Carbon nanofibers prepared by a novel co-extrusion and melt-spinning of phenol formaldehyde-based core/sheath polymer blends

A novel route based on the solvent-free core/sheath melt-spinning of polypropylene/(phenol formaldehyde–polyethylene) [PP/(PF–PE)] to prepare the carbon nanofiber (CNF) has been demonstrated in this study. The approach consists of three main steps: co-extrusion of PP (core) and a polymer blend of PF and PE (sheath), followed by melt-spinning, to form the core/sheath fiber, stabilization of core/sheath fiber to form the carbon fiber precursor, and carbonization of carbon fiber precursor to form the final CNF. Both scanning electron microscopy and transmission electron microscopy images reveal long and winding CNF with diameter 100–600 nm and length greater than 80 μm. With a yield of ~45% based on its raw material PF, the CNF exhibits regularly oriented bundles which curl up to become rolls of wavy long fibers with clean and smooth surface. Results from X-ray diffractometry, Raman spectroscopy, and selected area electron diffraction pattern further reveal that the CNF exhibits a mixed-phase carbon material with graphitic particles embedded homogeneously in an amorphous carbon matrix.     

Effects of aerosol heating rate on the properties of aggregates of lead zirconate titanate nanoparticles produced by spray pyrolysis

The dependence of the shape and size distribution of aggregates of lead zirconate titanate nanoparticles prepared by spray pyrolysis of a sol–gel precursor solution is reported. Decreasing the average heating rate from 300 to 160 °C s⁻¹ in the sub-200 °C section of the reactor decreased the proportion of non-spherical particle aggregates and decreased the maximum size from ~10 to ~5 μm. Microtome sectioning revealed an internal structure composed of <100 nm primary particles. Both solid and hollow particle aggregates were present.     

Effect of short-time thermal oxidation on the surface of Al−Li−Cu−Mg alloy (8090) sheet

The oxidation behaviour of 8090 Al−Li alloy sheet was studied after exposure for short times (<5 min) in laboratory air, moist air, moist argon and hydrogen at 530°C. Oxidation was greater at grain boundaries in hydrogen but not in air. Sites of rapid local oxidation (number density 9 to 8 × 10³ cm⁻²) were associated with insoluble particles. Four types of growth morphology were identified with these sites. Some growths believed to be spinel, were 10 to 25 μm diameter and grew to ≈1 mm in height at 2μm sec⁻¹. Pits beneath these growths were ≈25 μm diameter and 10 to 20 μm deep. A qualitative model is proposed for rapid oxidation in Al−Li alloys and the effect of these sites on weight gain measurements, surface contamination and mechanical properties is discussed.     

Evaluation of hydroxyapatite microspheres made from a borate glass to separate protein mixtures

A hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), transformed from a calcium-containing borate glass, has been investigated for its protein adsorption and chromatographic characteristics. Microspheres of the borate glass were transformed into HA by reacting them with a 0.25 M phosphate (K₂HPO₄) solution for 24 h at 37 °C (pH 9.0). The HA microspheres with a diameter of 45–90 μm were hand packed into a steel column (4.6 mm × 80 mm) and used to separate a binary protein mixture of bovine serum albumin (BSA) and lysozyme. HA microspheres, with a diameter <45 μm, were used for separating a protein mixture of BSA, myoglobin, and lysozyme. These microspheres had a diameter that was 20–30 times larger than commercial HA column packing spherical particles, 2–3 μm, but these microspheres had a six times larger surface area and a more uniform spherical shape. These advantages compensated for their larger size and the separation results were comparable to those commercially available HA columns in the separation of the proteins studied. These unique HA microspheres, made from microspheres of a borate glass, are considered to be useful as packing materials for protein separation in chromatography.     

Silver coated bioactive glass particles for wound healing applications

Bioactive glass particles (0.42SiO₂–0.15CaO–0.23Na₂O–0.20ZnO) of varying size (<90 μm and 425–850 μm) were synthesized and coated with silver (Ag) to produce Ag coated particles (PAg). These were compared against the uncoated analogous particles (Pcon.). Surface area analysis determined that Ag coating of the glass particles resulted in increased the surface area from 2.90 to 9.12 m²/g (90 μm) and 1.09–7.71 m²/g (425–850 μm). Scanning electron microscopy determined that the Ag coating remained at the surface and there was little diffusion through the bulk. Antibacterial (Escherichia coli—13 mm and Staphylococcus epidermidis—12 mm) and antifungal testing (Candida albicans—7.7 mm) determined that small Ag-coated glass particles exhibited the largest inhibition zones compared to uncoated particles. pH analysis determined an overall higher pH consider in the smaller particles, where after 24 h the large uncoated and Ag coated particles were 8.27 and 8.74 respectively, while the smaller uncoated and Ag coated particles attained pH values of 9.63 and 9.35 respectively.     

