Oamenii numesc nitrur\u0103 de bor hexagonal\u0103 \u201egrafit alb\u201d, deoarece structura cristalin\u0103 se bazeaz\u0103 pe acela\u0219i principiu: pl\u0103ci suprapuse care se deformeaz\u0103 prin forfecare. De aceea, un film uscat de h-BN pare alunecos la atingere. Compara\u021bia \u00ee\u0219i pierde \u00eens\u0103 relevan\u021ba de \u00eendat\u0103 ce procesul implic\u0103 c\u0103ldur\u0103, oxidare sau curent electric. Grafitul este un conductor \u0219i \u00eencepe s\u0103 se oxideze \u00een aer la temperaturi de aproximativ 500\u2013600 \u00b0C. BN-ul hexagonal r\u0103m\u00e2ne izolant, iar \u00een aer consider\u0103m c\u0103 intervalul practic de oxidare se situeaz\u0103 \u00eentre 900 \u0219i 1000 \u00b0C. \u00cen azot sau \u00een vid, temperatura de oxidare cre\u0219te mult mai mult, ajung\u00e2nd la 2000 \u00b0C \u0219i chiar mai mult. Acesta este motivul pentru care specific\u0103m BN \u00een locul carbonului atunci c\u00e2nd acoperirea trebuie s\u0103 reziste la c\u0103ldur\u0103 \u0219i s\u0103 r\u0103m\u00e2n\u0103 dielectric\u0103.<\/p>\n
Pulberea pe care o comercializ\u0103m pentru acoperiri este, de obicei, h-BN sub form\u0103 de pl\u0103cu\u021be, adesea cu dimensiuni de ordinul c\u00e2torva microni, uneori mai fin\u0103 pentru o pulverizare uniform\u0103. Amestecat\u0103 cu un liant, aceasta devine o vopsea de demulare pentru matri\u021be, \u0219tan\u021be, oale de turnare \u0219i tuburi de termocuplu. Trucul util \u00een cazul aluminiului topit este umectarea. Aluminiul se a\u0219eaz\u0103 pe nitrur\u0103 de bor cu un unghi de contact ridicat \u2014 \u00een jur de 160\u00b0 p\u00e2n\u0103 la 900\u00b0C, conform studiilor publicate privind pic\u0103turile sesile \u2014 astfel \u00eenc\u00e2t metalul nu se lipeste de ceramic\u0103 a\u0219a cum se lipeste de alumin\u0103 sau de o talp\u0103 murdar\u0103 de o\u021bel. \u00cendep\u0103rta\u021bi stratul de suprafa\u021b\u0103, turna\u021bi, \u00eendep\u0103rta\u021bi resturile. \u0218i grafitul poate ac\u021biona ca agent de demulare, p\u00e2n\u0103 c\u00e2nd arde \u0219i las\u0103 o pat\u0103 de carbon sau o ad\u00e2ncitur\u0103. Nitrur\u0103 de bor las\u0103 o pelicul\u0103 alb\u0103. Atelierele care acoper\u0103 jgheaburile \u0219i tuburile de imersie observ\u0103 diferen\u021ba dup\u0103 o s\u0103pt\u0103m\u00e2n\u0103, nu dup\u0103 o discu\u021bie de laborator.<\/p>\n
Conductivitatea termic\u0103 este satisf\u0103c\u0103toare \u0219i puternic anizotrop\u0103 \u00eentr-un monocristal. \u00cen cazul unei piese presate la cald sau al unui strat de acoperire, se ob\u021bine o valoare mai medie, dar totu\u0219i suficient de ridicat\u0103 \u00eenc\u00e2t ceramica din nitrur\u0103 de bor s\u0103 fie utilizat\u0103 acolo unde c\u0103ldura trebuie s\u0103 se deplaseze, iar curentul nu poate: disipatoare de c\u0103ldur\u0103, straturi de acoperire pentru settoare, izola\u021bie electric\u0103 la temperaturi ridicate. Aceast\u0103 combina\u021bie \u2014 conducerea c\u0103ldurii \u0219i blocarea curentului \u2014 nu este o proprietate a grafitului. Grafitul face ambele lucruri \u00een direc\u021bia gre\u0219it\u0103 pentru un izolator.<\/p>\n
BN-ul cubic este un material diferit. Acelea\u0219i elemente, re\u021bea cristalin\u0103 similar\u0103 cu cea a diamantului, duritate comparabil\u0103 cu cea a uneltelor de t\u0103iere. Nu comanda\u021bi c-BN dac\u0103 ave\u021bi nevoie de un strat de eliberare \u0219i nu v\u0103 a\u0219tepta\u021bi ca o pulbere de h-BN de calitate vopsitoare s\u0103 poat\u0103 prelucra o\u021belul. BN pirolitic este din nou o alt\u0103 categorie: pl\u0103ci \u0219i creuzete CVD pentru lucr\u0103ri cu semiconductori, foarte pur, foarte scump. Majoritatea cererilor noastre industriale se refer\u0103 \u00een continuare la pulbere hexagonal\u0103 \u0219i forme presate la cald.<\/p>\n
h-BN nu are propriet\u0103\u021bi miraculoase la temperaturi sc\u0103zute. La temperaturi sub aproximativ 600 \u00b0C, grafitul are adesea un coeficient de frecare mai mic. BN preia avantajul odat\u0103 ce grafitul \u00eencepe s\u0103 se oxideze. Umiditatea, uleiul \u0219i un strat gros, care se exfoliaz\u0103, distrug o pulbere de bun\u0103 calitate. Aplica\u021bi un strat sub\u021bire, uniform \u0219i uscat, reaplic\u00e2nd atunci c\u00e2nd albul dispare. Dac\u0103 materialul topit este aluminiu sau magneziu \u0219i scula trebuie s\u0103 r\u0103m\u00e2n\u0103 curat\u0103 \u0219i f\u0103r\u0103 interferen\u021be electrice, nitrur\u0103 de bor hexagonal\u0103 este lubrifiantul care r\u0103m\u00e2ne pe scul\u0103 chiar \u0219i dup\u0103 ce grafitul s-a transformat \u00een CO\u2082.<\/p>","protected":false},"excerpt":{"rendered":"
Hexagonal Boron Nitride Is Graphite That Does Not Conduct and Does Not Burn Off at 600\u00b0C People call hexagonal boron […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"set","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-gradient":""}},"ngg_post_thumbnail":0,"footnotes":""},"categories":[4],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/posts\/337"}],"collection":[{"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/comments?post=337"}],"version-history":[{"count":1,"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/posts\/337\/revisions"}],"predecessor-version":[{"id":338,"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/posts\/337\/revisions\/338"}],"wp:attachment":[{"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/media?parent=337"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/categories?post=337"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/ro\/wp-json\/wp\/v2\/tags?post=337"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}