Formation mechanism of ZrB2-Al2O3 nanocomposite powder by mechanically induced self-sustaining reaction

1 Fo ma ion mechanism o Z B2–Al2O3 nanocomposi e powde by mechanically induced sel -sus aining eac ion M. Jalaly 1,*, M.Sh. Ba ghi 1, M. Tamizi a 1, F.J. Go o 2 1. School o Me allu gy and Ma e ials Enginee ing, I an Uni e si y o Science & Technology (IUST), Na mak, Teh an 16846-13114, I an 2. Ins i u o de Ciencia de Ma e iales de Se illa (CSIC-US), Ame ico Vespucio 49, 41092 Se illa, Spain *Co esponding Au ho , Email: maisam_jalaly@ius .ac.i Tel: +989127387902, Fax: +982177240480 Abs ac Z B2–Al2O3 nanocomposi e powde was p oduced by alumino he mic educ ion in Al/Z O2/B2O3 sys em. In his esea ch, high ene gy ball milling was used o p oduce he necessa y condi ions o induce a mechanically induced sel -sus aining eac ion (MSR). The igni ion ime o he composi e o ma ion was ound o be abou 13 minu es. The syn hesis mechanism in his sys em was in es iga ed by examining he co esponding sub- eac ions as well as changing he s oichiome y o eac an s. The mal beha io o he sys em was also s udied. Keywo ds: Zi conium dibo ide; Mechanosyn hesis; Mechanism; Nanocomposi e 1. In oduc ion Z B2 is a well-known ma e ial belonging o he Ul a-High Tempe a u e Ce amics class [1]. The dis inc i e ea u es o his class o ma e ials make hem good selec ions o use in a ious applica ions such as hype sonic ligh s, a mosphe ic e-en y ehicles, and ocke p opulsion sys ems. Zi conium dibo ide has a ac ed much a en ion because o 2 i s supe io oxida ion esis ance, which is a consequence o he s abili y o Z O2 o med on hese ma e ials a high empe a u es in oxidizing a mosphe es [2]. Ce amic ma ix composi es consis ing o high empe a u e bo ides and some o he indus ial ce amic ma e ials ha e been o in e es in ecen yea s. Alumina is one o he mos common used ce amics in a ious applica ions such as g inding media, cu ing ools, c ucibles, ube u naces and line s, owing o i s se e al in insic cha ac e is ics like high ha dness, high mel ing poin , good chemical ine ness, high wea esis ance, and low cos . Ne e heless, some mechanical p ope ies o alumina a e no good enough o se e al applica ions. The mechanical s eng h o hese ma e ials can signi ican ly imp o e by he addi ion o s ong compounds like zi conium dibo ide [3]. TiB2–Al2O3 composi e ha was p epa ed by mixing alumina and dibo ide powde s, showed excellen mechanical p ope ies [4]. The mos impo an applica ions o Z B2 a e in he high- empe a u e ields whe e i is used as a e ac o y ma e ial; hence, he e ec o alumina on he oxida ion a e o Z B2 ce amic should be essen ially in es iga ed. Few epo s exis on he high empe a u e oxida ion esis ance o Z B2– Al2O3 composi es. Recen ly, Li e al. [5] examined he oxida ion kine ics o Al2O3/Z B2/Z O2 composi e p epa ed by mixing and ho -p essing. Sel -p opaga ing high empe a u e syn hesis (SHS) has ecen ly been used ex ensi ely o he p epa a ion o e ac o y ma e ials such as ca bides, silicides, ni ides, and a ious composi e ma e ials. This kind o syn hesis is cha ac e ized by i s signi ican nega i e en halpy and high adiaba ic empe a u e (Tad) o abo e 1800 K [6]. Li e a u e su ey shows a g ea a en ion o he me allo he mic educ ion o Z O2 and B2O3 in 3 p epa a ion o Z B2 because o i s cheape aw ma e ial as well as he high exo he mic na u e o he in ol ing sel -sus