Most of the previous answers were correct, but somewhat incomplete. From your question, I understand that the goal is to remove the PVA through thermal treatment, but typically the ultimate goal is to sinter the material to full density.

PVA is a polymeric binder, frequently used in ceramic slurries to increase resistance to cracking during drying, or mixed with dry powders to increase mechanical resistance in the green state.

PVA starts decomposing at T > 300 ºC until 600 ºC, so much lower than the sintering temperature of the ceramic material. You can read more about thermal decomposition of PVA here:Article A Thermal Degradation Mechanism of Polyvinyl Alcohol/Silica ...

Decomposition may occur in several steps, and may result in formation gases like CO, CO2, and H2O vapor. If you heat all the way up to the sintering temperature too quickly, material densification and PVA decomposition will occur simultaneously, but the decomposition gases will be trapped in the microstructure as the material densifies, resulting in trapped gas bubbles and thus sub-optimum densification. If there is significant amount of gas being formed, there is the risk that the sample will "explode". This is basically the same reason why any ceramics required a drying step prior to thermal treatment.

To avoid this, the sintering thermal cycle must contain a "de-binding step", during which the material is held at a fixed temperature slightly above the decomposition temperature of the binder (or any other organic or water).

Coming back to your question, the standard thermal cycle to sinter a generic ceramic pellet (~cm) including a debinding step, is to heat up to 600 ºC at

Dear Antonio,

Generally, the PVA will evaporate around 600oC.

In my research work, I have used this temperature.

You can read this paper, might be you will get some information regarding to your question.

https://www.researchgate.net/publication/257583127_Microwave_sintering_effect_on_structural_and_dielectrical_properties_of_Ba1-xSrPbxTiO3_x_02_for_Sr_and_Pb_ceramics?_sg=SUlqA5kN_Sns910RqxDVHQUoZUZ5DVrzgIh6b65ZJoy7xJUb-lPOqeh_NQOoTKyUgdU5htdNiTqqqGqWsFBC5JVxniUrAxLuDVVNNNDE.O9vJ9c3wltri3S2uBrZI3f_7eLlLxXhnHWWbBZlY8S7-q5r-Y3bGXAlmKeFG4GYMKQiVGhxlU41G3p8o9EoqhA

Venkata Ramana Mudinepalli Thank you sir!

Here we also use 600oC with 1oC/min and a dwell time of 1h.

Do a DSC and in the cycle add a long holding at the temperature where the mass loss starts in the DSC.

The duration of the holding dépends on the size of the pellet.

best

Most of the previous answers were correct, but somewhat incomplete. From your question, I understand that the goal is to remove the PVA through thermal treatment, but typically the ultimate goal is to sinter the material to full density.

PVA is a polymeric binder, frequently used in ceramic slurries to increase resistance to cracking during drying, or mixed with dry powders to increase mechanical resistance in the green state.

PVA starts decomposing at T > 300 ºC until 600 ºC, so much lower than the sintering temperature of the ceramic material. You can read more about thermal decomposition of PVA here:Article A Thermal Degradation Mechanism of Polyvinyl Alcohol/Silica ...

Decomposition may occur in several steps, and may result in formation gases like CO, CO2, and H2O vapor. If you heat all the way up to the sintering temperature too quickly, material densification and PVA decomposition will occur simultaneously, but the decomposition gases will be trapped in the microstructure as the material densifies, resulting in trapped gas bubbles and thus sub-optimum densification. If there is significant amount of gas being formed, there is the risk that the sample will "explode". This is basically the same reason why any ceramics required a drying step prior to thermal treatment.

To avoid this, the sintering thermal cycle must contain a "de-binding step", during which the material is held at a fixed temperature slightly above the decomposition temperature of the binder (or any other organic or water).

Coming back to your question, the standard thermal cycle to sinter a generic ceramic pellet (~cm) including a debinding step, is to heat up to 600 ºC at

Thank you all for your answers. I have another question to ask you. I'm working on KNN materials (sodium and potassium niobate), many authors sinter the pellets covering them with an alumina crucible to prevent the volatilization of alkaline ions. To do this, I suppose I need to do two thermal cycles: the first one to remove the PVA and the second one (where I cover the pellets with the crucibles) to perform the sintering process. To avoid any misunderstandings, I mean that these two heat treatments are two different thermal cycles (because I need to add the crucibles in the second step), so my question is: it is correct to operate as I described above (two thermal cycles) or it's better to do with a single thermal cycle? (with different heating rate and dwell time for the elimination of PVA and for the sintering) maybe starting already with inverted crucible which cover the pellets.

Dear Antonio,

While doing the thermal (sintering) process, you can remove PVA and sinter your sample in single step. Most of the PVA will evaporate at 600oC, so, after 600oC the remaining composition take place the reaction between the chemical and finally you can get the required dense pellet. What ever you do KNN or some other compositions, the sintering process is the same for all in the solid state method. If you have any further questions regarding your experiment, don't hesitate to ask me.

Dear Antonio, I assume that you want to sinter the KNN in the air. The debinder step is your least problem; o)

There, the comments by Daniel Marinha were very well presented. I would like to add only to that, we also relieve on larger cylinders only up to 450°C with moderate heating rates. The lower the heating rate is selected, the lower the decomposition process of the PVA. Holding times during the ramp up to 450°C have proved to be unnecessary, since the decomposition process then came to a standstill and only started again with further increase in temperature. Likewise, be aware that the gases in your capsule may escape in the first step. The second step (sintering) can be performed in a closed or open (slotted) capsule.

The sintering of pure KNN without doping or additives is a real challenge!!! On small tablets, this should be quite successful on a laboratory scale. But here too you will encounter the known problems (repeatability, alkali evaporation, phase shift, etc.). Alumina crucible may be a good choice for sintering, but there are also big differences depending on the manufacturer. A tip from me sintered KNN as a scattering agent. I hope my remarks were not too pessimistic for KNN.