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Abstract: Using the values of standard molar enthalpy of reaction for dimethylethyleneurea (dmeu),dimethylformamide (dmf), dimethylacetamide (dma), tetramethylurea (tmu),hexamethylphosphoramide (hmpa) and pyridine (py) with the acids BF3, SbCl5, ZnCl2 and AsCl3, it is shown that, in terms of acid-base behaviour, ZnCl2 is closer to BF3, which differs from SbCl5. Furthermore, the equation −Δr H m(ZnCl2) = − [1.26⋅Δr H m(BF3)]−56.99 correlates with the standard molar enthalpy of reaction for the same set of molecules with ZnCl2 and BF3. A similar equation was obtained to estimate the enthalpy of reaction with AsCl3: −Δr H m(AsCl3) = − [4.12⋅Δr H m(BF3)]− 417.82. It is also shown that, for hmpa and tmu, sterical hindrance is a prominent factor that influences the coordination chemistry of the acidic centres, whose deviation from the linearity can be considered as a measure for the steric contribution to Δr H m.

Abstract: The thermal decomposition reactions of crystalline chelates of general formula Ln(thd)3 (Ln=La,Pr, Nd, Sm and Gd; thd=2,2,6,6-tetramethyl-3,5-heptanedione) have been studied by isothermal thermogravimetry. Several models were proposed initially to calculate the kinetic parameters by isothermal method, thus the time reduced method was used to define the best kinetic models. The Avrami–Erofeev (Am=2, 3 and 4) and R1 and R2 models presented good agreement with experimental data, as well as, linear correlation coefficient (r) and standard deviation (s).

Abstract: Commercial humic acid (HA) was anchored onto silica gel (SiAPTS) previously modified with 3-aminopropyltrimethoxysilane (APTS). HA was anchored onto SiAPTS through two routes: adsorption and covalent chemical immobilization onto the surface. The adsorption occurred by adding SiAPTS to HA in an aqueous solution, producing SiHA1, while chemical immobilization was performed by reacting HA suspended in N,N-dimethylformamide with SiAPTS, to yield SiHA2. The infrared spectra confirm HA immobilization using both procedures and the termogravimetric results showed that the anchored compounds have significantly thermal stability increased. While natural HA presents a thermal stability up to 200C, the anchored compound presents a thermal stability near to 750C.

Abstract: Ethylenediamine molecule was chemically bonded on a silica gel surface previously anchored with 3-glycidoxypropyltrimethoxysilane. This new surface was employed to adsorb divalent cation from aqueous solutions at 298±1 K. The series of adsorption isotherms were adjusted to a modified Langmuir equation from data obtained by suspending the solid with MCl2 (M=Cu, Ni, Zn and Co) solutions, which gave the maximum number of moles adsorbed as 1.54, 0.56, 0.45 and 0.36 mmol g-1 for Cu, Ni, Co and Zn, respectively. Suspended aliquots of the chemically modified surface were calorimetrically titrated and the thermodynamic data showed the system is favored enthalpically and by free Gibbs energy.

The surface of natural talc was modified with organosilanes (H3CO)3SiR, for R= -(CH2)3NH2, -(CH2)3NH(CH2)2NH2and -(CH2)3NH(CH2)2NH(CH2)2NH2, resulting in the inorganic-organic hybrids TC1, TC2and TC3. These aminated talcs contain 4.38, 2.56 and 2.03 mmol g-1of immobilized organic chains for TCx(x=1 to 3), respectively. The chemisorption isotherm data obtained by a batch wise process were adjusted to a modified Langmuir equation, to give the maximum adsorption capacity TC1>TC2>TC3. The chelate effect was illustrated through calorimetric titration, giving the highest enthalpic values for TC2and TC3hybrids and favoured for sulfate counter anion. The enthalpic and entropic values indicated favourable reaction between copper-basic nitrogen center atoms on pendant chain covalently bonded to the inorganic backbone.

Thermogravimetric data were used to calculate the number of acidic Brönsted sites in lamellar α-titanium (α-TiP), γ-titanium (γ-TiP), α-zirconium (α-ZrP) and γ-zirconium (γ-ZrP) hydrogenphosphates. The numbers of acidic sites calculated for these lamellar compounds were 7.81, 5.67, 6.33 and 5.56 for α-TiP, γ-TiP, α-ZrP and γ-ZrP, respectively. These values are in good agreement with those found through potentiometric titration. The data obtained prove that thermogravimetric measurements can be used as a reliable analytical tool to follow the ion-exchange capacity of this kind of crystalline lamellar compounds.

The microcalorimetric method was used to calculate the metabolic enthalpy change per mol of glucose degraded by soil microorganisms, ΔHmet. This parameter has been calculated by microcalorimetry for many organic, inorganic and biochemical reactions, but there is only some information about its quantification for microbial growth reactions in soils. Values of ΔHmetwere calculated for different soil samples collected in Galicia (Spain) and Campinas (Săo Paolo, Brazil). Exponential microbial growth was stimulated in all soil samples by the addition of glucose and power-time curves were recorded. Results showed changes in the values of ΔHmetcalculated for all the soil samples, suggesting a dependence of this value with the microbial growth rate constant, with the percentage of growth, with the initial number of microorganisms of soil samples, with the quantity of glucose added and with the strain of bacteria growing in soil.

Abstract: A new analytical method based on thermogravimetry and applied to chemically functionalized surfaces is proposed. The mass losses of surfaces modified with alkoxysilane reagents, Sup-CH2CH2CH2−R (Sup=support andR=Cl, SH, NH2, NHCONH2, NHNHCOCH3 or (CH2)4NH), are interpreted by considering the physically adsorbed water, the silanol groups and the organic moiety. The elemental analyses calculated from these data are in agreement with those obtained by classical elemental analysis. The method is quick and reproducible, and requires the use of only a few milligrams of material.

A method was developed to estimate the density of the silanol groups attached to silica gel surfaces from thermogravimetric data. Depending on the mechanism of condensation of silanol groups during heating, after removing physically adsorbed water, the results obtained ranged from 4.3 to 6.7 OH nm-2for a series of silicas. The data are in good agreement with those obtained by other techniques. Thermogravimetry proved to be a reliable tool for this kind of study, with the great advantage of being a simple, quick and inexpensive method requiring only a few mg of the silica sample.