Fabrication of Graded, Spray, and Fused Coatings and Their High Temperature Erosion Performance

Thermally sprayed coatings are often used industrially to protect bulk metal structural and heat exchange surfaces against wear and corrosion at high temperature. Spray and fused coatings of Ni-based alloys are dense, with metallurgical coating adhesion and have provided excellent industrial corrosion resistance. This process allows the addition of hard particles to improve coating wear resistance in a functionally graded manner, and the first such coating is developed. There has been few wear studies of such functionally graded materials (FGMS), particularly as coatings. Because such materials provide a gradation in properties such as hardness and thermal expansion coefficient between the coating and the substrate, it is thought that they may have potential in aggressive environments such as high temperature energy conversion processes (resisting spallation and erosion).

In a low velocity fluidized bed erosion environment the effects of erodent particle size and bed temperature on the erosion rate through the section of a functionally graded spray and fused coating was studied. The coating consisted of a varying fraction of WC particles (0-42 vol.%) in a Ni-Cr-based, self-fluxing matrix. The erodent particle size varied from 200 to 600 μm, testing was between 25 and 600°C, with impact angles of 30° and 90°.     

Effect of erodent properties on the erosion of alumina

The effect of erodent particle properties for solid particle erosion in a series of alumina ceramics was investigated using alumina and SiC erodents. Using a new model analysis, the results were interpreted in terms of particle fragmentation effects and related erodent-target properties. An increase in the erosion rate with increase in the particle-target hardness ratio reported in the literature is related to these effects but is not actually a direct consequence of hardness. Changes in the velocity exponents for erosion were observed and can be explained by blunting due to crushing and fragmentation of larger erodent particles. The quasi-static model for erosion predicts a reduction in the velocity exponent as the particle-tip blunting increases. In steady state, SEM observations show that lateral crack controlled erosion mechanisms operate in all cases but, for certain combinations of erodent and target properties, damage accumulation by plastic punching occurs.     

Optical Probe for the In-Line Determination of Particle Shape, Size, and Velocity

A laboratory optical probe was developed to simultaneously determine the following particle characteristics: circularity, particle projection area, equivalent diameter of a circle, length of the particle outline or perimeter, maximum chord length, aspect ratio, and particle velocity. Using the projection area and the perimeter, the particle shape factor circularity can be determined. The aspect ratio was approximated by the ratio of the equivalent diameter to the maximum chord length. The basic measuring principle is multi-point scanning of the particle shadow image by a line of optical fibers. In addition, the particle velocity can be measured by a differential spatial filter of optical fibers. These fibers are step index fibers with a core diameter of 64 µm and cladding of 70 µm. The shadow image of a single particle was generated by a parallel laser beam. The uncertainty of the measured circularity and aspect ratio was investigated by using metal wires with diameters of 0.12 to 0.5 mm as test particles with known circularity and aspect ratio. The standard deviations were 1.9% for the circularity and 15.5% for the approximated aspect ratio. In addition, the optical probe system was investigated by measurements of solid particles with different shapes. As an example, the results of sand, marjoram seed, and metallic oxide particles are shown. Using 1000 sand particles, the correlation between equivalent diameter and particle velocity could be demonstrated. The presented configuration of the optical probe is applicable in the size range of 0.1 to 0.9 mm and up to a particle velocity of 5 m/s.     

Piroxicam benzoate--synthesis,HPLC determination,and hydrolysis

An improved method of piroxicam benzoate synthesis was described, and an isocratic reversed-phase high-performance liquid chromatography method for its determination was developed and fully validated. The method was found to be specific, precise (relative standard deviation 0.3%), accurate (mean recovery 99.9%), and robust. Limit of detection was estimated at 0.055 µg mL^-1 and limit of quantification at 0.185 µg mL^-1. The kinetics of piroxicam benzoate hydrolysis in aqueous buffer solutions (pH 1.1 and 10), simulated gastric and intestinal fluids was studied. The hydrolysis followed first-order kinetics. The following rate constants were obtained at pH 10: k = 1.8 × 10^-3 hr^-1 at 37°C and k = 3.4 × 10^-2 hr^-1 at 60°C. In acidic media, no significant hydrolysis was observed after 24 hr. During the 24-hr period in simulated intestinal fluid, only 10.9% of the starting ester was hydrolyzed.     

