High Aluminum Content Research Articles

Effect and mechanism of high Li2CO3 concentrations on the early hydration of sulfoaluminate cement-based materials

Lithium carbonate (Li2CO3) is a commonly used early strength agent for sulfoaluminate cement based grouting materials. Low concentrations of Li2CO3 (≤30 μmol Li/g in sulfoaluminate cement) can significantly accelerate the early hydration of sulfoaluminate cement. However, the effect of high Li2CO3 concentrations (>30 μmol Li/g in sulfoaluminate cement) on the early hydration of sulfoaluminate-cement-based materials (SCBMs) is unclear. In this study, the effects of high concentrations of lithium ion (Li+) and carbonate ion (CO32) on the early hydration of SCBMs (C4A3S¯–CaSO4–CaO) with different mineral compositions (systems T1 and T2) were investigated by hydration calorimetry, X-ray diffraction, and ion concentration measurements. The results revealed that both Li+ and CO32− promoted the hydration of C4A3S¯. Li+ and CO32− each reacted with aluminum and calcium in solution, and the formation of ettringite was suppressed when they were present. At low aluminum and high calcium concentrations in solution (system T1), ettringite formation was controlled mainly by the low concentration of aluminum. Less ettringite was generated, and the inhibition of ettringite formation by both Li+ and CO32− was weaker. At high concentrations of both aluminum and calcium in solution (system T2), ettringite formed more rapidly than in system T1, and Li+ and CO32− inhibited its formation to a greater extent. Li2CO3 affected the amount of ettringite by changing aluminum ion and calcium ion in slurry, thus leading to the change of hydration heat release. These new insights into the interaction between Li2CO3 and SCBMs contribute to the theoretical foundation for cement hydration control.

Investigation on the machining performance of copper-based diamond ultra-thin dicing blades manufactured by fused deposition modeling and sintering (FDMS)

Utilizing FDMS technology to manufacture ultra-thin diamond blades can enhance its machining performance. In this study, the machinability of ultrathin diamond blades manufactured by FDMS on a variety of materials, including ferrite magnets, synthetic sapphire, ceramic, and cemented carbide, was investigated. This study examined the fragmentation characteristics, chipping size, and surface morphology of the machined surfaces with the ultra-thin diamond blades. Experimental results showed that ultrathin diamond blades for dicing ferrite magnets and sapphire produced larger chipping sizes than the other two materials; while because of high aluminum content, alumina ceramics have a smoother dicing surface among other materials, the surface roughness of the alumina measuring surface reached 13.6 nm. On the other hand, as a result of the reinforcement of cobalt on the matrix properties and the wetting effect on the interface between matrix and diamond particles, the wear resistance and sharpness of the blade are improved, and the wear loss of the blade is only 0.011 g. Even though diamond blades for various materials produce different machining results, FDMS diamond blades can improve the machining performance of processed materials, the machined surface quality, and the exposure of diamond particles on the blades. In summary, this study affirms that FDMS improves diamond blade machining performance, promoting the industrialization of FDMS for the production of ultra-thin diamond blades.

Effect of clay minerals on asphaltene deposition in reservoir rock: Insights from experimental investigations

This study investigated the effect of crude oil characteristics and the presence of clays on the interaction and precipitation tendency of asphaltenes during solvent washing. As solvent n-pentane was used, hence, in this study, the behavior of n-pentane insoluble asphaltenes was investigated. The asphaltenes precipitation tendency and consequently its impact on formation damage were investigated with several experiments performed on sand samples mixed with two different crude oils, with and without added clays. The samples were then analyzed using various techniques including Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and porosity measurements. The results showed that the presence of clays increased the affinity of asphaltenes towards adsorption onto the clay surfaces, resulting in the plugging of pore spaces and inducing higher asphaltenes precipitation. The surface elemental composition of the samples indicated that the asphaltenes of one crude oil (Oil 1) had a higher concentration of aluminum (Al), calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), and silicon (Si), while the asphaltenes of the other crude oil (Oil 2) had a higher concentration of sulfur (S) and vanadium (V). These differences in elemental composition led to different precipitation tendencies and porosity reductions. Accordingly, the interactions of asphaltenes with reservoir rock found more for Oil 1 to Oil 2. The findings of this study provide insights into the factors that influence asphaltene precipitation during solvent washing, which can have implications for oil production and processing.

