3D microstructure of magnesium potassium phosphate ceramics from X-ray tomography: new insights into the reaction mechanisms

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3D microstructure of magnesium potassium phosphate ceramics from X-ray tomography: new insights into the reaction mechanisms

Magnesium potassium phosphate ceramics are chemically bonded ceramics employed as biomaterials, in nuclear waste encapsulation and for concrete repair. The microstructure dictates material performance and depends on the raw mix composition. Synchrotron X-ray computed microtomography was employed to describe the 3D microstructure and its time evolution during hardening and gain insights into the reaction mechanisms. Any excess water with respect to the stoichiometry of the reaction brought about an increase in porosity, but, notably, a reduction in the average pore size. Crystals filled the water ‘pockets’ in the ceramic volume by growing larger, although less densely packed, increasing the complexity of the pore shape. Platelet over elongated crystal habit was favoured. Such a change in shape is likely related to a change in reaction mechanism, as crystallization from a gel-like amorphous precursor is hindered and progressively substituted by a through-solution mechanism. It is proposed that the time evolution of the microstructure is dictated by the balance between crystallization from amorphous precursor, prevailing in relatively ‘dense’ systems (with stoichiometric water or in low excess), and water segregation, prevailing at higher water contents. The former mechanism was shown to produce an increase in porosity with time, because of the density mismatch between the amorphous and the crystalline phase

The preferences of participants in small-scale sport events: A conjoint analysis case study from Taiwan

The primary objective of this study was an investigation of participants\u27 preferences for a cycling orientated sport tourism event using conjoint analysis. Respondents in a survey were presented with a range of different event alternatives related to the characteristics of proposed small-scale cycling events to draw out useful conclusions about the ideal scenario of such a sporting event that would be the most attractive and desirable for those who compete. A questionnaire, in two parts, was developed and distributed to 195 bicyclers during an event in Kaohsiung, Taiwan and the data was analysed using SPSS Conjoint at the aggregate level (pooled data). Based on the preferences expressed by the athletes the three most important factors were: "preferred season to organizing the event", "parallel organised trade shows & exhibitions" and "entertainment & awards". The findings of this study provide event coordinators and sport marketers with practical insights into event planning and possibility of development of effective marketing strategies designed to reach and attract more participants to these types of activities. This investigation is unique since is one of the first to use a full design of seven parameters in the conjoint analysis model to comprehensively examine athlete\u27s preferences

Preliminary study of the pozzolanic activity of dumped mine wastes obtained from the North Bohemian basin in the Czech Republic

Three dumped raw materials, a tuff and two bentonites, obtained from two mining sites at the North Bohemian basin in the Czech Republic, have been studied in order to evaluate them as pozzolanic admixtures in lime mortars for employment in restoration of cultural heritage objects. After thermal activation (800 °C; 5 h), their pozzolanic properties were compared with those of commercial metakaolin. Quantitative phase analysis with the Rietveld method from X-ray powder diffraction patterns, morphological observations, as well as the Frattini and the modified Chapelle tests were performed. In addition, lime mortars, incorporating the fired materials, were prepared and subjected to simultaneous thermal analysis after a 28-day initial curing (20 ± 1 °C; 60 ± 5 % RH). The results showed that all three materials possess pozzolanic activity. However, when employed in lime mortars they did not result in formation of pozzolanic reaction products. Two methods were proposed to improve their reactivity; grinding to obtain finer particle size and removal of quartz content where necessary

Microstructural characterization of dental zinc phosphate cements using combined small angle neutron scattering and microfocus X-ray computed tomography

