Nanoscale Calcium Research Articles

Alginate-controlled formation of nanoscale calcium carbonate and hydroxyapatite mineral phase within hydrogel networks

A one-step method was used to make nanostructured composites from alginate and calcium carbonate or calcium phosphate. Nanometer-scale mineral phase was successfully formed within the gel network of alginate gel beads, and the composites were characterized. It was found that calcite was the dominating polymorph in the calcium carbonate mineralized beads, while stoichiometric hydroxyapatite was formed in the calcium phosphate mineralized beads. A combination of electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis and powder X-ray diffraction showed that alginate played an active role in controlling mineral size, morphology and polymorphy. For the calcium phosphate mineralized beads, alginate was shown to modulate stoichiometric hydroxyapatite with low crystallinity at room temperature, which may have important applications in tissue engineering. The results presented in this work demonstrate important aspects of alginate-controlled crystallization, which contributes to the understanding of composite material design.

Synthesis of brushite nanoparticles at different temperatures

AbstractPhase pure, stable nanocrystalline brushite particles with average diameter in the range of 23–87 nm were obtained by the reverse microemulsion technique employing a mixture of surfactants (Aliquat 336 & Tween 80) as template directing agents, and calcium nitrate tetrahydrate and biammonium hydrogen phosphate as precursors. Particle sizes and morphologies were tuned by adjusting the reaction parameters, precursor concentration and temperature. FTIR, TEM, and XRD were used to characterize morphological changes of as synthesized nanoparticles. FTIR and XRD analyses confirmed the formation of brushite nanoparticles. Variations in the reaction temperature resulted in changes in the particle morphology and distribution. At high temperatures (60°C), the sample exhibited high monodispersity and spherical morphology with the average grain size of 42 nm. At low temperatures (6°C), nanoflakes were formed. The results suggest that a reverse microemulsion system provides facile media for control of the phase and morphology of nanoscale calcium phosphate biominerals. A mechanism providing an insight into the formation of brushite particles has also been proposed.

The osteogenic effect of electrosprayed nanoscale collagen/calcium phosphate coatings on titanium

For orthopedic and dental implants, the ultimate goal is to obtain a life-long secure anchoring of the implant in the native surrounding bone. To this end, nanoscale calcium phosphate (CaP) and collagen-CaP (col-CaP) composite coatings have been successfully deposited using the electrospray deposition (ESD) technique. In order to study to what extent the thickness of these coatings can be reduced without losing coating osteogenic properties, we have characterized the mechanical and biological coating properties using tape tests (ASTM D-3359) and in vitro cell culture experiments, respectively. Co-deposition of collagen significantly improved coating adhesive and cohesive strength, resulting in a remarkably high coating retention of up to 97% for coating thicknesses below 100 nm. In vitro cell culture experiments showed that electrosprayed CaP and col-CaP composite coatings enhanced osteoblast differentiation, leading to improved mineral deposition. This effect was most pronounced upon co-deposition of collagen with CaP, and these coatings displayed osteogenic effects even for a coating thickness of below 100 nm.

Porous Polypyrrole Prepared by Using Nanoscale Calcium Carbonate as a Core for Supercapacitance Materials

Porous Polypyrrole Prepared by Using Nanoscale Calcium Carbonate as a Core for Supercapacitance Materials

On Processing and Impact Deformation Behavior of High Density Polyethylene (HDPE)–Calcium Carbonate Nanocomposites

AbstractDifferent processing approaches were adopted to obtain the best combination of strength and toughness. The approach that yielded superior properties was examined in detail to study the mechanical response of nanoscale calcium carbonate‐reinforced high density polyethylene in conjunction with unreinforced high density polyethylene. The reinforcement of high density polyethylene with nanoscale calcium carbonate increases impact strength and is not accompanied by decrease in yield strength. The addition of nanoscale calcium carbonate to high density polyethylene alters the micromechanism of deformation from crazing‐tearing in high density polyethylene to fibrillation in high density polyethylene–calcium carbonate nanocomposite.magnified image

