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Jan Hendrik de Boer
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<p>Jan Hendrik de Boer (19 March 1899 – 25 April 1971) was a Dutch <a href="/facts/Physicist/cQcgvSIm">physicist</a> and <a href="/facts/Chemist/N09K7Bdm">chemist</a>. </p><p>De Boer was born in <a href="/facts/Ruinen/BKM4KDtM">Ruinen</a>, <a href="/facts/De_Wolden/dyurRv2r">De Wolden</a>, and died in <a href="/facts/The_Hague/NRtu1Qqk">The Hague</a>. He studied at the <a href="/facts/University_of_Groningen/j7AbDh6z">University of Groningen</a> and was later employed in industry. </p><p>Together with <a href="/facts/Anton_Eduard_van_Arkel/gRF4Tz4U">Anton Eduard van Arkel</a>, de Boer developed a <a href="/facts/Chemical_transport_reaction/polRr3ls">chemical transport reaction</a> for <a href="/facts/Titanium/53ArnDoy">titanium</a>, <a href="/facts/Zirconium/y7gsoQFz">zirconium</a>, and <a href="/facts/Hafnium/rBNnlxDS">hafnium</a> known as the <a href="/facts/Crystal_bar_process/kw3GMBhY">crystal bar process</a>. In a closed vessel the metal reacts with <a href="/facts/Iodine/JlfMecMf">iodine</a> at elevated temperature forming the iodide. At a tungsten filament of 1700 °C the reverse reaction occurs, and the iodine and the metal are set free. The metal forms a solid coating at the tungsten filament and the iodine can react with additional metal, resulting in a steady turnover. </p> M + 2I2 (>400 °C) → MI4 MI4 (1700 °C) → M + 2I2 <p>This process is now known as <a href="/facts/Van_Arkel%E2%80%93de_Boer_process/kw3GMBhY">Van Arkel–de Boer process</a>. </p><p>However, in 1937 De Boer and <a href="/facts/Evert_Verwey/ygV3bJ8f">Evert Verwey</a> reported that many <a href="/facts/Transition-metal_oxides/DXtoVe1C">transition-metal oxides</a> (such as NiO) with a partially filled d-band were poor conductors, often insulating. This led to the concept of <a href="/facts/Metal%E2%80%93insulator_transition/gay8Tusb">metal–insulator transition</a>. </p><p>In 1940, De Boer became a member of the <a href="/facts/Royal_Netherlands_Academy_of_Arts_and_Sciences/3kMPbFAD">Royal Netherlands Academy of Arts and Sciences</a>, and foreign member in 1947. </p>