Si-rich Phase Research Articles

Spectroscopic identification of Ca-bearing uranyl silicates formed in C–S–H systems

Portland cement-based grouts used for radioactive waste immobilisation contain a Ca- and Si-rich binder phase, known as calcium–silicate–hydrate (C–S–H). Depending on the blend of cement used, the Ca/Si ratio can vary considerably. A range of C–S–H minerals with Ca/Si ratios from 0.6 to 1.6 were synthesised and contacted with aqueous U(VI) at 0.5 mM and 10 mM concentrations. Solid-state 29Si MAS-NMR spectroscopy was applied to probe the Si coordination environment in U(VI)-contacted C–S–H minerals and, in conjunction with U LIII-edge X-ray absorption spectroscopy analysis, inferences of the fate of U(VI) in these systems were made. At moderate or high Ca/Si ratios, uranophane-type uranyl silicates or Ca-uranates dominated, while at the lowest Ca/Si ratios, the formation of a Ca-bearing uranyl silicate mineral, similar to haiweeite (Ca[(UO2)2Si5O12(OH)2]·3H2O) or Ca-bearing weeksite (Ca2(UO2)2Si6O15·10H2O) was identified. This study highlights the influence of Ca/Si ratio on uranyl sequestration, of interest in the development of post-closure safety models for U-bearing radioactive waste disposal.

Relationship between macro-properties and amorphous gel of FA-based AAMs with different curing conditions after elevated temperature

This study investigated the effect of curing conditions (40 °C, 60 °C, and 80 °C curing temperature, 3 h, 5 h, and 8 h curing time) on the macro-properties (compressive strength, surface properties, and length change) of alkali-activated fly ash materials (FA-based AAM) at elevated temperatures (300 °C, 600 °C, 800 °C, and 1000 °C). The microstructure properties of samples before/after high-temperature treatment were studied by the FTIR, XRD, XRD- Rietveld, SEM-EDS, and 29Si NMR experiments. The results show that the compressive strength of samples shows a decreasing trend beyond elevated 600 °C. A similar phenomenon was found in the surface and length properties. Unlike samples with lower curing temperatures (40 °C) exit the lower residual mechanical properties beyond 600 °C, samples with higher curing temperatures have stable performance in the compressive strength, surface properties, and length change. And high curing temperature is favorable for the formation of amorphous gels with a Si-rich phase in FA-based AAM. Lower diffusion coefficient of water and high skeleton stability were obtained in the higher Si/Al ratio of N-A-S-H amorphous gel decreasing the evaporative rate of water to exacerbate the damage of microstructure at a low elevated temperature, while increasing the stability at high temperature.

Microstructure evolution and thermal shock properties of PEO coatings on a TiAl alloy

In this paper, plasma electrolytic oxidation (PEO) coatings were produced on Ti-48Al-2Cr-2Nb alloy in a silicate electrolyte. During the PEO process, four coating growth stages were revealed, which were anodic oxidation (I), breakdown of the anodized film (II), micro-arcing growth (III) and formation of glass phase with coating fusing (IV). It was found that the porous aluminium silicate phase preferentially grew at the Ti3Al regions of the substrate in stage II and the amount of Al2TiO5 phase increased rapidly in stage III. In stage IV, a Si-rich glass phase layer grew rapidly leading to a large increase in coating thickness. The thermal shock tests were conducted for both the substrate and PEO-coated samples from 1123 K to room temperature. The thermal shock resistance study showed that the oxide layer kept growing with the thermal shock cycles on the uncoated TiAl substrate. PEO coatings with predominate Al2TiO5 and aluminium silicate phases can withstand 55 thermal shock cycles without changing. The samples with a thin amorphous anodized layer cannot withstand the internal stress generated during thermal shock cycles due to the weak bond between the outmost layer and the substrate. The coating with thick glass outmost layer also peeled off because of the weak thermal shock resistance of the glass phase. The wear test results showed that, after thermal shock cycles, the PEO coating with suitable thickness and roughness has good wear resistance and potential application in wear protection.

