DTA Studies Research Articles

Hypoeutectic Silumin to Pressure Die Casting with Vanadium and Tungsten

AbstractThe basic aim of this study is to investigate the effect of vanadium and tungsten on the crystallization process, microstructure and mechanical properties of silumin grade EN-AC 46000. The research involved a derivative thermal analysis DTA of the crystallization process, the metallographic analysis as well as the mechanical properties. The metallographic analysis was carried out on pressure die castings and made in the DTA probe. Vanadium and tungsten were added simultaneously to silumin in amount of approximately 0.1; 0.2; 0.3 and 0.4%. The DTA studies have shown the similar shape of all crystallization curves. It has been shown the additives of vanadium and tungsten in pressure die cast silumin can significantly increase its tensile strength as an well as elongation.

Useful method to analyze data on overall transformation kinetics

We propose an easy and reliable method for analyzing data from DTA and DSC studies of crystallization at constant heating rate, q. It is demonstrated that important information can be obtained in log-log coordinates of plot of heating rate, logq, against peak temperature, logTp. The slope of the corresponding straight line is proportional to the dimensionless activation energy ℰ. It is demonstrated that there is a simple relation between the characteristic crystallization time τ, the heating rate q and the peak temperature Tp.

Effect of Cr and W on the Crystallization Process, the Microstructure and Properties of Hypoeutectic Silumin to Pressure Die Casting

Abstract This article presents the results of studies in the hypoeutectic silumin destined for pressure die casting with the simultaneous addition of chromium and tungsten. The study involved the derivative and thermal analysis of the crystallization process, metallographic analysis and mechanical properties testing. Silumin 226 grade was destined for studies. It is a typical silumin to pressure die casting. AlCr15 and AlW8 preliminary alloys were added to silumin. Its quantity allowed to obtain 0.1, 0.2, 0.3 and 0.4% of Cr and W in the tested alloy. Studies of the crystallization process as well as the microstructure of the silumin poured into DTA sampler allowed to state the presence of additional phase containing 0.2% or more Cr and W. It has not occurred in silumin without the addition of above mentioned elements. It is probably the intermetallic phase containing Cr and W. DTA studies have shown this phase crystallizes at a higher temperature range than α (Al) solid solution. In the microstructure of each pressure die casting containing Cr and W the new phases formed. Mechanical properties tests have shown Cr and W additives in silumin in an appropriate amount may increase its tensile strength Rm (about 11%), the yield strength Rp0.2 (about 21%) and to a small extent elongation A.

Investigation on synthesis, growth and characterization of Glycine oxalate: An organic nonlinear crystal for optical applications

A new semiorganic nonlinear optical material Glycine oxalate dihydrate (GOD) has been synthesized and crystals have been grown from its supersaturated solution by slow evaporation method using water as a solvent for the first time. Purity of the grown crystal can be increased by the method called recrystallization. Crystal structure and unit cell dimensions of GOD can be obtained using powder X-ray diffraction analysis. The functional groups of GOD and their modes of vibration were identified from Fourier transform infrared (FTIR) spectral analysis. Transparency of the grown crystal GOD was studied using Ultraviolet visible spectral analysis. Second harmonic generation efficiency was confirmed by Kurtz–Perry method. TGA and DTA studies were carried out to study about the thermal properties of the grown crystal.

Investigations on the growth and characterisation of an isomorphous ammonium tetroxalate dihydrate superacid crystal

Single crystals of ammonium tetroxalate dihydrate (ATOXAL) were grown by the slow evaporation solution growth technique. The crystal structure was confirmed by single crystal XRD analysis. The functional groups present were explored and ammonium ion reveals its group frequency at 1404cm−1 and 1489cm−1 respectively from the recorded FT-IR and FT-Raman spectra. Microhardness studies were carried out with the Vicker's microhardness tester. The TG, DTA and DSC studies divulged information about thermal behaviour. The HOPM studies supported the thermal anomalies in the crystal. The density was evaluated to be 1.639g/cc. The optical behaviour was examined with DRS, UV–vis, photoluminescence and photoconductivity studies. The optical band gap was assessed to be 3.963eV. Negative photoconductivity was exhibited. SEM micrographs showed the purity and crystalline nature of the grown crystals. Dielectric anomalies are seen in the variation of the dielectric constant with temperature suggesting the ferroelectric nature of the crystal.

