Main and interaction effects of matrix particle size,reinforcement particle size and volume fraction on wear characteristics of Al–SiCp composites using central composite design

The aim of this study was to investigate the effects of matrix particle size, reinforcement particle size, volume fraction, and their interactions on the wear characteristics of Al–SiC_p composites. Central composite design method was used to perform a series of experiments. The statistical analysis of experimental results showed that both main effect and interaction effect of factors investigated were effective on the wear behavior of Al–SiC_p composites. Wear loss decreased as volume fraction increased; however, beyond volume fraction of 17.5%, it increased due to reinforcement particle clustering depending on volume fraction and matrix particle size to reinforcement particle size ratio. With decreasing of matrix particle size and increasing of reinforcement particle size, wear loss also decreased. However, after a certain volume fraction, large sized reinforcement particles had a negative effect on the wear resistance.     

Study on physicochemical properties and in vitro bioactivity of tricalcium silicate–calcium carbonate composite bone cement

In this article, a novel bone cement composed of tricalcium silicate (Ca(3)SiO(5); C(3)S) and calcium carbonate (CaCO(3)) was prepared with the weight percent of CaCO(3) in the range of 0, 10, 20, 30, and 40%. The initial setting time was dramatically reduced from 90 to 45 min as the content of CaCO(3) increased from 0 to 40%, and the workable paste with a liquid/powder (L/P) ratio of 0.8 ml/g could be injected between 2 and 20 min (nozzle diameter 2.0 mm). The composite cement showed higher mechanical strength (24-27 MPa) than that of the pure Ca(3)SiO(5) paste (14-16 MPa). Furthermore, the composite cement could induce apatite formation and degrade in the phosphate buffered saline. The results indicated that the Ca(3)SiO(5)-CaCO(3) paste had better hydraulic properties than pure Ca(3)SiO(5) paste, and also the composite cement was bioactive and degradable. The novel bone cement could be a potential candidate as a bone substitute.     

Composition and properties of silver-containing calcium carbonate–calcium phosphate bone cement

The introduction of silver, either in the liquid phase (as silver nitrate solution: Ag(L)) or in the solid phase (as silver phosphate salt: Ag(S)) of calcium carbonate–calcium phosphate (CaCO₃–CaP) bone cement, its influence on the composition of the set cement (C-Ag(L) and C-Ag(S) cements with a Ca/Ag atomic ratio equal to 10.3) and its biological properties were investigated. The fine characterisation of the chemical setting of silver-doped and reference cements was performed using FTIR spectroscopy. We showed that the formation of apatite was enhanced from the first hours of maturation of C-Ag(L) cement in comparison with the reference cement, whereas a longer period of maturation (about 10 h) was required to observe this increase for C-Ag(S) cement, although in both cases, silver was present in the set cements mainly as silver phosphate. The role of silver nitrate on the setting chemical reaction is discussed and a chemical scheme is proposed. Antibacterial activity tests (S. aureus and S. epidermidis) and in vitro cytotoxicity tests (human bone marrow stromal cells (HBMSC)) showed that silver-loaded CaCO₃–CaP cements had antibacterial properties (anti-adhesion and anti-biofilm formation) without a toxic effect on HBMSC cells, making C-Ag(S) cement a promising candidate for the prevention of bone implant-associated infections.     

The influence of lithium fluoride on in vitro biocompatibility and bioactivity of calcium aluminate–PMMA composite cement

The objective of this study is to assess the influence of lithium fluoride on in vitro biocompatibility and bioactivity of calcium aluminate (CA)-polymethylmethacrylate (PMMA) composite cement exhibiting quick setting time ( < 15 min), low exothermic temperature (< 47 degrees C), and high compressive strength (> 100 MPa). The biocompatibility was measured by examining cytotoxicity tests such as the agar diffusion test with L929 cell line and the hemolysis test with fresh rabbit blood. To estimate the bioactivity of CA-PMMA composite cement, we determined hydroxyapatite (HAp) formation on the surface of composite cement in the simulated body (SBF) solution by using thin-film XRD, XPS, SEM, EPMA and ICP-AES. The results of biocompatibility tests indicated that all experimental compositions of this study had no cytotoxicity and no hemolysis so that there was no cytotoxicity with regard to non-reacted monomers (MMA and TEGDMA) and lithium fluoride. The results of bioactivity tests revealed that CA-PMMA composite cement without lithium fluoride did not form HAp on its surface after 60 days of soaking in the SBF. On the other hand, LiAl2(OH)7 . 2H2O and HAp were formed on the surface of CA-PMMA composite cement including 1.0% by weight of lithium fluoride after 7 and 15 days of soaking in the SBF, respectively. The 5 microm of LiAl2(OH)7 . 2H2O and HAp mixed layers were formed on the surface of specimen after 60 days of soaking in the SBF.     