Reactivity of raw, pyroprocessed and GGBS-blended alum sludge (AS) waste for sustainable cement production

This paper investigates AS waste to produce a construction binder of low environmental impact. It studies the reactivity of AS so that it can be used instead of traditional (higher impact) binders. Currently, most construction binders are Portland cement (PC) based, hence carrying a major environmental impact. Significant impact can be offset by using wastes as binders. Alum sludge (AS) waste is massively produced in drinking water plants, and its primary component is aluminium hydroxide (Al(OH)3). Both the raw and the calcined AS exhibit pozzolanic activity measured by the Chapelle test. The organic matter in raw AS inhibits pozzolanic reaction and hydrate formation, hence the raw AS specimens display low strength. Calcination removed the organic matter and induced the dehydroxylation of Al tetrahedra thereby increasing the pozzolanic activity of AS. The AS burned at 450 and 600 °C shows excessive reactivity which results in a flash set. However, at 800 °C, some amorphous Al(OH)3 transforms into semi-amorphous γ-Al2O3 avoiding flash set and allowing handling while maintaining significant reactivity that yields substantial strength. At 1000 °C, the conversion of amorphous Al(OH)3 into inert corundum significantly lowers reactivity. Therefore, pyroprocessing AS at 800 °C produces material of high reactivity: abundant calcium aluminate hydrates were evident in the pastes due to pozzolanic reaction and secondary hydration involving CO32− ions. Replacing 50% 800°C-AS with GGBS enhances strength and avoids strength reduction (caused by the conversion of carbonate AFm phases to Si-rich AFm phases, possibly stratlingite). A blend of 800°C-calcined AS and GGBS, in a lime or PC system, renders workable setting times and a high ultimate strength. Calcination is the key parameter affecting AS as binder replacement. When incorporated into lime or PC systems, improper calcination may cause problems such as flash setting and a strength reduction.

Corrosion mechanism and fatigue behavior of aluminum alloy with high silicon content

The corrosion and corrosion-assisted fatigue life degradation behaviors of Al–8Si alloy is investigated. The test results show that galvanic cells are formed in the inter-dendrites due to high Si concentration, leading to pitting corrosion. The Al2Cu phase and the Si-rich phase precipitate at the grain boundaries in the inter-dendrites, among which the Al2Cu phase is the most critical factor leading to intergranular corrosion. Subsequently, intergranular corrosion gradually develops into intragranular corrosion attributed to the higher dislocation energy in fine-grained Al grains. Additionally, it is found by comparing the corrosion potential and corrosion rate that high Si concentration would cause the decrease in corrosion resistance. Finally, the fatigue test results show that the corrosion could reduce fatigue life of Al–8Si alloy by 79.77% on average. Therefore, the corrosion-induced fatigue life degradation is very worth to be considered in structures.

Cold metal transfer welding of AlSi7Mg alloy sheets prepared by selective laser melting

Cold metal transfer (CMT) welding of AlSi7Mg alloy sheets prepared by selective laser melting (SLM) was employed using ER4047 and ER5356 filler wire. Effect of the filler wires on hydrogen pores, microstructures and mechanical properties of welded joints was studied. As a result, CMT welding of AlSi7Mg alloy sheets using ER5356 wire reduces the porosity, refines the grains, increases the fraction of high angle grain boundaries (HAGBs), modifies the eutectic Si-rich morphology, and improves the solid solution strengthening of Si elements in the α-Al matrix of the microstructures in the weld metal (WM). Additionally, the morphology of eutectic Si-rich phases in heat affected zone (HAZ) of the welded joint is noticeably changed from the continuous cellular networks in base metal (BM) to totally globularized particles, as a result of the increased welding heat effect with decreasing distance to the WM. Compared with the ER4047 wire, the welded joint with ER5356 wire achieves higher WM hardness and higher ultimate tensile strength (UTS), which have been increased by 13.9 % and 18.6 %, respectively. The enhanced mechanical properties of the welded joints with ER5356 wire are mainly attributed to the reduced porosity and the improved microstructures in the WM.

