第26卷第7期無(wú)機(jī)化學(xué)學(xué)報(bào)Vol 26 No. 72010年7月CHINESE JOURNAL OF INORGANIC CHEMISTRY1279-1283研究簡(jiǎn)高嶺土相轉(zhuǎn)變的非等溫動(dòng)力學(xué)周佳何明中*張愛(ài)華李淋傅鳳英(中國(guó)地質(zhì)大學(xué)材料科學(xué)與化學(xué)工程學(xué)院武漢430074)關(guān)鍵詞:高嶺土;相轉(zhuǎn)變;差示掃描量熱法;非等溫動(dòng)力學(xué);選代法中圖分類號(hào):064312文獻(xiàn)標(biāo)識(shí)碼:A文章編號(hào):10014861(201007-127905Non-Isothermal Kinetics for Phase Transformation of KaoliniteZHOU Jia HE Ming-Zhong" ZHANG Ai-Hua LI Lin FU Feng-YingFaculty of Material Science and Chemical Engineering, China University of Geosciences, Wuhan 430074)Abstract: The process of phase transformation of kaolinite was investigated by differential scanning calorimetry( SC)and X-ray power diffraction(XRD). The iterative procedure along with the minimum deviation was employedto determine the kinetic parameters of phase transformation of kaolinite. Results show that the kaolinite phasetransformation occurs from the metakaolin into mullite in the temperature range 975-1040 C. The kaolinite phaseransformation conforms to an accommodated nuclei production and nuclei growth model. The correspondingmechanism functions are f(a)=3(1-a)[-In(1-a)P and G(a)=[-In(1-a)]. The activation energy E, and pre-exponential factor A of kaolinite phase transformation are 840.44 k] mol-and 1 54x10--1 65x108-, respectivelyKey words: kaolinite; phase transformation; DSC; non-isothermal kinetics; iterative method高嶺土為三斜晶系,一般為無(wú)色至白色的細(xì)小并未給出。而 Traore等認(rèn)為高嶺土在950-1020℃鱗片,單晶呈假六方板狀或書(shū)冊(cè)狀,平行連生的集時(shí)成核與晶體生長(zhǎng)同時(shí)進(jìn)行,XRD和微晶實(shí)驗(yàn)證實(shí)合體往往呈蠕蟲(chóng)狀或手風(fēng)琴狀,是造紙、陶瓷、化該過(guò)程為非均相同時(shí)轉(zhuǎn)變?yōu)榧饩湍獊?lái)石,不能工、涂料醫(yī)藥和國(guó)防等幾十個(gè)行業(yè)中必須的礦物以 Arrhenius公式計(jì)算得到重結(jié)晶的動(dòng)力學(xué)參數(shù)。原料。高嶺土相轉(zhuǎn)變的研究是材料學(xué)和礦物學(xué)研本工作以廣東茂名高嶺土為原料,研究了髙溫下高究的熱點(diǎn)之一,高溫下高嶺土相轉(zhuǎn)變產(chǎn)生的莫來(lái)石嶺土由偏高嶺土轉(zhuǎn)變?yōu)槟獊?lái)石過(guò)程。通過(guò)迭代的等具有較低的熱傳導(dǎo)系數(shù)、熱膨脹系數(shù)、優(yōu)良的抗蠕轉(zhuǎn)化率法求算高嶺土相轉(zhuǎn)變的活化能,以最小偏差變和熱穩(wěn)定性等性質(zhì),可作為高溫材料廣泛應(yīng)用于法得到最可能機(jī)理函數(shù)最后求得指前因子,從而工業(yè)生產(chǎn)網(wǎng)。徐豐平等剛通過(guò)DSC數(shù)據(jù)運(yùn)用得到完整的動(dòng)力學(xué)三因子Kissinger和Oawa方程計(jì)算得到的高嶺土轉(zhuǎn)變?yōu)槟獊?lái)石相變活化能分別為9283k·mol和95541實(shí)驗(yàn)部分kJ·mol-,該過(guò)程為一級(jí)固相反應(yīng),其成核過(guò)程為以11試劑與儀器界面擴(kuò)散生長(zhǎng)為主,但具體的機(jī)理函數(shù)和指前因子收稿山期:201003-10。