Micrometric Powders Research Articles

Nanostructured bulk HPT β Ti-42Nb alloy as biomaterial for implants obtained directly from micrometric powders

The effect of high-pressure torsion (HPT) processing on mechanical properties in a β Ti-42Nb alloy micrometric powder consolidated in a nanostructured bulk disc through severe plastic deformation for biomedical applications is investigated. XRD, SEM and TEM/ASTAR characterization are used to characterize microstructure of the original micrometric powder and the consolidated disc of β Ti-42Nb alloy after HPT. The results show that severe plastic deformation processing improves Vickers hardness of β Ti-42Nb alloy, and leads to a low modulus bulk material with E = 63 GPa after HPT, comparable with that of as-cast alloy. The obtaining of nanostructured grain size around 55 nm bulk β Ti-42Nb alloy consolidated through HPT from micrometric atomized powder opens perspectives of applications as biomedical implants.

Reaction-sintered zircon-based nanostructured coatings obtained by suspension plasma spraying

Zircon (ZrSiO4) is an inexpensive and widely available material with excellent thermal properties that makes it an ideal candidate for thermal barrier coatings. Previous works have demonstrated the feasibility of obtaining coatings with a high retention of zircon by plasma spraying of ZrSiO4 and ZrSiO4/ZrO2 suspensions.Suspensions of ZrSiO4/Al2O3 and ZrSiO4/TiO2 were produced by dispersing a micrometric zircon powder into alumina and titania colloidal sols, optimising their colloidal stability and rheological behaviour. Optimised slurries were plasma sprayed onto metallic substrates, obtaining coatings with the typical morphologies obtained by suspension plasma spraying (SPS). Nanostructured coatings with nanoparticles embedded in the molten matrix were obtained at higher proportions of sprayed colloidal sol. The high retention of ZrSiO4 in the final coatings and the formation of new crystallographic phases of mullite and zirconium titanate by reaction of the by-products of zircon decomposition (SiO2 and ZrO2) and the Al2O3 and TiO2 colloids was demonstrated.

3D printing of shape memory Alloys for complex architectures of smart structures

Shape Memory Alloys (SMA) are materials used to design smart structures with intrinsic functional properties and improved efficiency. This is a key aspect of aerospace industry and makes SMA good candidates in this field. One of the most widespread SMA is the equiatomic NiTi alloy which, however, has the strong limitation of poor machinability, so only simple shapes can be obtained. Additive Manufacturing processes allow to overcome this limit and to design complex shapes. Compared to other metallic materials, the optimization of the process for NiTi alloy is complicated because, beside mechanical properties and presence of defects, considerable attention needs to be dedicated to the material functionality. The high temperatures involved in the additive process significantly affect the material properties due to possible evaporation of Ni and formation of precipitates that enable a shift of the phase transformation temperatures. This paper is focused on the optimization of the process parameters of the NiTi alloy printed through the Laser Powder Bed Fusion (L-PBF) to ensure optimal pseudo-elastic behaviour, which is essential for the design of structural dampers. This was accomplished starting from simple structures and then designing a damper that couples the pseudoelasticity of NiTi with load support capacity.The L-PBF is a powder-bed technique that selectively melts layers of micrometric metal powder. A pseudoelastic NiTi powder with 50.8 at. % of Ni content was selected and characterized through scanning electron microscope (SEM) and observations connected to an Energy Dispersive X-ray Spectroscopy (EDX) probe. After that, some cubic samples were manufactured, with the dimension of 3 × 3 × 15 mm3. A set of different laser powers and scanning speeds were used to find the set of process parameters that optimize the functional properties of the printed parts. Near fully dense specimens with density higher than 99.5 % were selected for further investigations. Differential scanning calorimetry (DSC) and mechanical tests were performed on as-built and heat-treated samples.Quasi-static mechanical tests were accomplished in compression mode, at different strains, up to 8 %. It was observed that the residual strain for cyclic loading at 4 % is lower than 1 %, so good recovery of the deformation was shown. Moreover, numerical analyses that mimic the pseudoelastic behaviour in compression tests were implemented.Finally, the best set of parameters was selected on the basis of the material's ability to recover deformations and its loss factor.

