Specific Surface Topography Research Articles

Tribology of Micro Milled Surfaces

Micro milling is an appropriate technology for the flexible production of precise micro molds with complex shapes for metal forming processes (e.g. micro deep drawing). Besides high form accuracy micro ball end milling also provides a specific surface topography which can enhance the tribological behavior during the forming processes. This paper is focusing on the tribological behavior of micro structured surfaces generated by micro milling compared to smooth surfaces. The coefficient of friction was investigated on a pin-on-disc test stand for different materials. The results of the tribological tests suggest a relationship between micro structure and coefficient of friction. Finally, the correlations between machining parameters and tribological behavior will be discussed.

Grindability and Surface Integrity of Cast Nickel-based Superalloy in Creep Feed Grinding with Brazed CBN Abrasive Wheels

The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters (i.e. wheel speed, workpiece speed and depth of cut) on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride (CBN) abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardness and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 °C is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the burn-free and crack-free ground surface.

Nanoscale topography of nanocrystalline diamonds promotes differentiation of osteoblasts

The excellent mechanical, tribological and biochemical properties of diamond coatings are promising for improving orthopedic or stomatology implants. A crucial prerequisite for such applications is an understanding and control of the biological response of the diamond coatings. This study concentrates on the correlation of diamond surface properties with osteoblast behavior. Nanocrystalline diamond (NCD) films (grain size up to 200 nm, surface roughness 20 nm) were deposited on silicon substrates of varying roughnesses (1, 270 and 500 nm) and treated by oxygen plasma to generate a hydrophilic surface. Atomic force microscopy was used for topographical characterization of the films. As a reference surface, tissue culture polystyrene (PS) was used. Scanning electron microscopy and immunofluorescence staining was used to visualize cell morphological features as a function of culture time. Metabolic activity, alkaline phosphatase activity, and calcium and phosphate deposition was also monitored. The results show an enhanced osteoblast adhesion as well as increased differentiation (raised alkaline phosphatase activity and mineral deposition) on NCD surfaces (most significantly on RMS 20 nm) compared to PS. This is attributed mainly to the specific surface topography as well as to the biocompatible properties of diamond. Hence the controlled (topographically structured) diamond coating of various substrates is promising for preparation of better implants, which offer faster colonization by specific cells as well as longer-term stability.

Surface topography induces 3D self-orientation of cells and extracellular matrix resulting in improved tissue function

The organization of cells and extracellular matrix (ECM) in native tissues plays a crucial role in their functionality. However, in tissue engineering, cells and ECM are randomly distributed within a scaffold. Thus, the production of engineered-tissue with complex 3D organization remains a challenge. In the present study, we used contact guidance to control the interactions between the material topography, the cells and the ECM for three different tissues, namely vascular media, corneal stroma and dermal tissue. Using a specific surface topography on an elastomeric material, we observed the orientation of a first cell layer along the patterns in the material. Orientation of the first cell layer translates into a physical cue that induces the second cell layer to follow a physiologically consistent orientation mimicking the structure of the native tissue. Furthermore, secreted ECM followed cell orientation in every layer, resulting in an oriented self-assembled tissue sheet. These self-assembled tissue sheets were then used to create 3 different structured engineered-tissue: cornea, vascular media and dermis. We showed that functionality of such structured engineered-tissue was increased when compared to the same non-structured tissue. Dermal tissues were used as a negative control in response to surface topography since native dermal fibroblasts are not preferentially oriented in vivo. Non-structured surfaces were also used to produce randomly oriented tissue sheets to evaluate the impact of tissue orientation on functional output. This novel approach for the production of more complex 3D tissues would be useful for clinical purposes and for in vitro physiological tissue model to better understand long standing questions in biology.

Enhancement of In Vitro Capillary Tube Formation by Substrate Nanotopography.

Vascular engineering remains a key thrust in advancing the field of tissue engineering of highly vascularized, complex, metabolic organs. A wide variety of strategies have been employed to control the formation of organized vascular structures in vitro and in vivo. Some of these methods include, but are not limited to, controlled growth factor delivery,[1] filamentous scaffold geometry,[2] protein micropatterning,[3] and enhanced scaffold biomaterials.[4] Many of these approaches are motivated by biomimicry of the in vivo microenvironment. Extracellular matrix (ECM) proteins, both in vitro and in vivo, provide mammalian cells with biophysical cues including specific surface chemistry and rich three-dimensional surface topography[5] with features on the nanometer length scale.[6] ECM substrates provide chemical and physical external cues that dictate a variety of cell responses. Therefore, it is not only the milieu of soluble, diffusible factors, but also the adhesive, mechanical interactions with scaffolding materials, both natural and synthetic, that control select cell functions including cell attachment, migration, proliferation, differentiation, and regulation of genes.[7–9] We hypothesized that physical features on nanofabricated substrates could promote the organization of endothelial cell lineages into well-defined vascular structures in vitro by inducing the contact guidance phenomenon, which is known to affect the morphology of endothelial cells.[10–12]We found that endothelial progenitor cells (EPCs) responded to ridge-groove grating of 1200 nm in period and 600 nm in depth through alignment, elongation, reduced proliferation, and enhanced migration. Although endothelial- specific markers were not significantly altered, EPCs cultured on substrate nanotopography formed supercellular band structures after 6 d. Furthermore, an in vitro Matrigel assay led to enhanced capillary tube formation and organization.

