Influence of temperature,ripening time and calcination on the morphology and crystallinity of hydroxyapatite nanoparticles

Nano-sized hydroxyapatite (HA) particles were prepared by chemical precipitation through aqueous solutions of calcium chloride and ammonium hydrogenphosphate. The influence of temperature, ripening time and calcination on the crystallinity and morphology of the HA nanoparticles were investigated. It was found that the crystallinity and crystallite size increased with the increase of synthetic temperature and ripening time. XRD and TEM results showed that the morphology change of HA nanoparticles was related to their crystallinity. High crystallinity of HA led to regular shape and smooth surface of the nanoparticles. The crystallinity of HA powders increased greatly after calcination at 650 °C for 6 h but the change of the crystallite size after calcination was dependent on the crystallinity and crystallite size of “as prepared” HA nanoparticles.     

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Comparative investigation on the structural,morphological, optical,and magnetic properties of CoFe2O4 nanoparticles

Herein, we report a sustainable production of magnetic cobalt ferrite nanoparticles by conventional (CHM) and microwave heating (MHM) method. Hibiscus rosa-sinensis extract was used as both reducing and stabilizing agent. Using plant extracts to synthesize nanoparticles has been considered as an eco-friendly method, since it avoids noxious chemicals. The plethora of plant extract mediated nanoparticles were compared by techniques, such as XRD, Rietveld, FT-IR, SEM, EDX, UV-Visible DRS, PL and VSM were carried out to analyze and understand their crystallite size, functional groups, morphology, optical and magnetic properties. The crystalline structure of cobalt ferrite nanoparticles revealed the cubic structure and the microwave heating of nanoparticles showed smaller crystallite size compared to the conventional heating, which was then confirmed by XRD analysis. To analyze the presence of functional groups and the phytochemical involvement of the plant extract was confirmed by FT-IR studies. Spherical morphology with less than 100 nm sized particles was confirmed by SEM and EDX analysis confirm the existence of Co, O, and Fe elements present in the samples. UV-Visible DRS studies were carried out to calculate the band gap of the as-synthesized nanoparticles, estimated from the Kubelka-Munk function, as 2.06, and 1.87 eV for CHM and MHM, respectively. Photoluminescence emission spectrum of the nanoparticles showed two different bands at 494 and 620 nm, which explores the optical properties of the nanoparticles, due to the quantum confinement effect. VSM analysis showed better ferromagnetic behavior, which can be used for magnetic applications.     

An innovative Azadirachta indica gum-mediated synthesis of cocoon-shaped nano-AgHAp from Lamellidens marginalis shells

In this work, the evaluations of noble nanoparticles for the structural and morphological characteristics are focused. The control of desired particles size and morphology for hydroxyapatite (HAp) and Ag-substituted hydroxyapatite (AgHAp) derived from Lamellidens marginalis shells using Azadirachta Indica (AI) gum as a potential surfactant for the synthesis of stable nanoparticles are reported. The morphological change with respect to the concentration of AI gum is analyzed. The functional group (FTIR) and crystallographic (XRD) characterization of the HAp and AgHAp nanoparticles confirm the presence of HAp with desired apatite functional peaks. The morphological evaluation (FE-SEM) exhibited the formation of cocoon-shaped nanoparticles for the AI gum-medicated synthesis. Higher AI gum concentration reduces the particle size along with the formation of unique surface morphology. The average diameter of the synthesized AgHAp nanoparticles was found to be ≤30 nm which is revealed from HR-TEM. The bacterial investigation against bacterial strains substantiates the higher resistance of bacterial growth for Staphylococcus aureus was observed than Escherichia coli for the AgHAp particles. Hence, embedding silver nanoparticles in the HAp is an efficient approach to enhance the long-term antibacterial effect of the orthopedic and dental applications.     

