Rotating Disc Apparatus Research Articles

Boronizing of cast martensitic chromium nickel stainless steel and its abrasion and cavitation-erosion behaviour

Boronizing of steels has been very effectively used in overcoming adhesive, sliding and abrasive wear. However, little information is available on boronized cast chromium–nickel steel (13Cr–4Ni) with regard to cavitation-erosion and abrasion resistance as well as their effect on mechanical properties. In this paper, the cavitation-erosion characteristics along with abrasive wear of boronized 13Cr–4Ni steel are studied in detail. Cavitation-erosion resistance was evaluated by using a rotating disc apparatus, whereas abrasive wear was studied as per ASTM G-65. These phenomena are being correlated with mechanical properties such as resilience and strain-energy. Drastic reduction in elongation and strain-energy of borided steel has resulted in poor cavitation-erosion resistance whereas improvement of the order of 300% was observed in abrasive wear resistance. All these results are being reported in this paper.

An investigation of the corrosive wear of stainless steels in aqueous slurries

Pumping installations made of stainless steels have been widely used for transporting slurries in chemical process industry. However, knowledge of the attack of stainless steels due to corrosive wear in two-phase liquid-particle flow is still incomplete. This paper studies the behaviors and mechanisms of corrosive wear for two austenitic stainless steels, 24Cr-25Ni-4Mo and 18Cr-12Ni-2Mo, using a rotating disc apparatus made by the authors. The two components, wear by slurry abrasion and corrosion, within the corrosive wear process, are first examined individually. Then the synergistic effect between wear and corrosion is investigated. The research we have done shows that corrosive wear rate of samples is closely related to such factors as the solution, type of abrasive, flow velocity, impingement angle and temperature. In addition, a threshold of flow velocity exists which is called the breakaway velocity V k, above which the corrosive wear rate increases rapidly. The combined effects of abrasion and corrosion result in a total wear loss larger than the added effects of each process alone. An analytical model is developed which would help to reveal the mechanisms of the corrosive wear processes.

Multisite surface reaction versus transport control during the hydrolysis of a complex oxide

Dissolution experiments of a tholeiite basalt glass carried out at different pH and T (up to 300°C) using a rotatingdisc apparatus show that, depending on pH and T, dissolution can be controlled by one of the following steps: (1) surface reaction; (2) transport of reactants in solution; and (3) mixed reaction. The activation energies of these different processes were found to be 60, 9 and 15–50 kJ mol −1, respectively. Taking account of these results, it appears likely that surface reactions are not rate limiting for the hydrolysis of most crystalline silicate minerals in hydrothermal and metamorphic processes, and that caution should be exercised when predicting rate of reactions at high temperatures solely on the basis of activation energies measured at low temperatures. Comparison of experimental and theoretical potentiometric titrations of the basalt glass and its constituent oxides indicates that the adsorption of H + and OH − ions at the basalt surface is metal cation specific and that the net adsorption can be predicted from the sole knowledge of the acidity constants of the network-forming constituent oxides. We found that in the acidic pH region dissolution is promoted by the adsorption of H + on al and Fe surface sites while in the basic region, dissolution is promoted by the adsorption of OH − on Si sites. The combination of the two distinct types of surface sites, Al and Fe on the one hand, and Si on the other hand, results in a dissolution rate minimum at a pH-value between the pH zpc of the two groups of oxide components. Linear regressions with a slope n=3.8 are observed both in acid and alkaline solutions in logarithmic plots of the rate of dissolution vs. the surface charge. The value of n, which represents the number of protonation or hydroxylation steps prior to metal detachment, has been found equal to the mean valence of the network-forming metals. Combining concepts of surface coordination chemistry with transition state theory afforded characterisation of the activated complexes involved in basalt dissolution processes. From the values obtained for the thermodynamic properties of activation for basalt dissolution it is assumed that the activated complexes formed during the H 2O-promoted dissolution of the basalt glass are more tightly bonded than those formed during H +- or OH −-promoted dissolution.

In-vitro enhancement of cholesterol dissolution by commonly used drugs.

A rotating disc apparatus was used to study the dissolution of cholesterol in sodium cholate solutions and ox bile. Drugs with structures that render them capable of lowering interfacial resistance were tested and shown to increase cholesterol dissolution rates in both systems. In sodium cholate solutions, loperamide (3 X 10(-4)M) increased the rate of dissolution by over six times, and a similar effect was observed with amitriptyline (3 X 10(-3)M), diphenhydramine (3 X 10(-3)M), dicyclomine (3 X 10(-3)M) and propantheline (3 X 10(-3)M). These drugs are as effective as benzalkonium chloride at these concentrations. Amitriptyline, propantheline, dicyclomine and diphenhydramine also increased cholesterol dissolution rates into ox bile. If these drugs are excreted into human bile in sufficient quantities and in an active form they may be able to enhance the speed of cholesterol gallstone dissolution therapy.

