Ban chat cua men va cac khuyet tat thu'dng gap khi nung gom trang men
Nguyin Thanh Dong Trw&ng Dai hoc Bach khoa Ha Noi
M
en la mot lop m6ng dang thuy tinh co do day thuomg tit 0,1 den 0,3 mm dugc phu tren be mat ciia xuong gom. Men c6 tac dung ngan ngira bui, nuoc, axit, kiem ngam vao xuong san pham, lam tang gia tri tham my va lam cho cac tinh chat ky thuat cua san pham dugc tot hom.Ve ban chat hoa hgc, men la mot vat chat dang thuy tinh dugc cau thanh tir cac oxyt nhu Si02, AI2O3, CaO, MgO, Na20, K2O...
Men tmoc khi nung la mot hon hgp bgt ran, min. Trong qua trinh nung men chuyen tir trang thai ran sang deo quanh, sau d6 sang trang thai bien mem roi chay 16ng.
Su bien d6i trang thai nhu vay tuong tu nhu khi niu chay thuy tinh. Men kh6ng CO nhiet do chay nhit dinh va nhiet do chay ciia men theo quan niem thong thuong la nhiet do ma men da chay thanh mot lop dan deu va bong tren bl mat san
pham. Nhiet do chay dan deu cua men can phii hgp voi khoang nhiet do nung de thu dugc lop men bong lang tren bl mat san pham sau khi nung.
Ban chat ciing nhu qua trinh hinh thanh cua men tuomg tu nhu thuy tinh nhung 6 giai doan cu6i cua qua trinh nung, do nhort cua men phai dii 16m de men bam chat vao xuong ma kh6ng bi troi kh6i be mat ciia n6.
Trong qua trinh nung san pham, giiia xuong va men CO phan iing hoa hgc de tao ra san pham phan iing la mot lop vat chat trung gian nam giiia xuong va men. Lop trung gian c6 tinh chat vat ly dung hoa giua xuong va men. Su c6 mat ciia n6 lam giam dang ke itng suat trong lop men do chenh lech ve he s6 gian no nhiet giiia xuong va men, qua d6 lam giam hien tugng niit va bong men.
Chieu day lop vat chat tmng gian d6i voi cac loai men khac nhau thuong dao dong
tu 0,01 den 0,3 mm.
Chat lugng ciia lop men phii anh huong dang ke den gia tri ciia san pham, dac biet la ve gia tri tham my. Tuy nhien, trong qua trinh nung tren be mat men thuomg xuat hien cac khuyet tat ma dien hinh la cac hien tugng bgt khi va cu6n men.
Bgt khi trong men dugc hinh thanh khi nung san pham. Cac bgt khi nay c6 thi la cac khi thoat ra tit cac 16 xop trong xuong, ciia nuoc b6c hgi hoac la san pham ciia cac phan iing chay tap chit hiru co, phan iing phan buy cua cac chat trong xuong va men g6m. Bgt khi tao nen cac mieng pheu iron kin va ho voi kich thuoc khac nhau tren be mat men.
Cac mieng pheu ho va nh6 dugc ggi la 16 chan kim, con 16m hon dugc ggi la lo chan long. Cac mieng pheu kin tao nen cau tnic san v6 tning, v6 cam 6 be mat men.
Bgt khi khong nhiing lam giam do b6ng va my quan cua men, ma con lam tang
So 03/2010
nguy CO dgng ban, dgng am tren be mat men.
Su hinh thanh cac bot khi tren be mat men c6 the dugc mo ta mot each don gian hoa nhu sau:
6 nhiet do cao, khong khi nim giira cac hat ran trong xuong, men ciing voi cac nguin khi do chay tap huu CO va phan buy nguyen lieu se toa ra khi men dang chay.
Do do nhot ciia men liic nay kha cao nen khi bi gift lai va nam 6 dang 16 xop kin trong men.
Khi tang nhiet do nung, do nhort ciia men giam xuong, cac bgt khi tang the tich do su gian no nhiet va do cac bgt khi nh6 lien ket lai thanh cac bgt 16m hom, chiing dich chuyen den gan be mat men.