aining eac ions compa ed o he o he syn hesis ou es [7-12]. Magnesium has been equen ly used o educe zi conium and bo on oxides [7- 11] due o good easibili y o MgO leaching, al hough aluminium has also been employed in a ew cases [3, 12] o inducing he educ ion eac ion in his sys em. Using Al as educing agen has also he ad an age o in-si u making o Z B2–Al2O3 which is a aluable composi e. When a sel -sus aining eac ion is induced by he high-ene gy ball milling o eac an s a e a c i ical milling pe iod, called he igni ion ime, such a mechanochemical p ocess is e e ed o as mechanically induced sel -sus aining eac ion (MSR) [6]. MSR and SHS a e di e en me hods, al hough he e a e common ea u es be ween bo h p ocesses. In con as o he con en ional SHS p ocedu e, MSR p ocess has he a o able side bene i o mixing o he eac an s as well as he subsequen homogeniza ion o he p oduc s oge he wi h in ensi e pa icle size educ ion o bo h eac an s and p oduc s, all jus in one single s ep. All esea ch wo ks ha we e pe o med on he Z B2 syn hesis by use o Al as educing agen , we e ca ied ou by he mally combus i e SHS me hods, a he han MSR eac ions [3, 11]. Fu he mo e, eac ion mechanism has no also been clea ly explained. The aim o he p esen wo k, he e o e, was o in es iga e he mechanosyn hesis o Z B2–Al2O3 powde by alumino he mic educ ion using Z O2 and B2O3 as s a ing ma e ials and by means o mechanically induced sel -sus aining eac ion (MSR), which has no been epo ed so a . The mechanis ic explana ion o Z B2 o ma ion in his 4 sys em was also ano he a ge , which has been accomplished h ough he in es iga ion o sub- eac ions, as well as he s udy o he in luence o he eac an s s oichiome y. 2. Expe imen al The aw ma e ials, monoclinic Z O2 (99%, Ald ich, USA), B2O3 (98%, Fluka, Ge many), and Al (99%, Ald ich, USA) powde s, we e used o p oduce zi conium dibo ide–alumina composi e powde . Elemen al zi conium (99%, Al a Aesa , Ge many) and bo on (97%, amo phous, Ald ich, USA) we e also used o s udying a sub- eac ion. The s a ing ma e ials we e subjec ed o he high ene gy ball milling in a modi ied plane a y ball mill (Pul e ise e7, F i sch, Ge many). The o a ional speed and ball- o- powde mass a io we e 600 pm and 30:1, espec i ely. The milling ial and balls (15 mm) we e made o ha dened ch omium s eel. All milling expe imen s we e conduc ed unde 5 ba o high-pu i y a gon gas. The ial was pu ged wi h a gon gas se e al imes, and he desi ed p essu e was adjus ed be o e he s a o he milling. The connec ion o he ial o he gas cylinde du ing he milling expe imen s was main ained by a o a ing union and a lexible polyamide ube. The p essu e change s. ime was moni o ed by a SMC solenoid al e (model EVT307-5DO-01F-Q, SMC Co ., Tokyo, Japan) o eco d he igni ion ime. A sha p peak due o he p essu e ise appea s when he MSR eac ion occu s. The posi ion o his peak ep esen s he igni ion ime. The sys em used in his wo k has al eady been shown elsewhe e [13]. The mal beha io o he as-blended mix u e was s udied by di e en ial scanning calo ime y (DSC) in a TA Ins umen Q600 analyze using a cons an hea ing a e o 20°C/min om oom empe a u e o 1400°C. The DSC measu emen was done unde a 5 lowing helium a mosphe e. Fu he mo e, iso he mal annealing o mix u es was ca ied ou a di e en empe a u es o 30 min unde a lowing a gon a mosphe e a a p essu e o 1 ba in a ho izon