Tổng hợp ferit MFe2O4 (với m là ni và co) bằng phương pháp hóa học ướt, nghiên cứu đặc trưng cấu trúc và từ tính

Vdi nhiJng uu diem cho san pham cd do tinh khiet cao, cac chat dau phan bd ddng deu, nhiet do phan img thap, kich thuoc hat san pham nhd, tranh dugc su ngung tu cua cac hat trong qua tri

BQ CONG THLTONG TRU^OfNG CAO DANG HOA CHAT

BAO CAO TONG KET

DE TAI NGHIEN ClTU KHOA HOC CONG NGHE CAP BO

MA SO: 101-69-RD

TONG HOfP FERIT MFe204 (VCfl M LA Ni VA Co) B A N G PHLTONG

PHAP HOA HOC UOfT, NGHIEN CtTU DAC T R U N G

CAU TRUC VA Ttr TINH

CHU NHIEM DE TAI: ThS VU DINH NGO Cac thanh vien tham gia:

- TS QUAN DINH KHOA

- PGS.TS NGO SY L C O N G

- ThS NGUYEN THI KIM DUNG

- ThS DAM THI THANH HtTONG

MUC LUC

Trang

MO DAU 1 PHAN I: TONG QUAN VE TINH HINH NGHIEN ClTU VA NHIEM VU

CUA DE TAI

1.1 Cac dac trirng cua vat lieu tir 2

1.1 1 Cac dac tnmg ciia vat lieu tir cijmg 2

1.1.2 Cac dac trung vat lieu tir mem 3

1.2 Dac trirng cau triic va tinh chat ciia cac ferit spinen 5

1.2.1 Cau tnic cac ferit spinen 5

1.2.2 Tinh chat tir va dien ciia ferit spinen 7

1.2.3 Tinh chat xuc tac 9

1.3 Tinh chat va irng dung cua ferit kich thirffc nano 9

1.3.1 Sir bien doi tinh chat tir cua cac vat lieu nano so vol vat lieu khoi 9

1.3.2 Nhung ung dung va huong nghien cuu chinh ve vat lieu tir nano 10

1.4 Mot so phvong phap tong hop coban ferit va niken ferit 11

1.4.1 Tong hgp coban ferit va niken ferit bang phuang phap gom 11

1.4.2 Tong hop coban ferit va niken ferit bang phuong phap hoa hoc uot 12

1.5 Mot so ket qua nghien ciru tong hop ferit cap hat nano 16

1.6 Muc tieu ciia de tai 18

PHAN THlT II: THU'C NGHIEM 19

2.1 Hoa chat, dung cu va thiet bi 19

2.1.1 Hoa chat 19 2.1.2 Dung cu va thiet bi 19

2.2 Cac phu-ong phap du-ffc su- dung di xac dinh dac tinh cua vat lieu 20

2.2.1 Phuong phap ghi gian do nhilu xa tia X 20

2.2.2 Phuong phap phan tich nhiet 20

2.2.3 Phuong phap kinh hien vi dien tir 20

2.2.4 Phuong phap xac dinh tir tinh vat lieu bang thiSt bi tir k^ mau rung 21

PHAN THlT III: KET QUA VA THAO LUAN 22

3.1 Tong hop niken ferit (CoFe204) cap hat nano bSng phiro'ng phap

dong ket tua

3.1.1 Khao sat anh huong ciia pH dung dich den kich thuoc hat 22

3.1.2 Khao sat anh huong ciia n6ng do dung dich dkn kich thuoc hat 24

3.1.3 Khao sat anh huong cua nhiet do kk tua va thoi gian khuSy 26

3.1.4 Khao sat anh huong ciia lugng dung moi trong dung dich ddng k6t tua 27

3.1.5 Khao sat anh huong cua nhiet do nung va thoi gian nung 28

3.2 Tong ho"p coban ferit (CoFe204) cap hat nano bang phu-ong phap

22

chira Fe^* va Mn^^ ham lu-tfng cao

39

3.2.2 Khao sat anh huong ciia thoi gian khuay den kich thuoc hat 34

3.2.3 Khao sat anh huong ciia ty le etanol /nuoc trong dung dich ket tiia 35

3.2.4 Khao sat anh huong ciia nhiet do nung va thoi gian nung 36

3.3 Xay du-ng quy trinh t6ng hop niken ferit va coban ferit cap hat

nano bang phno-ng phap dong ket tua qui mo phong thi nghiem

3.3.1 So do qui trinh tong hop 39

3.3.2 Giai thich qui trinh 39

3.3.3 Ket qua ap dung qui trinh 40

3.4 Tong hgp niken ferit (NiFe204) va coban ferit (CoFe204) cap hat

nano bling phirang phap sol-gel

3.4.1 Khao sat anh huong ciia pH dung dich den qua trinh tao gel va kich

thuoc hat ferit

3.4.2 Khao sat anh huong ciia thoi gian khuay 43

3.4.3 Khao sat anh huong cua nhiet do nung va thoi gian nung 44

3.4.4 Khao sat anh huong cua ti le chat nen 47

3.4.5 Qui trinh tong hop niken ferit va coban ferit cap hat nano bang

phuong phap sol- gel, qui mo phong thi nghiem

PHAN IV: THAM DO KHA NANG DUNG CUA BOT NANO FERIT 52

4.1 Che tao loi tu- va nam cham 52

4.2 Tham do kha nang sir dung bot ferit nano trong xir ly nirdc co

42

42

48

53 4.2 1 Phuong phap xac dinh ham luong Mn^"^ 53

4.2.2 Phuong phap xac dinh ham luong Fe^^ 54

4.2.3 Sii dung bpt nano ferit hap phu cac ion Mn^^, Fe^"^ trong nuoc 56

4.3 Tham do kha nang hap phu cac ion As^ va Pb^^ trong niro'c bSng bot

nano ferit

KET LUAN 60 TAI LIEU THAM KHAO 62

MdDAU

Vat lieu tir da dugc nghien ciru va sir dung rat rgng rai trong thuc te trong cac thiet bi phuc vu doi song con nguoi nhu: may bien the, dgng co dien, may phat dien den cac thiet bi dien tii hien dai nhu may tinh, may ghi am, may ghi hinh va ca trong cac ITnh vuc xiic tac cho cac qua trinh tong hgp hiju co, xir ly moi trudng Ciing voi sir phat trien ciia khoa hgc va cong nghe viec che tao vat lieu tir nano vdi tinh nang uu viet ngay cang dugc chii trgng trong nhirng nam gan day Trong sd cac vat lieu tir dugc chii y nhieu cd ferit tir dang cau tnic spinen AB2O4 Ferit tir la vat lieu quan trgng bdi chiing cd do tir tham, do bao hda tir tuong ddi cao, dien trd lai rat Idn thich hgp cho cac dung cu hoat ddng d tan sd cao vi giam su mat mat nang lugng tang tudi thg thiet bi

Vat lieu tir ferit spinen cd kich thuoc nano met cd the dugc dieu che theo nhieu phuong phap khac nhau Vdi phuong phap vat ly la nghien trdn nung ep nhieu lan, nhugc diem cua phuong phap vat ly la vat lieu bi bay hoi hao hut nhieu, nhiing chat tham gia che tao khdng cdn nhu ban dau, mat khac cdi nghien phai ciing vat lieu vdi ddi tugng nghien ciiu, kich thuoc hat khdng deu, thanh phan khdng ddng nhat, be mat rieng nhd, d nhiem mdi trudng Gan day de dieu che vat lieu tir nano ngudi ta thudng sir dung phuong phap hoa hgc udt Cd nhieu phuong phap hoa hgc de dieu che loai vat lieu nay nhu: phuong phap ddng ket tua va phan huy nhiet, phuong phap su dung tien chat, phuong phap sol-gel, thuy nhiet Vdi nhiJng uu diem cho san pham cd do tinh khiet cao, cac chat dau phan bd ddng deu, nhiet do phan img thap, kich thuoc hat san pham nhd, tranh dugc su ngung tu cua cac hat trong qua trinh thieu ket, vat lieu thu dugc chat lugng cao hon cac san pham che tao bang phuong phap gdm truyen thdng v.v Trong dd phuong phap ddng ket tiia va sol - gel dang dugc sir dung rat thanh cdng trong tdng hgp vat lieu nano dac biet la vat lieu tir

Vi vay chung tdi dang ky thuc hien de tai nghien cuu: Tong hgrpferU MFe204 (vdi

Mid Ni vd Co) cdp hgt nano bdng phuang phdp hod hoc udt, nghien ciru dgc trung cdu true vd tu tinh Vdi mong mudn cd the ddng gdp nhirng luan cir khoa hgc va ket qua thuc

nghiem trong Imh vuc mdi me - hda hgc nano va cdng nghe nano

PHAN I TONG QUAN VE TINH HINH NGHIEN ClTU VA NHIEM VU

CUA DE TAI

1.1 Cac dac trirng cua vat lieu tir

7.7.7 Cdc dgc trung ciia vgt lieu tir cirng [1,4,6,7,13,18]

Vat lieu tir ciing la loai vat lieu tir dugc phat hien va sir dung sdm nhat trong lich sir loai ngudi Ngudi Trung Qudc da che tao ra cac kim chi nam diing de xac dinh phuong hudng ngay tir nhimg nam 1046 - 771 TCN Dd la cac da nam cham

cd kha nang hiit sat va dinh hudng Bac - Nam va la ban thuc su xuat hien nhieu la the ky thir 7 trudc cdng nguyen ddng thdi d Trung Qudc va Hy Lap Cac kim chi nam trong la ban la mdt dang cua vat lieu tir ciing, la cac dxit sat Fe304 Ngay nay vat lieu tir cimg cd nhirng ling dung phd bien trong che tao cac nam cham vTnh cim hoac dugc sii dung lam vat lieu ghi tir trong cac d dia ciing, cac bang tir

