Paste Composition Research Articles

Tracing Aquatic Macrophyte Development in Nansi Lake, Northern China's Largest Freshwater Lake: Plant Macrofossils From 1855 to Present.

Examining the impacts of natural and anthropogenic influences on aquatic macrophytes in shallow lakes is crucial for their effective restoration and management. However, there is a lack of direct evidence regarding past species composition or detailed and continuous evidence of recent changes in aquatic macrophyte communities. This study utilized plant macrofossil remains deposited in the sediment, combined with macrophyte surveys from 1983 to 2010, to reconstruct the historical changes in the macrophyte community over approximately 160 years in Lake Weishan, a sub-lake of Lake Nansi located in the lower Yellow River (Huanghe River) Basin, northern China. Approximately 54.3% of the species historically recorded at the core site were identified through macro-remains analysis, including five previously unrecorded submerged taxa (Myriophyllum verticillatum, Ranunculus trichophyllus, Chara sp., Nitella sp., and Vallisneria spinulosa) discovered during monitoring surveys. The findings revealed four major shifts in the macrophyte community: A transition from a swampy environment dominated by emergent/wetland plants (ca. 1855-1875) to an expanded water body characterized by a rapid proliferation of submerged macrophytes (ca. 1875-1910), followed by mass disappearance of macrophytes (ca. 1910-2005) and subsequent significant resurgence (after 2005). Multiple factor analysis was employed to investigate the correlation between these shifts and changes in paleolimnological indicators (invertebrates, geochemistry, and grain size), as well as documented records related to hydrology, climate changes, and human activities. The results confirmed our hypothesis that climatically and anthropogenically induced hydrological alterations were likely the primary drivers influencing macrophyte composition alteration and succession dynamics in the lake. This study highlights the potential use of plant macrofossils for reconstructing long-term changes in macrophyte community components, abundance assessment, and ecosystem health evaluation within the lower Yellow River region. To effectively address persistent challenges such as water diversion and climate change, we propose integrating paleoecological methods into standard ecological monitoring protocols employed for water ecological quality assessment.

Novel carbon paste sensor modified with MWCNT and Ca-doped ZnO nanocomposite for therapeutic monitoring of Favipiravir in COVID-19 patients

Favipiravir (FAV) is a prodrug with a proven antiviral efficacy against coronavirus 2. Close therapeutic monitoring of FAV is crucial for COVID-19 patients due to its variable dosing, complex pharmacokinetics, and notable drug interactions. This study presents a novel, selective electrochemical sensor for FAV detection, using a carbon paste electrode (CPE) modified with multi-walled carbon nanotubes (MWCNTs) and calcium-doped ZnO nanoparticles (Ca-ZnO NPs). Characterization of the Ca-ZnO NPs was performed using Fourier-transform infrared spectroscopy (FT-IR), field emission-scanning electron microscope (FE-SEM), and X-ray photoelectron spectroscopy (XPS). Several operational parameters were optimized, including carbon paste composition, buffer selection, pH, and electrochemical waveform settings. Under optimized conditions, an oxidation signal of FAV was identified at approximately + 1.22 V versus an Ag/AgCl reference electrode in Britton-Robinson buffer (BRB) at pH 4.0. Differential pulse voltammetry (DPV) facilitated the detection of FAV across a wide dynamic concentration range of 0.6–100.0 µM, with detection and quantification limits of 0.17 and 0.51 µM, respectively. The developed method demonstrated high selectivity towards FAV, effectively distinguishing it from its acidic degradation product (ADP), qualifying it as a stability-indicating assay. Evaluations using the GAPI, AGREE, and RGB 12 metrics confirmed alignment with green and white analytical chemistry principles. Furthermore, this method was successfully applied to quantify FAV in human plasma, making it suitable for therapeutic drug monitoring (TDM) in COVID-19 patients.

Influence of Hydroxypropyl methylcellulose (HPMC) on the hydration characteristics and early phase composition of C3S-gypsum binary paste

To further understand the influence of HPMC on cement-based material (CBM) hydration, this study investigates the hydration characteristics and early product formation of C3S-gypsum binary pastes with HPMC. Results demonstrated that HPMC significantly delayed heat release peak occurrence, with the most pronounced effect on induction period duration, which was increased by 1-2 times with adding HPMC. Calculations employing the Krstulovic-Dabic hydration kinetic model show that HPMC most significantly extended the nucleation and crystal growth (NG) stage, increasing the duration by 21% in the 0.05% HPMC group. Additionally, the 0.035% HPMC group showed a 2.6% decrease in CSH gel and 14% in Ca(OH)2 generation after 1 day, while also reducing the chemically bound water (CBW) content by 20%, with CBW relative content variations correlating with hydration stage rate constants. This study confirms that HPMC delays C3S-gypsum hydration and reduces early product generation, aiding future regulation of CBM hydration processes.

