•Nanocrystalline regions in size of ∼5nm were found in the amorphous C-A-S-H gel.•A hydration model was proposed to clarify the hydration mechanism.•The developed cementitious materials are ...environmentally acceptable.
A deep investigation on the hydration mechanism of bauxite-calcination-method red mud-coal gangue based cementitious materials was conducted from viewpoints of hydration products and hydration heat analysis. As a main hydration product, the microstructure of C-A-S-H gel was observed using high resolution transmission electron microscopy. It was found that the C-A-S-H gel is composed of amorphous regions and nanocrystalline regions. Most of regions in the C-A-S-H gel are amorphous with continuous distribution, and the nanocrystalline regions on scale of ∼5nm are dispersed irregularly within the amorphous regions. The hydration heat of red mud-coal gangue based cementitious materials is much lower than that of the ordinary Portland cement. A hydration model was proposed for this kind of cementitious materials, and the hydration process mainly consists of four stages which are dissolution of materials, formation of C-A-S-H gels and ettringite, cementation of hydration products, and polycondensation of C-A-S-H gels. There are no strict boundaries among these four basic stages, and they proceed crossing each other. Moreover, the leaching toxicity tests were also performed to prove that the developed red mud-coal gangue based cementitious materials are environmentally acceptable.
To investigate how corneal hydration affects the Brillouin frequency of corneal stroma.
From a simple analytical model considering the volume fraction of water in corneal stroma, we derived the ...dependence of Brillouin frequency on hydration and hydration-induced corneal thickness variation. The Brillouin frequencies of fresh ex vivo porcine corneas were measured as their hydration was varied in dextran solution and water. Healthy volunteers (8 eyes) were scanned in vivo repeatedly over the course of 9 hours, and the diurnal variations of Brillouin frequency and central corneal thickness (CCT) were measured.
The measured dependence of Brillouin frequency on hydration, both ex vivo and in vivo, agreed well with the theoretical prediction. The Brillouin frequencies of human corneas scanned immediately after waking were on average ∼25 MHz lower than their daytime average values. For stabilized corneas, the typical variation of Brillouin frequency was ± 7.2 MHz. With respect to CCT increase or swelling, the Brillouin frequency decreased with a slope of -1.06 MHz/μm in vivo.
The ex vivo and in vivo data agree with our theoretical model and support that the effect of corneal hydration on Brillouin frequency comes predominantly from the dependence of the tissue compressibility on the water. Corneal hydration correlates negatively with the Brillouin frequency. During daytime activities, the influence of physiological hydration changes in human corneas is < ± 10 MHz. The sensitivity to hydration may potentially be useful in detecting abnormal hydration change in patients with endothelial disorders.
The strength-formation mechanism for industrial-construction residue cement stabilization of crushed aggregate (IRCSCA) is not clear. To expand the application range for recycled micro-powders in ...road engineering, the dosages of eco-friendly hybrid recycled powders (HRPs) with different proportions of RBP and RCP affecting the strengths of cement-fly ash mortar at different ages, and the strength-formation mechanism, were studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the early strength of the mortar was 2.62 times higher than that of the reference specimen when a 3/2 mass ratio of brick powder and concrete powder was mixed to form the HRP and replace some of the cement. With increasing HRP content substituted for fly ash, the strength of the cement mortar first increased and then decreased. When the HRP content was 35%, the compressive strength of the mortar was 1.56 times higher than that of the reference specimen, and the flexural strength was 1.51 times higher; XRD and SEM studies of the hydrated cement mixed with HRP showed that the amount of CH in the cement paste was reduced by the pozzolanic reaction of HRP at later hydration ages, and it was very useful in improving the compactness of the mortar. The XRD spectrum of the cement paste made with HRP indicated that the CH crystal plane orientation index R, with a diffraction angle peak of approximately 34.0, was consistent with the cement slurry strength evolution law, and this research provides a reference for the application of HRP to produce IRCSCA.
Here we show that bulk H, C and N elemental and isotopic analyses can be used to classify CM and CR chondrites. These meteorites in both groups form well-defined trends in plots of H content vs. δD ...and C/H vs. δD, and these trends appear to primarily reflect varying degrees of aqueous alteration. The subset of samples with evidence for thermal alteration plot well away from these trends. In CMs, both bulk H and N isotopic compositions, in particular, strongly correlate with petrologic indicators of the degree of alteration and have been used to classify 54 unheated or weakly heated meteorites on a scale of 2–3. However, extrapolation of the trends based on this scale to type 3.0 predicts relatively high water contents, and the schemes cannot be used to classify altered meteorite belonging to other chondrite groups. Here we propose a different classification scheme based on the degree of hydration (wt.% H in water and OH) of a meteorite that can be determined straightforwardly from a meteorite’s bulk H and C contents. Our estimates of the extent of hydration in CMs correlate well with petrologic estimates of the extent of hydration and with the previously determined phyllosilicate abundances. This is not the case for the CRs, which we suggest is due to cryptic alteration of some CRs at low temperatures.
