Po v\u00edce ne\u017e dvaceti letech str\u00e1ven\u00fdch v oboru \u017e\u00e1ruvzdorn\u00fdch materi\u00e1l\u016f, kdy jsem se zab\u00fdval nejr\u016fzn\u011bj\u0161\u00edmi materi\u00e1ly, kter\u00e9 mus\u00ed odol\u00e1vat vysok\u00fdm teplot\u00e1m a drsn\u00fdm podm\u00ednk\u00e1m, jsem si karbid k\u0159em\u00edku s nitridovou vazbou velmi obl\u00edbil. Nen\u00ed to zrovna efektn\u00ed technologie, o kter\u00e9 se mluv\u00ed v p\u0159edn\u00e1\u0161k\u00e1ch TED, ale v ka\u017edodenn\u00edm provozu tov\u00e1ren a z\u00e1vod\u016f je to z\u00e1chrana \u017eivota. Tento materi\u00e1l kombinuje hou\u017eevnatost karbidu k\u0159em\u00edku s nitridov\u00fdm pojivem, kter\u00e9 mu dod\u00e1v\u00e1 mimo\u0159\u00e1dnou odolnost, a stal se z\u00e1kladem pro v\u0161echny, kdo se pot\u00fdkaj\u00ed s extr\u00e9mn\u00edmi podm\u00ednkami. L\u00edb\u00ed se mi na n\u011bm, \u017ee \u0159e\u0161\u00ed probl\u00e9my bez velk\u00e9ho povyku - trvanliv\u011bj\u0161\u00ed oblo\u017een\u00ed, m\u00e9n\u011b prostoj\u016f a podobn\u011b. V tomto \u010dl\u00e1nku v\u00e1s sezn\u00e1m\u00edm s t\u00edm, z \u010deho se skl\u00e1d\u00e1, s jeho hlavn\u00edmi p\u0159ednostmi, s t\u00edm, kde se pou\u017e\u00edv\u00e1, a s n\u011bkolika v\u011bcmi, na kter\u00e9 je t\u0159eba si d\u00e1t pozor, na z\u00e1klad\u011b toho, co jsem vid\u011bl v ter\u00e9nu. Pokud jste in\u017een\u00fdr nebo technik a hled\u00e1te mo\u017enosti nastaven\u00ed vysok\u00fdch teplot, mohlo by v\u00e1m to d\u00e1t p\u00e1r u\u017eite\u010dn\u00fdch tip\u016f.<\/p>\n
<\/p>\n
Za\u010dn\u011bme od z\u00e1klad\u016f: jak vznik\u00e1 nitridov\u00e1 vazba sic. Kl\u00ed\u010dovou slo\u017ekou je karbid k\u0159em\u00edku neboli SiC, kter\u00fd poch\u00e1z\u00ed z Achesonova procesu. P\u0159i n\u011bm vezmete k\u0159emi\u010dit\u00fd p\u00edsek a uhl\u00edk, zah\u0159ejete je ve velk\u00e9 elektrick\u00e9 peci na teplotu 2000 stup\u0148\u016f Celsia nebo vy\u0161\u0161\u00ed a vzniknou tvrd\u00e9 krystaly SiC. Jsou tvrd\u00e9 jako h\u0159eb\u00edky. P\u0159i v\u00fdrob\u011b lepen\u00e9 verze sm\u00edch\u00e1te tato zrnka SiC s k\u0159em\u00edkov\u00fdm pr\u00e1\u0161kem a vytvarujete z nich, co pot\u0159ebujete - cihly, desky, mo\u017en\u00e1 i trubky. Pak je vyp\u00e1l\u00edte v atmosf\u00e9\u0159e pln\u00e9 dus\u00edku o teplot\u011b kolem 1400 a\u017e 1500 \u00b0C. K\u0159em\u00edk se zachyt\u00ed na dus\u00edku a zm\u011bn\u00ed se na nitrid k\u0159em\u00edku, Si3N4, kter\u00fd vytvo\u0159\u00ed vazebnou s\u00ed\u0165, kter\u00e1 v\u0161e dr\u017e\u00ed na sv\u00e9m m\u00edst\u011b. Je to p\u0159ev\u00e1\u017en\u011b SiC, \u0159ekn\u011bme 85% nebo tak n\u011bjak, a nitrid vypl\u0148uje mezery. Kdy\u017e se na to pod\u00edv\u00e1te pod mikroskopem, uvid\u00edte tyto jehli\u010dkovit\u00e9 krystaly nitridu, kter\u00e9 se ov\u00edjej\u00ed kolem \u010d\u00e1stic SiC a vytv\u00e1\u0159ej\u00ed strukturu, kter\u00e1 je pevn\u00e1, ale ne p\u0159\u00edli\u0161 k\u0159ehk\u00e1. Nen\u00ed t\u0159eba pou\u017e\u00edvat \u017e\u00e1dn\u00e1 dal\u0161\u00ed pojiva, kter\u00e1 by mohla p\u0159i vysok\u00fdch teplot\u00e1ch vyho\u0159et, co\u017e je p\u0159\u00edjemn\u00e9.<\/p>\n
