Calcined Alumina Thiab Refractories

Sufficient fine grinding of the α-Al2O3 aggregates can destroy their aggregated state and make them non-porous primary crystals, at which time the particle size means close to its grain size. Activated alumina is calcined alumina that has been sufficiently finely ground and has α-Al2O3 with an original crystal size of less than 1 μm as the basic composition (20% to >90 feem pua). Hauv kev tsim cov khoom siv alumina, kev sib tsoo muaj zog feem ntau yuav tsum tau, xws li kev sib tsoo qhuav hauv cov pob zeb ceramic-lined nrog cov pob zeb ceramic ua qhov sib tsoo nruab nrab rau ntau tshaj 24 teev. Yog vim li cas vim li cas nws thiaj li hu ua activated alumina feem ntau txhais tau hais tias nws yog ib qho yooj yim mus cuag lub siab tshaj plaws sintering ceev thaum sintered, tab sis lub sintering kub yog 100-200 degree qis dua qhov qis-Al2O3 hmoov; Nws yog ib qho yooj yim rau react thiab sinter nrog rau lwm yam nyob rau hauv cov khoom matrix, xws li combining nrog av nplaum nyob rau hauv lub matrix los ua mullite, reacting nrog calcium aluminate cement rau daim ntawv CA6, reacting nrog MgO los tsim spinel, thiab lwm yam. Raws li sintering txoj kev xav. , cov nplej loj heev cuam tshuam rau sintering tus nqi nyob rau hauv thawj theem, uas yog, tsim thiab loj hlob ntawm lub caj dab ntawm cov nplej. Yog hais tias lub grain loj yog txo mus rau 1/10 ntawm qhov qub loj (xws li los ntawm 5 μm mus rau 0.5 μm), sintering yuav 1000 zaug rau 10000 zaug yooj yim dua. Qhov no piav qhia txog kev ua haujlwm siab thermal ntawm activated alumina.

Cov txheej txheem sib tsoo siv ntau lub zog, yog li cov hmoov zoo dua, nws yuav kim dua. Cov tsos ntawm silicon micro (cov pos huab SiO2 generated thaum lub sij hawm zus tau tej cov silicon carbide los yog silicon hlau) tau zoo heev pab rau txoj kev loj hlob ntawm cov dej tsis muaj zog, tsawg-cement thiab ultra-low cement castables, tab sis cov nquag SiO2 no kuj txwv cov castables. Ua haujlwm kub. Yog tias tsis muaj kev vam meej ntawm kev ua haujlwm alumina, kev lag luam refractory castable niaj hnub tsis tuaj yeem txhim kho sai, thiab kev ua haujlwm kub yuav tsis tshaj 1600 degree.

 Generally speaking, powders can be divided into two categories according to the shape of particle size distribution (PSD for short): one type has a unimodal PSD, that is, the particle size distribution curve only surrounds a special particle size (close to but not necessarily Yes D50) peak: the other type is the PSD with multi-peak, that is, there are two or more distribution peaks on the PSD curve. Whether it is unimodal or bimodal, generally the wider the PSD range, the greater the powder bulk density or green body density. The PSD powder with unimodal and narrow range has the lowest bulk density. Of course, activated alumina also has the above two types. The unimodal activated alumina is characterized by a higher percentage (>80 feem pua) ntawm cov khoom<1μm (≈primary="" crystal="" size),="" and="" thus="" has="" a="" higher="" activity,="" and="" the="" average="" value="" of="" their="" particle="" size="" (≈grain="" size)="" is="" 0.30.="" around="" 5μm.="" the="" density="" of="" this="" activated="" alumina="" green="" body="" is="" low,="" usually="" only="" 54%="" 55%="" of="" the="" theoretical="" density="" of="" α-al2o3="" (3.98g/cm3),="" but="" its="" density="" after="" firing="" at="" 15001600="" ℃="" can="" reach="" 98%="" of="" the="" theoretical="" density,="" or="" even="" higher.="" unimodal="" activated="" alumina="" is="" easily="" and="" completely="" dispersed="" in="" water="" with="" the="" aid="" of="" dispersants="" such="" as="" sodium="" polyphosphate.="" the="" content="" of="" active="" particles="" smaller="" than="" 1="" μm="" in="" the="" multi-bee="" activated="" alumina="" varies="" greatly.="" usually="" between="" 20%="" and="" 7o%.="" the="" ratio="" of="" the="" number="" of="" active="" particles="" to="" the="" number="" of="" larger="" particles="" (="">1 μm) txiav txim siab nws qhov tsis muaj peev xwm sau thiab ua haujlwm. Rau multimodal activated alumina, qhov nruab nrab txoj kab uas hla D50 tsuas yog sawv cev rau nws fineness, tsis yog ib tug parameter uas characterizes nws cov khoom. Cov ntsuab ntom ntawm multimodal activated alumina feem ntau tuaj yeem ncav cuag 62 feem pua ​​​​68 feem pua ​​​​ntawm cov nqi theoretical, uas yog pom tseeb siab dua li ntawm unimodal activated alumina. Lub sintered ntom uas multimodal activated alumina tuaj yeem ua tiav nyob ntawm nws cov haujlwm. Thaum cov kev ua haujlwm siab dua multimodal alumina siv rau kev nias thiab sintering, txawm hais tias nws qhov kub thiab txias yog 100-150 degree siab dua li ntawm cov densified unimodal activated alumina, nws sintered ceev tsuas yog 94 feem pua ​​thiab 96 feem pua ​​ntawm cov nqi theoretical. Cov khoom tau yooj yim tshem tawm los ntawm cov khoom loj dua, yog li cov multimodal activated alumina yog yooj yim rau disperse hauv dej. Qhov dav ntawm PSD ntawm multimodal activated alumina ua rau -Al2O3 micropowder tau ntim rau hauv qhov khoob ntawm cov aggregates ntawm refractory bricks thiab cov castables thiab cov seem seem ntawm cov hmoov loj loj. Yog li ntawd, thaum siv castables, kom ua tiav tib lub fluidity, tus nqi ntawm cov dej ntxiv tuaj yeem txo los ntawm 4 feem pua ​​thiab 5 feem pua. Nyob rau hauv lub matrix ntawm lub castable, lub multimodal activated alumina ua raws li ib tug lubricant ntawm cov loj hais, uas yuav txo tau lub loosening ntawm lub castable, txawm thaum raug mus rau intensive mixing los yog siv. khaws cia sib cais.