Application of alginate gelation to aqueous tape casting technology

This work deals with a novel forming process for manufacturing ceramic tapes in an aqueous medium, that combines tape casting and gel-casting technologies. Aqueous tape casting suspensions of Al₂O₃ are prepared to a solid loading of 57 vol.% (84 wt.%) by adding 15 wt.% of a binder system consisting of acrylic emulsions and a small concentration (≤0.5 wt.%) of alginate. The as-cast tape is immersed in a CaCl₂ solution and the alginate undergoes gelation. This allows releasing of the tape from the carrier film so that no sticking occurs and crack formation is avoided. Sintered densities are ∼97% of theoretical, similar to those obtained by conventional aqueous tape casting.     

Development of porous ceramic bodies for applications in tissue engineering and drug delivery systems

Hydroxyapatite (OHAp) particles with a specific surface area of 9 m²/g were obtained through a thermal treatment at 900 °C followed by deagglomeration by ball milling in ethanol for 20 h. Slurries with a 50-vol.% solids loading were prepared by mixing the particles with water. Organic inclusions with particles sizes from 55 to 750 μm were added and ceramic bodies were consolidated by slip casting. Dense and porous ceramic bodies were obtained with densities as low as 30% and as high as 94% and pore sizes up to 750 μm. The possibility of manufacturing ceramic bodies with porosity gradients designed according to the features of the porous ceramic bodies was studied in order to adapt them to the severe requirements of tissue engineering scaffolds.     

Formation of TiB2 by volume combustion and mechanochemical process

Titanium diboride was produced both by volume combustion synthesis (VCS) and by mechanochemical synthesis (MCP) through the reaction of TiO₂, B₂O₃ and Mg. VCS products, expected to be composed of TiB₂ and MgO, were found to contain also side products such as Mg₂TiO₄, Mg₃B₂O₆, MgB₂ and TiN. HCl leaching was applied to the reaction products with the objective of removing MgO and the side products. Formation of TiN could be prevented by conducting the VCS under an argon atmosphere. Mg₂TiO₄ did not form when 40% excess Mg was used. Wet ball milling of the products before leaching was found to be effective in removal of Mg₃B₂O₆ during leaching in 1 M HCl. When stoichiometric starting mixtures were used, all of the side products could be removed after wet ball milling in ethanol and leaching in 5 M HCl when pure TiB₂ was obtained with a molar yield of 30%. Pure TiB₂ could also be obtained at a molar yield of 45.6% by hot leaching of VCS products at 75 °C in 5 M HCl, omitting the wet ball milling step. By MCP, products containing only TiB₂ and MgO were obtained after 15 h of ball milling. Leaching in 0.5 M HCl for 3 min was found to be sufficient for elimination of MgO. Molar yield of TiB₂ was 89.6%, much higher than that of VCS. According to scanning electron microscope analyses, the TiB₂ produced had average grain size of 0.27 ± 0.08 μm.     

Fabrication and evaluation of mechanical and tribological properties of boron carbide reinforced aluminum matrix nanocomposites

In this study, fabrication and characterization of bulk Al–B₄C nanocomposites were investigated. B₄C nanoparticles were mixed with pure Al powder by ball milling to produce Al–B₄C powder. Al–B₄C powders containing different amounts of B₄C (5, 10 and 15 wt.%) were subsequently hot pressed to produce bulk nanocomposite samples. Consolidated samples were characterized by hardness, compression and wear tests. Results showed that the sample with 15 wt.% B₄C had the optimum properties. This sample had a value of 164 HV which is significantly higher than 33 HV for pure Al. Also, ultimate compressive strength of the sample was measured to be 485 MPa which is much higher than that for pure Al (130 MPa). The wear resistance of the nanocomposites increased significantly by increasing the B₄C content. Dominant wear mechanisms for Al–B₄C nanocomposites were determined to be formation of mechanical mixed layer on the surface of samples.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.     

A modified synthesis method of manganese perovskite La0.67Ca0.33MnO3 by high energy ball milling and post heat treatment

A modified synthesis method of La_0.67Ca_0.33MnO₃ by high energy ball milling and post sintering is reported. The characteristics of samples from this modified method are also studied. The new synthesis method has some advantages including reducing the synthesis procedure into two simple steps, shortening the sintering time, and obtaining similar properties compared with conventional synthesis method. High energy ball milling was employed for 10 h to refine the starting materials into a sub-micron particle size (for comparison, samples milled for 30 and 50 h were also synthesized); during the process, ethanol was added as a milling medium for avoiding amorphization or crystallization, as well as suspending the starting powders for more profound milling. Finally, the as-milled powder was sintered in air to crystallize. The samples show metal-to-insulator transitions at around 260 K, with grain size from 200 nm to 8 μm, and exhibit large magnetoresistance up to 21% at a magnetic field of 3000 Oe near the transition temperature. The possible mechanism is discussed.     

