Utafiti huu umeunda polisiloksani mpya zenye madaraja ya phenylene na vikundi vya pembeni vya ethyl ili kushinda mgongano wa kimolekuli unaodumu katika silicone rubber kati ya unyumbufu wa joto la chini na uthabiti wa joto la juu. Watafiti walilenga kupunguza uharibifu wa joto la juu kwa vitengo vigumu vya phenylene vilivyowekwa kwenye backbone, huku wakihifadhi uhamaji wa mnyororo kwa vikundi vya pembeni vya methyl na ethyl. Polima zilizosanisiwa ziliunganishwa na fumed silica pamoja na hollow glass microspheres, zikafanywa coatings zenye unene wa 3,5 mm, na baada ya pre-treatment ya liquid nitrogen ya −196 °C zikajaribiwa katika mazingira ya plasma-arc wind tunnel yanayofikia 1150 °C.

Coating ya EMEQ-10, iliyojitokeza kuwa composition yenye uwiano bora zaidi, ilionyesha density ya 0,628 g/cm³, tensile strength ya 3,38 MPa na elongation at break ya asilimia 64,44. Katika high-temperature test baada ya cryogenic pre-treatment, back-surface temperature ya coating ilipimwa kuwa 42 °C, huku average mass ablation rate ikiwa 0,027 g/s. Uchunguzi wa surface na cross-section unaonyesha kwamba katika joto la juu hollow glass microspheres na mabaki ya polima yenye phenylene huungana na kutengeneza protective ceramicized layer iliyo dense, yenye continuity kubwa na ambayo watafiti waliielezea kuwa “kama scale armor”.

Hata hivyo, utafiti hauthibitishi kwamba material inaweza kutumika kwa kuendelea na kwa muda mrefu kati ya −196 °C na 1150 °C. Jaribio ni laboratory-scale cycle inayounganisha pre-treatment ya liquid nitrogen ya dakika 15 na staged plasma heating ya takribani sekunde 32. Real flight, long-term thermal cycling, vibration, humidity, radiation, atomic oxygen, fatigue na large-scale manufacturing conditions hazijatathminiwa. Zaidi ya hayo, utafiti ni preprint na bado haujapitia peer review.

Swali kuu la utafiti ni lipi?

Swali kuu ni kama coating inayotegemea silicone inaweza kubuniwa iwe flexible kiasi cha kutopasuka katika liquid-nitrogen temperature, na wakati huo huo iwe stable kiasi cha kuunda protective residue chini ya intense heat flux inayofikia 1150 °C.

Katika backbone ya silicone rubber ya kawaida, silicon na oxygen atoms hupishana. Kwa sababu Si–O–Si backbone ina low rotational-energy barrier, chains zinaweza kuendelea kusogea kwa kiasi fulani hata katika low temperature. Hali hii huipa silicone flexibility, lakini katika high temperature inaweza pia kurahisisha chain kujikunja na kutengeneza cyclic small molecules. Watafiti wanaelezea degradation process hii kama “back-biting” au intrachain cyclization.

Ili kuongeza high-temperature resistance, aromatic phenylene rings zinaweza kuongezwa kwenye polymer backbone. Phenylene units huifanya backbone kuwa rigid, huzuia kutengenezwa kwa volatile cyclic oligomers na huchangia carbonization. Lakini rigidity nyingi inaweza kupunguza chain mobility, kuongeza glass-transition temperature na kufanya material kuwa brittle katika cryogenic temperatures.

Njia ya kipekee ya utafiti ni kuunganisha sifa hizi mbili katika molecular architecture moja:

• Rigid main-chain units: Phenylene bridges zinaunga mkono high-temperature stability na carbonization.
• Flexible main-chain units: Siloxane segments huhifadhi mobility ya polymer chain.
• Flexible side chains: Methyl na hasa ethyl groups huvuruga regular packing kati ya chains na kuongeza low-temperature flexibility.

Kwa nini temperature range ya silicone za kawaida ni ndogo?

Watafiti wanaeleza typical service range ya conventional silicone rubber kuwa takribani −55 °C hadi 300 °C. Kwenye lower limit, crystallization na kupungua kwa chain mobility vinaweza kuwa muhimu; kwenye upper limit, backbone cyclization, formation ya volatile siloxanes, oxidation na surface loss vinaweza kutawala.

Figure 1 inalinganisha molecular approaches tatu. Structure inayotumia flexible main chain pamoja na flexible side groups huwa mobile katika low temperature, lakini inaweza degrade kwa urahisi katika high temperature. Structure yenye flexible main chain na rigid phenyl side groups inaweza kuongeza thermal stability, lakini inaweza kuwa brittle katika low temperature. Katika design ya watafiti, phenylene units zimewekwa ndani ya main chain, huku methyl na ethyl groups zikibaki katika side chains.

“Ethyl effect” ina maana gani?

