Differential Scanning Calorimetric Techniques Research Articles

(INVITED) Positron annihilation spectroscopy and third harmonic generation studies on MnO mixed lead zirconium silicate glass ceramics

This work is intended to report pertinent studies covering several aspects viz., spectroscopic, higher order non-linear optical studies and positron annihilation spectroscopic studies on lead zirconium silicate glass ceramics admixed with different contents of MnO. Lead zirconium silicate glasses mixed with small contents (up to 1.0 mol%) of MnO were prepared and crystallized by subjecting them to the prolonged heat treatment at crystallization temperature ∼ 830 °C. The structural analysis of the samples carried out using XRD, TEM, EDS and differential scanning calorimetric techniques has suggested that the glass ceramics are entrenched with coagulated poly-crystallites viz., Mn2SiO4, Pb2MnO4 and Pb3Mn7O15 that contain manganese ions in multiple oxidation states. These studies have also suggested that Mn2+ ions occupy octahedral as well as tetrahedral positions and the tetrahedral occupancy is predominant in the glass ceramic sample mixed 0.6 mol% of MnO (M6). Infrared, Raman, optical absorption and photoluminescence spectral investigations have further supported the above conclusions and indicated an increasing rigidity of the glass network (attributed to the enhanced tetrahedral occupancy of manganese ions) with increasing concentration of MnO up to 0.6 mol%. Positron annihilation lifetime spectroscopic studies (carried out with 22Na isotope source of strength 0.1 MBq) suggested the sample M6 contains the lowest magnitude of free volume space. This is attributed to the participation of the maximal concentration of Mn2+ ions in the glass network forming. Non-linear optical (NLO) studies using NIR Er-glass laser (λ = 1540 nm) indicated the highest intensity third harmonic generation (THG) beam in the glass ceramics doped with small contents (∼0.2 mol%) of MnO. Overall analysis of these results suggested that the samples with lower concentrations of MnO possess highly disordered internal structure and facilitated the increase of intensity of THG beam; Hence, such samples may be considered as potential candidates for the applications in the fabrication of various micro sized opto-electronic devices, for example, optical switches, optical cross-connectors, microbolometers, photovoltaics, light sensors etc.

Capturing low-pressure hydrogen using V[sbnd]Ti[sbnd]Cr catalyzed magnesium hydride

Catalyzed magnesium hydride is suggested as a potential absorbent material for hydrogen separation, purification, and other relevant applications. The present study reports an investigation on selective hydrogen absorption using ball-milled VTiCr-catalyzed MgH2 from a gaseous mixture. Temperature oscillation absorption method, thermogravimetric analysis and differential scanning calorimeter techniques are utilized to characterize the VTiCr-catalyzed MgH2, demonstrating a reversible capacity up to 4 wt%H when the temperature is oscillated between 150 and 350 °C. When the hydrogen partial pressure is increased from 0.04 to 0.4 bar the reaction (dehydrogenation and hydrogenation) temperatures increase, and so do the reversible hydrogen capacities. The reaction kinetics are stable during the first 10 cycles. Transmission electron microscopy analysis shows that the VTiCr catalyst is a few nanometers in size and is dispersed uniformly in MgH2 matrix. The results of this study demonstrate that nano-VTiCr catalyzed MgH2 can readily react with low-pressure hydrogen and cycle in the mixture atmosphere.

Thermodynamic stability of CaThF6(cr) by transpiration and e.m.f. techniques

In the present paper, we report the standard molar Gibbs energy of formation for CaThF6 measured by gas equilibration and e.m.f. methods. The HF(g) vapour pressure over the equilibrium reaction: $${\text{CaThF}}_{6} \left( {\text{cr}} \right) + 2 {\text{H}}_{ 2} {\text{O}}\left( {\text{g}} \right) = {\text{CaF}}_{2} \left( {\text{cr}} \right) + {\text{ThO}}_{2} \left( {\text{cr}} \right) + 4{\text{HF}}\left( {\text{g}} \right)$$ has been measured using transpiration technique. The above reaction mechanism has been established employing TG and XRD techniques. A fluoride e.m.f. cell: (−)Pt, CaF2(cr) + ThOF2(cr) + CaThF6(cr) |CaF2(cr)| NiO(cr) + NiF2(cr), Pt(+) has been constructed to measure Gibbs energy of formation of CaThF6 (cr) using CaF2 (cr) as a solid electrolyte. The isobaric heat capacity $${\text{Cp}}_{\text{m}}^{{\circ }} \left( T \right)$$ of the compound has been measured using differential scanning calorimetric technique. Based on the experimental results, thermodynamic functions for CaThF6 have been generated.

