Extent Of Reaction Research Articles

Interfacial rheology for probing the in-situ chemical reaction at interfaces of molten polymer systems

The design of new functional materials from immiscible polymers or multi-layered structures using reactive compatibilisation is an efficient approach that has been extensively employed in a wide range of applications. The adhesion/interfacial properties in these multiphase polymeric systems depend on the extent of reaction occurring at the interface. However, probing in-situ interfacial reactions in the molten state has proved challenging. In this study, interfacial shear rheology is used for the first time to directly probe the reaction at the interface between maleic anhydride-grafted polyethylene (PEgMA) and aminopropyl-terminated polydimethylsiloxane (PDMS-(PropNH2)2) used as model reactive polymer systems. Then the reaction at the interface was investigated using interfacial shear rheology based on a newly homemade, lightweight biconical setup. Thereafter, the time evolution of the interfacial tension with the progress of interfacial reaction was assessed using the pendant drop method. First, the extent of reaction was checked using differential scanning calorimetry (DSC) and dynamic rheology coupled with fast-scan FTIR spectroscopy. It has been demonstrated that the molecular weight of the aminated PDMS and the temperature of the medium markedly affect the rate of melt reaction at the interface and related interfacial rheological properties. Interestingly, the ability to assess the reactions at the interface in PEgMA/PDMS-(PropNH2)2 systems, even with low concentrations of reactive functionalities, demonstrates that interfacial rheology is a suitable, sensitive probe that could be applied to other reactive polymer systems, allowing better control of the resulting physical properties.

Impact of CO2 atmosphere on coal pyrolysis in indirectly heated fixed bed with internals

To clarify how CO2 affects pyrolysis characteristics in reactor with internals, pyrolysis of Yulin coal under N2 (inert) and CO2 (active) atmospheres is performed in fixed-bed reactors for two kinds of pyrolysis, i.e., with and without internals.CO2 exhibits different impact on tar yield for two types of pyrolysis, i.e., raising tar yield for pyrolysis in reactor without internals but lowering tar yield for that with internals. Tar yield pyrolysis under CO2 atmosphere is 6.31 wt% with internals, which is still higher 15.97% than that without internals at 1000 °C. In addition, CO2 atmosphere can produce more CO, high BET surface area char and high-quality of tar with more light tar (<C10), but less char, H2 and CH4 for both types of pyrolysis. The different impact of CO2 may be ascribed to the various flow routes for two kinds of reactors, and the extent of CO2-inclusive reactions, such as CO2-char gasification and reverse water gas shift (RWGS), is weakened by the adoption of internals due to occurring at lower temperatures and shorter residence time.

Microstructural and wear properties of WC-12Co cemented carbide fabricated by direct energy deposition

The microstructural and wear properties of WC–12Co (wt.%) cemented carbide bulk material manufactured by additive manufacturing direct energy deposition (DED) process were investigated and compared to those of WC-12Co coating material fabricated by high-velocity oxygen fuel (HVOF) thermal spray process. The feedstock powder, DED and HVOF materials were analyzed using scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDAX), X-ray diffraction (XRD) and an electron back-scattered diffraction (EBSD) technique. WC and α-Co phases were observed in the initial WC-12Co cemented carbide powder feedstock. After the DED process, WC phase growth and M12C phase were identified. However, the amount of M12C phase decreased after the HVOF process. The DED material had relatively higher porosity (BD: 11.58%; PD: 10.23%) as compared with HVOF (porosity: 1.66%). The hardness of the HVOF sample was measured as 1429 ± 49 HV, which was much higher than that of the DED (BD:1373 ± 68 HV, SD1: 1352 ± 62 HV) sample, due to the existence of porosity in the DED sample. A pin-on-disc tribometer was used to measure wear rates and coefficients of friction. The wear-worn surfaces were analyzed using SEM with an energy-dispersive spectrometer. The wear test results indicated that the DED material exhibited a lower wear rate (higher wear resistance) and a lower friction coefficient than those of the HVOF material. The difference in the wear behaviour of the DED and HVOF materials could be explained in terms of differences in WC size, the extent of reaction and decarburization during spraying, and the formation of the high oxide content.

