Aluminum Borate Whiskers Research Articles

Novel ceramic supports for catalyst with hierarchical pore structures fabricated via additive manufacturing-direct ink writing

The use of direct ink writing technology, combined with in-situ grown whiskers, has facilitated the development of 3D-printed ceramic catalyst supports-aluminum borate porous ceramics (ABPCs) with hierarchical pore structures. The optimal slurry consists of 0.2 wt% polycarboxylate, 19 wt% water addition, and 1.2 wt% sodium alginate. The most effective printing parameters are determined to be a 1.0 mm nozzle diameter, 10 mm/s printing speed, 4.0 kPa air pressure, and 0.4 mm layer height. After sintering at 1100 ℃, pure-phase aluminum borate (Al18B4O33) ceramics are achieved, leading to the formation of needle-like aluminum borate whiskers. The aspect ratio of whiskers, flexural strength, BET-specific surface area, and photocatalytic activity of ABPCs increase initially and then decrease with increasing sintering temperature. The ABPCs coated with a titanium oxide layer display a photocatalytic degradation rate of 83.92% for methyl orange solution. These results underscore the immense potential of ABPCs in high-temperature catalyst support applications.

Effect of Al4B2O9 and Al18B4O33 whiskers synthesized in situ on the evolution of microstructure and mechanical properties of white fused alumina and Cubitron glass-ceramic composites

The present paper reports on the influence of in situ crystallization of aluminum borate whiskers on the evolution of the microstructure and mechanical properties of electrocorundum (white fused alumina) and microcrystalline alumina (Cubitron 321™) glass-ceramic porous composites. The investigated composites were obtained by sintering the white fused alumina (WFA) and Cubitron 321™ abrasive grains, glass-ceramic bond and various amounts of precursor for whisker growth. The results showed that in the presented technology, the crystallization of the composite reinforcing phases proceeds differently in both types of composites, which affects their microstructure and mechanical properties. An increase in the mechanical tensile strength of 36% was observed for both types of composites; however, depending on the type of abrasive grain, the composites with the highest tensile strength differed in the amount of whisker precursor added. A significant increase in the Young's modulus values was also observed for composites containing 40 wt% precursor: by 45% for WFA and by 52% for Cubitron 321™.

Microstructure characteristics and their effects on fatigue behaviors of the bond zone between Al‐12Si/ABOw composites and Al‐12Si alloys

AbstractIn order to research the fatigue properties of the bond zone between aluminum borate whiskers (ABOw)‐reinforced composites and matrix Al‐12Si alloys, specially designed specimens consisted of Al‐12Si/ABOw composites and Al‐12Si alloys (named C/A specimen for short) were used in fatigue tests at different temperatures. The microstructure evolution of the bond zone of C/A specimen was studied through electronic microscope analysis. The results showed that the aluminum borate whiskers could cause segregation of alloying elements in the Al matrix and formation of numerous microscopic pores. Moreover, whiskers that were perpendicular to the load tended to cause interface between whiskers and Al matrix or Si particles cracking and thus lead to deterioration of fatigue performance. With the change of temperature from 25°C to 350°C, the toughness of Al matrix increased and the strength decreased, which also made the most serious stress concentration site of C/A specimen varied at different temperatures.

Aluminum borate whisker-based lattices with a hierarchical pore structure obtained via digital light processing

To satisfy the ever-increasing demand for aluminum borate porous ceramics with complex shapes and tunable pore structures in a diverse set of fields, aluminum borate whisker-based lattices with hierarchical pore structures were fabricated by a combination of in situ reaction and digital light processing three-dimensional (3D) printing. The optimal dispersant concentration and exposure parameters for 3D printing were determined based on analyses of the rheological properties and working curves of the Al2O3–B2O3 photosensitive slurries. The effects of the B2O3/Al2O3 molar ratio on the morphology and properties of aluminum borate lattices were investigated. The results showed that the addition of an excess of B2O3 was beneficial to the growth of aluminum borate whiskers. When the B2O3/Al2O3 molar ratio was set to 6:9, the resultant aluminum borate lattices exhibited a typical hierarchical pore structure, including inherent large pores in the lattices and small pores formed by interlocked aluminum borate whiskers generated in situ within the struts. This unique hierarchical pore structure endowed the ceramic lattices with a high compressive strength (1.18 MPa) and porosity (82.58%), as well as non-brittle fracture characteristics. Owing to these outstanding properties, aluminum borate whisker-based lattices are promising candidates for high-temperature thermal insulation, catalyst supports, acoustic absorption, and particle filtration.

