Στην διατριβή αυτή επιχειρείται µια συστηµατική και σε βάθος µελέτη της χηµικής και ορυκτολογικής σύστασης, καθώς και φυσικών και τεχνολογικών ιδιοτήτων των διαφόρων ελληνικών µαγνησιακών υλικών. Τα υλικά αυτά παρήχθησαν από τον µαγνησίτη της Β. Εύβοιας στο εργοστάσιο της ΒΙΟΜΑΓΝ στο Μαντούδι Ευβοίας, προκειµένου να εξαχθούν συµπεράσµατα όχι µόνο για τη βελτίωση των τελικών προϊόντων αλλά και για το σχεδιασµό και παραγωγή νέων προϊόντων, έτσι ώστε τα ελληνικά βασικά πυρίµαχα υλικά να παραµείνουν στην πρωτοπορία των διεθνών εξελίξεων. Συγκεκριµένα µελετήθηκαν: Πρώτες ύλες µαγνησίας. Εξετάστηκαν ελληνικές ποιότητες δίπυρης µαγνησίας, οι οποίες πορούν να διαχωριστούν σε δύο κατηγορίες σύµφωνα µε το µέσο του εµπλουτισµού του αγνησίτη από τον οποίο προέρχονται : Α) Οι ποιότητες δίπυρης µαγνησίας Ε21Α, Ε12Ε, ΝΕ3, οι οποίες παρήχθησαν από ικροκρυσταλλικό µαγνησίτη µε έψηση σε θερµοκρασίες 1850-1900οC σε περιστροφικούς κάµινους, ενώ πριν την έψησή του ο µαγνησίτης εµπλουτίστηκε µε οπτικό διαχωρισµό, βαρέα διάµεσα και µαγνητικό διαχωρισµό. Β) Οι ποιότητες δίπυρης µαγνησίας υψηλής καθαρότητας Μagflot Super Α και Magflot A1 που παρήχθησαν από µικροκρυσταλλικό µαγνησίτη εµπλουτισµένο µε τη µέθοδο της επίπλευσης, η οποία εξασφαλίζει οµοιογένεια και χαµηλό ποσοστό πυριτικών. Το παραγόµενο εµπλούτισµα µετατρέπεται σε καυστική µαγνησία η οποία ακολούθως πρικετοποιείται και τελικά ψήνεται σε φρεατώδη κάµινο στους 2000-2200οC. Μελετήθηκε επίσης, για λόγους σύγκρισης µε τα ελληνικά υλικά, Τετηγµένη µαγνησία, η οποία προέρχεται από την Κίνα Ποιότητες εµπορικών µαγνησιακών πλίνθων της ΒΙΟΜΑΓΝ, MbE21A και MbΜagflot Super A µε πρώτες ύλες δίπυρη µαγνησία Ε21Α και Μagflot Super A αντίστοιχα. Επίσης µελετήθηκε µπορικό µαγνησιοχρωµιτικό πυρίµαχο µε πρώτες ύλες Μagflot Super A και χρωµίτη Αφρικής. Νέες σπινελικές συνθέσεις και νέα µαγνησιοσπινελικά πυρίµαχα που παρήχθησαν στα πλαίσια της διατριβής, σε ηµιβιοµηχανική κλίµακα.Η χηµική σύσταση των πρώτων υλών που εξετάστηκαν µπορεί να περιγραφεί στα πλαίσια του συστήµατος MgO-CaO-SiO2, δεδοµένου ότι περιέχουν πολύ χαµηλές ποσότητες Fe2O3 και Al2O3. Αν και o λόγος τους CaO/SiO2 µπορεί να χρησιµοποιηθεί για την πρόβλεψη των ορυκτολογικών παραγενέσεών τους, λεπτοµερείς αναλύσεις µε περιθλασιµετρία ακτίνων-Χ, οπτική και ηλεκτρονική µικροσκοπία έδειξαν σηµαντικές παρεκκλίσεις από τις αναµενόµενες φάσεις. Οι µικροδοµές ποικίλουν αρκετά ως προς τον δεσµό MgO-MgO, τις ποσότητες και τις συστάσεις των φάσεων των πυριτικών δεσµών, αλλά και το µέγεθος των κρυστάλλων του περικλάστου. Οι ποιότητες Magflot και Τετηγµένης µαγνησίας Κίνας περιέχουν µικρότερα ποσοστά δευτερευουσών φάσεων από τις ποιότητες Ε21Α, Ε12Ε και ΝΕ3. Ο χηµισµός των ποιοτήτων Ε21Α, Ε12Ε και ΝΕ3 ευνοεί το σχηµατισµό δευτερευουσών ασβεστοπυριτικών φάσεων χαµηλού σηµείου τήξεως (όπως C3MS2, CMS) που µειώνουν την πυριµαχικότητα των υλικών. Η διαλυτότητα του CaO στο περίκλαστο ποικίλει µεταξύ των κρυστάλλων του ίδιου δείγµατος, ενώ ο σίδηρος συγκεντρώνεται στο περίκλαστο σχηµατίζοντας βουστίτη. Οι δεκαοκτώ νέες σπινελικές συνθέσεις που παρήχθησαν στα πλαίσια αυτής της διατριβής σε πιλοτική µονάδα στη ΒΙΟΜΑΓΝ στο Μαντούδι Ευβοίας, περιέχουν αλούµινα από 50% έως και 70% και ως προσθετικά, είτε πυριτικό ζιρκόνιο (0,5-2%) ή χρωµίτη (2-5%). Αύξηση του ποσοστού του Al2O3 στις σπινελικές συνθέσεις µε πυριτικό ζιρκόνιο αλλά και σε εκείνες µε χρωµίτη, οδηγεί σε αύξηση της φαινόµενης πυκνότητας καθώς και σε αύξηση του ποσοστού του σπινελίου. Το σταθεροποιητικό προσθετικό του πυριτικού ζιρκονίου επιδρά στο σχηµατισµό µιας πυρίµαχης φάσης υψηλού σηµείου τήξεως, CaOZrO2, η οποία ρυθµίζει την ποσότητα και το είδος των υπολοίπων δευτερευουσών φάσεων που σχηµατίζονται. Το Cr2O3 στις συνθέσεις σπινελίου µε προσθετικό χρωµίτη δεσµεύεται κυρίως στο πλέγµα του σπινελίου αυξάνοντας την πυκνότητά του, ενώ δρα και ως φύτρο σχηµατισµού του σπινελίου. Παράλληλα οι άµεσοι δεσµοί διάχυσης είναι ισχυρότεροι σε σχέση µε εκείνους των κρυστάλλων σπινελίου στις σπινελικές συνθέσεις χωρίς χρωµίτη και αυξάνουν την αντοχή του σπινελίου στη χηµική διάβρωση από τήγµατα µεταλλουργικών σκωριών Οι δευτερεύουσες ασβεστοπυριτικές και ασβεστοαλουµινούχες φάσεις που ανιχνεύθηκαν στις δεκαοκτώ σπινελικές συνθέσεις κυµαίνονται σε πολύ χαµηλά επίπεδα, ενώ δεν αποτελούν όλες, φάσεις ισορροπίας. Από τις νέες σπινελικές συνθέσεις παρασκευάστηκαν έξι νέες ποιότητες µαγνησιοσπινελικών πυριµάχων. Σε κάθε µία από τις συνθέσεις µε 10 και 20 %Al2O3 χρησιµοποιήθηκαν ως πρώτες ύλες: 1. Μagflot και σπινελική σύνθεση τύπου R551z (µε 50% αλούµινα-50% Μafglot και προσθετικό πυριτικό ζιρκόνιο), 2. Magflot και σπινελική σύνθεση τύπου R559z (µε 70% αλούµινα-30% Μagflot και προσθετικό πυριτικό ζιρκόνιο), 3. Magflot και σπινελική σύνθεση τύπου R573cr (µε 70% αλούµινα-30% Μagflot και προσθετικό χρωµίτη). Οι νέες συνθέσεις των µαγνησιοσπινελικών πυριµάχων παρασκευάστηκαν µε σκοπό τη βελτίωση της συµπεριφοράς τους στους θερµοκρασιακούς αιφνιδιασµούς, στη διάβρωση από τήγµατα αλλά και στην αντοχή τους στην εκτριβή µε στόχο την εφαρµογή τους στη βιοµηχανία (ως πορώδη εµβύσµατα για παραγωγή υπερκαθαρού χάλυβα, για αντικατάσταση των ανδαλουσιτικών πυριµάχων στους µεταλλουργικούς κάδους, για αντικατάσταση των µαγνησιοχρωµιτικών πυριµάχων στους κάµινους της τσιµεντοβιοµηχανίας κλπ.). Στις νέες συνθέσεις των µαγνησιοσπινελικών πυριµάχων πραγµατοποιήθηκαν χηµικές, ορυκτολογικές αναλύσεις καθώς και µετρήσεις φαινόµενης πυκνότητας, συντελεστή θερµικής διαστολής αλλά και δοκιµές σε θλίψη εν ψυχρώ. Από τα αποτελέσµατα που προέκυψαν οι ποιότητες S-MAL37z-20 και S-MAL37cr-20, που περιέχουν υψηλής πυκνότητας σπινελικές συνθέσεις (R559z και R573cr αντίστοιχα) και περιεκτικότητα σε Αl2O3 στη µάζα τους της τάξεως 20%, προτείνονται ως περισσότερο κατάλληλες σε σχέση µε τις υπόλοιπες, για αντοχή στους θερµοκρασιακούς αιφνιδιασµούς, και στη διάβρωση από σκωρίες, ενώ οι S-MAL55z-10, S-MAL55z-20 και S-MAL55cr-10 θεωρούνται περισσότερο κατάλληλες για αντοχή σε θλίψηΗ χηµική σύσταση των πρώτων υλών που εξετάστηκαν µπορεί να περιγραφεί στα πλαίσια του συστήµατος MgO-CaO-SiO2, δεδοµένου ότι περιέχουν πολύ χαµηλές ποσότητες Fe2O3 και Al2O3. Αν και o λόγος τους CaO/SiO2 µπορεί να χρησιµοποιηθεί για την πρόβλεψη των ορυκτολογικών παραγενέσεών τους, λεπτοµερείς αναλύσεις µε περιθλασιµετρία ακτίνων-Χ, οπτική και ηλεκτρονική µικροσκοπία έδειξαν σηµαντικές παρεκκλίσεις από τις αναµενόµενες φάσεις. Οι µικροδοµές ποικίλουν αρκετά ως προς τον δεσµό MgO-MgO, τις ποσότητες και τις συστάσεις των φάσεων των πυριτικών δεσµών, αλλά και το µέγεθος των κρυστάλλων του περικλάστου. Οι ποιότητες Magflot και Τετηγµένης µαγνησίας Κίνας περιέχουν µικρότερα ποσοστά δευτερευουσών φάσεων από τις ποιότητες Ε21Α, Ε12Ε και ΝΕ3. Ο χηµισµός των ποιοτήτων Ε21Α, Ε12Ε και ΝΕ3 ευνοεί το σχηµατισµό δευτερευουσών ασβεστοπυριτικών φάσεων χαµηλού σηµείου τήξεως (όπως C3MS2, CMS) που µειώνουν την πυριµαχικότητα των υλικών. Η διαλυτότητα του CaO στο περίκλαστο ποικίλει µεταξύ των κρυστάλλων του ίδιου δείγµατος, ενώ ο σίδηρος συγκεντρώνεται στο περίκλαστο σχηµατίζοντας βουστίτη. Οι δεκαοκτώ νέες σπινελικές συνθέσεις που παρήχθησαν στα πλαίσια αυτής της διατριβής σε πιλοτική µονάδα στη ΒΙΟΜΑΓΝ στο Μαντούδι Ευβοίας, περιέχουν αλούµινα από 50% έως και 70% και ως προσθετικά, είτε πυριτικό ζιρκόνιο (0,5-2%) ή χρωµίτη (2-5%). Αύξηση του ποσοστού του Al2O3 στις σπινελικές συνθέσεις µε πυριτικό ζιρκόνιο αλλά και σε εκείνες µε χρωµίτη, οδηγεί σε αύξηση της φαινόµενης πυκνότητας καθώς και σε αύξηση του ποσοστού του σπινελίου. Το σταθεροποιητικό προσθετικό του πυριτικού ζιρκονίου επιδρά στο σχηµατισµό µιας πυρίµαχης φάσης υψηλού σηµείου τήξεως, CaOZrO2, η οποία ρυθµίζει την ποσότητα και το είδος των υπολοίπων δευτερευουσών φάσεων που σχηµατίζονται. Το Cr2O3 στις συνθέσεις σπινελίου µε προσθετικό χρωµίτη δεσµεύεται κυρίως στο πλέγµα του σπινελίου αυξάνοντας την πυκνότητά του, ενώ δρα και ως φύτρο σχηµατισµού του σπινελίου. Παράλληλα οι άµεσοι δεσµοί διάχυσης είναι ισχυρότεροι σε σχέση µε εκείνους των κρυστάλλων σπινελίου στις σπινελικές συνθέσεις χωρίς χρωµίτη και αυξάνουν την αντοχή του σπινελίου στη χηµική διάβρωση από τήγµατα µεταλλουργικών σκωριών Οι δευτερεύουσες ασβεστοπυριτικές και ασβεστοαλουµινούχες φάσεις που ανιχνεύθηκαν στις δεκαοκτώ σπινελικές συνθέσεις κυµαίνονται σε πολύ χαµηλά επίπεδα, ενώ δεν αποτελούν όλες, φάσεις ισορροπίας. Από τις νέες σπινελικές συνθέσεις παρασκευάστηκαν έξι νέες ποιότητες µαγνησιοσπινελικών πυριµάχων. Σε κάθε µία από τις συνθέσεις µε 10 και 20 %Al2O3 χρησιµοποιήθηκαν ως πρώτες ύλες: 1. Μagflot και σπινελική σύνθεση τύπου R551z (µε 50% αλούµινα-50% Μafglot και προσθετικό πυριτικό ζιρκόνιο), 2. Magflot και σπινελική σύνθεση τύπου R559z (µε 70% αλούµινα-30% Μagflot και προσθετικό πυριτικό ζιρκόνιο), 3. Magflot και σπινελική σύνθεση τύπου R573cr (µε 70% αλούµινα-30% Μagflot και προσθετικό χρωµίτη). Οι νέες συνθέσεις των µαγνησιοσπινελικών πυριµάχων παρασκευάστηκαν µε σκοπό τη βελτίωση της συµπεριφοράς τους στους θερµοκρασιακούς αιφνιδιασµούς, στη διάβρωση από τήγµατα αλλά και στην αντοχή τους στην εκτριβή µε στόχο την εφαρµογή τους στη βιοµηχανία (ως πορώδη εµβύσµατα για παραγωγή υπερκαθαρού χάλυβα, για αντικατάσταση των ανδαλουσιτικών πυριµάχων στους µεταλλουργικούς κάδους, για αντικατάσταση των µαγνησιοχρωµιτικών πυριµάχων στους κάµινους της τσιµεντοβιοµηχανίας κλπ.). Στις νέες συνθέσεις των µαγνησιοσπινελικών πυριµάχων πραγµατοποιήθηκαν χηµικές, ορυκτολογικές αναλύσεις καθώς και µετρήσεις φαινόµενης πυκνότητας, συντελεστή θερµικής διαστολής αλλά και δοκιµές σε θλίψη εν ψυχρώ. Από τα αποτελέσµατα που προέκυψαν οι ποιότητες S-MAL37z-20 και S-MAL37cr-20, που περιέχουν υψηλής πυκνότητας σπινελικές συνθέσεις (R559z και R573cr αντίστοιχα) και περιεκτικότητα σε Αl2O3 στη µάζα τους της τάξεως 20%, προτείνονται ως περισσότερο κατάλληλες σε σχέση µε τις υπόλοιπες, για αντοχή στους θερµοκρασιακούς αιφνιδιασµούς, και στη διάβρωση από σκωρίες, ενώ οι S-MAL55z-10, S-MAL55z-20 και S-MAL55cr-10 θεωρούνται περισσότερο κατάλληλες για αντοχή σε θλίψη. / The present thesis deals with the systematic study of the chemical, mineralogical composition as well as the