Derivative Differential Thermal Analysis Research Articles

CA Modeling of Microsegregation and Growth of Equiaxed Dendrites in the Binary Al-Mg Alloy.

A two-dimensional model based on the Cellular Automaton (CA) technique for simulating free dendritic growth in the binary Al + 5 wt.% alloy was presented. In the model, the local increment of the solid fraction was calculated using a methodology that takes into account changes in the concentration of the liquid and solid phase component in the interface cells during the solidification transition. The procedure of discarding the alloy component to the cells in the immediate vicinity was used to describe the initial, unstable dendrite growth phase under transient diffusion conditions. Numerical simulations of solidification were performed for a single dendrite using cooling rates of 5 K/s, 25 K/s and 45 K/s and for many crystals assuming the boundary condition of the third kind (Newton). The formation and growth of primary and secondary branches as well as the development of component microsegregation in the liquid and solid phase during solidification of the investigated alloy were analysed. It was found that with an increase in the cooling rate, the dendrite morphology changes, its cross-section and the distance between the secondary arms decrease, while the degree of component microsegregation and temperature recalescence in the initial stage of solidification increase. In order to determine the potential of the numerical model, the simulation results were compared with the predictions of the Lipton-Glicksman-Kurz (LGK) analytical model and the experimental solidification tests. It was demonstrated that the variability of the dendrite tip diameter and the growth rate determined in the Cellular Automaton (CA) model are similar to the values obtained in the LGK model. As part of the solidification tests carried out using the Derivative Differential Thermal Analysis (DDTA) method, a good fit of the CA model was established in terms of the shape of the solidification curves as well as the location of the characteristic phase transition temperatures and transformation time. Comparative tests of the real structure of the Al + 5 wt.% Mg alloy with the simulated structure were also carried out, and the compliance of the Secondary Dendrite Arm Spacing (SDAS) parameter and magnesium concentration profiles on the cross-section of the secondary dendrites arms was assessed.

Investigation of Methylammonium Tin Strontium Bromide Perovskite Systems

The properties of methylammonium-tin-strontium bromide systems (CH3NH3Sn1-xSrxBr3, 0.0 ≤ x ≤ 0.1) were investigated. The X-ray diffraction analysis (XRD) revealed the presence of the untilted cubic Pm-3m perovskite and orthorhombic SnBr2 as major crystalline phases. The morphological analysis confirmed the XRD data by detecting the formation of polyhedral shaped crystallites attributed to MASnBr3 perovskite and elongated crystallites related to SnBr2 phase. Derivative differential thermal analysis (DDTA) and derivative thermogravimetric analysis (DTG) revealed a thermal stability of MASnBr3 phase till T = 250°C and showed the presence of more thermal events related to a multistep decomposition process. The addition of Sr-ions retained the cubic crystalline structure of the perovskite and enhanced its thermal stability at T = 150°C by reducing the weight loss rates. The optical spectra displayed values of absorption edges between 624 nm and 636 nm. The Tauc plots revealed a direct semiconducting behavior with band energy gaps at ∼2.02–2.03 eV. The emission photoluminescence (PL) spectra, measured at room temperature and excitation wavelength λexc = 380 nm as well as the excitation photoluminescence (PL) spectra, measured at room temperature and emission wavelength λem = 520 nm showed a dramatic increase of the intensity by adding the Sr-ions reaching a maximum for x = 0.025.

Thermal and kinetic parameters of 30Li2O–55B2O3–5ZnO–xTiO2–(10−x)V2O5 (0 ≤ x ≤ 10) glasses

In the present investigation, the effects of titanium and vanadium concentration on the thermal properties have been studied for 30Li2O–55B2O3–5ZnO–xTiO2–(10−x)V2O5 (0 ≤ x ≤ 10) glasses. To understand the crystallization mechanics, activation energy has been calculated using two different approaches, i.e., Kissinger model and Augis and Bennett model. Using the derivative differential thermal analysis, the inflection point temperature (Tf) and crystallization constants ky(T) and kf(T), for different heating rates, have also been obtained for all the glasses. Furthermore, kinetic parameters such as fluctuation free volume (fg) and change in bulk thermal expansion coefficient (αf) have been calculated for all the glass samples. The replacement of V2O5 by TiO2 induces phase separation in glasses.

