Fast thermolysis/FTIR spectroscopy

To emphasize the importance of coworker contributions, the history of our work in this area can be traced. Fast Thermolysis/FTIR Spectroscopy originated in our proposal to the Aerospace Sciences Directorate of the Air Force Office of Scientific Research in the Spring of 1982. At that time the Nicolet 60SX FTIR spectrometer, the first truly rapid-scanning FTIR spectrometer, was about to be introduced, and was needed to make the program viable. 

Fast Thermolysis/FTIR Spectroscopy gives considerable new mechanistic insight into the chemical and physicochemical processes that occur in materials undergoing rapid heating. The pressure and the composition of the atmosphere can be set as desired to gain an additional variable. 

Tendency to Form HQNO(g). Closely related to NO2 is the formation of HONO. At least one additional process, that of H participation, is required before HONO(g) is detected. Kinetic modelling indicates that HONO formation plays a key role in the N-N bond fission process [32]. The formation of HONO has been used in many previous studies of nitramines to rationalize products, but it was not detected directly before Fast Thermolysis/FTIR Spectroscopy was applied. HONO is a reactive and, thus, transient molecule which is not observed without rapid heating and near real-time product detection. However, both the cis and trans-HONO isomers can now be routinely observed from nitramines [30]. 

The temperature at which the higher temperature exotherm occurs with many of these compounds is quite sensitive to the applied pressure in the cell [77]. Because the fast thermolysis/FTIR spectroscopy experiment largely involves the condensed phase, the only way the static pressure in the cell can affect the temperature of the exotherm is by influencing the heterogeneous condensed phase/gas phase chemistry. Thus, we conclude from the pressure sensitivity that the thermal decomposition of alkylammonium nitrate salts involves an extensive amount of heterogeneous gas phase/condensed phase chemistry. This notion is consistent with many of the comments in this section, especially with regard to the participation of HNOo in the degradation chemistry. 

In thermolysis FTIR the sample (typically 200 /ug) is loaded onto a quartz boat, which is inserted straight into a platinum coil filament. With the beam focused several mm above the filament surface, the IR-active gas products from the fast heated sample can be detected in near real-time. Fast thermolysis/FTIR spectroscopy combines rapid-scan FTIR (20 scans/s) with pyrolysis of a material and realtime measurement of the gas spectra [376]. Temperature, mass changes and spectral data of IR active gases are thus measured simultaneously as a function of time during the rapid heating phase. High-resolution vapour phase libraries are used for identification. 

Variations on the theme of fast thermolysis/FTIR spectroscopy include temperature profiling/FTIR spectroscopy, in which the temperature changes of the condensed phase are measured simultaneously with the gas evolution fast-heat-and-hold/FTIR spectroscopy [378], in which isothermal decomposition is studied following rapid heating to a selected temperature and Simultaneous Mass and Temperature Change (SMATCH)/FTIR spectroscopy [379], which has clearly established the connection between the microscale fast thermolysis approach and steady-state combustion of the bulk material. In T-jump/FTIR spectroscopy the thermal decomposition of a material can be studied isothermally after heating at 2000°C/s [376]. 

Apart from the aforementioned sample preparation techniques (SFE, SPE and SPME), other sample collection modes are coupled directly to spectroscopy (e.g. fast pyrolysis and fast thermolysis-FTIR) and spectrometry (e.g. LD-ITMS). 

Brill et al. [376,380] have illustrated the application of T-jump/FTIR spectroscopy with rapid thermolysis of various organoazide polymers and hydroxyl-terminated polybutadiene with and without Ti02 and melamine additives. The T-jump/FTIR technique determines the chemistry of fast pyrolysis. 

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