Sintering behavior of 0.95MgTiO3-0.05CaTiO3 ceramics with high densification, high Q and enhanced mechanical properties for 5G massive MIMO technology: Effect of particle gradation

An increase in the requirements for microwave dielectric materials was brought on by the quick growth of communication technologies. In this study, the sintering problems including the narrow sintering densification range and high sintering temperature of 0.95MgTiO3-0.05CaTiO3 (95MCT) ceramics with high densification and high Q, as one of the candidate materials for 5G filters, were discussed and overcome through the particle gradation with sub-micrometric and micrometric powders according to closest packing models. It was found that sub-micrometric (0.7–1 μm) 95MCT powder particles agreed well with the Andreasen model, while micrometric (1–3 μm) particles agreed better with the Dinger-Funk model. With increasing of sub-micrometric powders, the activation energy decreased from 926.01 ± 75.49 to 569.49 ± 31.57 kJ/mol, and the relative density of samples which contained 20–60% fine powders were increased to 98%. The average grain size and grain homogeneity decreased from 7.36 μm to 2.54 μm and 3.36 to 1.79, respectively, to improve the mechanical properties. The results show that the powder grading further improved the comprehensive performance of 95MCT, and the best performance point was J1 which exhibited excellent microwave dielectric properties with εr = 21.1, Qf = 82000 GHz, τf = −0.9 ppm/°C, RD = 98.2%, σf = 178.7 MPa and HV = 8.78 GPa after sintering at 1225 °C for 3h.

Colloidal processing, sintering and properties of aluminum borate Al18B4O33 porous ceramics

Aluminum borate (Al18B4O33) is one of the mixed oxides with extensive applications as due to its good thermomechanical properties. Its application requires of accessible processing techniques to provide controlled microstructures and shapes. This work presents an aqueous colloidal route to manufacture porous aluminum borate ceramics from micrometric Al18B4O33 powder (∼2.0 μm) obtained by high temperature reaction of alumina and boric acid. Zeta potential measurements determine that isoelectric point of the Al18B4O33 powders suspended in water happens at pH = 8.5 achieving a maximum positive value of 60 mV for pH < 4. Rheological characterization of concentrated slurries showed a pseudoplastic flowing behavior with a thixotropic cycle, being the yield point and the thixotropy value strongly dependents on the solid content. Shear thinning curves were fitted to a Windhab model that confirmed a face-edge interactions of the particles in the suspension.Porous ceramic with a green density of 50 % and a narrow micronic (1–2 μm) porosity are obtained by slip-casting of the optimal concentrated suspension (33 vol%). Sintering above the formation temperature showed a decrease in the density of the compacts as a consequence of the acicular grain growth. Four sintering conditions were tested to follow the structural and compositional evolution. It has been observed that thermal treatments up to 1300 °C do not affect the composition but the microstructure. At 1400 °C presence of alumina is detected indicating the initial decomposition of Al18B4O33 and evaporation of boron. At 1500 °C decomposition and evaporation phenomena are massive. The porous compacts sintered below the decomposition temperature are characterized by scanning electron microscopy, mercury intrusion porosimetry and mechanical strength, indicating that at 1300 °C Al18B4O33 achieves the more uniform microstructure and the better mechanical response.It should be noted that for the first time the Zeta potential curve for aluminum borate powder is reported. The processing methodology employed in this study, has potential application to the manufacture of porous materials with insulating applications to replace traditional ceramic materials working in harsh conditions, especially in nuclear energy systems with complex geometry by casting techniques and even by 3D printing.

Ultra-High-Temperature Ceramic-Doped Inorganic Polymers for Thermo-Structural Fiber-Reinforced Composites.