al ubula u nace (IGM1360 model no. RTH-180-50-1H, AGNI, Ge many). S uc u al ea u es o he samples we e in es iga ed using X- ay di ac ion (XRD) analysis by means o a PANali ycal X'Pe di ac ome e (45 kV, 40 mA) wi h Cu Kα adia ion (λ=0.15406 nm) XRD analyse . The c ys alli e size o sample was es ima ed by b oadening analysis o XRD peaks using Williamson–Hall o mula [14]. Scanning elec on mic oscopy (SEM) images we e ob ained by a Hi achi S-4800 SEM- Field Emission Gun mic oscope. T ansmission elec on mic oscopy (TEM) images we e aken using a 200 kV Philips CM200 mic oscope equipped wi h a Supe Twin objec i e lens and a ungs en ilamen (poin esolu ion Ø=0.25 nm). Powde ed samples we e dispe sed in e hanol, and d ople s o he suspension we e deposi ed on o a holey ca bon ilm. 3. Resul s and Discussion 3.1. Mechanosyn hesis The ini ial pu pose o he p esen wo k was o syn hesize zi conium dibo ide-alumina composi e. In o de o achie e his goal, he ollowing eac ion was conside ed: Z O2 + B2O3 + (10/3)Al → Z B2 + (5/3)Al2O3 (1) ΔG°298= –722 kJ, ΔH°298= –746 kJ, Tad ≈ 2330 K 6 S oichime ic amoun s o s a ing ma e ials (Table 1) we e milled unde a o emen ioned condi ions. The change o in e nal p essu e o he ial e sus milling ime is shown in Fig. 1. The la ge p essu e ise obse ed a app oxima ely 13 min milling demons a es he occu ence o a highly exo he mic MSR eac ion. Fig. 2 shows he XRD pa e ns o Al, Z O2 and B2O3 powde mix u e as- ecei ed and a e di e en milling imes. The XRD pa e n o as-blended mix u e included only he sha p peaks o Al (ICCD PDF #03-0932), Z O2 (ICCD PDF #13-0307) and B2O3 (ICCD PDF #06-0297) compounds, which we e con e ed o Z B2 (ICCD PDF #34- 0423) and Al2O3 (ICCD PDF #11-0661) a e 13 min milling (jus a e igni ion). Small amoun s o Al and Z O2 we e s ill emained which is a ypical beha io o mechanosyn hesis eac ions, especially in he MSR si ua ions [12], due o he en apmen o some powde s in he dead zones o milling ial. As Fig. 2 shows, a e agonal Z O2 phase (nomina ed as T-Z O2) was de ec ed among he emaining ma e ials in he sample ha was milled o 13 min ( he igni ion poin ). In ac , zi conium dioxide ans o med om i s monoclinic c ys al s uc u e a oom empe a u e o a e agonal o m, due o he signi ican empe a u e ise esul ed om he highly exo he mic MSR eac ion. Because he cooling a e a e igni ion is e y high, he e a e aces o ans o med zi conia emained in he e agonal s a e a oom empe a u e. As shown in Fig. 2, a e y sligh amoun o elemen al Z was de ec ed in he XRD pa e n o he sample milled o 13 min, mos likely due o he incomple e eac ion o educed zi conium wi h bo on. Elemen al bo on, which may emain due o he incomple e eac ion wi h zi conium, could no be de ec ed, mos likely due o i s e y li le quan i y and/o i s amo phiza ion because o apid cooling a e igni ion. 7 By inc easing he milling ime, powde s apped in he dead zones can be g adually subjec ed o he ball impac s and locally eac ed. Fig. 2 shows he XRD pa e ns o samples milled o 1 and 2 hou s. A sligh amoun o zi conium dioxide was obse ed a e 1 h milling, bu i was en i ely disappea ed a e 2 h milling. The c ys alli e size o Z B2 a e 2 h ball milling was calcula ed o be app oxima ely 83 nm. The elec on mic oga phs o a sample milled o 2 h a e shown in Fig. 3. As hese mic og aphs shows, he p oduc powde con ains agglome a es which a e composed o pa icles o sub-mic ome ic and nanome ic sizes wi h a combina ion o semi-sphe ical and pla ele mo phology. The TEM mic og aph in Fig. 3 (b) shows da k polyhed on Z B2 pa icles su ounded by b igh alumina nanopa icles. A bigge , single c ys al o hexagonal Z B2 along wi h alumina nanopa icles is indica ed in a la ge magni ica ion in Fig. 3 (c). 