Mineral surface area in deep weathering profiles reveals the interrelationship of iron oxidation and silicate weathering

Abstract. Mineral specific surface area (SSA) increases as primary minerals weather and restructure into secondary phyllosilicate, oxide, and oxyhydroxide minerals. SSA is a measurable property that captures cumulative effects of many physical and chemical weathering processes in a single measurement and has meaningful implications for many soil processes, including water-holding capacity and nutrient availability. Here we report our measurements of SSA and mineralogy of two 21 m deep SSA profiles at two landscape positions, in which the emergence of a very small mass percent (&lt;0.1 %) of secondary oxide generated 36 %–81 % of the total SSA in both drill cores. The SSA transition occurred near 3 m at both locations and did not coincide with the boundary of soil to weathered rock. The 3 m boundary in each weathering profile coincides with the depth extent of secondary iron oxide minerals and secondary phyllosilicates. Although elemental depletions in both profiles extend to 7 and 10 m depth, the mineralogical changes did not result in SSA increase until 3 m depth. The emergence of secondary oxide minerals at 3 m suggests that this boundary may be the depth extent of oxidation weathering reactions. Our results suggest that oxidation weathering reactions may be the primary limitation in the coevolution of both secondary silicate and secondary oxide minerals. We value element depletion profiles to understand weathering, but our finding of nested weathering fronts driven by different chemical processes (e.g., oxidation to 3 m and acid dissolution to 10 m) warrants the recognition that element depletion profiles are not able to identify the full set of processes that occur in weathering profiles.

Exploring physical sciences learners’ graphical interpretation of rate and extent of reaction graphs

Graphs are very important in all areas of science, and they are an essential part of tertiary, high school, and primary school learning, worldwide. A solid understanding of graphical interpretation is essential for understanding today's world and becoming scientifically literate. The aim of this study was to explore grade 12 learners’ graphical interpretation of the rate and extent of reaction topic. A mixed-method methodology was adopted for this study. A purposive sampling technique was used to sample participants from the accessible population in King Cetshwayo District KwaZulu-Natal province in South Africa. One-hundred and forty-six (146) grade 12 Physical Sciences learners formed the sample. A validated two-tier diagnostic questionnaire and semi-structured interviews were used to collect data. Quantitative data were analysed using SPSS version 25 and inductive coding was used to qualitative data. The Johnstone triangle and the Peircean semiotic modes were employed as the theoretical framework. The findings indicated that learners rely on definitions to interpret graphs. Most of the learners failed to interpret the salient features of the graphs. The findings of this study are diagnostic, and they assist module designers and educators in determining challenges learners face when interpreting graphs in chemistry. Implications for instructional approaches particular to the rate of reaction graphs are discussed. Further studies are needed on instructional practices and their effect on students’ ability to interpret rate and extent of reaction graphs. Keywords: Graphical interpretation; rate and extent of reaction; Johnstone triangle

Design and operational guidelines of solar-driven catalytic conversion of CO2 and H2 to fuels

