Txoj Kev Tshawb Fawb Txog Kev Ntsuas Thermogravimetric
Kev tshuaj xyuas Thermogravimetric (TGA) yog ib txoj kev ntsuas tus cwj pwm ntawm cov khoom siv uas ntsuas qhov kev hloov pauv ntawm qhov hnyav ntawm cov qauv raws li qhov kub thiab/lossis lub sijhawm hauv ib puag ncig uas tswj tau. Cov txheej txheem no siv dav hauv chemistry, kev tsim khoom siv, tshuaj, polymers, thiab lub zog vim tias nws tuaj yeem muab cov ntaub ntawv tseem ceeb txog kev ruaj khov thermal, kev sib xyaw, cov dej/solvent content, decomposition, thiab reaction kinetics. Los ntawm TGA curve thiab nws cov derivatives (DTG), cov kws tshawb fawb tuaj yeem nkag siab txog tus cwj pwm ntawm cov khoom siv thaum cua sov, txias, lossis tswj hwm ntawm qhov kub thiab txias.
Cov ntsiab cai yooj yim ntawm TGA
Lub hauv paus ntsiab lus ua haujlwm ntawm TGA yooj yim heev: cov qauv raug ntsuas tas li siv lub microbalance uas koom ua ke rau hauv lub cuab yeej, tom qab ntawd cua sov rau qhov kub tshwj xeeb. Thaum qhov kub nce ntxiv, cov qauv tuaj yeem dhau los ntawm ntau yam txheej txheem xws li dej evaporation, solvent volatilization, oxidation, dehydration, depolymerization, lossis kev tsim cov inorganic residues. Tag nrho cov txheej txheem no muaj peev xwm ua rau qhov hnyav txo qis (piv txwv li, vim yog kev tso tawm ntawm cov molecules volatile) lossis, qee zaum, qhov hnyav nce ntxiv (piv txwv li, vim yog oxidation, uas ua rau qhov hnyav nce ntxiv vim yog kev khi ntawm oxygen).
Cov kev ntsuas no tau ua nyob rau hauv qab huab cua tswj hwm, xws li nitrogen (N₂) lossis argon (Ar) rau cov xwm txheej inert, thiab oxygen (O₂) lossis huab cua rau cov xwm txheej oxidative. Kev xaiv ntawm huab cua yog qhov tseem ceeb rau cov txheej txheem koom nrog: cov polymers uas ruaj khov hauv nitrogen tuaj yeem lwj sai hauv huab cua vim yog oxidation.
Cov khoom tseem ceeb ntawm TGA instrument
Feem ntau cov cuab yeej TGA muaj ntau qhov tseem ceeb:
1. Lub cub tawg (lub cub tawg ua kom sov): tsim cov cua sov uas tau teeb tsa kom sov rau qhov kub siab (feem ntau yog 800–1000°C, nyob ntawm lub cuab yeej).
2. Microbalance (micro balance): ntsuas qhov kev hloov pauv ntawm qhov hnyav nrog kev rhiab heev (txog li micrograms).
3. Lub lauj kaub/lub khob ntsuas qauv: lub thawv ntsuas qauv, feem ntau yog ua los ntawm alumina, platinum, lossis ceramic—xaiv raws li qhov ua tau thiab qhov kub ua haujlwm.
4. Lub kaw lus tswj roj: tswj hom roj, qhov nrawm ntawm kev ntws, thiab kev hloov pauv ntawm huab cua (piv txwv li ntawm N₂ mus rau O₂).
5. Lub tswj kub thiab lub sensor: tswj tus nqi cua sov thiab xyuas kom meej qhov kub thiab txias raug.
6. Cov software nrhiav cov ntaub ntawv: sau cov kab sib txawv ntawm qhov hnyav thiab qhov kub thiab txias thiab feem ntau muab kev tshuaj xyuas DTG, kev xam cov kauj ruam poob phaus, thiab kev kwv yees kinetics.
Hom ntaub ntawv thiab cov kab nkhaus tshwm sim
Qhov tshwm sim tseem ceeb ntawm TGA yog daim duab TG (qhov hnyav lossis feem pua ntawm qhov hnyav piv rau qhov kub/lub sijhawm). Muaj ntau yam tseem ceeb uas nyeem tau los ntawm daim duab no:
- Kub pib: qhov kub pib uas ua rau lub cev poob ntau heev (qhia txog kev puas tsuaj lossis ua pa).
- Kev poob phaus ntawm cov kauj ruam: qhov ntau ntawm kev poob phaus ntawm txhua theem.
– Cov Khoom seem/char: qhov hnyav seem ntawm qhov kub kawg (cuam tshuam nrog cov ntsiab lus inorganic, cov khoom sau, tshauv, lossis cov char tsim).
