Activator Concentration Research Articles

Durability properties of copper slag and coal bottom ash based I-shaped geopolymer paver blocks

Geopolymer mortar was prepared with aluminate and silicate-bearing minerals with caustic activators like fly ash (FA), and copper slag (CS). The impression focused on the entire replacement of extensive and energy-intensive Portland cement and traditional natural fine aggregates with coal bottom ash and CS in manufacturing of sustainable geopolymer paving blocks suitable for both rural and urban infrastructure. The designed paver blocks were tested for various durability tests such as water absorption, chemical resistance, abrasion resistance, efflorescence and initial rate of absorption. In overall, the findings indicate the recommendation of geopolymer paving blocks containing 70% of CS and 30% of CBA with different concentrations of alkali activators. Also, the aforesaid geopolymer paver blocks, were found to be efficient compared to conventional (FA and PC) based paver blocks as the same were resulted in reduced water absorption (up to 15%). Similarly GPC mixes, resulted in better resistance (as the same were yielded up to 15% and 70%) against abrasion and chemical attack compared to conventional paver blocks respectively. Based on experimental findings, irrespective of the cost, the designed GPC mixes demonstrated excellent resistance towards aforementioned durability aspects compared to the conventional mix based paver blocks.

Design and fabrication of Tb3+ doped Gd2O3-WO3-SiO2 scintillating glass

Developing novel scintillating glass with high density and intense radioluminescence is of critical importance for various radiation-related technologies. In this paper, Tb-doped Gd 2 O 3 -WO 3 -SiO 2 (GWS) scintillating glass was prepared and investigated. The optical and scintillation properties are explored. And the optimal concentration of Tb activators in glass excited by UV-light and X-ray is determined. Moreover, annealing glass enables a unique glass bleaching phenomenon. Benefitting from the increasement in transparency, a notable improvement in photoluminescence (~195% enhancement in intensity) and radioluminescence (~146% enhancement in intensity) could be realized. The optical and structural characterizations reveal a dramatic change of W chemical valance state from W 5+ to W 6+ , which is supposed to govern the decoloring process. Our research indicates that Tb-doped GWS scintillating glass can be a potential candidate for X-ray monitoring. • Tb doped scintillating glass derived from gadolinium orthosilicate was prepared. • An annealing mediated color bleaching process of the obtained glass was demonstrated and investigated. • The scintillating performance was improved and the potential application for radiation detection was explored.

Effect of Activator Type and Concentration, Water-to-Solid Ratio, and Time on the Flowability of Metakaolin-Based Geopolymer Pastes

Effect of Activator Type and Concentration, Water-to-Solid Ratio, and Time on the Flowability of Metakaolin-Based Geopolymer Pastes

Effect of the Synthesis Conditions on the Morphology, Luminescence and Scintillation Properties of a New Light Scintillation Material Li2CaSiO4:Eu2+ for Neutron and Charged Particle Detection

In the present article, the influence of the activator concentration and impurity content of raw materials on the luminescence and scintillation properties of Li2CaSiO4 was studied. Polycrystalline powder material was obtained by the sol–gel method. It was shown that europium had limited solubility in the host lattice with a limiting concentration proximate to 0.014 formula units. The maximum intensity of photoluminescence was observed with a divalent europium concentration of 0.002 formula units; the light yield under alpha-particle excitation was measured to be 21,600 photons/MeV for ~200 μm of coating, and under neutron excitation, it was calculated to be 103,800 photons/n, the scintillation kinetics was characterized by an effective decay time of 157 ns. These properties and the transparency in the visible spectrum make it possible to produce scintillation screens with a coating of Li2CaSiO4 for detecting neutrons, alpha particles and low-energy beta radiation. The low Zeff (~15) of this compound makes it less sensitive to gamma rays. The 480 nm blue emission peak makes this material compatible with most commercial PMT photocathodes, CCD cameras and silicon photomultipliers, which have a maximum quantum efficiency in the blue–green spectral region.

