Kinetic Crystallization

Cintica de cristalizacin por Anlisis TrmicoAnlisis TrmicoTodos aquellos mtodos de medida basados en el cambio, con la temperatura (o en funcin del tiempo a temperatura constante), de una propiedad fsica o mecnica de un material, mientras se le somete a un programa de temperaturas controlado.Conjunto de tcnicas mediante las cuales el cambio de una propiedad fsica o qumica de un material es medida en funcin del tiempo controlando la temperaturaTcnicas de anlisisTcnicaPropiedad medidaDetermine:Method:Termogravimetra (TG)MasaKinetic parameters (of the process)

Coats and RedfemMadhysudanan et al.Tang et al.Wajun et al.Anlisis Trmico Diferencial (DTA)TemperaturaDominant crystallization mechanism (in glass)AvramiCalorimetra diferencial de barrido (DSC)EntalpaThe kind of nucleation (homogeneous or heterogeneous), and the growth geometry (one, two or three dimensional growth)KissingerOzawaTakhorAugis and BernetGao and WangApproximation FreeTermooptometraPropiedad pticaAnlisis ElectrotrmicoConductividad ElctricaOtros---Termogravimetra (TG, DTG)Anlisis Termogravimtrico Registro, de manera continua, de la masa de una muestra (en atmsfera controlada), o bien en funcin de la temperatura, o bien en funcin del tiempo a T = cte.Anlisis Termogravimtrico diferencial Medida del gradiente en la variacin de masa con T t (T = cte).Termograma Representacin de la masa o porcentaje de cambio en funcin de T t.Termogravimetra (TG, DTG)Termograma Tpico:a) Curva primaria (TGA); b) curva derivada (DTGA)

Sistema de gas de purga:Gases de purga (N2, Ar, O2: depende del anlisis)

Termogravimetra (TG, DTG)Aplicaciones:Causas del cambio de peso:Reaccin de descomposicinReaccin de oxidacinVaporizacinSublimacinDesorcinAplicaciones del anlisis termogravimtrico:Control de calidad. Efecto de aditivosEstabilidad trmica en atmsfera inerteOxidacin en aire o atmsfera rica en oxgenoDegradacin trmica de polmerosEstudios de cintica de degradacin y anlisis de los productosIdentificacin de materialesTermogravimetra (TG, DTG)Termograma de descomposicin del CaC2O4 H2O a 5 C/min

Anlisis cuantitativo de una mezcla de iones Ca, Sr, Ba, precipitados como oxalatos monohidratados

