In the vast panorama of scientific discoveries, some capture the imagination for their simplicity and perfection, and among these there is the roundest object ever made by manobject known as the silicon-28 spherewhich represents a extraordinary achievement in metrologythe science of measurement.
But why would anyone bother to create such a perfectly spherical object? The answer lies in the quest for absolute precision and the definition of the standard kilogram.
The silicon-28 sphere was created as part of the Avogadro projectan international initiative to redefine the kilogram in terms of fundamental constants of nature, rather than as a physical artefact.
Until recently, the kilogram was defined by a platinum-iridium cylinder preserved in Sèvreshowever, in France this method had limitations, since the mass of the cylinder could vary over time due to contamination or material losses.
To overcome these limitations, scientists have tried to define the kilogram in terms of an immutable physical constant, and the choice fell on Avogadro’s number, which represents the number of atoms in a mole of substance.
By creating a sphere of silicon-28, a pure isotope of silicon, and precisely measuring its volume and mass, it is possible to calculate the number of atoms in the sphere and, consequently, redefine the kilogram.
The making of the silicon-28 sphere
The silicon-28 sphere was made with incredible precision, where its roundness is such that the difference between its maximum and minimum radius is less than 50 nanometersless than a thousandth of the thickness of a human hair, a geometric perfection that was achieved thanks to advanced processing and measurement techniquesinvolving scientists and engineers from all over the world.
The creation of this object is not only a technical feat, but also a symbol of international collaboration and the pursuit of knowledge: it represents a significant step forward in our ability to measure the world precisely and understand the fundamental laws of nature.
As we have already said before, the silicon-28 sphere is not only an object of extraordinary roundness, but also a masterpiece of engineering and materials science, the creation of which required the use of advanced technologies and the collaboration of scientists and engineers from all over the world, but what makes this sphere so special and what are the techniques used to create it?
Silicon-28 was chosen for its purity and stability, this isotope of silicon is particularly suitable for the creation of a perfect sphere thanks to its regular crystalline structure and the possibility of obtaining extremely pure samples.
The purity of the silicon-28 used in the sphere is greater than 99.9999%which means it contains very few impurities that could affect measurements.
The production of the sphere
The production of the silicon-28 sphere began with the growth of a pure silicon-28 crystal, this crystal was then cut and machined into a sphere. The processing of the sphere required the use of precision machines and advanced polishing techniquesand every stage of the process was carefully monitored to ensure that the sphere maintained its perfect shape.
One of the main challenges in creating the silicon-28 sphere was measuring its roundness. To obtain a perfect sphere, the radius of the sphere had to be precisely measured at several points. This was done using advanced measuring instruments, such as laser interferometerswhich can detect size variations on the order of nanometers.
The silicon-28 sphere is of fundamental importance in redefining the kilogram. Using this sphere, scientists can precisely calculate the number of atoms contained in a kilogram of silicon-28, allowing the kilogram to be defined in terms of a physical constantAvogadro’s number, rather than a physical artifact which may vary over time.
The creation of the silicon-28 sphere represents a significant step forward in metrology and materials science, opens up new possibilities for the definition of other units of measurement in terms of physical constants, and moreover the technology and techniques developed for the production of the sphere can be applied in other fieldslike the semiconductor manufacturing and nanotechnology.
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