Microscopy and surface analysis
Smearing under pressure makes it possible to assess the quality and properties of putties or pastes more precisely. The pressure creates so-called “tear-off edges”, which give an indication of the adhesion of the paste. This is particularly important as the way in which a paste tears or shears under mechanical stress allows conclusions to be drawn about its internal structure and bonding strength. Putties that are too sticky or runny tend to release the binding polymer and tiny particles when smeared, which can impair their adhesion.
This may indicate insufficient viscosity or poor distribution of the solid components. Such putties often behave like non-Newtonian fluids whose viscosity can vary under shear stress. Putties that are too viscous and show abrupt break-off edges, on the other hand, are often materials that tend to be brittle and require a higher shear stress to flow. Such properties may indicate that the paste does not flow optimally when applied under pressure, which can have a negative impact on even distribution and therefore adhesion.
Viscosity is therefore a critical parameter that must be taken into account when formulating and applying putties. A balanced viscosity, which is neither too high nor too low, ensures that the paste can be spread well and adheres sufficiently without causing unwanted cracking or tearing. Both putties look quite similar here, whereby the Value32 is a little greasier, i.e. less viscous.
Particle sizes
The particle sizes of thermal conductive additives such as Al₂O₃ (aluminum oxide) or ZnO (zinc oxide) play a decisive role in thermal putties, as they directly influence the thermal conductivity and processability of the material. Particle sizes in the micrometer or sub-micrometer range are generally used, as smaller particles offer a larger surface area that can improve heat transfer. A narrow particle size distribution is optimal, which helps to minimize voids between the particles and thus maximize the thermal efficiency of the material.
Good thermal putties can be recognized by several properties. Firstly, the material should have a high thermal conductivity, which means that the thermal conductive additives are effectively distributed in the matrix and tightly packed to ensure the most continuous heat flow possible. A uniform consistency without lumps indicates good dispersion of the particles, which in turn improves the thermal properties. In addition, good putty should have sufficient viscosity to allow easy application without the material softening or losing its shape under pressure.
The mechanical properties are also important; the material should not only be thermally efficient, but also sufficiently flexible to conform to irregular surfaces without breaking or tearing We now see all the products tested, each at 1000x magnification and with an additional particle measurement, although with such tough polymers, except for the HY 268, this is more of a measurement of bubble formation on the surface.
Material analysis
The matrix of thermal putties usually consists of polymeric materials (as in our two putties today), which act as a binder and evenly distribute the thermal conductive additives such as Al₂O₃ or ZnO. Frequently used polymers in these rather crumbly matrices are silicones or acrylates. These polymers offer good mechanical flexibility and stability, which makes it possible to use the putties in various applications such as electronics or heat sinks. Silicone-based matrices are particularly popular as they have excellent thermal stability and flexibility, which is important for balancing thermal stresses between different materials.
The choice of matrix often depends on the specific requirements of the application, including operating temperature, required mechanical properties and chemical resistance. A well-formulated matrix ensures that the thermal conductive additives are evenly distributed and that the putties maintain their thermal and mechanical properties throughout the lifetime of the application. So let’s take a closer look at what’s actually inside and what’s not.
Interestingly, the CX-H1300 does not contain any zinc oxide (ZnO), but only aluminum oxide (Al2O3) and a viscous silicone matrix:
Although aluminum oxide predominates in Value32, some zinc oxide is also present, even if only in tiny traces. The rest is also a kneadable silicone matrix, but it appears somewhat coarser and more inhomogeneous.
Kommentieren