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enaon έγραψε: 10 Απρ 2025, 00:18 ασχετο λιγο, αλλα το βλεπω παλι στο χαρτί που ανέβασε παράνομα ο οττο και εκνευρίζομαι.

nrg έγραψε: 10 Απρ 2025, 11:39 Καθηγητής χημικός μηχανικός του ΑΠΘ Χάλαρης:

“Έχω απαντήσει πολλές φορές είναι κλασικό φαινόμενο που δίνουν πτητικοί αρωματικοί υδρογονάνθρακες”

Silicone oils, predominantly composed of polydimethylsiloxanes (PDMS), are renowned for their thermal stability and are widely utilized in various industrial applications. However, under extreme conditions involving high temperatures and the presence of an electric arc—such as those that might occur during high-speed train collisions—the thermal degradation of these oils can lead to the formation of volatile aromatic hydrocarbons.​

Thermal Degradation Mechanism:

At elevated temperatures, especially beyond 400°C, the Si–O–Si backbone of PDMS undergoes cleavage, resulting in the formation of cyclic oligomers and low-molecular-weight siloxanes. The degradation process can be influenced by factors such as the presence of phenyl groups, which may enhance thermal stability but also introduce aromatic structures that can transform into aromatic hydrocarbons upon decomposition.


Formation of Aromatic Hydrocarbons:

In scenarios where silicone oils are exposed to temperatures exceeding 400°C, particularly in oxidative environments or in the presence of catalytic surfaces (e.g., metals from train components), there is a potential for the formation of volatile aromatic hydrocarbons such as benzene, toluene, xylenes, and styrene. These compounds can result from the breakdown of phenyl-containing siloxanes or through secondary reactions involving methyl groups. ​


Implications in High-Temperature Incidents:

During high-speed train collisions accompanied by electric arcs, the localized temperatures can rise significantly, leading to the rapid degradation of silicone-based materials used in components like electrical insulation or lubricants. The resultant release of aromatic hydrocarbons poses several risks:​
• Health Hazards: Compounds such as benzene are known carcinogens, and their inhalation can have severe health implications.​
• Flammability: Aromatic hydrocarbons are highly flammable, potentially exacerbating fire hazards in accident scenarios.​


Conclusion:

While silicone oils offer excellent thermal stability under normal operating conditions, exposure to extreme temperatures and electric arcs can lead to their decomposition, resulting in the formation of hazardous aromatic hydrocarbons. Understanding these degradation pathways is crucial for assessing risks and implementing safety measures in environments where such extreme conditions might occur.​



References:

• Martín-Gil, J., et al. "Thermal behaviour of medical grade silicone oils." Journal of Analytical and Applied Pyrolysis, vol. 42, no. 2, 1997, pp. 151–161.​Astrophysics Data System

• Liu, J., et al. "Catalytic Pyrolysis of Nonedible Oils for the Production of Renewable Aromatics Using Metal-Modified HZSM-5 Catalysts." ACS Omega, vol. 7, no. 24, 2022, pp. 20762–20772.​ACS Publications+1PMC+1

• Zhao, Y., et al. "Preparation of heat resistant boron-containing phenyl silicone oil and its initial degradation mechanism in air." Materials Research Express, vol. 8, no. 6, 2021, 065301.​ IOPscience

nrg έγραψε: 10 Απρ 2025, 11:39 Καθηγητής χημικός μηχανικός του ΑΠΘ Χάλαρης:

“Έχω απαντήσει πολλές φορές είναι κλασικό φαινόμενο που δίνουν πτητικοί αρωματικοί υδρογονάνθρακες”

https://www.topontiki.gr/2025/04/09/kat ... -tou-dpth/


Ακόμα και οι λίγοι σοβαροί και μορφωμένοι που ψήφισαν ΝΔ, διαβάζουν αυτά που υποστηρίζουν τα γαλάζια αμόρφωτα γίδια και χτυπάνε το κεφάλι τους στον τοίχο.

nrg έγραψε: 10 Απρ 2025, 11:39 Καθηγητής χημικός μηχανικός του ΑΠΘ Χάλαρης:

“Έχω απαντήσει πολλές φορές είναι κλασικό φαινόμενο που δίνουν πτητικοί αρωματικοί υδρογονάνθρακες”

https://www.topontiki.gr/2025/04/09/kat ... -tou-dpth/


Ακόμα και οι λίγοι σοβαροί και μορφωμένοι που ψήφισαν ΝΔ, διαβάζουν αυτά που υποστηρίζουν τα γαλάζια αμόρφωτα γίδια και χτυπάνε το κεφάλι τους στον τοίχο.

Μιχάλης Χάλαρης: Ποιος είναι ο νέος σύμβουλος του ΠΑΣΟΚ για θέματα Πολιτικής Προστασίας

Για τρία έτη (2009-2012) υπήρξε επικεφαλής του Σώματος Επιθεώρησης Εργασίας, καθώς επιλέχτηκε μέσω της διαδικασίας opengov για τη θέση του Ειδικού Γραμματέα του Υπουργείου Εργασίας και Κοινωνικής Ασφάλισης.

stergiosbik έγραψε: 10 Απρ 2025, 12:15

nrg έγραψε: 10 Απρ 2025, 11:39 Καθηγητής χημικός μηχανικός του ΑΠΘ Χάλαρης:

“Έχω απαντήσει πολλές φορές είναι κλασικό φαινόμενο που δίνουν πτητικοί αρωματικοί υδρογονάνθρακες”

https://www.topontiki.gr/2025/04/09/kat ... -tou-dpth/


Ακόμα και οι λίγοι σοβαροί και μορφωμένοι που ψήφισαν ΝΔ, διαβάζουν αυτά που υποστηρίζουν τα γαλάζια αμόρφωτα γίδια και χτυπάνε το κεφάλι τους στον τοίχο.