Beneficial effects of microwave assisted heating versus conventional heating in synthesis of cyclodextrin based nanosponges

The effects of microwave heating versus conventional heating on particle-size distribution, morphology and crystallinity of cyclodextrin nanosponges have been investigated. FTIR-ATR, XRPD, DSC and DTA studies outlined the structural differences between the nanosponges prepared by different methods. The microwave-synthesized nanosponges exhibited higher degree of crystallinity and narrow size distribution. HR-TEM indicates that nanosponges obtained from microwave method are highly crystalline and faceted versus their conventionally-prepared counterparts. Microwave-synthesized nanosponges were measured with approximately twice the loading capacity towards a model drug than similar-sized conventionally prepared particles. Extensive structural characterisation studies revealed the distinct and preferential effects of the microwave heating method.

Synthesis and characterization of nano hexagonal boron nitride powder and evaluating the influence on aluminium alloy matrix

An attempt is made to synthesize the nano h-BN powders by high energy ball milling and also aluminium reinforced h-BN composite by powder processing route. The impact of ball milling time on microstructure and particle size reduction of h-BN powder was investigated by FESEM, FTIR, XRD, UV-vis diffuse reflectance spectroscopy and particle size analyser.It was indicated that high energy ball milling is effective up to 10 hours in reducing the particles size a further increase in time is resulting in agglomeration. Microhardness of the composite increases in proportion to increases in weight percentage of reinforcement, h-BN exhibited a poor sinterability without any accelerating agentand with tin addition up to 0.5% low melting point metal.TGA and DTA study shows that there is reduction in melting point from 641°C to 638 °C with addition of 2% weight fraction of h-BN.Selection and Peer-review under responsibility of [Conference Committee Members of Recent Advances In Nano Science and Technology 2015.].

The B-Li System. Calorimetric and Theoretical Studies / Układ B-Li. Badania Kalorymetryczne I Teoretyczne

The standard enthalpy of formation of the B78Li22 alloy was measured with the use of the water reaction calorimetric method at 25 °C (298 K). An X-ray diffraction study of the prepared sample was conducted. The obtained diffraction pattern was different from the patterns for the B3Li and B14Li3 phases. The standard enthalpy of formation obtained for the B78Li22 alloy was -39.0 ± 0.7 kJ/mole of atoms. This value corresponds well with the formation enthalpies of the phases from the boron-lithium system. Theoretical calculations of the standard enthalpy of formation were conducted for the B78Li22 alloy and the phases from B-Li system, which were investigated earlier. A discussion of the deviations observed between both sets of data (experimental and calculated) was performed. Additionally, DTA studies were performed for 14 alloys of the concentrations from 40 to 100 at. % of Li.

Effect of post-growth annealing on the structural, optical and electrical properties of V2O5 nanorods and its fabrication, characterization of V2O5/p-Si junction diode

We report the synthesis of V2O5 nanorods by utilizing simple wet chemical strategy with ammonia meta vanadate (NH4VO3) and polyethylene glycol (PEG) exploited as precursor and surfactant agent, respectively. The effect of post-annealing on structural, optical and electrical properties of V2O5 nanorods was characterized by XRD, HRSEM-EDX, TEM, FT-IR, UV (DRS), PL, TG–DTA and DC conductivity studies. The X-ray diffraction analysis revealed that the prepared sample annealed at 150°C for 5h which exhibited anorthic phase of V5O9 and annealed at 300–600°C showed the anorthic phase change to orthorhombic phase of V2O5 due to the post-annealing effect. The surface morphology results indicated that increasing temperature caused a change from microrods to a nanorods shape in the morphology of V2O5. FT-IR spectrum confirmed that the presence of V2O5 functional groups and the formation of V–O bond. The optical band gap was found in the range 2.5–2.48eV and observed to decreases with various annealed temperature. The DC electrical conductivity was studied as a function of temperature which indicated the semiconducting nature. Further, the potential of V2O5 nanostructures were grown on the p-Si substrate using the nebulizer spray technique. The junction properties of the V2O5/p-Si diode were evaluated by measuring current (I)–voltage (V) and AC characteristics.

Dielectric Investigation of Ferroelectric Glass-Ceramics Containing Sodium Niobate and Barium Niobium Silicate Crystals

Glass-ceramics in the BaO-Na2O-Nb2O5-SiO2 system were fabricated by a controlled-crystallization process. During the process, different heat treatment conditions were applied. Phase formation, micro-structural arrangement, and dielectric properties of the glass-ceramics were investigated by XRD, SEM, and Dielectric spectroscopy techniques. The results of phase identification revealed that NaNbO3 (NN) with perovskite crystals formed at a treatment temperature close to the crystallization peak (Tcr) which was suggested by DTA study of the parent glass. At a higher treatment temperature, Ba3Nb6Si4O26 (BNS) with layered structure was found as the additional crystalline phase. Both crystalline phases distributed randomly throughout the whole bulk glass-ceramic specimens with no observation of phase clustering. The plots of dielectric constant versus temperature revealed the dielectric response of the ferroelectric NaNbO3 crystals. With the presence of Ba3Nb6Si4O26 phase, there was no pronounced effect on the phase transition of the NaNbO3 but it enhanced the dielectric constant at Tmax. The dielectric spectroscopic investigation revealed that dipolar polarization is responsible for overall dielectric contribution.