Comparative analysis and antibacterial properties of thermally sintered apatites with varied processing conditions

Hydroxyapatite (HA) and biphasic hydroxyapatite/beta-tricalcium phosphate (biphasic HA/β-TCP) were synthesized using thermal sintering. The parameters- sintering temperature (600°C, 900°C, and 1200°C), biological source used (fish bone, egg shells, and fish scales), and soaking time (2, 6, and 10 hours) were permuted to study their effects on the properties of the resultant apatite. Morphological study revealed that the smallest (60 nm) spherical particle and the largest (470 nm) irregular shaped particle were obtained from the fish bone sample sintered at 600°C and at 1200°C respectively. FTIR and XRD results showed that as the sintering temperature is increased, the phase transformation from HA to β-TCP takes place. Only the final products from fishbone sample at 600°C are pure carbonated HA. The crystallinity of synthesized particles ranged from 79% to 98%. Soaking time has no effect on phase composition of the apatite but has significant effect on crystallite size; increase in soaking time increases crystallite size and particle shape becomes more spherical. Interestingly, the fish bone sample sintered at 900°C has higher crystallinity and crystallite size compared to the fish scale sample sintered at the same temperature. EDX confirmed that non-stoichiometric apatite with Ca/P ratio ranging from 1.47 to 1.91 can be obtained by varying the sintering conditions. The antibacterial test revealed that both calcium apatite obtained from fish bones and fish scales have inhibited bacterial growth; apatite from fish bone works faster than fish scales. The in vitro cytotoxicity test ensured that all the calcium apatite except for eggshell are non-cytotoxic. Thus, apatite with excellent microbial activity can be obtained by using fish wastes, and by tuning the sintering parameters, the apatite with desired types and properties can be synthesized for different biomedical applications.     

Dense fine-grained biphasic calcium phosphate (BCP) bioceramics designed by two-step sintering

In this study, dense, fine-grained biphasic calcium phosphate bioceramics were designed via the two-step sintering method. The starting powder was nanosized calcium-deficient hydroxyapatite, whose phase composition, average particle size and morphology were characterized by XRD, FTIR, Raman spectroscopy, laser diffraction and FE-SEM. The phase transformations of the initial powder during heating up to 1200 °C were examined using TG/DSC. At first, conventional sintering was performed and the recorded shrinkage/densification data were used to find out the appropriate experimental conditions for two-step sintering. The obtained results show that two-step sintering yields BCP ceramics, consisting of hydroxyapatite and β-TCP, with full dense, homogeneous structure with average grain size of 375 nm. Furthermore, BCP ceramics obtained by the two-step sintering method exhibit improved mechanical properties, compared to conventionally sintered BCP.     

Kinetics of magnetite nanoparticles formation in a one step low temperature hydrothermal process

In the present study, a one step hydrothermal process was employed to synthesize magnetite nanoparticles using oleic acid as surfactant agent at 140 °C. Effects of reaction time and alkalinity were studied on particles size and morphology. By changing these parameters, some monodisperse spherical nanoparticles with mean particle size between 2.71 and 13.88 nm were synthesized and characterized via TEM, XRD, VSM, TGA and FT-IR techniques. Assuming the Avrami behavior of particles formation, a kinetics equation was proposed for the transformation rate at 140 °C. Using some simplifying assumptions, nucleation and growth rates were calculated for the hydrothermal formation of magnetite nanoparticles at 140 °C.     

Synthesis of dispersed CaCO3 nanoparticles by the ultrafine grinding

A one-step grinding process to obtain CaCO₃ nanoparticles from a micrometer-sized CaCO₃ was studied. A high-speed beads mill was employed to grind the particles, and poly(acrylic acid, sodium salt) was used to disperse the ground particles. The main parameters, which were investigated, were the slurry concentration, the rotor speed, the bead size, and the surfactant concentration. The larger bead size, higher slurry concentration, and faster rotor speed showed higher grinding efficiencies. However, there was severe agglomeration of the ground particles resulting in larger secondary particles as the grinding time increased after the certain point. The dispersion and enhanced grinding of particles were achieved by the surfactant. The particle size distribution of the ground particles had a narrow peak around 190 nm that was measured by the diffraction method. The primary particle size of the ground particles was around 40 nm.     

Continuous supercritical hydrothermal synthesis of controlled size and highly crystalline anatase TiO2 nanoparticles

