**3.2 The cross-linking and pyrolysis of polysilanes with functional groups**

The mass retaining ratio of EPS1 was much higher than that of EPS2 (Table 7), and was close to that of EPS1/DVB (1/0.5). It could be inferred that the double bonds on EPS1 had played important role in the cross-linking processes and were the cause of high mass retaining ratio. The ceramic yields of self-cross linking samples were dramatically higher, compared with specimens having DVB as curing agent. DVB might form inhomogeneous structure during curing process, leading to lower ceramic yield26. Therefore, it is not necessary to add curing agent to polysilane with double bonds, which is on its own a good ceramic precursor. The Zr-containing EPS3 also had a high mass retaining ratio and a moderate ceramic yield.


DVB: Divinylbenzene , as curing agent.

Table 7. Mass retaining ratio and Ceramic yield of EPS1, EPS2 and EPS3

Electropolymerization of Polysilanes with Functional Groups 17

modified with SiC ceramic27. The introduction of SiC can be achieved by the chemical vapor infiltration (CVI) and the polymer infiltration and pyrolysis (PIP)28. PIP has aroused much interest due to its low manufacturing temperature, ability for the design of precursor molecules, simplicity of formation and feasibility of fabricating complex components. The main precursors for SiC at present are polycarbosilane and polysilane (PS)4. The C/C–SiC composites were manufactured using PS with double bonds by the PIP technique9. The C/C-ZrC-SiC composites were prepared using Zr-containing polysilane. The ablation

The used C/C composites with a density of 1.29 g/cm3 were made by CVI of bulk needled carbon felt and temperature treatment at 2 300 ℃. The C/C–SiC composites and C/C-ZrC-SiC composites were densified by the following procedure: C/C composites → vacuum + pressure infiltration of precursor → cross-linking → pyrolysis → sintering. The process was repeated several times. The maximum density of the obtained C/C–SiC and C/C-ZrC-SiC

The specimens, with a size of ø30 mm×10 mm, were flushed vertically with a H2–O2 torch flame. The inner diameter of the nozzle tip was 4.68 mm. The distance between the nozzle tip and specimen surface was 15.8 mm. The pressure and flux of oxygen were 1.55 MPa and 2.1 L/min, and for hydrogen, they were 0.18 MPa and 1.68 L/min, respectively. The ablation

The thickness of the specimen before ablation (d1) was measured with a micrometer (precision 0.01 mm), and the mass (m1) was measured with an analytical balance (precision 0.1 mg). After ablation, the thickness at the lowest point (d2) and mass (m2) were measured. For the ablation time of t, the linear ablation rate was calculated by (d1-d2)/t, and the mass

1.3 1.4 1.5 1.6 1.7 1.8

The ablation test results are depicted in Fig.12 and Fig.13, which show that the linear and mass ablation rate of the C/C–SiC and C/C-ZrC-SiC were lower than that of the C/C composites at the same density. With the increase of infiltration times, the density of C/C– SiC specimens increased, and the ablation rate decreased. The linear ablation rates of the 1.75 g/cm3 C/C–SiC and 1.69 g/cm3 C/C-ZrC-SiC specimen were 21.7% and 20.6% those of

ρ(**g.cm-3**)

 C/C 180S C/C-ZrC-SiC 180S C/C-SiC 180S

behavior of the C/C–SiC composites and C/C-ZrC-SiC composites were measured.

composites were 1.75 g/cm3 and 1.69 g/cm3, respectively.

ablation rate was calculated by (m1-m2)/t.

**Linear ablation rates**(**mm.s-1**

Fig. 12. Linear ablation rate of specimens

)

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035

time was 180 s.

XRD pattern of the pyrolyzed product of EPS1 at 1300℃(Fig. 10) shows broad peaks of β-SiC (2θ =35.6°,60°,71.8°). That of EPS3 (Figure 11) shows the existence of β-SiC, ZrC, Si and SiO2.

Fig. 10. XRD spectrum of EPS1's pyrolyzed product

Fig. 11. XRD pattern of ceramic from EPS3

#### **3.3 Improvement of the anti-oxidative ablation property of C/C composites by using polysilanes with functional groups**

The poor oxidation resistance of C/C composites restricts its usage in oxidized environments. To improve its oxidative ablation resistance, the matrix of C/C composites is

XRD pattern of the pyrolyzed product of EPS1 at 1300℃(Fig. 10) shows broad peaks of β-SiC (2θ =35.6°,60°,71.8°). That of EPS3 (Figure 11) shows the existence of β-SiC, ZrC, Si and SiO2.

