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Bonding and structures
Published in Ash Ahmed, John Sturges, Materials Science in Construction: An Introduction, 2014
In 1869 the Russian chemist Dmitri Mendeleev first noted that the chemical elements exhibited a ‘periodicity of properties’. He had tried to organise the chemical elements according to their increasing atomic weights. He had assumed that their properties would progressively change as their atomic weights increased, but he found that their properties changed and then seemed to be repeated at sudden distinct steps, so that they could be arranged or grouped into distinct periods. One of his particular insights was that in 1869 there were elements that remained undiscovered, and which would, when found, occupy the missing places in his periodic scheme. This insight enabled him to predict accurately many of the properties that that an element was found to possess when it was isolated later. For example, he gave the name eka-silicon to the element germanium, which had not yet been discovered in 1869, and he successfully predicted several of its properties.
Elemental Semiconductors
Published in Lev I. Berger, Semiconductor Materials, 2020
The existence of germanium was predicted by D.I. Mendeleev (1871), who named the still unknown element as eka-silicon and described the chemical properties it must have. It was first isolated (1887) by Clemens A. Winkler from a silver ore (argyrodite, AggGeS6 in the form of the sulfide GeS2.3.297 The atomic number of germanium is 32 and its atomic weight is 72.61. Germanium consists of five stable isotopes, Ge70, Ge71, Ge74, Ge76, and Ge78. Electron configuration (ground state) is 4s24p2. Ionization energies for Ge0 → Ge+ → Ge2+ → Ge3+ are 8.13, 15.95, 34.22, and 45.70 eV, respectively.
Characteristics of the Metal–Metal Oxide Reaction Matrix
Published in Anthony Peter Gordon Shaw, Thermitic Thermodynamics, 2020
The modern periodic table, as we know it today, contains eighteen numbered groups. This was not always the case. In the 1870s, the Russian chemist Dmitri Ivanovich Mendeleev placed the elements that were known at the time into eight major groups [5,6]. He also predicted the existence of several elements before they were discovered. Four of them are scandium (eka-boron), gallium (eka-aluminum), germanium (eka-silicon), and technetium (eka-manganese). These anticipated elements appeared as blank spaces with the predicted atomic weights 44, 68, 72, and 100 (Figure 2.11). Mendeleev’s predicted values were fairly close to the actual ones that were later determined.
Nuclear Science for the Manhattan Project and Comparison to Today’s ENDF Data
Published in Nuclear Technology, 2021
The high potential value of plutonium for a bomb was independently perceived around 1939 to 1940 by scientists in the United States, Britain, and Germany, based on the understanding of fission embodied in Bohr and Wheeler’s 1939 paper, probably even before plutonium was first created in 1940. Early insights from the United States and Germany have been discussed by Bernstein,17 including by Louis Turner (Princeton) in 1940 and by von Weizsäcker in July 1940 on 239Np “Eka-Rhenium” produced from n + 238U capture (the 239Pu insight in Germany came 1 year later in 1941 by Houtermans). British insights around the same time are described as follows. At that time, it was typical to refer to plutonium as “94”; more exotically, Bretscher in Cambridge referred to it as “the body 94X239.” Scientists quickly appreciated its two main advantages: it would likely have even more favorable fission properties compared to 235U, and it could be bred and chemically separated from the abundant 238U isotope in a reactor, as opposed to the challenging isotope separation route for the minor 235U isotope. Histories of this era give credit to Egon Bretscher, Feather, and Rotblat for their first 1940 considerations of the utility of plutonium for a weapon (Ref. 18, p. 208). Surprisingly, this important insight is described by many sources, including in Gowing’s classic book,10 but without a reference to a Bretscher primary source. I was able to track down such a source in Bretscher’s papers held by Churchill College Cambridge’s Archives. Bretscher did indeed write with great perception and intelligence. In Report II, December 19, 1940, Bretscher and Feather19 wrote (p. 1):
Catalytic performance of modified multi-walled carbon nanotubes with manganese(III) porphyrin in aerobic olefin oxidation
Published in Journal of Coordination Chemistry, 2021
Saeed Rayati, Fatemeh Nejabat, Paria Radmanesh
Energy-dispersive X-ray spectroscopy (EDS) shows the presence of 2.6% Mn (0.47 mmol of manganese per each gram of heterogenized catalyst) on the surface of MWCNTs, which is in agreement with the metal value obtained from AAS analysis (Figure 4). Also, the peaks from the N (EKa = 0.19 keV), C (EKa = 0.2 keV) and Mn (EKa = 5.8 keV) were detectable in the EDS analysis, confirming the presence of the Mn porphyrin (indicated by the existence of manganese and other elements of porphyrin such as carbon, nitrogen and oxygen) onto the MWCNTs (Figure 4). The gold peak was due to the conductive layer deposited for SEM observation.