CTCF DNA-binding domain undergoes dynamic and selective protein–protein interactions

SummaryCTCF is a predominant insulator protein required for three-dimensional chromatin organization. However, the roles of its insulation of enhancers in a 3D nuclear organization have not been fully explained. Here, we found that the CTCF DNA-binding domain (DBD) forms dynamic self-interacting clusters. Strikingly, CTCF DBD clusters were found to incorporate other insulator proteins but are not coenriched with transcriptional activators in the nucleus. This property is not observed in other domains of CTCF or the DBDs of other transcription factors. Moreover, endogenous CTCF shows a phenotype consistent with the DBD by forming small protein clusters and interacting with CTCF motif arrays that have fewer transcriptional activators bound. Our results reveal an interesting phenomenon in which CTCF DBD interacts with insulator proteins and selectively localizes to nuclear positions with lower concentrations of transcriptional activators, providing insights into the insulation function of CTCF.

Premature delivery impacts the concentration of plasminogen activators and a plasminogen activator inhibitor and the plasmin activity in human milk.

Background and aimsPlasmin in human milk partially hydrolyzes milk proteins within the mammary gland and may enhance the hydrolysis of milk proteins within the infant’s stomach. This study examined the effects of extremely preterm (EP)-, very preterm (VP)-, and term-delivery on plasmin activity and the concentrations of plasminogen activators [urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA)], plasminogen activator inhibitor type 1 (PAI-1) and the complexes of PAI-1/uPA and PAI-1/tPA in human milk.Materials and methodsHuman milk samples were collected from mothers who delivered extremely preterm infants [24–27 weeks gestational age (GA), n = 20], very preterm infants (28–32 weeks GA, n = 12), and term infants (38–39 weeks GA, n = 8) during 2–72 days postnatally. Plasmin activity was determined using fluorometric substrate assay, whereas concentrations of uPA, tPA, PAI-1, the PAI-1/uPA complex and the PAI-1/tPA complex were quantified by ELISA.ResultsPlasmin activity, uPA and tPA were detected in all human milk samples, PAI-1 and the PAI-1/uPA complex were present in 42.5 and 32.5% of milk samples, respectively, and the PAI-1/tPA complex was not detected. Plasmin activity was correlated negatively with postnatal age and postmenstrual age (PMA) in the VP group and positively with postnatal age in the term group. uPA and tPA concentrations decreased with increasing postnatal age in both EP and VP groups but did not correlate in the term group. uPA concentration was correlated positively with GA in the VP group and tended to be elevated with increasing GA in the combined three groups. In contrast, tPA concentrations were correlated negatively with GA and PMA in the combined three groups (P < 0.008) and with PMA in the EP and VP groups. PAI-1 concentration tended to be correlated positively with postnatal age in the combined three groups. No correlation was detected with the PAI-1/uPA complex.ConclusionPremature delivery impacted the plasmin activity and the concentrations of uPA, tPA, and PAI-1 in human milk. Whether these changes in milk plasminogen activators and inhibitors have a role in balancing the proteolytic digestion of premature infants remains to be investigated.

Synthesis and characterization of metakaolin-based crystalline phase sodium aluminum silicon oxide geopolymers using concentrated alkaline medium

Crystalline phase geopolymers that include sodium aluminum silicon oxide were produced with high concentrations of NaOH activator in metakaolin–sodium silicate solution at 80 °C. Low-temperature geopolymerization provided these first-ever reported crystalline geopolymers when high NaOH concentration 12–15 M was used for the aqueous metakaolin medium. By changing the NaOH activator concentration to 10 M, amorphous geopolymers were formed, but crystalline geopolymers of sodium aluminum silicon oxide appeared in the NaOH concentration range. The crystalline phase had dense morphology of the formed bulk ceramics, respectively exhibiting 8.4 ± 0.5 MPa compressive strength at weight ratios of solid/liquid (S/L) and Na2SiO3/NaOH of mixtures for 0.45 and 1.0.