•Oxalate ions were added into cement pastes to reduce the calcium concentration of pore solution.•The influence of calcium concentration and pH on the length of induction period was investigated.•The ...influence of calcium concentration and pH on the silicate peak and the sulfate depletion peak was investigated.•Role of calcium ions and pH in cement hydration was discussed.
Pore solution provides the physical and chemical environment for cement hydration, in which calcium, silicon, and hydroxyl ions released by dissolution of cement clinker are transferred into the hydration products such as calcium silicate hydrates (C-S-H) and calcium hydroxide (CH). Therefore, both calcium ions and pH not only have significant influence on the dissolution of cement clinker but also on the precipitation of CH and C-S-H. However, how they influence the kinetics of cement hydration, especially at the very early stage, remains unclear. With the attempt to explore this influence potassium oxalate and oxalic acid were used to regulate the calcium concentration and pH within pore solution independently. Cement pastes with different formulations were investigated by the combination of calorimetric measurements and pore solution analysis.
The results suggest that simultaneous removal of calcium and hydroxyl ions can significantly increase the length of induction period and reduce the height of the silicate reaction peak in the calorimetric curves, whereas the removal of hydroxyl or calcium ions alone cannot. The calculation of saturation index of alite, CH, and C-S-H indicates that undersaturation degree of alite during induction period is well related to the length of induction period and simultaneous removal of calcium and hydroxyl ions is likely to cause lower undersaturation degree of alite, longer induction period, and postponed time of silicate peak. The increase of pH could result in a higher sulfate concentration and subsequently a higher aluminate peak, and a shorter time interval between silicate and aluminate peak.
•Hydration rate of cement was accelerated, and cumulative hydration heat was increased by GO.•Electrical resistivity of cement paste was increased by appropriate GO content.•Mechanical strengths of ...cement paste were enhanced by GO incorporation.•GO-cement paste presented dense microstructure and more hydrates networking.
The effects of graphene oxide (GO) on the early-age hydration process and mechanical properties of Portland cement paste were experimentally investigated in this study. Based on an isothermal calorimeter measurement, the hydration rate of cement was observed to increase with the increase of GO content by nucleation effect. On the other hand, the electrical resistivity development of GO-cement paste was monitored using a non-contact electrical resistivity device. The result showed that electrical the resistivity of GO-cement paste was evidently higher than that of plain cement paste. However, cement paste with excessive amounts of GO exhibited a decreased electrical resistivity due to the massive ion diffusion caused by GO. Compared to plain cement paste, the GO-cement paste exhibited obviously higher compressive and flexural strengths, but the enhancements in compressive strength began to decline when the GO amount was greater than 0.04%. The microstructure characterization indicated that GO can apparently densify the cement pastes with less porosity and hydrates networking, which is consistent with the results of hydration acceleration and strength enhancement.
Waste glass is a bulk solid waste, and its utilization is of great consequence for environmental protection; the application of waste glass to magnesium phosphate cement can also play a prominent ...role in its recycling. The purpose of this study is to evaluate the effect of glass powder (GP) on the mechanical and working properties of magnesium potassium phosphate cement (MKPC). Moreover, a 40mm × 40mm × 40mm mold was used in this experiment, the workability, setting time, strength, hydration heat release, porosity, and microstructure of the specimens were evaluated. The results indicated that the addition of glass powder prolonged the setting time of MKPC, reduced the workability of the matrix, and effectively lowered the hydration heat of the MKPC. Compared to an M/P ratio (MgO/KH
PO
mass ratio) of 1:1, the workability of the MKPC with M/P ratios of 2:1 and 3:1 was reduced by 1% and 2.1%, respectively, and the peak hydration temperatures were reduced by 0.5% and 14.6%, respectively. The compressive strength of MKPC increased with an increase in the glass powder content at the M/P ratio of 1:1, and the addition of glass powder reduced the porosity of the matrix, effectively increased the yield of struvite-K, and affected the morphology of the hydration products. With an increase in the M/P ratio, the struvite-K content decreased, many tiny pores were more prevalent on the surface of the matrix, and the bonding integrity between the MKPC was weakened, thereby reducing the compressive strength of the matrix. At less than 40 wt.% glass powder content, the performance of MKPC improved at an M/P ratio of 1:1. In general, the addition of glass powders improved the mechanical properties of MKPC and reduced the heat of hydration.
