Po v\u00edce ne\u017e dvaceti letech, kdy se zab\u00fdv\u00e1m v\u00fdb\u011brem maziv a funk\u010dn\u00edch pr\u00e1\u0161k\u016f pro tv\u00e1\u0159en\u00ed kov\u016f, keramiku a elektroniku, jsem dosp\u011bl k z\u00e1v\u011bru, \u017ee pr\u00e1\u0161ek z nitridu boru pat\u0159\u00ed k t\u011bm materi\u00e1l\u016fm, kter\u00e9 p\u0159i praktick\u00e9m pou\u017eit\u00ed nen\u00e1padn\u011b p\u0159ed\u010d\u00ed v\u0161echna o\u010dek\u00e1v\u00e1n\u00ed. Lid\u00e9 jej \u010dasto naz\u00fdvaj\u00ed \u201cb\u00edl\u00fdm grafitem\u201d, proto\u017ee jeho hexagon\u00e1ln\u00ed krystalov\u00e1 struktura vypad\u00e1 na pap\u00ed\u0159e podobn\u011b, ale v praxi se chov\u00e1 velmi odli\u0161n\u011b \u2013 a obvykle l\u00e9pe \u2013 kdy\u017e teploty stoupaj\u00ed nebo kdy\u017e je kontaminace uhl\u00edkem nep\u0159ijateln\u00e1. Provedl jsem zkou\u0161ky, sledoval jsem, jak na n\u011bj p\u0159ech\u00e1zej\u00ed v\u00fdrobn\u00ed linky, a vid\u011bl jsem rozd\u00edl v \u017eivotnosti lisovac\u00edch n\u00e1stroj\u016f, kvalit\u011b povrchu a stabilit\u011b procesu. Nen\u00ed to v\u017edy nejlevn\u011bj\u0161\u00ed varianta, ale na spr\u00e1vn\u00fdch m\u00edstech se vyplat\u00ed.<\/p>\n
Hexagon\u00e1ln\u00ed nitrid boru (h-BN) se vyr\u00e1b\u00ed reakc\u00ed oxidu boru nebo kyseliny borit\u00e9 s amoniakem nebo dus\u00edkem p\u0159i teplot\u00e1ch nad 1400 \u00b0C. V\u00fdsledn\u00fd pr\u00e1\u0161ek je b\u00edl\u00fd, m\u011bkk\u00fd a m\u00e1 podobu desti\u010dek, jejich\u017e vrstvy po sob\u011b snadno klou\u017eou. Tato vrstevnat\u00e1 struktura mu dod\u00e1v\u00e1 vynikaj\u00edc\u00ed mazivost, ale na rozd\u00edl od grafitu z\u016fst\u00e1v\u00e1 stabiln\u00ed na vzduchu a\u017e do teploty p\u0159ibli\u017en\u011b 1000 \u00b0C a v inertn\u00edch atmosf\u00e9r\u00e1ch i p\u0159i teplot\u00e1ch v\u00fdrazn\u011b p\u0159esahuj\u00edc\u00edch 1400 \u00b0C. Je tak\u00e9 elektrick\u00fdm izol\u00e1torem a m\u00e1 pro keramiku slu\u0161nou tepelnou vodivost \u2013 kolem 20\u201330 W\/m\u00b7K v rovin\u011b desti\u010dek. Tyto vlastnosti dohromady jej \u010din\u00ed u\u017eite\u010dn\u00fdm tam, kde by grafit oxidoval, vn\u00e1\u0161el uhl\u00edk nebo zp\u016fsoboval elektrick\u00e9 probl\u00e9my.<\/p>\n
P\u0159i tv\u00e1\u0159en\u00ed za tepla a vytla\u010dov\u00e1n\u00ed se pr\u00e1\u0161ek z nitridu boru stal jedn\u00edm z m\u00fdch nejobl\u00edben\u011bj\u0161\u00edch odformovac\u00edch prost\u0159edk\u016f. Grafit funguje dob\u0159e p\u0159i m\u00edrn\u00fdch teplot\u00e1ch, ale p\u0159i teplot\u00e1ch nad 700\u2013800 \u00b0C se za\u010d\u00edn\u00e1 sp\u00e1lit a m\u016f\u017ee zanech\u00e1vat zbytky, kter\u00e9 ovliv\u0148uj\u00ed povrchovou \u00fapravu. V r\u00e1mci jednoho pokusu s extruz\u00ed hlin\u00edku, na kter\u00e9m jsem se pod\u00edlel, jsme porovn\u00e1vali standardn\u00ed disperzi grafitu ve vod\u011b s disperz\u00ed 15 % h-BN na stejn\u00fdch sochorech ze slitiny 6061. Po 4 000 sochorech vykazovaly matrice pota\u017een\u00e9 grafitem viditeln\u00e9 opot\u0159ebovan\u00e9 r\u00fdhy a vy\u017eadovaly le\u0161t\u011bn\u00ed, zat\u00edmco matrice pota\u017een\u00e9 h-BN m\u011bly st\u00e1le hladk\u00e9 povrchy a vyr\u00e1b\u011bly d\u00edly s ni\u017e\u0161\u00ed drsnost\u00ed povrchu (Ra 0,8 \u00b5m oproti 1,6 \u00b5m). h-BN tak\u00e9 sn\u00ed\u017eil s\u00edlu pot\u0159ebnou k extruzi v pr\u016fm\u011bru p\u0159ibli\u017en\u011b o 12 %, co\u017e se prom\u00edtlo do ni\u017e\u0161\u00ed spot\u0159eby energie lisu a krat\u0161\u00edch prostoj\u016f p\u0159i v\u00fdm\u011bn\u011b matric.<\/p>\n
Podobn\u00e9 zlep\u0161en\u00ed jsme zaznamenali i p\u0159i tv\u00e1\u0159en\u00ed za tepla nerezov\u00e9 oceli p\u0159i teplot\u011b 950 \u00b0C. Srovn\u00e1vac\u00ed test na 200 d\u00edlech uk\u00e1zal, \u017ee u lisovac\u00edch n\u00e1stroj\u016f mazan\u00fdch h-BN byla po skon\u010den\u00ed s\u00e9rie m\u011b\u0159en\u00e1 hloubka opot\u0159eben\u00ed profilometrem o 28 % men\u0161\u00ed. D\u00edly byly tak\u00e9 \u010dist\u0161\u00ed \u2013 bez tmav\u00fdch grafitov\u00fdch skvrn, kter\u00e9 n\u011bkdy vy\u017eaduj\u00ed dodate\u010dn\u00e9 \u010di\u0161t\u011bn\u00ed. Nev\u00fdhodou byla cena: disperze h-BN byla asi 2,5kr\u00e1t dra\u017e\u0161\u00ed na litr, ale prodlou\u017een\u00e1 \u017eivotnost lisovac\u00edch n\u00e1stroj\u016f a sn\u00ed\u017een\u00ed po\u010dtu oprav to v tomto konkr\u00e9tn\u00edm p\u0159\u00edpad\u011b v\u00edce ne\u017e vykompenzovaly.<\/p>\n
V keramice a \u017e\u00e1ruvzdorn\u00fdch materi\u00e1lech se pr\u00e1\u0161ek z nitridu boru \u010dasto p\u0159id\u00e1v\u00e1 jako slinovac\u00ed p\u0159\u00edsada nebo jako vysokoteplotn\u00ed mazivo do peciho n\u00e1bytku. Pou\u017eil jsem jej v kompozitech z nitridu k\u0159em\u00edku a oxidu hlinit\u00e9ho, kde jsme pot\u0159ebovali lep\u0161\u00ed obrobitelnost po slinov\u00e1n\u00ed. P\u0159id\u00e1n\u00ed 3\u20135 % jemn\u00e9ho h-BN (pr\u016fm\u011brn\u00e1 velikost \u010d\u00e1stic 5\u201310 \u00b5m) zlep\u0161ilo snadnost brou\u0161en\u00ed vyp\u00e1len\u00fdch d\u00edl\u016f, ani\u017e by do\u0161lo k v\u00fdrazn\u00e9mu sn\u00ed\u017een\u00ed pevnosti. V jednom intern\u00edm srovn\u00e1n\u00ed vy\u017eadovaly \u0161ar\u017ee obsahuj\u00edc\u00ed h-BN o 18 % m\u00e9n\u011b \u010dasu na brou\u0161en\u00ed diamantov\u00fdm kotou\u010dem ve srovn\u00e1n\u00ed s kontroln\u00ed \u0161ar\u017e\u00ed a od\u0161t\u011bpov\u00e1n\u00ed hran bylo znateln\u011b sn\u00ed\u017eeno.<\/p>\n
\u0158\u00edzen\u00ed tepla je dal\u0161\u00ed oblast\u00ed, kde tento materi\u00e1l prokazuje jasn\u00e9 v\u00fdhody. V elektronice se h-BN pou\u017e\u00edv\u00e1 jako plnivo v materi\u00e1lech pro tepeln\u00fd kontakt a zal\u00e9vac\u00edch hmot\u00e1ch, proto\u017ee vede teplo a z\u00e1rove\u0148 z\u016fst\u00e1v\u00e1 elektricky izola\u010dn\u00ed. V jednoduch\u00e9m laboratorn\u00edm srovn\u00e1n\u00ed, kter\u00e9 jsme provedli p\u0159ed n\u011bkolika lety, dos\u00e1hlo silikonov\u00e9 mazivo napln\u011bn\u00e9 30 % oxidu hlinit\u00e9ho % hodnoty p\u0159ibli\u017en\u011b 1,1 W\/m\u00b7K. Stejn\u00e1 z\u00e1kladna napln\u011bn\u00e1 30 % h-BN % (s v\u011bt\u0161\u00edmi desti\u010dkami) dos\u00e1hla za identick\u00fdch testovac\u00edch podm\u00ednek p\u0159i pou\u017eit\u00ed chr\u00e1n\u011bn\u00e9ho m\u011b\u0159i\u010de tepeln\u00e9ho toku hodnoty 2,4 W\/m\u00b7K. Verze s h-BN tak\u00e9 z\u016fstala p\u0159i n\u00edzk\u00fdch teplot\u00e1ch m\u011bk\u010d\u00ed, co\u017e pomohlo sn\u00ed\u017eit kontaktn\u00ed odpor na nerovn\u00fdch povr\u0161\u00edch.<\/p>\n
Samoz\u0159ejm\u011b, nitrid boru nen\u00ed \u017e\u00e1dn\u00fd z\u00e1zrak. Je dra\u017e\u0161\u00ed ne\u017e grafit nebo mastek a velmi jemn\u00e9 frakce mohou b\u00fdt pra\u0161n\u00e9 a p\u0159i manipulaci vy\u017eaduj\u00ed dobr\u00e9 v\u011btr\u00e1n\u00ed. V n\u011bkter\u00fdch aplikac\u00edch tv\u00e1\u0159en\u00ed kov\u016f, kde je zapot\u0159eb\u00ed extr\u00e9mn\u00ed tlak, ho mohou disulfid molybdenu nebo speci\u00e1ln\u00ed syntetick\u00e1 maziva st\u00e1le p\u0159ekonat, a to u\u017e jen co se t\u00fd\u010de koeficientu t\u0159en\u00ed. Velikost \u010d\u00e1stic a \u010distota hraj\u00ed velkou roli \u2013 hrub\u0161\u00ed frakce poskytuj\u00ed lep\u0161\u00ed uvoln\u011bn\u00ed, ale hor\u0161\u00ed disperzi, zat\u00edmco frakce s vysokou \u010distotou jsou nezbytn\u00e9 pro elektroniku nebo kosmetiku.<\/p>\n
Zku\u0161enosti ukazuj\u00ed, \u017ee nejlep\u0161\u00edch v\u00fdsledk\u016f dos\u00e1hnete, kdy\u017e zvol\u00edte spr\u00e1vnou t\u0159\u00eddu materi\u00e1lu pro danou aplikaci. Pro tv\u00e1\u0159en\u00ed za tepla obvykle doporu\u010duji desti\u010dky o velikosti 10\u201320 \u00b5m s dobrou tekutost\u00ed. Pro term\u00e1ln\u00ed v\u00fdpln\u011b nebo kosmetiku se l\u00e9pe osv\u011bd\u010duj\u00ed t\u0159\u00eddy s velikost\u00ed pod 10 \u00b5m nebo dokonce submikronov\u00e9 s kontrolovanou povrchovou plochou. V\u017edy prove\u010fte \u0159\u00e1dn\u00e9 zkou\u0161ky na va\u0161em skute\u010dn\u00e9m za\u0159\u00edzen\u00ed a materi\u00e1lech, m\u00edsto abyste se spol\u00e9hali na obecn\u00e9 technick\u00e9 listy. V p\u0159\u00edpadech, kdy jsme tak u\u010dinili, pr\u00e1\u0161ky z nitridu boru opakovan\u011b p\u0159inesly m\u011b\u0159iteln\u00e9 zlep\u0161en\u00ed \u017eivotnosti n\u00e1stroj\u016f, spot\u0159eby energie nebo kvality produktu, kter\u00e9 ospravedlnily vy\u0161\u0161\u00ed n\u00e1klady na materi\u00e1l.<\/p>\n
Nikdy nenahrad\u00ed v\u0161echny ostatn\u00ed maziva nebo plniva, ale pokud proces zahrnuje vysok\u00e9 teploty, po\u017eadavky na \u010distotu nebo elektrickou izolaci spolu s tepeln\u00fdmi vlastnostmi, pr\u00e1\u0161ek z nitridu boru si v m\u00e9 v\u00fdbav\u011b vydobyl trval\u00e9 m\u00edsto. Kl\u00ed\u010dem je st\u00e1le tot\u00e9\u017e jako u jak\u00e9hokoli speci\u00e1ln\u00edho materi\u00e1lu: pochopit, jak ve va\u0161ich konkr\u00e9tn\u00edch podm\u00ednk\u00e1ch skute\u010dn\u011b funguje, \u0159\u00e1dn\u011b jej otestovat a pou\u017e\u00edt tam, kde je zv\u00fd\u0161en\u00ed v\u00fdkonu skute\u010dn\u00e9, nikoli pouze p\u0159edpokl\u00e1dan\u00e9.<\/p>","protected":false},"excerpt":{"rendered":"
After more than twenty years specifying lubricants and functional powders for metal forming, ceramics, and electronics, I\u2019ve come to treat […]<\/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":[11],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/posts\/329"}],"collection":[{"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/comments?post=329"}],"version-history":[{"count":1,"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/posts\/329\/revisions"}],"predecessor-version":[{"id":330,"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/posts\/329\/revisions\/330"}],"wp:attachment":[{"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/media?parent=329"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/categories?post=329"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/cs\/wp-json\/wp\/v2\/tags?post=329"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}