ANH HUONG CLA NHIET Dp LEN VI CAU TRUC VA CO CH£ KHUECH TAIV CUA IVIO HINH KHOI FciO., BANG PHU^ONG PHAP DONG

JOURNAL O F SCIENCE O F HNUE DOI: 10 I8I73'2354-I059.2016-0006 Namral Sci. 2016, Vol 6 1 . No. 4, pp. 33-38

This paper i.s available online at hnp-//stdb hnue edu.vn

ANH HUONG CLA NHIET Dp LEN VI CAU TRUC VA CO CH£ KHUECH TAIV CUA IVIO HINH KHOI FciO.,

BANG PHU^ONG PHAP D O N G LUC HOC PHAN TU"

Nguyen Trpng Diing, Pham Thi Hue, Nguyen Anh Due va Nguyin Chinh Cuong

Khoa Vdl li. Trirdng Dai hoc Supham Hd N6i

Tom tat: Bai bao nghien ciru sy anh huang ciia nhiel do ten vi cau triic, ca LIK khuech lan va xac dinh nhiet do chuyen pha cua mo hinh khoi Fe^Oj 3000 hat bang phuong phap dong lire hoe phan tli (MD) vdl the hrong lac cap Bom - Mayer va dicu kien bien tuan hoan Cac mau FcjOj vdi kfch thudc nano d nhiet do 300 K sau do tang nhiet dd Icn (600 K, 900 K, 1100 K, 1300 K, 1600 K, 1900 K, 2500 K, ."^000 K) Cac mau nay dvroe khao sat, phan lich thong qua ham phan bd xuyen tam (RDF), sd phdi tri. phan bo gde giua cae hat, tu do xac dmh nhiel dd chuy('n pha qua mdi quan he giiia nang lugng va nhi?t dp Kei qua cho thay. cd su anh huong cua nhici do len vi cau nuc va CO che khuech tan ciia md hinh.

Tir khod: Nhiel dd. vi cau tnie. ca che khuech Ian, nhiet dd chuyen pha. md hinh khdi F e s C .

1. Modau

Hien nay, viee nghien cfln vi cdu Inic, c a che khuech tdn, nhiet dd chuyen pha cua cac oxit kim loai: AI2O3, GeOi, SiO?, Fe^Oj [1-7] ed kich thudc nano dang dugc sy quan tam cua eac nha khoa hpc. Cac pxit kim loai nay cd kha nang ung dung rdi Idn trong cac ITnh vyc nhu: dien tu, y hoc, quang hgc, sieu ddn, cdng nghiep gdm va thuy tinh. Cac nghien cuu cd y nghia het sue quan trong khdng nhirng gdp phan vao nhirng hieu biet mdi ve vat lieu, ma cdn khang dmh khi Iang nhiet do dan den sy chuyen pha vi cau tnic tu trang thdi vd dinh hinh sang trang thai Idng (trang thai vd dinh hinh ta irang thai can bang gia ben cua vat iieu).

Cac nghien cflu hien tai chi mdi xem xet cac yeu id anh hudng nhu: nhiet dd, dp suat, sd hat, thdi gian thyc hien, c a c h l khuech tan [1-3] len qua trinh chuyen pha vi cau iriic, ca che khuech tan va nhiet dd chuyen pha cua md hinh. Ngoai ra, cac kel qua nay van chua dn dmh duac cdng nghe cung nhu xac dinh dugc cac yen td anh huang cy the [1-3. 8, 9]. Nghien cuu mdt each chi tiet ve sy anh huoTig cfla nhiet do len vi cau trflc va c a che khuech tan, tu do xdc dinh nhiet dd chuyen pha cua \at lieu dang la mdt ddi hoi cap thict. Vi vay, chung Idi licn hanh nghien ciju van dc ircn bang phucmg phap ddng Iyc hpc phan tu.

2. Noi dung nghien cuu 2.1. Phu-otig phap tinh toan

Ban ddu. md hinh khdi Fe^Oi 3000 hat dugc gieo ngau nhien nong mdi hinh tap phuang cd kich thudc nano. Sau dd, cho ehay 10000 budc thong ke hdi phuc bang phircmg phap dpng luc hgc phan tu vdi t h i tuong tac cap B o m - Mayer cd dang (1),

U„(r) = a i 9 i + B , e x p ( - ^ ) *'*

r l<ii

Ngaynhanbai: 13/2/2015. Ngay nhan dang: 15/3/2016.

