Thermal studies of chitin–chitosan derivatives

New poly(azo) amino-chitosan compounds were obtained from the azo coupling reaction of N-benzyl chitosan and diazonium salts. The thermal behavior of these compounds was studied by thermogravimetric analysis (TG), differential thermogravimetric analysis (DTG), TG coupled with a Fourier-transform infrared, and differential scanning calorimetry (DSC). TG/DTG curves of chitin–chitosan polymer showed two thermal events attributed to water loss and decomposition of the polysaccharide after cross-linking reactions. Thermal analysis of the poly(azo) amino-chitosan compounds showed that the decomposition temperatures decreased when compared to the starting chitin–chitosan and N-benzyl chitosan. DSC results showed an agreement with the TG/DTG analyses. Thermal behavior of poly(azo) amino-chitosans suggest that these compounds could be considered as potential thermal sensors.     

Thermal stability of Ti–MCM-41

Ti containing mesoporous MCM-41 materials have been synthesized through two methods: heating and non-heating [room temperature (RT)]. The synthesized materials have been characterized using X-ray diffraction, Fourier transform infrared, nitrogen sorption, and X-ray fluorescence methods and their thermal stabilities evaluated using thermogravimetric methods in inert atmosphere. The thermal stabilities have been analyzed based on the synthesis method, as well as on the amount of titanium in the MCM-41 materials. The thermal stability results suggest that uncalcined MCM-41 materials generally show higher mass loss than their calcined counterparts. Also, the RT-synthesized materials showed lower stability than the high-temperature synthesized samples for the uncalcined samples. It is also been found that MCM-41 materials show improved thermal stabilities as the amount of titanium is increased.     

Thermal study of CVD metal–organic precursors

Journal of Thermal Analysis and Calorimetry - The pressure of the saturated and unsaturated vapors of Zr(thd)4 and Y(thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) has been...     

Thermal analysis of protein–metallic ion systems

Advanced thermal analysis methods, such as temperature modulated DSC (differential scanning calorimetry) and quasi-isothermal TMDSC were used to analyze the protein–metallic ion interactions in silk fibroin proteins. The precise heat capacities were measured and theoretically predicted in this study. To remove bound water and simplify the system, a thermal cycling treatment through both standard DSC and TMDSC was used to detect the underlying heat capacity and reveal the phase transitions of the silk–metallic salts system. Results show that K⁺ metallic salts play the role of plasticizer in silk fibroin proteins, which reduces the glass transition (T_g) of the pure silk protein and negatively affects its structural thermal stability. On the other hand, Ca²⁺ metallic salts act as an anti-plasticizer, and increase the glass transition and the thermal stability of the silk protein structure. This indicates that the thermal analysis methods offer a new pathway to study protein–metallic ion systems, yielding very fruitful information for the study of protein structures in the future.     

Thermal study of Mn-containing silicate–phosphate glasses

Silicate-phosphate glasses of SiO₂–P₂O₅–K₂O–MgO–CaO system containing manganese cations were investigated to obtain information about the influence of manganese ions on the thermal behavior of such glasses. Amorphous state of glasses and the course of phase transformation and crystallization taking place during their heating were investigated by DSC, XRD, and FTIR methods. It was shown that an increasing content of manganese replacing calcium and magnesium in the structure of analyzed glasses causes decrease of glass transition temperature (T _g) and heat capacity change (Δc _p) accompanying the glass transformation. Simultaneously, thermal stability of the glasses increased. Products of multistage crystallization of glasses containing up to 8 mol% of MnO₂ were: marokite (CaMn₂O₄), phosphate of Ca₉MgK(PO₄)₇ type, and diopside (CaMgSi₂O₆). Product of crystallization of glasses containing higher amount of manganese was braunite (Mn₇O₈SiO₄). This was accompanied by change of structure of magnesium calcium silicates from diopside-type structure to akermanite-type silicates (Ca₂MgSi₂O₇). The data interpretation was based on bonds and chemical interactions of the individual components forming the glass structure.     