Effect of cement paste and saline solution composition on chemical and physical binding of chlorides

AbstractChloride ingress, along with chemical and physical binding in cement pastes, was studied in relation to the paste composition, saline solution, and hydration regime used. Unblended cement paste and pastes prepared with combinations of SF with MK and SF with BFS, replacing 30% of the cement mass, were exposed to NaCl and geothermal solutions for 7 days, either directly or following 7 days of water curing. The surface and middle parts of the samples were evaluated using TGA, XRD, FTIR, ion chromatography (Cl concentration), and ICP-OES (Na concentration). In addition, compressive strength (CS) measurements were performed. In MK-containing samples, Cl-AFm (hydrocalumite) formed mainly through an ion exchange mechanism, while in BFS-containing samples and the reference pastes, Cl-AFm phases primarily formed through the reaction of Cl− with C3A and Ca(OH)2 and increased physical adsorption of Cl− onto C-(A-)S-H were determined. Exposure to NaCl solution led to more chlorides being chemically incorporated into Cl-AFm, as well as higher levels of physically adsorbed and free chlorides in the pore solutions, compared to the geothermal solution. Pozzolanic reactions of additives, the acceleration of hydration induced by the solutions, especially by the geothermal one, and the densification of the matrix by the products of chloride reactions in blended samples resulted in CSs comparable to or higher than those reached after standard water curing. CSs of referential samples decreased following the decalcification of the initially formed C-(A-)S-H phases.

The Effects of Combined Use of Sodium Citrate and PCE Plasticizer on Microstructure and Properties of Binary OPC-CAC Binder.

This study examines the impact of sodium citrate and a plasticizing additive, along with their sequential introduction into a cement slurry or concrete mix, on the heat evolution of the cement slurry, the microstructure, phase composition of the cement paste, and the compressive strength of fine-grained concrete. The binder used in this research was a blended binder consisting of 90% Portland cement and 10% calcium aluminate cement. This type of binder is characterized by an increased heat evolution and accelerated setting time. The addition of sodium citrate at 5% of the binder mass alters the phase composition of newly formed compounds by increasing the quantity of AFt and AFm phases. The presence of sodium citrate significantly delays the hydration process of tricalcium silicate by a factor of 3.3. Initially, it accelerates belite hydration by 31.6%, but subsequently slows it down, with a retardation of 43.4% observed at 28 days. During the hardening process, the hydration of tricalcium aluminate and tetracalcium aluminoferrite is accelerated throughout the hardening process, with the maximum acceleration occurring within the first 24 h. During the first 24 h of hydration, the dissolution rates of tricalcium aluminate and tetracalcium aluminoferrite were 40.7% and 75% faster, respectively. Sodium citrate enhances heat evolution during the initial 24 h by up to 4.3 times and reduces the induction period by up to 5 times. Furthermore, sodium citrate promotes early strength development during the initial curing period, enhancing compressive strength by up to 6.4 times compared to the reference composition.

Microstructural evolution and degradation mechanisms of tricalcium silicate and tricalcium aluminate composite pastes under sulfate exposure

