Indlela Yokuhlaziya I-Thermogravimetric
Ukuhlaziywa kwe-Thermogravimetric (TGA) kuyindlela yokuchaza izinto ezisetshenziswayo elinganisa ushintsho kusisindo sesampula njengomsebenzi wokushisa kanye/noma isikhathi endaweni elawulwayo. Le ndlela isetshenziswa kabanzi kumakhemikhali, ubunjiniyela bezinto ezisetshenziswayo, kwezemithi, kuma-polymers, kanye namandla ngoba inganikeza ulwazi olubalulekile mayelana nokuzinza kokushisa, ukwakheka, okuqukethwe kwamanzi/okuncibilikisayo, ukubola, kanye ne-reaction kinetics. Nge-TGA curve kanye ne-derivatives yayo (DTG), abacwaningi bangaqonda ukuziphatha kwezinto lapho zishiswa, zipholile, noma zigcinwa ekushiseni okuthile.
Izimiso eziyisisekelo ze-TGA
Isimiso sokusebenza se-TGA silula: isampula ilinganiswa njalo kusetshenziswa i-microbalance ehlanganiswe nethuluzi, bese ishiswa ohlelweni oluthile lokushisa. Njengoba izinga lokushisa likhuphuka, isampula ingadlula ezinqubweni ezahlukahlukene njengokuhwamuka kwamanzi, ukuguquguquka kwe-solvent, ukuguquka kwe-oxidation, ukuphelelwa amanzi emzimbeni, ukususwa kwe-polymerization, noma ukwakheka kwezinsalela ezingaphili. Zonke lezi zinqubo zingabangela ukwehla kwesisindo (isb., ngenxa yokukhululwa kwama-molecule aguquguqukayo) noma, kwezinye izimo, ukwanda kwesisindo (isb., ngenxa yokuguquguquka kwe-oxidation, okwandisa isisindo ngenxa yokubopha kwe-oxygen).
Lezi zilinganiso zenziwa ngaphansi kwezindawo ezilawulwayo, njenge-nitrogen (N₂) noma i-argon (Ar) yezimo zokungangeni, kanye ne-oxygen (O₂) noma umoya wezimo zokungangeni. Ukukhetha umoya kubalulekile ekusebenzeni okuhilelekile: ama-polymer azinzile ku-nitrogen angawohloka ngokushesha emoyeni ngenxa yokungangeni.
Izingxenye eziyinhloko zethuluzi le-TGA
Amathuluzi e-TGA ngokuvamile aqukethe izingxenye eziningana ezibalulekile:
1. Isithando somlilo (isithando somlilo esifudumezayo): sikhiqiza ukushisa okuhleliwe kuze kufike emazingeni okushisa aphezulu (ngokuvamile angu-800–1000°C, kuye ngokuthi iyiphi ithuluzi).
2. I-Microbalance (i-micro balance): ilinganisa izinguquko zobuningi ngokuzwela okuphezulu (kuze kufike kuma-microgram).
3. Ipani/ibhodlela lesampula: isitsha sesampula, ngokuvamile esenziwe nge-alumina, iplatinum, noma i-ceramic—esikhethwe ngokuya ngokusebenza kanye nokushisa kokusebenza.
4. Uhlelo lokulawula igesi: lulawula uhlobo lwegesi, izinga lokugeleza, kanye nokuguquka komoya (isb. ukusuka ku-N₂ kuya ku-O₂).
5. Isilawuli sokushisa kanye nenzwa: silawula izinga lokushisa futhi siqinisekisa ukunemba kokushisa.
6. Isofthiwe yokuthola idatha: iqopha ubuningi uma kuqhathaniswa nokushisa/izikhathi futhi ivame ukunikeza ukuhlaziywa kwe-DTG, izibalo zokulahlekelwa ubuningi ezilandelanayo, kanye nokulinganisa i-kinetics.
Uhlobo lwedatha kanye nejika elivelayo
Umphumela oyinhloko we-TGA yi-TG curve (iphesenti lesisindo noma lesisindo uma kuqhathaniswa nezinga lokushisa/isikhathi). Amapharamitha amaningana abalulekile angafundwa kusukela kule curve:
– Izinga lokushisa lokuqala: izinga lokushisa lokuqala lapho kwenzeka khona ukulahlekelwa okukhulu kwesisindo (isibonakaliso sokuqala sokuwohloka noma ukuhwamuka).
– Ukulahlekelwa isisindo ngesinyathelo: inani lokulahlekelwa isisindo esigabeni ngasinye.
