Conventional Linear Heating Research Articles

The use of quasi-isothermal modulated temperature differential scanning calorimetry for the characterization of slow crystallization processes in lipid-based solid self-emulsifying systems.

PurposeSlow or incomplete crystallization may be a significant manufacturing issue for solid lipid-based dosage forms, yet little information is available on this phenomenon. In this investigation we suggest a novel means by which slow solidification may be monitored in Gelucire 44/14 using quasi-isothermal modulated temperature DSC (QiMTDSC).MethodsConventional linear heating and cooling DSC methods were employed, along with hot stage microscopy (HSM), for basic thermal profiling of Gelucire 44/14. QiMTDSC experiments were performed on cooling from the melt, using a range of incremental decreases in temperature and isothermal measurement periods.ResultsDSC and HSM highlighted the main (primary) crystallization transition; solid fat content analysis and kinetic analysis were used to profile the solidification process. The heat capacity profile from QiMTDSC indicated that after an initial energetic primary crystallisation, the lipid underwent a slower period of crystallization which continued to manifest at much lower temperatures than indicated by standard DSC.ConclusionsWe present evidence that Gelucire 44/14 undergoes an initial crystallization followed by a secondary, slower process. QIMTDSC appears to be a promising tool in the investigation of this secondary crystallization process.

Controlled rate thermal decomposition of synthetic bayerite under vacuum

Influences of the controlled decomposition rate and controlled residual pressure on the thermal decomposition process of synthetic bayerite were investigated by applying a method of controlled rate evolved gas detection (CREGD). Comparing with the conventional process under linearly increasing temperature, the thermal decomposition process of the synthetic bayerite at a controlled decomposition rate (∼10 −2 mg min −1) under controlled residual pressure (∼10 −3 Pa) was characterized by the lowered reaction temperature profile and small changes in the specific surface area of the sample during the course of reaction. Formation of an amorphous alumina as the decomposition product is another important result of the process control by the present CREGD. The amorphous alumina crystallizes to η-Al 2O 3 at around 1100 K. It is worth noting that the characteristics of the reaction process under controlled rate conditions and the formation of amorphous alumina as the decomposition product are very similar to those of mechanochemically activated bayerite under conventional linear heating.

The effect of humidity on thermal decomposition of terephthalate polyester

The thermal decomposition of engineering polyester in the atmospheres of controlled humidity has been successfully investigated by sample-controlled thermogravimetry (SCTG) and thermogravimety combined with evolved gas analysis using mass spectrometry (TG-MS). The thermal decomposition of poly(butylene terephthalate) (PBT) by conventional linear heating rate thermogravimetry (LHTG) was shown by a monotonous single decomposition step between 300 and 450 °C. The thermal decomposition was significantly influenced by the presence of water vapor, and the amount of the residues decreased with increasing the partial pressure of water in the atmosphere. Various heating rates and mass loss rates were used for kinetic analysis in LHTG and SCTG. The apparent activation energy of the thermal decomposition of PBT was evaluated by using Friedman–Ozawa method. In nitrogen atmosphere of controlled high-humidity, the apparent activation energy estimated by SCTG was the lower than that obtained by LHTG because the influence of water vapor acts more effectively in SCTG. The TG-MS equipped with a humidity generator controlling the atmosphere revealed the presence of hydrolysis products occurred concurrently during the thermal decomposition process. A detailed thermal decomposition of PBT and the effect of water vapor are discussed.

The effect of humidity on thermal process of zinc acetate

The thermal decomposition of zinc acetate dihydrate Zn(CH 3CO 2) 2·2H 2O in some humidity-controlled atmospheres has been successfully investigated by novel thermal analyses, which are sample-controlled thermogravimetry (SCTG), thermogravimety combined with evolved gas analysis using mass spectrometry (TG–MS) and simultaneous measurement of differential scanning calorimetry and X-ray diffractometry (XRD–DSC). The thermal processes of anhydrous zinc acetate in dry gas atmosphere by conventional linear heating experiment initiated with the sublimation around 180 °C, followed by the fusion and the decomposition over 250 °C. SCTG was useful to interpret clearly the successive reaction because the high-temperature parallel decompositions were effectively inhibited. The thermal behavior changed dramatically by introducing water vapor in the atmosphere and the thermal process was quite different from that in dry gas atmosphere. Zinc oxide (ZnO) was formed only in a humidity-controlled atmosphere, and could be easily synthesized at temperatures below 300 °C. XRD–DSC equipped with a humidity generator revealed directly the crystalline change from Zn(CH 3CO 2) 2 to ZnO. A detailed thermal process of Zn(CH 3CO 2) 2·2H 2O and the effect of water vapor are discussed.

