Time-temperature limits

ISO 2578, Plastics - Determination of time-temperature limits after prolonged exposure to heat, 1993. 

ISO 2578, Determination of Time-Temperature Limits after Exposure to Prolonged Action of Heat, ISO, Geneva, Switzerland, 1974. 

The only procedure to have been standardised generally is application of the Arrhenius relation (see below). IEC 21662 is a guide to evaluating the thermal endurance of electrical insulating materials and ISO 257863 applies the same principle to determining time/temperature limits to plastics. In both cases, the accent is more on finding maximum service temperatures rather than extrapolating to normal ambient temperature. Use of the same... 

Pump the blend over a vibrating or rotating screen to separate all lumps larger than the size that can be sterilized by the time-temperature limitation of the sterilization cycle. Discard the oversized lumps. (Calculate the maximum lump size by the Gurney, Laurie charts. See Perry and Chilton. 1 )... 

Chemical Properties. Molybdenum has good resistance to chemical attack by mineral acids, provided that oxidizing agents ate not present. The metal also offers excellent resistance to attack by several liquid metals. The approximate temperature limits for molybdenum to be considered for long-time service while in contact with various metals in the hquid state ate as follows ... 

Molten silver dissolves nearly 10 times its own volume of oxygen, ie, 0.32 wt % above its melting point, and ejects much but not all of the g violently as it solidifies. There appears to be no lower temperature limit at which oxygen does not dissolve in silver. 

Nonmolecular species, including radiant quanta, electrons, holes, and phonons, may interact with the molecular environment. In some cases, the electronic environment (3), in a film for example, may be improved by doping with impurities (4). Contamination by undesirable species must at the same time be limited. In general, depending primarily on temperature, molecular transport occurs in and between phases (5), but it is unlikely that the concentration ratios of molecular species is uniform from one phase to another or that, within one phase, all partial concentrations or their ratios are uniform. Molecular concentrations and species that are anathema in one appHcation may be tolerable or even desirable in another. Toxic and other types of dangerous gases are handled or generated in vacuum systems. Safety procedures have been discussed (6,7). 

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. 

One early program carried out at AUied-Signal, Inc. proposed the use of conductive polymers in remotely readable indicators (210). Conductivity changes induced in the conductive polymer could be read externally and the history of the sample known. Systems designed to detect time—temperature, temperature limit, radiation dosage, mechanical abuse, and chemical exposure were developed. 

Loss of throughput. The combustion of hydrogen to water produces 3.7 times more heat than the combustion of carbon to carbon dioxide. The increase in the regenerator temperature caused by excess hydrocarbons could exceed the temperature limit of the regenerator internals and force the unit into a reduced feed rate mode of operation. 

Freeze thermostat (low water temperature limit) Single-phase protection (preventing attempts to start with loss of one phase of a three-phase electrical supply) Time out (preventing too-frequent starting and motor burn). 

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