We plan to start powder injection molding experiment in our lab - mostly with ceramics, but also with metal powders. So far we were successful in preparing polymer based feedstock with high filling rate. Soon we will have a desktop injection molding machine to prepare "green body" samples. The next steps are 1. de-binding, 2. sintering. From the temperature viewpoint step 1. is less demanding (although it also has to be optimized carefully), but step 2. requires 1600-1650 oC for alumina, which is by far the most used engineering ceramic. Right now, I have an oven only up to 1550 oC, and even that has a small storage volume. According to the literature other techniques, such as SPS (spark plasma sintering), microwave ovens, induction ovens result in much shorter sintering cycles at comparable finaly density. SPS is, however, fairly expensive. I have seen articles where apparently household MW was modified to such application (with SiC susceptors), and some house-made induction ovens were published. At least in the beginning, I believe, it is a cheaper solution. Can anyone offer insight or suggestions?
Hi dear gyorgy banhegyi
i belive that u can do this .
We made a high alumina crucible ( 99.99) with this method. So, we used nano aluminium powder and alumina and nano aluminium oxide in the batch .
Mw =2100 watt and time max 20 min .
U can examin ....
Best regards.
Ali amirarjmand
Could any one please let me know some good literature links of Al2O3 coating on a carbon or grahene or on any other surface by microwave irradiation?
Debinding is the most critical stage in IM parts-whether its MIM (metal injection molded) or ceramics. This process is always trecherous as one is apt to develop microcracks if the heat-up rate is not adjusted properly.
Microwave sintering works best for shapes that is somewhat less dense. There are few companies in the US who would like to work with scientists like you on a fee-for-service basis. I am personally seeking out a company like that. If you need any further info. please feel free to contact me at: [email protected].
Thanks,
Sanjoy Das
Materials Engineer
Massachusetts (USA)
Dear Colleagues,
Thank you for the answers. My laboratory is located in Hungary (in the EU), so we could cooperate with Dr Rincón.
I am sure that it would be possible to buy commercial microwave oven or to have one developed for our purposes - but that is probably fairly expensive that's why I thought of tryin first a non-industrial equipment.
Ad Ali: what happened with the aluminium additive after sintering? I presume you used aluminium to absorb MW radation - as at room temperature the dielectirc loss of Al2O3 is too low.
Ad Sanjoy: thanks for your comment. Do you use regularly some kind of quality control method to check the brown body after debinding? Such as ultrasound, X-ray tomorgaphy etc. - or is it enough to stick to a temperature schedule?
my email address is [email protected]
I have used household MW oven for synthesis of ferrites. Precursors were microwave transparent, so I had to use susceptors. I had no means to modify the oven, so I designed the susceptor setup to suit the need. Yes indeed it is much cheaper option. However one needs to ensure that the temperature of cavity of household microwave does not exceed 300 degree centigrade. Above this, the MW oven is programmed for automatic shutdown. If your samples are small enough ( not more than few cm.) household MW oven is effectively useful.
Thank you very much for your kind proposal. I will contact you personally.
Yes, temperature control and heating rate control are issues. Silicon Carbide and most metal oxides are strong absorbers of microwaves.This leads to rapid rise in temperature, which is often difficult to control. In order to overcome this problem I have used metal powder instead. Metal powders (particularly Aluminium) are moderate absorber of microwaves. Temperature rises slowly so it is much easier to control heating rate. You can see the attached file.
It was an interesting article. I have some short questions: 1. How did you measure the temperature inside the oven? 2. How did you heat insulate the bottom of the MW oven from the heated up owder? 3. What was the density of the produced ferrite with respect to the theoreticl value - i.e. did you synthesize or also sinter the powder by microwave?
1. The quartz crucible was covered from top and a small hole in the centre of the lid allowed entry of a thin thermocouple. The heating rate( temperature of sample v/s time) was established for a particular value of power setup. 3 grams of powder sample was used to establish this heating rate. Temperature of sample was measured by switching off the oven and inserting the thermocouple in the powder after 30 sec, 60 sec,......., through the central hole. Once the heating rate was established all the powder was heated in batches of 3 gram.
2. Alumina brick has dual advantage. It is not only microwave transparent but also a good heat insulator.So while it allows microwaves to pass through it, it contains and retains heat inside it( in the sample inside the cavity). Cavity in the brick was designed in such a way that it isolated the the crucible bottom and susceptor from microwave oven. See the attached file.
3.I heated only powder. However, it is possible to extend this method for sintering too.
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