New inorganic nanostructured matrices for fiber-reinforced composites with enhanced high-temperature stability were developed from alkali aluminosilicate polymers doped with different ultra-high-temperature ceramic (UHTC) particles. The alkali aluminosilicate matrices were synthesized at room temperature with a high SiO2:Al2O3 ratio and then further functionalized by doping with 4-5 wt % of micrometric SiC, ZrB2, ZrC, and HfC powders and finally thermally stabilized as glass-ceramics at 750 °C. The different UHTC-doped matrices were characterized according to their dimensional and microstructural changes after thermal cycling in air flux at 1000 °C. The first results showed that carbide-based UHTC powders improved the thermal stability of the matrices, preventing the excessive swelling of the material and the formation of detrimental voids that might result in the lack of adhesion with reinforcing fibers. Contrarily, the addition of ZrB2 resulted in an excessive matrix swelling at high temperature, thus proving no efficacy compared to the undoped matrix. Impregnation tests carried out on C-fiber fabrics showed good processability, adhesion to the fibers, and fracture pull-out, especially for carbide-based matrices.

Microstructure, mechanical and thermal properties of YSZ thermal barrier coatings deposited by axial suspension plasma spraying

Yttrium-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are indispensable elements of present-day turbine propulsion systems. The ones deposited with atmospheric plasma spraying (APS) are characterized by required low thermal conductivity, but they are unable to survive frequent thermomechanical loading and therefore their application is limited to parts remaining stationary. Expanding capability of TBCs is sought in various areas, but the one realized through modification of most proliferated apparatus used for plasma spraying (PS) (from radial to axial injection) and substituting micrometric powders with the nano-structured suspension needs least changes in the industry established procedures and offers the highest property improvement. The present experiment covered the deposition of ZrO2-8Y2O3 YSZ TBC using both atmospheric and suspension PS processes. They were performed with commercial micrometric and nano-structured YSZ (8% Y2O3) powders. The coatings morphology and microstructure were characterized with 3D profilometry, scanning and transmission electron microscopy (SEM/TEM) methods. Finally, the coating’s hardness and heat conductivity were measured. This complex approach allowed to state that PS of micrometric t’-ZrO2 powder having an admixture of m-ZrO2 phase is capable of only partial improvement in its homogenization. However, the suspension PS process of nano-structured powder eliminated any traces of the monoclinic phase from the coating. The TEM microstructure observations indicated that the suspension PS coating is built by in-flight solidified droplets as well as by the melted ones flattened on arrival. A surface layer of liquefied material on solid droplets increases their adhesion to surface asperities promoting pseudo-columnar growth of the coating. The preservation of monotonic slow increase of thermal conductivity during heating of the suspension PS coating means, that its pseudo-columnar microstructure is better suited to withstand high strains during such treatment.

Novel method to investigate plastic flow in micrometer powder particles by integrated experimental and computational approach

Novel method to investigate plastic flow in micrometer powder particles by integrated experimental and computational approach

Mechanical and corrosion characteristics of 6061–T6 aluminum alloy samples reinforced with alumina micro and nanoparticles fabricated by friction stir processing

The present study investigates the mechanical and corrosion properties of reinforced 6061[Formula: see text]T6 aluminum samples after friction stir processing. Three different composites are fabricated: one without any powder and the others with micrometer and nanometer alumina powder (Al2O3) as reinforcing particles. The hardness, tensile, and potentiodynamic polarization tests are performed to compare the new samples with the base metal. The results show that friction stir processing has increased the tensile and ultimate strength of the composites by an average of 181% compared to the base metal which is due to the microstructure changes including grain distribution refinement and the elimination of defects and micro-voids through localized plastic deformation. The strength of the composites with additives is significantly affected by the size of the particles. The hardness of the processed samples has also increased compared to the base metal by 200%. Despite these enhancements, the corrosion resistance of new samples has decreased by 70%, which can be due to the numerous dislocations in the stress-induced stir zone, creating lattice deformations and causing the breakdown of the passive protective layer. The analysis of fracture surface topography through a Fractography method revealed a specific anaglyph consisting of dimples of various shapes, sizes, and dispersion and further confirmed the tensile test results.

