Carbonization of PAN grafted uniform crosslinked polystyrene microspheres

Micrometer-sized polystyrene/poly(styrene-divinylbenzene) and polystyrene/polydivinylbenzene composite particles of narrow size distribution were formed by a single-step swelling process of uniform polystyrene template particles with emulsion droplets of dibutyl phthalate containing benzoyl peroxide and divinylbenzene in the presence or absence of styrene, followed by polymerization of the monomer(s) within the swollen template particles at 70 °C. Porous poly(styrene-divinylbenzene) and polydivinylbenzene uniform microspheres were formed by dissolution of the polystyrene part of the former composite particles. Hydroperoxide conjugated microspheres were formed by ozonolysis of the former porous microspheres. Uniform poly(styrene-divinylbenzene)/PAN and polydivinylbenzene/PAN core/shell microspheres were prepared by room temperature redox graft polymerization of AN onto the hydroperoxide conjugated particles. Uniform carbon microspheres were prepared by carbonization of the core/shell particles at 800 and 1100 °C under dynamic N₂ atmosphere. On the other hand, a similar treatment of the core particles only resulted in destruction of the particle shape. Carbon microspheres of increasing surface area (up to ca. 1000 m²/g) were prepared by activation of the former carbon microspheres with CO₂ at 850 °C. The influence of the carbonization temperature of the core/shell particles and the activation time of the carbon particles on the carbon yield and surface area has been elucidated.     

Synthesis of silicate glass/poly(l-lactide) composite scaffolds by freeze-extraction technique: Characterization and in vitro bioactivity evaluation

The main objectives of the present study were to fabricate the silicate glass/poly(l-lactide) composite scaffolds for bone engineering applications, by using the freeze-extraction technique, and to evaluate the possibility for optimizing their degradation rate by changing their glass content. The scaffolds characterized by SEM-EDXA, FT-IR, TGA and XRD. Examination of the SEM microphotographs revealed that the pore size of the scaffolds decreased as the glass content increased. The neat polymer scaffold (PLA) had a highly interconnected porous structure with a maximum pore size of 200 μm. For the composite scaffold containing glass content up to 25 wt% (SP25) and up to 50 wt% (SP50), the maximum pore size was 40 μm and 20 μm respectively. The apparent porosity was 56.56%, 52.49% and 48.74% for PLA, SP25 and SP50, respectively. The results of the degradation study showed that the water absorption of the scaffolds decreased by increasing their glass content, It reached finally to 48.71%and 30.93% for SP25 and SP50, respectively. It revealed that also the weight loss of the scaffolds increased by increasing the glass content. The final weight loss was around 5.44%, 9.31% and 26.17% for the PLA, SP25 and SP50, respectively, indicating that it was possible to modulate the degradation rate of the scaffolds by varying their glass content. In addition, the pH measurement of incubation medium indicated that the glass could compensate the acidic degradation products of the polymer. In vitro bioactivity evaluation showed that the composite scaffolds were able to induce the formation of hydroxyapaptite layer on their surfaces, demonstrating their potential application in bone engineering.     

Controlled fabrication of nanosized TiO2 hollow sphere particles via acid catalytic hydrolysis/hydrothermal treatment

TiO₂ hollow spheres of controlled size were synthesized by combined acid catalytic hydrolysis and hydrothermal treatment, which involves the deposition of an inorganic coating of TiO₂ on the surface of carbon spheres prepared by a hydrothermal method and subsequent removal of the carbon spheres by calcination in air. The obtained TiO₂ hollow spheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and powder X-ray diffraction. The results revealed that the size and surface morphology of the TiO₂ hollow spheres can be controlled by adjusting the concentration of the aqueous solution of glucose used to produce the template carbon spheres. Increasing the concentration of the glucose solution increased the average diameter of the TiO₂ hollow spheres from 190 to 300 nm. TiO₂ hollow spheres prepared using a glucose solution with a concentration of 0.7 mol/L are uniform in size with a diameter of 220 nm and shell thickness of 28 nm. The phenol removal rate of the sample prepared by calcination at 600 °C is 1.35 times higher than that of TiO₂ made by the same method without using the carbon template.     

