Pycnometry is a technique used to measure the density of materials that are manufactured in many of today's products. Mass divided by volume is the way that most people refer to pycnometry but not all measurements are as straight forward as that for rigid and solid materials.
Porous and nonporous objects may share the same definition as density and can be measured by displaced volumes, but displaced medium can also consist of gas, liquid or fine powder.
Then there are the irregular shapes or objects with cracks that change the rules of pycnometry completely. For this reason, there are three separate ways to determine density depending on the type of sample you are choosing to measure.
Absolute density is a measured volume that excludes the pores and other void spaces between particles of the bulk sample. Liquid was once the technique of choice for filling in the pore spaces but is quickly being replaced with a method referred to as the 'helium density' because helium pycnometry is replacing the liquid method. Helium has been found to be much more accurate and easier to use.
Envelope density is when porous materials are included in the volume measurement due to irregular size and shaped objects. The envelope density values are less than absolute densities when the object is porous and even for non porous. Pycnometry instruments are able to measure an envelope density quickly and efficiently.
Bulk or tap density consists of vibrating the packaging and rearranging the particle size distribution and shape of the material. As interparticle voids are allowed in this measurement, tap density is always of less value than envelope density. The evaluation is very important to industries that need to make their products partially porous while still fulfilling their function.
British standards recognize the definitions of density in different terms. Absolute powder density is the mass of powder per unit of absolute powder volume. Apparent powder density refers to the mass of a powder that is divided by its apparent volume. The volume that is occupied by it excluding all pores and voids is called absolute volume.
Materials that utilize dense stage determination include Coke, film, resins, polyester fiber, clay, cement, carbon cloth, foam, metal parts, nickel and coating powder. The pycnometer products used to measure these products from the beginning of a raw compound to a finished product, shifts density several times but with a crucially accurate measurement.
Many products are rated by their decreased or increased amount of density. Home insulation for instance, wants as many closed air bubbles as possible while furnace and automobile filters require just the opposite. Without the aid of pycnometer instruments, this would be very difficult to evaluate.
Industry has become comfortable with the ways and means of measuring dense values and pycnometry makes this process simple. They will continue to work to make this technology even better as more products are designed.