Supercritical CO2 Synthesis of Porous Metalloporphyrin Frameworks: Application in Photodynamic Therapy.

A series of porous metalloporphyrin frameworks prepared from the 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) linker and four metal complexes, M(hfac)2 M = Cu(II), Zn(II), Co(II), and Ni(II) (hfac: 1,1,1,5,5,5-hexafluoroacetylacetonate), were obtained using supercritical CO2 (scCO2) as a solvent. All the materials, named generically as [M-TPyP] n , formed porous metal-organic frameworks (MOFs), with surface areas of ∼450 m2 g-1. All MOFs were formed through the coordination of the metal to the exocyclic pyridine moieties in the porphyrin linker. For Cu(II), Zn(II), and Co(II), incomplete metal coordination of the inner pyrrole ring throughout the structure was observed, giving place to MOFs with substitutional defects and leading to a certain level of disorder and limited crystallinity. These samples, prepared using scCO2, were precipitated as nano- to micrometric powders. Separately, a layering technique from a mixture of organic solvents was used to crystallize high-quality crystals of the Co(II) based MOF, obtained with the formula [{Co(hfac)2}2H2TPyP] n . The crystal structure of this MOF was elucidated by single-crystal synchrotron X-ray diffraction. The Zn(II)-based MOF was selected as a potential photodynamic therapy drug in the SKBR-3 tumoral cell line showing outstanding performance. This MOF resulted to be nontoxic, but after 15 min of irradiation at 630 nm, using either 1 or 5 μM concentration of the product, almost 70% of tumor cells died after 72 h.

Friction stir welding of severely plastic deformed aluminum using (Al2O3 + graphite) hybrid powders: grain structure stability and mechanical performance

Welding of severely plastic deformed aluminum sheets, with high stored strain energy, faces a serious concern, which is decrease in strength of weld and heat-affected zone (HAZ) due to instability in microstructure and related grain growth. In this work, two-passes constrained groove pressed (CGPed) Al-1050 sheets were welded via friction stir welding (FSW), without and with addition of a hybrid powder including 50 vol.% α-Al2O3 nanoparticles+50 vol.% graphite micrometric powders (∼1 vol.% of hybrid powders in stir zone). Al2O3 nanoparticles may result in grain refinement in stir zone by grain boundary pinning. Lubricating nature of graphite may reduce welding heat input resulting in lower degree of HAZ softening. Addition of hybrid powders improved thermal stability of grain structure and increased hardness of stir zone and strength of weld after three passes of FSW and at high rotation speed (ω) to traverse speed (v) ratio. With one-pass FSW, a sound weld was not achieved. However, higher weld efficiency (with transition of failure location from stir zone to HAZ) was obtained when three-pass FSW was carried out due to better material flow, superior distribution of powders, and elimination of cavities. Due to presence of graphite, effect of increase in pass number was negligible on HAZ softening. Finer distribution of hybrid powder was achieved at high ω/v ratios. Weld efficiency was improved from ∼50% (strength of 62 MPa) in one-pass FSW at ω/v = 25 r/mm to a maximum of ∼80% (strength of 101 MPa) after conducting three-pass FSW at ω/v = 70 r/mm.

