Title Poboljšanje svojstava Al2O3 keramike dodatkom nanočestica ZrO2 Title (english) The improvement of Al2O3 ceramics properties by the addition of ZrO2 nanoparticles Author Marijana Majić Renjo Mentor Lidija Ćurković (mentor)Committee member Krešimir Grilec (predsjednik povjerenstva)Committee member Lidija Ćurković (član povjerenstva)Committee member Stanislav Kurajica (član povjerenstva)Granter University of Zagreb Defense date and country 2016-10-07, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 666 - Glass industry. Ceramics. Cement and concrete 620 - Materials testing. Power stations. Economics of energy Abstract Aluminijev i cirkonijev oksid pripadaju skupini oksidnih tehničkih keramika. Zbog svojih dobrih svojstava našli su široku primjenu. Najveći nedostatak Al2O3 jest niska lomna žilavost. Nasuprot tome, ZrO2 relativno je žilav. Kako bi proizvodnja tehničke keramike bila ekološki i ekonomski prihvatljivija, razmatraju se nekonvencionalni tehnološki postupci, kao što je lijevanje suspenzija. Dosad se taj postupak uglavnom primjenjivao za proizvodnju tankostijenih predmeta od silikatne keramike, a danas se nastoji koristiti za dobivanje odljevaka različitih presjeka i dimenzija od monolitne i kompozitne oksidne keramike. Cilj ovog doktorskog rada bio je poboljšati mehanička i tribološka svojstva monolitne Al2O3 keramike, proizvedene postupkom lijevanja suspenzija, dodatkom nanočestica ZrO2. Pripravljene su tri skupine 70%-tnih suspenzija koje su sadržavale: (i) čisti Al2O3 prah, (ii) 99 % Al2O3 praha i 1 % ZrO2 praha te (iii) 90 % Al2O3 i 10 % ZrO2 praha. Karakterizirani su polazni keramički prahovi: određen je fazni sastav i veličina čestica. Suspenzije su pripravljene homogenizacijom u planetarnom kugličnom mlinu, nakon čega su im određena reološka svojstva na rotacijskom viskozimetru, kako bi se odredili optimalni udjeli komercijalnog disperzanta. Optimalni sastavi suspenzija potvrđeni su sedimentacijskim testovima. U sljedećoj fazi istraživanja pripravljene su stabilne suspenzije i njihovim lijevanjem u gipsani kalup oblikovani su sirovci monolitne Al2O3 i kompozitne Al2O3–ZrO2 keramike. Sirovcima je određena gustoća te analizirana mikrostruktura i elementni sastav površine SEM/EDS analizom. Nakon sinteriranja u laboratorijskoj peći, karakterizirani su sinterirani uzorci: određena je Arhimedova gustoća i skupljanje tijekom sinteriranja, analizirana je mikrostruktura i elementni sastav površine (SEM/EDS). U posljednjoj fazi istraživanja ispitana su mehanička svojstva sinteriranih uzoraka: izmjerena je tvrdoća po Vickersu te određena lomna žilavost metodom utiskivanja. Tribološka svojstava sinteriranih uzoraka monolitne Al2O3 i kompozitne Al2O3–ZrO2 keramike određena su erozijom česticama, uz dva erodenta i tri kuta upada. Mehanizmi erozijskog trošenja analizirani su usporedbom svojstava prije i poslije erozije: morfologije površine uzoraka (SEM/EDS), parametara hrapavosti i mase sinteriranih uzoraka. Dobiveni rezultati potvrdili su hipotezu da se mehanička i tribološka svojstva Al2O3 keramike mogu poboljšati dodatkom nanočestica ZrO2.
Abstract (english) Aluminium and zirconium oxide belong to the group of the oxide ceramics. Due to their advantages, their application is fairly wide. The biggest disadvantage of Al2O3 is its low fracture toughness. In contrast, ZrO2 is relatively tough. Unconventional technologies, such as slip casting, are being developed to make the production of technical ceramics more economically acceptable and environmentally friendly. This technology was mostly used for the manufacturing of thin-walled silicate items, but nowadays it is used for the production of objects of different cross-sections and sizes, made from monolithic and composite oxide ceramics. The objective of this thesis was to improve the mechanical and tribological properties of slip cast alumina with the addition of zirconia nanoparticles. Three groups of suspensions, with solid loading of 70 wt. %, were prepared: (i) pure Al2O3, (ii) 99 wt. % of Al2O3 and 1 wt. % of ZrO2 powder and (iii) 90 wt. % of Al2O3 and 10 wt. % of ZrO2 powder. Ceramic powders were characterized: phase composition and particle size were determined. Suspensions were homogenized in a planetary ball mill, whereupon their rheological properties were determined on a rotational viscometer, in order to found the optimal amount of a commercially available dispersant. The optimal compositions of prepared suspensions were confirmed by sedimentation tests. In the next phase of this investigation, stable suspensions were prepared and cast into plaster moulds to prepare green bodies of monolithic Al2O3 and composite Al2O3–ZrO2 ceramics. Density of green bodies was determined as well as their microstructure and elemental composition by SEM/EDS analysis. After the sintering in a laboratory kiln, sintered samples were characterized: Archimedes’ density as well as shrinkage while sintering were determined; microstructure and elemental composition were analysed (SEM/EDS). In the final phase of the research, mechanical properties were determined: Vickers hardness and fracture toughness by the indentation method. Tribological properties of the sintered samples of monolithic Al2O3 and composite Al2O3–ZrO2 ceramics were determined by solid particle erosion, using two erodents and three impact angles. Erosion wear mechanisms were analysed by comparing the properties before and after erosion: surface morphology (SEM/EDS), roughness parameters and weight of the sintered samples. Obtained results confirmed the h
Keywords
ehnička keramika
aluminijev oksid (Al2O3)
cirkonijev oksid (ZrO2)
aluminijev oksid ojačan cirkonijevim oksidom (ZTA)
kompozitna keramika
lijevanje suspenzija
erozija česticama
Keywords (english)
echnical ceramics
alumina (Al2O3)
zirconia (ZrO2)
zirconia toughened alumina (ZTA)
composite ceramics
slip casting
solid particle erosion
Language croatian URN:NBN urn:nbn:hr:235:366803 Study programme Title: Mechanical Engineering and Naval Architecture Type of resource Text File origin Born digital Access conditions Open access Terms of use Repository Repository of Faculty of Mechanical Engineering and Naval Architecture University of Zagreb Created on 2020-04-15 10:53:56
