Binary Precursors Research Articles

Using One-Part Geopolymer in Stabilizing High-Water-Content Soft Clay: Towards an Eco-Friendly and Cost-Effective Solution

To achieve environmental and economic goals in ground improvement, a one-part geopolymer (OPG), synthesized from binary precursors (fly ash [FA] and granulated blast furnace slag [GGBFS]) and a solid activator (solid sodium silicate [NS]), was used to replace ordinary Portland cement (OPC) for stabilizing high-water-content soft clay. The effects of different initial water content (50%, 80%, 100%, and 120%) and various OPG binder content (10%, 20%, 30%, and 40%) on the strength development of the OPG-stabilized soft clay were investigated through unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial tests. Additionally, the microstructure evolution and the distribution of pores in the OPG-stabilized soft clay were examined by the utilization of mercury intrusion porosimetry (MIP) and scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) techniques, respectively. The life cycle assessment (LCA) methodology was then used to analyze the environmental and economic advantages of employing an OPG binder for soil stabilization. It was revealed that the optimal content of OPG binder was contingent upon the water content of soft clay, with variations in requirements for strength development. Specifically, for soft clay not demanding early strength, a maximum binder content of 20% is proposed. Conversely, for soft clay that necessitated rapid strength gain, the OPG binder content escalated with increasing water content of the soft clay, in which soft clays with different water contents had corresponding required amounts of OPG binder. For soil with water content ranging from 50% to 80%, the recommended OPG binder content is 20%. While for soil with 100% and 120% water content, the designed OPG binder content is suggested to be 30% and 40%, respectively. The environmental assessment demonstrated that the utilization of OPG as a binder for the stabilization of soft clay reduces costs and carbon emissions in comparison to OPC. The present study provides substantial theoretical validation for the utilization of OPG as a novel binder to stabilize soft clay with elevated water content, which holds promise as an eco-friendly and cost-effective solution in ground improvement.

Copolymerization of Poly (Triazine Imide) Single Crystal Nanoplates with Enhanced Charge Transfer for Efficient Photocatalytic Overall Water Splitting

AbstractSolar‐driven photocatalytic overall water splitting represents a sustainable strategy to produce green hydrogen using metal‐free polymeric carbon nitride. However, conventional thermal polymerization with a single precursor for the synthesis of poly (triazine imide) faces challenges such as slow deamination rates and mass transfer, resulting in the formation of undesired structural defects, which usually serve as charge recombination sites and decrease the photocatalytic performance. Herein, highly crystalline poly (triazine imide) by thermal copolymerization of binary precursors of melamine and cyanuric acid in the presence of molten salts is reported. The results reveal that melamine and cyanuric acid easily generate melam (intermediates of carbon nitride) and subsequently facilitate the polycondensation process. Solid characterizations revealed that crystalline poly (triazine imide) nanoplates with extended π‐conjugation degrees and reduced intensity of structural defects would be obtained, which largely promotes separation and migration of photogenerated carriers, and inhibits the undesirable charge recombination at the defect sites. Accordingly, after in situ photo‐deposition of CoOx and Pt/Cr2O3 as O2 and H2 evolution co‐catalysts, respectively, the optimized crystalline poly (triazine imide) nanoplates achieve an excellent solar‐to‐hydrogen conversion of 0.30% under simulated sunlight irradiation.

Rapid Synthesis of Covalent Organic Framework at Room Temperature Incorporated Electrospun Nanofiber for Thin Film Microextraction of Quinolone Antibiotics in Honey and Chicken Samples.

In this work, the covalent organic frameworks-incorporated electrospun nanofiber membranes were used as a highly efficient adsorbent to enrich quinolone antibiotics in food samples. Covalent organic frameworks composed of 1,3,5-tris(4-aminophenyl) benzene and 2,5-dihydroxyterephthalaldehyde were rapid prepared only 20min at room temperature, then were further synthesized into electrospun polyacrylonitrile nanofiber membranes by electrospinning the binary precursors solution directly. Coupled with high-performance liquid chromatography with ultraviolet detector, the method exhibited good linearity in the range of 1-100 ng·mL-1 for four quinolone antibiotics, with low limits of detection 0.19-0.34 ng·mL-1 (signal-to-noise ratio = 3). The recoveries of four quinolone antibiotics were 86%-116%, and relative standard deviations of the intra- and interday for four quinolone antibiotics were 0.7%-9.0%, respectively. The practical application of the thin film microextraction method using nanofiber membranes as adsorbent for detecting four quinolone antibiotics in animal-derived food samples was demonstrated.