natural and technological properties of several Greek magnesia materials, derived from magnesite, in order to reach conclusions not only fοr the improvement of the final products but also for the development and manufacture of new ones which, in turn, will allow the greek basic refractories to remain at the forefront of the international developments . Specifically, have been studied: 1) Raw materials. The dead- burned magnesia grains examined are divided into two groups according to the mode of beneficiation of the raw magnesite. A). Dead –burned magnesias of E21A, E12E, NE3 were produced from natural microcrystalline magnesite by firing at temperatures in the range of 1800-2000 oC in rotary kilns. Prior to dead burning magnestite was beneficiated by conventional methods (optical sorting, heavy media, magnetic separation). B) Dead –burned magnesias of Magflot Super A and Magflot A1 were produced from natural microcrystalline magnesite beneficiated by the process of froth flotation, which ensures homogeneity and low silica. The obtained filter cake is calcined to caustic magnesia, which is subsequently briquetted and finally dead burned in shaft kiln at temperatures up to 2000 –2200 oC. Chinese fused magnesia has been also studied in order to be compared with greek materials. 2) Magnesia bricks produced by VIOMAGN; MbE21A from magnesia E21A and MbMagflot Super A from Magflot Super A. In addition, a magnesia chromite brick derived from raw materials of Magflot Super A and chromite from China was studied. 3) New spinel-based compositions and new magnesia-spinel refractory materials which have been produced for the needs of this study. The chemical composition of the materials examined here lie essentially in the MgO-CaO-SiO2 system, since they contain only trace amounts of Fe2O3 and Al2O3. Although their CaO/SiO2 ratios can be used to approximate their mineralogical compositions, detailed XRD, and optical and analytical SEM studies revealed significant deviations from the expected phase assemblages. Their microstructures vary widely in terms of proportions of direct MgO-MgO bonding, amounts and phase constitution of the siliceous bonding and size of the periclase crystals. The qualities of Magflot and Fused Chinese Magnesia contain secondary phases at lower levels compared to the qualities E21A, E12E and NE3. The chemical compositions of the qualities E21A, E12E and NE3 favored the formation of secondary calcium-silicate phases of low melting point. (such as C3MS2, CMS), which reduce the refractoriness of the materials. The solid solubility of CaO in periclase varies between crystals of the same sample. Iron was always found in solution to periclase as wustite. The new spinel-based compositions were produced in a pilot plant at Madoudi of Evia and contain alumina ranging from 50% to 70% and additives of either ZrSiO4 (0,5-2%) or chromite (2-5%). Increase in the amount of Al2O3 in the spinel compositions with ZrSiO4 and chromite lead to an increase in the bulk density as well as in the amount of spinel formed. The stabilizing additive of silica zircon favored the formation of a refractory phase with increased melting point, which controls the formation, the amount and the type of the other secondary phases. The Cr2O3 of spinel compositions which enters mainly the lattice, increases the density and acts as a core for the formation of the spinel. Furthermore, the direct diffusion bondings are stronger than those of the spinel crystals in the spinel compositions without chromite and increase the resistance of spinel against the chemical corrosion from fused metallurgic slags. The secondary calcium-aluminate and calcium- silicate phases, which were traced in the eighteen spinel-based compositions occur in low amount, and not all of them are equilibrium phases. From the new spinel-based compositions, six new magnesia-spinel refractory materials were produced. The compositions with 10 and 20% Al2O3 were derived from : 1 Magflot and spinel composition R551Z which contains 50% alumina-50% Magflot and silica zircon as additive. 2 Magflot and spinel composition R559z that contains 70% alumina – 30% Magflot and silica zircon as additive, 3 Magflot and spinel composition R573cr that contains 70% alumina – 30% Magflot and chromite as additive. The compositions of the magnesia spinel refractories produced are expected to show endurance in thermal shocks as well as in the corrosion from slags and friction, in order to have a wide application in steel, cement industry etc. Chemical, mineralogical analyses as well as estimation of bulk density, thermal coefficient factor and cold crushing strength parameter, of the new magnesia-spinel refractory materials, revealed that: a) the S-MAL37z-20 and S-MAL37cr-20 qualities which contain high density spinel compositions (R559z and R573cr respectively), and Al2O3 of about 20 (% wt) exhibit high endurance in rapid thermal changes and in corrosion, b) the S-MAL55z-10, S-MAL55z-20 and S-MAL55cr-10 qualities show high endurance in crushing.

