Classification proton hydrates

This leads us to suggest the following classification of proton hydrates based on the way in which the various protonic species are involved in the overall structural arrangement ... 

Every water molecule in a crystalline hydrate has, as its nearest neighbours [579], two proton acceptors and at least one electron acceptor. Where only a single electron acceptor is present, co-ordination of the H20 molecule is approximately planar trigonal, and, when two are present, tetrahedral co-ordination is adopted. Large deviations from these configurations seldom occur. Classification [579—582] of the water molecules in hydrates, on the basis of co-ordination of the lone pair orbitals, has been discussed further [579,581] and modified [580] (see Fig. 9 and Table 9). For example, the water in CuS04 5 H20 is located in three different environments two H20 molecules are in Class 1, type D two are in Class 1, type J, and the remaining one is in Class 2, type E. 

Acidity and basicity are relative properties. Many compounds are amphoteric and behave as acids or as bases according to a partner. Metal oxides are classified as acidic, amphoteric or basic. Experimentally, this classification corresponds to the adsorption of probe molecules[7, 8]. NH3 is a base probe molecule that reacts with the electron deficient metal atoms (Lewis acid) or the protons adsorbed on the hydrated surface, CO2 is usually considered as acidic and thus it is expected to adsorb more strongly on basic sites. According to this classification, Ti02 belongs to an amphoteric species and MgO to a basic species. A general difficulty for such classifications is that the order can vary with the choice of the probe. The Hard and Soft Bases and Acids theory[9, 10] responds to the necessity to refine the model with a second scale it is better to couple... 

For the bonding of the water of crystallization primarily the first coordination sphere of the H2O molecules must be considered, that is number and coordination of the proton acceptor groups and metal ions in the neighborhood of the water molecules. Various classifications are reported in the literature in order to describe the environment of H2O molecules in solid hydrates. The system mostly used is that of Chidambaram et al. which classifies H-bonded water molecules with respect to their lone-pair coordination (see Table 1 and Fig. 1). 

M stands for cations such as protons, alkali, or alkaline earths, n stands for then-valency, X indicates numbers between 2 and 40, and y indicates numbers between 1 and 20. The metal ions are exchangeable xSi02 comprises the tetfahedral [SiOJ units of the framework, and nH20 comprises all structural hydroxyl groups and the interlayer water molecules. This formulation refers to layered silicate hydrates of different structures, cationic forms, and degrees of hydration. It does not differentiate the M-SHs from other silicate types, such as nesosilicates, inosilicates, and phyllosilicates. Liebau [16] proposed a classification criterion (Table 2) based on the 0/Si ratio in the framework. The layered metal silicate hydrates with values between 2.25 and 2.1 are positioned between the traditional phyllosilicates (0/Si ratio 2.5) and the tectosilicates (0/Si ratio 2.0). 

Cement samples are often mixed with distilled water here the fresh cement paste initially exhibits one single and long relaxation component. This rapidly evolves towards shorter relaxation times (as cement grains dissolve into water) and into different relaxation components (as cement reactions create hydrates). Numerous experiments on hydrated white cements have led to the classification of hydrogen protons in two main categories ... 

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