Actually I am working on Titania (TiO2). I need to know what the most probable reasons are. As the pallet is taken out from the hydraulic press it is hard and intact. I place it in furnace for sintering and when it is removed it is either broken, or sometimes breaks afterwards.
DearAsma,
are you sure that you are not avoiding the anatase-rutile transformation around 600°C, at atm pressure? If your TiO2 powders are madeor are partially constitued by anatase crystals, they transform to rutile with a decrease of volume. This transformation may create cracks in the green , that are not recovered even after prolonged sintering.
I suggest to read the following review
The sintering processes has to be improved. The ramping rate should be slow may be 1oC/hr is advisable
You need to provide the size and shape of the pellet. You may use any type of binder (PVA/PVB) which may help you. May be during heating some organic gas (from impurity) is evolving and thus creating cracks. You need to heat the pellet slowly and gradually starting from room temperature. The pressure you are using may be too much and duration is just not enough. You may try low pressure (2-5 tons) and increase the duration (10-15 minutes). I think it might help you. Best of luck.
Yes, I agree the comments above that you have to optimise the pressure, time and temperature ramping. I would like to add that you also consider the thickness of your pallet as that also play a significant part in determining the stability of the pallet before, during and after the sintering process. I used to make pallets about 5 to 10mm thick for all sorts of conductive polymers and problems like this were sorted with good parameter optimisation. Hope that would help.
Yes, process optimization is crucial. Someone could suggest a solution if sintering cycle and other parameters are provided.
3 further adivices (or questions) to avoid or limit the destructive effects. (I suppose if they could be both residual stresses or shaping defects in your samples that bring to cracks):
1) Have you used a monoaxial or an isostatic press to shape your pellets? Isostatic of course would limitate directional stresses of powders in moulds.
2) Try to use a slower loading ramp (in uniaxial press), in successive steps, alternating small increments in loadings to full discharges in pressure, until the final pressure. This should allow the powders to flow and to release better air trapped inside
3) Maybe a controlled cooling rate after sintering may help too, as well as trying a mild annealing to rearrange the eventual inner residual stresses.
Good work!
DearAsma,
are you sure that you are not avoiding the anatase-rutile transformation around 600°C, at atm pressure? If your TiO2 powders are madeor are partially constitued by anatase crystals, they transform to rutile with a decrease of volume. This transformation may create cracks in the green , that are not recovered even after prolonged sintering.
I suggest to read the following review
This is the paper by A.H.Hanaor and C.C Sorrell J Mater Sci 2011
GG
Hey there, I also had a question and this was the quickest way to get in touch with experts on this matter.
I want to test al possiblities of pressing cellulose containing materials (wood, fibre, weed, paper and so on) with a heeted hydraulic pressing machine. I would like to translate this possibiltiess to develop innovative furniture.
My question is:
I am studying the procedé of pressing woodfibre pallets with a hydraulic heated press. What is the right amount of pressure (BAR,Kg/Cm2,PSI), temperature and duration of pressing for good results?
It would be really helpfull if someone can give me awnser. Thanks
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