The effects of initial particle moisture content, wood-cement ratio and density on physical (thickness swelling and water absorption) and mechanical properties (MOE, MOR, IB and edgewise compression) were investigated. Five initial particle moisture content levels - 0-6%, 8-15%, 25-30%, 40-50% and 60-80%; three wood-cement ratios - 1:1, 1:1.5 and 1:2; and three density levels at each wood-cement ratio - 1:1 -0.472 g/cm³, 0.528 g/cm³ and 0.622 g/cm³, 1:1.5 - 0.636 g/cm³, 0.707 g/cm³ and 0.809 g/cm³; and 1:2 - 0.763 g/cm³, 0.847 g/cm³ and 0.939 g/cm³ were used. Combinations of the above variables gave 45 treatments. Three replicate boards were made for each treatment thus giving a total of 135 panels for the study. A total of 135 test specimens were used for each property tested. Results from the tests were compared to the German and ISO Standards for similar boards and to the Canadian Waferboard Standard. Initial particle moisture content was highly significant in the development of physical and mechanical properties of magnesite cement-bonded particleboard. Increasing initial particle moisture content from 0-6% to 60-80% resulted in the reduction of the physical and mechanical properties of the boards. The highest initial particle moisture content of (60-80%) yielded the lowest physical and mechanical properties. For manufacture of boards of favourable mechanical properties, an initial particle moisture content of not more than 15% is recommended. On the other hand, a higher initial particle moisture content (>40%) is considered desirable if board thickness and water absorption are to be minimized. All the mechanical properties tested consistently increased by increasing wood-cement ratio and density and were highest at 1:2 wood-cement ratio and density level 3 of each wood-cement ratio. Thickness swelling and water absorption were consistently reduced by increasing wood-cement ratio and density. In both physical properties tests, the 1:2 wood-cement ratio and density level 3 yielded the lowest values. Thirty-two of the forty-five treatment combinations of initial particle moisture content, density and wood-cement ratio pass the MOE requirement of the German Standard DIN 52 362 for Portland cement-bonded particleboard; forty-one treatments met the minimum MOE Canadian Waferboard Standard requirements, while no treatment meet the MOR requirements for this Standard. Eleven of the forty-five treatments met the minimum IB Canadian Waferboard Standard requirements. All the 45 treatments pass the ISO building board requirements in thickness swelling, while 18 treatments pass the water absorption requirements for this Standard. Most of the treatment combinations compare favourably with results obtained in tests conducted in Europe for cement-bonded particleboard. / Forestry, Faculty of / Graduate

<p> The effects of small additions of Fe2O3, GeO2, Ta2O5, V2O5, TiO2, and SiO2 on the microstructure and fracture toughness of magnesia enriched doloma were investigated. Effects of up to 5% additive oxides on grain growth and sintering in MgO and CaO were determined in preliminary tests. One percent additions were made to 40%, 60% and 80% MgO dolomas and the fracture toughness at temperatures up to 1500°C determined using the single edge notched beam specimen. Fracture surfaces were studied on the scanning electron microscope to determine fracture mode. Silica and Ta2O5 doped material showed high toughness at 1500°C possibly due to microcracks, while TiO2 resulted in formation of a viscous grain boundary film producing high toughness at 1300°C followed by a rapid decline by 1500°C. In undoped samples increases in MgO resulted in the appearance of a toughness peak near 1300°C. This was attributed to grain boundary segregation of impurities.</p> / Thesis / Master of Engineering (MEngr)

Groundwater is a major and sometimes lone source of drinking water worldwide. The chemical composition of groundwater is a combined product of the composition of water that enters the aquifer and its reaction with various minerals present in the soil and rock mass, which alter the water composition with time and space. Some important factors influencing groundwater quality are (1) physiochemical characteristics o the rocks through which the water circulates; (2) geology of the location; (3) climate of the area; (4) role of microorganisms, which includes oxidative and reductive biodegradation of organic matter; (5)chemical, physical, and mineralogical characteristics of the overburden soils through which the rainwater percolates; and (6) human intrusion affecting the hydrological cycle and degradation in water quality through utilization of water for agricultural and industrial activities. By far the most serious naturally occurring groundwater-quality problem in India derives from high fluoride, arsenic and iron concentrations which are dissolved from the bedrocks by geochemical processes. Presence of excess fluoride in groundwater is identified as a naturally occurring health hazard by the World Health Organization (WHO). Prolonged ingestion of fluoride beyond certain permissible limit leads to ffluorosis, one of the common water-related diseases recognized by the WHO and the United Nations Children's Fund (UNICEF). Endemic fluorosis is now known to be global in scope, occurring on all continents and affecting many millions of people. According to estimates made in the early 1980s, around 260 million people in 30 countries worldwide were drinking water with more than 1 ppm of fluoride. The ultimate source of fluoride in water, soil or biosphere is associated with its distribution in rocks and its dispersion in groundwater. The three most important minerals of fluoride are fluorite (CaF2), cryolite (Na3AlF6) and fluorapatite (Ca5(PO4)3F); cryolite is a rare mineral where as by far the largest amount of fluorine in the earth's crust is in the form of fluorapatite (about 3.5% by weight of fluorine) which is processed almost exclusively for its phosphate content. Fluoride substitutes readily in hydroxyl positions in late-formed minerals in igneous rocks, and in primary minerals especially micas (such as biotites) and amphiboles (such as hornblende). The most important controlling factors influencing fluoride presence in groundwater include: distribution of easily weathered fluoride-bearing minerals, the accessibility of circulating water to these minerals, pH of the percolating water, calcium content of the leaching water, temperature of the percolating water and the soil, exchangeable ions in the percolating water, extent of fresh water exchange in an aquifer, evaporation and evapotranspiration, complexing of fluoride ions with other ions, presence of CO2 and other chemicals in draining water and residence time of the percolating water in soil. High fluoride levels are observed in the groundwater in 19 states of the country. Fluorite, apatite, rock phosphate, phosphorites, phosphatic nodules and topaz are major fluoride bearing minerals in India with varying levels of fluoride content. There are three major fluoride bearing areas in India :1) Gujarat-Rajasthan in the north-west and 2) Chandidongri-Raipur in central India 3) Tamil Nadu-Andhra Pradesh in the south; besides other areas in Karnataka, Bihar, Punjab and in the North-west Himalayas. The total mineral reserves of fluorite, rock phosphate and apatite in the country are estimated at 11.6, 71 and 2.82 million tonnes respectively. The distribution of areas with excess fluoride in groundwater concurs with that of fluorine-bearing minerals. Further high fluoride concentrations are observed from arid and semi arid regions of the country and the areas with advanced stage of groundwater development. An estimated 62 million people, including 6 million children suffer from fluorosis in India because of consuming fluoride-contaminated water. Endemic fluorosis is found to practically exist only in the villages due to lack of piped water supply. The Indian Drinking Water Standard specifies the desirable and permissible limits for fluoride in drinking water as 1.0 and 1.5ppm respectively. De-fluoridation of groundwater is the only alternative to prevent fluorosis in the absence of alternate water source especially for immediate and/or interim relief. De-fluoridation