Usually binder is introduced during granulation of powder by spray drying. There are a few active threads on this method in rg. You need special equipment for this - a spray-drying column.

It depends on your powder properties. Usually I added 3-5% PVA solution into powder about 5 wt.%. Then it needs to be granulated. The easiest and simple granulation is to pass the PVA added powder via a sieve. If you want to make a porous sample after sintering increase the amount of PVA solution.

I didn't know it could be that simple - a sieve? As I understand, the powder has to be dried first and then ground to coarse powder. Is it easy to crush and grind dried sample containing PVA? I expect it to strongly aggregate and resist a straightforward mortar-and-pestle crushing. Any tricks?

I have experience to do work with PVA. If you want to make a dense sample in your lab, then the easiest way is to make the PVA solution (5-10%) with water.  Add few drops of the solution in your powder and then mix them with mortar and pestle. After that it will be agglomerated. So, you should sieve it to get the fine powder. Now you can compact it in a die. Don't forget to lubricate the internal walls of the die with some lubricating agents such as zinc stearate so that sample may not stick the walls and can be removed easily.

It will effect the porosity, if you will increase the amount of the binder, but it is not too much because you are adding very few drops.

Dear Dr. Punia:

This question belongs to the basic Processing Ceramic.

There is reasonable number the question and by consequence a higher number of answers in the ResearchGate about PVA and PVB. Each one of them has a number of proper solvent. Prior to adding PVA the powder should be finalized.

Spry-dry system is really the ideal procedure. However, in a general way, directed to great amount of powder, several mobile parts difficult the clean of apparatus and typically exhibits a very low fly time.

Then, you can use an Agate-mortar. As mentioned above this procedure, also mentioned by me in some answer of RG, is non-adequate to the powder milling or mixture of powder or adding of doping agents. But, is fully functional.

Small portion of powder + PVA should be charged at mortar. Excessive amount of powder at mortar leads formation of powder shells being the superior shell sliding under shells positioned below. After, some laps of the pestle. The powder + PVA should be replaced at central region of the mortar. All start again. After, all start again and again. This procedure is tedious. After tens of minutes, the mixture is sieved, forming standard granules. Now, powder is additive with PVA and can go to pressing stage. After, green compacts should be placed in a glover-box to the complete elimination of solvent. Here, you have in mind that process is very slow, 8 - 24 hours. See, at this point is evident that is necessary the development of a proper protocol for the Lab. After this, follow the step of PVA decomposition. After, the green compact can be sintered. Here, as part of protocol of basic processing, sample return to the room temperature after each stage.

At end, I would like to comment that the application of lubricant to the wall die is conventional. There is a broad set of them. Typically, a compound that is soluble in apolar solvent, with easy volatilization as ketone and isopropyl alcohol. Some solid organic compounds to the temperature close to ambient can be dissolved up to the saturation level. After the application to the inner and contact areas of die with powder, the solvent volatilize fast, a functional film is deposited under the wall. Most common are stearic acid or citric acid, but there is another. Well, it is possible to use salts of this compounds but is necessary verify if after decomposition of this salt, particles of oxides formed can actuate as contaminant agents of the ceramic.

Kind regards

Marcos Nobre

Processing of pellets

Step-I              PVA preparation (10 wt%)

1.      50 ml distilled water + 5 gms of PVA powder

2.      Heated and stirred by spatula (completely dissolved)

Step-II            Pellets preparation   

1.      10 gms calcined powders + 1 ml PVA solution (equal to 0.1 gms PVA powder, 1 wt% to 10 gms powder)

2.      Powders should be mixed properly and weighed according to calculations

Ceramics are mixed with water, dispersant, binder ( like PVA/PVP), plasticiser ( like PEG) are mixed in ball mill to make slurry. PVA ( 1 Lakh to 1.2 Lakh of Molecular weight) is converted into 3-5 weight% solution. PVA will make clear suspension with water if mixed under stirring at 50 Degree C temperature. Slurry is being spray dried at controlled Inlet and outlet temperature with particular flow rate depending on different parameters of Spray driers. Proper control of all parameter only gives compressible pore free spherical granules, suitable for pressing.

There are a lot of different commercially available polyvinyl alcohol powders (CAS Registry Number: 9002-89-5). Different molecular weights mean different temperature of dissolution. It is necessary to dissolve as Ajeet Kumar suggested. It is necessary to use water base with 80oC to heat water + PVA and stirring. To mix inorganic (or oxide) powder with water solution of polyvinyl alcohol please use water solution of polyvinyl alcohol with ambient temperature. We call this kind of molding as semi-dry (=semi- (so to say) humid) pressing. Water solution of polyvinyl alcohol powders = glue for holding inorganic powder particles together. So there is no place for fanatism at stage of drying. Otherwise you will need to spend a significant part of your life destroying solid powder aggregates. I would not recommend to use any ball mill for mixing inorganic powder and water solution of polyvinyl alcohol because of foam formation.

There is no direct correlation between quantity of binder and final porosity. You should take into account activity of the powder and temperature of the firing. All these depend from prehistory of the powder and from what kind of oxide powder you plan to use. As I can assume water soluble binder can not be used for some kinds of ceramics, for example, based on oxygen-free compounds. Paraffin sometimes better. From 10.1023/A:1023838116298 : "As ceramic pieces intended for making endoprostheses caps for coxofemoral joints are large enough, the process of drying and preliminary heat treatment of intermediate pieces to remove the temporary technological binder (TTB) is significant. Therefore, the selection of a TTB is one of essential problems in the technology of producing ceramic endoprostheses caps. Furthermore, the distribution of binder and the rate and temperature interval of its decomposition have a significant effect on microstructure and properties of ceramics.".

