Activator Concentration Research Articles

Assessment of mechanical and micro-structural characterization of novel ambient cured cement-free composite concrete

To minimize the utilization of natural resources & consuming of huge energy and in order to control the global warming, industrial waste based geopolymer has attracted by the researchers. The manufacturing of GGBS-FA based Geopolymer Concrete (GFGPC) are essential due to its cost-effective reuse by recycling the industrial wastes. The impact of various quantities of Ground Granulated Blast-furnace Slag (GGBS), activator concentration, alkaline solution to solid ratios and liquid ratios of silicate to hydroxide of sodium on experimented mechanical strength and microstructural characterization are investigated. The novelty and research significance lie in adoption of ambient curing techniques, reduced time interval between Alkali Activator Solution (AAS) preparation and concrete casting from 24 h to 3–6. It was observed that with decrease of GGBS content from 70% to 30%, compressive strength at 28 days was reduced from 53 MPa to 36 MPa. A mix containing 40–50% GGBS, AAS to binder ratio of 0.45–0.55, 7 M(Molar) solution of Sodium Hydroxide (SH), ratio of sodium silicate (SS) to sodium hydroxide (SH) of 1.5–2.0 along with 3–6 h of time interval between AAS preparation and concrete casting were proposed as an optimum design mix with respect to compressive strength, workability and setting time. The empirical predictions of splitting-tensile strength and flexural strength of developed GFGPC were made based on the experimental laboratory results and made comparisons with respect to the equations of ACI 318, Eurocode 2, AS 3600 and IS 456 for OPC based conventional concrete (CCOPC) and others existing literature for GPC. Additionally, XRF, XRD, FESEM and EDS were conducted to investigate the microstructural properties and the reaction mechanism of GFGPC.

Effect of Composition on Characteristics of Powder Coating Sludge (PCS)-Metakaolin-Based Geopolymer

The aim of this research is to experimentally study the application of powder coating sludge (PCS) and metakaolin as geopolymer. The PCS is a lot of waste which is released after the powder coating production process. While metakaolin comprises SiO2 and Al2O3 which can be used to produce geopolymer. Therefore, this study aimed to determine a suitable geopolymer mix ratio, using PCS as part of the mixture. This research also investigated the effect of metakaolin/PCS ratio, sodium hydroxide (NaOH)/sodium silicate (Na2SiO3) ratio, curing time, NaOH concentration and solid/liquid ratio on compressive strength of geopolymer. The coefficient of thermal conductivity was tested by using a suitable composition. Kaolin in this experiment was calcined at 700 °C for 2 h. Alkaline activators for molding were NaOH and Na2SiO3. Samples were hardened in an electric oven at 80 °C for 4 h before being removed from the moulds and cured at room temperature within 7, 14 and 28 days. Metakaolin/PCS ratios of 90:10, 80:20, 70:30 and 60:40, and solid/liquid ratios of 0.8 and 0.6 were performed. Concentration of NaOH were 6, 8, 10, 12 and 14 molars and NaOH/Na2SiO3 ratios were 1:1.5, 1:2 and 1:2.5, respectively. The experiments were conducted in triplicate. Results of 3 PCS tests showed that the highest composition of Al2O3 and SiO2 were 3.37 and 1.99 % w/w, respectively. The sample which is based on 60 % metakaolin and 40 % PCS, 10 molars NaOH, NaOH/ Na2SiO3 of 1:1.25, solid/liquid of 0.6 and curing time of 28 days had a maximum compressive strength of 81 kg/cm2, while the coefficient of thermal conductivity was 0.1766 W/(mŸk). Therefore, it can be concluded that the PCS has the potential to partially replace metakaolin as geopolymers material.
 HIGHLIGHTS
 
 Geopolymer comprises alumina (Al2O3) and silica (SiO2) and the advantages of geopolymer production are environmentally friendly and reduce energy consumption 
 
 
 The appropriate metakaolin/PCS ratio and concentration of activators provide the highest compressive strength
 
 
 The geopolymer of this study has low thermal conductivity coefficient therefore it is a good insulation material 
 

Tunable concentration-dependent upconversion and downconversion luminescence in NaYF4: Yb3+, Er3+@ NaYF4: Yb3+, Nd3+ core-shell nanocrystals for a dual-mode anti-counterfeiting imaging application.