Microstructure and martensitic transformation in Si-coated TiNi powders prepared by ball milling

Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO₂ occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powders were recovered and Ti₄Ni₄Si₇ was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.     

Influence of different carbon nanotubes on the electrical and mechanical properties of melt mixed poly(ether sulfone)-multi walled carbon nanotube composites

Commercial Udel® poly(ether sulfone) (PSU) was filled with three different commercially available multiwalled carbon nanotubes (MWCNTs) by small scale melt mixing. The MWCNTs were as grown NC 7000 and two of its derivatives prepared by ball milling treatment. One of them was unmodified (NC 3150); the other was amino modified (NC 3152). The main difference beside the reactivity was the reduced aspect ratio of NC 3150 and NC 3152 caused by ball milling process. All PSU/MWCNT composites with similar filler content were prepared under fixed processing conditions and comparative analysis of their electrical and mechanical properties were performed and were correlated with their microstructure, characterized by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A non-uniform MWCNT dispersion was observed in all composites. The MWCNTs were present in form of agglomerates in the size of 10–60 μm whereas the deagglomerated part was homogeneously distributed in the PSU matrix. The differences in the agglomeration states correlate with the variations of properties between different PSU/MWCNT composites. The lowest electrical percolation threshold of 0.25–0.5 wt.% was observed for the shortened non-functionalized MWCNT composites and the highest for amine-modified MWCNT composites (ca. 1.5 wt.%). The tensile behavior of the three composites was only slightly altered with CNT loading as compared to the pure PSU. However, the elongation at break showed a reduction with MWCNT loading and the reduction was least for composite with best MWCNT dispersion.     

Rapid formation of lead magnesium niobate-based ferroelectric ceramics via a high-energy ball milling process

Pyrochlore-free nano-sized 0.90Pb(Mg_1/3Nb_2/3)O₃(PMN)-0.10PbTiO₃(PT) and 0.65PMN-0.35PT powders were synthesized from oxides via a high-energy ball milling process. Single perovskite phase PMN-PT were readily formed from the oxide mixture after milling for only 2 h. The grain size calculated from X-ray diffraction (XRD) patterns of all samples is about 20 nm, which is in agreement with the observation from scanning electron microscopy (SEM) (20-50 nm). PMN-PT ceramics were obtained by sintering the milled powders at temperature from 1000 to 1100°C for 2 h. The dielectric, ferroelectric properties of the PMN-PT ceramics derived from the synthesized powders were comparable with the reported results in the literature.     

Nanocomposites based on MWCNT and styrene–butadiene–styrene block copolymers: Effect of the preparation method on dispersion and polymer–filler interactions

Composites of Kraton-D® 1102 BT (a styrene–butadiene–styrene block copolymer) and multi-walled carbon nanotubes (MWCNTs) were prepared by melt mixing. The composites were characterized by electrical conductivity measurements (Coleman’s method), mechanical properties (DMA and stress–strain tests), thermal stability (thermogravimetry) and morphology of dispersion (SEM). Finally, the resulting composites were compared with those made by the solution casting method. The results showed a strong influence of the preparation methodology on the final properties of the composites due to changes in morphology. Composites prepared by casting showed a higher electrical conductivity than extruded ones; the composites with 6 wt.% of MWCNT prepared by extrusion presented conductivity of the same order of magnitude as the composite with 1 wt.% of MWCNT prepared by casting – 10⁻³ to 10⁻⁴ S cm⁻¹. However, the extruded samples presented better mechanical properties than the casting ones.     