Nonisothermal crystallization of high density polyethylene and nanoscale calcium carbonate composites

AbstractNonisothermal crystallization of high density polyethylene (HDPE)/maleic anhydride‐modified HDPE(manPE)/nanoscale calcium carbonate (CaCO3) nanocomposite was investigated by means of wide angle X‐ray diffraction (WAXD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC). WAXD indicated that the crystallinity was reduced with the addition of CaCO3. The spherulite size of HDPE increased in the presence of manPE, but decreased when CaCO3 was added from observation of POM. A modified Avrami analysis, Ozawa analysis, and Liu analysis were applied to the nonisothermal crystallization process. Crystallizability followed the order: HDPE/manPE/CaCO3 > HDPE/CaCO3 > HDPE/manPE > HDPE when undercooling was taken into account. Dependence of the effective activation energy on the relative crystallinity was estimated by the Friedman equation, and the results were used to calculate the parameters (Kg and U*) of Lauritzen‐Hoffman's equation by Vyazovkin's method. These results indicate that the addition of maleic anhydride groups and CaCO3 tend to promote the nucleation of spherulites on their surfaces and lead to epitaxial growth of the crystallites. But at the same time, manPE and CaCO3 particles may hinder the transport of the molecule chains resulting in a decrease of the crystallization growth rate. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

End of the Induction Period in Ordinary Portland Cement as Examined by High‐Resolution Scanning Electron Microscopy

The early stages of ordinary Portland cement (OPC) hydration were studied by cold field emission scanning electron microscopy and isothermal conduction calorimetry. Particular attention was paid to samples from the end of the induction period, where an additional peak in the tricalcium silicate hydration reaction has recently been discovered. Higher resolution images were obtained than is possible with currentin situimaging techniques, allowing for the observation of features on the 5‐nm scale. The peak in the hydration at the end of the induction period was associated with both the formation of pores in the surface of the cement grains and the formation of nanoscale calcium silicate hydrate (C–S–H) structures on those surfaces. The effects of grinding of OPC and additions of tricalcium aluminate and tetracalcium aluminoferrite on the peak at the end of the induction period were also examined. The results of the study were compared with the models in the literature used to describe the causes of the induction period and its end.

Effect of substrate temperature on mechanical properties of calcium phosphate coatings

The effect of substrate temperature and processing parameters on mechanical properties of nanoscale calcium phosphate coatings are being studied in order to refine the processing technique for Functionally Graded Hydroxyapatite (FGHA) coatings. Coatings were deposited on titanium substrates with a set substrate temperature of 450, 550, 650, or 750 degrees C in an Ion Beam Assisted Deposition (IBAD) system using a sintered hydroxyapatite (HA) target. Mechanical properties of the coatings deposited with a set substrate temperature such as, bonding/adhesion strength to the substrate, nanohardness, and Young's Modulus as well as coating thickness were evaluated and compared with commercial plasma spray HA coatings. It is concluded that depositing FGHA coatings would better be started at 550-650 degrees C to maintain superior properties of the film at the interface. It can also be concluded that the residual stresses caused by different Coefficient of Thermal Expansions (CTEs) between the substrate and coatings are not the only factor controlling the bonding strength and mechanical properties of these samples. Other parameters such as the nature of the interface layers and their bonding to each other as well as the density and grain structure of the coatings must be taken into consideration for an appropriate evaluation of mechanical properties of calcium phosphate coatings deposited on heated substrate.

