Journal of Thermal Analysis and Calorimetry: An International Forum for Thermal Studies (v.63, #3)
A Thermal Analysis Study of Hydroxy Benzoic Acid Derivatives Using Rising Temperature Thermogravimetry
by K. Chatterjee; D. Dollimore; K. Alexander (pp. 629-639).
Hydroxy benzoic acids were subjected to rising temperature thermogravimetric analysis. After optimizing the procedural variables, the kinetics of decomposition was determined and methyl paraben was taken as the calibration compound to characterize the evaporation patterns for the ortho and meta derivatives. The E act values for ortho, meta and para derivatives were 64.8, 78.2, and 119.1 kJ mol–1, respectively. The Antoine and Langmuir equations were utilized to determine the coefficient of evaporation k, which was 124525±0.8, units being in the SI system. The vapor pressure plots were generated for the ortho and meta derivatives; ΔH vap for these two compounds were obtained as 66.7 and 80.4 kJ mol–1, respectively.
Keywords: Antoine equation; Arrhenius equation; benzoic acids; evaporation; kinetics; Langmuir equation; thermogravimetry
Differential Scanning Calorimetry at Hydrothermal Conditions of Amorphous Materials Prepared by Drying Sodium Silicate Solutions
by H. Roggendorf; D. Böschel; B. Rödicker (pp. 641-652).
Concentrated sodium silicate solutions with a molar SiO2:Na2O ratio of 3.3 and a SiO2 content of 27 mass% were dried up to 63 d at temperatures between 40 and 100°C to residual water contents between 12 and 38 mass%. The dried solid materials were investigated by differential scanning calorimetry (DSC). Pressure tight autoclave crucibles were applied to suppress evaporation and boiling of the samples during heating. Two thermal events are discussed with respect to glass transition.
Keywords: drying; glass transition; hydrothermal conditions; sodium silicate solution; thermal analysis
The Melting Process of Acetylsalicylic Acid Single Crystals
by G. L. Perlovich; A. Bauer-Brandl (pp. 653-661).
Crystallisation is generally regarded as a nucleation — growth mechanism of a solid phase and often studied using thermo chemical methods. The present work postulates an analogy to melting processes, looking at melting as nucleation — growth of a liquid phase. The melting process of acetylsalicylic acid single crystals was investigated by DSC measurements under isothermal conditions. The fraction of material molten after a certain time period, α(t), was calculated by integrating the DSC curves. The resulting kinetic curves were fitted using the Avrami-Erofeev equation: –ln(1–α)=kt n, where parameter n was analysed. According to established methods, functions I('2')=[t('2')]/[t('2')+t('3')]100% and I('3')=[t('3')]/[t('3')+t('2')]100% were introduced, where t('2') and t('3') is the absolute time of consumption two- and three-dimension nuclei growth, respectively. Applying correlation analysis, relationships between two- or three-dimensional growth and the independent variables describing the single crystals (for strictly definite trajectories into the space of sizes) were found. Particular correlations were:a) Two-dimensional growth is a function of the total surface area of the crystal, S, and of the surface area of the (ac)-face, S ac; b) Three-dimensional growth is a function of S/M (where M is the mass of the single crystal). It is also a function of S ac/M and of S. The obtained experimental data are explained by the ‘layer’ structure of crystals of acetylsalicylic acid.
Keywords: acetylsalicylic acid; Avrami–Erofeev equation; isothermal melting process; single crystal; two- and three-dimension growth nuclei
Phase Diagrams of Perhydrotriphenylene and Aromatic Compounds II. Terthiophene and related thiophene oligomers
by G. Di Silvestro; C. M. Yuan; W. Porzio (pp. 663-669).
Terthiophene included in a perhydrotriphenylene (PHTP) adduct exhibits an UV spectrum different from that observed in the bulk or in solution. The X-ray diffraction pattern also differs significantly from that of pure PHTP. The UV spectrum is interpreted as due to an isolated molecule in a vacuum-like space, in agreement with a model developed from X-ray diffraction data. Knowledge of the phase diagram was essential for an interpretation of the optical properties and of some kinetic aspects of the formation of the inclusion compound phase. In this work, the phase diagrams of terthiophene (T3) are presented, and DSC evidence of the inclusion of quater- (T4), penta- (T5)and α,ω-dihexylquaterthiophene (DH4T) is discussed.