3.2. Reac ion mechanism 3.2.1. Du ing milling The mechanis ic s udy o he o ma ion o Z B2–Al2O3 composi e du ing milling in he p esen wo k can be di ided in o wo sec ions. The o e all eac ion (Rea.1) was ini ially in es iga ed by he s udy o in ol ed sub- eac ions. A he second s ep, he e ec o bo on oxide amoun on he na u e o he eac ion was s udied. To o m zi conium dibo ide, zi conium and bo on elemen s mus be ob ained h ough he educ ion o hei co esponding oxides. The sub- eac ions in ol ed in his sys em can be w i en as ollows: 8 2Al + B2O3 → 2B + Al2O3 (2) ΔG°298= –389 kJ, ΔH°298= –404 kJ, Tad ≈ 2310 K (4/3) Al + Z O2 → Z + (2/3) Al2O3 (3) ΔG°298= –15 kJ, ΔH°298= –20 kJ, Tad ≈ 500 K Z + 2B → Z B2 (4) ΔG°298= –318 kJ, ΔH°298= –322 kJ, Tad ≈ 3200 K In he abo e eac ions, aluminum educes bo on oxide and zi conium oxide o yield elemen al bo on and zi conium. Z B2 can be subsequen ly o med by he eac ion be ween hese wo elemen s. Acco ding o he adiaba ic empe a u es (Tad) and en halpy alues o he abo e eac ions, Reas. 2 and 4 mee he equi ed condi ions o sa is y Me zhano ’s c i e ion [12] o p oceed in a sel -sus aining manne . Howe e , he educ ion o Z O2 by Al (Rea. 3) does no sa is y hese condi ions, and i is hence an icipa ed o g adually p oceed as an o dina y eac ion. When Al, B2O3 and Z O2 a e all p esen in one sys em, Al educes bo on oxide in a sel - sus aining manne o yield elemen al bo on oge he wi h he elease o a g ea deal o hea ; his hea inc eases he sys em empe a u e inside he milling ial o such a le el which can igge he eac ion be ween Al and zi conia o o m elemen al Z . Consequen ly, Z B2 can be syn hesized by he eac ion be ween hese wo elemen s. The highly exo he mic eac ion o he educed B and Z (Rea. 4) can exe an addi ional amoun o hea o he sys em, hus causing he u he Z O2 educ ion o p oceed mo e easily. All hese h ee eac ions occu simul aneously; hus only one peak is obse ed in he p essu e- ime g aph o o e all eac ion (Rea. 1). This pos ula ion can be con i med 9 by he exis ence o a ace amoun o esidual zi conium as he XRD pa e n jus a e he igni ion ime (Fig. 2) shows. Al hough elemen al bo on was no de ec ed in he XRD pa e n, i may be p esen in consequence o incomple e eac ion o Z B2 o ma ion and emaining elemen al zi conium. Bo on can be possibly in e p e ed o ha e been p esen in an amo phous o m, i his possible mechanism is ac ual. In o de o examine he p oposed mechanism, hese sub- eac ions we e sepa a ely s udied. S oichiome ic amoun s o Al/B2O3, Al/Z O2 and Z /B we e mixed acco ding o he Reas. 2-4 and milled unde he same condi ions. Fo Rea. 2, he igni ion ime was ound o be abou 25 min (Fig. 4), which is a li le longe han he igni ion ime o Rea. 1, due o lowe exo he mici y o Rea. 2. Reac ion 1 includes Al/B2O3 igni ion along wi h Z /B igni ion which can cause he sys em o be mo e igo ous han eac ion1 (only Al/B2O3 igni ion). The e o e, he igni ion ime is sho e in he o e all sys em. The XRD pa e ns o ini ial ma e ials along wi h ha o sample milled up o he igni ion