1,720,961 research outputs found
The effect of 3D structure design on fire behavior of polyethylene terephthalate glycol containing aluminum hypophosphite and melamine cyanurate
No full textEffect of the shape of 3D printed samples on fire behavior of polyethylene terephthalate glycol (PET-G) and PET-G additivated with a mix of aluminum hypophosphite (AHP) and melamine cyanurate as flame retardant, was investigated. The additives improved fire performance (e.g., maximum average rate of heat emission, total oxygen consumption, heat release rate indices) irrespective of structural complexity, favoring carbonaceous char formation. However, at increasing structural complexity, they promoted higher release of smoke, compared to neat PET-G, because of a change in the prevalent retardation mechanism, which became dominated by the flame inhibition action of AHP. Consequently, the synergistic effect obtained combining the two additives, was hindered. Impact of product design on mechanisms of fire retardation helps in devising engineering solutions aimed at meeting required level of fire-safety performance, which should be tailored to the specific product
Design of polymeric binders to improve the properties of magnesium phosphate cement
No full textIn the context of reducing the environmental impact of cement manufacturing, magnesium phosphate cements raise interest as alternative binders in construction, for immobilization of wastes, and recycling purposes. Their use in applications is somehow limited by short setting time, brittleness and low water resistance; this calls for the use of additives. Two polymer additives were designed adopting emulsion polymerization, an environmentally friendly solution to make available polymers as water-based latex dispersions. The composites containing 5 wt% of polymer, exhibited better elastic behaviour, with up to twice the toughness of the reference sample and of a sample produced with commercial styrene-butadiene rubber latex. Moreover, the additives reduced the apparent porosity, promoted phosphate crystallization, modified the size and shape of crystals, and effectively retarded the reaction, extending working time. The acrylic emulsion developing keto-hydrazide self-crosslinking reaction imparted better properties to the composite, thanks to the synergistic effect with the MPC setting reaction
Bone diagenesis in the medieval cemetery of Vratislavs’ Palace in Prague
No full textDiagenetic modifications in human bones from the early-medieval cemetery discovered in the garden of Vratislavs’ Palace, in the central Malá Strana district of Prague, have been investigated combining histological analysis and instrumental analysis with X-ray diffraction, infrared, and 31P NMR spectroscopy. A total of 15 ribs samples were collected for the study. One sample belonged to a child, whereas, of the other samples from adults, 7 belonged to males, 5 to females, and for 2 the sex attribution was uncertain. A diagenetic pathway common to most of the studied samples was considered the result of a burial environment characterized by a nearly static water regime, with limited temperature excursions, moderately oxic to suboxic, and with pH fluctuations around the limit of apatite recrystallization window, in agreement with the fine textured clay-rich soil, its low hydraulic conductivity, and the measured soil pH. A second pattern, related to variations in the microenvironment, interested a limited number of samples with poorer histological preservation. This was interpreted as the result of higher pH and a better oxygenated environment, which favoured mineral recrystallization. Further reactivation of deterioration processes probably occurred later in some of the graves perturbed by works conducted in the seventeenth century. This work highlights the complementarity of the information obtained from the adopted techniques in order to gain insights into the post-mortem fate of the human remains and their sedimentary environment. In this respect, the quantification of the amount of phosphorus in the amorphous hydrated layer of apatite provided a unique type of information on the mineral component of bone and its reorganization during diagenesis, revealing that a relevant fraction can survive diagenesis, at variance with what previously supposed
Technical Note: Post-burial alteration of bones: Quantitative characterization with solid-state 1H MAS NMR
No full textThe identification of markers of the modifications occurring in human bones after death and of the sedimentary and post-sedimentary processes affecting their state of preservation, is of interest for several scientific disciplines. A new index, obtained from spectral deconvolution of the 1H MAS NMR spectra of bones, relating the number of organic protons to the amount of hydrogen nuclei in the OH– groups of bioapatite, is proposed as indicator of the state of preservation of the organic fraction. In the osteological material from three different archaeological sites, this index resulted positively correlated with the extent of collagen loss derived from infrared spectroscopy. Its sensitivity to changes in the physical and chemical characteristics of bone allows to identify distinct diagenetic pathways specific to each site and to distinguish different trajectories within the same site
The Assessment of Bone Deterioration with Nuclear Magnetic Resonance Spectroscopy in a Multidisciplinary Context: The Case of the UNESCO World Heritage Site of Sedlec, Czechia
No full textHuman remains from the skeletal collection of the UNESCO world heritage site of Sedlec (Czechia) have been investigated with 1H, 31P and 13C magic-angle-spinning nuclear magnetic resonance spectroscopy. The quantitative description of the component of the phosphorus signal attributed to the external amorphous hydrated layer of the mineral apatite particles is considered a sensitive index of the bone integrity, in general agreement with indicators of decay derived from other analytical techniques. Differences in proton and phosphorus resonances were related to deterioration effects, allowing for the identification of local conditions posing a threat to bone preservation
Monitoring Durability of Limestone Cement Paste Stored at Conditions Promoting Thaumasite Formation
Full text linkThe 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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigation of nano-microstructural changes in Maastricht limestone after treatment with nanolime suspension
No full textNanolimes are dispersions of nanosized Ca(OH)2 particles in alcohols often used for the consolidation of various types of cultural heritage objects. The consolidation effect is based on the transformation of Ca(OH)2 into CaCO3 phases during carbonation process. The detection of microstructural changes consequent to a consolidating treatment (essential to evaluate its effectiveness) was approached adopting the innovative combination of two advanced techniques, covering a range in pore size from the nanometric to the millimetric scale: small-angle neutron scattering (SANS) and synchrotron X-ray micro-computed tomography (μ-CT). The changes in the 3D microstructure of samples of Maastricht limestone, a well-known weak stone material considered as a sort of ‘standard’ in cultural heritage conservation studies, pure and treated with nanolime dispersions, have been described in a fully non-invasive fashion, overcoming the limitation of previous approaches. The application of nanolime resulted to have a limited positive effect in reducing the fine porosity. Its time evolution was attributed to the progress of the carbonation reaction. On the contrary, the treatment produced positive effects on the porosity in the size range covered with μ-CT, reducing the pore accessibility between 30 and 65 μm, suggesting an improvement of the mechanical properties. The combined use of SANS and μ-CT represents and novel methodological approach in support of cultural heritage conservation works
Quantification of microstructural changes in limestone cement paste stored in sulfate environment at low temperature
No full textPortland-limestone cement paste specimens were stored in magnesium sulfate solution at 5°C for 6 months; the occurring microstructural changes have been monitored on a monthly basis. Extent of deterioration was quantitatively assessed with different techniques. The X-ray micro-computed tomography was employed to describe non-invasively the pore structure and extend of deterioration. X-ray powder diffraction and infrared spectroscopy were used to characterize the phase changes occurred in the course of the sulfate attack. Compressive strength tests reflected the effect of the process on mechanical performance. The results indicate the rapid degradation of the system, owing, mainly, to crack formation, expansion, and finally loss of cohesion between the deteriorated parts of the specimens and the sound cement matrix, as a consequence of the formation of new phases. The progress of an irregular deterioration front was observed. The presence of complex phases (thaumasite, ettringite) was proved, however, the deteriorated parts of the specimens mostly consisted of gypsum
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