Muhammad Waqas Khalid

• Ph.D. (Materials Science and Engineering)
• Senior Researcher at Yeonhwa Advanced Materials

For the sake of recycling electrolyte of a polymer Li-ion battery, the salts like LiPF6 will be recycled with CO2 supercritical extraction method.

But how can we preserve the volatile organic solvent carbonates to be used again, as these solvents start evaporating as soon as a cell is opened?

I make polycrystalline diamond with tape casting followed by HPHT sintering. When i sintered the samples up till May, the sintering was good. When i sintered the samples in June and July at the same conditions, the sintering was not good. I used the same slurry making conditions, tape casting conditions, debinding conditions, heat treatment conditions, and sintering conditions.

The only changed parameter i can think of may be humidity, as humidity is very high in June, July and August in Korea.

What tests should i perform and at what stages? How to overcome this issue?

Thank you.

I am preparing polycrystalline diamond (PCD) with tape casting. The powder is 8~12 um.

After drying of tapes, I place several tapes in Ta cup without warm-pressing. Next, debinding is carried out. There are no cracks visible with naked eye. SEM analysis shows all the organics are evaporated.

After debinding, WC-Co substrate (4 um average particle size of WC) is placed in cup over debinded tapes. Heat treatment is done in vacuum above 1000 C for surface graphitization to help in sintering.

After that, high pressure high temperature sintering is carried out. When surface is observed after polishing, there are whitish parts on the dark gray diamond surface, mostly in circles. These discolored parts are mostly near the edge of sample, and sometimes inwards too, for example, in the center of a sample. Sometimes, these discolors are distributed throughout the sample.

What may the reason of these discolors?

Additionally, mostly there are also cracks near the edge of sample. What could be the reason for these cracks?

I usually use PEG-200 and PEG-300 that are in liquid form.

Recently I received PEG-100 from a company that usually do not make PEG-100, and made it once specially for us.

It is not in liquid state, or granules or flakes form, but it is one big solid that looks like in the picture attached.

I tried to melt it up to 100 C, but it did not melt.

How should I use it? My purpose is to use it as a plasticizer for aqueous tape casting, and to mix it with powder, binder and water.

Thank you.

I am using 4000 cP methyl cellulose for aqueous tape casting. Since it gives very viscous solution, I am dissolving it in 1.5 wt% in 98.5 wt% DI water. Still it is a very viscous solution. Because of a large quantity of inherent water coming from the MC binder solution, I cannot use more than 1 wt% binder active matter w.r.t powder in slurry, otherwise the powder settles down on container base and water floats on top and there is no mixing because of a lot of water.

What MC viscosity is better keeping in mind a higher possible weight percent dissolution in water? And in how much weightage should it be dissolved in water and at what temperature?

Since sedimentation of particles is very high, what do you recommend for usage of such sized particles for making a good slurry?

The total slurry contained 50 wt% Alumina (D50 = 0.5 um, 11 m2/g surface area), 50 wt% DI water. Powder was dispersed using NH4PMA aqueous solution. PVA aqueous solution was used as binder (20 wt% active matter w.r.t Al2O3), PEG-300 was used as plasticizer (20 wt% w.r.t Al2O3, 1:1 binder to plasticizer ratio). After mixing and debubbling, the slurry seemed good, and a good tape (~450 um thickness) without cracks was obtained after tape casting.

Debinding of single tape (40 mm x 40 mm x 450 um) at 1 C/min, 600 C, 2 h holding gave debinded tape without cracks, which could be sintered too without cracks.

I did lamination of 9 tapes via thermocompression using uniaxial warm-press. The temp. used was 80 C, and 15 MPa was the maximum pressure that could be applied.

I also tried with increasing number of tapes up to 15, and for those i used temp of 100 C so that a higher pressure could be applied, and the max. pressure that could be applied was 40 MPa, with change in dimesnions of the pressed tapes. I even tried only two layers pressed at 100 C, 40 MPa.

But: Every time debinding of laminated samples resulted in cracks. I tried with 1 C/min, 0.5 C/min, and 0.3 C/min heating rates up to 600 C. I also tried with giving steps, for example using 0.3 C/min heating rate and holding at 100 C for 2 h, at 300 C for 6 h, at 500 C for 4 h. But the samples always cracked. Please find attached the TG/DTA data of a single tape.

Please guide me how to achieve debinding without cracks. I'll appreciate your kind help.

Thank you.