Analysis of Geopolymer Mortar Compressive Strength Based on Fly Ash and GGBFS as Patch Repair Material

Damages that often emerge in concrete include cracks, delamination, spalling, wear, fracture, porous, voids (perforated). These damages need to be repaired, one of which is by patch repair. With consideration of strength and frugality, a self-made repair material was developed using mortar as a base material, i.e., geopolymer mortar. Geopolymer mortar is a mortar with natural materials and materials that have a high content of silica oxide and alumina (such as Fly Ash and GGBFS) as a binder that must be activated with an alkaline activator in the form of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The use of Fly Ash and GGBFS as a binder to replace cement in geopolymer mortar has a positive impact from an environmental point of view because it can reduce the use of cement and can reduce environmental pollution due to Fly Ash and GGBFS waste. In this research, the effect of variations in Fly Ash and GGBFS and variations in the molarity of NaOH on the compressive strength of geopolymer mortar were investigated, in order to obtain the optimum composition of the geopolymer mortar mixture that meets the requirements of compressive strength as a repair material. From the results of the research, the maximum compressive strength occurred in GF91 16 M mortar at 56 days of 73.77 MPa was obtained. Geopolymer mortar has a higher compressive strength and a cheaper price when compared to Sika Grout mortar so that the use of geopolymer mortar as a patch repair material is better than Sika Grout mortar in terms of strength and frugality.

Influence of the Joint Use of Phosphorus and Magnesium Fertilizers on the Background of Nitrogen and Potassium Fertilizers on the Productivity, Quality and Removal of Nutrition Elements in Spring Barley Depending on the Acidity of Sod-Podzolic Soil

In the long term (56 years) field experience revealed a great return from the combined use of lime, phosphorus and magnesium fertilizers compared with the background of nitrogen-potassium fertilizers on strongly acidic sod-podzolic poorly cultivated soil, with a high content of mobile aluminum in it (up to 130 mg/kg), due to the prolonged use of physiologically acidic fertilizers in the form of ammonium nitrate and potassium chloride. The use of phosphorous fertilizers on highly acidic untreated soil contributed to an increase in the yield of spring barley by 67%, on medium-acidic soil produced at a dose of 11.5 t CaCO3/ha – by 2.3 times, on slightly acidic soil produced at a dose of 19.0 t CaCO3/ha – by 2.6 times, when combined with magnesium fertilizers – by 2.5 and 2.9 times, respectively, according to compared with the yield on the background of nitrogen-potash fertilizers 1.78 t/ha (highly acidic soil). With the introduction of magnesium fertilizers on slightly acidic soil, the payback by adding grain of mineral fertilizers (N90P60K90) increased by 3 times, increasing to 13.9 kg/kg, with an increase in protein content compared to the background of nitrogen-potassium fertilizers by 1.2%. The use of nitrogen and phosphorus by spring barley plants increased 3.4 times, potassium – 3.0 times.

