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Thermal analysis is used to investigate 30 year old samples of concrete. In this study, thermal analysis data is combined with XRD data. The contents of these concrete samples are identified in terms of portlandite, calcite, dolomite, gypsum, and quartz. However, the calcium carbonate comes from the carbonation of the portlandite, from the fine and coarse aggregate used in the preparation of the concrete, and also from the second stage of the thermal decomposition of the dolomite. In the present study, samples of recycled Portland cement concrete are investigated which were low in calcite but high in dolomite content. The original presence of slag in these samples influences the long term leaching potential of the concrete. Leaching experiments reveal the presence of both calcium and magnesium ions in the leachate.

The binary mixtures of ibuprofen and stearic acid have been tested on the DSC at a heating rate of 5°C min -1 . All temperatures reported here are for endothermic peak temperatures. The heating curves are employed to construct a phase diagram. The resultant phase diagram shows the existence of a compound formed between the two materials and is essentially two simple eutectic systems compressed into one equilibrium diagram. The component in excess melts at a lower temperature than its single entity. There are two eutectic melting points at 42% ibuprofen and 65% ibuprofen. It would seem probable that the condensed phase compound has the formula AB 2 , where A is stearic acid (C 18 H 36 O 2 ) and B is ibuprofen (C 13 H 18 O 2 ). A relationship between the enthalpy of melting (ΔH m ) and %composition is found. However, the overlapped endothermic peaks pose difficulty in peak integration resulting in a deviation from a typical plot. DSC is a fast, useful, and reliable analytical tool to detect and investigate the eutectic compound in this study.

It is shown that thermal analysis and XRD data can identify the component of RPCCA which may be hydrated cement or slag (generally considered as an aggregate component). The other coarse aggregates present may be gravel or limestone. The fine aggregate often referred to as sand may be quartz or limestone in origin. The limestone may be dolomite and/or calcite in nature. The TG reveals the extent of the hydration product portlandite [Ca(OH) 2 ] in the sample, the amount of CaCO 3 present, and the amount of dolomite. XRD studies confirm the presence of these materials. In old concrete samples, the portlandite may be partially carbonated. TG data in CO 2 allows the presence of dolomite to be identified.

The variation of the activation energy (Eact) is reported for the evaporation of Ibuprofen-starch binary mixtures in nitrogen atmosphere. It is shown that all the features of Ibuprofen and starch are still present in the mixtures. That is, the loss of water from the starch, melting of the Ibuprofen, the evaporation of the Ibuprofen, and the degradation of the starch, appearing in this order as the heating mode is progressed. The temperature range for the evaporation of Ibuprofen is moved to a higher temperature as the Ibuprofen content in the mixture is increased. This is reflected in the energy of evaporation associated with each binary mixture. The kinetic analysis of the starch degradation is also affected in that the temperature range for the degradation increases with the Ibuprofen content. This again is reflected in an analysis of the activation energy as a function of the original Ibuprofen content in the mixture. The cause of this effect is discussed in the paper.

Mixtures of ibuprofen and starch were examined in a flowing atmosphere of dry nitrogen using a simultaneous TG–DTA unit. This showed that the two main features of heat treatment of ibuprofen, namely melting and evaporation, were retained. The loss of water from the starch on heat treatment could be noticed in the mixtures, and the thermal degradation of the starch to carbon could also be observed as a separate step. The temperature for the evaporation of the ibuprofen increased and the starch degradation temperature also rose with increasing ibuprofen content in the binary mixtures. The separation of these two processes enabled the percentage of composition of the mixture to be established.

The heat treatment of stearic acid shows a zero-order process which is in accord with an evaporation process. In this study, the melting points of three samples of stearic acid (A, B, and C) from the rising temperature experiments at the heating rate (β) of 2-12°C min -1 are found to be in the range of 57.4-73.5 C and that of stearic acid B in N 2 flow rate ranging from 50 to 1000 ml min -1 is 69.0-70.0 C. From the DTA signals, the β of 6-8 C min -1 and an N 2 flow rate of 100 ml min -1 were found to be the optimum conditions for the evaporation process of these materials. The enthalpy of vaporization (ΔH vap ) of stearic acid is calculated by the use of the Antoine [1] and Clausius-Clapeyron equations [2]. These ΔH vap values are equal to 115.7 and 81.6 kJ mol -1 for the temperature ranges of 349-415 and 457-649 K, respectively. These values can be compared to the activation energy (E act ) which is in the range of 87.0 to 101. 1 kJ mol -1 determined from the rising temperature experiments of three types of stearic acid subjected to various experimental conditions. Generally. E act ≥ΔH vap . It is predicted, and verified experimentally, that the equilibrium vapor pressure and the coefficient of vaporization have a logarithmic relationship.

