Ben Krasnow

Freeze-drying Jello gelatin with an improved cold trap

2012-01-29T11:33:00.003-08:00

I built an improved cold trap from an aluminum pan and a stainless steel bowl. It held more ice than my original copper pipe cold trap, but the 100ml of water from the gelatin still managed to almost plug up the trap.

Yeast cells under the microscope

2012-01-29T11:33:00.001-08:00

These bakers' yeast cells might be reproducing in the video. It's hard to tell if its just movement from the water under the cover slip

Creating aerogel with supercritical methanol

2012-01-29T11:32:00.000-08:00

In previous videos, I used supercritical CO2 to dry my homemade aerogels. This time, I soaked the aerogel in methanol, then raised the temperature and pressure of the methanol itself to make it supercritical. This allows the gels to be dried without an additional solvent exchange into CO2. The downside is that it requires a chamber full of methanol at 460*F and over 1200 psi, which is a much bigger hazard than using CO2.

The aerogels dried with methanol shrank less than the ones dried with CO2, but there was still a lot of cracking, and I have yet to create a high-quality monolith.

Piezoelectric bender used as a sensor and actuator

2012-01-29T11:30:00.000-08:00

Piezoelectric benders are devices that have piezoelectric material on either side of a long flexible metal strip. When the material contracts on one side of the strip and expands on the other (eq due to applied voltage), the strip will bend. In many cases, one end of the strip will be fixed, and the free end will be allowed to deflect to move an object or provide force on an object. In this circuit, I sense the voltage generated when the bender is flexed, then send power to the bender via L6203 H-bridge drivers to effect movement in response. Thus, the bender functions as a sensor and an actuator in the same application. Instead of using a transmit/receive switch, I used a passive network of resistors and diodes to limit the voltage coming back from the bender. An ATMega8 microcontroller senses this limited voltage then controls the L6203's to cause the bender to move.

Extracting caffeine with methylene chloride

2012-01-12T23:00:00.000-08:00

In a previous video, I showed how to extract caffeinated water from green coffee beans with supercritical CO2. Here, I show how to extract dry caffeine crystals from the caffeinated water (ie coffee, in this case). I used a vacuum filtration setup to create very strong coffee, then mixed it with methylene chloride in a seperatory funnel. The methylene chloride sinks below the water, taking most of the caffeine with it. By opening the funnel carefully, only the methylene chloride and caffeine can be transferred to a flask where the methylene chloride is boiled away. I then mounted a test tube in a rubber stopped and filled the tube with ice. With the stopped in the flask, I evacuated the flask and applied heat. The caffeine will sublimate and collect on the cold test tube. I scraped off the caffeine and measured the mass.

Making astronaut ice cream in my home shop

2012-01-12T22:59:00.000-08:00

In his recent post, Chris Gammell used astronaut ice cream as a fun example of how high tech innovation trickles down to consumer-level products. Seeing an image of astronaut ice cream in my G+ feed got me thinking about making some of my own. I managed to accomplish this with a harbor freight vacuum pump, some dry ice and various hoses and fittings. The process is known as freeze-drying and allows water to pass directly from ice to vapor, thus allowing the ice cream to maintain its physical structure while it is dried.

What should I freeze-dry next?

http://engineerblogs.org/2012/01/weekend-journal-the-trickle-down-techonomy/

Caffeine extraction from green coffee with supercritical CO2

2011-12-31T18:27:00.000-08:00

I finally succeeded in extracting caffeine from green coffee beans by using supercritical CO2. I built a high pressure chamber from 2" steel pipe fittings, and poured in 200mL of water. There is an aluminum screen above the water line, which held 0.75 lbs of moisturized green coffee beans in the upper part of the chamber. I added liquid CO2 to the chamber, then closed all valves and raised the temperature, making the CO2 pass into the supercritical phase. I left the system overnight at about 60*C, 3000 psi, then drained the water. It was very black due to impurities and some bean burning that occurred where my electric strip heater caused localized overheated zones in the chamber. The water was highly caffeinated, and tasted somewhat like coffee. I used a typical hydrocarbon extraction process to isolate the caffeine from the water (will show this in a later video).