Performance evaluation and mix design of ambient-cured fly ash-phosphogypsum blended geopolymer paste and mortar

A practical mix design and performance metrics for fly ash-phosphogypsum blended geopolymer paste and mortar is lacking. This study focused on investigating the physico-chemo-mechanical performance and mix design of ambient-cured fly ash-phosphogypsum geopolymer paste (FPGP) and mortar (FPGM). The geopolymer was formed by reacting binary powder precursor (fly ash+phosphogypsum) and alkaline activator (NaOH+Na2SiO3). The fly ash was substituted with varying weight proportions of phosphogypsum (i.e., 10 %, 20 %, 30 %, 40 %, 50 %). Experimental testing and analysis were done based on ASTM standards, XRF, XRD, SEM-EDS, ANOVA, and Python. The workability, setting time, flexural strength, compressive strength, morphology, and mineralogy were studied. The multivariate regression approach was used to model the relationship between compressive strength and alkaline liquid/precursor. The optimum mixture conditions for FPGP and FPGM were 30 wt% phosphogypsum, alkaline liquid/precursor of 0.4, 10 M NaOH, Na2SiO3/NaOH of 1.5, and binder/aggregate of 1.0. The results showed that the workability of FPGP ranged from 185 mm to 112 mm while that of FPGM ranged from 145 mm to 100 mm. The FPGP and FPGM had considerably lower initial and final setting times of (18 – 37 min, 81 – 155 min) and (14 – 29 min, 67 – 142 min), respectively. The compressive strength of FPGP ranged from 7.3 MPa to 27.24 MPa while that of FPGM ranged from 9.5 MPa to 43.27 MPa. There was a strong connection between compressive and flexural strength giving R2 values > 0.8. Based on the adjusted R2 values and ANOVA, the proposed mix design models were statistically significant since the p-value (0.000) was less than the 0.05 significance level and the value of F (197.953) was greater than the critical value of 1. At high curing duration, the concentration of NaOH and alkaline liquid/precursor facilitated the dissolution of Ca2+ in phosphogypsum and Si4+and Al3+ in fly ash forming a C-(N)-A-S-H matrix crucial to the strength development of geopolymers. The statistical metrics implied a good performance accuracy and reliability of the proposed model equations and can find practical applications in construction materials design. For optimal results, it is recommended to use the prediction models within the specific input parameters employed in this study.

Radiative recombination model for BiSeI microcrystals: unveiling deep defects through photoluminescence

Abstract Pnictogen chalcohalides are semiconductors that have emerged as promising materials for energy conversion due to their exceptional optoelectronic properties. Their electronic configuration (ns2), particularly for Bi- and Sb-based compounds, can be a key factor in efficient carrier transport and defect tolerance, similarly, to Pb-perovskites. In the present study, the Bi-containing chalcohalide, bismuth selenoiodide (BiSeI) was synthesized via isothermal heat treatment of binary precursors in evacuated quartz ampoules. The synthesized BiSeI microcrystals exhibited a characteristic needle-like morphology and a near-stoichiometric composition. Both indirect and direct band gap energies of BiSeI were determined by ultraviolet–visible–near-infrared diffuse reflectance spectroscopy, with room temperature values of 1.17 eV and 1.29 eV, respectively. This study presents the first experimental investigation of the photoluminescence properties of BiSeI microcrystals resulting in a recombination model involving multiple defect states. This work provides valuable insights into the defect structure and recombination mechanisms within BiSeI, paving the way for further exploration of its potential in optoelectronic devices.

SHS of copper Chevrel phase compounds

Chevrel phase (CP) compounds are a highly multifunctional class of materials but are underused due to the high energy processing required for their synthesis. Self-propagation high-temperature synthesis (SHS) is a low energy and quick alternative for synthesizing this material system. In this investigation, copper-based CPs were synthesized via SHS using either elemental or binary precursor powders. The elemental precursors produced non-stoichiometric Cu2.76Mo6S8, and consisted mainly of grown MoS2 platelets. The binary precursor, on the other hand, produced stoichiometric Cu2Mo6S8. The influences of mixing and precursor concentration are discussed as well as the reaction mechanisms operating for the elemental system and the binary system, separately. The investigation into this synthesis process aims to provide a better understanding of the Chevrel SHS mechanism to accurately control the product.