– Insalela/i-char: isisindo esisele ekushiseni kokugcina (okuhlobene nokuqukethwe okungaphili, ukugcwalisa, umlotha, noma ukwakheka kwe-char).
– Izinga lokushisa lokuzinza: izinga lokushisa lapho isisindo singaguquguquki.
Ngaphezu kwalokho, i-derivative yokuqala ye-TG curve iveza i-DTG (Derivative Thermogravimetry), okuyisilinganiso sokushintsha kwesisindo uma kuqhathaniswa nezinga lokushisa. I-DTG peak isiza ukuhlukanisa izigaba ezihambisanayo futhi yenza kube lula ukuhlonza izinga lokushisa lapho kwenzeka khona izinga eliphezulu lokuwohloka.
Kwezinye izinhlelo, i-TGA ihlanganiswa nezinye izindlela ezifana ne-FTIR (TGA-FTIR) noma i-MS (TGA-MS) ukuze kutholakale amagesi akhishwa ngesikhathi sokushisa, ngaleyo ndlela kwenze ukuchazwa kwendlela yokusebenza kube okuqinile kakhudlwana.
Izindlela zokuhlola: izinyathelo ezijwayelekile
Empeleni, ukuhlaziywa kwe-TGA kwenziwa ngezigaba ezilandelayo:
1. Ukulungiswa kwesampula: isampula iyomiswa uma kudingeka, igaywe ukuze ifane, bese ikalwa (ngokuvamile 5–20 mg, kuye ngokuthi yenziwe kanjani kanye nethuluzi).
2. Ukukhethwa kwe-crucible: isib. i-alumina yamasampula amaningi; i-platinum yezidingo ezikhethekile; gwema ukusabela phakathi kwesampula ne-crucible.
3. Izindawo zomoya: ukungafundi ukucubungula i-pyrolysis/ukubola ngaphandle kwe-oxidation; umoya/i-oxygen ukuze kufundwe ukuqina kokusha noma kwe-oxidative.
4. Uhlelo lokushisa: kungaba ukushisa okuqondile (isb. 10°C/min), ukushisa ngesinyathelo ngokubamba okushisayo, noma umjikelezo wokushisa nokupholisa.
5. Ukulinganisa kanye nokuqoshwa kwedatha: isofthiwe iqopha ijika le-TG/DTG.
6. Ukuhlaziywa kwemiphumela: thola isigaba sokulahlekelwa yisisindo, bala iphesenti lezingxenye, bese uhumusha izinqubo ezenzekayo.
Ukukhetha izinga lokushisa kubalulekile: amazinga aphezulu asheshisa ukuhlolwa kodwa angaguqula ukuqala kube izinga lokushisa eliphezulu futhi enze ukuhlukana kwesigaba kube kubi kakhulu; amazinga aphansi anikeza isisombululo esingcono kodwa kuthatha isikhathi eside.
Izinhlelo zokusebenza eziyinhloko ze-TGA
1. Nquma amanzi kanye nokuqukethwe okuguquguqukayo
Izinto eziningi ziqukethe amanzi akhululekile, amanzi aboshwe, noma i-solvent esele. Ezingeni lokushisa eliphansi (isb., 30–150°C), ukulahlekelwa yisisindo kuvame ukubangelwa ukuhwamuka kwamanzi/i-solvent. Lokhu kubalulekile emithini yemithi (okuqukethwe kwamanzi ezintweni ezisizayo), ukudla, kanye nama-polymer.
2. Ukulinganisa ukuzinza kokushisa kanye nokuwohloka
I-TGA ingabonisa izinga lokushisa lokuqala kokuwohloka, isigaba sokuwohloka, kanye nezinsalela. Kuma-polymer afana ne-PVC, isibonelo, isigaba sokuqala singaba yi-dehydrochlorination, kulandelwe ukuqhekeka kweketanga kanye nokwakheka kwe-char.
3. Thola ukwakheka kwezinto ezixubile
Izinto ezihlanganisiwe noma ezixubile zivame ukulahlekelwa kancane kancane yisisindo: izingxenye eziphilayo ziyabola, kuyilapho isigcwalisi esingaphili sihlala njengesinsalela. Ngakho-ke i-TGA ingalinganisa ingxenye yesisindo sengxenye ethile (isb., i-carbon black, i-fiber, amaminerali, noma okuqukethwe umlotha).
4. Izifundo ze-oxidation kanye nokusha
Esimweni esifaka i-oxidation, izinto zekhabhoni noma ze-polymer zingasha, zishiye umlotha ngemuva. I-TGA isiza ekunqumeni izinga lokushisa lokushisa, izinga le-oxidation, kanye nokulinganisa okuqukethwe umlotha.