Antimicrobial properties, cytotoxicity, colour and mechanical behavior of light-cured resin composites containing modified Novaron

Background The NOVARON, a silver-based antimicrobial agent derived from inorganic ion exchangers developed by Toagosei and registered by FDA, has effectively indicated the antimicrobial power of silver against a variety of microbes. The objective of this study was to investigate the effect of a silver-supported material (Novaron (N)) on the mechanical behaviour, antimicrobial properties, cytotoxicity and colour of light-cured resin composites. Methods Silanized aluminum borate whisker (ABWs) (4 wt%) and nano-zirconia (nano-ZrO2) (2 wt%) were mixed with the resin matrix to obtain the control groups; 4 wt% surface-modified Novaron particles were incorporated into the above matrices as the experimental groups. The surface hardness was tested. Furthermore, the antimicrobial abilities evaluated in vitro with Streptococcus mutans (S. mutans), Fusobacterium nucleatum (F. nucleatum) and Candida albicans (C. albicans) using the live/dead, MTT and colony-forming units (CFUs) assay. Furthermore, the effects on fibroblast growth and colour were test in this study. Results The data of the Novaron and control groups were analyzed by Student’s t-test. The results showed that the activities of S. mutans, F. nucleatum and C. albicans biofilms on the composites surface were greatly reduced (p < 0.05) and no significant difference was found in the culture medium (p > 0.05). Extracts taken from the cell culture medium of the specimens were used to evaluate cell viability. The composites did not have an adverse effect on fibroblast growth and colour in this study. The results showed that 4 wt% Novaron incorporated into the resin composites could increase the surface hardness (p < 0.05). Therefore, Novaron is a potential antimicrobial agent applying in light-cured and inorganic nanoparticles reinforced dental resin materials.

Preparation and characterization of aluminum borate whiskers reinforced ceramics with MnO2 addition

AbstractCeramics with aluminum borate whiskers (ABWs) were prepared from H3BO3 and Al2O3 reagent, with and without 6 wt% MnO2 used as an addition. The microstructures, phase composition, and crystal structure of the ceramics were analyzed via scanning electron microscopy, energy dispersive spectroscopy, and X‐ray diffraction, respectively. The results show that MnO2 is an effective addition for enhancing the flexural strength of ceramics. The MnO2 could lead to the distortion of lattice, and improve the mechanical strength via a solid solution strengthening mechanism. Moreover, the content of H3BO3 and the sintering temperature were also key factors in the manufacture of optimal ceramics. The ceramic made from 6 wt% MnO2 addition, 25 wt% H3BO3, and sintered at 1200°C, showed the highest flexural strength of 88.5 (±1.9) MPa, and had a bulk density of 1.64 g/cm3 and porosity of 44.2%.

Interfacial reaction of aluminum borate whisker reinforced Mg-10Gd-3Y-1Zn-0.4Zr (wt%) alloy matrix composite

Magnesium matrix composites usually possess high strength and stiffness as well as low coefficient of thermal expansion, which makes them promising in lightweight and energy-saving strategies. Although the interfacial bonding state has a crucial influence on the properties of magnesium matrix composites, the interfacial reaction mechanism of Mg-RE alloy matrix composites is still unclear. Herein, the interfacial reaction and microstructure of Mg-10Gd-3Y-1Zn-0.4Zr (wt%) alloy matrix composite reinforced with aluminum borate whisker (Al18B4O33w) were reported by heating the matrix to a semisolid region and inducing the interfacial reaction to continue. After heat treatment at 600 °C for 6 h, the thickness of the interface layer increased from 50‐120 nm to about 335 nm, and the main interfacial reaction product was (Mg0.4Al0.6)Al1.8O4. With the increase of heating time to 12 h, a new double interface layer with (Mg0.4Al0.6)Al1.8O4 in the inner layer and MgO in the outer layer was formed. The difference of interfacial reaction products during isothermal heat treatment was related to the concentration gradient of Mg atoms along the radial direction of the whiskers and the hindrance of the migration of Mg atoms by reaction products formed in the early stage. These findings provide a further understanding of the interfacial reaction of Al18B4O33w reinforced Mg-RE alloy matrix composites.

