Thermal analysis of Codex Huamantla and other Mexican papers

The application of thermal analysis and other techniques to determine the thermal and mechanical history of an object is extended to investigate the method of manufacturing of ancient papers. The Humboldt Fragment number six of the Codex Huamantla and other Mexican papers are analyzed by means of Differential Scanning Calorimetry (DSC) and Thermogravimetry-Mass Spectroscopy (TG-MS). The results reveal mechanical treatment or beating of the raw material and also indicate, that the two cultures exchanged knowledge about the paper making. The simplicity and speed of thermoanalytical methods make them a good choice to screen samples for composition and origin. With the addition of more elaborate techniques, such as X-ray analysis, IR spectroscopy, evolved gas analysis by mass spectrometry and microscopy, a definitive classification can be reached easily.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayPresented in part at the 4th Meeting of the Materials Research Society, Cancun May 16–20, 1994 Mexico.The authors wish to express their gratitude and appreciation to Senora Zita Basich, Museo Nacional de Antropologia, I.N.A.H., S.E.P. Cazada m. Gandhi, Mexico 5, D. F. and to Dr. Peter Masson, Ibero-Amerikanisches Institut Preussischer Kulturbesitz, Berlin, Potsdamer Strasse 37, Germany.     

Fractional and component analysis of crude oils by the method of dynamic microdistillation—Differential scanning calorimetry coupled with thermogravimetry

High-resolution differential scanning calorimetry was used to accurately establish the temperature intervals of oxidation/distillation of the major components of crude oils. Some theoretical aspects of the method of dynamic microdistillation, enabling consecutive distillation (oxidation) of the main components of hydrocarbon mixtures, are discussed. The experimental TG-DSC curves show that the temperature scan of the run can be divided into six regions, of which the first belongs to simple distillation of the sample's liquid constituent (the distillate) and the others to oxidative cracking distillation of the solid (heavy) residue. The latter occur in the order paraffins + light oils, middle base oils, heavy base oils, condensed aromatics (resins) and asphaltenes. The probable oxidation mechanisms of different classes of petroleum hydrocarbons operating in different temperature regions are discussed. Full quantitative fractional and group component analysis of a number of crude oils of different chemical classes and geological age was carried out by the combined TG-DSC techniques under specially chosen experimental conditions (those of dynamic microdistillation).     

Unexplored capabilities of chemiluminescence and thermoanalytical methods in characterization of intact and degraded hyaluronans

Three intact and four degraded hyaluronans were investigated by using chemiluminometry, differential scanning calorimetry, and thermogravimetry. Degradation of hyaluronan was induced by a system containing H₂O₂ alone (882 mM); 55 mM H₂O₂plus 1.25 μM CuCl₂; NaOCl alone (10 mM); and NaOCl plus CuCl₂ and ascorbic acid (10 mM, 0.1 μM, and 100 μM, respectively). The four different oxidative systems yielded biopolymer fragments represented by similar viscosity characteristics. The results obtained by using chemiluminescence and thermoanalytical methods indicate that hyaluronans of similar rheological properties could be distinguished from each other.     

Thermal behavior of vanadyl complexes with Schiff bases derived from trans-N,N′-bis(salicylidene)-1,2-cyclohexadiamine (t-Salcn)

Several Schiff bases coordinated to vanadyl, VO(Schiff base), were synthesized, characterized and studied by thermogravimetry in order to evaluate their thermal stability and thermal decomposition pathways. The number of steps and, in particular, the starting temperature of decomposition of these complexes depend on the equatorial ligand. The intermediates of the thermal decomposition processes were characterized by their IR spectra.     

Thermal treatment of whewellite—a thermal analysis and Raman spectroscopic study

Thermal transformations of natural calcium oxalate monohydrate known in mineralogy as whewellite have been undertaken using a combination of thermal analysis and Raman microscopy with the use of a thermal stage. High resolution thermogravimetry shows that three mass loss steps occur at 162, 479 and 684 °C.Evolved gas mass spectrometry shows that water is evolved in the first step and carbon dioxide in the second and third mass loss steps. The changes in the molecular structure of whewellite can be followed by the use of the in situ Raman spectroscopy of whewellite at the elevated temperatures. The whewellite is stable up to around 161 °C, above which temperature the anhydrous calcium oxalate is formed. At 479 °C, the oxalate transforms to calcium carbonate with loss of carbon dioxide. Above 684 °C, calcium oxide is formed.     