The production of size-controlled and highly crystalline anatase titanium dioxide (TiO₂) nanoparticles was carried out under supercritical hydrothermal conditions (400 °C and 30 MPa) in a continuous flow apparatus with a residence time of 1.7 s. An industrially useful titanium sulfate (Ti(SO₄)₂) solution was used as the starting solution. KOH was used to change TiO₂ solubility and pH and thereby control the particle size. The apparatus comprised two micromixers operating at high temperature. The first mixer was configured to prepare a supercritical aqueous KOH solution from supercritical water (SC-H₂O) and KOH. The second mixer combined this KOH solution with aqueous Ti(SO₄)₂. In situ pH control and homogeneous nucleation were achieved in the second mixer. This two-step high-temperature micromixing process produced reasonably small and homogeneous particles. The particles were characterized by transmission electron microscopy (TEM) on the basis of morphology, average size, and size distribution, together with the coefficient of variation (CV). Powder X-ray diffraction (XRD) was used to determine the crystal structure and crystalline size. The weight loss of material was found through thermogravimetric (TG) measurement. The crystal structure of the product was assigned to the anatase single phase. The average particle size could be adjusted in the range 13–30 nm while maintaining a CV of 0.5 by changing the KOH concentration. At low pH, the powder XRD results for crystallite size were in good agreement with the average particle size measured by TEM, confirming that the products were single crystals of TiO₂ nanoparticles. When the reactor temperature was increased from 400 to 500 °C, the weight loss decreased from 4.5 to 2.5%, keeping the average particle size and high crystallinity of the TiO₂ particles unchanged.     

Effect of atomization methods on the size and morphology of Gd0.1Ce0.9O2−δ powder synthesized by aerosol flame synthesis

Nano-sized gadolinium doped ceria (GDC) powders were successfully synthesized by aerosol flame deposition (AFD) with two different atomization methods; ultrasonic and electrostatic atomization. The effect of the atomization method on the size and morphology of GDC particles were investigated. It was observed that the diameter range of the GDC small primary particles synthesized by the ultrasonic atomization method was 10–50 nm while with the electrostatic method was 5–25 nm. In addition, the size of primary large particle found to be decreased from 200 nm to 50 nm with increasing electric field up to 15 kV. The GDC powder synthesized by the electrostatic atomization exhibited reduced crystallite size, particle size, and similar electrical conductivity compared to GDC powder synthesized by ultrasonic atomization. This work demonstrated the benefits of the electrostatic atomization for producing smaller-sized GDC nanopowders for the application in intermediate temperature solid oxide fuel cells.     

Enhanced in vitro inhibition of MCF-7 and magnetic properties of cobalt incorporated calcium phosphate (HAp and β-TCP) nanoparticles

The Co²⁺ (0.1 M) incorporated hydroxyapatite (HAp) and beta tricalcium phosphate (β-TCP) nanoparticles were synthesized by the microwave assisted technique and sintering of HAp respectively. The samples were thermally treated at temperatures ranging from 200 to 1000°C. The partial substitutions of Co²⁺ at the Ca²⁺ site of HAp were confirmed from the slight shift (～0.2°) in the (002) and (211) XRD peaks. The morphology of the nanoparticles was transformed from nanospheres to twinned particles on thermal treatment. In addition, the particle size of Co-600 was increased (from ～50 nm to ～100 nm) due to the recrystallization process. Further, the thermal treatment enhanced the crystallinity (41.15 to 90.16%), retentivity (M_r) and coercivity (H_c) of the nanoparticles. The cobalt incorporated HAp and β-TCP possessed paramagnetic property. The excellent bioactivity of β-TCP has been confirmed by the mineralization in simulated body fluid (SBF). Compared to HAp, β-TCP possessed better compatibility towards C2C12 cells on cobalt incorporation as evidenced by the in vitro cell viability. Moreover, both HAp and β-TCP have significantly inhibited the growth of MCF-7 on increasing the interaction time (72 h). Hence, the inhibition characteristics of Co²⁺ incorporated calcium phosphate (CaP) towards MCF-7 (without affecting the normal cells) demonstrate its competency as a potential material for cancer therapy over the already existing nanoparticles.     

Synthesis of CaCO3 nanoparticles by controlled precipitation of saturated carbonate and calcium nitrate aqueous solutions

Calcium carbonate nanoparticles (CCNP) were synthesised by precipitation from saturated sodium carbonate and calcium nitrate aqueous solutions. The effect of agitation rate, mixing time, calcium/carbonate ions concentration and temperature on particle size and morphology were investigated. Particles were characterised using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Increasing the mixing time from 30 to 180 min resulted in a decrease in particles size. Mixing rate variation between 300 and 14 000 rpm decreased the particle size. Temperature increase favoured a significant growth in particle size and in the formation of aragonite beginning from 80°C. Calcium and carbonate ion concentrations are key parameters controlling the CCNP particle size. Calcite is the main polymorph obtained as revealed by XRD analysis. © 2011 Canadian Society for Chemical Engineering     