POTENSI DAUN JAHE MERAH SEBAGAI BAHAN DASAR PEMBUATAN ELEKTRODA SUPERKAPASITOR

Red ginger leaf waste (Zingiber Officinale Var Rubrum) has been successfully processed as an active carbon base material for supercapacitor electrodes. The process of making carbon electrodes starts from the preparation of the original material, drying, refining, chemical activation, integrated pyrolysis and neutralization. The focus of this research is on the chemical activator ZnCl2 which is used with different concentrations of (0.1 and 0.5) M. Activated carbon powder is printed using a press to produce carbon in the form of solid coins of uniform size. The optimization of the carbon element in the sample is carried out through a pyrolysis process at high temperature with a one-stage integrated technique. Where, carbonization in the N2 gas environment is carried out starting from room temperature 30°C up to 600°C followed by physical activation until the high temperature reaches 800°C in CO2 gas environment. Characterization of activated carbon samples from red ginger leaves begins with determining the amount of shrinkage that occurs in the pyrolysis process by measuring the mass, diameter and thickness of the carbon coins. Furthermore, the electrochemical properties were tested using two methods, namely cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) in a symmetrical two-electrode system. The electrochemical characterization was carried out under the influence of an aqueous electrolyte of 1M KOH and 1M Na2SO4 at a low potential window of 0-1 V. The optimum conditions of electrochemical properties were found in the red ginger leaf activated carbon sample with a ZnCl2 activator concentration of 0.5M for the electrolyte. KOH with a specific capacitance value of 115.9 F/g. while for electrolyte Na2SO4 found in ZnCl2 activator 0.1M with a value of 72 F/g. Through these results, red ginger leaves are known to have great potential as a base material for activated carbon electrodes to improve the performance of supercapacitors.

Original KGd2F7 nanocrystals in fluoro-oxide glass ceramics by Dy3+/Sm3+ co-doped for white light emission

Serial fluoro-oxide glass ceramics (GCs) containing 0.6 mol% Dy 3+ and various Sm 3+ from 0 mol% to 1.5 mol% co-doped novel KGd 2 F 7 nanocrystals were firstly fabricated through high temperature melt-quenching method. Then the microscopic structure of the GCs was revealed by transmission electron microscopy (TEM). And the rare-earth ions (RE 3+ ) of Dy 3+ and Sm 3+ were successfully doped in monoclinic-phase KGd 2 F 7 nanocrystals, which can be verified by energy-dispersive X-ray spectroscopy (EDX) mappings. The photoluminescence spectra of the GCs were probed systematically utilizing 365 nm excitation light. The yellow (573 nm), green (486 nm), and red (648 nm) multiple emissions were observed in the co-doped GCs, and the intensity of red became stronger because of the higher Sm 3+ doping concentrations. This contribution of multiple emissions is due to the co-absorption of both Dy 3+ and Sm 3+ for 365 nm and the presence of energy transfer (ET). Moreover, the ET between Dy 3+ and Sm 3+ was confirmed from the variations of emission spectra and measured decay curves of emissions. Furthermore, the maximum energy transfer efficiency (ETE) from Dy 3+ to Sm 3+ can reach ~60.34% and the internal quantum yield (QY) is computed to be around 31.82% upon excitation of 365 nm. The chromaticity coordinates (CIE (Commission Internationale de L′Eclairage)− 1931) of the GCs can be tuned effectively through changing activator concentrations. Ideal white light emission is at the CIE (0.3357, 0.3342), which was achieved for 0.6 mol% Dy 3+ /0.9 mol% Sm 3+ doped GCs sample. The results indicated that Dy 3+ /Sm 3+ co-doped GCs with both high thermal and chemical-physical stabilities have strong potential application in white light-emitting diodes and fluorescent display devices. • The Dy 3+ /Sm 3+ co-doped fluoro-oxide glass ceramics containing novel KGd 2 F 7 nanocrystals were firstly fabricated. • The Dy 3+ and Sm 3+ ions were successfully doped in monoclinic-phase KGd 2 F 7 nanocrystals. • The standard white light emission was obtained by changing the concentration of Sm 3+ . • The energy transfer process from the Dy 3+ to Sm 3+ has been verified to dipole-dipole interaction mechanism. • The fluoro-oxide glass ceramics containing KGd 2 F 7 nanocrystals exhibit high thermal stability.

Synthesis and Characterization of Li2MgGeO4:Ho3.