- Kub ruaj khov: qhov kub thiab txias thaum lub cev hnyav tsis hloov pauv.
Tsis tas li ntawd xwb, thawj qhov derivative ntawm TG nkhaus ua rau muaj DTG (Derivative Thermogravimetry), uas yog tus nqi ntawm kev hloov pauv ntawm qhov hnyav piv rau qhov kub thiab txias. Lub ncov DTG pab cais cov theem sib tshooj thiab pab txhawb kev txheeb xyuas qhov kub thiab txias uas tus nqi degradation siab tshaj plaws tshwm sim.
Hauv qee lub tshuab, TGA kuj tseem siv ua ke nrog lwm cov txheej txheem xws li FTIR (TGA-FTIR) lossis MS (TGA-MS) los txheeb xyuas cov pa roj uas tso tawm thaum lub sijhawm cua sov, yog li ua rau kev txhais lus ntawm lub tshuab muaj zog dua.
Cov txheej txheem sim: cov kauj ruam dav dav
Hauv kev xyaum ua, kev tshuaj xyuas TGA yog ua tiav los ntawm cov theem hauv qab no:
1. Kev npaj cov qauv: cov qauv yuav tsum tau qhuav yog tias tsim nyog, zom kom sib npaug, thiab hnyav (feem ntau yog 5–20 mg, nyob ntawm cov khoom siv thiab cov cuab yeej).
2. Kev xaiv crucible: piv txwv li alumina rau feem ntau cov qauv; platinum rau cov kev xav tau tshwj xeeb; tsis txhob muaj kev sib xyaw ntawm cov qauv thiab crucible.
3. Qhov chaw huab cua: inert los kawm txog pyrolysis/degradation yam tsis muaj oxidation; cua/oxygen los kawm txog kev kub hnyiab lossis kev ruaj khov ntawm oxidative.
4. Qhov kev pab cuam kub: tuaj yeem yog cua sov linear (piv txwv li 10 ° C / feeb), cua sov kauj ruam nrog kev tuav isothermal, lossis lub voj voog cua sov-txias.
5. Kev ntsuas thiab kev kaw cov ntaub ntawv: cov software kaw cov kab TG/DTG.
6. Kev tshuaj xyuas cov txiaj ntsig: txiav txim siab theem ntawm kev poob phaus, xam feem pua ntawm cov khoom, thiab txhais cov txheej txheem uas tshwm sim.
Qhov kev xaiv ntawm qhov kub thiab txias yog qhov tseem ceeb: qhov kub thiab txias ua rau qhov kev ntsuam xyuas sai dua tab sis tuaj yeem hloov qhov pib mus rau qhov kub siab dua thiab ua rau qhov sib cais theem zuj zus; qhov kub thiab txias qis muab kev daws teeb meem zoo dua tab sis siv sijhawm ntev dua.
Cov ntawv thov tseem ceeb ntawm TGA
1. Txheeb xyuas cov dej thiab cov khoom uas yaj tau yooj yim
Ntau yam khoom muaj dej dawb, dej khi, lossis cov kuab tshuaj seem. Hauv qhov kub qis (piv txwv li, 30–150 ° C), kev poob loj feem ntau yog vim dej/cov kuab tshuaj evaporation. Qhov no yog qhov tseem ceeb rau cov tshuaj (cov dej hauv cov khoom siv), cov khoom noj, thiab cov polymers.
2. Ntsuas qhov ruaj khov thiab kev puas tsuaj ntawm thermal
TGA tuaj yeem qhia qhov kub thiab txias pib ntawm kev puas tsuaj, theem ntawm kev puas tsuaj, thiab cov seem. Hauv cov polymers zoo li PVC, piv txwv li, theem pib yuav yog dehydrochlorination, ua raws li kev sib cais saw thiab kev tsim char.
3. Txheeb xyuas cov khoom sib xyaw ua ke
Cov khoom sib xyaw ua ke lossis cov khoom sib xyaw feem ntau muaj kev poob phaus maj mam: cov khoom organic lwj, thaum cov khoom inorganic tseem nyob ua cov seem. Yog li ntawd, TGA tuaj yeem kwv yees qhov feem pua ntawm cov khoom tshwj xeeb (piv txwv li, cov pa roj carbon dub, fiber, minerals, lossis tshauv).
4. Kev tshawb fawb txog kev oxidation thiab kev sib xyaw ua ke
Hauv huab cua uas muaj oxidizing, cov khoom siv carbon lossis polymer tuaj yeem hlawv, thiab tseem muaj tshauv nyob tom qab. TGA pab txiav txim siab qhov kub thiab txias ntawm kev hlawv, qhov nrawm ntawm kev oxidation, thiab kev kwv yees cov tshauv uas muaj nyob hauv.