Joining of mullite ceramics with yttrium aluminosilicate glass interlayers

Pellets of yttrium aluminosilicate glass (Y₂O₃:Al₂O₃:SiO₂ = 30:20:50 mol%) powder were used as the filler interlayers (0.4 mm thick) to join two mullite substrates. The glass interlayer partially melted at joining temperature to bond the substrates and then crystallized during cooling to have better bonding strength. The results showed that joining could be performed at 1390–1420 °C for 1–5 h with applied pressure of 0.02 MPa. After joining, the thickness of glass layers varied between 250 μm and 80 μm, depending upon the temperatures. The glass interlayer crystallized into cristobalite, mullite and Y₂Si₂O₇. When joining mullite/3 mol%yttria–zirconia substrates using the same glass pellet, a layer of zircon/mullite was formed at the interface, indicating that reaction occurred between glass and substrates. The formation of zircon usually accompanied with cracks in the substrates. These cracks deteriorated the strength. The achievable three-point bending strengths were 139 MPa for joined mullite and 76 MPa for joined mullite/3 mol%yttria–zirconia.     

Synthesis of monodisperse porous poly(divinylbenzene) microspheres by distillation-precipitation polymerization

Highly crosslinked monodisperse porous poly(divinylbenzene) (PDVB) microspheres were prepared by distillation-precipitation polymerization in acetonitrile containing up to 25 vol% of toluene as porogen with 2,2′-azobisisobutyronitrile (AIBN) as initiator in the absence of any stabilizer or surfactant. The porous polymer microspheres were formed through a precipitation manner during the distillation of the solvent from the reaction system. Monodisperse porous polymer particles with spherical shape and smooth surface were synthesized with diameters in the range of 1.86 and 3.06 μm, total porosity of up to 0.30 cm³/g and specific surface area as high as 762 m²/g. The growth procedure of porous PDVB microsphere was characterized by SEM technique for morphological observation and isotherm nitrogen adsorption for the determination of the special surface area and porosity. The resultant porous polymer microspheres had a novel structure with the gradual increasing of pore volume during distillation of the solvent out of the reaction system.     

Effect of heat treatment on 7Na2O-23B2O3-70SiO2 glass

Porous 7Na₂O-23B₂O₃-70SiO₂ glass was successfully fabricated by acid leaching treatment and phase-separation. The 2 mol/l hydrochloric acid (HCl) solution treatment was used for 24 h. Thermal analysis and X-ray diffraction were used to identify the temperature range of heat-treatment. The average pore size and the pore volume were investigated by a nitrogen adsorption instrument, and SEM was used to characterize the appearance of the porous glass. The results show that the average size of pores changed from 3.75 nm to 3.03 nm when heat treated at 640-680 °C for 6 h. In addition, when heat treated at 640 °C for 6-24 h, the pore size fell from 3.75 nm to 3.66 nm. The surface area and pore volume become larger with the increase in both temperature and heat treatment time.     

Fabrication and characterization of ZnO modified bioactive glass nanoparticles

Bioactive glass nanoparticles in the system (SiO₂-CaO-P₂O₅-ZnO) were synthesized following the sol-gel technique. The prepared glass nanoparticles of 1, 3 and 5 wt% of ZnO (coded: GZ1, GZ3 and GZ5, respectively) were characterized by TEM, FTIR, XRF, TGA and DSC. All glass powders had particle sizes less than 100 nm. Textural analysis revealed that for GZ1, GZ3 and GZ5, the average pore diameters, measured by the high-speed gas sorption analyzer, were 15.9, 15.4 and 15.2 nm, respectively, while the average pore diameters measured by the mercury intrusion porosimetry were 47, 50 and 63 nm, respectively. All glass powders were highly porous (75, 76 and 75%) with surface areas of 233, 94 and 118 m²/g for GZ1, GZ3 and GZ5, respectively. All glass powders induced an apatite layer on their surfaces upon immersion in simulated body fluid (SBF) as verified by SEM and TF-XRD.     

Fabrication of porous SiC ceramics having pores shaped with Si grain templates

SiC porous ceramics were prepared by heating mixtures of Si powder and carbon black at 900 °C for 24 h in Na vapor. The grains of the Si powder were not only the source of Si for SiC but also served as templates for the pores in the SiC porous ceramics. Angular-shaped pores with sizes of 2-10, 10-150 and 50-150 μm were formed by angular Si grains with sizes of ≤10, ≤50 and ≤150 μm, respectively. The porosity of the SiC porous ceramics was around 55-59%. Spherical pores were also formed when spherical Si grains were used. A bending strength of 14 MPa was measured for the SiC porous ceramics prepared with the Si grains (≤50 μm).     