Grain refinement and mechanical properties enhancement of AZ91E alloy by addition of ceramic particles

Improved mechanical properties and structural uniformity of Mg-based alloys can be achieved by use of grain-refining additives prior to casting. Ceramic particles of α-Al₂O₃ and SiC can serve as such additives to refine the microstructure of Mg–Al-based alloys. However, direct introduction of ceramic particles into Mg matrix is limited by the poor wetting of those particles by liquid Mg and their massive agglomeration. Mg/α-Al₂O₃ and Mg/SiC master alloys were prepared using a method based on the insertion of the ceramic particles into a molten Mg bath through a Mg-nitride layer formed on the surface of the molten bath. The mixture of Mg/ceramic particles was cooled to room temperature under a nitrogen atmosphere. Mg-15%Al₂O₃ and AZ91E + 10%SiC master alloys were obtained. These master alloys were used to refine AZ91E alloys by introducing various amounts of ceramic particles to manufacture AZ91E + 1%Al₂O₃, AZ91E + 1%SiC, and AZ91E + 3%SiC alloys. These were cast using high-pressure die casting and gravity die casting. The alloy AZ91E + 1%Al₂O₃ was grain refined to ~20 μm and the alloys AZ91E + SiC were grain refined to ~50 μm as against 110 μm in non-refined counterparts. The mechanical properties of the modified alloys are substantially better than those of a non-refined AZ91E alloy which is the result of a combination of grain refinement and reinforcement of the matrix by ceramic particles. Alloy AZ91E + 1%Al₂O₃ exhibited the best mechanical properties.     

Foaming behavior of Ti6Al4V particle-added aluminum powder compacts

The foaming behavior of 5 wt.% Ti6Al4V (Ti64) particle (30–200 μm)-added Al powder compacts was investigated in order to assess the particle-addition effects on the foaming behavior. Al compacts without particle addition were also prepared with the same method and foamed. The expansions of Ti64 particle-added compacts were measured to be relatively low at small particle sizes and increased with increasing particle size. At highest particle size range (160–200 μm), particle-added compacts showed expansion behavior similar to that of Al compacts without particle addition, but with lower expansion values. Expansions studies on 30–45 μm size Ti64-added compacts with varying weight percentages showed that the expansion behavior of the compacts became very similar to that of Al compact when the particle content was lower than 2 wt.%. However, Ti64 addition reduced the extent of drainage. Ti64 particles and TiAl₃ particles formed during foaming increased the apparent viscosity of the liquid foam and hence reduced the flow of liquid metal from cell walls to plateau borders. The reduced foamability in the compacts with the smaller size Ti64 addition was attributed to the relatively high viscosities, due to the higher cumulative surface area of the particles and higher rate of TiAl₃ formation between liquid Al and Ti64 particles.     

Hot deformation of ultrafine-grained Al6063/Al2O3 nanocomposites

Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1–1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation activation energy at temperature ranges of T < 300 °C and 300 °C ≤ T < 450 °C was determined to be 74 and 264 kJ mol⁻¹, respectively. This observation indicated a change in the deformation mechanism at around 300 °C. At the higher temperatures, significant deformation softening was observed due to dynamic recrystallization of non-equilibrium grain boundaries. The reinforcement nanoparticles, however, renders the high strength of the material at the elevated temperatures mainly by dislocation pinning.     

Proliferation and function of MC3T3-E1 cells on freeze-cast hydroxyapatite scaffolds with oriented pore architectures

Previous work by the authors showed that hydroxyapatite (HA) scaffolds with different types of oriented microstructures and a unique ‘elastic–plastic’ mechanical response could be prepared by unidirectional freezing of suspensions. The objective of the present work was to evaluate the in vitro cellular response to these freeze-cast HA scaffolds. Unidirectional scaffolds with approximately the same porosity (65–70%) but different pore architectures, described as ‘lamellar’ (pore width = 25 ± 5 μm) and ‘cellular’ (pore diameter = 100 ± 10 μm), were evaluated. Whereas both groups of scaffolds showed excellent ability to support the proliferation of MC3T3-E1 pre-osteoblastic cells on their surfaces, scaffolds with the cellular-type microstructure showed far better ability to support cell proliferation into the pores and cell function. These results indicate that freeze-cast HA scaffolds with the cellular-type microstructure have better potential for bone repair applications.     