Synthesis and characterization of cellulose acetate–calcium carbonate hybrid nanocomposite

A hybrid nanocomposite composed of calcium carbonate (CaCO₃) and cellulose acetate (CA) was fabricated by bubbling CO₂ gas into the mixture of CA and Ca(OH)₂ solution. Cellulose acetate–calcium carbonate (CA–CC) nanocomposite was characterized by spectral, thermal and optical methods. FTIR and XRD analysis confirmed the formation of the hybrid nanocomposite and XRD confirmed the formation of CaCO₃ with calcite polymorph. Thermal analysis showed CA–CC nanocomposite has better thermal stability than pristine CA. The CaCO₃ nanoparticles were in sphere shape with 100–1000 nm diameter.     

Effect of calcium–silicon ratio on microstructure and nanostructure of calcium silicate hydrate synthesized by reaction of fumed silica and calcium oxide at room temperature

A C–S–H series with calcium–silicon ratio 0.6–3.0 was synthesized by pozzolanic reaction. Phase composition, nanostructural and morphological characteristics were determined using XRD, XRF, SEM and ²⁹Si NMR. Most of the samples were phase-pure, poorly crystalline C–S–H. Significant changes in the nanostructure of the C–S–H samples were observed when the calcium–silicon ratio reached values of 0.8, 1.0 and 1.5. At calcium–silicon ratio 0.8 the basal XRD peak began to develop, crosslinking between layers was seen below this ratio but not above, and there was a substantial decrease in mean silica chain length at this ratio. At calcium–silicon ratio 1.0 there was a pronounced microstructural change from granular to reticular and another substantial decrease in mean chain length (indicated by an abrupt increase in the Q¹ peak intensity and decrease in the Q² peak intensity). At calcium–silicon ratio 1.5 the basal XRD peak began to diminish again, the mean silica chain length decreased further, and isolated tetrahedra (Q⁰) were observed.     

Influence of α-calcium sulfate hemihydrate particle characteristics on the performance of calcium sulfate-based medical materials

This paper presents a systemic study on the effect of α-calcium sulfate hemihydrate (α-hemihydrate) particle characteristics on the performance of calcium sulfate-based materials (CSBM) that widely used in the medical field. The hydration performance and water requirement for normal consistency of α-hemihydrate were investigated. The mechanical strength, microstructure, and pore structure of the hardened CSBM were also examined. The performance of CSBM was greatly affected by the α-hemihydrate crystal properties. α-Hemihydrate crystals with good gradation and a length/diameter ratio of 1–3:1 tended to have perfect fluidity, lower water requirement for normal consistency, and low crystallization velocity. Moreover, in the hardened CSBM hydrated from such α-hemihydrate crystals, the crystal size of the dehydrate was large, and the crystals were interconnected. The strength of the hardened CSBM was sufficient because of low porosity, small pore diameter, and dihydrate crystals firmly in contact. This study serves as a foundation for preparing high performance for CSBM medical applications.     

Study of particle–matrix interaction in Al/AlB2 composite via nanoindentation

Aluminum diboride (AlB₂) particles enhance wear resistance of functionally-graded aluminum-AlB₂ composites. A critical factor governing the wear resistance of these composites is the mechanical interaction between the diboride particles and the aluminum matrix. To study this interaction nanoindentation experiments were performed on 3–10 µm size AlB₂ particles embedded in the aluminum matrix of an as-received Al–5 wt.%B alloy and a centrifugally cast one. Under large nanoindentation loads (2–8 mN) diboride particles could be pushed into the matrix. The results show that on a per unit area basis, smaller particles are more difficult to push-in than larger particles. Strain gradient plasticity (SGP) theory was used to explain the size dependence of the push-in force.     