> 20 40 60 80 100 Deg./2θ

30 40 50 60 70 80

**3.3 Improvement of the anti-oxidative ablation property of C/C composites by using** 

The poor oxidation resistance of C/C composites restricts its usage in oxidized environments. To improve its oxidative ablation resistance, the matrix of C/C composites is

ZrC

Si Si

SiC

2θ(。)

SiO2

SiC

Fig. 10. XRD spectrum of EPS1's pyrolyzed product

SiC

ZrC

Fig. 11. XRD pattern of ceramic from EPS3

**polysilanes with functional groups** 

SiO2

modified with SiC ceramic27. The introduction of SiC can be achieved by the chemical vapor infiltration (CVI) and the polymer infiltration and pyrolysis (PIP)28. PIP has aroused much interest due to its low manufacturing temperature, ability for the design of precursor molecules, simplicity of formation and feasibility of fabricating complex components. The main precursors for SiC at present are polycarbosilane and polysilane (PS)4. The C/C–SiC composites were manufactured using PS with double bonds by the PIP technique9. The C/C-ZrC-SiC composites were prepared using Zr-containing polysilane. The ablation behavior of the C/C–SiC composites and C/C-ZrC-SiC composites were measured.

The used C/C composites with a density of 1.29 g/cm3 were made by CVI of bulk needled carbon felt and temperature treatment at 2 300 ℃. The C/C–SiC composites and C/C-ZrC-SiC composites were densified by the following procedure: C/C composites → vacuum + pressure infiltration of precursor → cross-linking → pyrolysis → sintering. The process was repeated several times. The maximum density of the obtained C/C–SiC and C/C-ZrC-SiC composites were 1.75 g/cm3 and 1.69 g/cm3, respectively.

The specimens, with a size of ø30 mm×10 mm, were flushed vertically with a H2–O2 torch flame. The inner diameter of the nozzle tip was 4.68 mm. The distance between the nozzle tip and specimen surface was 15.8 mm. The pressure and flux of oxygen were 1.55 MPa and 2.1 L/min, and for hydrogen, they were 0.18 MPa and 1.68 L/min, respectively. The ablation time was 180 s.

The thickness of the specimen before ablation (d1) was measured with a micrometer (precision 0.01 mm), and the mass (m1) was measured with an analytical balance (precision 0.1 mg). After ablation, the thickness at the lowest point (d2) and mass (m2) were measured. For the ablation time of t, the linear ablation rate was calculated by (d1-d2)/t, and the mass ablation rate was calculated by (m1-m2)/t.

Fig. 12. Linear ablation rate of specimens

The ablation test results are depicted in Fig.12 and Fig.13, which show that the linear and mass ablation rate of the C/C–SiC and C/C-ZrC-SiC were lower than that of the C/C composites at the same density. With the increase of infiltration times, the density of C/C– SiC specimens increased, and the ablation rate decreased. The linear ablation rates of the 1.75 g/cm3 C/C–SiC and 1.69 g/cm3 C/C-ZrC-SiC specimen were 21.7% and 20.6% those of

Electropolymerization of Polysilanes with Functional Groups 19

[5] Subramanian, K., A review of electrosynthesis of polysilane. *Journal of Macromolecular Science-Reviews in Macromolecular Chemistry and Physics* 1998, C38, (4), 637-650. [6] Kashimura, S.; Ishifune, M.; Yamashita, N.; Bu, H. B.; Takebayashi, M.; Kitajima, S.;

magnesium electrodes. *Journal of Organic Chemistry* 1999, 64, (18), 6615-6621. [7] Elangovan, M.; Muthukumaran, A.; Kulandainathan, M. A., Novel electrochemical

[8] Wu, S.; Chen, L.; Zhang, F.-j., Polysilane with double bonds by electrochemical synthesis.

[9] Wu, S.; Chen, L.; Qian, L.; Zhang, J.; Pan, J.; Zhou, C.; Ren, M.; Sun, J., Ablation

[10] Cao, S.-w.; Xie, Z.-f.; Wang, J.; Wang, H.; Tang, Y.; Li, W.-h., Research progress in

[11] Chen, Y.; Du, L., *Organic Quantitative Microanalysis*. Science Press, China: Beijing,

[12] Gozzi, M.; Yoshida, I., Structural evolution of a poly(methylsilane)/tetra-allylsilane mixture into silicon carbide. *European Polymer Journal* 1997, 1301-1306. [13] Yang, G.; Gao, S.; Gu, Q.; Xu, N., Purification of carbosilane dendrimers by column chromatography. *Nanjing Gongye Daxue Xuebao, Ziran Kexueban* 2010, 32, (1), 19-22.

