Differential Scanning Calorimetry Equipment Research Articles

Effect of curing cycles using wet prepreg processing on mechanical properties

For the fabrication of polymer-based composite materials, the interpretation of an appropriate fabrication process is essential to improve the productivity and manufacturing process. In this study, the wet prepreg forming process was used to fabricate carbon fiber reinforced plastic (CFRP) and different curing cycles were demonstrated for an optimal process. To determine the range of curing temperature, a pretreatment on differential scanning calorimetry (DSC) analysis was performed. After that, tensile and ILSS tests were adopted to investigate the mechanical properties and thermal analysis on a matrix carried out by the DSC equipment. Different volumes of the matrix residue on fractured fiber, which represent the matrix-reinforcement adhesion strength, were observed by a scanning electron microscope (SEM). Also, a void aggregation was found in high curing temperature situation due to excessive exotherm. Both the tensile strength and ILSS held a certain trend with the changing curing cycles. The highest tensile strength (469 MPa) and glass transition temperature (Tg) at 91.58[Formula: see text]C occurred at 80[Formula: see text]C and 12 h curing temperature and time, respectively. The result of ILSS had an almost opposite tendency of the tensile strength. A correlation between Tg and mechanical properties was observed and it can be extensively applied to optimize the manufacturing process.

Use of DSC in degree of conversion of dimethacrylate polymers: easier and faster than MIR technique

This work aims to determine the degree of conversion of polymers obtained using diurethane dimethacrylate (UDMA) monomer by two different techniques: differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (MIR). The measurements were made in triplicate on both equipment, which resulted in average values for MIR 79.52 ± 3.57% (camphorquinone photoinitiator) and 78.15 ± 1.86% (fluorescein photoinitiator) and for DSC 80.85 ± 1.06 and 78.27 ± 1.71%. The DSC technique showed higher accuracy and lesser standard deviation. Furthermore, this technique is easier and faster than the MIR, and in situ polymerization is not necessary on the DSC equipment.

Thermal properties of some Egyptian kaolin pastes for pelotherapeutic applications: Influence of particle geometry on thermal dosage release

Abstract The present study aims to evaluate the potentiality of 7 selected structural highly ordered kaolinite-rich samples from Egyptian Carboniferous sedimentary deposits (located at Abu Zenima district, west central Sinai peninsula) to use them in medicinal semisolid formulations as peloids. The effect of particle geometry and kaolinite crystallite size are studied to check their influence on thermal dosage performance. The studied samples exhibit a variable mineralogy. Kaolinite is the main constituent (ranging from 81 to 94%), followed by quartz (up to 14%), lesser amounts of anatase and halite, and traces of hematite, magnetite, alunite and gypsum. The kaolinite order “Hinckley Index” varies from 1.28 to 1.50. 1:1 (w/w) kaolin mud pastes were prepared with purified water in Eppendorf tubes using a touch vibration vortex mixer for 2 min. The cooling kinetics of pastes were measured by using a differential scanning calorimetry equipment (Shimadzu DSC-50Q). Specific heats were calculated, following Cara et al. (2000). The granulometry and geometric surface area were measured by laser diffraction (Mastersizer 2000LF, Malvern Instruments) in the range 0.02 and 1500 μm. All analyzed samples showed a clear predominance of particles under 4 μm (ranging from 82 to 94%), with median size (D50) ranging from 0.93 to 1.35 μm. The heat retention time during cooling from 50 °C to 32 °C reached up to 30.82 min, oscillating around an average of 28.72 min, and the temperature corresponding to the minimal dosage time (T20) was not exceed below 34.7 °C. A good correlation (R2 = 0.875) was found between heat retention time and specific heats. There is no correlation between kaolinite content and thermal properties, but R2 values around 0.6 are found with granulometry (finer the particles, greater the heat retention time t32 and the specific heat). Even if sample H5 (Gabal Hazbar deposit) is not the richest in kaolinite, it exhibits the best thermal dosage performance, in accordance with the granulometry (D50 = 0.93 μm), and geometric surface area (3.73 m2/g).

