Thermomechanical Analysis Measurements Research Articles

Structural interpretation of the viscous flow and relaxation kinetics in the As-Se and Ge-Se chalcogenide systems

This study investigates the behaviour of As₂₀Se₈₀ and Ge₂₅Se₇₅ chalcogenide glasses near the glass transition temperature using differential scanning calorimetry (DSC) and thermomechanical analysis (TMA), addressing a gap in the literature for these compositions. Precise TMA measurements of viscosity in the range of 10⁶ – 10¹³ Pa·s clarified existing data and improved the quality of fits describing the temperature-dependent viscosity for both compositions. The DSC method enabled a comprehensive analysis of structural relaxation behaviours, which were described using the Tool-Narayanaswamy-Moynihan (TNM) model with the determination of its four parameters. The study discusses the viscosity and structural relaxation behaviours of both glass-formers in relation to their structure, referencing previous results for other binary chalcogenide glasses in the As-Se and Ge-Se systems. The findings indicate significant changes in viscosity and activation energy of structural relaxation with the addition of As or Ge, while the non-linearity and non-exponentiality parameters remain largely unaffected.

Measuring thermomechanical response of large-format printed polymer composite structures via digital image correlation

Large-format additive manufacturing (LFAM) is a branch of additive manufacturing (AM) research with the ability to create large structures typically measuring several meters in scale. LFAM is advantageous for tooling applications, not only because it offers the ability to create complex geometries not easily made using subtractive manufacturing processes, but the cost savings of pelletized feedstock used by these systems result in larger parts printed at faster speeds than traditional AM systems. Fiber reinforced polymer (FRP) is a commonly used feedstock material in LFAM structures because it reduces the distortion experienced during printing. However, FRP introduces highly anisotropic thermomechanical properties and contributes to a nonhomogeneous microstructure that can result in critical distortion of dimensions during tooling. Measuring the global thermomechanical response of LFAM structures requires a more representative method that accounts for not only anisotropic properties but also the nonhomogeneous nature of the final part. This is where traditional techniques to measure thermomechanical response, such as thermomechanical analysis (TMA), fall short as they assume homogeneity. This study evaluated the coefficient of thermal expansion (CTE) of LFAM structures as measured by TMA as compared to a novel digital image correlation oven (DIC Oven) system. The LFAM structures were made from 20 % by weight carbon fiber reinforced acrylonitrile butadiene styrene (CF-ABS). TMA measurements showed significant variations in CTE across a single LFAM bead, confirming the need for a global technique that captures overall thermomechanical response. The CTE values measured using the DIC Oven compared well to average TMA values obtained from localized measurements across the sample. The DIC Oven was also used to quantify the effects of different layer orientations on thermomechanical properties, which cannot be easily captured using TMA. A predictive model was also developed by using localized TMA values across an LFAM bead to predict the overall thermomechanical response of an LFAM structure.

On thermal-expansion properties of more-orthotropic prepreg laminates with and without interleaf layers

More-orthotropic laminates are increasingly used in today’s carbon-fiber-epoxy composite airframe structures. A recent study reported on a considerable discrepancy between measured and calculated coefficients of thermal expansion (CTEs) for M21E/IMA prepreg laminates, which was found to increase with the laminates’ degree of orthotropy ξ=Ex/Ey. In this paper it is analyzed whether the observed effect is related to more-orthotropic laminate stackings in general or to the particular inner laminate architecture of M21E/IMA laminates, which is characterized by discrete interleaf layers. Therefore, a quasi-isotropic and three more-orthotropic laminates, made from 8552/AS4 and M21E/IMA prepreg, were analyzed by means of thermo-mechanical analysis (TMA) and classical-laminate theory (CLT). Calculated and measured CTEs are compared and the effect of orthotropy is quantified. Potential affectations of TMA measurements and CTE determination due to edge effects and sample size are examined by means of finite-element analyses.

Thermokinetic behavior of Ga-doped GeTe4 glasses

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used in conjunction to study thermokinetic behavior of (GeTe4)y(GaTe3)100-y bulk infrared glasses (for y between 40 and 100). The DSC data were utilized to describe the glass transition and crystallization kinetics in terms of the Tool-Narayanaswamy-Moynihan and Šesták-Berggren models, respectively. The kinetic data are of sufficient quality to enable predictions utilizable for preparation of Ge-Ga-Te ceramics and glass-ceramics. Whereas the compositional evolution of the positions of glass transition and crystallization effects was found to be small, the activation energies obtained for the two processes have shown that in case of the crystallization process the applied heating rate q+ has large influence on the position of the corresponding kinetic peak on the temperature axis (Tc) and, consequently, on the values of glass stability and glass-forming criteria calculated by using this value. For this reason, a new viscous-flow-related criterion, which utilizes the joint DSC and TMA measurements and is independent from applied q+, was derived to consider the thermal stability of the glassy materials with regard to their processing (fiber-drawing or shape-molding). Based on the newly developed criteria, the (GeTe4)67(GaTe3)33 glass (positioned near the eutectic) was found to be optimal with respect to the fiber-drawing procedure.

