Piezoelectricity is the charge that accumulates in solid materials in response to applied mechanical stress. Substances that exhibit piezoelectric properties to a greater or lesser extent are crystals (Tourmaline, Quartz, Topaz, Rochelle salt and sugar cane), certain ceramics and biological matter such as bone, DNA and various proteins. Quartz and Rochelle salt exhibit the greatest amount of piezoelectrical properties and since the ingredients and instructions for making Rochelle salt are relatively straightforward I decided to make some to play with. I found some helpful guides here and here, but diverged from both guides several times without ill effect. Here are my instructions for making Rochelle salt (Potassium Sodium Tartrate), which yielded at least 5 tablespoons full of the salt and several large single crystals in a few days.

I've recorded two mechanical force tests of a single crystal using both a digital and analog oscilloscope here.

Step 1: Making Washing Soda

The recipe calls for cream of tartar (Potassium Bitartrate or Potassium Hydrogen Tartrate) and washing soda (soda ash or Sodium Carbonate). Cream of tartar is a byproduct of winemaking; as the grapes age this acidic salt forms on the barrels of wine and is collected and used in a variety of household purposes, from preventing sugars from crystallizing to an ingredient in baking powder to stabilizing egg whites in recipes. Washing soda is highly alkaline (pH of 11) and often used as a water softener. It can be extracted from the ashes of plants and is sometimes used to make German pretzels. Washing soda can be made by heating baking soda (Sodium Bicarbonate or Sodium Hydrogen Carbonate) in an oven to break and evaporate the bonds of hydrogen to leave the Sodium Carbonate.


