Kategori: Electronics

DIY graphene videos

In the recent days videos from people who actually made some DIY graphene has started to pop up on youtube and in this post I will introduce you to a few of them.

Robert Murray-Smith

One of the very first people who I think deserves a mentioning is Robert Murray-Smith. Robert is a MacGyver of DIY chemistry and he would of course not be doing something as trivial as buying graphite oxide when you can make it your self from graphite. Robert has posted a whole series of movies where he makes graphite oxide and components necessary for making your own DIY super capacitor. The first videos have terrible sound picture and sound quality but along the way Robert has bought a new camera and more recent videos look and sound much better. Robert has also written some books you can buy online at kobobooks.

Additional videos about graphene and super capacitors from Robert.

Graphene

Super capacitors

Eric Goeken

Eric Goeken is the first DIYer to post a video where he successfully produce some light scribe graphene the same way I discussed in my first post about DIY graphene. He bought some graphite oxide powder online and went from there.

Additional videos about graphene from Eric.

unitedstatesgraphene

The user behind unitedstatesgraphene doesn’t go out with his real name in public but he seems to be on his way to make light scribe graphene all the way from graphite as described by Robert. He has gotten to the point where the graphite oxide is drying on the CD-substrate waiting to go into the light scribe burner.

I wish them all the best of luck and I look forward to follow their progress.

Annonser

Calibrating a Figaro TGS822 sensor, by drawing…

After consulting with the boys and girls at chemicalforums.com about how to produce an ethanol gas with a 300 ppm without having to buy a lot of fancy gear and thus finding out that it was more difficult then I initially thought I have reluctantly decided that I don’t think I will be able to pull it of. There for I have decided to work with what I got. What I got is air and a datasheet.

The data sheet provided by Figaro for the TGS822 only goes down to 50ppm, however the graph looks pretty logarithmic linear to me so I decided to add the 10-50ppm part my self making a bold assumption that it will be logarithmic linear in that interval as well.

From the data sheet we get the relation between RL and RS which is a voltage divider circuit.

Rs_vs_RlFrom the graph in the data sheet we can also see that the resistance of the sensor in air is RS (air) = R0 * 19.

If we combine these two facts we can express R0 as a relation of RS (air) and the value of RS (air) can be deduced by reading the voltage of the sensor and using the voltage divider formula.

RS (air) / 19 = R0 in my case RS (air) = 78kΩ. => R0 = 4105Ω

When we have R0 we can make a table to relate resistance (RS) to ppm by reading the scaling factor of RS/R0 from the graph for different gas concentrations.

Rs in air = 78000 Ro = 4105,26315789474
ppm Scaling factor Rs = Ro * Scaling factor
0 19 78000
10 15 61578,947368421
10 10 41052,6315789474
20 9 36947,3684210526
20 7 28736,8421052632
30 6 24631,5789473684
30 5,7 23400
40 4,7 19294,7368421053
50 4 16421,0526315789
60 3,5 14368,4210526316
70 3,2 13136,8421052632
80 3 12315,7894736842
90 2,7 11084,2105263158
100 2,5 10263,1578947368
150 2 8210,5263157895
200 1,6 6568,4210526316
300 1,2 4926,3157894737
400 0,9 3694,7368421053
500 0,75 3078,9473684211
600 0,67 2750,5263157895
700 0,58 2381,052631579
800 0,52 2134,7368421053
900 0,47 1929,4736842105
1000 0,4 1642,1052631579
2000 0,2 821,0526315789
3000 0,15 615,7894736842
4000 0,1 410,5263157895

The TGS822 sensor is affected by both temperatures and humidity and it should be complemented with a thermistor and hygrometer so that it is possible to compensate for temperature and humidity. I don’t have any thermistor or hygrometer yet but if we use the ”calculate R0 from RS (air)” every time we start the sensor then perhaps we will also compensate for temperature and humidity, this is something further experimenting will tell.