Keywords: inclusion compounds; perhydrotriphenylene; phase diagrams; quater-, penta- and α,ω-dihexylquaterthiophene
Work of Fracture and Strain-induced Cold Crystallization Behavior of Amorphous Copolyester Sheets
by J. Karger-Kocsis; E. J. Moskala; P. P. Shang (pp. 671-678).
The toughness of amorphous copolyester sheets was assessed by the essential work of fracture (EWF) concept. While the yielding-related work of fracture terms did not change significantly, the necking-related parameters strongly decreased with decreasing entanglement density of the copolyesters having different amounts of cyclohexylenedimethylene (CHDM) units in their backbones. Furthermore, copolyesters with high CHDM content and thus less entanglement density showed full recovery of the necked region beyond the glass transition temperature, i.e. the ‘plastic’ zone in the related specimens formed by cold drawing and not by true plastic deformation. By contrast, the copolyester with negligible amount of CHDM did not show this shape recovery. Modulated differential scanning calorimetry (MDSC) revealed that the necking in the latter system was accompanied by strain-induced crystallization. The superior work hardening in the necking stage of the respective poly(ethylene terephthalate) (PET) specimens can thus be ascribed to stretching of the entanglement network with superimposed crystallization.
Keywords: amorphous copolyesters; cold crystallization; cold drawing; entanglement; essential work of fracture; modulated DSC; necking
TG and Flammability Studies on Polymer Blends Containing Acrylonitrile–butadiene–styrene and Chlorinated Poly(vinyl Chloride)
by P. Carty; J. R. Creighton; S. White (pp. 679-687).
The effects which an iron(III) based smoke suppressing compound have on the thermal stability of some acrylonitrile–butadiene–styrene/chlorinated poly(vinyl chloride) (ABS/CPVC) polymer blends have been investigated. Thermogravimetric analysis (TG) experiments have shown that there are three distinctive stages occurring during the thermal breakdown of these blends both when the iron compound is absent and present in the polymer formulations. The most important effect which the iron compound has when it is present in these blends is to modify the decomposition chemistry which takes place and the effect becomes more pronounced as the concentration of CPVC present in the blends increases. Other important effects are that the iron compound stabilises the blends so that mass loss is significantly reduced (by up to 50% in some cases) and the onset temperature of decomposition is raised. Flammability data generated during earlier work is supported by the TG results obtained in this work especially in the important area of smoke formation and suppression.
Keywords: changes in decomposition chemistry; flammability data; iron(III) smoke suppressant; polymer blend (ABS/CPVC); TG results
Dissolution De L'hydroxyapatite et Du Phosphate Tricalcique β Dans Les Solutions D'acide Nitrique
by A. Ben Cherifa; J. Rogez; M. Jemal; J. C. Mathieu (pp. 689-697).
Using an isoperibol calorimeter for rapid reactions and a Calsol type microcalorimeter for slow processes, are applied to determine the enthalpies of solution of two synthetic phosphate products in nitric acid. Namely, β tricalcium phosphate Ca3(PO4)2 and the calcium hydroxyapatite Ca10 (PO4)6 (OH)2 are measured by varying pH value of the solvent. Some dissolution mechanisms are proposed for various pH values. They are ensured by complementary reactions of solution of Ca(NO3)2, Ca(H2 PO4)2 and H3 PO4 in the same solvents. An extrapolation of solution enthalpies to pH=7 leads to the enthalpy of solution of these products in the pure water. These values are Δsol H °=–138.3 kJ mol–1 for Ca3 (PO4)2 and –393.6 kJ mol–1 for Ca10 (PO4)6 (OH)2 .