NIU ket thiic nung 6 khoang nhiet do nay va bat diu thuc hien qua trinh lam nguoi thi cac bgt khi bi co lai ve the tich, no keo mang men m6ng ben tren xuong dan den viec hinh thanh cac mieng pheu kin nam ben tren bgt khi. Nhin be mat lop men trong truomg hgp nay c6 dang san v6 tning, v6 cam va do b6ng 16rp men bi giam di. Cac mieng pheu nim tren bgt khi thuomg c6 kich thuoc 25 - 40mm hoac 16m hom va c6 the thay dugc bang mat thuong.
Neu tiep tuc tang cao
nhiet do nung thi do nhot ciia men cang giam va kich thuoc bgt cang tang len. Bgt di chuyin thuan Igi qua lop men it nhot de thoat ra ngoai. Tai be mat men, bgt bi vo ra va de lai cac mieng pheu khuyet men. Khi d6, neu do linh dgng ciia lop men khong du cao thi t6c do dan men tir cac vi tri xung quanh vao vi tri khuyet men cham, dan den nhieu mieng pheu khong dugc lap day men khi lam nguoi, tao thanh cac mieng pheu ho voi kich thuoc 16m nho khac nhau ggi la cac 16 chan long, chan kim.
Trang thai bgt khi thoat ra kh6i be mat men ggi la trang thai soi men va nhiet do tuomg ling la nhiet do s6i men. Giai doan nay neu tien hanh luu nhiet dii lau, tham chi CO the tang nhiet do nung san pham len mot it thi cac mieng pheu da hinh thanh se dugc ban lai nhanh ch6ng va bl mat men dugc bong lang hon.
Cuon men la hien tugng tren be mat san pham c6 nhiing viing tr6ng voi hinh dang, kich thuoc khac nhau kh6ng dugc phii men. Men 6 ria cac vung tr6ng thuomg nh6 len va day hom.
Cuon men xuat phat tu vet niit men hoac tu vi tri tr6c men 6 viing nhiet do thap do men lien ket yeu voi xuomg. Khi men chay, do do
nhot, sue cang be mat ciia men cao ciing nhu do tham uort ciia men kh6ng t6t nen cac khe niit, diem tr6c men kh6ng nhung kh6ng dugc ban lai ma con bi keo rgng ra va de lai cac viing khuyet men. Neu do nhot, siic cang bl mat ciia men giam xuong, do thim uort ciia xuong boi men tit hom thi cac vet niit, vit tr6c men c6 the dugc ban lai hoan toan hoac mot phin.
Cac nguyen nhan gay nen pha huy cau tnic lop men 6 viing nhiet do thap c6 anh huong quyet dinh den hien tugng cuon men. Neu be mat men kh6ng hinh thanh cac vet nut, vet troc thi rat kh6 xay ra hien tugng cu6n men.
B I mat ciia xuong bi ban nhu dgng bui, dinh vet dau mo lam cho men kho bam vao xuomg ciing la mot trong cac nguyen nhan gay nen hien tugng cuon men.
C6 the tang do bam dinh ciia men vao xuong de men kh6ng bi troc ra 6 viing nhiet do thap bang each dua vao men cac chat lien ket nhu dat set deo va cac loai keo hiiu CO. Set bentonit dua vao men voi lugng 1 -3% lam tang dang ke do ben ciia lop men ciing nhu do bam dinh ciia men vao xuomg. Tuy nhien dua mot lugng 16m set deo vao men lai c6 the gay nen cac vet niit, vet troc 6 lorp men khi say hoac nung 6 nhiet do thap.
Thong tin khoa hoc cong nghe Binh Dirong p 29'
Mot so dang khuyet tat men thu'O'ng gap
L5 chan leng L5 cMn kim
Bot klii CO lai S^i v6 cam khi lain ngnoi
Lo dian Idng Lo chaji kim
Lop men
Lop tnuig gian V i t l i b i c a ^
Xwong gom ^
Ldpmen
LdptfUDjgiaD