Hi, I’m Ketosense

Im_ketosense

During the weekend I have managed to put together a first very early prototype of my ”Ketosense”. It does register when a person is blowing in to the ”gas chamber” where the sensor is located and something that feels encouraging is that my wife gets significantly higher readings then me. Since I’m still a carbohydrate junky and she is not that is exactly what we want. However we do have some hurdles to cross before this thing is useful.

To-do-list

  • Calibrate the sensor
  • Determine sensor characteristics for gas concentrations between 0-50 ppm
  • Build a better moth piece

Calibrating the sensor

Calibrating the sensor is the major thing that needs to be done. In the sensor data sheet there is stated exactly how the resistance of the sensor behaves at different gas concentrations but everything relates to one calibration point, the sensor resistance Rs = Ro at 300 ppm of ethanol. Based on this value we can calculate the relation between sensor resistance and gas concentration for all other gas concentrations. Further in the data sheet it is stated that Rs at 300 ppm of ethanol is between 1-10 kΩ and that is quite a wide range and I don’t want to make a generalization of 5k before I even tried to calibrate it. Right now I don’t rely have a clue how to create a 300 ppm ethanol gas mix but hey, thats just another problem to solve.

Sensor characteristics for gas concentrations between 0-50 ppm

The datasheet for the TGS822 doesn’t have any data for how the sensor behaves at low gas concentrations between 0-50 ppm. In the graph displaying the Rs/Ro relation it looks like the function for the sensor resistance follows a Log-linear model so if I can determine the Ro (Rs at 300 ppm ethanol) of my sensor and also have the Rs for < 10 ppm of gas, which I presume is the ethanol content of normal room air, then I should be able to deduce some info for how the sensor should behave in that range as well.

Moth piece

I quickly understood that to get a good reading you needed to give the sensor some time to take the reading. This means we have to trap the gas around the sensor in some sort of chamber for a while to get a good reading. Right now I have a plastic cup with a tube and some tape over the opening and it does the job. However it is actually to air tight and I have to remove the tape from the opening to vent out the gas after getting a reading for the sensor to be able to reset it self. Another issue with the cup design is the condensation. Breath has quite a high moisture level and after just a few readings with this moth piece you start so see condensation on the inside of the cup and readings from the same person are different from time to time which they obviously shouldn’t be. Both humidity and temperature affects the sensor resistance so I am thinking of getting a humidity/temperature and add that so I can compensate for those factors but I believe that a better design of the moth piece can be just as or even more effective.

Measured sensor characteristics MQ-3 and TGS822

The 48 hour burn in of both sensors has now been completed and I have been able to do some initial measurements of the sensors characteristics. So far both the sensors does seem to react to acetone but that is not rely surprising. The sensor resistance range (Rs) does vary a lot between them, the TGS822 has a span of 300Ω – 78 kΩ while the MQ-3 has a more narrow resistance span of 22.6 – 1.5 kΩ. Since I am interested in low concentrations of gas I want to have as wide range as possible and have therefor selected to go on working with the TGS822 sensor first.

One aspect of the sensors that makes the them a bit annoying to work with is that they have a warmup period of 3-5 minutes before the resistance has stabilized it self and they also take quite a long time to return back to the initial value after a measurement has been done. The time it takes for the sensor to reset is related to how high the gas concentration was.IMG_3363

Figaro TGS822

  • Rs = 78 kΩ, 22 degrees C, 20% Humidity, normal air.
  • Rs = 300 kΩ when blowing into the sensor.
  • Rs = 300 kΩ after ail polish remover puff.

A good value for voltage divider resistor with the TGS822 should be 10k. A 10k resistor would give an output to the Arduino of just above 0.5 V at no gas detection up to a full 5 V for high gas concentrations.

Reset time, Resistance in kΩ/time after acetone puff.