The effect of added dissolved calcium on calcite dissolution kinetics in aqueous solutions at 25°C

The kinetics of calcite dissolution in solutions containing dissolved Ca 2+ has been investigated at 25°C, using a rotating disc apparatus. In acid solutions no effect of Ca 2+ in solution is observed. The rate is dependent on the transport of H + to the surface. In neutral to alkaline solutions the dissolution reaction is controlled by mixed kinetics and the conventional empirical representation of the dissolution rate results through the interaction of chemical and transport gradients in the diffusion boundary layer. The chemical reaction rate is a function of the gradient between the equilibrium and the surface concentrations of calcium carbonate, whereas the transport reaction can be described in terms of a series of gradients between the surface and the bulk of dissolved calcium and carbonate species. The presence of dissolved Ca 2+ decreases the rate of the transport reaction, making the dissolution process more transport-controlled. The chemical rate constant is independent of the Ca 2+ concentration in solution. The chemical rate constant for Carrara marble dissolution is determined to ∼2·10 −2 cm s −1 and the diffusion coefficient for the transport reaction to ∼7.6·10 −6 cm 2 s −1. In natural systems with high Ca 2+ concentrations and in absence of inhibitors of the surface chemical reaction, the dissolution of calcite may approach a transport-controlled reaction, especially in environments with restricted flow.

Cavitation erosion characteristics of nickel-based alloy-composite coatings obtained by plasma spraying

Nickel-based alloy and composite coatings were obtained on an 18-8 stainless steel substrate by a plasma spraying technique. They were sintered in a vacuum furnace (10 −2 Pa) to improve toughness and to reduce hardness. The cavitation erosion resistance of these coatings was evaluated using a rotating disc apparatus. The results of the investigation reveal that sintered coatings are several times better than “as-sprayed” plasma coatings. The sintered coatings can help in increasing the length of the incubation period.

Separation Based on Shape Part I: Recovery Efficiency of Spherical Particles

The use of an inclined rotating disc apparatus, employed to separate spherical from non-spherical particles, is studied theoretically and experimentally. The effects of feed rate F s, speed of rotation of the disc n, angle of inclination of the disc θ, angular co-ordinate of the feed point α, and the feed point position on the efficiency of recovery of spherical particles η s are investigated. A rate-type equation is proposed to describe the variation of η s with F s and n. The ‘rate constant’ K is theoretically related to θ by a linear equation. The experimental results generally confirm the features of the model. The results indicate F s, n and θ to be critical variables. Further, it is found that η s is critically affected by the angular co-ordinate of the feed point α, whereas the radial co-ordinate of the feed point is a non-critical variable.

Temperature dependence of calcite dissolution kinetics between 1 and 62°C at pH 2.7 to 8.4 in aqueous solutions

The kinetics of calcite dissolution in aqueous KCl-solutions far from equilibrium, between 1 and 62°C in the pH-range 2.7 to 8.4 have been investigated using a rotating disc apparatus. At neutral and alkaline pH in the mixed kinetic regime the empirical apparent activation energy (EAAE) for the surface chemical reaction rate constant is 54 ± 4 kJ mole−1 for Carrara marble and 46 ± 4 kJ mole−1 for Iceland spar. Under similar conditions the EAAE of the transport rate constant increases with decreasing temperature, but has a mean value of 27 ± 2 kJ mole−1. The corresponding diffusion coefficient has a mean EAAE of 37 ± 3 kJ mole−1 and this high EAAE is consistent with transport dependence on product diffusion in this H+-independent regime.In contrast, in acid solutions, where the rate approaches end-member transport control, the EAAE of the diffusion coefficient is 16 kJ mole−1, also decreasing with increasing temperature. This is compatible with H+-diffusion to the surface being rate-controlling.In inhibitor-free natural systems, calcite dissolution kinetics far from equilibrium can be described in terms of three regimes: an H+-dependent regime (pH < 4 at 25°C), a transition regime (4 < pH < 5.5 at 25°C) and an H+-independent regime (pH > 5.5 at 25°C). At lower temperatures these boundaries move to higher pH values. The presence of inhibitors in natural systems may enhance surface controlled kinetics.

Dissolution at porous interfaces III. Pore effects in relation to the hydrodynamics at a rotating disc surface

The dissolution rate-increasing effect of pores drilled into a dissolving tablet surface was studied in a rotating disc apparatus. The increase of the dissolution rate due to one pore, ΔR, was measured as a function of the pore diameter, the pore position and the rotation speed of the tablet surface. From the obtained results the critical pore diameters were determined. They appeared to be inversely proportional to the friction velocity at the surface, a hydrodynamic variable dependent both on the radial position on the surface and on the rotation speed. In addition, ΔR was found to be related to the friction velocity on the one hand and to the extent the pore size exceeds the critical pore diameter on the other.