Synthesis of g‐C3N4‐Decorated Magnesium Ferrite Nanoparticle Composites for Improved Ethanol Sensing

AbstractThe nanocomposites of g‐C3N4 nanosheet decorated magnesium ferrite nanoparticles were synthesized by a facile solvothermal method. X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and thermal gravimetric analysis and differential scanning calorimeter (TG‐DSC) techniques were used to characterize the structure and morphology of the as‐prepared nanocomposites. The results indicated that the MgFe2O4 nanoparticles were highly dispersed on the surface of the g‐C3N4 nanosheet. The gas‐sensing properties of the samples were tested, and the response value (Ra/Rg) of the MgFe2O4/g‐C3N4 nanocomposite with 15 wt.% g‐C3N4 content‐based sensor to 500 ppm of ethanol was 112 at 300 °C, which is 5 times higher than that of pure MgFe2O4. Moreover, the MgFe2O4/g‐C3N4‐15‐based sensor showed impressive selectivity, fast response and recovery characteristics, and good linearity in range of ethanol concentration (10–500 ppm).

Comparative evaluation on the thermal behaviors and kinetics of combustion of heavy crude oil and its SARA fractions

In situ combustion (ISC) plays a significant role in the exploitation of heavy crude oil. In this study, the thermal behaviors and kinetics of combustion of heavy crude oil and its saturates-aromatics-reins-asphaltenes (SARA) fractions were comparatively evaluated using thermogravimetry (TG) and differential scanning calorimeter (DSC) techniques. The results indicated that saturates and aromatics were vulnerable to severe mass loss at the low-temperature oxidation (LTO) stage; however, resins and asphaltenes encountered appreciable mass loss in the fuel deposition (FD) interval to form a great amount of coke, which consequently contributed to high-temperature oxidation (HTO) reactions. Saturates made an inconsequential thermal release to the HTO reactions. Aromatics showed apparent exothermic effect both at the LTO and HTO stages, which was consistent with crude oil. Compared with saturates and aromatics, resins and asphaltenes gave considerably higher heat release in the HTO region, especially asphaltenes. By comparing the DSC curve of heavy crude oil with fitting curve of SARA superposition based on their proportion in crude oil, apparent inhibiting (promoting) effect among SARA fractions at the LTO stage (FD and HTO stages) were detected in terms of heat release, which should be of much significance for using SARA fractions to model ISC process. The kinetic parameters determined by Ozawa–Flynn–Wall (OFW) method were almost identical to those obtained by distributed activation energy model (DAEM). The activation energies of crude oil fluctuated and varied in the range of 45–95 kJ/mol during combustion, disclosing its intricate combustion processes and multiple reaction mechanisms. Unlike other three fractions, the FD and HTO activation energies of asphaltenes descended consecutively with conversion degree, which is favorable for boosting the sustainability of combustion front.

Determination of the thermodynamic properties of the Li2CaThF8 in Li-Ca-Th-F system by the solid-state electrochemical cell method

In the present paper, we have reported the standard molar Gibbs energy of formation for Li2CaThF8(s) measured by solid electrolyte galvanic cell technique with CaF2 as solid electrolyte. The heat capacity, Cp, of the compound has been measured using the differential scanning calorimetric technique. Based on the experimentally obtained thermodynamic parameters, thermodynamic functions for Li2CaThF8(s) have been generated.

