Mostafa Rezazadeh Shirdar

The application of surface response methodology to the pretreatment of WC substrates prior to diamond coating

High cobalt (Co) content greater than 10% in tungsten carbide is desirable because Co improves the toughness of the cutting tool. However, the additional Co poses a huge challenge in surface preparation given that the Co content must be reduced to less than 1% on the substrate surface prior to applying a diamond coating. The excessive presence of Co on the substrate surface during coating suppresses diamond nucleation and causes the deterioration of diamond film adhesion. Many attempts have been made to overcome this issue, including the use of chemical etching, mechanical blasting, and heat treatment, but the successful pretreatment of WC-12%Co is still very limited. In this paper, a single-step chemical pretreatment using a mixture of sulfuric acid and hydrogen peroxide solutions was carried out on WC-12%Co. Two independent variables, i.e., etching time and acid temperature, were varied in the experiments to reduce Co contents as well as to roughen the substrate surface. The experimental plan was based on a central composite design. Variance analysis was employed to verify the precision of the mathematical models and their relative parameters. The predicted models generated by the response surface methodology (RSM) were compared with the experimental results, and close agreement was observed. The models demonstrated the significance of both factors, namely, acid temperature and etching time, in reducing Co contents to less than 1% as well as a roughening of the substrate surface within the desirable range.

Green synthesis of silver nanoneedles using shallot and apricot tree gum

Abstract A green synthesis method to produce silver nanoneedles was described using shallot and apricot tree gum (ATG). A fast, simple, and low cost method was used to synthesize silver with nanoparticle and nanoneedle shape from the silver nitrate solution. Shallot as a reducing agent and apricot tree gum (ATG) as a stabilizer and a capping agent were utilized to reduce and form silver ions into silver atoms with needle and particle shape. Moreover, high crystalline structures of silver nanoparticles (AgNPs) with diameters of 8–20 nm and silver nanoneedles with average diameters of 50–60 nm and lengths of 5–10 μm were consequently synthesized by shallot and the mixture of shallot and ATG. A self-assembly mechanism was proposed to indicate the formation of needle-like structures of spherical AgNPs via carbon chains of ATG. The results indicate that the presence of ATG with shallot can transfer the reduced AgNPs into the silver nanoneedle. The findings were characterized using X-ray diffraction (XRD), ultra violet visible (UV-Vis) spectrometry, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) techniques.

Evaluating hydrothermal synthesis of fluorapatite nanorods: pH and temperature

ABSTRACT In this study, the fluorapatite was synthesised by a hydrothermal technique in different pH and temperature using apricot tree gum surfactant. The fluorapatite was synthesised in different shapes such as spherical, Chrysanthemum flower and rod. The effect of two factors (pH and temperature) on the shape and dimension of synthesised fluorapatite was investigated through the full factorial design. An experimental strategy was developed based on the analysis of variance to create mathematical models for the shape and dimension of synthesised fluorapatite. Findings revealed that the pH of hydrothermal solution is more significant factor than temperature in terms of shape and dimension of the synthesised fluorapatite. It was illustrated that similar nanorods structure to the human tooth enamel can be achieved in pH of 10 and temperature of 70 °C The transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) spectroscopy were carried out for characterisation of synthesised fluorapatite.

In situ synthesis of hydroxyapatite-grafted titanium nanotube composite

ABSTRACT The present study is an investigation to demonstrate the effectiveness of in situ approach in the synthesis of hydroxyapatite-grafted titanium nanotube composite (HA-TNT). This method involves combining the process of HA sol–gel and rapid breakdown anodisation of titanium in a novel solution consisting of NaCl and N3PO4. This new synthesis approach produced a uniform dispersion of Anatase and Rutile phases of TiO2 nanotubes with minimal agglomeration in the matrix of crystalline HA. The characterisation of homogenised HA-TNT composite was investigated via field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD). FESEM and TEM images indicated the nanostructure of composite with TiO2 nanotube diameter of approximately 10 nm. XRD and EDS analyses confirmed the formation of HA crystalline with the Ca/P ratio of 1.58 and formation of Anatase and Rutile phase of TiO2 nanotubes.

Optimization of Pre-Treatment Parameters before Diamond Coating Using Non-Dominated Sorting Genetic Algorithm (NSGA-II)

In this study a single step of the chemical pre-treatment is implemented to tungsten carbide (WC 6 [%]) at the surface of the substrate in order to solve poor adhesion problem. During the pre-treatment process, numerous parameters such as etching time, acid temperature and concentration affect on the surface roughness and Cobalt content of WC-Co substrate are investigated. Optimal selection of these parameters is one of the significant issues to achieve high-quality work-piece in etching process. Thus, the statistical model based on nonlinear polynomial equations is developed for the different responses. Non-dominated Sorting Genetic Algorithm (NSGA-II) with the use of MATLAB Software codes is used to solve multi-objective optimization problem in order to provide a preferred solution for a process engineer in a short period of time.