Sunlight-powered catalytic conversion of CO2 and (green) H2 into fuels and chemicals via Sabatier and reverse water gas shift (RWGS) processes offers a promising solution to reduce greenhouse gas emissions and increase renewable energy utilization. The success of this approach relies on the development of efficient catalysts and reactors. Prior research on reactor design is based on fixed-bed concepts using conventional transition metal thermocatalysts that typically require high-temperature activation. The utilization of photothermal catalysts yields fast reaction kinetics and enhanced product selectivity at relatively low temperatures, and, therefore, requires new design and operational guidelines. A comprehensive steady-state model is described to assess the performance of solar-driven photothermal catalytic Sabatier and RWGS processes, with an emphasis on the development of a 1D heat and mass transfer model for a plate-shaped transparent flow reactor. The model allows for the prediction of the temperature profile, pressure drop and reaction extent along the reactor channel, CO2 and H2 conversion, total fuel yield, as well as system efficiency for a variety of design and operational choices. The effects of these parameters are strongly coupled, and a low packed bed porosity of 40% combined with high gas inlet pressure at 18–20 bar leads to both, high fuel yield and high system efficiency, for both the Sabatier and RWGS processes. The maximum system efficiency is predicted via simultaneous optimization of relevant variables within meaningful ranges while also respecting the practical temperature constraints of both the glass and catalysts. Compared with the baseline case, the optimized scenario achieves higher efficiencies of 26.3% (vs 6.7%) and 10.1% (vs 5.4%) for the Sabatier and RWGS processes, respectively, at 20 kW/m2 irradiance. The model also identifies optimal reactor conditions under different concentrated solar irradiance, thus offering design and operational guidelines for solar-driven catalytic conversion of CO2 and H2 processes.

Assessment of the oxygen reactivity in a gas storage facility by multiphase reactive transport modeling of field data for air injection into a sandstone reservoir in the Paris Basin, France

The first objective of this study is to present unique field data on a three-year pilot test during which air containing 8 mol% O2(g) was injected as a cushion gas into a natural gas reservoir, a carbonate-cemented sandstone aquifer located in the Paris Basin (France). 10-year system survey showed that: the oxygen was fully depleted several months after injection completion, meanwhile CO2(g) was detected around 2–6 mol%; the pH decreased from 8 to 6, while reducing conditions shifted to mildly oxidizing ones with increasing concentration of sulfates in equilibrium with gypsum. 3 years after injection completion, the pH gradually returned to its near initial state and sulfates were reduced by 2 to 3 times. The second objective is to develop a multiphase reactive transport model based on the field data. Simulations were constructed using the HYTEC reactive transport code, progressing from 0D-batch to 2D-reservoir configurations. The model reproduced the gas-water-rock reactive sequence: 1/ full depletion of the injected O2(g) due to pyrite oxidation, 2/ leading to acidity production and dissolved sulfates, 3/ acidity buffering by calcite dissolution, 4/ followed by gypsum precipitation and CO2(g) exsolution. The model demonstrated that pyrite kinetics was the most significant factor governing not only the amount of O2(g), CO2(g) and dissolved minerals, but also the spatial extent of these chemical reactions and, hence, the gas spread inside the reservoir. The formulated advective Damköhler number for oxygen consumption indicated advection- and reaction-dominant regimes explaining the gas composition and extension. The developed field-based model could be used as a workflow for other gas storage facilities, e.g. biomethane, compressed air, and CO2. For underground biomethane storage, the O2(g) contents recommended in Europe, i.e. the EASEE-gas specification 2005-001-02, should have a low impact on gas composition and reservoir geochemistry when the reservoir contains efficient pH-buffers such as calcite.

The asymmetric effect of COVID-19 on investor sentiment: evidence from NARDL model

PurposeThis study aims to investigate the asymmetric impact of daily announcements regarding COVID-19 on investor sentiment in the stock market.Design/methodology/approachThis study uses a Non-Linear Autoregressive Distribution Lag (NARDL) model that relies on positive and negative partial sum decompositions of the Coronavirus indicators. Five investor sentiments had been used and the analysis is conducted on the full sample period from 24th February 2020 to 25th March 2021.FindingsThe results show that new cases have a greater impact on investor sentiment compared to daily announcements of new deaths related to COVID-19. In addition to revealing a significant impact of new COVID-19 new cases and new death announcements on a daily basis on investor sentiment over the short- and long-term, this paper also highlights the nonlinearity and asymmetry of this relationship in the short and long run. Investors' sentiments are more affected by negative news regarding Covid 19 than positive news.Originality/valueFinancial markets have been severely affected by COVID-19 pandemic. This study is the first to measure the extent of reaction of investors to positive and negative announcements of COVID-19. Interestingly, this study examines the asymmetric effect of daily announcements on new cases and new deaths by COVID-19 on investor sentiments and derive many implications for portfolio managers.

