Al2O3-ZrO2 microspheres were prepared by internal gelation method. The effects of Al3+ on the stability of solution and performance of gel spheres were studied. Al3+ had a great influence on the stability of the solutions, and the more of the amount of Al3+, the shorter of the stabilization time. Because Al3+ did not copolymerize with Zr4+ during the sol-gel transformation, the strength of gel sphere added with Al3+ was low and deformed easily as it was squeezed. The results of our experiments well verify Glasser team’s speculation and conclusions. At the same time, based on the experimental results, we prepared Al2O3-ZrO2 composite microspheres with higher content of Al2O3 by controlling the pH of the solution. The change curve of viscosity with time and the stabilization time of the solution with different Al3+ dosage were given, which could provide references for industrial mass production. Samples without hydrothermal treatment cracked severely, while the samples hydrothermally treated kept structural integrity with no cracks after calcined. Al2O3-ZrO2 microspheres with no segregation and phase separation were prepared and alumina evenly distributed in the zirconia matrix. When the content of Al2O3 was low, the tetragonal phase was stable. And the cubic phase was obtained when the content of Al2O3 was more.
A series of tests were performed to investigate the macroscopic properties and the stabilization mechanism of calcium lignosulphonate modified expansive soil. Compared with natural soil, soil modified by 4% calcium lignosulphonate showed 56.5% increased 28 days unconfined compressive strength and 23.8% decreased free expansion rate. The X-ray diffraction analysis results indicate the existence of cation exchange and the reduction of montmorillonite interplanar spacing. The X-computed tomography results demonstrate that calcium lignosulphonate decreased the porosity and optimized the pore distribution. The calcium lignosulphonate also increased the stability of the suspension system according to the Zeta potential results. Moreover, the results of rheological tests show that the moderate amount of calcium lignosulphonate enhanced the yield stress and the plastic viscosity, proving the formation of a strong connection between soil particles.
The sulfur-containing activated carbons (SACs) were prepared by CO2 activation and sulfur impregnation. The sulfur-containing samples were then oxidized in air. The SACs were characterized by N2 adsorption, elemental analysis, thermogravimetric analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. The CO2 activation provided precursor carbons with high porosity, which in turn were sulfurized effectively. Oxidation in air at 200 °C enlarged pores and redistributed amorphous sulfur in the hierarchical pores. A typical SAC containing 17.89% sulfur exhibited a surface area of 1 464 m2/g. This work may open up a valid route to prepare highly microporous SACs with high sulfur loading for applications where the presence of sulfur is beneficial.
We used density functional theory (DFT) calculations to study the influence of alkali earth metal element (AE) doping on the crystal structure and electronic band structure of α-Si3N4. The diversity of atomic radii of alkaline earth metal elements results in structural expansion when they were doped into the α-Si3N4 lattice. Formation energies of the doped structures indicate that dopants prefer to occupy the interstitial site under the nitrogen-deficient environment, while substitute Si under the nitrogen-rich environment, which provides a guide to synthesizing α-Si3N4 with different doping types by controlling nitrogen conditions. For electronic structures, energy levels of the dopants appear in the bottom of the conduction band or the top of the valence band or the forbidden band, which reduces the bandgap of α-Si3N4.
The phosphogypsum particles coated with organic emulsion were prepared by coating three kinds of organic emulsion of silicone-acrylic, styrene-acrylic and acrylic. The structure and mineralogical characteristics, acid and alkali resistance, water resistance and dissociation degree of coated phosphogypsum were studied by means of SEM-EDAX, optical microscope, gravimetric analysis and chemical detection. The results showed that the initial emulsion can be used directly for coating and granulation of phosphogypsum. The spray re-coating was carried out by using diluted emulsion with the water-to-emulsion mass ratio of 1:1. The organic emulsion coated phosphogypsum crystal can be clearly observed, and the mixing zone at internal boundary between the organic emulsion and phosphogypsum crystal was distinguishable under the optical microscope. SEM photos showed that the surface of coated phosphogypsum particles was smooth. And the basic elements of C, O, S and Ca can be detected by EDAX. Organic emulsion can be solidified into filmnetwork between the phosphogypsum crystals inside of the coated particles, and it can play a protective role in improving the acid resistance, alkali resistance and water resistance of phosphogypsum, and reduce the degree of dissociation of phosphogypsum in water.