收修改稿日期:201003-29。H中國(guó)煤化工要成分為:4628%CNMHG家自然科學(xué)基金資助項(xiàng)目No50972135)。通訊聯(lián)系人。 E-mail hezhong@26com第一作者:周佳,男,24歲,碩士研究生;研究方向:熱分析動(dòng)力學(xué)。1280無(wú)機(jī)化第26卷SO2;3815%AlO3,平均粒度為2μm。德國(guó) Netzsch公司STA409PC綜合熱分析儀。荷蘭 PANalyticalh(u)=u+18u+88a+96uu+20u+120u+240u+l20公司 X Pert PRO Dy2198X射線衍射儀。迭代過(guò)程可分為三步:步驟一,假設(shè)Hl)=1或12實(shí)驗(yàn)條件h(a)=1,代人方程5)或(6中,并以lnBH(叫)對(duì)1T或綜合熱分析儀:高嶺土用量為1840-18831mg;ln{h(u)7對(duì)/進(jìn)行線性回歸,通過(guò)斜率可求得升溫速率分別為510.150.25及30℃·min;掃描初始的活化能Ea,即為常規(guī)的等轉(zhuǎn)化率法所求得的溫度范圍為30-1200℃;空氣流量為30 mLmin余X射線衍射儀:CuKa靶;管電流80m;管電E值;步驟二,將E1值以及不同升溫速率條件下同壓40kV;步長(zhǎng)002°;掃描角度10.009-65.00定義式中,求取u及相應(yīng)的H(a)或h)的值,再將2基本原理Hal)或h(l)的值代入方程5或(6中線性回歸,可求得新的E值;步驟三,以E代替E,重復(fù)步驟二21迭代法計(jì)算活化能直至E-E1<0.01 kJ mol時(shí),即可認(rèn)為所求得的在升溫速率恒定時(shí),非等溫動(dòng)力學(xué)方程有如下活化能值為真實(shí)值。在不同的a處采取相同的步形式:驟得到a與En的關(guān)系,如果在主要的a范圍內(nèi)-Aexp(pr fa(1)0.2≤a≤08,活化能的數(shù)值基本不變,則可以認(rèn)為該反應(yīng)可以用單一的動(dòng)力學(xué)模型來(lái)描述式(1)中,a為轉(zhuǎn)化率a為動(dòng)力學(xué)機(jī)理函數(shù)B為升22判定最可能的機(jī)理函數(shù)溫速率;E為活化能;A為指前因子;T為該轉(zhuǎn)化率主曲線法是一種判定最可能的機(jī)理函數(shù)的方下的反應(yīng)溫度R為普適氣體常數(shù)設(shè)u=ERT,對(duì)法,它是以實(shí)驗(yàn)曲線和標(biāo)準(zhǔn)曲線的最大重疊或曲線相式(1進(jìn)行移項(xiàng)并兩端同時(shí)進(jìn)行積分得:近作為判定的依據(jù)最小偏差法則是以實(shí)驗(yàn)值和理論G(a)=-2du= op Au)(2值大小差別作為判定依據(jù),從定量方面來(lái)看更具優(yōu)BRBR勢(shì)。最小偏差法求算最可能的機(jī)理函數(shù)過(guò)程如下溫度積分公式Pu)在數(shù)學(xué)上得不到精確解,常常由以a=0.5作為參考點(diǎn),由式(2可以得到近似公式代替。采用Doye近似式得Oawa方程:Au)Auos)=G(a)G(0.5)000484AE為了更加精確地計(jì)算Pua),可采用一個(gè)準(zhǔn)確度1.0516高的溫度積分近似表達(dá)式均。采用 Coats-Redferm近似式得到KAS方程:Pus+8+8+90B-ARt+20u+120u+240u+120將迭代法計(jì)算得到的活化能的平均值和各a由于式(3和式4引人了溫度積分近似公式,在(016≤a≤084間隔00)0處對(duì)應(yīng)的溫度T值代入計(jì)算E時(shí)會(huì)產(chǎn)生一定的誤差。本文采用迭代法啊即式(9左端計(jì)算出 Lupus的值構(gòu)成實(shí)驗(yàn)值;將45Oawa選代法和KAS迭代法來(lái)求算E。若P(a)取種機(jī)理對(duì)應(yīng)的Ga)代入式9的右端計(jì)算出GaySenum-Yang近似可得:Ga的值,構(gòu)成理論值。計(jì)算實(shí)驗(yàn)值和理論值之間Ozawa迭代方程的標(biāo)準(zhǔn)偏差,根據(jù)標(biāo)準(zhǔn)偏差的大小可以找到合適的B=m04848.1051機(jī)理函數(shù)。標(biāo)準(zhǔn)偏差的計(jì)算公式如下KAS迭代方程∑∑G(a Plr)G0.5)P(xA(k)=(n-1)(m-1)(11)式(1中國(guó)煤化工n分別為數(shù)據(jù)點(diǎn)和H()和h()隨著u的變化而變化,它們分別為方程升(5)和(6)進(jìn)行選代的定義函數(shù)其定義式為ah小CNMH能的機(jī)理函數(shù)時(shí),exp(-uh(u/uHu0.00484exp(-1.0516u))23指前因子求解確定機(jī)理函數(shù)G(a)之后將其代入到式(2)中,第7期周佳等:高嶺土相轉(zhuǎn)變的非等溫動(dòng)力學(xué)移項(xiàng)并兩邊取對(duì)數(shù)得:偏高嶺土轉(zhuǎn)變成為莫來(lái)石,這與文獻(xiàn)口報(bào)道的相符。