Lanthanide-doped luminescent nanocrystals display both upconversion luminescence (UCL) and downconversion luminescence (DCL) properties, which offer potential applications in the second near-infrared window (NIR-II) images and biology sensors. Both UCL and DCL are sensitive to concentrations of activators. However, few works reveal the mechanism of concentration-dependent UCL and DCL. Herein, we synthesize core-shell upconversion nanocrystals (UCNCs) NaYF4: Yb3+(20%), Er3+ (2%)@NaYF4: Yb3+ (x%), Nd3+ (y%) with varying concentration of Nd and Yb ions. The UCL and DCL spectra are recorded under excitation of 980 nm and 808 nm lasers. The results indicate that the luminescence of core-shell UCNCs is influenced by the non-radiative rate between activators (Yb3+ and Nd3+) and the back energy transfer rate from Er3+ ions to activators. UCL tends to be obtained at a relatively low concentration of Yb3+ and Nd3+ ions (about 5%), whereas NIR emission tends to be obtained at a relatively high concentration of Yb3+ and Nd3+ ions (not higher than 20%). Dual-mode anti-counterfeiting imaging is successfully fabricated using core-shell UCNCs, which can be detected and distinguished by visible and infrared detectors. The visible versus infrared brightness of dual-mode anti-counterfeiting imaging can be tuned by varying the concentration of activators (Yb3+, Nd3+). Our work demonstrates concentration-dependent UCL and DCL in core-shell UCNCs, which provides reference to obtain NIR emission in the NIR-II region and adds encrypted dimensions for anti-counterfeiting patterns in the field of file encryption.

Tunable and Enhanced NIR-II Luminescence from Heavily Doped Rare-Earth Nanoparticles for In Vivo Bioimaging

The last decade has witnessed the booming development of optical imaging in the second near-infrared (NIR-II, 1000-1700 nm) window for disease screening and image-guided surgical interventions, due to the merits of multi-color observations and high spatio-temporal resolution in deep tissue. Therefore, bright and multispectral NIR-II probes are required and play a key role. Here, we report the synthesis of a set of bright rare-earth based NIR-II downshifting nanoparticles (DSNPs) with hexagonal phase (β phase). As compared with the widely reported DSNPs (β-NaYF4@NaYF4:20Yb/(0.5-2)A@NaYF4; A = Ho, Pr, Tm or Er) previously, we reveal that the concentrations of both sensitizers and activators can be further highly doped, not limited by the concentration quenching effect. Our results demonstrate that the optimized formula in the heavily doped DSNPs (β-NaYF4@NaYbF4:A@NaYF4, A = 20Ho, 3Pr, 4Tm or 10Er) leads to 1.2- to 4.2-folds NIR-II luminescence enhancement. Especially for the heavily Er-doped DSNPs with long-wavelength photons extending to the NIR-IIb window (1500-1700 nm), we can further boost their luminescence through introducing a beneficial cross-relaxation and host matrix with higher phonon energy (cubic phase NaYF4@NaYbF4:10Er/5Ce@NaYF4), leading to a total of ∼11.4-fold enhancement. The resulting biocompatible, bright NIR-II emitting DSNPs enable us to in vivo monitor the cerebral vessels through the intact scalp and skull, as well as two-color dynamic tumor imaging with high spatial resolution. This work suggests the potential of the heavily doped DSNPs for multiplexed imaging in cerebrovascular abnormalities toward the diagnosis and therapy of the cerebral diseases.

Stability of superplasticizer on NaOH activators and influence on the rheology of alkali-activated fly ash fresh pastes

This paper investigates the effect of the five different superplasticizer (SPs), Melamine sulfonate (M), naphthalene-based (N), lignosulfonate (L), polyether-type (P-Ⅰ), and polyester-type polycarboxylate super-plasticizers (P-Ⅱ), on the rheology of fly ash pastes activated by different molarity of NaOH activator. The fluidity, viscoelasticity, inter-microstructure, and mechanism were evaluated for AAM fresh pastes. And the stability of SPs in the different molarity (0.01 M, 0.1 M, 1 M, 2 M, 3 M,5 M, and 10 M) of NaOH activators was investigated by the ATR-FTIR experiment. The results show that all SPs were the effective admixtures under low molarity (0.1 M) of NaOH activators, while N-SPs performed better in case of high molarity (10 M) of NaOH activators in AAM fly ash pastes. However, with the increase in the concentration of NaOH activators, the structure of SPs is destroyed into small molecules and has negligible effects on the rheology properties of fresh pasts. Unlike other SPs, the electrophilic effect of Ar and strong electricity of the sulfonic acid group of N-SPs may provide more adsorption sites and decrease the interaction between sulfonic groups.

