Po viac ako dvadsiatich rokoch, po\u010das ktor\u00fdch som sa zaoberal v\u00fdberom maz\u00edv a funk\u010dn\u00fdch pr\u00e1\u0161kov pre tv\u00e1rnenie kovov, keramiku a elektroniku, som dospel k n\u00e1zoru, \u017ee pr\u00e1\u0161ok z nitridu b\u00f3ru patr\u00ed medzi tie materi\u00e1ly, ktor\u00e9 po skuto\u010dnom pou\u017eit\u00ed nen\u00e1padne prekon\u00e1vaj\u00fa o\u010dak\u00e1vania. \u013dudia ho \u010dasto naz\u00fdvaj\u00fa \u201cbielym grafitom\u201d, preto\u017ee jeho hexagon\u00e1lna kry\u0161t\u00e1lov\u00e1 \u0161trukt\u00fara vyzer\u00e1 na papieri podobne, ale v praxi sa spr\u00e1va \u00faplne inak \u2013 a zvy\u010dajne lep\u0161ie \u2013 ke\u010f teploty st\u00fapaj\u00fa alebo ke\u010f je kontamin\u00e1cia uhl\u00edkom neprijate\u013en\u00e1. Vykonal som testy, sledoval som, ako na\u0148 prech\u00e1dzaj\u00fa v\u00fdrobn\u00e9 linky, a videl som rozdiel v \u017eivotnosti foriem, kvalite povrchu a stabilite procesu. Nie je to v\u017edy najlacnej\u0161ia vo\u013eba, ale na spr\u00e1vnych miestach sa to oplat\u00ed.<\/p>\n
Hexagon\u00e1lny nitrid b\u00f3ru (h-BN) sa vyr\u00e1ba reakciou oxidu b\u00f3ru alebo kyseliny boritej s amoniakom alebo dus\u00edkom pri teplot\u00e1ch nad 1400 \u00b0C. V\u00fdsledn\u00fd pr\u00e1\u0161ok je biely, m\u00e4kk\u00fd a m\u00e1 podobu do\u0161ti\u010diek, ktor\u00fdch vrstvy sa \u013eahko k\u013a\u017eu jedna po druhej. T\u00e1to vrstevnat\u00e1 \u0161trukt\u00fara mu dod\u00e1va vynikaj\u00facu mazivos\u0165, ale na rozdiel od grafitu zost\u00e1va stabiln\u00fd na vzduchu a\u017e do teploty pribli\u017ene 1000 \u00b0C a v inertn\u00fdch atmosf\u00e9rach aj pri teplot\u00e1ch vysoko nad 1400 \u00b0C. Je to tie\u017e elektrick\u00fd izolant a m\u00e1 slu\u0161n\u00fa tepeln\u00fa vodivos\u0165 na keramiku \u2013 okolo 20\u201330 W\/m\u00b7K v rovine do\u0161ti\u010diek. Tieto vlastnosti spolu ho robia u\u017eito\u010dn\u00fdm tam, kde by grafit oxidoval, vn\u00e1\u0161al uhl\u00edk alebo sp\u00f4sobil elektrick\u00e9 probl\u00e9my.<\/p>\n
Pri kovan\u00ed za tepla a extrudovan\u00ed sa pr\u00e1\u0161ok z nitridu b\u00f3ru stal jedn\u00fdm z mojich ob\u013e\u00faben\u00fdch separa\u010dn\u00fdch prostriedkov. Grafit funguje dobre pri stredn\u00fdch teplot\u00e1ch, ale pri teplot\u00e1ch nad 700\u2013800 \u00b0C sa za\u010d\u00edna vypa\u013eova\u0165 a m\u00f4\u017ee zanecha\u0165 zvy\u0161ky, ktor\u00e9 ovplyv\u0148uj\u00fa povrchov\u00fa \u00fapravu. V jednej sk\u00fa\u0161ke extrudovania hlin\u00edka, na ktorej som sa podie\u013eal, sme porovnali \u0161tandardn\u00fa disperziu grafitu vo vode s disperziou 15 % h-BN na rovnak\u00fdch sochoroch zo zliatiny 6061. Po 4 000 polotovaroch vykazovali matrice potiahnut\u00e9 grafitom vidite\u013en\u00e9 opotrebovan\u00e9 dr\u00e1\u017eky a vy\u017eadovali le\u0161tenie, zatia\u013e \u010do matrice potiahnut\u00e9 h-BN mali st\u00e1le hladk\u00e9 povrchy a vyr\u00e1bali diely s ni\u017e\u0161ou drsnos\u0165ou povrchu (Ra 0,8 \u00b5m oproti 1,6 \u00b5m). h-BN tie\u017e zn\u00ed\u017eil silu potrebn\u00fa na extrudovanie v priemere pribli\u017ene o 12 %, \u010do sa prejavilo ni\u017e\u0161ou spotrebou energie lisu a krat\u0161\u00edmi prestojmi pri v\u00fdmene mat\u00edc.<\/p>\n