Polystyrene degraded and functionalized with acrylamide for removal of Pb(II) metal ions

The present study describes the synthesis of a new material prepared by low-temperature thermocatalytic degradation of polystyrene (PS) by using zeolite clinoptilonite as a degradation template and subsequent functionalization with acrylamide (AAm) for the removal of lead (Pb(II)) metal ions from aqueous solutions. Infrared spectroscopy (FTIR), field emission scanning electron microscopy, thermogravimetric analysis and differential scanning calorimeter techniques confirm the successful functionalization of PS oligomers, before applying this material as an alternative adsorbent. A preliminar absorption study using functionalized PS oligomers as an adsorbent indicates that material has a good potential to absorb heavy metal of Pb(II) from the aqueous solutions. Equilibrium data show a maximum adsorption capacity of 33.85 mg g−1 with a percentage removal of 90.94%, which fitted well with Freundlich model and kinetic data were best described by pseudo-second-order model. Desorption studies revealed that PS oligomers functionalized with acrylamide as monomer source can be recovered using 0.5 M EDTA as regenerating agent, with a maximum recovery of Pb(II) metal ions of 97.28%. These results reveal that PS oligomers functionalized with acrylamide could be recommended as a promising adsorbent for Pb(II) metal ions contained in aqueous systems.

Hydrothermal synthesis of Eu3+-doped Gd2O3 nanophosphors and its Judd-Ofelt analysis

A series of Gd2-xO3:x% Eu (x = 0 to 10 mol%) were synthesized by hydrothermal method. The structural, morphological and optical properties of as-synthesized samples were studied by X-ray diffraction, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), FT-IR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), UV/Vis spectroscopy and photoluminescence (PL) spectroscopy techniques. The effect of the doping concentration has been studied by experimental and theoretical methods. When the phosphors were exposed to UV radiation (250 nm), they exhibited a sharp red emission at 611 nm which corresponds to the hypersensitive 5D0→ 7F2 transition of Eu3+ ions. The Judd-Ofelt parameters (Ω2, Ω4 and Ω6) and other spectral parameters were calculated using Judd-Ofelt theory from emission spectra. The pristine phosphors are expected to have tremendous applications in the field of semiconductor devices, field emission displays and optical devices.

Cu(II), Zn(II), Cd(II) and Hg(II) Complexes of Pantroprazole (PPZH): Synthesis and Characterization

Several metal complexes of pantoprazole, [Cu(PPZ)(H2O)Cl], [Zn(PPZ)2], [Cd(PPZ)2].1.5H2O and [Hg(PPZ)(H2O)Cl] have been synthesized and characterized. Elemental analysis, IR, UV-Visible spectral analysis, magnetic measurement, thermogravimetric analysis, differential scanning calorimetric and cyclic voltammetric techniques were used for their characterization. The lipophilic weak base pantoprazole (PPZ) act as a potential bidentate ligand forming coordination complexes with divalent metal ions through anionic imidazolyl N- and O atom of sulfinyl >S=O group. All complexes possess tetrahedral geometry.
 Dhaka Univ. J. Sci. 66(2): 151-156, 2018 (July)

Growth, spectroscopic studies, and third order non-linear optical analysis of an organic dicarboxylic acid based single crystal: Urea Oxalic acid

A non-centro symmetric single crystal of Urea Oxalic acid (UOA) has been grown from aqueous solution by the process called slow evaporation technique. Single crystal X-ray diffraction (SXRD) evinces UOA corresponding to the triclinic crystal system with the space group P. The diverse functional groups existing in UOA are vividly discovered with Fourier transform infrared (FTIR) and FT-Raman spectrum analysis. Ultraviolet (Uv)-visible spectral analysis reveals that the crystal has the cut-off wavelength of 263 nm. The thermal stability of the grown crystal has been studied by thermo gravimetric analysis and differential scanning calorimetric technique. The Vicker's micro hardness test was also carried out employing one of the as-grown crystals are assessed. The dielectric behavior of the grown crystal was thoroughly analyzed for different temperatures. Fluorescence emission spectrum (PL) has been recorded and lifetime was also studied. The scanning electron microscope (SEM) technique was also carried out and determined the surface morphology topography of the UOA crystal. The theoretical study has been done by quantum mechanical calculations of DFT using Gaussian software package. The structural, vibrational and electronic properties of the title compound had been presented using the B3LYP method with 6-311++G (d, p) basis set. The linear polarizabilities (α) and the first order hyperpolarizability (β) values of the investigated molecule have been calculated. The HOMO-LUMO energies show that the chemical activity of the molecule and molecular electrostatic potential maps (MEPs) and NLO activity confirm to the superiority of the material. The third order nonlinear optical characteristics of UOA have been investigated using z-scan technique.