Synthesis of NaP Zeolite Based on Bauxite Red Mud Using Hydrothermal Method on Mole Ratio of SiO2/Al2O3 Variations

Red mud is a bauxite industrial waste of reddish-brown mud with high alkalinity. Red mud has relatively high silica and alumina content, so it can be utilized as a raw material in the synthesis of zeolite. This study aims to synthesize high-purity NaP zeolite from red mud at various SiO2/Al2O3 mole ratios. The synthesis begins with neutralizing the red mud, followed by decomposition using the alkaline fusion method at a ratio of red mud:NaOH = 1:1 (w/w). The filtrate produced by the alkaline fusion was adjusted to the mole ratio of SiO2/Al2O3 = 2.0; 2.5; 3.0; and 4.0, respectively, by adding sodium silicate, followed by a hydrothermal process using an autoclave at 120oC for 16 hours. The synthesized zeolites were characterized using XRD and FTIR spectrophotometry. The XRD results showed that the zeolite produced in all variations of the SiO2/Al2O3 mole ratio studied was a type of high-purity NaP with no other zeolite crystalline phases found as impurities. The structure formed is tetragonal with a degree of crystallinity of 74.54%; 76.47%; 78.94%; 75.64%, and crystal size 80.2286; 54.3437; 37.7099 and 40.1226 nm for zeolite with SiO2/Al2O3 mole ratio 2.0; 2.5; 3.0; and 4.0, respectively. Based on the results of the study, pure NaP zeolite can be synthesized from red mud material using the hydrothermal method at the ratio of moles SiO2/Al2O3 = 2.0 – 4.0.

High aluminum content in bone of marine mammals and its relation with source levels and origin

Although aluminum is widely distributed in the earth's crust, its environmental availability and wildlife assimilation rates are only partially known. Here we analyze aluminum concentrations in bone from 10 species of marine mammals inhabiting 3 geographic areas subject to different aluminum inputs: the Río de la Plata estuary (Uruguay), the coastal waters of Mauritania and the Galapagos archipelago (Ecuador). Overall, concentrations were unusually high as compared to those of terrestrial animals, with lowest concentrations in the Galapagos archipelago, then the Río de la Plata estuary and finally Mauritania. The aluminum source varied between regions, prevailing anthropogenic sources in the Río de la Plata Estuary and natural sources (wind-blown dust) in Mauritanian waters. The type of source determined contamination levels: anthropogenic sources were most significant for coastal species and showed a decline with distance of habitat from shoreline, while natural sources had a higher influence on open waters because of the dearth of biogenic silica that eliminates aluminum from the water column. Since aluminum remains in bone for several decades, marine mammal bone reflects historical levels of aluminum and therefore is a good bioindicator of the aluminum concentration of the marine environment.

Geochemistry and mineralogy of prehistoric pottery shards found at Gua Kelew, Nenggiri Valley, Kelantan, Malaysia

Gua Kelew is one of the newly discovered caves by archaeological researchers in Malaysia. This cave has the potential to become one of Malaysia’s prehistoric sites from the findings from site surveys and archaeological excavations. Among the artifacts that were found are stone tools, earthenware, ceramics, snail shells, cave paintings and animal bones. The discovered earthenwares were analyzed for their mineral content in order to determine whether they were made locally around the cave or brought from elsewhere. The outcome of this analysis is vital as the data would provide proof that the community living in the cave or the surrounding area had its own technology for manufacturing the earthenwares. However, if the earthenwares were brought from elsewhere, it is believed that trade or the exchange of goods between communities living inland and near the coast had occurred. Composition of the earthenware samples was obtained by X-Ray Diffraction (XRD) analysis for mineral content and also X-Ray Flouresence (XRF) analysis for major, minor and trace elements. Findings from the XRD analysis show that the mineral content in the earthenware samples are quartz, calcite and anorthoclase, while the XRF analysis shows a high content of silica and aluminium. The analysis also discovered that all of the earthenwares found in Gua Kelew used the same raw materials obtained from the same area. Based on the graph plot analysis, the data exhibits differences in the elements between the earthenware samples and the surrounding area’s clay samples. Hence, it is suggested that the earthenwares found in Gua Kelew were not produced in the Hulu Kelantan area. This also indicates that the earthenwares may have been brought from another location to the area through trade deal between the local and foreign communities.

