Your question also defines at least part or your answer.  Do you need a temperature gradient?  If not, a simple muffle furnace does well.  What temperature do you need?  That will determine which model of furnace you might require to achieve the temperature.  Do you need to carry out the growth in a controlled atmosphere?  That also will define the model of oven.   Here is a nice tutorial with further references.  http://www.icmr.ucsb.edu/programs/documents/Sefat1.pdf

Thank you dear Joseph for a prompt answer. I am trying to grow barium hexaferrite with soaking temperature of about 1250 degrees. I have a platinum crucible 30 ml . I also want to have oxygen flux continuously over the charge. So will a simple muffle furnace can do the job. 

Well, it sounds as though you need one with gas purge capabilities which will raise the price of one compared with a "simple" muffle furnace.  However, as long as it can purge gas and reach Temp, you should be fine.

Thanks for expert suggestion

Dear Basharat,

My suggestion would be to have a distinct working atmosphere from your furnace, this could be easily achieved using an alumina tube through a tubular furnace (vertical or horizontal)

This setup allow you to tune your growing atmosphere independently of your heating elements (oxydizing, reducing, inert). Air-proff connection +/- cooled inlet/outlet of gases at each ends of your tube should be set.

About heating, flux growth often requires extended cooling times, so if you plan to heat around 1250C, using SiC heaters would be a good and lasting solution.

If you have a lot of money ;-) , platinum heaters would be fine also (taking care of Pt R(T) change).

The choice of your final setup would also depend on the way you plan to split crystals out of flux (accessibility of your crucible).

Best of luck,

 Thank you dear Gérard for a good technical suggestion. Does it mean that the alumina tube will be fitted inside the furnace and  gases can be injected into the tube. If I understand it rightly , it means that the my  Pt crucible will lie in another large aluminium a crucible.

Yes if you have a tube furnace, the alumina (Al2O3) tube goes through from on end to another (top to bottom), then you can flow gases as you want.

The diameter of the alumina tube should allow your 30 ml Pt crucible to fit in, vertical setup is the easier. Pt crucible supported by a smaller Al2O3 tube inside the working tube.

Thanks once again. How will be the platinum crucible (cylindrical shape) placed in the vertices geometry. I mean if the alumina the tube is hollow throughout where  will I put my crucible . Either at the bottom or suspended in the middle. 

http://onlinelibrary.wiley.com/doi/10.1002/bbpc.19730770205/abstract

If you have planned the growth in vertical furnace then it would appropriate to suspend the crucible at the middle then move it towards lower temperature to solidify the melt. We have grown Antimonide bulk (III-V, II-VI) in vertical furnace by the vertical directional solidification (VDS), at this moment I don’t have more idea for your growth of materials, even though, you may see vertical furnace in our publications in ResearchGate. If suitable then we will discuss in details.

Thanks Dr. Gadkari we are planning to grow single crystals of hexaferrite.  I think that horizontal tube furnace will be appropriate for our purpose. Initially we will place the charge inside the platinum crucible and heat the furnace upto 1250 then hold it for some time and then cool at 5 degrees per hour . Meanwhile we will allow a continuous flow of oxygen gas .  I think we don't need to hang crucible in the middle. 

I would like you to suggest us whether to go for vertical or horizontal one. Your suggestion will be highly appreciable. 

OK,

There are two methods of cooling the melt, 1) Keep the crucible stationary and lower the furnace temperature by varying gradient, which already you follow. 2) Keep the furnace temperature stationary and slowly takeout the crucible out of the hot zone. In this case vertical furnace is appropriate. In my opinion, the vertical furnace will give better results. However, horizontal tube furnace may be used as the vertical furnace. Only crucible suspension mechanism is  required and the shape of crucible is also important. Have you seen furnace designed and fabricated by us? Its mechanism may  help you.

Have better success !

Thank you for fruitful suggestions. Yes definitely I would like to see  your furnace design.

I am trying to establish a single crystal growth lab. in this part of India. I have a project sanctioned by DST. So before I go for purchases, I want to utilize the money in a justified manner. 

Your Pt crucible could be in an thermally homogeneous place in you want to perform programmed slow cooling or translated toward a cooler zone as suggested by pr Gadkari (more kind of a Bridgman growth)

It can be hang by a wire (check that the wire will survive with T, atmosphere, time) or supported by a smaller tube fitting inside your working tube, use a hook and a handle to set it in /out the furnace.

How do you plan to take your crystals out of the solidified flux ? 

Dear Gerard,

Yes I will place the crucible in a thermally equilibrium position and then after every thing melts cool down at a controlled rate. The crystal embedded in the solidified flux will be taken out by washing the solid in boiling nitric acid or the acid sol.  which will not attack the Pt. crucible and the crystals.

It is very nice that you have DST project and your plane to develop single crystal growth  lab and you are on write track. The single crystal semiconductor bulk crystal growth lab has been developed from the Indian government projects. However, if you need any help from us then information us. Hope you will complete your project with a great success! 

Hai,

I am not going to give a answer. I have a question.

We are going to grow oxide material using flux growth method.

The molten salt (solution) is poured into platinum crucible. Then platinum crucible is also place into another alumina crucible. The two crucibles are place into quartz tube and then sealing it and place to furnaces (Box or zone furnaces).

My questions are

1. How do seal platinum crucible with lid, after pouring solution?

2. How do seal alumina crucible with lid

3. Is it possible to seal quartz tube, after place two crucibles?

4. If it is not possible to seal quartz tube, shall i place into zone furnace?

5. Which furnace is suitable for for this experiment?

Give me your answers.

Regards

K. Moovendaran