Geomechanical Behaviour of Clay Stabilised with Fly-Ash-Based Geopolymer for Deep Mixing

Geopolymer has recently become an attractive alternative to traditional binders (e.g., cement and lime) used for chemical soil improvement, with several environmental benefits including lower toxic emissions and energy consumption. This paper presents an evaluation of the geomechanical behaviour of soft clay treated with fly-ash-based geopolymer incorporating slag for deep soil mixing (DSM) applications. The geomechanical properties of stabilised clay were evaluated using unconfined compressive strength (UCS) tests and durability against wetting–drying. Thermal conductivity and pH tests along with microstructural analysis using scanning electron microscopy (SEM) were also performed to provide insights into the effect of geopolymer on treated clay. The results indicate that the inclusion of geopolymer with the increase in curing time and activator content considerably improves the geomechanical performance of geopolymer-treated soft clay in terms of stress–strain response and attainable peak compressive strength. Although it was found that a small percentage of geopolymer can enhance the initial compressive response, a larger dosage of geopolymer up to 30% was necessary to maintain stable durability performance over successive wetting–drying cycles. Such improved durability performance is related to the enhanced soil structure due to the cementation development and overall reduction in thermal conductivity. The reduction in thermal conductivity of treated clay was found to be activator-dependent and was suppressed steadily with the increase in activator concentration. Overall, geopolymer-treated clay showed promising potential for DSM applications due to its enhanced strength and durability responses.

Broadband Near-Infrared-Emitting Phosphors with Suppressed Concentration Quenching in a Two-Dimensional Structure

For inorganic luminescent materials with activators, the energy yield is usually observed to decrease with an increase in activator concentration, which is known as the concentration quenching effect. To inhibit this phenomenon, a common strategy is to increase the distance between activators. Most previous reports have focused on the three-dimensional crystal lattice, and there have been few reports about two-dimensional layered structure. Herein, we synthesized a novel Cr3+-activated near-infrared (NIR) phosphor Li2Sr2Al(PO4)3 (LSAPO) with layered structure, and in such a two-dimensional structure, we proved experimentally that the concentration quenching was suppressed. Under 460 nm excitation, LSAPO:Cr3+ gave a broad NIR emission band (700-1200 nm) centered at 823 nm with a full width at half-maximum (fwhm) of 178 nm and a broad absorption band, indicating its potential application in NIR spectroscopy. Moreover, by codoping Cr3+ and Yb3+ ions, we further widened the emission bandwidth to ∼230 nm of fwhm, the internal quantum efficiency increased from 54% to 61%, and the thermal stability was improved. The fabricated NIR device with a LSAPO:Cr3+,Yb3+ phosphor coupled with blue chips can be applied in night-vision technologies and medical fields.

The effects of cations and concentration on reaction mechanism of alkali-activated blast furnace ferronickel slag

The effects of ion species and alkalinity on the alkali activated furnace ferronickel slag (FNS) were studied in this paper. NaOH and KOH with different concentration (2 M & 6 M) were used as activator. XRD , FT-IR and BET results show that more C-A-S-H gels were produced than the crystalline phases at lower activator concentration, while more crystalline phases formed at high concentration. Isothermal calorimetry and ICP results show that the effects of cations are different at different concentration. At lower concentration, higher reaction rate and higher concentrations of Si and Al were found in NaOH activated FNS although the alkalinity of NaOH is lower. This is due to the stronger polarization ability of Na + than K + can stabilize Si and Al anions in the solution and improve the reaction rate. At higher concentration, isothermal calorimetry shows large differences between NaOH and KOH while only small differences was found in ICP data. This indicates that cations have greater impact on the reaction process at higher concentration. A hypothesis was proposed to explain the anomalous phenomenon at higher concentration. At high concentration, there are not enough water molecules in the solution for ion hydration. Na + with higher ionic polarization and hydration heat will strongly bind to dissolved anions and accelerate the reaction near the FNS particle. While K + bind to less water molecules which enable faster diffusion of anionic species and promote the later reaction. • The effect of cations on the reaction kinetics of alkali-activated furnace slag is different at different concentrations. • At 2 M concentration, Na + with a high charge density could stabilize the Si and Al anions and the reaction rate is higher. • At 6 M concentration, the strong polarization ability of Na + decrease the molar conductivity of NaOH solution.