Effect of filler level and particle size on dental caries-inhibiting Ca–PO4 composite

Secondary caries and restoration fracture are common problems in restorative dentistry. The aim of this study was to develop Ca–PO₄ nanocomposite having improved stress-bearing properties and Ca and PO₄ ion release to inhibit caries, and to determine the effects of filler level. Nanoparticles of dicalcium phosphate anhydrous (DCPA), two larger DCPA powders, and reinforcing whiskers were incorporated into a resin. A 6 × 3 design was tested with six filler mass fractions (0, 30, 50, 65, 70, and 75%) and three DCPA particle sizes (112 nm, 0.88 μm, 12.0 μm). The DCPA nanocomposite at 75% fillers had a flexural strength (mean ± SD; n = 6) of 114 ± 23 MPa, matching the 112 ± 22 MPa of a commercial non-releasing, hybrid composite (P > 0.1). This was 2-fold of the 60 ± 6 MPa of a commercial releasing control. Decreasing the particle size increased the ion release. Increasing the filler level increased the ion release at a rate faster than being linear. The amount of ion release from the nanocomposite matched or exceeded those of previous composites that released supersaturating levels of Ca and PO₄ and remineralized tooth lesions. This suggests that the much stronger nanocomposite may also be effective in remineralizing tooth lesion and inhibiting caries. In summary, combining calcium phosphate nanoparticles with reinforcing co-fillers in the composite provided a way to achieving both caries-inhibiting and stress-bearing capabilities. Filler level and particle size can be tailored to achieve optimal composite properties. Disclaimer: Certain commercial materials and equipment are identified to specify the experimental procedure. This does not imply recommendation or endorsement by NIST or ADAF.     

Preparation and properties of cast aluminium alloy–sillimanite particle composite

An attempt has been made to explore the possibility of using natural mineral namely sillimanite for synthesizing aluminium alloy composite through a solidification technique. The sillimanite particles were characterized in terms of X-ray, differential thermal analysis in order to examine their suitability for preparing the composite. An aluminium alloy (BS:LM6) was used as the matrix alloy. The sillimanite particles of mean size 140 μm (major axis) were used as reinforcement. The sillimanite particles were added into the matrix melt by creating a vortex with the help of a mechanical stirrer and the melt temperature was maintained between 750 and 800°C. The cast composite was characterized in terms of microstructural, mechanical and abrasive wear properties. It was noted that the sillimanite particles were reasonably uniformly distributed within the matrix and exhibited good mechanical bonding with the matrix. The strength of the composite was noted to be marginally lower than that of the base alloy but the hardness and the wear resistance of the composite were found to be significantly higher than those of the base alloy.     

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO₂ (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO₂ = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO₂ = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO₂ = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.     

Detailed analysis of particle–substrate interaction based on a centrifugal method

The interaction between particles and inclined substrates in a centrifuge was investigated theoretically and experimentally. First, the balance of the force acting on a particle adhering to the substrate, with an inclination angle from 0 to 90° to the horizontal, was formulated separately in the normal and tangential directions. The adhesion force was then derived based on the point-mass model as a function of the angular velocity. Next, the balance of the moments of the forces acting on a particle adhering to the substrate was formulated; theoretical equations for the adhesion force and the effective contact radius were then derived from the angular velocities, obtained at any two inclination angles, based on the rigid-body model. Finally, the removal fraction curves of spherical/nonspherical particles with median diameters of less than 10 µm were experimentally obtained by increasing the angular velocity at each inclination angle. The experimentally obtained angular velocities were substituted into the theoretical equations to compare the point-mass and rigid-body models. The effects of the particle shape on the adhesion force and effective contact radius and that of the inclination angle on the removal fraction curves based on the theoretical equation were also investigated.     