Interview with me on the Amp Hour podcast

2011-12-26T21:22:00.000-08:00

http://www.theamphour.com/2011/12/26/the-amp-hour-75-sprauncy-saccadic-spintherism/

Wooden pens

2011-12-25T18:45:00.001-08:00

I made these wooden pens (the metal parts came from a kit).

LED mounted in a contact lens for possible virtual / augmented reality displays

2011-12-19T02:15:00.001-08:00

Every so often, internet news aggregator sites run a story about a research group that put an LED into a contact lens, then inserted it into a rabbit's eye. I figured that I would try the same thing, but put the lens into my own eye. I accomplished this by laminating a coil of wire and an 0402 surface-mount LED between two ordinary soft contact lenses. I was hoping the lenses would stick to each other, but they did not, so I ended up fixing the edges together by pinching the plastic together with hot tweezers. This held well enough to capture a minute of video with the LED illuminated in my eye. For video purposes, I mounted the LED facing outward. An actual VR/AR display would have the LED facing inward.

I powered the LED by using a very primitive spark-gap transmitter built from a mechanical relay to send RF energy into a larger coil held near my eye. The large coil coupled the energy into the contact lens coil and pulsed the LED.

http://nextbigfuture.com/2011/11/single-pixel-contact-lens-display.html

http://www.cs.uic.edu/~kenyon/Papers/Soft%20Contact%20Search%20Coil.Vision%20Research.Kenyon.pdf

Trying to visualize beta particles in supercritical CO2 (still no success)

2011-12-07T00:49:00.000-08:00

In an earlier video, I tried to visualize alpha particles in supercritical CO2, similar to an isopropanol vapor cloud chamber. Someone commented that the alpha particles will not travel very far (maybe 10 microns) in liquid or supercritical CO2, and recommended that I try beta particles, which should have a path length of almost 10mm. Unfortunately, I still don't see any bubble or droplet trails using strontium-90 and thallium-204 sources. It's possible that the ionizing effect of the radiation particles does not interact with the CO2 phase change as it does by condensing droplets in a cloud chamber. Also, cloud chambers are very finicky, and if this CO2 visualization method is as finicky or worse, it may take some more time to figure out the right combination of environmental variables.

Laser microphone for audio surveillance via window panes

2011-11-24T01:20:00.000-08:00

I bounced a laser beam off of a window in my house and recovered the audio from inside the room via the beam deflection. I used a Hamamatsu S7815 amplified photodiode and connected it with a 9V battery to my stereo's microphone input jack. The audio quality was very low -- probably due to the double-pane windows in my house. Speech was just barely intelligible.

I also tested the procedure of bouncing a laser beam off of a framed picture that is hanging on the wall inside the room to be monitored. The reflected beam will hit a wall somewhere else in the room, and the dot can be monitored by a telescope from remote. The goal would be to measure the beam wobble via the telescope and recover the audio without needing a stringent geometric relation to the target room. This didn't work at all, but I think with a sensitive detector, it has potential.

More about laser microphones:
http://www.williamson-labs.com/laser-mic.htm

Making silica aerogel at home

2011-11-13T14:27:00.001-08:00

I followed instructions in the silica TMOS recipe from http://www.aerogel.org and successfully produced some small pieces of aerogel in my home shop.

The two main difficulties are: 1. Getting TMOS or TEOS (the key chemical ingredient), and 2. Building a supercritical drying chamber. The components for the chamber can be bought from http://www.mcmaster.com or another source of industrial pipe fittings. You'll also need a supply of liquid carbon dioxide. I used a 20-lbs cylinder, which I bought from a local welding store. Most of the cost is in the cylinder itself, since a refill costs only $20 to $30. You may find a welding supply shop that will rent the cylinder.