Synthesis and sintering of Y2O3-doped ZrO2 powders using two Pechini-type gel routes

Yttria-tetragonal zirconia polycrystal (ZrO₂ + 4.5 mol% Y₂O₃) nanocrystalline powder was synthesized by two Pechini-type gel routes, the in situ polymerized complex (IPC) method and the PEG/AF method. FTIR spectra confirmed coordination of metal ions with the polymer by different routes, depending on the method used. The crystallite size of the powder increased from 5 nm to 8 nm when the temperature was increased from 450 °C to 600 °C and calcination times increased from 2 h to 24 h. The morphology of the powders differed only when the organic impurities were not completely eliminated. After calcination, the morphology of the powders produced by the two methods showed porous agglomerates composed of smaller particles. All the resulting microstructures were very similar, regardless of the method employed to obtain the powder or the calcination times and temperatures.     

Manufacture and characterization of ultra and microfiltration ceramic membranes by isostatic pressing

This paper describes the manufacture of tubular UF and MF porous and supported ceramic membranes to oil/water emulsions demulsification. For such a purpose, a rigorous control was realized over the distribution and size of pores. Suspensions at 30 vol.% of solids (zirconia or alumina powder and sucrose) and 70 vol.% of liquids (isopropyl alcohol and PVB) were prepared in a jar mill varying the milling time of the sucrose particles, according to the pores size expected. The membranes were prepared by isostatic pressing method and structurally characterized by SEM, porosimetry by mercury intrusion and measurements of weight by immersion. The morphological characterization of the membranes identified the formation of porous zirconia and alumina membranes and supported membranes. The results of porosimetry analysis by mercury intrusion presented an average pore size of 1.8 μm for the microfiltration porous membranes and for the ultrafiltration supported membranes, pores with average size of 0.01-0.03 μm in the top-layer and 1.8 μm in the support. By means of the manufacture method applied, it was possible to produce ultra and microfiltration membranes with high potential to be applied to the separation of oil/water emulsions.     

Polyvinylpyrrolidone-assisted synthesis of microscale C-LiFePO4 with high tap density as positive electrode materials for lithium batteries

Carbon-coated LiFePO₄ (C-LiFePO₄) with micron particle size (6 μm) and high tap density (1.6 g cm⁻³) was prepared from spherical FePO₄·2H₂O powder via the co-precipitation method. The C-LiFePO₄ powder was calcined at temperatures between 650 and 800 °C. The 6 μm C-LiFePO₄ prepared at 800 °C exhibited an excellent rate capability, delivering 150 mAh g⁻¹ on discharge at the 0.1 C-rate and 108 mAh g⁻¹ at the 5 C-rate. The volumetric capacity of the 6 μm C-LiFePO₄ corresponded to 225 mAh cm⁻³, since the large secondary particles (6 μm) C-LiFePO₄ sufficiently allowed tight packing of the particles. The 6 μm C-LiFePO₄ powder with high tap density makes an attractive positive electrode candidate for lithium-ion batteries designed for high energy density.     

Sintering kinetics of a 18.8Li2O 8.3ZrO2 64.2SiO2 8.7Al2O3 glass ceramic

The LZSA (Li₂O-ZrO₂-SiO₂-Al₂O₃) glass ceramic system has shown high potential as low temperature co-fired ceramics, the so called LTCC, for several applications, such as screen-printed electronic components, due to its low sintering temperature (< 1000 °C). However, a good microstructural control must be achieved in order to obtain a low porosity material. The 18.8Li₂O 8.3ZrO₂ 64.2SiO₂ 8.7Al₂O₃ LZSA glass ceramic composition was prepared by melting, quenching in water, and grinding in order to obtain a very fine powder (3.78 μm mean particle size). Subsequently, compacted bodies were obtained by uniaxial pressing (40 MPa) and drying. Sintering kinetics was investigated by optical dilatometry measurements and scanning electron microscopy (SEM) observations. The activation energy for sintering was found to be 314 kJ.mol⁻¹, whilst a maximum linear shrinkage of 22% and porosity of 3.5% were obtained with 10 min swelling time at 800 °C.     

