Επικαιροποίηση γνώσεων αποφοίτων Α.Ε.Ι. Επιχειρησιακό Πρόγραμμα «Εκπαίδευση και Δια Βίου Μάθηση» Επικαιροποίηση γνώσεων αποφοίτων Α.Ε.Ι. ΠΕΓΑ_ΤΕΧΝΟΛΟΓΙΚΕΣ ΕΦΑΡΜΟΓΕΣ ΚΑΙ ΠΕΡΙΒΑΛΛΟΝΤΙΚΗ ΣΥΜΠΕΡΙΦΟΡΑ ΣΥΓΧΡΟΝΩΝ ΥΛΙΚΩΝ   ΔΙΔΑΚΤΙΚΗ ΕΝΟΤΗΤΑ 3.1. Διεργασίες υαλοποίησης από βιομηχανικά απόβλητα και παραγωγή Δρ. Συμεών Αγαθόπουλος, Αναπληρωτής Καθηγητής Πανεπιστήμιο Ιωαννίνων 1

Ύαλος είναι ένα υλικό που έχει ψηχθεί από ένα τήγμα χωρίς να κρυσταλλωθεί American Society for Testing and Materials (ASTM) Κινητική Μετασταθής κατάσταση Κατάσταση θερμοδυναμικής ισορροπίας Ύαλος Κεραμικό Quenching rates Air cooling (>30min) Water cooling >1min Splat cooling ~1sec Fast cooling 105 K/s (Roller splat-cooling)

Ύαλος είναι ένα υλικό που έχει ψηχθεί από ένα τήγμα χωρίς να κρυσταλλωθεί American Society for Testing and Materials (ASTM) Κινητική Μετασταθής κατάσταση Κατάσταση θερμοδυναμικής ισορροπίας Ύαλος Κεραμικό Φάσεις υάλων Κεραμικές φάσεις Quenching rates Υαλοκεραμικό Air cooling (>30min) Water cooling >1min Splat cooling ~1sec Fast cooling 105 K/s (Roller splat-cooling) IPS e.max Press IPS e.max Ceram IPS e.max CAD IPS Empress Η κινητική ακυρώνει τη θερμοδυναμική!!!

Υαλοκεραμικά υλικά Υαλοκεραμικό Ύαλος Κεραμικό Κινητική Μετασταθής κατάσταση Κατάσταση θερμοδυναμικής ισορροπίας Υαλοκεραμικό Ύαλος Κεραμικό Φάσεις υάλων Κεραμικές φάσεις Πολύ ειδική σχέση υάλου και κρυσταλλικών φάσεων Οι κρυσταλλικές φάσεις που θα σχηματιστούν έχουν ήδη «καθοριστεί» από τη δομή της υάλου Ομογενής κρυστάλλωση Phase separation Bulk crystallization Surface crystallization Ετερογενής κρυστάλλωση Σχεδιασμός αρχικής σύστασης υάλου Δομή υάλου (IR, Raman, NMR) Ελεγχόμενη διεργασία κρυστάλλωσης Θερμική Ανάλυση DSC: Μηχανισμός, Ea Κρυσταλλικές φάσεις Πυρηνοποίηση Κρυσταλλική ανάπτυξη

CONVERSION OF LOW-SILICA FLY-ASH INTO BULK NUCLEATED FINE GRAINED MONO-MINERAL GLASS-CERAMIC PORTUGAL Dept. Ceramics & Glass Engineering, University of Aveiro Polytechnique Institute of Viana do Castelo K.C. Vasilopoulos D.U. Tulyaganov S. Agathopoulos M.J. Ribeiro M.A. Karakassides J.M.F. Ferreira D. Tsipas UZBEKISTAN Scientific Research Institute of Space Engineering Tashkent GREECE Lab. Physical Metallurgy Dept. Mechanical Engineering Aristotle University of Thessaloniki Dept. Materials Science & Engineering University of Ioannina I. Koutselas Dept. Materials Science University of Patras

