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A Comparison of Grinding Media Composition

By Alyssa Conn, OPS Diagnostics, LLC

  Stainless Steel Glass Zirconium Silicate Zirconium Oxide (Yttria stabilized) Zirconium Oxide (Ceria stabilized)
Density g/cc 7.9 2.25 4.65 6.0 6.20
Durability Medium Low Medium High High
Approximate Hardness on Vickers Scale 700 533 690 1280 1150
Compatibility (Low 1-High 4) 1 2 3 4 4
Cost(Low 1-High 4) 3 1 2 4 4
SPECS  (Low 1-High 4) 4 1 2 3 3
Comment Some types may be retrieved with magnets May be derivatized using silane chemistry Partially modifiable with silane chemistry Resistant to corrosive chemicals such as phenol Resistant to corrosive chemicals such as phenol

Discussion

Several different types of media are available for grinding samples. Selecting the right type is important to the disruption process, as there are advantages and disadvantages of each medium depending on the application.  When choosing a media type, the density, durability and chemical resistance are often the most important factors to consider.

Stainless Steel: Most dense of all the grinding media, stainless steel balls are popular for their moderate cost and wide range of sizes. Furthermore, stainless steel balls are machined with high precision and can be removed from vials using magnets (some but not all stainless steel types). One disadvantage is that they may react with phenol and acids, which may interfere with sample processes.

Glass: Widely-used for their low cost, glass beads are ideal for the homogenization of microorganisms. The size range for glass is from microns to centimeters. They are inert but may be modified or derivatized by adding functional groups using silane chemistry. Disadvantages include lower precision, density and durability.

Zirconium Silicate: This type of grinding media is of high precision (roundness) and moderate cost, making them ideal for most disruption processes. Zirconium silicates are higher in density than glass, but lower than stainless steel and zirconium oxide. They also contain silica; therefore they may be partially modified or derivatized using silane chemistry.

Zirconium Oxide, Yttria Stabilized: Exceptionally hard (1150 HV) and dense (6.0 g/cc), these grinding balls are the highest quality of all the grinding media as well as the most durable. They are extremely inert and of the highest precision, and can be obtained in a variety of sizes.

Zirconium Oxide, Ceria Stabilized: Similar to Yttria Stabilized Zirconium Oxide, this type of grinding media is also of high precision, density, and quality. They are more expensive, yet also more durable. They may be used for special applications as a result of the availability of a variety of shapes, including satellites