of drinking water in India is usually achieved by the Nalgonda technique or activated alumina process. The Nalgonda method involves addition of aluminum salts (aluminium sulphate and/or aluminium chloride), lime and bleaching powder to water, followed by rapid mixing, flocculation, sedimentation, filtration and disinfection. Only aluminum salt is responsible for removal of fluoride from water .Fluoride removal is achieved in a combination of complexation with polyhydroxy aluminium species and adsorption on polymeric alumino hydroxides (floc). Activated alumina(Al2O3) was proposed for de-fluoridation of water for domestic use in 1930’s and since then it has become one of the most advocated de-fluoridation methods. Activated alumina is a semi crystalline porous inorganic adsorbent and an excellent medium for fluoride removal. When the source water passes through the packed column of activated alumina, fluoride (and other components in the water) is removed via exchange reaction with surface hydroxides on alumina; this mechanism is generally called adsorption although ligand exchange is a more appropriate term for the highly specific surface reactions involved. The fluoride removal capacity of alumina is highly sensitive to pH, the optimum being about pH5.5-6. Significant reduction in fluoride removal by activated alumina is also observed in presence of sulfate and silicate ions. The column needs periodic regeneration once break point(where the effluent concentration is, for example, 2ppm at normal saturation) is reached. For regeneration, the medium is backwashed for 5-10 min and then subjected to two step regeneration with base (NaOH) followed by acid(H2SO4). A major cause for concern with the Nalgonda method is the possibility of formation of residual aluminum and soluble aluminum fluoride complexes in the treated water and a potential breach of the 0.2ppm Indian drinking water standard for aluminium. Concerns with the activated alumina filter method are that the process is pH dependent, with an optimum (pH) working range of 5-6. Further, the activated alumina column requires periodic recharge using caustic soda and acid solutions to rejuvenate the fluoride retention capacity of the column. After 3-4 regenerations the medium has to be replaced. If the pH is not readjusted to normal following the regeneration process, there is a possibility that the aluminum concentration in the treated water may exceed the 0.2ppm standard. Due to the aforementioned drawbacks of the currentde-fluoridation technologies in India that chiefly rely on aluminum based compounds, magnesia(magnesium oxide, MgO) is selected to develop an alternate sustainable de-fluoridation method. The potential of MgO for de-fluoridation has been examined owing to its very limited solubility(6.2mg/L), non-toxicity and excellent fluoride retention capacity. A review of the previous studies on fluoride removal using MgO reveals that the relevant information is essentially scattered. Though studies demonstrated the fluoride removing ability of MgO and brought into focus certain aspects of the fluoride removal mechanism and change in water quality upon MgO addition, vital issues necessary for efficient design and successful field implementation of the de-fluoridation processusing MgO were not addressed. The significant limitations in the earlier works include: influence of process variables(such as MgO dosage, initial fluoride concentration, contact time, temperature, initial solution pH, presence of co-ions and ionic strength) on fluoride retention characteristics (such as removal rate, equilibrium time, capacity) of MgO were not systematically determined, optimum operating parameters/conditions (such as MgO dosage, stirring and settling time) for effective de-fluoridation process applicable to a wide range of groundwater chemical composition and fluoride concentrations were not defined, mechanism of fluoride retention by MgO was not fully understood, issue of lowering the pH of MgO treated water within potable water limits was not comprehensively addressed, safe disposal methods of fluoride bearing sludge were not explored. Failure to address the above issues has impeded the adoption of the MgO treatment method for fluoride removal from water. Scope of the study Present study aims to develop a new sustainable de-fluoridation method, applicable to a wide range of groundwater chemical compositions and fluoride concentrations, based on co-precipitation/precipitation-sedimentation-filtration processes using light MgO. Efforts are made to implement the method at domestic level in a rural area with incidence of high fluoride concentration in groundwater and to understand the status and geochemistry of fluoride contamination in the area. The main objectives of the study include: To determine the fluoride retention characteristics of MgO viz.,rate, equilibrium time and capacity of fluoride retention. To examine the influence of process variables on fluoride retention characteristics of MgO and to determine the optimum operating parameters for effective de-fluoridation process. To understand the mechanism and rate limiting step of MgO de-fluoridation process. To propose methods and specifications to lower the pH of MgO treated water within permissible limits to ensure its potability. To design a simple to use, single-stage domestic de-fluoridation unit. To propose procedures for implementation of the new de-fluoridation method in field. To evaluate the efficiency of the new de-fluoridation method as a useful remedial measure in the fluoride affected areas. To understand the geochemical factors governing the quality of the fluoride rich groundwater and to ascertain the status and geochemistry of fluoride contamination in the area where felid implementation of de-fluoridation method is planned. To characterize the fluoride bearing sludge and propose methods for safe disposal and reuse of fluoride bearing sludge. Organization of the thesis Chapter1 presents an overview of the various aspects of excess fluoride presence in groundwater, remedial measures, and emphasizes the need for a new sustainable de-fluoridation method and defines the scope of present study. Chapter 2 performs a detailed investigation to determine the fluoride retention characteristics of MgO under the influence of various process variables at transient and equilibrium conditions using batch studies. The process variables that have been considered are, contact time, initial fluoride concentration, dosage of MgO, temperature, initial pH, presence of co-ions and ionic strength. Studies to determine the optimum operating parameters for efficient de-fluoridation and to understand some basics of reaction mechanisms involved are also part of this chapter. Chapter 3 examines the true nature of the reaction mechanism between fluoride ions and MgO in aqueous media and the rate-limiting step of the de-fluoridation process by investigating the hydration process of MgO and its influence/relation on fluoride removal. Chapter 4 addresses issues that will assist applying the MgO treatment method for fluoride removal in field such as 1)methods and specifications for lowering the pH of the MgO treated water within permissible limits, 2)design of a simple to use, single-stage de-fluoridation unit, and 3)characterization of the resultant fluoride bearing sludge. Chapter 5 performs a detailed investigation to evaluate the efficiency of the new de-fluoridation method in laboratory and field, and to understand the origin and the geochemicall mechanisms driving the groundwater fluorine enrichment in the area where field implementation of the de-fluoridation unit was planned. Chapter 6 explores an environmentally safe route for the disposal and re-use of fluoride bearing sludge in soil based building materials such as, stabilized soil blocks (produced by cement stabilization of densely compacted soil mass) which are alternative to burnt bricks. Chapter 7 summarizes the major results, observations and contributions from the study.