The correlation of sulfonation reaction kinetics with the degree of sulfonation (DS) and its effects on microstructure and morphology of electrospun fibers for the membrane of fuel cells.

Sulfonation is among the frequently used surface modification methods to endow new surface properties on polymer fibers. Direct sulfonation is the simplest chemical modification via incorporation of sulfonate functional groups onto fibers' surfaces at ordinary conditions. However, the process of functionalization compromises other properties of the electrospun membrane due to the extent of sulfonation reaction that occurred. This study was carried out to determine the effects on microstructure and morphology of crosslinked electrospun polybenzoxazine (PBz) fibers by correlating the reaction kinetics using a specific reaction parameter with the degree of sulfonation (DS). The kinetics of sulfonation reaction for PBz fibers is an electrophilic-based, first-type substitution mechanism where only one sulfonic acid (-SO3H) group is attached to each of the repeating units in the aromatic structure of PBz under ordinary conditions. From a previous study, the rate of change of ion exchange capacity (IEC) was derived as a logarithmic correlation that increased rapidly for some time and became constant. This study employed the derived empirical relationship based on reaction kinetics to correlate the degree of sulfonation (DS) with IEC at varying reaction time. DS was calculated as 55%, 66% and 77%, for 3, 6 and 24 h, respectively. The maximum IEC of 2.71 with the corresponding DS of 100% was obtained theoretically but since sulfonation reaction kinetics at ordinary conditions proceeds at slower phase, it can only attain 86% DS with maximum IEC of 2.44 at a calculated time of 48 h. Sulfonation was confirmed by the functional groups present in the structural composition of PBz fibers using ATR-FTIR which were quantified based on the absorbance in the IR spectra showing an increased peak height with increased reaction time for the first 6 h. Morphological analyses using SEM images revealed an increase in fiber diameter with increased sulfonation time. In addition, the higher reaction time showed the effects of longer acid exposure which compromised the fibers' structural integrity with the presence of broken fibers and defects on fibers' surfaces after 24 h. The electrospun PBz fibers sulfonated for 6 h achieved the highest IEC value with DS of 66% which was enough to attain the balance of degree of sulfonation with electrochemical and morphological properties.

Probing the mechanism of flavin action in the oxidative decarboxylation catalyzed by salicylate hydroxylase.

Salicylate hydroxylase (NahG) is a FAD-dependent monooxygenase in which the reduced flavin activates O2 coupled to the oxidative decarboxylation of salicylate to catechol or uncoupled from substrate oxidation to afford H2O2. This chapter presents different methodologies in equilibrium studies, steady-state kinetics, and identification of reaction products, which were important to understand the SEAr mechanism of catalysis in NahG, the role of the different FAD parts for ligand binding, the extent of uncoupled reaction, and the catalysis of salicylate's oxidative decarboxylation. These features are likely familiar to many other FAD-dependent monooxygenases and offer a potential asset for developing new tools and strategies in catalysis.

Shape–Constrained Moving Horizon Estimators for Reaction Systems

In reaction systems, state estimators are used to improve the quality of estimates using measurements and process models with the number of moles or concentrations as states. The model of reaction systems can be reformulated in the extent domain with the reaction and flow extents as states. This work exploits the properties of the extents, such as nonnegativity and monotonicity, and formulates nonlinear and linear Shape-Constrained Moving Horizon Estimators (SCMHE) for reaction systems. It is shown that the linear SCMHE is a quadratic programming problem, and hence, it is computationally less expensive. The performance of the SCMHE schemes is compared with the Extended Kalman filters (EKF) and MHE in the concentration domain via simulation studies using two examples, namely, gas-phase isothermal batch reactor and lactic acid production in a fed-batch reactor. It is shown that the linear SCMHE provides better performance than EKF with a similar average computational time, while nonlinear SCMHE is computationally cheaper and performs better than the MHE in the concentration or mole domain.

