Nima uchun juda sof (past{0}}kul) PFA darajasidagi isitgich yuqori-namlik muhitida dielektrik parchalanishini erta ko‘rsatishi mumkin?

Kam ekstrakt va ionli ifloslantiruvchi moddalarni talab qiladigan muhim ilovalar uchun juda toza PFA darajalari (past-kul, yarimo'tkazgich-navbati) ko'rsatilgan. Bu navlar kul tarkibiga ega<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.

Namlikni yutish va dielektrik parchalanish mexanizmi
PFA harorat va kristallanishga qarab 100% RHda og'irlik bo'yicha 0,03-0,10% suv oladi. So'rilgan suv molekulalari harakatchan bo'lib, elektr maydonida ion tokini o'tkazishi mumkin. Elektr maydonining kuchi material bardosh bera oladigan darajadan yuqori bo'lsa, odatda quruq PFA uchun 15-25 kV / mm, dielektrik parchalanish sodir bo'ladi. Yutilgan namlik 80% RHda 10-15 kV / mm gacha va 100% RHda 5-10 kV / mm gacha parchalanish kuchini pasaytiradi.

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 Bu reaksiya bo'sh suvni ishlatadi va uni kimyoviy jihatdan birlashtiradi. Bog'langan suv erkin suvga qaraganda kamroq harakatchan va o'tkazuvchandir. To'ldiruvchi zarrachalar, shuningdek, elektronlar uchun tarqalish nuqtalari bo'lib xizmat qiladi va parchalanish yo'li uzunligini oshiradi. Juda toza PFA tarkibida bunday plomba moddalari mavjud emas (kul<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.

Standart PFA va Utra-Sof PFA dielektrik kuchi
PFA darajasidagi kul tarkibi (%) 60 daraja suvni singdirish, 80% RH (%) 80% RH da dielektrik quvvati (kV/mm) Izolyatsiya qarshilik tushish vaqti (<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
Yuqori-tozalik 0.05-0.10 0.06-0.08 11-13 5000-8000 soatOziq-ovqat, farmatsevtika
Ultra-sof (past{1}}kul) 0,005–0.01 0.08–0.10 8–10 2,000–4,000 soat Yarimoʻtkazgich, muhim laboratoriyalar
Ultra{0}}sof, qurituvchi plomba bilan (maxsus) 0,01–0,02 (to‘ldiruvchi qo‘shilgan) 0,04–0.06 11–14 6,000–10,000 soatYuqori namlik + Yuqori tozalik
0,20–0.40 0.04–0.06 13–16 10,000–15,000 hTropik, tashqi muhit sozlamalari bilan standart namlik
Yarimo'tkazgichlarni ishlab chiqarish bo'yicha dala dalillari
Yarimo'tkazgichli zavod ultra{0}}sof PFA isitgichlarini (kul<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.

Namlik xizmatida Ultra-Sof PFAni kamaytirish
Ultra{2}}sof PFA isitgichlari kerak bo'lgan yuqori namlik holatlarida (masalan, texnologik namlik bilan yarimo'tkazgichli ho'l skameykalar) dielektrik ishonchliligini oshirishning uchta usuli:

Azotni tozalash: Isitgichning sovuq tomoniga doimiy quruq azot oqimini qo'llang. Ijobiy bosim nam havoning PFA-metall interfeysiga tegishidan saqlaydi. Azotni tozalash izolyatsiyaga qarshilik muddatini 5-10X oshiradi.

Kamroq vatt zichligi: Pastroq kuchlanishda (208V va . 480V) ishlash va/yoki kattaroq isitgichdan (past Vt/sm²) foydalanish orqali elektr maydon kuchlanishini kamaytiring. Pastroq maydon kuchi oqish oqimi uchun harakatlantiruvchi kuchni kamaytiradi.

Namlik oluvchi: Sovuq hududda molekulyar elak paketini (zeolit ​​yoki silika jeli) o'rnating. Qabul qiluvchi PFA orqali oqadigan har qanday namlikni oladi. Qabul qiluvchini har 6 oydan 12 oygacha o'zgartiring.

Yuqori tozalik va yuqori namlikni talab qiladigan ilovalar uchun (masalan, farmatsevtik nam reaktorlar) qoʻshimcha namlikni barqarorlashtiruvchi plomba-bilan ultra{2}}sof PFA dan foydalaning. Turli ishlab chiqaruvchilar 0,01-0,02% kaltsiy oksidi yoki sintetik gidrotalsit bilan "yuqori{5}}namlik" ultra{6}}sof PFA ishlab chiqaradilar. Ushbu navlar 85% RHda 12-14 kV / mm dielektrik quvvatga ega, bu oddiy PFAga o'xshash, shu bilan birga past olinadigan moddalarni saqlaydi.

Xulosa: Standart PFA yuqori namlikda Ultra-Pure'dan ustundir
Juda toza (past kul) To'ldirgichga namlikni yutuvchi moddalar qo'shilmasa, PFA isitgichlari yuqori namlik sharoitida (80% RH dan katta yoki unga teng) odatdagi PFAga qaraganda tezroq buziladi. Ion o'tkazuvchanligi polimer matritsasidagi erkin suv bilan ortadi va dielektrik quvvati 12-15 kV / mm dan 8-10 kV / mm gacha kamayadi. 0,1–0,5% kulli standart PFA nam xizmatda ultra-sof PFAga qaraganda 2–4 ​​marta uzoqroq saqlanadi. Muhandislar barcha vaziyatlarda "tozaroq yaxshiroq" deb o'ylamasliklari kerak. Quruq ilovalar uchun ultra{14}}sof PFA eng yuqori darajadagi tozalikni taklif qiladi. Nam ilovalarda oddiy PFA yoki namlikni barqarorlashtiruvchi-ultra sof plomba moddasi afzalroqdir. Agar past olinadigan moddalar va yuqori namlik qo'llanilishi kerak bo'lsa, azotni tozalash yoki namlik olish moslamalarini ta'minlang. Namlikdan kelib chiqadigan dielektrik parchalanish- materialning emas, balki dizayndagi cheklovdir. Nazariy tozalik idealini emas, balki atrof-muhitga qarab PFA darajasini tanlang. Bir oz kul - namlikda yoqimli narsa.