Heating-cooling Rates Research Articles

Влияние термоциклирования на фазовые превращения в сплаве Ti-49,8%Ni, деформированном при 200 и 600°C

Results of investigation of rolling temperature regime and further thermal cycling on the martensite transformations in the Ti-49.8%Ni alloy are presented. Temperature range of the phase transitions in the alloy is defined by joint effect of two opposite processes, namely phase transformation strengthening and structure relaxation during thermal cycling. It is demonstrated that in the alloy rolled at 200°C change of heating-cooling rate during thermal cycling does not lead to shift of range of the phase transformations, which is in contrast with high temperature (600ºС) deformation.

Synthesis of BSCFO Ceramics Membrane Using a Simple Complexing Method and Experimental Study of Sintering Parameters

A new complexing agent Ethylene Diamine N,N′,N′,N′-Tetra N-Acetyl Diamine(EDTNAD), was used for Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3–δ (BSCFO) synthesis. Some chemicals such as ammonia, nitric acid and citric acid were eliminated in comparison to the commonly used EDTA method. This agent makes complexing synthesis method a single step and causes more homogeneity in the liquid and solid phase. The sintering process was studied at temperatures between 1000 to 1200°C, heating-cooling rates of 1, 2, 5, 10°C/min and dwell time of 2, 5, 10 and 15 h. As-sintered membranes were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and density analysis. From the SEM images and X-ray diffraction of the BSCFO disks, it could be seen that above 1100°C, crystal intensity decreased, and melting and deformation of the disk occurred. The results show that in restricted temperature range, 1000–1100°C, 10% temperature increase leads to about a 4.5% density increase but a 200% increase in dwell time leads to about a 4% density increase. It could be concluded that the effect of temperature on grain growth, porosity and density is more than that of dwell time. Results also showed that the heating-cooling rate has no significant effect on grain size and density.

902 形状記憶複合帯板の3方向曲げ挙動(OS9-1 形状記憶材料の特性と応用)

In order to develop the new function of the shape memory materials, the shape memory composite (SMC) with the shape memory alloy (SMA) and the shape memory polymer (SMP) was fabricated, and the three-way bending motion and recovery force were investigated. The results obtained can be summarized as follows. (1) Two kinds of SMA tapes which show the shape memory effect (SME) and superelasticity (SE) were heat-treated to memorize the round shape. The shape-memorized round SMA tapes were arranged facing in the opposite directions and were sandwiched between the SMP sheets. The SMC belt can be fabricated by using the appropriate factors: the number of SMP sheets, the pressing force, the heating temperature and the holding time. (2) The three-way bending movement in the fabricated SMC belt is observed based on the SME and SE of the SMA tapes and the glass transition of the SMP sheet during heating and cooling. (3) If the SMC belt is heated and cooled by keeping the bent form, the recovery force increases during heating and decreases during cooling based on the three-way properties of the SMC. (4) The development and application of high-functional SMCs are expected by the combination of the SMA and the SMP with various kinds of phase transformation temperatures, volume fractions, configurations and heating-cooling rates.

Two-Way Bending Properties of Shape Memory Composite with SMA and SMP

A shape memory composite (SMC) was fabricated with a shape memory alloy (SMA) and a shape memory polymer (SMP), and its two-way bending deformation and recovery force were investigated. The results obtained can be summarized as follows: (1) two kinds of SMA tapes which show the shape memory effect (SME) and superelasticity (SE) were heat-treated to memorize the round shape. The shape-memorized round SMA tapes were arranged facing in the opposite directions and were sandwiched between the SMP sheets. The SMC belt can be fabricated by using the appropriate factors: the number of SMP sheets, the pressing force, the heating temperature and the hold time. (2) The two-way bending deformation with an angle of 56 degrees in the fabricated SMC belt is observed based on the SME and SE of the SMA tapes during heating and cooling. (3) If the SMC belt is heated and cooled by keeping the bent form, the recovery force increases during heating and degreases during cooling based on the two-way properties of the SMC. (4) The development and application of high-functional SMCs are expected by the combination of the SMA and the SMP with various kinds of phase transformation temperatures, volume fractions, configurations and heating-cooling rates.

Temperature calibration of heat flux DSC's on cooling

The temperature calibration of a TA Instruments 3200-2920 DSC has been performed on cooling using the isotropic → nematic, isotropic → cholesteric and other liquid crystal → liquid crystal transitions of thermally stable, high purity liquid crystals. The thermal stability of these liquid crystals has been verified by measuring the temperature of the mentioned transitions during cyclic heating and cooling experiments. Correspondence has been established between the real and indicated temperature during cooling for all combinations of heating and cooling rates of practical interest: correction values were determined to the indicated temperature in order to obtain the real temperature on cooling. These correction values were calculated as the average from the temperatures of four or five different liquid crystal transitions for each heating-cooling rate combination. The accuracy of the temperature calibration on cooling is ca. 0.2‡C for heating and cooling rates up to 20‡C min−1.

Measurement of Phase Transitions by Photothermal Radiometry: The Semiconductor-To-Metal Transition of Vanadium(IV) Oxide, VO2

A new experimental method of investigating phase transitions of solids, photothermal radiometry, is described. The effects of modulation frequency, laser intensity, and heating-cooling rates on the first-order semiconductor-to-metal phase transition of a microcystalline vanadium dioxide sample have been studied. The PTR signal increases with temperature in both phases, and a negative peak occurs at the phase transition. The intensity of signal is inversely proportional to the square root of frequency at laser-beam chopping frequencies lower than 100 Hz, indicating that the sample is thermally thick, and the signal is controlled by the thermal conductivity and the heat capacity and is independent of the optical properties of the material. The relative peak intensity decreases slightly in the low-frequency range with increasing frequency and more sharply at higher frequencies. The measured temperature of the phase transition decreases linearly with the intensity of illuminating light, from which the static component of the temperature rise at the surface can be determined. From the increase of linewidth with the laser intensity one may estimate the amplitude of the temperature modulation at the surface. The measured temperature of the phase transition increases with increasing heating rate and decreases with increasing cooling rates. The effects of variable light intensity and heating-cooling rates can be eliminated by extrapolation, and the exact temperature of the phase transition is obtained.

Study of the compatibility of plasticizers with poly(vinyl chloride) by dielectric spectroscopy

Dielectric spectroscopy has been applied for studying the compatibility of plasticizers with poly (vinyl chloride) as well as for detecting the phase-inhomogeneities of plasticized systems. Commercial plasticizers having different polarity and compatibility with the polymer have been investigated. The effect of insufficient processing as well as storage and annealing on the physical structure of the compounds are also discussed. For obtaining dielectric spectra, the real and imaginary parts of the dielectric permittivity of liquid plasticizers and plasticized compounds were recorded continuously as a function of temperature in the range from −170 up to +200°C at fixed frequencies and heating-cooling rates. Exudation, the weight loss of the plasticizer, as well as mechanical properties were measured comparatively. It is a generally accepted fact that the compatibility of a plasticizer with a given polymer depends upon their dielectric properties. According to our observations, the temperature dependence of the dielectric permittivity of the plasticizer is of great importance from this point of view, especially in the range of application of the plasticized system. Comparing the dielectric dispersion spectrum of a liquid plasticizer to that of the corresponding plasticized compound, conclusions about the compatibility can be derived. A special polarization is found to be originated from the phase-separation and from the inhomogeneities. Besides the dielectric polarization arising from the polymer chain and plasticizer dipoles, the dielectric spectra show the existence of an interfacial, Maxwell-Wagner type polarization, which is found to be dependent on the inhomogeneities of the texture of the compound.