Abstract
This study aimed to investigate the suitability of some concrete components for producing \"high- performance heavy density concrete\" using different types of aggregates that could enhances the shielding efficiency against - rays. 15 mixes were prepared using barite, magnetite, goethite and serpentine aggregates along with 10% silica fume, 20% fly ash and 30% blast furnace slag to total OPC content for each mix. The mixes were subjected to compressive strength at 7, 28 and 90 days. In some mixes, compressive strengths were also tested up to 90 days upon replacing sand with the fine portions of magnetite, barite and goethite. The mixes containing magnetite along with 10% SF reaches the highest compressive strength exceeding over M60 requirement by 14% after 28 days. Whereas, the compressive strength of concrete containing barite was very close to M60 and exceeds upon continuing for 90 days. Also, the compressive strength of high-performance concrete incorporating magnetite fine aggregate was significantly higher than that containing sand by 23%. On the other hand, concrete made with magnetite fine aggregate had higher physico-mechanical properties than that containing barite and goethite. High-performance concrete incorporating magnetite fine aggregate enhances the shielding efficiency against - rays.
Key Words
heavyweight aggregates; high- performance concrete; linear attenuation coefficient (u); half- value layer (HVL); tenth- value layer (TVL)
Address
Ahmed S. Ouda: Housing and Building National Research Center (HBRC), Dokki, Giza, Egypt
Abstract
In the present article, the thermal buckling of zigzag single-walled carbon nanotubes (SWCNTs) is studied using a nonlocal refined shear deformation beam theory and Von-Karman geometric nonlinearity. The model developed simulates both small scale effects and higher-order variation of transverse shear strain through the depth of the nanobeam. Furthermore the present formulation also accommodates stress-free boundary conditions on the top and bottom surfaces of the nanobeam. A shear correction factor, therefore, is not required. The equivalent Young\'s modulus and shear modulus for zigzag SWCNTs are derived using an energy-equivalent model. The present study illustrates that the thermal buckling properties of SWCNTs are strongly dependent on the scale effect and additionally on the chirality of zigzag carbon nanotube. Some illustrative examples are also presented to verify the present formulation and solutions. Good agreement is observed.
Key Words
carbon nanotube; computer modelling and simulation; thermal properties
Address
Abdelwahed Semmah:Faculté des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria
O. Anwar Bég: Gort Engovation- Propulsion, Nanomechanics and Biophysics, Southmere Avenue, Bradford, UK
S. R. Mahmoud:Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia, Mathematics Department, Faculty of Science, University of Sohag, Egypt
Abdelouahed Tounsi:Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Abstract
A study that demonstrates how to investigate the molded part quality and the consistency of injection process based on the rheological concept is proposed. It is important for plastic material whose melt viscosity is variable with respect to the processing condition. The formulations to couple the melt viscosity with injection pressure and fill time are derived first. Taking calculations of the measured pressure and the time by using these formulations, the melt viscosity in injection process can be determined on machine. As the relation between the injection speed and the melt viscosity is constructed, the influences of the setting parameter of injection machine on the molded part quality can be investigated through evaluating the state of the melt viscosity. In addition, a pressure sensor bushing (PSB) designed with a quick installation feature is also provided and validated. The results show that a higher injection speed improves the tensile strength of the molded part but also the consistency of the molded part quality. This work provides an alternative to evaluate the molding quality scientifically.
Key Words
rheology; melt viscosity; consistency of molded part quality; injection molding process
Address
Chung-Chih Lin and Chieh-Liang Wu: Department of Mechanical and Computer-Aided Engineering, National Formosa University 63208, No.64, Wen-Hwa Road, Hu-Wei town, Yunlin county, Taiwan
Abstract
The microwave dielectric properties of CeO2 nanoparticles (0.5, 1.0 & 1.5 wt%) doped Mg2TiO4 (MTO) ceramics have been investigated at cryogenic temperatures. The XRD patterns of the samples were refined using the full proof program reveal the inverse spinel structure without any secondary phases. The addition of CeO2 nanoparticles lowered the sintering temperature with enhancement in density and grain size as compared to pure MTO ceramics. This is attributed to the higher sintering velocity of the fine particles. Further, the microwave dielectric properties of the MTO ceramics were measured at cryogenic temperatures in the temperature range of 6.5-295 K. It is observed that the loss tangent (tan )of all the samples increased with temperature. However, the CeO2 nanoparticles doped MTO ceramics manifested lower loss tangents as compared to the pure MTO ceramics. The loss tangents of the pure and MTO ceramics doped with 1.5 wt% of CeO2 nanoparticles measured at 6.5K are found to be 6.6
Address
Ranjan K. Bhuyan, Santhosh K. Thatikonda, Pamu Dobbidi and Mohan V. Jacob: Department of physics, Indian Institute of Technology Guwahati, Guwahati -39, India
J.M. Renehan: Electronics Materials Lab., School of Engineering and Physical Sciences, James Cook University, Townsville, QLD 4811 Australia
Abstract
Processable conducting polyaniline derivative with free amine functional groups was successfully synthesized from the monomer o-phenylenediamine in aqueous hydrochloric acid medium using ammonium persulfate as an oxidative initiator. The synthesized poly(o-phenylenediamine) (PoPD) in critical condition was found to be completely soluble in common organic solvents like dimethyl sulfoxide, N,N-dimethyl formamide etc. From the intrinsic viscosity measurement, the optimum condition for the polymerization was established. The polymer was characterized by ultraviolet visible spectroscopy, Fourier transform infrared spectroscopy, proton magnetic resonance spectroscopy (1HNMR) and thermogravimetric (TGA) analyses. The weight average molecular weights of the synthesized polymers were determined by the dynamic light scattering (DLS) method. From the spectroscopic analysis the structure was found to resemble that of polyaniline derivative with free amine functional groups attached to ortho/meta position in the phenyl ring. However, very little ladder unit was also present with in the polymer chain. The moderate thermal stability of the synthesized polymer could be found from the TGA analysis. The average DC conductivity of 2.8 x 10-4 S/cm was observed for the synthesized polymer pellet after doping with hydrochloric acid.