The thermal behaviour of nickel, copper and zinc complexes with the Schiff bases cis- and trans-N,N′-bis(salicylidene)-1,2-ciclohexadiamine (Salcn)

The Schiff base complexes were prepared and characterised by UV, IR and NMR (¹H and ¹³C) spectroscopy, elemental analysis and X-ray powder diffractometry. Free ligands and some new complexes were submitted to thermal analysis (TG and DSC) under dynamic air atmosphere. The differences in the decomposition profiles were related to the structure of isomers and decomposition intermediates were characterised according to their X-ray diffraction pattern.     

Crystallisation process on the stage of the gel-to-solid transformation in thermo-reversible polyethylene gels

The crystalline phase in gels and solid (gel derived) samples of ultra-high molecular weight polyethylene was studied using the low-frequency Raman spectroscopy and the differential scanning calorimetry methods. The Raman data evidence the presence in gels of tiny crystallites whose thickness (3-5 nm) depends on the sort of solvent used. After removal of the solvent by drying or squeezing the original gels, there appear some extra ordered regions (6-12 nm in size) coexisting in solid material with the primary crystallites which remain unchanged. It is concluded that the gel-to-solid transformation is accompanied by a secondary crystallisation process which is weakly (if ever) dependent on the incipient crystalline entities in gels.     

Synthesis,Structural Study and Phase Transitions Characterization by Thermal Analysis and Vibrational Spectroscopy of an Ammonium Rubidium Arsenate Tellurate

The Rb_2.42(NH₄)_0.58(HAsO₄)(H₂AsO4)·Te(OH)₆ crystals(denoted by RbNAsTe) crystallize in the monoclinic system, space group P2₁/n with the following parameters:a=1.3059(5) nm, b=0.6755(3) nm, c=1.6675(6) nm, β=94.126(4)°, Z=4 and V=1.46733(10) nm³. Thermal analyses(DSC, DTA and TG) confirm the presence of the phase transition and the temperature of the decomposition. The vibrational spectroscopy study at room temperature show the presence and the independence of anionic groups, cationic groups, and give more importance to the hydrogen bonds. Raman spectra were recorded in the temperature range of 298-503 K. The temperature dependence of the Raman line shift, intensity reduction and the half width detects the phase transitions and confirms their nature. So, the phase transition at 453 K corresponds to the superprotonic-ionic conduction phase transition, and those at 483 and 491 K correspond to the decomposition of our material.     

Continous gradient temperature Raman Spectroscopy identifies flexible sites in proline and alanine peptides

Continuous gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements that occur near phase transitions. Herein we apply GTRS and DSC to the solid dipeptides Ala-Pro, Pro-Ala, and the mixture Ala-Pro/Pro-Ala 2:1. A simple change in residue order resulted in dramatic changes in thermal stability and properties. Characteristic Pro vibrations were observed at ∼75 °C higher temperature in Pro-Ala than Ala-Pro. The appearance/disappearance of characteristic vibrational modes with increasing temperature showed that a double peak in the Ala-Pro major phase transition (174–184 °C) was due to a gauche to anti 165° rotation of H₃CC*NH₃ about C*. CH₂ rocking and wagging frequencies present in Pro-Ala were not observed in Ala-Pro. For Ala-Pro, the Ala ⁺NH_3, and Pro COO⁻ sites were flexible whereas the Pro ring moiety was not; since the OCN (C)₂ amide bond is planar the CNC moiety keeps the Pro ring rigid. For Pro-Ala, CH₂ sites in the Pro ring were flexible and the OCNH amide bond is perpendicular to the Pro ring. Since the mass of the Pro ring is significantly larger than the mass of the flexible Ala ⁺NH₃ moiety, Pro-Ala absorbs more thermal energy, corresponding to a higher phase transition temperature (240–260 °C). Ala-Pro, Pro-Ala, and Ala-Pro/Pro-Ala 2:1 exhibited α-helix, β-sheet, α-helix secondary structure conformations, respectively.     

Synthesis,crystal structure,vibrational and dielectric properties of di-benzyl-ammonium selenite monohydrate

The new hybrid compound [C₆H₅CH₂NH₃]_2·SeO_3·H₂O was synthesized and found to crystallize in the triclinic space group P$\overline{1}$. This structure can be described as an alternation between organic and inorganic chains connected by two types of N−HO and O−HO hydrogen bonds. The two and antiparallel cations [C₆H₅CH₂NH₃]⁺are arranged in a face-to-face pattern with a distance of 3.911(10)Å between them, indicating the existence of π-π interaction. The thermal properties show that the mass losses take place in three steps, which correspond to dehydration and degradation of the title compound. The IR and Raman spectra prove the existence and independence of the organic and inorganic groups as well as a water molecule. The equivalent circuit is modeled by a combination series of two parallel R–CPE circuits. Dielectric studies show that this material is ionic-protonic conductor at low temperature and becomes electronic one at high temperature.     