<p>Katalytisk förbränning är en lovande teknik för användning vid kraftgenerering, särskilt för</p><p>gasturbiner. Genom att använda katalytisk förbränning kan man nå mycket låga emissioner av kväveoxider</p><p>(NOX), kolmonoxid (CO) och oförbrända kolväten (UHC) samtidigt, vilket är svårt vid</p><p>konventionell förbränning. Förutom att man erhåller låga emissioner, kan katalytisk förbränning stabilisera</p><p>förbränningen och kan därmed användas för att uppnå stabil förbränning för gaser med låga</p><p>värmevärden. Denna avhandling behandlar huvudsakligen högtemperaturdelen av den katalytiska</p><p>förbränningskammaren. Kraven på denna del har visat sig svåra att nå. För att den katalytiska förbränningskammaren</p><p>ska kunna göras till ett alternativ till den konventionella, måste katalysatorer</p><p>med bättre stabilitet och aktivitet utvecklas.</p><p>Målet med denna avhandling har varit att utveckla katalysatorer med högre aktivitet och stabilitet,</p><p>lämpliga för högtemperaturdelen av en katalytisk förbränningskammare för förbränning av naturgas.</p><p>En mikroemulsionsbaserad framställningsmetod utvecklades för att undersöka om den kunde ge</p><p>katalysatorer med bättre stabilitet och aktivitet. Bärarmaterial som är kända för sin stabilitet, magnesia</p><p>och hexaaluminat, framställdes med den nya metoden. Mikroemulsionsmetoden användes också</p><p>för att impregnera de framställda materialen med de mer aktiva materialen perovskit (LaMnO3) och</p><p>ceriumdioxid (CeO2). Det visade sig att mikroemulsionsmetoden kan användas för att framställa katalysatorer</p><p>med bättre aktivitet jämfört med de konventionella framställningsmetoderna. Genom att</p><p>använda mikroemulsionen för att lägga på aktiva material på bäraren erhölls också en högre aktivitet</p><p>jämfört med konventionella beläggningsstekniker.</p><p>Eftersom katalysatorerna ska användas under lång tid i förbräningskammaren utfördes också en</p><p>åldringsstudie. Som jämförelse användes en av de mest stabila materialen som rapporterats i litteraturen:</p><p>LMHA (mangan-substituerad lantan-hexaaluminat). Resultaten visade att LMHA deaktiverade</p><p>mycket mer jämfört med flera av katalysatorerna innehållande ceriumdioxid på hexaaluminat som</p><p>framställts med den utvecklade mikroemulsionstekniken.</p> / <p>Catalytic combustion is a promising technology for power applications, especially gas turbines.</p><p>By using catalytic combustion ultra low emissions of nitrogen oxides (NO_X), carbon monoxide (CO)</p><p>and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional</p><p>combustion technologies. Besides achieving low emission levels, catalytic combustion can</p><p>stabilize the combustion and thereby be used to obtain stable combustion with low heating-value</p><p>gases. This thesis is focused on the high temperature part of the catalytic combustor. The level of</p><p>performance demanded on this part has been proven hard to achieve. In order to make the catalytic</p><p>combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity</p><p>have to be developed.</p><p>The objective of this work was to develop catalysts with higher activity and stability, suitable</p><p>for the high-temperature part of a catalytic combustor fueled by natural gas. A microemulsion-based</p><p>preparation method was developed for this purpose in an attempt to increase the stability and activity</p><p>of the catalysts. Supports known for their stability, magnesia and hexaaluminate, were prepared using</p><p>the new method. The microemulsion method was also used to impregnate the prepared material with</p><p>the more active materials perovskite (LaMnO₃) and ceria (CeO₂). It was shown that the microemulsion</p><p>method could be used to prepare catalysts with better activity compared to the conventional</p><p>methods. Furthermore, by using the microemulsion to apply active materials onto the support a</p><p>significantly higher activity was obtained than when using conventional impregnation techniques.</p><p>Since the catalysts will operate in the catalytic combustor for extended periods of time under</p><p>harsh conditions, an aging study was performed. One of the most stable catalysts reported in the</p><p>literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for</p><p>comparison purposes. The results show that LMHA deactivated much more strongly compared to</p><p>several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the</p><p>developed microemulsion method.</p>

Among the most impressive developments observed in the last 20 years, the improvement of the installation methods of monolithic refractories is certainly to be taken into account. However, this evolution, from vibratable castables to shotcrete and drycrete was not applied to materials based on magnesia, which are still mostly commercialized as ramming mixes, or as pouring castables with poor properties due to excessive water use. The major issues associated to this lack of technology is the scarcity of submicrometric powders compatible to magnesian systems, and the expansion followed by hydration of the magnesia, which is a disruptive reaction. By a thorough research on the literature, some potential additives were identified to be tested as anti-hydration additives. Hydration tests of powders in autoclave, complemented by pH and rheological measurements on magnesia pastes have identified five possible additives which can be used to inhibit the hydration: tartaric acid, citric acid, boric acid, magnesium fluoride and microsilica. Salts from the organic acids can also be successfully used. Of these, microsilica also presented the advantage of providing the submicrometric particles necessary to improve the flow of the castable, and to improve the bond of the castable. The three acids are very effective in inhibiting the formation of magnesium hydroxide, but affect negatively flow properties and mechanical resistance after cure. Microsilica prevented hydration cracks due to the reaction between the silicic acid generated under basic environment with the newly formed brucite, leading to the precipitation of a magnesium-silica-hydrated phase of poor crystallinity between the magnesia grains. This phase does not promote volumetric change, and also enable water release at a wider temperature range. Due to its nature close to serpentine minerals, it forms forsterite and enstatite at low temperatures, thus generating suitable strength between room temperature and at least 1400 °C. Magnesium fluoride changed the nature of this magnesium-silica-hydrated phase, by being incorporated to it and forming a phase more similar to the humite minerals. These minerals present higher MgO:SiO2 molar ratio than serpentine, and their formation requires a lower content of microsilica for a same effect against hydration, which is beneficial for the overall properties of the castable. The properties of the castable, as well as the influence of a number of other variables (for instance, refractoriness under load, creep, cold crushing strength, cold modulus of rupture, bulk density and apparent porosity) were also studied and hereby reported. It is believed that this technology can be further developed for industrial use, provided that some issues regarding the properties at high temperatures are solved. Not only had the study and comprehension of the nature of the bond between microsilica and magnesia, and the role of magnesium fluoride been pioneered by this work, but also the methodology used to evaluate the hydration after the drying process of castings, which was close to real refractory components.