5. I-kinetics yokusabela kokushisa
Ngokwenza i-TGA ngamazinga okushisa amaningi, abacwaningi bangalinganisa amapharamitha e-kinetic njengamandla okusebenza besebenzisa izindlela ezifana ne-Kissinger, i-Ozawa-Flynn-Wall, noma i-Friedman (izindlela ze-isoconvertional). Lokhu kubalulekile ekuboniseni isikhathi sokuphila kwento ekushiseni okunikeziwe.
Izici ezithonya imiphumela kanye nokuchazwa
Imiphumela ye-TGA ayinqunywa nje kuphela ngezinto ezibonakalayo, kodwa futhi nangezimo zokuhlola. Ezinye izinto ezibalulekile zifaka:
– Isisindo sesampula: isampula enkulu kakhulu ingabangela ukuthambekela kokushisa kanye nokusabalala kwegesi okuhamba kancane, ukuze ijika libonakale lishintsha noma linwebeka.
– Usayizi wezinhlayiya kanye nokulingana kwazo: izinhlayiya ezinkulu zingavimbela ukuphuma kwamagesi aguquguqukayo.
– Uhlobo lokubethela: izitsha ezivaliwe/ezimboziwe zingagcina igesi futhi zishintshe indlela yokusabela uma kuqhathaniswa nezitsha ezivulekile.
– Izinga lokugeleza kwegesi kanye nohlobo lwegesi: kudingeka ukugeleza kwegesi okwanele ukuze imikhiqizo eguquguqukayo ingagcinwa eduze kwesampula.
– Izinga lokushisa: lithinta ukuxazululwa kwesigaba kanye namazinga okushisa ahlukile (ukuqala, i-peak DTG).
– Ukulinganiswa kwezinga lokushisa kanye nebhalansi: amaphutha okulinganisa angabangela ukuchazwa okuyiphutha.
Ngakho-ke, umbiko omuhle we-TGA uvame ukufaka imininingwane yokuhlolwa: isisindo sesampula, izinga lokushisa, izinga lokushisa kanye nomoya, uhlobo lwepani, kanye nobubanzi bokushisa.
Izinzuzo kanye nemikhawulo
Izinzuzo ze-TGA zifaka phakathi izidingo ezincane zesampula, ukuhlaziywa okusheshayo, ukuzwela okuphezulu ekushintsheni kobuningi, kanye nekhono lokufunda izinqubo zezinyathelo eziningi. Kodwa-ke, umkhawulo wayo ukuthi i-TGA ayibonisi ngqo uhlobo lwenhlanganisela elahlekile—ibonisa kuphela ukuthi ubukhulu buyashintsha. Ukuze kutholakale "okwenzekayo noma okwenziwayo," amasu ahambisanayo njenge-FTIR/MS noma okunye ukuhlaziywa kokwakheka avame ukudingeka.
Ngaphezu kwalokho, ezinye izinqubo zokushisa azibangeli izinguquko ezinkulu zobukhulu (isb. ukuguqulwa kwengilazi kuma-polymers), ngakho azifaneleki ukuhlaziywa yi-TGA kuphela futhi zifaneleka kakhulu ukusebenzisa i-DSC noma i-DMA.
I-Penutup
Ukuhlaziywa kwe-thermogravimetric kuyithuluzi elibalulekile kwisayensi yezinto zokwakha kanye nobunjiniyela, elikwazi ukumaka ngokunembile izinguquko zobuningi bezinto ezibonakalayo ngokuhamba kwesikhathi kanye nokushisa. Ngama-curve e-TG kanye ne-DTG, i-TGA inikeza ulwazi olujulile ngokuqukethwe okuguquguqukayo, ukuzinza kokushisa, izigaba zokubola, izinsalela ezingaphili, kanye ne-kinetics yokusabela kokushisa. Ngezimo ezifanele zomkhathi, amazinga okushisa, kanye nokulungiselela amasampula, i-TGA inganikeza isisekelo esiqinile sokuthuthukiswa komkhiqizo, ukulawulwa kwekhwalithi, kanye nokuqonda izindlela zokubola kwezinto ezibonakalayo. Ukuhlanganisa i-TGA namasu okuhlonza igesi njenge-FTIR noma i-MS kuthuthukisa kakhulu ukuhumusha, okwenza i-TGA ibe enye yezindlela zokuchaza ukushisa ezisebenziseka kakhulu ocwaningweni lwanamuhla.
