Preliminary Analysis of the Citations to Articles Published in Two Academic Journals

The citations to articles published in Applied Physical Letters (APL) and Journal of the American Ceramic Society (JACS) were analyzed. For each journal, 199 articles published in 1995 were randomly selected and the number of citations in each year, CY, to these articles during 1996 ~ 2004 were recorded. It was found that CY reaches its maximum in 1997 for APL and in 1999 for JACS. During the first three years after the year when the articles were published, the number of self-citations to the articles published in APL is about two times of that in JACS. These results seem to indicate that the impact factor, which is defined as the ratio of the number of citations to a journal to the number of articles published in this journal over a two-year period, is not comparable for different journals in different fields.

Refined ettringite (Ca6Al2(SO4)3(OH)12∙26H2O) structure for quantitative X-ray diffraction analysis

A revised structure model of ettringite is presented, in order to provide quantitative X-ray diffraction (QXRD) of this mineral in cement pastes. The model is derived from two different existing structure models, both of which are suitable for restricted use but are inferior to the refined ettringite structure presented. In the first published ettringite structure proposed by Moore and Taylor [Acta Crystallogr. B 26, 386–393 (1970)], none of the 128 positions for H are given in the unit cell, which results in reduced scattering power for use of this model for quantification purposes. For the precise quantification of ettringite in samples together with anhydrous phases, the scattering factors of all atoms including the H positions are indispensable. The revised structure model is based on the data of Moore and Taylor, supplemented by the H positions determined by Berliner (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic, Society, 1998, pp. 127–141) on the basis of a neutron diffraction structural investigation of deuterated ettringite at 20 K. Berliner’s (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic Society, 1998, pp. 127–141) thermal parameter should not, however, be used, since a normal application is at room temperature. In order further to improve the structure model of ettringite, Rietveld refinement with the rigid body approach for OH and H2O molecules and SO4 tetrahedra was employed. The refined and improved ettringite structure model was tested for quantitative phase analysis by the determination of actual ettringite contents in mixtures with an internal standard. Synthesized and orientation-free prepared ettringite powders were investigated by X-ray powder diffraction analysis and quantified in four different blends with zircon. The quantification results with the new structure model demonstrate the superior quality of the revised ettringite structure.