Katika utafiti, “ethyl effect” inaelezwa kama uwezo wa ethyl side groups kutengeneza steric space zaidi kati ya polymer chains na kufanya regular chain packing kuwa ngumu zaidi. Ethyl group ni bulky zaidi kuliko methyl group. Kuongezeka kwa ukubwa huku kunaweza kuzuia neighboring chain segments kukaribiana, hivyo kuongeza free volume na segmental mobility.

Mechanism hii imetoa matokeo mawili:

1. Glass-transition temperature ya polima ilishuka na flexibility yake katika cryogenic conditions ikaboreshwa.
2. Ingawa ethyl groups zinaweza kukatika kwa urahisi zaidi katika high temperature, bond cleavage hii ilihamasisha interchain crosslinking badala ya intrachain cyclization na kuchangia kutengenezwa kwa more stable carbonized network.

Kwa hiyo ethyl group haikufanya kazi tu kama “more flexible side chain”. Pia ilibadilisha chemical pathway inayotawala wakati wa degradation.

Ni polymer series zipi zilisanisiwa?

Watafiti waliandaa series mbili za polysiloxane:

• EMQ-X series: Ina phenylene-bridged units na methyl siloxane units. Phenylene fraction ilibadilishwa kuwa asilimia 5, 10, 15 na 20 mol.
• EMEQ-Y series: Phenylene fraction iliwekwa constant kwenye asilimia 10 mol, huku ethyl-containing siloxane units zikibadilishwa kati ya asilimia 5, 10, 15 na 20 mol.

Katika detailed comparisons, EMQ-10 na EMEQ-10 samples zilitumika. EMQ-10 ni phenylene-bridged polysiloxane yenye takribani asilimia 10 mol phenylene na isiyo na ethyl side group. EMEQ-10 ni three-component structure yenye takribani asilimia 10 mol phenylene na asilimia 10 mol ethyl. Flexible segments zilizobaki hasa ni methyl siloxane units.

Polima zilisanisiwaje?

Starting materials zifuatazo zilitumika:

• 1,4-bis(dimetilhidroksisilil)benzene: Ilitoa rigid phenylene-bridged unit.
• Hexaethylcyclotrisiloxane: Ilitoa siloxane units zenye ethyl side groups.
• Octamethylcyclotetrasiloxane: Ilitoa flexible siloxane units zenye methyl side groups.
• Hydroxyl-terminated polydimethylsiloxane: Ilitumika kama chain terminator ya kudhibiti chain length.
• Methylsilanolate: Ilitumika kama initiator ya anionic ring-opening polymerization.

Katika reported one-pot method ya EMEQ-10, methyl siloxane, ethyl siloxane na phenylene-containing components zilitumika kwa takribani ratio ya 0,8:0,1:0,1. Mixture ilichanganywa mechanically kwa 250 rpm, ika-dehydrate kwa 110 °C kwa dakika 5 na ika-polymerize kwa atmospheric pressure kwa saa 3,5. Kisha temperature iliongezwa hadi 180 °C na process ikaendelea kwa saa 1. Mwishoni, system ilishikiliwa chini ya vacuum ya −0,10 MPa kwa dakika 30; residual initiator na unreacted monomers zikaondolewa.

Process hii ilitoa gramu 143,3 za EMEQ-10 transparent na viscous, huku yield ikiripotiwa kuwa asilimia 85,6. Number-average molecular weight ilipimwa kuwa 106.600 g/mol na polydispersity index 2,31.

Coating iliandaliwa vipi?

Polysiloxane iliyosanisiwa ilichanganywa na fumed silica, hollow glass microspheres na kiasi kinachofaa cha n-hexane. Fumed silica ilitoa mechanical reinforcement na rheology control, huku hollow glass microspheres zikiongezwa kwa low density na low thermal conductivity.

Tetraethyl orthosilicate na dibutyltin dilaurate zilitumika kufanya coating icure katika room temperature. Mixture ilipakwa kwenye aluminium-alloy surface iliyotayarishwa kwa sanding na ikacure kwa siku 7 katika room temperature. Katika main thermal-protection tests, coating thickness ilichaguliwa kuwa 3,5 mm.

Je, molecular structure iliyolengwa iliundwa kweli?

Nuclear magnetic resonance analyses ziliunga mkono kuingia kwa targeted phenylene, methyl na ethyl groups ndani ya polymer structure. Katika EMQ-10 sample, proton signal iliyoonekana karibu 7,57 ppm ilihusishwa na protons kwenye phenylene ring.

Katika EMEQ-10 sample, signals za ziada zinazohusiana na ethyl group zilionekana:

• Takribani 0,54-0,48 ppm: Methylene protons katika Si–CH₂–CH₃ structure.
• Takribani 0,97-0,94 ppm: Methyl protons katika ethyl group.
• Katika carbon NMR spectrum, takribani 6,78-6,64 na 7,67-7,32 ppm: Carbon signals za ethyl group.

Katika silicon-29 NMR analysis, silicon atoms zilizofungwa moja kwa moja kwa phenyl group zilitoa signal karibu −1,32 ppm; silicon centers zilizo karibu na phenylene group na zilizo mbali zaidi zikatoa signals karibu −19,5 na −20,88 ppm. Additional signals katika EMEQ-10 zilihusishwa na silicon centers zenye ethyl side groups.

