Monday, April 25, 2011

How to make Oobleck

Oobleck is a suspension of cornstarch and water that can behave like a solid or a liquid depending on how much pressure you apply. Try to grab some in your hand and it will form a solid ball in your palm just until you release the pressure, then it will flow out between your fingers. Materials that behave this way are classified as non-Newtonian liquids because their flow properties are not described by a constant viscosity.  The name Oobleck comes from the 1949 children’s book, Bartholomew and the Oobleck, by Dr. Seuss. In the story a sticky liquid falls from the sky as a result of the king becoming bored with normal weather.

Recipe for Oobleck

To mix up some Oobleck grab a box of cornstarch, some water and a mixing bowl. In general, a mixture of about 1.5 cups of cornstarch to 1 cup of water is a good starting point. You will have to tweak these amounts to get the perfect mixture. Keep in mind that the mixing process can get messy so be prepared to clean up.
  • Cornstarch
  • Pitcher of water
  • Aluminum pie pans
  • Measuring cups
  • Mixing spoon
  • Newspaper for covering tables
  • Food coloring or tempera paint (for fun)
Pour the cornstarch into a large mixing bowl and slowly add the water. You are shooting for a mixture that feels kind of like honey and tears a bit when you run your hands across the top. You will have to experiment with more or less cornstarch or water until you get the right mixture. If you want to color your Oobleck add some tempera paint. You can use food coloring if that’s all you have on hand. Food coloring tends to stain more than the paint, especially if you have a spill while preparing your Oobleck.

One thing to keep in mind is that Oobleck is a suspension, not a solution. The cornstarch does not dissolve in the water like salt or sugar would. Instead, the tiny starch particles are suspended in the liquid. If you let it sit long enough in a glass, the cornstarch will settle to the bottom leaving a layer of clear water on the top. This is why it is very important to not pour Oobleck down the drain. Should the suspension separate in your drain pipes, you will be left with a hard clump of cornstarch that will block the drain. The best way to get rid of you Oobleck is to simply put it in your trash can.

What does non-Newtonian mean?

All fluids have a property known as viscosity that describes how the fluid flows – commonly thought of as how thick or thin a fluid is. For instance, honey is much more viscous than water. When a fluid’s viscosity is constant it is referred to as a Newtonian fluid. Oobleck is an example of a fluid whose viscosity is not constant, it changes depending on the stress or forces applied to it. If you poke it with your finger and apply a large force, it becomes very viscous and stays in place. If you gently pour it, applying little force, it will flow like water. This kind of fluid is called a dilatant material or a shear thickening fluid. It becomes more viscous when agitated or compressed.

Another non-Newtonian liquid is ketchup. Ketchup behaves in just the opposite way from oobleck. It becomes less viscous when agitated. Liquids like this are called thixotropic. If you leave a bottle of Ketchup on a shelf, it becomes thicker or more viscous. Nearly everyone has experienced this while trying to pour the liquid from a new bottle – it refuses to move. If you shake the bottle or stir it up it becomes less viscous and pours easily.

Why does Oobleck behave the way it does?

The most generally accepted explanation for the behavior of Oobleck is offered by Cary Sneider in “Oobleck: What do Scientists Say?”. When sitting still the granules of starch are surrounded by water. The surface tension of the water keeps it from completely flowing out of the spaces between the granules. The cushion of water provides quite a bit of lubrication and allows the granules to move freely. But, if the movement is abrupt, the water is squeezed out from between the granules and the friction between them increases rather dramatically.

Experiments to try

The first thing you have to do is simply place your hands into the Oobleck and start squeezing it. Have some fun! Try to make a ball by moving it around quickly in your palms. Once you stop applying pressure to the mixture it will flow out of your hands like a liquid.

Try filling a pie plate with a think layer of Oobleck and then slapping the surface with your open hand. Because of the dilatant properties, becoming more viscous when a force is applied, the liquid will all stay in the plate. Try the same experiment with water and compare the results!

If you have a lot of cornstarch and a small pool (or a large one like in the video) you can supersize this experiment. Since the liquid becomes more viscous when pressure is applied you can actually walk or run on the surface without sinking. Of course, once you stop moving you will begin slowly sinking into the liquid.

Another fun experiment is to fill the cone of a speaker with some Oobleck. Connect the speaker to a low frequency sound source and watch as the Oobleck seems to come alive. Typically low frequencies get the fluid up and moving better than higher pitched sounds. A plastic subwoofer works the best, or you can use a sheet of plastic wrap to protect a paper cone speaker.

Tuesday, April 19, 2011

How to Make Charcoal Briquettes from Waste Materials

Charcoal made out of the modified pit method can be used in making charcoal briquettes. Charcoal briquettes are charcoal dust compactly massed by a binder of either cassava flour, corn or sweet potato starch.

As fuel, charcoal briquettes have higher heating value than wood or plain charcoal. They are almost smokeless when burning and give off intense and steady heat. They can be used in the smelting of iron ore since it is compact and dense.

Aside from their used as fuel, charcoal briquettes can be converted to other industrial products. In the chemical industry, they are used in the manufacture of carbon disulfide, carbon electrodes, carbon tetrachloride, carbon carbide, sodium cyanide and activated charcoal for purifying air or water.

Materials and Equipment
 To make the charcoal briquettes, you need well-charred charcoal made through the modified pit method and cassava corn or camote starch as binder.

Hammer mill or wooden mallets, pail, mild and a tapahan type dryer are also needed.