Getting the TMOS is difficult since chemical suppliers are generally unwilling to sell to individuals.

The process to make aerogel is:

1. Mix TMOS, methanol, and ammonium hydroxide. Pour this mixture into molds, and wait for a gel to form.
2. Submerge the gel in methanol, and wait a day for the remaining water in the gel to diffuse into the methanol.
3. Discard the methanol, and replace with fresh methanol. Wait a day, and repeat. Repeat this process a few times over three days.
4. Transfer the gel into the supercritical drying chamber, and fill the chamber with methanol.
5. Add liquid CO2, then open the chamber's bottom valve to remove the methanol. Make sure the gels are always covered with liquid CO2.
6. Wait a day for methanol to diffuse into the liquid CO2.
7. Open the bottom valve and remove more methanol.
8. Repeat the methanol draining procedure while making sure the gels stay submerged in liquid CO2. Repeat the CO2 draining/exchange a couple times over 2-3 days.
9. Raise the chamber temperature to cause the CO2 to become supercritical. Slowly vent the chamber while applying heat to ensure the CO2 moves from the supercritical phase to the gas phase. Continue venting the chamber slowly, then remove the finished aerogels.

Carbonated fruit: apple slices

2011-11-11T12:34:00.000-08:00

In a previous video, I used a stainless steel water bottle as a pressure chamber to add argon and carbon dioxide to beer. This time, I used pure CO2 to carbonate some apple slices. They're very tasty!

http://www.evilmadscientist.com/article.php/co2inator

Supercritical CO2 does not help visualize ionizing radiation

2011-11-06T20:54:00.000-08:00

I tried to build a cloud chamber with supercritical CO2, thinking that ionizing radiation (alpha particles) would cause localized condensation of the CO2 at the point where the fluid is coming out of the supercritical state. It didn't work, unfortunately. I tested this idea with the americium-241 source from a smoke detector. I will continue experimenting with CO2 ionization chambers, and it might be possible to visualize the particles with superheated liquid CO2.

A helpful commenter pointed out that alpha particles will not travel very far in a fluid as dense as liquid CO2, so I will try again with a beta emitter.

Supercritical drying chamber for aerogel production

2011-10-29T18:16:00.000-07:00

I built a pressure chamber from 2" pipe fittings and 1/8" brass valves to contain supercritical CO2 for drying applications. One project is to try aerogel production which generally requires that solvent be removed via supercritical drying. Normal evaporation would deform the aerogel structure as the surface tension of the solvent pulls the gel's structure tighter together and makes it dense. Since supercritical fluids have gaseous properties, they can diffuse out through the gel without affecting the structure the way that a liquid would.

Liquid lens video

2011-10-21T23:21:00.001-07:00

Repost for new video on liquid lenses:

This is a project that I built a few years ago when I learned about liquid lenses. They are quite useful for optical paths with small diameters.

http://www.supertex.com/pdf/datasheets/HV892.pdf

http://varioptic.com/en/products.html

http://benkrasnow.blogspot.com/2009/07/experimenting-with-liquid-lens.html

Microstepping a stepper motor with the SLA7062

2011-10-20T12:05:00.000-07:00

Stepper motors can be made to rotate more smoothly by providing simulated sine waves. The SLA7062 chip uses internal PWM to provide sinusoidal current waveforms to unipolar stepper motors. I have this working fairly well, but the PWM frequency is acoustically apparent and annoying.

How to TIG weld aluminum beverage cans together

2011-10-04T22:24:00.000-07:00

I show how to weld aluminum cans together with a cheap import TIG welder. I am not a professional welder, so some of my advice may be unconventional or even wrong, but these methods work well for me. With a 3/32" electrode and large gas lens, I don't have to change the torch setup for nearly any kind of common welding. Let me know if you have any questions or would like me to make more welding videos.

Some things that I have learned:

Don't use pure tungsten electrodes. The new rare-earth blends work very well on nearly all metals.

Sharpen the electrode to a very fine point for low-current welding, and sharpen it like a pencil for higher (eg over 100A) welding.