Azadirachta indica (Neem) leaf powder as a biosorbent for removal of Cd(II) from aqueous medium

A biosorbent, Neem leaf powder (NLP), was prepared from the mature leaves of the Azadirachta indica (Neem) tree by initial cleaning, drying, grinding, washing to remove pigments and redrying. The powder was characterized with respect to specific surface area (21.45 m 2 g −1), surface topography and surface functional groups and the material was used as an adsorbent in a batch process to remove Cd(II) from aqueous medium under conditions of different concentrations, NLP loadings, pH, agitation time and temperature. Adsorption increased from 8.8% at pH 4.0 to 70.0% at pH 7.0 and 93.6% at pH 9.5, the higher values in alkaline medium being due to removal by precipitation. The adsorption was very fast initially and maximum adsorption was observed within 300 min of agitation. The kinetics of the interactions was tested with pseudo first order Lagergren equation (mean k 1 = 1.2 × 10 −2 min −1), simple second order kinetics (mean k 2 = 1.34 × 10 −3 g mg −1 min −1), Elovich equation, liquid film diffusion model (mean k = 1.39 × 10 −2 min −1) and intra-particle diffusion mechanism. The adsorption data gave good fits with Langmuir and Freundlich isotherms and yielded Langmuir monolayer capacity of 158 mg g −1 for the NLP and Freundlich adsorption capacity of 18.7 L g −1. A 2.0 g of NLP could remove 86% of Cd(II) at 293 K from a solution containing 158.8 mg Cd(II) per litre. The mean values of the thermodynamic parameters, Δ H, Δ S and Δ G, at 293 K were −73.7 kJ mol −1, −0.24 J mol −1 K −1 and −3.63 kJ mol −1, respectively, showing the adsorption process to be thermodynamically favourable. The results have established good potentiality for the Neem leaf powder to be used as a biosorbent for Cd(II).

Development of advanced quantitative analysis methods for wear particle characterization and classification to aid tribological system diagnosis

Classification of wear particles is performed in two steps, i.e. first a particle to be classified is characterized by surface feature parameters such as roughness, directionality, homogeneity, periodicity, etc. and then, the particle is assigned to a specific class using these parameters. However, a significant limitation of this approach is that surface parameters are often not unique to a specific surface topography and their values may change significantly with scale, orientation angle and position at which the particle data was acquired. Various attempts were made to overcome this limitation by selecting a core set of parameters which ensures that wear particles are accurately classified. However, the parameter selection is usually cumbersome and requires lengthy computation. Furthermore, there is no guarantee that parameters selected are sensitive enough to separate particles belonging to different classes. Thus, a new classification technique based entirely on dissimilarity measures (e.g. Euclidean, Baddeley's distances), calculated between surface images of an unclassified particle and classified particles, was developed. The classification process is based on assigning a particle to a class of particles with the smallest dissimilarity measure. This idea arises naturally from the two facts: (i) compactness, similar objects are in close proximity to each other in their representation space, while different objects are far apart, and (ii) true representation, if objects are close to each other in their representation space they belong to the same class. In this paper, an overview of recent advances and developments in the area of particle classification based on dissimilarity measures is presented with a particular emphasis on constructing a simple and accurate classifier.

Sputtering and ion-induced electron emission of graphite under high-dose nitrogen bombardment

The dependence of the sputtering yield Y and the electron emission coefficient γ of isotropic graphites (POCO-AXF-5Q and Russian MPG-LT) on ion fluence and ion incidence angle θ at near room temperatures and the dependence of γ on target temperature under high dose 30 keV N 2 + ion irradiation were measured. It was found that Y and γ are stabilized at fluences F⩾1×10 19 N/cm 2. A specific target surface topography develops. At steady-state conditions, the N concentration in MPG-LT is 19 at.% and in POCO16 at.%. In the angular range θ=0–80°, Y and γ increase and the angular dependence of Y is slightly stronger than that of γ. Sputtering yields of POCO are 1.5 times higher than those of MPG-LT. The reasons of the difference between the experimental and calculated sputtering yields using the TRIM.SP code are discussed. The dependence of γ on the target temperature manifests a step-like increase at ≃250 °C which may be due to radiation induced structure transformation in the modified surface layer.

