A. Justo

Bio: A. Justo is an academic researcher from University of Seville. The author has contributed to research in topics: Pyrophyllite & Eutectic system. The author has an hindex of 11, co-authored 27 publications receiving 280 citations.

Thermal analysis of ground kaolinite and pyrophyllite

Abstract: The aim of this work was to study the DTA effects produced between 950 o and 1500 o C after the dry-grinding of kaolinite and pyrophyllite. When ground kaolinite is heated, the exotherm at ≃1000 o C is shifted to lower temperature as the grinding time increases; the effects at ≃1250 o and ≃1460 o C disappear, and two new closer exothermic effects are detected at around 1200 o C after grinding in a hard porcelain mill. When ground pyrophyllite is heated, the former effect also disappears, a new effect is detected at ≃1200 o C, and a new intense exothermic effect appears at 982 o C, associated with mullite formation at lower temperature

Thermal study of vermiculites and mica-vermiculite interstratifications

Abstract: Simultaneous DTA-TG has been carried out on a set of natural vermiculite samples. Based on their dehydration behaviour the samples can be divided in two groups: (a) those with DTA endothermic peak temperatures at 140°–150°C and 240°–270°C (pure vermiculties) and (b) those with peak temperatures at 95°–115°C (vermiculite with mica or mica-vermiculite interstratifications). The low temperature at which the endothermic effect in group (b) appears is discussed on the basis of dilution due to the inert layers of mica, differences in chemical composition, and lowering of interlamellar water bond energy.

X‐Ray Identification and Crystal Structures of Clay Minerals

Abstract: mented, if not .particularly new. Chapter 15, on the boron hydrides, has been almost entirely rewritten by the translators, with curious results. Historically, Syrkin and Dyatkina were among the first authors to revive the bridged structure for diborane and related molecules, and their views on the electronic structure of the bridge are clearly not entirely acceptable to the translators, who give prominence to Pitzer's subsequent ideas, and ignore altogether the extension of the bridge theory to beryllium and aluminium borohydrides. The effect is confusing, and the altered chapter has lost in clarity what it may have gained in modernity. The more theoretical chapters are not quite so good. I t is, of course, wellnigh impossible to do justice to the wave mechanics of atoms and molecules in 140 pages without oversimplifying or passing over the mathematical and physical difficulties. One must admire the ambitious a t tempt of the authors to do this, and much of the fundamental theory--for instance, the exclusion principle and the variation method--is well explained. But surely some mention should have been made of the fixed-nucleus approximation, and the fact tha t the Aufbauprinzip is only an approximation, even for atoms ? Chapters 5 and 6 show up the resonance theory at its worst, though this does not seem to have been the intention of the authors. We now know that the 'unexcited structures' of large aromatic molecules make scarcely any contribution to the ground state; and counting resonance structures is a theoretically unjustifiable procedure. Also, t h e theory of ionic-covalent resonance, in its simple form, has not stood up to recent critical examination, and can no longer be taken very seriously. These last two criticisms, however, are mainly based on work which has been done since the book was written, and can hardly be laid at the door of the authors. Chapter 7 has been added in translation, and is a good chapter in its own right, t-hough, as one might have expected, it is not particularly well integrated into the rest of the book. The printing is good, and the translation intelligent, though it is regrettable t h a t Mulliken's name should have been misspelt every time it is mentioned--more than twenty times. Taken as a whole, the book is an important contribution to the literature, and is to be recommended to everyone interested in molecular structure. H. C. LONGUET-HIGGINS Department of Chemistry University of Manchester England

Chemically modified kaolinite. Grafting of methoxy groups on the interlamellar aluminol surface of kaolinite

Abstract: The interlayer aluminol surface of kaolinite has been modified by the reaction of methanol, at temperatures between 200 and 270 °C, with both the dimethyl sulfoside intercalate of kaolinite (Kao–DMSO) and the N-methylformamide intercalate of kaolinite (Kao-NMF). The product was a methoxy-functionalized organomineral material, which was resistant to thermal decomposition in both air and N2 atmospheres up to temperatures > 350 °C, and also to water hydrolysis. Based on results from thermal analysis, IR analysis, NMR spectroscopy (13C CP MAS, 29Si CP MAS and 27Al MAS) and elemental analysis, a structural model has been proposed, in which every third interlayer surface hydroxy group on the aluminol surface of kaolinite has been replaced by a methoxide group. The methyl groups which point away from this surface are keyed into the (SiO)6 macro-rings of the adjacent silicate surface, resulting in a non-centrosymmetric two-dimensionally ordered organomineral assembly.