Evolved gas profile

Thermal-programmed solid insertion probe mass spectrometry (TP-SIP-MS) has been proposed [247,248], in which the solid insertion probe consisting of a water-cooled microfumace enters the mass spectrometer via an airlock. The sample is contained in a small Pyrex tube (i.d. 1 mm, length 20 mm). The TIC trace gives a characteristic evolved gas profile for each compound in a mixture of materials, and the mass spectra associated with each TIC peak give a positive identification of that component as it is vaporised. TP-SIP-MS is appropriate for analysis of small solid particles which are volatile, or produce volatile decomposition products. The technique is a form of evolved gas analysis. 

Figure 1.3 Evolved gas profiles (EPG) for PTFE, Aflas and PP upon heating at 10 °C / min. Ordinate axis values are arbitrary and simply relative...

EGP Evolved gas profile FD-MS, EDMS Field desorption mass... 

Mass spectrometer data Computation of fractional extent parameter a from MS data is explained with the help of a theoretical evolved gas profile shown in Figure 15.20a and b. In this case, the fractional extent of reaction a can be defined as... 

B. Results from TG-FTIR and STA-FTIR. It is possible to display a number of features of the decomposition pattern in real time and for each of these to be on the same time base for strict comparison purposes. Thus in addition to the weight profile (and its derivative) and the DSC signal, various gas evolution profiles can be plotted. The first of these is the Evolved Gas Profile (EGP) using the Gram-Schmidt orthogonalization method (8). This plots the mean of the integrated IR absorbance in the spectra as a function of time. It should be noted that the shape of the EGP... 

Figure 3. The Specific Gas Profiles for "resin (1160 -1185 cm" ) and "activator (877 - 904 cm ) and the total Evolved Gas Profile generated during a TGA/FT-IR run of a "slow step cured epoxy sample. (Reproduced with permission fi om ref 6. Copyright 1993 Elsevier Science Publishers B.V.)...

SAFETY PROFILE A highly corrosive irritant to the eyes, skin, and mucous membranes. Mildly toxic by inhalation, Explosive reaction with alcohols + hydrogen cyanide, potassium permanganate, sodium (with aqueous HCl), tetraselenium tetranitride. Ignition on contact with aluminum-titanium alloys (with HCl vapor), fluorine, hexa-lithium disilicide, metal acetylides or carbides (e.g., cesium acetylide, rubidium ace-tylide). Violent reaction with 1,1-difluoro-ethylene. Vigorous reaction with aluminum, chlorine + dinitroanilines (evolves gas). Potentially dangerous reaction with sulfuric acid releases HCl gas. Adsorption of the acid onto silicon dioxide is exothermic. See also HYDROGEN CHLORIDE (AEROSOL) and HYDROCHLORIC ACID. 

Acetyl- and isocyanate-bonded chemicals did not stabilize the components degrading at 325 °C, but showed the same thermogra-vimetric and evolved gas analysis profiles as did the controls. Because ester and urethane bonds are not as stable toward pyrolysis as ether linkages at high temperatures, there was a partial release of bonded chemical at low temperatures (117). 

Thermal analysis of PS, poly-p-methylstyrene and polyalpha-methylstyrene was carried out using evolved-gas analysis by IR and mass spectrometry and direct-pyrolysis analysis by mass spectrometric techniques. Evolved-gas analysis, both by IR and mass spectrometry, revealed features due mainly to the corresponding monomers or stable, volatile and low relative molec.wt. degradation products. In direct-pyrolysis mass spectrometry, however, primary decomposition products and heavier fragments such as dimers and trimers could also be detected. The ion-temp, profiles of the corresponding monomer ions revealed information about the thermal stability of the polymers. 25 refs. (XXVIII Colloquium Spectroscopicum Internationale, York, UK, June/July 1993)... 

Decomposition of poly(ethylene terephthalate) as recorded using TG-DTA-FTIR. (A) Simultaneous TG-DTA curves. (B) IR absorption spectra of the evolved gases at various temperatures. (C) Specific gas profiles of the evolved gases. 