Cac vat lieu tir ciing thuong pham diing de che tao nam cham vTnh ciiu xuat hien lan dau tien vao nhirng nam tir 1740 den 1750 d chau Au va thuc su phat trien manh tir cudi the ky 19, dau the ky 20 den nay

Vat lieu tir ciing cd nhieu dac trung tir hgc: luc khang tir, tich nang lugng cue dai, cam ling tir du va sir phu thugc cua tinh chat tir vao nhiet do, do ben, do chdng mai mdn Tren hinh 1.1 ghi dudng cong tir tre cua vat lieu tir ciing

Hinh 1.1 Dudng cong tir tre vd cdc ddc trung ciia vdt lieu tu cung

*Lirc khang tir: Luc khang tir, ky hieu la He la dai lugng quan trgng dac

trung cho tinh tir cimg cua vat lieu tir cimg Vdi vat lieu tir cirng la khd tir hda va

khd khir tir nen cd luc khang tir cao Dilu kien tdi thieu la tren 100 Oe, nhung vat lieu tir cimg phd biln thudng cd lire khang tir co hang ngan Oe trd len Ngudn gdc cua lire khang tir Idn trong cac vat lieu tir ciing chu yeu lien quan den den di hudng tir tinh thi Idn trong vat lieu Cac vat lieu tir ciing thudng cd cau tnic tinh the cd tinh ddi xiing kem hon so vdi cac vat lieu tir mem va chiing cd di hudng tir tinh the rat Idn

Luc khang tir cua vat lieu tir ciing thudng dugc tinh bang cdng thirc:

*Tich nang lu-ong tir cu-c dai: La dai lugng dac trung cho do manh yeu ciia vat

lieu tir, dugc dac trung bdi nang lugng tir cue dai cd the tdn trir trong mdt don vj the tich vat lieu tir Dai lugng nay cd don vi la don vi mat do nang lugng IJ/m^] Tich nang lugng tir cue dai dugc xac dinh tren dudng cong khii tir thugc ve gdc phan tu thir 2 tren dudng cong tir tre, la mdt diem sao cho gia tri ciia tich cam img tir B va tir trudng H la cue dai Vi the, tich nang lugng tir cue dai thudng dugc ky hieu la

{B.H)max- De cd tich nang lugng tir cao, vat lieu can cd lire khang tir Idn va cam ling

tir du cao

*Cam irng tu- du-: Cam ling tir du, thudng ky hieu la B^ hay J^, la cam img tir

cdn du sau khi ngat tir trudng

*Nhiet do Curie: Day la nhiet do ma tai dd vat lieu bi mat tir tinh, trd thanh

chat thuan tir Mgt sd vat lieu tir ciing dugc img dung trong cac nam cham hoat dgng d nhiet do cao nen nd ddi hdi nhiet do Curie rat cao Loai vat lieu tir ciing cd nhiet do Curie cao nhat hien nay la nhdm cac vat lieu tren nen SmCo

7.7.2 Cdc dgc trung vgt lieu tie mem [4,6,7,13,18 ]

Day la vat lieu tir phd bien, de tir hda va khii tir Vat lieu tir mim thudng dugc diing lam vat lieu hoat ddng trong trudng ngoai, vi du nhu loi bien thi, loi nam cham dien, cac loi dan tir

Hinh 1.2 Mpt s6 ung dung cua vdt lieu tu mem trong ky thuat (Cong ty Hitachi)

Tren hinh 1.3 ghi dudng cong tir tri va cac dac trung vat lieu tir mem

Hinh 1.3 Dudng cong tir tre ciia vdt lieu tu mem

*Luc khdng tie: Luc khang tir cua cac vat lieu tir mem nhd hon cd 100 Oe Nhung

vat lieu cd tinh tir mim tdt, tham chi cd lire khang tir rat nhd (tdi co 0,01 Oe)

*Cdm ieng tie bao hda, Bs hay tu dp bdo hoa M^: Vat lieu tir mem thudng cd

tir do bao hda rat cao Loai cd tir do cao nhat la hgp kim FegsCoss cd tir do bao hda

dat tdi 2,34 T

*Dp tie tham ban dau La thdng sd rat quan trgng ndi len tinh tir mem ciia

vat lieu tir mim Do tham tir ban dau dugc dinh nghia bdi cdng thiic:

lim

^ ' H" 0 dll

Vat lieu tir mem cd do tir tham ban dau tir vai tram den vai ngan, cac vat lieu

cd tinh tir mem tdt cd the dat tdi vai chuc ngan, tham chi hang tram ngan Do tir thSm (permeability) la dai lugng dac trung cho kha nang phan irng cua vat lieu tir dudi tac dung cua tir trudng ngoai

*Dp thdm tie cue dgi: Ta biet rang vat lieu sat tir khdng nhirng cd do tir tham

Idn ma cdn cd do tir tham la mdt ham ciia tir trudng ngoai Do tir tham cue dai la mdt thdng sd quan trgng Cd nhirng vat lieu sat tir mem cd do tir tham cue dai rat cao, tdi hang vai tram ngan vi du nhu permalloy, hay hgp kim nano tinh the Finemet

*Tdn hao dong Fucd: Nhu da biet, vat lieu tir mem dugc sir dung trong tir

trudng ngoai, va neu sir dung trong trudng xoay chieu, se sinh ra cac ddng dien Foucault gay mat mat nang lugng va tda nhiet Cdng suat tdn hao Fucd dugc tinh theo cdng thiic:

p _ '^ / •'

^ Foiiedult o

S.-i.p

Trong dd:

Bs' Cam img tir bao hoa ciia loi; d: Do day ciia loi; kf: He so dac tnmg

/ Tan so tir truang xoay chieu; y: Khoi lugng rieng vat lieu; p: Dien tro suat Tir cdng thiic nay ta ly giai dugc viec cac loi bien the tdn Si (FeSi) dugc che tao thanh cac la mdng nham lam giam do day, giam tdn hao ddng xoay Ddng thdi, loi FeSi chi cd the sir dung cho bien the tAn sd thap vi d tin sd cao, tdn hao se rat Idn (do FeSi cd dien trd suat thap), trong khi cac ferit cd the sir dung d cac tdn sd rat cao do chung cd ban chat gdm, cd dien trd suat rat Idn, lam giam tdn hao ddng xoay

*T6n hao tre: Khi vat lieu tir mem dugc sir dung trong tir trudng ngoai, nd se bi tir

hda va tao ra chu trinh tre, va se cd nang lugng bj tdn hao cho viec tir hda vat lieu

*Dgc trung tan so: Khi sii dung d tan sd cang cao, pham chat ciia vat lieu

cang bi suy giam, do dd sir thay ddi cua pham chat theo tan sd la mdt thdng sd rat dang quan tam

*Tiegido: Ve mat ban chat, tir giao la su thay ddi hinh dang vat lieu tir dudi

tac dung cua tir trudng ngoai Viec khu tir giao giiip cho viec tao ra tinh tir mim tdt

Cd nhiing vat lieu cd tir giao bang 0 nhu vat lieu vd djnh hinh nen Co

1.2 Dac tru-ng cau triic va tinh chat cua cac ferit spinen 14,6,13,16,18,25]

7,2.7 Cau true cdc ferit spinen

Cac ferit spinen cd cdng thiic MFe204, trong dd M^"" la cac cation kim loai hda tri 2 nhu Fe^^, Ni^"", Cu^"", Mg^^, Zn^^Co^* Cac ferit cd cau tnic tinh thi spinen Cau tnic nay bao gdm cac nguyen tir oxi gdi gem chac dac lap phuong mat tam va cac cation M ^ va Fe^^ lan lugt chiem cir cac hdc bat dien (O) va tir dien (T+,T-) tao nen tir phan mang oxi

Hinh 1.4 Te bdo mgng cua tinh the ferit spinen

Moi tl bao mang cd 8 phan tii MFe204, trong dd cd 32 nguyen tii oxi, 16 nguyen tir Fe''^ va 8 nguyen tir M^"^, 64 hdc T (T+, T-) va 32 hdc O

Nhu vay, mdi tinh thi spinen cd 96 hdc T va O, trong khi dd chi cd 24 cation, chiem 1/4 sd hdc

NIU 8 cation M^^ chilm cac hdc T, cdn 16 cation Fe^^ chiem cac hdc O thi ferit tuong ling cd cau tnic spinen thuan MlFeFe]04

NIU 8 cation M^^ chilm cac hdc O, 8 cation Fe^* nam hdc O va 8 cdn lai nam hdc T thi spinen tuong img cd cau tnic spinen dao FelMFe]04

NIU 24 cation dugc phan bd mdt each ngau nhien vao ca hdc O va hdc T thi ferit tuong irng cd cau tnic spinen trung gian

B

Hinh 1.6 Cdc hoc trong tu dien vd bdt dien trong ferit spinen

Sir phan bd cac ion kim loai vao cac hdc tii dien hay hdc bat dien phu thugc vao cac yeu td: ban kinh cac ion kim loai, sir phu hgp ve cau hinh dien tir ciia ion kim loai va nang lugng tmh dien cua mang

+ Cau hinh electron ciia ion M^^: Tuy thugc vao cau hinh electron cua ion

M ^ ma cac cation nay cd the chiem d hdc tii dien hay hdc bat dien va vi vay tao nen cau tnic spinen thuan hoac spinen dao Vi du, Zn^^, Cd^^ cd cau hinh dien tir d"',

sd phdi tri thuan Igi la 4, nen chiem chu yeu d hdc tii dien va tao nen ferit cd cau tnic

:2+ ,2+

spinen thuan Cdn Ni va Fe cd cau hinh dien tir tuong img la 3d va 3d , sd phdi tri

thuan Igi la 6, nen chiem hdc bat dien va tao nen ferit cd cau tnic spinen daọ

+ Ban kinh cac cation: Vi hdc T cd kich thude be hon hdc O nen neu ban kinh cua M^^ Idn hon ciia Fê"^ thi M^^ cd xu hudng chiem cac hdc O va ngugc laị