Sulfate attack precipitates instability and degradation within calcium silicate (aluminate) hydrate (C-(A)-S-H) gel, the primary binding phase in cementitious materials. This degradation intricately correlates with the clinker phase composition, particularly the ratios of tricalcium silicate (C3S) and tricalcium aluminate (C3A). In this study, C3S and C3A were synthesized through solid-state sintering to create C3S-C3A pastes. The research aimed to examine the impact of varying C3A substitution levels and Na2SO4 exposure durations on the microstructure and performance of these composite pastes. The findings reveal that C3A markedly accelerates both the early hydration kinetics and the overall hydration degree of C3S within the C3S-C3A system, with this effect becoming more pronounced with increasing C3A content. Furthermore, the inclusion of C3A elevates the Al[4]/Si ratio, mean chain length (MCL), and Ca/Si of the C-S-H gel. This leads to an increase in the overall porosity of the composite matrix while simultaneously diminishing its chloride-binding capacity. Exposure to Na2SO4 disrupts the incorporation of Al3+, released during C3A hydration, into the bridging sites of the C-S-H structure, causing a decrease in the Al[4]/Si of the C-(A)-S-H gel. The leached aluminum subsequently reacts with SO42- to form ettringite and other deleterious compounds. Additionally, Na2SO4 exposure induces a significant reduction in the Ca/Si within the composite pastes, with the magnitude of decalcification inversely proportional to the initial Ca/Si—implying that higher C3A content exacerbates the decalcification process. During the process of sulfate attack, the formation of gypsum and AFt complicates the pore structure of the matrix, providing more adsorption sites for the binding of Cl-.

The characteristic of andesite waste powder (AWP) as a replacement for fly ash geopolymer paste

Abstract Large-scale production of andesite has created much waste. Andesite waste material has SiO2 (Si) as a main component and causes pozzolanic activity. During the mining, processing, and polishing steps, almost 70% of this waste is thrown away. This research studied the potential of andesite waste material (AWP) as a substitution for fly ash. Six compositions of geopolymer paste with AWP were mixed to determine the ability of andesite waste powder (AWP) to be a silica source material in geopolymer paste. AWP ranged from 0%, 10%,20%,30%,40% and 50% from the unit weight of fly ash. 10 Molar of NaOH and Na2SiO3 were used as an alkaline activator. The ratio between Na2SiO3 and NaOH was constant at 2. The water-to-solid ratio was kept constant at 35%. Flow test and compressive strength of geopolymer were tested according to ASTM C1437 and ASTM C109, respectively. The result showed that the AWP affected the workability of the geopolymer paste. The geopolymer unit weight increases at 10% of AWP and decreases gradually when the AWP content rises. The geopolymer achieves a maximum compressive strength of 41.55 MPa over 28 days when 30% AWP is used. As a silica source, AWP can be used to replace fly ash geopolymer, based on the study’s results.

Comparative study on different methods of activation of recycled powder grouts

Abstract The high-value utilization of recycled powder (RP), primarily derived from construction and demolition waste, has been limited due to its low reactivity. In this study, the effect of RP subjected to three types of inorganic alkalis (sodium hydroxide, sodium carbonate, and calcium hydroxide [CH]), two alkanolamines (diethanolisopropanolamine [DEIPA] and triisopropanolamine [TIPA]), elevated temperatures, and their combined activation on the technical properties of RP grouts was analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to investigate the development of the mineral composition and micromorphology of the grout pastes. The results indicated that alkali and thermal activation of RP had negative effects, while combined activation improved the fluidity of the grout pastes. The compressive strength of alkali-activated groups was slightly enhanced at 1 day but significantly decreased at 28 days. In contrast, the compressive strength of grouts activated with CH, alkanolamines, and thermal treatment was found to be improved at all ages. The compressive strength of the grout paste containing 40% combined-activated RP was measured at 43.1, 73.3, and 95.7 MPa at 1, 3, and 28 days, respectively, which represented increases of 20.4, 19.6, and 17.7%, respectively, compared to the non-activated grout. Combined activation demonstrated the most improvement in the microstructural density of the grouts when compared to the single-activation mode.

Investigation on the mechanical and microstructure properties of masonry cement-red mud-carbide slag-based paste

The high alkalinity and complex phase composition of red mud pose significant challenges for its direct utilization. The construction industry is widely regarded as the most viable option for large-scale consumption of red mud to mitigate its continuous accumulation globally. Activation treatment is a crucial prerequisite for preparing cementitious materials from red mud, but traditional methods either require high-temperature calcination of red mud or the use of substantial amounts of strong alkaline substances as alkaline activators, thereby increasing costs and hindering the large-scale application of red mud. This paper presents an alternative method where 4% carbide slag is used as an activator to prepare cement-red mud-carbide slag-based composite pastes, substituting 10%-90% of masonry cement with red mud. As the red mud content increases, the compressive and flexural strengths of the hydrated pastes significantly decrease; the compressive strength of the material with 10% red mud is 13.4 times that of the material with 90% red mud. The addition of 4% carbide slag enhances the compressive and flexural strengths of the red mud-based cementitious material, with increases of 1.67%, 17.9%, and 34.6% in compressive strength at 3d, 7d, and 28d, respectively, and increases of 2.38%, 6.67%, and 7.36% in flexural strength. This indicates that carbide slag is beneficial for activating the reactivity of red mud. There is an incremental relationship between the flexural and compressive strengths of the cementitious material, and a fitting formula can be used to quantify the relationship between red mud content and these strengths. Microstructural analysis confirms that the addition of carbide slag significantly optimizes the pore structure, promoting the formation of Ca(OH)2 and C-S-H gel, which leads to improved mechanical properties of the red mud-containing composites. This study provides a feasible solution for the large-scale application of red mud in the cement industry.

Unveiling the degradation mechanisms in silicon heterojunction solar cells under accelerated damp-heat testing

Silicon heterojunction (SHJ) solar cells have become one of the mainstream solar cells in the current photovoltaic market due to their high efficiency. Still, concerns about their long-term reliability are seen as a potential issue restricting further marketisation. In particular, the sensitivity of silicon heterojunction solar cells to high temperatures and moisture is a concern. Sodium (Na) in combination with humidity is widely considered one of the causes of degradation in silicon heterojunction solar cells. Yet, a comprehensive understanding of the mechanisms behind Na-induced decay remains lacking. This study will investigate humidity-induced degradation of industrial SHJ solar cells at elevated temperatures using various sodium-containing salts [sodium bicarbonate (NaHCO3), sodium chloride (NaCl), and sodium nitrate (NaNO3)] to improve our fundamental understanding of Na-induced degradation. We will show that SHJ solar cells exposed to NaHCO3 and NaCl show a significant reduction in efficiency, while solar cells exposed to NaNO3 show minimal degradation. Further analysis indicates that NaHCO3 may interact with the transparent conductive oxide (TCO) layer, leading to a reduction in surface passivation and a deterioration of the metal-TCO interface. NaCl primarily affects the Ag contact, resulting in a reduction of the adhesion of the screen-printed contact. Moreover, the TCO composition, particularly the oxygen content, influences its chemical tolerance. These results show that Na-related degradation is more complicated than initially thought. The chemistry is strongly influenced by the negative ions, as well as the composition of TCO and metal paste. These factors are determined by the bill of materials and the contaminants introduced during cell/module fabrication and operation of the SHJ module. The findings of this paper may lead to the development of new accelerated testing protocols for SHJ technology to ascertain long-term reliability in the field.

Study on the interaction between limestone filler and rice husk ash on the rheological properties of cement composite pastes

As an active supplementary cementitious material, rice husk ash (RHA) can improve several properties of cement paste. However, it has a significant negative impact on the flowability of cement pastes. This study aims to improve the rheological properties of cement-RHA paste by adding an additional admixture: limestone filler (LF). The rheological curve was measured using a rheometer, and the effects of LF and RHA on the rheological properties (dynamic and static yield stresses, consistency, and structural build-up) were investigated. The calculation and analysis of water film thickness (WFT) and the interaction forces between the particles in the paste were conducted to reveal the intrinsic mechanism. The results show that LF can effectively eliminate the adverse effect of RHA on rheological properties. When the RHA content is 10 %, the addition of 5 %, 10 %, and 20 % LF reduces the yield stress by 43.86 %, 69.64 %, and 87.11 %, respectively, and decreases the consistency by 28.17 %, 40.85 %, and 73.24 %, respectively. The high porosity of RHA leads to significant water absorption, which affects the WFT between paste particles much more than LF. The WFT decreases with RHA, resulting in a higher yield stress. The higher specific surface area (SSA) of RHA reduces the spacing between paste particles, and the enhanced interactions between particles significantly increase the initial yield stress (20 min). The addition of LF reduces the inter-particle forces and the structural build-up, lowering the yield stress, which results in a good complementary effect between LF and RHA on the rheological properties. This study can provide guidance for the design of mix proportions considering the workability of the cement-LF-RHA composite system.

The Role and Mechanism of Rice Husk Ash Particle Characteristics in Cement Hydration Process.