The heat treatment of an α-cellulose and a microcrystalline cellulose (Avicel®) in nitrogen gives a one-stage degradation to carbon. This degradation suffers a temperature transposition in the presence of pharmaceutical excipients, namely dibasic calcium phosphate, stearic acid, magnesium stearate, and silicon dioxide. It is possible to produce a kinetic evaluation of these thermal analysis studies in terms of a comparative method by constructing the theoretical TG trace of the binary mixture based on a presumed no-interaction between the two components. There is a variation in behavior to be noted in the different forms of cellulose, and also different values are shown for the Arrhenius parameters. Such variations are also noted in the Avicel® degradation in the presence of other materials. These observations should be of use in the characterization of pharmaceutical excipients. The Arrhenius parameters for α-cellulose degradation using D3 (three-dimensional diffusion) mechanism at the temperature range from 580 to 630 K are 289.32 kJ mol−1 and 1.85×1023 for Eact and A, respectively. The Arrhenius parameters for Avicel® degradation using F1 (first-order) mechanism at the temperature range from 562 to 604 K are 291.35 kJ mol−1 and 1.26×1025 for Eact and A, respectively.

Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to 251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (Δvap H) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol−1. TheE act for the zero order reaction is in the range of 81.8–87.0 kJ mol−1 and is calculated by use of the derivative method. The value ofE act is about twice that for ΔH vap in Ibuprofen and differs from other compounds, whereE act ≈Δ H vap . It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the vapor state.

In a previous publication, the thermogravimetric (TG) analysis of ascorbic acid was considered. Simultaneously with the production of the TG data, time-temperature plots were also generated on the work station which allowed the process to be classified as exothermic or endothermic and identified the energy change with the reaction sequence. This aspect is investigated in the present study. To maximize the energy change, the model mixtures were assessed at a mass ratio of 1∶1. The analytical implications of this approach are explored. To avoid complications in this kind of analysis, the present study is restricted to the behavior of binary systems heat treated in nitrogen.

A new approach to establishing kinetic parameters for solid state decompositions is outlined based on the equation of Harcourt and Esson. It enables the integral method to be used without the need to make approximations. It is applied here to a study of certain pharmaceutical excipients used in the formulation of tablets.

The thermal decomposition of ascorbic acid and its excipients in tablet formulations was studied under an atmosphere of nitrogen using a thermogravimetric balance. To maximize the tendency of an interaction, binary mixtures (1:1 by weight) of drug and excipient and between excipients were utilized. Two new methods were employed to assess the change in reactivities, and the thermal behavior of the materials under investigation. In the first method, named the αs−αr method, the solid state reactivity of the sample was compared to that of a reference. The term α refers to the extent of the reaction. The second method is called the W p W t method. In this method, the effect of the excipients on the decomposition pattern of ascorbic acid can be shown. The terms Wp and Wt refer to the percentage of residual solid material obtained experimentally (Wp) and theoretically (Wt). The ratio W p W t is reported at various values of temperature.

The concept of concurrently using two or more techniques of thermal analysis on a single substance has been promoted by advances in microprocessor control. This has made it possible to program and collect the data and process the information in many ways. Strictly speaking, the nomenclature “simultaneous” applied in such circumstance is not always correct. The mass change in thermogravimetry (TG) is generally the first signal received. The signal from the differential thermal analysis (DTA) probe will be received a little later as the heat has to diffuse through the sample and the crucible before reaching the sensing thermocouple. The sample is defined as the material (usually a solid) under investigation. Likewise, in evolved gas analysis (EGA), the gases are sampled but it then takes a finite time for the gas to be analyzed. In the mass spectrometer, there is an interface to allow the gas to be analyzed. In gas chromatography (GC), the signal of gas analysis takes considerable time to process, and consequently the gas analysis signal is intermittent and not received in “real time.” In common with all other thermal analysis techniques, the following parameters must be considered: the sample characteristics, its mass, the sample holder, the temperature range for study, the rate of heating, and the atmosphere. It must be remembered that a single thermal analysis method may not give the investigator sufficient information. Thus DTA will indicate if a transformation is exothermic or endothermic. It needs thermogravimetric analysis to indicate if there is mass change as well as gas analysis to identify any gaseous products involved. Although “simultaneous techniques” is the approved term used by the International Union of Pure and Applied Chemistry (IUPAC), the recommended nomenclature for such simultaneous techniques is to use a hyphen to separate the two techniques, e.g., TG-DSC. This has led to such techniques being called “hyphenated” techniques. Keywords: thermal gravimetry; differential thermal analysis; principles; practical aspects; simultaneous techniques; commercial equipment; gas analysis; gas chromatography; infrared spectrometry; method automation; disadvantages