Melting of basaltic lithologies in the Earth's lower mantle

As basaltic rocks formed at the base of the oceanic floor are transported back to the Earth's mantle along subduction zones, they undergo transitions and introduce compositional and thermal heterogeneities in the deeper parts of the mantle. Studying the melting phase relations of basaltic lithologies at elevated pressures and temperatures provides insights into what potentially happens at different depths in the lower mantle now and throughout the past billion years of active plate tectonics. Using laser heated – diamond anvil cell experiments combined with in situ X-Ray Diffraction measurements at synchrotron sources, we revisit the crystallization and melting properties of natural basaltic samples at 60–100 GPa and up to 4000 K. Diffraction patterns highlight the major phases: bridgmanite and Ca-perovskite, followed by crystallization of Si-rich phases (mainly stishovite) and Calcium Ferrite (CF-type) Na and Al-rich phase. Recovered samples were prepared using focused ion beam techniques for detailed chemical analyses of the extracted thin sections by electron microscopies in order to resolve sub-micron features and understand the chemical partitioning of elements induced by melting at high pressure and temperature conditions. We confirm that the liquidus phase is Ca-perovskite, which segregates during melting and is recovered as rings that encapsulate a melt pool throughout the studied pressure range. The melt pocket shows a concentric structure consisting of an alumino-silicate envelope surrounding an Fe-rich silicate part. At the center of samples, an Fe-O-S metal pond is often observed. We associate the observation of segregation of liquid phases to capillary forces. The differentiation of melt pockets into three melts is tentatively attributed to Marangoni effects, i.e. temperature-induced surface tension gradients in the samples. Central metal ponds are indirectly best interpreted as related to the disproportionation reaction of Fe2+ into Fe3+ and Fe(0) in bridgmanite whereas the two silicate-melt pools could be associated to the formation of two immiscible liquids upon melting of basalts. On the basis of these observations, we propose that melting of basaltic lithologies at lower mantle pressures could lead to important chemical differentiation mostly characterized by Fe enrichment at increasing depth.

Effect of Zirconium micro-addition and multi-pass friction stir processing on microstructure and tensile properties of Mg–Zn–Si alloys

The aim of this study is to investigate the microstructure and tensile properties of Mg-0.5Zn-0.2Si-XZr (X: 0, 0.25, 0.5 wt.%) in the as-cast and multi-pass friction stir processed (FSPed) conditions. Micro addition of Zr element resulted in the average grain size (AGS) reduction from 1.65 ± 0.3 mm in Mg-0.5Zn-0.2Si alloy to less than 700 μm through the formation of Zr-rich particles evenly distributed in the structure and constitutional supercooling effect. However, the refinement efficiency of Zr was reduced by the formation of Si-containing intermetallic phases through the Si poisoning effect. Thus, agglomeration of these brittle compounds, specifically at the grain boundaries, resulted in quasi-brittle fracture mode in the as-cast samples. On the other hand, applying the FSP on Zr-free alloy improved both microstructure and mechanical properties due to grain refinement and porosity content reduction. In other words, in the optimum condition, the AGS reduced to about 5 μm and yield strength (YS), ultimate tensile strength (UTS) and total elongation percentage (EL%) improved up to 70%, 90%, and 566%, respectively, compared to the as-cast sample. On the other hand, in the Zr-modified alloys, the fragmentation and even redistribution of Zr-rich and Si-rich phases, particularly after the 2nd FSP pass, enhanced the dynamic recrystallization (DRX) through the particle stimulated nucleation (PSN) mechanism and restricted the grain growth through the Zener pinning effect. Therefore, the AGS of 2 ± 0.1 μm, UTS of 182 Mpa, and EL of 36% were achieved.

Micromechanical Modeling of AlSi10Mg Processed by Laser-Based Additive Manufacturing: From as-Built to Heat-Treated Microstructures.