Tac gia hen lac: Nguyen Trong Diing, dia chi e-mail: dungntsphn(i:r;gmaii com

Nguyen Trong Dijng, Pham Thi Hue, Nguyen Anh Due vii Nguyen Chinh Cmmg trong dd: q„ qj la dien tich cua cac ion; r la khoang cdch tu nguyen tfl thu^ i den nguyen lu ihu j va I R,j la cac Ihdng sd dupc chon. Vdi md hinh FC2O1 cac thdng sd dugc chpn Id qrc=+3c, qri=-2e, BFCFI 0 eV. BF..O= 2453 cV, B,w, = 1500 eV. R,j = 29 pm

I

Mo hinh

FejO,

Bdng 1. SS nguyen tie trong mo hinh FezOi N (hat)

3000

NFe (hat) 1200

NO (hat) 1800

De thu duac ket qua chinh xac, chung tdi su dyng dieu kien bien tuan hoan nham bd qua bd hieu irng b l mat Ban dau, md hinh khdi F c j O j d nhiet dd 7000 K dugc ha nhict dd xudng 300 K sau 20000 budc vdi budc dich chuyen dT = 5 (dT la budc dich chuyen trong md phong. ung vdi moi budc mo phong cd dp dich chuyen nhiet dp 5 K). Cho md hinh chay dn dmh sd hat, the tich va nhict do (NVT) 20000 budc d nhiet dd 300 K de he dal trang thai on dinh, tilp luc lang nhiet dd len (600 K, 900 K, 1100 K, 1300 K. 1600 K, 1900 K, 2500 K, 3000 K) sau 20000 budc vdi budc dicli chuyen dT = 1.

Sau khi thu dupc cac mdu a nhiel do tuang ung, cho cac mau chay N V T 20000 budc de cac mau dn dmh nhiet do, rdi cho chay 100000 budc dn dinh sd hai. the tich va nang lugng (NVE) cho den khi cac mau dat bang thai can bang Trong qua trinh nghien cuu, cac mau dupc tien hanh vdi ciing mgt dieu kien nhu. sd hat, the tieh, dp suat vd nang lugng khdng ddi trong sudt qua trinh thuc hien.

Ket qua dugc khdo sat chi tiet thdng qua ham phdn bd xuyen tam (RDF), sd phdi tri, nang lugng, phan bd gdc va mdi quan he giiia nang lugng va nhiet dd (xdc djnh nhiet do chuyen pha tu Irang thai

\ d dinh hinh sang trang thai ldng) 2.2. Ket qua va (hao luan

Md hinh khdi F e ! 0 , 3000 hat d nhiel dd (300 K. 600 K, 900 K, 1100 K, 1300 K, 1600 K, 1900 K, 2500 K, 3000 K) duge md phdng bang phuang phap ddng luc hoc phan tu vdi the tuang lac cSp Bom - Mayer va dieu kien bien tuan hoan. Ket qua hinh dang cua mau d u a c the hien nhu Hinh I.

Hinh I. Hinh dang mdu FcjO,} & nhiet dp 300 K

Hinh 1 cho thay, mau FciOi o nhiet dp 300 K cd dang hinh l^p phuang, cd kich thudc nano, c6 sy ton tai cua nguyen tu Fe va O (mau cua nguyen hr sal la miiu do. cdn miiu cua nguyen Ur 0x1 la mau xanh), Khi tang nhict do tir 300 K Icn (600 K, 900 K, 1100 K, 1300 K, 1600 K, ! 900 K, 2500 K, 3000 K), kich Ihudc cua cac mau thu dugc a nhiet dp tuang flng dugc t h i hien tren Bang 2.

Nhiet 96 (K) Kich thiro-c (nm)

Bang 2. Kich thu&c cua mo hinh Fe,0, & cdc nhiet d

1 300

1 3.354

600 3,357

900 3,359

1100 3,356

1300 1600

3,355 1 3,361

9 khdcnhau 1900 3.359

2500 3,358

3000 3,39!.

Ket qua trong Bang 2 eho thjy, kich thuoc mo hinh FcjO, khi tang nhict do lir 300 K Icn (600 K(,' 900 K, 1100 K, 1300 K. 1600 K, 1900 K. 2500 K. 3000 K) biSn ddi trong khoang til 3.354 nm din 34

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Anh hu-e'mg ciia nhiel do len v I'l hinh khiii Fc-fJj bangphicemgphdp I, 3,398 nm Chung td, khi tang nhiet dd tir 300 K ten nhiet dd 3000 K Ihi kich thudc cua cac mdu tang.