Thermoplastic Composite Materials Approach for More Circular Components: From Monomer to In Situ Polymerization, a Review

To move toward eco-sustainable and circular composites, one of the most effective solutions is to create thermoplastic composites. The strong commitment of world organizations in the field of safeguarding the planet has directed the research of these materials toward production processes with a lower environmental impact and a strong propensity to recycle the polymeric part. Under its chemical properties, Nylon 6 is the polymer that best satisfies this specific trade-off. The most common production processes that use a thermosetting matrix are described. Subsequently, the work aimed at investigating the use of thermoplastics in the same processes to obtain comparable performances with the materials that are currently used. Particular attention was given to the in situ anionic polymerization process of Nylon 6, starting from the ε-caprolactam monomer. The dependencies of the process parameters, such as temperature, time, pressure, humidity, and concentration of initiators and activators, were therefore investigated with reference to the vacuum infusion technique, currently optimized only to produce thermosetting matrix composites, but promising for the realization of thermoplastic matrix composite; this is the reason why we chose to focus our attention on the vacuum infusion. Finally, three production processes of the polymeric matrix and glass fiber composites were compared in terms of carbon footprint and cumulative energy demand (CED) through life-cycle assessment (LCA).

Electronic and optical responses, Compton spectroscopy and manifestation of trapping centres of LiF:Mg,Ti

Electronic structure to judge trapping centres and activation energies in Mg-doped (2–8%) and Mg,Ti co-doped (2–3% each) LiF phosphors are presented using full-potential linearized APW method. Compton measurement for LiF is performed for appropriate choice of exchange-correlation potentials used in electronic properties. It is seen that 2–6% of Mg activator leads to formation of electronic traps with activation energy between 0.79 and 0.49 eV. At high concentration (>6%) of Mg, the formation of trap centres vanishes. Co-doping of 2% Mg,Ti permits the formation of trap centres, which is in contrast to higher concentrations. Mg-3s states play key role in the building of electronic trap centres. Higher concentration of Ti and Mg activators in LiF leads to the widening of 3d and 3s states, respectively. Analysis of optical response (frequency-dependent dielectric constants, trapping centres, and absorption coefficients) of 2% Mg-doped and 2% Mg,Ti co-doped LiF suggest their dosimetric applications and in ultra-violet detection.

Characteristics of Carbon from Oil Palm Shell Activated by Low Concentration of Zinc Chloride Activator

Currently, a large amount of oil palm shell has been dumped as waste from palm oil processing in Indonesia. Using a low concentration of zinc chloride (ZnCl2), thermal treatment during pre-carbonization was applied in the preparation of activated carbon from oil palm shells at various temperatures and reaction durations. This study, therefore, aims to investigate the physical and chemical characteristics of activated carbon prepared. Oil palm shells collected from a plantation in Palembang were carbonized by two methods, one-stage carbonization (at 300°C for 3 hours) and two-stage carbonization (at 300°C for 3 hours, then at 600°C for an hour) before chemical activation using ZnCl2, at a concentration of 10 and 15%wt. Activation of oil palm shell charcoal was conducted at 600, 700, and 800°C and reaction times of 60, 120, and 180 minutes. The results showed two-stage carbonization, high temperature, and prolonged reaction time is bound to increase burn-off as well as methylene blue adsorption, and decrease the yield and volatile matter content of the activated carbon prepared. Meanwhile, high ZnCl2 concentration increased the ash content and the methylene blue adsorption. In addition, the two-stage carbonization had higher iodine adsorption compared to the one-stage carbonization. The activated carbon with high iodine (769.3 mg/g) and methylene blue adsorption (133.7 mL/g) levels was obtained by two-stage carbonization using 15%wt ZnCl2 at a temperature and reaction time of 800°C and 180 minutes, respectively.