Synthesis and characterization of titanium-45S5 Bioglass nanocomposites

Titanium-45S5 Bioglass nanocomposites were synthesized by the combination of mechanical alloying and powder metallurgy process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vicker’s microhardness as high as 770 HV_0.2 for Ti-20 wt.% 45S5 Bioglass, which is more than three times higher than that of a conventional microcrystalline titanium (225 HV_0.2). Additionally, titanium-10 wt.% of 45S5 Bioglass nanocomposites (i_c = 1.20 × 10⁻⁷ A/cm², E_c = −0.42 V vs. SCE) were more corrosion resistant than microcrystalline titanium (i_c = 2.27 × 10⁻⁶ A/cm², E_c = −0.36 V vs. SCE). In vitro biocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured on the disks of the materials and cell growth was examined. The morphology of the cell cultures obtained on Ti-10 wt.% 45S5 Bioglass nanocomposite was similar to those obtained on the microcrystalline titanium. Mechanical alloying and powder metallurgy process for the fabrication of titanium-45S5 Bioglass nanocomposites with a unique microstructure, higher hardness, lower Young’s modulus and better corrosion resistance, in comparison to microcrystalline titanium, were developed. On the other hand, Ti-10 wt.% 45S5 Bioglass composites posses higher fracture toughness compared to 45S5 Bioglass. The proper modification of chemical composition and microstructure of Ti-bioceramic nanocomposites can expand the use of titanium in the biomedical fields.     

Synthesis of nanocrystalline magnesium aluminate (MgAl2O4) spinel powder by the urea-formaldehyde polymer gel combustion route

Nanocrystalline MgAl₂O₄ spinel powder was synthesized by the urea-formaldehyde (UF) polymer gel combustion route. A transparent gel formed from magnesium nitrate, aluminium nitrate and UF after drying underwet self-sustained combustion when initiated with a burning splinter. The combustion product on calcinations at 850 °C formed MgAl₂O₄ spinel. Calcination of the combustion product resulted in particle coarsening. The powder obtained by planetary ball milling of the spinel had a median particle size of 1.58 μm. The spinel particles are agglomerates of nanocrystallites of size in the range 10-30 nm. The compacts prepared by uni-axial pressing of the spinel powder sintered to >99% TD at 1600 °C.     

Mechanochemical preparation of palladium chalcogenides

Palladium chalcogenides of PdS, Pd₁₇Se₁₅, PdSe₂, PdTe, Pd₃Te₂ and PdSeTe were prepared by milling elemental mixtures, using a planetary-type ball mill at room temperature. These chalcogenides were obtained within 30 min. Pd₁₇Se₁₅ was also obtained when the elemental mixture was immersed in methanol or ethanol at room temperature for 10 days.     

Influence of dry grinding in a ball mill on the length of multiwalled carbon nanotubes and their dispersion and percolation behaviour in melt mixed polycarbonate composites

Ball milling of carbon nanotubes (CNTs) in the dry state is a common way to produce tailored CNT materials for composite applications, especially to adjust nanotube lengths. For Nanocyl^TM NC7000 nanotube material before and after milling for 5 and 10 h the length distributions were quantified using TEM analysis, showing decreases of the mean length to 54% and 35%, respectively. With increasing ball milling time in addition a decrease of agglomerate size and an increase of packing density took place resulting in a worse dispersability in aqueous surfactant solutions. In melt mixed CNT/polycarbonate composites produced using masterbatch dilution step, the electrical properties, the nanotube length distribution after processing, and the nano- and macrodispersion of the nanotubes were studied. The slight increase in the electrical percolation threshold in the melt mixed composites with ball milling time of CNTs can be assigned to lower nanotube lengths as well as the worse dispersability of the ball milled nanotubes. After melt compounding, the mean CNT lengths were shortened to 31%, 50%, and 66% of the initial lengths of NC7000, NC7000-5 h, and NC7000-10 h, respectively.     

Characterization of Se88Te12 nanostructured chalcogenide prepared by ball milling

The present work deals with the structural and optical studies of Se₈₈Te₁₂ chalcogenide nanoparticles prepared by ball milling. Polycrystalline Se₈₈Te₁₂ chalcogenide prepared by melt quenching was used as a starting material. The ball milling was performed in a Laboratory 8000 M-Mixer/Mill (SPEX) mill using hardened steel balls and a vial with a ball-to-powder weight ratio of 10:1. After various times of milling, a small amount of material was taken from the container to be characterized by Transmission Electron Microscopy and optical measurements in thin film form within the wavelength region 400-1000 nm. Optical absorption measurements indicate that the absorption mechanism is due to direct transition. It has been observed that the optical band gap increases with the increase of milling time. The results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level.     