Study of rosin softening point through thermal treatment for a better understanding of maritime pine exudation

The temperature of pine rosin softening point was studied to better understand the phenomenon of resin exudation on the surface of pine boards. This problem may decrease strongly the aesthetical performance of wood used outside and is an important concern for the industry. To perform a reliable measurement of rosin properties with a small amount of sample, differential scanning calorimetry (DSC) and thermo mechanical analysis (TMA) techniques were investigated and the results compared. DSC curves on industrial rosin and acetone rosin extractives from maritime pine show a behavior similar to a glass transition in polymers. TMA measurements carried out on the same industrial rosin showed that the softening point is in the midpoint of the transition phase observed by DSC. The softening point temperature is about 45 °C for industrial rosin and about 50 °C for rosin extractives from maritime pine boards. These values are significantly lower than those usually found on other rosins measured by the ASTM E28-14 standard using the ring-and-ball method. When using heat treatment, it was observed for the first time that the thermal history of the sample can change its softening point temperature. With these results, it could be possible to develop a new strategy to reduce rosin exudation for exterior wood siding.

Effects of acrylic adhesives property and optimized bonding parameters on Sn[sbnd]58Bi solder joint morphology for flex-on-board assembly

Acrylic resin with a fast curable property has been used in low temperature ACFs applications. However, its poor thermo-mechanical property was a concern for solder ACFs applications. In this study, a novel thermomechanical analysis (TMA) method was introduced to measure its polymer rebound amounts due to pressures removal after a thermo-compression (TC) bonding process. Polymer resin was laminated between two silicon chips (7∗7mm2), and then a compressive mode TMA measurement was done on the prepared samples. Constant compressive pressures were applied until the temperature was gradually increased to target temperature, and the forces were removed at the target temperatures. The polymer rebound was measured by monitoring the z-axis dimension change after the compressive forces was removed. In addition, the effects of bonding temperatures (from 150 to 250°C) and the bonding pressures (1, 2 and 3MPa) on the SnBi58 (139°C melting point) solder joints morphologies and joint resistances were evaluated to investigate acrylic resin property and find out the optimized bonding conditions for low Tg acrylic-based solder ACFs applications.

In situ shrinkage measurement during pressure‐assisted sintering of low temperature co‐fired ceramic panels

AbstractShrinkage measurements of miniaturized low temperature co‐fired ceramics (LTCC) samples under load typically lead to collapsing of the samples, which hampers the characterization of shrinkage up to full densification. In this paper, a measurement setup is presented, which allows for in situ shrinkage measurements of practical, large LTCC panels during pressure‐assisted sintering in a sintering press. The shrinkage behavior of two commercial LTCC systems (GreenTape 951 and Ceramtape GC) has been measured under loads of up to 1 MPa. No crushing of the specimens was observed and reproducible characterization of shrinkage up to full densification has been performed. Based on comparisons to thermomechanical analyzer measurements in this and other studies, it was found that the in situ approach is much better suited for shrinkage characterization of LTCC under load. Reproducibility and accuracy of the method are discussed and practical as well as more academic applications are proposed.

Thermal properties and viscous flow behavior of As2Se3 glass

Thermal deformation of the As2Se3 bulk samples polished to optical quality has been investigated in the undercooled liquid region using thermomechanical analyzer (TMA). During the non-isothermal measurements the change of sample height has been monitored under compression at different heating rates (1–5 °C/min). The coefficient of linear thermal expansion, glass transition temperature and two characteristic extrapolated temperatures T0, as beginning of sample deformation caused by viscous flow, and Tf, as temperature at which the deformation is stopped by crystal growth and the sample reaches the final height hf, were obtained from TMA measurements. It was found that the value of activation energy obtained from the shift of characteristic temperature Tf with heating rate using the Kissinger method is very close to activation energy of crystal growth obtained by direct monitoring using microscopic methods. The influences of applied force, sample dimensions and heating rate on the overall TMA crystallization curve are discussed. For the first time, theoretical simulations of crystal growth were used to correlate the course of the TMA curve with the direct microscopic observation of the crystallization process.