Effect of artificial ageing on the hardness of cast ZA-27/graphite particulate composites

The aim of this present investigation is to study the effect of artificial ageing on the hardness of cast ZA-27 zinc-aluminium alloy/graphite particulate composites containing graphite particles of size 90–150 μm and of contents ranging from 0% to 5% by weight. The age-hardening characteristics of the unreinforced ZA-27 alloy as well as of the graphite-reinforced composite materials were determined using hardness measurements. The ageing temperatures were 75°C, 100°C and 125°C for ageing durations of 6, 12 and 18 hours respectively. The results show that for any particular graphite content and ageing temperature, hardness seems to increase monotonically with ageing time, although it probably tends towards an asymptotic value. For the non-aged composites, graphite content plays a significant role in determining their hardness values, whereas for all the aged composites, the effect of graphite content on hardness is not so marked.     

Impact of high‐velocity oxy‐fuel sprayed TiAlN surface coating on mechanical and slurry erosion performance of aluminium alloys

TiAlN coatings were deposited on AA1050 and AA5083 aluminium alloys by high‐velocity oxy‐fuel (HVOF) spray process and evaluated for their mechanical and slurry erosion performance. In comparison to base alloys, the mechanical properties were found to enhance upon coating. The effect of working parameters namely impingement angle, impact velocity, erodent size and erodent feed rate on the slurry erosion wear rate has been investigated. The slurry erosion wear rate of the uncoated samples was found to decrease with an increase in the impingement angle whereas for coated samples the slurry erosion wear rate first increased, reached to a maximum value at 60° and then decreased with further increase in the impingement angle. For uncoated and coated samples the slurry erosion wear rate was found to increase with an increase in impact velocity, erodent size and erodent feed rate. Finally, the morphology of the eroded surfaces was analyzed using scanning electron microscopy and the possible erosion mechanisms have been studied.     

Abrasive Blasting of Metal Matrix Composites

This paper investigates the feasibility of dry erosion by blasting alumina erodent on aluminum composite reinforced with silicon carbide particles. The erosion rate is dependent on the erodent velocity and the matrix hardness. Two different material removal mechanisms are observed due to different attack angles. Blasting between 30-60° is recommended for optimum erosion rate and surface quality. Material removal mechanisms and surface quality of blasted and ground composites are compared. Although its erosion rate is two orders of magnitude less than that for rough grinding, dry blasting is suitable as a finishing process of composites with irregular contours.     

MASS TRANSFER OF SULFUR DIOXIDE TO CONDENSING AQUEOUS AEROSOLS

Sodium chloride aerosols were generated from a 1.0 percent solution and passed through a tubular furnace, then recondensed at 29°C in a cooling section in the presence of SO₂. The dry particles ranged from 0.711 to 0.843 µm and the condensed droplets were in the 1.66 to 2.88 µm range. Final droplet size was varied by controlling the temperature of the nebulizer solution between 17 and 50°C. The SO₂ concentration in the gas phase of the condensing cloud was varied between 0.5x10 - ³ and 2.5 xl0 - ³ atm.

Cloud droplets were separated from the gas stream in a point-to-plane electrostatic precipitator and the droplets analyzed colorimetrically for total sulfur content.

Concentrations of SO₂ in the aqueous phase were about one order of magnitude greater than values obtained from equilibrium constants. The collection rate of SO₂ at 29°C appeared to be first order in SO₂ gas phase concentrations.

A model for this process was constructed, based on the hydrate formation in the gas-water interface[SO₂]_g + n[H₂O]ℓ ⇋ [SO₂ · n(H₂O)]ℓ

The order of the hydrate n was estimated to be 4.0.     

PARTICLE CONCENTRATION MEASUREMENTS BY LASER IMAGING FOR A TURBULENT DISPERSION

A laser imaging system has been developed which can be used for investigating the particle concentration variation in explosive test apparatus such as the Ciba-Geigi and Hartmann Bomb during turbulent dispersions of air-particle mixtures. The pulsed UV (337 nm) laser imaging system using a 500X optical and electronic magnification system has a measurement volume of 900 µm by 675 µm and an in-focus depth of field of 780 µm for a 32 µm diameter particle. Particles in the measurement control volume are imaged every 33 ms during the dispersion process and viewed in real time but stored for later analysis on a video tape system.