Fabrication of Synthetic Zeolite from Sinabung Mountain Volcanic Ash via Sol-Gel Method

Fabrication of synthetic zeolite from Sinabung Mountain volcanic ash by Sol-Gel method. The zeolite is obtained by extraction of alkalis sodium silicate and sodium aluminate. At first volcanic ash was characterized using XRF and XRD analyses. The XRF analysis shows that silica is 44.8%. In contrast, XRD analysis showed a sharp peak at a 2Ѳ corner area of 27.55o to express bonded with silica mineral salt. At the same time, the silica characterization is done by FT-IR analysis. The FT-IR analysis shows the presence of Si-O-Si groups at wave numbers 1064.71 cm-1, 786.96 cm-1 and Si-OH at wave 3749.62 cm-1 and 3448.72 cm-1, identifying the presence of silica. The synthetic zeolite characterization analysis obtained is FT-IR, XRD, SEM-EDX, and BET analysis. In the FT-IR analysis, the O-Si-O group was obtained at wave 987,85 cm-1 and O-Al-O at wave 447,89-585,30 cm-1, identifying X zeolite. Diffractogram XRD showed a sharp peak at 66.8°, 28.12°, and 45.84°, forming mixed crystalline X and zeolite A. SEM-EDX analysis shows that zeolite morphology is tight and homogeneous and has a high aluminium content of 24.79 and Si 16.12. While for nitrogen desorption, adsorption analysis on pore size, surface area and pore volume are 3,22 nm, 61,86 m2/g and 0,095 cc/g. The result of synthetic zeolite isotherm adsorption-desorption shows type V showing mesoporous size.

Neoproterozoic Collision Granitoids in the Southwestern Margin of the Siberian Craton: Chemical Composition, U−Pb Age, and Formation Conditions of the Gusyanka Massif

The paper provides evidence that collisional magmatism related to the Neoproterozoic (880−860 Ma) orogenic event occurred in the southwest of the Siberian Craton. Newly obtained data are presented on the major-component and trace-element composition, U−Pb (SHRIMP II) zircon age, and Sm−Nd isotope composition for rocks of the Gusyanka granitoid massif in the Yenisei fault zone of the Yenisei Ridge. The concordant U−Pb zircon age of the Gusyanka massif is 871 ± 11 Ma indicates that its rocks were formed in the mid-Early Neoproterozoic, simultaneously with the rocks of the Kalama and Eruda massifs in the Tatarka−Ishimba fault system, during the same stage of the collisional events at approximately 880–860 Ma. The calc-alkaline granites, granodiorites, and leucogranites of the Gusyanka massif are classified, on the basis of their high alumina content and trace element composition, as S-type and were derived from a metapelitic source. Many trace-element parameters of rocks of the Kalama and Eruda massifs correspond to those of low-potassium I-type granites, which were most likely derived from mafic rocks and tonalites. The granitoids of the Gusyanka massif, on the one hand, and the Kalama and Middle Tyrada massifs, on the other, differ contrastingly in Nd isotope composition. The source of the former was either metapelites of the Tungusik Group or metasedimentary rocks of the Sukhoi Pit Group, with the involvement of juvenile material. The melts of granites of the Kalama and Middle Tyrada massifs might have been derived from a source with the involvement of an older, possibly Paleoproterozoic, crustal material and a juvenile mafic source. Thus, the orogenic events at 880−860 Ma led to the generation of melts at different levels of the Paleo- to Mesoproterozoic crust of the trans-Angara region of the Yenisei Ridge. The geodynamic history of the region is correlated with the synchronous successions and similar style of tectono-thermal events along the peripheries of the large Precambrian cratons of Laurentia and Baltica, and this is consistent with paleocontinental reconstructions of the close spatiotemporal relations between these cratons, Siberia, and their incorporation into Rodinia.