Data Disp syst 2007 1

i still don't get how those of you going mortar-and-pestle way don't have problems with crushing and seiving - the powder containing a binder should not be that easily crushed but rather form splats of powder under the pestle? I recently tried to dry a small portion of the slurry we use for spray drying with a rotational evaporation and crushing was really tedious. It helped a lot to freeze the powder to -20°C but still it was very difficult to obtain sufficiently fine "granulate".

For making pellets in laboratory scale processing normally we make 2-5 % PVA solution in distilled water (2gm PVA in 98 ml water). For getting clear solution you need to boil the water at hot plate. Take small amount of powder (~10-15 gm) to be pelletised in agate mortar (5-6 inch diameter is better) and sprinkle few drops (5-10) of PVA solution on it with the help of thin glass rod. Grind the powder with the help of pestle for few minute (5-10 minutes) till fine powder is obtained. Again add few drops of PVA and repeat the process. Depending upon the type and fineness of the powder you may need to do this few times till the formation of agglomerates is eliminated. Now powder is ready for pelletization. Make the pellets immediately otherwise it will dry and you may need to add PVA again.  

My experience is that if the quantity of PVA added is less than cracking at the edges of the pellets is observed. If you have added extra amount of PVA solution, you will observe layering in the central and middle region of the pellet. Allow to dry the powder for few minute in such a situation. 

Use of some suitable lubricant on the wall of the die will help during removal of the pellet. 

Heat the pellets at 500 degC overnight (~10 hours) in a oven/furnace for the removal of the PVA binder before sintering. 

Can we use PVA as binder for making pallets of polypyrrole powder. The pallet stick to die and when we cut it , the surface become nonuniform.

you suggested to heat the pallet for 500 degC overnight. What if sample in pallet will get spoiled or wil lose its property.  For if it has low Tg and Tc points.

PVA removal is done mostly for ceramic  samples which are stable at higher temperatures. For organic samples, normally one need not to add any binder as they have sufficient adhesion and flow characteristics. Such compounds can be directly pelletized without adding any binder and mostly at smaller loads. 

I'm not talking for organic samples, rather about glassy samples which are brittle in nature. For which sometimes its hard to make pallet. If we heat the sample above its Tg then its properties will be lost.

Rajinder, PVA burns off above 228 C, so perhaps you can use a lower temp. than 500 C, but for longer time.

heating at 400C is sufficient. At lower temperature some part of amorphous carbon may remains

I want to convert ordered mesoporous carbon into graunles or pellets. What is the way  to get that ?

I find 4Wt % of PVA for GDC pellets develop cracks after sintering. should i increase or decrease the weight percentage of PVA. How to avoid the cracks?

You can use 5 Wt% of PVA , PVA  does not affect much on electrical properties.

i will try with 5 Wt %. thank you suman

U can add 3-5% PVA as the binder but remember before sintering heat the pellete at 650 degc for 2hr for the removal of binder and the most important thing is  heating process must be slow.

I have followed the same sintering process. But still  cracks were present in the sintered sample. Thank you Smaranika

Different reasons exist for cracks. Overpressure during forming. Using of nanosized piwders. Phase transformation.  You should try to find out the reasons.

Mr.Palani , is your question is like this " Can you use the pellets pressed with PVA as binder for electrical conductivity measurement?"

If so, Answer is yes. But before using the pellets directly, heat the pellets @ 650 C for 1-2hrs with slow heating rate. then you can carry out the required measurement.

Hello professor Akhilesh and other contributors of this thread,

I need to prepare SnP2O7 in film form with thickness of 1.0 - 1.5 mm and average diameter of 25 mm. Can you guys help to clarify few points,

1. Instead of PVA, could we use PEO or any clay like laponite?

2. After adding clay, do we need to ball mill or mix it using a pestle and mortar?

3. What is the optimum pressure to applied to get a mechanically stable pellet (just share your experience with your material's pellet making, that should help me to understand the pressure value to be used during pellet making).

4. Anyone in this forum ever tried to prepare ceramics using tape casting?

Could you guys help me understand the process by answering these questions.

Thanks in advance for your help with this,

Rajesh

Hi,

It is totally depends on your powder properties. Usually we added 3-5% PVA solution into powder and proper mixing of PVA and sample powder is required.

Hello Sunil,

Thank your for sharing your thoughts!

Is it really necessary to remove the PVA binder from the pellet before press sintering? I am preparing a ceramic composite (oxide + organic) pellet

can polyvinyl alcohol is used as an binder in electrolyte.please give the answer

Can anyone please suggest where I can buy PVA? Need to make pellets with 5% PVA solution.

Thank you

Dear Mizelle,

You can contact to the chemical supplier at your institute and mention this " CAS9002-89-5 ". This is unique number of PVA chemical and you can give order of any company make. Follow this link for further clarifications.

https://www.fishersci.com/shop/products/polyvinyl-alcohol-15/S25473

Can any one elaborate why PVA why not any other instead of PVA

Can we use direct PVA powder with few drops of water in the prepared sample powder to make fine pellet? will it affect the properties of the material sample?

@Asif Ali Haider

Powdered PVA WILL NOT BE ABLE TO MAKE COHESIVE PELLET WITH LITTLE WATER DROPS. THE REASON IS THAT PVA WILL NOT BE ABLE TO SWELL AND HOLD THE POWDER. INSTED YOU MAY TRY DEXTRINE POWDER AND WATER DROPS.

Mayank Rawal Thanks to explain.

So I am not working with PVA but with PVAc, but my question is analogous:

How big is the impact of the average Mw. of the polymer on the binder solution. It should at least have an influence on the colligative properties, which means there is an influence on drying time.

I was wondering why nobody discussed this before, maybe the impact isn't that big?

How to calculate quantum capacitance, and double-layer capacitance from DFT calculations?