Podobn\u00e9 zlep\u0161enia sme zaznamenali aj pri kovan\u00ed za tepla z nehrdzavej\u00facej ocele pri teplote 950 \u00b0C. Porovn\u00e1vacia sk\u00fa\u0161ka na 200 dieloch uk\u00e1zala, \u017ee formy namazan\u00e9 h-BN vykazovali po cykle o 28 % men\u0161iu h\u013abku opotrebenia meran\u00fa profilometrom. Diely boli tie\u017e \u010distej\u0161ie \u2013 bez tmav\u00fdch grafitov\u00fdch \u0161kv\u0155n, ktor\u00e9 niekedy vy\u017eaduj\u00fa dodato\u010dn\u00e9 \u010distenie. Nev\u00fdhodou bola cena: disperzia h-BN bola pribli\u017ene 2,5-kr\u00e1t drah\u0161ia na liter, ale pred\u013a\u017een\u00e1 \u017eivotnos\u0165 foriem a zn\u00ed\u017een\u00e1 potreba dodato\u010dn\u00fdch \u00faprav to v tomto konkr\u00e9tnom pr\u00edpade viac ne\u017e kompenzovali.<\/p>\n
V keramike a \u017eiaruvzdorn\u00fdch materi\u00e1loch sa pr\u00e1\u0161ok z nitridu b\u00f3ru \u010dasto prid\u00e1va ako sp\u00e1jkovacie \u010dinidlo alebo ako vysokoteplotn\u00e9 mazivo do v\u00fdmuroviek pec\u00ed. Pou\u017eil som ho v kompozitoch z nitridu krem\u00edka a oxidu hlinit\u00e9ho, kde sme potrebovali lep\u0161iu obrobite\u013enos\u0165 po spekan\u00ed. Pridan\u00edm 3\u20135 % jemn\u00e9ho h-BN (priemern\u00e1 ve\u013ekos\u0165 \u010dast\u00edc 5\u201310 \u00b5m) sa zlep\u0161ila \u013eahkos\u0165 br\u00fasenia vyp\u00e1len\u00fdch dielov bez v\u00fdraznej straty pevnosti. V jednom internom porovnan\u00ed si d\u00e1vky obsahuj\u00face h-BN vy\u017eiadali o 18 % menej \u010dasu br\u00fasenia na diamantovom kot\u00fa\u010di v porovnan\u00ed s kontrolnou d\u00e1vkou a od\u0161tiepovanie hr\u00e1n bolo v\u00fdrazne zn\u00ed\u017een\u00e9.<\/p>\n
Riadenie tepeln\u00e9ho re\u017eimu je \u010fal\u0161ou oblas\u0165ou, v ktorej sa prejavuje jeho jasn\u00e1 pridan\u00e1 hodnota. V elektronike sa h-BN pou\u017e\u00edva ako plnivo v materi\u00e1loch na vytvorenie tepeln\u00e9ho rozhrania a v zalievac\u00edch hmot\u00e1ch, preto\u017ee vedie teplo a z\u00e1rove\u0148 zachov\u00e1va elektrick\u00fa izol\u00e1ciu. V jednoduchom laborat\u00f3rnom porovnan\u00ed, ktor\u00e9 sme vykonali pred nieko\u013ek\u00fdmi rokmi, dosiahlo silik\u00f3nov\u00e9 mazivo naplnen\u00e9 30 % oxidu hlinit\u00e9ho % hodnotu pribli\u017ene 1,1 W\/m\u00b7K. Rovnak\u00e1 z\u00e1klad\u0148a naplnen\u00e1 30 % h-BN % (s v\u00e4\u010d\u0161\u00edmi platni\u010dkami) dosiahla pri identick\u00fdch testovac\u00edch podmienkach s pou\u017eit\u00edm chr\u00e1nen\u00e9ho meradla tepeln\u00e9ho toku hodnotu 2,4 W\/m\u00b7K. Verzia s h-BN tie\u017e zostala pri n\u00edzkych teplot\u00e1ch m\u00e4k\u0161ia, \u010do pomohlo zn\u00ed\u017ei\u0165 kontaktn\u00fd odpor na nerovn\u00fdch povrchoch.<\/p>\n