Properties of Palm Oil Ash Geopolymer Containing Alumina Powder and Field Para Rubber Latex

Most geopolymer binder is produced using raw materials comprising powder with high silica and alumina content. Additionally, fine aggregate is prepared with river sand for high bulk density. This research proposes using palm oil ash (POA) for the main binder and palm oil clinker (POC) for the fine aggregate. The chemical composition of POA has high levels of silica but low alumina, so it must undergo partial replacement with alumina powder (AP). POA and POC are waste by-products of electrical power plants. The properties to be investigated include compressive strength, bulk density, water absorption, and microstructure. The effect of mixture composition, i.e., POA and field Para rubber latex (FPRL), on those properties is of particular interest. POA was substituted by AP and FPRL at 2.5%, 5%, 7.5%, and 10%, and at 1%, 3%, 5%, and 10%, respectively. Geopolymer mortars were cured at ambient temperature for 24 hours and kept at ambient temperature until testing. The compressive strengths of the geopolymer mortars were tested at 1, 7, and 28 days. The results showed that the optimal mixture consisted of 5% AP in the case of AP only and 1% FPRL in the case of FPRL only, while the ternary optimal mixture of 1% FPRL and 7.5% AP achieved higher compressive strengths than the control (CT) sample at 28.16, 19.98, and 25.30 MPa, respectively, after 28 days of curing. Bulk density increased with the addition of AP and FPRL. The microstructures of the geopolymer samples investigated using SEM-EDX showed the presence of different elements with different mixtures and displayed a dense, compact geopolymer matrix with high compressive strength. Using large amounts of POA in combination with AP and FPRL improved the environmental aspects of landfill disposal. Doi: 10.28991/CEJ-2023-09-05-017 Full Text: PDF

Effects of GaN channel downscaling in AlGaN–GaN high electron mobility transistor structures grown on AlN bulk substrate

In this work, two series of AlGaN/GaN/AlN high electron mobility transistor (HEMT) heterostructures have been grown by molecular beam epitaxy on AlN bulk substrates. The effects of reduction in the GaN channel thickness as well as the AlGaN barrier thickness and composition on structural and electrical properties of the heterostructures have been studied. The material analysis involved high-resolution x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. In a first series of HEMT structures grown with an aluminum content of 30% in the AlGaN barrier, the channel downscaling results in a reduction in the GaN strain relaxation rate but at the expense of degradation in the mean crystal quality and in the electron mobility with a noticeable increase in the sheet resistance. An opposite trend is noticed for the three-terminal breakdown voltage of transistors, so that a trade-off is obtained for a 50 nm width GaN channel HEMT, which exhibits a sheet resistance of 1700 Ω/sq. with transistors demonstrating three-terminal breakdown voltage up to 1400 V for 40 μm gate to drain spacing with static on resistance Ron = 32 mΩ cm2. On the other hand, a second series of HEMT structures with high aluminum content AlGaN barriers and sub-10 nm GaN channels have been grown perfectly strained with high sheet carrier densities allowing to preserve sheet resistances in the range of 880–1050 Ω/sq.

Fabrication and characterization of a novel mullite-stainless steel composed hollow fibre membrane for oil/water separation

