Volume 11 (2011): Issue 1 (March 2011)

The effect of rice husk ash with different grinding time on the engineering properties of concrete was studied. Eight rice husk ashes with different grinding were used in this investigation. Rice husk ash was used to partially replace Portland cement Type I at 15% by weight of cementitious material. The 100-mm concrete cube specimens were cast and cured in water for 7 and 28 days. The compressive strength of concrete was designed to achieve of grade 40 N/mm² at 28 days. A superplasticizer was added to all mixes to provide workability in the range of 110 - 120 mm. However, the water to cement ratio (w/c) of the concrete was maintained at 0.49. Based on the results, the morphology of the rice husk ashes were changed by grinding. These appear to be an optimum grinding time of approximate 90 minutes which the compressive strength increased significantly. Generally, incorporation of RHA at varies grinding time can be decrease or increased the engineering properties of concrete extremely.

Titanium and titanium alloys are frequently used in orthopaedic implants in load bearing situations because they possess favourable properties, such as a good ductility, tensile and fatigue strength, modulus of elasticity matching that of bones, low weight, and good biocompatibility. The drawback of Ti implants is their poor osseointegration and osteoconductive properties. The present paper describes the techniques to improve the bioactivity of titanium and enhance the bone-implant bonding ability by the electrochemical anodization to fabricate titania nanotube arrays (TiO₂). The naturally formed oxide layer has bio-inert character and does not readily form a strong interface with surrounding tissue. It has been proved that osseointegration of titanium implants can be improved by rough surfaces of Ti implants [1,2]. The nanotubular surface enhances adhesion, growth and differentiation of the cells. The nanotubular arrays increase the roughness of titanium implants on the nanoscale, providing the surface similar to that of a human bone. Bone-forming cells tend to adhere to the surfaces that are similar to natural bone both in chemistry and roughness. Nanotubular layers provide a high surface-to-volume ratio with controllable dimensions which are able to differentiation of mesenchymal stem cells into osteoblastic cells. Moreover, the anodized nanotubular arrays on titanium surface can be used as reservoirs for drugs (anti-inflammatory, and improving bone-growth) with prolonged drug release ability. Also, there is possibility to further enhance bioactivity of titanium implant with nanotubular surface by hydroxyapatite deposition into the titania nanotubes which further promotes bone ingrowth. The application of nanotubular structures of oxide layers can be optimized taking into consideration some important parameters as osseointegration rate and interface strength determined by nanotube mean size and length.

The paper critically reviews so far investigations focused on nanooxidation of titanium and titanium alloys. The numerical model of nanotubular arrays with the use of Finite Element Method (FEM) is proposed for an assessment of the load transfer and stress distribution under applied loading which could be a critical factor when considering the described application of nanotubes.

Titanium and its alloys are widely used as biomaterials for orthopaedic applications. Research connected with their best corrosion and wear resistance, biocompatibility and bioactivity are still being conducted. The current research is also focused on the design and manufacturing of the porous materials based on e.g. Ti-13Nb-13Zr alloy, which can be applied for implants. One of the most effective manufacturing methods of the porous materials are powder metallurgy techniques. The aim of the presented work was the design of powder preparation procedure and design a parameters of pressing and sintering processes in order to obtain the porous structure from Ti-13Nb-13Zr alloy. Investigation results of the microstructure morphology, pore size and porosity of the obtained porous material on the base Ti-13Nb-13Zr alloy in dependence of the pressing and sintering parameters are also shown and discussed.

Mechanical behaviour was compared for glass/polyester laminates manufactured in the boatbuilding plant using three methods: hand lay-up, vacuum bagging, infusion. Specimens were tested in dry condition and following accelerated water immersion test (70°C- corresponding to the exposure of 30 years at 19°C). In three point bending test 40-50% reduction in laminate strength was observed due to water immersion. The highest degradation was in samples manufactured using hand lay-up method, the differences in strength between both vacuum methods were insignificant. Interlaminar shear strength was reduced by 25% for infusion method which is recommended as the most efficient. Matrix plasticization and debondings as well as surface microcracks were responsible for reduction in strength for water conditioned specimens. However, no microstructural difference in type or intensity of internal damage was observed for the three sample types.

The nanometric materials and technologies resulted in nanostructures are reviewed. The examples of nanomaterials are shown. The typical nanotechnologies, including plastic deformation, mechanical attrition, controlled detonation, hot plasma jet synthesis, laser vaporisation, CVD and PVD, mechanical milling, annealing, ultrasonic irradiation, nanolithography, electrocrystallisation, electrospinning, sol-gel method, cryogenic laser-enhanced melting, and hydrogen-enhanced amorphisation, are presented. Typical applications in technics and medicine are given.

Porous CaTi_0.9Fe_0.1O_3-δ (CTF) perovskites were synthesized by the standard solid state method at different sintering temperatures with carbon black (CB), corn starch (CS) and potato starch (PS) as pore-forming agents. The ceramic samples of porosity between 9% and 42% with 5 - 40 μm pore sizes, were obtained by a 6 h sintering at either 1130° C or 1200° C of precursor powder prepared at 1470° C. X-ray diffraction analysis proved the existence of orthorhombic single-phase perovskites crystalline structure. Electrical conductivity at 800° C was between 1.42×10^-2 S cm^-1 and 1.86×10^-3 Scm^-1. The conductivity markedly depended on the sample porosity. It should be noted that 30% of porosity, resulted in reduction of conductivity by less than one order of magnitude. Activation energy of conductivity varied between 0.41 and 0.56 eV. Cornstarch has been chosen as the most suitable pore-forming agent for obtaining the cathode of good properties. The best amount of the cornstarch has been proposed as between 5 and 10%.