The effect of wind on the snow cover

AbstractResults of wind-tunnel investigations of the propagation of air within snow showed that the process responsible for causing horizontal air flux in the pore space of snow was not necessarily related to specific surface topography. The reasons for this flux formation are: (i) the near-surface wind characteristics, such as the frequency of the pressure variation related to the turbulent character of the near-surface wind; (ii) the structure of the near-surface snow, responsible for the air exchange between the atmosphere and the pore space; and (iii) the temperature difference between the snow and the atmosphere, forming the air-density difference which augments or decreases the air exchange. This paper summarizes the experimentally observed effects that the wind and the air flux generated in the pore space had on snow. These included isothermal temperature distributions throughout the artificial snow cover, snow-density change and snow recrystallization.

Development of the Lateral Effect Photo Diode Technique to Measure Oil Film Thickness

A measurement technique was developed using the lateral effect photodiode method to determine oil film thickness and oil retention measurement. A position-sensing photodiode determined the change in position of a focused laser beam. The beam was reflected off a diffuse body and calibrated to varying surface deflections. The calibration showed accuracy to 1 um. Samples of tool steel were prepared with a specific surface topography and then applied with a predetermined amount of heavy white mineral oil. The resulting film of the mineral oil was then observed, measured and recorded using the lateral effect photo diode method. Experiments were also run with a pin-on-disk machine to measure the oil film thickness produced at varying sliding speeds. The experiments showed that the lateral effect photo diode technique can measure oil films in a lab environment. Presented at the 51st Annual Meeting In Cincinnati, Ohio May 19–23, 1996

Hydroxyl groups as IR active surface probes on MgO crystallites

Highly dispersed MgO was produced under diverse non-equilibrium conditions, among them those of chemical gasphase deposition. The resulting powders were then degassed in HV at temperatures up to 800°C. These procedures permit the production of MgO samples which strongly differ in both specific surface area and surface topography. Correspondingly an enormous variety of surface sites is made available. Their distribution was studied by FT-IR spectroscopy using OH groups as surface probes. A unique correlation could be established between the characteristic absorption pattern in the OH stretching region on one hand and the experimental conditions applied in the course of the production and of the pretreatment procedure on the other. This required an assignment of the IR spectra in terms of coordination and hydrogen bonding of surface OH groups on MgO. The strategy of assignment involved adsorption experiments with HX (X = OH, H, SH, NH 2), thermal desorption studies, the evaluation of both the isotope effect ∼ν (OH)/∼ν (OD) and the first overtone 2∼ v (oh) as well as ab initio calculations related to hydrogenated and hydrated MgO clusters.

Planter Depth-Control: I. Predictions and Projected Effects on Crop Emergence

ABSTRACT PLANTER depth control with four wheel designs was evaluated on the basis of the predicted effects on simulated emergence for four crops. A linked front and rear depth control wheel design performed similar to rear and front depth control wheels. Side wheels produced the best performance, but they are too wide for solid-seeded planting narrow rows in crop residues. Depth control wheel position varied the simulated emergence as much as 36%. The simulation models proved useful in evaluating depth control mechanisms and could be extended to field situations by using specific surface topography and seed emergence data for response prediction.

Amyloid A: amphipathic helixes and lipid binding.

Polypeptide segments, composed of alpha helixes with specific surface topography termed amphipathic helixes, have been proposed as the basic lipid-associating domains of apolipoproteins from the plasma lipoproteins. A computer search for proteins having sequences that could form amphipathic helixes indicated that amyloid A, a pathologically occurring protein usually associated with "secondary" amyloidosis, also contained amphipathic helixes. In studies reported here, amyloid A is shown to associate spontaneously with phospholipid vesicles with the following results: (a) the formation of a protein-lipid complex isolated by equilibrium density gradient ultracentrifugation, (b) a 100% increase in alpha helicity as measured by circular dichroism, (c) a 9-nm shift in the fluorescence maximum due to the single tryptophan residue located in the amphipathic region, indicating the tryptophan is moving from a polar to a nonpolar environment, and (d) the formation of stacked disk-like protein-lipid complexes as visualized by negative stain electron microscopy. The temperature dependence of the circular dichroic spectrum of the amyloid A-phospholipid complex suggests that the complex is formed by insertion of protein between the fatty acyl chains of the lipid. These findings suggest that the amphipathic helix is an important structural unit in lipid-associating proteins and that this unit can be recognized on the basis of its amino acid sequence. In addition, these studies have implications for the origin and function of amyloid A protein.

The Afferent Innervation of the Heart.

The detailed personal observations of the author coupled with a comprehensive review of the major studies in the world literature along these lines place this particular compilation in the category of an authoritative treatise on the subject of afferent innervation of the heart. The histological material dealing with afferent receptor fields and individual receptors is particularly outstanding, although some questions may still be raised as to whether all of the neural components comprising the receptor fields and specialized ending are strictly afferent in nature. In addition it would have been helpful to include illustrations of specific heart surface topography in the description of the distribution of afferent areas along the heart wall. The experimental work confirming the similarity between the afferent endings found in animal hearts and those existing in the human can be regarded as a significant contribution. The tie-up of these peripheral fields with the central nervous system