Samozrejme, nitrid b\u00f3ru nie je \u017eiadny z\u00e1zrak. Je drah\u0161\u00ed ako grafit alebo mastek a ve\u013emi jemn\u00e9 frakcie m\u00f4\u017eu by\u0165 prachov\u00e9 a pri manipul\u00e1cii si vy\u017eaduj\u00fa dobr\u00e9 vetranie. V niektor\u00fdch aplik\u00e1ci\u00e1ch tv\u00e1rnenia kovov, kde je potrebn\u00fd extr\u00e9mny tlak, ho disulfid molybd\u00e9nu alebo \u0161pecializovan\u00e9 syntetick\u00e9 maziv\u00e1 st\u00e1le m\u00f4\u017eu prekona\u0165 u\u017e len \u010do sa t\u00fdka koeficientu trenia. Ve\u013ekos\u0165 \u010dast\u00edc a \u010distota maj\u00fa ve\u013ek\u00fd v\u00fdznam \u2013 hrub\u0161ie frakcie poskytuj\u00fa lep\u0161ie uvo\u013e\u0148ovanie, ale hor\u0161iu disperziu, zatia\u013e \u010do frakcie s vysokou \u010distotou s\u00fa nevyhnutn\u00e9 pre elektroniku alebo kozmetiku.<\/p>\n
Zo sk\u00fasenost\u00ed viem, \u017ee najlep\u0161\u00edch v\u00fdsledkov dosiahnete, ak zvol\u00edte triedu materi\u00e1lu zodpovedaj\u00facu danej \u00falohe. Pri tv\u00e1rnen\u00ed roztaven\u00e9ho kovu zvy\u010dajne \u0161pecifikujem do\u0161ti\u010dky s ve\u013ekos\u0165ou 10\u201320 \u00b5m a dobrou sypnos\u0165ou. Pre tepeln\u00e9 v\u00fdplne alebo kozmetiku sa lep\u0161ie osved\u010duj\u00fa triedy s ve\u013ekos\u0165ou men\u0161ou ako 10 \u00b5m alebo dokonca submikr\u00f3nov\u00e9 s kontrolovanou povrchovou plochou. V\u017edy vykonajte riadne testovanie na va\u0161om skuto\u010dnom zariaden\u00ed a materi\u00e1loch, namiesto toho, aby ste sa spoliehali na v\u0161eobecn\u00e9 technick\u00e9 listy. V pr\u00edpadoch, ke\u010f sme tak urobili, pr\u00e1\u0161ky z nitridu b\u00f3ru opakovane priniesli merate\u013en\u00e9 zlep\u0161enia v \u017eivotnosti n\u00e1strojov, spotrebe energie alebo kvalite v\u00fdrobkov, ktor\u00e9 ospravedlnili vy\u0161\u0161ie n\u00e1klady na materi\u00e1l.<\/p>\n
Nikdy nenahrad\u00ed v\u0161etky ostatn\u00e9 maziv\u00e1 \u010di plniv\u00e1, ale ak proces zah\u0155\u0148a vysok\u00e9 teploty, po\u017eiadavky na \u010distotu alebo elektrick\u00fa izol\u00e1ciu popri tepeln\u00fdch vlastnostiach, pr\u00e1\u0161ok z nitridu b\u00f3ru si v mojej v\u00fdbave vysl\u00fa\u017eil trval\u00e9 miesto. K\u013e\u00fa\u010dom je st\u00e1le to ist\u00e9 ako pri akomko\u013evek \u0161peci\u00e1lnom materi\u00e1li: pochopi\u0165, \u010do vlastne rob\u00ed vo va\u0161ich konkr\u00e9tnych podmienkach, riadne ho otestova\u0165 a pou\u017e\u00edva\u0165 tam, kde je zv\u00fd\u0161enie v\u00fdkonu skuto\u010dn\u00e9, a nie len predpokladan\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\/sk\/wp-json\/wp\/v2\/posts\/329"}],"collection":[{"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/comments?post=329"}],"version-history":[{"count":1,"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/posts\/329\/revisions"}],"predecessor-version":[{"id":330,"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/posts\/329\/revisions\/330"}],"wp:attachment":[{"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/media?parent=329"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/categories?post=329"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/boronnitrideceramic.com\/sk\/wp-json\/wp\/v2\/tags?post=329"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}