+ Nang lugng tuong tac tinh dien: Cac cation trong mang ludi tinh the ion cd

xu hudng sap xep sao cho tdng nang lugng tuong tac tmh dien la Idn nhat va lire đy tinh dien giira cac cation la be nhat

Phan mang oxi bi bien dang khi cac cation tham nhap vao cac hdc T va hdc Ọ The tich hdc T be hon hdc O nen khi cac cation tham nhap vao hdc T se lam cho khdng gian hdc T tang len bSng each ndi rgng ca 4 ion oxi (gian nd khdng gian tii dien) Sir gian nd nay cd thi xac dinh dugc nhd phuong phap XRD hoac nhieu xa notron De dac trung cho

su gian nd khdng gian tir dien ngudi ta dua vao mgt khai niem ggi la thdng sd oxị Sir dich chuyin cac ion Ố nhu vay se lam tang the tich hdc T va giam the tich hdc O, ket qua la lam cho thi tich hai hdc T va O trong mang ludi gan bang nhaụ

Mdi lien he giira thdng sd oxi (W) va kich thude hdc T (rA), kich thude hdc

O {TQ) dugc bilu dien bang he thiic:

rA=(W-0.25).a-ro rB=(0.625-W).a - ro Trudng hgp mang lap phuong ly tudng thi W = 0.375

A la hang sd mang ludi spinen (A), rA va r^ la ban kinh khdi cau nam trong

khdng gian tii dien va khdng gian bat dien, ro la ban kinh ciia oxị

7.2.2 Tinh chat tie vd dien cua ferit spinen

Do cau tnic cac spinen gdm 2 phan mang, cac mdmen tir d phan mang A va

B phan bd phan song song Dieu nay dugc giai thich nhd sir phu thugc gdc ciia

tuong tac sieu trao đi (tuong tac am): AOB « 125^ AOA ~ 80°, BOB « 90°, do đ tuong tac phan sat tir giira A va B la manh nhit

Trong spinen dao, do ion Fê^ ed mat ca d ca hai phan mang vdi sd lugng nhu nhau nen mdmen tir chi do M^^ quyet dinh

Hinh 1.7 Su sdp xep spin trong cdc ferit spinen đo

Do vay vdi M ISn lugt la Mn^^ Fe^^ Co^^ Ni^^ Cu^^, Zn^* vdi sd dien tir d tuong img la 5, 6, 7, 8, 9, 10, ta lan lugt cd cac ferit vdi mdmen tir tren mdt don vi

cdng thiic tinh ra [IQ lan lugt la 5, 4, 3, 2, 1, 0 Thuc nghiem da khang dinh ket qua

nay (hinh 1.7) Mdt sd thdng sd cua ferit spinen don gian dugc liet ke tren bang 1.1

8,50 8,39 8,38 8,34 8,64 - 8,24 8,36

Mat dp (g/cm ^)

5,00 5,24 5,29 5,38 5,38 4,52 Cac spinen cd kha nang dan dien d nhiet do cao, sir dan dien phu thugc ban chat cac cation, dien tich va sir phan bd cac cation trong cac hdc T va O Vi du trudng hgp Fe304 la chat din dien do Fe^"^ va Fe^^ dugc phan bd trong cac hdc bat dien tiep xiic nhau qua canh do dd kha nang dan dien kha tdt, trong khi dd Mn304

cd cac cation Mn^^ va Mn^* phan bd trong hoc T nen din dien kem hon

Cau hinh electron ciia cac kim loai nhat la sir xen phii cac AOd ciia mdi kim loai khac nhau nen co che din dien cd thi dang lo trdng (LiMn204) hoac dang electron tu do nhu LiV204

8

Kha nang din dien ciia spinen cdn phu thugc vao dieu kien xir ly nhiet va phuong phap dieu che

Theo do dan dien ngudi ta chia spinen ra 3 nhdm:

Nhdm aluminat cd do dan dien nhd nhat, nhdm cromit do dan dien trung binh, nhdm ferit cd do din dien nhd nhat Rieng Fe304 cd do dan dien gan bang do dan dien ciia kim loai

1.2.3 Tinh chdt xiic tdc

Cac vat lieu clu tnic tinh thi spinen da dugc nghien cim va ling dung trong nhilu ITnh vuc: cdng nghiep gdm sir, vat lieu ky thuat nhiet da thu dugc nhung ket qua tdt Trong nhirng nam gin day ngudi ta cdn nghien ciiu sir dung cac spinen nano trong cac ITnh vuc xiic tac cho cac phan irng hda hgc tdng hgp hiru co- hda dlu, xuc tac xir ly mdi trudng, chi tao dien cue, sensor nhay khi

Trong cac cdng trinh [55, 56, 57] cac tac gia tdng hgp va nghien cim hoat tinh xiic tac ciia cac spinen bac 2-3, Zn[FexCr2.x04] trong cac phan ling dehidro hda etylbenzen thanh stiren, ngoai ra cdn mdt sd he spinen dugc nghien cim trong cac phan ling oxi hda hidrocacbon, dehidro hda hidrocacbon, oxidehidro hda hidrocacbon thanh olefin; nghien cuu sir dung spinen trong cac hop xiic tac xir ly khi thai ddng co xang Ben canh dd, cac spinen cdn dugc nghien ciiru che tao ldp phii dien cue catot hoac diing lam dien cue, che tao cac sensor nhay khi hidrocacbon dd la cac spinen: LiMn204, LiMnCo04, Mn2.xCOxNi1.xO4

Viec tdng hgp dugc cac loai vat lieu hat nano, mang mdng nano da md ra kha nang ling dung cang rdng va hieu qua ciia cac loai spinen dac biet trong ITnh vuc xiic tac, dien hda, dien xiic tac

1.3 Tinh chat va irng dung ciia ferit kich thiroc nano [7,8,11,13,18]

Cac spinen ndi chung va ferit spinen ndi rieng dang vat lieu khdi cd nhieu ling dung trong cdng nghiep do chung cd tinh chat qui nhu tinh chat tir, kha nang ben nhiet, kha nang xiic tac Tuy nhien, cac spinen cau tnic nano la nhirng vat lieu mdi, ngudi ta dang nghien ciiu de md rdng kha nang ling dung ciia loai vat lieu nay, dac biet trong cac ITnh vuc vat lieu tir nano, chat ldng tir, xuc tac cac phan irng hda hgc, xu ly mdi trudng v.v

1.3.1 Su Men doi tinh chat tie ciia cdc vgt lieu nano so vdi vgt lieu khoi

Khi giam kich thude ciia cac hat tinh the den cd micro, cac tinh chat vat ly ciia vat lieu van tuan theo cac qui luat nhu trong vat lieu khdi, nhung khi dat den kich thuoc nano thi cac tinh chat bieu hien theo cac qui luat khac thudng vdi nhieu tinh chat vat ly thii vi va cd nhieu img dung trong thuc te, trong dd dae biet la cac

tinh chat tir, xiic tac Cac tinh chat vat ly khac thudng ciia vat lieu nano chu yeu gay ra bdi hai yeu td:

* Kich thude ciia cdc hgt tinh the: Kich thude hat tinh the giam lam cho %

nguyen tir, ion nam tren be mat tang len nhanh va hang sd mang giam xudng Cac ion hay nguyen tir nam tren be mat tuong tac vdi cac ion hay nguyen tir xung quanh hoan toan khac vdi cac nguyen tir nam ben trong, nen vi tri ciia chiing bi thay ddi, dan den cac tinh chit khac bi thay ddi theo

Mat khac, su giam kich thude hat tinh the cdn anh hudng den cap trao ddi: co chi lugng tii ciia tuong tac trao ddi trong cac hat ciia vat lieu tir gay ra sir dinh hudng ciia mdmen tir tren toan bd tinh the, nhung ciing gay ra sir anh hudng den cac hat ben canh ggi la tuong tac cap trao ddi Ddi vdi cac vat lieu khdi, cac hat cd kich thude micro trd len cap trao ddi nhd hon rat nhieu so vdi tuong tac nhiet ddng trong mdi hat Vi vay, tinh chat vT md dugc xac dinh bdi qui luat nhiet ddng vT md trong cac hat Khi kich thude cac hat giam xudng den don vi nano, tuong tac trao ddi cd thi so sanh hoac Idn hon tuong tac nhiet ddng, cac hat trao ddi vdi nhau Trong trudng hgp nay cac hat rieng le mat tinh chat tir rieng cua nd, cau tnic tir tinh va tinh chat mdi dugc tao ra Qui luat khdng che tir tinh khac so vdi vat lieu cd cap hat Idn

* Su bdt giu luang tie: Cac electron bi giam cam trong cac hd the nam trong

cac hat Sir giam cam lugng tir nay tao nen cac tinh chat khac thudng ciia vat lieu nano nhu:

+ Dien trd cua vat lieu nano Idn hon rat nhieu so vdi vat lieu khdi Dieu nay rat

cd Igi ddi vdi cac ferit tir hoat ddng d viing tan sd cao vi giam sir mat mat nang lugng

+ Tuy nhien, khac vdi vat lieu khdi cd dien trd giam nhe khi hoat ddng trong tir trudng cd tan sd cao, dien trd ciia vat lieu nano lai giam manh d dieu kien do (hieu irng tir trd Idn)

+ Mau sac ciia vat lieu dang nano khac dang khdi Do vay cd the tdng hgp cac gdm sieu min, mau sac phong phii

Vdi nhirng dac diem ndi bat, sir ra ddi ciia ITnh vuc vat lieu tir nano tao nen cudc each mang trong ITnh vuc vat lieu tir