Reference material for temperature calibration of differential scanning calorimeters above 1400 °C

Platinum crucible pans are widely used for differential scanning calorimetry (DSC) at temperatures above the aluminum melting point (about 660 °C) due to good signal quality, chemical inertness and easiness of cleaning. However, reference materials commonly used for the calibration of DSC equipment operating with platinum pans exhibit phase transition temperatures no higher than about 1000 °C. In this work, the solid–solid, reversible, $$\alpha ^{\prime }_{\mathrm{H}}\rightarrow \alpha$$ phase transition of calcio-olivine, $$\hbox {Ca}_{2}\hbox {SiO}_{4},$$ was found to produce a marked DSC peak with an onset temperature of $$1453^{+1}_{-2}\,^{\circ }\hbox {C}$$ and a relatively small hysteresis. This compound is compatible with platinum crucibles and fulfills the requirements to be used as reference material for high-temperature calibration of differential scanning calorimeters.

Using DSC for the detection of diffusion-controlled phenomena in Cu-based shape memory alloys

The thermally induced reversible diffusionless martensitic transformation, that governs the mechanism of shape memory alloys (SMAs), can be conveniently illustrated, on differential scanning calorimetry (DSC) curves, by a close variation loop of heat flow with temperature. Cooling-induced direct (forward) martensitic formation causes an exothermic maximum, while martensite reversion, on heating, is associated with an endothermic peak. The occurrence of diffusion-controlled phenomena is emphasized by discontinuities of heat flow variations, such as those observed in the case of Cu–Zn–Al SMAs, experiencing thermoelastic martensitic transformation. When heating such a martensitic Cu–Zn–Al SMA, four solid-state transitions were observed on DSC curves, under the form of: (1) an endothermic minimum ascribed to martensite reversion to parent phase; (2) an endothermic minimum associated with transitory formation of bainite; (3) an exothermic maximum corresponding to the precipitation of equilibrium α-phase and (4) an endothermic peak representing the order–disorder transition of parent phase. The first transition is diffusionless, while the other three are diffusion-controlled. The DSC equipment was used to investigate the effects of: (1) heat treatment temperature, (2) number of cycles of thermomechanical treatment and (3) thermal cycling within the temperature range where diffusion-controlled solid-state transitions occur in a Cu–Zn–Al SMA, the results being corroborated with that obtained by optical (OM) and transmission (TEM) electron microscopy.

Solution Heat Treatment Optimization of Fourth-Generation Single-Crystal Nickel-Base Superalloys

The optimization of the solution heat treatment (SHT) of fourth-generation single-crystal nickel-base superalloys LDSX-6B and LDSX-6C is presented. The methodological approach to optimizing the SHT process is particularly highlighted. Differential scanning calorimetry (DSC) measurements and electron-probe microanalysis (EPMA) mapping were carried out to investigate material properties in the as-cast condition and after SHT. The DSC equipment was also adopted as a vacuum furnace to evaluate the suitability of the SHT ramp profile and to check the safety margins with regard to incipient melting during SHT. SHT trials were carried out in a laboratory-scale vacuum furnace, after which the heat-treated samples were subjected to DSC experiments, microstructural analysis, and EPMA mapping to assess the effects of SHT peak temperatures and soak periods. From the DSC and EPMA results, as-cast LDSX-6B shows a lower degree of elemental microsegregation; hence, this alloy is relatively easier to homogenize in the SHT trials. In contrast, as-cast LDSX-6C was found to have a higher degree of elemental microsegregation; therefore, it is much more difficult to homogenize and is highly prone to incipient melting. The results of this study indicate that an increase in the SHT peak temperature and/or soak period will lead to an improved compositional homogeneity in the material as expected. After SHT, both alloys retained some residual elemental microsegregation and the LDSX-6C alloy showed precipitation of topologically close-packed (TCP) phase at the dendrite cores. The most appropriate and economic SHT process may be determined based on the methodological approach presented in this study and the requirements of the materials during service.

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr 2N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.

