Yuav ua li casraunpaj siabkev ua tau zoo lanthanum hexaboride (LaB6)
Lanthanum hexaboride (LaB6) tau lees paub tias yog cov khoom kub kub zoo tshaj plaws nyob rau tam sim no, uas muaj cov yam ntxwv ntawm kev khiav haujlwm qis, kev ruaj ntseg tshuaj zoo, siab melting point, siab hardness, siab emission tam sim no ntom thiab muaj zog tiv thaiv ion foob pob tawg. LaB6 muaj ntau yam kev siv, thiab tau ua tiav hauv ntau tshaj 20 kev ua tub rog thiab kev siv tshuab siab, xws li radar, aerospace, hluav taws xob kev lag luam, thiab lwm yam. Nws cov khoom lag luam feem ntau suav nrog peb hom hmoov, polycrystal thiab ib qho siv lead ua. Tshwj xeeb, lanthanum hexaboride ib leeg siv lead ua yog cov khoom siv zoo tshaj plaws rau kev ua lub zog hluav taws xob siab, magnetron, electron beam, ion beam thiab accelerator cathode.
Lub cev thiab tshuaj muaj zog ntawm LaB 6
Qhov muaj nyob ntawm lanthanum hexaboride: muaj B 85.8-88 (wt)%, nws yog ntshav thaum muaj B 85.8%, thiab xiav thaum muaj B 88%; Qhov ceev yog 4.7g / cm3, chav kub tsis kam yog 15-27 μΩ, Vickers hardness yog 27.7 GPa, kev ua haujlwm yog 2.66 eV, emission tas li yog 29A /cm2 ua·K2.
Lanthanum hexaboride yog opaque thiab pom lub teeb liab liab liab thaum qhuav, thiab sib sib zog nqus liab thaum ntub. Lanthanum hexaboride muaj cov qauv siv lead ua cubic, raws li pom hauv daim duab 1:
Daim duab 1 Crystal qauv ntawm LaB6
Los ntawm daim duab, nws tuaj yeem pom tias cov yam ntxwv ntawm cov pob zeb siv lead ua ntawm lanthanum hexaboride yog:
1) Boron atoms tsim cov qauv peb-dimensional cubic moj khaum, muaj cov lanthanum atoms loj dua.
2) Lub moj khaum boron yog octahedron, thiab ntawm txhua qhov vertex ntawm lub voos xwmfab, muaj octahedron tsim los ntawm boron atomic moj khaum, uas txuas rau ib leeg los ntawm nws cov vertices.
3) Txhua boron atom nyob ib sab ntawm tsib boron atoms, plaub nyob rau hauv nws cov octahedron thiab ib tug nyob rau hauv kev coj ntawm ib tug ntawm lub ntsiab axes ntawm lub voos xwmfab, yog li muab ib tug homopolar lattice qauv nrog ib tug sib koom tes ntawm 5.
4) Txhua boron atom muaj peb valence electrons muab rau tsib daim ntawv cog lus.
5) Kev sib koom tes ntawm cov hlau atoms daig hauv boron lattice yog 24.
Cov qauv siv lead ua ntawm borides txiav txim siab lawv cov khoom tshwj xeeb:
1) Vim yog lub zog sib txuas ntawm boron atoms (lattice tas li 4.145 Å), nws yog ib qho kev sib xyaw refractory nrog lub melting point ntawm 2210 degree.
2) Nyob rau hauv chav tsev kub, nws tsuas reacts nrog nitric acid thiab aqua regia; Oxygen tsuas yog oxidation ntawm 600-700 degree .
3) Nyob rau hauv ib qho kev ntsuas kub, qhov coefficient ntawm expansion mus zero.
4) Kev ruaj ntseg zoo hauv huab cua, thiab qhov chaw paug thaum siv tuaj yeem rov qab los ntawm kev kho cua sov.
5) Kev ua haujlwm zoo rau ion foob pob thiab muaj peev xwm tiv taus lub zog siab.
6) Vim tias qhov tsis muaj valence bonds ntawm hlau atoms thiab boron atoms, valence electrons ntawm hlau atoms yog dawb. Yog li borides muaj cov conductivity siab, thiab qhov tsis kam ntawm lanthanum hexaboride yog ib yam li cov hlau lead. Qhov kub coefficient ntawm nws cov resistivity yog qhov zoo.
7) Yog tias hexaborides raug tso cai tuaj rau hauv kev sib cuag nrog cov hlau refractory ntawm qhov kub thiab txias, boron yuav diffuse mus rau hauv cov hlau lattices thiab tsim interstitial boron alloys nrog cov hlau. Nyob rau tib lub sijhawm, boron moj khaum yuav vau, cia cov hlau atoms evaporate.
8) Thaum cov borides tau rhuab mus rau ib qho kub, cov hlau atoms ntawm cov khoom siv lead ua evaporate, tab sis tam sim ntawd rov qab los ntawm cov hlau atoms diffusing los ntawm sab hauv lub lattice, thaum lub boron moj khaum tseem tsis hloov, txo qhov poob ntawm cov khoom nquag. .
Vim yog qhov zoo li saum toj no, LaB6 tau ua rau hauv cov khoom siv hluav taws xob hauv cov cuab yeej siv niaj hnub no thiab siv dav hauv kev lag luam pej xeem thiab kev tiv thaiv:
1) Electronic emission cathodes. Vim tias cov khoom siv hluav taws xob tsawg tsawg, cov khoom siv cathode nrog lub siab tshaj plaws emission tam sim no ntawm nruab nrab kub tuaj yeem tau txais, tshwj xeeb tshaj yog cov khoom siv hluav taws xob zoo, uas yog cov ntaub ntawv zoo tshaj plaws rau cov hluav taws xob hluav taws xob hluav taws xob siab tshaj cathodes.