Dense nanostructured calcium phosphate coating on titanium by cold spray

This article deals with the understanding of building-up mechanisms of bioactive nanocrystalline hydroxyapatite coatings by Cold Spray, revealing very promising results in contrast to more conventional techniques such as Plasma Spray. A full characterization of feedstock and coatings is provided. The agglomerated structure of the powder proved to be suitable to obtain successfully thick hydroxyapatite coatings. A crystallite size below ∼20 nm in the powder and the as-sprayed coatings is calculated by the Rietveld X-ray refinement method and agreed by Transmission Electron Microscopy. Some wipe tests were carried out on Ti6Al4V substrates in order to study the deposition of single particles and the nanoscale features were evaluated. The resulting structure indicates that there is no delimitation of particle boundaries and the overall coating has been formed by effective compaction of the original nanocrystallites, leading to consistent and consolidated layers.     

Phase content,tetragonality, and crystallite size of nanoscaled barium titanate synthesized by the catecholate process: effect of calcination temperature

A modified catecholate process has been applied to synthesize high purity barium titanate powders in the submicron range. A barium titanium-catechol complex, Ba[Ti(C₆H₄O₂)₃] was prepared from TiCl₄, C₆H₄(OH)₂ and BaCO₃, freeze-dried, and calcined for 3 h at temperatures between 600 and 1300 °C. Phase transformation and crystallite size of the calcined powders were investigated as a function of the calcination temperature by X-ray diffraction methods, and particle morphology and size were studied by scanning electron microscopy. With increasing calcination temperature, BaTiO₃ transformed from the (pseudo)cubic to the ferroelectric tetragonal phase. The tetragonality (c/a-1) increases with increasing calcination temperature and increasing crystallite size, respectively. Higher temperatures clearly favoured particle growth and the formation of large and hard agglomerates. The crystallite size of the tetragonal phase increased from <60 nm at 600–800 °C to 1237±344 nm at 1300 °C.     

Alumina nanocrystalline ceramic by centrifugal casting

Centrifugal casting is an established molding method to prepare ceramics with high strength and high reliability and it has been well demonstrated in Al₂O₃. However, it has not yet been applied to Al₂O₃ nanocrystalline ceramic with < 100 nm grain size, primarily due to the unavailability of high-quality α-Al₂O₃ nanoparticles. In addition, ultrafine nanoparticles may be difficult to cast from the solution unless high-speed ultracentrifuge (e. g., >60,000 rpm) is used. Here we addressed these two challenges by home-made dispersed α-Al₂O₃ nanoparticles with 10 nm average particle size and HCl-assisted casting under a “normal” centrifuge condition and report the first attempt to produce Al₂O₃ nanocrystalline ceramic by centrifuge casting and pressureless sintering. The sintering kinetics and microstructure were analyzed, which assists the design of optimal two-step sintering schedule. We showed that dense Al₂O₃ nanocrystalline ceramic with 65 nm average grain size and ultra-uniform microstructure (the standard deviation of the grain size distribution to the average grain size is 0.358) can be obtained by two-step sintering at 1175 °C without holding followed by holding at 1025 °C for 20 h. The ultra-uniform microstructure may result from the denser and more uniform packing of particles in the green bodies produced by centrifugal casting. The two-step sintered Al₂O₃ nanocrystalline ceramic has a microhardness of 19.9 GPa. The microhardness indicates potential softening (inverse Hall-Petch relationship) of Al₂O₃ nanocrystalline ceramic at such a grain size.     

Growth of hydroxyapatite plate-like nanoparticles by additive free precipitation for the deposition of aligned coatings

In recent years, nanoparticles' morphology has been tailored to tune nanoparticle specific properties for several applications. In particular, plate-like particles have been synthesized to create an analog of nacre microstructure exhibiting outstanding mechanical performance attributed to nacre's micro and nano hierarchy. However, the synthesis of equiaxed hydroxyapatite (HA) plates for constructing an oriented architecture has remained as an astounding challenge. In this study, we designed an additive-free chemical precipitation route in which the pH was increased stepwise to maintain the particles' equiaxed 2d shape. Our results showed that the produced particles exhibited HA's crystal structure and highly sustained the equiaxed/rectangular plate morphology of the octacalcium phosphate (OCP) phase, formed as an interphase during the precipitation. The reaction time, reactant concentration, and heat treatment were found essential in controlling the particles' morphology, size, and crystal symmetry. The crystal features of the particles were dissected via high-resolution scanning and transmission electron microscopes (HRSEM and HRTEM) and X-ray diffraction (XRD) analysis. Moreover, the Williamson-Hall plot and Rietveld Size-strain algorithm were implemented to calculate the crystallite size and strain of the particles. HRSEM and HRTEM micrographs showed that ultrathin (10–20 nm) 2d HA particles with mean lengths of 140–150 nm grew through the c-axis. In the last stage, we attempted to use the particles to deposit oriented coatings by electrophoretic deposition (EPD).     