The unique microstructure of the alloy AlSi10Mg produced by the laser-based powder bed fusion of metals (PBF-LB/M) provides high-strength and high-strain-hardening capabilities of the material. The microstructure and mechanical properties of 3D-printed, i.e., additively manufactured, AlSi10Mg are significantly altered by post-building heat-treatment processes applied in order to tailor the final properties of the parts. Using an accurate computational model to predict and improve the mechanical performance of 3D-printed samples considering their microstructural features can accelerate their employment in envisaged applications. The present study aims to investigate the correlation between microstructural features and the mechanical behavior of as-built, direct-aged, and T6 heat-treated samples of PBF-LB/M AlSi10Mg under tensile loading using experiment and microstructure-sensitive modeling approaches. Nanoindentation tests are used to calibrate the parameters of the constitutive models for the Al and Si-rich phases. The experimental investigations revealed that heat treatment significantly changes the sub-grain morphology of the Si-rich phase, and this can have a considerable effect on the mechanical behavior of the components. The effect of the modeling of the Si-rich phase in the representative volume elements on the prediction of mechanical behavior is investigated using the J2 plasticity model. The combination of the crystal plasticity model for Al and the J2 plasticity model for the Si-rich phase is used to predict the tensile properties of the as-built and heat-treated states. The predicted results are in good agreement with the experimental results. This approach can be used to understand the microstructure–property relationship of PBF-LB/M AlSi10Mg and eventually tailor heat treatment for PBF-LB/M AlSi10Mg based on the requirement of the application.

The microstructure tailoring and property improving of directed energy deposited Al-Zn-Mg-Cu alloy modified with various Si and ZrO2 contents

Al-Zn-Mg-Cu alloys are traditional lightweight materials with extraordinary mechanical properties. Nevertheless, the manufacturing of Al-Zn-Mg-Cu alloys by directed energy deposition (DED) technique is still a tough problem since these alloys are prone to hot-cracking during the rapid solidification process of DED. In this paper, the co-incorporation of Si and ZrO 2 into the Al-Zn-Mg-Cu alloy was adopted for alleviating solidification shrinkage and enhancing mechanical properties. After the addition of Si, cracks are completely eliminated and the microstructure is refined due to the formation of Si rich eutectic phases. The average grain size is further decreased when ZrO 2 was added and the elevation of ZrO 2 amount facilitates the declination. The combined effects of Si and ZrO 2 induce the enhanced tensile properties (241 MPa in tensile strength, 160 MPa in yield strength and 4.1% in elongation) of the Al-Zn-Mg-Cu alloy modified with 2.9 wt% Si and 1.5 wt% ZrO 2 , which are further improved after T6 treatment (304 MPa in tensile strength, 225 MPa in yield strength and 4.3% in elongation). This paper indicates that the present approach can enable the manufacturing of crack free hard-to-weld Al-Zn-Mg-Cu alloys with ultrafine grains by DED through adding appropriate ceramic inoculants. • Si and ZrO 2 were added for crack elimination and mechanical property enhancement. • Columnar grains are transformed into equiaxed grains after adding ZrO 2 . • The tensile strength is increased to 304 MPa after T6 treatment.

Effect of passivation on the high-temperature oxidation behavior of hot-formed steel

In this study, the effect of passive film on the high-temperature oxidation process of a PHS1500 hot-formed steel was investigated through molybdate passivation and austenitizing high-temperature oxidation experiments. The corrosion resistance and phase composition of the passive film were tested by electrochemical impedance test and X-ray photoelectron spectroscopy. The structure and phase composition of the oxide layer were also systematically analyzed. The passive film affects the oxide layer structure of hot-formed steel through the influence of the Si-rich phase formation. After the molybdate passivation treatment, the oxidation resistance of hot-formed steel significantly improved.

Calcification-Carbonation Method for Bayer Red Mud Treatment: Carbonation Performance of Hydrogarnets.