Keywords: enthalpies of solution; isoperibol calorimeter; microcalorimeter; synthetic phosphate
Modulated Differential Scanning Calorimetry Observation of Physical Ageing in Polymers
by M. Song (pp. 699-707).
Modulated-temperature differential scanning calorimetry (M-TDSC) is becoming a useful tool in the characterisation of thermal behaviour of polymers. In this paper, we discuss whether the non-reversing M-TDSC signal can be used, quantitatively and directly, to study the process of physical ageing in polymers. Difference exists between the values of relaxation enthalpy determined by using average heat capacity, <C p>, signal as for conventional DSC and non-reversing heat capacity, C n p, signal. When the signal of reversing heat capacity of unaged sample is considered as baseline for <C p> and C n p signals, the difference disappears. It is concluded that non-reversing M-TDSC signal can be used to observe the process of physical ageing semi-qualitatively and directly. With increasing annealing time, the peak of the imaginary part, C″p, of the complex heat capacity becomes narrow, but peak area changes little. This indicated that C″p is not correlated with relaxation enthalpy. It may be related to entropy change during the modulation. However, the entropy change is quite small.
Keywords: entropy; glass transition; modulated DSC; physical ageing
Incorporation of Cadmium Ions and Cadmium Sulfide Particles into Sol-gel Zirconium Phosphate. Synthesis, thermal behavior and X-ray characterization
by C. Ferragina; P. Cafarelli; R. Di Rocco (pp. 709-721).
The inorganic ion-exchanger α-zirconium phosphate was synthesized by the sol-gel method and its properties relating to the exchange of Cd2+ and the intercalation of CdS particles were studied. The Cd2+-exchange process is a fast process and the material obtained exhibits an increased interlayer distance d with respect to its precursor (9.56 vs. 7.56 Å). The resulting Cd-containing material was exposed to aH2S gas flow to give CdS particles in the exchanger. The zirconium phosphate containing CdS particles still possesses a layered structure, with a pattern almost identical to that of the initial ion-exchanger precursor. Moreover, the material may exchange further Cd2+ and hence lead to a higher CdS particle content. The thermal behavior of this ion-exchangers containing Cd2+ or CdS particles was studied.
Keywords: intercalation compounds; ion-exchanger; layered composite; thermal behavior
Transition Metal Complexes with Pyrazole-based Ligands. Part 8. Characterization and thermal decomposition of zinc(II) complexes with di- and trisubstituted pyrazoles
by K. Mészáros Szécsényi; V. M. Leovac; Ž. K. Jaćimović; V. I. Češljević; A. Kovács; G. Pokol; S. Gál (pp. 723-732).
We report the synthesis and the characterization (elemental analysis, FT-IR spectroscopy, thermal methods and molar conductivity measurements) of the mixed complexes of zinc with acetate and 3-amino-5-methylpyrazole, HL 1, [Zn(OAc)2(HL1)2], or 3-amino-5-phenylpyrazole, HL 2 [Zn(OAc)2(HL2)2], or 4-acetyl-3-amino-5-methylpyrazole, HL 3, [Zn(OAc)(L3)(HL3)]2, with isothiocyanate and HL 2 [Zn(SCN)2(HL2)2], or HL 3 [Zn(SCN)2(HL3)2], and with nitrate, isothiocyanate and 3,5-dimethyl-1-carboxamidinepyrazole, HL 4 [Zn(NO3)(NCS)(HL4)2].The thermal decomposition of the complexes is generally continuous resulting zinc oxide as end product,except [Zn(OAc)(L3)(HL3)]2 in which case a well-defined intermediate was observed between 570–620 K. On the basis of the IR spectra and elemental analysis data of the intermediate a decomposition scheme is proposed.
Keywords: 4-acetyl-3-amino-5-methylpyrazole; 3-amino-5-methylpyrazole; 3-amino-5-phenylpyrazole; FT-IR spectroscopy; thermal decomposition; zinc(II) complexes
The Mechanism of the Thermal Transformation From Goethite to Hematite
by D. Walter; G. Buxbaum; W. Laqua (pp. 733-748).
