"There is a demand from the aerospace and energy industries for the production of turbines that operate at higher temperatures, i.e., temperatures higher than 1100.degree. C. Operation at such higher temperatures would translate into higher efficiency, high economy and less pollution. New materials such as La.sub.2Zr.sub.2O.sub.7, SrZrO.sub.3 and BaZrO that are more stable at higher temperatures and present a low thermal conductivity have been proposed recently to address this need but their fracture toughness is lower than zirconia-based TBCs making them more prone to delamination near the BC interface.
"In order to provide higher combustion temperatures, it is important to engineer TBCs with lower thermal diffusivity, thermal conductivity and elastic modulus values, when compared to those of the current TBCs. A low elastic modulus of the ceramic topcoat makes it possible to reduce the thermal stresses at the top coat/BC interface arising from the difference in thermal expansion coefficients between the two layers. As the BC is not responsible for the thermal protection performance of the TBC, the ceramic top coat will have to be re-engineered or further developed in order to produce a structure which will lower the thermal transfer from the combustion gases to the metallic parts of the turbine. Moreover, there is always a demand for more reliable TBCs that will last longer and confer a better thermal protection of the metallic substrate in gas turbines as well as in diesel engines, internal combustion engines, and in general any metal surface that is coated for thermal protection.
"It has been very, widely established that zirconia-based coatings are not suitable for use as a TBC, principally because zirconia-based coatings are known to sinter and densify in high temperature environments. The smaller the crystal size the faster they sinter. For these reasons the zirconia-based coatings would be expected to become very rigid and would be expected to crack under thermal shock conditions.
"It will thus be appreciated that thermal spray coatings have important applications and that a wide variety of thermal, mechanical and chemical properties of coatings may be desired."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Applicant has discovered that controlling thermal spray deposition parameters, including particle size distribution, and morphology, temperature, and particle velocities, produces nanostructured coatings that have important applications by virtue of a variety of thermal, mechanical and chemical properties, including a high macroscopic abradability, low thermal diffusivity, low thermal conductivity and low elastic modulus. These properties are provided by selection of a composition size and morphology of a ceramic particle and thermal spray parameters used to form the nanostructured coating, with a view to controlling a spatial distribution of porous nanostructured inclusions separated by solidified, non-porous inclusions.
"Accordingly a method is provided for producing a coating, the method comprising obtaining a ceramic powder of porous particles, collecting particles from the ceramic powder that have high porosity and selected sizes; and thermal spraying the collected particles while controlling parameters of the thermal spray to impart temperatures and velocities on the collected particles, wherein the selected size, and imparted temperatures and velocities ensure that parts of the collected particles are not melted, whereby a nanostructured coating is produced having a spatial distribution of porous nanostructured inclusions.
"Controlling the distribution and amount of porous nanostructured inclusions further permits the abradable coatings to be of a desired resistance to crumbling (fragmentation) permitting application in harsh operating environments and permits control over elasticity modulus properties to permit low thermal stress interfaces with a TBC.
"Thus, there is provided an abradable thermal spray coating comprising a ceramic material, the coating having a microstructure comprising about 10-80% by area, based on surface area of a cross-section of the coating, of a particulate phase comprising agglomerated semi-molten nanoparticles of the ceramic material.
"There is also provided a thermal barrier coating comprising a ceramic material with a microstructure having about 10-80% by cross-sectional area of porous nanostructured inclusions (semi-molten nanoparticles) distributed uniformly throughout.
"Concerning thermal barrier coatings, new materials such as La.sub.2Zr.sub.2O.sub.7, SrZrO.sub.3 and BaZrO that are more stable at higher temperatures and present a low thermal conductivity have been proposed and may be applied as a top coat over the nanostructured zirconia-yttria coating to help improving the overall stability of the coating system and further lowering its thermal conductivity.
"In one particularly preferred embodiment, agglomerated ceramic nanoparticles of ZrO.sub.2-7 wt % Y.sub.2O.sub.3 thermally sprayed at a temperature of about 2500-2700.degree. C. and a velocity of from about 200 m/s to about 250 m/s advantageously provides a nanostructured coating having about 30-35% by area of particulate phase based on surface area of a cross-section of the nanostructured coating.
"Further features of the invention will be described or will become apparent in the course of the following detailed description."
URL and more information on this patent, see: Lima, Rogerio S.; Marple, Basil R.; Moreau, Christian. Thermal Spray Coating of Porous Nanostructured Ceramic Feedstock. U.S. Patent Number 8486520, filed
Keywords for this news article include: Nanoparticle, Nanotechnology, Emerging Technologies,
Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2013, NewsRx LLC
Most Popular Stories
- Bipartisan Budget Deal Gets Key Support in House
- TFA Recruiting DACA Recipients
- Bitcoin Clones Lurch Onto Financial Scene
- Clinton to Keynote Annual Simmons Leadership Conference
- Scotch Whisky Sales Raise Distillers' Spirits
- Holiday Shopping Off to a Slow Start This Season
- Fake Deaf Interpreter Was Hallucinating, Has Schizophrenia
- Health Coverage Disparities Emerge Among States
- Podesta Likely to Reject Keystone XL
- Tea Party Glum in Face of Bipartisan Budget Deal