# What’s the purest element or compound (mass more than a peanut) ever made by humans ? **URL:** \ **Category:** Factual Questions\ **Created:** [June 3, 2020, 4:23am UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963 "2020-06-03T04:23:55Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [June 3, 2020, 4:23am UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963/1 "2020-06-03T04:23:55Z")
For the purpose of this question, let’s assume a peanut weighs 0.5 grams. What’s the purest element or compound with a mass greater than a peanut, ever to be purified by humans ? It can be a solid, liquid or gas. And it must have the same chemical structure for compounds (isomers not acceptable). It also has to be in one piece. My guess will be silicon for integrated circuits. Thanks ---
**Author:** ![Tabco](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tabco/32/7644_2.png) [@Tabco](https://boards.straightdope.com/u/Tabco)\ **Post date:** [June 3, 2020, 4:57am UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963/2 "2020-06-03T04:57:32Z")
I seem to recall a project whose goal was to make perfect (or very nearly perfect) spheres of silicon crystals in order to assist with the official definition of the kilogram. I think they’re supposed to be pure silicon. [Link to NIST webpage about the project.](https://www.nist.gov/si-redefinition/kilogram/kilogram-silicon-spheres-and-international-avogadro-project) ETA: Upon reading the webpage it appears the spheres are only 99.9995% Si-28 with the remainder being other isotopes. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [June 3, 2020, 5:08am UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963/3 "2020-06-03T05:08:29Z")
> [@Tabco](#): > > ETA: Upon reading the webpage it appears the spheres are only 99.9995% Si-28 with the remainder being other isotopes. Other isotopes of silicon. The OP doesn’t seem to be distinguishing between isotopes. I can’t tell what the overall purity of the IAP spheres is, but electronic grade silicon goes to one part in 100 billion (99.999999999%). I think the OP is probably right that this will be hard to beat. ---
**Author:** ![road\_lobo](https://avatars.discourse-cdn.com/v4/letter/r/d78d45/32.png) [@road\_lobo](https://boards.straightdope.com/u/road_lobo)\ **Post date:** [June 3, 2020, 9:06am UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963/4 "2020-06-03T09:06:29Z")
> [@am77494](#): > > It can be a… gas. … It also has to be in one piece. Can a gas be in one piece? ---
**Author:** ![Lord\_Mondegreen](https://avatars.discourse-cdn.com/v4/letter/l/91b2a8/32.png) [@Lord\_Mondegreen](https://boards.straightdope.com/u/Lord_Mondegreen)\ **Post date:** [June 3, 2020, 9:31am UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963/5 "2020-06-03T09:31:08Z")
> [@road\_lobo](#): > > Can a gas be in one piece? For various values of “one” and “piece.” (Also your definition of to “be” and “in.” 😃 ) Maybe if the gas is contained within a, well, container, and the gas is a pure element or compound. But that silicon number would be hard to beat, even if you tried with really light (hydrogen I guess) or really heavy gas (can’t remember which is heaviest. Radon, maybe?) displacing the rest. Before reading the thread I probably would have guessed Gold for the solid, but now it seems like it is an amateur. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 3, 2020, 1:20pm UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963/6 "2020-06-03T13:20:50Z")
You might be able to top those silicon numbers with the best lab-grown sapphires. At one point, the plan for LIGO called for each of the mirrors to be a 40-kg sapphire crystal with no crystalline defects at all. Granted, defects are not the same thing as impurities, but it’s hard to get the defect rate that low unless the impurity concentration is extremely low, too. ---
**Author:** ![filmstar-en](https://avatars.discourse-cdn.com/v4/letter/f/50afbb/32.png) [@filmstar-en](https://boards.straightdope.com/u/filmstar-en)\ **Post date:** [June 3, 2020, 1:32pm UTC](https://boards.straightdope.com/t/what-s-the-purest-element-or-compound-mass-more-than-a-peanut-ever-made-by-humans/854963/7 "2020-06-03T13:32:38Z")
This seems to be the state of the art in terms of purity. They managed to refine the Silicon-28 so that the other isotopes of silicon were removed, but it still had some other contaminants measured in nano-grams. It is used as a technique to define a Kilogram in terms of the number of atoms the sphere contains. This verifies the measurements of electrical Kibble balances, the worlds most accurate weighting machines. I cannot think of another application that would require such an extremely high degree of purity in any material. > **[Sphere Made to Redefine Kilogram Has Purest Silicon Ever Created](https://www.scientificamerican.com/article/sphere-made-to-redefine-kilogram-has-purest-silicon-ever-created/)** > > New measure, to take effect in 2018, relies on crystal that is free of impurities > [@](#): > > Researchers at the National Institute for Metrology Research, Italy, and the Australian Nuclear Science and Technology Organisation checked a sample of the sphere for 65 elemental impurities using neutron activation analysis. This bombards the sample with neutrons, which causes atoms to form radioactive isotopes. As each element has a particular decay path, neutron activation analysis can determine the nature and amount of each element within the sample. > > The ‘largest’ impurity the team found was copper—approximately 70 nanograms per gram of sample. This adds up to about one copper atom for every three billion silicon atoms. Other elements were found in even tinier amounts—picograms to femtograms per gram of silicon—including chromium, cobalt, gallium, arsenic, bromine, lanthanum, tungsten and gold. The researchers found no traces of any of the other elements, down to their detection limits. > > With all the impurities accounted for, 1kg of the material would weigh 0.7μg less than it should if every atom were silicon. This makes the sphere, which is highly enriched in the element’s most abundant isotope silicon-28, even purer than a previously made orb used for the latest determination of the Avogadro constant.