Evaluation of crystallization kinetics of glasses by non-isothermal analysis

Based on Johnson-Mehl-Avrami transition equation, this paper proposes a new non-isothermal method for evaluating the crystallization kinetics of glasses. An equation relating the kinetic parameters of the crystallization activation energy, E, and the frequency factor, v, to the inflection-point temperature, Tf, and the heating rate, β, of differential thermal analysis (DTA) experiment is established. The inflection-point temperature, Tf, can be easily determined from the derivative differential thermal analysis (DDTA) curves. The validity of the proposed method is ascertained by applying it to Li2O·2SiO2 glass. The acquired values of the crystallization kinetic parameters by this method are excellent agreement with the isothermal analysis results. In contrast, the traditional non-isothermal methods give much higher values.

Determining crystallization kinetic parameters of Li 2O–Al 2O 3–SiO 2 glass from derivative differential thermal analysis curves

The kinetic parameters such as crystallization activation energy, E, and the frequency factor, ν, of Li 2O–Al 2O 3–SiO 2 glass were determined by a new non-isothermal method. The method is described by the equation ln T f 2/β = E/RT f + ln(E/R)− ln ν , where β is the heating rate and T f is the inflection-point temperature of differential thermal analysis (DTA). The value of T f is determined as the maximum peak temperature on derivative differential thermal analysis (DDTA) curves. Values of E and ν of Li 2O–Al 2O 3–SiO 2 glass were also determined by two existing non-isothermal methods, namely the Kissinger plot and the Ozawa plot, and compared with those determined by isothermal method. Values of E and ν determined by the proposed equation were 332 kJ/mol and 1.4×10 13 s −1, respectively. They are excellent agreement with the isothermal analysis results, 336 kJ/mol and 1.8×10 13 s −1, respectively. In contrast, both the Kissinger equation and the Ozawa equation give much higher values of E and ν.

Thermal stability of the amorphous system Ge20As14(SexS1−x)52I14

Results of thermal investigations of the amorphous five-component chalcogenide system Ge20As14(SexS1−x)52I14 are presented. Differential thermal analysis (DTA), derivative differential thermal analysis (DDTA), and dilatometry were employed to determine the temperatures of softening and partial crystallization of the samples. Thermal treatment of the samples at 1000°C and recording of the corresponding thermogravimetric (TG) and derivative thermogravimetric (DTG) curves allowed an elucidation of the full mechanism of their decomposition, which proceeds via seven characteristic phase transitions.

Effect of the size factor and alloying on oxidation of aluminum powders

The effect of particle size and alloying with rare-earth elements on oxidation of aluminum-based powders was studied by methods of derivative differential thermal analysis of the change in the specific surface and x-ray diffraction analysis. It is shown that the character of oxidation is determined by processes occurring in the barrier layer of interaction products on the particle surface.

The use of the derivative differential thermal analysis curve to compute the kinetic parameters of a reaction

A method based on the use of the two temperatures of the inflection determined on a single derivative differential thermal analysis (DDTA) curve and of the temperature of the extremum determined on the differential thermal analysis (DTA) curve is proposed for computing the activation energy and the order of reaction of a chemical process. The obtained formulae do not contain the heating rate. If the conversion degree corresponding to the three temperatures required by the formulae are known, the third kinetic parameter, A, may be also computed. The formulae are fitted to the reaction order model.

Glass transition temperature and ionic conductivity in Ag2O-Ga2O3-P2O5 glasses

with y = 0.0, 0.1, 0.2, 0.3, 0.4 The glasses were obtained by melting pure reagents in a platinum crucible in an electric oven. The melts were quenched by casting them between two brass plates. Glass transition temperatures were detected by differential thermal analysis (DTA) and derivative differential thermal analysis (DDTA), the measurements being made in air at a scan rate of 10°Cmin -1 on powdered (-32 + 42 mesh) glass samples. A

Thermal decomposition kinetics of solids from DDTA curves

It is shown that the activation energy for solid thermal decompositions which follow a first order kinetic equation can be determined in a very simple manner from a single derivative differential thermal analysis (DDTA) curve. The experimental results are in good agreement with those obtained by other workers.

Activation energy for the crystallization of glass from DDTA curves

A simple method, based on the measurements of two peak temperatures on a single derivative differential thermal analysis (DDTA) curve for determining the activation energy for bulk or surface crystallization in glasses is described. The devitrification of Li2O-2SiO2 glass has been investigated; the experimental results agree well with those obtained by alternative techniques and with the activation energy of viscous flow in the crystallization-range temperatures.

Simple Method for Derivative Differential Thermal Analysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSimple Method for Derivative Differential Thermal AnalysisE. S. Freeman and David. EdeimanCite this: Anal. Chem. 1959, 31, 4, 624–625Publication Date (Print):April 1, 1959Publication History Published online1 May 2002Published inissue 1 April 1959https://doi.org/10.1021/ac50164a055RIGHTS & PERMISSIONSArticle Views253Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (263 KB) Get e-Alerts Get e-Alerts