Thermal Analysis DTA

Thermogravimetric Analysis (TGA). TGA follows the loss in weight of a sample as it is heated, and measures the amount of volatUes versus temperature. Carried to pyrolysis temperature, in nitrogen or in oxygen, it can be used to determine the percent of organic matrix versus inorganic fillers, as well as percent moisture or solvents. 

HPPE = high-pressure polyethylene PTFE = polyetrafluoroethylene 

Thermal Stability. The above techniques (DTA, DSC and TGA) provide measures of thermal stability of polymers. TGA provides a direct measure by observing the temperature(s) at which actual weight loss occurs. DTA/DSC can be used to determine safe storage - and use-temperatures of materials that decompose exothermally by finding the temperature at which exothermic decomposition occurs. These techniques are used extensively in the study of reactive monomers, catalysts and explosives. 

A particularly useful application is the oxidation stability test in which the thermal activity of a specimen is followed in oxygen until a sudden large exotherm occurs. If the sample contains an oxidation inhibitor the onset of the exotherm will be delayed, compared to that of an uninhibited sample. The amount of this delay is a measure of the amount of oxidation inhibitor remaining. 

Analytical pyrolysis consists of heating a sample, preferably suddenly, in a vacuum, and analyzing the vapors produced. It is very much an art, but identification of the vapors - olefins such as ethylene, vinyl chloride, MCN, aldehydes, etc. - provides obvious clues to the composition of the material from which they are broken down. Analysis of the vapors is usually by gas chromatography (GC) or infrared (IR) spectrophotometry. 

The temperature at the start of an exotherm is a measure of the thermal sensitivity of the sample, and the lower the temperature at which this occurs the more sensitive is the material to thermal energy. The difference (AT) be- 

(onset,(°C) Temp,(peak) (°C) Lead MP(°C) Sample weight (mg) 

Azide Exotherm, onset (°C) Exotherm peak (°C) A°C Explosion temperature, (°C)(5 sec delay) 

It has been noted that silver azide explodes at a lower temperature when tested in copper blasting caps than when tested in aluminum blasting caps. It has been observed that the thermocouple catalyzes a strong exothermic reaction just above the azide melting point, whereas when the thermocouple is encapsulated the exothermic reaction is milder [27]. 

This technique measures the temperature difference between a sample and a reference, as temperature is increased. A plot of the temperature difference (thermogram) reveals exothermic and endothermic reactions that may occur in the sample. Temperature for thermal events, such as phase transitions, melting points, crystallization temperatures, and others, can he determined by this method. Maximum temperature capability of DTA is in excess of 1000 °C under air or other gas atmospheres. A typical heat-up rate for DTA is in the range of 10—20 °C/min, although slower rates are possible by using a typical optimum sample weight of 50—100 mg. The sample should be ground to particles finer than 100 mesh. 

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Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

The glass-tiansition tempeiatuiesfoi solution-polymeiized SBR as well as ESBR aie loutinely determined by nuclear magnetic resonance (nmr), differential thermal analysis (dta), or differential scanning calorimetry (dsc). 

Melting temperatures of as-polymerized powders are high, ie, 198—205°C as measured by differential thermal analysis (dta) or hot-stage microscopy (76). Two peaks are usually observed in dta curves a small lower temperature peak and the main melting peak. The small peak seems to be related to polymer crystallized by precipitation rather than during polymerization. 

Thermal Properties. The thermal stabiUty of cellulose esters is deterrnined by heating a known amount of ester in a test tube at a specific temperature a specified length of time, after which the sample is dissolved in a given amount of solvent and its intrinsic viscosity and solution color are deterrnined. Solution color is deterrnined spectroscopically and is compared to platinum—cobalt standards. Differential thermal analysis (dta) has also been reported as a method for determining the relative heat stabiUty of cellulose esters (127). 

Dijferential Thermal Analysis (DTA) A sample and inert reference material are heated at a controlled rate in a single heating block. If an exothermic reaction occurs, the sample temperature will... 

Differential thermal analysis (DTA) Onset temperature of exotherms, heat of reaction, Cp, approximate kinetics... 