Keep the electrode balance control electrode negative ("weld") and only shift toward electrode positive ("clean") when absolutely necessary.

The welder's pulse feature turned out to be not as useful as I originally thought. It just seems to complicate things. It's definitely possible to make great welds without it.

Use fat electrodes. Some people claim that using an electrode that is "too large" for the weld current will cause the arc to wander. Nope. Just grind it to a sharp point. Thin electrodes 1/16" and .040" overheat much too easily, and provide no apparent benefit. .040" electrodes are very frustrating.

Use thin filler rod. It's much easier to feed thin rod quickly than feed fat rod slowly. As I mentioned in the video, it's easier to sneak a thin filler rod into the puddle while keeping the torch close to the surface.

Effect of long-term high pressure CO2 on acrylic

2011-10-01T21:02:00.001-07:00

I left my supercritical CO2 chamber charged up with 750 psi liquid CO2 (not supercritical) for about a week. I then depressurized the chamber, and opened it. At first, the acrylic seemed fine with just minor surface crazing. After a few hours, I was surprised to find the acrylic had deformed in a major way and was full of CO2 bubbles. Weird!

Supercritical CO2 caffeine extraction (negative result -- more work needed)

2011-09-19T18:49:00.000-07:00

I tried to extract caffeine from green coffee beans using supercritical CO2, but I had no success. The beans underwent a strange transformation, becoming white and rubbery after 6 hours at 80*C in supercritical CO2. I also used water and ethanol as a cosolvent, thinking that the caffeine would end up in solution in the water/ethanol mix after the CO2 became subcritical.

Do you have any advice about how this process is supposed to work?

Argon beer, an alternative to the usual CO2 carbonation

2011-09-09T10:37:00.000-07:00

Most beer is carbonated with 100% CO2. Some beers, notably Guinness and some other porter/stouts, contain a mixture of nitrogen and CO2 in a ratio commonly 75/25 N2/CO2. The nitrogen is less soluble in water, and allows the beer to be served at a higher pressure without dissolving too much gas into the beer itself. The higher serving pressure churns up the beer as it exits the spout, and creates a creamy head that is the signature of a good Guinness pour. Some pubs use 75/25 gas to push normally carbonated beers out of the tap, but the beers themselves contain only CO2.

In this video I wondered what would happen if I used argon instead of nitrogen. I started by using %100 argon since the solubility of Ar is between that of N2 and CO2. As it turns out, the Ar is not soluble enough to produce a decent head on the beer. Additionally, the complete lack of CO2 makes the beer taste sweet (like it's flat) since the CO2 is necessary to form carbonic acid in water, and this is an important flavor component of beer.

Xenon has anesthetic properties at atmospheric pressure, while the other noble gasses can become anesthetic at higher pressures. Does anyone want to explore xenon beer, or have any experience with xenon used as an anesthetic?

A close look at supercritical carbon dioxide CO2

2011-09-03T14:07:00.000-07:00

I built a pressure vessel from aluminum and acrylic and filled it by placing pieces of dry ice inside. The dry ice melts under high pressure, and forms a liquid and gas phase. When the vessel is heated, the CO2 becomes supercritical -- meaning the liquid and gas phases merge together into a new phase that has properties of a gas, but the density of a liquid.

Supercritical CO2 is a good solvent, and is used for decaffeinating coffee, dry cleaning clothes, and other situations where avoiding a hydrocarbon solvent is desirable for environmental or health reasons.

If you have a suggestion for what I should do with the supercritical CO2, please leave a comment.

Here are a few engineering calculations that I used to determine the pressure capacity of the chamber:

1. Hoop stress in the aluminum ring:
http://www.engineeringtoolbox.com/stress-thick-walled-tube-d_949.html
The aluminum alloy and heat treatment is unknown unfortunately, which makes a huge difference in its material properties. Since it is a structural tube, I will assume 6061-T4, which has a yield strength of about 40 ksi.