Principles and Characteristics Simultaneous thermal analysis techniques, such as TG-DSC/DTA offer vital information on polymer structure based on heat flow behaviour and mass change [290], but little direct information on the composition of evolved gas products. A more complete thermal profile is provided when a thermal analyser is coupled to an identification tool. Henderson et al. [433] have recently described TG-DSC/DTA with evolved gas analysers (MS and FTIR). The skimmer coupling is the most advanced commercial way of combining a thermobalance or simultaneous TG-DSC/DTA instrument with a quadrupole mass spectrometer [338]. For descriptions of interface techniques in this coupled instrumentation, cfr. ref. [411]. Simultaneous TG-DSC-MS is capable of operation up to 2000°C [434]. 

Davidson [15] applied programmed pyrolysis - evolved gas IR spectroscopic techniques to determine whether for polymethylmethacrylate (PMMA) the evolution profiles of various pyrolysis gases against temperature were sufficiently distinctive to allow reliable identification of different types and to distinguish between different batches of the same type. The results showed that the different types and batches could be reliably identified. Reactions accounting for some of the compounds evolved... 

The electrolytes Na", and Cl are second only to glucose in being the most frequently run hospital tests. Many clinical chemistry analyzers now contain an ISE module for electrolyte analysis. Most commonly the module will consist of a Na -glass electrode, a valinomycin/PVC electrode, a Ag/AgCl pellet or a quaternary ammonium ion/PVC electrode and a reference electrode. A selective electrode for the bicarbonate ion continues to elude workers in the field. An indirect measurement of HCOf must be made. The sample is usually reacted with acid to evolve carbon dioxide gas which is measured with a traditional Severinghaus type CO2 electrode. Alternatively, the sample is treated with base to convert HCO to CO3 and a carbonate ion-selective electrode is used In this manner, the complete primary electrolyte profile is obtained electrochemically. 

Equation (9.41) constitutes a fundamental solution for purely convective mass burning flux in a stagnant layer. Sorting through the S-Z transformation will allow us to obtain specific stagnant layer solutions for T and Yr However, the introduction of a new variable - the mixture fraction - will allow us to express these profiles in mixture fraction space where they are universal. They only require a spatial and temporal determination of the mixture fraction/. The mixture fraction is defined as the mass fraction of original fuel atoms. It is as if the fuel atoms are all painted red in their evolved state, and as they are transported and chemically recombined, we track their mass relative to the gas phase mixture mass. Since these fuel atoms cannot be destroyed, the governing equation for their mass conservation must be... 

The separation of the two sets of desorption products may indicate that they are from different sites. That is, branching of the selective and nonselec-tive oxidation takes place on adsorption of butene. This can be confirmed if the two sets of products can be varied independently. This is shown by two experiments. The first experiment makes use of the fact that butene and butadiene adsorb on the same sites. Butadiene is first adsorbed onto the catalyst (5). The catalyst is then heated to 210°C, desorbing all of the unreacted butadiene, but leaving on the surface the precursors of the combustion products. Since desorption of the unreacted butadiene does not involve a net chemical reaction, the adsorpton sites involved are not affected. The catalyst is then cooled to 22°C, and cis-2-butene is adsorbed. If selective oxidation and combustion take place on the same site, the adsorbed butene would undergo both reactions. If they take place on separate sites, and butene adsorbs only on the selective oxidation site (because the combustion site is covered by species from butadiene adsorption), the adsorbed butene would form only butadiene. Subsequent desorption yields a profile similar to that for a single adsorption of ds-2-butene (Fig.l, curve b). More importantly, within experimental errors, the amount of butadiene evolved is the same as in a ds-2-butene adsorption experiment, and the amount of C02 evolved is the same as in a butadiene adsorption experiment. Thus, the adsorbed butene forms only butadiene. These results show that under these experimental conditions (i.e., in the absence of gas-phase oxygen), the production of butadiene and carbon dioxide takes place on separate sites. 

ACGIH TLV TWA 2 mg(Al)/m3 DOT CLASSIFICATION 4.3 Label Dangerous When Wet SAFETY PROFILE Hydrides of some metals (such as ASH3) are extremely toxic. Dangerous fire hazard. An unstable material which is spontaneously flammable in air or O2. Evolves explosive H2 upon contact with moisture. Severe explosion hazard by chemical reacdon wherein H2 gas is produced, also in contact with methyl ethers contaminated by CO2. Mixtures with tetrazole derivadves are explosive. Reacts with oxidizing materials. On contact with acid or acid fumes, it can emit toxic fumes. See also HYDRIDES and ALUMINUM COMPOUNDS. 

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