Measurement of surface tension and specific heat of Ni-18.8 at.% Si alloy melt by containerless processing

The surface tension and specific heat of superheated and undercooled Ni-18.8 at.% Si alloy melt have been measured by the oscillating drop method and the drop calorimetry technique in combination with electromagnetic levitation, respectively. The surface tension follows a linear relationship with temperature within the range of 1370–2100 K. The surface tension at the melting temperature and the temperature coefficient are determined to be 1.796 N/m and −3.858 × 10⁻⁴ N/m/K, respectively. The specific heat is determined to be 40.80 ± 1.435 J/mol/K over the temperature range 1296–2000 K. The maximum undercooling of 178 K is achieved in the experiments. Based on the measured data of surface tension and specific heat, the viscosity, solute diffusion coefficient, density and thermal diffusivity of liquid Ni-18.8 at.% Si alloy are calculated.     

Continuous high-pressure torsion using wires

A newly developed severe plastic deformation method, continuous high-pressure torsion (CHPT), was modified for continuous processing of metallic wires. In this study, using the CHPT, wires of high-purity aluminum (99.99%) and copper (99.999%) with diameters of 2 mm and total lengths of 100 mm were successfully processed by employing the same features as conventional high-pressure torsion (HPT) technique. The results of hardness measurements, 35 Hv for Al and 116 Hv for Cu, after CHPT at an imposed equivalent strain of ~13 were consistent with those of conventional HPT using disk and ring specimens, as well as with those of CHPT using sheet specimens. Transmission electron microscopy (TEM) demonstrated that the microstructural elements are elongated in the shear direction after CHPT. The average grain size reaches the steady-state level, ~1.3 μm, in Al, but the microstructure is at the non-steady state in Cu with subgrain sizes in the range of 0.3–4 μm.     

Freeze extrusion fabrication of 13–93 bioactive glass scaffolds for bone repair

A solid freeform fabrication technique, freeze extrusion fabrication (FEF), was investigated for the creation of three-dimensional bioactive glass (13–93) scaffolds with pre-designed porosity and pore architecture. An aqueous mixture of bioactive glass particles and polymeric additives with a paste-like consistency was extruded through a narrow nozzle, and deposited layer-by-layer in a cold environment according to a computer-aided design (CAD) file. Following sublimation of the ice in a freeze dryer, the construct was heated according to a controlled schedule to burn out the polymeric additives (below ~500°C), and to densify the glass phase at higher temperature (1 h at 700°C). The sintered scaffolds had a grid-like microstructure of interconnected pores, with a porosity of ~50%, pore width of ~300 μm, and dense glass filaments (struts) with a diameter or width of ~300 μm. The scaffolds showed an elastic response during mechanical testing in compression, with an average compressive strength of 140 MPa and an elastic modulus of 5–6 GPa, comparable to the values for human cortical bone. These bioactive glass scaffolds created by the FEF method could have potential application in the repair of load-bearing bones.     

Hydroxyapatite formation from cuttlefish bones: kinetics

Highly porous hydroxyapatite (Ca₁₀(PO₄)₆·(OH)₂, HA) was prepared through hydrothermal transformation of aragonitic cuttlefish bones (Sepia officinalis L. Adriatic Sea) in the temperature range from 140 to 220°C for 20 min to 48 h. The phase composition of converted hydroxyapatite was examined by quantitative X-ray diffraction (XRD) using Rietveld structure refinement and Fourier transform infrared spectroscopy (FTIR). Johnson–Mehl–Avrami (JMA) approach was used to follow the kinetics and mechanism of transformation. Diffusion controlled one dimensional growth of HA, predominantly along the a-axis, could be defined. FTIR spectroscopy determined B-type substitutions of CO₃ ²⁻ groups. The morphology and microstructure of converted HA was examined by scanning electron microscopy. The general architecture of cuttlefish bones was preserved after hydrothermal treatment and the cuttlefish bones retained its form with the same channel size (~80 × 300 μm). The formation of dandelion-like HA spheres with diameter from 3 to 8 μm were observed on the surface of lamellae, which further transformed into various radially oriented nanoplates and nanorods with an average diameter of about 200–300 nm and an average length of about 8–10 μm.     