Effect of redox agents on the reaction behavior of pyrite in sodium aluminate solution at elevated temperatures

As the main sulfide mineral in diasporic bauxite, pyrite readily reacts with sodium aluminate solution in Bayer digestion at elevated temperatures, adversely affecting the utilization of high-sulfur bauxite for alumina production by the Bayer process. For better understanding of the reaction mechanism during Bayer digestion, this paper focuses on the impacts of oxidant and reductant on the reaction extents of pyrite at elevated temperatures. The extents of reaction between pyrite and sodium aluminate solution are 57.9, 38.3 and 99.0 % at 260 °C for 40 min with no, oxidant and reductant addition, respectively. In the presence of oxidant, a dense layer formed on the surface of unreacted pyrite retarding the reaction with sodium aluminate solution, which follows the Kröger and Ziegler diffusion control model at 240–260 °C. However, the presence of reductant favors the decomposition of pyrite due to the formation of hematite and then transformation to magnetite, and the development of “chemical etching channel”. Finally, the above results were experimentally verified by digesting high-sulfur diasporic bauxite at 260 °C for 60 min, in which the inhibition of pyrite reaction with oxidant addition is affected by the organic content of the bauxite. These results may facilitate the development of a technique for directly treating the high-sulfur diasporic bauxite for alumina production with the Bayer process bypassing desulfurization pretreatment.

Pore formation mechanism and intermetallic phase transformation in Ti–Al alloy during reactive sintering

The mechanism of pore formation associated with intermetallic reaction is studied in sintered Ti50Al50 alloy with two different heating rates i.e. 1 °C/min and 10 °C/min. The heating rate significantly influences the pore parameters and the intermetallic reactions. The pore size and porosity increase with the extent of exothermic reactions during sintering. The intermetallic Ti2Al5 phase forms by a low-temperature solid-state diffusion of Al at the surface of Ti skeletons, while TiAl3 and TiAl2 intermetallic phases form at a high temperature owing to Ti2Al5 phase reaction with Al and Ti, respectively. A considerable change in thermal and volume expansion take place in the alloy heated with 10 °C/min compared to 1 °C/min. Therefore, it is found that the heating rate during sintering greatly influences the porous properties of Ti50Al50 by controlling the degree of exothermic reactions.

Cricket Batting Test Robotic-Based Equipment Using Sensor Cameras with Grid System

Technology development in the 5.0 era has been rapid, including in education and sports. One example of technology in sports education is a sports skills test kit. This study aims to develop and test the cricket batting test robotic-based equipment using sensor cameras with the grid system. The experiment was carried out by measuring student responses regarding using a robotic-based batting test tool using a camera sensor with a grid system. This student response is useful for knowing the extent of student responses and reactions to the products used so that they can be used as reflection material and references in designing products. The research method used in this study is Research and Development. The instrument used in this study is a test instrument in the form of an observation sheet. Product validation is divided into two, media validation and learning evaluation. The final assessment results are 160 and 162, indicating that the product is very suitable for use. They are synchronized by looking for whether there is an effect of student responses on student abilities. The results show 53,4% of the effect of students' positive responses on the object's ability. Based on the study's results, it was stated that the development of the tool was feasible to use and validated by media transfer and evaluation experts. In addition, this research is also developing research inspired by previous research. Further research is needed on implementing modified tools to see the effectiveness of training using an Android-based cricket batting test tool using a sensor camera with a grid system.

Are all chemical reactions in principle reversible? Thermodynamic distinction between “conceptually complete” and “practically complete” reactions

Abstract Among the chemical reactions having a pronounced thermodynamic driving force to the formation of products, a distinction has to be made between processes which attain a chemical equilibrium state very much shifted towards the products and those where the final equilibrium state corresponds to the truly complete consumption of reactant(s), i.e. where a true chemical equilibrium is actually not attained under the given conditions. Based on a few selected examples, two thermodynamic arguments are led which rationalise the above distinction from different points of view: a phase-rule point of view and a Gibbs energy minimization approach. “Conceptually complete” reactions involve pure phases and, as a consequence, establishing chemical equilibrium would imply a negative variance, what is avoided by the complete consumption of one or more phases. In the Gibbs energy approach, “conceptually complete” reactions and “practically complete” ones can be distinguished (at fixed temperature and pressure) by the different way to attain the minimum Gibbs energy condition, respectively with sharp (not differentiable) and flat (zero derivative) minimum points as a function of the extent of reaction ξ.