Montreal Cognitive Assessment for the diagnosis of Alzheimer's disease and other dementias.

Dementia is a progressive syndrome of global cognitive impairment with significant health and social care costs. Global prevalence is projected to increase, particularly in resource-limited settings. Recent policy changes in Western countries to increase detection mandates a careful examination of the diagnostic accuracy of neuropsychological tests for dementia. To determine the diagnostic accuracy of the Montreal Cognitive Assessment (MoCA) at various thresholds for dementia and its subtypes. We searched MEDLINE, EMBASE, BIOSIS Previews, Science Citation Index, PsycINFO and LILACS databases to August 2012. In addition, we searched specialised sources containing diagnostic studies and reviews, including MEDION (Meta-analyses van Diagnostisch Onderzoek), DARE (Database of Abstracts of Reviews of Effects), HTA (Health Technology Assessment Database), ARIF (Aggressive Research Intelligence Facility) and C-EBLM (International Federation of Clinical Chemistry and Laboratory Medicine Committee for Evidence-based Laboratory Medicine) databases. We also searched ALOIS (Cochrane Dementia and Cognitive Improvement Group specialized register of diagnostic and intervention studies). We identified further relevant studies from the PubMed 'related articles' feature and by tracking key studies in Science Citation Index and Scopus. We also searched for relevant grey literature from the Web of Science Core Collection, including Science Citation Index and Conference Proceedings Citation Index (Thomson Reuters Web of Science), PhD theses and contacted researchers with potential relevant data. Cross-sectional designs where all participants were recruited from the same sample were sought; case-control studies were excluded due to high chance of bias. We searched for studies from memory clinics, hospital clinics, primary care and community populations. We excluded studies of early onset dementia, dementia from a secondary cause, or studies where participants were selected on the basis of a specific disease type such as Parkinson's disease or specific settings such as nursing homes. We extracted dementia study prevalence and dichotomised test positive/test negative results with thresholds used to diagnose dementia. This allowed calculation of sensitivity and specificity if not already reported in the study. Study authors were contacted where there was insufficient information to complete the 2x2 tables. We performed quality assessment according to the QUADAS-2 criteria.Methodological variation in selected studies precluded quantitative meta-analysis, therefore results from individual studies were presented with a narrative synthesis. Seven studies were selected: three in memory clinics, two in hospital clinics, none in primary care and two in population-derived samples. There were 9422 participants in total, but most of studies recruited only small samples, with only one having more than 350 participants. The prevalence of dementia was 22% to 54% in the clinic-based studies, and 5% to 10% in population samples. In the four studies that used the recommended threshold score of 26 or over indicating normal cognition, the MoCA had high sensitivity of 0.94 or more but low specificity of 0.60 or less. The overall quality and quantity of information is insufficient to make recommendations on the clinical utility of MoCA for detecting dementia in different settings. Further studies that do not recruit participants based on diagnoses already present (case-control design) but apply diagnostic tests and reference standards prospectively are required. Methodological clarity could be improved in subsequent DTA studies of MoCA by reporting findings using recommended guidelines (e.g. STARDdem). Thresholds lower than 26 are likely to be more useful for optimal diagnostic accuracy of MoCA in dementia, but this requires confirmation in further studies.

Study of anneal hardening in cold worked Cu–Au alloy

An experimental study was carried out on cold worked Cu-12.7 wt.%Au alloy and pure copper, in order to compare the properties change during thermo-mechanical treatment. Hardness, microhardness, and electrical conductivity were studied as a function of annealing temperature and annealing time with the purpose of investigating the intensity of anneal hardening effect in cold worked Cu-12.7 wt.%Au alloy. Isochronal (up to 350 °C) and isothermal (at 250 °C for 100 h) annealing of cold worked alloy caused a two-stage increase in all of the measured properties. The mechanism responsible for this increase was analyzed using DTA, XRD, and TEM studies. The four stages observed in DTA heating curve were discussed in connection with the occurring processes. The reduction in the lattice parameter of cold worked Cu-12.7 wt.%Au alloy during annealing at 260 °C caused by the solute clustering, was observed. TEM studies did not show any presence of precipitates, other than disk-shaped areas with a higher degree of ordering. The achievement of high mechanical properties and high electrical conductivity in cold worked Cu-12.7 wt.%Au alloy after low temperature annealing was ascribed to the comparative effects of short-range ordering and solute segregation to lattice defects.