Deviation of dissolution behaviour of benzoic acid from theoretical predictions with lowering of temperature: limitations as a model dissolution substance

Benzoic acid dissolution was found to be non-ideal on lowering the dissolution temperature and serious deviation from classical diffusion was observed. Experimental dissolution rates, measured using a rotating disc apparatus, differed from the values predicted using the Levich equation, the deviations becoming more pronounced and negative as the temperature was reduced. Measurement of dissolution rates at varying rotational velocities (ω) of the disc enabled application of a test for diffusional behaviour: plots of dissolution rate against ω 1 2 were linear only at 37°C but were curved at 25°C and below. Since the deviation was negative at high ω-values, it could not have been due to turbulence, the rate-limiting process evidently being an interfacial reaction. In further tests, the addition of a complexing agent, caffeine, to increase the dissolution rate eliminated the curvature at 25°C when the caffeine concentration was high but not at low concentrations, thus confirming the postulation of an interfacial process. Additional evidence was provided by an Arrhenius plot of the experimental data which deviated at low temperatures whereas at 25–37°C, the slope was in accord with an activation energy value suited to transport control.

Kinetics of dissolution of calcium hydroxyapatite: II. Dissolution in non-stoichiometric solutions at constant pH

The influence of the total concentrations of calcium and phospate ions on the rate of dissolution of calcium hydroxyapatite microcrystals in sub-saturated solutions at constant pH has been studied. The rate of dissolution is found to be a function of [Ca] α[PO 4], where α is 3 for very dilute solutions. For more concentrated solutions α is close to 1.67. The results obtained explain the empirical results found in experiments in which a disc of calcium hydroxyapatite is dissolved in a rotating disc apparatus. The concentrations close to the dissolving surface have been calculated from the bulk concentrations, the diffusion coefficients, and the angular velocity of the disc. The “two-site dissolution” is shown to be an artifact due to mathematical curve fitting, which reproduces the experimental data quite well, but which has no relation to the surface processes governing the dissolution.

Polarisation in electrodialysis. Rotating-disc studies

Polarisation in an electrodialysis stack is difficult to examine because of the complex flow of the fluids through the stack. A rotating-disc apparatus has been built, for which the fluid mechanics are both well-known and convenient. Using anion-exchange membranes, the current against voltage plots at high voltages show considerable “water-splitting”, with large fluxes of H+ and OH– ions. The results correlate well with the treatments of Levich and of Cowan, and the enhancement of the anion fluxes by the water-splitting can be explained. Using cation-exchange membranes there is much less water-splitting, with anomalously high cation flux enhancement. Though these characteristics are desirable in practice, they are not explicable by the same approach as seems successful with anion membranes.

The influence of temperature on red cell deformability

This study was undertaken to examine the influence of temperature on physical properties of red cell membranes. Red cells adhering to cover slips were subjected to fluid shear stress in a rotating disc apparatus for 1 min or for 10 min at temperatures ranging from 2 degrees to 50 degress C. They were fixed while subject to shear stress by addition of glutaraldehyde and then processed for examination and photography by reflected-light microscopy. Cell dimensions were obtained with a computerized planimeter. At shear stresses under 2 dynes/sq cm, cells changed shape from biconcave discs to tear drops, the dimensions of which were influenced very little by temperature or duration of shear stress. Above 2 dynes/sq cm, filamentous processes or “tethers” developed at attachment points of cells to cover slips. Tether length and the percentage of cells possessing tethers increased markedly with increasing temperature and duration of shear stress. At approximately 48 degrees C, a dramatic change occurred over a narrow temperature range such that cells were markedly elongated and irregularly deformed by a shear stress of 1 dyne/sq cm or less. These observations demonstrate that elongation of human red cells subjected to fluid shear stress in a rotating disc system is markedly influenced by temperature as well as by magnitude and duration of shear stress. They also indicate that significant increases in red cell membrane fluidity occur between 2 degrees and 24 degrees-37 degrees C and again between 48 degrees and 50 degrees C.