Vanadium films were deposited on Si(100) substrates at room temperature by direct current (DC) magnetron sputtering. The microstructure and surface morphology were studied using scanning electron microscopy (SEM) and atomic force microscope (AFM). The oxidation resistance of films in air was studied using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that the amorphous vanadium film with a flatter surface had higher oxidation resistance than the crystalline film when exposed to atmosphere. The rapid formation of the thin oxide layer of amorphous vanadium film could protect the film from sustained oxidation, and the relative reasons were discussed.
The SrCO3/AgI photocatalysts were prepared via a co-precipitation method by using SrCO3 as a co-photocatalyst and AgI as a photo sensitizer. X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectrometer, UV-vis diffuse reflectance spectroscopy and electrochemical impedance spectroscope were used to analyze the structure, micro-morphology, chemical compositions, optical properties and photo-generated carrier behaviors of the as-prepared samples, respectively. The photocatalytic degradation mechanism of the as-developed composites was also proposed. Analysis results show SrCO3, an insulator, can improve the photocatalytic performances and recyclability of AgI for degrading tetracycline under visible light. As the theoretical molar ratio of Sr(NO3)2 to AgNO3 increases, the degradation efficiency of the hybrids first increases and then descends. When the theoretical molar ratio of that is 1: 1, it acquires the maximum of 66.6% within 8 min. This is higher than 32.0% of pure AgI and 34.0% of SrCO3. Moreover, after three times degradations it is 63.0%, which is higher than 13.6% of AgI. The improvement of the photocatalytic performance of the sample is attributed to the construction of hybrids. The main activated species in catalysis process are superoxide radicals.
On parabolic flights, the growth of ettringite, [Ca3Al(OH)6·12H2O]2·(SO4)3·2H2O, a major reaction product of cement with water which forms instantaneously, was crystallized under microgravity conditions and studied. In the experiments, Ca(OH)2/Al2(SO4)3 solutions were combined and reacted for 10 s, followed by immediate filtration of the suspension and subsequent quenching with acetone. For the ettringite crystals, the size, aspect ratios, quantity and morphology were determined and the results were compared with those from identical experiments performed under terrestric gravity. Under microgravity, generally smaller crystals (l–2.9 µm) precipitated in larger amount than under normal gravity (1–3.5 µm). The aspect ratios of the crystals grown under terrestric or microgravity condition were comparable at about 5.6. It is assumed that the reason for the smaller ettringite crystals is the absence of convection leading to more initial nuclei, but slower crystal growth which is diffusion limited. Apparently, no preference relative to the ion transport to the different faces of the crystals exists. The results contribute to the understanding of the mineralization of inorganic salts under microgravity conditions for which hitherto only a handful of examples were reported.
Ultra-high performance cement-based composites (UHPCC) is promising in construction of concrete structures that suffer impact and explosive loads. In this study, a reference UHPCC mixture with no fiber reinforcement and four mixtures with a single type of fiber reinforcement or hybrid fiber reinforcements of straight smooth and end hook type of steel fibers were prepared. Split Hopkinson pressure bar (SHPB) was performed to investigate the dynamic compression behavior of UHPCC and X-CT test and 3D reconstruction technology were used to indicate the failure process of UHPCC under impact loading. Results show that UHPCC with 1% straight smooth fiber and 2% end hook fiber reinforcements demonstrated the best static and dynamic mechanical properties. When the hybrid steel fiber reinforcements are added in the concrete, it may need more impact energy to break the matrix and to pull out the fiber reinforcements, thus, the mixture with hybrid steel fiber reinforcements demonstrates excellent dynamic compressive performance.
Cement-based materials (CBMs), such as paste, mortar and concrete, are highly alkaline with an initial high pH of approximately 12.0 to 13.8. CBMs have a high pH due to the existing oxide mineral portlandite and alkali metal contents in Portland cement. The high pH of concrete provides excellent protection and reinforces the steel bars against corrosion. The pH of concrete does not remain constant due to ageing and other defect-causing factors, such as chloride ingress, alkali leaching, carbonation, corrosion, acid attack, moisture and biodegradation process. Reducing the concrete pH has negative impact on the strength, durability and service life of concrete buildings. However, the high pH of concrete may also cause concrete structure deterioration, such as alkali silica reaction, porosity and moisture related damages in concrete structures. The pH of CBMs can be influenced by high temperatures. For instance, the extremely high volume (85%–100%) of slag-blended cement pastes shows considerable pH reduction from 12.80 to 11.34 at 800 °C. As many concrete structure deterioration are related to concrete pH, using an accurate and reliable method to measure pH and analyse the durability of reinforced concrete structure based on pH values is extremely important. This study is a comprehensive review of the pH of CBM in terms of measurement, limitations and varying values for different CBM types.