Synthetic pigments of goethite (BayferroxR) of different particle size were investigated by DTA, IR, DSC, TG and X-ray diffraction measurements. It follows that a so-called ‘hydrohematite’ described in the literature does not exist as a discrete intermediate during the dehydration course from goethite to hematite. Instead we observed a dependence of the dehydration mechanism on the particle size. Transformation enthalpies and activation energies for the dehydration process will be given. A plausible dehydration mechanism, which is compatible with our DTA/DSC results, is deduced from TEM investigations.
Keywords: dehydration; DTA/DSC; goethite; hematite; IR; TEM; TG; XRD
Thermogravimetric Analysis and Thermal Ageing of Crosslinked Nitrile Rubber/Poly(ethylene-co-vinyl Acetate) Blends
by H. Varghese; S. S. Bhagawan; S. Thomas (pp. 749-763).
The thermal behaviour of nitrile rubber (NBR)/poly(ethylene-co-vinyl acetate) (EVA) blends was studied by thermogravimetry. The effects of blend ratio, different crosslinking systems (sulphur, peroxide and mixed), various fillers (silica, clay and carbon black) and filler loading on the thermal properties were evaluated. It was found that the initial decomposition temperature increased with the addition of NBR to EVA. Among the various crosslinking systems studied, the peroxide cured system showed the highest initial decomposition temperature. This is associated with the high bond dissociation energy of C–C linkages. The addition of fillers improved the thermal stability of the blend. The mass loss at different temperatures and activation energy of degradation were also studied. The thermal ageing of these blends was carried out at 50 and 100°C for 72 h. It was seen that the properties are not affected by the mild ageing condition. Also, the peroxide cured system was found to exhibit better retention in properties, than other crosslinking systems.
Keywords: nitrile rubber and poly(ethylene-co-vinyl acetate); thermal ageing; thermogravimetric analysis
Analysis of the Thermokinetics Under Dynamic Conditions by Relative Rate of Thermal Decomposition
by A. Mianowski (pp. 765-776).
A novel parameter of the relative rate of thermal decomposition has been defined on the basis of an analysis of equation relating the logarithm of the conversion degree on the temperature. The dependence of this parameter on temperature in the dynamic conditions has been analyzed and discussed. The dependence of the relative rate of thermal decomposition is a linear relationship involving two coefficients. These coefficients can be related to the enthalpy and activation energy. The parameter developed has been used for the analysis of a series of consecutive reactions of thermal decomposition of calcium oxalate monohydrate.
Keywords: calcium oxalate monohydrate; conversion degree; relative rate; thermal decomposition; thermokinetics
Kinetic Analysis of Dissociation of Smithsonite from a Set of Non-isothermal Data Obtained at Different Heating Rates
by P. Budrugeac; J. M. Criado; F. J. Gotor; C. Popescu; E. Segal (pp. 777-786).
The isoconversional methods (Friedman and Flynn-Wall-Ozawa) as well as the invariant kinetic parameters method (IKP) were used in order to work the TG data corresponding to the thermal dissociation of smithsonite. As a result we mention a mechanism change at T≈671 K. For T>671 K, which corresponds to heating rates in the range 0.57– 8.06 K min–1, a reaction order model with 1<n≤1.4 describes the experimental data.
Keywords: invariant kinetic parameters method; isoconversional method; smithsonite; thermal dissociation
The Thermal Stability of Ciprofloxacin Complexes with Magnesium(II), Zinc(II) and Cobalt(II)
by M. Zupančič; R. Cerc Korošec; P. Bukovec (pp. 787-795).
The thermal behaviour of Mg(II), Zn(II) and Co(II) compounds of ciprofloxacin was studied by thermogravimetry (TG) and differential thermal analysis (DTA) in order to determine or to confirm some structural characteristics of substances. The complexes decompose in two steps: dehydration and pyrolytic decomposition of the anhydrous complexes to form metal oxide or metal fluoride. The dehydration process of one magnesium(II) compound takes place in two steps suggesting a marked difference in the bonding of water molecules. The different bonding mode of the ciprofloxacin molecules in both magnesium compounds leads to different residues of the thermal decompositions.
