern and the extent of the longer range density fluctuations as revealed by X-ray and neutron measurements at small scattering vectors. The use of structural modelling in the interpretation of the diffraction data is discussed and representative models are compared with experiment. The extent of the (dis)agreement of each model with experiment is compared quantitatively and the paper concludes by identifying the most accurate structural model of vitreous silica known to the author at the present time.