Structure–property relationships of hyperbranched polyimide–silica hybrid membranes with different degrees of modification

AbstractThe physical and gas transport properties of hyperbranched polyimide (HBPI)–silica hybrid membranes with different degrees of modification prepared with a dianhydride, 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride, a triamine, 1,3,5‐tris(4‐aminophenoxy) benzene, and a coupling agent, 3‐aminopropyltrimethoxysilane, were investigated. With increasing degree of modification, the inherent viscosity of the hyperbranched poly(amic acid) increased, and the density of the HBPI decreased; this suggested the formation of crosslinking through the coupling agent. Dynamic mechanical analysis and thermomechanical analysis measurements indicated that the mobility of the HBPI molecular chains decreased in the rubbery region and that the free‐volume holes of the HBPI increased in the glassy region because of the increased degree of crosslinking through the coupling agent. The CO2 permeability and CO2/CH4 permselectivity of the HBPI–silica hybrid membranes increased with increasing silica content, with the latter increase being remarkable for the HBPI–silica hybrid membranes with a higher degree of modification. This suggested that the pronounced improvement in the CO2/CH4 permselectivity of the highly modified HBPI–silica hybrid membranes was likely caused by the contributions of both the intrinsic high‐fractional free volume attributed to crosslinking through the coupling agent and the characteristic distribution and interconnectivity of free‐volume holes created by hybridization with silica. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Relaxation studies of amorphous alloys with creep induced magnetic and structural anisotropy

Amorphous ferromagnetic (Fe,Co,Ni) ribbons of various compositions have been prepared by rapid solidification and annealed with applied tensile stress. This process yields both creep-induced magnetic anisotropy and structural anisotropy. Post-annealing has been done to investigate the relaxation process. X-ray diffraction and thermomechanical analysis measurement of post-annealed samples reveal a clear underlying relaxation process in the material, proving that structural anisotropy corresponds to the elastic strain induced by creep annealing.

Crystallization in glasses monitored by thermomechanical analysis

Abstract Thermomechanical analysis (TMA) can be used as a sensitive tool to follow crystallization behavior in non-crystalline materials. Newly developed method is based on slowing down of sample deformation caused by viscous flow above the glass transition due to macroscopic crystal growth. It is shown that a typical TMA sigmoidal curve reasonably well corresponds to direct measurement of crystal growth kinetics by means of optical microscopy. The method has been used to study crystallization kinetics in Ge38S62 glass. The TMA measurement is able to detect earlier stages of crystallization than obtained by differential scanning calorimetry measurement. The activation energy obtained from the shift of extrapolated end of TMA curve with heating rate (E = 263 ± 7 kJ mol−1) is similar to the activation energy of α-GeS2 crystal growth in Ge38S62 glass (EG = 247 ± 23 kJ mol−1) obtained from direct optical microscopy measurements.

A novel method to study crystallization of glasses

A novel method to study crystallization behavior in non-crystalline materials has been developed. The method is based on slowing down of sample deformation by viscous flow above the glass transition due to macroscopic crystal growth. This process might be detected by thermomechanical analysis (TMA). The influences of sample length, applied force and heating rate have been examined. Newly developed method has been used to study crystallization in (GeS 2) 0.3(Sb 2S 3) 0.7 glass. It was found that a typical TMA measurement reasonably well corresponds to previously reported crystal growth kinetics by means of optical microscopy. The activation energy obtained from the shift of extrapolated TMA onset temperature with heating rate ( E = 286 ± 8 kJ mol −1) is very similar to the activation energy of Sb 2S 3 crystal growth in (GeS 2) 0.3(Sb 2S 3) 0.7 glass ( E G = 288 ± 7 kJ mol −1) from optical microscopy measurements. The TMA curve does not match with non-isothermal DSC curve taken at comparable experimental conditions. It seems that TMA measurement reflects early stages of crystal growth that are not associated with thermal effects measured by DSC.

Compatibilization of immiscible poly(vinyl chloride) (PVC)/polystyrene (PS) blends with maleic anhydride–styrene–vinyl acetate terpolymer (MAStVA)

In this study, compatibilizing effects of maleic anhydride–styrene–vinyl acetate (MAStVA) with various terpolymer ratios on immiscible blends of poly(vinyl chloride) (PVC) and polystyrene (PS) blends were investigated by viscometry method, thermo-mechanical analysis (TMA) and infrared spectroscopy (FTIR). The viscosimetric measurements were carried out for PVC, PS, a (70:30) blend of PVC/PS and a blend of PVC/PS/MAStVA containing 2–10% of the terpolymer in the range of concentrations (0.25–2.00 g dL −1) where tetrahydrofuran (THF) is the solvent. The interaction parameter (Δ b) was used to study the miscibility and compatibility of polymer blend in solution, obtained from the modified Krigbaum and Wall theory. TMA and FTIR measurements were also used to investigate the miscibility of this pair of polymers. In consequence of the study, it was observed that a considerable improvement was achieved in the miscibility of PVC/PS blends by adding among 4 and 10 wt.% of compatibilizer.