FT-IR spectra za EMQ-10 na EMEQ-10 zilionekana kufanana kwa kiasi kikubwa. Vibrations maalum za ethyl group zili-overlap na strong Si–CH₃ bands, hivyo hazikuweza kutenganishwa kwa wazi. Kwa hiyo chemical-structure confirmation haikutegemea FT-IR pekee, bali combined assessment ya proton, carbon na silicon NMR results.

Ethyl group iliathirije molecular weight na viscosity?

Number-average molecular weight ya EMQ-10 ilipimwa kuwa 90.400 g/mol, huku EMEQ-10 ikiwa 106.600 g/mol. Viscosity ya EMEQ-10 ilikuwa 14,57 Pa·s, huku ya EMQ-10 ikiwa 7,35 Pa·s. EMEQ-10 ilikuwa na viscosity karibu mara mbili.

Tofauti hii haiwezi kuhusishwa na presence ya ethyl group pekee; kuongezeka kwa molecular weight pia huongeza viscosity. Comparison ya utafiti inaonyesha kwamba pamoja na ethyl modification, polima yenye higher molecular weight na higher viscosity ilipatikana.

Phenylene fraction ilibadilishaje low-temperature behavior?

Katika EMQ-X series, glass-transition temperature iliongezeka kutoka −118,10 °C hadi −96,92 °C kadiri phenylene fraction ilivyoongezeka. Kuongezeka kwa glass-transition temperature kunaonyesha kwamba movement ya polymer segments huanza kuzuiliwa katika temperature ya juu zaidi. Kwa maneno mengine, increasing phenylene content iliunga mkono high-temperature stability lakini ikapunguza low-temperature flexibility.

Matokeo haya yanathibitisha moja kwa moja silicone dilemma iliyoelezwa mwanzo wa utafiti: backbone rigid zaidi iliongeza heat resistance lakini ikadhoofisha cryogenic flexibility.

Ethyl fraction ilibadilishaje low-temperature behavior?

Katika EMEQ-Y series ambako phenylene fraction iliwekwa constant kwenye asilimia 10 mol, glass-transition temperature ilishuka kutoka −110,05 °C hadi −114,78 °C kadiri ethyl fraction ilivyoongezeka. Lower glass-transition temperature inaonyesha kwamba chain mobility inaweza kuhifadhiwa hadi temperatures za chini zaidi.

Watafiti wanaeleza decrease hii kwa ethyl groups kutenganisha neighboring chains, kuongeza free volume na kuzuia formation ya ordered crystalline regions. Mechanism hii haitegemei direct imaging ya molecular motion, bali tafsiri ya DSC trends na molecular structure.

Phenylene iliathirije high-temperature stability?

Katika EMQ-X series, temperature ya asilimia 5 mass loss iliongezeka kutoka 441,59 °C hadi 480,51 °C kadiri phenylene fraction ilivyoongezeka. Temperature ya maximum degradation rate iliongezeka kutoka 534,04 °C hadi 557,64 °C.

Temperature ya asilimia 5 mass loss ni kipimo kinachoonyesha wakati thermal degradation inaanza kwa kiwango kinachoonekana. Maximum degradation temperature inaonyesha point ambako mass loss rate ni kubwa zaidi. Kuongezeka kwa values zote mbili kunaunga mkono kwamba phenylene units huchelewesha decomposition ya polymer backbone.

Je, ethyl groups zilipunguza high-temperature stability?

Kadiri ethyl fraction ilivyoongezeka katika EMEQ-Y series, temperature ya asilimia 5 mass loss ilishuka kutoka 457,16 °C hadi 432,16 °C, na maximum degradation temperature ikashuka kutoka 548,16 °C hadi 526,69 °C. Kwa hiyo ethyl groups ziliongeza low-temperature flexibility lakini zikapunguza initial thermal-degradation temperatures kwa kiasi fulani.

Watafiti wanaeleza trend hii kwa Si–C bond energies. Bond energy iliyotolewa kwa methyl-group Si–C bond ni 317,9 kJ/mol, wakati ya ethyl-group Si–C bond ni 276,0 kJ/mol. Lower bond energy inaweza kufanya Si–CH₂–CH₃ bond ikatike kwa urahisi zaidi.

Hata hivyo, EMEQ-10 iliacha carbonaceous residue zaidi kuliko EMQ-10 yenye phenylene fraction hiyo hiyo. Hivyo earlier bond cleavage haimaanishi kila mara final protection mbaya zaidi. Cleavage ya ethyl groups huenda ilifungua reaction pathways mpya za interchain crosslinking na formation ya carbonized network.

TG-IR analysis ilionyesha nini kuhusu degradation mechanism?

Katika TG-IR experiments zilizochanganya thermogravimetric analysis na infrared spectroscopy, chemical signatures za gases zilizotoka wakati polima inapashwa joto zilifuatiliwa. Bands karibu 1026 na 1084 cm⁻¹ zilihusishwa na cyclic siloxane products, huku 3016 cm⁻¹ band ikihusishwa na methane.