A New Approach to the Study of the Reactivity of Solid-Acid Catalysts: The Application of Constant Rate Thermal Analysis to the Desorption and Surface Reaction of Isopropylamine from NaY and HY Zeolites

A new and potentially valuable approach to the study of the acidity and reactivity of the surfaces of solid acid materials is described. The technique uses a combination of constant rate thermal analysis (CRTA) with the rate jump technique (CRTA-RJ) for temperature programmed desorption (TPD) and reaction (TPRx). CRTA, where the sample temperature is changed to force the rate of reaction to remain constant through a process, offers a number of advantages over conventional linear heating thermal methods by minimizing temperature and concentration gradients in the sample and reducing the effects of diffusion. CRTA and CRTA-RJ were applied to the TPD and TPRx of isopropylamine from NaY zeolite and its acidic form, HY. Activation energies of both the physical desorption of the amine and the surface-catalyzed Hoffman elimination reaction were calculated as a function of surface coverage and the advantages and limitations of the techniques are discussed. Comparisons are made with analogous TPD experiments using...

Reduction of Iron Oxide Catalysts: The Investigation of Kinetic Parameters Using Rate Perturbation and Linear Heating Thermoanalytical Techniques

The mechanisms and kinetics of the reduction of powdered Fe2O3 and Fe3O4 samples have been investigated under nonisothermal conditions to provide a detailed insight into the processes occurring. Both conventional linear heating temperature-programmed reduction (TPR) and constant rate temperature-programmed reduction (CR-TPR) techniques were utilized. Fe2O3 was found to reduce to Fe in a two-step process via Fe3O4. The mechanism of the prereduction step of Fe2O3 to Fe3O4 was found to follow an nth order expression where nucleation or diffusion was not the rate-controlling factor while the main reduction step to metal was described by a model involving the random formation and growth of nuclei. A CR-TPR rate perturbation method, “rate-jump”, was applied to the measurement of variations in apparent activation energy throughout the reduction processes, under near-equilibrium conditions and the activation energy measurements are compared with those obtained under conventional linear heating conditions.

Thermal decomposition of calcium copper acetate hexahydrate by simultaneous measurement of controlled-rate thermogravimetry and mass spectrometry (CRTG–MS)

The thermal decomposition of calcium copper acetate hexahydrate, CaCu(CH 3CO 2) 4·6H 2O, in an inert atmosphere has been studied successfully by means of thermogravimetry (TG) or controlled-rate thermogravimetry (CRTG), both combined with simultaneous evolved gas analysis (EGA) using mass spectrometry (MS). CRTG is useful to simplify the complicated successive reactions and to study the mechanism of the thermal decomposition. The determination of the residual intermediates provides powerful information to analyze the decomposition mechanism. Compared with the conventional linear heating method the CRTG–MS method offers an invaluable interpretation for the complex process in the thermal events. The features of the thermal decomposition observed by the conventional TG were different from those by CRTG, so that the decomposition seems to proceed through different mechanisms in TG and CRTG. The X-ray diffraction profiles of the intermediate products support this expectation. The decomposition mechanism of CaCu(CH 3CO 2) 4·6H 2O was proposed.

Use of Solid Insertion Probe Mass Spectrometry and Constant Rate Thermal Analysis in the Study of Materials: Determination of Apparent Activation Energies and Mechanisms of Solid-State Decomposition Reactions

Thermally induced reactions are of great importance in the manufacture and characterization of a very wide range of increasingly complex materials covering areas as diverse as ceramics and heterogeneous catalysts. Subsequently, there is a need for improved thermoanalytical methods that can provide enhanced resolution and a greater understanding of the energetics and mechanisms involved. This paper describes a new solid insertion probe mass spectrometer (SIP-MS) system that is designed to meet these needs by operating high vacuum with small sample masses. The SIP-MS system supports both conventional linear heating and a range of sample-controlled thermal analysis (SCTA) techniques including constant rate thermal analysis (CRTA). Its ability, in conjunction with the latter technique, to obtain reliable apparent activation energy measurements throughout a process under near-ideal experimental conditions is demonstrated. In addition, the system can discriminate between different reaction mechanisms and provid...

Sample controlled thermal analysis: Temperature programmed reduction of bulk and supported copper oxide

The reduction of bulk and supported copper oxide was investigated using Constant Rate-Temperature Programmed Reduction (CR-TPR) and conventional linear heating rate TPR. Linear heating profiles indicated that the reduction of supported samples was more facile than that of the bulk oxide. CRTA results revealed that both supported and bulk oxide samples were reduced via a mechanism involving a nucleation step and/or auto-catalysis. The increased reducibility of the supported samples is attributed to a higher dispersion which provides a larger reactive surface area and a high concentration of defects at which reduction is initiated.