What are the consequences What is the maximum pressure Vapor pressure of solvent as a function of temperature Gas evolution Differential Thermal Analysis (DTA) / Differential Scanning Calorimetry (DSC) Dewar flask experiments... 

Difl erential thermal analysis (DTA) and differential scanning calorimetry (DSC) are the other mainline thermal techniques. These are methods to identify temperatures at which specific heat changes suddenly or a latent heat is evolved or absorbed by the specimen. DTA is an early technique, invented by Le Chatelier in France in 1887 and improved at the turn of the century by Roberts-Austen (Section 4.2.2). A... 

Reactivity (instability) information Acceleration rate calorimetry Differential thermal analysis (DTA) Impact test Thermal stability Lead block test Explosion propagation with detonation Drop weight test Thermal decomposition test Influence test Self-acceleration temperature Card gap test (under confinement) JANAE Critical diameter Pyrophoricity... 

The experiment duration is mueh longer than for differential thermal analysis (DTA) tests. 

Shock-modified zirconia powder was reacted with lead oxide in controlled differential thermal analysis (DTA) experiments and compared to the unmodified material by Hankey and co-workers [82H01]. This reaction yields... 

Fig. 7.10. The solid state reactivity of shock-modified zirconia with lead oxide as studied with differential thermal analysis (DTA) shows both a reduction in onset temperature and apparent increase in reaction rate. The shock-modified material has a behavior much like the much higher specific surface powder shown in B (after Hankey et al. [82H01]).

Thermogravimetric analysis has also been used in conjunction with other techniques, such as differential thermal analysis (DTA), gas chromatography, and mass spectrometry, for the study and characterisation of complex materials such as clays, soils and polymers.35... 

R.L. Bohon, AnalChem 35 (12), 1845-52 (1963) CA 60,1527 (1964) Approx heats of expin, Qv were detd on mg amounts of propints and expls by differential thermal analysis (DTA). Small-screw-cap metal cupsi sealed with a Cu washer served as constant vol sample containers the initial cup pressure could be controlled from 0 to approximately lOOOpsia. The calibration constant was calcd for each run from the total heat capacity of the cup and the relaxation curve, thereby compensating for equipment variations. 

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

Reactivity (instabiiity) information Acceleration rate calorimetry Differential thermal analysis (DTA) Impact test Thermal stability Lead block test... 

When solids react, we would like to know at what temperature the solid state reaction takes place. If the solid decomposes to a different composition, or phase, we would like to have this knowledge so that we can predict and use that knowledge In preparation of desired materials. Sometimes, intermediate compounds form before the final phase. In this chapter, we will detail some of the measurements used to characterize the solid state and methods used to foUow solid state reactions. This will consist of various types of thermal analysis (TA), including differentlEd thermal analysis (DTA), thermogravimetric analysis (TGA) and measurements of optical properties. 

Recently we investigated ferromagnetic properties of CoPt bimetallic nanoparticles [232,233]. CoPt3 nanoparticles can be prepared by a two-step reduction using NaBH4 as a reductant. The bimetallic nanoparticles were characterized by thermogravimetry (TG) and differential thermal analysis (DTA), FT-IR, TEM) and XRD. Structural and spectroscopic studies showed that the bimetallic nanoparticles adopt an fee crystalline structure with an average particle size of 2.6 nm. SQUID studies revealed... 

In addition to these standardised test methods set by regulation (in particular the transport regulations of dangerous substances), there are laboratory methods that can provide more details regarding substance behaviour. In particular, there is differential thermal analysis (DTA), thermal gravimetric analysis, calorimetry and thermomanometry, which will not be described here. 

Phase diagrams give valuable information about the compounds that can form in a system of components. These compounds can then be prepared and studied. For the experimental determination of phase diagrams the following methods are used. In differential thermal analysis (DTA) a sample of a given composition is heated or cooled slowly... 

See entry differential thermal ANALYSIS(DTA) (reference 1) See other a-nitro... 

See entry differential thermal analysis (dta) See other oxosalts of nitrogenous bases... 

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