Hydrogarnets are vital intermediate products in the calcification- carbonation method, which is designed for Bayer red mud treatment. Their carbonation performance greatly depends on SiO2 substitution. In this study, different SiO2-substituted hydrogarnets were synthesized and characterized. Then, batch experiments were performed to evaluate the potential effects of important parameters such as CO2 pressure, and SiO2 substitution degree (x) on the carbonation process. The SiO2 substitution degrees of the hydrogarnets synthesized at 60, 120, 180, and 240°C were 0.27, 0.36, 0.70, and 0.73, respectively. As the SiO2 substitution degree increased, the hydrogarnet carbonation extents gradually declined. With an increase in CO2 pressure, the hydrogarnet carbonation percentages increased gradually and rose from 80.33% to 98.19% within 120min. The phases detected in the carbonized products were strip-like aragonite as well as some calcite; the Al-rich and Si-rich phases in the carbonized products were amorphous.

Cooperative effect of Mg and Si contents on the microstructural evolution, mechanical performance, and deformation behavior of cast Al–Li–Mg–Si alloys

In this study, the cooperative effect of Mg and Si contents on the microstructural evolution, mechanical properties, and deformation behavior of the cast Al–Li–Mg–Si alloys is investigated. Five different Al–Li–Mg–Si alloys are prepared by conventional casting method, which are referred to as Alloy A-E. The results show that with the increase in the Mg content, the amount of lath-like Mg2Si precipitates and bulk-like AlLiSi particles increases, which leads to an improvement in the strength and ductility of alloys. The amount of intergranular Si-rich phases in Alloy D increases with the increase in the Si content. Further, a higher Si content in Alloy E promotes the formation of bulk-like AlLiSi. The geometric phase analysis (GPA) results reveal strain partitioning behavior at the interface of Mg2Si precipitates and AlLiSi particles, which follows the Orowan looping or dislocation cutting strengthening mechanism. The geometrically necessary dislocation (GND) density calculation results suggest that the lath-like Mg2Si precipitates play a critical role in the deformation behaviors of Alloy A-C. The hindering effect of lath-like Mg2Si precipitates on the movement of dislocations decreases the GND density gap between high-angle grain boundaries or junctions and grain interior and improves the resistance to deformation. However, the deformation behaviors of Alloy D and E with higher Si content are mainly governed by the intergranular Si-rich phases. Finally, a methodological framework is established to elucidate the effect of precipitates and/or intergranular phases on the deformation behaviors of materials using a combination of GPA and GND density calculation methods.

Stable hexagonal ternary alloy phase in Fe-Si-H at 28.6–42.2 GPa and 3000 K

Hydrogen (H) and silicon (Si) are considered as important light elements for the planetary cores. A large amount of H is able to alloy with pure Fe metal at high pressures. Si can also alloy well with Fe. However, it remains uncertain how much H can alloy with iron silicides and if it alloys how H can alter the crystal structures of Fe-Si alloys at high pressures-temperatures ($P\text{\ensuremath{-}}T$). We performed experiments on Fe-9Si and Fe-16Si alloys (9 and 16 wt % Si, respectively) in a H medium up to 42.2 GPa and 3000 K in diamond-anvil cells coupled with pulsed laser heating and gated synchrotron x-ray diffraction techniques. We found conversion of the Fe-Si alloys into Fe-rich (fcc and dhcp $\mathrm{Fe}{\mathrm{H}}_{x}$), Si-rich (B20 and B2 FeSi), and intermediate (${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}{\mathrm{H}}_{x}$) phases. The new ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}{\mathrm{H}}_{x}$ phase has a structure similar to the hexagonal ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}$ phase but with expanded volumes, and thus, possible H incorporation. Both the observed volume expansion and the H content estimated by density-functional theory calculations support a significant amount of H with H/Fe \ensuremath{\approx} 0.6 in the crystal structure. Because ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}$ is known to break down above \ensuremath{\sim}1300 K at \ensuremath{\sim}18 GPa, our results suggest that hydrogen stabilizes the hexagonal structure at high $P\text{\ensuremath{-}}T$. These results have implications for the crystallization of Fe-rich liquid at the solid-to-liquid boundary of planetary cores and possible existence of chemical heterogeneities in the solid cores.