Thermomechanical analysis of laboratory ash, combustion ash and deposits from coal combustion

Mineral impurities in coal form ash and a part of the fly ash form deposits in pulverized coal-firing furnaces. Understanding of the transformation of mineral matter in coals to flyash and deposit formation has improved knowledge and helped industrial engineers better handle ash-related problems. In Australia, ash fusibility tested in accordance to the standardized procedure or measured by Thermo-Mechanical Analysis (TMA) has been widely used to compare and predict slagging potential of various coals. The current study aims at obtaining an understanding of the sensitivity of TMA analysis to the physical, chemical and morphological properties of coal combustion deposits. In the study combustion residues including ash prepared in a laboratory oven at a temperature of 815 °C, flyash collected in a pilot scale furnace and deposits collected from a utility furnace generated from one Australian coal are used for TMA analysis. Ash samples with various levels of iron content were obtained from different milling performance, ash samples with various silicon and alumina contents were prepared by mixing ash with quartz, kaolinite and bauxite. Results indicated that TMA measurements on coal ashes are very sensitive to iron content and can be used to indicate iron related slagging problems in pf-fired boilers. For ash deposits, both the physical properties such as their homogeneous/heterogeneous nature and ash chemistry affect TMA measurement.

Mg-Doped Sapphire Crystal Fibers Grown by Laser-Heated Pedestal Growth Method

We grew sapphire crystal fibers doped with various Mg concentrations from 0.5 to 4 mol % by the laser-heated pedestal growth method. It was easy to grow defect-free 0.5 mol % Mg-doped sapphire crystal fibers longer than 50 mm; however, the length of the defect-free region decreased as the amount of MgO doping increased. The growth rates also influenced the quality of the fibers. Microscopic observations of cross sections of the grown fibers revealed that the defects were always concentrated in the central regions of the fibers. Using an electron probe X-ray microanalyzer, we also found Mg in the central regions of the fibers. We discuss the influence of thermocapillary convection and the growth rate on the Mg distribution, and the reason for the formation of defects by constitutional supercooling is described. Using thermomechanical analyzer measurements, we suggest that the strength of the sapphire can be enhanced by MgO doping, which increases Young's modulus.

Thin Silicon Films on Polymeric Substrate

AbstractLaser crystallization of amorphous silicon film on polymeric substrate is reported. Intrinsic amorphous films 1000 Å thick have been deposited on Polyethersulphone (PES) by PECVD technique in the deposition temperature range of 120‐200 °C. Dehydrogenation and crystallization of the thin films have been obtained by high energy (10 J) XeCl pulsed excimer laser. The irradiation conditions have been varied to study their influence on dehydrogenated and crystallized material properties. Electrical and optical properties of as‐deposited and crystallized films have been investigated. Structural characterization (SEM, XRD, AFM) has been performed. Average crystallite size and grain distribution have been evaluated.For the substrate, the glass transition temperature (Tg) and the coefficient of thermal expansion (CTE) have been evaluated by DSC (Differential Scanning Calorimetry) and TMA (Thermo Mechanical Analysis) measurements and the compatibility with the deposition and crystallization processes have been verified.

Thermomechanical Properties during Cure of Glass-Polyester RTM Composites: Elastic and Viscoelastic Modeling