The early hydration of calcium aluminate cement (CAC) with different kinds of zinc (II), such as ZnSO4·7H2O, ZnO, Zn(NO3)2·6H2O and ZnCl2, was analyzed. Changes in consistency, setting time, hydration heat flow, hydration heat amount, ion concentration in solution, and hydration products were found upon the addition of different Zn2+. The water consumption of standard consistency of CAC is decreased with different Zn2+. Zn2+ can delay the initial hydration of CAC. The induction period of cement with Zn2+ is longer than that of CAC, especially the reaction time of the acceleration period is extended. Zn2+ can promote hydration hydrate of CAC at 24 h. The characteristic diffraction peaks of CA and CA2 in CAC with different Zn2+ are significantly reduced. It can inhibit the formation of CAH10 and promote the formation C3AH6 and AH3 in hydration products at 24 h.
The gas tungsten arc welding based additive manufacturing (GTAW-AM) was carried out by printing 316L austenitic stainless steel on carbon steel substrate with different arc currents (140, 160, 180 A). Microstructure and corrosion resistance of additive manufactured components were investigated. The results show that the microstructure of the GTAW-AM austenitic stainless steel is obviously changed by the arc current. With arc current increasing from 140 to 180 A, the austenite grains become coarse due to the effect of welding heat input. Meanwhile, the quantity of ferrites in the austenite matrix is decreased and the morphology transforms from lath to skeleton. Moreover, a phases are finally formed under the arc currents of 180 A owing to high welding heat input. Therefore, as the microstructure transform into coarse-grained austenites, low-quantity ferrites and new-generated a phases, the GTAW-AM austenitic stainless steel presents a significantly decrease in corrosion resistance. And the reduction of corrosion resistance is mainly due to the formation of a phase as a result from consuming the large amounts of Cr element from the matrix.
Aluminum alloy 6061 was welded with zinc coated low carbon steel by cold metal transfer (CMT). The microstructure composition, morphology and growth process of the welding joint and the HAZ were researched. The weld area on the side of the galvanized steel sheet mainly contains Fe2Al5. And on the side of the aluminum alloy substrate, it is mainly filled with a needle-like FeAl3. At the same time, Al8Fe2Si is formed at the edge of FeAl3. The zinc-rich region on the side of the aluminum alloy mainly contains an aluminum-zinc solid solution and an aluminum-zinc co-crystal, and the current size had no significant effect on the type and morphology of the compounds produced in the interface layer.
The hot deformation behavior of an ultralow-carbon microalloyed steel was investigated using an MMS-200 thermal simulation test machine in a temperature range of 1 073–1 373 K and strain rate range of 0.01–10 s−1. The results show that the flow stress decreases with increasing deformation temperature or decreasing strain rate. The strain-compensated constitutive model based on the Arrhenius equation for this steel was established using the true stress-strain data obtained from a hot compression test. Furthermore, a new constitutive model based on the Z-parameter was proposed for this steel. The predictive ability of two constitutive models was compared with statistical measures. The results indicate the new constitutive model based on the Z-parameter can more accurately predict the flow stress of an ultralow-carbon microalloyed steel during hot deformation. The dynamic recrystallization (DRX) nucleation mechanism at different deformation temperatures was observed and analyzed by transmission electron microscopy (TEM), and strain-induced grain boundary migration was observed at 1 373 K/0.01 s−1.
Aluminum alloy plates were explosively cladded to stainless steel plates with trapezoidal grooves on the mating surface. The process parameters viz, loading ratio, standoff distance and flyer plate thickness were varied based on the Taguchi analogy. The variation in the process parameters alters the kinetic energy dissipation and the deformation work performed at the interface, and dictates the interfacial wave amplitude and the mechanical strength of the dissimilar explosive clad. The optimum level of process parameters for attaining higher tensile and shear strength is computed by signal-to-noise ratio. Further, a mathematical model is developed for calculating tensile and shear strength of the clad, based on the regression analysis using statistical software Minitab-16, and the level of fit is determined by analysis of variance.
