Thermal stability definition

Good heat transfer on the outside of the reactor tube is essential but not sufficient because the heat transfer is limited at low flow rates at the inside film coefficient in the reacting stream. The same holds between catalyst particles and the streaming fluid, as in the case between the fluid and inside tube wall. This is why these reactors frequently exhibit ignition-extinction phenomena and non-reproducibility of results. Laboratory research workers untrained in the field of reactor thermal stability usually observe that the rate is not a continuous function of the temperature, as the Arrhenius relationship predicts, but that a definite minimum temperature is required to start the reaction. This is not a property of the reaction but a characteristic of the given system consisting of a reaction and a particular reactor. 

The cationic polymerization of cardanol under acidic conditions has been referred to earlier [170,171], NMR studies [16] indicated a carbonium ion initiated mechanism for oligomerization. PCP was found to be highly reactive with aldehydes, amines, and isocyates. Highly insoluble and infusible thermoset products could be obtained. Hexamine-cured PCP showed much superior thermal stability (Fig. 12) at temperatures above 500°C to that of the unmodified cardanol-formaldehyde resins. However, it was definitely inferior to phenolic resins at all temperatures. The difference in thermal stability between phenolic and PCP resins could be understood from the presence of the libile hydrocarbon segment in PCP. 

The definition of thermal stability of inorganic zinccontaining (Zn(OH)2), organic carbamide-formaldehyde (CFO) components and ZnCFO composite was carried out by the method of differencial-thermal analysis on the derivatograph "Q-1500 D" of F. Paulik, J. 

Thermal Stability. Lithium-ion batteries can be poisoned by water, and so materials going into the cell are typically dried at 80 °C under vacuum. Under these conditions, the separator must not shrink significantly and definitely must not wrinkle. Each battery manufacturer has specific drying procedures. The requirement of less than 5% shrinkage after 60 min at 90 °C (in a vacuum) in both MD and TD direction is a reasonable generalization. 

Mesophase that is thermodynamically stable over a definite temperature or pressure range. Note The range of thermal stability of an enantiotropic mesophase is limited by the melting point and the clearing point of an LC compound or by any two successive mesophase transitions. 

Thermal stability as measured by these ramped TGA experiments of the sort previously described are not the definitive test of a polymer s utility at elevated temperature. Rather, for a polymer to be useful at elevated temperatures, it must exhibit some significant retention of useful mechanical properties over a predetermined lifetime at the maximum temperature that will be encountered in its final end use application. While many of the bisbenzocyclobutene polymers have been reported in the literature, only a few have been studied in detail with regards to their thermal and mechanical performance at both room and elevated temperatures. Tables 7-10 show some of the preliminary mechanical data as well as some other physical properties of molded samples of polymers derived from amide monomer 32, ester monomer 40, diketone monomer 14 and polysiloxane monomer 13. The use of the term polyamide, ester etc. with these materials is not meant to imply that they are to be regarded as merely modified linear thermoplastics. Rather, these polymers are for the most part highly crosslinked thermosets. 

Thermal Stability. In general, pnre AN may be considered stable up to its mp (169.9°) Reports of early investigators, such as Berthelot (Refs 1 8), that the salt begins to decompose at temps as low as 100°, were apparently correct because the substance was not pure. In the days when nitric acid (used for the manuf of AN) was prepd from Chile saltpeter, some nitrites and chlorides, as well as other impurities, remained in the AN, and it was apparently due to them that the stability of the product was not satisfactory. Tram it Velde (Ref 49) found that as little as 0 1% of Amm or Na chloride increases greatly the probability of decompn of AN, while 1—2% of such impurities are definitely the cause of increase of decompn of molten AN... 

The definition of polymer thermal stability is not simple owing to the number of measurement techniques, desired properties, and factors that affect each (time, heating rate, atmosphere, etc). The easiest evaluation of thermal stability is by the temperature at which a certain weight loss occurs as observed by thermogravimetric analysis (tga). Early work assigned a 7% loss as the point of stability, more recently a 10% value or the extrapolated break in the tga curve has been used. A more realistic view is to compare weight loss vs time at constant temperature, and better yet is to evaluate property retention time at temperature one set of criteria has been 177°C for 30,000 h, or 240°C for 1000 h, or 538°C for 1 h, or 816°C for 5 min (1). 

Often safety data or material safety data sheets mention the thermal stability as an intrinsic property of a substance or mixture. In fact, this is an oversimplification of a concept that must be defined in a more comprehensive way. Basically, a substance or a mixture is thermally stable in a situation where the heat released can be removed in such a way that no temperature increase occurs. This definition... 

By using very thin samples, the oven aging of polypropylene can be appreciably accelerated. Specimens of definite and reproducible shape and thickness were made by using a microtome. The first phase of the work evaluated the influence of sample thickness from 0.2 to 12 mils on oven life at different temperatures. In the second phase, this modified technique was used to study the effectiveness of three anti-oxidant/DLTDP systems as thermal stabilizers for polypropylene. The results obtained over a wide spectrum of antioxidant/DLTDP combinations are shown in three-dimensional graphs. 

We became interested in poly(l-trimethylsilyl-l-propyne) [poly(TMSP)] after the initial report of its synthesis (9). Poly(TMSP) possesses many of the qualities needed in a practical deep-UV resist material a high silicon content (—25%) thermal stability excellent film-forming properties and a chromo-phore, the conjugated backbone, that absorbs strongly in the deep-UV region. Our initial work with poly(TMSP) showed that it had one serious drawback its sensitivity toward degradation by deep-UV radiation was poor, and doses of >1 J/cm are required for the definition of a positive-tone pattern. 

A discussion of photostability is not as straightforward as that of thermal stability due to the complexity of photoexposure. Correlation between devices of the same type, either in the same laboratory or at different locations, can be very good if they are operated under the same test conditions. Test results between devices with different sources of radiation (e.g., xenon arc and fluorescent tube) will vary according to the spectral absorption characteristics of the product being tested. Thus it is possible that some products may decompose at an equal rate in systems having different types of irradiation sources however, other products may react quite differently. Although the proposed test is reasonably simple to conduct, there are some practical problems not definitively resolved (e.g., selection of adequate irradiation source and calibration). This chapter will focus on practical problems related to the use of the current guideline. 

Section I deals with the chemistry of explosives. It starts with definitions and nomenclature of organic chemicals, based on molecular structure, which is included to bring nonchemists up to speed on being able recognize and describe pure explosive compounds and mixtures and not to be intimidated by chemists jargon. It then describes the many forms in which these explosive chemicals are used. Using molecular structure as the common thread, the text then goes into the estimation of the stoichiometry of oxidation reactions, the prediction of explosive detonation velocity and pressure properties, and the quantitative analysis of thermal stability. 

All decomposition reactions are endothermal except that of FeU04, presumably because this is the only reaction which involves oxidation of the double oxide. No significant diflFerence was noted in the DTA or TGA curves of the two NiU04 phases. It is interesting to note the alternating pattern in the decomposition reactions of the uranates. The iron, nickel, and zinc double oxides tend to decompose directly into their constituent oxides, while the manganese, cobalt, and copper compounds decompose to other double oxides. The pattern is not carried over into the decomposition temperatures. In this instance, the thermal stability of the double oxides appears to vary directly with the characteristic transition element oxidation states Gr(III) > Mn, Go (III, II) > Ni, Zn(II) > Gu(II, I). The iron compounds constitute a definite exception to this pattern. 

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