^ Ticp tuc phantfch cac dac trung vi cau tnic cua cac mau (vi tri, do cao cac dmh cua ham phan bd xuyen tam), kit qua dugc Ihl hicn tren Bang 3.

Bang 3.

Nhiet do (K) 300 600 900 1100 1300 1600 1900 2500 3000 Thuc nghiem

[i]va[8i

Vi tri, do cao dinh hdm phdn bd xuyen tdm cua md hinh

rif (""•

Fe-Fe 3.5 3,46 3.22 3,38 3,26 3.28 3,3 3,36 3,36 3.35 va 3,11

Fe-0 1,98 1,98 1,98 1,98 1,98 1,98 1,98 1,98 1.96 1,93 va 1.91

0-0 1.1 2,7 2,74 2,74 2.78 2.78 2.8 2,82 2,88 2.91 va 2,6

o cdc nhiet do khdc nhau g i j ' ^ l

Fe-Fe 2,85 2,8 2,83 2,85 2,82 2.8 2.79 2,8 2,61

Fe-0 8.84 7,98 7,26 6,95 6.57 6.15 5.8 5.2 5.01

0-0 2.31 2.29 2.3 2,29 2.3 2,26 2,23 2,21 2,09

Quan sat Bang 3 ta Itiay, md binh FeAiO nhiet dd (300 K. 600 K. 900 K, 1 100 K, 1300 K. 1600 K. 1900 K, 2500 K, 3000 K) cd vi in' dinh dau lien cua ham phan bd xuyen tam ludn chiem uu the Khi Iang nhiet dp. vi tri thu nhal cua ham phan bd xuyen tam cua Fe-O cd gia tri khdng ddi va dd cao cua ham phan bd xuyen lam cd gia tri giam dan. Dieu dd chung td, khoang each ndi phan tu cua Fe-O khdng phy thudc vao nhiel dd va mat do cac nguyen tu (phan tu) Fe-0 giam dan. Ndi mdt each khac, lien ket Fe-0 khdng cd trat ty xa ma ludn tdn tai trat ty gan, dp cao cua ham phan bd xuyen tam thu nhat d nhiet dp 300 K cd gia tn tdn nhat, khi Iang nhiet do thi dd cao cua ham phan bd xuyen Iam thu nhat cd xu hudng giam dan. Tuang ty, ddi vdi hen ket Fe-Fe. 0-0 rhi vi tri dmh dau tien cua ham phdn bd xuyen tam Fe-Fe giam, O-O tang va do cao cua ham phan bd xuyen tam deu giam khi tang nhiet dp. Dieu dd cbo tliay, ed sy anh huang cua nhiet dd ten lien ket Fe-Fe, O-O va ten tinh ddng nhat ve mat vi eau true trong md hinh hat Fe20j la dang ke. Qua qua Irinh khao sat cho ihay, trong vung nhiet dp tir 2500 K den 3000 K tiii dp cao dinh thu nhal cua ham phan bd xuyen tam cua Fe-0 cd xu hudng giam manh nhat, tai vung nhiet do nay mau Fe:03 xay ra qua trinh chuyen pha tiJ trang thai vd dinh hinh sang trang thai ldng. De khang dinh sy anh hudng cua nhiet do ten qua trinh chuyen pha vi cau tnic, ehflng Idi phan tich sd phdi tri, nang luang cfla md hinh d cac nhiet do khac nhau, ket qua dugc the hien tren Bang 4.

Nhiet d o (K) 300 600 900

" HOO

•; 1300 1600 1900 2500 3000

^ Thue nghiem

,. filva[8]

Bdng 4. So phdl tri, nang lutmg ua mo hinh & cdc nhiet do khdc n ZTB

Fe-Fe 11,29 11,23 11,2 11,31 11,3 11,3 11,3 11.5 11 13,5 va 11,44

Fe-O 5,32 5,34 5,43 5,44 5,47 5,46 5,48 5,5 5,33 5,25 va 5,44

0-Fe 3,55 3,56 3,62 3,63 3,65 3,64 3,66 3.66 3,55 4 v a 3 , 6 3

O-O 15,6 15,59 15,73 15,75 15,81 15,74 15,83 15,84 15,39 I 2 v a 9 , 9

hau Nang luoTig

(eV - 88690,3 - 88480,9 - 88276,6 - 8 8 1 2 5 - 8 7 9 8 1 , 9 - 87767,9 - 87509,9 - 87025,7 - 86433,2