Termogravimetra (TGA, DTGA)YearTitle / Author / SourceAbstract1992THE KINETICS AND MECHANISM OF WATER EVOLUTION FROM MOLTEN DL LITHIUM POTASSIUM TARTRATE MONOHYDRATESreelekha D. Bhattamisra, Genevieve M. Laverty, Nikolai A. Baranov, Vladimir B. Okhotnikov and Andrew K. GalweyPublished 15 December 1992 doi:10.1098/rsta.1992.0112Phil. Trans. R. Soc. Lond. A 15 December 1992 vol. 341 no. 1662 479-498A kinetic and microscopic investigation of the thermal dehydration of dl lithium potassium tartrate monohydrate is reported and the reaction mechanism discussed. This work forms part of a more comprehensive study concerned with the influence of reactant structure on the reactivity and the mechanism of chemical change. The other hydrated reactants with which this salt will be compared contain the d and meso forms of the tartrate anion and crystallize with different structures. dl lithium potassium tartrate monohydrate lost the single molecule of water of crystallization in one predominantly deceleratory process that was studied between 350-460 K. Reaction was accompanied by melting to yield a residual glassy anhydrous product that was amorphous to X-ray diffraction. An initial, relatively rapid release of water (6%) was followed by a deceleratory process that led to a zero-order reaction (that, in crystals, extended between 18% and 80%) before completion by an approximately first-order stage. Dehydrations of crushed powder reactant samples differed from single crystals in being relatively more rapid (an eight-fold increase); the deceleratory process was long and the zero-order process shorter (50-85%). The activation energy for dehydrations of crystal and of powder was 330 $\pm $ 30 kJ mol$^{-1}$. This pattern of kinetic behaviour was not in accordance with expectation for a homogeneous reaction, the rate was not directly related to reactant concentration terms. Alternative analyses of the obedience of data to rate expressions applicable to solid state reactions were equally unsuccessful. Our mechanistic interpretation of the rate data, therefore, considered a priori the factors expected to participate in the control of water evolution from the melt. It is concluded that the vitreous or molten phase is not homogeneous and, therefore, behaviour is different from reactions in an isotropic fluid or in a solid. Two models are proposed to explain our observations. In the two phase equilibrium mechanism it is assumed that the reactant particles are composed of two phases, zones of hydrate are embedded in dehydrated material that retains a constant but small proportion of water. (These phases participate in an equilibrium analogous to that of liquid/vapour.) The surface boundary layer model envisages the initial development of a peripheral barrier zone through which the constant rate of water diffusion is rate controlling. This class of reaction, proceeding in a fluid but the absence of added solvent, has received relatively little attention. The present discussion is intended to identify the characteristic behaviour and draw attention to the necessity to consider such mechanisms in discussions of reactions of solids where there is the possibility of melt participation.1994THERMAL STABILITY OF LIXCOO2, LIXNIO2 AND -MNO2 AND CONSEQUENCES FOR THE SAFETY OF LI-ION CELLSJ DAHN, E FULLER, M OBROVAC, U VONSACKENJournal: Solid State Ionics , vol. 69, no. 3-4, pp. 265-270, 1994DOI: 10.1016/0167-2738(94)90415-4LiCoO2, LiNiO2 and LiMn2O4 are all stable in air to high temperature. By contrast, LixCoO2, LixNiO2 and LixMn2O4 (x E-1 for stressed glass and E-3 > E-2 approximate to E-1 for stress-free glass, where E-1, E-2 and E-3 were associated to the gamma-TeO2, alpha-TeO2 and alpha-Li2Te2O5 phases, respectively. The observed distinct (n) over bar (1) < (2) < (3) in both glasses is an indicative that nucleation and growth takes place by more than one mechanism in the early stages of the crystallization.2011Thermal analyses to assess diffusion kinetics in the nano-sized interspaces between the growing crystals of a glass ceramicsAuthor(s): Fotheringham, Ulrich; Wurth, Roman; Ruessel, ChristianSource: THERMOCHIMICA ACTA Volume: 522 Issue: 1-2 Special Issue: SI Pages: 144-150 DOI: 10.1016/j.tca.2011.03.023 Published: AUG 10 2011According to a hypothesis by Russel and coworkers, the absence of Ostwald ripening during isothermal crystallization of lithium aluminosilicate (LAS) and other glass ceramics indicates the existence of a kinetic hindrance of