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5
МЕЖФАЗНЫЕ СЛОИ И ПРОЦЕССЫ ВЗАИМОДЕЙСТВИЯ В НИХ
УДК 541.6+536.46
INVESTIGATION OF CARBONIZATION PROCESS KINETICS IN INTERFACE LAYERS OF PHOSPHORUS-CONTAINING COMPOUNDS BY X - RAY PHOTOELECTRON SPECTROSCOPY
V.I. KODOLOV, A.M. LIPANOV, S.G. SHUKLIN. I.N. SHABANOVA, JU.V. RUTZ, E.SH. SHAJAKHMETOVA
Basic Research - High Educational Center of Chemical Physics and Mesoscopy, Ural Branch, Russian Academy of Sciences, Izhevsk, Russia
ABSTRACT. The processes proceeding in surface and interface layers of organophospho-rus substances, including phosphorus containing polymeric materials, during their thermolysis and pyrolysis are investigated by X - ray photoelectron spectroscopy and TG -DTA analysis. Methods of samples production and results interpretation for kinetic relation obtaining are proposed. The temperature regions, in which chemical particles diffusion into surface layers during heating in spectrometer chamber is not prevailing in comparison with the chemical process, are determined. The destruction and carbonization processes of phosphorus-containing (methyl- or phenylphosphonic acids) and the phosphorus vanadium containing (polyamide modified by P-V fire retardant) substances as well as the destruction (dechlorination) of P, CI containing polybutadiene are considered The kinetics characteristics of some reaction being preliminary stage of carbonization, for instance, kinetic parameters of dehydrochlorination and methyldechlorination for phosphorus chlorine containing polybutadiene, are found. The mechanism of above substances carbonization is discussed and the consequence of reactions during this processes supported. It is found out that the processes in interface regions proceed more than 10 times comparing to a volume.
INTRODUCTION
The carbonization conditions of organic substances, when there are phosphorus-containing compounds in them, were determined in [1 - 2]. It is shown that the formation of carbon graphite - like products obtained in the above processes proceed at lower temperature. Besides, there are many publications concerning the investigations of kinetics processes of polymers destruction, including phosphorus-containing polymers, for example [3]. Further, it is of interest to study kinetics of processes proceeding in the interface layers of phosphorus containing substances including the carbonization of these substances.
ХИМИЧЕСКАЯ ФИЗИКА И МЕЗОСКОПИЯ. Том 3, Ne 2
INVKST1GA I ION OF CARBONIZATION PROCESS KINETICS IN INTERFACE LAYERS OF PHOSPHORWS-C OBTAINING COMPOUNDS BY X - RAY PHOTOELECTRON SPECTROSCOPY
experimental
Samples of organophosphorus acids, model mixtures of them and aromatic hydrocarbons or olygoincric compounds, phosphorus-containing polymeric films are studied by TG - DTA analysis and X i<n photoelectron spectroscopy.
Hie sample are placed on metal plates. The spectra are obtained using X - ray pho-toclcctron magnciK- .pectrometer (AlKaradiation) and X - ray electron spectrometer ES-2401 (MgK„ lodiation) which have been equipped with the chamber for samples heating.
TCI D'l A investigations are carried out on standard equipment for the determination of temperature regions of carbonization stages.
RESULTS AND DISCUSSION
The investigation of carbonization process in surface and interface layers of organophospho-rus compounds, as well as the processes of their destruction, is carried out by X-ray photoelectron spectroscopy, diffractometry and derivatography (TG-DTA analysis). The research methods including the study of processes kinetics are the following:
Examination of initial substances - organophosphorus acids, model systems containing these acids, olygomers containing organophosphorus groups, polymer systems and materials containing phosphorus by X-ray photoelectron spectroscopy, IR-spectroscopy and diffractometry methods.
Investigation of thermal transformation of phosphorus-containing substances and materials using TG-DTA analysis with the display of temperature areas, where the changes in the composition and structure of substances occur. The preparation of samples obtained in these temperature areas in order to study the process in surface and interface layers.
X-ray photoelectron investigation of phosphorus-containing substances (samples) obtained during heating and IR-laser effect on the samples mentioned.
X-ray photoelectron investigation of model systems, which are the films up to 20 mem thick with particles of fine powders of phosphorus-containing fire-retardant systems distributed in them, and the films from phosphorylated polymers.
The calculations of kinetic parameters are carried out in accordance with the changes of content (in per cent) of separate bonds in interface and boundary layers of substances. The reactions of the changes in bond content are considered by their prediction on the basis of possible intermediate and end products experimental and theoretical data. The rate of per cent content changes is determined according to proportional temperature and time fluctuations of heat effect and under the isothermal effect.
Investigation results are the following:
Processes proceeding under thermal effect on phosphorus-containing substances lead to the formation of polyphosphoric acids or their derivatives which stimulate carbonization
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V.I. KODOLOV, A.M. LIPANOV, S.G. SHUKLÏN, l.N. SHABANOVA, JU.V. RUTZ,
E.SH. SHAJAKHMETOVA
processes at lower, in comparison with the processes in volume, temperatures. For example, the formation of graphite-like substances from phenylphosphonic acid can be observed at about 473K. (Fig.l, Fig.2).
