Precursors gravimetric analysis

Conversion of the as-deposited film into the crystalline state has been carried out by a variety of methods. The most typical approach is a two-step heat treatment process involving separate low-temperature pyrolysis ( 300 to 350°C) and high-temperature ( 550 to 750°C) crystallization anneals. The times and temperatures utilized depend upon precursor chemistry, film composition, and layer thickness. At the laboratory scale, the pyrolysis step is most often carried out by simply placing the film on a hot plate that has been preset to the desired temperature. Nearly always, pyrolysis conditions are chosen based on the thermal decomposition behavior of powders derived from the same solution chemistry. Thermal gravimetric analysis (TGA) is normally employed for these studies, and while this approach seems less than ideal, it has proved reasonably effective. A few investigators have studied organic pyrolysis in thin films by Fourier transform infrared spectroscopy (FTIR) using reflectance techniques. - This approach allows for an in situ determination of film pyrolysis behavior. 

Since all polymeric intermediates, and in many instances also the final ceramics, are amorphous, only thermal and spectroscopic methods can be utilized to characterize the thermal conversion. The most extensive studies have been performed on the polymer N-methylpolyborosileizane (PBS-Me), made from the single source precursor TADB. The pyrolysis has been monitored in situ by differential thermal analysis combined with thermo-gravimetric analysis and mass spectrometry (DTA/TG/MS). For ex situ investigations, batches of the polymer were treated at different temperatures, cooled to room temperature, and characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy. 

Abstract In situ spectroscopy is an important tool to characterize polymers synthesized via a precursor route. Highly conjugated polymers such as po y(p-phenylene vinylene) (PPV) and PPV derivatives are commonly prepared from a precursor polymer because the final polymers are very insoluble and intractable. Preparation in the precursor form enables the polymer materials to be cast as films. The PPV polymers are obtained from the precursor forms using a thermal elimination reaction. The exact conditions of the reaction are important as they influence the properties of the resultant polymer. The details of this thermal elimination reaction have been analyzed using thermal gravimetric analysis (TGA) coupled with infrared analysis of the evolved gas products. In situ infrared spectroscopy of the precursor films during thermal conversion to the polymers has provided further details about the elimination reaction. We have characterized PPV synthesized from a tetrahydrothiophenium monomer (sulfonium precursor route) and via the xanthate precursor route. PPV derivatives under study include poly(2,5-dimethoxy-p-phenylene vinylene) and poly(phenoxy phenylene vinylene). 

Figure 10.2 Thermal gravimetric analysis of the ZBLAN precursor. Reproduced from reference 21 by permission of Elsevier...

Compound (17-G-V) is used in analysis for the gravimetric determination of nickel. Phosphine complexes of the type tro/is-NiX and (L—L)NiX2 are used as precursors for numerous catalytic reactions some of these have also been discussed as potential anti-tumor agents.2 An unusual class of compounds are the metalladithi-olenes, for example, (17-G-VI) and (17-G-VII), which are readily oxidized to give, formally, Ni111 and Ni1 species. These compounds show metallic conductivity and may show low-temperature superconductivity.3... 

Two types of infrared spectroscopic analysis have been applied. The first is to follow the changes in the evolved gas product infrared spectra during heating. The precursor polymer is heated in a thermal gravimetric analyzer (TGA) and the evolved gases are directed into a gas cell in the infrared spectrometer. This TGA-IR method enables us to characterize the composition of the species evolved during the thermal elimination reaction. 

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