5. Kev ua haujlwm ntawm cov tshuaj tiv thaiv thermal
Los ntawm kev ua TGA ntawm ntau qhov kub thiab txias, cov kws tshawb fawb tuaj yeem kwv yees cov yam ntxwv kinetic xws li lub zog ua kom muaj zog siv cov txheej txheem xws li Kissinger, Ozawa-Flynn-Wall, lossis Friedman (isoconversional methods). Qhov no yog qhov tseem ceeb rau kev ua qauv lub neej ntawm cov khoom siv ntawm qhov kub thiab txias.
Cov yam tseem ceeb uas cuam tshuam rau cov txiaj ntsig thiab kev txhais lus
Cov txiaj ntsig ntawm TGA tsis yog txiav txim los ntawm cov khoom siv xwb, tab sis kuj los ntawm cov xwm txheej ntawm kev sim. Qee yam tseem ceeb suav nrog:
– Qhov hnyav ntawm cov qauv kuaj: cov qauv kuaj loj dhau yuav ua rau qhov kub thiab txias hloov pauv thiab cov pa roj kis qeeb qeeb, yog li ntawd qhov nkhaus zoo li hloov lossis dav dua.
- Qhov loj me ntawm cov khoom me me thiab qhov sib xws: cov khoom loj tuaj yeem tiv thaiv kev tawm ntawm cov pa roj volatile.
– Hom Crucible: cov crucible kaw/npog tuaj yeem khaws cov pa roj thiab hloov txoj kev ua tshuaj piv rau cov crucible qhib.
- Tus nqi roj ntws thiab hom roj: xav tau roj ntws txaus kom cov khoom uas yaj tau tsis txhob nyob ib puag ncig cov qauv.
- Tus nqi cua sov: cuam tshuam rau qhov kev daws teeb meem ntawm theem thiab qhov kub thiab txias (pib, qhov siab tshaj plaws ntawm DTG).
- Kev ntsuas kub thiab qhov sib npaug: qhov yuam kev ntawm kev ntsuas tuaj yeem ua rau muaj kev txhais lus tsis raug.
Yog li ntawd, daim ntawv qhia TGA zoo feem ntau muaj cov ntsiab lus ntawm kev kuaj: qhov hnyav ntawm cov qauv, qhov kub thiab txias, huab cua thiab qhov ntws, hom lauj kaub, thiab qhov kub thiab txias.
Cov txiaj ntsig thiab kev txwv
Qhov zoo ntawm TGA suav nrog cov qauv me me uas yuav tsum tau kuaj, kev tshuaj xyuas sai, kev nkag siab zoo rau kev hloov pauv ntawm cov pawg, thiab lub peev xwm los kawm txog ntau kauj ruam. Txawm li cas los xij, nws qhov kev txwv yog tias TGA tsis qhia ncaj qha txog hom tshuaj uas ploj lawm - nws tsuas yog qhia tias pawg hloov pauv. Txhawm rau txiav txim siab "dab tsi evaporates lossis tsim," cov txheej txheem nrog xws li FTIR / MS lossis lwm yam kev tshuaj xyuas cov khoom sib xyaw feem ntau xav tau.
Ntxiv mus, qee cov txheej txheem thermal tsis ua rau muaj kev hloov pauv loj heev (piv txwv li kev hloov pauv iav hauv cov polymers), yog li lawv tsis haum rau kev tshuaj xyuas los ntawm TGA ib leeg thiab tsim nyog dua los siv DSC lossis DMA.
Kev kaw
Kev tshuaj xyuas thermogravimetric yog ib qho cuab yeej tseem ceeb hauv kev tshawb fawb txog cov ntaub ntawv thiab kev tsim kho, uas muaj peev xwm kos duab qhov kev hloov pauv ntawm cov khoom siv raws sijhawm thiab qhov kub. Los ntawm cov kab TG thiab DTG, TGA muab cov ntaub ntawv tob txog cov ntsiab lus volatile, thermal stability, degradation stages, inorganic residues, thiab thermal reaction kinetics. Nrog rau cov huab cua zoo, cov nqi cua sov, thiab kev npaj qauv, TGA tuaj yeem muab lub hauv paus ruaj khov rau kev tsim khoom, kev tswj xyuas zoo, thiab kev nkag siab txog cov txheej txheem degradation ntawm cov khoom. Kev sib xyaw ua ke TGA nrog cov txheej txheem txheeb xyuas roj xws li FTIR lossis MS ua rau kev txhais lus zoo dua, ua rau TGA yog ib qho ntawm cov txheej txheem thermal characterization ntau yam hauv kev tshawb fawb niaj hnub no.
