Papers by Keyword: Microtopography

Abstract: Cholesterol is a main component in mammalian cell membranes and lipoproteins. High level of cholesterol in blood can damage arteries and potentially linked with cardiovascular diseases. Cholesterol is also major constituent of gall stones. Cholesterol crystals were grown by single diffusion gel growth technique using neutral silica gel set by acetic acid. Solution of cholesterol prepared in acetone was poured as a supernatant solution on set gel. Transparent, thin, platelet type crystals were grown. Powder XRD and FT IR studies were carried out for the confirmation of crystal system and chemical bonding. The surface micro topographical study was carried out by using SEM and AFM and interesting features were observed. As cholesterol possesses high dielectric constant, it functions as an insulting cover for the transmission of electric impulses in the nervous tissues; therefore, the dielectric study was carried to understand its dielectric behavior in the frequency range from 50 Hz to 5 MHz. The dielectric constant decreased as the frequency of applied field increased. The a.c. conductivity and a.c. resistivity were also calculated.

Abstract: For perfect surface roughness description is not enough to know characteristics of surface profile. It is necessary to use topography methods, so called microtopography. Thereby, surface roughness in microtopographycal understanding must be described with three coordinates, whose in Cartesian coordinates system compose point under consideration height h, abscissa and ordinate, determines point position in the plane. Most efficient methods in irregular surface roughness research are random function theory methods. Therefore, microtopography, analogically to profile, may consider as random function, but two dimensional function, i.e. two variable x and y random field h(x,y). From analogy with random process, random field can be normal – ordinates are distributed by normal (Gaussian) distribution. Moreover, random field can be homogeneous and heterogeneous. Random field is deemed homogeneous if its mean value is discretionary and correlation function depends only from distance between surface points. Important characteristic of random field is correlation function, whose depends of two variables t1 and t2 – orthogonal Cartesian coordinates of vector t. Random field is homogeneous and isotropic when its characteristics are equivalent in any direction. There are three types of surface anisotropy: • General event of surface anisotropy. Characteristics of this event roughness parameters are depend of surface split direction. • Surface roughness with direct anisotropy. Those surfaces are with typical traces of tool and they proper two mutually perpendicular surface roughness directions. • Extended anisotropy area – special event of anisotropy roughness. Of analytical opinion, gainfully anisotropy roughness see as extended occasional isotropy area. This let easy cross from anisotropy surface to isotropy and contrariwise, thereby embrace amount class of surface roughness. Let’s formulate microtopography model of rough surface [1]. Surface roughness is described with homogeneous normal random field h(x,y) that has uninterrupted correlation function and uninterrupted deriviates. We may consider that E{h(x,y)}=0. The mean random field value is plane called mean plane. For describing random field we must know mathematical expectation and field correlation function, what in fact reduces on determining dispersion and rationed correlation function r(t1, t2). Homogeneous random field dispersion D{h} doesn’t depends of direction and can be founded in any surface split. Given model of rough surface let inspect surfaces produced by abrasive instruments and friction surfaces after wear-in period.

Abstract: The influence of ultrasonic vibration on the surface roughness and micro-topography of ceramics plate is discussed in this paper. Grinding assisted by two-dimensional ultrasonic vibration is developed to deal with the processing difficulty of ceramic materials due to its hard-brittle property. The experimental results show that the surface roughness value obtained in two-dimensional ultrasonic grinding nano-ZrO2 ceramic plate specimen is obviously smaller than that in common grinding, and the scratched grooves on the machined surface in ultrasonic grinding is wider and relatively smoother than that in common grinding. Consequently, it proves that the two-dimensional ultrasonic machining is a feasible, high-efficient machining method for hard-brittle materials.

Abstract: Based on the fractal theories, using image processing software (IPS) to handle the scan electron microscope photos of particles, this paper gives a simple and applied method to pick up the boundary line’s fractal dimension (FD) of particles’ projective numerical images. Take example for Al(OH)3 material particles, adopting respectively relative Box-counting (BC) method and relative C-S method, we have calculated the boundary FD values of the research objects and compared FD with other quantitative token parameters, which shows FD is a sort of more refined quantitative token parameter. Finally, utilizing the method of Generator, we get some fractal figures which have nearly same FD values with Al(OH)3 material particles, utilizing that we can simulate and analyze the complexity of the boundary and surface micro-topography of Al(OH)3 material particles.

Abstract: The biomaterial surface represents the first contact point for proteins and cells and is thus critical to optimise the features to transmit the best signals for tissue and organ regeneration. Both chemistry and topography are surface characteristics that can be modified by the manufacturing process and provide signals to cells. While chemistry and crystallinity have received attention for thermally sprayed hydroxyapatite coatings, the control of the surface microtopography has not been addressed. This study collected a range of implants with a coating and assessed the topography on dental implants, orthopaedic screws and hip prostheses. The surface was found to be composed of large topographic features (angular particulate and smooth areas) and micron sized aspects (fine grains, cracks and ridges). Thermal spray experiments were designed to determine the influence of processing conditions on droplet spreading. This knowledge was then applied to see the effect of different parameters on the final coating topography. The parameters investigated for their influence on the surface topography included substrate roughness, substrate temperature, spray distance and particle size. The particle size showed the largest influence on altering the roughness, Ra of the coating. A two-fold increase in particle size doubled the roughness from Ra of 4.8 µm when the powder was sprayed under the same conditions.