Transforming silicon slag into high‐capacity anode material for lithium‐ion batteries

AbstractThe conception of cheaper and greener electrode materials is critical for lithium (Li)‐ion battery manufacturers. In this study, a by‐product of the carbothermic reduction of SiO2 to Si, containing 65 wt% Si, 31 wt% SiC, and 4 wt% C, is evaluated as raw material for the production of high‐capacity anodes for Li‐ion batteries. After 20 h of high‐energy ball milling, C is fully converted to SiC and a micrometric powder (D50 ∼1 μm) is obtained in which submicrometric SiC inclusions are embedded in a nanocrystalline/amorphous Si matrix. This material is able to maintain a capacity &gt;1000 mAh g−1 (&gt;3 mAh cm−2) over 100 cycles. No crystalline Li15Si4 phase is formed upon cycling as shown from the differential dQ/dV curves. The good mechanical resiliency of the electrode is evidenced by monitoring its morphological changes from sequential focused ion beam scanning electron microscopy analyses. However, a progressive and irreversible increase in the electrode mass and thickness is observed over cycling (reaching 125% and 60% after 200 cycles, respectively), which is mainly attributed to the accumulation of solid electrolyte interphase products in the electrode.

Transforming Silicon Slag into High-Capacity Anode Material for Lithium-Ion Batteries

Silicon is mainly produced by carbothermic reduction of silica. This process generates a by-product called silicon slag, which consists mainly of a mixture of Si, SiC and C. This silicon slag represents considerable energy and material losses. On the other hand, the production of cheaper and more environmentally friendly electrode materials is essential for Li-ion battery manufacturers. In this study, it is demonstrated that this waste containing 65 wt% Si, 31 wt% SiC and 4 wt% C can be valorized as low-cost high-capacity LiB anode material. After 20 h of high-energy ball-milling, C is fully converted to SiC and a micrometric powder is obtained in which submicrometric SiC inclusions are embedded in a nanocrystalline/amorphous Si matrix (Fig. 1a). This material displays a specific discharge capacity ≥1100 mAh g-1 at a current density ≤ 0.9 A g-1 (Fig. 1b) and an areal capacity ≥3.5 mAh cm-2 for at least 100 cycles (Fig. 1c). Moreover, calendering has no negative impact on the electrode performance (Fig 1d). The dQ/dV curves (Fig. 1e) do not shown intense-sharp anodic peak at about 0.45V characteristic of the delithiation of the c-Li15Si4 phase, suggesting that its formation is here prevented. This may be beneficial for the electrode cycle life as the formation of c-Li15Si4 phase is well-known to accentuate the particle cracking. However, a progressive and irreversible increase of the electrode mass and thickness is observed over cycling (reaching 125% and 60% after 200 cycles, respectively) (Fig. 1f), which is mainly attributed to the accumulation of solid electrolyte interphase (SEI) products in the electrode. Figure 1

A Low-Cost and Green Si-Based Anode Material for Lithium-Ion Batteries

The conception of cheaper and greener electrode materials is critical for Li-ion battery manufacturers. In this study, it is shown that a by-product of the carbothermic reduction of SiO2 to Si, containing Si, SiC and C materials, can be valorized as a low-cost and high-capacity anode material for Li-ion batteries after an appropriate high-energy ball milling treatment. The latter results in the production of a micrometric powder (D50 ~1 mm) in which submicrometric SiC inclusions are embedded in a nanocrystalline/amorphous Si matrix. Such a microstructure prevents the deleterious formation of c-Li15Si4 phase, which is well known to accentuate particle cracking. As a result, the electrode is able to maintain a capacity >1000 mAh g-1 (>3 mAh cm-2) over 100 cycles. Moreover, calendering has no negative impact on the electrode performance. However, a significant and irreversible increase of the electrode mass and thickness was observed over cycling, which is mainly attributed to the accumulation of SEI products. In order to have deeper insights into the microstructural evolution of the electrode during cycling, a focused ion beam (FIB) milled microcavity (45×20×50 µm3) was created in the center of the pristine electrode. This cavity was observed by SEM at different cycling periods of a single electrode (Fig. 1a). This investigation method allows following the same electrode along different steps of its cycling, nearly as for an in-situ method. Additionally, backscattered-electron (BSE) imaging was performed on broad ion beam (BIB) polished cross-section of the electrode after different periods of cycling (Fig. 1b). The morphological change is characterized at the electrode and particle scales by monitoring the thickness, mass, porosity and macrocracking of the electrode, SEI layer thickness and particle morphology. On the basis of these investigations, a more comprehensive view of the degradation phenomena of the electrode is established. Figure 1