Keywords: ciprofloxacin; DTA; metal complexes; quinolones; TG
Kinetics and Mechanism of Topochemical Transformations of Phosphoric Salts
by V. V. Samuskevich (pp. 797-805).
A study was made on the topochemical processes of hydration-dehydration, ammonation-deammonation, disproportionation and anionic condensation (certain of which can proceed concurrently) that occur during the production, storage and exploitation of phosphoric salts and phosphate materials. These processes which can be accompanied by complicated structural transformations and sometimes by melting were shown to be satisfactorily described by the known kinetic regularities. The detected deviations, that are associated with the anomalous influence of temperature, the gaseous phase, the size and habit of the crystals and the ageing of samples on the process rate, were explained in terms of the localization peculiarities of the reactions proceeding on the surface or in the bulk of the reactant.
Keywords: kinetics; localization; phosphoric salts; topochemical reactions
Thermal and Infrared Study of Desorption of Pyridine and Pyridine Derivatives from Ni-exchanged Montmorillonite
by E. Jóna; M. Kubranová; A. Sirota; M. Kopcová (pp. 807-813).
Thermal analysis (TG, DTG) and infrared absorption spectra were used to study desorption of pyridine (py), 4-methylpyridine (4-Mepy) and 4-ethylpyridine (4-Etpy) from Ni(II)-exchanged montmorillonite (Ni-MMT). It is shown that the bonds between the derivatives of pyridine (R-py) and the montmorillonite exhibit predominantly Lewis acid character. The thermal stability of studied samples and the total amounts of R-py inserted in the porous structure of Ni-MMT increase in the following sequence: py/Ni-MMT<4-Mepy/Ni-MMT<4-Etpy/Ni-MMT, i. e. the influence of the substituent on the pyridine ring is evident.
Keywords: desorption of pyridine derivatives; infrared spectra; Ni(II)-montmorillonite; thermal study
Effect of the Drawing Process on the Thermal Stability of Gelatine-polyacrylonitrile Graft Copolymer Fibres
by G. Janowska; T. Mikołajczyk (pp. 815-822).
The thermal stability of gelatine-polyacrylonitrile graft copolymers fibres obtained under various conditions of deformation has been studied. The thermal properties of examined fibres depend on the synthetic component of the fibre forming material – polyacrylonitrile which appears in the form of grafted PAN chains and PAN homopolymer. It was stated that the highest thermal stability have those fibres which formation process included two stages of drawing with the use of deformation close to the maximal values, with the value of the total draw ratio amounting to 691%. It should be supposed that with such a drawing process, already in its first stage, are created advantageous conditions for the formation of paracrystalline regions to a larger extent and their orientation along the fibre axis.
Keywords: DSC; DTA; gelatine; gelatine-polyacrylonitrile graft copolymer fibres; polyacrylonitrile; thermal analysis; thermal properties; thermal stability; TG
Synthesis, Characterization and Thermal Decomposition of p-iodo-phenylalanine Complexes of Cobalt or Nickel
by W. J. Wang; S. R. Luan; Y. R. Chen; L. Z. Cal; Y. Q. Jia; S. K. Ruan; J. F. Duan (pp. 823-830).
New complexes of the non-natural amino acid (p-iodo-phenylalanine) with divalent cobalt and nickel ions have been synthesized. The composition of the complexes is [M(IC6H4CH2CHNH2COO)2]×2.5H2O (M=Co, Ni) and the crystal structure belongs to orthorhombic system. Infrared spectra indicate the nature of bonding in the complex. The first stage in the thermal decomposition process of the complex shows the presence of crystal water. The thermal decomposition process of cobalt complex differs from that of nickel. The intermediate and final residues in the thermal decomposition process have been analyzed to check the pyrolysis reactions. Thermal analysis indicates that the iodine atom of the ligand may coordinate to the metal ion in the lattice.