Katika nitrogen atmosphere, bands za EMEQ-10 zinazohusishwa na cyclic siloxanes zilikuwa dhaifu kuliko za EMQ-10. Watafiti wanaeleza hili kwa bulky ethyl groups kuzuia sterically chain kujikunja na kufanya cyclization.

Cleavage ya weaker Si–C bonds katika ethyl group huenda iliunga mkono interchain crosslinking badala ya intrachain cyclization. Kwa njia hiyo, more stable and interconnected network iliundwa wakati wa pyrolysis.

Katika air atmosphere, bands zinazolingana na carbon monoxide na carbon dioxide zilionekana kwa polima zote mbili. Signals hizi zilikuwa stronger katika EMEQ-10. Methylene hydrogens katika ethyl group kuondolewa kwa urahisi zaidi na oxygen-derived radicals huenda kulisababisha ethyl carbons kubadilishwa zaidi kuwa CO na CO₂ products.

Density na mechanical properties za coatings zilikuwa vipi?

Densities za coatings zenye fumed silica na hollow glass microspheres zilipimwa kati ya 0,628-0,675 g/cm³. Lowest density ya 0,628 g/cm³ iliripotiwa kwa optimized EMEQ-10-based composition.

Tensile strength ya EMQ-10 coating ilikuwa 2,51 MPa, huku EMEQ-10 coating ikiwa 3,38 MPa. Ongezeko katika EMEQ-10 lilikuwa asilimia 34,66. Elongation at break ilipimwa kuwa asilimia 61,70 kwa EMQ-10 na asilimia 64,44 kwa EMEQ-10.

Values hizi zinaonyesha kwamba ethyl modification haikuongeza low-temperature mobility pekee, bali pia tensile strength ya composite coating iliyotayarishwa. Hata hivyo, molecular weight, crosslink density, filler distribution na degree of cure pia huenda zilichangia mechanical results.

Matokeo ya thermal conductivity ni yapi?

Katika high-temperature thermal-conductivity test iliyofanywa 250 °C, values zifuatazo ziliripotiwa:

Hata hivyo, Figure 6d katika main text inaonyesha values za 0,146, 0,152 na 0,143 W/(m·K) kwa PMQ-10, EMQ-10 na EMEQ-10 mtawalia. Utafiti hauelezi wazi tofauti ya test conditions kati ya values za 0,126, 0,119 na 0,116 W/(m·K) zilizotolewa kwa 250 °C na second group of values katika Figure 6d. Kwa hiyo result sets hizi mbili hazipaswi kuunganishwa kimya kimya; inapaswa kuzingatiwa kwamba huenda zinatokana na different but unspecified test conditions.

Plasma-arc wind-tunnel test ilifanywaje?

Tabia ya coatings chini ya high heat flux ilijaribiwa katika plasma-arc micro wind tunnel. Maximum heat flux iliyoripotiwa ilikuwa 0,45 MW/m² na maximum specific enthalpy 2,60 MJ/kg.

Staged-heating program ilikuwa hivi:

1. Initial temperature 250 °C.
2. Kuongezeka hadi 550 °C ndani ya sekunde 10 za kwanza.
3. Kuongezeka hadi 1150 °C katika sekunde 12 zinazofuata.
4. Kushikiliwa 1150 °C kwa sekunde 10.

Total high-temperature exposure ilikuwa takribani sekunde 32. Jaribio hili linawakilisha short-duration, intense aerothermal load; si continuous-service test ya masaa au siku.

PMQ-10 control coating ilifanya vipi?

Commercial PMQ-10 coating yenye phenyl kwenye side chain ilionyesha continuous ablation wakati temperature ilipofikia 1150 °C katika second 22. Carbonaceous layer iliyoundwa kwenye surface ilivunjika kwa kiwango kikubwa na kujitenga na coating.

Phenyl groups za PMQ-10 zimeunganishwa kama side chains kwenye flexible siloxane backbone. Kulingana na watafiti, structure hii haikuweza kutengeneza continuous na mechanically strong microcrystalline regions katika high temperature; ikaacha porous, brittle na irregular residue.

Kwa nini EMQ-10 na EMEQ-10 zilifanya tofauti?

Katika coatings za EMQ-10 na EMEQ-10 ambako phenylene units zimewekwa moja kwa moja kwenye main chain, connected surface scales zilizotenganishwa na cracks ziliundwa baada ya wind-tunnel test. Watafiti walilinganisha appearance hii na ngozi ya mamba na kuiita “scale-armor-like ceramic layer”.

Formation ya structure hii inaelezwa kwa processes mbili zinazotokea pamoja:

• Katika inner regions, gas ilitoka wakati polima inadegrade na porous pyrolysis layer ikaenda kuundwa.
• Kwenye surface, phenylene-containing residues, fumed silica na melted glass microspheres zili-oxidize na kuwa dense ceramic scales.

