Development of an improved XRD sample holder

Li, Chi-Tang; Albe, William R.

doi:10.1017/s0885715600017942

Cited by 4 publications

(3 citation statements)

References 2 publications

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“…All data were collected in the 2θ range of 3° to 70°, with a step scan of 0.02° and a counting time of 8 seconds per step. For each analysis, 10 mg of sample was powdered in alcohol and then mounted into the central hole (10 x 10 x 0.5 mm) of a nominally zero-background Si-sample holder (Li and Albe, 1993). The identification of crystalline phases for each pattern was performed by comparison…”

Section: Methods To Track Thermally-induced Chemical Changesmentioning

confidence: 99%

Thermal weakening of the carbonate basement under Mt. Etna volcano (Italy): Implications for volcano instability

Heap

Mollo

Vinciguerra

et al. 2013

Journal of Volcanology and Geothermal Research

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The physical integrity of a sub-volcanic basement is crucial in controlling the stability of a volcanic edifice. For many volcanoes, this basement can comprise thick sequences of carbonates that are prone to significant thermally-induced alteration. These debilitating thermal reactions, facilitated by heat from proximal magma storage volumes, promote the weakening of the rock mass and likely therefore encourage edifice instability. Such instability can result in slow, gravitational spreading and episodic to continuous slippage of unstable flanks, and may also facilitate catastrophic flank collapse. Understanding the propensity of a particular sub-volcanic basement to such instability requires a detailed understanding of the influence of high temperatures on the chemical, physical, and mechanical properties of the rocks involved. The juxtaposition of a thick carbonate substratum and magmatic heat sources makes Mt. Etna volcano an ideal candidate for our study. We investigated experimentally the effect of temperature on two carbonate rocks that have been chosen to represent the deep, heterogeneous sedimentary substratum under Mt. Etna volcano. This study has demonstrated that thermalstressing resulted in a progressive and significant change in the physical properties of the two rocks. Porosity, wet (i.e., water-saturated) dynamic Poisson's ratio and wet Vp/Vs ratio all increased, whilst P-and S-wave velocities, bulk sample density, dynamic and static Young's modulus, dry Vp/Vs ratio, and dry dynamic Poisson's ratio all decreased. At temperatures of 800 °C, the carbonate in these rocks completely dissociated, resulting in a total mass loss of about 45% and the release of about 44 wt.% of CO 2 . Uniaxial deformation experiments showed that high in-situ temperatures (> 500°C) significantly reduced the strength of the carbonates and altered their deformation behaviour. Above 500 °C the rocks deformed in a ductile manner and A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTthe output of acoustic emissions was greatly reduced. We speculate that thermally-induced weakening and the ductile behaviour of the carbonate substratum could be a key factor in explaining the large-scale deformation observed at Mt. Etna volcano. Our findings are consistent with several field observations at Mt. Etna volcano and can quantitatively support the interpretation of (1) the irregularly low seismic velocity zones present within the sub-volcanic sedimentary basement, (2) the anomalously high CO 2 degassing observed, (3) the anomalously high Vp/Vs ratios and the rapid migration of fluids, and (4) the increasing instability of volcanic edifices in the lifespan of a magmatic system. We speculate that carbonate sub-volcanic basement may emerge as one of the decisive fundamentals in controlling volcanic stability.

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Section: Methods To Track Thermally-induced Chemical Changesmentioning

confidence: 99%

Thermal weakening of the carbonate basement under Mt. Etna volcano (Italy): Implications for volcano instability

Heap

Mollo

Vinciguerra

et al. 2013

Journal of Volcanology and Geothermal Research

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“…The mixtures (1.5 to 2 mL) then were hardened at 60 to 90 ~ on 2 cm • 4 cm polished Si-metal wafers that had been cut perpendicular to (100) and glued to glass slides. The Si-substrates produce low-background XRD intensities (Li and Albe 1993), and the polished surface, together with the effects of the gel, help maximize preferred orientation of the crystals. It is evident from the XRD patterns that the illite crystals are highly oriented in the preparation, with their basal surfaces parallel to the surface of the slide, because no reflections with hk > 0 were observed, and because a small amount of clay (2.5 mg) often yielded large XRD intensities for 00l reflections.…”

Section: Methodsmentioning

confidence: 99%

Measurement of Fundamental Illite Particle Thicknesses by X-Ray Diffraction Using PVP-10 Intercalation

Eberl

Nüesch²,

Šucha

et al. 1998

Clays and clay miner.

