Dispersion In Air of Micron and Nanometer Sized Particulate Systems:

PREDICTING AGGLOMERATE STRENGTH

N. StevensH. El-Shall*, K. Powers*, A. Ranade**, and Y. Rabinovich*

*University of Florida** Particle Systems, LLC

Center for Particulate & Surfactant Systems (CPaSS)

IAB Meeting University of Columbia, New York, NY

August 20, 2009

Agglomeration is responsible for Dosing errors for inhaled drugs

Defects in powder coatings Formulation errors Bulk transfer powder hang-up

Decreased effectiveness of products

Poor performance obscurants

Dispersion is important to: Health, Industry,Environment, Defense and Emerging Areas:

Industrial RelevanceIndustrial Relevance

Bottom Line: Improper dispersion will impact cost and quality

Agglomeration and Powder ProcessingAgglomeration and Powder Processing

Specific Objectives: develop a methodology/protocol to

predict the dispersability of powders based on agglomerate

strength measurements

State of the Art:

ad-hoc approach, using brute force, wastes energy

Powder Drying

Dispersion

Powder production

Powder processing

Final Product

WetDry

bottle neck

DevelopDevelop relationship between agglomerate strength, interparticle forces, and dispersion for more energy and material efficient processes & equipment design

Shear Strength– Aerodisperser, Sonic nozzle, and/ or Calibrated ultrasonic technique*

Interparticle Forces – AFM Particle Morphology, fracture surfaces, neck characterization-

SEM, TEM, Image analysis

DevelopDevelop a model using a Design of Experiments Used successfully for modeling dispersion of IR Obscurants

Research ApproachResearch Approach

* “* “Determination of agglomerate strength distributions : Part 1. Calibration via ultrasonic forces” by S. G. Thoma, M. Ciftcioglu and D. M. Smith, Powder TechnologyVolume 68, Issue 1, October 1991, Pages 53-61

0.7( ) 1.8( ) 3.9( ) ...airborne spacerC f RH C

Effect of Drying Technique on Agglomerate StrengthEffect of Drying Technique on Agglomerate Strength

Drying Method Mean (µm) Agglomeration (%)

Primary Particle Size (Al)

10 -

SC-CO2 17 85%

Sublime Dry 51 88%

Freeze Dry 158 96%

Convection Dry 344 98%

• Almost every technique results in agglomeration• Do agglomerates have different strengths?• What is the best way to characterize this?

Agglomerate Strength CharacterizationAgglomerate Strength CharacterizationDry Aerosol System:Dry Aerosol System:

Aerosizer or Sonic NozzleAerosizer or Sonic Nozzle•Agglomerate strength Agglomerate strength monitored w.r.t. shearing monitored w.r.t. shearing forceforce

•Control over shearing forceControl over shearing force

•Broad range of nozzle Broad range of nozzle designsdesigns

•Monitor changes in PSD Monitor changes in PSD with laser diffractionwith laser diffraction

•Monitor whole PSD or size Monitor whole PSD or size of interestof interest

MethodologyMethodologyCalibrateCalibrate

Agglomerate StrengthAgglomerate StrengthAnalyseAnalyse ReportReport

Glass Ballotini:

•Known breaking strength

•Used to calibrateshear force of nozzle

Test Powders:

•Model - alumina•Industrial powders

Agglomerate Strength Distributions:

•Quantitative•d50 and PSD vs.

shear force

HypothesisHypothesis

Supercritical Drying Evaporation

MODEL FOR DEAGGLOMERATION

•Use model to develop energy & material efficient processes & equipment•Long term goal: model deagglomeration from first principles

Evaporative Drying

Super Critical Drying

50( ) ( ) ( ) ( )....de aggF f A D B RH C D Energy

Outcomes/ DeliverablesOutcomes/ Deliverables•Agglomerate strength measuring technique and protocol

•Effect of processing methods on agglomerate strength

•Correlation between of interparticle forces and agglomerate strength

•A model to correlate powder dispersion in air to powder characteristics and dispersion techniques

The authors acknowledge the financial support of CPaSS, the National Science Foundation (NSF), and the CPaSS Industrial Partners.

AcknowledgementsAcknowledgements