Preparation and electromagnetic characteristics of silica coated Fe–Ni–Mo alloy flakes

The Fe–Ni–Mo alloy flakes were firstly prepared from water atomized powders. Subsequently, by a facile sol–gel technique using tetraethylorthosilicate (Si(OC₂H₅)₄) as a precursor, we successfully synthesized silica coated Fe–Ni–Mo alloy flakes. These products were characterized by Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Furthermore, their electromagnetic parameters, complex permittivity and complex permeability within 2–12 GHz were measured. The results show that both and values of the silica coated flakes substantially decrease with the increase of coating times. Meanwhile, the μ′ values of silica coated samples are larger than those of the as-milled sample at the high frequencies. However, the maximum μ′ exhibits a decline while resonance frequency shifts to high values with the increase of coating times. The calculated reflection loss (RL) curve reveals that a proper thickness of coating can redound to improve the absorbing performances of silica coated Fe–Ni–Mo alloy flakes in high frequency range.     

Effect of calcium on primary silicon particle size in hypereutectic Al–Si alloys

Abstract

Modification of hypereutectic Al-Sialloy, B390 alloy for the refinement of primary silicon particles, and its effects on tensile and impact properties were examined. Calcium was found to have an effect on the size of primary silicon particles. Primary silicon particle size was refined as calcium content decreased. Control of calcium content by the addition of Ti₂Cl₆ to the melt resulted in successful refinement of primary silicon particles. The minimum size of primary silicon particles was 20.3 μmwitha residual calcium content of 16 ppm. The microstructure was composed of very fine 20.3 μm primary silicon particles, compared to 24.5 μm primary silicon particles obtained using the AlCuP method, previously reported as the most effective method. Refinement of primary silicon particles led to an improvement in the mechanical properties of the alloy, especially elongation.     

Structure and optical properties of ordered mesoporous copper oxide–silica composite films

In this study, ordered mesoporous copper oxide–silica (CuO–SiO₂) composite films with CuO/SiO₂ molar ratio ≤6% have been prepared. Small-angle X-ray diffraction and transmission electron microscopy investigations show that the mesoporous CuO–SiO₂ composite films have a hexagonally ordered pore array nanostructure. Wide-angle X-ray diffraction analysis reveals that the copper oxide and silica in the composite films are non-crystalline. The non-crystalline CuO in the mesoporous composite films has an obvious blue-shift phenomenon of the absorption edge. The calculated band gap energy for CuO is 3.2?eV, which is much higher than its bulk counterparts (1.21–1.5?eV).     

The ballistic impact characteristics of Kevlar® woven fabrics impregnated with a colloidal shear thickening fluid

This study reports the ballistic penetration performance of a composite material composed of woven Kevlar® fabric impregnated with a colloidal shear thickening fluid (silica particles (450 nm) dispersed in ethylene glycol). The impregnated Kevlar fabric yields a flexible, yet penetration resistant composite material. Fragment simulation projectile (FSP) ballistic penetration measurements at 244 m/s have been performed to demonstrate the efficacy of the novel composite material. The results demonstrate a significant enhancement in ballistic penetration resistance due to the addition of shear thickening fluid to the fabric, without any loss in material flexibility. Furthermore, under these ballistic test conditions, the impregnated fabric targets perform equivalently to neat fabric targets of equal areal density, while offering significantly less thickness and more material flexibility. The enhancement in ballistic performance is shown to be associated with the shear thickening response, and possible mechanisms of fabric-fluid interaction during ballistic impact are identified.     

Performance characteristics of concrete based on a ternary calcium sulfoaluminate–anhydrite–fly ash cement

This paper reports an assessment of the performance of concrete based on a calcium sulfoaluminate–anhydrite–fly ash cement combination. Concretes were prepared at three different w/c ratios and the properties were compared to those of Portland cement and blast-furnace cement concretes. The assessment involved determination of mechanical and durability properties. The results suggest that an advantageous synergistic effect between and ettringite and fly ash (Ioannou et al., 2014) was reflected in the concrete’s low water absorption rates, high sulfate resistance, and low chloride diffusion coefficients. However, carbonation depths, considering the dense ettringite-rich microstructure developed, were higher than those observed in Portland cement concretes at a given w/c ratio. It was concluded that the amount of alkali hydroxides present in the pore solution is as important factor as the w/c ratio when performance of this type of concrete is addressed.