Fabrication of CaSiO3 bioceramics with open and unidirectional macro-channels using an ice/fiber-templated method

Porous CaSiO₃ bioceramics with open and unidirectional macro-channels of pore size more than 200 μm are of particular interest for biomedical applications. An ice/fiber-templated method was employed for the fabrication of CaSiO₃ bioceramics with interconnected lamellar pores and macro-channels of pore size more than 200 μm. The pores formed by ice crystals transformed from cellular to lamellar, while the pores formed by fibers were aligned macro-channels, which were also in alignment with the lamellar pores. Keeping the initial slurry concentration constant and increasing the packing density of fibers, the volume fraction of macro-channels and open porosity increased, and the compressive strength decreased. Maintaining the packing density of fibers and increasing the initial slurry concentration, the pore sizes of lamellar pores and open porosity decreased, and the compressive strength increased. The results indicated that it was possible to manufacture porous CaSiO₃ bioceramics with the macro-channels of 250–350 μm, lamellae spacing of 50–100 μm, open porosity of 71.12–83.94% and compressive strength of 0.87–3.59 MPa, indicating the suitability for tissue engineering.     

Reactive infiltration processing (RIP) of ultra high temperature ceramics (UHTC) into porous C/C composite tubes

A novel reactive infiltration processing (RIP) technique was employed to infiltrate porous carbon fibre reinforced carbon (C/C) composite hollow tubes with ultra high temperature ceramic (UHTC) particles such as ZrB₂. The C/C composite tubes had initial porosity of ∼60% with a bimodal (10 μm and 100 μm) pore size distribution. A slurry with 40-50% ZrB₂ solid loading particles was used to infiltrate the C/C tubes. Our approach combines in situ ZrB₂ formation with coating of fine ZrB₂ particles on carbon fibre surfaces by a reactive processing method. A Zr and B containing diphasic gel was first prepared using inorganic-organic hybrid precursors of zirconium oxychloride (ZrOCl₂·8H₂O), boric acid, and phenolic resin as sources of zirconia, boron oxide, and carbon, respectively. Then commercially available ZrB₂ powder was added to this diphasic gel and milled for 6 h. The resultant hybrid slurry was vacuum infiltrated into the porous hollow C/C tubes. The infiltrated tubes were dried and fired for 3 h at 1400 °C in flowing Ar atmosphere to form and coat ZrB₂ on the carbon fibres in situ by carbothermal reaction. Microstructural observation of infiltrated porous C/C composites revealed carbon fibres coating with fine nanosized (∼100 nm) ZrB₂ particles infiltrated to a depth exceeding 2 mm. Ultra high temperature ablation testing for 60 s at 2190 °C suggested formation of ZrO₂ around the inner bore of the downstream surface.     

Preparation of a carbon monolith with hierarchical porous structure by ultrasonic irradiation followed by carbonization, physical and chemical activation

A two-step direct and simple method for the preparation of a hierarchical porous carbon monolith with micropores, mesopores and macropores is described. The two stages give more flexibility in the preparation of a porous carbon monolith. In step I a macroporous interconnected carbon monolith is prepared by ultrasonic irradiation during sol-gel polycondensation. The effects of sol-gel temperature, catalyst concentration and ultrasonic power on the structure of the monolith are investigated. In step II, mesopores are induced in the monolith by Ca(NO₃)₂ impregnation followed by CO₂ activation. The effect of activation temperature is also studied. A hierarchical interconnected carbon monolith with mean pore size diameter of 1.2 μm, BET surface area of 624 m²/g, mesopore volume of 0.38 cm³/g and micropore volume of 0.22 cm³/g has been obtained from Ca(NO₃)₂ impregnation of the macroporous carbon monolith followed by CO₂ activation at 850 °C.     

Effect of Al2O3 particle size on preparation and properties of ZTA ceramics formed by gelcasting

Zirconia-toughened alumina (ZTA) ceramics were prepared using three different kinds of Al₂O₃ powders (marked PW-A average particle size: 7.53 μm, marked PW-B average particle size: 1.76 μm, marked PW-C average particle size: 0.61 μm) by gelcasting. Effect of Al₂O₃ particle size on zeta potential, dispersant dosage and solid volume fractions of ZTA suspensions as well as the mechanical properties of ZTA green bodies and ceramics were investigated. The optimum dosages of dispersant for ZTA suspensions prepared by PW-A, PW-B and PW-C are 0.4 wt%, 0.5 wt% and 0.7 wt%, respectively. The highest solid volume fractions of ZTA suspensions can reach 62 vol% (SP-A), 60 vol% (SP-B) and 52 vol% (SP-C), respectively. The green bodies show a bending strength as high as 20 MPa, which can meet the requirement of machining. The Al₂O₃ powder with fine particle size is beneficial to the improvement of mechanical properties. The ZTA ceramics prepared by PW-B Al₂O₃ powder show the highest bending strength (680 MPa) and toughness (7.49 MPa m^1/2).     