7.i.2 Nhitng ung dung vd hudng nghien cieu chinh ve vgt lieu tie nano

Nhiing irng dung va hudng nghien ciiu chinh hien nay vdi cac hat nano tir la:

- Nghien ciiu tdng hgp va kha nang ling dung cua eae hat nano tir trong ITnh virc che tao cac linh kien dien tii sieu nhd, cdn ggi la ky thuat dien tir-spin, sir dung ddng thdi hai thugc tinh dien tich va spin cua dien tii trong ciing mdt linh kien, md

ra tuong lai rdng Idn cho che tao linh kien dien tir, ban din v.v

10

- Nghien ciru che tao cac vat lieu tir hat nano, mang mdng nano trong cdng nghe ghi am, ghi hinh tren cac bang tir, dTa cimg, dTa mem, cac dau dgc, dau ghi, cac thiet bi nghe nhin, cac the tir vdi ldp phu nano cd the tang mat do thdng tin d dTa len rat nhieu lan ma lai giam kich thude cua thiet bi

- Nghien ciiu che tao cac chat ldng tir thdng minh sir dung trong cdng nghe nhan dang va tach te bao, chat dinh vi trong ky thuat chuan doan benh, chat dan thude trong dieu tri benh la nhirng ITnh vuc nghien cuu rat sdi ddng

- Nghien ciiu cac ling dung trong ITnh vuc xiic tac cho tdng hgp hiru co - hda dlu vdi do chgn Igc va hieu suat rat cao, cac xiic tac cho cdng nghe xir ly mdi trudng: xir ly khi, xii ly nude

1.4 Mot s6 phu-OTig phap t6ng hop coban ferit va niken ferit

7.^.7 Tdng hap coban ferit vd niken ferit bdng phuang phdp gdm

KT thuat tdng hgp ferit bing phuong phap gdm da dugc nhieu tac gia nghien ciiu, dl tdng hgp theo phuong phap nay ngudi ta thudng diing cac nguyen lieu dau

la cac oxit: CoO, NiO va Fe203, chiing dugc dinh lugng chinh xac, nghien trdn kT

dk cd sir ddng nhit cao ciia phdi lieu phan img De qua trinh phan ling tdt hon,

ngudi ta ep phdi lieu thanh vien, ap lire ep den hang tram KG/cm Nhiet do nung

1250 - 1300V, tuy thugc thanh phin phdi lieu

Phan ling tao ferit d nhiet do tren 1200°C nhu sau:

CoO + FcjOs = CoFe204 NiO + Fe203 = NiFe204 Trong phan ling tren NiO, CoO cd cau tnic lap phuong, sd phdi tri Ni^^ va O^" deu bang 6 cdn Fe203 gidng AI2O3 cau tnic 2 phan mang, phan mang oxi gdi gem chac dac luc phuong, phan mang Fe ^ chiem 2/3 cac hdc bat dien, cdn lai cac hdc tii dien deu trdng Cac oxit CoO, NiO cd nhiet do ndng chay cao (CoO cd tpc: 1810 °C; NiO cd cd tnc : 1955 °C) va cac spinen CoFe204 va NiFe204 deu cd nhiet do ndng chay cao ~ 2000 °C vi vay phan ling xay ra khi nung hdn hgp cac oxit xay ra chi 0 pha ran Phan irng dien ra khi cac cau tii tiep xiic vdi nhau, tai vi tri tiep xiic, cac cation Ni^"^ va Co^"^ khuech tan tir phia NiO va CoO di vao cac hdc T cua pha Fe203 cdn Fe^* khuech tan theo chieu ngugc lai Ngay khi ldp NiFe204 hoac CoFe204 hinh thanh se la nhirng mam phat trien nen pha mdi NiFe204 hoac CoFe204

De qua trinh phan img thuan Igi, cac oxit phai trdn deu tdi da, sir tiep xiic cac pha vdi be mat Idn vi vay nghien min cac hdn hgp bdt ban dau la yeu td anh hudng Idn den tdc do phan img Su tiep xiic cang tdt khi ep mau vdi cudng do hgp ly (yeu cau khdng qua nen gay sir phan ldp phdi lieu)

Qua trinh chuyen ddng nhiet, sir khuech tan cac cation, sir bien ddi cau tnic tao ra cac khuyet tat mang ludi tai viing tiep xiic trd nen manh d nhiet do cao vi vay vdi phan img pha ran duy tri nhiet do cao la yeu td cd tinh quyet dinh den tdc do phan ling Khi pha spinen va ket tinh tao tinh the hoan chinh, nang lugng ciia he giam xudng, he spinen trd nen ben virng

Pha CoO Co^^

Pha Fe203 Fe^"

Pha spinen CoFe204

Hinh 1.8 Mo td ca che khuech tdn trong phdn dng tgo spinen

Phuong phap gdm truyen thdng da dugc ling dung rat phd bien trong tdng hgp nhieu loai vat lieu [1,3,17,18] La phuong phap don gian, de td chirc san xuat d qui md cdng nghiep nhung la phuong phap tieu tdn nhieu nang lugng nghien, va nhiet nang cho nung phdi lieu d nhiet do cao San pham ket tinh vdi tinh the Idn, de phan ling xay ra hoan toan thudng phai nghien- nung nhieu lan

7.-^.2 Tong hgp coban ferit vd niken ferit bang phuang phdp hda hpc udt

a Tong hgp coban ferit vd niken ferd bdng phucrng phdp dong ket tua

Day la mdt trong nhirng phuong phap dang dugc sir dung kha phd bien de tdng hgp vat lieu mdi ndi chung, va tdng hgp cac vat lieu kich thude nano met ndi rieng Nguyen tac cua phuong phap nay la tiln hanh kit tiia ddng thdi (dung ti le hgp thirc san pham can tdng hgp) dudi dang hidroxyt hoac mudi khdng tan nhu: oxalat, cacbonat [5, 6,7,13,] cd the phan img chuyen thanh san pham trong qua trinh nung

Vi tich sd tan ciia cac ket tiia khdng gidng nhau, kha nang tao phirc giQ-a cac cation kim loai va anion lam ket tiia cang khdng gidng nhau do dd de khdng che thanh phan san pham nhu mong mudn ddi hdi cd nhimg tinh toan va thuc nghiem vdi do chinh xac cao

Mat khac ket tiia cua cac kim loai khac nhau bat dau va kit thiic d cac gia trj

pH khac nhau nen trat tu trdn lan cac chat khi lam ket tiia cd anh hudng idn din sir

12

khuech tan cac chat ket tiia Vi du, khi ddng ket tiia dudi dang hidroxyt coban (II)

va hidrotxyt sat (111) neu ta diing dung dich NaOH + amoniac dd vao hdn hgp dung dich mudi ciia chiing thi trudc het xay ra sir ket tiia ciia hidroxyt sat 111, den khi bat dau ket tua hidroxyt coban thi lugng sat trong dung dich khdng cdn phii hgp vdi ti

le 1/2 nhu mong mudn de tao pha spinen

De thuc hien ket tua ddng thdi bao dam cho sir tiep xiic tdt cac chat phan ling chiing ta phai thuc hien qui trinh ngugc lai, nghTa la dd hdn hgp dung dich mudi kim loai vao dung dich NaOH+ amoniac

Nhieu cdng trinh nghien ciiru mdi day ve ITnh vuc ferit spinen cap hat nano da dung phuong phap ddng ket tiia de tdng hgp [5,6,11,26,29]

Cac ket qua khao sat cho thay nhiet do phan ling tao ra pha spinen ciia phuong phap ddng ket tua thap hon kha nhieu so vdi phuong phap gdm truyen thdng Cac ket qua nghien ciru cua chiing tdi da cdng bd cGng kha thdng nhat vdi cac cdng trinh da nghien ciru trudc day Phan ling tao ferit coban va ferit niken thudng d khoang 700°C- 800°C da cho tinh thi kha hoan thien, d p hat tir 15- 30

nm Dieu dd dugc giai thich, qua trinh ddng ket tiia de tao cac prescusor ddng ket tiia cho phep trdn lan cac chat phan irng d qui md phan tii, nguyen tu vdi kich thuoc cac hat cd hat keo vai chuc nm do dd chiing de phan ling de tao ferit khi nung d nhiet do tren 700°C

Co che hinh thanh tien chat ciia ket tiia hidroxyt tir cac mudi kim loai khi ddng ket tua, ngay trong qua trinh say ~ 110°C da hinh thanh cac lien ket kim loai-oxi- kim loai dau tien theo co che dugc de nghi nhu sau:

OH OH

I I

Ni(0H)2 + 2Fe(OH)3 '^°"^' > H-[0- Fe-0- Ni-0- Fe - 0]n-H ^°°°'' >

NiFe204 (ferit spinen);

OH OH

I I

Co(OH)2 + 2Fe(OH)3 '^°°'' > H-[0- Fe-0- Ni-0- Fe - 0]n-H '''"'' >

CoFe204 (ferit spinen);

Tir cac tien chat cd cac lien ket ban dlu, khi nung ngay d nhiet do ~ 700°C

da phan img tao ra cac tinh the spinen NiFe204 hoac CoFe204 cap hat nano

Vdi cac tien chat la cac mudi it tan oxalat, cacbonat hinh thanh trong qua trinh ddng ket tua d dieu kien dung dich kha loang, tien hanh ddng thdi nen cd sir bao phii, lien ket ciia cac phan tu, khi nung, chiing phan huy tao ra pha trung gian cd

be mat mdi sinh, khuyet tat nhieu nen phan img dien ra theo co chi pha rin cd mat

pha khi, lam giam nhiet do phan img xudng kha nhieu so vdi phan img pha ran don thuan

b Tong hap coban ferit vd niken ferit bdng phucrng phdp sol-gelfl 7,20,30,35,43]

Qua trinh sol-gel hda gdm 2 giai doan:

