Linear shrinkage techniques

In another work (MucciUo, 2002) linear shrinkage studies were reported on reactive neodymium-doped zirconia with 3, 5 and 8 mol% Nd powders prepared by the sol-gel technique. The calcined powder with a uniform distribution of particles and an average particle size of 3 /xm was found microscopically to be agglomerated. Linear shrinkage studies on the powder compacts exhibited a total shrinkage of around 30% up to 1650°C. 

The TMA technique can be used for Tg-value determinations, resin cure studies, penetration experiments or orientation effect determinations. The most important application is thought to be the linear thermal expansion coefficient (l.e.c.) determination of engineering polymers. An example of this application is given in chapter 3.1.2. The results of a polymer shrinkage experiment monitored by TMA are described in chapter 3.1.3. 

The TMA technique provides a means by which the behavior of a sample may be characterized in response to specific experimental circumstances and allows a detailed fingerprint to be recorded as small sample history differences give rise to different dimension-temperature behaviors. Properties that are of immediate relevance to end users, including linear thermal expansion coefficient, thermal shrinkage and the shrinkage force, may be obtained by direct measurement from TMA characterization. 

For the resin shrinkage measurements, various techniques utilizing different physical principles are used. These techniques can be divided into two major categories linear and volumetric resin shrinkage measurements. 

Certainly in the case of many co-injection techniques, differences in mould shrinkage and thermal expansion can lead to problems such as sink marks, warpage and residual stresses. With over-moulding techniques, differences in shrinkage or the coefficient of linear thermal expansion (CLTE) can produce high stresses between restrained materials. The result in both cases can be the same, premature failure. 

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