poin (25 min) a e shown in Fig. 5. I can be seen ha he igni ed sample con ains aluminum oxide, which is an indica ion o he easibili y o he educ ion o bo on oxide by Al. Small amoun s o he s a ing ma e ials we e also obse ed, pe haps due o hei en apmen in he dead zones o he ial, as men ioned ea lie . Howe e , elemen al bo on was no de ec ed in he XRD pa e n, mos likely due o i s amo phiza ion as a esul o he high empe a u e ise du ing he MSR eac ion and high cooling a e a e igni ion. The o ma ion o amo phous bo on as a esul o me allo he mic educ ion o bo on oxide has al eady been desc ibed in he li e a u e [15,16]. 16 ea men s, which can make he condi ions sui able o Z and Al o o m zi conium aluminides. 4. Conclusion High ene gy ball milling echnique was success ully applied o mechanosyn hesis o Z B2–Al2O3 nanocomposi e by means o he alumino he mic educ ion. Syn hesis in Al/B2O3/Z O2 sys em ound o possess a sel -sus aining na u e ha ing an igni ion ime o 13 min. Examina ion o he sub- eac ions e ealed ha bo on oxide is easily educed by Al, while Al canno educe Z O2 o Z in a sel -sus aining manne . I was concluded ha he g ea deal o hea gene a ed h ough he educ ion o bo on oxide by Al oge he wi h he la ge amoun o hea eleased by he eac ion be ween he educed B and Z , is capable o ac i a ing he educ ion o Z O2. This mechanism was ound o be in good ag eemen wi h he gene al end obse ed du ing he mal ea men o he sys em wi h an excep ion o o ma ion o in e media e zi conium aluminides in he la e case. The amoun o bo on oxide was ecognized o be a c i ical pa ame e which can al e he magni ude o eac ion hea and consequen ly cause he sys em o unde go a ansi ion om a g adual s a e o a sel -sus aining one. Acknowledgemen s This wo k was inancially suppo ed by he Spanish go e nmen unde g an No. MAT2011-22981, which was inanced in pa by he Eu opean Regional De elopmen Fund o 2007-2013. The wo k has been based on an ini ia ion p oposed by he School o Me allu gy and Ma e ials Enginee ing o I an uni e si y o science and echnology as he Ph.D hesis subjec o M . M. Jalaly who was g an ed he pe mission o accomplish 17 his expe imen s wi h he acili ies and co-supe ision o P o . F.J. Go o in Ins i u o de Ciencia de Ma e iales de Se illa, Se illa, Spain. Re e ences [1] M.A. A iles, J.M. Co doba, M.J. Sayagues, F.J. Go o , Mechanochemical syn hesis o Ti1- xZ xB2 and Ti1-xH xB2 solid solu ions, Ce amics In e na ional 37 (2011) 1895–1904. [2] W.G. Fah enhol z, G.E. Hilmas, Re ac o y Dibo ides o Zi conium and Ha nium, Jou nal o Ame ican Ce amic Socie y 90 (2007) 1347–1364. [3] S.K. Mish a, S.K. Das, V. She baco , Fab ica ion o Al2O3–Z B2 in si u composi e by SHS dynamic compac ion: A no el app oach, Composi es Science and Technology 67 (2007) 2447– 2453. [4] J. Liu, P.D. Ownby, Enhanced mechanical p ope ies o alumina by dispe sed i anium dibo ide pa icula e inclusions, Jou nal o Ame ican Ce amic Socie y 74 (1991) 241–243. [5] B. Li, J. Deng, Y. Li, Oxida ion beha io and mechanical p ope ies deg ada ion o ho - p essed Al2O3/Z B2/Z O2 ce amic composi es, In e na ional Jou nal o Re ac o y Me als & Ha d Ma e ials 27 (2009) 747–753. [6] A.K. Khan a, L.C. Pa hak, S.K. Mish a, M.M. Godkhindi, Sin e ing o ul a ine zi conium dibo ide powde p epa ed by modi ied SHS echnique, Ad ances in Applied Ce amics 104 (2005) 282–284. [7] K. Nishiyama, T. Nakamu , S. U sumi, H. Sakai, M. Abe, P epa a ion o ul a ine bo ide powde s by me allo he mic educ ion me hod, Jou nal o Physics: Con e ence Se ies 176 (2009) 012043. [8] N. Se oudeh, N.J. Welham, Fo ma ion o zi conium dibo ide (Z B2) by oom empe a u e mechanochemical eac ion be ween Z O2, B2O3 and Mg, Jou nal o Alloys and Compounds 420 (2006) 225–228. 