Low-cost mullite-kaolinite material has recently received more attention as an alternative to conventional ceramic materials such as alumina and silica to prepare ceramic hollow fibre membranes (CHFMs) due to its high alumina contents and silica and thermal/chemical stability. However, weak bending strength is still one of the key bottlenecks that delay their commercial applications. In this work, we successfully fabricate a novel mullite-SS HFM with enhanced bending strength using mullite-kaolinite power with different stainless steel alloy (SS) 316 L contents of 0.0, 2.5, 5.0, 7.5, 10 and 12 % (w/w) as a reinforcement material by phase inversion/sintering techniques. The SS alloy was a potential material to enhance the mechanical strength of mullite HFMs due to its excellent mechanical properties. The effects of the major fabrication parameters of SS contents, mullite contents, and fabrication parameters such as air gap distance and bore fluid flow rates were well studied and evaluated through the fabrication process. Fabricated mullite-SS HFMs were characterized by morphology, porosity, pore size/pore size distribution, and bending strength. Afterwards, they were evaluated in an oil/water separation system regarding water flux and oil rejection rate. Based on the findings, there was a gradual increase in the bending strength from 32.1 to 79.8 MPa with increased SS contents from 0 to 12 % (w/w). At 10 % (w/w) SS, the satisfactory morphology with the balance between the bending strength of 66.7 MPa and porosity of 29 % was obtained. This bending strength was significantly higher than reported for mullite-kaolinite HFMs in previous works. Moreover, At 10 % (w/w) SS, the oil–water rejection performance of 96.9% and the water permeation of 290 L/m2. h was satisfactory at the sintering temperature of 1300 °C. These findings suggest the advantage of this membrane for various water treatment applications, such as oil/water separation, due to its outstanding physical properties.

The role of chemistry and fineness of metakaolin on the fresh properties and heat resistance of blended fly ash-based geopolymer

Sensible thermal energy storage using concrete as a storage medium is a promising technology that helps minimize energy in power plant. The purpose of this study is to evaluate the potential benefits of metakaolin (MK) as a partial substitute for fly ash-based geopolymer for heat resistance. As a partial substitute (5 and 20 wt.%) for fly ash (FA), nine metakaolins containing different alumina contents were selected. In order to assess their potential for storing high-temperature thermal energy, physical and microstructural analyses were performed before and after heat exposure up to 500 °C. Low packing density limits the workability of some metakaolins and increases water demand in pastes. The mechanical properties of geopolymer weaken as the temperature is raised (< 500 °C). The high alumina content of some metakaolins, however, helps to mitigate strength loss during high temperatures. A higher dosage of metakaolin has also shown to prevent this deterioration of strength. A reduction in strength under heating is caused by both dehydration and dehydroxylation. The higher fineness and alumina content of MK have demonstrated significant potential to enhance the heat resistance of FA-based geopolymers. As a result, the geopolymer paste developed is suitable for being used in heat-resistant applications.Article HighlightsFly ash was the main precursor of as prepared alkali-activated binders.Adding metakaolin enhances the resistance of hardened materials under thermal load.The higher the alumina content inside metakaolin is, the higher the performance is.

Petrology and Geochemical Features of Crystalline Rocks in Ora-Ekiti, Southwestern Nigeria

This research investigates and reports on the petrology and geochemical characteristics of crystalline basement rocks in Ora-Ekiti, Southwestern Nigeria. Exhaustive geological investigation reveals migmatite, banded gneiss, granite gneiss and biotite gneiss underlie the area. In reducing order of abundance, petrographic examination reveals that migmatite contains quartz, muscovite and opaque minerals. Banded geniuses contain quartz, biotite, plagioclase, and opaque minerals. Granite geniuses contain quartz, plagioclase, biotite, microcline and opaque; while biotite geniuses contain biotite, plagioclase, opaque minerals, and quartz. Silica contents in migmatite (69.50%-72.66%; ca. 71.23%), banded gneiss (71.66%-77.1%; ca. 75.23%), biotite gneiss (72.32%-76.18%; ca. 73.83%) and granite gneiss (69.82%-73.15%; ca. 71.95%) indicate the rocks are siliceous. High alumina contents in migmatite (12.18%), banded gneiss (10.28%), biotite gneiss (11.46%) and granite gneiss (9.97%) are comparable to similar rocks in the basement complex. All the rocks show Ba, Sr and Rb enrichment. Harker diagrams of Al2O3 versus SiO2 and CaO versus SiO2 show negative trends while Na2O versus SiO2, K2O versus SiO2 and TiO2 versus SiO2 plots showed positive trends. This variation probably depicts extensive crystal fractionation in the magmatic systems that produced the rocks prior to metamorphism or partial melting of the precursor rock. SiO2 versus (Na2O + K2O) classifies the rocks as granite to granodiorite. The rocks are high K-calc-alkaline and calc-alkalic on SiO2-K2O plot. This shows the rocks are potassic meaningthat they are formed from a potassium-rich source. The plot of Al2O3/(Na2O + K2O) versus Al2O3/(CaO +Na2O + K2O) reveals the crystalline rocks are orogenic and originated from granitoid with meta luminous affinity. The rocks consist of gneisses of no economic minerals, but the petrology reveals them as common rocks typical of metamorphic terrains and geochemical features of the rocks reveal they are felsic and of granitic composition.

