Browse

1 - 10 of 71 items :

  • Biomaterials x
  • Mechanical Engineering x
Clear All

Abstract

In this work, Zn-Ni alloys have been deposited on steel from sulfate bath, by electrodeposition method. The effect of Zn content on deposits properties was studied by cyclic voltammetry (CV), chronoaperometry (CA), linear stripping voltammetry (ALSV) and diffraction (XRD) and scanning electronic microscopy (SEM). The corrosion behavior in 3.5 wt. NaCl solution was examined using anodic polarization test and electrochemical impedance spectroscopy. X-ray diffraction of show that Zn-Ni alloys structure is composed of δ phase and γ phase, which increase with the decrease of Zn content in deposits. Results show that deposits obtained from bath less Zn2+ concentration exhibited better corrosion resistance.

Abstract

The purpose of this paper is to establish the intersection curves between cylinders, using Mathematica program. The equations curves which are inferred by mathematical methods are introduced in this program. This paper takes into discussion the case of four cylinders.

Abstract

The paper presents a numerical method of kinematical analysis of the articulated quadrilateral mechanism. Starting from Euler’s relation concerning the distribution of speeds written in projections on the fixed reference system axes, a system of differential equations describing the movement of the mechanism was obtained. This system of differential equations was then solved using numerical integration methods and the variation with respect to time of the position kinematical parameters, of the velocities (the first order kinematical parameters), and of the accelerations (the second order kinematical parameters), was obtained. Matrix writing of the differential equations was used in order to make the differential equations set out in the paper easier to solve using the electronic computer.

Abstract

The paper deals with the complete kinematical analysis of the mechanism that enters the machine tool structure designed to generate, in particular, plane surfaces. A machine tool of this kind is called shaping machine. For this purpose, Euler’s relations concerning the velocities distribution, written in projections on the fix reference system axes will be used. Starting from these relations we will get to a system of the first order linear differential equations whose unknowns are the kinematical parameters of the mechanism elements. The variation in time of these parameters will be obtained by solving the differential equations system the differential equations system using numerical integration methods.

Abstract

Refractory concretes with the usual cement content (about 20%) present, besides their well-known advantages, several important disadvantages which make such concretes unfit for certain applications. The relatively high CaO content in concretes, the presence of even small amounts of SiO2 and Fe2O3 in cement reduce in the first place the concretes refractoriness; if their relatively high porosity is also taken into account, the concretes behavior is further damaged in regard to the structural and thermal-chemical stability. especially at their high operating temperatures. This work is an attempt to correct the shortcomings shown by reducing the cement dosage and using appropriate admixtures in the technological process of concrete making.

Abstract

The paper shows data related to coexistence of various binding systems, which could be present during the hardening of special concretes. It is taken into account the Ultra Low Aluminous Cement Concretes additivated with different materials (phosphates and mineral ultra dispersed powders - Condensed Silica Fume, Hydrated Alumina etc). In correlation to the pH-value, these substances can favour the forming of new binding systems besides the hydraulic binder (which is not important in this case). The new system is the coagulation binding form. The coagulation binding system has a very important role in the advanced compactness and in the increasing mechanical strengths of concrete structures.

Abstract

0.88Pb(Zr0.52Ti0.48)O3 – 0.12Pb(Mn1/3Sb2/3)O3 – 0,02 at%E piezoelectric ceramics, with E = Pr3+ were synthesized by using a conventional method, namely a solid state reaction technique. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were employed for the structural and microstructural investigations. Piezoelectric methods were used for the dielectric and piezoelectric properties determination. The results of XRD show a perovskite structure and XRD patterns, indexing on a tetragonal cell structure, was carried out for the most common phases. The SEM micrographs of the sintered compositions reveal a homogenous structure with a sharp or rounded grain boundary. The modified PZT ceramic presents still superior piezoelectric properties. Based on the results obtained, one can conclude that the analysed piezoelectric ceramics are useful for device applications.

Abstract

In this work, nickel oxide was fabricated on glass substrate at 450 °C by spray pyrolysis technique. The NiO layers were obtained with 0.05M molarity, which were deposited by various deposition rates 20, 40, 60 and 80 ml. The effects of deposition rate on the structural, electrical and optical properties were examined. All fabricated NiO thin films were observed a nanocrystalline a cubic structure with a strong (111) preferred orientation, it is only phase was observed in all deposited NiO. The film elaborated with 60 ml have a minimum value of crystallite size was 15.8 nm. All NiO thin films have an average transmittance is about 70 % in the visible region. The NiO thin films have a verity in the band gap energy from 3.34 to 3.51 eV because the effect of deposition, the minimum value was found at 80 ml, this condition have a lowest Urbach energy. The NiO thin films have an electrical resistivity was decreased from 0.625 to 0.152 (Ω.cm) with increasing the deposition rate from 20 to 80ml. The best results of NiO thin films are obtained in the deposition NiO films by 40 and 80 ml.

Abstract

This paper presents the most used processes for the synthesis of hydroxyapatite from aqueous solutions: chemical precipitation, the hydrothermal process and the sol-gel method. The experimental part includes the synthesis of hydroxyapatite by chemical precipitation. The obtained results confirm the obtaining of a ceramic with a high purity and a high degree of crystallization.

Abstract

The paper proposes to establish the intersection curve and the unfoldings of three cylinders. The intersection of the curves was determined by the classical method, using the AutoCAD program, and the unfolded surfaces were realized by analytical methods. For this the Mathematica program was used.