In ceramic engineering, the most common method for producing ceramic components is to form a green body comprising a mixture of the ceramic material and various organic or inorganic additives, and then to fire it in a kiln to produce a strong, vitrified object.
The measurement of bulk density of, for example, green ceramic tiles during production is a fundamental parameter for the quality of the product. The bulk density of a green ceramic body provides valuable information needed to control the quality of a ceramic piece (after firing) with respect to its final size and the porosity and cracks in the body and is proportional to the final mechanical resistance. It is therefore important that optimum measurement procedures are followed in determining density.
Bulk density is defined as the total mass of a body divided by the bulk volume. Bulk volume (or envelope volume) is defined as all space that is interior to the macroscopic “envelope” surface of the body. For a green body, the bulk volume includes the volume of solid particles, the volume of any temporary additives and liquid present, and the volume of empty pore space. This is what the Ceramscan can measure using its laser.
The porosity of freshly pressed ceramic bodies conditions green tile behaviour during the process (drying, glazing, and firing) and largely determines the properties of the final product. This makes it necessary to control tile porosity during shaping. Due to the difficulty of measuring ceramic tile porosity, bulk density is the physical magnitude that is actually measured to control the pressing stage.
Many ASTM methods for determining bulk density of refractory materials and glasses are described in books published by the ASTM. Most of these methods are based on volume displacement by Archimedes’ principle; that is, since both refractory materials and glasses are compatible with water, their bulk density can be easily determined by volume displacement in water. However, this test method is not suitable for green body ceramics, which will disintegrate easily in water. For green body ceramics, mercury pycnometry is recognised as the benchmark method for measuring the bulk volume of a body. Mercury is an excellent displacement liquid – its high wetting angle and large surface tension prevents it from penetrating into small pores in green bodies.
The most common method used to measure green tile bulk density has been by mercury displacement. The main advantages of this method are its ease of use and apparent high precision. Nevertheless, it has the drawbacks of being destructive, discontinuous, and manual. Furthermore, the high toxicity of mercury implies a grave health for workers performing industrial compaction controls and as such it is now illegal to use industrially in most parts of the world. This means that companies must look for alternatives to the use of mercury in tile bulk density measurement.
Why measure Volume, Density and Product Dimensions using a Ceramscan?
• Fluid displacement techniques are not suitable for porous materials. The Ceramscan is a non-contact laser-based measurement that is not affected by sample porosity.
• Mercury displacement techniques represent a toxic risk to the environment and are therefore illegal in many countries. The Ceramscan has been verified as accurate as mercury displacement methods.
• Gas displacement techniques usually measure very small samples or otherwise attract a high instrument price. The Ceramscan has the largest measurement envelope in its class.
• X-ray techniques are expensive and present a health and safety issue and therefore require fully trained operators. The Ceramscan uses an eye-safe laser and therefore is the safest procedure for density determination.