Phase transition and structure of (C3N2H5)2SbF5 single crystal

New crystal of the formula (C3N2H5)2SbF5 was obtained and characterized with DSC, DTA, TGA, structural and dielectric studies. DSC and dielectric studies revealed a structural phase transition of the first order at 216K on cooling and 220K on heating. The entropy of the transition ΔS equal to 11.5J/mol·K gives evidence that the phase transition is order-disorder type. X-ray studies showed that transition undergoes from orthorhombic phase I with a space group of Pmmn to monoclinic phase II with a space group P21/m. The phase transition is proposed to be ferroelastic type. The molecular mechanism of the phase transition is related to ordering of imidazolium cations in phase II that are disordered in phase I.

Metal adsorption by agricultural biosorbents: Adsorption isotherm, kinetic and biosorbents chemical structures

Biosorption of Cu(II), Co(II) and Fe(III) ions from aqueous solutions by rice husk, palm leaf and water hyacinth was investigated as a function of initial pH, initial heavy metal ions concentration and treatment time. The adsorption process was examined by two adsorption isotherms: Langmuir and Freundlich isotherms. The experimental data of biosorption process were analyzed using pseudo-first order, pseudo-second order kinetic models. The equilibrium biosorption isotherms showed that the three studied biosorbents possess high affinity and sorption capacity for Cu(II), Co(II) and Fe(III) ions. Rice husk showed more efficiency than palm leaf and water hyacinth. Adsorption of Cu(II) and Co(II) was more efficient in alkaline medium (pH 9) than neutral medium due to the high solubility of metal ion complexes. The metal removal efficiency of each biosorbent was correlated to its chemical structure. DTA studies showed formation of metal complex between the biosorbents and the metal ions. The obtained results showed that the tested biosorbents are efficient and alternate low-cost biosorbent for removal of heavy metal ions from aqueous media.

Comparison of physicochemical and electrochemical characterization of PVC incorporated ZT and ZM composite membranes and their applicability on TMS theoretical equation

PVC incorporated ZT/ZM composite materials have been synthesized via qualitative sol–gel method of material synthesis. Both the composite materials have the combination of inorganic ion-exchanger of different metal salt as well as same organic polymers, which is used to design a new class of organic–inorganic composite ion exchange membrane with much better chemical and mechanical properties, good ion-exchange capacity, higher thermal stability, reproducibility, selectivity etc. The physicochemical, electrochemical, mechanical and thermal properties of both the membranes were characterized by SEM, XRD, FTIR and simultaneous TGA–DTA studies were carried out to understand the ion exchange behavior of materials. The above analysis demonstrated the functional groups, material nature, thermal stability, surface structure, porosity, elemental percentages, ion transportation etc. The electrochemical properties have been studied by TMS theoretical approach which easily determined the important parameters of membranes like transport number, mobility ratio, charge density, charge effectiveness etc. The observed ionic potential and graphical fixed-charge density of both the membranes follows KCl < NaCl < LiCl and KCl > NaCl > LiCl order respectively.

Optimization of methylene blue using Ca2+ and Zn2+ bio-polymer hydrogel beads: A comparative study

Recently noted that the methylene blue cause severe central nervous system toxicity. It is essential to optimize the methylene blue from aqueous environment. In this study, a comparison of an optimization of methylene blue was investigated by using modified Ca2+ and Zn2+ bio-polymer hydrogel beads. A batch mode study was conducted using various parameters like time, dye concentration, bio-polymer dose, pH and process temperature. The isotherms, kinetics, diffusion and thermodynamic studies were performed for feasibility of the optimization process. Freundlich and Langmuir isotherm equations were used for the prediction of isotherm parameters and correlated with dimensionless separation factor (RL). Pseudo-first order and pseudo-second order Lagegren's kinetic equations were used for the correlation of kinetic parameters. Intraparticle diffusion model was employed for diffusion of the optimization process. The Fourier Transform Infrared Spectroscopy (FTIR) shows different absorbent peaks of Ca2+ and Zn2+ beads and the morphology of the bio-polymer material analyzed with Scanning Electron Microscope (SEM). The TG & DTA studies show that good thermal stability with less humidity without production of any non-degraded products.

