Time-temperature dependence

Relatively high (typically 980—1200°C) temperatures are required to decompose spent acids at reasonable burner retention times. Temperatures depend on the type of spent acid. A wide variety of spent acids can be processed in this way, but costs escalate rapidly when the sulfuric acid concentration in spent acid (impurity-free basis) falls below about 75%. A few relatively uncontaminated spent acids can be reused without decomposition by evaporating the excess water in concentrators, or by mixing in fresh sulfuric acid of high concentration. Weak spent acids are frequently concentrated by evaporation prior to decomposition. 

Vulcanisation being a chemical reaction, is time/temperature dependant. In factory operations, vulcanisation is usually carried out in an autoclave using steam under pressure at temperatures up to 160°C. If the lined unit is a vessel too large to fit in an autoclave and has an adequate pressure rating, all outlets can be sealed and it can itself be pressurised. If this technique is employed then care must be taken, as a failure of the steam supply with consequent condensation, can cause a vacuum and subsequent collapse of the vessel. 

The time/temperature-dependent change in mechanical properties results from stress relaxation and other viscoelastic phenomena that are typical of these plastics. When the change is an unwanted limitation it is called creep. When the change is skillfully adapted to use in the overall design, it is referred to as plastic memory. 

In the first one, the desorption rates and the corresponding desorbed amounts at a set of particular temperatures are extracted from the output data. These pairs of values are then substituted into the Arrhenius equation, and from their temperature dependence its parameters are estimated. This is the most general treatment, for which a more empirical knowledge of the time-temperature dependence is sufficient, and which in principle does not presume a constancy of the parameters in the Arrhenius equation. It requires, however, a graphical or numerical integration of experimental data and in some cases their differentiation as well, which inherently brings about some loss of information and accuracy, The reliability of the temperature estimate throughout the whole experiment with this... 

If treatment of the experimental data used by Ehrlich (27), by Ageev, Ionov, and Ustinov (28), and by Lapujoulade (66) is employed, a mere empirical knowledge of the time-temperature dependence is sufficient (see Section I). Most authors, however, use an analytical approach to the treatment of the desorption data, where a simple analytical expression of the time-temperature function is essential. In such a case, the following two schedules are employed due to their feasibility and relative simplicity from the mathematical point of view (i) The temperature T of the adsorbent increases linearly with time t ... 

Crystallization of the polymer when the propellant formulation is subjected to low temperatures can be annoying (12). Formation of additional periodic attractions between molecules has the same effect as additional crosslinking. Upon crystallization, the propellant becomes hard and brittle with low strain capability. If the effect is caused by crystallization of the polymer, the original physical properties are obtained when the propellant is heated above the melting point of the polymer. These effects are time-temperature dependent and can have a significant effect on the selection of operating and storage temperatures... 

The experiments show that the time-temperature dependence of viscosity in the non-Newtonian region of flow may be represented as ... 

Schwakzl, F., and A. J. Staverman Time-temperature dependence of linear viscoelastic behavior. J. Appl. Phys. 23, 838—843 (1952). 

All the examples described above show that confinement in different cases may be responsible for nonmonotonic relaxation kinetics and can lead to a saddle-like dependence of relaxation time versus temperature. However, this is not the only possible reason for nonmonotonic kinetics. For instance, work [258] devoted to the dielectric study of an antiferromagnetic crystal discusses a model based on the idea of screening particles. Starting from the Arrhenius equation and implying that the Arrhenius activation energy has a linear dependence on the concentration of screening charge carriers, the authors of Ref. 258 also obtained an expression that can lead to nonmonotonic relaxation kinetics under certain conditions. However, the experimental data discussed in that work does not show clear saddle-like behavior of relaxation time temperature dependence. The authors of Ref. 258 do not even discuss such a possibility. 

The screen for each chemical kinetic calculation simultaneously displays a variety of characterizations in multiple windows and allows analysis of time/temperature-dependent species and reaction information including species concentrations, species steady-state analysis, individual reaction rates, net production/destruction rates, reaction equilibrium analysis and the temperature/time history of the system. The interactive user-sorting of the species and reaction information from the numerical simulations is mouse/cursor driven. An additional feature also allows interactive analysis and identification of dependent and independent species and reaction pathways, on-line reaction network analysis and pathway/flowchart construe-... 

