Characterization of a novel bioactive composite using advanced X-ray computed tomography

A novel bioactive, porous silica–calcium phosphate nanocomposite (SCPC) that can be used to treat large bone defects in load-bearing positions has been tested and has shown great potential for applications in tissue engineering. Porosity is essential to the performance of the composite material as a tissue engineering scaffold, as porous scaffolds provide a physical, 3-D template to support new tissue formation. However, porosity characterization using conventional techniques such as porosimetry or scanning electron microscopy requires extensive preparation of samples and may destroy important features during preparation and analysis stage. In this work, the new composite is characterized using an advanced high resolution X-ray computed tomography, which is a non-destructive testing technique that allows construction of the 3-D topology of the microstructure. The results clearly show the effectiveness and versatility of this technique in characterizing the porous architecture of the novel composite biomaterial. The pore distribution, morphology and interconnectivity in the composite scaffolds were found to be ideal for use in tissue engineering applications.     

Flocculation and viscoelastic behavior of industrial papermaking suspensions

The effects of the surface charge type and density C496, C492 and A130LMW polyacrylamides (PAMs) on the rheological behavior of real industrial papermaking suspensions were quantitatively related to the degree of flocculation for the same industrial papermaking suspensions. The floc sizes were larger but less dense when anionic PAM was used, and this due to the repulsive forces between the anionic PAM and colloidal particles, leading to the development of open structure flocs of less density. On the other hand, rheological measurements showed that the papermaking suspension is thixotropic with a measurable yield stress. The results showed that the magnitude of the critical stress, τ _c , complex viscosity, η*, elastic modulus, G′, and viscous modulus, G″, depend on the number of interactions between the PAM chains and particle surface and the strength of those interactions. Cationic PAM showed higher values of η*, G′, G″ and τ _c compared to anionic PAM. This behavior is in good agreement with Bingham yield stress, τ _B , adsorption and effective floc density results. Similar to oscillatory measurements, creep measurements also showed that the deformation was much lower for the cationic PAM based suspensions than for the anionic PAM based suspensions. Furthermore, the results revealed that increasing the cationic PAM surface charge decreases the floc size but increases the adsorption rate, elasticity and effective floc density proposing differences in the floc structures, which are not revealed clearly in the Bingham yield stress measurements.     

Thermo-mechanical and metallurgical aspects in friction stir processing of AZ31 Mg alloy—A numerical and experimental investigation

Friction stir processing of AZ31 Mg alloy was investigated by numerical modeling and experiments. A CFD based, fully coupled, 3D, thermo-mechanical model was built to better understand the effect of process parameters on temperature, material flow and strain rate. In order to account for material softening phenomena at elevated temperatures and extremely high strain rates that occur during the FSP process, experimentally measured peak temperatures were utilized to introduce a correction function in the flow stress constitutive relation. The numerical results showed that rotational speed as compared to translational speed had a more dominant effect on temperature field and strain rate. In addition, the asymmetric material flow around the tool axis caused higher peak temperature and strain rate on the advancing side (AS), while the material in the path of tool pin was swept around the retreating side (RS). FSP experiments confirmed peak temperatures measured at sheet surface near shoulder perimeter on AS were always higher than corresponding RS peak temperatures, under the selected range of process parameters. In addition to thermo-mechanical aspects, the metallurgical characteristics of FSP i.e. mainly the grain size evolution was studied by optical and electron microscopy. Experiments revealed that the coarse bimodal microstructure of as-received AZ31 Mg was subdivided into a defect-free, fine grain microstructure at the rotational speed of 1000 rpm, while a defect-free but a relatively coarse and bimodal microstructure evolved in the material at rotational speeds higher than 1000 rpm. Furthermore, in the selected range of process parameters the increases in translational speed resulted in finer grain sizes without the formation of voids or defects.     

On the High Temperature Testing of Superplastic Materials

The simplest test in characterizing the behavior of superplastic materials is the uniaxial tensile test. Since superplasticity is achieved at relatively high temperatures, heat involvement adds so many unpredictable problems to the simplest testing technique. In spite of the vast number of research activities directed towards studying the various aspects of superplastic deformation, there is a lack of a standardized testing procedure that can tackle the various issues associated with high temperature testing. In this work, we attempt to shed some light on the controversial issues associated with high temperature superplastic testing. The effects of various testing procedures and parameters on the accuracy of the results are investigated. We address the issues related to gripping and test sample geometry, heat and temperature effects, and comment on the available testing and analysis procedures. We hope that this study highlights the urgent need to develop a standardized testing approach that takes into account all the important issues affecting high temperature testing. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6–9, 2005.     