atomic reorganization in the interstitial spaces between the crystals.Methods of Thermal Analysis (Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA)) which are sensitive to the local atomic rearrangements in the interstitial spaces (including viscous flow) are applied to find support for the idea of kinetic hindrance and the formation of a core shell structure acting as diffusion barrier.Both the DSC-measured calorimetric glass transition and the DMA-measured viscoelastic properties indicate an increase in the time constants of atomic rearrangements and diffusion by at least two orders of magnitude during ceramization. This fits to the above idea.2011Title: Dynamic processes in a silicate liquid from above melting to below the glass transitionAuthor(s): Ferreira Nascimento, Marcio Luis; Fokin, Vladimir Mihailovich; Zanotto, Edgar Dutra; et al.Source: JOURNAL OF CHEMICAL PHYSICS Volume: 135 Issue: 19 Article Number: 194703 DOI: 10.1063/1.3656696 Published: NOV 21 2011We collect and critically analyze extensive literature data, including our own, on three important kinetic processesviscous flow, crystal nucleation, and growthin lithium disilicate (Li2O2SiO2) over a wide temperature range, from above T m to 0.98T g where T g 727 K is the calorimetric glass transition temperature and T m = 1307 K, which is the melting point. We found that crystal growth mediated by screw dislocations is the most likely growth mechanism in this system. We then calculated the diffusion coefficients controlling crystal growth,DUeff, and completed the analyses by looking at the ionic diffusion coefficients of Li+1, O2, and Si4+estimated from experiments and molecular dynamic simulations. These values were then employed to estimate the effective volume diffusion coefficients, DVeff, resulting from their combination within a hypothetical Li2Si2O5 molecule. The similarity of the temperature dependencies of 1/, where is shear viscosity, and DVeff corroborates the validity of the Stokes-Einstein/Eyring equation (SEE) at high temperatures around T m . Using the equality of DVeff and Deff, we estimated the jump distance 2.70 from the SEE equation and showed that the values of DUeff have the same temperature dependence but exceed Deff by about eightfold. The difference between Deff and DUeff indicates that the former determines the process of mass transport in the bulk whereas the latter relates to the mobility of the structural units on the crystal/liquid interface. We then employed the values of (T) reduced by eightfold to calculate the growth rates U(T). The resultant U(T) curve is consistent with experimental data until the temperature decreases to a decoupling temperature TUd1.11.2Tg, when Deff begins decrease with decreasing temperature faster than DUeff. A similar decoupling occurs between Deff and Deff (estimated from nucleation time-lags) but at a lower temperatureTdTg. For T > T g the values of Deff exceed Deff only by twofold. The different behaviors of Deff(T) and DUeff(T) are likely caused by differences in the mechanisms of critical nuclei formation. Therefore, we have shown that at low undercoolings, viscosity data can be employed for quantitative analyses of crystal growth rates, but in the deeply supercooled liquid state, mass transport for crystal nucleation and growth are not controlled by viscosity. The origin of decoupling is assigned to spatially dynamic heterogeneity in glass-forming melts.Calorimetra diferencial de Barrido (DSC)YearTitle / Author / SourceAbstract2011Title: Interpretation of crystallization kinetics results provided by DSCAuthor(s): Svoboda, Roman; Malek, JiriSource: THERMOCHIMICA ACTA Volume: 526 Issue: 1-2 Pages: 237-251 DOI: 10.1016/j.tca.2011.10.005 Published: NOV 10 2011Differential scanning calorimetry (DSC) measurements were used to study crystallization in the Se(70)Te(30) glass under non-isothermal conditions. The crystallization kinetics was described in terms of the nucleation-growth Johnson-Mehl-Avrami and autocatalytic Sestak-Berggren models.An extensive discussion of all aspects of a full-scale kinetic study for a complex crystallization process was performed. Number of suggestions regarding the experimental part (sample and glass preparation, temperature programs, data acquisition, etc.) was introduced to maximize precision and reproducibility of the experimental data. Complexity of the crystallization process was in this particularly described case represented by very closely overlapping