CONVERSION OF LOW-SILICA FLY-ASH INTO BULK NUCLEATED FINE GRAINED MONO-MINERAL GLASS-CERAMIC The study aims at exploiting the potential of using this FA as precursor in production of bulk-nucleated Glass-Ceramics (GCs) recycling of the fly ash (FA) derived from the thermal power stations of Ptolemaida (Greece)

CONVERSION OF LOW-SILICA FLY-ASH INTO BULK NUCLEATED FINE GRAINED MONO-MINERAL GLASS-CERAMIC Pyroxene Production of pyroxene based glasses from Fly-Ash was undertaken. Di – Ca-Tschermak s.s. The parent glass approached the composition of CaMg0.75Al0.4Fe0.1Si1.75O6. This composition derives from CaMg0.75Al0.5Si1.75O6, which belongs to diopside–Ca-Tschermak solid solutions. ? How ? Genika gia fly ash kai xarths Augite Fine grained mono-mineral glass-ceramics of augite were crystallized from glasses which comprised Fly-Ash and additives of SiO2, Al2O3 and MgCO3, using Cr2O3 as nucleating agent Cr2O3 The influence of Cr2O3-content on the development of crystalline phases, the properties and the microstructure of the resultant glass-ceramics, crystallized at different temperatures, was investigated.

CONVERSION OF LOW-SILICA FLY-ASH INTO Microstructure Chemical composition (wt%) SiO2 : 30.03 Al2O3 : 13.67 CaO : 38.87 Fe2O3 : 5.32 MgO : 4.42 Na2O : 0.63 K2O : 0.59 SO3 : 6.17 TiO2 : 0.30 Xarakthristika FA Particle size Distribution

CONVERSION OF LOW-SILICA FLY-ASH INTO THERMAL ANALYSIS (DTA/TG) 516oC Calcium hydroxide decomposition 830oC Calcium carbonate decomposition 1172oC Calcium sulfate decomposition 1320oC Melting

CONVERSION OF LOW-SILICA FLY-ASH INTO X-RAY DIFFRACTION

Thermal treatment (900ºC-1000ºC, 1h) EXPERIMENTAL PROCEDURE Raw Materials Tips Milling Homogeneous mixtures of batches (~100 g), obtained by ball-milling, were preheated at 900ºC for 1 h for decarbonization Homogenization Calcination (900ºC, 1h) The powders were melted in alumina crucibles at 1500º-1550ºC for 1 h in air Melting (1500-1550ºC, 1h ) Glasses in bulk form were produced by casting of molten glass on preheated bronze moulds. Monolithic Frit Annealing (550ºC, 1h) To release the residual stresses, the glass blocks were immediately (i.e. before cooling to room temperature) annealed at 550ºC for 1 h. Glass Thermal treatment (900ºC-1000ºC, 1h) The glass blocks were cooled down to room temperature afterwards. Glass-Ceramics The glass-frit was used only for DTA

PREPARATION OF GLASSES Raw Materials SiO2 Al2O3 MgCO3 Cr2O3 (technical grade powders) Fly-Ash (as-received fine powder) + 4 new Glasses (batch composition wt%) GC1 GC2 GC3 GC4   Fly-Ash G1 G2 G3 G4 CaO 38.869 22.850 22.736 22.679 22.622 SiO2 30.030 45.456 45.229 45.115 45.001 Al2O3 13.667 11.015 10.960 10.932 10.905 SO3 6.172 3.628 3.610 3.601 3.592 Fe2O3 5.323 3.129 3.114 3.106 3.098 MgO 4.424 13.030 12.956 12.932 12.900 Na2O 0.626 0.368 0.366 0.365 0.364 K2O 0.586 0.344 0.343 0.342 0.341 TiO2 0.303 0.178 0.177 0.176 Cr2O3 -  0.000 0.500 0.750 1.000 process

THERMAL ANALYSIS Dilatometry (not shown) It determined glass transition (Tg) & softening points (Ts) Both Tg and Ts were slightly affected on Cr2O3-content Tg ranged between 665oC - 690ºC Ts ranged between 761oC - 778ºC  Cr2O3 DTA A single exothermic crystallization peak (Tp) was registered 900oC-1000oC The peak is shallow and occurs at high temperature in the case of G1 but it is much sharper and occurs at lower temperatures in G2 and more pronouncedly in G3 and G4

