The plasma spray-coating process of .25 canbe used to

Chapter 5, Problem 5.26

(choose chapter or problem)

The plasma spray-coating process of 5.25 canbe used to produce nanostructuredceramic coatings.Such coatings are characterized by low thermal conduc-tivity, which is desirable in applications where the coat-ing serves to protect the substrate from hot gases suchas in a gas turbine engine. One method to produce ananostructured coating involves spraying sphericalparticles, each of which is composed of agglomeratedAl2O3nanoscale granules. To form the coating, parti-cles of diameter Dp?50 ?m must be partiallymoltenwhen they strike the surface, with the liquid Al2O3providing a means to adhere the ceramic material tothe surface, and the unmelted Al2O3providing themany grain boundaries that give the coating its lowthermal conductivity. The boundaries between individ-ual granules scatter phonons and reduce the thermalconductivity of the ceramic particle to kp?5W/m?K.The density of the porous particle is reduced to??3800 kg/m3. All other properties and conditions areas specified in 5.25.(a) Determine the time-in-flighcorresponding to 30%of the particle mass being melted.(b) Determine the time-in-flighcorresponding to theparticle being 70% melted.(c) If the particle is traveling at a velocity V?35 m/s,determine the standoff distancesbetween the noz-zle and the substrate associated with your answersin parts (a) and (b).