On the time and temperature dependent photoluminescence of Nd3+ and Gd3+ doped Lu3Al5O12

This work concerns the energy transfer between neodymium and gadolinium in the host material Lu3Al5O12. To this end, a solution combustion method was used to synthesize eight members of the solid solution with the compositions (Lu2.97-xNd0.03Gdx)Al5O12 (x = 0.003, 0.006, 0.015, 0.03, 0.06, 0.15, 0.3, 0.6). Phase purity of the samples was confirmed, while the reflection spectra showed a brilliant white body color which is essential for UV emitting phosphors. It turned out that the emission spectra and intensity strongly depend on the Gd3+ concentration and that (Lu2.82Nd0.03Gd0.15)Al5O12 showed the highest emission intensity upon excitation the host material or the sensitizer ion (Nd3+) by radiation at 160 or 227 nm respectively. In addition, temperature and time dependent photoluminescence of the 6P7/2→8S7/2 (Gd3+) transition was investigated from 3 to 500 K. This dismantled that the 6P7/2 energy level, which is split into four sublevels is occupied step wisely with increasing temperature. Overall, it is shown that the emission intensity and decay time of Gd3+ in the UV-B range is strongly depend on activator concentration and temperature.

Optimising Crystallisation during Rapid Prototyping of Fe3O4-PA6 Polymer Nanocomposite Component

Polymer components capable of self-healing can rapidly be manufactured by injecting the monomer (ε-caprolactam), activator and catalyst mixed with a small amount of magnetic nanoparticles into a steel mould. The anionic polymerisation of the monomer produces a polymer component capturing magnetic nanoparticles in a dispersed state. Any microcracks developed in this nanocomposite component can be healed by exposing it to an external alternating magnetic field. Due to the magnetocaloric effect, the nanoparticles locally melt the polymer in response to the magnetic field and fill the cracks, but the nanoparticles require establishing a network within the matrix of the polymer through effective dispersion for functional and uniform melting. The dispersed nanoparticles, however, affect the degree of crystallinity of the polymer depending on the radius of gyration of the polymer chain and the diameter of the magnetic nanoparticle agglomerates. The variation in the degree of crystallinity and crystallite size induced by nanoparticles can affect the melting temperature as well as its mechanical strength after testing for applications, such as stimuli-based self-healing. In the case of in situ synthesis of the polyamide-6 (PA6) magnetic nanocomposite (PMC), there is an opportunity to alter the degree of crystallinity and crystallite size by optimising the catalyst and activator concentration in the monomer. This optimisation method offers an opportunity to tune the crystallinity and, thus, the properties of PMC, which otherwise can be affected by the addition of nanoparticles. To study the effect of the concentration of the catalyst and activator on thermal properties, the degree of crystallinity and the crystallite size of the component (PMC), the ratio of activator and catalyst is varied during the anionic polymerisation of ε-caprolactam, but the concentration of Fe3O4 nanoparticles is kept constant at 1 wt%. Differential Scanning Calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), XRD (X-ray diffraction) and Thermogravimetric analysis (TGA) were used to find the required concentration of the activator and catalyst for optimum properties. It was observed that the sample with 30% N-acetyl caprolactam (NACL) (with 50% EtMgBr) among all of the samples was most suitable to Rapid Prototype the PMC dog-bone sample with the desired degree of crystallinity and required formability.

Effect of superplasticizer on the strength of fly ash based geopolymer concrete

In this research, the effect of a polycarboxylate based superplasticizer on the strength of Geopolymer Concrete (GPC) was investigated. A fixed amount of superplasticizer (1.5 % of Fly Ash weight) was utilized along with alkali activators Sodium Hydroxide (NaOH) and Sodium Silicate (Na2SiO3). The Ultrasonic Pulse Velocity Test determined the strength development of concrete. The quality of the GPC improved when a higher concentration of alkali activator was applied based on the Concrete Quality Designation. In detecting the color development of GPC, samples were put through MATLAB and specimens became lighter as time passes due to dehydration (a process where water escapes from the sample). Stress strain diagrams were generated which generally indicate that GPC specimens are ductile. The researchers were able to assess the workability of the mix designs using a rating from 1 to 5, with 1 being the least workable and 5 being the most workable.

