Synergistic effect of acetic acid and NOXfor objects made of lead and its alloys; Indoor corrosive environments in museums and depositories

Complex corrosion simulation to evaluate synergistic effect have to cover large number of factors. To do so, environmental and corrosion datasets collected by monitoring sites of interest have been used to tailor complex artificial ageing of lead and lead alloys, using lead, tin and tin-lead coupons. Material composition was based on objects of interest which are tin-lead alloy based although naming lead objects is used widespread for vast of them. To evaluate results corrosion rate based on weight loss, phase composition of corrosion product and colour change of the coupon surface were utilized. For thin corrosion layers formed micro Raman and FTIR did not provide suitable results, and GIXRD have been used. Although limited number of conditions were used for the simulations, synergistic effect was observed for lead under specific conditions. Synergistic effect do occur on lead when exposed to NOX and acetic acid fumes of relatively low concentrations (18 μg·m-3 and 500 ppb respectively). In addition, there is grouping of colourimetric data collected according to test regimes-phase composition of corrosion product respectively. This information albeit preliminary suggests that colourimetric spectroscopy may be suitable as fast and easy corrosion monitoring

Influence of linseed oil on the microstructure and composition of lime and lime-metakaolin pastes after a long curing time

This study investigates the effect of linseed oil on the microstructure of lime and lime-metakaolin pastes after 68 months of curing under controlled conditions. The hydrophobicity imparted by linseed oil to the pastes’ bulk was confirmed by measuring water drops’ contact angle. The results of thermal analysis, X-ray powder diffraction, and Fourier transform infrared spectroscopy showed that linseed oil significantly hindered the carbonation reaction in both lime and lime-metakaolin pastes and promoted the development of amorphous phases. The obtained results also indicated that linseed oil could foster the pozzolanic reaction in the lime-metakaolin system by stabilizing and/or promoting the development of hydration products resulting in reduced shrinkage in comparison with the reference

Impact of gonadectomy on blood pressure regulation in ageing male and female rats

Sexual dimorphism in blood pressure has been associated with differential expression of the angiotensin II (AII) receptors and with activity of the nervous system. It is generally accepted that aging affects kidney function as well as autonomic nervous system and hormonal balance. Given that hypertension is more prevalent in men than women until women reach their seventh decade we hypothesised that females would be relatively protected from adverse effects of ageing compared to males, and that this would be mediated by the protective effect of ovarian steroids. Intact and gonadectomised male and female normotensive Wistar rats aged 6, 12 and 18 months were used to study renal function, blood pressure, heart rate and blood pressure variability. We observed that intact females had lower levels of proteinuria and higher (12.5%) creatinine clearance compared to intact males, and that this difference was abolished by castration but not by ovariectomy. Ovariectomy resulted in a change by 9% in heart rate, resulting in similar cardiovascular parameters to those observed in males or gonadectomised males. Spectral analysis of systolic blood pressure revealed that high frequency power spectra were significantly elevated in the females vs. males and were reduced by ovariectomy. Taken altogether the results show that females are protected from age-related declining renal function and to a lesser extent from rising blood pressure in comparison to males. Whilst ovariectomy had some deleterious effects in females, the strongest effects were associated with gonadectomy in males, suggesting a damaging effect of male hormones

Polyamorphism and frustrated crystallization in the acid-base reaction of magnesium potassium phosphate cements

Magnesium potassium phosphate cements are a class of acid-base cements for bioengineering and civil engineering applications. The kinetics of their chemical reaction was investigated in situ with isothermal conduction calorimetry and powder X-ray diffraction, quantifying amorphous and crystalline products. The first reaction step, dissolution of MgO, with an apparent activation energy of 71 kJ mol-1, dictates the time evolution of two amorphous intermediate precursors and the crystalline product. The early crystallization of the latter has been described with an Avrami equation with an apparent activation energy of 81 kJ mol-1, pointing to a mechanism of deceleratory nucleation and growth in one direction, compatible with the acicular crystal habit observed with electron microscopy. The observed polyamorph transformation is controlled by a complex interplay between kinetic and thermodynamic factors, in which the changes in the chemical environment (increase in pH) driven by the MgO dissolution, play a crucial role. It is proposed that the onset of the amorphous-amorphous transformation hinders crystallization by decreasing ion mobility, raising the energy barriers to structural reorganization. The rate of MgO dissolution depends on the reactivity of the powder and the parameters of the mix (such as the amount of liquid) and influences the reaction pathways, impacting on material performance

Investigation of setting reaction in magnesium potassium phosphate ceramics with time resolved infrared spectroscopy