Novel carbon-ceramic composite membranes with high cation exchange properties for use in microbial fuel cell and electricity generation

Actually, there are different configurations used in microbial fuel cells (MFCs) with presence or absence of an ion exchange membrane between their electrodes. Specifically, MFCs that use membranes have the objective of avoiding the diffusion of oxygen and substrate between the anodic and cathodic compartment, and to achieve a correct transfer of protons from one chamber to another. In this regard, the current study seeks to prepare and characterize new composite membranes using as precursors three types of carbonaceous materials such as bone char, coconut shell activated carbon and bituminous activated carbon and natural clay. The composite membranes of bituminous activated carbon and clay showed more promising specific conductivity (42%) than the one made with pure clay. The physicochemical properties of the membranes and their precursors were elucidated by SEM/EDX analysis, IR spectroscopy, nitrogen adsorption isotherms at 77 K and optical microscopy. Further, membranes performance was assessed using microbial fuel cells (MFCs) where the composite membranes prepared with clay-bituminous carbon reached the highest voltage values (0.95–1.02 V) in open circuits, while that reached a maximum power density of 0.699 W/m3 at a current density of 4.012 A/m3 in closed circuit. This behavior is associated with the high content of silicon and aluminum in bituminous activated carbon, which favored the proper functioning of membranes in the MFCs. Specifically, with this type of cells, energy recovery of 0.0057 kWh/m3 and 0.1322 kWh/kg chemical oxygen demand (COD) removed, which indicates an extra economic income of the order of $0.0025/kg COD. Finally, the produced power was demonstrated in prototypes to power LED and four digital clocks. This novel clay-bituminous activated carbon showed promising cost-effectiveness and sustainable energy generation, which may be suitable for wastewater treatment.

Designing p-region of AlGaN ultraviolet light-emitting diodes for the improved performance

We have used aluminum indium gallium nitride (AlInGaN) graded layers instead of the conventional combination of three p-type layers i.e., AlGaN final quantum barrier (FQB), AlGaN electron blocking layer (EBL), and top p-AlGaN hole injecting layer to increase the performance of ultraviolet light-emitting diodes (UV LEDs). In this study, the effects of graded quaternary layers (GQLs) on efficiency droop have also been investigated. These GQLs improve the injection of holes into the quantum wells. Our simulated results show that our proposed structure (LED K2) has a high peak efficiency of ∼ 68% and a significantly reduced efficiency droop of ∼41% than LED K1. The radiative recombination rate in the multiquantum wells (MQWs) of LED K2 is improved by ∼90% which can be attributed to enhanced carrier overlap or recombination in the multiquantum wells. The concentration of electrons in the active region of LED K2 is increased by ∼ 56% as compared to LED K1. This is due to the high aluminum (Al) content in GQLs of LED K2 which minimizes the electron leakage.