Boundaries kati ya scales huenda zilisaidia coating kusambaza thermal stress kuelekea edges badala ya kuvunjika kama rigid ceramic moja. Utafiti unaunga mkono mechanism hii kwa morphology na chemical analyses; lakini stress distribution haikupimwa moja kwa moja.

Numerical results katika wind tunnel zilikuwa zipi?

Katika wind-tunnel test bila cryogenic pre-treatment, lowest mass ablation rate haikuwa ya EMEQ-10 bali EMQ-10 yenye 0,023 g/s. EMEQ-10 ilionyesha lower back-surface temperature na lower Figure 6d thermal conductivity. Kwa hiyo “best” result inategemea performance metric inayotumika.

Ni layers zipi ziliundwa kwenye coating cross-section?

SEM cross-sectional images zilionyesha kwamba coating iliyowekwa chini ya heat flux iliunda regions tatu kutoka surface kuelekea substrate:

1. Ceramic layer: Outer region inayokabili plasma moja kwa moja. Hollow glass microspheres ziliyeyuka, zikaungana na polymer residues na kutengeneza dense surface yenye pores ndogo zaidi.
2. Pyrolysis layer: Intermediate region ambako polima ilikuwa partially degraded na baadhi ya microspheres ziliyeyuka au kuvunjika. Ni porous kwa sababu ya kutoka kwa degradation gases.
3. Undamaged layer: Region karibu na substrate ambako temperature rise ilikuwa limited zaidi. Glass microspheres kwa kiasi kikubwa zilibaki intact na distributed ndani ya matrix.

Microspheres nyingi katika undamaged layer zilikuwa takribani micrometers 20-50. Kadiri surface ilivyokaribiwa, melting na coalescence ya microspheres iliongezeka. Morphological change hii inaonyesha strong temperature gradient kupitia coating thickness.

Kwa nini porous inner layer inaweza kuwa na faida?

Gases zilizotoka wakati wa pyrolysis ziliunda porous structure katika inner region. Kwa kuwa gas-filled voids zina lower thermal conductivity kuliko solid material, region hii inaweza kuchelewesha heat kufika substrate.

Lakini porosity si faida kila wakati. Ikiwa surface layer ni porous na loose kupita kiasi, inaweza ku-erode kwa urahisi na plasma flow. Structure iliyopendekezwa na utafiti inategemea coexistence ya insulating porosity ndani na dense, erosion-resistant ceramicization nje.

XPS analysis ilionyesha nini kuhusu surface chemistry?

X-ray photoelectron spectroscopy ilitumika kuchunguza carbon, oxygen na silicon bonds katika surface baada ya ablation. Carbon fraction kwenye EMQ-10 na EMEQ-10 surfaces ilipatikana kuwa kubwa kuliko kwenye PMQ-10.

Watafiti wanaeleza tofauti hii kwa phenylene units kwenye main chain kupoteza hydrogen katika high temperature na kubadilika kuwa aromatic carbon clusters. Phenylene groups zilizuia siloxane backbone kugawanyika kuwa volatile cyclic oligomers na kusaidia kuhifadhi carbonaceous framework.

Katika carbon spectrum ya coatings zote tatu, C–Si bonds zilitawala; contributions ndogo za C–O pia zilikuwepo. C=O bond ilitambuliwa katika EMEQ-10 pekee na kuhusishwa na incomplete combustion wakati wa ablation.

Oxygen na silicon spectra zilionyesha kwamba major inorganic component katika surface residue ilikuwa SiO₂. Si–O bond fraction ya PMQ-10 iliripotiwa kuwa chini kuliko ya EMQ-10 na EMEQ-10. Watafiti wanaeleza hili kwa PMQ-10 kuwa na cyclization zaidi, kutengeneza volatile oligomers na baadaye ku-deposit kama loose silica.

“Scale armor” mechanism inaundwaje?

Mechanism iliyopendekezwa na utafiti inafuata sequence hii:

1. High heat flux huanzisha Si–C bond cleavage, oxidation na pyrolysis kwenye polymer surface.
2. Phenylene units hupoteza hydrogen na kutengeneza aromatic na carbon-rich microcrystalline regions.
3. Fumed silica na melted glass microspheres huungana kuzunguka carbonaceous framework hii.
4. Hard ceramic scales zenye silicon na oxygen nyingi huundwa kwenye surface.
5. Narrow boundaries kati ya scales husaidia coating kusambaza thermal expansion na contraction stresses katika boundaries nyingi ndogo badala ya crack moja kubwa.
6. Porous pyrolysis layer ya chini huzuia heat transfer; undamaged lower layer huhifadhi bonding na aluminium surface.

Mechanism hii inaendana na SEM, elemental distribution, XPS na ablation morphology. Hata hivyo, crystal structure ya microcrystalline regions haijaonyeshwa moja kwa moja kwa detailed diffraction analysis; maelezo ya “aromatic cluster” na stress distribution ni mechanism interpretation iliyotengenezwa na watafiti kutokana na experiments.

Cryogenic pre-treatment ilifanywaje?

