Poukisa yon aparèy chofaj PFA Klas Trè Pi (Ba-Sann) ka montre yon pann dyelèktrik pi bonè nan anviwònman ki gen gwo-imidite?

Pou aplikasyon esansyèl ki mande pou ekstrè ki ba ak polyan iyonik, yo espesifye klas PFA trè pi (ba-sann, semi-conducteurs-). Klas sa yo gen kontni sann<0.01% (versus 0.1-0.5% for normal PFA). Paradoxically, very pure PFA heaters can show sooner dielectric breakdown than conventional PFA heaters in high humidity conditions (≥80% RH). That's because conventional PFA contains trace metal oxides (calcium oxide, magnesium oxide, aluminium oxide) that are water-absorbing fillers or stabilisers. These oxides react with moisture to generate hydroxides which devour water molecules and maintain high electrical resistance. These moisture scavenging organisms are absent in very pure PFA. The absorbed water molecules stay free in the polymer matrix, enhancing the ionic conductivity and reducing the dielectric strength. In high humidity environments, the electrical dependability of normal PFA can be better than ultra-pure PFA.

Mekanis nan absòpsyon imidite ak pann Dielectric
PFA pran 0.03-0.10% dlo pa pwa nan 100% RH depann sou tanperati ak kristalinite. Molekil dlo yo absòbe yo mobil, epi yo ka fè kouran iyonik nan yon jaden elektrik. Si fòs jaden elektrik la pi wo pase materyèl la ka kenbe tèt ak, anjeneral 15-25 kV / mm pou PFA sèk, pann dyelèktrik pral rive. Imidite absòbe diminye fòs pann nan 10-15 kV / mm nan 80% RH ak 5-10 kV / mm nan 100% RH.

Standard PFA usually comprises 0.1 to 0.5 percent inorganic fillers, often calcium oxide, magnesium oxide, or aluminium silicate, which are used as acid acceptors to stabilise the polymer during processing. These oxides are hygroscopic : CaO + H2O -->Ca(OH)2 Reyaksyon sa a itilize dlo gratis epi li konbine l sou fòm chimik. Dlo lié se sibstansyèlman mwens mobil ak kondiktif pase dlo gratis. Patikil filler yo sèvi tou kòm pwen gaye pou elektwon, ogmante longè chemen an pann. Trè pi PFA pa gen okenn file sa yo (sann<0.01%). The water that is absorbed is left as free water and creates conduction paths. Less filler content also means less physical impediments to electron avalanche.

Estanda PFA vs Utra-Pure PFA Dielectric fòs
PFA Klas Sann kontni (%) Absòbsyon dlo nan 60 degre, 80% RH (%) Dielectric fòs (kV/mm) nan 80% RH Rezistans izolasyon gout tan (<100 MΩ) at 85°C, 85% RHTypical Application Standard (industrial) 0.15 – 0.30 0.05 – 0.07 12 – 15 8,000 – 12,000 hours Industrial general, high humidity
Segondè -pite 0.05-0.10 0.06-0.08 11-13 5000-8000 èdtanManje, famasetik
Ultra-pi (ba-sann) 0.005–0.01 0.08–0.10 8–{10 2,000–4,000 èdtan Semiconductor, laboratwa kritik
Ultra-pi ak filler desiccant (espesyal) 0.01–0.02 (filler ajoute) 0.04–0.06 11–14 6,000–10,000 èdtanHigh Imidite + High Purity
Estanda ak scavenger imidite 0.20–0.40 0.04–0.06 13–16 10,000–15,000 hTropical, anviwònman deyò
Prèv jaden ki soti nan Faktori Semiconductor
Fabrikasyon semi-kondiktè a enstale aparèy chofaj PFA ultra-pi (sann<0.01%) in a wet bench with 85% RH, 85°C process temperature. Heaters lasted an average of 2,500 hours before the insulation resistance dropped below 100 MΩ and triggered ground fault alarms. For the same application the fab converted to normal PFA heaters (ash 0.2%) with an expectation of reduced life due to greater extractables. All the conventional heaters surprisingly survived 9000 hours. Analysis indicated that conventional heaters had magnesium oxide filler that absorbed moisture and so maintained high resistance. Ultra-pure heaters had no filler and free water built up at the interface to the PFA-metal resulting in leakage. The fab now uses normal PFA for high humidity procedures and reserves ultra-pure PFA for dry processes (<30% RH) when extractables are the main focus.

Diminisyon nan Ultra-PFA PFA nan sèvis imid
Pou sitiyasyon imidite ki wo (egzanp semi-kondiktè ban mouye ak imidite pwosesis pwodui) kote yo mande aparèy chofaj ultra-PFA pi, twa mitigasyon amelyore fyab dyelèktrik:

Purge Azòt: Aplike yon kouran konstan nitwojèn sèk sou bò frèt aparèy chofaj la. Presyon pozitif la anpeche lè imid manyen koòdone metal PFA-. Azòt purge ogmante izolasyon rezistans lavi 5-10X.

Pi ba dansite watt: Diminye estrès jaden elektrik la lè w kouri nan yon vòltaj ki pi ba (208V vs . 480V) ak/oswa itilize yon aparèy chofaj pi gwo (pi ba W/cm²). Fòs nan jaden ki pi ba diminye pouvwa a kondwi pou aktyèl flit.

Capteur imidite: Enstale yon pake molekilè Van (zeolit ​​oswa jèl silica) nan rejyon frèt la. Getter la pran nenpòt imidite ki koule nan PFA a. Chanje getter la chak 6 a 12 mwa.

Pou aplikasyon ki bezwen pite segondè ak imidite ki wo (pa egzanp, reyaktè imid pharmaceutique), sèvi ak PFA ultra-pi ak plis imidite-estabilize. Divès manifakti yo fè "wo -klas imidite" ultra-PFA pi ak 0.01-0.02% oksid kalsyòm oswa idrotalsit sentetik. Klas sa yo gen fòs dielectric nan 12-14 kV / mm nan 85% RH, menm jan ak PFA nòmal, pandan y ap kenbe ekstrè ki ba.

Konklizyon: PFA estanda pi wo pase Ultra-Pure anba gwo imidite
Trè pi (sann ki ba) Kote absòbe imidite yo pa ajoute nan filler la, aparèy chofaj PFA yo gen tandans kraze pi bonè pase PFA nòmal nan anviwònman imidite ki wo (pi gran pase oswa egal a 80% RH). Konduktivite iyonik la ogmante pa dlo gratis nan matris polymère a ak fòs dyelèktrik la diminye soti nan 12-15 kV / mm a 8-10 kV / mm. PFA estanda ak 0.1–0.5% sann pral siviv 2–4× pi long pase ultra-PFA pi nan sèvis imid. Enjenyè pa ta dwe sipoze "pi bon kalite se pi bon" atravè tout sitiyasyon. Pou aplikasyon sèk, PFA ultra-pi bon kalite ofri pi wo degre pwòpte. Nan aplikasyon imid, PFA nòmal oswa ultra-pi ak imidite-filler estabilize pi bon. Si tou de ekstrè ki ba ak imidite segondè yo dezirab pou aplikasyon an, bay pirj nitwojèn oswa getters imidite. Imidite -pann dielectric pwovoke se yon limit nan konsepsyon an, pa nan materyèl la. Chwazi klas PFA selon anviwònman an, pa yon ideyal pite teyorik. Yon ti sann se yon bèl bagay nan imidite.