Surface Of Base Material Research Articles

Adsorption of human salivary mucin MG1 onto glow‐discharge plasma treated acrylic resin surfaces

It has been suggested that altering the surface properties of acrylic resin material may change the nature of the adsorbed pellicle affecting denture retention and microbial adherence. This study aimed at evaluating the adsorption of salivary high molecular-weight mucins, a major component of denture pellicle, onto modified acrylic resin surfaces. (Poly) methylmethacrylate specimens were treated by glow discharge plasma technique, using hydrophilic 2-Hydroxyethylmethacrylate monomer or oxygen (O(2)) gas and hydrophobic Hexamethyldisiloxane monomer, at different discharge powers. Acrylic samples were incubated with high-molecular weight mucin, MG1 purified from saliva, the adsorbed fractions were transferred to nitrocellulose membranes by slot-blot technique, stained by periodic acid-Schiff and colour intensities were analysed by a colour densitometer. Higher amounts of mucins were adsorbed on all the surfaces modified by glow-discharge plasma treatment. Within the limitations of this study, it was concluded that glow-discharge plasma altered the surfaces of acrylic resin denture base materials and significantly increased the adsorption of high molecular-weight mucins at varying levels depending on plasma parameters.

Effects of Surface Roughness and Manganese Phosphate Coating on Friction and Wear Characteristics

The effects of surface roughness on the friction characteristics of FC250 cast iron coated with manganese phosphate was examined by using a ring-on-disk test machine. A rotating test piece and a stationary one were used under test conditions, with only the rotating piece coated. The test piece surfaces either had a roughness (Rz) of 0.8, 3.2 or 6.3μm, and the contact pressure at which the pieces were pressed to each other was gradually increased from 1MPa to 9MPa. A manganese phosphate coating is easily worn out, and then a part of the base material is exposed. This makes the surface's friction stable. It was shown clearly that the frictional force strongly depends on the load as well as on the base material's surface roughness. The friction coefficient was as high as 0.04-0.05 when both pieces had the same roughness, but was as low as 0.007 when the pieces had different roughnesses.

Depth-resolved analysis of Ni–P plated aluminium hard disks by radiofrequency glow discharge optical emission spectroscopy (rf-GD-OES)

A parametric evaluation of the discharge conditions which affect the quality of radiofrequency glow discharge optical emission spectroscopy (rf-GD-OES) depth profiles of Ni–P plated aluminium hard disks is described. This technique has been shown previously to provide good depth resolution for metallic and oxide layers, also being able to examine contaminants at the layer interfaces. A range of discharge parameters is investigated relative to their contributions to analyte responses and resultant depth profile characteristics. The optimal discharge operating parameters for this application were determined to be an rf power of 40 W and an argon discharge gas pressure of 6 Torr. The depth-resolved analysis of the Ni–P layer plated on the Al–Mg alloy substrate reflects the microscopic non-uniformity of the surface of the Al alloy base material. Diamond stylus profilometry is employed to extract crater profiles and sputtering rates obtained over a range of discharge conditions of rf power and argon discharge gas pressure. SEM, TEM and EDX images of specimen cross sections are used to examine the physical structure of the layer interfaces on a microscopic scale. For each of the aluminium hard disks investigated in this study, the interface breadths (Δz) obtained at the Ni–P/Al–Mg interface is ultimately limited by the roughness of the aluminium disk substrate to which the overlayer is applied. Optimized discharge conditions are employed to profile hard disks extracted from two commercial drives of different technological generations. Distinct compositional differences are observed that correlate with improvements in the base technology over the years 1992–1998.

Heat and fluid flow in pulsed current GTA weld pool

In this study the heat transfer, fluid flow and phase change of the weld pool in pulsed current gas tungsten arc (GTA) welding were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered, namely self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc force. Furthermore, the effect of deformed free surface due to the arc pressure acting on the weld pool surface was considered. Heat and mass transfer equations, including the generalized Navier-Stokes equation and electric transport equation, were solved by a finite difference method. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model for pulsed current welding was applied to AISI 304 stainless steel and compared with the results of the constant current.

EFFECT OF VARIOUS DRIVING FORCES ON HEAT AND MASS TRANSFER IN ARC WELDING

In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered: self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI304 stainless steel and compared with the experimental results.

ＹＡＧレーザを用いた微細加工におけるドロス生成に関する研究

YAG laser has actively been used for precision micro machining, since it has become possible to get stable and high quality beam and the spot diameter can be focused less than 100 micrometers. High energy beam machining with YAG laser or CO2 laser is heat energy machinig accompanied with heating, fusion, evaporation processes, therefore the adhesions of spatter and dross to base material lead to the deterioration of machining integrity. In this paper, the dross generation mechanism in precision micro cutting of thin plate with pulsed YAG laser is experimentally investigated.Main conclusions obtained are as follows:(1) In a single pulse machining, the spatter scatters on the base material surface at irradiation side and the dross sticks around the hole at exit side.(2) Oxygen assist gas makes the mobility of melting material increase, which leads to the decrease of the adhesion of dross.(3) The height of dross is greatly affected by the beam overlap rate, and it takes maximum when the beam overlap rate is about 93%.(4) The dropout phenomenon of dross is occurred when the beam overlap rate is more than 96%.(5) The generation of dross is restrained by shortening the gap distance between the nozzle of assist gas and the workpiece.