DEVITRIFICATION OF GLASSES GLASS-CERAMICS DEVITRIFICATION OF GLASSES 2 stage heat treatment 24ο 900-1000ο (5ο/min) (1ο/min) 1h 700ο 2h 700ºC for 1 h 900ºC-1000oC for 2 h Nucleation Crystal growth

GLASS-CERAMICS DENSITY Sample d (g/cm3) Parent glass 900oC 950oC 2.91 2.93 2.96 GC2 3.05 3.04 GC3 2.92 3.11 3.08 GC4 3.10 The difference of density between the parent glasses and the GCs index the degree of devitrification and the formation of crystalline phases Higher % of Cr2O3 causes better crystallization, occurred at lower temperatures

GLASS-CERAMICS HEAT-TREATED AT 900oC X-ray diffraction GLASS-CERAMICS HEAT-TREATED AT 900oC The diffractograms show that heat treatment at 900ºC predominantly results in single crystalline phase GCs of augite (Ca,Mg,Fe,Na)(Mg,Fe,Al,Ti)(Al,Si)2O6 Thermal Expansion Coefficient (for the range 200oC-700oC) (measured from dilatometry curves) GC2900oC: 8.81  10-6 K-1 GC3900oC: 9.55  10-6 K-1 GC4900oC: 9.36  10-6 K-1

GLASS-CERAMIC C3 (0.75% Cr2O3) CRYSTALLIZED AT 900oC GLASS-CERAMICS MICROSTRUCTURE GLASS-CERAMIC C3 (0.75% Cr2O3) CRYSTALLIZED AT 900oC Fine microstructure Submicron crystals are perfectly bordered one to the other Note: This SEM image was taken after etching of a mirror-polished surface with HF

GLASS-CERAMIC C3 (0.75% Cr2O3) CRYSTALLIZED AT 900oC GLASS-CERAMICS APPEARANCE GLASS-CERAMIC C3 (0.75% Cr2O3) CRYSTALLIZED AT 900oC

GLASS-CERAMICS ELECTRICAL IMPEDANCE SPECTROSCOPY Measurements were conducted between 500-1000ºC in the experimental setup using a Hewlett Packard 4284A bridge and changing the frequency between 100 and 106 Hz Diataksh EIS

GLASS-CERAMICS ELECTRICAL IMPEDANCE SPECTROSCOPY ARRHENIOUS PLOTS OF GC3 & GC4 The GC4 is more conductive and has lower Ea than the GC3 (1.21 eV, 1.54 eV, respectively). The calculated electrical resistivity at 1000ºC is: 1.40x106 cm for GC3 5.78x105 cm for GC4 These values are comparable (at 1000ºC) to conventional electrical insulators made of alumina (7x106 cm) and cordierite-anorthite composites (4.6x105 cm).

GLASS-CERAMICS ELECTRICAL IMPEDANCE SPECTROSCOPY GC3 (0.75% Cr2O3) MEASURED AT 800oC In the present impedance spectra, obtained for the glass G3 heat treated at 800ºC, two semicircular arcs were registered. That type of curves indicate contribution of two electrical conductivity phenomena. In the present case, we assign: the 1st arc to glass phase the 2nd arc to crystal grains

CONVERSION OF LOW-SILICA FLY-ASH INTO BULK NUCLEATED FINE GRAINED MONO-MINERAL GLASS-CERAMIC √ √ √ √ √ The difference of density between the parent glasses and the GCs, assumed to be an index of the degree of devitrification and the formation of the crystalline phases, is well correlated with Cr2O3-content. The relatively high values of CTE and electrical resistivity qualify the investigated materials for further consideration with regards to their potential application in electro-vacuum techniques in contact with metals (since they generally approach metals’ thermal properties). The characteristic “grass” greenish colour is attributed to the presence of Cr2O3 in combination with CaO. The appearance of the glass-ceramics suggest their use as decorative tile for architectural uses.