<p>You can do this reaction with bicarbonate directly it just takes more by weight since there is less sodium for the neutralization, and produces more CO2. Also by making washing soda you know it is anhydrous and its weight is correct for the reaction. Baking soda will gain some water weight which affects measurements.</p><p>I just did this to verify what my reading suggested. My initial method was (SLOPPY) simply dissolve some tartar in water and teaspoon baking soda into it till it stopped violently fizzing. I wanted to give this a shot to see if some peoples issues were balance related. </p><p>The crystals I generated the first time were just a mess with only a needle like growth, and all at once. The growth didn't happen till the volume was drastically reduced and it looked a lot more like freezing than crystallizing. </p><p>I re-dissolved and tested my solution and found the PH was quite basic(~9.5). I adjusted this by adding tartaric acid back into the liquor. Pure Rochelle salt in solution should be a little basic(~7-8) but not what I had. I recrystallized and the crystal habit now looks correct.</p><p>To play with the piezoelectric effect you should really have single monolithic crystals and identify which 2 surfaces are going to react electrically. Consider tinfoil, 2 foam blocks, alligator clips and a vice to make electrical contact.</p><p>This reaction can also be done using NaOH in place of the soda, but I see no real point in using a harder to find, more dangerous, chemical to do what baking soda will do just as well. </p><p>The chemistry of this</p><p>KC4H5O6 cream of tartar is an acid salt, which separates into the potassium ion and some stuff in water </p><p>We add an alkali with sodium ions like NaHCO3 sodium carbonate</p><p>We have a neutralization reaction and some typical products, salt and water. </p><p><strong>KC4H5O6 + NaHCO3 = KNaC4H4O6 + CO2 + H2O</strong></p><p>A handy link to the balanced equation and a molar mass calculator so you can plug in numbers and get weights out.</p><p><a href="http://www.webqc.org/balance.php?reaction=KC4H5O6%2BNaHCO3%3DKNaC4H4O6%2BCO2%2BH2O" rel="nofollow">http://www.webqc.org/balance.php?reaction=KC4H5O6%...</a></p>
Why do you have to use sodium carbonate for this experiment instead of bicarbonate? What happen if plain baking soda was used instead? I'm assuming it will not work to make Rochelle salts but I actually didn't come to this page learn how to make them. I just want to know what happens when you mix bicarbonate and bitartrate, chemically speaking. If somebody understand this chemical reaction can you please explain it? Thanks!
<p>Update: I have now come to the conclusion that I did not create this correctly. I have no idea what happened, but what I do know is that the substance is not piezoelectric (I determined that the millivolts reading I had was caused by my crappy multimeter. I know because it shows the same type of reading if put on metal when in the millivolts range. My only guess as to how this happened is that I purchased a defunked/bad quality multimeter). With that being said, do not even bother telling me that my &quot;crystal&quot; has been made incorrectly because I all ready know. However, I am entirely open to suggestions as to why/how this happened. As of now, I have started a new batch and am hoping they turn out all right. Again, awesome job on the instructable. </p>
<p>I would just like to say, great instructable! I made a batch of these today, but I am having some problems. First, I did no have enough cream of tartar so I sdcaled back the proportions. Second, when I measured them they were in the milliamps range. Note that they have not cooled for an entire day yet. Does It look like I did this correctly?</p>
<p>Hello thanks for the post, I wonder if the greater the greater applied pressure will be generated voltage or you could find a limit? theoretically I applied 20 tons (know it will break) would generate a higher voltage at the output?</p>
<p>I'm just curious, how did you measure the voltage on these crystals? Did you just stick multimeter probe at different spots on the crystal at the same time and pressing on it? I'm planning to make a project on this and see what kind of movement I can apply on crystals to generate current/voltage. thanks.</p>
<p>Thanks for all this information :) Im using about 67g of Cream of tartar in about 100ml of tap water. To make my Sodium Carbonate ive used red hot coals and a pie try filled with about a quarter inch of Baking Soda. I stirred it 25 mins in and checked it again at 45 mins which seems it was already done. The texture was more granular. I let it sit on the coals for about 80 mins total just to be safe. After removing from the coals there was a noticeable difference in appearance. Baking Soda has a shine to it and you can see some sparkle in it. With the Sodium Carbonate it was noticeably dull with no sparkles. After simmering the tartar and water i added the Sodium Carbonate and there were instant bubbles and it over flowed once... my bad. The liquid becomes clear after. After straining the fluid and dumping it back into the container for cooling &quot;fog&quot; started to grow on the container I dumped the hot liquid into. Just waiting for the liquid to cool enough to crystallize. Hopefully i can get one to start growing some. </p>
<p>Seems you really do have to boil it really good to concentrate it. Had a little sample on a spoon and was very viscous. So i torched it for a bit untill it almost stopped bubbling. Put it outside to cool an after there was crystals. I tried to crush one and almost broke the skin. I think i have accomplished this. </p>
<p>Note you can still buy sodium carbonate from amazon.com and maybe some dollar stores as well as walmart. But when I made my rochelle salt I bought one pound of potassium tartrate and poured it into about a quart or two of water. I added sodium carbonate in small amounts until it turned clear. It fizzes a lot and using a tall jar or large pickle jar is good so it does not fizz over. Once it is clear you don't need to add any more sodium carbonate. I got some a large metal strainer and place a coffee filter and strained it in a large bowl to make sure I got most of the excess carbonate and stuff out. Note it takes a while for two quarts of water to evaporate. So far I seeded a couple of small crystals that are slowly growing. </p>
I used store bought washing soda from an art supply store. I let the solution cool at room tempetature and stirred constantly at a leasurely pace.<br><br>Instead of forming crystals on top, the solution began to set up like concrete on the bottom of the glass container while I was stirring. The liquid was opaque, but I could hear and feel my spoon scraping against the growing rock. When I finally poored off the liquid, the rock was about a centimeter thick, with a pitted, uneven surface. <br><br>I tested the rock with a volt meter and it did show more voltage when I pressed harder with the probes<br><br>I don't have a pix on this device, but I will come back and include one tomorrow. For now, here's another picture to enjoy
These instructions don't seem to work for me. 7 hours later I still have a clear liquid in the fridge, no crystallization. Other instructions seem to think 2 hours at 300 is not enough to result in washing powder and suggest 4 hours. I think just adding that directly to the cream of tartar in simmering water also isn't echoed by other similar instructions. am I missing a step? If I added too much of the powder, would it still crystallize if additionally saturated (that's the only place I could've gone wrong, even had a helper chemistry student)? Any ideas or suggestions why im not seeing crystals?