Nguyen Trong Dung. Pham Thi Hul, Nguyin Anh Diic va Nguyen Chinh Cuong Kit qua Iren Bang 4 eho Ihdy, khi lang nhiel dd Ihi sd phdi tri trung binh, mai dd ciia cac lien ket (Fc-Fc, 0 - 0 ) giam, ciia lien k i t ( F c - 0 , 0-Fc) tang va nang lugng cua cac mdu tang. Khi tang nhict do len 3000 K thi mat dp cac lien kit d i u giam dgl ngdt. cac mau da chuyen sang trang thai tdng. Kit hop vdl cac kit tu^n tren eho thdy, khi tang nhiel do Ihi kich thude, nang luang cua cac mau tang. Ngoai ra, d l phan Iich vi cdu tnic cfla cac mdu, chiing tdi cdn su dung p h u a n g phap true quan hod de nghien cuu so dan vi vi cdu Inic cua cdc mau, ket qua dugc the hien iren Hinh 2.

Hinh 2. So dtfn vi cdu true trong mo liinh Fe20}

( ^ a n sat Uen Hinh 2 ta thdy. Irong md hinh Fe^Oi tdn tai chu yeu la cac don vi cau mic 4 d Hinh 2a (Fe04, luang ung I nguyen ni Fe Uen ket vdi 4 nguyen nr O), dan vi cdu tnic 5 a 1 linh 2b (FeOs), dan vi cdu true 6 d Hinh 2c (FeO^). Sd nguyen tu ed dan vi cau true irong cdc mau d nhiet dp khac nhau dugc the hien iren Bang 5.

Bang 5, So nguyen tiled dffn vi cdu true (4, 5. 6, N h i i t do (K)

So nguyen tlj c6 don vi cau tnic 4 So nguyen tu co don vi cau true 5 So nguyen tii co don vi cau tnic 6 So nguyen tu vo dinh hinh

300 417 1452 895

*

236

*

600 392 1484 828 296

900 428 1457 840 275

1100 456 1452 873 219

cda mo 1300 416 1457 880 247

hinh & nliiet do khdc nhau 1600

520 1443 823 214

1900 516 1407 876 201

2500 613 1432 740 215

30N 833 1368

*

524 275,

Ket qua d Bang 5 cho Ihay, khi lang nhiet dp, sd nguyen tu cd d(m vi cau tnic 4 tang, sd nguyen tu cd dan vj cau tnic (5, 6) giam, sd nguyen tu vd dmh hinh tiing chflng td cdc mau cd xu hirdng chuyen dan sang trang thai Idng. De khao sat sy phan bd gdc giua cac nguyen tu Fe va O, ket qua dugc the hien tren Bang 6.

Nhist dp (K) Phan bo goc (do)

Fe-O-Fc 0-Fe-O

300 95 75

Bdng 6. i 600

95 75

irphdn b 900

95 75

0 gdc cua md him 1100

95 75

1300 95 75

Fefii 1600

95 75

1900 95 75

2500 95 75

3000 95 75 Bang 6 cho thay, khi iang nhiet dp, sy phan bo gdc Fe-O-Fc, O - F e - 0 giua cac nguyen tfl Fe va 0 khdng ddi. Ndi each khac, sy phan bd gdc gifla cac nguyen tu Fe, O khdng phu thupc vao nhi^Idp.

Ngoai ra, cd the xdc dinh duac nhiet dp chuyen pha cfla md hinh FcjOs thdng qua ket qua tren Bang 7

vaHlnh 3.

Nhi?t

d6(K)

III

_{- S8690.3} ³⁰⁰ Bdng 7. Nans luffni 600

- 8 8 4 8 0 , 9 900 - 8 8 2 7 6 . 6

1 1 0 0

- 8 8 1 2 5 1 3 0 0

- 8 7 9 8 1 . 9 1 6 0 0

- 8 7 7 6 7 . 9 1 9 0 0

- 8 7 5 0 9 . 9 2 5 0 0

- 8 7 0 2 5 . 7 3O00

- 86433

Anb huemgcua nbiei de} ten vi cdu true vd at che khuech ldn cuu me) hinh kboi Fe:(), hang pbuerug pbeip