Regulative effect of Mg/Si ratio on microstructure evolution and mechanical properties of cast Al-Li-Mg-Si alloys

The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si, Al-2.5Li-1Cu-1.6Mg-0.8Si, and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated. The results show that the primary phases and their morphologies in the as-cast alloys are found to vary with the Mg/Si ratio. The improvement of Mg/Si ratio of as-cast alloys promotes the formation of Mg2Si primary phase at the expense of the AlLiSi primary phase. Moreover, a tiny amount of TB-Al7.5Cu4Li phase transforms into S-Al2CuMg phase with the increase of Mg content. In addition, the increase of Mg/Si ratio also causes the Cu-rich intergranular phase distributed along crystal boundary to Si-rich intergranular phase. After ageing treatment, the precipitation sequence as a function of Mg/Si ratio is as follows: δ/δ′+AlLiSi (Mg/Si is ∼1) → δ/δ′+β′-Mg2Si+AlLiSi (Mg/Si is ∼2) → δ/δ′+β′-Mg2Si (Mg/Si is ∼3). A good combination of strength and ductility can be obtained in Al-2.5Li-1Cu-2.4Mg-0.8Si alloy after solution and ageing. The rod-like β′-Mg2Si precipitate has a positive influence on the comprehensive mechanical properties of the alloy.

High strength-ductility synergy induced by sub-rapid solidification in twin-roll cast Al–Mg–Si alloys

Regulating the morphology and composition of Fe-containing phases can significantly improve the mechanical properties of Al–Mg–Si alloys. Here, we successfully prepared the high-performance AA6061 alloys by the route of sub-rapid solidification (SRS) based on twin-roll casting (TRC). Excellent tensile strength (∼372 MPa) and elongation (∼19%) were achieved in the peak-aged TRC sample, which increased simultaneously compared with the counterpart (∼351 MPa and ∼14%) fabricated via ingot casting (IC). It was found that the strength-ductility synergy of the TRC sample was caused by the high cooling rate, wherein the SRS can refine the microstructure significantly and promote the reaction from the AlFeSi to the AlFeMgSi (Mg:Fe:Si = 1:1.5:2.5) phase. The centerline segregation in the TRC strip could be well mitigated during solution treatment because the reduced size and Mg-incorporation accelerated the redissolution of AlFeMgSi phases. The alleviative segregation greatly promoted supersaturated solution, and thus contributing to the synergy of strength and ductility. Meanwhile, the Si-rich AlFeMgSi phase could decompose into the Fe-rich α-AlFeSi (Fe:Si > 1) during solution treatment, which expanded the solid solubility of Si and Mg. Therefore, an enhanced aging hardening response was obtained in the peak-aged TRC sample, showing the high number density and volume fraction of β” phase. The results would provide guidelines for developing high-performance Al–Mg–Si alloys based on the SRS during TRC.

Research on high-temperature oxidation resistance, hot forming ability, and microstructure of Al–Si–Cu coating for 22MnB5 steel

Abstract High-temperature oxidation resistance, hot formability, element distribution, and microstructure of Al-10% Si-(0.5–3.0%)Cu coating were investigated by means of glow discharge spectroscopy, optical microscope, scanning electron microscope, and energy-dispersive spectroscopy. Results show that the addition of Cu can increase high-temperature oxidation resistance above 950°C and improve hot formability so that no crack spreads into substrate steel as hot forming at 33.3% strain. Oxidation film structure is continual and compacting, and Si highly concentrates in the surface layer. The distribution of Cu has skin effect with peaking content 8.2% in the surface layer. After hot stamping, Al and Si diffuse into substrate steel, and Cu diffuses from inner to outer coating. Al–Si–Cu coating has smoother surface, straighter diffusion layer, and finer metal compound than Al–Si coating. Surface and diffusion layers are identified as aluminum oxide, Si-rich, and Cu phase and Al7SiFe2, Al3Fe, and CuAl3, respectively. Al-rich phase and the metal compound are composed of α-Al dissolving Fe, Si, and Cu and Al–Si matrix, Cu3Al, respectively.