Nyn\u00ed k tomu, co zp\u016fsobuje tak dobr\u00fd v\u00fdkon. Tepeln\u011b tento materi\u00e1l snese n\u00e1por a\u017e 1650 \u00b0C na vzduchu a n\u011bkdy i vy\u0161\u0161\u00ed, pokud se atmosf\u00e9ra sni\u017euje. P\u0159i oxidaci vytv\u00e1\u0159\u00ed na povrchu vrstvu oxidu k\u0159emi\u010dit\u00e9ho, kter\u00e1 funguje jako \u0161t\u00edt proti dal\u0161\u00edmu po\u0161kozen\u00ed. Tepeln\u00e1 vodivost je docela dobr\u00e1, mezi 20 a 40 watty na metr kelvinu, tak\u017ee zvl\u00e1d\u00e1 tepeln\u00fd tok bez probl\u00e9m\u016f v takov\u00fdch v\u011bcech, jako jsou v\u00fdm\u011bn\u00edky tepla. Rozta\u017enost je n\u00edzk\u00e1, asi 4kr\u00e1t 10 a\u017e minus 6 na stupe\u0148 C, co\u017e znamen\u00e1, \u017ee p\u0159i divok\u00fdch v\u00fdkyvech teplot snadno neprask\u00e1. Z mechanick\u00e9ho hlediska je pevn\u00fd - pevnost v tlaku p\u0159es 200 megapascal\u016f - a mimo\u0159\u00e1dn\u011b odoln\u00fd proti ot\u011bru, proto\u017ee SiC je t\u00e9m\u011b\u0159 stejn\u011b tvrd\u00fd jako diamant. Vzorky jsem podrobil erozn\u00edm test\u016fm s roztavenou struskou a vy\u0161ly z nich mnohem l\u00e9pe ne\u017e v\u011bci z oxidu hlinit\u00e9ho.<\/p>\n
Z chemick\u00e9ho hlediska je to tak\u00e9 \u0161ampion. Kyseliny, louhy, roztaven\u00e9 kovy - ty ho p\u0159\u00edli\u0161 nerozh\u00e1z\u00ed. P\u0159i pr\u00e1ci s hlin\u00edkem odol\u00e1v\u00e1 fluorid\u016fm, kter\u00e9 by jin\u00e9 \u017e\u00e1ruvzdorn\u00e9 materi\u00e1ly se\u017eraly za\u017eiva. Hustota se pohybuje kolem 2,7 a\u017e 3,1 gramu na centimetr krychlov\u00fd, tak\u017ee nen\u00ed p\u0159\u00edli\u0161 t\u011b\u017ek\u00fd, a p\u00f3rovitost je 10 a\u017e 20 procent, co\u017e mu umo\u017e\u0148uje trochu d\u00fdchat, ani\u017e by se rozpadl. Ale tady je upozorn\u011bn\u00ed: pokud se nach\u00e1z\u00edte v parn\u00e9m prost\u0159ed\u00ed s teplotou nad 1400 \u00b0C, nitrid m\u016f\u017ee reagovat s vodou a degradovat. S t\u00edm je t\u0159eba po\u010d\u00edtat.<\/p>\n
Kde se to projevuje v re\u00e1ln\u00e9m sv\u011bt\u011b? Na mnoha m\u00edstech. Ve v\u00fdrob\u011b oceli se skv\u011ble hod\u00ed pro \u010d\u00e1sti vysok\u00fdch pec\u00ed, jako jsou oblasti kolem tuyer\u016f nebo kom\u00edn\u016f, kde doch\u00e1z\u00ed k neust\u00e1l\u00e9mu zah\u0159\u00edv\u00e1n\u00ed a otlouk\u00e1n\u00ed materi\u00e1lu. Vzpom\u00edn\u00e1m si na jednu zak\u00e1zku, kde jsme vyzd\u00edvku pece vym\u011bnili za SiC, a ta vydr\u017eela dvakr\u00e1t d\u00e9le - z pot\u0159eby vyzd\u00edvky ka\u017ed\u00fdch \u0161est m\u011bs\u00edc\u016f se stala vyzd\u00edvka del\u0161\u00ed ne\u017e rok. To je velk\u00e1 \u00faspora. U kov\u016f, jako je m\u011b\u010f nebo hlin\u00edk, se pou\u017e\u00edv\u00e1 v kel\u00edmc\u00edch a kan\u00e1lech; povrch nepropou\u0161t\u00ed kov, tak\u017ee se neucp\u00e1v\u00e1. V keramice se z n\u011bj vyr\u00e1b\u011bj\u00ed dobr\u00e9 podp\u011bry pec\u00ed a police, kter\u00e9 se p\u0159i vysok\u00e9m \u017e\u00e1ru nedeformuj\u00ed pod z\u00e1t\u011b\u017e\u00ed.<\/p>\n