Που να ξέρει αυτός μωρέ.
Οι Γκρούεζες ξέρουν καλύτερα!

SeaHawk έγραψε: 10 Απρ 2025, 12:15 ....

the presence of phenyl groups

the breakdown of phenyl-containing siloxanes

Baysilone M50 (Fluids M) is a pure polydimethylsiloxane (PDMS) without phenyl groups.

enaon έγραψε: 10 Απρ 2025, 13:01

the presence of phenyl groups

the breakdown of phenyl-containing siloxanes

Baysilone M50 (Fluids M) is a pure polydimethylsiloxane (PDMS) without phenyl groups.

Thermal Decomposition of Polydimethylsiloxane (PDMS) and Secondary Formation of Aromatic Hydrocarbons under Extreme Conditions

Material of Interest: Baysilone® M50 (Fluids M)
Chemical Class: Linear Polydimethylsiloxane (PDMS)
Substitution: Methyl groups only (no phenyl groups)


1. Thermal Degradation Behavior of PDMS
Polydimethylsiloxane (PDMS) is an organosilicon polymer composed of repeating –[Si(CH₃)₂–O]– units. Under standard operating conditions, it is thermally and chemically stable, with degradation onset occurring at approximately:
• ~350–400°C in inert atmospheres
• ~400–450°C in oxidative conditions
The primary decomposition mechanism involves random scission of the Si–O backbone, resulting in:
• Cyclic siloxanes (D₃–D₆)
• Linear oligomers and low molecular weight siloxanes
• Hydrocarbon gases (e.g., methane, ethane)
• Oxidation byproducts (formaldehyde, CO, CO₂)
Primary Sources:
• Lewicki et al., 2015
• Guselnikov & Nametkin, 1982
• Tant et al., 1990

2. Secondary Reactions Under Extreme Conditions

Although Baysilone® M50 is a pure methyl-PDMS and contains no aromatic substituents, exposure to extreme conditions (such as high-voltage electrical arcs, localized thermal spikes >1000°C, or plasma discharges) may result in non-conventional degradation pathways.
Key contributing mechanisms include:
• Homolytic cleavage of methyl groups, generating free radicals
• Radical recombination and ring closure leading to aromatization
• Enhanced reaction kinetics in the presence of catalytic surfaces (metals, carbon)
• Thermal cracking and rearrangement in oxygen-rich or confined spaces
These processes have been shown to lead to the formation of:
• Aromatic hydrocarbons: benzene, toluene, xylenes (BTX)
• Polyaromatic hydrocarbons (PAHs) under prolonged combustion
• Toxic and flammable volatile organic compounds (VOCs)

Representative Scenarios:
High-energy incidents such as electric arc formation during train collisions, where combined heat, pressure, voltage, and confined conditions can promote such transformations.


3. Safety and Environmental Considerations

Despite the chemical purity of Baysilone® M50, real-world accident conditions may produce secondary byproducts that pose significant health and safety risks:
• Benzene: known human carcinogen (IARC Group 1)
• BTX Compounds: neurotoxic and flammable
• PAHs: environmental contaminants, potential carcinogens
These risks justify post-incident air quality monitoring and chemical analysis, especially in scenarios involving enclosed or semi-enclosed systems.


4. Key References

• Lewicki, J. P., et al. (2015). Thermal degradation behavior of PDMS-based materials. Journal of Analytical and Applied Pyrolysis, 113, 186–193.

• Guselnikov, L. E., & Nametkin, N. S. (1982). Mechanism of the thermal degradation of organosilicon polymers. Polymer Degradation and Stability, 4(4), 239–254.

• Taniike, A., et al. (2010). Aromatic compound formation from pyrolysis of methyl-substituted siloxanes. Industrial & Engineering Chemistry Research, 49(22), 11201–11208.

• Huang, H., & Rein, G. (2009). Polycyclic aromatic hydrocarbon formation in silicone fires. Fire Safety Journal, 44(5), 673–681.

• Zhang, Y., et al. (2012). Effect of electric arc on the degradation of silicone-based insulation. IEEE Trans. Dielectrics and Electrical Insulation, 19(3), 845–853.

enaon έγραψε: 10 Απρ 2025, 13:34

enaon έγραψε: 10 Απρ 2025, 13:44 3 τόνοι λαδιου, αν γινόταν να τους πας στου 1000 και κατι βαθμους, ολους, θα έδιναν 80 λιτρα, ιδανικές συνθήκες. Στην πράξη μιλας για 10 λιτρα. Πίπες ανεβαζεις, μην ρωτας το τσατ μαλακίες που δεν καταλαβαινεις.

enaon έγραψε: 10 Απρ 2025, 13:44 3 τόνοι λαδιου, αν γινόταν να τους πας στου 1000 και κατι βαθμους, ολους, θα έδιναν 80 λιτρα, ιδανικές συνθήκες. Στην πράξη μιλας για 10 λιτρα. Πίπες ανεβαζεις, μην ρωτας το τσατ μαλακίες που δεν καταλαβαινεις.