CH7_vatlieuceramic - 113 Chng 7 Vt liu v c ceramic nh ngha...

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113 Ch ¬ng 7 VËt liÖu v« c¬ - ceramic §Þnh nghÜa: VËt liÖu v« c¬ lμ sù kÕt hîp gi÷a kim lo¹i Me, Si víi ¸ kim B,C,N,O b»ng c¸c liªn kÕt ion vμ céng ho¸ trÞ Ph©n lo¹i: nhiÒu c¸ch ph©n lo¹i Theo ®Æc ®iÓm kÕt hîp: 3 nhãm chÝ nh: Gèm vμ kim lo¹i chÞu löa Thuû tinh vμ gèm thuû tinh Xi m¨ng vμ bª t«ng Theo cÊu tróc: 2 nhãm: ®¬n pha: thuû tinh SiO 2 (ch ¬ng 1 ), gèm ®¬n oxit VËt liÖu ®a pha: hÇu hÕt c¸c vËt liÖu v« c¬ H×nh 7.1. Kh¶ n¨ng kÕt hîp Pha chÝ nh lμ c¸c pha tinh thÓ liªn kÕt víi nhau bëi pha thuû tinh (v« ®Þnh h×nh) : gèm & VL chÞu löa, sø, gèm thuû tinh. Ngoμi ra cßn cã pha khÝ do c«ng nghÖ chÕ t¹o kh«ng tr¸nh khái còng cã thÓ do chñ ®éng ® a vμo: gèm xèp, thuû tinh xèp, bª t«ng xèp c¸c pha tinh thÓ cã thÓ cã % kh¸c nhau, chøa khuyÕt tËt, nhiÒu vÕt nøt, chóng quyÕt ®Þnh tÝ nh chÊt cña ceramic. 7.1. Quan hÖ gi÷a cÊu tróc vμ tÝ nh chÊt cña ceramic Do cÊu tróc cña vËt liÖu v« c¬ t¹o thμnh tõ c¸c kim lo¹i vμ ¸ kim liªn kÕt ion vμ liªn kÕt céng ho¸ trÞ, vÝ dô: trong oxit : Mg-O, Zr-O , Ti-O , Al-O, B-O , Si-O, C-O % liªn kÕt ion: 80 67 63 60 45 40 22 cßn l¹i lμ liªn kÕt céng ho¸ trÞ VËt liÖu v« c¬ bÒn ho¸ häc, bÒn nhiÖt , c¸ch nhiÖt tèt, mét sè cã tÝ nh chÊt quang ®Æc biÖt TÝ nh chÊt c¬ häc (nh¾c l¹i biÓu ®å kÐo) §μn håi gißn: do cÊu tróc, VL bÞ ph¸ huû gißn §é bÒn lý thuyÕt σ LT = (2E. γ /a) 1 /2 E- m«dun ®μn håi γ - søc c¨ng bÒ mÆt; a- kho¶ng c¸ch nguyªn tö σ LT - vËt liÖu coranh®«ng 50. 1 0 3 MPa, thuû tinh SiO 2 ~ 8. 1 0 3 MPa §é bÒn thùc tÕ: do cã nøt tÕ vi 1 0 -3 ÷ 1 00 µ m ®é bÒn thùc tÕ = 1 / 1 00 ®é bÒn lý thuyÕt : Khi chÞu t¶I kÐo σ O th× thùc tÕ σ = 2. σ O (l/r) 1 /2 l: dμI nøt; r: b¸n kÝ nh cong ®Çu vÕt nøt. σ thùc trong vËt liÖu phô thuéc vμo σ O vμ tû lÖ thuËn l vμ tû lÖ nghÞch víi r. Khi nøt dμi, ®Çu nhän: σ [ σ LT ] nøt t¨ng ph¸ huû Chó ý vËt liÖu v« c¬ chÞu nÐn tèt h¬n chÞu kÐo ( 1 0 lÇn) §é bÒn vËt liÖu v« c¬ kh«ng ph¶i do n¨ng l îng liªn kÕt nguyªn tö cÊu t¹o nªn nã mμ do sè l îng, chiÒu dμi, chiÒu s©u vÕt nøt (h×nh d¹ng). VËt liÖu v« c¬ tinh thÓ: h¹t cμng nhá th× ®é bÒn cμng cao Bät khÝ 0, 1 -0,5% h¹t nhá trßn t¨ng ®é bÒn, >0,5% bät cμng dμi cμng nhiÒu ®é bÒn gi¶m m¹nh. Bät khÝ lμm gi¶m ®é dÉn nhiÖt. Me Si O N C B kim lo¹ i ceramic P l
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114 7.2. C¸c vËt liÖu v« c¬ ®iÓn h×nh 7.2.1. Gèm vμ vËt liÖu chÞu löa Gèm b»ng s¶n phÈm ®Êt nung: NhiÖt ®é nung g¹ch 900 o C, 1 400, t¹o tõ c¸c nguyªn liÖu tù nhiªn: KaolinÝ t Al 2 O 3 .2SO 2 .2H 2 O VËt liÖu bét t¹o h×nh nung vËt liÖu gèm CÊu tróc: gåm c¸c pha tinh thÓ liªn kÕt b»ng pha v« ®Þnh h×nh tû lÖ v« ®Þnh h×nh trong g¹ch ngãi 20-40 %, trong sø 50-60%, Al 2 O 3 1 % Bät khÝ trong g¹ch ngãi 1 0-50%, trong sø 5%
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