  • 32 kΩ after 7 minutes
  • 41 kΩ after 10 minutes
  • 51 kΩ after 13 minutes
  • 54 kΩ after 15 minutes
  • 58.4 kΩ after 18 minutes
  • 62 kΩ after 21 minutes

MQ-3 sensor

  • Rs = 22.6 kΩ, 22 degrees C, 20% Humidity, normal air.
  • Rs = 15 kΩ when blowing into the sensor.
  • Rs = 1.05 kΩ after ail polish remover puff.

Reset time, Resistance in kΩ/time after acetone puff.

  • 10.5 kΩ after 8 minutes
  • 14.5 kΩ after 16 minutes
  • 17.9 kΩ after 26 minutes
  • 18.9 kΩ after 31 minutes

Blowing at the sensor with clean air did not seem to have any effect on the reset time.

DIY Graphene

I came across a much inspiring video about some scientists at UCLA who successfully made some graphene and using only commercially available equipment doing it.

After watching this I just had to look in to what it would take to make some graphene and perhaps a super capacitor or two of my own. Graphene is a fascinating material and I believe there are hundreds of uses for it yet to be discovered, but again to be able to discover something to use it for I need to have some. So what do I need to rustle up some graphene?

Shopping list for DIY graphene

  • Graphite oxide
  • Light scribe capable DVD burner 
  • Light scribe DVD
  • Substrate
  • Sonicator
  • Pippette

Additional items for super capacitor

  • Ion-porous separator
  • Electrolyte

Graphite oxide

In the report written by Maher F. El-Kady & co they stated that they used a mix of 3.7mg graphite oxide in 1 mL water.

I did some empirical testing on how much water it takes to cover an area as large as a CD and it was around 10ml. So to make a piece of graphene the size of a CD we need 37 mg graphite oxide.

I have found one supplier, although it wasn’t easy, that sells graphite oxide for 120$ per gram and is willing to ship it to me. The price for the graphite oxide per CD would be somewhere around 0.12 * 37 = 4.4$.

Light scribe capable DVD burner / Light scribe DVD

This is probably the object on the list that would be the easiest to get a hold of. A Light scribe capable DVD-writer cost about 40$ here in Sweden and the Light scribe media is about 1$ a piece.

Substrate

Although it would be possible to make the graphene straight on to the DVD media it would not be very practical since one of the properties of graphene is that it is thin and flexible and a DVD is pretty far both from thin and flexible. What makes a bit more sense is to have some material between the DVD and the graphite oxide that acts as a carrier and also perhaps as an electrode. Maher F. El-Kady & co tried a bunch of different substrates and here I belive there is plenty of room to experiment.

Substrates tried by Maher F. El-Kady & co

  • polyethylene terephthalate (PET)
  • aluminum foil
  • a porous nitrocellulose membrane
  • regular photocopy paper

Sonicator

To state that the researchers at UCLA used only commercially available equipment while making their Light scribe graphene (LSG) is a bit of a stretch. Although graphite oxide is water-soluble you can’t just put some graphite oxide powder in water and give it a stir like it was a cup of Nescafé, that would not disperse it good enough. What you need to do is to smash the graphite oxide powder with ultrasound using a sonicator probe and that is not something everyone has in their kitchen drawers at least not me.

The EpiShear™ Probe Sonicator

However using a proper sonicator probe might not be rely necessary in this case it might suffice using a ultrasonic cleaner instead and those are both much easier to obtain and also a lot cheeper (around 45-55$).

Pipette

Perhaps not so hard to get but I have to remember to get one. It might be possible to get the graphite oxide solution on to the substrate using some other thing but I think a pipette is a good investment.

Conclutions

So far it feels like making your own graphene is far from impossible but at the same time it is not super easy. I would have to make some investments as well. 0.5 g of graphite oxide would in theory allow me to make 13 ”graphene DVDs” but I would say that a more reasonable number is 8-10 DVDs.