MOI quail lie giuD naivj luong nhii^t do

• (E.T)

1000 1500 2000 Nhiet do

2500 3000

Hinh 3. Nhiet do chuyen pha eua mo hinh FeiOj

Quan sat Bang 7 vd Hinh 3 ta thay, khi tang nhiel dp, nang luang ciia cdc mau giam ddn, rieng tai vung nhiel do tir 1900 K den 3000 K nang lugng ciia md hinh FcjO, tang rat nhanh va xac dinh dugc nhiet dd chuyen pha efla md hinh la 2257.92 K tucmg ung vdi muc nang luong -87323,46 eV. C5n eu- vao eac kel qua khaq sdt vd phan tich iren cho thay sy anh hudng cfla nhiet do len vi cau true va ca che khuech tan cua md hinh lit dang ke.

3. Kit luan

Bang phuang phap dpng lyc hgc phan tu, sy anh hudng cua nhiet dd len vi cau tnic, ca che khuech tan va xae dinh nhiet dp chuyen pha cua md hinh klidi FejOi 3000 hat a nhiet do (300 K. 600 K, 900 K, 1 too K, 1300 K, 1600 K, 1900 K, 2500 K. 3000 K) duoc tiln hanh khao sat va phan tich thu dugc mdt sd ket qua sau:

- Viec lya chgn the tuang lac cap Bom - Mayer, cac thdng sd de md phong md hinh khdi Fe^Oi 3000 hat cd ket qua phii hgp vdi thuc nghiem [1, 8] va ket qua khao sat tnrdc day [3],

- Khi tang nhiet dp, kich ihudc, nang luang cua md hinh tang va nhiet dp ehuyen pha cua md hinh duac xac dinh Id 2257,92 K.

- Trong khoang nhiet dp tu 300 K den 2257,92 K md hinh tdn tai a trang that vd dinh hinh, cd cau tnic Clia vat lieu khdt.

- Co sy anh huong cua nhiel do ten qua trinh chuyen pha vi cau tnic. ca che khuech tan cua md hinh.

- Cd sy khac biet ve mat cau tnic cua cac lien ket Fe-Fc, Fc-0, 0 - 0 trong md hinh a cac nhiet dp khac nhau.

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[2] S M. Yusuf, M. D. Mukadama, J. M. DcTercsa, M. R. Ibarra. J Kohlbrechcr, A.

Heinemann, A. Wiedenmann, 2010. Structural and magnetic properties of amorpheius iron oxide. Physica B405, pp. 1202-1206.

[3] B. T. H. L. Khanh, V. V Hoang and H. Zung, 2008. Structural pioperties of amorphous Fe20, nanoparticles Eur Phys..!. D, pp 325-332.

[4] Tcruo Hcnmi, Kazuhiko Tangc, Tetsuo Mingawa and Naganori Yoshinaga, 1981 Effecl of S1O2/AI2O3 ratio on the thermal reactions of allophane II infrared and X-ray powder elitJraciion data Clays and Clay Minerals, Vol. 29, No. 2. pp. 124-12S

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Nguyen Trong Diing. Pham Th] Hud. Nguyen Anh Diic va Nguyen Chinh Cmmg [5] Troy K, Townscnd. Erwin M Subin, Nigel D, Browning and Frank E. Osterioh, 2011,

Photocalalylic water oxidation with suspended alpha-Fe>0, particles-effects nfnano scaling.

Energy Environ, Sci., 4. pp. 4270-4275.

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ABSTRACT

The influence of temperature on microstruclure and diffusion mechanisms of Fe20.t bulk models using the molecular dynamics method

This paper looks at Ihe influence of temperature on microstmcture, diffusion mechanisms and transition lemperatuies of Fe:iOibulk models (3000 particles) using the Molecular Dynamics method (MD) with the Bom-Mayer couple-interaction pulenlial and penodic boundary conditions. Models of nano-sized FcjOi underwent a tempcramre increase of 300 K lo 600 K, 900 K. 1100 K, 1300 K, 1600 K, 1900 K, 2500 K and 3000 K. These models were examined and analyzed using the radial dislnbution function (RDF), coordinanon numbers and the disposition of the angle between parbcles. Transition temperatures were then determined by examining the relationship between the energy and temperature The results show thai temperamre does influence microstmcture and diffiision mechanisms of models.

Keywords: Temperahire, microstmcture, diffusion mechanisms, transition temperature, FeiO?

bulk model.