Coatings zilishikiliwa katika liquid nitrogen kwa takribani −196 °C kwa dakika 15, kisha zikarejeshwa room temperature na kupashwa hadi 1150 °C katika plasma-arc wind-tunnel program hiyo hiyo.

Baada ya liquid nitrogen, hakuna coating iliyoonyesha obvious crack au separation kutoka substrate kwa naked eye. Hata hivyo, subsequent wind-tunnel test ilionyesha kwamba significant differences zilitokea katika internal structure za coatings zilizoonekana macroscopically intact.

PMQ-10 ilifanya vipi baada ya cryogenic cycle?

PMQ-10 ilionyesha severe ablation damage katika plasma test baada ya liquid-nitrogen pre-treatment. Back-surface temperature ilikuwa 52 °C na average mass ablation rate 0,108 g/s.

Result hii inaonyesha kwamba PMQ-10 haikuweza kuhifadhi stable surface layer si katika high temperature pekee, bali pia ilipowekwa kwanza chini ya cryogenic contraction na kisha rapid heating.

EMQ-10 ilifanya vipi baada ya cryogenic cycle?

Mass ablation rate ya EMQ-10 bila cryogenic pre-treatment ilikuwa 0,023 g/s, lakini iliongezeka hadi 0,045 g/s baada ya cryogenic treatment. Back-surface temperature ilikuwa 50 °C.

Ingawa obvious cracks hazikuonekana mwanzoni kwa naked eye, watafiti wanaona uwezekano kwamba microscopic internal cracks ziliendelea katika phenylene-bridged but ethyl-free structure. Katika high temperature, cracks hizi huenda zilizuia timely na continuous formation ya surface ceramic layer, kisha layer ikavunjika na kujitenga.

Internal microcracks haziku-imaged directly katika section hii. Kwa hiyo microcrack explanation ni proposed mechanism ya kutafsiri observed performance loss.

EMEQ-10 ilifanya vipi baada ya cryogenic cycle?

EMEQ-10 haikuonyesha obvious ablation mark katika high-temperature test baada ya −196 °C pre-treatment. Back-surface temperature ilipimwa kuwa 42 °C na average mass ablation rate 0,027 g/s.

Kwa EMEQ-10 bila cryogenic treatment, ablation rate ilikuwa 0,035 g/s na back-surface temperature 43 °C. Kutokudhoofika kwa results baada ya cryogenic treatment, na hata measured mass loss kuwa lower, kunaonyesha kwamba composition hii ilikuwa stable zaidi dhidi ya low-temperature contraction katika single cycle.

Watafiti wanahusisha tofauti hii na higher tensile na shear strength ya EMEQ-10. Segmental mobility inayotolewa na ethyl groups huenda ilisaidia coating kubeba internal stresses kutoka cryogenic contraction bila kutengeneza microcracks.

Shear strength ilibadilikaje na temperature?

Katika coatings zote tatu, measured shear strength iliongezeka kadiri temperature ilivyopungua. Values zilizotolewa katika Figure 9d ni hizi:

Katika graph axis, values zimepewa kama “tensile-shear strength”, lakini unit haisomeki wazi katika main figure. Kwa hiyo table imehifadhi numbers katika form ya utafiti na haijaongeza unit isiyoweza kuthibitishwa.

EMEQ-10 ilionyesha highest au miongoni mwa highest strength katika temperatures zote. Watafiti wanahusisha increase ya low temperature na kupungua kwa chain mobility na formation ya more ordered structural regions.

Je, coating ilijitenga na substrate?

Kulingana na supplementary data ya utafiti, coatings zote zilionyesha cohesive failure ndani ya coating body badala ya separation kwenye coating–substrate interface katika mechanical tests za room temperature na cryogenic conditions. Observation hii inaonyesha kwamba bonding na aluminium surface haikuwa weaker kuliko internal strength ya coating.

Hata hivyo, results hizi zilizopatikana kwa laboratory preparation method moja hazitoi direct adhesion guarantee kwa large surfaces, complex geometries, vibration, humidity, contamination au manufacturing tolerances.

Utafiti unaunga mkono matokeo gani?

• Kuongeza phenylene units kwenye polysiloxane main chain kuliinua degradation onset na maximum degradation temperature.
• Kuongeza phenylene fraction kupita kiasi kuliinua glass-transition temperature na kupunguza low-temperature flexibility.
• Ethyl side groups zilishusha glass-transition temperature na kuboresha structural stability baada ya cryogenic cycle.
• Ingawa ethyl groups zilipunguza initial thermal-degradation temperature, zilichangia formation ya more crosslinked carbonaceous residue kwa kukandamiza intrachain cyclization.
• Phenylene-bridged EMQ-10 na EMEQ-10 coatings zilionyesha lower mass ablation rate na lower back-surface temperature kuliko side-chain-phenyl PMQ-10.
• EMEQ-10 ilionyesha 42 °C back-surface temperature na 0,027 g/s mass ablation rate katika short-duration plasma test baada ya cryogenic pre-treatment.
• Coexistence ya dense ceramic surface layer na porous inner pyrolysis layer ilichangia thermal protection na erosion resistance.

