Showing papers on "Surface finish published in 1986"

Crystal truncation rods and surface roughness.

Abstract: We present x-ray-diffraction profiles from a variety of different crystals which are characteristically diffuse in the direction perpendicular to the surface through which the incident and diffracted beams pass, but sharp in both parallel directions. We show that these effects arise from truncation of the crystal lattice at the surface. To explain the precise form of the momentum-transfer dependence of the intensity across the reciprocal-space zone, it is necessary to include the effects of surface roughness on an atomic scale. Such measurements therefore allow highly sensitive roughness determinations to be made. Understanding the origin of these streaks of intensity will have significant impact on the practice of x-ray crystallographic determinations of surface structure.

Roughness coefficients for routing surface runoff

Abstract: Hydraulic roughness coefficients have been derived from runoff plot data originally collected for erosion studies. The data were collected from different agricultural and natural surfaces by applying constant rainfall rates from rainfall simulators. The derived roughness coefficient is actually an “effective” roughness coefficient that includes: the effect of raindrop impact; the effect of channelization of flow; the effects of obstacles such as litter, crop ridges, rocks, and roughness from tillage; the frictional drag over the surface; and the erosion and transport of sediment. A ready reference of friction factors for overland flow is presented in tabular format with a description of the various surfaces and land uses. Surface conditions varied from very smooth asphalt to extremely rough, litter‐strewn agricultural and rangeland areas.

A simple model of neutrally stratified boundary-layer flow over complex terrain with surface roughness modulations (MS3DJH/3R)

Abstract: The MS3DJH series of simple models of flow over low hills and other terrain features described in earlier papers (see Taylor et al, 1983) required that the terrain was of uniform surface roughness In the present paper, we describe an approximate theory of flow above variations in surface roughness using a similar structure to that established by Jackson and Hunt (1975) for flow over hills This then allows us to include the calculation of flow perturbations due to roughness variations within a modified version of our model which we designate as MS3DJH/3R Comparisons are made with alternative calculations for simple two-dimensional flows; and sample three-dimensional calculations are presented The model retains its essential features of high spatial resolution and low computing cost

Surface melting and roughening of adsorbed argon films.

Abstract: Des multicouches d'argon adsorbees sur du graphite montrent des anomalies de chaleur massique attribuees a la rugosite de surface et a la fusion superficielle

Aerodynamic roughness over an inhomogeneous ground surface

Abstract: The aerodynamic roughness parameter z 0 over inhomogeneous ground surfaces, such as cities, rural towns and so on, is determined by analyzing the wind data at AMeDAS observatories in the Tohoku and Kanto districts of Japan, by making use of Rossby number similarity theory It is found that the aerodynamic roughness parameter is proportional to the average size of the roughness elements A practical method of estimating the aerodynamic roughness parameter over an extensive area with various inhomogeneities is developed In this method, the Digital National Land Information data bank is employed As an example, the roughness parameter distribution around Tsukuba Academic City is presented

Turbulent boundary layers on rough surfaces

Abstract: The influence of three-dimensional, stochastic roughness on the properties of turbulent boundary layers has been investigated experimentally in order to obtain an improved understanding and description of such effects on the boundary-layer flow over turbomachinery blading. Four rough surfaces were examined: a surface representative of newly-finished turbo-machinery blading, a variant of this surface with different roughness parameters, a sand-cast surface and a mesh surface with a deterministic roughness geometry. A skin-friction correlation has been obtained, and trends in this correlation and the roughness function caused by changes in roughness parameters have been identified.

Application of speckle-correlation methods to surface-roughness measurement: a theoretical study

Abstract: The properties of a speckle pattern are determined by the light source, the rough surface, and the optical system. The degree of correlation of the intensities of two slightly different speckle patterns can be applied to measure surface roughness since it depends on the variance of the surface height distribution. The two speckle patterns are produced by illuminating a rough surface with coherent light of either two different wavelengths or two different angles of incidence. A unified description of the theory for the spectral and angular speckle-correlation methods is presented, and explicit solutions are derived for both far-field and image-plane geometries. The theoretical results essentially yield a factorization of the degree of speckle correlation into a roughness-dependent and a space-dependent part. By maximizing the space-dependent part, one obtains the requirements for experimental arrangements with optimal measuring conditions. Examples of possible setups for each method are presented, and cross references to earlier work published in this field are given.

Effects of cathode surface roughness on the quality of electron beams

Abstract: The effects of the roughness of the cathode surface on the emittance of an electron beam are examined. Tentative scaling laws are suggested which yield the bounds on the beam emittance due to surface roughness for both temperature‐limited and space‐charge‐limited regimes. These formulas are found to be consistent with numerical integration of electron trajectories over a wide range of parameters. In general, roughness‐induced beam emittance may be reduced by a factor of 2–5, if the cathode is operated in the space‐charge‐limited regime rather than in the temperature‐limited regime.

Fine diamond turning of KDP crystals.

