Aránzazu Espina

Intercalation of n-alkylamines by lamellar materials of the α-zirconium phosphate type

Abstract n-Alkylamines have been intercalated by α-titanium phosphate by exposing the solid to the vapour of the amines. The formula of the intercalation compounds is Ti(OPO 3 ) 2 .2C n H 2n+1 NH 3 .H 2 O (n=1–9). X-ray diffraction patterns and information on the disposition of the guests within the interlayer region have been derived. The n-alkylamines form a bimolecular film in which the carbon chains incline at roughly 59° to the titanium phosphate layers. The terminal amino groups are protonated by the -POH groups of the host. The results obtained are discussed together with the extracted from literature referring to the n-alkylamines intercalation in α-zirconium phosphate and α-tin phosphate.

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.

Intercalation ofn-alkylamines into α-titanium phosphate from aqueous solutions

The intercalation reactions betweenn-alkylamines and α-titanium phosphate in aqueous media have been investigated. The compounds with the maximum intercalation have the formula α-Ti(HOPO3)2 · 2 CnH2n+1NH2 · H2O (n=1–10). Defined crystalline phases with lower amine content are described, the general formula being α-Ti(HOPO3)2 ·mCnH2n+1NH2 ·pH2O (m=1.0 1.3, 1.5, 1.7). Whenm=1.0 then-alkylamines form a monomolecular layer. Whenm>1.0 the layer is bimolecular. The inclination angle and the packing density of then-alkylamines in the interlayer space is determined.

Survival cryopreservation of hop shoot tips monitored by differential scanning calorimetry

Differential scanning calorimetry is used for monitoring the survival conditions of hop (Humulus lupulus L.) shoot tips under cryopreservation. The survival is related to the absence of formation and growing of ice crystals during the cooling process as shown by the absence of heat effect from ice formation. Samples with different degrees of humidity were obtained through a controlled process of dehydration.

Fast method for the experimental determination of vaporization enthalpy by differential scanning calorimetry

A simple method is proposed to estimate the vaporization enthalpy of the palmitic acid (hexadecanoic acid) at its normal boiling temperature. Differential scanning calorimetry (DSC) was the technique used to directly measure these thermodynamic properties. The advantages of this method are its speed and small amount of sample required. In order to avoid evaporation and to ensure equilibrium conditions, the experiments were carried out including a-alumina in contact with the fatty acid. The effect of the alumina concentration is discussed. The obtained experimental data (Tbp=625.4±0.5 K, DvapH=237.6±5.9 J g-1) is compared with that obtained by using thermodynamic equations.

Revisiting the thermal decomposition of layered γ-Titanium phosphate and structural elucidation of its intermediate phases

The thermal transformations of gamma-titanium phosphate, Ti(PO(4))(H(2)PO(4)) x 2 H(2)O, have been studied by thermal analyses (thermogravimetry (TG) and differential thermal analysis (DTA)) and variable-temperature (31)P magic-angle spinning (MAS)/CPMAS and 2D (31)P-(31)P spin-exchange NMR. The structure of this material has been refined from synchrotron powder X-ray diffraction data (monoclinic, P2(1), a = 5.1811(2) A, b = 6.3479(2) A, c = 23.725(2) A, beta = 102.57(1) degrees). Vyazovkins model-free kinetic algorithms have been applied to determine the apparent activation energy to both dehydration and dehydroxylation of gamma-titanium phosphate. In these processes, several overlapped steps have been detected. Structural models for Ti(PO(4))(H(2)PO(4)) x H(2)O and Ti(PO(4))(H(2)P(2)O(7))(0.5) intermediate layered phases have been proposed.

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.

Differential scanning calorimetry applied to the storage at ultra low temperatures of olive and hop in vitro grown shoot-tips

Abstract Differential scanning calorimetry was used for monitoring the survival conditions of olive in vitro grown shoot-tips under cryopreservation (−196°C), as well as for establishing the storage conditions at temperatures higher than liquid nitrogen. Olive survival is related to the absence of formation and growing of ice crystals during the cooling process. These results are compared with those obtained in hop. The final storage temperature is given as a function of the shoot tip survival to the dehydration step and the absence of ice crystal growth during cooling and warming.