Carbon-based quantum dots for green-lubrication technology

Nadeem, Irfan (author), Cavaleiro, Albano (mentor), Kalin, Mitjan (mentor)

Friction and wear contribute significantly to energy loss and component failure in mechanical systems. As such, reducing friction and achieving superlubricity in engineering materials is a promising strategy to decrease material losses and energy consumption in industrial systems. Recently, the use of aqueous green lubricants to achieve superlubricity has gained interest due to their potential to reduce energy consumption and carbon footprint. However, it is still a challenge to achieve superlubricity with high load-bearing capacity in aqueous-lubricated systems. In particular, for self-mated steel contacts, the contact pressure rarely exceeds 50 MPa during super-low friction, due to excessive wear during the long running-in period. Additionally, maintaining superlubricity under different sliding conditions over extended durations is a major obstacle for real-scale applications. This thesis addresses these challenges by investigating the tribological performance of graphene quantum dots (GQDs) as nano-additives in aqueous glycerol between various friction pairs. The results show that GQDs in aqueous glycerol achieve super-low friction and even superlubricity in self-mated steel contacts at a contact pressure as high as 316.5 MPa. Carboxyl-functionalized GQDs (CGQDs) have been shown to provide robust and durable superlubricity in self-mated steel contacts that is maintained over a prolonged time and adapts to different sliding conditions without an additional supply of CGQDs-based nanolubricants. Furthermore, nitrogen-doped GQDs (NGQDs) as an additive in aqueous glycerol provide superlubricity with friction coefficients ranging between 0.005 and 0.009 in friction pairs of steel and silicon-doped hydrogenated amorphous carbon (a-C:H:Si). This comprehensive investigation of the lubrication mechanisms and the effects of various tribological parameters on the performance of GQDs and their functionalized forms aims to improve the energy efficiency and longevity of lubricated engineering contacts. By providing new insights into the role of GQDs in reducing friction, this thesis work represents a significant step toward implementing energy-efficient and green lubrication technologies for industrial applications.

• Language: English
• Keywords: graphene quantum dots, superlubricity, green tribology, boundary lubrication, aqueous glycerol, diamond-like carbon, amorphous-carbon coatings
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FS - Faculty of Mechanical Engineering
• Publisher: [I. Nadeem]
• Year: 2024
• Number of pages: 1 zv. (loč. pag.)
• PID: 20.500.12556/RUL-166191
• UDC: 539.92:621.892(043.2)
• COBISS.SI-ID: 224024835
• Publication date in RUL: 24.12.2024

Secondary language

• Language: Slovenian
• Title: Kvantne pike na osnovi ogljika za tehnologijo zelenega mazanja

Abstract

Trenje in obraba pomembno prispevata k izgubi energije in odpovedi komponent v mehanskih sistemih. Zmanjševanje trenja in doseganje supermazalnosti pri inženirskih materialih je obetavna strategija za zmanjšanje izgub materiala in porabe energije v industrijskih sistemih. V zadnjem času je uporaba zelenih maziv na osnovi vode za doseganje supermazalnosti pridobila zanimanje zaradi njihovega potenciala za zmanjšanje porabe energije in ogljičnega odtisa. Kljub temu pa je težko doseči supermazalnost z visoko nosilnostjo v vodno mazanih sistemih, še posebej v primeru kontaktov jeklo/jeklo, kjer kontaktni tlak redko preseže 50 MPa med super-nizkim trenjem, zaradi prekomerne obrabe med dolgo trajajočo fazo utekanja. Poleg tega je vzdrževanje supermazalnosti pod različnimi drsnimi pogoji skozi daljša obdobja velik izziv za realne aplikacije. Ta naloga se osredotoča na reševanje teh izzivov z raziskovanjem tribološke zmogljivosti kvantnih pik iz grafena (GQD) kot nano-aditivov v vodni raztopini glicerola med različnimi kontaktnimi pari. Rezultati kažejo, da GQD v vodni raztopini glicerola dosežejo super-nizko trenje in celo supermazalnost v kontaktih jeklo/jeklo pri kontaktnem tlaku do 316,5 MPa. GQD funckionalizirane s karboksilnimi skupinami (CGQD) so pokazale robustno in trajno supermazalnost pri kontaktih jeklo/jeklo, ki se ohranja skozi daljše obdobje in se prilagaja različnim drsnim pogojem brez dodatnega dovajanja nanomaziv na osnovi CGQD. Poleg tega, aditivi na osnovi z dušikom dopiranih GQD (NGQD) v vodni raztopini glicerola zagotavljajo supermazalnost s koeficienti trenja med 0,005 in 0,009 pri kontaktnih parih iz jekla in s silicijem dopiranega hidrogeniranega amorfnega ogljika (a-C:H:Si). Ta raziskava mehanizmov mazanja in vpliva različnih triboloških parametrov na zmogljivost GQD in njihovih funkcionaliziranih oblik skuša prispevati k izboljšanju energetske učinkovitosti in trajnosti mazanih inženirskih kontaktov. Z zagotavljanjem novih vpogledov v vlogo GQD pri zniževanju trenja, naloga predstavlja pomemben korak k implementaciji energetsko učinkovitih in zelenih tehnologij mazanja za industrijske aplikacije.

• Keywords: grafenske kvantne pike, supermazljivost, zelena tribologija, mejno mazanje, vodni glicerol, diamantu podoben ogljik, amorfno-ogljične prevleke