Mortars and pestles come in a variety of shapes and sizes. A few of these from the Fisher Scientific catalog are shown below. On the left is a typical porcelain mortar and in the middle is an agate mortar and pestle set. A Diamonite (synthetic sapphire) set is shown on the right.
The kind of mortar and pestle used in the preparation of a solid state material is very important. If the sample being ground is harder than the material comprising the mortar, significant contamination of the sample can be expected. For this reason, porcelain (fired clay) is not typically used for solid state synthesis. In addition, porcelain is a porous material and can be difficult to clean. Agate (a form of quartz) is usually the material of choice, but there are also other alternatives such as the Diamonite set shown above. A three inch (76 mm) porcelain mortar and pestle set costs around $20 U.S. and an agate or Diamonite set costs around $200. Most inorganic or organic laboratories have porcelain mortars and pestles, but you won't find many (smart) solid state chemists using these!
In a typical solid state synthesis, the reactants are placed in a mortar and ground by hand with the pestle. Acetone or an alcohol are sometimes added to ease grinding. Grinding is continued until the mixture is homogeneous, the particles are no longer getting smaller, and the solvent has evaporated. With good technique, powders with an average diameter of 10 microns (10-3 cm) can be prepared.
If one has many samples to prepare and each requires frequent grinding or one has very large samples, this method of particle size reduction becomes very tedious (and physically taxing). In this case, a better solution is a machine called a ball mill which automatically grinds samples.
This page was last updated Monday, March 30, 2015.
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