Comparison of two calorimetric methods to determine the loss of organic matter in Galician soils (NW Spain) due to forest wildfires

Seven forest soils, Cambisols under pinus, located at Galicia (NW Spain) and affected by forest wildfires were collected to determine the loss of organic matter due to the effect of burning, using calorimetric methods. The enthalpy of combustion, ΔH, of the organic matter of the burnt and the corresponding unburnt soils was calculated from the thermograms obtained with a differential scanning calorimeter (DSC-7, Perkin-Elmer). From these data, the loss of organic matter during the fires was calculated. On the other hand, the organic matter content for each burnt and unburnt soil studied was determined by thermogravimetry (TG) and, in the same way, the loss of organic matter was obtained. High linear, significant correlations were found between the enthalpy of combustion of the soil organic matter (SOM) and the organic matter content measured by thermogravimetry. Consequently, comparison of the loss of organic matter obtained by both methods indicated that the quantitative results are similar. Both techniques allow to determine the degradation level of the soils affected by forest wildfires, taking the loss of organic matter during the fire as a degradation index.     

阿司匹林的热解机理及热动力学研究

在用热重法研究了阿司匹林的热稳定性实验的基础上,通过量子化学方法(ab initio DFT)计算了阿司匹林分子的键级,据此计算结果提出了阿司匹林的热解机理,按此机理得到的理论计算值与实验结果一致;运用Freeman-Carroll、Kissinger和Ozawa三种方法分别计算了阿司匹林的热解动力学参数:活化能(E)、反应级数(n)和指前因子(A),其热解动力学方程为: dα/dt=4.74×1011[exp(－(100.34±5.18)×103/RT)](1－α)2.8±0.3;用差示扫描量热法测定的该物质的熔点、摩尔熔化焓和摩尔熔化熵分别为(409.19 ± 0.22) K、(29.17 ± 0.41) kJ•mol-1和(71.09±1.06) J•mol-1•K-1.     

Characterisation of macroporous poly(methyl methacrylate) coated with plasma-polymerised poly(2-hydroxyethyl acrylate)

Macroporous poly(methyl methacrylate) networks with varying cross-linking density and porosity were coated with plasma-polymerised poly(2-hydroxyethyl acrylate) grafted on the pores surface. The result is a mechanically reinforced hydrogel (PMMA-gr-plPHEA) whose properties are characterised in this work using several experimental techniques. Bulk PMMA and bulk PHEA were also characterised as reference materials. The diffusion and water sorption properties of these hydrogels were studied through equilibrium water sorption isotherms and desorption starting with the sample equilibrated in immersion in liquid water or in a vapour atmosphere. Glass transition, dynamic-mechanical relaxation and thermal degradation were characterised in order to study the interphase interaction in these biphasic systems. All these experimental techniques suggested that plasma-polymerised PHEA is more homogeneously interpenetrated with highly cross-linked macroporous PMMA than if the porous substrate is a loosely cross-linked polymer network.     

Spectroscopic, thermal, magnetic and structural characterization of K3VF6 prepared at room temperature

A straight forward room-temperature synthesis of V(III) containing complex fluoride K₃VF₆, using KF and vanadium(III) acetylacetonate is reported. The pale green colored powder was characterized by chemical analysis, powder X-ray diffraction; diffuse reflectance spectroscopy, infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, scanning electron microscopy, photoluminescence spectroscopy, magnetic susceptibility measurements and photoluminescence spectroscopy. The powder X-ray diffraction pattern was fitted in P2₁/n space group (monoclinic) with a = 12.106 (1) Å, b = 17.685 (0) Å, c = 11.802 (0) Å, β = 92.23° (1). Differential scanning calorimetry showed phase transitions, occurring at 158 °C and 190 °C. In the FT-IR spectrum, characteristic band for the VF₆³⁻ group was observed at 508 cm⁻¹. The bands observed in the 335-361 cm⁻¹ region and at 504 cm⁻¹ in the room temperature Raman spectrum of K₃VF₆ corresponded to the F_2g and A_1g modes, respectively. The ratio of the frequencies (F_2g/A_1g) observed in the diffuse reflectance spectrum was fitted on the Tanabe-Sugano diagram to determine the Racah parameter B value of 712 cm⁻¹. Magnetic ordering was not observed down to the lowest measured temperature of 5 K.     

