Properties of Al2O3 nano-particle reinforced copper matrix composite coatings prepared by pulse and direct current electroplating

Cu–Al₂O₃ nano-composite coatings have high potential for use in applications in which high mechanical properties together with high corrosion resistance are required. In the present study it is intended to produce copper nano-alumina composite coatings with various nano-alumina contents in order to investigate the effect of alumina reinforcement particles on corrosion resistance and mechanical properties such as hardness and wear resistance. The composite coatings were deposited using direct current (DC) and pulse current (PC) plating. The microstructures of the coatings produced from both methods were examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The wear behaviors, micro hardness, coating thickness, corrosion rate and coating porosity were examined using appropriate methods. Compared to DC deposition, PC plating facilitated higher amounts of particle incorporation with more uniform distribution. The results indicated that the mechanical properties of the applied coatings with incorporated nano-alumina reinforcement were far more superior as compared to its own matrix as well as non-composite copper coatings. It was also found out that increasing the amount of nano-alumina content in the coating, led to enhanced general properties of the coatings.     

Influence of Xanthan–Curdlan Hydrogel Complex on Freeze‐Thaw Stability and Rheological Properties of Whey Protein Isolate Gel over Multiple Freeze‐Thaw Cycle

The effect of adding xanthan–curdlan hydrogel complex (XCHC) at 2 concentrations (0.25 and 0.5% w/w) on the freeze‐thaw stability of heat‐induced whey protein isolate (WPI) gel was investigated. Samples were stored at 4 °C for 24 h before subjected to 5 freeze‐thaw cycles alternating between ?16 °C (18 h) and 25 °C (6 h). Adding XCHC to the WPI solution resulted in the reduction of a significant amount of syneresis up to 5 repeated freeze‐thaw cycles. Addition of XCHC decreased the amount of syneresis from 45% in the control sample (pure WPI gel) to 31.82% and 5.44% in the samples containing 0.25% and 0.5% gum, respectively, after the 5th freeze‐thaw cycle. XCHC increased the storage modulus (G′) of the gels and minimized the changes of the G′ values over the 5 freeze‐thaw cycles, indicating improvement of the stability of the system. Furthermore, the minimum protein concentration for gel formation decreased in the presence of the XCHC. Scanning electron microscopy (SEM) images showed that addition of XCHC resulted in the formation of a well‐structured gel with numerous small pores in the network, which consequently improved the water retention ability during the temperature abuses up to 5 freeze‐thaw cycles. These results have important implications for using XCHC in the formulation of the frozen WPI‐based products with improved freeze‐thaw stability and rheological properties.     

Online ultrasonic film casting of LLDPE and LLDPE/clay nanocomposites

Transparent cast films of linear low density polyethylene (LLDPE) with nanoclay up to 10 wt % were prepared in one step process using an ultrasonically assisted compounding extruder operating at various ultrasonic amplitudes combined with film casting machine operating at various take up speeds. Thermal, rheological, morphological, and mechanical properties and gas permeability of these films were studied. Ultrasonic treatment introduced an increase in the complex viscosity and storage modulus and a reduction in the tangent loss of LLDPE/clay nanocomposite melts. Cast films prepared by ultrasonic treatment at an amplitude of 7.5 μm showed the highest mechanical properties in both the machine and transverse directions and the lowest oxygen permeability. X‐ray diffraction patterns along with the SEM and TEM images revealed the presence of the exfoliated structure due to the ultrasonic treatment for cast films containing up to 7.5 wt % of clay loading. NMR studies of LLDPE cast films showed an increase of branching due to the ultrasound treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Additive Manufacturing of Ceramics Enabled by Flash Pyrolysis of Polymer Precursors with Nanoscale Layers

We show that a polymer‐based route to ceramics can be implemented into additive manufacturing by reducing the time for pyrolysis to about a second, which we call flash pyrolysis. Repetitive deposition of nanometer scale coatings of the ceramic, in this way, is employed to create defect‐free infiltrations of carbon fiber composites. The mechanical strength of the fibers is retained in the composite. Excellent wetting properties of the polymer precursor permits three‐dimensional, conformal coating through the three stages of infiltration: nanoscale coating of the single fibers, filling of interstitial spaces between the fibers, and a buildup of the coating over the entire composite. The flash pyrolysis method will enable a new genre of polymer‐derived ceramics made into net shape by this unusual method of additive manufacturing.     

Development of a Virtual Reality Structural Analysis System

This paper discusses the development of virtual structural analysis program (VSAP). This is a virtual environment (VE) based structural analysis system developed through a collaborative effort between the School of Architecture + Design and the Department of Computer Science at Virginia Polytechnic Institute and State Univ. (Virginia Tech). The VSAP was developed by linking a visualization routine using the simple VE library and a structural analysis software, the PC-SAP4. Details of the design of four user interfaces for the VSAP are presented. These user interfaces are: the immersive pen and tablet interface, the desktop interface, the portable immersive interface, and the cave automatic VE immersive interface. Usability studies for each interface were conducted. Results of these studies indicated that the users of VSAP were highly satisfied with the experience. In addition, all the developed interfaces were found to be successful for their specific application.     

