Search results for "MINERALOGY"

Rate-limiting reaction of C 3 S hydration - A reply to the discussion “A new view on the kinetics of tricalcium silicate hydration” by E. Gartner

2018

Abstract In the case of coupled solids-solution reactions, any mean accelerating or decelerating one of the reaction, will also change the other reaction(s) in the same way, through the coupling mediated by the solution. The observation of any kinetic change by one of these means should not lead to too rapid conclusion on the limitation of kinetics and it must be done with great caution. Contrary to what Gartner mentioned, the acceleration of C3S hydration by the addition of calcium silicate hydrate seeds, is not a trivial evidence suggesting that hydration kinetics “has to be” limited by the C-S-H precipitation and that the C3S dissolution can be neglected. In our paper, efforts have been …

Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate

1994

This paper describes recent experimental results concerning investigation of the parameters which determine, on the one hand, the kinetics of hydration of tricalcium silicate and the thermodynamic, morphological and structural characteristics of C-S-H and, on the other hand, the evolution of the particle interactions at the origin of setting. It is shown that, in both cases, lime concentration in solution is the most important parameter. As a consequence, the chemical evolution of the system, which controls the lime concentration in solution, determines the nature of particle interactions and the physical evolution of the suspension or paste. In return, the contacts, between particles, resu…

Glass Transition and Food Technology: A Critical Appraisal

2002

ABSTRACT: Most low water content or frozen food products are partly or fully amorphous. This review will discuss the extent to which it is possible to understand and predict their behavior during processing and storage, on the basis of glass transition temperature values (Tg) and phenomena related to glass transition. Two main conclusions are provisionally proposed. Firstly, glass transition cannot be considered as an absolute threshold for molecular mobility. Transport of water and other small molecules takes place even in the glassy state at a significant rate, resulting in effective exchange of water in multi-domains foods or sensitivity to oxidation of encapsulated materials. Texture pr…

ChemInform Abstract: Kimberlite, Carbonatite, and Potassic Magmatism as Part of the Geochemical Cycle

2013

Interplay between Chemical Composition and Cation Ordering in the Magnetism of Ni/Fe Layered Double Hydroxides

2013

We report the synthesis of a family of ferrimagnetic NiFe layered double hydroxides (LDHs) with a variable Ni(2+)/Fe(3+) in-plane composition of [Ni(1-x)Fe(x)(OH)2](CO3)(x/2)·yH2O (x = 0.20, 0.25, and 0.33) by following a modified homogeneous precipitation. These layered magnets display high crystallinity, homogeneous hexagonal morphologies, and micrometric size that enable their quantitative exfoliation into single layers by sonomechanical treatment of the solids in polar solvents. This was confirmed by dynamic light scattering, UV-vis spectroscopy, high-resolution transmission electron miscroscopy, and atomic force microscopy methodologies to study the resulting steady suspensions. Our ma…

Adhesion and adhesion hysteresis of mica surfaces covered with bola-amphipiles in dry and humid air

1998

Abstract Bola-amphiphiles with spherical hydrophilic chinuclidinium head groups form laterally ordered monolayers on mica by adsorption from solution. To measure the surface adhesion, JKR-type compression/decompression cycles have been performed with the surface forces apparatus (SFA). In an inert atmosphere, the adhesion energy on increasing the contact area is much lower than predicted by wetting experiments. Furthermore, the pronounced adhesion hysteresis varies from sample to sample in a wide range, indicating a defect-rich surface. On increase of the relative humidity (rh), the reproducibility improves and the values for the adhesion energy measured on compression and decompression con…

Thermal analyses of commercial magnesium stearate pseudopolymorphs

2005

Abstract Two commercial magnesium stearate powders in two well-characterised structural states are investigated using DSC and coupled TGA–DTA under dry nitrogen flow. They consist of either a mixture of crystalline hydrates or a poorly crystallised so-called anhydrate. Following the degassing of unbound water, 1 or 3 weight-loss peaks are observed below about 100 °C, each associated with one heat loss peak at the same temperature. The present results and a review of graphical data from literature show that the so-called anhydrate always contains a significant amount of water. At the beginning of the dehydration process, the heat loss is the same as the standard heat of vaporisation of water…

Non-exponential relaxation in disordered materials: Phenomenological correlations and spectrally selective experiments

1998

Abstract In most glass-forming materials external perturbations are relaxed in a non-exponential fashion. It is shown that the degree of non-exponentiality is phenomenologically correlated with the departure from simple thermally activated behavior as measured by the fragility index m. In model glass formers such as the Ge-As-Se ternary alloy, and to some degree for amorphous materials in general, the correlations with these properties are observed also for other characteristic features. These include the specific heat step and the aging kinetics in the glass transformation range. While phenomenological correlations have proven very useful for rationalizing the properties of many glass form…

Incommensurate nature of the multilayered molecular ferromagnetic metals based on bis(ethylenedithio)tetrathiafulvalene and bimetallic oxalate comple…

2004

The salt [ET]x[MnRh(ox)(3)].CH(2)Cl(2) (x = 2.526(1)) has been obtained and characterized. This paramagnetic metal is essentially isostructural to the ferromagnetic metal [ET]y[MnCr(ox)(3)].CH(2)Cl(2) (y approximately equal to 3) and provides a definite answer on the origin of the structural disorder present on such systems. As in the ferromagnetic analogue, this material shows high electrical conductivity at room temperature (13 S.cm(-1)) and metallic behavior.

Chemical modification of porous calcium hydroxyapatite surfaces by grafting phenylphosphonic and phenylphosphite acids

2006

Abstract It is well known that the incorporation of organic molecules can provide an effective route to modify the surface properties of apatite ceramics. The present study shows that phosphonates can react with calcium ions to control the formation of the hydroxyapatite structures. The grafting of C6H5PO(OH)2 (PPOH) and C6H5PO(OH)H (PPH) was used to increase the specific surface area as well as the porosity of hydroxyapatite materials. The higher specific surface area for HAp treated by PPOH is around 267 m2/g compared to the pure HAp (140 m2/g). The phenyl (C6H5) groups are removed by thermal treatment around 500 °C. After treatment at 800 °C, organoapatites (PP-HAp) are converted to stoi…