Controllable preparation of graphene glass fiber fabric towards mass production and its application in self-adaptive thermal management

Direct synthesis of graphene on nonmetallic substrates via chemical vapor deposition (CVD) has become a frontier research realm targeting transfer-free applications of CVD graphene. However, the stable mass production of graphene with a favorable growth rate and quality remains a grand challenge. Herein, graphene glass fiber fabric (GGFF) was successfully developed through the controllable growth of graphene on non-catalytic glass fiber fabric, employing a synergistic binary-precursor CVD strategy to alleviate the dilemma between growth rate and quality. The binary precursors consisted of acetylene and acetone, where acetylene with high decomposition efficiency fed rapid graphene growth while oxygen-containing acetone was adopted for improving the layer uniformity and quality. Notably, the bifurcating introducing-confluent premixing (BI-CP) system was self-built for the controllable introduction of gas and liquid precursors, enabling the stable production of GGFF. GGFF features solar absorption and infrared emission properties, based on which the self-adaptive dual-mode thermal management film was developed. This film can automatically switch between heating and cooling modes by spontaneously perceiving the temperature, achieving excellent thermal management performances with heating and cooling power of ∼501.2 and ∼108.6 W m−2, respectively. These findings unlock a new strategy for the large-scale batch production of graphene materials and inspire advanced possibilities for further applications.

A Review of Biomass Wood Ash in Alkali-Activated Materials: Treatment, Application, and Outlook

The utilisation of Portland cement has aroused tremendous concerns owing to its production exerting a lot of pressure on the environment. Alternative eco-binders have been developed to replace it, among which alkali-activated materials (AAMs) have drawn great attention, especially due to the possibility of encompassing industrial and agricultural waste, which significantly improves the sustainability and cost-efficiency of the material. Biomass wood ash (BWA) is a by-product generated from power plants and, along with the advocation for biomass fuel as a renewable energy resource, there have been increasing applications of BWA in building and construction materials. This review examines the use of BWA as a precursor source in AAMs. Due to its low chemical and hydraulic reactivity, more active binary precursors are usually introduced to guarantee mechanical properties. Whereas the increment of BWA content can have a negative influence on material strength development, it is still a promising and feasible material, and new approaches should be developed to improve the effectiveness of its utilisation. Currently, study of BWA-based AAMs is still in the beginning stages and more research is needed to investigate the effects of BWA characteristics on the property evolution of AAMs, focusing on the durability and analysis of eco-efficiency. Overall, this review provides a comprehensive overview of the characterisation of BWA and its potential applications in AAMs, and meanwhile, based on the analysis of present research trends, proposes some prospective directions for future research.

Microphase Separation 3D Printing of Binary Inorganic Polymer Precursors to Prepare Nanostructured Carbon‐Ceramic Multimaterials

AbstractTraditionally, combining carbon and ceramic materials has been challenging due to their different chemical and physical properties. Despite the development of numerous methodologies for their synthesis, these techniques frequently necessitate intricate, multi‐stage protocols and specialized equipment. This study introduces a novel approach for fabricating nanostructured carbon‐ceramic multimaterials through polymerization‐induced microphase separation 3D printing. By combining inorganic precursors, polycarbosilane, and acrylonitrile (AN) within a photocurable resin, heterogeneous nanostructured materials composed of PAN‐preceramic and sacrificial polymer phases are 3D printed. Upon pyrolysis, PAN‐preceramic domains transformed into a carbon‐ceramic matrix while sacrificial polymer domains thermally decomposed to yield nanoscale voids. The utilization of synchrotron X‐ray spectroscopy and microscopy techniques revealed that the phase compositions and microstructure of the resulting multi‐materials are significantly influenced by the initial composition of the resins. The co‐existence of ceramic and carbon phases within a single 3D printed material brought together a combination of properties from both phases, such as the low thermal conductivity of ceramics and the relatively high electrical conductivity of carbon, along with the exceptional chemical resistance. The insights into the microstructure, atomic configuration, and property relationships of the resulting materials have broad implications for the development of multi‐phase nanostructured hybrid materials.