This paper presents the results of investigating the lycopodium particle concentration variations during the dispersion process of 0.200 grams of lycopodium particles in the Hartmann Bomb explosive test apparatus. Data were taken at the center line and at a radius ratio of 0.5 at a height of 0.102 m (4 inches) above the base of the Hartmann lucite tube. Twenty-five separate dispersions were made at each radius ratio and were based on a reservoir pressure of 103 kPa (15 psig) and 0.200 g of lycopodium powder. The average number of lycopodium particles based upon 25 dispersions at 33 ms intervals in the 473.9 × 10⁶ m³ control volume are reported for a total elapsed time of 15 seconds. The maximum average particle concentration observed was 6.4 particles at 133 ms for r/R = 0.0 and 6.5 particles in 333 ms for r/R = 0.5. Based upon uniform dispersion model for 0.200 g of lycopodium powder, 6.8 particles per control volume, would be expected. The time averaged data followed a Poisson Distribution for each time increment after 0.73 s for both radius ratios of r/R = 0.0 and 0.5 (based upon 95% confidence interval and Kolmogorov-Smirnov test). Data from 0 to 0.73 seconds could not be assigned confidence levels as the data did not follow a Poisson Distribution or any other known statistical distribution. No significant particle agglomeration was observed for the dispersion of lycopodium particles. In any one dispersion the number of lycopodium particles in the control volume was observed to vary widely during each 033 second measurement cycle.

To further investigate the particle dispersion, the flow pattern characteristics in the Hartmann dispersion apparatus were studied using flow visualization techniques based upon a matched Reynolds number (3.13 × 10⁶) dispersion of fluorescent dye by turbulent water injection. The matched Reynolds number flow visualization work further indicated the Hartmann Bomb dispersion method produces local pockets of nonuniformly-mixed mixtures during initial stages of the dispersion process, and this work further points out the shortcomings of integrating optical probes.     

RE-ENTRAINMENT OF DUSTS FROM THE DUST LAYER ON THE THE DEPOSITED DUSTS IN THE CYCLONE DUST COLLECTORS

There were many papers concerning the experimental results of the collection efficiency, but up to this time there are a few papers concerning the experimental results of the re-entrainment or dispersion of the dust particles from the dust layer by the turbulent rotational air flow in the dust bunker for the cyclone dust collector. Then in this paper, the author described the experimental results of the re-entrainment of the test dust ( talc X_R50 = 8.O µm ) for the four kinds of the throat diameter D₃ = 50, 80, 100 and 150 mm. Especially it is very importance to take into consideration of flow rate Qb into the dust bunker which is a function of D₃ and cyclone diameter D₁ and the maximum tangential velocity Vet in the dust bunker which depends on D₁,D₃ and Qb.     

PREDICTION OF PRESSURE DROP IN PNEUMATIC TRANSPORT SYSTEMS AT VARIOUS PIPE ORIENTATIONS USING AN EMPIRICAL CORRELATION FOR THE PARTICLE VELOCITY

A new empirical correlation for the particle velocity which incorporates the angle of inclination is proposed here. This correlation coupled with the expression for the solids friction factor obtained from the force balance on the particle was used to predict the pressure drops in the 0.0266 m and 0.0504 m systems held at various angles of inclination. Particles used in these systems included glass particles of 67, 450, and 900 µm weight mean diameter. The existence of minimum points in the predicted pressure drop curves as a function of gas velocity was corroborated by these two expressions.     

CONTRIBUTIONS OF ROAD DUST RESUSPENSION TO THE AIRBORNE PARTICLE CONCENTRATIONS IN TAIPEI

The high concentrations of airborne particles have been one of the main air pollution problems in Taipei, Taiwan. In this study, the possible sources of airborne particles were investigated using concentration profile and chemical composition. The vertical concentration profile of TSP was measured at 1.5 m, 11 m, and 38 m above ground. The concentrations of TSP at 1.5 m above ground are always greater than 300 µg/m³; and even up to 1230 µg/m³, while those at 11 m above ground are only half of these values. The concentrations at 38 m above ground are only about half of those at 11 m above ground. Similar concentration profiles are found for Mg, Ca, Pb, Fe, and Zn measured and the enrichment factors with respect to the composition of road dust are generally less than 3. Therefore, there is a not upward flux of airborne particles from ground. The net upward fluxes are estimated to be about 100 ton/yr/km¹ from the vertical concentrations profiles and particle size distributions. The particle resuspension rates due to wind flow from a Teflon filter were also determined at the same time. The resuspension rates of particles by wind were found to be on the order of 10^-6 to 10^-5sec^-1. These particle resuspension fluxes are much smaller than those calculated by concentration profile. Other mechanisms, e.g. traffic-induced resuspension, are needed to be included in further study.     

Reaction Kinetics of C60 Fullerene Ozonation

It has been verified that the reaction between O₃ and C₆₀ follows the general second order reaction rate which is valid for all the reactions between ozone and unsaturated olefinic bonds: v = k[C=C][O₃]. The reaction rate constant k has been measured ≈(1.5 ± 0.3) × 10⁴ L mol^-1 s^-1. The value of this rate constant has the same order of magnitude of the rate constant measured for instance in the ozonation of 1,4-diphenylbutadiene.     