Structural, optical, thermal and mechanical properties of Urea tartaric acid single crystals

Urea tartaric acid (UT) an organic nonlinear optical (NLO) material was synthesized from aqueous solution and the crystals were grown by the slow evaporation technique. The single crystal X-ray diffraction (XRD) analysis revealed that the UT crystal belongs to the orthorhombic system. The functional groups of UT have been identified by the Fourier transform infrared spectral studies. The optical transparent window in the visible and near the IR regions was investigated. The transmittance of UT has been used to calculate the refractive index (n) as a function of the wavelength. The nonlinear optical property of the grown crystal has been confirmed by the Kurtz powder second harmonic generation test. The birefringence of the crystal was determined using a tungsten halogen lamp source. The laser induced surface damage threshold for the grown crystal was measured using the Nd:YAG laser. The anisotropic in mechanical property of the grown crystals was studied using Vicker’s microhardness tester at different planes. The etch pit density of UT crystals was investigated. The thermal behavior of UT was investigated using the TG–DTA and DSC studies.

Studies on the growth, spectral, structural, electrical, optical and mechanical properties of Uronium 3-carboxy-4-hydroxybenzenesulfonate single crystal for third-order nonlinear optical applications

Organic Uronium 3-carboxy-4-hydroxybenzenesulfonate (UCHBS) nonlinear optical single crystal was grown by solution growth technique. The solubility and nucleation studies were performed for UCHBS at different temperatures 30, 35, 40, 45, 50 and 55°C. The crystal structure of UCHBS was elucidated from single crystal X-ray diffraction study. High resolution X-ray diffraction technique was employed to study the perfection and internal defects of UCHBS crystal. Infrared and Raman spectra were recorded to analyze the vibrational behavior of chemical bonds and its functional groups. The physico-chemical changes, stability and decomposition stages of the UCHBS compound were established by TG–DTA studies. The dielectric phenomenon of UCHBS crystal was studied at different temperatures with respect to frequency. Linear optical properties of transmittance, cut-off wavelength, band gap of UCHBS were found from UV–visible spectral studies. Third-order nonlinear optical susceptibility, nonlinear refractive index, nonlinear optical absorption coefficient values were measured by Z-scan technique. The mechanical properties of UCHBS crystal was studied by using Vicker’s microhardness test. The growth features of UCHBS crystal were analyzed from etching studies.

DTA study of the crystallization of Li2O–Nb2O5–SiO2–TiO2 glass

In this study, the crystallization of 30Li2O·15Nb2O5·50SiO2·5TiO2 (mol%) glass was examined. The parent glass was prepared by the standard melt quenching method, and the investigations were performed under non-isothermal and isothermal conditions using the DTA, XRD, SEM and EDS methods. The results revealed primary crystallization of this glass and the dendritic morphology of crystal growth. Three crystalline phases were formed in the glass matrix during crystallization, whereby LiNbO3 was formed as the primary phase, followed by Li2Si2O5 and SiO2 as the secondary. The surface and volume mechanisms of crystallization occur. The condition that both the mechanisms were dominant was determined. In the case of volume crystallization, the characteristics of the nucleation process were examined. The kinetic parameters of crystallization under different mechanisms of crystallization were determined.

Investigations on effects of the incorporation of various ionic liquids on PVA based hybrid membranes for proton exchange membrane fuel cells

PVA (Polyvinylalcohol) based hybrid membranes were prepared by incorporating inorganic fillers and ionic liquids (ILs) like 1–butyl–3–methylimidazolium Bis (trifluoromethanesulfonyl)imide (BMITFSI) and 1–ethyl–3–methylimidazolium tetrafluoroborate (EMI–BF4) using sol–gel method. Hybrid composite membranes were investigated with respect to its structural and thermal properties, water uptake capability and proton conductivity. TG–DTA studies confirmed the thermal stability of membranes and both ILs based membranes are stable up to 370 °C. As compared between two ILs, EMI–BF4 contained membranes showed better thermal stability and a complete degradation of main chain polymer backbone is occurred at about 640 °C. Thus, the thermal stability of the membranes was importantly enhanced by the presence of both EMI–BF4 and SiO2. From the experimental data, the conductivity of PVA based hybrid membranes depends on the ILs and its concentration. Significantly, the maximum conductivity of PVA/PMA/SiO2/BMITFSI and PVA/PMA/SiO2/EMI–BF4 hybrid membranes at 60 °C were 0.83 × 10−3 S/cm and 0.58 × 10−3 S/cm with constant relative humidity of 50%, respectively. It was found that, the proton conductivity essentially reduced with an increasing ILs fraction accompanied with the increase in cross–linking density, which impedes the proton conductivity due to the enhanced compact nature of membranes.