Synthesis of nanocrystalline yttria doped ceria powder by urea-formaldehyde polymer gel auto-combustion process

Nanocrystalline yttria doped ceria powder has been prepared by auto-combustion of a transparent gel formed by heating an aqueous acidic solution containing methylol urea, urea, cerium(III) nitrate and yttrium(III) nitrate. The TGA and DSC studies showed the combustion reaction of the gel initiated at 225 °C and completed within a short period of time. XRD spectrum of the combustion product reveals the formation of phase pure cubic yttria doped ceria during the combustion process. Loose agglomerate of yttria doped ceria particle obtained by the combustion reaction could be easily deagglomerated by planetary ball milling and the powder obtained contains particles in the size range of 0.05-3.3 μm with D₅₀ value of 0.13 μm. The powder particles are aggregate of nanocrystallites with a wide size range of 14-105 nm. Pellets prepared by pressing the yttria doped ceria powder sintered to 95.2% TD at 1400 °C.     

Fabrication of transparent conductive carbon nanotubes/polyurethane-urea composite films by solvent evaporation-induced self-assembly (EISA)

Transparent and conductive carbon nanotubes (CNTs)/polyurethane-urea (PUU) composite films were prepared by solvent evaporation-induced self-assembly (EISA). Pristine CNTs were treated with acids (H₂SO₄/HNO₃ = 3:1, v:v), acylated with thionyl chloride, and purified after filtration. These acylated CNTs (0.05 wt.% in dimethylformamide, DMF) were deposited onto the 3-aminopropyl triethoxysilane (APTES)-modified glass substrate by DMF EISA at 100 °C with the withdrawal rate of 3 cm/h. The CNT layers of 200–400 nm thicknesses were transferred to the PUU films by solution casting or resin transfer molding (RTM) at ambient temperature. Optical transmittances of the composite films were 60–75% at 550 nm wavelength and their sheet resistances were 5.2 × 10⁰–2.4 × 10³ kΩ/square, and which varied significantly with type of CNTs and the transferring methods of CNT layers.     

Preparation, microstructure and properties of reaction-bonded AlN ceramics

AlN ceramics were prepared via a reaction-bonding technique, using Al and AlN powders as the starting materials. The effects of processing parameters and CaO as an additive were investigated. An AlN ceramic sintered at 1800°C with 0.5 wt.% CaO is highly densified and its dielectric constant and dielectric loss tgδ are 9.4 and 0.002 at 1 MHz, respectively. Its electrical resistivity and Vickers hardness are 2.88×10¹² Ω cm, 1210 kg/mm², respectively.     

Effect of Ni addition on formation of amorphous and nanocrystalline phase during mechanical alloying of Al-25 at.%Fe-(5,10) at.%Ni powders

Al-Fe-Ni ternary powder mixtures containing 25 at.%Fe-5 at.%Ni and 25 at.%Fe-10 at.%Ni were mechanically alloyed by a high-energy planetary ball mill. Structural evolution of these powders during milling was investigated by X-ray diffraction technique and transmission electron microscopy. Almost complete amorphous phase in Al₇₀Fe₂₅Ni₅ system is observed at the early milling stage. The amorphous phase transforms into metallic compound Al₅(Fe,Ni)₂ and then the compound changes to ordered Al(Fe,Ni) phase. The last milling products in Al₇₀Fe₂₅Ni₅ system are amorphous phase plus nanocrystalline of the disordered Al(Fe,Ni) phase changed from the ordered Al(Fe,Ni) phase. During milling of Al₆₅Fe₂₅Ni₁₀ system, α-Al and α-Fe solid solutions formed at the early stage change to the ordered Al(Fe,Ni) compound and at last the ordered phase changes to the disordered Al(Fe,Ni) phase. Ten percent of Ni addition promotes retardation of the formation of the amorphous phase.     

Synthesis, low-temperature sintering and the dielectric properties of the ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2)

ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. Fine particle powders were prepared by chemical processing to activate the formation of compound and to improve the sinterability. One wt.% of V₂O₅ and B₂O₃ with the mole ratios of 3:1 were used to lower the sintering temperature of ceramics. The effect of Sn content on phase structure and dielectric properties were investigated. The results show that the substituting Sn for Ti accelerates the hexagonal phase transition to cubic phase, and an inverse spinel structure Zn₂(Ti_1−xSn_x)O₄ solid solution forms. The best dielectric properties obtained at x = 0.12. The ZnO-0.88TiO₂-0.12SnO₂ ceramics sintered at 900 °C exhibit a good dielectric property: ?_r = 29 and tan δ = 9.86 × 10⁻⁵. Due to their good dielectric properties, low firing characteristics, ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) can serve as the promising microwave dielectric capacitor.