Durability of slag-based alkali-activated materials: A critical review

As the world becomes increasingly aware of the devastating effects of climate change, the need for sustainable building materials that are both durable and environmentally friendly increases. Geopolymer and alkali-activated materials formed by a chemical reaction between an alkaline activator solution and an aluminosilicate source have gained popularity in recent years. The alkaline activator solution dissolves the aluminosilicate source, which then undergoes a polycondensation reaction to form a three-dimensional geopolymeric gel network. The development of this network ensures the strength and durability of the material. Today, this phenomenon of durability has been studied in detail to enable the development of superior construction materials, taking into account degradation mechanisms such as carbonation, leaching, shrinkage, fire, freezing and thawing, and exposure to aggressive environments (chlorides, acids, and sulphates). Although there are many unsolved problems in their engineering applications, slag-based alkali-activated materials appear to be more advantageous and are promising as alternative materials to ordinary Portland cement. First of all, it should not be ignored that the cure sensitivity is high in these systems due to compressive strength losses of up to 69%. Loss of strength of alkali-activated materials is considered an important indicator of degradation. In binary precursors, the presence of fly ash in slag can result in an improvement of over 10% in compressive strength of the binary-based alkali-activated materials after undergoing carbonation. The binary systems can provide superior resistance to many degradation mechanisms, especially exposure to high-temperature. The partial presence of class F fly ash in the slag-based precursor can overcome the poor ability of alkali-activated materials to withstand high temperatures. Due to the desired pore structure, alkali-activated materials may not be damaged even after 300 freeze–thaw cycles. Their superior permeability compared to cementitious counterparts can extend service life against chloride corrosion by more than 20 times. While traditional (ordinary Portland cement-based) concrete remains the most widely used material in construction, geopolymer concrete’s superior performance makes it an increasingly emerging option for sustainable and long-lasting infrastructure.

Feasibility of recycled concrete aggregate stabilized with one-part geopolymers as semi-rigid inclusion columns

Recycled concrete aggregate (RCA) is a voluminous solid waste material derived from the construction sector and is typically stockpiled in landfills. In recent years, the ground improvement industry has grappled with challenges stemming from the depletion of natural quarry materials, resulting in a skyrocketing of their prices and increased project costs. This research investigated the feasibility of using RCA stabilized by one-part geopolymers to produce an innovative semi-rigid inclusion column system for ground improvement of soft soils. Na2SiO3-anhydrous was used as a sole solid activator for the activation of fly ash (FA), slag (S) or a binary precursor (FA+S) in the stabilization of RCA. The unconfined compressive strength (UCS) and microstructure of the stabilized mixtures have been examined with respect to different binder formulations and curing conditions. The permanent deformation characteristics of mixtures under cyclic loading were evaluated through repeated load triaxial (RLT) tests to replicate the moving wheel loads imposed on the semi-rigid inclusion columns. In addition, the cost and environmental impacts of the optimum mixtures suggested in this research were studied. The test results indicated that stabilizing RCA with as low as 5% one-part alkali-activated FA, S or (FA+S) met the minimum strength requirement (1.034 MPa) for ground improvement work. Compared with standalone FA and S geopolymer stabilized RCA mixtures, (FA+S) geopolymer stabilized RCA mixtures were identified as preferred industrial formulations due to their prolonged setting time for ease of mixing and handling when used in stone column applications. It was found that curing temperature and duration played a pivotal role in the strength gain of the mixtures. The RLT test results demonstrated that implementing the optimum RCA + 5%(FA+S) mixture as identified in this study for semi-rigid inclusion columns, led to a reduction in permanent strain values by approximately 90% compared to conventional unbound stone columns. The comparison between the optimum mixture highlighted in this study with other stabilization methods showed that the semi-rigid inclusion columns had great potential to enable large-scale production, cost and emission reduction in future ground improvement projects.