ID = 1.1", OD= 1.5" (to the inner edge of the bolt circle)
Chamber pressure = 3000 psi
Hoop stress at inner edge = 10ksi

So, there is a safety factor of 4, but the additional material outside the bolt circle will actually add to this factor. In theory, the aluminum will yield at 12000 psi chamber pressure.

2. Bending force on the acrylic windows:
Acrylic ultimate strength: 10 ksi. It doesn't yield. It is elastic, then breaks. Modulus: 400 ksi
http://www.efunda.com/formulae/solid_mechanics/plates/calculators/cpS_PUniform.cfm#Results
The plate is not a thin plate, but the results show only a 0.004" deflection at the center under a chamber pressure of 3000 psi.

http://www.xcalcs.com/cgi-bin/tutti/x3calcs.cgi?d=i_4_0_1_0_0&l=en

This shows a stress of about 4.3 ksi for a 1.25" thick acrylic plate with 1.35" radius. The pressure-bearing radius is larger than the inner radius of the aluminum ring. This has a safety factor of 10/4.3 = 2.3. In theory the acrylic will break apart when the chamber reaches 7000 psi.

3. Stress on the bolts:

Total window area is about (pi)(1.35)^2 = 5.7", so total force when chamber pressure is 3000 psi is (5.7)(3000) = 17,200 pounds! I will use six bolts, so each bolt must hold 17,200/6 = 2860 pounds.
http://www.derose.net/steve/resources/engtables/bolts.html

1/4-20 bolts are NOT strong enough -- even at grade 8!

5/16 bolts would be OK in grade 8, but I wanted a higher safety margin, and I don't like 5/16 bolts.

I chose 3/8" grade 8 bolts, which have a working load of almost 7000 pounds. I wanted to be sure bolt failure could not possibly be the failure mode that breaks the whole system. I also used grade 8 nuts, which should ensure the failure happens within the fastener, not by shearing the threads out of the nut or bolt. I am not positive about this, though.

4. Pipe threads:

I wasn't sure what 1/8" pipe threads are capable of holding, but McMaster sells such fittings that are rated for 5000 psi (like the gauge that I used), so I assume a brass part can hold such a load. I cut threads into the aluminum so it's possible that the pipe thread in aluminum could fail (ie the gauge or valve could be pushed out, shearing the threads right out of the aluminum ring). It might be possible to add up all of the area of the pipe thread cross-sectional area, but it seems silly and unlikely to be at all accurate.

5. Temperature concerns:

The acrylic has a glass transition temperature of at least 180*F, but it should not be heated anywhere near this temperature or else its ultimate strength rating may not be valid. I would say 130*F is the upper safe limit.

6. Effect of supercritical CO2 on the acrylic and O-ring:

I used buna-n O-rings, which may affected by exposure to SC CO2. They are very unlikely to fail in the short term, and I can change the O-rings for every experiment if I want.

The acrylic showed signs of crazing after just one supercritical CO2 cycle. I think the crazing is unlikely to affect the acrylic's ability to hold pressure, but there is a slight concern.

The most likely failure mode would occur when the acrylic reaches its ultimate strength, and suddenly breaks. Unlike pressure vessels made from ductile materials, which can be designed to yield and leak before breaking, the acrylic will suddenly blast apart without leaking first. If the equations and material specs are correct, 3000 psi should be OK, but I would not want to go much higher.

Magnesium burning inside dry ice

2011-09-03T13:09:00.000-07:00

This has been done many times, but is still fun and easy. This is the first time that I have tried it myself. The reaction produces Magnesium Oxide and Carbon

2 Mg(s) + CO2 yields 2 MgO(s) + C(s)

Getting started with the Altera DE1 FPGA board: Create and download a simple counter

2011-08-25T16:38:00.000-07:00

This is my first experience with FPGA programming, and so I made this video to show how easy it is to get started. Many of the tutorials on the web and the DE1 manual make the process seem more difficult than it actually is (as usual).