Katalytisk förbränning är en lovande teknik för användning vid kraftgenerering, särskilt för gasturbiner. Genom att använda katalytisk förbränning kan man nå mycket låga emissioner av kväveoxider (NOX), kolmonoxid (CO) och oförbrända kolväten (UHC) samtidigt, vilket är svårt vid konventionell förbränning. Förutom att man erhåller låga emissioner, kan katalytisk förbränning stabilisera förbränningen och kan därmed användas för att uppnå stabil förbränning för gaser med låga värmevärden. Denna avhandling behandlar huvudsakligen högtemperaturdelen av den katalytiska förbränningskammaren. Kraven på denna del har visat sig svåra att nå. För att den katalytiska förbränningskammaren ska kunna göras till ett alternativ till den konventionella, måste katalysatorer med bättre stabilitet och aktivitet utvecklas. Målet med denna avhandling har varit att utveckla katalysatorer med högre aktivitet och stabilitet, lämpliga för högtemperaturdelen av en katalytisk förbränningskammare för förbränning av naturgas. En mikroemulsionsbaserad framställningsmetod utvecklades för att undersöka om den kunde ge katalysatorer med bättre stabilitet och aktivitet. Bärarmaterial som är kända för sin stabilitet, magnesia och hexaaluminat, framställdes med den nya metoden. Mikroemulsionsmetoden användes också för att impregnera de framställda materialen med de mer aktiva materialen perovskit (LaMnO3) och ceriumdioxid (CeO2). Det visade sig att mikroemulsionsmetoden kan användas för att framställa katalysatorer med bättre aktivitet jämfört med de konventionella framställningsmetoderna. Genom att använda mikroemulsionen för att lägga på aktiva material på bäraren erhölls också en högre aktivitet jämfört med konventionella beläggningsstekniker. Eftersom katalysatorerna ska användas under lång tid i förbräningskammaren utfördes också en åldringsstudie. Som jämförelse användes en av de mest stabila materialen som rapporterats i litteraturen: LMHA (mangan-substituerad lantan-hexaaluminat). Resultaten visade att LMHA deaktiverade mycket mer jämfört med flera av katalysatorerna innehållande ceriumdioxid på hexaaluminat som framställts med den utvecklade mikroemulsionstekniken. / Catalytic combustion is a promising technology for power applications, especially gas turbines. By using catalytic combustion ultra low emissions of nitrogen oxides (NOX), carbon monoxide (CO) and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional combustion technologies. Besides achieving low emission levels, catalytic combustion can stabilize the combustion and thereby be used to obtain stable combustion with low heating-value gases. This thesis is focused on the high temperature part of the catalytic combustor. The level of performance demanded on this part has been proven hard to achieve. In order to make the catalytic combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity have to be developed. The objective of this work was to develop catalysts with higher activity and stability, suitable for the high-temperature part of a catalytic combustor fueled by natural gas. A microemulsion-based preparation method was developed for this purpose in an attempt to increase the stability and activity of the catalysts. Supports known for their stability, magnesia and hexaaluminate, were prepared using the new method. The microemulsion method was also used to impregnate the prepared material with the more active materials perovskite (LaMnO3) and ceria (CeO2). It was shown that the microemulsion method could be used to prepare catalysts with better activity compared to the conventional methods. Furthermore, by using the microemulsion to apply active materials onto the support a significantly higher activity was obtained than when using conventional impregnation techniques. Since the catalysts will operate in the catalytic combustor for extended periods of time under harsh conditions, an aging study was performed. One of the most stable catalysts reported in the literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for comparison purposes. The results show that LMHA deactivated much more strongly compared to several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the developed microemulsion method. / QC 20101104

Catalisadores de Ni (10% em massa) suportado em matrizes mistas MgO-SiO2 foram aplicados na rea&ccedil;&atilde;o de reforma a vapor de glicerol. Os efeitos do teor de MgO como aditivo e do m&eacute;todo de prepara&ccedil;&atilde;o foram avaliados frente &agrave;s propriedades f&iacute;sico-qu&iacute;micas e texturais dos materiais; assim como &agrave; atividade, seletividade, estabilidade e forma&ccedil;&atilde;o de carbono na reforma a vapor do glicerol. Os catalisadores foram preparados com diferentes teores m&aacute;ssicos de MgO (10%, 30% e 50%) sobre SiO2 comercial, utilizando processo via seca (mistura f&iacute;sica) e via &uacute;mida (impregna&ccedil;&atilde;o sequencial com diferentes solventes: &aacute;gua, etanol e acetona). Foram utilizadas as t&eacute;cnicas de caracteriza&ccedil;&atilde;o de espectroscopia de energia dispersiva de raios X, fisissor&ccedil;&atilde;o de nitrog&ecirc;nio, difratometria de raios X, termogravimetria, difratometria de raios X in situ com O2, redu&ccedil;&atilde;o a temperatura programada com H2, difratometria de raios X in situ com H2, dessor&ccedil;&atilde;o a temperatura programada com H2 e microscopia eletr&ocirc;nica de varredura. Foi observado que o Ni(II) interage de forma variada com os suportes com diferentes teores de MgO, e que a polaridade do solvente de impregna&ccedil;&atilde;o utilizado no processo de prepara&ccedil;&atilde;o influencia as propriedades dos catalisadores. A fim de verificar a atividade, seletividade e deposi&ccedil;&atilde;o de carbono; os catalisadores foram testados na rea&ccedil;&atilde;o de reforma a vapor de glicerol a 600oC, por um per&iacute;odo de 5h e raz&atilde;o molar &aacute;gua:glicerol de 12:1. Ap&oacute;s as rea&ccedil;&otilde;es, os catalisadores foram novamente submetidos &agrave;s an&aacute;lises de termogravimetria, difratometria de raios X e microscopia eletr&ocirc;nica de varredura, visando a caracteriza&ccedil;&atilde;o dos dep&oacute;sitos de carbono obtidos durante o processo catal&iacute;tico. Os catalisadores de matrizes mistas se mostraram ativos e apresentaram seletividades similares para os produtos gasosos CH4, CO e CO2, al&eacute;m de um alto rendimento em H2. Observou-se que a adi&ccedil;&atilde;o de MgO no suporte, aumentou a dispers&atilde;o do Ni(II) no material, que por sua vez, influenciou na quantidade de carbono depositado ao longo da rea&ccedil;&atilde;o. A polaridade do solvente de impregna&ccedil;&atilde;o tamb&eacute;m teve influ&ecirc;ncia na dispers&atilde;o met&aacute;lica, sendo que, quanto menor a polaridade do solvente, maior foi a dispers&atilde;o obtida no catalisador, e menor a deposi&ccedil;&atilde;o de carbono na rea&ccedil;&atilde;o. O material que apresentou o melhor desempenho catal&iacute;tico frente ao rendimento de H2 e &agrave; deposi&ccedil;&atilde;o de carbono, foi o catalisador preparado com 30% de MgO com etanol como solvente de impregna&ccedil;&atilde;o. / Ni catalysts (10wt%) supported on MgO-SiO2 were assessed in glycerol steam reforming reaction. The effects of MgO as additive and preparation method were evaluated on physico-chemical and textural materials properties; as their activity, selectivity, stability and carbon formation in glycerol steam reforming. The catalysts were prepared with different amounts of MgO (10wt%, 30wt% and 50wt%) on commercial SiO2 by dry process (physical mixture) and wet process (sequential impregnation with water, ethanol and acetone as solvents). Samples were characterized by energy dispersive X-ray spectroscopy, nitrogen physisorption, X-ray diffraction, thermogravimetry, in situ X-ray diffraction with O2, temperature programmed reduction with H2, in situ X-ray diffraction with H2, temperature programmed desorption with H2 and scanning electron microscopy. It was observed that the Ni(II) interacts differently with supports with different MgO content, and the polarity of impregnation solvent used in preparation process influences on catalysts properties. In order to evaluated the activity, selectivity and carbon deposition, the catalysts were tested in glycerol steam reforming reaction at 600oC for 5h and water:glycerol molar ratio of 12:1. After reaction, carbon deposits obtained during the catalytic process were characterized by thermogravimetry, X-ray diffraction and scanning electron microscopy. Mixed matrices catalysts were active in glycerol steam reforming and showed similar selectivity for the gaseous products (H2, CH4, CO and CO2), with a high H2 yield. It was observed that the addition of MgO increased Ni(II) dispersion on material, which influenced on the quantity of carbon deposited during reaction. Polarity of impregnation solvent had also influence on metallic dispersion, and smaller the solvent polarity, higher the dispersion obtained in the catalyst, and lower the carbon deposition on reaction. The material that showed the best catalytic performance in H2 yield and carbon deposition, was the catalyst prepared with 30wt% of MgO with ethanol as impregnation solvent.