Keywords: complex of amino acid with cobalt or nickel; crystal structure; infrared spectra; synthesis; thermal decomposition
The Effect of Magnesium Chloride Hydrate on the Fire Retardation of Cellulosic Fibers
by W. A. Esmail; A. M. Y. Darwish; O. A. Ibrahim; M. F. Abadir (pp. 831-838).
Thermal analysis was used to investigate the effect of the addition of magnesium chloride hexahydrate as a fire retardant to cellulosic fibers. The kinetics of the decomposition of the cellulosic material were first studied. The decomposition of the dry salt was also investigated and three steps disclosed. Then, the fabrics were impregnated into salt solutions of different concentrations and the loss in mass was followed by thermal analysis. The percent loss in mass was compared to that of pure cellulosic fabric at different temperatures. It was found that there is an appreciable improvement in fire retardation at a minimum percent add-on of the salt of 35%.
Keywords: cellulose; fire retardation; magnesium chloride hydrate
Thermal Analysis of Manganese(II) Complexes With Glycine
by R. Mrozek; Z. Rzączyńska; M. Sikorska-Iwan (pp. 839-846).
The thermal decomposition behaviour of the manganese(II) complexes with glycine: Mn(gly)Cl2(H2O)2, Mn(gly)2Cl2, Mn(gly)Br2(H2O)2, Mn(gly)2Br2(H2O)2 was investigated by means of TG-DTG-DTA, Hi-Res-TA and DSC techniques. The evolved gas analysis was carried out by means of the coupled TG-FTIR system. Heating of the complexes results first in the release of water molecules. Next, the multi-stage decomposition process with degradation of glycine ligand occurs. Water, carbon dioxide and ammonia were detected in the gaseous products of the complexes decomposition. The temperature of NH3 evolution from the complexes is higher than from free glycine. The final residue in the air atmosphere is Mn2O3 which transforms into Mn3O4 at 930°C. In a nitrogen atmosphere, the complexes decompose into MnO.
Keywords: DSC; manganese(II)complexes with glycine; TG-DTG; TG-FTIR; thermal analysis
Thermal Analysis of Hexachloroplumbate and Chlorides Containing Complex Divalent Lead 2,2'-bipyridine Cations
by M. Kabir; J. Szychliński; A. Konitz (pp. 847-854).
Lead(II) 2,2'-bipyridine hexachloroplumba tetetrahydrate was synthesized and investigated by DTA, TG and DTG. IR spectroscopy and other methods enabled the identification of some of the decomposition products. Comparative studies on the corresponding chlorides: [Pb(bipy)]Cl2 and [Pb(bipy)3]Cl2, which can be considered as precursors of the hexachloroplumbate, were also undertaken. X-ray measurements enabled the tentative determination of the crystal structure of [Pb(bipy)]Cl2. Hexachloroplumbate decomposes with the liberation of chlorine, water and organic ligands, and the process is accompanied by the simultaneous transition of Pb(IV)→Pb(II). Chlorides release only ligands upon heating. Residues comprised always PbCl2.
Keywords: lead(II) 2,2'-bipyridine hexachloroplumbate and chlorides; thermal analysis; X-ray structure
Application of Thermal Analysis to the Study of Some Waste Agricultural Products for the Preparation of Active Carbons
by T. Lupascu; I. Dranca; V. T. Popa; M. Vass (pp. 855-863).
TG, DTG and DTA methods were used for the investigation of some waste agricultural products, such as grape seeds, walnut shells, plum and peach stones, which can serve as raw materials for the production of active carbons. It was demonstrated that thermo analytical methods are appropriate to study the thermal characteristics of the above wastes and the data obtained can be applied to the technological processes of active carbon preparation.
Keywords: active carbons; thermal analysis; waste agricultural products
Thermal and Spectral Features of Yttrium and Heavy Lanthanide Complexes with 2,4-dimethoxybenzoic Acid
by W. Ferenc; A. Walków-Dziewulska (pp. 865-877).
