Plasma Spraying Conditions Research Articles

Prediction of in-flight particle parameters during plasma spraying of ceramic powders

A theoretical prediction model is presented to estimate the in-flight velocity, temperature, and size of a ceramic particle traversing through a plasma flame. The model accounts for the various phenomena that can influence the transport rate calculations in plasma spraying operations, which typically involve very fine particles (<50 μm) subjected to an extremely non-isothermal environment. The mathematical formulation simultaneously considers internal heat conduction in particles, accounts for the steep temperature gradients that prevail in plasma–particle systems, and incorporates the Knudsen discontinuum effects on both heat and momentum transfer. The significance of these factors is illustrated through some example calculations performed under typical plasma spraying conditions. Comparison with experimental data reveals that the present method, although simple and easy to use, enables accurate predictions to be made and can be a very useful tool in the model assisted development of various plasma–particle processing systems.MST/1533

Investigation of products arising from enzymatic digestion of advanced glycated albumin by high-performance liquid chromatography/mass spectrometry

The structural investigation of the products arising from 28 days incubation of albumin with high glucose concentration and further enzymatic hydrolysis has been carried out by means of high-performance liquid chromatography/mass spectrometry (HPLC/MS) under plasmaspray conditions. By this approach many different compounds have been detected, and for most of them, possible structures have been proposed on the basis of literature data and molecular weight assignments.

Influence of the morphology of ZrO 2 particles stabilized with Y 2O 3 on thermomechanical properties of plasma-sprayed coatings

Plasma spraying conditions of two size distributions (Pratt and Whitney Aircraft 1375 size specification −106+10 μm and −90+45 μm respectively) of Y 2O 3-stabilized ZrO 2 (8 wt.%) with different morphologies (fused and crushed, sintered and crushed, agglomerated, agglomerated and sintered) have been studied. The torch was custom made (cylindrical nozzle diameter, 8 mm) working with an Ar-H 2 mixture (75 standard 1 min −1 and 15 standard 1 min −1 respectively) at two power levels: 28 and 40 kW. A study of particles collected in water showed very different behaviour. The dense particles were almost completely melted but showed porosities and thus had a density that decreased with increasing torch power. Part of the fine agglomerated powders (diamter less than 40 μm) exploded on penetration but were partly densified, and the agglomerated and sintered as well as the agglomerated large particles (diameter greater than 40 μm) exhibited a molten shell surrounding an unmolten core; the shell for the agglomerated and sintered particles was thicker than that of the agglomerated particles. The molten shell is due to enhanced heat propagation with such porous particles. The highest densities, the best cohesion (characterized by their hardness under a load of 5 N), the lowest porosities and the smallest pore diameters of the coatings were obtained with the particles in the size range −106 + 10 μm which had been either sintered or melted. In good correlation with these results the highest thermal diffusivities at room temperature were also obtained with dense particles.

Behavior of Alumina Particles in Atmospheric Pressure Plasma Jets

The distribution of Al2O3 particle size, velocity and temperature was mapped over the flow field of a 31.5 kW plasma torch. The effects of varying the powder loading were studied. The powder feed rate was varied between.45 and 2.05 kg/hr independent of the carrier gas flow rate. The particle flow field was non-symmetric due to the method of particle injection. The data indicate that powder feed rate does not significantly affect either the temperature or velocity of the particles, for typical plasma spray conditions, and that the assumption of a dilute particle flow field is valid.

Applications of computer simulation techniques to problems encountered in conventional plasma spraying

A computer simulation technique requiring only modest computational power for predicting optimum plasma spraying conditions is described. The technique is illustrated by applying it to a model plasma gun and determining the “safe range” of working distances for forming good coatings; the data are summarized in the form of a new type of phase diagram.

Effect of plasma-spraying conditions on the adhesion of steel coatings

1. The strength of adhesion of a plasma-sprayed steel coating is 2.5–3 times that of a steel coating prepared by the welding-arc process. 2. The following process parameters may be recommended for the plasma-jet deposition of steel (U8A) coatings: L=120 mm, I=450 A, V=30 V, Q=17 liters/min, and G=0.86 m/min (at a wire diameter of 1.8 mm).