Resin transfer molding (RTM) is a widely used technique for the manufacturing of composite parts. A proper selection of process parameters is the key to yield successful molding results and obtain a good part. During composite consolidation, resin cure, also called chemical conversion, plays a decisive role on the final mechanical properties of the part. The modeling of resin kinetics and the evolution of composite properties during cure are crucial for process optimization. In this paper, the curing of a thermosetting polyester resin is studied by differential scanning calorimetry (DSC). A semiempirical autocatalytic model is developed to describe the kinetics of the chemical reaction. The model accounts for the maximum degree of polymerization as a function of cure temperature and induction time, i.e., the time required to attain total inhibitor degradation. The evolution of mechanical properties during resin cure for two glass-polyester composites is also studied with a dynamical mechanical thermal analyzer (DMTA) and a thermomechanical analyzer (TMA). Given that for a low chemical conversion, the elastic properties of the resin remain low, an initial degree of polymerization called after gel point (AGP) is introduced in the analysis of the mechanical properties during cure. A normalized elastic modulus is defined from the value at AGP, taken as a reference. The normalized elastic modulus is then compared to the polymerization degree. For pure resin samples, the logarithm of chemical conversion is found to be almost linearly related to the logarithm of the elastic modulus. Based on this comparison, a thermochemical model is proposed to describe the evolution of mechanical properties during the cure of composite samples with different fiber volume fractions. The viscoelastic behavior is also determined by performing stress relaxation tests with the DMTA. Resin specimens are tested for different cure states below the glass transition temperature, and master curves of stress relaxation during cure are constructed by applying the time-temperature superposition principle. The measurements depict the relaxation modulus of polyester resins as sharply affected by the degree of polymerization. Based on the experimental data, a relaxation modulus is modeled in a thermorheologically simple manner using exponential and power laws. Finally, a linear volume change model is constructed based on the TMA measurements of thermal expansion and resin shrinkage. The volume changes resulting from composite expansion-contraction and resin polymerization shrinkage are modeled as a function of temperature and degree of polymerization. The purpose of this work is to develop appropriate models of chemo- and thermomechanical behaviors of glass-polyester composites during cure. A resin cure kinetics model is developed by adding the glass transition effects to the J.L.B. model. For the mechanical properties, two new models are presented to account for the elastic and viscoelastic behaviors of the resin and the composite. Finally, the coefficients of the volume changes model are measured to account for the composite thermal expansion-contraction and resin chemical shrinkage. These models will be used in future investigations for thermal and curing optimization of composites processed by resin transfer molding.

Miscibility behavior and hydrogen bonding in blends of poly(vinyl phenyl ketone hydrogenated) and poly(2‐ethyl‐2‐oxazoline)

AbstractThe miscibility behavior of poly(2‐ethyl‐2‐oxazoline) (PEOx)/poly(vinyl phenyl ketone hydrogenated) (PVPhKH) blends was studied for the entire range of compositions. Differential scanning calorimetry and thermomechanical analysis measurements showed that all the PEOx/PVPhKH blends studied had a single glass‐transition temperature (Tg). The natural tendency of PVPhKH to self‐associate through hydrogen bonding was modified by the presence of PEOx. Partial IR spectra of these blends suggested that amide groups in PEOx and hydroxyl groups in PVPhKH interacted through hydrogen bonding. This physical interaction had a positive influence on the phase behavior of PEOx/PVPhKH blends. The Kwei equation for Tg as a function of the blend composition was satisfactorily used to describe the experimental data. Pure‐component pressure–volume–temperature data were also reported for both PEOx and PVPhKH. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 636–645, 2004

Effects of water content and temperature on the crystallization behavior of FGD scrubber sludge

Massive quantities of flue gas desulfurization scrubber sludges, both sulfate- and sulfite-rich, are generated by coal burning power plants. Environmentally friendly but economical disposal of this sludge is of great importance to the coal industry. To achieve the goal of effective utilization of the scrubber sludges, we have begun to explore developing value-added materials from these sludges. In this paper, we report how water-to-scrubber sludge (w/s) ratio and the fabrication temperature affected the crystal growth behavior of the sludge under pressure. This was accomplished by conducting scanning electron microscopy, X-ray diffraction, Fourier transform infrared, differential scanning calorimetry, and thermomechanical analyzer measurements on the samples formed at 24.2 MPa. Our results suggest that the hydration of hemihydrate, generated from the sludge, resulted in the formation of two phases of calcium sulfate in our materials formed at four different temperatures using two different w/s ratio settings. At T<130 °C, parallelogram-shaped (columnar) gypsum (CaSO 4·2H 2O) and rectangular-shaped (acicular) β-hemihydrate (CaSO 4·0.5H 2O) crystals dominated our materials for w/s=0.2. However, for w/s=0.6, needle-shaped but orientated crystallites formed in the samples. At T>130 °C, the samples mainly exhibited hemihydrate phase in the form of fibrous growths formed by the splitting of gypsum crystallites. The samples fabricated at 90°C exhibited a higher degree of interlocking of the crystallites, which imparted better mechanical property to our materials as depicted by the fracture strength.

Thermomechanical analysis of a polymer dispersed liquid crystal containing a thermoplastic elastomer

Bulk samples of polymer dispersed liquid crystals (PDLCs) containing polystyrene (PS) and a thermoelastic elastomer as polymer matrices, have been prepared by a thermally-induced phase separation method. Thermomechanical analysis measurements revealed that the PDLC containing the thermoplastic elastomer possessed rubber-like elasticity even in the mesomorphic temperature range of the LC while the PDLC based on PS showed plastic deformation during the measurement.