consecutive competing surface and bulk nucleation-growth mechanisms. Mutual interactions of both mechanisms as well as all other observed effects were explained in terms of thermal gradients, surface crystallization centres arising from the sample preparation treatments and changing amount of volume nuclei originating from the combination of pre-nucleation period and the very glass preparation phase. Advanced error analysis was performed for each step of the kinetic study.Objective of the presented study was to demonstrate extensity of information the differential scanning calorimetry is able to provide and, furthermore, to show how a thorough kinetic analysis may lead to reliable, valid and detailed description of complex processes as well as to interpretations of any observable trend occurring in experimental data.2012Title: Lithium rich phosphate glass: Crystallization kinetics, structural and conduction characteristicsAuthor(s): Dabas, Prashant; Hariharan, K.Source: JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 358 Issue: 2 Pages: 252-260 DOI: 10.1016/j.jnoncrysol.2011.09.024 Published: JAN 15 2012Crystallization kinetic studies of Li+ ion conducting mol% 60Li(2)O-40P(2)O(5) glass indicate a 2-dimensional crystal growth mechanism as compared to the 3-dimensional growth mechanism for LiPO3 glass (mol% 50Li(2)O-50P(2)O(5)). Spectroscopic studies reveal that the structures of these two glass compositions differ considerably resulting in different mechanisms for crystal growth. Isothermal ionic conductivity studies further support 2-dimensional crystallization in mol% 60Li(2)O-40P(2)O(5) glass. Above the glass transition temperature the ionic conductivity deviates from the usual Arrhenian temperature dependence due to the additional effect of the movement of the phosphate polymeric chains in the glass network. The ionic conductivity of the glass ceramic corresponding to the mol% 60Li(2)O-40P(2)O(5) glass behaves in an Arrhenian fashion with an activation energy of 1.21 eV, much higher than that of 0.77 eV for the glass. Further, it is established using canonical scaling that the mechanism for ionic conduction is temperature independent.2012Title: Effect of Simultaneous Nucleation and Crystal Growth on DSC Crystallization Peaks of GlassesAuthor(s): Rodrigues, Alisson M.; Costa, Alberth M. C.; Cabral, Aluisio A.Source: JOURNAL OF THE AMERICAN CERAMIC SOCIETY Volume: 95 Issue: 9 Special Issue: SI Pages: 2885-2890 DOI: 10.1111/j.1551-2916.2012.05333.x Published: SEP 2012In this study, the change of the height of the crystallization peak, (delta T)p, and the reciprocal of the crystallization peak temperature, 1/Tp, were investigated as a function of nucleation heat-treatment time for two silicate glasses: (2BaO center dot TiO2 center dot 2SiO2B2TS2) and lithium disilicate (Li2O center dot 2SiO2LS2). Then, monolithic pieces were heat-treated in a differential scanning calorimetry furnace. The results demonstrated that these glasses behave similarly with respect to peak crystallization temperature, i.e., 1/Tp decreases with the heating rate for nucleation (phi n). However, the results with B2TS2 samples demonstrated that (delta T)p increases with rising heating rates for nucleation (shorter nucleation heat treatment times), fn, whereas (delta T)p was found to decrease with phi n in the LS2 specimens. This unexpected behavior is attributed to the extensive overlapping of the I(T) and U(T) curves shown by fresnoite glass.2012Title: Study of the crystallization kinetics of LAS glass by differential scanning calorimetry, X-ray diffraction, and beam bending viscometryAuthor(s): Ovono, D. Ovono; Berre, S.; Pradeau, P.; et al.Source: THERMOCHIMICA ACTA Volume: 527 Pages: 158-164 DOI: 10.1016/j.tca.2011.10.021 Published: JAN 10 2012The crystallization kinetics of a commercial lithium-aluminum silicate (LAS) glass were characterized by differential scanning calorimetry (DSC) under non-isothermal conditions, by in-situ X-ray diffraction, and by three point beam bending viscosimeter (BBV). Non-isothermal DSC experiments were conducted at different heating rates. Results show that the crystal growth is controlled by a thermally activated process of the Arrhenius type. The activation energies obtained from isoconversional analysis are close to that extracted using the Johnson-Mehl-Avrami equation. While X-ray diffraction volume fraction data confirm the DSC analysis, it also shows that the crystallite size changes only at the end