Sharif Digital Repository

The precipitation process considered here, involved the addition of orthophosphoric acid solution to a calcium hydroxide solution. Several parameters such as the effects of atmosphere controlling, pH, adding extra acid solution, the amount of stirring speed, and post-chemical treatment were studied. In order to study the thermal stability of synthesised powders, they were sintered for 2 h at 1200 °C and the as-precipitated and sintered powder samples were examined using SEM, XRD, FTIR and ICP methods. The results clearly revealed that the final precipitated powder is hydroxyapatite (HA) with good purity, stoichiometry and successful thermal stability. SEM high magnification micrographs... 

Commercially pure titanium samples were exposed to grit blasting and acid-alkali treatments to obtain a variety of surface compositions and morphologies. Contact roughness test and microstructural studies were employed to study the surface topography of the samples. The nature and chemical composition of surface phases were evaluated using X-ray diffraction and microanalysis techniques. Selected samples first exposed to in vitro environment were then tested to determine the surface morphology and surface microstructure. Based on the data presented in this work, it is suggested that grit blasting process utilized prior to chemical treatment stage, yields a high quality surface morphology.... 

The surface defluorination of Teflon in powdery form was performed using a chemical treatment. The reaction parameters including the reaction time, sodium, naphthalene concentrations were optimized using a Taguchi method to obtain maximum functionality on the particles surface. The surface functionality of the treated particles was analyzed by FTIR, energy dispersive X-ray analysis (EDX) and surface energy. Both treated (g-PTFE) and untreated (PTFE) Teflon were added to polyamide 66 (PA66) at various loadings up to 6 wt%. Mechanical, differential scanning calorimetry (DSC) and tribological analyses for different PA66/Teflon composites were carried out. The chemical treatment enhanced the... 

Pectin from two different plant sources: apple and sugar beet was studied. Apple pectin was modified by chemical treatments such as: acid, alkali and ammonia, so as to obtain an ester level equal to or less than 50 %, which is described as low methoxyl (LM) pectin. LM pectin form gels with significant characteristic. In this study, de-esterification of apple pectin with acid treatment resulted in gel specification with higher molecular weight and viscosity. Acid treatment resulted in pectin with average molecular weight of 32000 Dalton. Pectin was extracted from sugar beet pulp by acid and alkali treatments. The quality of gel formation and water uptake was improved using sugar source... 

Gamma irradiation systems are used extensively in the industry in order to sterilize medical devices, disinfect hygienic products and increase the shelf life of agricultural products. The method of gamma irradiation is superior to the older methods of heat or chemical treatment because it is by far a simpler operation. In this method, only one parameter, the exposure time is controlled, whereas in the other mentioned methods five or six different parameters need to be controlled. The design of irradiation systems generally includes the size and the location of products, and the arrangement of source rack pencils. In order to optimize the design of the gamma irradiation systems, it is needed... 

Spontaneous water imbibition into the matrix blocks is known as the main mechanism for increased oil recovery from naturally fractured oil reservoirs. The rate of oil recovery and its ultimate value is mostly affected by wettability of the rocks and their pore structure. Oil viscosity also greatly influences the rate of oil recovery. A novel experimental model was utilized to study the imbibition mechanism under different wettability conditions. Matrix blocks made from different grain types and size distributions of glass beads were saturated with two different types of synthetic oil, to mimic the oil-saturated matrixes. The wetting characteristic of the models used in this study were... 

An experimental investigation was conducted on the oxidative desulfurization of model sulfur compounds such as dibenzothiophene and benzothiophene in toluene as a simulated light fuel oil with a mixture of hydrogen peroxide as the oxidant and various acids as the catalyst. The influences of various parameters including reaction temperature (T), acid to sulfur molar ratio (Acid/S), oxidant to sulfur molar ratio (O/S), type of acid, and the presence of sodium tungstate and commercial activated carbon as a co-catalyst on the fractional conversion of the model sulfur compounds were investigated. The experimental data obtained were used to determine the reaction rate constant of the model sulfur...