Giai doan dau tien la su thiiy phan va ddng tu tien chat de hinh thanh sol (sol:

la dang huyen phii ddng nhat cua cac hat oxit cd kich thude sieu nhd trong chat ldng) Tien chat de tdng hgp sol nay la cac hgp chat hoat dgng ciia kim loai hay a kim nhu alkoxide cua silic, nhdm, titan Giai doan nay cd the dieu khien bang sir thay ddi pH, nhiet do, thdi gian phan ling, xiic tac, ndng do tac nhan, ti le H2O

Giai doan 2: Cac hat sol cd the Idn len va ddng tu hinh thanh nen mang polime lien tuc hay gel chira day cac bay hat dung mdi

De thu dugc san pham cudi ciing ngudi ta tien hanh lam khd gel Gel cd the nung ndng de loai trir cac phan tir dung mdi (gay ap lire len mao quan va sup dd mang gel), san pham thu dugc ggi la xerogel

Hoac gel cd the say khd sieu tdi han cho phep loai bd cac phan tii dung mdi

va gifl- nguyen cau tnic mang gel San pham cudi ciing thu dugc la arogel

So vdi phuong phap tdng hgp vat lieu truyen thdng cho chat lugng san phim chua cao, khd dieu khien ti le cac chat trong san pham cudi ciing kich thude hat thu dugc Idn, can nhiet do tdng hgp cao Phuong phap sol-gel cd nhieu thuan Igi hon nhu:

- Cho san pham tinh khiet: vi qua trinh tdng hgp sir dung cac loai hda chat 0 dang min nen cd the ap dung kT thuat tinh che nhu: Chung cat, thang hoa, sac ky va ket tinh lai

- Tinh ddng nhat ciia san pham cao: Do sir phan tan cua cac chat ban dau d mirc

do phan tir nen ti le hda hgc ciia san pham dat dugc nhu mong mudn

- De dieu chinh cac tinh chat ciia san pham cudi ciing thdng qua sir thay ddi cac thdng sd nhu nhiet do, ndng do, pH

- Nhiet do tdng hgp vat lieu thap: Vi san pham gel bdt ddng nhat va kich thude hat nhd nen sir Idn len cua tinh thi cd thi thu dugc d nhiet do thap

Vi hau het cac alkoxide deu khdng hda tan trong nude nen sir thiiy phan ciia cac alkoxide chi xay ra khi them nude vao dung dich khdng phai la nude cua cac alkoxide (nhu etanol) Sir thiiy phan ciia cac alkoxide xay ra thuan Igi khi tinh Nucleophin (tinh ai lire) ciia cac tac nhan cang Idn

Sau khi thuy phan se thu dugc mdt monome hoat ddng, su ddng tu tilp theo xay ra theo mgt trong ba co che sau:

14

- Sir oxo hda: Phan img giira 2 phan tOr M-OH hinh thanh mdt cau ndi oxo

va tach ra mgt phan tir nude:

M-OH + M-OH -^ M(M-OH)M-OH M(M-OH)M-OH -^ M-O-M-(HOH) M-O-M-(HOH) -^ M-O-M + H2O

Su alool hda: Phan ling giira M-OH va alkoxide ket qua hinh thanh mdt khdi "ol" san phim nay tiep theo dd chiu sir chuyen rdi proton de hinh thanh nhdm ROH dl tach hon

M-OH + M-OR -> M(M-OH)M-OR

M(M-OH)M-OR -^ M-O-M-(HOR)

M-O-M-(HOR) -> M-O-M + ROH Sir ol hda: khi ion kim loai trung tam chua dat den sd phdi tri bao hda (khi dugc phdi tri bdi cac phan tii nude hoac dung mdi), mdt cau ndi hidroxo cd the dugc hinh thanh

M-OH + M - ( H O R ) ^ M(M-OH)M + ROH

va M-OH + M-(HOH) -> M(M-OH)M + H2O

Vi du: sir thuy phan va ddng tu ciia TEOS: Si(OC2H5)4 xay ra nhu sau:

I

Su loai nude hoac ruou de hinh thanh cac cau lien ket mdi cua oxi va kim loai

-Si-OR + HOH ^ -Si-OH + ROH

I X I

I I X I I

-Si-H + -Si-OH ^ - S i - O - S i - + HOH

I I \ I I

Cac ket qua tdng hgp ferit bang phuong phap sol- gel sir dung cac alcoxide silic (TEOS) da kha thanh cdng tao nen cac hat ferit nano phan tan tren nen Si02, la khdi lien tuc khdng cd tir tinh Kha nhieu tac gia da di theo hudng nay de tdng hgp cac ferit vdi thanh phan khac nhau [30,43,48]

c Phuang phdp dong tgo phuc [ 5,6,11,17,29,36]

Nguyen tac ciia phuong phap nay la cho cac mudi kim loai tao phirc ciing nhau vdi phdi tii trong dung dich Sau dd tien hanh phan huy nhiet phirc chat cd thanh phan hgp thirc vdi ferit mudn dieu che Phuong phap nay dat dugc sir phan bd

ly tudng cac cau tir trong he phan img vi rang trong mang ludi tinh the ciia phirc ran

dd cd sir phan bd hoan toan cd trat tu ciia cac ion

Uu diem ciia phuong phap ddng tao phirc: Trong hdn hgp ban dau dua vao nung (hdn hgp cac phirc chat) da bao dam ti le hgp thirc ciia cac cau tir dung nhu trotig vat lieu mong mudn

Nhugc diem: Tim cac phiic chat da nhan khdng phai de dang va cdng viec tdng hgp phiic chat tuong ddi phiic tap ddi hdi nhieu phdi tir dat tien Do dd vdi cac vat lieu ddi hdi phai bao dam chinh xac ti le hgp thiic thi mdi can thiet tdng hgp theo phuong phap nay Vi du, de tdng hgp ferit niken chiing ta cd the bat dau tir phiic chat cd cdng thirc Ni3Fe6(CH3COO)i7030H.12C5H5N Dieu ly thii la phiic nay

cd the tinh che thanh dang nguyen chat bang each ket tinh lai trong pyridin

1.5 Mpt so kit qud nghien cuu tdng hap ferit cap hgt nano

* Lee, Seung Wha va cac cdng sir [35] da tdng hgp Zn-Co-ferit bang phuong

phap sol-gel Tac gia da xac dinh dugc rang, hang sd mang tang khi ham lugng Zn^"" tang MIU vat lieu cd cdng thiic Coo,9Zno,iFe204 dugc nung d 673K, 523K, 573K deu cd cau tnic ferit spinen Tuy nhien, mau dugc nung d 673K the hien tinh ferit tir, cdn mau nung d 573K, 523K the hien ddng thdi tinh sieu thuan tir va ferit tir, do bao hda tir va lire khang tir Idn nhat tuong irng 81,1 emu/g va 132,8 Oe

* Hong Wen Wang va cac cdng sir [41] da cdng bd cac ket qua nghien curu tdng hgp tinh the Ni-Zn-ferit cap hat nano bang phuong phap thuy nhiet Ket qua nhieu xa XRD cho thay mau vat lieu Nio,5Zno,5Fe204 cd cau tnic ferit spinen khi ngay khi nung d 120°C trong Ih Kich thude trung binh cua hat tinh the ferit spinen

la 15^20nm

* Updhyay, Chandan va cac cdng su [45] da tdng hgp Nii.xZnxFe204 (x=0,0, 0,25, 0,5, 0,75) bang phuong phap ddng ket tiia va thuy nhiet Mau vat lieu cd tnic ferit spinen, kich thude hat tinh the trung binh tir 12nm Sir phan bd ciia cac cation trong tinh the khdng chi phu thude vao ham lugng Zn^"^, kich thude hat ma cdn phu thugc vao giai doan ddng ket tiia Cac mau vat lieu ma cac tac gia nay thu dugc ti le

Fe ^ chiem cii cac hdc tii dien nhieu hon so vdi vat lieu khdi

* Elsa E Sileo va eae cdng sir [36] da cdng bd eae ket qua nghien ciiu tdng hgp Nii.x ZnxFe204 (x = 0,0; 0,2; 0,4; 0,5; 0,7) bang phuong phap tien chat citrat Gel thu dugc khi trdn cac mudi natri ciia Ni(ll), Zn(ll), Fe(lll) va axit citric dugc nung d 200°C va sau dd thieu ket d 1000°C Ket qua gian dd nhilu xa tia X cho thay: sau khi nung gel thu dugc pha don tinh the, cap hat nano, qua trinh thieu ket

lam tang kich thude hat Ket qua nghien cim cho thay hang sd mang tang khi ham

lugng Zn ^"^ tang

^ 16

* Bang phuong phap micelle ngugc Shannon A.Morrison va cac cdng sir da tdng hgp dugc Ni-Zn-ferit d nhiet do thudng ma khdng ddi hdi them mdt qua trinh thieu ket nao khac He chat hoat ddng be mat dugc sir dung de tdng hgp cac hat nano theo micelle ngugc la natri dioctyl sulfosuccinate (AOT) dugc pha trong dung mdi 2,2,4- trimetyl pentan (isooctan) Kich thude hat thu dugc tir 6,2 ^ 6,8nm, tir tinh khdng cao, do bao hda ve tir tinh d 300K la 25,9 emu/g

* H.H.Nien va cac cdng sir [47] da cdng bd cac ket qua nghien ciiu tdng hgp Mn-Zn-ferit bang phuong phap nghien trdn co hgc, nung: Mn-Zn-ferit tren nen Sn02 va Ti02 dugc chuan bi theo ky thuat ceramic thdng thudng Cac bdt MnC03, ZnO va nghien trong 12 gid tren may nghien Bdt san pham cudi ciing dugc nung trong khdng khi d 900°C trong 3 gid Sau khi nung bdt dugc nghien lai Trong sudt qua trinh nghiin udt cac bdt Sn02, Ti02, CaO va Si02 ndng dugc them vao Sau dd bdt dugc ep vien (dang dTa, dudng kinh 10,7mm cao 2mm) trudc khi nung