In[E,/BR)+InAu)=-InA +InG(a)(12)當(dāng)升溫速率為一定值時(shí),把溫度積分近似表達(dá)式,活化能平均值和各轉(zhuǎn)化率對(duì)應(yīng)的溫度代入式12的左端,設(shè)定的轉(zhuǎn)化率代人上式的右端用叫l(wèi)nE2A(BR)+nPu)對(duì)lna)作圖,可得到一條直線根據(jù)直線的截距可得到lnA的值,計(jì)算得到不同升溫速率下的lnA,就得到指前因子的變化范圍。3結(jié)果與討論31XRD分析圖2升溫速率為20℃·min時(shí)高嶺土的 TG-DSC圖1是高嶺土原樣(曲線a以及經(jīng)過(guò)850℃(曲曲線線b和1200℃(曲線c)煅燒后樣品的XRD圖,曲Fig 2 TG-DSC curves of kaolinite at heating rate of20℃·mi線a衍射峰的峰型尖銳且對(duì)稱性好,與標(biāo)準(zhǔn)卡片No.4-1784對(duì)比可知樣品為高嶺土;曲線b幾乎沒(méi)33相轉(zhuǎn)變動(dòng)力學(xué)有明銳的衍射峰,呈現(xiàn)典型的無(wú)定形結(jié)構(gòu),沒(méi)有明圖3為不同升溫速率下900~1100℃高嶺土的顯的晶型存在,即高嶺土經(jīng)過(guò)850℃煅燒后轉(zhuǎn)變成SC曲線。根據(jù)DSC曲線所對(duì)應(yīng)的數(shù)據(jù),運(yùn)用21非晶態(tài)偏高嶺土;曲線c與標(biāo)準(zhǔn)卡片No060238對(duì)中求活化能的4種方法對(duì)高嶺土相轉(zhuǎn)變過(guò)程的活照,證實(shí)該晶態(tài)物質(zhì)為莫來(lái)石,表明樣品經(jīng)過(guò)1200化能進(jìn)行計(jì)算,得到不同轉(zhuǎn)化率時(shí)相對(duì)應(yīng)的活化能℃煅燒后重新結(jié)晶并生成新的晶態(tài)物質(zhì)山。的值,見(jiàn)表1。3:5℃mis6:30℃mim110028/(°)圖1高嶺土樣品及不同煅燒溫度樣品的XRD圖圖3不同升溫速率下高嶺土相轉(zhuǎn)變的DSC曲線Fig 1 XRD pattems of kaolinite sample and samplesFig 3 DSC curves of the kaolinite phase transformationcalcined at different temperaturesat different heating rates3.2TG-DSC分析由表1可以看出,由Oawa法和KAS法所得活圖2是升溫速率為20℃·min4時(shí)高嶺土在化能結(jié)果相差2104kJmo,而由Oawa迭代法和30-1200℃之間的 TG-DSC曲線,由圖可知高嶺土KAS迭代法計(jì)算的結(jié)果基本一致所得活化能相差在40-700℃之間發(fā)生熱分解反應(yīng),其對(duì)應(yīng)為高嶺僅0.52 k].mol-。鑒于兩種迭代法分別為Owa法土分子內(nèi)羥基的脫除,實(shí)際平均失重率(13.56%)和KAS法的改進(jìn)故取二者所得活化能的平均值作與理論失重率(13%6%)相吻合。在975~1040℃之為高嶺土相轉(zhuǎn)變所需活化能,即E=840.44 kJ mol。間,DSC曲線上有一個(gè)尖銳的放熱峰,而在相同溫中國(guó)煤化衛(wèi)數(shù)據(jù)代入式左度區(qū)間熱重曲線計(jì)算表明失重率小于01%,故在端此溫度區(qū)間樣品應(yīng)發(fā)生了相轉(zhuǎn)變過(guò)程。CNMc45種機(jī)理對(duì)應(yīng)的∴x如0.5的值。根據(jù)最綜合XRD和 TG-DSC的結(jié)果表明,在975~小偏差法對(duì)實(shí)驗(yàn)值和理論值進(jìn)行處理,表2中列出1040℃之間,樣品發(fā)生了相轉(zhuǎn)變過(guò)程,由非晶態(tài)的了其中較優(yōu)的6種機(jī)理及其對(duì)應(yīng)的標(biāo)準(zhǔn)偏差,由表無(wú)機(jī)化學(xué)學(xué)報(bào)第26卷表1計(jì)算得到的高嶺土相轉(zhuǎn)變所對(duì)應(yīng)的活化能E表3高嶺土相轉(zhuǎn)變?cè)诓煌訜崴俾蕰r(shí)對(duì)應(yīng)的Table 1 Activation energies for ph指前因子transformation of kaoliniteTable 3 Pre-exponential term of the phasetransformation of kaolinite atE./(k·mol)different heating ratesOzawaInP.l/Tβ/(℃·min) Intercept