In this work, the synthesis and characterization of Li2MgGeO4:Ho3+ ceramics were reported. The X-ray diffraction measurements revealed that the studied ceramics belong to the monoclinic Li2MgGeO4. Luminescence properties were analyzed in the visible spectral range. Green and red emission bands correspondent to the 5F4,5S2→5I8 and 5F5→5I8 transitions of Ho3+ were observed, and their intensities were significantly dependent on activator concentration. Luminescence spectra were also measured under direct excitation of holmium ions or ceramic matrix. Holmium ions were inserted in crystal lattice Li2MgGeO4, giving broad blue emission and characteristic 4f-4f luminescent transitions of rare earths under the selective excitation of the ceramic matrix. The presence of the energy transfer process between the host lattice and Ho3+ ions was suggested.

Experimental Study on the Mechanical Properties and Microstructure of Metakaolin-Based Geopolymer Modified Clay.

Clay is found in some countries all over the world. It usually has low compressive strength and cannot be used as a bearing material for subgrade soil. In this paper, the influence of basicity on a metakaolin-based polymer binder to improve clay was studied. The effects of the molar concentration of the alkali activator, different concentration of the metakaolin-based geopolymer and curing time on unconfined compressive strength were studied. The alkali activator-to-ash ratio was maintained at 0.7. The percentage of metakaolin added to the soil relative to metakaolin and soil mixture was 6%, 8%, 10% and 12%. The sodium hydroxide concentrations are 2M, 4M, 6M and 8M. Unconfined compressive strength (UCS) was tested on days 3, 7, 14 and 28, respectively. Compared with original clay, the results show that the unconfined compressive strength increases with the increase in metakaolin content and molar concentration of NaOH. The maximum compressive strength of the sample with NaOH concentration of 8M and percentage of 12% was 4109 kN on the 28th day, which is about 112% higher than that of the original clay. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that the cementing compound covered the clay particles due to the reaction of the geopolymer with the clay, resulting in the formation of adhesive particles. The main purpose of this study is to verify the effectiveness and stability of metakaolin-based geopolymer binder polymerization under normal temperature and a strong alkali environment. The results can provide parameters for the application and promotion of metakaolin-based geopolymers in soil improvement engineering.

Characterization of class C and F fly ashes based geopolymers incorporating silica fume

Geopolymers have been proposed as an alternative to ordinary concrete with their appropriate mechanical performances and eco-friendly impacts. In current study investigated the interaction between the class C and F fly ashes on the properties of silica fume incorporated geopolymers. For that purpose, the concentration of the alkali activator were determined according to compressive and flexural strengths. Then, the geopolymers prepared with different fly ash/silica fume ratios at specified alkali activator concentration. Mechanical, physical, chemical and microstructural properties of these geopolymers were evaluated by FT-IR, XRD, TGA, and SEM-EDX. The mechanical properties of geopolymers were enhanced remarkably by NaOH molarity and it was detected that the compressive strength and flexural strength values reached the highest (21.13 ± 1.11 MPa and 6.61 ± 0.56 MPa, respectively) at 10 M. Results were compared according to the fly ash type and the fly ash/silica fume ratios of the geopolymers. Due to the high water demand of silica fume, prominent cracks were seen in the geopolymers including 100% silica fume. Besides, inadequate mechanical properties were obtained when 100% fly ash was used. Consequently, it was clearly revealed that the properties of geopolymers obtained with only fly ash or silica fume were improved by the use of both. Finally, higher mechanical properties (σC: 31.91 ± 1.90 MPa, σF: 8.34 ± 0.23 MPa) and less cracks in the bodies were obtained with class F fly ash (75% wt.).

The Influence of NaOH Activator Concentration on the Synthesis of Activated Carbon from Banana Peel for Pb(II) Adsorption

Lead has been known as one of the heavy metals with a high adverse effect to the environment and human health. This study reports the activity of activated carbon from biomass of banana peel as an adsorbent to resolve the hazardous lead-contaminated wastewater. The influence of the activator was studied via the alteration of NaOH concentration from 1, 3, and 5 M, where the sample was denoted as AC-1, AC-3, and AC-5. Some techniques, including FTIR, XRD, and SEM were applied to characterize the sample with the highest adsorption capacity. FTIR result affirmed the presence of hydroxyl group on the activated carbon with NaOH 1 M (AC-1) that was beneficial for adsorption. XRD and SEM confirmed that the activated carbon possessed crystalline and amorphous phases with sheet-like morphology. Regarding Pb(II) adsorption, the higher concentration of activator caused the decline of adsorption capacity as the contact time prolonged. The highest adsorption capacity and efficiency were obtained using 1 M NaOH activator with a contact time of 1 hour, which was 3.71 mg/gram and 97.86%, respectively.

