Char, analysis

Char Analysis. Analyses of char samples were performed on specimens prepared at 2CPC/minute and held at temperature for 30 minutes. Below 55CPC carbonaceous char is present. Above 55CPC in air and above 60CPC in nitrogen the residue consists of zinc, zinc oxide, glass and other inorganic species as shown in Table III. 

Table II Results of char analysis for pyrolysis of straw...

Char Analysis. The fragile char was carefully separated with a scalpel from the light color, unreacted portion of the wood pellet, and each fraction weighed. A cpialitative chemical analysis of some char samples was performed using a Fourier Transform Infrared Spectrometer (FTIRS) with preparation as described in Bousman (15). The surface areas of some chars were also characterized using CO2 adsorption. 

Figure 3 shows a linear dependance of phenyl content in the polymer with excess carbon content in the char based on the 1200 °C char analysis with high temperature nitrogen loss accounted for. 

Although aimed at the introductory class, this simple experiment provides a nice demonstration of the use of GG for a qualitative analysis. Students obtain chromatograms for several possible accelerants using headspace sampling and then analyze the headspace over a sealed sample of charred wood to determine the accelerant used in burning the wood. Separations are carried out using a wide-bore capillary column with a stationary phase of methyl 50% phenyl silicone and a flame ionization detector. 

Table 17. Properties and Analysis of Liquid Fuel and No. 6 Fuel Oil Liquid fuel produced by flash pyrolysis using char recycle (Fig. 10).

Various techniques have been used for the determination of oligomers, including GC [135], HPLC [136-138], TLC for polystyrene and poly a-methyl-styrene [139] and SEC for polyesters [140,141]. GC and PyGC-MS can also profitably be used for the analysis of the compositions of volatile products formed using different flame retardants (FRs). Takeda [142] reported that volumes and compositions of the volatile products and morphology of the char were affected by FRs, polymers (PC, PPE, PBT) and their reactions from 300... 

In a Japanese plasma wind tunnel, SPA specimens were tested up to 3.8 MW/m2 at 0.7 bar aerodynamic pressure (Fig. 12). After a test duration of 60 s, no obvious damage was visible. The surface temperature of about 2600°C was reduced to 100°C within 20 min. Further analysis showed a maximum charred depth of the ablator of 15 mm. The carbonization process did not change the geometric dimensions, the new heat protection system can be considered absolutely stable to deformation. The carbonized layer still has a noticeable pressure resistance and transfers the load applied by the dynamic pressure to the structure. 

In similar work, Sturgeon et al. [125] compared direct furnace methods with extraction methods for cadmium in coastal seawater samples. They could measure cadmium down to 0.1 pg/1. They used 10 pg/1 ascorbic acid as a matrix modifier. Various organic matrix modifiers were studied by Guevremont [116] for this analysis. He found citric acid to be somewhat preferable to EDTA, aspartic acid, lactic acid, and histidine. The method of standard additions was required. The standard deviation was better than 0.01 pg/1 in a seawater sample containing 0.07 pg/1. Generally, he charred at 300 °C and atomised at 1500 °C. This method required compromise between char and atomisation temperatures, sensitivity, heating rates, and so on, but the analytical results seemed precise and accurate. Nitrate added as sodium nitrate delayed the cadmium peak and suppressed the cadmium signal. 

Reaction of K3Co(CN) with PMMA. A 1.0 g sample of PMMA and 1.0g of the cobalt compound were combined in a standard vessel and pyrolyzed for 2 hrs at 375°C. The tube was removed from the oven and the contents of the tube were observed to be solid (PMMA is liquid at this temperature). The tube was reattached to the vacuum line via the break-seal and opened. Gases were determined by pressure-volume-temperature measurements on the vacuum line and identified by infrared spectroscopy. Recovered were 0.22g of methyl methacrylate and 0.11 g of CO and C02. The tube was then removed from the vacuum line and acetone was added. Filtration gave two fractions, 1.27g of acetone insoluble material and 0.30g of acetone soluble (some soluble material is always lost in the recovery process). The acetone insoluble fraction was then slurried with water, 0.11 g of material was insoluble in water. Infrared analysis of this insoluble material show both C-H and C-0 vibrations and are classified as char based upon infrared spectroscopy. Reactions were also performed at lower temperature, even at 260°C some char is evident in the insoluble fraction. 

The reaction between CIRh(PPh3)3 and PMMA produces both chloroform soluble and chloroform insoluble fractions (6-7). The soluble fraction contains a material which is very much like PMMA but also contains anhydride by FT-IR analysis. This polymeric fraction also contains rhodium, ligated by methyl and methoxy as well as triphenylphosphine. The chloroform insoluble fraction is about 25% of the total material and will not dissolve in any common laboratory solvent. Charring of PMMA under such conditions has not been previously seen. The char contains rhodium and is also found to retain chloroform, indicative of cross-linking. TGA analysis indicates that the chloroform may be driven off at about 150°C and the remainder is non-volatile at 600°C. 

Char Preparatioa Chars were prepared both by isothermal pyrolysis of 5 g samples of resin in a quartz boat heated in an atmosphere of flowing (0.5 SCFM) N2 in a quartz tube oven (N2 pyrolysis chars) and by open combustion of 1 g samples of resin exposed to 2.8 watts/cm2 of radiant energy from an electric heating panel (4-5) (combustion or burn chars). All chars were finely ground with a glass mortar and pestle prior to analysis. 

The above TGA and elemental analysis studies are consistent with Van Krevelen s two step model for polymer charring (2) in which a polymer first rapidly decomposes at 500°C to fuel gases and a primary char residue characterized by modestly high hydrogen content. On further heating above 550°C, this primary char is slowly converted in a second step to a nearly pure carbon residue by the loss of this hydrogen. 

Table III. Analysis of Carbon and Hydrogen Content of Char Samples for Modified Polyphenylene Oxide With and Without Zinc Coating...

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