Fig 14 Thermal Conductivity

the coating, as far as porosity and density, and the resulting thermal conductivity, are shown in Figure 14. Variations in the power are made to deposit the powders with similar densities.

Notice that there are some differences in the lower power coatings, particularly with Zircoa. The properties change little at lower power (less dense) processing. We have quite a range in the thermal conductivity and with the Cerac powder we are able to get thermal conductance down to about .6 whereas we seem to have hit a limit of .93 with the Zircoa powders. For comparison is the Amdry bond coat powder which has an obvious higher conductance because it is a metallic material with much higher thermal conductivity than the thermal barrier materials. We designed our work around the relationship between thermal conductivity and porosity of the coating based on a NASA Lewis published report, which is shown in Figure 15. It shows the thermal conductivity dropping from 2 ,:2v to less than .5 with porosities increasing up to 40%. Thé optimum level for the maximum change is about 12-15% porosity and we were aiming for that type of porosity in our coatings. We have plotted on this previously published curve the actual data of the thermal conductivity of both the Zircoa and the Cerac powder at the power levels described in the previous figure. As can be seen, the data fits the curve fairly well. Differences between the NASA data and our results are due more to the techniques used to measure the porosity of the material. We have had a

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