Thermodynamics and kinetics of hydrogen absorption–desorption of highly crystalline LaNi5

Lanthanum penta-nickel (LaNi5) has been considered as potential candidates for hydrogen storage application at room temperature (20 °C). The intermetallic could store more than 1.36 mass % hydrogen. Substantially, work has been done on the hydrogenation–dehydrogenation kinetics and thermodynamics of LaNi5. It has been reported that the hydrogen storage capacity reduced after single activation due to the deep trap of hydrogen. The kinetics and thermodynamics of trap hydrogen need to be quantified to understand the nature of trap and the required temperature to release the trapped hydrogen. In the current study, thermodynamics and kinetics of hydrogenation–dehydrogenation of high phase purity crystalline LaNi5 were investigated. Sievert’s apparatus was used to investigate the pressure composition-temperature measurement to find out the cyclic hydrogen storage capacity and the thermodynamic parameters. The thermodynamic data obtained were evaluated using high-pressure differential scanning calorimetric technique. The trap hydrogen and their desorption kinetics were studied using thermogravimetric–thermal analysis–mass spectrometric techniques.

Influence of Low Pressure Plasma Treatment on the Durability of Thermoplastic Composites LDPE-flax/coconut under Thermal and Humidity Conditions

The aim of this work is to study the influence of low pressure plasma (LPP) treatment on the durability of thermoplastic composites using flax and coconut fibers as reinforcement. Two different aging conditions were evaluated, high temperature (73 °C) and high temperature plus water immersion. In both cases five aging times (1, 2, 8, 30 and 60 days) were evaluated. Composite materials were prepared with treated and untreated flax and coconut fibers with 30 % of fiber content and a low density polyethylene (LDPE) matrix. Composites were manufactured using a rotor mixer and a hot plates press. The influence of the aging conditions on each type of fiber, flax or coconut, as well as the plasma treatment effect in all composite materials were studied by determining water absorption and mechanical properties. Mechanical properties were assessed by three point bending tests and the water uptake was determined by weight measurements. Thermal properties were also studied by Differential Scanning Calorimetric (DSC) technique. Finally, the liquids where the specimens were submerged in were evaluated by ultraviolet spectroscopy to analyse cellulose or lignin amounts dissolved. In all cases, durability was mainly affected by the humidity but not so much by high temperatures, obtaining better bending strength and Young’s modulus in the LPP treated materials, especially those with flax fiber reinforcement.

Comparative study of nisoldipine-loaded nanostructured lipid carriers and solid lipid nanoparticles for oral delivery: preparation, characterization, permeation and pharmacokinetic evaluation

Nisoldipine (ND) has low oral bioavailability (5%) due to first-pass metabolism. Previously, solid lipid nanoparticles (SLNs) of ND were reported. In this study, nanostructured lipid carriers (NLCs) of ND are developed to enhance the oral bioavailability. ND-NLCs were prepared using hot homogenization-ultrasonication method, using oleic acid and trimyristate as liquid lipid and solid lipid, respectively. Prepared NLCs are evaluated for an optimal system using measuring size, zeta potential, entrapment efficiency, in-vitro release and in-situ absorption studies. Further, in vivo pharmacokinetic (PK) studies of NLC were conducted in rats comparison with SLN and suspension as controls. Size, ZP and EE of optimized NLCs were found to be 110.4 ± 2.95 nm, –29.4 ± 2.05 mV and 97.07 ± 2.27%, respectively. Drug loaded into NLCs was converted to amorphous form revealed by differential scanning calorimeter (DSC) and X-ray diffractometry (XRD) technique and nearly spherical in shape by scanning electron microscopy (SEM) studies. Drug release and absorption of ND were prolonged from ND-NLCs and ND-SLNs. From the PK results, NLCs showed 2.46 and 1.09-folds improvement in oral bioavailability of ND compared with suspension and SLNs formulations, respectively. Taken together, the NLCs and SLNs are used as carriers for the enhancement of oral bioavailability of the ND.