Reactive rice husk ash (RHA) is used as a supplementary cementitious material (SCM) to prepare cement composite pastes. The impact of RHA content and the internal curing effect on the hydration process of the cementitious system was studied. The hydration heat, degree, and product content of the cement-RHA composite system at 3, 7, and 28 d were analyzed using hydration microcalorimetry, thermogravimetry, and XRD (Rietveld) analysis. The results show that with the increase in RHA, the main exothermic peaks move forward, and the values increase. The induction period is prolonged, and the acceleration period is shortened. The induction period of 15% RHA is extended to 3 h. The hydration heat of cement composite pastes is mainly divided into three stages. Namely, the first stage (0-18 h) is the superposition of the RHA nucleation effect and chemical effect, the second stage (18-51 h) is the superposition of the dilution effect and internal curing effect, and the third stage (51-72 h) is the internal curing effect with the water-release. The internal curing effect of RHA has a certain periodicity, which is related to its content. The water-release age in the early stage (24 h) advances with the increase of content, and the water-release effect in the later stage (7-28 d) is also significant with the increase of content. The higher the content, the more significant the promotion of the internal curing effect on cement hydration and the pozzolanic reaction of RHA.

Recycling some byproducts for fabrication of green cement with good mechanical strength and high efficiency for wastewater treatment

This research aims to produce green cement, as an alternative to traditional cement, with outstanding performance. Five alkali-activated cement pastes were fabricated based on NaOH-activation of slag (GGBFS), bypass (B), and/or silica fume (S). Codes of five pastes are C, C-20B, C-30B, C-10B10S, and C-20B10S, as C is the control paste containing 100% slag. The compressive strength of the fabricated pastes was measured at different curing regimes: Conventional curing for 3 months and autoclave curing at 4 bar/153◦C, 7 bar/178◦C, and 10 bar/198◦C for 4 h. XRD, TGA/DTG, SEM/EDX, and BET/BJH techniques were utilized to clarify the phase development, morphological and texture features of the formed alkali-activated composite pastes. Besides, the removal capacity of some pastes for methylene blue and indigo-carmine dyes from aqueous media was evaluated. The results confirmed that C and C10B10S (80%GGBFS + 10%B + 10%S) pastes have significant mechanical properties and distinctive meso-porosity that can remove both anionic and cationic dyes.

Analysis of Brucine using Poly(L-Arginine) modified biosynthesized CuO nanoparticle composite sensor

The study investigated the sensitive and selective electrochemical behavior of Brucine (BC) using electrochemically polymerized L-Arginine (LA) modified with a composite comprising biosynthesized copper oxide (CuO) nanoparticles (NPs) and carbon paste electrode (PAMCuONPs/CPE). PAMCuONPs/CPE showed an optimum reversible redox-peak at 0.2 M phosphate buffer solution (PBS) at pH 2.5, allowing detection of BC. The characterization of PAMCuONPs/CPE and bare CuONPs composite carbon paste electrode (BCuONPs/CPE) was performed using scanning-electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) methods were employed to evaluate the performance of PAMCuONPs/CPE. Experimental parameters, including pH, and variation of concentration, were investigated. PAMCuONPs/CPE exhibited an electrochemical performance with a limit of detection (LOD) of 0.12×10−6 M and a limit of quantification (LOQ) of 0.43×10−6 M. It demonstrated good reproducibility, repeatability, and stability. PAMCuONPs/CPE was successfully validated in determining BC in real samples.

Esh-Shaheinab: The archetype of the Sudanese Neolithic, its premises and sequels.

Esh-Shaheinab is a landmark in the African Neolithic. This site gave the name Shaheinab Neolithic to the Neolithic period in central Sudan, becoming its archetype. Excavated in the late 1940s by A.J. Arkell, it bears witness to the processes of domestic animal introduction from the Middle East into North and East Africa. Its excavation also uncovered the remains of an earlier Mesolithic or Early Khartoum (ca. ninth-sixth millennia BC) and a Late Neolithic occupation (ca. fourth millennium BC), providing essential insights into the Neolithic's premises and sequels. Although the influence of Esh-Shaheinab has been recognized for more than seventy years, our knowledge of its material culture has remained as it was then. In 2001, one of the present authors (EAAG) had permission to restudy the ceramic collection at the National Museum in Khartoum and subsequently export samples for laboratory analyses. Here, for the first time, we provide a multi-scale analysis of the Esh-Shaheinab ceramic material from the Early Khartoum to the Late Neolithic periods by integrating the chaîne opératoire approach into the local landscape. By combining the results of macroscopic and microscopic analyses, we performed petrographic investigations on the composition and manufacturing technology of the ceramic pastes using polarized optical microscopy (POM) and scanning electron microscopy (SEM-EDS). Organic residue analysis (ORA) was also carried out, to provide information on diet, vessel use, and subsistence practices. The results of our combined analyses showed that the inhabitants of Esh-Shaheinab developed an adaptation specific to the ecological niche they inhabited. They lived in the western valley of the Nile, which was narrower and offered different environmental conditions than the eastern bank. This resulted in partial continuity in manufacturing traditions and ceramic recipes, including more mixed wadi materials and a strong emphasis on wild meat consumption as the narrower alluvial plain restricted animal herding.

