Time-temperature index

Figure 8.35. Porosity versus time-temperature index of maturity (TTI) for various carbonate rock units. The TTI values are based on Lopatin s (1971) method. The onset and end of oil generation (the "oil generation window") in terms of TTI units are from Waples (1980). The log linear equations of best fit between porosity and TTI data are also shown. = porosity. (After Schmoker, 1984.)...

Temperatures within the sedimentary section calculated as a fimction of time are used to estimate the maturation level of the organic matter. The kinetic model of vitrinite maturation (Sweeney and Burnham 1990) is the primary method of maturity estimation. Comparison of measured vitrinite reflectance Rg) with the calculated values and present-day temperature profile (Fig. 6.6) is used to control modeling parameters. The time-temperature index (TTI) (Lopatin 1971 Waples 1980) is also computed as a simple method to describe the paleothermal regime. 

Hunt J. M., Lew an M. D. and Hennet R. J. C. (1991) Modeling oil generation with time-temperature index graphs based on the Arrhenius equation. Am. Assoc. Petrol. Geol. Bull. 75, 795-807. 

Aromaticity is the most important property of a carbon black feedstock. It is generally measured by the Bureau of Mines Correlation Index (BMCI) and is an indication of the carbon-to-hydrogen ratio. The sulfur content is limited to reduce corrosion, loss of yield, and sulfur in the product. It may be limited in certain locations for environmental reasons. The boiling range must be low enough so that it will be completely volatilized under furnace time—temperature conditions. Alkane insolubles or asphaltenes must be kept below critical levels in order to maintain product quaUty. Excessive asphaltene content results in a loss of reinforcement and poor treadwear in tire appHcations. 

Over the years many attempts have been made to provide some measure of the maximum service temperature which a material will be able to withstand without thermal degradation rendering it unfit for service. Quite clearly any figure will depend on the time the material is likely to be exposed to elevated temperatures. One assessment that is being increasingly quoted is the UL 746B Relative Temperature Index Test of the Underwriters Laboratories (previously known as the Continuous Use Temperature Rating or Index). 

ISO 2578 [3] calculates a Temperature Index (TI) which is the temperature at which the chosen threshold is reached in (usually) 20,000 hours. The Relative Temperature Index (RTI) is a comparative value with a reference material. The HIC is the halving interval the temperature change needed to halve the time to the end point from the TI. 

From a time-temperature equivalence principle (see below), any material history may be represented by an isothermal equivalent, corresponding to a point U (tu, Tu) in the (t, T) graph. If the point U is below the TSC curve, the material will not undergo failure in the particular conditions. In contrast, if the point U is above the TSC curve, the material will undergo failure because its index % will change sign. 

The most important testing protocol for resistance to deterioration of critical physical properties upon exposure to heat, especially over prolonged periods of time, was designed by the Underwriters Laboratories (UL) [1], The UL temperature index is used to qualify materials for applications (such as use in electrical equipment) regulated by UL. The main purpose of these tests is to ensure that a polymer can be used safely for a prolonged period of time in these applications. A larger value of the UL temperature index implies greater stability, defined in... 

Fluoropolymer manufacturers and suppliers have developed time-temperature-shear-rate data for melt viscosity or melt flow rate (index) to provide an assessment of the thermal stability of these polymers. Figures 6.1 and 6.2 show the melt viscosity of a few commercial grades of polyvinylidene fluoride as a function of temperature at a fixed shear rate. The relationships between melt viscosity and shear rate, and shear stress versus shear rate, are presented in Figs. 

Relative long-time experiments are often performed according to the Underwriters Laboratories (UL) testing protocol [29]. The results, the retention of certain properties upon exposure to heat, are expressed in UL temperature index values. The time and material consuming UL testing procedure is usually preceded by short-time mass retention measurements, mainly performed with TGA equipment. 

UL temperature index, °C/ /T (electrical) Deflection temperature "C 182 h/ po(°F 264 psi) Dielectric strength (short time), KV/cm (volts/mil) Dielectric constant 60Hzh(fHz Dissipation factor X lCt 60Hz/i04Hz Arc resistance, seconds Oxygen index... 

EPI has its maximal value of unity for well-watered conditions, optimal temperatures for net CO2 uptake, and saturating PAR — under other conditions, EPI represents the fraction of maximal net CO2 uptake expected. To calculate EPI for some species in the field, its net CO2 uptake over 24-h periods should be measured in the laboratory while varying one factor at a time, and the environmental conditions in the field should be specified, preferably on a daily basis. Models can be used to predict certain field conditions, such as soil water status as a function of rainfall and time, and monthly averages can sometimes be used, such as for calculating the Temperature Index (3). 

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