Strength and microstructural evolution of alkali-activated slag-based cemented paste backfill: Coupled effects of activator composition and temperature

The activator concentration/silica modulus and curing temperature play critical roles in the engineering performance of alkali-activated slag-based cemented paste backfill (AAS-CPB). Different types of AAS-CPB samples, as well as CPBs made of OPC, were tested at different curing times and temperatures (10 °C, 20 °C, 30 °C, and 40 °C). The results show that the strength of AAS-CPB is more sensitive to changes in curing temperature, and the strength of AAS-CPB is consistently higher than that of CPB made of OPC. Moreover, the strength evolution of AAS-CPB is strongly affected by the coupled effect of curing temperature and activator concentration/silica modulus. An increased activator concentration and a reduced silica modulus can improve the early strength of AAS-CPB under a low curing temperature, but it can also weaken the improvement in the late strength of AAS-CPB under warmer curing temperatures. These findings could contribute to successful application of AAS binder to the mine backfill operation.

A modified, optimized kinetic photometric thrombin generation assay components to measure the potency of thrombin in plasma

The purpose of the present study was to improve, optimize and modification, a kinetic photometric assay of Factor IIa activity with regard to blood sample types, calibration, analytic corrections, and activation reagents, in order to establish a rapid routine, less time consuming, and suitable method for the evaluation of large numbers of clinical samples. Our modified method was based on the continuous monitoring of the Factor IIa released from the reacting substance, in the presence of a specific chromogenic peptide substrate (S2238). The optimization of pH and of the concentrations of substrate, activator (CaCl2), EDTA, and tissue factor was carried out as well as blood sample types (Platelet-rich and platelet-poor plasma samples) so as to ensure the best compromise between reliability, specificity, and sensitivity, However, the Factor IIa activity was compared in the plasma of different donors. In conclusion, our modified and optimized FIIa generation assay is a rapid and simple method for the diagnosis and monitoring of different clinical cases, at the same time it can be easily adapted to clinical chemistry analyzers.

Strength Analysis and Optimization of Alkali Activated Slag Backfills Through Response Surface Methodology

The significant difference in water-to-binder ratio, activator type and concentration between alkali-activated slag (AAS) paste/mortar/concrete and AAS-based cemented paste backfill (AAS-CPB) means that previous results related to the properties and mix optimization of AAS materials cannot be directly translated to AAS-CPB. This study statistically identifies the effect of key influential variables such as silicate modulus, slag fineness and activator concentration on 3- and 28 day unconfined compressive strength (UCS) of AAS-CPB by central composite design (CCD) established in response surface methodology (RSM). In this study, the prominence of independent variables and their relations are investigated by using ANOVA (analysis of variance) having a significant level of 0.05. ANOVA results certify that there is a strong link between the level of variable contribution on UCS performance of AAS-CPB and curing age. Obviously, silicate modulus and activator concentration are the most major variables influencing UCS at 3 and 28 days, respectively. Increased fineness of slag and higher pH of pore solution enhance 3 day UCS, but restrain the further hydration of unreacted slag and subsequent the gain in strength at advanced curing ages. The combination of independent variables of silicate modulus (0.295), slag fineness (12630.2), activator concentration (0.45) gives the optimum responses.

A multi-objective optimisation approach for activity excitation of waste glass mortar

Waste glass is promising to be recycled and reused in construction for sustainability. Silicon dioxide is the main component of glass, however, its pozzolanic activity is latent mainly due to its stable silica tetrahedron structure. To excite the activation of waste glass, chemical activation and mechanical grinding of waste glass powder (WGP) were investigated. As the supplementary, hydrothermal and combined (mechanical-chemical-hydrothermal) treatments were conducted on part of the WGP samples. The unconfined compression strength (UCS), expansion caused by alkali–silica reaction (ASR), and the microstructural morphology of WGP were investigated. The results showed the dosage threshold (around 2%) of the chemical activators (alkali and sodium sulfate) and the combined activation were optimal. Besides, a firefly algorithm (FA) based multi-objective optimisation model (MOFA) was applied to seek the Pareto fronts based on three objectives: UCS, ASR expansion, and Cost of mixture proportion. The objective functions of UCS and expansion were established through training the machine learning (ML) models where FA was used to tune the hyperparameters. The cost was calculated by a polynomial function. The ultimate values of root mean square error (RMSE) and correlation coefficient (R) showed the robustness of the ML models. Moreover, the Pareto fronts for mortars containing 300 μm and 75 μm WGPs were successfully obtained, which contributed to the practical application of waste glass in mortar production. In addition, the sensitivity analysis was conducted to rank the importance of input variables. The results showed that curing time, activator's content, and WGP particle size were three essential parameters.