[14] Vermeulen, L. A.; Smith, K.; Wang, J. B., Electrochemical polymerization of

[15] Krzysztof, M.; Dorota, G.; S., H. J.; Kyu, K. H., Sonochemical Synthesis of Polysilylenes

[16] Okano, M.; Takeda, K.; Toriumi, T.; Hamano, H., Electrochemical synthesis of

[17] Colombo, P.; Mera, G.; Riedel, R.; Soraru, G. D., Polymer-Derived Ceramics: 40 Years

[18] Yamaoka, H.; Ishikawa, T.; Kumagawa, K., Excellent heat resistance of Si-Zr-C-O fibre.

[19] Li, X.; Edirisinghe, M. J., Evolution of the ceramic structure during thermal degradation of a Si-Al-C-O precursor. *Chemistry of Materials* 2004, 16, (6), 1111-19. [20] Amoros, P.; Beltran, D.; Guillem, C.; Latorre, J., Synthesis and characterization of

[21] Xing, X.; Liu, L.; Gou, Y.; Li, X., Research progress of polymethylsilane in precursor of

[22] Shibuya, M.; Yamamura, T., Characteristics of a continuous Si-Ti-C-O fibre with low

silicon carbide ceramics. *Guisuanyan Xuebao* 2009, 37, (5), 898-904.

alkyltrichlorosilane monomers to form branched Si backbone polymers.

by Reductive Coupling of Disubstituted Dichlorosilanes with Alkali Metals.

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SiC/MC/C ceramics (M = Ti, Zr, Hf) starting from totally non-oxidic precursors.

oxygen content using an organometallic polymer precursor. *Journal of Materials* 

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*Guisuanyan Xuebao* 2008, 36, (7), 973-977,984.

*Electrochimica Acta* 1999, 45, (7), 1007-1014.

polygermanes. *Electrochimica Acta* 1998, 44, (4), 659-666.

*Journal of Materials Science* 1999, 34, (6), 1333-1339.

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*Gongcheng* 2007, 23, (3), 1-5.

China, 1978.

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Yoshiwara, D.; Kataoka, Y.; Nishida, R.; Kawasaki, S.; Murase, H.; Shono, T., Electroreductive synthesis of polysilanes, polygermanes, and related polymers with

synthesis and characterisation of poly(methyl vinylsilane) and its co-polymers.

properties of C/C-SiC composites by precursor infiltration and pyrolysis process.

hetero-elements containing SiC ceramic precursors. *Gaofenzi Cailiao Kexue Yu* 

the 1.78 g/cm3 C/C specimen, respectively. And the mass ablation rates of the 1.75 g/cm3 C/C–SiC and 1.69 g/cm3 C/C-ZrC-SiC specimen were 78.6% and 31.6% those of the 1.78 g/cm3 C/C specimen, respectively. Therefore, introduction of SiC into C/C composite greatly improved its oxidative ablation-resistive property, and the adulteration of Zr element enhances the effect even more. It is worthwhile to investigate the impact of attaching refractory metals, such as Ta, Zr, Hf, Th, et al. solely or combinatorially to polysilanes on the anti-oxidative ablation property of the C/C composites.

Fig. 13. Mass ablation rate of specimens

### **4. Conclusions**

The electroreduction MeSiCl3 and Allyl chloride monomers carried out with Mg electrodes in a single compartment cell gave polysilane with double bonds. The preferred MeSiCl3/Allyl chloride ratio was 3:1. The molecular weight and yield of the products were affected by the concentration of monomer, the amount of electricity, the electrode's interval time and concentration of supporting electrolyte. By introducing cyclopendienyl ligands as side groups of polysilanes, the polysilanes with refractory metals were obtained by the combination of Cp with the metal elements. The synthesized polysilanes with self-curable ability and high ceramic yields are excellent ceramic precursors.