Molten-salt assisted synthesis and characterization of Mg2B2O5 and Al18B4O33 whiskers

ABSTRACT In this work, magnesium borate (Mg2B2O5) and aluminum borate (Al18B4O33) whiskers with a high aspect ratio were successfully synthesized using a molten salt method. The phase transformation and morphology involution of the whiskers were studied by XRD, IR-FT, TG-DSC, and SEM-EDS with different boron/metal ratios and reaction temperatures. The results show a rich boron environment and appropriate reaction temperature to be the crucial factors with respect to the composition and morphology of the borate whiskers. Mg2B2O5 whiskers with a diameter of several hundred nanometers and a 10–60 length–diameter ratio were obtained when the B/Mg ratio was 1.5:1 and the reaction temperature was 800°C. For Al18B4O33 whiskers, a synthesis temperature of 1000°C and a B/Al ratio of 3:9 were found to be optimal with respect to the whisker morphology. A liquid-solid (LS) mechanism is proposed as the growth mechanism of the whiskers on the basis of the experimental phenomena.

High-strength and high-modulus Al18B4O33W/GWZ1031K magnesium matrix composite prepared by squeeze casting

High-strength and high-modulus Mg-10Gd-3Y-1Zn-0.4Zr (GWZ1031K, wt.%) alloy matrix composite reinforced with aluminum borate whiskers (Al18B4O33w) was fabricated by squeeze casting. The microstructure, interfacial characteristics, mechanical properties and fracture behavior of the composite were investigated. The results indicate that the grains of Mg matrix were significantly refined from 29±2 μm to 2 ± 0.5 μm by the randomly distributed whiskers in the composite. For the first time, two adjacent and distinct interfacial reaction layers were found between the whisker and matrix, which resulted from the interfacial reaction and element diffusion. Compared with the matrix alloy and other Al18B4O33w reinforced Mg matrix composites, the tensile strengths at room and high temperatures, Vickers hardness and Young's modulus of the composite were significantly improved. The yield strength (YS), ultimate tensile strength (UTS) and Young's modulus of the material at room temperature reached 364 ± 13 MPa, 380 ± 16 MPa and 77.8 ± 2.1 GPa respectively, realizing the integration of high strength and high modulus. The fracture analysis indicated a mixed fracture mode of macro brittle fracture and micro ductile fracture of the composite.

Lightweight and thermally insulating aluminum borate nanofibrous porous ceramics

Aluminum borate porous ceramics are excellent candidates for high-temperature insulation applications. Current research on aluminum borate-based porous ceramics mainly focuses on porous ceramics made up of aluminum borate whiskers, whose low aspect ratio leads to a relatively dense porous structure; this results in porous ceramics with low porosity and relatively high thermal conductivity. In this study, we report the manufacturing of aluminum borate nanofibrous porous ceramics by an agar-based gel casting method using electrospun nanofibers with a high aspect ratio as the three-dimensional skeleton structure. We explored the effect of the alumina/boron oxide molar ratio on the microscopic morphology and crystal phase composition of the aluminum borate nanofibers and that of the sintering temperature on the micro and macro properties of porous ceramics based on the nanofibers. The results showed that aluminum borate nanofibers with an alumina/boron oxide molar ratio of 7:2 had the densest microscopic morphology, and the corresponding porous ceramics exhibited a higher porosity (91%) and lower thermal conductivity (0.11 W m−1 K−1) after sintering at 1200 °C than aluminum borate porous ceramics with aluminum borate whiskers as the skeleton. The successful synthesis of aluminum borate nanofibrous porous ceramics provides new insights into the development of high-temperature insulators.

Surface synthesis of aluminum borate whiskers on the ZTA ceramics and its application to joining

In this study, aluminum borate whiskers were prepared on the zirconia-toughened alumina (ZTA) substrates for the first time. This result was achieved by calcining a mixture of B2O3 powders with and without adding the MnO2 flux in air. The morphologies of as-prepared whiskers were carefully characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The length-diameter ratio of whiskers prepared by adding MnO2 flux is larger than those prepared by using only B2O3 powders, and the growth mechanisms of whiskers follow solid–liquid–solid theory. In addition, aluminum borate whiskers were successfully used to join ZTA ceramics. By adding the MnO2 flux in the interlayer, the strength of the joints can be significantly improved. The highest flexural strength for the ZTA/whiskers/ZTA joints bonded using B2O3 + 5 wt% MnO2 powders reached 162 ± 11 MPa at 1100 °C after holding for 4 h.