Laser-induced dynamic wetting behavior and interfacial evolution of AlSi5 alloy on Ti6Al4V alloy

Compared with isothermal wetting, laser-induced wetting behavior exhibited a significant contrast within the spreading mechanism owing to the short thermal cycle and migration driven by the thermal gradient. In this study, laser-induced wetting behavior of AlSi5 alloy on Ti6Al4V substrate was investigated. The process was captured by a self-built dynamic data acquisition device and interfacial microstructure evolution was explored. The mechanism for spreading was evaluated by finite element simulation, spreading dynamic and thermodynamic analysis. The wetting process was controlled by reaction product at the early stage and dominated by adsorption of elements at a later stage. The wettability was promoted with increasing irradiation time until 1.4 s. After prolonged irradiation, IMC composed of TiAl3 phase evolved from granular to rod-shape. Continue to irradiate, multiple Ti-Al phases and Ti5Si3 precipitates were produced. At central zone, Al atoms were more likely adsorbed onto Ti substrate, which facilitated the growth of Ti-Al phases. At front zone, the adsorption rate of Si atoms onto Ti substrates was accelerated and the decomposition of Si-rich phase further promoted the spreading. The elucidated relationship between wetting and microstructure could provide a reliable guide for obtaining relatively good wetting without generating over-thick compounds.

+Effect of niobium on microstructure and properties of 6016 aluminum alloy

6016 aluminum alloys with different niobium contents were prepared by smelting and casting. The alloys were rolled and heat treated, and the effect of niobium on microstructures and properties of the alloys were studied. The results show that the as-cast alloy consists of Mn-rich phases, Cu-rich phases, Mg-rich phases, Si-rich phases and small blocks of Zn-rich phases, and Nb element is solidly dissolved in these phases and matrix. After solution and pre-aging treatment, recrystallization occurs in the rolled alloy. The grain size of the rolled alloy is obviously smaller than that of the as-cast alloy, and the second phase precipitates dispersively. After solution treatment or solution treatment + pre-aging treatment, the tensile strength and plasticity of the alloy are significantly improved. With the increase of niobium content, the number and size of the second phase increase. The alloy with 1%Nb in T4P condition has the better comprehensive mechanical properties, and its elongation after fracture, tensile strength, yield strength, plastic strain ratio and strain hardening index are as following respectively: 34.20%, 372.77MPa, 208.54MPa, 0.82, 0.32.

Effects of torrefaction and water-washing on the mineral transformation behavior during co-combustion of straw and coal: A CCSEM analysis

Biomass can be torrefied to improve the fuel quality prior to its utilization. In addition, a large number of soluble alkali metals can be removed by water washing, to solve slagging and other ash-related problems. In this study, computer-controlled scanning electron microscopy (CCSEM) was used to analyze the mineral composition and elemental distribution of straw, torrefied straw char, and torrefied-water washed straw char. The mineral transformation behavior and the distribution of main elements, when these biomass species were individually co-combusted with coal, were also studied in detail. The comparison of the mineral composition of bulk ash obtained from torrefied straw combustion and straw combustion revealed that the quartz phase decreased and the aluminosilicates of K-, Na-, and Ca–Fe–K increased in the former compared to that in the latter. After the torrefied straw was washed with water, the quartz and Si-Rich phases increased. K aluminosilicate decreased and the quartz phase increased when the torrefied sample was co-combusted with coal at both mixing ratios of 1:1 and 1:4 compared to straw/coal co-combustion. When the torrefied-water washing sample and coal were co-combusted at a 1:1 ratio, the quartz phase decreased, and the Si-Rich and mullite phases increased. When the straw/torrefied char/torrefied-washed char was co-fired with coal at the 1:4 ratio, the amount of K aluminosilicate was less compared to that observed at the 1:1 ratio. It can be concluded that both torrefaction and torrefaction-washing can reduce the content of low-melting-point aluminosilicates in the mineral composition of the studied biomass after co-combustion, which can be beneficial to alleviate the ash slagging problem.