J.R. García

Formation of crystalline titanium(IV) phosphates from titanium(III) solutions

Crystalline phases of titanium (IV) phosphate have been obtained from titanium(III) chloride in phosphoric acid solutions. The {alpha}-titanium phosphate synthesis is possible at low temperature (60--80 C). {gamma}-Titanium phosphate is obtained by reflux with very concentrated phosphoric acid in 3--5 hours by oxidation with O{sub 2}. The influence in these reactions of several factors (concentration of reagents, molar ratio P:Ti in the reaction mixture, temperature and reaction) was studied. The {alpha}-titanium phosphate formation takes place in several steps through the sequential formation of amorphous titanium(IV) phosphate, {gamma}-titanium phosphate and/or a semicrystalline titanium(IV) hydroxophosphate, Ti(OH){sub 2}(HPO{sub 4}){center_dot}H{sub 2}O.

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.

Hydrolytic stability of amorphous titanium and zirconium phosphates

Abstract Spherically granulated amorphous titanium and zirconium hydroxophosphates, Ti(OH)P and Zr(OH)P, with different molar P:M(IV) ratio varying in a range of (0.51.1):1, have been synthesized and their hydrolytic behavior has been studied as a function of the chemical composition of the material, type of exchangers sale form, pH and concentration of electrolyte, type of electrolyte, temperature of model solution and some other factors. It was found that the hydrolysis of Ti(OH)P and Zr(OH)P in neutral and alkaline media is a complex process occurring by nucleophilic mechanism of phosphate group substitution. The governing factors are steric hindrances for nucleophilic attack and the value of the effective positive charge on titanium and zirconium atoms.

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.

Intercalation of α,ω-Alkyldiamines into Layered α-Titanium Phosphate from Aqueous Solutions

Abstract This paper reports a study on the mechanism of intercalation of α,ω-alkyldiamines, NH 2 (CH 2 ) n NH 2 (n = 2–9), into layered α-titanium phosphate, α-Ti(HPO 4 ) 2 ·H 2 O. The intercalates synthesis was performed by titrating the host with aqueous solutions of alkyldiamine at 25%C. Crystalline phases showing a general formula α-Ti(HPO 4 ) 2 ·xNH 2 (CH 2 ) n NH 2 ·H 2 O (x ≤ 1) have been obtained. In every case, a monolayered arrangement of α,ω-alkyldiamine molecules into the host layers is formed. The average inclination angle of the alkyldiamine molecules to the phosphate layer and the intercalates packing density have been determined.

Reactivity of alpha-titanium phosphate/n-alkylamine intercalation compounds with mono- and polymeric aluminum species

Abstract The reaction of Al(H2O)63+ and [Al13O4(OH)24(H2O)12]7+ with α-Ti(PO4)2·2RNH3·H2O (R = C3H7, C4H9) has been investigated. The processes can be considered as RNH 3 + Al(H 2 O) 6 3+ or RNH 3 + [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ ion exchange. With Al(H2O)63+, saturation is reached and an α-Ti[Al(H 2 O) 6 ] 2 3 (PO 4 ) 2 ·nH 2 O phase is formed. With [Al13O4(OH)24(H2O)12]7+, materials were obtained with the highest aluminum content, having the formula α-Ti[Al13O4(OH)24(H2O)12]x(PO4)2·(2−7x)RNH3·nH2O (x = 0.20, R = C3H7; x = 0.14, R = C4H9). These compounds maintain ion-exchange properties. The porosity of the materials obtained is discussed.

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.

Polyhydrated phases in the exchange of H+ and K+ in α-titanium phosphate

The exchange of H+ by K+ in α-titanium phosphate, Ti(HPO4)2·H2O, was studied. The exchange isotherm and the hydrolysis and titration curves were obtained, and the evolution of the material was followed by X-ray diffraction. The existence of partially substituted phases was not detected. Phases saturated in potassium and highly hydrated, Ti(KPO4)2·3H2O (interlayer distance 10.4 A) and Ti(KPO4)2·2H2O (9.6 A), were obtained. The experimental results are explained by taking account of the structures of the materials.

Double magnetic phase transition inND4Fe(DPO4)2andNH4Fe(HPO4)2

B. F. Alfonso,1 C. Pique,1 C. Trobajo,2 J. R. Garcia,2 E. Kampert,3 U. Zeitler,3 J. Rodriguez Fernandez,4 M. T. Fernandez-Diaz,5 and J. A. Blanco6 1Departamento de Fisica, Universidad de Oviedo, E-33204 Gijon, Spain 2Departamento de Quimica Organica e Inorganica, Universidad de Oviedo, E-33006 Oviedo, Spain 3Institute for Molecules and Materials, High Field Magnet Laboratory, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands 4CITIMAC, Facultad de Ciencias, Universidad de Cantabria, E-39005 Santander, Spain 5Institute Laue-Langevin, BP 156X, F-38042 Grenoble, France 6Departamento de Fisica, Universidad de Oviedo, E-33007 Oviedo, Spain Received 3 June 2010; revised manuscript received 14 September 2010; published 20 October 2010

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.