Dr. Marvin Groeb – Abrasive Solutions

Category: Abrasive Snippets

  • Abrasive Snippets – Part 3 – SiC Grains (FEPA 300, 400, 1000)

    This is part of a series of posts about abrasives. This is mostly cool SEM pictures, but I find them interesting. It’s quite difficult to image small grains at large magnifications, so there’s very limited information and pictures online about them. Head over to the archive to see the other snippets on abrasives.

    Today’s abrasive is SiC. Silicon carbide is a fantastic engineering material, and also quite hard. Depending on the polytype, you get between 2000 and 3000 HV, which makes it kinda like the 3rd or 4th hardest commercially available abrasive. It is also super temperature resistant and very chemically inert. Again, depending on the polytype, it is either green (4H-SiC) or black (6H-SiC).

    What’s the difference? The crystal structure. While SiC is typically hexagonal oriented, the different polytypes show different stacking orders. While 6H is stacked ABCACB, 4H is stacked ABCB

    Crystal structure of 6H-SiC.

    This property is called polymorphism, many minerals exhibit this, but SiC is unique in terms of there being 250 different known polymorphs.

    The SiC we are looking at was bought at a German sharpening supply, sharpeningstones.de. They declare it as FEPA 300, 400 and 1000 grit, which would correspond to (roughly) 34, 17 and 4.5 µm.

    FEPA 300 SiC

    SEM Micrographs of FEPA 300 SiC particles. Instrument: Zeiss GeminiSEM 560.

    FEPA 400 SiC

    SEM Micrographs of FEPA 400 SiC particles. Instrument: Zeiss GeminiSEM 560.

    FEPA 1000 SiC

    SEM Micrographs of FEPA 1000 SiC particles. Instrument: Zeiss GeminiSEM 560.

  • Abrasive Snippets – Part 2 – CBN Grains (8-12 micrometre)

    This is part of a series of posts about abrasives. This is mostly cool SEM pictures, but I find them interesting. It’s quite difficult to image small grains at large magnifications, so there’s very limited information and pictures online about them.

    This post is about 3 different CBN abrasives. They are all nominally 8-12 µm sized. Curiously, they are different colours. Manufacturer: Ceratonia, Germany.

    The first type is an amber coloured one. It’s blocky, and supposedly very nice lapping of steels or galvanic applications.

    SEM micrographs of 8-12 µm CBN grains, amber coloured. Instrument: Zeiss GeminiSEM560.

    The second time is a black one, supposedly self sharpening and ideal for super alloys and hardened steels.

    SEM micrographs of 8-12 µm CBN grains, black coloured. Instrument: Zeiss GeminiSEM560.

    The third type is a brownish coloured one. I managed to pour half of my sample over myself, nice work Dr.Marv. Monocrystalline and very hard.

    SEM micrographs of 8-12 µm CBN grains, brownish coloured. Instrument: Zeiss GeminiSEM560.

  • Abrasive snippets – Part 1- 0.25 µm Diamond (PCD/MCD)

    This is part of a series of posts about abrasives. This is mostly cool SEM pictures, but I find them interesting. It’s quite difficult to image diamond at large magnifications, so there’s very limited information and pictures online about them.

    This post is about very small diamond – nominal size is 0.25 µm, so 250 nm. This is already bordering on a nanoparticle, with all the difficulties that go along with this. Particles clump together like crazy, because weak surface forces such as van der waals forces are already larger than the mass of the particle. Sample preparation is a pain. And once you manage to prepare a nice monolayer on a very even substrate, diamond is non conductive, and very prone to charging effects. Luckily, the Zeiss GeminiSEM560 we have installed at Kern Microtechnik is an absolute champ at low voltage images.

    Without further ado: 0.25 µm polycrystalline diamond.

    SEM micrographs of 0.25 µm polycrystalline diamond. Sensor used is a SE1 InLens type. It shows very fine surface detail, but flattens the picture minimally. Low accelerating voltage and beam current with frame integration to reduce noise (about 100 frames / <1 sec frame time). At > 50kx magnification, beam deconvolution is used. Instrument: Zeiss GeminiSEM560

    And the 0.25 µm monocrystalline diamond:

    SEM micrographs of 0.25 µm monocrystalline diamond. Sensor used is a SE1 InLens type. It shows very fine surface detail, but flattens the picture minimally. Low accelerating voltage and beam current with frame integration to reduce noise (about 100 frames / <1 sec frame time). At > 50kx magnification, beam deconvolution is used. Instrument: Zeiss GeminiSEM560