Differential Foreign Body Reactions between Branched and Linear Glucomannan Scaffolds.

The extent and patterns of foreign body reaction (FBR) influence the function and feasibility of biomaterials. Polysaccharides, as an important biomaterial category, have received increasing attention in diverse biomaterials design and biomedical applications due to their excellent polymeric and biocompatible characteristics. Their biological effects are usually associated with their monosaccharide composition or functional groups, yet the contribution of their glycan structure is still unknown. Herein, two glucomannans, similar in composition and molecular weight with differences in glycan structure, linear-chain (Konjac glucomannan, KGM), and branched-chain (Bletilla striata polysaccharide, BSP), were adopted to explore the host-biomaterials interaction. After acetyl modification, these polysaccharides were fabricated into electrospun scaffolds to reduce the impacts derived from the physical properties and surface morphology. According to a systematic study of their biological effects on immune cells and host response in a subcutaneous implantation model in vivo, it was revealed that acetyl KGM (acKGM) scaffolds caused a stronger FBR than acetyl BSP materials. Additionally, acKGM could stimulate macrophages to release pro-inflammatory cytokines, suggesting the influence of sugar chain arrangement on FBR and providing clues for the fine regulation of immune response and novel biomaterials design.

Synthesis of Hybrid Epoxy Methacrylate Resin Based on Diglycidyl Ethers and Coatings Preparation via Cationic and Free-Radical Photopolymerization

A series of difunctional epoxy methacrylate resins (EAs) containing at least one epoxy and at least one methacrylate group were synthesized by means of an addition reaction between epoxy-terminated diglycidyl ethers and methacrylic acid. In order to investigate the impact of polymer architecture on the course of addition reactions and further coating properties, several different types of diglycidyl ethers, i.e., linear, containing aliphatic or aromatic rings, with a short or polymeric backbone, were employed in the synthesis. The carboxyl-epoxide addition esterification reactions have been found to, in a relatively straightforward manner, control the extent of acrylation depending on the substrate feed ratio and reaction time. The structure of obtained pre-polymers was evaluated by FT-IR and NMR methods. At the same time, the extent of addition reactions was validated via quantitative analysis, including non-volatile matter content (NV), acid value (PAVs), and epoxy equivalent value (EE) analysis. The modification was carried out in a manner likely to create a compound with one epoxy and one carbon-carbon pendant group. Hence, due to the presence of both functionalities, it is possible to crosslink compositions based on synthesized EAs via two distinct mechanisms: (i) cationic polymerization or (ii) free-radical polymerization. Synthesized epoxy methacrylate pre-polymers were further employed for use in formulate photocurable coating compositions by the cationic or radical process. Furthermore, the photopolymerization behavior and properties of cured coatings were explored regarding some structural factors and parameters. The investigated polymeric materials cure in a short time to obtain coatings with good properties, which is why they can be successfully used to produce protective and decorative coatings for many industries.

