agglomeration breakup can be monitored. The Coriolis meter has a fast response, which may help to smooth out the powder feed.

Another sensor development, applicable to the spray plume region, is the imaging pyrometer. The two-color imaging pyrometer has advanced capabilities for noncontact thermometry suitable for nanoscale thermal spray. The ability to image the plume provides information such as plume alignment; changes in the spray pattern because of changes in the spray parameters; particle velocity, temperature, and size distributions without having to scan the plume; and powder feed-rate fluctuations (the relatively rapid frame rate can resolve fluctuations of 10 Hz or less). The large number of particles sensed in each image also speeds up the acquisition of statistical information concerning average particle velocity and temperature (for the entire particle field or for various regions in the plume).

An important issue that NIST still must examine is imaging at lower temperatures—how much of the plume is not registering because of cold material.

Finally, Dr. Ridder discussed a substrate-based sensor, a surface temperature pyrometer using an InGaAs photodetector. Substrate temperature is a key factor in splat formation and coating buildup. Substrate preheat affects coating adhesion in a poorly understood way (e.g., does substrate preheat boil off moisture, changing the substrate’s stress state?).

The opportunities, barriers, and potential applications identified by Dr. Ridder are as follows:

• Controlling spray parameters to preserve nanostructures in coatings requires addressing feed problems such as periodic change in flow, feeder rates, and liquid precursor chemistry and concentrations.

• Torch-based sensors need to consider arc parameters, powder mass flow-rate control, gas mass flow-rate control, and spray gun position control.

• Spray plume-based sensing systems need to monitor and control particle spray pattern, particle size distribution, particle velocity and velocity distribution, and particle temperature and temperature gradients.

• The accuracy with which the two-color imaging pyrometer can image the entire plume needs to be quantified. Cold material in the plume may prevent the full plume from being imaged.

• Affordable real-time detectors are needed. An example is the InGaAs photodetector for surface temperature of the substrate.

• Changing substrate conditions will require dynamic coupling of the plasma environment with the deposition to the substrate.

Walter Milligan of Michigan Technological University then completed the session with a discussion of modeling of consolidation processes in his presentation “Modeling of Nanopowder Consolidation.” Fe-base alloys and cryo-milled Al alloy powders have been created by ball milling. Ball milling can produce bulk quantities of powders economically with low capital equipment costs. Ceramics, intermetallics, and metal powders with particle size from 1 to 20 microns and grain sizes from 5 to 30 nm can be produced.

Front Matter (R1-R7)

Introduction (1-2)

Session 1: Synthesis, Assembly, and Processing (3-8)

Session 2: Fabrication and Production (9-16)

Session 3: Applications (17-22)

Session 4: Structure, Properties, and Characterization (23-24)

Session 5: Modeling and Simulation (25-28)

Workshop Wrap-up (29-32)

Appendix A: Workshop Participants and Agenda (33-38)

Appendix B: List of Attendees (39-40)