New Approach to the Investigation of Mechanisms and Apparent Activation Energies for the Reduction of Metal Oxides Using Constant Reaction Rate Temperature-Programmed Reduction

A new system has been developed for the study of both bulk and surface metal oxides by temperature programmed reduction (TPR) under both conventional linear heating and constant rate thermal analysis (CRTA) conditions. It is shown that constant rate temperature-programmed reduction (CR-TPR) is capable of producing higher resolution of overlapping events, provides more insight into reduction mechanisms, and allows easier quantification of reduction processes than conventional TPR. The CR-TPR curves for both bulk and supported copper oxides confirmed that reduction followed a nucleation or autocatalytic mechanism. Bulk nickel oxide was found to reduce via a similar mechanism. Advantages of the CR-TPR “rate-jump” technique to determine reaction energetics are illustrated by investigation of the apparent activation energy (Ea) of CuO reduction, and the results are compared with those obtained under linear heating conditions. Both approaches yield reasonable values of Ea under the appropriate experimental cond...

Controlled-rate thermal analysis

Binder burnout has been carried out by a controlled heating programme which depends on the composition of the binder system used. The present paper gives the principle of constant decomposition rate thermogravimetry, which falls within controlled-rate thermal analysis, and the advantage of this technique when evolved gas analysis is used in discriminating the process of super hard material burnout by comparison with the conventional linear heating method is described. In this technique, the sample temperature is varied to maintain a constant rate of mass loss by control of the heating of the infrared image furnace. Since the constant decomposition rate control (CDRC) allows a much better control of the sample environment, which generally depends on the rate of gas evolution, it is possible for uniform conditions to exist throughout the sample, and the total burnout time can be reduced considerably without crack formation. The efficiency of this CDRC was proved by the obtained temperaturevs. time curve and SEM observations of the heat-treated sample after the debinding process.

Applications of new high resolution evolved-gas analysis systems for the characterisation of catalysts using rate-controlled thermal analysis

The advantages of using rate-controlled thermal analysis (RCTA) methods in the thermal characterisation of catalysts are described. The use of these methods is demonstrated by the temperature programmed reduction of vanadium pentoxide, the measurement of the number and type of acid sites in clays by temperature programmed desorption of cyclohexylamine, and temperature programmed reaction, which is illustrated by the dehydration of propan-2-ol over an acid-activated montmorillonite clay. It is shown that the new system has advantages in the study of the kinetics of reactions and in improving resolution when used to characterise the thermal decomposition of catalyst precursors. New evolved-gas analysis systems for characterising heterogeneous catalysts are described, in which a variety of RCTA methods is used. The systems are computer-controlled and use a variety of furnaces, permitting samples from a few microgrammes to fifty milligrammes to be studied, under pressures ranging from ultra high vacuum to one atmosphere. The furnace chosen for a particular experiment is linked to one of a number of gas detectors (hygrometers, katharometers and mass spectrometers), the output of which completes the control loop. The most important component of the system is the versatile software which supports a range of RCTA modes, including conventional linear heating rate, constant reaction rate, and other control strategies developed in this work.

Reaction‐Controlled Binder Burnout of Ceramic Multilayer Capacitors

Reaction‐controlled binder burnout of ceramic multilayer capacitors (CMCs) is conducted in a series of small‐scale experiments. the burnout process is followed by monitoring the weight of the CMCs. The observed maximum weight loss rate, obtained with a conventional linear heating process, is used to design a weight‐time program for a reaction‐controlled process. In this process the actual CMC weight is controlled to closely follow the weight program by means of continuous control with the batch temperature. The advantages of this procedure are discussed. The results of the present study, although being restricted to oxidative burnout of a special product, are thought to be of some use for other ceramic burnout situations. The relevant parts of controller design are discussed together with some comments on scale‐up.

Analysis of the shape index of DTG or DTA curves under a hyperbolic or logarithmic schedule

It is shown that the reacted fraction, αm, at the maximum reaction rate of solid state transformation analyzed under a hyperbolic or a logarithmic heating schedule depends only on the reaction mechanism-being independent of the actual value of E/RT. On the other hand, it has been demonstrated that the corresponding “shape index”, S, defined as the slope ratio of the tangents to the DTG or DTA traces depends only on the reaction mechanism and does not depend either on E/RT or on the curve broadening. The above statements are not accomplished if the DTG or DTA traces are obtained by means of a conventional linear heating program.