Isothermal Kinetic Study and Shelf-Life Prediction of Triple Base Propellant Using Vacuum Stability Test in Combination with HPLC and GPC

ABSTRACT In this study, isothermal decomposition kinetic of a triple-base propellant (TBP) has been investigated by vacuum stability test (VST). The volumes of the evolved gas have been recorded step by step to monitor gas evolution in VST at 80°C, 90°C, 100°C, 110°C, 120°C, and 150°C. This semi-continuous data-recording mode makes it possible to use the Berthelot equation for shelf-life prediction of TBP. Activation energy has been calculated in both model-free and model-fitting methods, and F0/R1 is determined as the best model for thermal decomposition of TBP at VST. High-performance liquid chromatography has been used to determine stabilizer (methyl centralite) content of the TBP at various extents of reactions (α). The critical amount of stabilizer was specified at 2% α. Arrhenius average temperatures have been calculated at various climate categories and used as actual storage temperatures. Molecular weight (Mw) reductions of nitrocellulose were determined by gel permeation chromatography during aging. According to the results, the shelf-life of TBP has been estimated using the Berthelot equation at 2% α in various climate categories. Shelf-life of studied TBP differs from 14 to about 36 (years) in extremely hot dry (A1) to intermediate (A3) climate categories.

Investigation of Setting Time and Microstructural and Mechanical Properties of MK/GGBFS-Blended Geopolymer Pastes.

In this study, geopolymer pastes with 60% metakaolin (MK) and 40% ground granulated blast-furnace slag (GGBFS) were synthesized. To determine the influence of the alkaline activator concentration, modulus, and the liquid/solid (L/S) ratio on setting time and compressive strength, the geopolymerization process and microstructures of MK/GGBFS-blended geopolymer pastes were analyzed using isothermal calorimetry, X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. Acid dissolution was employed to measure reaction extent. The results showed that the initial setting time of the geopolymer pastes was between 68 and 226 min, and the initial setting and final setting time was apart about by 10 min. For the same variable, the total heat released was positively correlated to the reaction extent. Available silicate content increased the reaction rate and intensity at the initial stage, whereas the OH- concentration controlled the reaction extent in the long term. A limited reaction extent existed in the geopolymeric reaction even if the system contained sufficient alkali content and medium. An increase in the L/S ratio increased the reaction extent. The highest reaction extent of 86.3% was found in the study. Additionally, increasing the L/S ratio reduced the compressive strength by increasing the porosity.

Mechanism and assessment of the pozzolanic activity of melting-quenching lithium slag modified with MgO

The current energy consumption and waste emission are mainly produced from the process of cement manufacturing. Lithium slag (LS), a solid waste from lithium smelting, has been utilized as concrete additives with a low rate of approximately 10 %, and the remaining nearly 90 % of LS are stored as industrial solid waste, which not only occupies large amounts of land, but also causes serious resource waste and environmental pollution. For the purpose of developing a kind of cleaner binders using LS to reduce cement consumption and environmental pollution, a novel activation method of “chemical modification-melting granulation-mechanical pulverization” was conducted in this present study. Alkali cations, such as Mg2+, Ca2+, etc., are beneficial to improve the pozzolanic activity of LS according to previous results. Thus, a chemical modification was first performed by preparing the melted-quenched mixtures of LS and MgO in different ratios, and coded as MGLS. The characterization results of MGLS demonstrate that MgO modification can enhance the pozzolanic activity of LS by accelerating the dissolution of the amorphous networks. Pastes of PPC and P-MGLS (70 % PPC + 30 % MGLS) were prepared for UCS tests (a maximum allowable rate of 30 % for LS as concrete additives, according to engineering experience), showing clear retardations of strength development for P-MGLS pastes due to the low extent of pozzolanic reaction in the early period of 3 ∼ 7 d. The 7 ∼ 90 d strengths significantly increase with the content of MgO for P-MGLS pastes, and the P-MGLS15 paste cured for 90 d gains the UCS value of 52.49 MPa, even higher than that of PPC paste at 90 d, due mainly to the enhanced pozzolanic reaction with large amounts of CSH/CAH gels formed by MgO modification, and a compact microstructure, as well as higher values of Ca/Si and Al/Si ratios are measured in the CSH/CAH gels of P-MGLS15 paste, indicating that more reactive constituents can be released to enhance the formation of pozzolanic products for the pastes richer in MgO. Results of the present study may provide a potential way for the applications such as construction building, backfill mining, etc., that can be developed using MGLS, which also promotes the sustainability for cement and environmental industries.