Assembling phenyl-modified colloidal silica on graphene oxide towards ethanol redispersible graphene oxide powder.

Recently, ethanol has shown promising potential in the large-scale reduction of graphene oxide (GO) into graphene. However, dispersion of GO powder in ethanol is a challenge due to its poor affinity, which hinders permeation and intercalation of ethanol between GO molecule layers. In this paper, phenyl-modified colloidal silica nanospheres (PSNS) were synthesized by phenyl-tri-ethoxy-silane (PTES) and tetra-ethyl ortho-silicate (TEOS) using a sol-gel method. PSNS was then assembled onto a GO surface to form a PSNS@GO structure by possible non-covalent π-π stacking interactions between the phenyl groups and GO molecules. The surface morphology, chemical composition, and dispersion stability were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Raman spectroscopy, X-ray diffractometry, nuclear magnetic resonance, and particle sedimentation test. The results showed that the as-assembled PSNS@GO suspension had excellent dispersion stability with an optimal PSNS concentration of 5 vol% PTES. With the optimized PSNS@GO, ethanol can permeate between the GO layers and intercalate along with PSNS particles via formation of hydrogen bonds between assembled PSNS on GO and ethanol, achieving a stable dispersion of GO in ethanol. The optimized PSNS@GO powder remained redispersible after drying and milling according to this interaction mechanism which is favorable for large scale reduction processes. Higher PTES concentration may result in agglomeration of PSNS and formation of wrapping structures of PSNS@GO after drying and worsen its dispersion capability.

The CO2 fertilization effect on leaf photosynthesis of maize (Zea mays L.) depends on growth temperatures with changes in leaf anatomy and soluble sugars.

Understanding the potential mechanisms and processes of leaf photosynthesis in response to elevated CO2 concentration ([CO2]) and temperature is critical for estimating the impacts of climatic change on the growth and yield in crops such as maize (Zea mays L.), which is a widely cultivated C4 crop all over the world. We examined the combined effect of elevated [CO2] and temperature on plant growth, leaf photosynthesis, stomatal traits, and biochemical compositions of maize with six environmental growth chambers controlling two CO2 levels (400 and 800 µmol mol-1) and three temperature regimes (25/19°C, 31/25°C, and 37/31°C). We found that leaf photosynthesis was significantly enhanced by increasing growth temperature from 25/19°C to 31/25°C independent of [CO2]. However, leaf photosynthesis drastically declined when the growth temperature was continually increased to 37/31°C at both ambient CO2 concentration (400 µmol mol-1, a[CO2]) and elevated CO2 concentration (800 µmol mol-1, e[CO2]). Meanwhile, we also found strong CO2 fertilization effect on maize plants grown at the highest temperature (37/31°C), as evidenced by the higher leaf photosynthesis at e[CO2] than that at a[CO2], although leaf photosynthesis was similar between a[CO2] and e[CO2] under the other two temperature regimes of 25/19°C and 31/25°C. Furthermore, we also found that e[CO2] resulted in an increase in leaf soluble sugar, which was positively related with leaf photosynthesis under the high temperature regime of 37/31°C (R 2 = 0.77). In addition, our results showed that e[CO2] substantially decreased leaf transpiration rates of maize plants, which might be partially attributed to the reduced stomatal openness as demonstrated by the declined stomatal width and stomatal area. These results suggest that the CO2 fertilization effect on plant growth and leaf photosynthesis of maize depends on growth temperatures through changing stomatal traits, leaf anatomy, and soluble sugar contents.

Cement-Based Materials Modified by Colloidal Nano-Silica: Impermeability Characteristic and Microstructure.

Colloidal nano-silica (CNS) was used to improve the mechanical and impermeability characteristics of mortar in this study. The samples were prepared with 0%, 1%, 2% and 3% (solid content) CNS addition. The mechanical strength and permeability of each mixture was studied, and the mechanism behind was revealed by hydration heat evolution, XRD, DSC-DTG, 29Si MAS-NMR and SEM-EDS analysis. The compressive strength and impermeability characteristics of mortars incorporating CNS were significantly improved. The experimental results demonstrated that the incorporation of CNS promoted the early hydration process of cement, thus increasing the polymerization degree of hydrated calcium silicate, decreasing the porosity, and improving the microstructure of mortar. Furthermore, 3% CNS decreased the Ca/Si ratio of the interfacial transition zone (ITZ) from 3.18 to 2.22, thus the enrichment of CH was reduced and the density and strength were improved. This was mainly because of the high pozzolanic activity of CNS, which consumed plenty of calcium hydroxide and converted to C-S-H. Besides, nanoscale CNS and C-S-H particles filled the voids between hydrates, thus refining the pore size, increasing the complexity of pores, and improving the microstructure of ITZ which contributed to the improvement of the impermeability.