This paper aims to develop a surface modification process to improve the surface properties of the middle trough. The coatings were prepared by plasma cladding with Fe-Cr-B-Si-based alloy powders (Ig 6 and Ig7). The organizational structure and micro-hardness of the coatings were analyzed by laboratory equipments. The friction and wear tests were performed to investigate the friction-wear properties of middle trough. The coatings have higher hardness and good friction-wear properties than the substrate. The hardness and friction wear properties of the coating with Ig7 powder are better than those with Ig6 powder. The experimental results show that the surface properties of the middle trough are improved by Fe-Cr-B-Si-based alloy coating, which can improve the middle trough service life. The plasma cladding can be widely used in the surface-modification of middle trough to reduce the waste of resources.
In order to optimize the tool coating material and reduce the tool wear rate, the coating material and wear mechanism for carbide tools are proposed and analyzed based on thermodynamics theory. We deduced the Gibbs free energy function method and analyzed the enthalpy value of the coating material of cemented carbide tools. The rules of diffusion wear and oxidation wear for WC-Co-based carbide tools were analyzed based on the diffusion dissolution theory and the calculation method of the thermal effect of chemical reaction. The diffusion wear and oxidation wear of WC-Co-based carbide tools when machining Ti-6Al-4V were studied with SEM-EDS. The results indicate that a good prediction accuracy of both diffusion wear and oxidation wear can be achieved by the method of thermodynamic theory analysis method. The conclusion will provide useful references for the optimization of cutting parameters and the improvement of the tool life.
In order to restrain the carbon pollution, the feasibility of CaZrO3 coating was studied. The precursor powder was synthesized via solid-state reaction using metal calcium as a raw material. The protective coating on graphite was prepared by impregnation sintering method, and the effects of slurry viscosity, graphite density and coating thickness for coating were compared. The phase composition and microstructure of coatings were characterized, and the thermodynamic process was analyzed when the coating composition changed from CaZrO3 to ZrC. The results show that vacuum sintering can result in the decomposition of CaZrO3 and an intact ZrC coating with beautiful porous structure can be obtained.
The microstructure, localized corrosion (LC) and stress corrosion cracking (SCC) behavior of 7003 aluminum alloy (AA7003) under various aging treatments (peak aging (PA), double peak aging (DPA), regression and re-aging (RRA)) were investigated by means of transmission electron microscope (TEM), scanning electron microscopy (SEM), electrochemical impendence spectroscopy (EIS) and slow strain rate tensile test. The results of TEM showed a discontinuous distribution of grain boundary precipitates of AA7003 under DPA and RRA treatments, which is beneficial for increasing the resistance of LC and SCC. Meanwhile, LC was found initiating firstly on intermetallics which caused the dissolution of surrounding matrix, then pitting holes were formed and developed into matrix. In addition, the SCC process of AA7003 could be divided into two stages, i e, initial pre-cracking and breeding cracking. The EIS analysis, cross-section morphologies and fracture surfaces of specimens indicated that DPA and RRA treatments significantly decreased the crack growth rate during breeding cracking stage, especially for RRA treatment.
Re-swelling capacity is a key factor influencing the self-sealing efficiency of superabsorbent polymers (SAPs) in concrete. In this paper, a new parameter (re-swelling ratio, η), the volume ratio of the crack which was filled with the expansive SAPs and the dry SAPs, was given to quantify the re-swelling capacity of a single SAPs particle. An innovative immersion test was used to study the η value of SAPs in the hardened cement paste with an artificial crack. Moreover, the influence of the crack width and particle size on the sealing efficiency of SAPs in the cracked paste was investigated by a water permeability test. The results showed that the mass ratios of the expansive SAPs in an artificial crack were less than those in a free state. The η value of SAPs in the hardened paste with an artificial crack increased with the increase of the crack width due to the restricting effects of the crack. The expansive SAPs in the cracked paste could totally seal or partly seal the crack within the original void. Moreover, the sealing efficiency of SAPs slightly increased with the rise of the crack width (0.25 to 0.5 mm) and the reduction of the particle size. This research demonstrates that the crack width in concrete and the particle size of SAPs are the key factors influencing the re-swelling behavior of SAPs which should be taken into consideration when designing the self-sealing concrete containing SAPs.
Split Hopkinson pressure bar (SHPB) has been used to study the dynamic failure pattern of flattened mortar Brazilian disc under impact load. Each disc contains several prefabricated cracks paralleled to each other. Dynamic FEM has also been adopted to simulate such failure behavior. The mechanism of crack initiation, propagation and cut-through have been scrutinized with both experimental and numerical approaches. Influence of the number of the prefabricated cracks on the specimen strength and acoustic emission (AE) performance can be observed and studied. The results show that the strength decreases and AE counts increases, when the number of the prefabricated cracks increases.