18 [9] S.K. Mish a, S. Das, L.C. Pa hak, De ec s uc u es in zi conium dibo ide powde p epa ed by sel -p opaga ing high- empe a u e syn hesis, Ma e ials Science and Enginee ing A364 (2004) 249–255. [10] B. Akgun, H.E. Camu lu, Y. Topkaya, N. Se inc, Mechanochemical and olume combus ion syn hesis o Z B2, In e na ional Jou nal o Re ac o y Me als and Ha d Ma e ials 29 (2011) 601–607. [11] Y.B. Lee, H.C. Pa k, K.D. Oh, C.R. Bowen, R. S e ens, Sel -p opaga ing high- empe a u e syn hesis o Z B2 in he sys em Z O2-B2O3-Fe2O3-Al, Jou nal o Ma e ials Science Le e s 19 (2000) 469– 471. [12] L. Takacs, Sel -sus aining eac ions induced by ball milling, P og ess in Ma e ials Science 47 (2002) 355–414. [13] F.J. Go o , M. Achimo ico a, C. Real, P. Balaz, In luence o he milling pa ame e s on he mechanical wo k in ensi y in plane a y mills, Powde Technology 233 (2013) 1–7. [14] G. K. Williamson, W. H. Hall, X- ay line b oadening om iled aluminium and wol am, Ac a Me allu gica 1 (1953) 22-31. [15] V. Sunda am, K. V. Logan, R. F. Speye , Alumino he mic eac ion pa h in he syn hesis o a TiB2-Al2O3 composi e, Jou nal o Ma e ials Resea ch 12 (1997) 1681-1684. [16] J. Wang, Y. Gu, Z. Li, W. Wang, Z. Fu, Syn hesis o nano-sized amo phous bo on powde s h ough ac i e dilu ion sel -p opaga ing high- empe a u e syn hesis me hod, Ma e ials Resea ch Bulle in 48 (2013) 2018-2022. 19 Fig. 1. P essu e inside he ial e sus milling ime o Al/Z O2/B2O3 sys em. Fig. 2. X- ay di ac ion pa e ns o as-blended and milled samples o Al/Z O2/B2O3 sys em. 20 Fig. 3. Elec on mic og aphs o Al/Z O2/B2O3 sys em a e 2 h milling, (a) SEM and (b) TEM images. Fig. 4. P essu e inside he ial e sus milling ime o Al/B2O3 and Z /B sys ems. 21 Fig. 5. X- ay di ac ion pa e ns o ini ial and milled samples o Al/B2O3 sys em. Fig. 6. X- ay di ac ion pa e ns o ini ial and milled samples o Al/Z O2 sys em. 22 Fig. 7. X- ay di ac ion pa e ns o ini ial and milled samples o Z /B sys em. Bo on canno be obse ed among ini ial mix u e due o i s amo phous s a e. Fig. 8. Calcula ed adiaba ic empe a u e and oom empe a u e en halpy o Rea. 5 se ies e sus B2O3 mola amoun . 23 Fig. 9. X- ay di ac ion pa e ns o he di e en composi ions (y = 0.7–0.9 in Rea. 5) a e milling. Fig. 10. DSC cu e o as-blended mix u e in Al/Z O2/B2O3 sys em. 24 Fig. 11. X- ay di ac ion pa e ns o he blended powde s in Al/Z O2/B2O3 sys em a e hea ing a 700, 950 and 1050°C (30 min dwelling a maximum empe a u e and hen cooling o oom empe a u e). Fig. 12. X- ay di ac ion pa e ns o he blended powde s in Al/Z O2/B2O3 sys em a e hea ing a 1150, 1300, 1400 and 1500°C (30 min dwelling a maximum empe a u e and hen cooling o oom empe a u e). 25 Table 1. The weigh (g) o componen s in ol ed in he Reac ion 5 o he di e en y alues. y 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 B2O3 - 0.127 0.238 0.335 0.420 0.495 0.563 0.624 0.679 0.729 0.774 Z O2 2.435 2.260 2.108 1.975 1.858 1.754 1.661 1.578 1.502 1.434 1.371 Al 0.712 0.759 0.801 0.837 0.869 0.897 0.922 0.945 0.965 0.984 1.001