Size effect of PLGA spheres on drug loading efficiency and release profiles

Drug delivery systems (DDS) based on poly (lactide-co-glycolide) (PLGA) microspheres and nanospheres have been separately studied in previous works as a means of delivering bioactive compounds over an extended period of time. In the present study, two DDS having different sizes of the PLGA spheres were compared in morphology, drug (dexamethasone) loading efficiency and drug release kinetics in order to investigate their feasibility with regard to production of medical combination devices for orthopedic applications. The loaded PLGA spheres have been produced by the oil-in-water emulsion/solvent evaporation method following two different schemes. Their morphology was assessed by scanning electron microscopy and the drug release was monitored in phosphate buffer saline solution at 37°C for 550 h using high performance liquid chromatography. The synthesis schemes used produced spheres with two different and reproducible size ranges (20 ± 10 and 1.0 ± 0.4 μm) having a smooth outer surface and regular shape. The drug loading efficiency of the 1.0 μm spheres was found to be 11% as compared to just 1% for the 20 μm spheres. Over the 550 h release period, the larger spheres (diameter 20 ± 10 μm) released 90% of the encapsulated dexamethasone in an approximately linear fashion whilst the relatively small spheres (diameter 1.0 ± 0.4 μm) released only 30% of the initially loaded dexamethasone, from which 20% within the first 25 h. The changes observed were mainly attributed to the difference in surface area between the two types of spheres as the surface texture of both systems was visibly similar. As the surface area per unit volume increases in the synthesis mixture, as is the case for the 1.0 μm spheres formulation, the amount of polymer-water interfaces increases allowing more dexamethasone to be encapsulated by the emerging polymer spheres. Similarly, during the release phase, as the surface area per unit volume increases, the rate of inclusion of water into the polymer increases, permitting faster diffusion of dexamethasone.     

A sol–gel-derived α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystal interlayer modified 316L porous stainless steel to support TiO<Subscript>2</Subscript>, SiO<Subscript>2</Subscript>, and TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> hybrid membranes

A homogeneous α-Al₂O₃ crystal membrane was fabricated by the sol–gel technique on 316L porous stainless steel (PSS) substrate with an average pore size of 1.0 μm. The preparation process was optimized by carefully choosing the binder, the concentrations of the casting solutions and the sintering temperatures of the membranes. Compared to methylcellulose and polyethylene glycol 20000, polyvinyl alcohol 1750 was found to be the most effective binder to fabricate a homogeneously structured Al₂O₃ membrane without defects. The concentration to prepare an uniform coverage membrane with a thickness of ~10 μm was 0.032 mol/L. When sintered at 1000 °C, γ-Al₂O₃ membrane with ~3 μm grains was obtained. When sintered at 1200 °C, γ-Al₂O₃ completely transformed into α-Al₂O₃ and the grains grew to ~5 μm. Accordingly, the process was applied to a bigger pore-sized PSS with an average pore size of 1.5 μm to fabricate an α-Al₂O₃ intermediate layer to initially modify its surface. A single α-Al₂O₃ crystal layer with a thickness of ~5 μm and an average pore size of 0.7 μm was achieved. Subsequently, TiO₂, SiO₂, and TiO₂–SiO₂ hybrid membranes were tried on the modified PSS. Defect-free microfiltration membranes with average pore sizes of ~0.3 μm were readily fabricated. The results indicate that the sol–gel method is promising to initially modify the PSS substrates and the sol–gel-derived α-Al₂O₃ crystal layer is an appropriate intermediate layer to modify the PSS and to support smaller grain-sized top membranes.     

Microstructural studies of self-supported (1.5–10 μm) Pd/23 wt%Ag hydrogen separation membranes subjected to different heat treatments