Crucial information on reaction products in magnesium potassium phosphate ceramics, essential for material design, is lacking. Setting reaction has been followed with time resolved infrared spectroscopy, supported by 2D correlation spectroscopy. We found evidence of a first amorphous orthophosphate precursor, possibly MgKPO4·H2O, forming early, and of a second intermediate amorphous phase, more structurally similar to MgKPO4·6H2O, forming later. Crystallization of MgKPO4·6H2O occurs from this last phase. Presence of amorphous Mg(OH)2 and magnesium phosphates identified as precipitates from diluted suspensions, was excluded. This complex set of parallel reactions, bears analogies with reaction of zinc phosphate cements and is consistent with recent NMR results

Properties enhancement of magnesium phosphate cement by cross-linked polyvinyl alcohol

A novel ceramic composite has been obtained by introducing polyvinyl alcohol in magnesium-based chemically-bonded ceramics and exploiting the cross-link reaction with glutaraldehyde during setting. The properties of the obtained material and the interaction of the polymer with the cement reaction have been investigated. Several beneficial effects were observed. Namely, an extension of the working time, a reduction in the water sensitivity, a decrease in the rate of the heat evolution during hardening. The latter has been ascribed to the intervention of surface adsorption processes, which hindered the dissolution of MgO, as well as the nucleation and growth of the magnesium phosphate products, in concert with the film forming ability of the polymer. Thanks to the complementarity of their mechanical properties, the cement and the additive operated in a synergistic fashion, allowing for the obtainment of a material possessing higher strength and better elastic properties. Three-dimensional quantitative image analysis from synchrotron X-ray microcomputed tomography evidenced the development of a more compact microstructure, comprising a higher number of crystals of smaller size. As a consequence, the pore network exhibited a higher fraction of small pores and lower pore connectivity. These characteristics contributed to hinder the water absorption, as confirmed by the fluid transport simulations within the volume. The observed correlation between the solution pH and the polymer cross-link density offers the way to effectively modulate the material performance by acting on the chemical environment thanks to its compatibility with the cross-link reaction

Investigation of amorphous and crystalline phosphates in magnesium phosphate ceramics with solid-state 1H and 31P NMR spectroscopy

Magnesium phosphate ceramics are chemically-bonded ceramics for bioengineering and civil engineering applications. Information about the nature of the reaction products, especially the amorphous fraction, and their role in the setting reaction, essential for linking reaction mechanisms to microstructure and performance of ceramics, is lacking. By exploiting 1H and 31P magic-angle spinning nuclear magnetic resonance spectroscopy, in addition to the crystalline reaction product (MKP), two amorphous phases, characterized by two distinct proton and phosphorous environments, have been identified. The results pointed to amorphous hydrated orthophosphate compounds which are the precursors of MKP. They show different 1H spin-lattice relaxation dynamics, and, higher water mobility with respect to MKP. Although these amorphous precursors should not be crypto-structural variants of MKP, they likely host similar structural units. Conversion into MKP is thought to occur through relatively minor rearrangements, as in Ca phosphate hydrates. The new information provided in this work allows us to propose a model for the setting reaction based on an existing theory involving a densification process, analogue to sol-gel processing of ceramics, coherent with results from small angle neutron scattering and mechanisms predicted by reaction kinetics analysis

Amorphous-crystalline transformation control on the microstructural evolution of magnesium phosphate cements

Magnesium phosphate cements are chemically-bonded ceramics exhibiting high strength and good adhesive properties. In-situ investigation of the reaction of Mg-K phosphate cements, indicated that microstructural evolution is controlled by a cement densification process entailing amorphous-to-crystalline transformation during hardening. Owing to the replacement of the amorphous fraction with a material of higher density, possessing elongated crystal habit, an increase in porosity with time occurs, at variance with previous models. The beneficial effect provided by the developed interlocked lath-shaped microstructure, constituted by crystals embedded in the amorphous matrix, prevails over the detrimental role of the increased porosity, explaining the increase in mechanical strength

Nucleation of amorphous precursor in magnesium phosphate cements: Clues to the reaction pathway

In-situ X-ray techniques indicated that in its early stages, the reaction pathway of magnesium phosphate cements involves the formation of an amorphous precursor, first detected as nanoparticles which organize themselves into larger domains. Crystallization occurs from this precursor (already containing the structural motives of the crystalline counterpart) by increasing the long-range order through relatively minor structural rearrangements. The process is compatible with multi-steps nucleation involving non-classical mechanisms, as observed in Ca-carbonates and phosphates, therefore, indicating ways to control the transformation to improve cement design