Effect of TIPA on mechanical properties and hydration properties of cement-lithium slag system.

Effect of triisopropanolamine (TIPA) on compressive strength and hydration properties of cement-lithium slag (LS, 30%) paste was studied. The results demonstrated that the addition of TIPA is advantageous for compressive strength at 7 d, 28 d and 60 d. The reason was related to the pore complexity and hydration process of cement and LS. TIPA reduced the total porosity, and increased the fractal dimension, making the pore structure more complicated. In addition, TIPA promoted the pozzolanic reaction of LS and the hydration of cement, expediting the formation of C-S(A)-H gel. TIPA accelerated the dissolution of aluminate ions, silicate ions and ferric ions in the pore solution, thereby accelerating the pozzolanic reaction of LS. During the hydration of cement-LS paste, TIPA facilitated the conversion of ettringite to the AFm-like phase and produced more C-A-S-H gel by promoting the dissolution of aluminate ions.

Preparation of ultrafine fly ash by wet grinding and its utilization for immobilizing chloride ions in cement paste.

In this study, to promote the chloride binding capacity of coal fired fly ash (RFA) in cementitious materials, wet grinding was employed and ultrafine fly ash (UFA) with D50 = 2.1 µm was prepared; SEM, XRD, TG, FTIR, and XPS were used to evaluate the chemical and physical change in the process of wet grinding. Then, two kinds of binders composed of cement and FA were designed, and the chloride immobilization was comparatively studied in terms of chemical binding, physical binding, and migration resistance. The hydration behavior and hydrates were investigated in terms of TGA, XRD, NMR, and MIP. Results revealed that UFA exhibited higher pozzolanic reactivity due to the increase of specific surface area, destruction of original molecular structure, and exposure of active reaction sites. And chloride immobilization in cement-UFA system was much greater than that in cement-RFA system at ages of 7 d and 28 d. The mechanism behind was discussed in three aspects: (a) chemical binding was promoted because of the more produced chloroaluminates facilitated by the release of aluminum from UFA; (b) physical adsorption was strengthened at 7 d but weakened at 28 d, resulting from the opposite influence on the amount of C-S-H gel at different ages; (c) migration resistance was improved by the reduction of pore volume and the increase in the complexity of pore structure. This investigation provided one new method for processing FA to promote the chloride immobilization of cement-FA system.

Effect of sodium gluconate on molecular conformation of polycarboxylate superplasticizer studied by the molecular dynamics simulation.

Sodium gluconate (SG) has been accepted as one of the main additional components in polycarboxylate superplasticizer (PCE) system, due to its excellent retarding effect. While the negative effect on dispersion of PCE was reported in the literature, the reason was not completely revealed. In this study, molecular dynamics simulation was used to investigate the mutual influence between SG and PCE in calcium hydroxide (CH) solution. Radial distribution function (RDF) was used to analyze the effects of SG on the complexation of PCE with Ca2+. Radius of gyration (Rg) was adopted to characterize the conformations of the backbone and side chains of PCE in CH solution. Finally, several adsorption and dispersion models were proposed. The results showed that the presence of SG would perturb adsorption of PCE, which was one of the main reasons that affected the dispersion ability of PCE. SG could preferentially combine with Ca2+ so that less amount of Ca2+ is available for combination of PCE, and this could extend the main chain of PCE and show advantage for PCE adsorption. Besides, adding SG could squeeze the side chains of PCE, which would put a negative effect on the dispersion. These findings gave deeper insight into understanding the dispersion mechanism of PCE-SG system.

Effect of Polyacrylic Acid on Rheology of Cement Paste Plasticized by Polycarboxylate Superplasticizer.

Viscosity-enhancing agents (VEA) have been widely employed in high flowability cement-based materials, so as to ensure that no bleeding and segregation would occur. However, in most cases, interaction between VEA and superplasticizer would be unavoidable. In this study, the effect of polyacrylic acid (PAA), known as one of the most commonly used VEAs, on rheology performance of cement paste containing polycarboxylate superplasticizer (PCE), was studied. The initial fluidity was assessed with mini slump, and rheological behavior of cement paste was evaluated with rotor rheometer. Adsorption amount was examined with total organic carbon (TOC) analyzer, and the zeta potential was also tested. The interaction between PAA and PCE in the presence of calcium ion (Ca2+) was analyzed with conductivity, X-ray photoelectron spectroscope (XPS), and dynamic light scattering (DLS). The results illustrate that PAA can adsorb onto the surface of cement particles to plasticize cement paste, being similar to PCE. In the presence of Ca2+, PAA can be curled and crosslinked, as a result of the combination between carboxyl groups (COO−) and Ca2+, thereby affecting the adsorption performance and conformation behavior. It is interesting that negative impact of PAA on dispersion efficiency of PCE can be demonstrated; one reason is the reduced adsorption amount of PCE by PAA competitively adsorbing onto the cement surface, and another possible reason is the invalided PCE by adsorption of PAA. Additionally, molecular weight of PAA should be considered if being used as VEA in PCE system.