Synthesis and cathodoluminescence properties of porous wood (fir)-templated zinc oxide

Wood (fir)-templated ZnO with hierarchically porous structure has been successfully synthesized through a simple hydrothermal process. Morphology and porosity of the products were investigated by FESEM, TEM, and N₂ adsorption, respectively. The optical properties were measured by cathodoluminescence (CL) at room temperature. The morphologies of bulk and ground flake ZnO show an inheritance from the fir microstructure. Experimental results suggest that a higher calcination temperature will influence the grain size and porosity. The pore size decreases from 20 to 10 μm in the bulk ZnO, while increases from 50 nm to several micrometers in the flake ZnO when the calcination temperature changes from 600 to 1200 °C. CL spectra also show temperature-dependent properties at ultraviolet (UV) band and blue band. The intensity of visible emission originated from oxygen vacancies is proportional to the calcination temperature, while that of UV emission is inverse proportional due to quantum confinement effect.     

Fabrication and characterization of porous silver powder prepared by spray drying and calcining technology

High porosity porous silver powder with about 100 µm average size and 5 µm pore size was fabricated by spray drying and calcining technology. Effects of calcining temperature and process of spray-dried powder on the phases, grain size, particle morphology and pore microstructure of silver powder were investigated. The results showed that porous silver with approximately spherical shape and via hole structure was obtained using 0.25 mol Ag₂CO₃ solution of ammonia water, which was spray-dried at 200 °C and calcined at 400 °C for 30 min with heat treatment technology curve of gradient temperature in air. And there were not Ag₂CO₃, Ag₂O and AgO phases existing in the porous silver. However, using 0.25 mol Ag₂CO₃ solution of ammonia water, the porous silver powder could not be fabricated by spray pyrolysis technology with a solution feed rate of 300 mL/h, flux of carrier gas of 0.30 MPa, and 640 °C furnace set temperature.     

In vitro assessment of degradation and bioactivity of robocast bioactive glass scaffolds in simulated body fluid

In this study porous three-dimensional scaffolds of borate (13-93B3) bioactive glass were prepared by robocasting and in vitro degradation and bioactivity was evaluated. Grid like scaffolds with interconnected pores was assembled using robotic deposition technique which is a direct ink writing method. After binder burnout, the constructs were sintered for 1 h at 560 °C to produce scaffolds (porosity≈60%) consisting of dense glass struts (300±20 μm in diameter) and interconnected pores of width 580±20 μm. Hydroxyapatite formation on borate bioactive glass scaffolds was investigated in simulated body fluid (SBF) using three different scaffold/SBF (S/S) ratios (1, 2 and 10 mg/ml) at 37 °C. When immersed in SBF, degradation rate of the scaffolds and conversion to a calcium phosphate material showed a strong dependence to the S/S ratio. At high solid concentration (10 mg/ml) surface of the glass scaffolds converted to the calcium rich amorphous calcium phosphate after 30 days. At lower solid concentrations (2 and 1 mg/ml) an amorphous calcium phosphate layer formation was observed followed by the conversion to hydroxyapatite.     

Poly(l-lactic acid) short fibers prepared by solvent evaporation using sodium tripolyphosphate

A porous material consisting of biodegradable polymer fibers may be one of the best candidates for implants used in the regeneration of damaged tissue, because it has a continuous pore structure that would allow ingrowth of nutriments, tissues, blood vessels or cells. In the present work, short fibers of biodegradable poly(l-lactic acid) (PLLA) were successfully prepared by the dropwise addition of PLLA dissolved in methylene chloride to a poly(vinyl alcohol) (PVA) solution containing sodium tripolyphosphate with stirring. It was suggested that droplets of the PLLA solution form spheres coated with PVA, which are then deformed into fibrous shapes due to stirring. The length of fibers was 200-800 μm and was controlled by the stirring rate, the PLLA concentration of the droplets and the PVA concentration. A PLLA porous block could be easily prepared by sintering the PLLA fibers at 173 °C for 10 min. The material had a continuous pore structure with the average pore size of approximately 40 μm and porosity of about 80%.