Mechanical Characteristics of Superplastic Deformation of AZ31Magnesium Alloy

As the lightest constructional metal on earth, magnesium (and its alloys) offers a great potential for weight reduction in the transportation industry. Many automotive components have been already produced from different magnesium alloys, but they are mainly cast components. Production of magnesium outer body components is still hindered by the material’s inferior ductility at room temperature. Magnesium alloys are usually warm-formed to overcome this problem; however, it was observed that some magnesium alloys exhibits superior ductility and superplastic behavior at higher temperatures. More comprehensive investigation of magnesium’s high temperature behavior is needed for broader utilization of the metal and its alloys. In this work, the high temperature deformation aspects of the AZ31B-H24 commercial magnesium alloy are investigated through a set of uniaxial tensile tests that cover forming temperatures ranging between 23 and 500 °C, and constant true strain rates between 2 × 10⁻⁵ and 2.5 × 10⁻² s⁻¹. The study targets mainly the superplastic behavior of the alloy, by characterizing flow stress, elongation-to-fracture, and strain rate sensitivity under various conditions. In addition, the initial anisotropy is also investigated at different forming temperatures. The results of these and other mechanical and microstructural tests will be used to develop a microstructure-based constitutive model that can capture the superplastic behavior of the material. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6–9, 2005.     

Analytical Modeling of Strain Rate Distribution During Friction Stir Processing

Friction Stir Processing (FSP) is becoming an acceptable technique for modifying the grain structure of sheet metals. One of the most important issues that hinder the widespread use of FSP is the lack of accurate models that can predict the resulting microstructure in terms of process parameters. Most of the work that has been done in the FSP field is experimental, and limited modeling activities have been conducted. In this work, an analytical model is presented that can predict the strain rate distribution and the deformation zone in the friction stir processed zone as a function of process parameters. In the model, the velocity fields within the processed zone are determined by incorporating the effects of both the shoulder and the pin of the tool on the material flow. This is achieved by introducing state variables and weight functions. The model also accounts for different interfacial conditions between the tool and the material. The effects of different process parameters and conditions on the velocity fields and strain rate distributions are discussed. The results clearly show that the model can successfully predict the shape of the deformation zone and that the predicted strain rate values are in good agreement with results reported in the literature. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Baltimore, MD, June 25-28, 2007.     

Maximum Stress Triaxiality Ratio Criterion for Mixed Mode Crack Initiation in Anisotropic Materials

The maximum stress triaxiality ratio criterion, originally proposed for mixed mode crack initiation in isotropic materials, is adapted for anisotropic materials using an anisotropic yield function.     

Visible light‐driven metal‐oxide photocatalytic CO2 conversion

In this work, nine photocatalysts were prepared by a conventional solid‐state reaction method. The samples were characterized by X‐ray diffraction, UV–Vis diffuse reflectance spectroscopy, surface area measurements based on the Brunauer–Emmett–Teller theory, and scanning electron microscopy. The tested materials (BaBiO₃, Bi₂WO₆, SrTiO₃, KNbO₃, NaNbO₃, Sr₄Nb₂O₉, YInO₃, CaIn₂O₄, and YFeO₃) showed great potential for use as photocatalysts in the efficient reduction of CO₂ into a renewable hydrocarbon fuel as well as in water splitting. Our results showed that among the nine tested photocatalysts, three could generate CH₄. In particular, it was observed that KNbO₃, as a result of its high surface area and the suitable band gap, showed the highest CH₄ generation, (86.842 ppm g^?1 h^?1). Some of the tested photocatalysts could generate H₂ and O₂ at a very promising rate; Sr₄Nb₂O₉ and NaNbO₃ were the best two photocatalysts, with an average O₂ production rate of 69.476 ppm g^?1 h^?1 and 57.928 ppm g^?1 h^?1, respectively. Further, NaNbO₃ showed the highest H₂ production average with a rate of 220.128 ppm g^?1 h^?1. The photocatalysts presented herein represent a significant improvement because of the reactor type and the preparation techniques implemented in this study. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrochemical Immuno-Vascular Solid State Point of Care Testing （POCT）

In this work, it is proposed a POCT and innovative method of immunoassay for the detection of C-reactive protein and IgG, using Amperometry coupled to solid state kit, connected to a micro-flow system with comparable sensitivity to a high sensitivity CRP ELISA （hsCRP） and IgG ELISA, with 1-3 min turnaround time to result. Samples of CRP （0 to 250 ng·mL-1） and IgG or diluted spiked human serum are injected through a solid state polymeric kit, micro-flow sensor channels of a SWCT SPE nano-modified biosensor. Preparing two kits immuno-assays, in the same micro-column, built on oxirane groups of polymeric bead surface, with biological support to CRP and IgG biomarkers recognition, in a real time scheme, at the end of analyte injection the initial rate of change in current intensity I/A was proportional to CRP respectively IgG concentration, with low detection limit （LOD） of 0.1 ng·mL-1. It was revealed that CRP/IgG concentrations in serum that might be expected in both normal and pathological conditions can be detected in a real-time-efficient, multi-immunoassay with solid state detection kit technology with determined CRP/lgG concentrations in close agreement with those determined using a commercially available high sensitivity EL1SA.