New chalcone based liquid crystals with allylidene amino linking unit: Synthesis and characterization

In this study, the synthesis, structural characterization and mesomorphic properties of newly thirteen calamitic shaped compounds derived from allylidene amino chalcone and 4-n-alkoxy benzoyloxy benzoic acid. Comp.H1 to H3 exhibited nonliquid crystalline nature, while comp.H4 to comp.H18 displayed enantiotropical smectic C phase. Phase transition temperatures of present synthesised compounds were determined by optical polarising microscopy (POM), differential scanning calorimetric (DSC) and powder X-ray diffraction (PXRD) techniques. Thermal stabilities of smectic to isotropic phase are 150.0 °C and temperature range of mesophase is in decreasing order from comp.H3 to comp.H18 respectively. The presences of SmC phase are the type of broken fan and needle type in present synthesized series. It is also shown that presence of chalcone amino allylidene central linking group favors a calamitic liquid crystalline behaviour in molecules with lower member to higher member aliphatic side chain in alkoxy group (-OR).

High performance epoxy nanocomposite adhesive: Effect of nanofillers on adhesive strength, curing and degradation kinetics

In the current study, the synergistic effect of a multi-walled carbon nanotube (MWCNT) and a nanoclay (C30B) on the mechanical, morphological and thermal behaviour of an epoxy based adhesive was investigated. The adhesive strength was investigated by conducting lap shear tests and from the test results it was observed that, Ep/1.0 C30B adhesive possessed the highest adhesive strength among all the adhesive formulations investigated and showed a 52% enhancement as compared to the pristine epoxy. Fracture analysis of different adhesive systems was investigated using scanning electron microscopy (SEM). SEM micrographs revealed that nanomaterials with different shapes and dimensions provide distinct features on the fracture surfaces due to the different energy dissipation mechanisms which they promote. The morphological variations of the epoxy based nanocomposite adhesives were investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The curing kinetics of the different nanofiller reinforced epoxy adhesives were examined using a non-isothermal differential scanning calorimetric (DSC) technique. The activation energy (Ea) was calculated by applying Kissinger's method and found to be increased for the Ep/1.0 CNT/1.0 C30B adhesive system as compared to the pristine epoxy. This increment can be attributed to the physical impediment impacted by the nanomaterials on the curing reaction of the epoxy resin. The degradation kinetics of the adhesive systems were also studied using thermogravimetric analysis (TGA). The corresponding activation energies (E) of the adhesive systems obtained by Kissinger's model were found to increase with addition of nanofillers, thus indicating improved thermal stability.

Influence of CuO nanoparticle on palm oil based alkyd resin preparation and its antimicrobial activity

An alkyd resin has been synthesized from palm oil that reacted with glycerol and phthalic anhydride by alcoholysis-polyesterification process and co-catalyzed by CuO nanoparticle. The CuO nanoparticle was pre-prepared in the glycerol via sol gel method, which creates a new reaction condition for resin preparation. The resins were characterized by fourier transform infrared spectroscopy (FTIR), where a new ester linkage bond (C-O-C) was noticed for resin sample. The antimicrobial activity and the curing behaviour of the resin were determined by Kirby-Bauer and differential scanning calorimeter technique. It was found that, the addition of CuO speeded up the reaction rate and played antimicrobial role. Moreover, it shortens the reaction time of alcoholysis and polyesterification process.

Thermodynamic stability of SrThF6(cr) and BaThF6(cr)

In the present paper we report the standard molar Gibbs energy of formation of SrThF6 and BaThF6 measured by gas equilibration method employing transpiration technique. The chemical equilibrium between MThF6 (cr) (M = Sr, Ba) and moisture: MThF6(cr)+2H2O(g)=MF2(cr)+ThO2(cr)+4HF(g) has been employed to determine thermodynamic stability of these compounds. The equilibrium constant ‘Kp’ at different temperatures was calculated using partial pressure of HF(g) measured at a fixed vapour pressure of water p(H2O). The Gibbs energy of formation for SrThF6(cr) and BaThF6(cr) could be expressed as: ΔfG°m (SrThF6, cr)(±8 kJ mol−1) = −3288 + 0.3776 T and ΔfG°m (BaThF6, cr) (±7 kJ mol−1) = −3292 + 0.378T. The isobaric heat capacity of these compounds was measured employing differential scanning calorimetric technique. Based on the experimental results thermodynamic functions for SrThF6 and BaThF6 have been generated.