Combined effect of operating variables on performance and kinetic of lead flotation

ABSTRACT This study aims to investigate the effects of pH and chemical reagents to model and optimize the flotation process of a complex lead ore containing 2.44 wt% Pb. For this purpose, the effects of pulp pH, collectors (PAX and R404), depressant (FeSo4), and activator (Na2S) concentrations were studied using response surface methodology. Furthermore, the influence of these parameters was studied on flotation kinetics parameters. The optimization studies indicated that the desired Pb recovery (84.1%) and grade (26.6%) was obtained from the test, which was performed with the optimum flotation conditions: 75 g/t PAX, 80 g/t FeSo4, 735 g/t Na2S, 20 g/t R404 and pH 9.5. The results of statistical analyses showed that the pulp pH, PAX concentration, and interactions between pH-R404 concentration and PAX concentration-R404 concentration were the most influential parameters on concentrate grade and recovery. From the kinetic studies, it was observed that the flotation rate coefficient and ultimate recovery were strongly dependent on the pulp pH. The flotation rate coefficient increased with enhancing the pH from 8 to 9.5 and after that reduced with increasing the pH to 11.

Stochastic gene transcription with non-competitive transcription regulatory architecture.

The transcription factors, such as activators and repressors, can interact with the promoter of gene either in a competitive or non-competitive way. In this paper, we construct a stochastic model with non-competitive transcriptional regulatory architecture and develop an analytical theory that re-establishes the experimental results with an improved data fitting. The analytical expressions in the theory allow us to study the nature of the system corresponding to any of its parameters and hence, enable us to find out the factors that govern the regulation of gene expression for that architecture. We notice that, along with transcriptional reinitiation and repressors, there are other parameters that can control the noisiness of this network. We also observe that, the Fano factor (at mRNA level) varies from sub-Poissonian regime to super-Poissonian regime. In addition to the aforementioned properties, we observe some anomalous characteristics of the Fano factor (at mRNA level) and that of the variance of protein at lower activator concentrations in the presence of repressor molecules. This model is useful to understand the architecture of interactions which may buffer the stochasticity inherent to gene transcription.

Anaerobic activation of microorganisms indigenous to oil reservoirs to enhance oil recovery

Microbial enhanced oil recovery focuses on the activation, isolation, and screening of aerobic functional bacteria. Air injection is required to activate aerobic microorganisms for use in indigenous microbe oil displacement technology. In practice, however, oil reservoirs are oxygen-free, as the oxygen in the air is rapidly consumed by reducing substances and aerobic microorganisms attached to the water injection well at the front end of the reservoir. In the reservoir, most of the microorganisms metabolize anaerobically, and they are concentrated in the area where the residual oil collects in the rear of the facility. The aim of this study was to investigate the factors such as electron acceptors, activator components, and activator concentrations that influence anaerobic metabolism in indigenous microorganisms. Core flooding tests and field trials were conducted to evaluate the anaerobic microbial activation efficiency. The organic nitrogen source in the activator was crucial to anaerobic bacterial metabolism. Yeast powder was the preferred nitrogen source, and other optimal operating parameters included a C/N ratio of 20:1 and an activator concentration of 3 g·L−1. Under these conditions, the anaerobic emulsification index surpassed 90%. Core flooding tests demonstrated that microbial enhancement may provide up to 13.5% oil recovery. A total of 3471.15 BBLs of oil was recovered by injecting anaerobic activator into the Zhan3-15 well, and emulsified oil droplets were detected in the fluid. The results of this study could provide technical support for the practical anaerobic activation of reservoir microorganisms and the improvement of microbial enhanced oil recovery.

