Particle Characterization of Abrasives

Transcription

1 Particle Characterization of Abrasives Mark Bumiller

2 Factors Affecting Abrasion Mechanics Difference in hardness between the two substances: a much harder abrasive will cut faster and deeper Grain size (grit size): larger grains will cut faster as they also cut deeper Grain shape: sharp corners help Adhesion between grains, between grains and backing, between grains and matrix: determines how quickly grains are lost from the abrasive and how soon fresh grains, if present, are exposed

3 Factors Affecting Abrasion Mechanics Contact force: more force causes faster abrasion Loading: worn abrasive & cast off work material fill spaces between abrasive grains, reducing cutting efficiency while increasing friction Use of lubricant/coolant/metalworking fluid: Can carry away swarf (preventing loading), transport heat (may affect physical properties of the workpiece or the abrasive), decrease friction (with the substrate or matrix), suspend worn work material and abrasives allowing for a finer finish, conduct stress to the workpiece.

4 Macro vs. Microgrits Macrogrits: Greater than ~ 60 µm Traditional size test is sieving Microgrits: Less than ~ 60 µm Traditional testing is sedimentometer 2 mm 40 µm

5 Macrogrits

6 Microgrits

7 ISO 6344 Macrogrits P12 to P220

8 Inexpensive Time consuming Alternative: Dynamic Image Analysis by CAMSIZER Higher throughput Complete distribution Shape information Particle images Sieve Analysis Size and shape from 30 µm 30 mm

9 Dynamic Image Analysis By choosing proper size parameter, Xc min, results can match historic sieve Data. Also generates shape data proven To correlate with abrasive performance.

10 Sand: Round vs. Edgy by CAMSIZER Similar in size. Shape difference seen in b/l and sphericity. Edgy would make better abrasive. Sphericity Breadth/length (b/l)

11 ISO 6344 Microgrits P240 to P1200

12 ISO 6344 Microgrits P1500 to P2500

13 Sedimentometer Sample is pre-wet, then placed in settling medium at top of tube, time is recorded Time is recorded when the first material reaches the collecting tube Times are recorded as sample reaches various graduations in settling tube Example: If the 2mm height was reached in 4 minutes, that means 8% of the material is 39.8 microns and coarser Still in use, but being replaced by newer technology (laser diffraction)

14 Laser Diffraction Powders (in air) and suspensions 30 nm 3000 µm Quick, easy, reproducible Highly automated Most popular particle sizing technique LA-950 highest performance available but workhorse dependability Dry powder feeder

15 Laser Diffraction Data Silicon Carbide Diamond Abrasives slurry

16 Chemical Mechanical Polishing (CMP) Smooth (planarize) silicon wafer surface with combination of chemical & mechanical forces Uses abrasive & corrosive colloidal slurry, polishing pad, and retainer ring CMP slurry contains small abrasive particles Large particles in slurry cause scratches (defects) Want to know mean size + presence of larger particles

17 Particle Sizing Techniques Technique Nano-Particle Measurement Oversize Measurement Analysis Speed Dilution Required? Laser Diffraction Very good Excellent Excellent Yes Dynamic Light Scattering Excellent Very poor Very good Yes Acoustic Spectroscopy Very good Excellent Good No Light Obscuration Very good Good Poor Yes Disc Centrifuge Very good Excellent Very poor Yes Microscopy (SEM, TEM) Excellent Very poor (statistics) Very poor No

18 Laser Diffraction Data Ludox colloidal slurry (31 nm) Geltech silica (1.65 µm) 0.05 wt % Geltech in Ludox

19 Acoustics: DT-1201 Experiment Attenuation [db/cm/mhz] α = 10 log f [ MHz] L[ cm] I I in out Attenuation [db/cm/mhz] diameter 1 micron diameter 0.5 micron Frequency [MHz]

20 Acoustics: DT-1201 Experiment Materials: Ludox colloidal silica, Geltech silica, commercially available CMP slurries Spike SS25 CMP slurry with Geltech silica Note: all measurements made with no dilution, major benefit of acoustics

21 Acoustics: DT-1201 Experiment Attenuation spectra for single component silica slurries Corresponding particle size distributions

22 Acoustics: DT-1201 Experiment Particle size distributions of silica Cabot SS25, diluted down to 12 wt %, with various additions of silica Geltech 0.5

23 Image Analysis Experiment Samples: small, medium, large abrasive particles Measure size & shape using static image analysis (PSA300) Prepare sample using Sampler Disperser Calculate size, shape, custom calculation to define angularity

24 Image Analysis Experiment Small abrasive, high angularity (left), low angularity (right) Medium abrasive, high angularity (left), low angularity (right) Large abrasive, high angularity (left), low angularity (right)

25 Shape Parameters

26 Spike Parameter* * Stachowiak, W., Image Analysis of Abrasive Grits, Tribology and Interface Engineering, Vol 44

27 PSA300 Calculation Find sharp edges at the tips of the particles Count number of tips (child count) Number of tips alone not sufficient, long particles w/2 tips not as good as hexagon w/6 tips Define angularity roundness as child count x roundness Thus triangle w/3 points less angular than octagon of 4 sharp edges & 4 rounded edges

28 PSA300 Calculation

29 PSA300 Calculation

30 PSA300 Calculation

31 Image Analysis Results

32 Conclusions For particle size analysis Laser diffraction offers many benefits over sedimentometer CAMSIZER offers many advantages over sieves DT-1201 for undiluted size and zeta potential For particle size and shape CAMSIZER for 30 µm 30 mm PSA300 for 0.5 µm 2000 µm View at any time at: