Man kallar hexagonalt bornitrid f\u00f6r \u201dvit grafit\u201d eftersom kristallstrukturen bygger p\u00e5 samma princip: staplade skikt som glider mot varandra. Det \u00e4r d\u00e4rf\u00f6r en torr h-BN-film k\u00e4nns hal. J\u00e4mf\u00f6relsen blir dock inte l\u00e4ngre relevant s\u00e5 fort arbetet utf\u00f6rs i h\u00f6g temperatur, under oxiderande f\u00f6rh\u00e5llanden eller under sp\u00e4nning. Grafit \u00e4r en ledare och b\u00f6rjar oxidera i luft vid cirka 500\u2013600 \u00b0C. Hexagonalt BN f\u00f6rblir isolerande och i luft betraktar vi 900\u20131000 \u00b0C som det praktiska oxidationsintervallet. I kv\u00e4ve eller vakuum g\u00e5r gr\u00e4nsen mycket h\u00f6gre, mot 2000 \u00b0C och \u00e4nnu h\u00f6gre. Det \u00e4r anledningen till att vi specificerar BN ist\u00e4llet f\u00f6r kol n\u00e4r bel\u00e4ggningen m\u00e5ste t\u00e5la v\u00e4rmen och f\u00f6rbli dielektrisk.<\/p>\n
Det pulver vi s\u00e4ljer f\u00f6r bel\u00e4ggningar \u00e4r vanligtvis plattformigt h-BN, ofta i storleksordningen n\u00e5gra mikrometer, ibland finare f\u00f6r en j\u00e4mn sprutning. Blandat med ett bindemedel blir det en sl\u00e4ppf\u00e4rg f\u00f6r formar, pressverktyg, sk\u00e4nkar och termoelementr\u00f6r. Det anv\u00e4ndbara knepet med sm\u00e4lt aluminium \u00e4r v\u00e4tningen. Aluminium ligger p\u00e5 bornitrid med en h\u00f6g kontaktvinkel \u2013 omkring 160\u00b0 upp till 900\u00b0C enligt publicerade studier med stillast\u00e5ende droppar \u2013 s\u00e5 metallen fastnar inte p\u00e5 keramiken p\u00e5 samma s\u00e4tt som den fastnar p\u00e5 aluminiumoxid eller en smutsig st\u00e5lskena. Skumma av, h\u00e4ll, knacka bort skallen. Grafit kan ocks\u00e5 fungera som sl\u00e4ppmedel, tills det brinner och l\u00e4mnar en kolfleck eller en grop. BN l\u00e4mnar en vit film. Verkst\u00e4der som bel\u00e4gger avloppsr\u00f6r och doppr\u00f6r m\u00e4rker skillnaden efter en vecka, inte efter ett f\u00f6redrag i ett laboratorium.<\/p>\n
V\u00e4rmeledningsf\u00f6rm\u00e5gan \u00e4r god och starkt anisotropisk i en enkristall. I en varmpressad komponent eller en bel\u00e4ggning f\u00e5r man ett mer genomsnittligt v\u00e4rde, men \u00e4nd\u00e5 tillr\u00e4ckligt h\u00f6gt f\u00f6r att bor-nitridkeramik ska anv\u00e4ndas d\u00e4r v\u00e4rme m\u00e5ste ledas bort men str\u00f6m inte kan leda: v\u00e4rmespridare, setterbel\u00e4ggningar, elektrisk isolering f\u00f6r h\u00f6ga temperaturer. Denna kombination \u2013 att leda v\u00e4rme och blockera str\u00f6m \u2013 \u00e4r inte en egenskap hos grafit. Grafit g\u00f6r b\u00e5da delarna p\u00e5 fel s\u00e4tt f\u00f6r att fungera som isolator.<\/p>\n
Kubiskt BN \u00e4r ett annat material. Samma grund\u00e4mnen, diamantliknande gitter, h\u00e5rdhet som hos sk\u00e4rverktyg. Best\u00e4ll inte c-BN om du menar en sl\u00e4ppbel\u00e4ggning, och f\u00f6rv\u00e4nta dig inte att ett h-BN-pulver av lackkvalitet ska kunna bearbeta st\u00e5l. Pyrolytiskt BN \u00e4r \u00e5terigen en annan kvalitet: CVD-plattor och sm\u00e4ltdeglar f\u00f6r halvledararbete, mycket rent, mycket dyrt. De flesta av v\u00e5ra industriella best\u00e4llningar g\u00e4ller fortfarande hexagonalt pulver och varmpressade former.<\/p>\n
h-BN \u00e4r inte n\u00e5gon mirakell\u00f6sning vid l\u00e5ga temperaturer. Vid temperaturer under cirka 600 \u00b0C har grafit ofta den l\u00e4gre friktionskoefficienten. BN tar \u00f6ver n\u00e4r grafiten b\u00f6rjar oxidera. Fukt, olja och ett tjockt, flagnande skikt f\u00f6rst\u00f6r ett bra pulver. L\u00e4gg p\u00e5 ett tunt, j\u00e4mnt och torrt skikt och applicera p\u00e5 nytt n\u00e4r det vita f\u00f6rsvinner. Om sm\u00e4ltan best\u00e5r av aluminium eller magnesium och verktyget m\u00e5ste f\u00f6rbli rent och elektriskt isolerat \u00e4r hexagonalt bornitrid det sm\u00f6rjmedel som fortfarande finns kvar efter att grafit har omvandlats till 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\/sv\/wp-json\/wp\/v2\/posts\/337"}],"collection":[{"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/comments?post=337"}],"version-history":[{"count":1,"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/posts\/337\/revisions"}],"predecessor-version":[{"id":338,"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/posts\/337\/revisions\/338"}],"wp:attachment":[{"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/media?parent=337"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/categories?post=337"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sv\/wp-json\/wp\/v2\/tags?post=337"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}