Analysis of the Impact and Mechanism of Polyacrylate-Based Composite Paste on the Performance of Recycled Aggregate.

This study developed three composite slurries for coating recycled aggregate by incorporating polyacrylate emulsion, fly ash, and gypsum into a cement-based mixture. The filling and pozzolanic effects of fly ash help to improve microcracks in the recycled aggregates. The polyacrylate emulsion forms a strong bonding layer between the cement matrix and the aggregates, enhancing the interfacial bond strength. Based on relevant studies, the following mix designs were developed: Slurry 1 consists of pure cement paste; Slurry 2 contains 15% fly ash and 3% gypsum added to the cement paste; Slurry 3 adds 22% polyacrylate emulsion to the slurry. The study first compared the effects of the three composite slurries on the crushing value and water absorption of recycled aggregates, and then analyzed their impact on the mechanical properties, permeability, and drying shrinkage of concrete. Finally, the mechanisms behind the enhancement were investigated using the Vickers Hardness Test (HV), Mercury Intrusion Porosimetry (MIP), and scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS). The results showed that the polyacrylate emulsion composite slurry had the most significant improvement effect. For recycled aggregate AL, the crushing value decreased from 28.8% to 22.5% and the saturated surface-dry water absorption decreased from 15.1% to 13.8% after cement slurry modification. After coating with the composite slurry, the crushing value further dropped to 18.2% and the water absorption to 9.5%. Two aspects of the performance of recycled aggregates are enhanced with the polymer composite slurry: first, fly ash provides nucleation sites for CH, reducing the tendency for directional CH alignment. Second, the long chains of PAE (polyacrylic ester) encapsulate cementitious particles, effectively filling surface defects on the recycled aggregates, improving the bonding strength at the new-to-old interface, and significantly enhancing the performance of both recycled aggregates and recycled concrete.

Stereolithography Printing and Mechanical Properties of Polyethylene Glycol Diacrylate/Hexagonal Boron Nitride Ceramic Composites

To enhance the mechanical properties of bioceramic composite bone scaffolds, a composite paste of polyethylene glycol diacrylate (PEGDA) and hexagonal boron nitride (h‐BN) with a solid content of up to 42 wt% was developed in this study. The part was produced using stereolithography (SLA). The SLA printing parameters and material ratios of the paste were optimized through a homogeneous design and mechanical property tests. The results indicate that the single‐line curing width of the PEGDA/h‐BN paste in the XY plane ranged from 172 to 209 μm, while the curing depth of a single layer along the Z‐axis ranged from 99 to 154 μm. Laser power was identified as the primary factor influencing both the width and depth of curing. The compressive strength of the printed sample of PEGDA/h‐BN ceramic composite paste was measured at 222.4 ± 5.6 MPa, which is 61 times greater than the compressive strength of a pure PEGDA structure and comparable to that of cortical bone (100‐230 MPa). Finally, the superior biocompatibility of PEGDA/h‐BN ceramics was confirmed through cytotoxicity experiments. Consequently, PEGDA/h‐BN ceramic composites meet the mechanical properties and biocompatibility requirements necessary for bone tissue applications, indicating promising potential in the field of bone tissue engineering.