Thermal analysis of air-cooled PEM fuel cells

Air-cooled proton exchange membrane fuel cells (PEMFCs), having combined air cooling and oxidant supply channels, offer significantly reduced bill of materials and system complexity compared to conventional, water-cooled fuel cells. Thermal management of air-cooled fuel cells is however a major challenge. In the present study, a 3D numerical thermal model is presented to analyze the heat transfer and predict the temperature distribution in air-cooled PEMFCs. Conservation equations of mass, momentum, species, and energy are solved in the oxidant channel, while energy equation is solved in the entire domain, including the membrane electrode assembly (MEA) and bipolar plates. The model is validated with experiments and can reasonably predict the maximum temperature and main temperature gradients in the stack. Large temperature variations are found between the cool incoming air flow and the hot bipolar plates and MEA, and in contrast to water-cooled fuel cells, significant temperature gradients are detected in the flow direction. Furthermore, the air velocity and in-plane thermal conductivity of the plate are found to play an important role in the thermal performance of the stack.     

Preparation and characterization of a temperature-sensitive nonwoven poly (propylene) with antibacterial properties

In this study, a temperature-sensitive fabric with antibacterial properties was prepared by the formation of silver nanoparticles (AgNPs) on nonwoven poly (propylene) (PP) grafted with poly (N-iso-propylacrylamide) (PNIPAAm-PP). First, PNIPAAm was grafted onto corona-treated nonwoven PP. Afterwards, silver nanoparticles were synthesized on the temperature-sensitive hydrogel layer grafted to the surface of nonwoven PP by the reduction of silver ions (Ag⁺). Fourier transform infra-red spectroscopy confirmed the presence of PNIPAAm on the nonwoven PP. scanning electron microscopy-energy dispersive X-ray spectroscopy was used to investigate surface morphology and the presence of silver particles in the samples. Inductively coupled-plasma atomic emission spectroscopy revealed that the Ag content in Ag-functionalized PNIPAAm-PP was significantly higher than Ag-functionalized corona-treated PP with the same concentration of silver solution. Moreover, the results of the swelling rate experiment confirmed that PNIPAAm-PP maintained temperature-sensitive properties after functionalizing with Ag. The results showed that the formation of AgNPs with enhancement in antibacterial property was possible onto PNIPAAm-PP.     

Vibration Studies of a Cantilevered Structure Subjected to Human Activities Using a Remote Monitoring System

Long cantilevered balconies used as seating areas in auditoriums, theaters, churches, and stadiums are often susceptible to excessive vibrations because of crowd movements. Measurement and analysis of the responses of such structures when subjected to human movements can provide a reasonable estimate of their dynamic properties. However, it is generally very difficult to artificially excite such massive structures with a measured input force at the same level as that exerted by a crowd. In addition, it is not yet well understood how human occupants’ presence may change the dynamic properties of these structures. This paper presents details of a remote vibration monitoring system (RVMS) installed on a large cantilevered balcony structure to collect the vibration records generated by rhythmic crowd activities. The results of the studies conducted indicate that the presence of human occupants resulted in a consistent reduction in the natural frequencies of the structure and an increase in the damping ratios for higher modes. Conclusions were also drawn regarding the applicability of the damping ratios recommended by a number of standards and design guides for the structure used in this study.     

Improvement of mechanical properties and in vitro bioactivity of freeze-dried gelatin/chitosan scaffolds by functionalized carbon nanotubes

Functionalized multiwall carbon nanotubes (f-MWCNTs) were used to reinforce the freeze-dried gelatin (G)/chitosan (Ch) scaffolds for bone graft substitution. Two types of G/Ch scaffolds at a ratio of 2:1 and 3:1 by weight incorporated with 0.025, 0.05, or 0.1 and 0.2 or 0.4?wt% f-MWCNT, respectively, were prepared by freeze drying, and their structure, morphology, and physicochemical and compressive mechanical properties were evaluated. The scaffolds exhibited porous structure with pore size of 80–300 and 120–140?µm for the reinforced scaffolds of G/Ch 2:1 and 3:1, respectively, and porosity 90–93% which slightly decreased with an increase in f-MWCNTs content for both types. Incorporation of f-MWCNTs led to 11- and 9.6-fold increase in modulus, with respect to their pure biopolymer blend scaffolds at a level of 0.05?wt% for G/Ch 2:1 and 0.2?wt% for G/Ch 3:1, respectively. The higher content of f-MWCNTs resulted in loss of mechanical properties due to agglomeration. The highest value of compressive strength and modulus was obtained for G/Ch 2:1 with 0.05?wt% f-MWCNT as 411?kPa and 18.7?MPa, respectively. Improvement of in vitro bioactivity as a result of f-MWCNTs incorporation was proved by formation of a bone-like apatite layer on the surface of scaffolds upon immersion in simulated body fluid. The findings indicate that the f-MWCNT-reinforced gelatin/chitosan scaffolds may be a suitable candidate for bone tissue engineering.