On the design of a piezoelectric self-sensing smart composite laminate

The structural health monitoring of composite laminates is a rapidly emerging need in structural applications. Different real-time sensors integrated into laminates have been proposed, such as fiber Bragg gratings and piezoceramics. However, their presence negatively affects the mechanical properties of the hosting laminate.This work proposes a non-invasive method for piezoelectric functionalization of composite laminates by interleaving lead zirconate titanate micrometric powder between glass-fiber-reinforced polymer plies. The effects of different powder volume fractions on the electromechanical properties were evaluated in terms of the electrical response and laminate inherent strength. The lead zirconate titanate powder laminates demonstrated an electrical sensitivity value that was up to 439% higher compared with that of the embedded commercial disk laminate (12.4 V/kN versus 2.3 V/kN). Impact tests revealed that the resistance of the interleaved lead zirconate titanate powder laminates is comparable to that of the pristine laminates, whereas a fragile commercial disk leads to delamination. Furthermore, an analytical model was proposed to predict the piezoelectric voltage coefficient g33 as a function of the electrical properties, volumetric powder fractions, and polarization process. The model matched the experimental g33 coefficients (R2=0.97), demonstrating its capability to predict the electromechanical behavior of piezoelectric composites and define their design guidelines.

UV-LED Curable Acrylic Films Containing Phosphate Glass Powder: Effect of the Filler Loading on the Thermal, Optical, Mechanical and Flame Retardant Properties.

In this work, we thoroughly investigate the effects of the incorporation of a phosphate glass micrometric powder on the morphology, as well as on the thermal, optical, mechanical and flame retardant properties of UV-LED curable acrylic films. To this aim, the filler loading was changed within 10 and 50 wt.%. UV-LED initiated curing was selected as a fast and reliable system, as the standard UV-curing process was not suitable because of the presence of the glass powder that decreased the quantum efficiency during the UV exposure, hence preventing the transformation of the liquid system into a solid network. The glass powder slightly increased the glass transition temperature of the acrylic network, hence showing a limited effect on the chain segments mobility; besides, increasing filler loadings were responsible for a progressive decrease of the transparency of films, irrespective of a marginal effect on their refractive index. Conversely, the presence of increasing amounts of phosphate glass improved the thermal and thermo-oxidative stability of the cured products. Besides, phosphate glass was capable of remarkably enhancing the flame retardance of the acrylic network at 50 wt.% loading, which achieved self-extinction in vertical flame spread tests (and was V-0 rated). This formulation, as assessed by forced-combustion tests, also displayed a remarkable decrease of peak of Heat Release Rate and Total Heat Release (by 44 and 33%, respectively) and of Total Smoke Release and Specific Extinction Area (by 53 and 56%, respectively). Further, the filler promoted an increase of the stiffness and surface hardness of the films, at the expense of a decrease in ductility. All these findings may justify the potential use of these composite films as flame retardant coatings for different flammable substrates.

Structural and morphological investigations of barium zirconium titanate particles synthesized by the Pechini method

Abstract Barium zirconium titanate systems are lead-free, environmentally friendly materials exhibiting relaxor behavior with increasing Zr content. Therefore, the study proposed preparing and characterization of an ecologically favorable Pb-free relaxor from Ba(Zr0.5Ti0.5)O3 (BZT). The results reported here are based on the research of BZT micrometric powders prepared by the Pechini method. The phase evolution was monitored by X-ray diffraction from 800 °C to 1300 °C, and results show that the formation of BZT starts around 1050 °C and continues until 1300 °C. The Rietveld refinement of data at 1300 °C confirms that BZT has a cubic structure. The thermal and structural properties of BZT samples were identified by thermogravimetric analysis and Fourier-transform infrared spectroscopy. Scanning electron microscopy results reveal that the synthesized particles are micron-sized (2–2.8 µm), rounded, polygonal-shaped, and agglomerated.