Synthesis and Optical Characterization of CdS Nanowires by Chemical Route

Cadmium sulphide (CdS) nanostructured materials were synthesized by a wet chemical route without using any capping agent. X-ray diffraction pattern showed the typical interplanar spacings corresponding to the cubic phase of CdS. The peaks were identified to originate from (100), (220), and (311) planes of CdS, respectively. Transmission electron microscopy studies showed the nanowire formation with an average length 1-5 μm and the average diameter was in the range 25-30 nm. UV-visible transmission spectrum of the films deposited on glass substrates was recorded in the region 300-800 nm at room temperature. Transmission spectrum showed 75%-90% transmittance in the visible region. The values of direct band gap were obtained as 3.07 eV and 3.00, 2.89, 2.86 eV for unannealed and annealed at 100°C, 150°C, 200°C films, respectively. It showed the blue shift with respect to the bulk value. Room temperature photoluminescence was also measured, which showed a broad band lying in the range 510-625 nm.     

PARTICLE SIZE ANALYSIS FOR OFLOXACIN, PREDNISOLONE ACETATE, AND AN OPHTHALMIC SUSPENSION CONTAINING THE OFLOXACIN/STEROID DRUG COMBINATION

Image analysis (LA), Photon Correlation Spectroscopy (PCS), and Single Particle Optical Sizing (SPOS) have been applied to the analysis of particle size for ofloxacin, prednisolone acetate and an ofloxacin/prednisolone acetate ophthalmic suspension. LA shows that ofloxacin particles suspended in mineral oil are on the order of 10 µor less. LA of prednisolone acetate in H₂O shows that the steroid particles are agglomerated and range in size from 20 to 50 µ. SPOS is used to verify LA results for prednisolone acetate. LA of the ofloxacin/steroid balled milled suspension yields a particle size of ∼ 1 µ with a few particles on the order of 5 µ, PCS analysis of three batches of ball-milled ofloxacin/steroid suspension shows that increased ball-milling time increases the reproducibility of the mean diameter value as determined by PCS. It is also observed by PCS that the mean diameter of the steroid achieves a constant value with ball-milling from 11 to 14 days (1386.4 to 1383.4 nm). Extended ball-milling past the 14 day time point (18 days) appears to reduce sample inhomogeneity, thereby eliminating larger particulates with a subsequent reduction in the mean diameter to 1097.4 nm, Results for PCS analysis of the ball-milled ofloxacin/steroid suspension are verified by SPOS.     

The effects of mischmetal, cooling rate and heat treatment on the hardness of A319.1, A356.2 and A413.1 Al–Si casting alloys

The present study investigated the effect of mischmetal as a modifier, as well as the effects of cooling rate and heat treatment on the hardness of non-modified and Sr-modified A319.1, A356.2 and A413.1 Al–Si casting alloys. The main aim of the study was to determine the effect of mischmetal in terms of mischmetal-containing intermetallic phases, as well as the effects of the chemical composition of the alloys, cooling rate and heat treatment on the corresponding hardness values obtained for the alloys in question. Two cooling rates were employed to provide estimated hardness levels of 85 and 110–115 BHN, levels conforming to levels most commonly observed in commercial applications of these alloys.

The hardness measurements revealed that the hardness values of the as-cast alloys were higher at high cooling rates than at low cooling rates. Non-modified alloys (i.e. those with no Sr addition) displayed slightly higher hardness levels compared to the Sr-modified alloys. Also, the hardness decreased with the addition of mischmetal at both cooling rates.

Two peak hardness values were observed at 200 °C/5 h and 240 °C/5 h at high cooling rates in the non-modified A319.1 alloy after aging at different temperatures between 155 °C/5 h and 240 °C/5 h, while the Sr-modified alloy showed only one peak at 200 °C/5 h. Two maximum hardness values were observed at 155 °C/5 h and 180 °C/5 h in both non-modified and Sr-modified alloys at low cooling rates. The alloys containing 0 and 2 wt% mischmetal additions exhibited the highest hardness values at both cooling rates; the hardness decreased with further mischmetal additions.

Peak hardness was observed at 180 °C/5 h in the non-modified and Sr-modified A356.2 alloys under both cooling rate conditions after aging at different temperatures between 155 °C/5 h and 240 °C/5 h. The alloys free of mischmetal exhibited relatively higher levels of hardness than those containing mischmetal. The hardness decreased with increasing mischmetal addition. At the high cooling rates, the non-modified alloys displayed higher hardness values than the Sr-modified alloys, while an opposite trend was observed at the low cooling rate.

