Vapor pressure is a fundamental property of a pure substance. This property is the pressure of a compound’s vapor in thermodynamic equilibrium with its condensed phase (solid or liquid). When phase ...equilibrium condition is met, phase coexistence of a pure substance involves a continuum interplay of vaporization or sublimation to gas and condensation back to their liquid or solid form, respectively. Thermogravimetric analysis (TGA) techniques are based on mass loss determination and are well suited for the study of such phenomena. In this work, it is shown that TGA method using a reference substance is a suitable technique for vapor pressure determination. This method is easy and fast because it involves a series of isothermal segments. In contrast to original Knudsen’s approach, where the use of high vacuum is mandatory, adopting the proposed method a given experimental setup is calibrated under ambient pressure conditions. The theoretical framework of this method is based on a generalization of Langmuir equation of free evaporation: The real strength of the proposed method is the ability to determine the vapor pressure independently of the molecular mass of the vapor. A demonstration of this method has been performed using the Clausius–Clapeyron equation of state to derive the working equation. This algorithm, however, is adaptive and admits the use of other equations of state. The results of a series of experiments with organic molecules indicate that the average difference of the measured and the literature vapor pressure amounts to about 5 %. Vapor pressure determined in this study spans from few mPa up to several kPa. Once the
p
versus
T
diagram is obtained, phase transition enthalpy can additionally be calculated from the data.
The influence of high amounts of calcium carbonate filler on the crystallization behavior of polypropylene (PP) is investigated by differential scanning calorimetry (DSC) and fast scanning DSC ...measurements. The non-isothermal crystallization process at industrially relevant cooling rates of about 100 K/s is significantly influenced by the calcium carbonate filler. Isothermal crystallization measurements indicate a new crystallization process in the temperature range between 45 and 80 °C caused by the filler content. To find an explanation for the origin of this process, we have analyzed the interaction between polymer and filler, the crystalline structure, and the crystallization kinetics. From the experimental results, we conclude that the newly observed crystallization process is governed by an additional nucleation process for the growth of α-phase crystals.
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•A description of the content dependence of the glass transition temperature of compatible systems with hydrogen bonds.•Description of the formation of molecular clusters on the glass ...transition of mixtures with hydrogen bonds.•Interpretation of the Gordon-Tayler Equation for hydrogen bonds containing systems.•Comparison of model simulations and experimental results for carbohydrate- carbohydrate and carbohydrate-water systems.
A thermodynamic approach is presented to describe the compositional dependence of the glass transition in amorphous systems with strong molecular interactions due to hydrogen bonds. Such systems form temporary molecular clusters. In result, a generalized Gordon Tayler equation is derived. It is shown that the factor k is related to the molecular interactions. This factor is linked to the average number of molecules that form a preferred sized cluster. This model is tested for carbohydrate mixtures and various sugar-water solutions.
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•Cooling rate dependence of the glass transition of silicate glass.•Measurement of nearly 6 decades of cooling rates by Fast DSC.•Fictive temperature at the glass transition compared ...with shear viscosity.•Proportionality between shear viscosity and cooling rate holds.
First results of the cooling rate dependent vitrification process of a silicate melt in the cooling rate range between 0.1 and 30,000 K/s are presented. These results are compared with the temperature dependence of the shear viscosity. The results indicate that rule of the proportionality between shear viscosity and cooling rate holds for the silicate glass. It is also indicated that the thermal retardation time is significantly larger than the shear stress relaxation time derived from viscosity measurements.
The major challenge to overcome when processing metallic glasses (MGs) is to avoid crystallization. Therefore, time-temperature-transformation (TTT) diagrams are used, but they are often derived from ...experiments in which heating or cooling rates are limited and do not cover the full range of processing conditions, especially those encountered in additive manufacturing (AM) where the rates are very high. Here, an industrial-grade Zr-based MG (AMZ4) is investigated via fast differential scanning calorimetry (FDSC). The critical cooling and heating rates of AMZ4 are experimentally measured and TTT diagrams are determined upon heating and cooling. The critical heating rate of 45,000 K/s is 18 times the critical cooling rate, which indicates the presence of a self-doped glass (SDG) that includes quenched-in nuclei. The results illustrate that AMZ4 is very sensitive to crystallization, even in laser-based AM conditions, where heating and cooling steps need to be distinguished.
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•Sample preparation of rubber for Fast Differential Scanning Calorimetry (FDSC).•Crystallization of a rubber with low glass transition temperature is analyzed by FDSC.•Isothermal ...crystallization between the glass transition and melting is measured.•The ratio between crystalline fraction and rigid amorphous fraction is determined.•The model of crystallization in self-assembled confinements is introduced.
The crystallization kinetics of commercial high cis-1.4-polybutadiene (BR) is measured by conventional differential scanning calorimetry (DSC) and fast differential scanning calorimetry (FDSC). This rubber has a glass transition temperature below -100 °C and is technically used for a wide application range.
In a crystallinity range between 10 % and 30 % the ratio between the crystal and rigid amorphous fraction was determined to be about unity.
Using the FDSC allows the quantitative characterization of the crystallization half time in the temperature range between the glass transition and the melting point even at low temperatures. For this, a discrete measurement method was applied. A single crystallization process was determined with the maximum crystallization rate at -50 °C.
For crystallization below -40 °C, the measurements show that the melting temperature of the initially formed crystals is relatively low. The Avrami exponent is about unity. We observed comparable kinetics of nucleation and growth. A relatively large amount of an amorphous fraction with restricted mobility (the rigid amorphous fraction) is formed during crystallization at low temperatures. This finding leads to the model of self-assembled confinements for the low temperature BR crystallization.
•The initial crystallinity of polymers (αini) is an important property measured by DSC.•The literature proposes a method to determine αini by temperature modulated DSC.•It is shown that this method ...is not useful for polymer analysis.•Alternative methods by conventional DSC are recommended.
The determination of the crystallinity of polymer samples is a typical use of the DSC and it is evaluated from the heat flow curves by various methods A received polymer sample will have an initial crystalline content, which could be zero if the sample was totally amorphous or which is smaller than unity for semicrystalline polymers. The problem with assessing the initial level of crystallinity, is that crystallization may occur during heating, so that the total measured melting enthalpy is the sum of the original amount plus that formed by cold crystallization, for example. Several claims in the literature recommend that the determination of crystallinity can be improved by using temperature modulated DSC (TMDSC). In this contribution we analyze the TMDSC method to determine the initial crystallinity of polymers proposed by Sauerbrunn and Thomas. The conclusion from this result shows that the apparent advantage of the TMDSC technique only arises when a poor baseline selection is made for the evaluation of the DSC curve. It is shown that the method for determination of the initial crystallinity by TMDSC results from incorrect conclusions. The occasionally discussed advantages of this technique are not real. Different techniques for evaluation of conventional DSC curves are referred.
The structural stability of a gold-based bulk metallic glass (Au49Ag5.5Pd2.3Cu26.9Si16.3) was investigated by fast differential scanning calorimetry (FDSC). A chemically homogeneous glass (CHG) ...containing no quenched-in nuclei was produced using sufficiently fast cooling from the melt. To characterize the stability of this glass, the structural variations during annealing in the glassy state were investigated and a sequence of five different events observed. These are structural relaxation, an incubation period, nucleation, crystallization, and finally reorganization. The kinetics of these processes and the stability of the crystalline structures are discussed.
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