0.5 g graphite oxide, 60$

Light scribe DVD writer, 40$

Light scribe DVD (10 pieces), 10$

Ultrasound cleaner, 50$

Pipette, 5$

A total of 165$ and then add some stretch to that budget brings it to a grand total of 200$.

Update: To see videos where the process described in this post is put into practice check out my another post ”DIY Graphene Videos” about some of the other people online who are working hands on with DIY Graphene experiments.

Sources:

http://www.sciencemag.org/content/suppl/2012/03/14/335.6074.1326.DC1/El-Kady-SOM.pdf

http://cleantechnica.com/2012/06/21/polish-researchers-develop-low-cost-graphene/

http://dangerousprototypes.com/forum/viewtopic.php?t=3803&p=38342

The sensors has arrived

Yesterday the sensors I had ordered arrived, I had ordered the Figaro TGS822 and the MQ-3 from Hanwei Electronics. Since this type of sensors require a burn-in of 24-48 hours I wired them and applied some power. I had a suspicion that the sensors were actually going to be identical in function but perhaps I was wrong since they do actually use different amounts of current. The TGS822 sensor draws 117 mA while the MQ-3 draws 102 mA. It might just be that different individuals use different amount of current, further experimenting will tell if they also measure differently.

One thing that I didn’t expect was that the pins of the sensors are placed along the side of the round sensor following the curvature. This makes it impossible to stick them into a breadboard, since the pins will not line up with the holes in the breadboard, so I had to solder some wires to the connectors.

Sensors

There are a bunch of different sensors out there, based on price and sensitivity I have chosen to buy two different sensors the TGS822 from Figaro sensors and the MQ-3 from HANWEI ELETRONICS. If i wasn’t on a budget I would also have ordered a WSP2110 –  air polution detection since I believe that a combination with on of the TGS882 or MQ-3 with the WSP2110 could be a good match where the WSP2110 is has a sensitivity range between 1-50 ppm and the other two has a range between 10-1000 ppm. So the combined result of both could give us a more granular scale at lower concentration levels.

Figaro Sensors

TGS822 – Alcohol (ethanol) gas sensor, gas sensors is a tin dioxide (SnO2) semiconductor.

From datasheet for TGS 822

From datasheet for TGS 822

HANWEI ELECTRONICS CO.,LTD

MQ-3 – Alcohol Gas Sensor, is also a SnO2 sensor so it should have similar detection abilities as the TGS822 but acetone is not mentioned in the data sheet. According to one manufacturer this sensor has a detection range between 10-1000 ppm for alcohol and then about the same apply for acetone.

MQ-3 Sensor

From data sheet for MQ-3 sensor

MQ303A – Alcohol Gas Sensor, is essentially the same sensor as the MQ-3 however it works on a lower voltage. One serious disadvantage with this one is that a manufacturer states that the sensitivity of this sensor is 20-1000 ppm.

When you compare the MQ303A with the MQ-3 sensor’s range of 10-1000 ppm I think I will go with the MQ-3 sensor instead of the MQ303A since the concentrations we want to measure is between 0-200 ppm.

WSP2110 –  air polution detection, this sensor has a different ceramic substrate of subminiature Al2O instead of th SnO2 used in the other sensors and is more sensitive but also has a smaller detection range then the others, 1-50 ppm. it is also a lot more expensive as the other sensors.

ME3A – C2H5OH – This sensor works with a completely different type of chemical process.

”Detects gas concentration by measuring current based on the electrochemical principle, which utilizes the electrochemical oxidation process of target gas on the working electrode inside the electrolytic cell, the current produced in electrochemical reaction of the target gas are in direct proportion with its concentration while following Faraday law”

It seems to be very sensitive and detects between 0-1.000mg/L alcohol per liter, however it also have a price of /piece. Since this sensor works with a completely different technique I am not even sure if it detects acetone as well as ethanol and it is also way to expensive so just forget about this one.