CaOHy can be utilized as high efficient heterogeneous solid catalyst for transesterification of palm oil to biodiesel at room temperature.
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•Hydration-dehydration process can improve ...the catalytic activity of CaO.•Over 94% FAME yield is achieved under optimization of reaction conditions at room temperature.•CaOHY exhibits high potential as solid catalyst for low cost industrial biodiesel production.
This research presents an efficient technique to enhance the catalytic activity, surface area and total basicity of CaO with hydration-dehydration process to be the catalyst for the transesterification of palm oil to biodiesel. The catalytic performance of the resulted catalyst was tested via transesterification reaction of palm oil at room temperature (30 ± 2 °C) and was compared against commercial CaO and CaO derived from natural calcium carbonate sources. Under the optimal reaction conditions (catalyst loading of 5 wt%, methanol to oil molar ratio 12:1), FAME yields were approximately 94% for CaOHY and 60.5%, 55.3%, 49.5% and 51.4% for CaOcom, CaOegg, CaOgol and CaOriv as catalysts, respectively. Catalyst reusability and scaling up of biodiesel production from 50 mL to 1.5 L were also investigated. The obtained biodiesel product after purification and treatment process showed high quality fuel properties within the range of biodiesel standard and similar with high-speed diesel. Furthermore, the used CaOHY as a solid heterogeneous catalyst at room temperature was not only low-cost but also environmentally-friendly, showing a high potential in the biodiesel production.
Purpose
(1) To compare the effects of wet and dry crosslinking (CL) on swell‐resistance of porcine corneal grafts; (2) for grafts obtained by dry physical CL methods, to evaluate some of their ...surgically relevant properties.
Methods
Experiment 1. The cornea was cut out of a frozen porcine eyeball with epithelium and Descemet's membrane removed. 30 such grafts were distributed into 10 groups of treatment (3 per group): five groups of wet grafts (wet control; Riboflavin/ultraviolet‐A CL at doses 5.4 and 54 J/cm2; glutaraldehyde CL at concentrations 0.1 and 1%) and five groups of air‐dried grafts (dry control; ultraviolet‐C (UVC) at doses of 5.4 and 54 J/cm2; dehydrothermal (DHT) CL at 80 and 105 °C). All grafts were immersed in distilled water for 24h, then their light transmission and swelling ratio were measured.
Experiment 2. 18 grafts (6 groups: wet non‐hydrated control; wet control; dry control; UVC 54 J/cm2; DHT 105°C; DHT 105°C + UVC 54 J/cm2) were immersed in water for 24 hr, then distant visual quality at 5 m, central thickness (CT) and suture retention strength (SRS) were tested. ANOVA and post‐hoc Tukey HSD tests were used.
Results
Exp. 1. There was a significant difference in water content and light transmission between all groups at 24h hydration (p < 0.05, ANOVA). DHT 105°C grafts had significantly lower water content and the highest light transmission in comparison to all other groups (p < 0.05 for each comparison, Tukey HSD).
Exp. 2. At 24 hr hydration, DHT+UVC treated grafts allowed distinguishing optotypes 0.4–0.6 (decimal). CT varied from 600 to 1200 microns for DHT+UVC and UVC groups, respectively. Control grafts swelled up to 6000 microns in the center. SRS of all grafts was significantly higher than the strength of the Nylon 9‐0 thread (p<0.05, Tukey HSD).
Conclusions
Dry physical CL methods allow obtaining corneal grafts with increased swell‐resistance compared to wet CL methods, while maintaining the strength sufficient for their surgical fixation.
Liposomes (or lipid vesicles) are a versatile platform as carriers for the delivery of the drugs and other macromolecules into human and animal bodies. Though the method of using liposomes has been ...known since 1960s, and major developments and commercialization of liposomal formulations took place in the late nineties (or early part of this century), newer methods of liposome synthesis and drug encapsulation continue to be an active area of research. With the developments in related fields, such as electrohydrodynamics and microfluidics, and a growing understanding of the mechanisms of lipid assembly from colloidal and intermolecular forces, liposome preparation techniques have been enriched and more predictable than before. This has led to better methods that can also scale at an industrial production level. In this review, we present several novel methods that were introduced over the last decade and compare their advantages over conventional methods. Researchers beginning to explore liposomal formulations will find this resource useful to give an overall direction for an appropriate choice of method. Where possible, we have also provided the known mechanisms behind the preparation methods.
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