A principal limitação do uso de MgO em refratários é a facilidade com que reage com água formando hidróxido de magnésio (Mg(OH)2) que, devido à sua menor densidade, causa tensões destrutivas nesses materiais. Para outras aplicações, no entanto, a reação de hidroxilação do MgO é necessária, como em produção de agentes antichamas, em compósitos poliméricos e na correção de pH de solos. Observações empíricas na literatura demonstraram que diferentes fontes de MgO possuem reatividades e sensibilidades à hidroxilação distintas. Este estudo analisou o impacto de variáveis externas (por exemplo, a liberação de calor que ocorre durante a reação ou o volume das amostras) que ainda não foi completamente compreendido. O impacto auto-catalítico da temperatura reacional e da exotermia da reação foi avaliado. Por meio de medidas de temperatura in situ e de grau de hidroxilação termogravimétrico, também foram estudados os impactos do volume das amostras testadas e da concentração de sólidos nas suspensões, por meio de medidas de temperatura in situ e termogravimetria. Analisou-se também as principais diferenças estruturais entre duas principais fontes de MgO (sínter de MgO e magnésia cáustica): morfologia de partículas, densidade e área superficial específica. Em seguida, os mecanismos de hidroxilação em suspensões aquosas e seus efeitos foram avaliados por meio de testes de hidroxilação seguidos de termogravimetria, difração de raios-X, medidas de condutividade iônica, densidade, área superficial específica e microscopia eletrônica, e relacionado com as características físico-químicas e morfológicas das respectivas fontes de MgO. Pôde-se constatar que diferenças significativas entre a temperatura nominal do meio reacional e no interior da amostra podem afetar a cinética de hidroxilação do material. O volume e a concentração de sólidos variáveis também podem acentuar consideravelmente os efeitos da exotermia e gerar gradientes de hidroxilação. Também se verificou que a morfologia e a quantidade do Mg(OH)2 formado mudam significativamente dependendo do precursor e em função das condições de tempo-temperatura. / The use of MgO in refractories is restrict due to the easy reaction with water forming magnesium hydroxide (Mg(OH)2). Its lower density causes compressive stresses that can crack their structure. On the other hand, for applications such as the production of flame retardant agents for polymer composites and pH correcting of contaminated soil, this reaction is necessary. Empirical observations in the literature have shown that different sources of MgO have district levels of chemical reactiveness. The present study analyzed the main structural differences between the two main sources of MgO (magnesia sinter and caustic magnesia): particle morphology, density and specific surface area. The mechanisms of hydroxylation of these raw materials in aqueous suspensions and their effects were followed by hydroxylation tests, X-ray diffraction, ionic conductivity, density, specific surface area and scanning electron microscopy. They were associated with the physical characteristics morphological, chemical of these MgO sources. The impact of external variables (e.g., heat release during the reaction or the sample volume), that was not yet completely understood, was also evaluated through temperature measurements carried out in situ and hydroxylation degree accessed by thermogravimetry. The effects of samples volume and solid concentration in aqueous suspension were also investigated. The results showed that differences between the ambient temperature and reaction inside sample temperature can affect the kinetics of hydroxylation of the material. The samples volume and solids concentration can also enhance significantly the effects of heat release and generate gradients of hydroxylation. It was also found out that the morphology and the amount of Mg(OH)2 formed can change depending on the precursor and on the time-temperature conditions.

A formação de espinélio de aluminato de magnésio (\'MG\'\'AL IND.2\'\'O IND.4\'; espinélio), através da combinação de óxido de alumínio (\'AL IND.2\'\'O IND.3\'; alumina) com geradores de poros à base de óxido de Magnésio (\'MG\'\'O\'; magnésia) ou hidróxido de magnésio (\'MG\'(\'OH)IND.2\'; HM), resulta em estruturas de elevada porosidade (acima de 50%) e com baixa tendência a densificar mesmo em temperaturas elevadas (1500-1650°C). Devido a isso, esse sistema tem grande potencial de aplicação tecnológica para isolamento térmico e filtração em altas temperaturas. Considerando sua utilização em larga escala como isolante térmico verifica-se a necessidade de desenvolvimento de novas rotas de síntese mais eficazes. A reação de hidroxilação do \'MG\'\'O\' pode ser controlada, utilizando como matéria-prima tanto a magnésia sínter como com a magnésia caustica, desta forma, a expansão de peças de cerâmicas porosas feitas a base de \'MG\'\'O\' também podem ser controladas. Deste modo, neste trabalho pretende-se investigar uma nova rota para a obtenção de espinélio utilizando o \'MG\'\'O\' como ligante hidráulico e incorporar poros, in situ, utilizando-se da decomposição do HM em uma matriz de alumina. Os resultados mostraram que a área superficial específica (ASE) da magnésia influencia fortemente nas propriedades mecânicas do material moldado, comprovando que para as ASEs maiores a magnésia é viável como ligante hidráulico, sendo 0,6 MPa para o modulo de ruptura por compressão diametral, o melhor resultado deste trabalho, enquanto o sistema à base de cimento de aluminato de cálcio (CAC) teve 0,5 MPa de módulo de ruptura, e o sistema à base de \'alfa\'-Bond teve 0,3 MPa de módulo, ambos sistemas de ligantes hidráulicos conhecidos na literatura. A grande diferença no módulo de ruptura por compressão diametral mostrou que o tempo de cura e a ASE da magnésia influenciaram-no fortemente.Enquanto, as amostras com alta ASE de magnésia, em torno de ~60 \'M POT.2\'/g, tiveram 0,6 MPa de módulo de ruptura, as amostras com baixa ASE, ~1 \'M POT.2\'/g, não tiveram alteração no módulo de ruptura. Verificou-se também um aumento gradual no módulo de ruptura segundo a ASE, para um valor intermediário de ASE, ~30 \'M POT.2\'/g, o módulo foi de 0,4 MPa, valor ainda comparável a outros sistemas que se utilizam ligantes hidráulicos. Observou-se que a expansão das amostras durante a cura foi influenciada pela sua ASE, quanto maior a ASE, maior a expansão. Os resultados de PTG e do módulo de ruptura combinados com as imagens de MEV e os difratogramas, das amostras calcinadas, mostraram a influência da temperatura e da ASE na formação da cerâmica porosa por essa rota, sendo a temperatura uma variável de controle já conhecida, observada no diagrama de equilíbrio de fases. Entretanto, a influência da ASE do \'MG\'\'O\' para o controle da formação do espinélio é desconhecido da literatura / Magnesium aluminate spinel (\'MG\'\'AL IND.2\'\'O IND.4\'; spinel) formation by the combination of aluminum oxide (\'AL IND.2\'\'O IND.3\'; alumina) with magnesium oxide (\'MG\'\'O\', magnesium) or magnesium hydroxide (\'MG\'(\'OH) IND.2\'; HM), results in structures of high porosity (above 50%) and with low tendency to densify even at elevated temperatures (1500-1650°C). Due to this, this system has great potential of technological application for thermal insulation and filtration in high temperatures. Considering its large scale use as thermal insulation, it is necessary to develop new and more efficient routes of synthesis. The hydroxylation reaction of \'MG\'\'O\' can be controlled using both sinter magnesia and caustic magnesia as a feedstock, so the expansion of porous ceramic pieces made with \'MG\'\'O\'can also be controlled. Thus, in this work we intend to investigate a new route to obtain spinel using \'MG\'\'O\' as a hydraulic binder and to incorporate pores, in situ, using the decomposition of HM in an alumina matrix. The results showed that the specific surface area (ASE) of the magnesia strongly influences the mechanical properties of the molded material, proving that for the larger ASEs the magnesia is viable as a hydraulic binder, being 0.6 MPa for the diametral compression rupture modulus, the best result of this work, while the calcium aluminate cement (CAC) system had 0.5 MPa of modulus of rupture, and the \'alfa\'-Bond based system had 0.3 MPa of modulus, both systems of hydraulic binders known in the literature. The large difference in the diametral compression rupture modulus showed that the curing time and the ASE of the magnesia strongly influenced it. While high ASE magnesia samples, around ~60 \'M POT.2\'/g, had 0.6 MPa of modulus of rupture, samples with low ASE, ~1 \'M POT.2\'/g, had no change in modulus of rupture. There was also a gradual increase in the ASE burst modulus, for an ASE intermediate value ~30 \'M POT.2\'/g, the modulus was 0.4 MPa,a value still comparable to other systems using hydraulic binders. It was observed that the expansion of the samples during curing was influenced by their ASE, the higher the ASE, the greater the expansion. The results of PTG and the rupture modulus combined with SEM images and the diffractograms of the calcined samples showed the influence of temperature and ASE on the formation of the porous ceramic by this route, the temperature being a known control variable, observed in the phase equilibrium diagram. However, the influence of \'Mg\'\'O\' ASE on the control of spinel formation is unknown in the literature