The complexes of yttrium and heavy lanthanides with 2,4-dimethoxybenzoic acid of the formula: Ln(C9H9O4)3×nH2O, where Ln=Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(III), n=2 for Tb(III), Dy(III), Ho(III), Er(III), Tm(III) and Y(III), and n=0 for Yb(III) and Lu(III), have been synthesized and characterized by elemental analysis, IR spectroscopy, themogravimetric studies, as well as X–ray and magnetic susceptibility measurements. The complexes have a colour typical of Ln 3+ salts (Tb, Dy, Tm, Yb, Lu, Y – white, Ho – cream, Er – pink). The carboxylate group in these complexes is a bidentate, chelating ligand. The compounds form crystals of various symmetry. 2,4-Dimethoxybenzoates of Yb(III) and Lu(III) are isostructural. 2,4-Dimethoxybenzoates of yttrium and heavy lanthanides decompose in various ways on heating in air to 1173 K. The hydrated complexes first lose water to form anhydrous salts and then decompose to the oxides of respective metals. The ytterbium and lutetium 2,4-dimethoxybenzoates decompose in one step to form Yb2O3 and Lu2O3.The solubilities of the 2,4-dimethoxybenzoates of yttrium and heavy lanthanides in water and ethanol at 293 K are of the order of: 10–3 and 10–3 –10–2 mol dm–3, respectively. The magnetic moments for the complexes were determined over the range of 77–298 K. They obey the Curie–Weiss law. The results show that there is no influence of the ligand field on the 4f electrons of lanthanide ions.
Keywords: 2,4-dimethoxybenzoates of heavy lanthanides thermal stability; IR spectroscopy; magnetic moments; X-ray diffraction
Heat Capacities of Hydroxy and Aminoderivatives of Benzene
by M. Čenský; M. Lipovská; H.-G. Schmidt; V. Růžička; G. Wolf (pp. 879-899).
Heat capacities in the liquid phase C l of methylbenzeneamines and heat capacities in the solid phase C s of benzenediols and of 4-methylbenzeneamine were measured by commercial Setaram heat conduction and power compensated calorimeters. Results obtained cover the following temperature range (depending on the compound and state of aggregation): 2-methylbenzeneamine 313 to 371 K, 3-methylbenzeneamine 263 to 371 K, 4-methylbenzeneamine 133 to 353 K, 1,2-benzenediol 153 to 353 K, 1,3-benzenediol 173 to 353 K, 1,4-benzenediol 133 to 403 K. The heat capacity data obtained in this work were merged with experimental data from literature, critically assessed and sets of recommended data were developed by correlating selected data as a function of temperature.
Keywords: benzenediols; heat capacity in liquid and solid phase; methylbenzeneamines; temperature dependence
Changes in the Thermal Behaviour of NBR Due to Accelerated γ-radiation-induced Ageing
by P. Budrugeac; D. Fatu (pp. 901-906).
Thermal investigation has allowed us to show the changes undergone by a sort of nitrile-butadiene rubber (NBR) as a consequence ofγ-radiation-induced ageing. The parameters of the processes, which occur at progressive heating of the investigated samples, were determined. It was shown that for γ-irradiated samples the activation parameters corresponding to the thermo-oxidative process leading to solid products are correlated through the relation of compensation effect. Also, it was shown that, by γ-irradiation, NBR undergoes a relatively rapid change of its thermal behaviour which can be due to structural changes.
Keywords: compensation effect; γ-radiation-induced ageing; non-isothermal kinetics
Thermal Behaviour Studies on Some Heterotrinuclearpolyacids
by L. Ghizdavu; A. Fodor; G. Şt. Szász (pp. 907-912).
An improved method for the synthesis of four heterotrinuclearpolyacids of the type: Hx[EM′yM″zO40⋅nH2O (E=P, Si; M′=Mo, W; M″=V, W) was elaborated. The studied compounds were characterized by elemental analysis, IR spectra and thermal behaviour over 20–800°C temperature range.
Keywords: heterotrinuclearpolyacids; IR spectra; polyoxometalates; thermal behavior