Nejedn\u00e1 se jen o starou \u0161kolu. Najdete ho ve spalovn\u00e1ch, kde se pracuje s nep\u0159\u00edjemn\u00fdmi plyny, nebo v chemick\u00fdch reaktorech s korozivn\u00edmi l\u00e1tkami. V posledn\u00ed dob\u011b se s t\u00edm setk\u00e1v\u00e1m v ekologick\u00fdch energetick\u00fdch za\u0159\u00edzen\u00edch, jako jsou zply\u0148ova\u010de biomasy nebo sol\u00e1rn\u00ed za\u0159\u00edzen\u00ed. M\u016f\u017eete ji tvarovat v podstat\u011b do \u010dehokoli - standardn\u00edch cihel nebo kus\u016f na zak\u00e1zku - a instalovat pomoc\u00ed speci\u00e1ln\u00edch malt. Stoj\u00ed to v\u00edc, mo\u017en\u00e1 p\u011bt a\u017e deset dolar\u016f za kilo, ale rychle se to vyplat\u00ed na t\u011b\u017ek\u00fdch m\u00edstech.<\/p>\n
P\u0159esto nen\u00ed dokonal\u00fd. Spr\u00e1vn\u00e9 proveden\u00ed vy\u017eaduje pe\u010dlivou kontrolu; pokud se nitridace neprovede a\u017e do konce, vzniknou slab\u00e1 m\u00edsta. P\u0159i \u0159ez\u00e1n\u00ed nebo brou\u0161en\u00ed se zved\u00e1 prach, kter\u00fd je \u0161patnou zpr\u00e1vou - m\u016f\u017ee b\u00fdt karcinogenn\u00ed - tak\u017ee pou\u017e\u00edvejte masky a ods\u00e1v\u00e1n\u00ed. V\u00fdroba spot\u0159ebov\u00e1v\u00e1 energii, ale recyklace se zlep\u0161uje; na n\u011bkter\u00fdch m\u00edstech se ze star\u00fdch d\u00edl\u016f stahuje 70% SiC. V\u00fdzkum tak\u00e9 posouv\u00e1 hranice, nap\u0159\u00edklad p\u0159id\u00e1v\u00e1n\u00edm l\u00e1tek, aby byl odoln\u011bj\u0161\u00ed proti prasklin\u00e1m, nebo pou\u017e\u00edv\u00e1n\u00edm 3D tisku ke sn\u00ed\u017een\u00ed odpadu.<\/p>\n
Karbid k\u0159em\u00edku s nitridov\u00fdm pojivem je jedn\u00edm z t\u011bch materi\u00e1l\u016f, kter\u00e9 funguj\u00ed, kdy\u017e je pot\u0159eba. Z toho, s \u010d\u00edm jsem se setkal, jsem zjistil, \u017ee dok\u00e1zal zvr\u00e1tit slo\u017eit\u00e9 situace, jako nap\u0159\u00edklad v t\u00e9 zinkovn\u011b, kde v\u00fdrazn\u011b zv\u00fd\u0161il \u00fa\u010dinnost. Pokud uva\u017eujete o jeho pou\u017eit\u00ed, p\u0159izp\u016fsobte ho sv\u00fdm podm\u00ednk\u00e1m - teplu, chemik\u00e1li\u00edm, nam\u00e1h\u00e1n\u00ed - a ov\u011b\u0159te si specifikace od lid\u00ed, jako je Saint-Gobain. M\u00e1 velkou budoucnost, proto\u017ee se sna\u017e\u00edme naj\u00edt lep\u0161\u00ed a ekologi\u010dt\u011bj\u0161\u00ed zp\u016fsoby, jak v\u011bci d\u011blat.<\/p>","protected":false},"excerpt":{"rendered":"
Nitride Bonded Silicon Carbide: A Reliable Ally Against Heat and Wear in Industry You know, after spending over twenty years in the refractories business, tinkering with all sorts of materials that have to stand up to blistering temperatures and harsh conditions, I’ve developed a real appreciation for nitride bonded silicon carbide. It’s not the kind […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-44","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/posts\/44","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/comments?post=44"}],"version-history":[{"count":1,"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/posts\/44\/revisions"}],"predecessor-version":[{"id":45,"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/posts\/44\/revisions\/45"}],"wp:attachment":[{"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/media?parent=44"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/categories?post=44"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/buyscialishrx.com\/cs\/wp-json\/wp\/v2\/tags?post=44"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}