Abstract: Frequency doubling optical components for the Nova laser system are made from single-crystal potassium dihydrogen phosphate (KDP). While developing a manufacturing process for these components, we found that single-point diamond turning could be used to directly produce finished parts with no need for additional surface polishing. A surface roughness of better than 8-A rms and 36-A P-V was measured on a test sample generated with certain machine and tool parameters. Further improvement in surface finish may be possible by employing refined diamond turning procedures and equipment.

Dry etching method

Abstract: PURPOSE:To enable to improve the uniformity and controllability of etching and the productivity of a device by using NF3 gas with a proper amount of N2 gas addition CONSTITUTION:When resist masks 1 are performed on an SiNx film 2 on an Si substrate 3 using NF3 gas with 2-50% of N2 gas addition and an etching is performed on the film 2 under the prescribed gas pressure by an RIE method, the uniformity of etching is remarkably improved to prevent the roughness of the etching surface, A a microscopic processing can be performed, the charac teristics of the NF3 gas of making hard reaction byproducts accumulate are held, and moreover, there is no possibility of the formation of an energy level by O atoms on the crystal surface as in the case of O2 gas addition By this way, a dry etching, by which a high-quality, high-integration and high-yield device can be obtained, can be realized

Principles of Grinding

Abstract: There are many types of grinding: “precision” and “rough,” internal, external, surface, centerless; using wheels or belts; and conventional or “super” abrasives I believe they all act the same When a moving abrasive surface contacts a workpiece, if the force is high enough, material will be removed from the part and the abrasive surface will wear Those two things will always occur; however, the force level determines how fast the mutual removal rates will be, how rough the remaining surface will be, and whether the workpiece will be metallurgically damaged or not The purpose of this section is to provide relationships between variables and to illustrate how changes to a system affect its performance

On the effective roughness length for use in numerical three-dimensional models

Abstract: We present analytical and numerical calculations of the effective roughness length (ERL) over a flat surface with varying roughness elements, for use in large-scale models. It is shown that ERL is mostly determined by the roughest elements present inside the averaging domain and that, more surprisingly, the ERL increases as the first level of the numerical model gets closer to the surface and its altitude approaches the value of the largest local roughness length. This effect further increases the drag coefficient, in addition to the well-known increase due to the lowering of the first model level.

Healing of a Rough Surface at Low Temperature

Abstract: The smoothening kinetics of a rough surface due to surface diffusion is studied theoretically. After a long time t, the surface is predicted to be flat on lengthscales smaller than R(t) ~ t1/3. At higher lengthscales the roughness is almost the same as at t = 0. The method is analogous to the Lifshitz-Slyozov theory of nucleation in a supersaturated solution. Our result R ~ t1/3 disagrees with existing theories of smoothening.

A microtribometer for measurement of friction and adhesion of coatings

Abstract: A new apparatus is described which enables the tribological properties of a surface to be measured. A modified cartridge of the record player is driven to swing sinusoidally in parallel to the surface at a frequency of 30 Hz with an amplitude of 8–200 μm. The stylus load is applied from 0 to 1 N. As the stylus is pressed to the surface, a voltage signal which reflects the frictional properties of the surface is generated in the cartridge. The analysis of the signal with the increase of the load yields the coefficient of friction. When the load is high enough, the surface or the coating on the substrate is broken and the signal of both the fracture and the resultant roughness is picked up. The coefficient of friction for an MgO coated glass substrate was 0.26. The adhesion forces of Ag, Al, MgO, and TiN films on glass substrates were 0.7, 1.2, 1.7, and 3.3 GPa in shear stress, respectively.

The significance of surface topography in engineering

Abstract: All machining processes leave characteristic topographic features on the surfaces of components. This paper reviews a wide range of examples in which the surface topography of a component has been found to bear a significant effect on its function. Problems in manufacture which are related to surface roughness requirements are also disccused.

The Influence of Surface Roughness on Resistance to Flow Through Packed Beds

Abstract: Experiments were performed to determine the effect of roughness on flow through randomly packed beds of spheres. Three different packings were investigated, one of smooth spheres, and two others composed of spheres with roughness elements added to the surface. The relative roughness, defined as the height of the added elements divided by the diameter of the smooth spheres, was .012 and .026 for these two cases. The experiments covered a range of Reynolds numbers based on the sphere diameter from near unity where the flow is dominated by viscosity to 1600 where the flow is dominated by inertia. It was found that the pressure drop is substantially increased by the presence of surface roughness over the entire range of Reynolds numbers studied. The observed behavior is quite different from that which has been proposed previously by drawing analogy with flow in rough pipes, since the flow at low Reynolds number as well as high Reynolds number was affected by roughness.