Electrochemical boost via thermally reduced graphene oxide for tailoring composite paste electrodes

Carbon-based composite materials are employed in diverse electrochemical applications, such as in catalysis, (bio)molecular sensing, and energy storage. In practice, electrode material needs to be highly conductive to allow high-speed electron transference to electrolyte species and possess high-surface area to obtain greater measured signals and power capabilities, as well as long useful life and stability. In this sense, graphene derivatives emerge as interesting candidates, even more so if they constitute part of practical, economical and versatile paste electrodes.This work presents a detailed analysis of the electrochemical performance of paste electrodes fabricated with multilayer partially reduced graphene oxide (rGO). The rGO was strategically produced via thermal treatment as a key factor that minimizes both mass loss and energy consumption. The results obtained through diffraction, microscopy and spectroscopy techniques show an effective partial reduction in the range of 100 to 400 °C. Furthermore, the enhanced electrochemical performance of rGO was determined by exploring the specific capacitance from cyclic voltammetry (CV) and galvanostatic charge–discharge measurements (GCD) as well as charge transfer resistance via electrochemical impedance spectroscopy (EIS). Our results evidence how an integral performance with suitable chemical, structural and morphological properties achieved for GO heat-treated at 200 °C leads to an improved electronic conductivity when a small part is combined with graphite in paste electrodes. This latter combination provides higher versatility compared to other alternatives since it arises as an economical and effective carbonaceous matrix for (bio)electrochemical sensors, hybrid supercapacitors or other desired nanotechnological applications.

The Concept of Using 3D Printing Technology in Ceramic Foundry Filter Manufacturing

The article presents the concept of using 3D printing technology in ceramic foundry filter manufacturing. They are a crucial component for obtaining an acceptable quality of nickel superalloys by carrying out the process using the precision casting method. Commonly used filters of this type have a number of disadvantages. They are characterized by irregularity of the filtering structure, high brittleness, lack of resistance to mechanical shocks, and impacts of a stream of liquid metal. All these factors create a risk of introducing the material from the damaged filter into the casting mold, which translates into contamination of the casting alloy, and thus the occurrence of casting defects such as nonmetallic inclusions. The hope for a change in this state of affairs is the use of additive manufacturing technology in their production, which by assumption will allow to obtain a product with a repeatable shape, high mechanical resistance, and a specially designed structure regulating the flow of liquid metal into the mold during casting. The suitability of robocasting and binder jetting technology for producing filtration structures was initially assessed. The results have presented the selection of ceramic powder, as well as the development of the composition of the ceramic paste. The parameters of paste preparation and 3D printing individual processes were described. Moreover, the representative microstructures and basic mechanical properties of samples obtained by both of the compared technologies were presented. Furthermore, the final effect of prototype casting filters with a repeatable shape, manufactured with the use of both technologies, was presented, which were transferred for further technological research in a foundry producing critical aircraft engine parts. The possibilities of using each technology in various applications were also discussed.

Wear and roughness analysis of two highly filled flowable composites.

This in vitro study aimed to evaluate surface roughness and wear of highly filled flowables and traditional packable composites. Additionally, the effect of polymerization time on these parameters was evaluated. Two flowable higly filled composites (CMf-Clearfil Majesty ES flow-low viscosity, Kuraray and GUf-Gaenial Universal Injectable, GC) and two packable composites (CM-Clearfil Majesty ES-2, Kuraray and GU-Gaenial A'CHORD, GC) were used to create 160 specimens (n = 40;8 × 6×4mm). For each tested material, two subgroups were considered according to the polymerization time (n = 20): 10s or 80s. After setting, the specimens were subjected to chewing simulations (240.000 cycles, 20N), and wear was measured by the laser integrated in the chewing simulator. The surface roughness was measured using a rugosimeter, before and after chewing cycles. Two representative specimens per group were observed under scanning electron microscope (SEM). Data were collected and statistically analyzed (p < 0.05). Wear analysis highlighted statistically significant differences between the groups: CMf10-CMf80 (p = 0.000), CMf10-CM10 (p = 0.019), CMf10-GUf10 (p = 0.002), CM10-CM80 (p = 0.000), CM80-GUf80 (p = 0.02), GUf10-GUf80 (p = 0.000), GUf10-GU10 (p = 0.043) and GU10-GU80 (p = 0.013). Statistically significant differences in surface roughness were highlighted between the groups: CMf10-CMf80 (p = 0.038), CMf80-CM80 (p = 0.019), CMf80-GU80 (p = 0.010), CM80-GUf80 (p = 0.34) and GUf80-GU80 (p = 0.003). Surface roughness and wear of highly filled flowable composites were comparable to that of traditional paste composites. Furthermore, a longer curing time leads to an improvement in the mechanical properties of the composites. Highly filled flowables can be a valid alternative to paste composites in occlusal areas due to its similar surface roughness and wear values, especially when overcured.