Thermal behavior of modified urea–formaldehyde resins

The thermal stability of pure urea–formaldehyde resin (PR) and modified urea–formaldehyde (UF) resins with hexamethylenetetramine-HMTA (Resin 1), melamine-M (Resin 2), and ethylene urea (EU, Resin 3) including nano-SiO₂ was investigated by non-isothermal thermo-gravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) supported by data from IR spectroscopy. Possibility of combining inorganic filler in a form of silicon dioxide with UF resins was found investigated and percentage of free formaldehyde was determined. The shift of DTG peaks to a high temperature indicates the increase of thermal stability of modified UF resin with EU (Resin 3) which is confirmed by data obtained from the FTIR study. The minimum percentage (6%) of free formaldehyde was obtained in Resin 3.     

Thermal characterization of titanium–titanium boride composites

Journal of Thermal Analysis and Calorimetry - Numerical simulation of mixed convection heat transfer in a lid-driven triangular cavity filled with power law nanofluid and with an opening was...     

Thermal behaviour of melamine-modified urea–formaldehyde resins

Thermal behaviour of industrial UF resins modified by low level of melamine was followed by TG-DTA technique on the labsys ^TM instrument Setaram together with the ¹³C NMR analysis of resin structure and testing boards in current production at Estonian particleboard factory Pärnu Plaaditehas AS. DTA curve of UF resin which has been cocondensed during synthesis with even low level of melamine shows the shift of condensation exotherm and water evaporation endotherm to considerable higher temperatures. The effect of melamine monomer introduced to UF resin just before curing was compared. The effect of addition of urea as formaldehyde scavenger was studied.     

Thermal behaviour of Fe-doped silicate–phosphate glasses

Thermal behaviour and structure of glasses from the SiO₂–P₂O₅–K₂O–MgO–CaO system modified by Fe₂O₃ addition were studied by DSC, XRD and FTIR methods. It has been found that the replacement of MgO and CaO modifiers by Fe₂O₃ in the structural network of silicate–phosphate glass results in decrease of the glass transition temperature (T _g) and heat capacity change (ΔC _p) accompanying the glass transformation. Simultaneously, the ability for crystallization, its course and the type of the forming phases depend on the relative proportions between iron and phosphorus as components forming the silicate–phosphate structure. The type of the crystal phases forming in the course of heating the considered glass has been found to be in agreement with the character of the domains occurring in this glass, confirmed by FTIR examinations.     

Thermal Studies of the Hardening of the Systems Calcium Silicates–Electrolyte–Water

Thermal studies, sometimes together with X-ray analysis, were applied to investigate the process of hydration in the systems calcium silicates (tricalcium silicate or dicalcium silicate) - water - electrolyte. Alkali metal or alkaline-earth metal salts were used as electrolytes. Results and conclusions are presented concerning the action of electrolytes upon the kinetics of hardening of the calcium silicates and the composition and phase transformation of calcium hydrosilicate in the presence of low proportions of electrolytes (0.5, 2 and 5 mass%), these effects being due to ionic substitution. A higher proportion of electrolyte (above 2%) in the systems calcium silicate-water can determine the formation of a complex salt, e.g. calcium hydroxysalts or double hydrosilicates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal characterization of bacterial cellulose–phosphate composite membranes

Cellulose–phosphate composite membranes have been prepared from bacterial cellulose membranes (BC) and sodium polyphosphate solution. The structure and thermal behavior of the new composites were evaluated by X-ray diffraction (XRD), ³¹P-nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry (TG) and thermomechanical analysis (TMA). From XRD analyses the Iα and Iβ cellulose crystalline phases were identified together with crystalline sodium phosphate that covers the cellulose microfibrils as revealed by SEM. ³¹P NMR spectra show peaks assigned to Q⁰ and Q¹ phosphate structures to be compared to the Q² units that characterize the precursor polyphosphate. Glass transition temperature, T _g, obtained from TMA curves and thermal stability obtained from TG and DSC measurements, were observed to be dependent on the phosphate content.     