Inhibited Surface Diffusion in Nanoporous Multi-Principal Element Alloy Thin Films Prepared by Vacuum Thermal Dealloying

Nanoporous structures with 3D interconnected networks are traditionally made by dealloying a binary precursor. Certain approaches for fabricating these materials have been applied to refractory multi-principal element alloys (RMPEAs), which can be suitable candidates for high-temperature applications. In this study, nanoporous refractory multi-principal element alloys (np-RMPEAs) were fabricated from magnesium-based thin films (VMoNbTaMg) that had been prepared by magnetron sputtering. Vacuum thermal dealloying (VTD), which involves sublimation of a higher vapor pressure element, is a novel technique for synthesizing nanoporous refractory elements that are prone to oxidation. When VMoNbTaMg was heated under vacuum, a nanoporous structure was created by the sublimation of the highest vapor pressure element (Mg). X-ray photoelectron spectroscopy depth profiling indicated significantly less ligament oxidation during VTD as compared to traditional dealloying methods. Furthermore, np-RMPEAs exhibited outstanding stability against coarsening, retaining smaller ligaments (~25 nm) at elevated temperature (700 °C) for a prolonged period (48 h).

"Preparation of CuІY from Binary CuII Precursors and its CO Adsorption Performance"

"Preparation of CuІY from Binary CuII Precursors and its CO Adsorption Performance"

Scalable Synthesis of Selenide Solid-State Electrolytes for Sodium-Ion Batteries.

Solid-state sodium-ion batteries employing superionic solid-state electrolytes (SSEs) offer low manufacturing costs and improved safety and are considered to be a promising alternative to current Li-ion batteries. Solid-state electrolytes must have high chemical/electrochemical stability and superior ionic conductivity. In this work, we employed precursor and solvent engineering to design scalable and cost-efficient solution routes to produce air-stable sodium selenoantimonate (Na3SbSe4). First, a simple metathesis route is demonstrated for the production of the Sb2Se3 precursor that is subsequently used to form ternary Na3SbSe4 through two different routes: alcohol-mediated redox and alkahest amine-thiol approaches. In the former, the electrolyte was successfully synthesized in EtOH by using a similar redox solution coupled with Sb2Se3, Se, and NaOH as a basic reagent. In the alkahest approach, an amine-thiol solvent mixture is utilized for the dissolution of elemental Se and Na and further reaction with the binary precursor to obtain Na3SbSe4. Both routes produced electrolytes with room temperature ionic conductivity (∼0.2 mS cm-1) on par with reported performance from other conventional thermo-mechanical routes. These novel solution-phase approaches showcase the diversity and application of wet chemistry in producing selenide-based electrolytes for all-solid-state sodium batteries.

Controllable Growth of 2D V3S5 Single Crystal by Chemical Vapor Deposition

Abstract2D intercalated vanadium chalcogenides have attracted intensive interest based on their physical properties and potential applications. However, controllable synthesis of the intercalated vanadium chalcogenides via chemical vapor deposition is still a big challenge. Here, a binary metal precursor co‐reaction growth mechanism to manipulate the evaporation rate of vanadium precursors is reported, thus the intercalated 2D V1+XS2 – V3S5 single crystal can be controllably synthesized. The quality of 2D V3S5 nanosheets is identified by Raman spectroscopy and high‐resolution scanning transmission electron microscopy. Interestingly, a phase transition in 2D metallic V3S5 nanosheets is observed at 20 K. Meanwhile, the resistance upturn and unsaturated negative magnetoresistance induced by electron–electron interaction is confirmed. This work proposes a new strategy to synthesize the 2D intercalated VxSy single crystals with different compositions for studying their excellent properties and potential applications.

Impact of Low-Reactivity Calcined Clay on the Performance of Fly Ash-Based Geopolymer Mortar