### **5. References**


the 1.78 g/cm3 C/C specimen, respectively. And the mass ablation rates of the 1.75 g/cm3 C/C–SiC and 1.69 g/cm3 C/C-ZrC-SiC specimen were 78.6% and 31.6% those of the 1.78 g/cm3 C/C specimen, respectively. Therefore, introduction of SiC into C/C composite greatly improved its oxidative ablation-resistive property, and the adulteration of Zr element enhances the effect even more. It is worthwhile to investigate the impact of attaching refractory metals, such as Ta, Zr, Hf, Th, et al. solely or combinatorially to

1.3 1.4 1.5 1.6 1.7 1.8

 C/C 180S C/C-ZrC-SiC 180S C/C-SiC 180S

ρ(**g.cm-3** )

The electroreduction MeSiCl3 and Allyl chloride monomers carried out with Mg electrodes in a single compartment cell gave polysilane with double bonds. The preferred MeSiCl3/Allyl chloride ratio was 3:1. The molecular weight and yield of the products were affected by the concentration of monomer, the amount of electricity, the electrode's interval time and concentration of supporting electrolyte. By introducing cyclopendienyl ligands as side groups of polysilanes, the polysilanes with refractory metals were obtained by the combination of Cp with the metal elements. The synthesized polysilanes with self-curable

[1] Hayase, S., Polysilanes for semiconductor fabrication. *Progress in Polymer Science* 2003, 28,

[2] Roewer, G.; Herzog, U.; Trommer, K.; Muller, E.; Fruhauf, S., Silicon carbide - A survey

[4] Chandrasekhar, V., Polysilanes and Other Silicon-Containing Polymers. In *Inorganic and Organometallic Polymers*, Springer Berlin Heidelberg: 2005; pp 249-292.

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of synthetic approaches, properties and applications. In *High Performance Non-Oxide* 

polysilanes on the anti-oxidative ablation property of the C/C composites.

0.5

ability and high ceramic yields are excellent ceramic precursors.

*Ceramics I*, 2002; Vol. 101, pp 59-135.

1.0

1.5

2.0

**Mass ablation rates**(**mg.s-1**

Fig. 13. Mass ablation rate of specimens

**4. Conclusions** 

**5. References** 

(3), 359-381.

)

2.5

3.0

3.5


**2** 

 *Egypt* 

**Electropolymerization of Some Ortho-**

**from Aqueous Acidic Solution; Kinetics,** 

S.M. Sayyah\*, A.B. Khaliel, R.E. Azooz and F. Mohamed *Polymer Research Laboratory, Chemistry Department, Faculty of Science,* 

*Beni-Suef University 62514, Beni-Suef City,* 

**Mechanism, Electrochemical Studies and Characterization of the Polymer Obtained** 

**Substituted Phenol Derivatives on Pt-Electrode** 

One of the promising methods for waste water remediation is The electrochemical oxidation of hazardous organic species [Fleszar & Jolanta, *1985;* Comninellis, 1994]. Phenols due to their slow degradation, bioaccumulation and toxicity constitute a large group of organic pollutants. The quantitation of phenolic compounds in environmental, industrial and food samples is currently of great interest, which can be found in soils and groundwater [Wang et al., 1998]. Also, these compounds are important synthesis intermediates in chemical industry such as resins, preservatives, pesticides, etc. Another, the main sources of phenolic waste are in glass fiber insulation manufacture on petroleum refineries. Phenol and substituted phenolic compounds such as catechol, chlorophenol are hydroquinones and discharged in the effluent from a number of chemical process industries. Today, these compounds are found in relatively high amount in domestic and industrial wastewater, discharged mainly from the mechanical industries. Many treatment technologies are in use

The electrooxidation of phenolic compounds can be occurs as follows: in the first step of electrooxidation of phenols, phenoxy radicals are generated, then these species can be either oxidized further or be coupled, forming ether and oligomeric or polymeric compounds [Wang et al ,1991; Iotov, & Kalcheva, 1998]. Electropolymerization of phenol beings with the formation of the phenoxy radical, or it can react with a molecule of phenol to give predominantly a para-linked dimeric radical. This radical may be further oxidized to form a neutral dimmer or it may attach another molecule. The dimer may be further oxidized create oligomers to polymers. Formation of the insoluble polyphenol results in deactivation of electrode surface. The relative rates of the two pathways (polymerization and forming quinonic structure) depend on the phenols concentration, the nature of electrode, pH, solvent, additives, electrode potential and current density [Gattrell & Kirk,1993]. Electropolymerization of phenols occur on different electrodes, such as Fe, Cu, Ni, Ti, Au, Pt

or have been proposed for phenol recovery or destruction.

**1. Introduction** 