Utafiti hauthibitishi nini?

• Hauthibitishi kwamba material inaweza kufanya kazi continuously na long-term kati ya −196 °C na 1150 °C.
• Resistance katika 1150 °C inategemea short plasma test yenye hold ya takribani sekunde 10 tu.
• Hakuna flight validation iliyofanywa kwenye real spacecraft, hypersonic vehicle au rocket.
• Fatigue life baada ya thousands of cryogenic-hot cycles haijatathminiwa.
• Atomic oxygen, vacuum, ultraviolet radiation, radiation, humidity, rain, salt, vibration na impact effects hazijajaribiwa pamoja.
• Applicability ya coating kwenye large na curved parts au consistency ya mass production haijaonyeshwa.
• Haijathibitishwa kwamba scale-armor-like layer itaundwa kwa namna hiyo hiyo katika heat fluxes zote na thicknesses zote.
• Haijaonyeshwa kwamba EMEQ-10 ni superior kuliko EMQ-10 kwa kila performance metric; katika test bila cryogenic pre-treatment, EMQ-10 ilitoa lower mass ablation rate.
• Existence ya patent application haimaanishi kwamba technical au commercial success ya material imeidhinishwa rasmi.

Kwa nini ni muhimu kwa Uturuki?

Molecular-design approach ya utafiti ina direct methodological value kwa watafiti nchini Uturuki wanaofanya kazi katika space and aviation, defense industry, rocket-engine environment, cryogenic fuel systems, high-temperature pipe na equipment coatings, fire-resistant composites na low-density insulation materials.

Hasa, utafiti unaonyesha umuhimu wa kusawazisha conflicting requirements katika molecular scale badala ya ku-maximize property moja. Phenylene units ziliunda residue katika high temperature, huku ethyl groups zikisaidia adaptation kwa cryogenic contraction. Fumed silica na glass microspheres zilibadilisha polymer chemistry kuwa multiscale composite structure.

Kwa transition kuelekea real aviation application nchini Uturuki, long-term thermal cycling, mechanical vibration, thermal shock, humidity, vacuum, radiation, oxidation, flame, adhesion aging na scale-up tests zinapaswa kufanywa kwa local formulations. Utafiti huu si ready-to-use product approval, bali strong example ya material design na laboratory validation.

Mbinu na Matokeo ya Utafiti

Muundo wa utafiti

Utafiti ni experimental material study inayounganisha new polymer synthesis, molecular characterization, thermal analysis, composite-coating production, mechanical testing, short-duration plasma-arc ablation test, cryogenic pre-treatment na post-ablation surface-cross-section examinations.

Experimental na control groups

EMEQ-10 synthesis parameters

Matokeo kuu ya structural na mechanical

Muhtasari wa thermal trends

Matokeo kuu ya plasma test

Ujumbe wa kisayansi wa figures

• Figure 1: Inalinganisha flexible-flexible, flexible-rigid na rigid-flexible molecular designs na kuonyesha approach ya “main-chain rigidity + main-chain flexibility + side-chain flexibility”.
• Figure 2: Inaonyesha ring-opening polymerization, formation ya EMQ na EMEQ chains na conversion kuwa composite coating.
• Figure 3: Inaunga mkono incorporation ya phenylene, methyl na ethyl units katika chemical structure kwa NMR na FT-IR signals.
• Figure 4: Inaonyesha kwamba kadiri phenylene inavyoongezeka, glass-transition na degradation temperatures huongezeka; kadiri ethyl inavyoongezeka, glass transition hushuka na degradation onset pia hushuka.
• Figure 5: Inaonyesha EMEQ-10 kutoa less cyclic siloxane product katika nitrogen atmosphere na more prominent CO na CO₂ katika air atmosphere.
• Figure 6: Inaonyesha PMQ-10 ku-erode continuously chini ya plasma, huku EMQ-10 na EMEQ-10 zikitengeneza scale-armor-like layer; pia inaonyesha differences za back-surface temperature na ablation rate.
• Figure 7: Inaonyesha ceramic, pyrolysis na undamaged layers, pamoja na microspheres kuyeyuka kuelekea surface na kutengeneza dense outer layer.
• Figure 8: Inalinganisha distribution ya C–Si, C–O, SiO₂ na Si–O bonds katika post-ablation surface.
• Figure 9: Inaonyesha performance loss ya PMQ-10 na EMQ-10 baada ya −196 °C pre-treatment, na lower back-surface temperature pamoja na lower mass ablation rate ya EMEQ-10.

Nguvu za utafiti

• Unaunganisha molecular design, composite production na high-heat-flux testing katika experimental chain moja.
• Haupunguzi low-temperature na high-temperature performance kuwa metric moja.
• Unatumia commercial side-chain phenyl silicone kama control group.
• Unabadilisha phenylene na ethyl amounts systematically katika separate polymer series.
• Unaunganisha NMR, DSC, TG, TG-IR, SEM na XPS results katika mechanism moja.
• Unalinganisha moja kwa moja jinsi cryogenic pre-treatment inaweza kubadilisha subsequent ablation behavior.
• Unatoa quantitative application-related metrics kama mass ablation rate, back-surface temperature, density na mechanical strength.