Objective To characterize the microstructure of two zinc phosphate cement formulations in order to investigate the role of liquid/solid ratio and composition of powder component, on the developed porosity and, consequently, on compressive strength. Methods X-ray powder diffraction with the Rietveld method was used to study the phase composition of zinc oxide powder and cements. Powder component and cement microstructure were investigated with scanning electron microscopy. Small angle neutron scattering (SANS) and microfocus X-ray computed tomography (XmCT) were together employed to characterize porosity and microstructure of dental cements. Compressive strength tests were performed to evaluate their mechanical performance. Results The beneficial effects obtained by the addition of Al, Mg and B to modulate powder reactivity were mitigated by the crystallization of a Zn aluminate phase not involved in the cement setting reaction. Both cements showed spherical pores with a bimodal distribution at the micro/nano-scale. Pores, containing a low density gel-like phase, developed through segregation of liquid during setting. Increasing liquid/solid ratio from 0.378 to 0.571, increased both SANS and XmCT-derived specific surface area (by 56% and 22%, respectively), porosity (XmCT-derived porosity increased from 3.8% to 5.2%), the relative fraction of large pores ≥50 μm, decreased compressive strength from 50 ± 3 MPa to 39 ± 3 MPa, and favored microstructural and compositional inhomogeneities. Significance Explain aspects of powder design affecting the setting reaction and, in turn, cement performance, to help in optimizing cement formulation. The mechanism behind development of porosity and specific surface area explains mechanical performance, and processes such as erosion and fluoride release/uptake

Is the construction of a sanitary landfill acceptable in a karstic area? The case of the sanitary landfill site in Fokida, Central Greece

Για τη μελέτη της καταλληλότητας μιας συγκεκριμένης θέσης ως Χ.Υ.Τ.Υ. πραγματοποιήθηκαν οι εξής ερευνητικές εργασίες. Εκπόνηση λεπτομερούς γεωλογικής χαρτογράφησης σε αρχική κλίμακα 1:5.000 και στη συνέχεια κατασκευή γεωλογικής- υδρογεωλογικής τομής που περνάει από τη θέση του Χ.Υ.Τ.Υ. Στη συνέχεια εκτελέσθηκε γεωτρητικό πρόγραμμα τόσο με βαθιά γεώτρηση για τη διαπίστωση ύπαρξης στάθμης υπόγειου υδροφόρου ορίζοντα όσο και δειγματοληπτικές γεωτρήσεις με δοκιμές εισπίεσης. Επιπλέον, εφαρμόσθηκαν μέθοδοι εκτίμησης της τρωτότητας υποκείμενου υδροφόρου στρώματος (DRASTIC και EPIC). Τέλος υπολογίσθηκε ο ετήσιος όγκος απορριμμάτων που θα τοποθετούνται στο Χ.Υ.Τ.Υ., ο οποίος δίνει και το μέγεθος του ρυπαντικού φορτίου.This paper investigates the suitability of a specific site for the construction of a sanitary landfill. The following works were performed: detailed geological mapping at a scale of 1:5,000, a geological-hydrogeological cross-section of the sanitary landfill, drilling exploration including the construction of a deep borehole for the detection of any perched aquifer, core logging and in situ permeability tests, implementation of the DRASTIC and EPIC methods to estimate the aquifer’s vulnerability. Finally estimation of the total annual amount of solid waste that will be deposited into the sanitary landfill and determination of the pollution load

Monitoring Durability of Limestone Cement Paste Stored at Conditions Promoting Thaumasite Formation

The durability of Portland-limestone cement with high limestone content was monitored at conditions promoting thaumasite formation. Pore structure and deterioration characteristics were assessed with X-ray micro-computed tomography and correlated with material's strength. Changes in crystalline and amorphous phases of the cement paste were investigated with X-ray powder diffraction and solid state nuclear magnetic resonance spectroscopy. Rapid deterioration was observed, evolving as a front causing concentric crack patterns followed by detachment of the part of specimen in contact with the corrosive solution. This ultimately led to loss of structural integrity after 4 months of exposure. During sulfate attack, thaumasite, ettringite and gypsum formed at the expense of portlandite, calcite and monocarboaluminate hydrate. Furthermore, polymerization of silicate chains in C-S-H and deterioration of C-S-H also occurred