* O.Pena va cac cdng sir [49] da cdngbd cac ket qua nghien ciiu dieu che NiMn2.xC0x04 spinen bang phuong phap ceramic thdng thudng Tir cac chat dau la C03O4, NiO, CuO va MnO kich cd d 1050°C trong 1 gid Vat lieu sau dd dugc nghien lai dugc ep va thieu ket trong 2 gid vdi tdc do gia nhiet la 50°C/phiit va lam lanh trong khdng khi vdi tdc do 20°C/phut vdi hdn hgp dau img vdi cac gia tri x khac nhau Vdi gia tri x thay ddi tir 0,2; 0,5 den 1,5, cac hgp chat thu dugc deu la cd cau tnic spinen Thdng sd mang ciia san pham NiMn2-xCOx04 cd tang len chut it theo sir tang ham lugng Co

* Souad Ammar va cac cdng sir [29] da cdngbd cac ket qua nghien ciiu tdng hgp CoFe204 bang phuong phap thuy phan trong rugu da chirc Cac chat dau dugc diing la mudi FeCl3 va Co(CH3COO)2.4H20 theo ti le 2:1 dugc them vao 250ml cua 1,2 - propandiol Cac phan tir nano CoFe204 thu dugc cd dudng kinh 5,5 nm Hdn hgp dugc dun ndng cd diem sdi 160°C va tdc do 6°C/phiit Pha ferit dugc hinh thanh thdng qua pha trung gian Hdn hgp dugc it nhat khuay trdn trong 5 gid den khi san

pham cudi ciing la pha ran tinh khiet Sau khi dk ngudi den nhiet do phdng, cac

phan tii dugc tach bang phuong phap Iy tam, nia bang etylenglyeol va axeton va dugc lam khd trong khdng khi d 50°C Sau dd dugc nung d 327''C Chup gian dd nhieu xa tia X xac dinh CoFe204 la don pha, thdng sd mang a = 8,390 A° Phan tich hoa hgc va phd tia X chi ra pha nay giau ion Fe (111) vdi lugng Co it hon 5% Cac thdng sd tir tinh do dugc do bao hda tir 13 - 15 emu/g; lire khang tir 13,2 - 14,5 Oe;

do tir du 0,36-0,38 emu/g

* A S.Albuquerque va cac cdng sir [22] tdng hgp niken ferit NiFe204 bing phan irng ddng ket tiia Tiep theo, da xac dinh cau true va kich thude san phim bing

phuong phap nhieu xa tia X, xac dinh tir tinh cua hat bang phuong phap tir ke mlu rung Bdt niken ferit dugc tdng hgp bang each hoa tan sat va niken nitrat trong nude cat vdi thanh phan moi diing hgp thirc Sau 1 gid khuay, them NaOH (2,5 M) vao dung dich, san pham ket tiia sau dd dugc nia bang nude cat va etanol Bdt min nhan dugc sau qua trinh lam khd d 70°C trong 20 gid Cac mau vdi kich cd phan tir trung binh khac nhau dugc tao ra bang each nung tir 300°C tdi 600°C trong 2 gid d khdng khi Phan tich nhieu xa tia X cac mau bdt cd dudng kinh trung binh la 8 - 15 nm vdi cac mau nung d 300, 400, 500 va 600°C Phep do tir ke mau rung chi ra ban chat tir khac nhau lien quan den tinh the vat lieu Cac mau cd nm cd do bao hda tir 5 ~ 24 emu/g d 27°C va tir 1 6 - 2 8 emu/g d -268,8°C Mlu nung 400°C ed lire khang tir

168 Oe d 27°C, mlu nung 300V cd lire khang tir 9450e d -268,8°C

*C) trong nude viec nghien cuu ve vat lieu tir nano spinen chua nhieu, nhat la cac nghien ciiu mdt each he thdng ve phuong phap tdng hgp loai vat lieu nay Cac cdng trinh

da dugc cdng bd ciia nhdm nghien ciiu trung tam KHVL thugc khoa Vat ly Trudng DHKHTN- DHQGHN, tmng tam KHVL Dai hgc BKHN va Vien KHCNVN ehu ylu nghien ciiu cac ferit nano chiia dit hiem, cac peropkite vi vay viec nghien cim tdng hgp cac ferit spinen cua coban va niken la mdt hudng nghien cuu tiem nang, vira ed y nghTa khoa hgc vira cd y nghTa thuc tien trong giai doan hien nay va nhimg nam tiep theo

1.6 Muc tieu va noi dung nghien ciru ciia de tai

Muc tieu: Nghien eiiu tdng hgp vat lieu nano ferit MFe204vdi (M la Ni, Co)

bang phuong phap hoa hgc udt, khao sat cac yeu td anh hudng den qua trinh tdng hgp va tinh chat ciia san pham thu dugc, xay dung qui trinh tdng hgp loai vat lieu nay qui md phdng thi nghiem

Npi dung nghien cieu:

1 Tdng hgp ferit ciia Ni, Co tir cac cac mudi eiia chiing bang mdt sd phuong phap hoa hgc: ddng ket tiia, sol-gel

2 Nghien ciiu dieu kien che tao ferit kich thude hat nanomet, khao sat cac dac trung cau tnic cua san pham bang cac phuong phap vat ly hien dai DTA-TG, XRD, SEM, TEM,

3 Khao sat tinh chat tir ciia san pham thu dugc bang thiet bi tir ke mau rung VSM

4 Xay dung qui trinh tdng hgp niken ferit va coban ferit cap hat nano d qui

md phdng thi nghiem

5 Tham dd kha nang irng dung cua san pham

18

PHAN THU* II: THlTC NGHIEM

2.1 Hoa chat, dung cu va thiet bi

2.7.7 Hod chdt

Cac hoa chat dugc sir dung trong nghien ciiu la loai tinh khiet phan tich cua Merck (Diic), Trung Qudc va Phap Cu the nhu sau:

- Ni(N03)2.6H20, Co(N03)2.6H20 loai PA cua Merck (Diic)

- Fe(N03)3.9H20 loai PA cua Merck (Dire)

- Ethanol; 1,2 - Propandiol loai PA ciia Merck (Dire)

- HNO3 loai PA dac cua Merck (Diic)

- Amoniac dac loai PA cua Merck (Diic)

- NaOH ran loai tinh khiet PA cua Trung Qudc

- Tetraethoxysilane (TEOS) ciia Merck (Diie)

- Cac loai thude thii, chi thi phan tich cua Dire, Phap, Trung Qudc

2.7.2 Dung cu vd thiet bi

* Dung cu

- Cac binh dinh miic cac loai

- Cdc thuy tinh, binh ndn, doa thuy tinh

- Buret, pipet cac loai va dng ly tam

- Cdi ma nao

* Thilt bj

- May ly tam Hettich EBA 8 cua Prolabo (Phap)

- Can phan tich (± 0,000Ig) Mettler Toledo (Thuy ST)

- May khuay tir gia nhiet Veia ciia Cole Parmer Instrument Company (My)

- Til say chan khdng Labtech cua Han Qudc (cd dieu khien nhiet do)

- Ld nung (cd dieu khien nhiet do) - Diic

- May ep mau 300kN ciia Italia

- Cac he thiet bj nghien eiiu cau tnic va tinh chat tir ciia vat lieu

2.2 Cac phu-ong phap dirp-c sir dung de xac djnh dac tinh ciia vat heu dieu che dirge

2.2.7 Phuang phdp ghi gian do nhieu xg tia X

Cac mau san pham dugc ghi gian dd nhieu xa tia X (Gian dd XRD) tren may SIEMENS D5005 cua Dire tai Trung tam Hoa hgc vat lieu, Khoa Hoa hge - Trudng DHKHTN- DHQGHN Cac che do ghi gian dd nhieu xa tia X nhu sau:

+ Gdc quay 26 tir 20 H- 80°

+ Tdc do 0,037giay, 40 kV- 40 mA

+ Andt Cu, Xcu (KJ = 1,54056 A

+ Kieh thude hat dugc tinh toan theo phuong trinh Scherre

d = K.X/B.cosO vdi d- kich thude hat tinh the

B- FWHM- be rdng tai V2 chieu cao ciia pic

e- Gdc Bragg; 20/2

K = 0,89

a = dhki (h^ + k^ + 1^)'^^; h = 3; k = I = 1

2.2.2 Phuang phdp phan tich nhiet

Cac mau san pham dugc ghi gian dd phan tich nhiet tren may Labsys TG/DSC SET ARAM - cua Phap - tai Trung tam Hoa vat lieu, Khoa Hoa - Trudng Dai hgc Khoa hgc tu nhien Cac che do ghi gian dd phan tich nhiet nhu sau:

+ Tdc do ddt ndng 10° C/phut

+ Nang nhiet do tir 25°C tdi 1200°C

+ Mdi trudng khdng khi

2.2.3 Phuang phdp kinh hien vi dien tie

a Cac mau san pham dugc chup anh SEM vdi thiet bi va che do chup nhu sau: + Kinh hiln vi dien tir quel S- 4800, sd hieu HI - 9022- 0003

+ Kilu anh JPG

+ Dien thi tir 0 H- 2000V

+ Do phdng dai tir 30 ^ 120000 lln

+ Khoang each lam viec: 2400|im

+ Ddng phat ra: 12900 nA

+ Khi quyen chan khdng

b Cac mau san pham dugc chup anh TEM (JEOL 1010 - Nhat Ban) va tai Phdng thi nghiem Hda hgc Polime trudng dai hgc OSAKA - Nhat Ban vdi ehe do