Effect of SiO2 Coating on Microstructure and Mechanical Behavior of Al-ABOw Composite Synthesized by Powder Metallurgy Technique

In this investigation, powder metallurgy route was employed to synthesize SiO2 (5, 10 and 15 vol%) coated aluminium borate whisker (ABOw) reinforced aluminium composites. Commercial pure aluminium powder was used as matrix material and SiO2 coated ABOw was used as reinforcements. M icrostructures of the composites were characterized using scanning electron microscopy and high resolution scanning electron microscopy. Energy dispersive spectroscopy was employed to confirm the weight percentages of elements present in the composites. Transmission electron microscopic analysis was performed to observe morphological changes in the composites. X-ray diffraction analysis was carried out to confirm the phases of developed reinforcement and composites. A universal testing machine was employed for the observation of mechanical properties, viz. flexural strength, Young’s modulus and diametral compressive strength, and it was found that the mechanical strength improved by 50-55% in the case of 10 vol% SiO2 coated Al-ABOw composite. The effect of SiO2 coating on the hardness of fabricated composite was also evaluated and the maximum microhardness value was observed to be 46.2 HV in 10 vol% SiO2 coated composite. Themicrostructural analysis showed that excellent grain refined structures with improved mechanical strength were obtained.

Microstructure, mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

Abstract The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker (ABOw) (5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 °C. The sintered composites were characterized for microstructural features by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al−10wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Experimental study on low‐cycle fatigue behaviours of the specimen consisting of the composites (Al‐12Si/ABOw) and matrix Al‐12Si alloys

AbstractThe low‐cycle fatigue tests of the specimen, which was composed of half composites reinforced by aluminium borate whisker (ABOw) and half unreinforced matrix alloys, were performed under different temperatures. The results showed that the specimen exhibited obvious cyclic hardening at low temperature while increasingly remarkable cyclic softening with the increase of temperature. Meanwhile, the micromorphology of the fracture surface revealed apparent brittle characteristics at low temperature but dominated ductile characteristics at high temperature. The analysis of curves of total strain amplitude versus fatigue life indicated that the dominant fatigue damage mechanism changed from the elastic damage to the plastic damage with the increase of total strain amplitude. In addition, the description of fatigue behaviours based on energy criterion suggested that the capacities of specimen to absorb and dissipate plastic strain energy improved with increasing of temperature but may also be weakened by the strengthening effect of composite part.

Joining Alumina and Sapphire by Growing Aluminium Borate Whiskers In-Situ, and the Whiskers' Orientation Relationship with the Sapphire Substrate.

Bonding between polycrystal alumina and sapphire with (0001), (10 0), (11 0), (1 02) orientations is successfully achieved by growing aluminium borate whiskers in the joint. The morphology of the whiskers in the joint is characterised by (Scanning Electron Microscopy) SEM. The relationship between the growing direction of the aluminium borate whiskers and the orientation of the sapphire substrate is investigated. The effect of the growing direction of the aluminium borate whiskers on the mechanical properties of the joint is discussed. The results show that the whiskers on the sapphire with (10 0) orientation grow perpendicular to the surface of the substrate while the whiskers show a random growth on the other substrates. It is found that there is an orientation relationship between the whiskers (220) and sapphire (10 0) and the morphology of the whiskers has great influence on the mechanical properties of the joint. The joint between polycrystal alumina and sapphire with (10 0) orientation exhibits the highest strength, which reaches 26 MPa.

Growth behavior of aluminum borate whiskers on zirconia toughened alumina (ZTA) particle surface

In this work, B4C-covered zirconia-toughened alumina (ZTA) particles are prepared and oxidised at 1050 °C for different times (0, 2, 4, and 8 h) in air. The X-ray diffraction and electron probe micro-analysis results show that the covering layer is mainly composed of oxide B2O3 intermetallics, residual B4C particles, and Al18B4O33 whiskers. The scanning electron microscopy results show that the growth of Al18B4O33 whiskers on the ZTA particles enhances with increasing heat preservation time; the optimum holding time is determined to be 8 h Al2O3 in the ZTA particles diffuse into the covering layer and combine with B2O3 to form Al18B4O33 whiskers; the Al18B4O33 whiskers grow via the liquid-solid mechanism.

