INVAR and ELINVAR

The iron-nickel alloys called "invar" and "elinvar" were developed for use as metrical standards because of their "zero value" thermal expansion properties. The mechanism of their zero thermal expansion coefficients may be so-called "nickelide" bonding...where the iron atoms, in the alloyed lattice, donate a d electron, from the iron open d shell, in to the d shell of a neighboring Ni center bonded to the iron atoms through s-type delocalization. The inner d shell electron transfer completes the d shell of Ni as a closed dectet with zero angular momentum (Unsold's theorem) and creates a singly negatively charged nickelide center and a singly positively charged iron center (compare to CsAu with its auride anions). Heating such an alloy may possibly not be accompanied by lattice vibrations and thermal expansion...but perhaps maybe it instead may result in the addition of heat energy as it is deposited in an inner d shell electronic excitation within a continuum of states between the nickelide centers' d shell and the iron cationic centers' d shell. Nickelide bonding may also occur in diatomic molecules containing Ni and other 3d transition metals. This is just a hypothesis.

AZIDE of AMMONIUM

The azide of ammonium has a NH stoichiometry. Exploring the PT phase diagram of NH starting from ammonium azide at room PT would be maybe a fruitful project. Perhaps ammonium azide can be induced to phase transition in to a cubic NH pattern of octahedral or tetrahedral or cubic mutual coordination of H and N. It would thus be a 3D H bonded network. The same type of reasoning could be applied to hydrogen peroxide in the PT phase diagram of OH. Achieving a substance with 3D H bonding in its structure would be an important milestone for chemistry as it is so important in biological chemistry etc. where it is known in 0D or 1D only. Also cubic NH may be recoverable at room PT or some condition of P and T in which it could be used as a benign or environmentally friendly rocket propellant alternative to ammonium perchlorate that is now the rocket propellant of choice. The cubic NH substance might cleanly react with liquid oxygen to yield water and nitrogen gases and a lot of energy. I have been thinking about this type of project for 25 years.

TEA

There are 2 ways to make tea. I love tea. (1) you can fill a transparent glass container (an old apple juice container say) with tap water to the top and put several tea bags in the opening and push them in to the water...then seal the container and invert it with the tea bags suspended in the water...and put it in a window sill in bright sunlight...it takes about 30 minutes...then it is steeped as "photochemical" tea and you can drink it iced with a lemon wedge...(2) the other more common way to make tea is to heat water in a teapot and add the heated water to a cup and put a teabag in...this is the less desirable thermal tea...thermal tea does not taste as nice as photochemical tea...photochemical tea is a much more pure and clear taste...thermal tea can be cloudy...where cloudy tea often causes headaches and is bitter.

VERY LARGE and VERY SMALL

I believe that all of the microscopic physical constants are known to high accuracy and to high precision...perhaps to more than 8 significant figures. However the 2 key parameters in Einstein's equations of relativity are not known to high accuracy and to high precision. G, the gravitational constant is known for certainty to only 4 significant figures and there is some dispute about these numbers. The other parameters in Einstein's theory are "lambda", the cosmological constant, and "c" the speed of light. "lambda" appears to be known only to its closest power of ten...but "c" is known to high accuracy and high precision. It is no wonder that there is so much dispute about how much matter and energy the Universe is comprised of and how much of the Universe is not matter and energy...because we know so little about the basic parameters in Einstein's theory of relativity. You do not need to know about tensorial calculus to understand that the General Theory of Relativity has a lot of physical imprecision in its equations. But the Eddington constants may help to resolve these uncertainties maybe. At the extremes of mass, i.e. binary star systems, the equations of relativity are reported to work well...but in situations of less extreme and more moderate masses perhaps less is well known about gravity...and our understanding of it is not necessarily accurate..