Mipaka ya utafiti

• Utafiti ni preprint ambayo haijapitia peer review.
• Repeat numbers na error bars hazijaelezwa wazi kwa measurements zote katika main text.
• Statistical significance tests, p values na confidence intervals hazijaripotiwa.
• Exposure ya 1150 °C ni short-term na haiwakilishi long-term service life.
• Cryogenic pre-treatment ni single cycle na dakika 15 za liquid-nitrogen exposure.
• Hakuna real flight environment au full-scale part test iliyofanywa.
• Microcracks zinazodaiwa kuundwa katika EMQ-10 baada ya cryogenic treatment hazija-imaged directly.
• Difference ya measurement conditions kati ya thermal-conductivity values za Figure 6d na values zilizotolewa katika text kwa 250 °C haijaelezwa.
• Microcrystalline regions katika scale-armor layer hazijathibitishwa moja kwa moja kwa detailed crystal-phase analysis.
• Baadhi ya waandishi wameripoti conflict of interest na patent application inayohusiana na material imewasilishwa.

Dokezo la Chanzo na Mbinu

Jina kamili asili la utafiti: Synergistic Phenylene/Ethyl Units Breaking the Silicone Dilemma for Aerospace Thermal Protection Spanning from –196 ° to 1150 °C

Waandishi: Jin-Chen You, Yi Qin, Geng-Qiao Huang, Zhen-Kai Zhang, Yi-Chao Li, Shi-Ping Xiang, Yong Xiao, Hai-Ya Chen na Yi-Yong Huang.

Mpangilio wa waandishi: Jin-Chen You ni wa kwanza, Yi Qin wa pili, Geng-Qiao Huang wa tatu, Zhen-Kai Zhang wa nne, Yi-Chao Li wa tano, Shi-Ping Xiang wa sita, Yong Xiao wa saba, Hai-Ya Chen wa nane na Yi-Yong Huang wa tisa.

Equal contribution: Jin-Chen You na Yi Qin wamechangia kwa usawa katika utafiti.

Corresponding authors: Shi-Ping Xiang na Yi-Yong Huang.

Taasisi:

• Department of Chemistry, School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology, Wuhan, China.
• Hubei Provincial Enterprise-University Joint Innovation Center for Aerospace Thermal Protection Materials, Space Focus Co., Ltd., Xiaogan, China.
• State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China.

DOI: Kwa SSRN 7199946 version iliyochunguzwa, 10.2139/ssrn.7199946.

Jarida: Publication katika peer-reviewed journal haijathibitishwa.

Jukwaa la uchapishaji: SSRN.

Platform operator: Elsevier Inc.

Mwaka wa uchapishaji: 2026.

Aina ya chanzo: Preprint ambayo haijapitia peer review yenye experimental polymer na coating research.

Kiungo rasmi:https://ssrn.com/abstract=7199946

Version note: SSRN search results pia zina record nyingine namba 6932544 yenye title na author list hiyo hiyo. SSRN inaeleza kwamba records mbili za version zipo kwa entry 7199946. Kwa kuwa version order na DOI relationship ya records hizi haijaelezwa wazi, utafiti uliopakiwa namba 7199946 ndio umetumika kama msingi hapa.

Conflict of interest: Jin-Chen You, Yi Qin, Geng-Qiao Huang, Shi-Ping Xiang, Yong Xiao, Hai-Ya Chen na Yi-Yong Huang wameripoti conflict of interest. Utafiti unaeleza kwamba patent application namba 202511551709.5 imewasilishwa na imeingia review process. Zhen-Kai Zhang na Yi-Chao Li hawakuripoti conflict of interest.

Data status: Watafiti wanaeleza kwamba primary data zipo katika main study na supplementary information. Supplementary materials zimeripotiwa kuwa na detailed methods, 16 supplementary figures na 8 supplementary tables; si supplementary files zote zimo katika main study iliyopakiwa.

Makala hii imeandaliwa kwa kutegemea text ya utafiti uliopakiwa, molecular structures, experimental conditions, graph values, spectroscopic analyses, microscopy images na mechanism interpretations za watafiti. Hakuna new scientific result, flight success, commercial product approval au long-term safety guarantee ambayo haipo katika utafiti imeongezwa.

Utafiti ni preprint ambayo haijapitia peer review; results zinapaswa kusomwa kwa kuzingatia limitation hii. Usemi wa −196 °C hadi 1150 °C hauwakilishi continuous service range, bali laboratory cycle ambako liquid-nitrogen pre-treatment na short-duration plasma-arc heating zimefanywa mfululizo. Kwa real aerospace application, repeated thermal cycling, long-duration heat flux, vibration, vacuum, radiation, oxidation, humidity, impact, large-scale manufacturing na flight validation zinahitajika.