Impact of geopolymers on hard sludge formation on the secondary side of PWR steam generators under transient conditions

In modern steam generators (SG), some tube degradation phenomena are promoted by the formation of hard sludge (HS) on top of tubesheet. These phenomena reduce the efficiency of nuclear power plants (NPP). In some cases, SG deposits are primarily constituted by HS. This HS usually presents high concentrations of aluminum and silicon (up to 6.0 ± 0.1 wt% of Al and 2.7 ± 0.1 wt% of Si), together with high microhardness values (above 800 HV) at specific locations. In fact, there is evidence that the presence of aluminum and silicon is at the origin of the problematic of HS in SG during normal operation.Geopolymers are inorganic polymer materials constituted by a 3D-network of interlinked silica and alumina tetrahedra. Geopolymers present cementitious properties similar to HS. Geopolymers are formed under highly alkaline conditions and low temperature, by the polymerization of aluminosilicate and/or silicate oligomers. During NPP transient periods, geopolymer formation could be favor by the physicochemical conditions in the gaps arisen due to the different thermal contraction of SG tubes, deposits and tubesheet. Thus, it could be though that part of the HS formed in the crevice between tube and tubesheet of SG could correspond to geopolymers. In order to demonstrate this hypothesis, the mayor constituents of HS (magnetite, aluminum and/or silicon sources) have been autoclaved in representative secondary circuit transient conditions (cooldown). The effect the Si to Al ratio, the aluminosilicate source, the presence of magnetite and the chemical conditions in the crevice is also studied. The chemical, structural and morphological characterization of the resulting solids shows the presence of aluminosilicate compounds in some of the tested experimental conditions. However, these aluminosilicate compounds do not act as cementing agents agglomerating magnetite particles and therefore, they do not contribute to HS formation.

The Heteroepitaxy of Thick β-Ga2O3 Film on Sapphire Substrate with a β-(AlxGa1-x)2O3 Intermediate Buffer Layer.

A high aluminum (Al) content β-(AlxGa1-x)2O3 film was synthesized on c-plane sapphire substrate using the gallium (Ga) diffusion method. The obtained β-(AlxGa1-x)2O3 film had an average thickness of 750 nm and a surface roughness of 2.10 nm. Secondary ion mass spectrometry results indicated the homogenous distribution of Al components in the film. The Al compositions in the β-(AlxGa1-x)2O3 film, as estimated by X-ray diffraction, were close to those estimated by X-ray photoelectron spectroscopy, at ~62% and ~61.5%, respectively. The bandgap of the β-(AlxGa1-x)2O3 film, extracted from the O 1s core-level spectra, was approximately 6.0 ± 0.1 eV. After synthesizing the β-(AlxGa1-x)2O3 film, a thick β-Ga2O3 film was further deposited on sapphire substrate using carbothermal reduction and halide vapor phase epitaxy. The β-Ga2O3 thick film, grown on a sapphire substrate with a β-(AlxGa1-x)2O3 buffer layer, exhibited improved crystal orientation along the (-201) plane. Moreover, the scanning electron microscopy revealed that the surface quality of the β-Ga2O3 thick film on sapphire substrate with a β-(AlxGa1-x)2O3 intermediate buffer layer was significantly improved, with an obvious transition from grain island-like morphology to 2D continuous growth, and a reduction in surface roughness to less than 10 nm.

High entropy coating from AlCoCrCuFeNi alloy, obtained by laser alloying

The structural-phase state of the Al-Co-Cr-Cu-Fe-Ni system high-entropy alloy obtained by laser alloying of technically pure aluminium surface layers was investigated by XRD, EDX and metallographic analyses. It is shown that in the process of laser alloying the formation of an an ordered multicomponent substitution solid solution based on BCC lattice took place, which is typical for high-entropy alloys. The process of heterogeneous crystallization of high-entropy alloys AlCoCrCuFeNi and Al3CoCrCuFeNi was modeled taking into account cooling rates of the melt. It is established that the formation of the obtained structure is a consequence of high cooling rates of the melt and high content of aluminum in the laser alloying zone. The microhardness of the alloyed surface was higher compared to high-entropy alloys of this system obtained under equilibrium conditions and was equal to 6.59 GPa. Additional reasons that may affect the high values of microhardness are analysed.