20

chup nhu sau: Do phan giai: 5 = 3 A°, do phan giai x50- x600.000

2.2.4 Phuang phdp xdc dinh tie tinh vgt lieu bdng thiet bf tie ke mdu rung

He do VSM tai phdng thi nghiem tir va sieu dan thugc Vien Khoa hgc Vat lieu - Vien Khoa hgc va Cdng nghe Viet Nam va trung tam khoa hgc vat lieu - Khoa Vat ly - Trudng DHKHTN-DHQGHN He do nay cd cac tinh nang nhu sau:

+ Cd kha nang do tir do phu thugc nhiet do va phu thude vao tir trudng ngoai vdi do nhay la ~ lO""* emu, tir trudng cue dai len den 13kOe, dai nhiet do do tir 77 K din 1000 K

+ He cd kha nang do tir do phu thude nhiet do va phu thugc tir trudng ngoai vdi do nhay lO""* emu

+ Tir trudng cue dai la 13kOe

+ Dai nhiet do do tir 77 ^ lOOOK

+ Cudng do tir trudng 1 T

PHAN THir III: KET QUA VA THAO LUAN

3.1 Tong hgp niken ferit (NiFe204) cap hat nano bang phirong phap dong ket tiia

Cac hoa chat sir dung trong nghien eiiu la loai tinh khiet phan tich: Ni(N03)2.6H20, Fe(N03)3.9H20, 1,2-propandiol, etanol, NH4OH, NaOH cua hang Merck (CHLB Dire)

D I dieu che NiFe204 bang phuong phap ddng ket tua, dung dich ciia cac cation Ni^^ va Fe^^ vdi ti le 1/2 (ndng do Ni^^ tir 10"^M din 5.10"^M, ndng do tuong ling ciia Fe^^ tir 2.10'^M den lO'^M) da dugc chuan bi Qua trinh ddng ket tiia dugc tiln hanh trong dung mdi hdn hgp rugu - nude pH cua dung dich ddng ket tua dugc dilu ehinh bing hdn hgp NaOH + NH4OH sao cho sau khi ket thiic phan ling dat 9.0 ^ 9.5 Trong qua trinh ddng kit tiia, nhiet do ciia dung dich dugc duy tri d 60°C trong dilu kien khuay manh lien tue trong thdi gian 45 phiit

Sau phan ling, ket tiia dugc tach bang li tam tren may Hettic (CHLB Dire), nia 2^3 lan bang nude cat va axeton (mau dat trung tinh), say trong tii say chan khdng Labtech (Han Qudc) d 80°C trong 24h, nung trong Id nung Nabertherm (CHLB Dire) d 500 ^ 1000°C vdi thdi gian luu 0,5 H- 6h Gian dd XRD cua cac mlu niken ferit dugc ghi tren may D8 Advance Bruker ciia CHLB Dire, vdi gdc 29 tir 20

^ 80°, tdc do 0,03°c/s, andt Cu, XQU ( K J = 1,54056A Kich thude hat trung binh

(nm) eiia cac tinh the niken ferit dugc tinh theo phuong trinh Scherrer

5.7.7 Khdo sdt dnh hudng cdapH dung dich den kich thude hgt

Qua trinh thi nghiem dugc tien hanh vdi dieu kien la:

- Ndng do eua cac chit dlu: Ni^^ la 0.025M, Fe^^ la 0.05M

- Nhiet do dung dich: 60°C

- 1,2 propandiol vdi ti le the tich so vdi dung dich chat dau bang 1/10

- Thdi gian phan ling: 45 phiit

- Dieu kien tach va rira ket tiia: nia bang nude cat va axeton

- Dieu kien say: 24h d nhiet do 80°C trong tii say chan khdng

- Dieu kien nung: tdc do nang nhiet 10°C/phiit, duy tri 0 700°C trong thdi gian 2h, sau dd lam ngudi mau bang each ngat Id va mau ngudi den nhiet do phdng

- Gia tri pH ciia dung dich sau ket tua dugc duy tri: 8,5; 9,0; 9,5; 10,0; 11,0; dieu chinh pH bang dung dich hdn hgp NH3 + NaOH

* Ket qua nghien ciiu cau tnic pha tinh the bang nhieu xa tia X

22

20 50 60

2 - T h © t a - S c a I

Hinh 3.1 Gian do nhieu xg tia X cua cdc mdu Z),

Ket qua chup gian dd nhieu xa tia X (hinh 3.1) cho thay pha tinh the cua mau thu dugc don pha spinen, kich thude hat dugc tinh bang phuong trinh Scherrer thu dugc trong khoang 15 - 21nm

3.1 Sic phu thuoc cua kich thude hgt niken ferit vdo gid tri pH dung dich

Man

pH

Kich thude hatTB

theo Seherrer(nm)

Hieu suat dieu che

tinh theo Ni^^, %

D, 8,97 21,96

98,5

D2

10,14 19,15

96,2

D3

11,36 18,22

95,1

D4

11,90 16,71

94,3

D5

>14 15,7

93,2

Nhu vay kich thude hat phu thugc vao pH dung dich ddng ket tua, khi pH cao thi kich thude trung binh hat giam xudng, do tdc do thiiy phan cac mudi tang, sir tao mam tinh the tang nhanh nhung qua trinh phat trien cac mam tinh the khdng kip lam tang kieh thude hat tuy vay, neu ket tua d pH cao sir dung dung dich NaOH hoac NH3 se lam giam hieu suat thu san pham do mat mat d khau lam sach do dd chiing tdi lira chgn pH cudi qua trinh ket tiia tir 9,0 - 9,5 de thue hien cac nghien cuu sau nay

* Chup anh SEM mau cho thay kich thuoc hat tuong ddi phii hgp vdi phuong phap tinh toan theo phuong trinh Scherrer khoang 20nm

Hinh 3.2 Anh SEM cua mdu sdn phdm Hinh 3.3 Ket qud ghi vong tic tre cua niken ferit duac ddng kit tua dpH cuoi mdu sdn phdm niken ferit duac diiu chi a

bdng 9.0 pH cuoi bdng 9.0

* Kit qua khao sat tir tinh bing ghi vdng tir tri tren thiet bi tir ke mlu rung

cho thiy, vdi mlu tdng hgp pH = 9 cho tir tinh tdt, do bao hda tir kha cao, thude nhdm tir vat lieu tir mem

Tir kit qua khao sat d tren chiing tdi lira chgn pH dung dich ddng ket tua sau khi ket thue phan ling trong khoang 9,0 - 9,5

i.7.2 Khdo sdt dnh hudng cua nong dp dung dich den kich thude hgt

Trong thi nghiem nay, cac dieu kien dugc cd dinh nhu d tren, ehiing tdi chi

2.10"^ -^lO'^M, kit tua sau khi ly tam, nia, sly khd dugc nung d 700°C Sau dd mau san phim dugc ghi gian dd XRD va do tir tinh Kit qua thuc nghiem chi ra d bang 3.2 va cac hinh 3.4

Bdng 3.2 Suphu thugc cua kich thude hgt NiFe204 vdo nong dp cation

Ndng do

cac chat

dau

Ni(N03)2, (M) Fe(N03)3, (M) Kieh thude hat nm

Hieu suat thu hdi (%)

10-^

2 10"^

18,7 92,12

1,5.10"^

3 10-^

18,5 94,3

2 10"^

4 10"^

18,4 96,2

2,5.10"^

5 10"^

17,9 97,5

4 10'^

8 10"^

21,2 97,4

5 10"^ 10-^ 23,7 97.6

Nhin vao kit qua trong bang 3.2 va hinh 3.4 thay rang kieh thude hat ferit phu thugc ndng do

24

Ni(N0i)2 va Fe(NOdi khdc nhau

Khi ndng do nhd hon 2,5.10'^M, kich thude tinh the phu thude vao ndng do khdng Idn, do dung dich ket tiia kha loang nen kha nang phat trien tinh the cham Theo thuc nghiem kieh thude tinh the nhd nhat khi sir dung ndng do dung dich Ni^"" khoang 2,5.10"^M va Fe^* khoang 5.10"^M Khi ndng do tang len, kha nang phat trien tinh the thuan Igi nen kich thude hat tang rd ret Chiing tdi chgn cac ndng

do Ni^^ 2,5.10"^M va Fe^"^ 5.10"^M de thuc hien cac nghien ciiu tiep theo

J-TMI* ' SOM

Hinh 3.5 Gian do XRD (a) vd dudng cong tu tri (b) ciia mdu NiFe204 long

hap a nong dp Ni^^ 2,5.10'^Mvd Fe^" 5.10'^M

Tir ket qua thuc nghiem cho thay kich thude hat niken ferit dieu ehe dugc img vdi ndng do dung dich cac chat dau Ni^"^ 2,5.10'^M va Fe^^ 5.10"^M, vdi khoang ndng do nay cho san pham sau nung d 700°C d dang tinh thi don pha spinen NiFe204, kich thude khoang 17 nm theo Scherrer

Ket qua ghi tir ke mau rung VMS cho thay day la ferit cd tir tinh manh, lire khang tir He = 160 Oe, do tir du Mr = 14 emu/g, do bao hoa tir kha cao Ms = 48 emu/g, la ferit tir mem, ket qua nay cang tuong duong vdi cac cac kit qua cua mgt

sd cdng trinh da cdng bd tren tap chi nude ngoai

3.1.3 Khdo sdt dnh hudng cua nhiet dp kit tiia vd thdi gian khuay

Qua trinh thuc nghiem cho thay nhiet do duy tri trong qua trinh ket tua va thdi gian khuly anh hudng tdi kieh thude hat niken ferit Trong thi nghiem nay chung tdi nghien cuu cac mau ddng ket tiia d cac nhiet do phdng, 45 C, 60 C, 75 C

va 90°C, thdi gian khuly tir 30 phiit, 45 phiit, 60 phiit, 75 phiit Cac dilu kien thi nghiem khac dugc cd dinh nhu da tiln hanh d tren Ket qua thuc nghiem xac dinh kich thude tinh thi ferit thu dugc neu trong bang 3.4, hinh 3.6 khi ddng ket tiia d nhiet do tir

