Modifikacija spektralno selektivnih absorberskih premazov neodvisnih od debeline za učinkovitejšo pretvorbo sončne energije v toploto

Vidrih, Žiga (author), Marinšek, Marjan (mentor), Jerman, Ivan (co-mentor)

Pričujoče magistrsko delo obravnava modifikacijo od debeline neodvisnih spektralno selektivnih absorberskih premazov. Trenutno se praktična uporaba tovrstnih premazov srečuje vsaj s tremi izzivi. V industriji se največkrat uporabljajo: i) neselektivni premazi, kar pomeni izgubo termične energije s sevanjem, ii) absorberski premazi, izdelani na osnovi organskih topil, ki okolje bremenijo z visokimi izpusti hlapnih organskih komponent (VOC - volatile organic compounds), iii) premazi z absorberskimi površinami, na katerih se nabira prah in umazanija, kar ima za posledico zmanjšan izkoristek pretvorbe sončne energije v toploto. Učinkovitost delovanja premazov lahko izboljšamo z uporabo črnih ali barvnih spektralno selektivnih premazov na osnovi anorganskih pigmentov ali optimiziranih grafenskih pigmentov v kombinaciji z vezivi, ki omogočajo nizko termično emisivnost. Emisivnost dodatno znižamo z uporabo luskastih kovinskih pigmentov. Znano je, da aluminijeve luske, primerne za absorberske premaze, reagirajo z vodo v vezivih na vodni osnovi, zato je potrebna zaščitna modifikacija njihove površine, ki ohrani refleksijske lastnosti Al lusk v IR območju. Emisije VOC v okolje pa zmanjšamo s formulacijo premazov na vodni osnovi namesto na osnovi hlapnih organskih topil. Pripravili smo več različnih spektralno selektivnih absorberskih premazov; premaz s funkcionaliziranimi grafenskimi nanotrakovi, GNR premaz z vezivom na vodni osnovi in GNR premazi z različnimi masnimi deleži pigmenta Black 444. Vsem so skupni grafenski nanotrakovi (GNR - graphene nanoribbons), ki smo jih sintetizirali z oksidacijo ogljikovih nanocevk. Morfologijo GNR in pripravljenih premazov smo preučili z vrstično elektronsko mikroskopijo. Premazom smo določili tudi vrednosti absorpcije sončne svetlobe in toplotne emisije (αS in εT vrednosti), ki smo jih nato uporabili za izračun izkoristka pretvorbe sončnega sevanja v toploto. Z vključitvijo različnih deležev Cr3+ ionov smo dodatno modificirali spinelni pigment Black 444. Uspešnost vključitve Cr3+ ionov v strukturo pigmenta smo karakterizirali s FTIR spektroskopijo. Nove optične lastnosti dopiranih pigmentov smo preverili z UV/VIS in IR spektrofotometrijo. Aluminijeve luske smo oplaščili z različnimi grafenskimi pigmenti in komercialnim pigmentom Black 444. Pokritost lusk s pigmenti smo analizirali z vrstično elektronsko mikroskopijo in Raman-ovo spektroskopijo. Njihovo antikorozijsko obstojnost pa smo testirali z izvedbo hitrega korozijskega testa in testa s simulacijo slane komore.

• Language: Slovenian
• Keywords: absorberski premazi, spektralna selektivnost, sončni zbiralniki, grafen, aluminijeve luske
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2021
• PID: 20.500.12556/RUL-128962
• COBISS.SI-ID: 74790915
• Publication date in RUL: 19.08.2021

Secondary language

• Language: English
• Title: Modification of spectrally selective absorber coating components insensitive of thickness for more efficient conversion of solar energy into heat

Abstract

The present master thesis deals with the modification of thickness insensitive spectrally selective absorber coatings. Currently, the practical application of such coatings faces at least three challenges. The most commonly used in industry are: i) non-selective coatings, which means loss of thermal energy by radiation, ii) absorber coatings based on organic solvents that burden the environment with high emissions, iii) coatings with absorbing surfaces on which dust and dirt accumulate, resulting in reduced efficiency of solar to heat conversion. The performance of the coatings can be improved by using black or colored spectrally selective coatings based on optimized graphene pigments in combination with binders which allow low thermal emissivity. Emission is further reduced by using flaky metallic pigments. It is known that aluminum flakes, suitable for absorber coatings, react with water in water-based binder, so a protective modification of the flake surface is required to preserve the reflective porperties of Al flakes in the IR range. VOC (volatile organic compounds) emissions to the environment are reduced by formulating water-based coatings instead of volatile organic solvents. We have prepared several different spectrally selective absorber coatings; functionalized graphene nanoribbons coating, GNR coating with a weater-based binder and GNR coatings with different weight fractions of Black 444 pigment. The morphology of GNR and prepared cotings was examinated by scanning electron microscopy. The coatings were also determinated by the values of solar absorption and heat emission (αS and εT values), which were then used to calculate the efficency of the conversion of solar radiation into heat. The spinel pigment Black 444 was modifed by the inclusion of different proportions of Cr3+ ions. The success of incorporation of Cr3+ ions into the pigment structure was detected by FTIR spectroscopy. New optical properties of doped pigmets were verified by UV/VIS and IR spectrophotometry. The aluminium flakes were coated with various graphene pigments and the commercial pigment Black 444. The coverage of the flakes with pigments was analyzed by scanning electron microscopy and Raman spectroscopy. Their anti-corrosion resistance was tested by performing a rapid corrosion test and a salt chamber simulation test.

• Keywords: absorber coatings, spectral selectivity, solar collectors, graphene, aluminium flakes