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Abstract~The thicknesses of fundamental illite particles that compose mixed-layer illite-smectite (I-S) crystals can be measured by X-ray diffraction (XRD) peak broadening techniques (Bertaut-WarrenAverbach [BWA] method and integral peak-width method) if the effects of swelling and XRD background noise are eliminated from XRD patterns of the clays. Swelling is eliminated by intercalating Na-saturated I-S with polyvinylpyrrolidone having a molecular weight of 10,000 (PVP-10). Background is minimized by using polished metallic silicon wafers cut perpendicular to (100) as a substrate for XRD specimens, and by using a single-crystal monochromator. XRD measurements of PVP-intercalated diagenetic, hydrothermal and low-grade metamorphic I-S indicate that there are at least 2 types of crystallite thickness distribution shapes for illite fundamental particles, lognormal and asymptotic; that measurements of mean fundamental illite particle thicknesses made by various techniques (Bertant-Warren-Averbach, integral peak width, fixed cation content, and transmission electron microscopy [TEM]) give comparable results: and that strain (small differences in layer thicknesses) generally has a Gaussian distribution in the lognormal-type illites, but is often absent in the asymptotic-type illites.

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“…The holders are constructed of very large single crystals of silicon or quartz that are cut in such a manner as to expose a chosen crystalline face (Li and Albe, 1993). The face that is chosen corresponds to a Bragg direction that has low or unobserved intensity for that crystal.…”

Section: Mounting the Powder Specimen In The X-ray Diffractometermentioning

confidence: 99%

Practical Aspects

Reibenspies¹,

Bhuvanesh²

2009

Principles and Applications of Powder Diffraction

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Generation of X-rays: general concepts and terminologyX-rays are produced by the collision of high-velocity electrons with a stationary or rotating metallic target. The most useful X-rays for the home laboratory have energies between 4 and 21 keV, which relates to wavelengths of 3.1-0.59 Å (1 Å = 10 −10 m). X-rays with energy below 4 keV are readily absorbed by air, while X-rays above 21 keV will return condensed powder patterns that can be difficult to interpret.In practice, the metallic target is made of chromium (Cr), cobalt (Co), copper (Cu) or molybdenum (Mo). These metals produce X-rays in the 4-21 keV range while providing stable heat conduction and corrosion resistance. The production of X-rays generates large quantities of heat, which must be dissipated rapidly in order to prevent the metallic targets from melting; therefore, the metals must be durable and conductive to both heat and electricity.The continuous and characteristic spectrum of X-ray radiation is produced when highvelocity electrons strike the metallic target. The continuous spectrum or Bremsstrahlung radiation is produced when the path of the electron that enters the target is altered by interactions with the metal atoms (McCall, 1982). The bending or braking action causes the electrons to lose momentum and release X-ray radiation. The Bremsstrahlung radiation displays a continuous spectrum due to the fact that not every electron will decelerate in a similar manner. The electrons that are completely stopped by the impact will release all of their energy at once, and thus produce the maximum energetic and lowest wavelength X-ray. The energy is thus described by the equation:where λ is in Å (10 −10 m) and V is the applied voltage. If one plots the intensity of the Bremsstrahlung radiation against increasing wavelength, one would etch a curve that begins at λ min and rapidly increases to a maximum of a few tenths of an Angstrom above λ min and then slowly decreases as one proceeds to longer wavelengths. The characteristic spectrum, on the other hand, is composed of sharp intensity maxima at critical wavelengths and is superimposed on the continuous spectrum. These narrow peaks are characteristic of the metal used in the target material and are associated with the Principles and Applications of Powder Diffraction. Edited

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Development of an improved XRD sample holder

Cited by 4 publications

References 2 publications

Thermal weakening of the carbonate basement under Mt. Etna volcano (Italy): Implications for volcano instability

Thermal weakening of the carbonate basement under Mt. Etna volcano (Italy): Implications for volcano instability

Measurement of Fundamental Illite Particle Thicknesses by X-Ray Diffraction Using PVP-10 Intercalation

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