It is determined that in surface layers modified by phosphorus-containing substances of polymer materials the chemisorbed molecules of carbon impurities, water and molecules of other environmental substances have a great influence on carbonization process stimulation.
It is ascertained that the introduction of phosphorus-metal-containing redox systems into polymer materials or model systems accelerates the processes of carbonized layers formation in near surface layers (Fig. 3). Here, the oxidation of phosphorus - containing and the reduction of metal-oxide groups are noted.
/
1 \
1 11__— 523K C N v
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Fig.l. Changes of Cls line intensity during alkylphosphonic acid destruction
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Fig.2. Changes of carbon (Cls) and phosphorus (P2p) lines intensity relations during the transformation of naphtalene-methylphosphonic acid mixture under heat action
170 XMMMMECKAfl 0M3MKA M ME30CK0flMR Tom 3, № 2
INVESTIGATION OF CARBONIZATION PROCESS KINETICS IN INTERFACE LAYERS OF PHOSPHORUS-CON rAISING COMPOUNDS BY X-RAY PHOTOELECTRON SPECTROSCOPY
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4 -
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Fig.3. Changes of carbon (Cls) and phosphorus (P2p) lines intensity relations during the transformation of model system containing phosphorus, sodium vanadate and naphtalene
When foaincokes are formed the formation of carbonized surface of the bubble walls of growing carbon-containing foam takes place. As the healing temperature increases, the increasing of phosphorus-containing substances at the sample surface is noted. The increasing of phosphorus-containing products is followed by a higher intensity interaction with a polymer matrix and this positively influences on the rate of foamcoke formation processes.
It is determined that during the pyrolysis of epoxy resin ED-20 modified by phosphorus-nitrogen-containing compounds the intensity of liquid products being formed begins at 573K, this is confirmed by a sharp increase of Cls lines for CH groups. Carbon products accumulate on sample surfaces masking all the other pyrolysis products; therefore, it can be assumed that carbonization process begins at the same temperature as the growth of liquid product quantity. Not more than 12% of carbon from a total content is found on the spall (inner) surface of the samples. Apparently, the interaction of phosphorus-nitrogen-containing compounds with epoxy resin proceeds at the temperature mentioned because the intensity of nitrogen lines with the binding energy 402.1 eV decreases together with the intensity of phosphorous binding energy.
It is determined that chemical processes in a surface layer prevail over the diffusion of chemical particles from inner layers of the polymer film to its surface at 423-473K. Therefore, kinetic parameters (rate constant, activation energy and order of destruction reactions) can be calculated. So, kinetic parameters of phosphorus-chlorine-containing polybutadiene dechlorination are determined. The process in a surface layer is more complex as it consists of dehy-drochlorination and dechloralkylation reactions. The constants of these reactions are 1.5-2
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times higher, and the activation energy - 3-4 times lower in comparison with the results obtained during the process investigation in volume [3].
CONCLUSION
The system of process kinetics investigation methods using X-ray photoelectron spectroscopy is proposed. The increase of carbonization rates during the transformation of phosphorous-containing compounds and materials is noted. In this case the carbonization process rate can increase in 10 times and more.
REFERENCES
1. A.M. Lipanov, V.I. Kodolov. In: Proc. 1st APISCEU. Beijing: IAP, 1990. P. 516-520.
2. V.K. Bulgakov, V.I. Kodolov, A.M. Lipanov. Modeling of polymeric materials combustion. Moscow: Chemistry, 1990 (in Russian).
3. V.Ju. Repkin, S.A. Tjurin, A.D. Lykov et al. Vysokomol. soed., 1987. V.29A, №3. P. 523 (in Russian).
SUMMARY. The processes proceeding in surface and interface layers of organophospho-rus substances, including phosphorus containing polymeric materials, during their thermolysis and pyrolysis are investigated by X - ray photoelectron spectroscopy and TG -DTA analysis. Methods of samples production and results interpretation for kinetic relation obtaining are proposed. The temperature regions, in which chemical particles diffusion into surface layers during heating in spectrometer chamber is not prevailing in comparison with the chemical process, are determined. The destruction and carbonization processes of phosphorus-containing (methyl- or phenylphosphonic acids) and the phosphorus vanadium containing (polyamide modified by P-V fire retardant) substances as well as the destruction (dechlorination) of P, CI containing polybutadiene are considered The kinetics characteristics of some reaction being preliminary stage of carbonization, for instance, kinetic parameters of dehydrochlorination and methyldechlorination for phosphorus chlorine containing polybutadiene, are found. The mechanism of above substances carbonization is discussed and the consequence of reactions during this processes supported. It is found out that the processes in interface regions proceed more than 10 times comparing to a volume.
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