Availability of aluminosiliceous materials is essential for the production and promotion of geopolymer concrete. Unlike fly ash, which can only be found in industrial regions, clays are available almost everywhere but have not received sufficient attention to their potential use as a precursor for geopolymer synthesis. This study investigates the effectiveness of calcined clay as a sole and binary precursor (with fly ash) for the preparation of geopolymer mortar. Fly ash-based geopolymer containing between 0 and 100% low-grade calcined clay was prepared to investigate the effect of calcined clay replacement on the geopolymerization process and resultant mortar, using a constant liquid/solid ratio. Reagent-grade sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were mixed and used for the alkali solution preparation. Six different mortar mixes were formulated using sand and the geopolymer binder, comprising varying fly ash-to-calcined clay ratios. The combined effect of the two source materials on compressive strength, setting time, autogenous shrinkage, and porosity was studied. The source materials were characterized using XRD, SEM, FTIR, and XRF techniques. Isothermal calorimetry was used to characterize the effect of low-grade calcined clay on the geopolymerization process. The addition of calcined clay reduced the surface interaction between the dissolved particles in the alkali solution, leading to slow initial reactivity. Geopolymer mortar containing 20% calcined clay outperformed the reference geopolymer mortar by 5.6%, 17%, and 18.5% at 7, 28, and 91 days, respectively. The MIP analysis revealed that refinement of the pore structure of geopolymer specimens containing calcined clay resulted in the release of tensional forces within the pore fluid. Optimum replacement was found to be 20%. From this study, the mutual reliance on the physical and inherent properties of the two precursors to produce geopolymer mortar with desirable properties has been shown. The findings strongly suggest that clay containing low content of kaolinite can be calcined and added to fly ash, together with appropriate alkali activators, to produce a suitable geopolymer binder for construction applications.

On the use of one-part geopolymer activated by solid sodium silicate in soft clay stabilization

The application of geopolymers in ground improvement has garnered significant attention in recent years. However, most geopolymer preparations have focused on the two-part method, which not only has negative environmental impacts but also falls short of meeting practical requirements. This study aimed to address these limitations by employing solid sodium silicate (Na2O·nSiO2, n is the molar ratio, NS) to activate binary precursors (fly ash [FA] and ground granulated blast furnace slag [GGBFS]), along with water, to synthesize a one-part geopolymer (OPG) for soft clay stabilization. The primary factors on the properties of the OPG binder were firstly identified through macro- and micro-tests. Subsequently, the optimization of the OPG mixing proportion was achieved by reducing the molar concentration of NS, and was further used for soft clay stabilization. The effects of the FA/GGBFS ratio (0, 0.1, and 0.2), curing period (7, 14, and 28 days), and binder content (0.15, 0.20, and 0.25) on the mechanical properties of the OPG-stabilized soft clay were then evaluated using unconfined compressive strength (UCS) tests. Furthermore, mercury intrusion porosimetry (MIP), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS), and X-ray diffraction (XRD) techniques were employed to examine the evolution of microstructure, hydrate composition, and mineral/phase of the OPG-stabilized soft clay samples. The experimental results indicated that an appropriate OPG stabilizer proportion was achieved with an FA/GGBFS ratio of 0.1, water/precursor ratio of 0.8, molar ratio of NS of 1.0, and molar concentration of 3 mol/L. The high-early-strength feature of OPG binder contributed to the rapid strength development of the stabilized soft clay at an early age. A noticeable pozzolanic reaction was observed in the OPG-stabilized soft clay sample with an FA/GGBFS ratio of 0.1. Additionally, a binder content of 0.20 was recommended for the stabilization of soft clay due to its optimal balance between economic benefits and meeting the required UCS criteria in soil stabilization. Finally, a reliable nonlinear relationship between UCS and porosity of OPG-stabilized soft clay was established to assess the mechanical properties and stabilization effects of the OPG-stabilized soft clay for practical applications. This study greatly enhances the scientific understanding of geopolymerization in the OPG system by using a combination of the binary precursor of FA and GGBFS and the solid NS activator. It sheds light on the stabilization mechanism of OPG-stabilized soft clay. The outcomes of this study make a valuable contribution to the advancement of environmentally friendly soil stabilizers, promoting green and low-carbon practices in the field of ground improvement.

Hybrid geopolymer paste from high calcium fly ash and glass wool: Mechanical, microstructure, and sulfuric acid and magnesium sulfate resistance characteristics