Preparation and thermal insulation performance of cast-in-situ phosphogypsum wall.

INTRODUCTION: The mass accumulation of phosphogypsum has caused serious environmental pollution, which has become a worldwide problem. Gypsum is a kind of green building material, which is lighter, has better heat and sound insulation performance, and is easier to recycle compared to cement. The application of cast-in-situ phosphogypsum wall could consume a large amount of pollutant, and improve the efficiency of building construction. METHODS: The preparation and thermal insulation performance of cast-in-situ phosphogypsum wall were investigated. The property of phosphogypsum-fly ash-lime (PFL) triad cementing materials, the adaptability of retarders and superplasticizers, and the influences of vitrified microsphere as aggregates were explored. Thus, the optimum mix was proposed. Thermal insulation performance tests and ANSYS simulation of this material was carried out. RESULTS: Optimal structures based on heat channels and the method of calculation determining related parameters were proposed, which achieved a 12.3% reduction in the heat transfer coefficient of the wall. CONCLUSION: With good performance, phosphogypsum could be used in cast-in-situ walls. This paper provides the theoretical basis for the preparation and energy-saving application of phosphogypsum in the walls of buildings.

Stabilization/solidification on chromium (III) wastes by C(3)A and C(3)A hydrated matrix.

Hazardous wastes are usually used in the Portland cement production in order to save energy, costs and/or stabilize toxic substances and heavy metals inside the clinker. This work focus on the stabilization/solidification on chromium (III) wastes by C(3)A and C(3)A hydrated matrix. The immobilization rate of chromium in C(3)A and the leaching characteristics of the C(3)A hydrated matrixes containing chromium were investigated by ICP-AES. The results indicated that C(3)A had a good solidifying effect on chromium using the clinkering process, however, the Cr leaching content of Cr-doped C(3)A was higher than that of hydrated C(3)A matrix in Cr(NO(3))3 solution and was lower than that of the hydrated C(3)A matrix in K(2)CrO(4) solution, no matter the leachant was sulphuric acid & nitric acid or water. To explain this, C(3)A formation, chemical valence states of chromium in C(3)A, hydration products and Cr distribution in the C(3)A-gypsum hydrated matrixes were studied by XRD, XPS and FESEM-EDS. The investigation showed that part of Cr(3+) was oxidized to Cr(6+) in the clinkering process and identified as the chromium compounds Ca(4)Al(6)O(12)CrO(4) (3CaO·Al(20O(3)·CaCrO(4)), which resulted in the higher leaching of hydrated matrix of Cr-doped C(3)A.

Influence of sintering temperature on the characteristics of shale brick containing oil well-derived drilling waste.

INTRODUCTION: The influence of sintering temperature on the physico-mechanical characteristics (such as water absorption, apparent porosity, bulk density, weight loss on ignition, firing shrinkage, and compressive strength), leachability, and microstructure of shale brick containing oil well-derived drilling waste (DW) was investigated. METHODS: The experiments were conducted at a temperature ranging from 950°C to 1,050°C with 30% DW addition. RESULTS: The results indicate that increasing the sintering temperature decreases the water absorption and apparent porosity and increases the shrinkage, density, and compressive strength of sintered specimens. Moreover, the physico-mechanical properties of samples sintered at 1,050°C meet the requirements of the MU20 according to GB/T 5101-2003 (in China). The heavy metal concentrations of the leachate are much lower than the current regulatory limits according to GB16889-2008. CONCLUSION: The results from XRD and SEM show that increasing sintering temperature results in an increase of the high temperature liquid phase, which may have a significant effect on the densification process of the samples.

[Environment load from China's cement production].

Based on the life-cycle theory, a quantitative evaluation of the environment load caused by cement manufacturing in China was carried out with the application of the CML. environmental impact assessment method. The results show that global warming potential, energy depletion potential and abiotic depletion potential make the main contribution to the environment impact, their environmental loads corresponding to identical environmental impact sorts being 2.76%, 2.34% and 1.39% of the overall load of the whole world, respectively. In 2004, the environment load from cement manufacturing in China is roughly 1.28% of the overall load of the whole world, in which the environmental loads from the shaft kiln processing, wet rotary processing and new-type dry processing being 0.84%, 0.12% and 0.32%, respectively. And it can be reduced to about 1% by replacing backward production processes with the dry method production process.