Composition and density of nanoscale calcium–silicate–hydrate in cement

Although Portland cement concrete is the world's most widely used manufactured material, basic questions persist regarding its internal structure and water content, and their effect on concrete behaviour. Here, for the first time without recourse to drying methods, we measure the composition and solid density of the principal binding reaction product of cement hydration, calcium-silicate-hydrate (C-S-H) gel, one of the most complex of all gels. We also quantify a nanoscale calcium hydroxide phase that coexists with C-S-H gel. By combining small-angle neutron and X-ray scattering data, and by exploiting the hydrogen/deuterium neutron isotope effect both in water and methanol, we determine the mean formula and mass density of the nanoscale C-S-H gel particles in hydrating cement. We show that the formula, (CaO)1.7(SiO2)(H2O)1.80, and density, 2.604 Mg m(-3), differ from previous values for C-S-H gel, associated with specific drying conditions. Whereas previous studies have classified water within C-S-H gel by how tightly it is bound, in this study we classify water by its location-with implications for defining the chemically active (C-S-H) surface area within cement, and for predicting concrete properties.

Effects of the reinforcement and toughening of acrylate resin/CaCO3 nanoparticles on rigid poly(vinyl chloride)

AbstractNovel composite particles based on nanoscale calcium carbonate (nano‐CaCO3) as the core and polyacrylates as the shell were first synthesized by in situ encapsulating emulsion polymerization in the presence of the fresh slush pulp of calcium carbonate (CaCO3) nanoparticles. Subsequently, these modified nanoparticles were compounded with rigid poly(vinyl chloride) (RPVC) to prepare RPVC/CaCO3 nanocomposites. At the same time, the effects of the reinforcement and toughening of these modified nanoparticles on RPVC were investigated, and the synergistic effect of modified nanoparticles with chlorinated polyethylene (CPE) was also studied. The results showed that in the presence of nano‐CaCO3 particles, the in situ emulsion polymerization of acrylates was carried out smoothly, and polyacrylates successfully encapsulated on the surface of nano‐CaCO3 to prepare the modified nanoparticles, breaking down nano‐CaCO3 particle agglomerates, improving their dispersion in the matrix, and also increasing the particle–matrix interfacial adhesion. Thus, the effects of the reinforcement and toughening of these modified nanoparticles on RPVC were very significant, and the cooperative effect of the nanoparticles with CPE occurred in the united modification system. Scanning electron microscopy analyses indicated that large‐fiber drawing and network morphologies coexisted in the system of joint modification of nanoparticles with CPE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3940–3949, 2007

Effects of microscale calcium carbonate and nanoscale calcium carbonate on the fusion, thermal, and mechanical characterizations of rigid poly(vinyl chloride)/calcium carbonate composites

AbstractA Haake torque rheometer equipped with an internal mixer has been used to study the influence of microscale calcium carbonate (micro‐CaCO3) and nanoscale calcium carbonate (nano‐CaCO3) on the fusion, thermal, and mechanical characteristics of rigid poly(vinyl chloride) (PVC)/micro‐CaCO3 and PVC/nano‐CaCO3 composites, respectively. The fusion characteristics discussed in this article include the fusion time, fusion temperature, fusion torque, and fusion percolation threshold (FPT). The fusion time, fusion temperature, and FPT of rigid PVC/calcium carbonate (CaCO3) composites increase with an increase in the addition of micro‐CaCO3 or nano‐CaCO3. In contrast, the fusion torque of rigid PVC/CaCO3 composites decreases with an increase in the addition of micro‐CaCO3 or nano‐CaCO3. The results of thermal analysis show that the first thermal degradation onset temperature (Tonset) of rigid PVC/micro‐CaCO3 is 7.5 °C lower than that of PVC. Meanwhile, the glass‐transition temperature (Tg) of rigid PVC/micro‐CaCO3 is similar to that of PVC. However, Tonset and Tg of PVC/nano‐CaCO3 composites can be increased by up to 30 and 4.4%, respectively, via blending with 10 phr nano‐CaCO3. Mechanical testing results for PVC/micro‐CaCO3 composites with the addition of 5–15 phr micro‐CaCO3 and PVC/nano‐CaCO3 composites with the addition of 5–20 phr nano‐CaCO3 are better than those of PVC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 451–460, 2006