Functional porous carbon derived from waste eucalyptus bark for toluene adsorption and aqueous symmetric supercapacitors

It is of great significance to synthesize functional porous carbon from renewable waste biomass resources to solve the problems of energy storage and environmental pollution. Herein, the eucalyptus bark was converted into porous carbon materials for toluene adsorption and aqueous symmetric supercapacitors by hydrothermal treatment combined with KOH activation. Toluene adsorption experiments indicated that the toluene adsorption capacities of BPCs increased with increase of activated temperature and activator concentration, and the toluene adsorption capacities of BPCs were inversely related to adsorption temperature and relative humidity. The effects of structural characteristics and functional groups on toluene adsorption were analyzed in detail. Besides, the supercapacitance performance of samples under different preparation conditions was tested, the BPC-3-600 electrode exhibited the best specific capacitance of 263.2 F g−1 at 0.5 A g−1 and 207.5 F g−1 at 10 A g−1 in a three-electrode system using 6 M KOH as the electrolyte. Moreover, the aqueous symmetric supercapacitor assembled in 6 M KOH showed a high specific capacitance of 191.2 F g−1 at 0.2 A g−1 and an outstanding capacitance retention of 105.1 % at 5 A g−1 after 10,000 cycles. Most importantly, the supercapacitor assembled in 1 M Na2SO4 can provide an energy density as high as 10.5 Wh kg−1 at a power density of 159.5 W kg−1, and a remarkable energy density of 5.2 Wh kg−1 can be retained even at a power density as high as 12,480.0 W kg−1.

Quantification of the Activator and Sensitizer Ion Distributions in NaYF4 :Yb3+ , Er3+ Upconverting Nanoparticles Via Depth-Profiling with Tender X-Ray Photoemission.

The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles (UCNPs). Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X-ray photoelectron spectroscopy depth-profiling with tender X-rays (2000-6000eV), providing probe depths ideally matched to UCNP sizes, is used to measure the depth-dependent concentration ratios of Er3+ to Yb3+ , [Er3+ ]/[Yb3+ ], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements of the lanthanide ion concentrations to construct models of the UCNPs' dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core-only UCNPs synthesized with XCl3 ·6H2 O precursors (β-phase) exhibit a homogeneous distribution of lanthanide ions, but a slightly surface-enhanced [Er3+ ]/[Yb3+ ] is observed for UCNPs prepared with trifluroacetate precursors (α-phase). Examination of Yb-core@Er-shell UCNPs reveals a co-doped, intermixed region between the single-doped core and shell. The impact of these different dopant ion distributions on the UCNP's optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNPs.

Yb- and Er concentration dependence of the upconversion luminescence of highly doped NaYF4:Yb,Er/NaYF4:Lu core/shell nanocrystals prepared by a water-free synthesis

High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%–98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%–40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ∼9% and ∼25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ∼9% (20% Yb3+) to ∼7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ∼7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.

Influence of the type and concentration of the activator on the microstructure of alkali activated SiMn slag pastes

The influence of the type and concentration of the activator on the composition of the products formed and the microstructural development of alkali activated SiMn slag pastes and their evolution with curing time are studied. About 15–17 million tons of SiMn slag is produced per year, so valorising this residue is interesting for the economic and environmental scope. For this purpose, NaOH and WG with different concentrations of Na2O have been used as activators. The hydration products have been studied by X-ray diffraction analysis (XRD) and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDX) has been used to study the microstructure and elemental composition of hydrated phases. The advance of the degree of hydration with time and with the activator concentration is consistent with the mechanical behaviour of these pastes observed in previous studies. All the pastes show high microcracking due to the stresses caused by the shrinkage, as it has been observed in previous studies. Elemental composition data do not show significant differences regarding the type of activator with respect to the main elements and their relationship in the reaction products except for Mn. The main reaction product formed in the alkaline activation of SiMn slag is C-S-H with a low Ca/Si ratio, this being higher for pastes activated with NaOH compared to those with WG. In addition, the modification of the C-S-H structure is demonstrated by the presence of small amounts of Al and Mn and that Mg is not incorporated into it. The presence of hydrotalcite is not detected by XRD, but small amounts have been confirmed by TGA/DTG and SEM/EDX.