Incorporation of Stratification Effects on the Oceanic Roughness Length in the Derivation of the Neutral Drag Coefficient

Abstract: Based on the assumption that, over the sea, the roughness length of the wind profile scales with the wind stress, a new formulation that describes the drag coefficient as a function of the given neutral drag coefficient and stability is derived. The new formulation is compared to an earlier formulation where roughness changes with stability were ignored. The two are then illustrated with data collected from both the Marine Remote Sensing Project (1979) and the Tower Ocean Wave and Radar Dependence Experiment (1984). It was found that when the surface roughness was allowed to depend on wind stress (and therefore stability), the stratification correction to the neutral drag coefficient was larger than for the case when the roughness length was not allowed to vary.

Surface fractal dimension of small metallic particles.

Abstract: The surface structure of small metal particles is characterized by use of electron microscopy techniques. It is found that the surface has a very extensive roughness which can be described by means of a fractal dimension. We report a new method to measure the fractal dimension by image-processing techniques, and computer measurements. Different values of the fractal dimension are found for gold, platinum, and palladium particles depending on particle preparation and surface treatment. It is found that the fractal dimension of small metallic particles changes after a methanation reaction.

Fundamentals Of Laser Processing Of Materials

Abstract: Energy deposition and heating during laser processing of materials are a consequence of the balance between the deposited energy, governed by optical parameters of the surface and characteristics of the laser radiation, and the heat diffusion, determined by thermophysical parameters and the interaction time. The kinetics of laser-induced plasma with maximum values of absorptance is described giving indication that maximum efficiency and optimum quality only can be achieved in a narrow range of intensity. The optical feedback resulting stochastically in temporal and spatial changes of intensity distribution controls surface finish and reproducibility that diagnostics and monitoring of laser intensity and mode structure during processing are essential requirements for optimum processing results. The heat flow governs the load and the losses of the heat affected zone with the different analytic and numerical models for the mathematical analysis of the multiparameter problem laser materials processing providing a testing comparison with the physical picture and an easy estimation of process parameters in applications.

Roughness Measurement of X-Ray Mirror Surfaces

Abstract: In order to fabricate an X-ray mirror telescope, we investigated the roughness of mirror surfaces using X-ray scattering. With Al-K (8.34A) X-rays we measured the scattering profiles of plate glass. The spectral structure of surface roughness was revealed by the angular distribution of the X-ray scattering. The power spectral density functions of the surface-height distribution for these materials (except for a gold evapolated surface) were represented by the power-law spectra with power indices ranging from -1 to -2. The rms heights were derived to be 1.8-8.3A for a wavelength range as expected from the power-law spectrum. The results obtained with this method were found to be consistent with those with an ordinary optical profilometer.

Ionization assisted physical vapor deposition of zirconia thermal barrier coatings

Abstract: Yttria stabilized zirconia has been deposited by electron beam physical vapor deposition under a range of process conditions. The influence of rf plasma assistance, pressure, surface finish, and source to substrate distance on structure, phase, uniformity, and adhesion has been studied. Coatings were found to be predominantly cubic; their texture could be modified by plasma assistance. Also plasma assistance was found to improve adhesion, permit control of coating structure and densification, and provide the possibility to increase pressures, to improve coating thickness uniformity without loss of structure control. Excellent adhesion was obtained even on polished substrates at low temperatures (<400 °C), which when coupled with the fact that the coating tends to replicate the original surface finish, suggests that good aerodynamic efficiencies and performance should be achieved with thermal barrier coatings produced by this method.

Morphology of Au/GaAs interfaces

Abstract: The interface morphology of gold contacts on ultrahigh vacuum (UHV) cleaved, air‐exposed, and chemically prepared GaAs surfaces has been studied by electron microscopy. Diodes formed on atomically clean cleaved (110) GaAs surfaces, subsequently annealed at 405 °C, were found to have flat interfaces. In contrast, diodes formed on air‐exposed and chemically prepared GaAs surfaces, also subsequently annealed at 405 °C, were found to have rough and uneven interfaces with a large number of protrusions extending into the semiconductor. They have different orientation relationships with the GaAs substrate than the diodes prepared in situ in UHV. The results of this study show that, upon annealing, the interfacial chemistry and morphology depend strongly on the surface preparation of GaAs before gold deposition.

Quantitative analysis of streaks in reflection high-energy electron diffraction: GaAs and AlAs deposited on GaAs(001).

Abstract: Reflection high-energy electron diffraction (RHEED) has long been considered a qualitative tool for assessing the roughness of a surface and for determining whether thin films are deposited epitaxially Though this technique is known to be exceedingly surface sensitive, no quantitative statements could be made In this paper we report measurements of the specular diffraction beam from near-singular GaAs(001) surfaces with submonolayer deposits of GaAs and AlAs By fitting the shapes of these beams to a kinematic calculation, exact to within the column approximation, we determine the coverages of the surfaces and estimate the average island size in the overlayer The results show the sensitivity of RHEED to the details of the island or step distribution on the surface By comparing the AlAs and GaAs profiles it is apparent that Al is much less mobile on the (001) surface than is Ga Finally we report the observation of surface roughening during the 2 x 4 to c(4 x 4) GaAs(001) phase transition