Effect of nano-CaCO 3 on mechanical properties of PVC and PVC/Blendex blend

The effects of nanoscale calcium carbonate (nano-CaCO 3) particles on the mechanical properties of different ductile polymer matrices were investigated. Polyvinyl chloride (PVC) and PVC/Blendex (BLENDEX ® 338) blend were used as the matrix in this study. The nano-CaCO 3 particles were observed to be dispersed uniformly on the nanoscale in both PVC and PVC/Blendex blend by means of transmission electron microscopy. The impact strength, flexural modulus and Vicat softening temperature of PVC and PVC/Blendex blend were significantly enhanced after addition of 0–15 phr nano-CaCO 3, but the tensile properties of the two matrices showed different changes in the presence of nano-CaCO 3. The yield strength and elongation at break of PVC could be increased by the addition of nano-CaCO 3, while those of PVC/Blendex were decreased. Dynamic mechanical thermal analysis showed that the addition of nano-CaCO 3 led to an increase in storage modulus and glass transition temperature for both PVC and PVC/Blendex blend.

Absorption behavior of vinyl chloride/calcium carbonate and pressure/temperature/conversion relationship for vinyl chloride suspension polymerization in the presence of calcium carbonate

The absorption of vinyl chloride (VC) on surface-treated light-grade and nano-scale calcium carbonate (CaCO 3), and VC suspension polymerization in the presence of CaCO 3 were carried out in a 5 L autoclave. It showed that the absorption of VC on CaCO 3 increased with the partial pressure of VC up to a critical point. Nano-scale CaCO 3 was more effective in absorbing VC than light-grade CaCO 3 at the same temperature and partial pressure of VC due to its greater surface area. The absorption behavior of VC/CaCO 3 follows Langmuir isothermal equation. In view of the absorption of VC on CaCO 3, Xie’s model [J. Appl. Polym. Sci. 34 (1987) 1749] was modified to relate pressure, temperature, the amount of CaCO 3 and conversion for VC suspension polymerization in the presence of CaCO 3. The model simulation showed that VC conversions at the pressure drop point and at a certain pressure drop decreased with the increase of the amount of added CaCO 3, and the influence of nano-scale CaCO 3 was greater than that of light-grade CaCO 3. The simulated VC conversions fitted well with that obtained from VC suspension polymerizations in the presence of different amounts of light-grade or nano-scale CaCO 3.

Tensile Properties of Polypropylene Filled with Nanoscale Calcium Carbonate Particles

To bring the positive effect of nanoscale calcium carbonate into play, macromolecular chains were introduced onto the particles by irradiation grafting polymerisation so that the hydrophobicity of the particles was increased and the loosen agglomerates became stronger. Tensile testing results demonstrated that polypropylene composites incorporated with the grafted nano-CaCO3 particles exhibited improved stiffness, strength and toughness at low filler content when proper grafting polymers are introduced. Species of grafting polymers adhered to the nanoparticles is an important factor affecting the modification effect of the matrix polymer. Therefore, composites performance can be purposely tailored accordingly.

The decomposition kinetics of the SiO 2 coated nano-scale calcium carbonate

The model-free and model fitting approaches have been applied to the data for non-isothermal decomposition kinetics of SiO 2 surface coated calcium carbonate as well as the reference. The decomposition mechanisms as revealed by computation show great differences. Nano-sized reference samples decompose according to the contracting volume mechanism (R 3) while the surface SiO 2 coated calcium carbonate shows the one-dimensional diffusion (D 1) behavior, possibly because of the framework constituted by surface SiO 2 layer hinders the diffusion of the dissociate products into the outer atmosphere. At the mean time, the activation energy is increased by 30–35 kJ/mol in the process controlled by diffusion compared with the reference. However, the usual model fitting approach may also yield highly uncertain values of Arrhenius parameters when applied to non-isothermal data, so that a combination of master plot method and model-free kinetic approaches based on the isoconversional method that yields the dependencies of the activation energy on the extent of the conversion were also used to evaluate the credulity of the kinetic parameters achieved by model fitting methods.