Microstructure and Mechanical Behaviour of ABOw Reinforced Aluminium Matrix Composite Synthesized by Powder Metallurgy route

In present study, the effect of Aluminum borate whiskers (ABOw) content (5, 10 and15 wt.%) on the development of Al-ABOw composite using powder metallurgy route has been investigated. Firstly, Aluminum borate whiskers (ABOw) were produced using sol-gel method. The commercial pure aluminum powder was used as matrix material in this investigation. Amongst, the various casting technology, the powder metallurgy route is most economical and extensively used by researchers. The microstructures of composites were observed using optical microscopy (OM), scanning electron microscopy (SEM). Transmission electron microscopy (TEM) analysis was performed for the observation of ABOw powder morphologies. The XRD analysis was carried out to confirm the phases and peak intensity of developed alloy and composites. The sintering was carried out at 600°C for all samples. After that, the bending test was carried out to calculate flexural strength of alloy and composites. The flexural strength 172±5 MPa was obtained maxima in composite with 10 wt.% ABOw along with improved hardness around 40.2HV. The result shows that, the composite exhibited better interfacial bonds, uniformity in microstructure and optimum flexural strength.

Effect of sintering temperature on microstructure and flexural strength of alumina borate whiskers

Aluminium borate whiskers have been synthesized by hydrolysis route using Alumina (Al2O3) and boric acid (H3BO3). The effect of sintering temperature was studied in the range of 950 to 1400 °C on the formation of microstructures and associated mechanical strength of the synthesized whiskers. The microstructural evolution has been characterized using Differential Thermal Analysis (DTA-TGA), X-ray Diffraction Analysis (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (EDS) and Transmission Electron Microscopy was utilized to ascertain the formation of whiskers. The optimum temperature for whisker formation was found to be 1300 °C and around 1400 °C whiskers are about to lose the microstructure as the formation of glassy phase of Alumina borate start at this temperature. The room temperature and high temperature mechanical properties have been evaluated by cold modulus of rupture (CMOR) and hot modulus of rupture (HMOR) strengths. The results showed that highest HMOR and CMOR values reached 42 and 51 MPa respectively at sintering temperature of 1300 °C.

Microstructural evolution and kinetics analysis of aluminum borate ceramics via solid‐state reaction synthesis

AbstractAluminum borate ceramics (ABCs) with a skeleton structure of rod‐like crystals were established via a solid‐state reaction synthesis. The influence of heat treatment systems on the phase composition and microstructural evolution of an anisotropic grain were firstly studied. Next, the impact of boric acid content on the activation energy of reaction, microstructure, mechanical properties, and neutron shielding capability were investigated. The results demonstrate that orthorhombic Al18B4O33 formed between 900°C and 1000°C which was the stable phase during heating treatment. In addition, increasing the boric acid content was favorable for reducing the activation energy of forming aluminum borate, resulting in increased in situ formation and growth of aluminum borate whiskers in fired samples. Next, mircropores could be generated by the decomposition of boric acid at high temperatures, which had a considerable influence on the physical properties of the sample. Furthermore, the Monte Carlo particle transport program simulation and neutron shielding experiments showed that the prepared ABCs could shield neutron effectively manifested as possessing a high neutron absorption cross‐section in the case of porous materials. Moreover, ABCs have potential application value as thermal insulation material in the nuclear energy field.

3D-printed ceramic structures with in situ grown whiskers for effective oil/water separation

In this work, ceramics 3D printing combined with in situ grown whiskers are proposed for effective oil/water separation in multiple conditions, including (i) free oil/water mixture, (ii) oil purification, and (iii) separation of an oil-in-water emulsion. 3D printing allows the realization of geometrically complex alumina structures, inclusive of honeycomb meshes, sponges, woodpile scaffolds with flexible configuration of inner channels and struts. Aluminum borate whiskers, featured with superhydrophilicity and underwater superoleophobicity, are synthesized on those printed alumina substrates, acting as the pivotally functional coating. These combined structures possess excellent oil/water separation efficiency (over 99%) and high flowrate. The all-ceramic structures also exhibit remarkable durability in cycling tests and resistance to harsh environment, such as organic solvent, elevated temperature and highly corrosive solution, compared with metal/polymer counterparts. Finally, these all-ceramic filters can be quickly restored by high-temperature heat treatment to remove attached oil or water, so that the filters can be reused to avoid waste generation.