30 - 45°C thi kieh thude hat NiFe204 Idn hon 23 nm, nlu duy tri nhiet do 60 - 90°C thi kich thude thay ddi khdng dang kl nen chiing tdi chgn nhiet do tien hanh ket tiia d nhiet do d 60°C

Bang 3.4 Anh hudng cua nhiit dp dung dich dong kit tiia din

kich thude hgt NiFe204

Nhiet do dung dich khi ket tiia, °C

Kieh thude hat trung binh, nm

Thdi gian khuay (phut)

Kieh thude hat trung binh, nm

30 23,4

15 22,62

45 23,2

30 21,44

60 18,6

45 18,8

75 18,09

60 23,93

90 17,8

75 23,62

Hinh 3.6 la gian dd XRD cac mlu san pham NiFe204 sau nung 700 C dugc tiln hanh ddng kit tua d nhiet do 30°C va d 60°C Mlu kit tiia d nhiet do 60°C khi nung kit tinh tdt, kich thude hat khoang 18 nm

Vl thdi gian khuly trudc khi tach bang li tam cho thay, thdi gian khuay khoang 45 phiit cho kich thude hat san pham nhd nhat, hinh 3.7 la gian dd XRD eiia cac mlu ferit da nung 700°C/lh, vdi thdi gian khuay khac nhau

Hinh 3.6 Gidn do XRD mdu NiFe204 Hinh 3.7 Gidn do XRD cdc mdu NiFe204 v&i thai ddng kit tua o nhiet do 60 "C vd 30"C gian khudy khdc nhau Mi:15phut, M2: 30 phutMh

45 phut, M4: 60 phut

26

Nhu vay ket qua khao sat anh hudng cua nhiet do va thdi gian khuay cho thay neu giir nhiet do dung dich phan ling khoang 60°C, thdi gian khuay khoang 45 phiit se cho kich thuoc tinh the spinen nhd nhat, don pha

Bdng 3.5 Thong so cdu true tinh the vd tu tinh cua NiFe204 nano vdi thdi

gian khudy khdc nhau

26 (dp)

35,712 35,731 35,698 35,710 35,712

d

(A)

2,513 2,512 2,510 2,510 2,510

kich thude hgt (nm)

ii,(a

21,44 18,80 23,93 23,62

a

(A)

8,3247 8,3313 8,3346 8,3247 8,3247

Luc khdng tie He (Oe)

Ms (emu/g)

3.1.4 Khao sdt dnh hudng ciia luang dung mdi trong dung dich ddng ket tiia

Chiing tdi da khao sat anh hudng dung mdi 1,2 -propandiol trong dung dich khi ddng kit tiia vdi ti le thi tich so vdi dung dich dau 10%, 15% va 20% Ket qua khao sat cho thay khi tang ham lugng dung mdi 1,2-propandiol tir 10% len den 20% thi kich thude hat thay ddi khdng nhieu 6 day dung mdi cdn ddng vai trd nhu chat hoat ddng be mat lam giam tdc do thiiy phan va kha nang ket tu hat khi ddng ket tiia

Nhin vao bang 3.6 va gian dd nhieu xa cho thay cac mau khdng su dung dung mdi thi kich thude hat Idn hon so vdi mau cd sir dung dung mdi

50 60

2 - T h e t a - S c a l e

Hinh 3.7 Gidn do nhiiu xg tia Xcua cdc mdu niken ferU duac dong kit tiia

khi CO (Gd vd khdng co (Gi vd Gz) 1,2-propandiol

Bdng 3.6 Thong so mgng tinh thi vd kich thude hgt cua mdu niken ferd

dsii (A)

2,510 2,513 2,513

a (A)

8,3247 8,3346 8,3346

Kich thude tinh the, nm

27,8 29,1 18,90

Tir nhirng ket qua khao sat d tren chiing tdi chgn ti le dung mdi cho dung dich ddng ket tiia la 10% dung dich dau

5.7.5 Khdo sdt dnh hudng cua nhiet dp nung vd thdi gian nung

De khao sat nhiet do nung mau chiing tdi tien hanh phan tich nhiet san pham sau ket tua tren thiet bi ghi DTA-TG:

' -,

Hinh 3.8 Gidn do phdn tich nhiit {DTA-TG) cua sdn phdm dong kit tiia

Tir gian dd phan tich nhiet ehiing tdi thay cd ba hieu img giam khdi lugng d 142,9794°C; 256,3606°C va 295,5225°C Khdi lugng hao hut tdng cdng tren gian dd phan tich nhiet la 26,445%, sir hinh thanh pha spinen khoang tren 450°C

Tir ket qua phan tich nhiet chiing tdi da khao sat che do nung mau d cac nhiet do: 500, 600, 700, 800, 900 va 1000°C Gian dd XRD tren hinh 3.9-a cho thiy khi tang nhiet do nung cau tnic tinh thi hoan thien tdt hon Khi nung d 450^500°C mac dil tinh the spinen da hinh thanh nhung pha vd dinh hinh cdn nhieu Vdi nhiet do nung ~700°C tinh the NiFe204 da kha hoan thien, kich thude hat khoang 13nm va

nhung kich thuoc hat tang do cd sir ket tu Nhu vay khi dieu ehl NiFe204 bing

28

phuong phap ddng ket tua thi sir hinh thanh pha spinen d nhiet do thip hon nhilu so vdi viec tdng hgp tir cac oxit theo phuong phap gdm truyin thdng

Khi tang nhiet do nung lire khang tir cang tang len, do bao hoa tir tang khdng nhieu, do tir du cang tang kha rd (H3.9-b) Dieu nay cho thiy d nhiet do nung cao cac ion Ni^^ va Fe^^da sap xep lai vi tri mdt phan cd thi chilm d cac hdc bat dien, mdt phan chiem hdc tii dien nhung ti le nay thay ddi nen tir tinh cang biln ddi Qua khao sat nhiet do tdi uu cho qua trinh nung san phim khoang 700°C la phii hgp

Hinh 3.9 Gidn do XRD (a) vd dudng cong tu tri (b) ciia cdc mdu NiFe204 duac

nung a cdc nhiit dp khdc nhau tu 500"C^1000"C

Bang 3.7 Thong so cdu triic tinh thi vd tu tinh ciia NiFe204 nano

duac nung a cdc nhiit dp khdc nhau

-9,02

- - -

-c,

500 0,718 35,692 2,510 11,5 8.3247

20 28.6 0,8

C2

600 0,496 35,669 2,510 16,646 8.3247

116 36,0 5,0

Cs

700 0,619 35,691 2,513 13,34 8.3346

108 40,3 4,5

C4

800 0,453 35,682 2,510 18,22 8.3247

113 36,0 6,0

Cs

850 0,437 35,677 2,513 18,9 8.3346

171 40,0 4,0

Q

900 0,368 35,671 2,515 22,43 8.341

210 38,0 10,0

Cj

1000 0,347 35,693 2,510 23,39 8.3247

150 46,0 12,0

Viec khao sat anh hudng ciia thdi gian nung din clu tnic hat va tir tinh ciia san pham chiing tdi tien hanh nung mlu vdi tdc do nang nhiet 10°C/phut trong Id nung cd dat chuong trinh nung, thdi gian luu d nhiet do nung cao nhit dugc thay ddi tir: 0,5, 1, 2, 3,

4, 5, 6 gid, san pham sau nung dugc lam lanh tu nhien trong Id din nhiet do phdng Kit qua khao sat dugc chi ra tren gian dd nhilu xa tia X (hinh 3.10-a), chup anh SEM, TEM tren hinh 3.11 va bang 3.8 Khi thdi gian nung mlu tang thi kich thude tinh thi tang len

do sir hoan thien va phat trien tinh thi lam kich thude hat tang len

30 40 50 60 70

2-Theta-Scale

Hinh 3.10 Gidn do XRD (a) vd dudng cong tu tri (b) cua cdc mdu NiFe204 nung

700 C vdi thdi gian liru khdc nhau

C h u n q i if20Qk GE.JW)

Hinh 3.11 Anh SEM (a) vd dnh TEM (b) ciia mdu NiFe204 nano tong hgrp vdi

cdc diiu kien toi uu

30

Nhu vay, thdi gian luu d nhiet do nung cao nhat cang dai kieh thude hat cang tang Nhiing tinh thi hinh thanh trong mau niken ferit vdi thdi gian luu tir 0,5H-lh kha nhd nhung clu tnic chua hoan thien, pha vd dinh hinh cdn nhieu Neu keo dai thdi gian nung den 6h thi kich thude hat khoang 24nm

Ket qua khao sat dudng tir tre cac mau nung d cac thdi gian khac nhau cho thay: Luc khang tir eiia eae mlu khi thdi gian luu 1 H- 2h dat 70 H- 75 Oe, la ferit tir mem, do tir du nhd, do bao hoa tir 31 emu/g Khi nung dai hon 3 gid, lire khang tir tang len dat gia tri tren 1310e -^ 160 Oe, dilu nay do d thdi gian luu dii Idn, cac cation sap xep d cac vi tri cau tnic, tinh the spinen phat triln kieh thude lam tang He, tuy vay khi nhiet do cao va thdi gian luu dai, miic do di hudng tinh thi giam xudng lam cho He cang giam, do bao hoa tir va do tir du cang bien ddi nhung khdng nhilu Nhu vay qua trinh nung ed anh hudng Idn tdi kieh thude hat va tir tinh cua vat lieu

Bang 3.8 Thong so cdu true tinh thi vd tu tinh cdc mdu NiFe204nung a

700 C vdi thdi gian nung khdc nhau Mau

Thdi gian nung (gid)