Abstract Contribution of the Jahn-Teller system to the elastic moduli and ultrasonic wave attenuation of the diluted crystals is discussed in the frames of phenomenological approach and on the basis of quantum-mechanical theory. Both, resonant and relaxation processes are considered. The procedure of distinguishing the nature of the anomalies (either resonant or relaxation) in the elastic moduli and attenuation of ultrasound as well as generalized method for reconstruction of the relaxation time temperature dependence are described in detail. Particular attention is paid to the physical parameters of the Jahn-Teller complex that could be determined using the ultrasonic technique, namely, the potential barrier, the type of the vibronic modes and their frequency, the tunnelling splitting, the deformation potential and the energy of inevitable strain. The experimental results obtained in some zinc-blende crystals doped with 3d ions are presented. 

The next step is simulation of the relaxation time temperature dependence, the procedure similar to what was considered by Sturge [2], As a result, one will obtain the magnitudes of the potential barrier, Vq, the mnnelling splitting, rF, the vibrational frequency, vq, the deformation potential, b), and the energy of inevitable... 

Now we will overview some experiments that reveal the specificities of the Jahn-Teller effect in diluted crystals. First of all, we will discuss a justification of their relaxation origin. We have mentioned before that the first experiments were done on the crystals of aluminum oxide (corundum), yttrium aluminum garnet, yttrium iron garnet, and lithium gallium spinel doped with a number of 3d ions [10,11]. The main result was the discovery of attenuation maximum which was considered to be observed at cot 1 and reconstruction of the relaxation time temperature dependence. In some experiments reported later both the velocity and attenuation of ultrasound were measured as functions of the temperature. They were done on ZnSe and ZnTe crystals doped with transition metals. These crystals have the zinc-blende structure with the Jahn-Teller ion in tetrahedral coordination. The following... 

In spite of the often large contribution of secondary filler aggregation effects, measurements of the time-temperature dependence of the linear viscoelastic functions of carbon filled rubbers can be treated by conventional methods applying to unfilled amorphous polymers. Thus time or frequency vs. temperature reductions based on the Williams-Landel-Ferry (WLF) equation (162) are generally successful, although usually some additional scatter in the data is observed with filled rubbers. The constants C and C2 in the WLF equation... 

The results of EPR measurements on type 316 stainless steel quenched and reheated for 2, 4, 5, 20, and 40 h at 600 °C are shown in Fig. 7.66 (Ref 105). Areas within the anodic peaks increase with heat treatment time the associated values of Pa are 0.05, 0.29, 0.77, 3.90, and 7.36 C/cm2. The time-temperature dependence of EPR values for this steel are shown in Fig. 7.67, in which the C-curve represents the time limit beyond which the sensitized steel fails the ASTM A 262E test (boiling H2S04 + CuS04) (Ref 105). For this correlation, heat treat-... 

Figure 6. Pictorial representation of the phase-pure rutile titania nanocrystals showing time-temperature dependent morphological transformations under controlled hydrothermal synthesis. (Redrawn from Manorama et al. [104] with permission from publisher, Elsevier. License Number 2627071184341).

MDR WITH Square-Root Time-Temperature Dependence [26]... 

Yun, H.M., J.C. Goldsby, and J.A. DiCarlo. 1995c. Time-temperature effects on the rupture and creep strength of oxide fibers, to be published. Yun, H.M., and J.A. DiCarlo. 1996. Time/temperature dependent tensile strength of SiC and Al203-based fibers. Pp. 17-25 in Advances in Ceramic-Matrix Composites III, Vol. 74 in Ceramic Transactions, N.P. Bansal and J.P. Singh (eds.). Westerville, Ohio American Ceramic Society. 

Ada Adachi, T., Osaki, M., Yamaji, A., Gamou, M. Time-temperature dependence of the fracture toughness of a poly (phenylene sulphide) polymer. Proc. of the Institution of Mech. Engineers, Part L J. Mater. Design and Applications 217 (2003) 29-34. 

Ada Adachi, T., Osaki, M., Yamaji, A., Gamou, M. Time-temperature dependence of the fracture... 

H-M. Yun and J.A. DiCarlo, Time/Temperature Dependent Tensile Strength of SiC and AlaOs-Based Fibers , Ceramic Transactions, 74, 1996, p. 17-26. 

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