Monitoring the dielectric properties of Mn-ferrite nanoparticles by controlling crystallite size and applying static magnetic field

Mn-ferrite (MnFe₂O₄) nanoparticles were synthesized by a co-precipitation method. Temperature annealing and ball milling were used to change the crystallite size. X-Ray diffractograms (XRD) con?rmed the single phase spinel structure for all samples and calculations showed that the crystallite size is in the range of 8–33 nm. Transmission electron microscope (TEM) images reveals 17–43 nm particle sizes. The frequency and crystallite size dependence of resistivity ρ_ac, dielectric constant ε' and dielectric loss ε'' of all samples were studied without magnetic field and under a dc magnetic field that ranges from 0.1 T to 0.5 T in both the parallel and perpendicular directions to the applied electric field. For all samples, ρ_ac, ε' and ε'' were found to decrease with increasing the applied electric field frequency. ρ_ac decreases while ε' and ε'' increase with increasing the crystallite size. On the other hand, they have the reverse trend with applied magnetic field. All factors that affect these parameters were discussed to explain their behavior. Interestingly, it was found that the resistivity depends linearly on the applied magnetic field. This enables these samples to be used as magnetic sensors. Finally, the sensor sensitivity was controlled by changing the crystallite size of the samples. This work establishes valid ideas for promising applications in the field of magnetic sensors.     

Carboxylic acid-functionalized, core-shell polystyrene@polypyrrole microspheres as platforms for the attachment of CdS nanoparticles

Polypyrrole-coated polystyrene latex particles bearing N-carboxyl functional groups (PS@PPyCOOH) were prepared by the in-situ copolymerization of pyrrole (Py) and the active carboxyl-functionalized pyrrole (PyCOOH) in the presence of 390 nm diameter-sized polystyrene (PS) latex particles. Uncoated PS particles were prepared by emulsion polymerization of styrene. The initial comonomer fractions (in mol%) were 25/75, 50/50, 75/25 and 100/0 for pyrrole and PyCOOH, respectively. The PS@PPyCOOH_x particles, where x stands for the initial molar fraction of PyCOOH (x = 0, 25, 50 or 75%), were characterized in terms of particle size, surface morphology, chemical composition and electrochemical redox activity using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), FTIR, TGA and cyclic voltammetry respectively. TEM showed an increase of the latex particle diameter after coating by the conducting polymer layer, from 390 nm for uncoated PS to 430 nm for PS@PPyCOOH₅₀ particles, allowing an estimation of the PPyCOOH shell thickness to 20 nm. FTIR and XPS detected PyCOOH repeat units at the surface of the latex particles, indicating that this monomer had indeed copolymerized with pyrrole. The core-shell structure of the PS@PPyCOOH_x particles was confirmed by etching the polystyrene core in THF, leading to the formation of hollow conducting polymer capsules. Positively charged CdS nanoparticles were electrostatically assembled onto the surface of PS@PPyCOOH₅₀ particles, as a function of pH. It was found that, contrarily to unfunctionalized PPy-coated latex particles, PS@PPyCOOH₅₀ particles could be evenly decorated with stabilized CdS nanoparticles, at pH 5.The films of the PS@PPyCOOH@CdS-coated ITO electrodes are shown to be electroactive and electrochemically stable.     

Structural,optical, morphological properties of silver doped cobalt oxide nanoparticles by microwave irradiation method

The synthesis of silver doped cobalt oxide nanoparticles by microwave-assisted method and their structural, optical, antibacterial activities are presented in this study. The doping concentrations were chosen as 5, 10, 15, and 20 wt percentages. The sample was undergone powder X-ray diffraction studies and the result shows the good crystalline nature of the sample. Also, the average crystallite size increases from 13.95 nm, 21.26 nm, 26.13 nm, and 28.35 nm with different doping concentrations. The transmission electron microscopy image shows cubic and spherical morphology. The optical properties were tested by UV–vis–NIR absorption spectrum. It indicates the decrease of band gap value. From the antibacterial activity studies, the 20 wt % Ag doped nanoparticles exhibit better activity.     

Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.