So what are porous ceramics? Here at ThermoPore, the term porous ceramic defines a molded, open-cell, porous material made from aluminum oxide (AL2O3) or silicon carbide (SiC). By molded, we mean a rigid body that has 3D features. By open-cell, we mean a material that enables air (or fluid) to flow from one side of the part to the other as water flows through a sponge. The porous network that enables fluidic communication throughout the ceramic material is created in a basic two step process whereby a "green" part is first formed and subsequently fired at high very temps to bond adjacent ceramic particles to one another.
The production of a porous ceramic part begins with material selection. The majority of ThermoPore’s porous ceramic parts are made from aluminum oxide, but some parts made from silicon carbide do find use in special applications that warrant its 1800° F (982° C) operating temperature (400° F/204° C more than aluminum oxide). After the base ceramic raw material is selected, a pore size is selected, and the parts shape is designed. From these inputs, either prototype or production tooling is created for the creation of a “green” part.
The "green" part is the intermediate part that is created during the part's production. As an example of preparing a “green” part, imagine filling a coffee cup with a handful of special ceramic marbles – special because these marbles stick to one another if they are subjected to a compression cycle. Also special since they do not change shape during the compression cycle. Like we said – they’re special. So imagine that the marbles poured inside the coffee cup were subjected to a compression operation. What’s happens? Assuming that the coffee cup didn’t crack (did we say that the coffee cup is special also) the ceramic marbles contained within the cup will bind to each other without changing their shape. In other words, each marble will stick to its adjacent neighbor without eliminating the air space between each of the marbles. Now, if we remove the marble mass from the cup, you’ll have the equivalent of a “green” porous ceramic component. So what’s different about this “green” part that we just made as compared to a regular finish part? Well, truth be told, the ceramic marbles in the "green” part are only loosely bonded to one another following the compression operation? So how do you increase the bond strength of adjacent ceramic particles in the “green” part? Simple, just place it in a really, really hot oven.
Once removed from the tool, the “green” part exhibits the basic shape of a finished part. However, the green part lacks structural integrity. Remember, the spheres are only lightly bonded to one another at this point in time. However, by subjecting the ceramic part to a complex thermal cycle that undergoes temps in excess of 2000° F (1090° C), porcelain bonds are created amongst adjacent ceramic particles. Think of these porcelain bonds as binding agents that provide overall structural integrity to the finished part. Once fired and cooled, the "green" part is transformed into a finished part with plenty of strength.
By using the basic production process described above with raw materials of different size or shape, ThermoPore can produce porous ceramic components with different pore size (the size of the opening between adjacent particles), pore volume (the percentage of air per unit volume present in the porous part). In addition, by using various raw materials at the onset of the sintering process or by creating a raw material blend composed of multiple raw material types, ThermoPore can create porous ceramic components that offer a variety of functional attributes. So call us today to get your project started or peruse the eCatalog to learn more about readily available shapes and sizes of available production tooling that can be used to get your project going.