Geopolymer is a sustainable binder composed of source materials containing aluminosilicates under strongly alkaline conditions promising for use in place of cement in building materials due to its low carbon footprint. Although high calcium fly ash can be used as a source material for geopolymer binder, it has rarely been studied with other wastes especially, glass wool waste. Therefore, this study presents the use of glass wool (GWF) from the insulating materials waste and high calcium fly ash (HCFA) as binary precursors to produce geopolymer paste. HCFA was replaced by GWF at a ratio of 10–40% by weight. The sodium silicate-to-sodium hydroxide (NS/NH) ratio of 1.0 and a liquid-to-binder ratio of 0.6 were used. The geopolymer pastes were cured at room temperature before mechanical, microstructural, and durability property analyses. The results showed that the setting time and slump flow increased with increasing GWF content. The incorporation of GWF had little effect on the early strength of the geopolymer paste, but the 28-day compressive strength was significantly enhanced up to ∼67% (30% replacement) higher than that of the HCFA geopolymer paste. Likewise, the flexural strength increased with increasing GWF replacement content. The total porosity of the hybrid geopolymer paste was lower than that of the HCFA one resulting from the reaction and filling effect of the geopolymer matrix. The XRD, FTIR, and SEM-EDX analyses showed the presence of geopolymerization products with calcium silicate hydrate regardless of the geopolymer mixture composition. This suggested that GWF could react with alkaline activators to form geopolymer products even though some unreactive GWF was observable when GWF replaced at 40% by weight. Furthermore, an increase in GWF content led to better resistance to sulfuric acid and magnesium sulfate attack, which was observed within 180 days. All of these results suggested that GWF was an effective secondary precursor for improving the fresh and hardened properties of HCFA-based geopolymer paste. In addition, the residue acts as a reinforcing material in the matrix paste. Consequently, improved resistance to acid corrosion and sulfate expansion were significant.

Thermoelectric Properties of Ba2–xEuxZnSb2, a Zintl Phase with One-Dimensional Covalent Chains

The compound Ba2ZnSb2 has been predicted to be a promising thermoelectric material, potentially achieving zT > 2 at 900 K due to its one-dimensional chains of edge-shared [ZnSb4/2]4- tetrahedra and interspersed Ba cations. However, the high air sensitivity of this material makes it difficult to measure its thermoelectric properties. In this work, isovalent substitution of Eu for Ba was carried out to make Ba2-xEuxZnSb2 in order to improve the stability of the material in air and to allow characterization of thermal and electronic properties of three different compositions (x = 0.2, 0.3, and 0.4). Polycrystalline samples were synthesized using binary precursors via ball milling and annealing, and their thermoelectric properties were measured. Samples showed low thermal conductivity (<0.8 W/m K), a high Seebeck coefficient (350-550 μV/K), and high charge carrier mobility (20-35 cm2/V) from 300 to 500 K, consistent with predictions of high thermoelectric efficiency. Evaluation of the thermoelectric quality factor suggests that a higher zT can be attained if the carrier concentration can be increased via doping.

Bonding effect of a Zr/Si coating prepared on zirconia using a sol-gel method

Statement of problemZirconia has been widely used as a dental prosthetic material. However, bonding to zirconia is challenging, and whether a Zr/Si coating would improve bonding is unclear. PurposeThe purpose of this in vitro study was to prepare a Zr/Si coating on zirconia ceramics using a sol-gel method and to determine whether the bonding to resin is improved. Material and methodsPresintered zirconia specimens were prepared and divided into 5 groups: 4 experimental groups with ratios of the binary sol-gel precursor (zirconium oxychloride/tetraethoxysilane) set as 2:1 (Z2), 1:1 (Z1), 0.5:1 (Z0.5), and 0.25:1 (Z0.25) and Group C as the control group. In addition to surface roughness measurements, scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD) were carried out to characterize the surface. Each group was divided into 2 subgroups according to whether a silane coupling agent was applied. Half of the bond specimens were stored in deionized water for 24 hours; the remaining half were aged using 5000 thermocycles. The shear bond strength (SBS) of resin bonded to specimens was tested for the initial and durable bond strength, and the bonding interface was also observed by SEM after debonding. Data were subjected to 1-way ANOVA and the post hoc Tukey honestly significant difference test (α=.05). ResultsThe Zr/Si coating formed on zirconia ceramics. Z0.5 had the greatest mean ±standard deviation roughness (2.13 ±0.15 μm) and had the highest silicon content (21.7 ±0.21%). t-ZrO2, m-ZrO2, c-SiO2, and ZrSiO4 were detected by XRD in Z1. The SBS values were decreased by aging but were significantly increased by Zr/Si coating, especially for Z0.5, with the application of silane (initial: 22.92 ±2.79 MPa; aged: 9.91 ±0.92 MPa). ConclusionsThe Zr/Si coating significantly improved the initial and aged bond strength, and the optimal Zr/Si ratio of the sol-gel appeared to be 0.5:1.