The Influence of Temperature on Red Cell Deformability

This study was undertaken to examine the influence of temperature on physical properties of red cell membranes. Red cells adhering to cover slips were subjected to fluid shear stress in a rotating disc apparatus for 1 min or for 10 min at temperatures ranging from 2 degrees to 50 degress C. They were fixed while subject to shear stress by addition of glutaraldehyde and then processed for examination and photography by reflected-light microscopy. Cell dimensions were obtained with a computerized planimeter. At shear stresses under 2 dynes/sq cm, cells changed shape from biconcave discs to tear drops, the dimensions of which were influenced very little by temperature or duration of shear stress. Above 2 dynes/sq cm, filamentous processes or "tethers" developed at attachment points of cells to cover slips. Tether length and the percentage of cells possessing tethers increased markedly with increasing temperature and duration of shear stress. At approximately 48 degrees C, a dramatic change occurred over a narrow temperature range such that cells were markedly elongated and irregularly deformed by a shear stress of 1 dyne/sq cm or less. These observations demonstrate that elongation of human red cells subjected to fluid shear stress in a rotating disc system is markedly influenced by temperature as well as by magnitude and duration of shear stress. They also indicate that significant increases in red cell membrane fluidity occur between 2 degrees and 24 degrees-37 degrees C and again between 48 degrees and 50 degrees C.

The drag reduction of chrysotile asbestos dispersions

AbstractThe drag reduction (DR) of dispersions of Chrysotile asbestos fibers in aqueous solutions of Aerosol OT and in ethylene glycol, and of glass microfibers in water at a pH of 3 were studied as a function of concentration and temperature with a rotating disc apparatus. Only the dispersions of asbestos in aqueous Aerosol OT showed DR comparable to poly(ethylene oxide) WSR 35 (∼500,000 MW), and these dispersions were more fully studied. As was the case with Polyox WSR 35, the asbestos dispersions achieved maximum DR at a concentration of about 200 ppm. They showed no DR temperature dependence at constant Reynolds number at high concentrations but displayed a decreasing DR with increasing temperatures at low concentrations. However, the temperature effect was much smaller for the asbestos dispersions than for Polyox. The asbestos dispersions also showed a much smaller decrease of DR with time at a given disc rotation than was previously measured for poly(ethylene oxide). Electron microscope evidence indicated that less than 10% of the fibers were fully separated, and it is probable that these were the fibers which were primarily active in DR. Hence, if complete separation and dispersion could be accomplished without breaking the fibers, Chrysotile asbestos would be a most potent, not very shear‐degradable DR species.

The drag reduction of dilute polymer solutions as a function of solvent power, viscosity, and temperature

AbstractThe frictional drag reduction of high molecular weight poly(ethylene oxide) and polystyrene solutions under turbulent flow conditions has been studied as a function of temperature, solvent power, and solvent viscosity. A rotating‐disc apparatus was used to make the drag reduction measurements. For aqueous poly(ethylene oxide) solutions, at concentrations well above that needed to produce maximum drag reduction, all drag reduction data reduced to a common curve when per cent drag reduction was plotted against the Reynolds number for the flow. However, for poly(ethylene oxide) solutions below this optimum concentration, the drag reduction‐versus‐Reynolds number curves showed decreasing drag reduction with increasing temperature. The data are explained primarily in terms of the inverse temperature solubility characteristics of poly(ethylene oxide) in water. The per cent drag reduction of polystyrene in nonaqueous liquids was found to be greater in good solvents than in poor ones. It was also found that increases in solvent viscosity and decreases in temperature increased the per cent drag reduction. The results are discussed in relation to the current drag reduction theories and are shown to be in opposition to Virk's theory. It is concluded from the data that drag reduction is very likely a function of a relaxation time phenomenon involving the polymer molecules and the flow system. The results also emphasize the importance of considering solvent power, viscosity, and temperature in the design of an efficient drag reduction system.

Sediment Impact On Turbine Material: Case Study Of Modi River, Nepal

Hydropower is considered as one of the most economical and stable base energy source compared with other sources of energy of Nepal. Researches coherent to this field are not new but yet it is not sufficient, lots of tiles have to be kept for better understanding of hydropower effecting elements. Sand is the most affecting element that damages the turbine blades, so research on relation of sand and turbine is most. This research is done to find out the impact of sediment on turbine material. Modi River sediment at eight different stations has been taken as sample and its erosion rate in turbine blade sample specimen has been accounted in this study. Rotating disc apparatus has been utilized to find out the total impact of sand on turbine material. Four same kind of test turbine material is used on single rotating disc all at a time at same condition to define sand impact. Thirty gram (gm) of sediment mixed with three liters of water is used to strike sample pieces for five minutes. Two different tests of sediment samples of 8 different locations were studied. After all the test it is observed that the first test sand sample of location 1 and turbine material 1 has the highest impact with a weight loss of 7.764 mg and least impact in sand sample location 1 and sand sample 3 with a weight loss of 3.5 mg. Average weight loss of turbine material in first location is 5.929 mg which is the greatest impact and 4.0083 at eight locations which is the least. Relating to turbine material first rotating disc turbine specimen P0A has been affected highly with weight loss of 9.289 mg and less eroded on P5A rotating turbine specimen with weight loss of 1.2 mg. DOI: http://dx.doi.org/10.3126/kuset.v8i1.6047 KUSET 2012; 8(1): 88-96