Use of 4D-printing and shape memory alloys to fabricate customized metal jewels with functional properties

PurposeThis paper aims to examine customized NiTi jewels with functional properties fabricated through four-dimensional (4D)-printing.Design/methodology/approachTwo opened rings are fabricated through selective laser melting starting from 55.2Ni-Ti (wt.%) micrometric powder. After the additive process the two rings present the one-way shape memory effect (OWSME). A specific training is accomplished on one of the two printed rings to promote the two-way shape memory effect (TWSME). Both the samples, namely, the rings, respectively, presenting the OWSME and TWSME property, follow a series of post-processing routes to improve the surface finish. Furthermore, a thermal treatment at high temperature is used to create a thin colored oxide layer on the sample surface.FindingsResults show that the change of shape owing to the OWSME and TWSME properties allows the customized 4D-printed rings to be adaptable to environmental changes such as load and temperature variations. This adaptability improves comfort and fit of the jewels.Originality/valueTo the best of the authors’ knowledge, in this work, first cases of additively manufactured NiTi jewels are reported to propose innovative solutions in the design and processing industry of jewels.

Manufacturing of Photoactive β-Bismuth Oxide by Flame Spray Oxidation

Photoactive tetragonal bismuth oxide powder with different semiconducting characteristics was synthesized from Bi-pellets by flame spray oxidation. The effect of feedstock particle size and standoff distance (SOD) on the physical properties of β-Bi2O3 keeping constant the fuel/oxygen ratio is here reported. The flame spray oxidized powder was collected either from evaporated or in-flight particles quenched in water. The combination of flame spray processing parameters led to different β-Bi2O3 phase contents, oxidation characteristics, size distribution (nanometric and micrometric sized), morphology, and optical properties of the sprayed powder. The highest micrometric β-Bi2O3 content quenched in water was obtained at a SOD of 30 cm using a particle size distribution of 12-60 μm of Bi-feedstock. The obtained powder from in-flight particles collected in water allowed us to analyze the oxidation characteristics of bismuth. Micrometric powder shows the synthesis of snowman-like Bi/β-Bi2O3 Janus particles. The nanometric sized Bi2O3 powder was continuously obtained by spray oxidation, where its collection efficiency depends on processing parameters and showed spherical morphology and a highly pure tetragonal phase with narrow visible light absorbance (Eg = 2.26 eV). These optical characteristics indicate that the obtained β-Bi2O3 powder is suitable for high-performance visible-light photocatalyst.

Effect of alloy powder on the properties of ZTA particles reinforced high chromium cast iron composites

Micrometer scale zirconia toughened alumina particles (ZTAp) reinforced high chromium cast iron (HCCI) matrix composites were prepared by the non-pressure infiltration casting process, which solved the poor compounding of micrometer scale ceramic particle preforms under seepage. The effects of the microstructure and the mechanical properties of ZTAp reinforced HCCI matrix composites by micro-powder contents in the preforms were systematically investigated. Alloy powder content of 65 wt.%, 55 wt.%, 45 wt.%, 35 wt.% and 25 wt.% was added to the composite material respectively. Phases of the composites was identified by optical microscope (OM), energy dispersive spectrometer (EDS) and x-ray diffraction (XRD). The best compressive properties of the composites were obtained when the content of alloy powder at 45 wt.%, which the strain reached 6.32% with a stress of 1229.63 ± 39.05 MPa. The fracture mechanism of the ZTAp reinforced HCCI composites mainly was brittle fracture and the ductile fracture was minor. This study shows that the addition of micrometer powder was contributed to improve the organization and properties of the ZTAp reinforced HCCI matrix composites. The reinforcement mechanism of composites not only depends on the load sharing of the reinforcing particles, the strength of the matrix was also critical.