2) High brightness point teeb qhov chaw.
3) High stability thiab ntev lifespan system Cheebtsam. Nws txoj kev ua tau zoo heev ua rau nws daim ntawv thov nyob rau hauv ntau lub tshuab hluav taws xob, xws li hluav taws xob beam engraving, electron beam heat sources, electron beam welding guns, and accelerators, for the production of high-performance components in engineering fields.
Kev npaj ntawm LaB 6
(1) Kev npaj ntawm LaB6 hmoov
1) Pure element synthesis txoj kev
Txoj kev no yog txoj kev tshawb fawb thawj zaug, tsim nyog rau kev tshawb fawb daim duab qhia theem, tab sis tsis haum rau kev siv ntau lawm.
2) Synthesis ntawm cov tebchaw uas muaj La thiab cov tebchaw uas muaj B
Txoj kev no yog ib txoj kev lag luam, thiab muaj cov qauv tshuaj tiv thaiv sib txawv nyob ntawm cov reactants:
3) Txo cov La compounds nrog ntshiab B
(2) Kev npaj ntawm LaB6 cov ntaub ntawv polycrystalline
LaB6 polycrystals feem ntau yog npaj los ntawm sintering thiab kub nias txoj kev. Nyob rau hauv cov xwm txheej uas tus qauv muaj voids, sintering tsuas yog siv rau kev npaj. Sintering siv LaB6, ZrB2, lossis ZrC crucibles. Txhawm rau tiv thaiv kev nkag mus ntawm B, nws tsis pom zoo siv B crucible. Feem ntau sintered nyob rau hauv ib qho chaw hydrogen. Qhov kub nias siab yog 400 atm, qhov kub thiab txias yog 2000 degree, thiab lub sijhawm tuav yog 1-2 teev. Qhov loj ntawm lub billet feem ntau yog φ 100mm × 30mm.
(3) Kev npaj ntawm LaB6 Ib Leeg Crystal
Tam sim no, cov txheej txheem kev npaj ntawm ib qho muaju tuaj yeem raug sau tseg raws li txoj kev ua kom yaj, cov txheej txheem hnyav, thiab cov txheej txheem roj-theem.
1) Zone melting txoj kev
Zone melting txoj kev yog txoj kev siv ntau tshaj plaws rau kev npaj lub ntiaj teb tsis tshua muaj boride ib leeg muaju. Thaum sivLaB 6Raws li cov khoom siv hluav taws xob hluav taws xob, nws yog ib qho tsim nyog los npaj ib qho crystals nrog siab purity. Txawm hais tias tsis muaj qhov tseeb kev sib raug zoo ntawm cov impurities nyob rau hauv LaB6 thiab nws cov kev pab cuam lub neej raws li ib tug emitting electrode, qhov siab dua qhov purity ntawmLaB 6, ntev nws lub neej kev pab cuam. Yog li ntawd, kev npaj cov khoom siv high-purity yog qhov tseem ceeb heev.
Yuav kom npaj high-purityLaB 6, ib qho kev ncua ntawm qhov chaw melting txoj kev uas tsis muaj lub crucible feem ntau yog saws, tiv thaiv los ntawm inert gas, raws li qhia nyob rau hauv daim duab 2:
Daim duab 2 Schematic daim duab ntawm cheeb tsam melting txoj kev
Cov txheej txheem melting hauv cheeb tsam rau kev npaj ib lub pob zeb muaj xws li xov tooj cua zaus cua sov, hluav taws xob hluav taws xob cua sov, cua sov arc, thiab laser beam cua sov.
2) Cov txheej txheem hnyav
Cov txheej txheem hnyav kuj yog txoj hauv kev los npaj ib qho siv lead uaLaB 6, uas suav nrog ob txoj hauv kev: aluminium hnyav txoj kev thiab tsis tshua muaj lub ntiaj teb hnyav txoj kev. Qhov ob yog qhov zoo sib xws, tshwj tsis yog tias tom kawg siv cov ntsiab lus tsis tshua muaj hauv ntiaj teb es tsis txhob siv txhuas, raws li qhia hauv daim duab hauv qab no:
Daim duab 3 Schematic daim duab ntawm txhuas hnyav txoj kev
3) Gas theem nag lossis daus (CVD) txoj kev
Gas theem nag lossis daus txheej txheem yog cov txheej txheem ntawm kev siv cov tshuaj gaseous mus rau cov tshuaj tiv thaiv nyob rau saum npoo ntawm cov khoom siv, tsim cov khoom deposits. Lub schematic daim duab ntawm nws lub hauv paus ntsiab lus yog raws li nram no:
Daim duab 4 Schematic daim duab ntawm CVD txoj hauv paus ntsiab lus
Cov tshuaj tiv thaiv cov qauv siv rau kev tsim cov LaB6 los ntawm CVD txoj kev suav nrog:
HNRE tau ua tiav LaB6 hmoov nrog lub purity ntawm ntau tshaj 99% los ntawm pretreatment ntawm boron carbide raw cov ntaub ntawv thiab tshuaj purification ntawm LaB6 hmoov. Peb kuj tau tsim qhov kub-siab ob chav gradient sintering txheej txheem rau siab ceev LaB6 polycrystalline blocks. Qhov ntom ntawm polycrystalline ntau yog ntau dua 95%, thiab cov nplej loj yog li 20 μm. Peb lub hollow cathode ua los ntawm LaB6 polycrystal block muaj cov yam ntxwv ntawm siab emission tam sim no ceev, ntev cathode lub neej thiab ruaj khov cathode kev ua tau zoo.