Thermal Synthesis of the Zn1–xCOxO Pigments

In our laboratory, the synthesis of new inorganic pigments is followed by thermal analysis using a derivatograph apparatus. First information about the temperature region of the formation of the pigments investigated is provided by thermal analysis. The attention was directed to the preparation of the pigments based on zinc oxide in new green hues which can be used as medium colour pigments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal studies of sodium tetrahydroborate–potassium tetrafluoroborate mixtures

The results of DSC studies of NaBH₄–KBF₄ mixtures are presented. It is shown by chemical analysis, XRD analysis, IR spectroscopy, and ¹¹B and ⁹F MAS NMR that the decomposition of the mixtures starts at ~563 K to yield polyhedral borohydride compounds (predominantly B₁₂H₁₂^2-) in the solid residue. This temperature is much lower than the decomposition temperature of pure NaBH₄ (749 K). The mechanism of formation of the B₁₂H₁₂^2- anion has been proposed and confirmed. According to this mechanism, boron atoms from KBF₄ are involved in the formation of this anion.     

Thermal and structural properties of surfactant–picrate compounds

The novel surfactant?Cpicrate compounds were synthesized and characterized by thermal and XRD analysis. The synthesis, based on the electrostatic interactions of components in polar solvents, was carried out using picric acid and cationic surfactants (dodecyltrimethylammonium, didodecyldimethylammonium, and tridodecylmethylammonium halide). The idea was to investigate the dependence of physico-chemical properties and thermal transitions of picrate?Csurfactant compounds with raising number of dodecyl chains sited on the same ammoniumm head group. The equimolar mixed aqueous solutions are characterized as lyotropic, strongly promoted by picrate anion. The main crystal structure feature of investigated picrates is layered structure with stacked aromatic rings of one picrate molecule on the top of the other one via strong ?С??? interactions and connection to the alkylammonium molecules with their nitro groups by C?CH??O hydrogen bonds. Surfactant?Cpicrate bilayer-like structures are interrupted with layers of polar heads and picrate counterions and the observed width of such a bilayers are functions of more complex structural behaviors which ensures alternation in space of equal numbers of positive and negative charges. Although some of the surfactants used posses thermotropic porperties, like examined tridodecylmethylammonium chloride, no thermotropic mesomorphism is detected in solid state of investigated surfactant?Cpicrate compounds. The thermodynamic parameters of solid?Cliquid thermal transitions depend linear on the number of dodecyl chains, and for double- and triple-tailed picrate compounds the marked temporal hysteresis of the melt crystallization is registered.     

Thermal properties and combustibility of elastomer–protein composites

The article describes the measurements results of the influence of waste keratin on the properties of cross-linked styrene-butadiene rubber especially taking its thermal properties and flammability into consideration. The biopolymer used was thoroughly examined by means of derivatography, elementary analysis, FTIR spectroscopy, Zetasizer nano S90, and Zetasizer 2000. It has been found that the presence of protein facilitates the cross-linking of the elastomer investigated and the elastomeric-protein materials are characterized by good thermal and mechanical properties as well as a considerably increased resistance to thermooxidative aging. Under the influence of keratin, the flammability of the composites obtained is decreased.     

Thermal properties and combustibility of elastomer–protein composites

This article presents the test results of thermal properties and flammability of crosslinked nitrile rubber in the presence of zinc oxide or nano-zinc oxide containing waste keratin, using the test results obtained by means of a derivatograph, DSC, and oxygen index. The influence of modified montmorillonite (NanoBent) on selected properties of investigated elastomer–protein composites has also been studied. The composites' thermal stability and flammability depend on the method of composite preparation and the quantity of added keratin. The addition of waste keratin reduces the flammability of NBR–keratin composites.     

Thermal Oxidation Kinetics of Ni100–xPx Powders

The oxidation of Ni_100–xP_x(7.3 at%<x<25.0 at%) powders in air in the temperature range 350–450°C was determined by kinetics and X-ray diffraction. The isothermal kinetics was modeled using theGinstling–Brounstein equations. The oxidation process was found to be thermally activated with activation energy 127.8 kJ mol^–1 for x=7.3 at% to 157.7 kJ mol^–1 for x=25.0 at%. It was found that the rate constants for x=7.3 at% were approximately 100 times lower than those for x=25.0 at%. This revised version was published online in July 2006 with corrections to the Cover Date.