Evaluation of enthalpy change due to hydrogen desorption for lithium amide/imide system by differential scanning calorimetry

Enthalpy change (Δ H) due to hydrogen desorption (H-desorption) for the lithium amide/imide system was evaluated by differential scanning calorimetry (DSC) measurement. In order to obtain the accurate and precise value of Δ H, we have paid special attention to following two points for correcting raw experimental data. One is to determine a cell constant of DSC equipment, which was evaluated by using the TiO 2-doped MgH 2 compound as a reference because of its quite similar hydrogen desorption properties to that of the lithium amide/imide system. The other is to estimate the sample amount corresponding to the H-desorption reaction from weight loss in the thermogravimetric (TG) analysis. By performing both the corrections, the Δ H value due to the H-desorption reaction from LiNH 2 + LiH to Li 2NH + H 2 was evaluated to be 67 kJ/mol H 2.

Comparison of methods to determine the degree of gelatinisation for both high and low starch concentrations

A general procedure was developed to measure the degree of gelatinisation in samples over a broad concentration range. Measurements based on birefringence, DSC (Differential scanning calorimetry), X-ray and amylose–iodine complex formation were used. If a 10 w/w % wheat starch–water mixture was used, each method resulted in approximately the same degree of gelatinisation vs. temperature curve. In case the gelatinisation of a 60 w/w % wheat starch–water mixture was followed as a function of the temperature, each method resulted in a different degree of gelatinisation vs. temperature curve. DSC and X-ray measurements are preferred, because they can be used to determine when the final stage of the gelatinisation process has been completed. Birefringence and amylose–iodine complex formation measurements are suitable alternatives if DSC and X-ray equipment is not available, but will lead to different results. The differences between the methods can be explained by considering the phenomena that take place during the gelatinisation at limiting water conditions. Based on the experimental data obtained with DSC and X-ray measurements, the gelatinisation of 10 w/w % and 60 w/w % wheat starch–water mixtures started at the same temperature (approximately 50 °C). However, complete gelatinisation was reached at different temperatures (approximately 75 °C and 115 °C for, respectively, 10 w/w % and 60 w/w % wheat starch–water mixtures) according to the experimental DSC and X-ray data. These results are in accordance with independent DSC measurements that were carried out. The Flory equation was adapted to provide a quantitative explanation for the curves describing the degree of starch gelatinisation as a function of the starch–water ratio and the temperature. The gelatinisation curves that were obtained with the model are in good agreement with the experimentally determined curves. The parameters T m 0 , Δ H u and χ 12 that resulted in the lowest sum of the squared residuals are 291 ± 63 °C, 29.2 ± 3.9 kJ/mol and 0.53 ± 0.05 (95% confidence interval). These values agree with other values reported in literature.

Surface gas nitriding of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.08Si alloys

Abstract The paper presents results from thermochemical surface gas nitriding of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.08Si alloys using differential scanning calorimetry equipment. The experiments were carried out in nitrogen atmosphere at temperatures of 950 and 1050°C for 1, 3 and 5 h. Results for the surface hardness, the microhardness profiles and the thickness of the nitrided layers were obtained. Microstructure analyses were made by optical microscopy. X-ray diffraction analyses indicated new phases formed (TiN, TiN0.3, Ti2N and TiO2), depending on the time and the temperature of nitriding. The obtained thickness of the nitrided layers was in the range 60–320 μm depending on the process parameters. The Vickers microhardness along the cross-section depth varied between 610 and 1700.

Differential Scanning Calorimetry Evaluates Relative Proportions and Strength of Acid-Sites in Catalytic Materials and Adsorbents Alumina and Amorphous Silica-Alumina

Abstract Differential scanning calorimetry (DSC) is employed to evaluate the relative proportions and strength of acid-sites in gammaalumina and amorphous silica-alumina through presorption of tri-ethylamine (TEA) followed by its thermal desorption in the DSC equipment. From the data obtained, total acid-sites in silica-alumina is found to be 2.3 times as large as those present in gamma-alumina, and 5–5% of total acidity in alumina is of Bronsted type whereas in silica-alumina this type comprises 28.9%' The Bronsted acidity strength in alumina and silica-alumina is identical although greatly different in quantity. Lewis acidity in silica-alumina is significantly stronger than that in alumina.