Effective regulation of upconversion luminescence in NaErF4 and NaErF4@SiO2 core-shell particles

Upconversion luminescence materials have gained extensive attentions owing to their unique luminescence characteristics of converting near-infrared excitation to visible light emission. However, how to improve the doping concentration of activator (usually <3 mol%) in traditional sensitizer-activator system is still a great challenge due to the luminescence quenching effect. In this work, NaErF4 crystals with diverse crystal phases and morphologies were prepared by simple hydrothermal method, constructing a 100% doping concentration system of activator (Er3+). With the increase of F− content, the phase of NaErF4 transfers from cubic to hexagonal, and the morphology changes from nanospheres to hexagonal microflakes, meanwhile, the upconversion luminescence intensity also increases gradually. In addition, in order to further inhibit the luminescence quenching effect of NaErF4 bare core, a series of NaErF4@SiO2 core-shell samples with different SiO2 shell thickness were successfully prepared. Compared with NaErF4 bare core, the morphology and structure of the NaErF4@SiO2 core-shell samples have no obvious change, but the UC luminescence intensity is significantly enhanced. Interestingly, the change of NaErF4 crystal phase and SiO2 shell thickness can both bring about multicolor luminescence. In addition, different from the traditional NaYF4:Yb, Er co-doping system, the as-prepared hydrophilic NaErF4 and NaErF4@SiO2 samples showed a greater red to green ratio (R/G > 1), which may expand their potential applications in biological imaging and sensing fields.

Fresh Properties and Sulfuric Acid Resistance of Sustainable Mortar Using Alkali-Activated GGBS/Fly Ash Binder.

In this study, sorptivity, setting time, resistance to sulfuric acid, and compressive strength of mortars that use alkali-activated GGBS and fly ash as binders, were evaluated experimentally. The activation of binders, was achieved at room temperature of 22 ± 2 °C using combinations of sodium silicates (Na2SiO3) and sodium hydroxide (NaOH) solutions in ratios of 1.5, 2.0, and 2.5. The parameters considered in terms of their effects on fresh and hardened properties include: NaOH molarity, activator ratio Na2SiO3/NaOH, mortar sample age, and relative amount of GGBS/fly ash in binder combination. Sorptivity, change in mass, and compressive strength were determined for mortar samples that were submerged in 10% sulfuric acid solution for 7 days, 28 days, and 90 days. The binder for mortar samples tested at each of the specified ages consisted of 100% GGBS (G100), 75%GGBS+25% fly ash (G75F25), or 50% GGBS + 50% fly ash (G50F50). The binder was activated using Na2SiO3 solution, combined with 10 M, 12 M, 14 M, or 16 M NaOH solution. It was found that sorptivity decreases with increase in curing age, for all activator ratios, concentrations, and relative amounts of GGBS/fly ash. Binder consisting of 75%GGBS + 25% fly ash with NaOH concentration of 12 M had the lowest sorptivity. Exposure of alkali-activated GGBS/fly ash mortar samples to sulfate attack did not cause loss in mass nor visible signs of damage/deterioration. All binder combinations experienced increase in compressive strength after curing in 10%sufluric acid solution, with the optimum G75F25 mix achieving a 28-day strength of 80.53 MPa when NaOH molarity is 10 M, which increased to 91.06 MPa after 90 days. Variation in concentration of NaOH didn’t cause significant change in the magnitudes of 28-day or 90-day compressive strengths of G50F50. However, despite slow dissolution of fly ash and immersion in 10% sulfuric acid solution, G50F50 developed 28-day compressive strength of 56.23 MPa and 90-day compressive of 86.73 MPa, which qualifies G50F50 as high strength mortar for practical purposes.