SlopeA/s01853.746487668098769125876930378.7550.90130.99711.5954x10-78763093590996416082×10015847.7374870.2787870.5873870.528278.7582843.705I866.1215866.3178866.370998740996016002×10x8788097400995916489×100.2584038448625462862838903837617185963628599135859885605050787181.0394099451.5374x10M78.7321.1104099221.5591×100.3582180408430072843.2307843.256604819.0368840097184030538403465B: Heating rate, r: Correlation coefficient, A: Pre-ex0458163485837.187083745908374364factor8242551845.5847845.760884583414結(jié)論0.1437841.26118414913841.51050681563708364387836.7474836688在動(dòng)態(tài)空氣氣氛條件下,本文所用高嶺土在0.6581041868309262831.21288311839975~1040℃的溫度范圍內(nèi)相轉(zhuǎn)變生成莫來(lái)石的過(guò)07803856282406678243341824.3245程符合 Arrhenius公式,其相轉(zhuǎn)變的活化能E=0.757960288815.78558160323816043284044 kJ mol-;以最小偏差法得到最可能機(jī)理函8786264280550048057538805.7665數(shù),機(jī)理為隨機(jī)成核和隨后生長(zhǎng),機(jī)理函數(shù)的微0857734398791997779223367839493分和積分表達(dá)式分別為f(a)=31-a)-n(1-a)3和Average819.4014840.44478406957840.78Ga)--ln(1-a);指前因子A的范圍為154×10B=5,10,15,20,25,30℃min3裘2高嶺土相轉(zhuǎn)變對(duì)應(yīng)的較優(yōu)機(jī)理Table 2 Better mechanism of phase transformation致謝:“納米礦物材料及應(yīng)用教育部工程研究中心”的of kaolinite嚴(yán)春杰教授為本實(shí)驗(yàn)提供高嶺土樣品,在此表示衷心感謝。0.0668參考文獻(xiàn)007461000837[] WANG Xue-Jing(王雪靜), ZHANG』a-Min(張家敏).Uxiao-Bo(李曉波)etal. China non- Metall. Mining Indu(Zhongguo Feyjushu Kuangye Daokan), 2007, 5: 18-20007752] WEI Cun-D魏存弟), MA Hong-Wen(馬鴻文, YANG DianNo. Order number k: Mechanism number. A: StandardFan(楊殿范},etal. Chin. Ceram. Soc..( guisuanyandeviation.Xuebo),20053(1):77-81可知第11號(hào)機(jī)理所對(duì)應(yīng)的標(biāo)準(zhǔn)偏差最小,應(yīng)為高(3] Aksay A, Dabbs d m, Sarikaya M. J. Am. Ceram Soc,1991,嶺土相轉(zhuǎn)變過(guò)程的最可能機(jī)理,該機(jī)理為隨機(jī)成核14(1023412346和隨后生長(zhǎng)機(jī)理,對(duì)應(yīng)的機(jī)理函數(shù)為G(a){-n(1- XU Feng-Ping(徐豐平, CHEN Nan-Chun(陳南春,AOHaa)p,相應(yīng)的微分式為fa)=3(1-a0-m(1-a。Mei(放寒梅).lnd. Miner.Poe.( Huagong Kuangou Yu由23的計(jì)算方法得到不同升溫速率下的指前因子A如表3所示。從表3可知斜率均接近1,相1n中國(guó)煤化工 P. Thermochim. ACNMHG關(guān)系數(shù)r≥092,線性關(guān)系較好,這也進(jìn)一步表明[6]Doyle C D J. AppL Polymer Sci, 1961. 5(15): 285-292了本文求得的高嶺土相轉(zhuǎn)變機(jī)理的準(zhǔn)確性。計(jì)算得 [7) Coats A W, Redfern JP,Mne,194014914A6869該指前因子A范圍為1.54×10%-1.65×10ys-[8]Gao Z, Nakada M, Amasaki I. Thermochim. 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