溶融亜鉛めっき薄鋼板の高速アーク溶接における気孔の低減

As for the blowholes to be generated in high speed fillet welding of hot-dipping galvanized and annealed steel sheet lap joints, the types of materials to cause them as well as their formation mechanism were examined. It seems to us that the formation of blowholes is not caused by the organic substances usually stuck to the surface of base materials but by the vaporization of zinc. As the result of chemical analysis of the gases sampled from the blowholes by breaking them, it was found that the main contents were hydrocarbon including methane gas. Hydrogen gas was also detected at the same time but it was only about a tenth of methane gas so that the possibility of hydrogen gas causing blowholes is low. The results of chemical analysis of zinc at both blowhole wall faces and root parts seem to indicate that zinc is supplied from heat affected zones to the origin of blowholes wherefrom it pushes up the top side of blowholes for their growth. From the above, the blowholes can be presumed to be caused by the vaporization of zinc. Intending to oxidize zinc as a means to control its vaporization, the effect of adding oxygen gas to the mixed gas of Ar-CO2 was examined. As the result, it was found that the effective addition rate of oxygen gas for the reduction of blowholes was about 5% and especially effective in the case of joint gaps of 0.2 to 0.4 mm. However, too much addition of oxygen gas spoils this effect. Therefore, using the consumable electrodes of different melting points, the vaporization characteristics of zinc oxide were examined. By selecting the type of filler metal having the melting point of about 1, 400°C and using the mixed gas including oxygen gas, the effectiveness of reducing blowholes was clarified.

The nature of a denture base: A key factor in denture sore mouth

Sections of both the polished and the impression basal surfaces of polymethyl methacrylate, vulcanite, and cast-gold denture base materials were examined and photographed using scanning electron microscopy. An attempt was made to draw attention to some of the key factors related to the tissue tolerance to these materials.

The pulse height defect in silicon surface barrier detectors

A simple model is proposed which can be used to explain the existence of the dead layer, or window, that has been observed on silicon surface barrier detectors. Particles that are stopped in silicon detectors create a dense plasma of holes and electrons along their trajectory, and the charge collection process cannot procede until these carriers have diffused radially away from the plasma. The holes, having a reduced mobility in the thin p-type inversion layer on the surface of n-type base material will diffuse away more slowly than will holes in the bulk or depletion region, and this mechanism will inhibit the charge collection process in the surface layer. If the bulk hole mobility is omegab, and the surface hole mobility is omegas, the collection of carriers from the thin p-type surface will be reduced by the fraction (omegas/omegab)2, and if the thickness of the p-type layer is Zp the effective window thickness will be given by (omegas/omegab)2Zp. It is seen that the results of such calculations agree favorably with the measurements reported by Forcinal, Seiffert and Coche. Making use of recent measurements of the stopping powers for bromine and iodine ions, it is possible to calculate the residual defect for fission fragments as measured by Wilkins, Fluss, Kaufman, Gross and Steinberg.

Aluminizing Process of Marine Engine Steel and Surface Alloys

Hot corrosions of marine engine steels have often been experienced in operations with fuel oil C.Fuel oil C has approximately 40∼400ppm vanadium, 50ppm Na and 3∼3.5wt% sulphur.The controlling factors against its corrosive effect are oil ash deposits containing V2O5, Na2SO4, SO3 at elevated temperature 500 to 700°C, pulsating combustion pressure, and so on.It is the aim of the present paper to describe an aluminized process as protective to hot corrosions of heat resistant steels on marine engine service.The results obtained from this study were as follows.(1) None of the alloys used in the typical marine engine and investigated in the present experiment has satisfactory resistance to vanadium attack corrosions, although austenitic alloys-14 Cr-14 Ni-2W and territic alloy-2 Si-11 Cr-1 Mo, have been found as having comparatively high resistance.In general the resistance may be the function of the base composition, i. e., the Ni; Cr; Fe.(2) At service temperature, 600°C, the alloy's resistance to vanadium attack as well as to the scaling loss and such mechnical properties as fatigue life, shockwearing, etc., has been remarkably improved by the aluminized process.(3) However, it is less effective if micro cracks are initiated in the intermetallic compound formed on the surface of base material during the pulsating heats.It is likely that the intermetallic compound layer is stable against crack-initiations during the heating process if proper base materials, such as austenitic alloys 14 Cr-14 Ni-2 W, are selected, whose thermal expansion is approximate to that of the surface layer.