Charcoal briquettes can be produced manually or mechanically. For a small-scale briquettes maker, the manual method will suffice. The method is simple and can easily applied in places where coconuts abound.
First, prepare or have ready smokeless charcoal. This type of charcoal is shiny and gives a metallic sound when tapped. Powder the charcoal into dust particles by hammering with a mallet or wooden hammer or by passing through a hammer mill.

Cook cassava corn or camote starch under moderate heat. The starch should have a syrupy consisting which is neither too thick nor too thin. This will be used as binder.

Mix thoroughly the charcoal dust and the binder in a pail or any available container. When the mixture has reached an even consistency, knead in the same ways making dough for bread.

Molding the resulting mixture into desired shape and size using the hands or an improved wooden molder such as a sungkahan.

The dry briquettes under the sun. Better still, oven cook them in an improvement tapahan type dryer using pieces of wood, coconut shells and dusks and other waste materials for fuel.

Making of charcoal briquettes can be practically costly if undertaken in areas where coconut shells or other suitable materials are discard as waste.

Materials for Briquetting
Only materials which would produce soft and poor quality charcoal should be used for charcoal briquetting. It is not advisable to convert hard charcoal into charcoal briquette. Big charcoal manufacturing establishments, could put up charcoal briquettting units to convert charcoal fine and small broken charcoal particles into briquettes.

Studies show that in charcoal manufacturing establishments, fine waste constitutes 10 to 15 percent of usable charcoal. To ensure a smokeless charcoal briquette, the charcoal fine must be well-charged, that is, it must contain at least 75 percent fixed carbon and not more than 24 percent volatile matter.

For big scale (one ton per hour and up) briquetting, charcoal fines and lump charcoal may be combined as raw materials.

Materials recommended for charcoal briquetting are:
  1. Charcoal fines accumulated during charcoal manufacturing, handling, and transporting;
  2. charcoal from low-density wood and bulky materials like coconut husks, corn cobs, etc.;
  3. charcoal from wood wastes during logging, lumbering and veneering such a log ends, stumps, branches, twigs, barks and trimmings;
  4. charcoal from the fine agro-forestry waste materials such as sawdust, ricehull, and coconut coir dust; and
  5. charcoal from tree plantations.
These materials abound in the country. Their use in charcoal briquetting creates jobs and generates more income and recycles waste in the countryside into a useful commodity.

Binders for Charcoal Briquetting
1. Smokeless binders :
  • Meal binders such as cassava starch, corn starch, and other starches are smokeless but not moisture resistant. they are normally used in the range of 4 to 6 percent on the oven-dry basis. In some cases, small amounts of moisture resistant binders are used.
2. Smoky binders :
  • Smoky but moisture resistant binders are tar, pitch, asphalt, sugar cane molasses, and others. Recommended percentage for wood- tar pitch and coal-tar pitch is less than 30 percent. Briquettes with these blinders are smoky when ignited. But this characteristic is not a drawback for briquettes used in smelting and heating. For home use it could be very annoying.
Manufacture of Charcoal Briquettes

a. Mechanical Process
Charcoal is manufactured either mechanically or manually. A lot- size briquetting machine installed at the Forest Products Research and Development Institute (FPRDI) produces better quality briquettes faster. The steps in manufacturing charcoal briquettes are:

a1. Preparation of Charcoal Fines:
Use charcoal material with low moisture content and high fixed carbon content. If lump charcoal is used, pass these through a primary crusher, then through a disintegrator. This process is skipped if charcoal is fine like those obtained from sawdust, rice hull, and other agro-forestry fine materials such as those accumulated during charcoal manufacturing.

a2. Mixing Charcoal Fines with Binder
Charcoal fines is mixed with binder which could be any of gelatinized starch of pastry consistency, liquid tar, molasses, or heated asphalt. Mixing usually use a kneader type, double- shaft mixer. This process is one of the most critical operations in the manufacture of charcoal briquettes. Efficient mixing is essential to obtain a strong product.

a3. Briquetting of the Mixture
After thorough mixing of charcoal fines and the binders, mixture is fed into the molds where pressure is applied to make the particles compact. The size and shape of the briquettes go with the molds. The most common is the ovoid-type or pillow-shaped briquettes.

a4. Drying of the Briquettes
Briquettes are dried first before packaging, to make them strong. They are dried in a batch-type or continuous dryer.

b. Manual Process
For small-scale briquette manufacturing, the manual method is recommended. Although, this method is time-consuming and produces irregularly shaped briquettes, it is good alternative for small- scale operators who cannot afford an expensive briquetting unit. It is also ideal for housewives and amateur charcoal briquettes makers who are willing to experiment.

The same operations and principle used in the mechanical method are applied in the manual method. The only difference is the use of the hand in the manual technique.

First, the charcoal fines and binder are separately prepared. Charcoal fines are pulverized into soft or low quality charcoal with a hammer or mallet. The binder is made by simply sun-drying sliced cassava or sweet potato for about one week the pulverizing them until they turn into starch. Corn starch may also be used. It is cooked into a syrup consistency, neither too thick nor too thin.

In a pail or any suitable container, mix thoroughly the charcoal fine and the binder by kneading. The mixture is molded into desired shapes and sizes by hand. An improvised wooden molder may also be used.

Dry the molded briquettes under the sun for about three days. Or better still, dry them in an improvised “tapahan” type dryer fueled by wood, coconut shell or husk or other waste material. When the briquette moisture goes down to 10 percent, the briquettes are removed from the dryer.
source:, photo from