M. Suárez

Synthesis of γ-titanium phosphate. study of the solids obtained by using water or acetone as washing agents

Abstract The preparation of γ-titanium phosphate from mixtures of β and γ phases by treatment with NaCl and subsequent reverse reaction with HCl, is described. The hydration process of β-TiP was studied. Solids with a P 2 O 5 /TiO 2 ratio greater than one were obtained and their thermal behaviour and hydration capacity were determined. The materials were characterised by chemical analysis, thermal analysis (DTA and TG) and X-ray diffraction.

Characterization of monumental carbonate stones by thermal analysis (TG, DTG and DSC)

Abstract Thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC), were found to be suitable instrumental techniques for the study of monumental rocks because they need small amounts of sample and provide extensive qualitative and quantitative information. From DTG curves, the calcite/dolomite ratio in the samples as well as the differences between limestones and dolomites can be quantitatively determined. DSC curves are adequate for the identification of the degradation products in the monumental stones since they are usually salts (sometimes hydrates) which present first-order processes under 600°C. This technique makes it possible to carry out quantitative and semiquantitative analysis of the degradation of monumental rocks since it provides data about its mineralogic composition.

Thermodynamic treatment and calorimetric study of H+Li+ion exchange on α-titanium phosphate

Abstract The thermodynamics of H + Li + ion exchange on α-Ti(HPO4)2·H2O have been studied, and titration curves and exchange isotherms have been obtained at 298.15, 313.15, and 328.15(±0.1) K. The exchanger hydrolysis and the corrected isotherms have been calculated. The equilibrium constants, the standard molar Gibbs free energies, enthalpies, and entropies of the reactions have been all determined. The molar enthalpies of the exchange reaction have been measured calorimetrically. The thermodynamic and calorimetric results are compared.

Thermal behaviour of α-titanium phosphate/n-alkylamine intercalation compounds

Abstract The thermal decomposition of the intercalation compounds α-Ti(OPO 3 ) 2 · 2C n H 2n+1 NH 3 · H 2 O ( n = 1–6) is studied. Decomposition takes place in seven steps. The crystallization water is lost in the first step and the condensation of the hydrogenphosphate groups into pyrophosphate takes place in the last step. In the remaining five steps, the intercalated amine is desorbed, the last product being TiP 2 O 7 in every case. Materials of formula TiH 2−y (OPO 3 ) 2 ·yC n H 2n+1 NH 3 (y = 2.0, 1.7, 1.3, 1.0) have been characterized. When y =2.0, 1.7 or 1.3 the n -alkylamines form a bimolecular film. The interlayer distance of the intercalates decreases with decreasing amine content of the solids. Likewise, the inclination angle of the alkyl chains with respect to the phosphate layer decreases. When y = 1.0 the n -alkylamines form a monomolecular film.

Thermodynamic treatment of H+/K+ ion-exchange on γ-titanium phosphate

Abstract The H + /K + ion-exchange process in γ-Ti(HPO 4 ) 2 ·2H 2 O was studied, titration and hydrolysis curves and exchange isotherms being obtained at 278.15, 298.15, 313.15 and 328.15 (±0.1) K. Three differentiated processes of substitution and crystalline phases of 25, 50 and 100% of conversion were reached. The equilibrium constants, the standard molar Gibbs free energies, enthalpies and entropies of the exchange reaction were determined.

Thermodynamic treatment of H+/Sr2+ ion-exchange in γ-titanium phosphate

Abstract The H + /Sr 2+ ion-exchange in γ-Ti(HPO 4 ) 2 · 2H 2 O was studied. Exchange isotherms and pH curves were obtained at 298.15, 313.15 and 328.15(± 0.1) K. The half-exchanged phase TiHSr 0.5 (PO 4 ) 2 · 3H 2 O (interlayer distance 1.34 nm) was detected. The equilibrium constants and the standard molar Gibbs free energy, enthalpy and entropy of the exchange reaction were determined.

Quantitative extraction of uranium(VI) in aqueous solutions with n-alkylamine intercalates of γ-titanium phosphate

The intercalation compounds Ti(C3H7NH2)(HPO4)2·H2O (18.4 Å) (γ-TiP/n-Pr) and Ti(C4H9NH2)(HPO4)2·H2O (20.5 Å) (γ-TiP/n-Bu) have been prepared using γ-titanium phosphate, Ti(HPO4)2·2H2O (11.6 Å), as precursor. The retention of UO22+, in aqueous solutions by γ-TiP is very low being only a superficial adsorption phenomenon. When the intercalated materials are used, the retention is quantitative until 95% of the cation exchange capacity in the γ-TiP/n-Pr case (c.e.c.=6.30 mequiv./g), and over 80% for the γ-TiP/n-Bu compound (c.e.c.=6.04 mequiv./g).

Intercalation of n-alkylamines in α-hafnium phosphate

Abstract The preparation of α-hafnium phosphate and its intercalation behaviour toward n-alkylamines is studied. The formula of the saturated intercalation compounds is α-Hf(OPO3)2·2CnH2n+1NH3·H2O (n=1−6). The inclination angle of the n-alkylamines and the packing density in the interlayer space of the n-alkylamines is determined. The results are compared to those described for α-titanium phosphate and α-zirconium phosphate.

Layered hafnium phosphates. Synthesis, characterization, crystalline structure and intercalation behaviour

Abstract This review compiles the recent investigations on layered hafnium phosphates in the α and γ varieties. Their preparation, properties and crystalline structures are described. The behaviour of both compounds during the intercalation of n -alkylamines ( n =1–6) and the cyclic amines aniline, benzylamine, cyclohexylamine, piperidine, pyridine, n -methylpiperidine and 4-methylpiperidine, in the vapour and liquid phases, is reported. The formula of the intercalates and the estimation of the guests arrangement in the interlayer space is discussed.

H+Ca2+ Ion-exchange process in α-titanium phosphate

Abstract The behavior of α-titanium phosphate in the H + Ca 2+ ion-exchange by addition of CaCl2, (CaCl2+HCl),(CaCl2+Ca(OH)2) and Ca(OH)2 was studied. The conversion is not total in the absence of Ca(OH)2, the addition of (CaCl2+HCl) giving a maximum value of 36% and that of CaCl2 a value of 64%. In the presence of Ca(OH)2 the full substitution can be reached though the process occurs with hydrolysis of the exchanger and precipitation of calcium phosphate and titanium oxide. The results are compared with those obtained in α-zirconium phosphate.