Crystallization kinetics of MgO–Y2O3 composite nanopowder synthesized via combustion sol–gel method

The aim of this study is to synthesize MgO–Y2O3 nanocomposite by combustion sol–gel method from sucrose as a combustion agent. The influence of the ratio of sucrose (Su) to the transition metals (TM) on the phase and particle size of the composite nanopowder was investigated using a combination of X-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy techniques. In order to prediction of phase growth, the kinetics of crystallization of MgO–Y2O3 nanocomposite was also studied in the isothermal conditions using a differential scanning calorimetric technique. Results show that increasing the concentration of sucrose reduced the particle size from 29.3 to 21.6 nm. The ratio of Su to the TM optimized on 4 value. The Avrami exponent was found to be about 3 indicating 3-dimensional growth. The activation energy of crystallization was also determined to be 34.9 ± 0.01 kJ mol−1. Finally, the TEM results confirmed the 3-dimensional growth of MgO–Y2O3 nanopowders.

Single Ion Conducting Blend Polymer Electrolytes Based on LiPAAOB and PPEGMA

Single-ion polymer electrolytes are expected to play an important role in the development of next-generation lithium batteries. The current work focuses on the designing of novel solid single-ion conducting inorganic polymer electrolytes based on lithium polyacrylic acid oxalate borate (LiPAAOB) and poly(ethyleneglycol) methacrylate (PEGMA). PEGMA is polymerized into PPEGMA via free radical polymerization and LiPAAOB is prepared from poly(acrylic acid), oxalic acid and boric acid. Blend polymer electrolytes were produced by mixing of LiPAAOB with PPEGMA at different weight fractions to enhance the single ion conductivity of the system. To exploit the flexible chemistry and increase segmental mobility of the blend electrolyte, the composition was changed up to 80% with respect to PPEGMA. FT-IR and differential scanning calorimeter technique verifies the interaction between the host and guest polymers. Thermogravimetry analysis verified that the thermal stability of the blends increased up to approximately 200 °C. Scanning electron microscopy images confirm the homogeneity of the blend electrolytes. Cyclic voltammetry studies showed that electrochemical stability electrochemical stability window is approximately 5 V versus Li/Li+. The effect of PPEGMA on to the Lithium ion conductivity was investigated using dielectric impedance analyzer. The maximum single ion conductivity was measured as 1.3 × 10−4 S/cm at 100 °C for the sample LiPAAOB-80PPEGMA. Clearly these results confirmed the positive effect to the increment in ionic conductivity of the blend electrolytes with the addition of PPEGMA.

Thermal stability of xylose reductase from Debaryomyces nepalensis NCYC 3413: deactivation kinetics and structural studies

Abstract Deactivation kinetics, as well as the operational stability of enzymes, is crucial in economic feasibility of industrial enzymatic processes. In this study, thermal inactivation profiles of Debaryomyces nepalensis NCYC 3413 xylose reductase (DnXR) were obtained at different temperatures. Thermodynamic parameters of the deactivation process were determined by measuring the residual activity of the enzyme. Structural characteristics of the enzyme were determined using circular dichroism, differential scanning calorimetric techniques. Enzyme retained 75–80% activity at 35 °C after incubation for 5 h. At higher temperatures, the residual activity reduced at a faster rate where only 10% of the initial activity was retained in 10 min at 50 °C. Values of ΔH* (-300.47 kJmole−1), ΔG* (−530.66 kJ mole−1) and ΔS* (714.51 × 10−3 kJ K−1 mole−1) indicated that thermal deactivation of DnXR is enthalpy driven. In the presence of cofactor NADPH, melting temperature of the enzyme increased by 2 °C with a decrease in rate of thermal deactivation. Substrate found not to have a positive effect on thermal stability. This is the first report providing information on the thermal deactivation kinetics, thermodynamic parameter estimation and the influence of cofactor on thermal stability of Debaryomyces nepalensis NCYC 3413 xylose reductase.