The decrease in the hardness values may be attributed to the interaction of the mischmetal with the alloying elements Cu and Mg to form the various intermetallic phases observed. In tying up these elements, the volume fraction of the precipitation-hardening phases formed in the A319.1 and A356.2 alloys (i.e. the Al₂Cu and Mg₂Si phases) is significantly reduced, thereby decreasing the hardness. The addition of mischmetal was also reported to change the precipitation sequence of the Mg₂Si phase in the A356.2 alloy. In the case of the A413.1 alloy, the low content of alloying elements resulted in a weak response of the alloy to the age-hardening process at all aging temperature/time conditions (155 °C/5 h–240 °C/5 h), and at both cooling rates. Thus, no peak hardness was observable in these alloys.     

Effect of Particle Properties on Slug Flow Conveying in a Horizontal Pneumatic Pipeline

The influence of particle properties on slug flow conveying was experimentally examined by using polyethylene particles of different densities from 825 kg/m³ to 945 kg/m³ in a horizontal pipeline 5.5 m in length, inside diameter of 32 mm, for air speeds below 8 m/s. It was found that hardness affects the slug flow conveying in such a way that for soft particles lower limiting velocity as well as boundary air velocities for suspension flow and slug flow increases. Additionally, it was found that the frictional characteristics of a particle influence its flow pattern. Also, there are two types of slug flow, that is, a solitary slug flow and a consecutive slug flow. In a solitary slug flow, there is at most only one plug in the pipeline. In a consecutive slug flow, the particles are conveyed continuously as slugs. There is always at least one slug in the pipeline.     

Content analysis and stability evaluation of selected commercial preparations of St. John's wort

Content analysis and stability studies were performed for the commercial products of St. John's wort. Six marketed formulations were analyzed for their hypericin and pseudohypericin content. These products were standardized to contain 0.3% hypericin. Results revealed total hypericin as 7.72-38.57% of the labeled claim with varying concentrations of pseudohypericin. Stability studies were carried out under three different storage conditions: 1) 25 ± 2°C, 60 ± 5%RH for six months, 2) 40 ± 2°C, 75 ± 5%RH for six months, and 3) 50°C for one month. Tablet formulations were also analyzed for their hardness and friability. Stability studies revealed significant decrease in the content of the marker compounds with time.     

RESEARCH ON AN AERODYNAMIC PARTICLE SEPARATOR (THE EPS)

This report presents an account of the research work carried out in support of the development of a new particle separator.* The EPS, as it is designated, produces multiple fractions simultaneously at a high throughput rate. The cut sizes are roughly in the range 10 to 200 µm. The principle is that particles dissimilar with respect to any of size, density, or shape will follow different and distinct trajectories when injected into a uniform laminar flow of air.

The report outlines the theoretical analyses and experimental measurements made to verify the design concepts. A detailed model of the flow field permits the calculation of particle trajectories, and hence the prediction of coarse grade efficiency and sharpness of cut. The measurements made with glass spheres and other irregular particles (e.g., carbon, cement) provide a general verification of the analytical results.

Sharpness of cut values better than 0.8 are achieved down to cut points of about 10µm. Maximum throughput rates are not yet known, but separations have been made at 480 kg/hr in a separation zone 100 mm wide. Scale-up to larger capacity is straightforward.     

Synthesis and enzymatic degradation of epichlorohydrin cross-linked pectins

The water solubility of pectin was successfully decreased by cross-linking with increasing amounts of epichlorohydrin in the reaction media. The initial molar ratios of epichlorohydrin/ galacturonic acid monomer in the reaction mixtures were 0, 0.37, 0.56, 0.74, 1.00, 1.47, and 2.44. The resulting epichlorohydrin cross-linked pectins were thus referred to as C-LP0, C-LP37, C-LP56, C-LP75, C-LP100, C-LP150, and C-LP250, respectively. Methoxylation degrees ranged from 60.5 ± 0.9% to 68.0 ± 0.6%, and the effective cross-linking degrees, determined by quantification of the hydroxyl anions consumed during the reaction, were 0, 17.8, 26.0, 38.3, 46.5, 53.5, and 58.7%, respectively. After incubating the different cross-linked pectins (0.5% w/v) in 25 mL of 0.05 M acetate-phosphate buffer (pH 4.5), containing 50 µL of Pectinex® Ultra SP-L (pectinolytic enzymes), between 60 and 80% of the pectin osidic bounds were broken in less than 1 hr. Moreover, increasing the cross-linking degree only resulted in a weak slowing on the enzymatic degradation velocity.