The microstructure of self-supported 1.5–10-μm thick Pd/23 wt%Ag membranes grown by magnetron sputtering have been studied after heat treatment and hydrogen permeation tests using electron microscopy and synchrotron X-ray diffraction. After hydrogen flux stabilization and permeance measurements at 300 °C, the membranes were annealed in air at 300 °C or in N₂/Ar at 300/400/450 °C for 4 days and then tested for hydrogen permeation. The permeation results show that changes in permeability depend on the treatment atmosphere and temperature, as well as membrane thickness. Air treatment at ~300 °C generally induced a positive effect on permeation in the thickness range of 1.5–10 μm. Significant microstructural changes, including grain growth, strain relief, void formation, and growth of nodules occurred in the membranes. The changes in microstructure are more severe for the thinner membranes, and may be attributed mainly to the oxidation processes at or near the surface. For samples annealed in N₂/Ar, enhanced permeation was only obtained with treatment at ~450 °C for 5 and 10 μm. The changes in the microstructure generally increased with heat-treatment temperature, and decreased with membrane's thickness. The membrane with enhanced permeation was accompanied by significant grain growth, strain relief, and surface roughening. For all the membranes, the relative changes in the microstructure were substantially more prominent on the permeate surface than on the feed surface. Details of the analysis are presented and discussed.     

Microstructural heterogeneity in hexagonal close-packed pure Ti processed by high-pressure torsion

Microstructural evolution was studied quantitatively by electron backscattering diffraction in commercial purity Ti processed by high-pressure torsion (HPT) at room temperature. The results show that a heterogeneous microstructure develops during HPT processing with regions of both nanocrystalline grains (<100 nm) and coarse grains (~1–30 μm). Tensile {10[`1] \overline{1} 2} twins were observed in the center of the disk after the first turn of HPT. The microhardness near the disk center increases with increasing HPT turns and the hardness after 5 turns is reasonably homogeneous at radial positions >1 mm. The mechanism of grain refinement is characterized by dynamic recrystallization and the continuous formation of a necklace-like array of fine grains gradually consumes the larger grains in subsequent passes.     

Formation of water-soluble and biocompatible TOPO-capped CdSe quantum dots with efficient photoluminescence

Hollow hydroxyapatite (HA) microspheres (diameter = 100–800 μm) were prepared by reacting solid Li₂O–CaO–B₂O₃ glass spheres in 0.25 M K₂HPO₄ solution at 37°C. The influence of subsequent heating on the microstructure, surface area, and compressive strength of the HA microspheres was evaluated using scanning electron microscopy, the BET method, and nano-mechanical testing. The surface area and rupture strength of the as-prepared microspheres were 135 m²/g and 1.6 ± 0.6 MPa, respectively. On heating for 8 h at 600°C, the surface area decreased to 27 m²/g, but there was no increase in the compressive strength (1.7 ± 0.4 MPa). Heating to 800°C (8 h) resulted in a marked decrease in the surface area (to 2.6 m²/g) and a sharp increase in the compressive strength (to >35 ± 8 MPa). These hollow HA microspheres may be useful as devices for drug or protein growth factor delivery or as scaffolds for engineered tissues.     

Effect of particle size on kinetics crystallization of an iron-rich glass

The effect of glass particle size on the crystallization kinetics of an iron-rich glass from a nickel leaching waste has been investigated by means of differential thermal analysis (DTA). The results show that the crystallization of a pyroxene phase occurs by bulk nucleation from a constant number of nuclei. The crystallization mode and the dimensionality of crystals are strongly dependent on the glass particle size, 100 μm being the critical size. Glass fractions with particle size >100 μm show three-dimensional crystal growth controlled by diffusion, whereas a particle size <100 μm leads to an interface reaction mechanism with two-dimensional growth of crystals.     

Microstructural characterisation of metallurgical grade porous silicon nanosponge particles

Porous silicon finds numerous applications in the areas of bio-technology, drug delivery, energetic materials and catalysis. Recent studies by Vesta Sciences have led to the development of porous silicon nanosponge particles from metallurgical grade silicon powder through their own patented chemical etching process (Irish patent no. IE20060360). This discovery paves the way for a more economical production method for porous silicon. The study presented here studies the structural morphology of the porous silicon nanosponge particles using high resolution electron microscopy techniques combined with porisometry type measurements, where appropriate. The related surface pore structure is examined in detail using Scanning Electron Microscopy and Transmission Electron Microscopy techniques while the internal pore structure is explored using Focused Ion Beam milling and ultramicrotomed cross-sections. Three samples of the silicon particles were analysed for this study which include the starting metallurgical grade silicon powder and two samples that have been chemically etched. Analysis of the etched samples indicates a disordered pore structure with pore diameters ranging up to 15 nm on porous silicon particles ranging up to 5 μm in size. Crystallographic orientation did not appear to affect the surface pore opening diameter. Internal pore data indicated pore depths of up to 1 μm dependant on the particle size and etching conditions applied.