8. Profile Fitting of Powder Diffraction Patterns

Howard, Scott A.; Preston, K. D.

doi:10.1515/9781501509018-011

Cited by 100 publications

(66 citation statements)

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“…R wp is the square root of the quantity minimized, scaled by the weighted intensities between the observed and computed algorithm. R exp represents the "best possible R wp " quantity, such that R exp is the smallest obtainable value of R wp [26]. It is considered that R-values are best used as indicators of the progress of refinement [24] rather than on a comparative basis.…”

Section: Materials Characterizationmentioning

confidence: 99%

Comparison of the retarding mechanisms of zinc oxide and sucrose on cement hydration and interactions with supplementary cementitious materials

Ataie

Juenger

Taylor-Lange

et al. 2015

Cement and Concrete Research

114

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Section: Materials Characterizationmentioning

confidence: 99%

Comparison of the retarding mechanisms of zinc oxide and sucrose on cement hydration and interactions with supplementary cementitious materials

Ataie

Juenger

Taylor-Lange

et al. 2015

Cement and Concrete Research

114

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“…The CSD size along the c * axis was optimized, while keeping all other structural parameters to their optimal values derived from the simulation of the high-angle region. Fit quality was evaluated with the usual R wp and Goodness of Fit (GoF = R 2 wp /R 2 exp ) factors (Howard and Preston, 1989). The trial-and-error approach used here by necessity prevents the calculation of a covariance matrix.…”

Section: Powder Xrdmentioning

confidence: 99%

Zn sorption modifies dynamically the layer and interlayer structure of vernadite

Grangeon

Manceau

Guilhermet

et al. 2012

Geochimica et Cosmochimica Acta

113

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International audienceIn surficial environments, the fate of many trace metals is influenced by their interactions with the phyllomanganate vernadite, a nano-sized and turbostratic variety of birnessite. To advance our understanding of the surface reactivity of vernadite, synthetic vernadite (δ-MnO2) was equilibrated at pH 5 or 7, reacted with dissolved Zn to produce Zn-sorbed δ-MnO2 with Zn/Mn atomic ratios from 0.003 to 0.156, and characterized structurally. The octahedral layers in the Zn-free vernadite contain on average ∼0.15 vacancies, ∼0.13-0.06 Mn3+ and ∼0.72-0.79 Mn4+. The layer charge deficit is compensated in the interlayer by Mn3+ bonded over Mn vacancy sites and Na+ located in the interlayer mid-plane. The average lateral dimension of coherent scattering domains (CSDs) deduced from X-ray diffraction (XRD) modeling is ∼5 nm, consistent with that observed by transmission electron microscopy for individual crystals, indicating that the amounts of edge sites can be estimated by XRD. The average vertical dimension of CSDs is ∼1 nm, equivalent to 1.5 layers and less than the observed 3-4 layers in the particles. Zinc sorption at pH 5 and 7 on pre-equilibrated vernadite induced crystal dissolution reducing the lateral CSD size ∼15-20%. Zinc K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and XRD show that Zn occurs in the interlayer above vacancies as a triple-corner-sharing surface complex, which is fully tetrahedral at low Zn/Mn ratios and increasingly octahedral at higher ratios. As Zn/Mn increases, the site density of layer Mn3+ decreases from 0.13 ± 0.01 to 0.03 ± 0.01 at pH 5 and from 0.06 ± 0.01 to 0.01 ± 0.01 at pH 7, and that of layer vacancies correspondingly increases from ∼0.15 to 0.24 and 0.21 at pH 5 and 7, respectively. These changes likely occur because of the preference of Zn2+ for regular coordination structures owing to its completely filled third electron shell (3d10 configuration). Thus, sorption of Zn into the interlayer causes the departure of layer Mn3+, subsequent formation of new reactive layer vacancies, and an increase in surface area through a reduction in particle size, all of which dynamically enhance the sorbent reactivity. These results shed new light on the true complexity of the reactive vernadite surface, and pose greater challenges for surface-complexation modeling of its sorption isotherms

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“…Peak separation and profile analysis were carried out by the Origin PFMk using the Pearson VII algorithm (cf. Howard and Preston, 1989). Background values were calculated by means of a non-linear function (polynomial 2nd order function; Lanson, 1997).…”

Section: Clay Mineralogymentioning

confidence: 99%

Influence of steam sterilisation on soil chemical characteristics, trace metals and clay mineralogy

et al. 2006

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8. Profile Fitting of Powder Diffraction Patterns

Cited by 100 publications

References 0 publications

Comparison of the retarding mechanisms of zinc oxide and sucrose on cement hydration and interactions with supplementary cementitious materials

Comparison of the retarding mechanisms of zinc oxide and sucrose on cement hydration and interactions with supplementary cementitious materials

Zn sorption modifies dynamically the layer and interlayer structure of vernadite

Influence of steam sterilisation on soil chemical characteristics, trace metals and clay mineralogy

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