Could someone please help me?! I made the solution and it has been on the refrigerator for more than a day, it has only become very dense and I need those crystals ASAP!!! Can someone tell me if there's something wrong with it, should i make more, is it a matter of time...?!?!?! Please!
<p>Put it in a less cold place. </p>
Is that made right?
<p>Is it possible to generate enough electricity to light up a LED using the crystals? Connecting them in series or with some capacitors?</p>
<p>I have a question. What generates more energy? PZT or Rochelle Salts?</p>
<p>can one influence the growth of such a crystal electricity, like a pulsed dc signal being sent through it?</p>
<p>At this step you are not reaching saturation but rather neutralization of the the cream of tartar solution that is why it stops fizzing (i.e. giving off CO2) after a certain amount of washing soda. </p>
<p> back in the 1970s cheap crystal earphones using &quot;rochelle salt&quot; were commonly available in electronics shops so I did know of it a long time ago .. but until now had no idea what rochelle salt is actually made of ... I only knew it was strongly piezoelectric.</p><p>another material you could probably try is PZT salvaged from a cigarette lighter </p><p>(the ones that use a small electric spark to ignite the gas)</p>
<p>Fantastic! Can I ask, what does &quot;9.6v after being tapped&quot; mean? Does it mean it genereates a single pulse? What happens if you press it for a longer time?</p><p>...and how is there any polarity in this, I mean where exactly do you measure?</p><p>Thank you!!! :-)</p>
&quot;9.6v after being tapped&quot; means physically hitting the crystal. The mechanical force to the crystal presses the structure together momentarily against it's polarity, forcing it to realign, and in doing so it releases energy in all directions.
One of the most awesome things i have seen so far, piezoelectricity here i come! thanks emdAniels
Congrats! You clearly put a lot of effort into this!
This is awesome! Maybe I'll screw around with these and see if I can't make mats with LEDs that light up when walked upon.
I think crystals are the technology of the future, simply because all known reality is composed of vibration-see Maxwell's Equations. Even solid matter is not solid. Therefore, certain crystals should do some pretty interesting things when resonated at the right frequency. <br> <br>Thanks for posting your project.. I must try it some time. <br>
Could you use it somehow inside wind turbines to replace generators ?
If you guys like this you should check out John Hutchinson's Crystal battery using Rochelle salts. its pretty cool
Whoa.. I was just thinking that It's so inexpensive to make. What if you were to create a large slab and place it in-between 2 concrete slabs the size of a single lane highway. You could put small grooves in the top slab to induce vibration as cars passed over it (like a rumble strip). Make enough for at least a &frac14; mile and wire them up in series / parallel (figure out what will give max power). Anybody know why this won&rsquo;t work ? Maybe the useful life of the crystal is too low and it will just shatter after a short time. If that is the case, maybe you could introduce an inert polymer into it to maintain structural integrity. Gosh if only I didn&rsquo;t have a day job and limited funds or I&rsquo;d be trying it right now 
That would be pretty cool! Unfortunately it's really brittle so it would most likely break from the pressure. You'd probably want to sandwich it between sheets of conductive foam to cushion it and catch the electricity generated. You should try it!
my mother wants to know if you color Rochelle Salt if you added food coloring? anyone know?
Haven't tried with food coloring yet! A quick search of google doesn't come up with a lot of info for it either.
Congratulations on your win! I'm front Ottawa as well =)
Thanks! You should come to the Mod Lab maker meetups at Artengine! Great group of people there. :)
i tryed makeing some using collins video but it stoped fizing and it wasnt cleer it was yellowy color any idea why?
Regarding the yellow color, I might start by checking the purity of the cream of tartar. There are some manufacturers that sell cream of tartar with filler to reduce costs. I heard that McCormick brand sells a good cream of tartar, but I haven't tested it.
cool thank you for the speedy reply.
Brilliant ! have not come across this compound before, even though I have experience in crystal growing -much [ trial and error]:-) <br><br>Your recipe is very reliable, I do however have a ? Washing soda [na2co3.10h20] is a very accessible chem. Your calcination? method is logical but energy dependant? Na2Co3 has an R.A.M of 106.0 the decahydrate is 286.0 =[2.7] <br><br>if you use same proportions but use same scoop for both chems it work out well<br><br>Apologies if I am Saying what you are already aware of:-0
Thanks inspector gadget! It's true- both will work out well. I didn't have access to the Arm &amp; Hammer Washing Soda or any other decahydrate washing soda from a store so I had to make my own. If you can buy washing soda and want to skip the steps of making it yourself it should still work out fine.
I Made Far Too Much Of The Stuff Then I Needed -But With Selective Growing There The Size Of Alum Crystals.
I'd like to see how you mount or connect these crystals to actually tap into the voltage generated.
I just added two mechanical force tests of a single crystal using both a digital and analog oscilloscope to my website: http://www.emilydaniels.com/2011/11/further-testing-of-rochelle-salt/
Hi! I tried some time ago to make a speaker out of this:<br>http://www.youtube.com/watch?v=nRFgY4_3lHU<br><br>And it worked pretty well :)
Nice! Thanks for sharing!
wow. This has my head buzzing! Could you make a mini-alternator type generator, like to recharge a small battery for a little radio, or cell phone by putting many small crystals on a wire, and a wheel at equal distances, turn a crank to strike the crystals against a flywheel, to run electrical appliances? How about LED lights? Many options here!
yes with some imagination you can construct the things listed. Just keep in mind your results might not be what you expect. Even though stated on this instructable that a crystal could put off 9V it would take a large crystal with a large stressor. there is a reason why these crystal are typically used as sensors allot. The voltage output is too small to run a load but high enough for accurate readings. You might want to look into using it in combination with a BEAM Robotics project. <br>Hope your ideas are a success though and have fun.
Actually, the voltage output is high enough - 9.6 V is more than any USB-powered device uses! It's the current output that's too low to be useful (or, ultimately, the power).
Well the voltage out put is roughly 9.5V peak-to-peak AC shown is studies, so the actual rms value (DC volt equalent) will be 70.7% of that of one peak. one peak being 4.25 V max assuming this is a sine wave AC output. The voltage rms there for is 3.35V. This is less than the 5Vdc output of a USB cord. As for current you will need to determine the internal resistance of the crystal as well load resistance apply the total resistance into the ohms law formula and that will give you your current. the crystal itself creates a potentual difference (voltage) not current. you must have a complete circuit to have current.<br>
I wanted to add though that the use of a piezoelectric crystal as a energy source would be good in a BEAM application using a Miller Solar Engine or other similar engine, just replace the solar cell with the crystal. In this fashion you should be able to store up the needed energy to run a load. Experiment and Explore! :)

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