Thermal decomposition of syngenite, K2Ca(SO4)2·H2O

The thermal decomposition of syngenite, K₂Ca(SO₄)₂·H₂O, formed during the treatment of liquid manure has been studied by thermal gravimetric analysis, differential scanning calorimetry, high temperature X-ray diffraction (XRD) and infrared emission spectroscopy (IES). Gypsum was found as a minor impurity resulting in a minor weight loss due to dehydration around 100 °C. The main endothermic dehydration and decomposition stage of syngenite to crystalline K₂Ca₂(SO₄)₃ and amorphous K₂SO₄ is observed around 200 °C. The reaction involves a solid-state re-crystallisation, while water and the K₂SO₄ diffuse out of the existing lattice. The additional weight loss steps around 250 and 350 °C are probably due to presence of larger syngenite particles, which exhibit slower decomposition due to the slower diffusion of water and K₂SO₄ out of the crystal lattice. A minor endothermic sulphate loss around 450 °C is not due to the decomposition of syngenite or its products or of the gypsum impurity. The origin of this sulphate is not clear.     

Thermal transitions of gluten-free doughs as affected by water, egg white and hydroxypropylmethylcellulose

The thermal performance of a gluten-free bread dough consisting of a blend of non allergenic corn and cassava starches (75:25) with hydroxypropylmethylcellulose (HPMC) as gluten mimetic hydrocolloid in conjunction with egg white (EW) was determined by differential scanning calorimetry. In order to analyse the effects of different levels of the components (water: 80-110%, HPMC: 0-2% and EW: 0-10% over the starch blend) on the thermal transitions of the dough, a Doehlert design and a response surface methodology were used.The analysis of variance showed that EW did not affect the onset temperature of gelatinisation and HPMC did not affect the peak and conclusion temperatures. HPMC-water interactions mainly controlled the onset temperature of starch gelatinisation. On the other hand, the peak and conclusion temperatures were determined by the additive and opposite effects of water and EW.     

Assessing the progress of degradation in polyurethanes by chemiluminescence and thermal analysis. II. Flexible polyether- and polyester-type polyurethane foams

The thermooxidative and thermal stability of polyether- and polyester-type polyurethane foams were investigated by non-isothermal chemiluminescence (CL), differential scanning calorimetry (DSC) and thermogravimetry (TG). In the presence of air and humidity, the effect of various routes and conditions of polyurethane ageing (induced thermally or by light) on the chemiluminescence, DSC and thermogravimetry patterns was assessed. The rate constants determined from non-isothermal thermogravimetry and chemiluminescence measurements at 250 °C and their not very pronounced dependence on the atmosphere of degradation indicated that depolymerisation of the polyurethane containing the aliphatic polyester and aromatic polyisocyanate moieties preceded or occurred in parallel with thermal oxidation. Under conditions of 50% relative humidity, samples of the polyester-type polyurethane, aged either by light or thermally, as well as specimens of the polyether-type polyurethane, aged by light, gave increased amounts of carbonaceous residue when heated in nitrogen to 550 °C.     

DSC and Raman studies of the side chain length effect of ubiquinones on the thermotropic phase behavior of liposomes

Differential scanning calorimetry and Raman spectroscopy have been used to examine the effects of ubiquinones (UQn) on the thermotropic phase behavior of dipalmitoylphosphatidylcholine (DPPC) in multilamellar vesicles, for UQ/DPPC molar ratios ranging from 0.01 to 0.1. The influence of the side chain length has been investigated by comparing the effect of a series of UQ with 2 (UQ2), 4 (UQ4), 6 (UQ6) and 10 isoprene units (UQ10).In the presence of increasing amount of UQ2 or UQ4, concomitant shift of the gel to liquid crystalline phase transition towards lower temperatures and vanishing of the pretransition are observed. Short-chain ubiquinones are thus inserted parallel to phospholipid chains, their benzoquinone ring being close to the DPPC polar headgroups. In addition, broadening and skewing of the main transition peak support the fact that UQ2 and UQ4 are laterally self-organized in highly concentrated regions located at the boundary of lipid domains. The lipid thermotropic behavior is not affected by the presence of other analogues of the series, UQ6 and UQ10. They remain homogeneously dispersed within the midplane of the phospholipid bilayer. Such a chain length dependence on the location and the organization of ubiquinones analogues may be correlated with their biological activities in biomembranes.     

甲磺酸帕珠沙星的热分解机理及动力学

采用热重(TG)和差示扫描量热(DSC)法测定了甲磺酸帕珠沙星(PZFX)在氮气氛和空气氛中的热分解过程,测定了PZFX及其在热分解过程中不同阶段残余物的红外光谱,运用量子化学GAMESS软件计算了PZFX分子的键级,推断了PZFX的热分解机理.结果表明PZFX的热分解过程的起始步骤是甲磺酸的分解.采用Ozawa方法计...