of the heat treatment protocol, during a hold at temperatures as high as 1000 degrees C. In this latter case, the crystal growth follows the Ostwald ripening mechanism. Finally, the viscosity measured in the crystallization region by BBV provides the activation energy for viscous flow, and it is slightly higher than the values obtained by DSC2013Title: NONSTOICHIOMETRIC CRYSTALLIZATION OF LITHIUM METASILICATE-CALCIUM METASILICATE GLASSES. PART 1-CRYSTAL NUCLEATION AND GROWTH RATESAuthor(s): Fokin, Vladimir M.; Reis, Raphael M. C. V.; Abyzov, Alexander S.; et al.Source: JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 362 Pages: 56-64 DOI: 10.1016/j.jnoncrysol.2012.11.020 Published: FEB 15 2013The initial stages of the crystallization kinetics of lithium metasilicate (LS) in glasses of the Li2O center dot SiO2-CaO center dot SiO2 join - which has a simple eutectic - was investigated at high undercoolings, somewhat above the glass transition temperatures. Calcium metasilicate crystals precipitate and grow only in the advanced stages of crystallization. The variation of glass composition from the eutectic (26.5 mol% Li2O) towards lithium metasilicate (50 mol% Li2O) results in a sharp increase of the internal nucleation rate of LS crystals, whereas the growth rates increase only weakly. This strong increase of the nucleation rate is primarily caused by a decrease of the thermodynamic barrier for nucleation - due to an increase of the thermodynamic driving force for crystallization and a decrease of the nucleus/liquid interfacial energy - as the glass composition approaches the crystal composition.Calorimetra diferencial de Barrido (DSC) YearTitle / Author / SourceAbstract2013Title: Non-isothermal kinetics study on synthesis of LiFePO4 via carbothermal reduction methodAuthor(s): He, Lihua; Liu, Xuheng; Zhao, ZhongweiSource: THERMOCHIMICA ACTA Volume: 566 Pages: 298-304 DOI: 10.1016/j.tca.2013.06.014 Published: AUG 20 2013Non-isothermal kinetics of lithium ion phosphate synthesis via carbothermal reduction method with raw materials Li2CO3, FePO4 center dot 2H(2)O and C6H12O6 center dot 2H(2)O is studied by thermogravimetry-differential scanning calorimetry (TG-DSC) technology. The results indicate the synthesis process can be divided into two stages: dehydration and LiFePO4 formation. The apparent activation energy and natural logarithm frequency factor (In A-value) for dehydration reaction is respectively 83.4 +/- 4.7 kJ mol(-1) and 22.1 +/- 1.5 s(-1), and that for LiFePO4 formation reaction is in turn 184.2 +/- 10.4 kJ mol(-1) and 28.3 +/- 1.9 s(-1). Additionally, the mechanism for dehydration and LiFePO4 formation stages is Avrami's A(1.5) and A(4), respectively. Furthermore, the dehydration process is diffusion controlled, and the crystallization of LiFePO4 formation is controlled by nuclei being formed randomly and growing in three-dimensions, and the kinetic equations for each stage are shown as follows:Dehydration stage : [-ln(1 - a)](2/3) = 3.96 x 10(9) exp (-8.34 x 10(4)/RT) t;LiFePO4 formation stage : [-ln(1 - a)](1/4) = 1.95 x 10(12) exp (-1.84 x 10(5)/RT) t;where a is the fractional conversion, T the calcination temperature (K), t the calcination time (s), R the gas constant (8.314J mol(-1) K-1).2013Title: Nucleation and crystallization kinetics of rapidly quenched lithium pyrophosphate glassAuthor(s): Dabas, Prashant; Hariharan, K.Source: SOLID STATE IONICS Volume: 243 Pages: 42-49 DOI: 10.1016/j.ssi.2013.04.017 Published: JUL 15 2013Times Cited: 0 (from Web of Science)Title: Nucleation and crystallization kinetics of rapidly quenched lithium pyrophosphate glassAuthor(s): Dabas, Prashant; Hariharan, K.Source: SOLID STATE IONICS Volume: 243 Pages: 42-49 DOI: 10.1016/j.ssi.2013.04.017 Published: JUL 15 201366.7Li(2)O-33.3P(2)O(5) mol% glass prepared by twin-roller rapid quenching has been chosen to investigate the nucleation and crystallization kinetics using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and high temperature X-ray diffraction (XRD) as the experimental tools. Such studies assume importance in designing materials for solid state ionic devices. The glass exhibits a nucleation rate of 3.1 x 10(18) M-3 s(-1) at a typical temperature of 583 K and crystal growth rate of 2.1 x 10(-2) nm s(-1) at 643 K. Non-isothermal DSC studies reveal that the glass undergoes bulk crystallization with an activation energy of 114 kJ mol(-1). The crystallized phase is identified as lithium pyrophosphate (Li4P2O7). Crystallization kinetic studies reveal that Li4P2O7 crystallizes three dimensionally with increasing number of nuclei. Interestingly, lithium metaphosphate (LiPO3) appears as a secondary phase in the glass matrix, however, the final glass ceramic product obtained after prolonged heat treatment of the glass is single phase Li4P2O7. The secondary phase also grows three dimensionally with an activation energy of 365 kJ mol(-1), but with constant number of nuclei in contrast to Li4P2O7. The high nucleation and growth rate with lower activation energy for crystallization of Li4P2O7 underscore that the glass is extremely prone to nucleation and crystallization.2013Title: Effect of ionic liquid on the crystallization kinetics behaviour of polymer poly(ethylene oxide)Author(s): Chaurasia, S. K.; Singh, R. K.; Chandra, S.Source: CRYSTENGCOMM Volume: 15 Issue: 30 Pages: 6022-6034 DOI: 10.1039/c3ce40576a Published: 2013Modification in the crystallization kinetics behaviour of the polymer poly(ethylene oxide) due to the incorporation of an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate; BMIMPF6) has been studied. The PEO + x wt% BMIMPF6 polymer films were prepared by a solution casting technique. Crystallization kinetic parameters, such as relative crystallinity (X-t), crystallization half time (t(1/2)), crystallization rate constant (K), crystallization rate (G) and Avrami exponents (n), have been determined by both isothermal and non-isothermal techniques using DSC. The experimental results based on both non-isothermal and isothermal methods show that the melt crystallization of PEO slows down significantly with the incorporation of BMIMPF6 in the membranes. The growth of crystallized spherulites has also been monitored by polarizing optical microscope (POM), which confirms that the growth rate of crystallized spherulites slows down on the addition of BMIMPF6 in the polymeric membranes.2013Determining the Kinetic Parameters for Isothermal Crystallization in a Lithium Disilicate (Ls2) Glass by OM and DSCLeyliane S. Everton1, Aluisio A. Cabral1,2,*Article first published online: 28 NOV 2013DOI: 10.1111/jace.12638 2013 The American Ceramic Society. Journal of the American Ceramic SocietyIt is well known that the variation in the crystallized fraction, x(t), can be determined directly by optical microscopy (OM) or indirectly by differential scanning calorimetry (DSC) under isothermal conditions. In this work, the kinetic crystallization parameters E (activation energy) and n (Avrami index) of a quasi-stoichiometric lithium disilicate glass (Li2O2SiO2LS2) were studied. First, bulk samples were heat treated in a vertical tube furnace between 500C and 530C for different periods of time, and were carefully prepared. Furthermore, the same samples were then heated in a calorimeter from room temperature to 850C at 10C/min. The following E andn values were obtained: (i) OM: 462.2 1.23 kJ/mol and 4; and (ii) DSC: 187.5 0.45 kJ/mol and 2.4. The results indicated that the activation energy was reduced due to the formation of new crystals and growing of the preexisting crystals during the DSC experiments, and that the predominant crystallization mechanism in the samples changed according to the chosen thermal history.Cintica de CristalizacinLa nucleacin y cristalizacin pueden definirse como los procesos trmicos y cinticos en virtud de los cuales, a partir de una fase estructuralmente desordenada, se forma una fase slida estable con una ordenacin geomtrica regular.Este proceso de ordenacin, es consecuencia de una disminucin de la energa libre del sistema cuando un fundido es enfriado por debajo de su temperatura de liquidus (TL = Temperatura de fusin).

Metodologa

Cintica de CristalizacinProceso Petrrgico. Cristalizacin primaria de un vdrio: obtencin del vidrio y tratamientos trmicos posteriores se incluyen dentro de un nico proceso de enfriamiento

Proceso Vitrocermico. Cristalizacin secundaria de un vdrio: aplicacin de ciclos trmicos posteriores y diferentes al de la obtencin del vidrio.

Cintica de CristalizacinEnfriamientos bruscos (quenching) a las temperaturas elegidas (picos exotrmicos ATD.

Enfriamientos lentos, va petrrgica, en el intervalo Temperatura de Fusin (TL) 800C.

Seleccin y caracterizacin de las muestras

Molienda y homogenizacin

Fusin

Muestras

Recocido

Muestras

Anlisis Qumico y caracterizacin

Precursor

Preparada porReaccin qumica

Muestra a partir de Fusin por arco

Preparacin y/u obtencin por otros medios