
SF6 au sulfur hexafluoride ni maji yaliyojumuisha sulfur moja na fluorine sita. Maji haya yalitambuliwa kwanza mwaka 1900 katika makabila ya Faculte de Pharmacie de, Paris. Mwaka 1937, General Electrical Company ilipata kujua kuwa SF6 inaweza kutumika kama chombo cha insulasi. Baada ya Vita vya Pili vya Dunia, asilimia ya miaka ya 20th, utaratibu wa kutumia sulfur hexafluoride kama chombo cha insulasi katika mifumo ya umeme ulianza kupanda sana. Allied Chemical Corporation na Pennsalt walikuwa wale wa kwanza wa kimataifa kutoka Amerika, ambao wakuanza kutengeneza maji haya kwa biashara mwaka 1948. Katika miaka ya 1960, kutumia sulfur hexafluoride gas katika switchgear ya kiwango cha juu kilianza kupenda. Tangu malipo ya maji haya yanapongezeka, wengi wa watengenezaji katika Ulaya na Amerika wakianza kutengeneza SF6 kwa kiwango kikubwa, hivyo ndani ya wakati ule. Tangu awali, SF6 gas ilikutumiwa tu kwa ajili ya insulasi katika mfumo wa umeme. Lakini mapema ikajulikana kuwa maji haya yana uwezo mkubwa wa kuchoma arc. Kwa hiyo, maji haya pia vilianza kutumika katika circuit breaker kama chombo cha kuchoma arc. Substation ya kwanza ya SF6 ya insulasi vilivyotengenezwa vilianza kufanyika Paris mwaka 1966. Circuit breakers ya kiwango cha mviringo ya sulfur hexafluoride zilipewa kwenye soko tangu 1971.
SF6 gas inatengenezwa kwa biashara kwa njia ya mzunguko wa fluorine (uliotengenezwa kwa electrolysis) na sulfur.
Katika mchakato wa kutengeneza maji haya, viwango vingine kama vile SF4, SF2, S2F2, S2F10 pia hutanengwa kwa asilimia ndogo. Si viwango vingine tu, vitendawili kama vile hewa, moisture, na CO2 pia hupatikana katika maji, katika ufanyikio. Vitendawili vyote na viwango vyote huvifunishwa katika hatua mbalimbali za safi kutoa bidhaa sahihi na safi ya mwisho.
Kutafuta vigezo vya kimya vya SF6 gas, tutanipiga kwa undani msimu wa molekuli ya SF6. Katika molekuli haya, sulfur moja imekuwa nyuma na fluorine sita.
Sulfur ana nambari ya atomi 16. Electronic configuration ya sulfur atom ni 2, 8, 6 i.e. 1S2 2S2 2P6 3S2 3P4. Atomu ya fluorine ana nambari ya atomi 9. Electronic configuration ya fluorine ni 1S2 2S2 2P5. Kila sulfur atom katika molekuli ya SF6 anachukua bond ya covalent na 6 atoms za fluorine. Hivyo, sulfur atom anapata bond zote za covalent 6, i.e. pairs of electrons 6 katika outer shell yake, na kila fluorine atom anapata electrons 8 katika outer most shell yake.
NB: – Hapa tunaweza kuziona, katika sulfur hexafluoride outer shell ya sulfur atom ina electrons 12 badala ya 8. Hiyo inamaanisha kwamba hapa sulfur haiongezeki kwa octal rule muhimu ya atomic structure ambayo inaelezea, atom sahihi unahitaji electrons 8 katika outermost shell yake. Hii si kesi ya maana. Baadhi ya elements katika 3rd period na chini zinaweza kujenga compound ambayo inazidi 8 electrons katika outer most shell yake. The molecular structure of this gas is shown below,
Hivyo, SF6 kamili inakusanya tabia sahihi ya structure. Effective radius ya molecule ya sulfur hexafluoride ni 2.385 A. This electronic configuration and structure of this gas make SF6 extremely stable. The gas can be stable without any decomposition in its molecular structure up to 500oC. It is highly non-flammable. H2O and Cl cannot react with this gas. It also does not react with acid.
The SF6 gas is one of the heaviest gases. Density of this gas at 20oC at one atmospheric pressure, is about 6.139 kg/m3 which is about 5 times higher than air at same conditions. The molecular weight of this gas is 146.06. The variation of pressure with temperature is linear for sulfur hexafluoride and it is small within the service temperature, i.e. from – 25 to + 50oC. The volumetric specific heat of this gas is also high. It is around 3.7 times more than that of air, and that is why this gas also has a tremendous cooling effect in electrical equipment. The thermal conductivity of this gas is not very high it is even lower than air. Still it is quite suitable for cooling effect in circuit breaker. It is because, during dissociation of sulfur hexafluoride molecules around the electric arc, these molecules absorb a high amount of heat. This heat is then released when the molecules reform at the periphery of the arc. This process helps to transfer heat from a hot region to cool region very rapidly. That is why; this gas has an excellent cooling effect at high temperature although the thermal conductivity of SF6 is not very high.
SF6 gas ni elektronegative sana. Kwa sababu ya electronegativity sana, inatengeneza electrons free ambazo zinatengenezwa kwa sababu ya arcing kati ya contacts za circuit breaker. Combination of free electrons with molecules produces heavy and big ions, which have very low mobility. Because of the absorption of free electrons and low mobility of ions SF6 has very excellent dielectric property. The dielectric strength of SF6 gas is about 2.5 times more than that of air.