Learn node: Solder as an amalgam of open online sources


Posted on 5th March 2008 by Judy Breck in chemistry | engineering | general science | sciences

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The triangle of information shown in this learn node is a phase diagram thermodynamic calculation for solder Bi-Pb-Sn. So who care about something like that? In the advancing complexity of metallurgy, depth of detail is important. This is the explanation of the NIST host of the diagram, whose Web site explains the mission:

The NIST Metallurgy Division is working closely with materials suppliers and users to develop the measurement and standards infrastructure needed in diverse technological areas – from steelmaking to the fabrication of nanostructured multilayers for magnetic recording heads. . . .

solderiron.jpgLearning about solder might seem more likely to involve technique, like that offered in the PDF which contains the illustration of “Tinning the soldering iron” from About Soldering—making Clip Leads—CLK from MIT’s Open Courseware. A sample of third sort of soldering knowledge available online is this popular Soldering Guide, a tutorial supported by Google ads.

Within the open Internet, patterns of related ideas for the subject of solder can be an amalgam from diverse sources.

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Learn node: Removing dangerous arsenic from drinking water

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Posted on 11th January 2008 by Judy Breck in agriculture | chemistry | environment

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This learn node clusters material about the dangerous presence of arsenic in ground water of the United States as illustrated the map here from the U.S. Geological Survey’s Water Quality Assessment Analysis of Trace Elements webpage. Information on the world wide arsenic in drinking water problem is abundant on the World Health Organization Arsenic in drinking water Fact Sheet.

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A look at an example of the arsenic problem in drinking water is provided by the American Museum of Natural History’s 2007-08 special exhibit on Water, which describes a situation where arsenic foiled attempts to get good water by drilling below bacterial contamination:

In Bangladesh, millions of deep wells were drilled to end use of bacteria-laced surface water. It worked: for instance, infant mortality dropped sharply. But many of the wells turned out to contain high levels of naturally occurring arsenic—an extremely toxic chemical element with serious health effects. Today, experts are working to develop inexpensive methods of removing arsenic from the water.

So how would you get arsenic out of water? Three pages from a Stiochiometry tutorial at Carnegie Mellon University’s openlearning initiative describes a method developed by Prof. Fakhrul Islam, a chemist at Bangladesh’s Rajshahi University. The tutorial is Arsenic remediation: Using powder to absorb arsenic from water.

Learn node: Materials science: mixture or solution


Posted on 1st September 2007 by Judy Breck in chemistry | engineering | general science

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The sketch in this learn node is from a course taught at MIT. You can virtually sit in on the lectures from the course by clicking this link: Fundamental Concepts of Material Science. The above sketch is from page 7 of lecture L2 PDF that you can download from the list you will get when you click the link. The sketch teaches us:

Mixture: Inhomogeneous multi-phase system where the components are not mixed on a molecular level.
Solution: Homogeneous system, components are mixed on a molecular level.

The difference between a solution and a mixture is a basic idea that the illustration above gives us � so that we can go on in our own learning to other concepts linked to the subject. The PDF of the lecture is an excellent place to move on in this learning; it has 13 pages of basics. The elemental new power of learning in the network ecology online is a matter of grasping a node like this one about “mixture or solution” and linking to related nodes to build concepts and experience thinking.

MORE LEARN NODES about mixtures and solutions from Rice University: “The word mixture can be defined as a heterogeneous association of substances that cannot be represented by a single chemical formula. This definition does not limit mixtures to solids mixed with liquids, nor is every mixture considered to be a solution. . . .”

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