1,1′-二羥基-5,5′-聯(lián)四唑金屬鹽的制備及熱分解動(dòng)力學(xué)

王杰群, 王鵬程, 陸 明

(南京理工大學(xué)化工學(xué)院, 江蘇 南京 210094)

1 引 言

調(diào)節(jié)推進(jìn)劑的燃燒性能是固體推進(jìn)劑研究的熱點(diǎn)之一。為達(dá)到推進(jìn)劑燃速調(diào)節(jié)范圍寬和壓強(qiáng)指數(shù)低的目的,一般采用添加燃燒催化劑的方法[1],而其中常用的惰性催化劑對(duì)推進(jìn)劑能量損失較大[2],而含能催化劑因克服惰性催化劑的缺點(diǎn)得到了廣泛關(guān)注和研究[3-4]。含能催化劑有很多種類,其中的唑類金屬鹽具有密度大、蒸氣壓低、極性強(qiáng)、熱穩(wěn)定性好、性能可調(diào)等特點(diǎn),同時(shí)可降低推進(jìn)劑的特征信號(hào),有望成為推進(jìn)劑的良好組分[4]。Li等[5]合成3,6-雙(1-氫1,2,3,4-四唑-5-氨基)-1,2,4,5-四嗪(BTATz)鉛鹽,使雙基推進(jìn)劑(DB)推進(jìn)劑在8～12 MPa范圍內(nèi)產(chǎn)生“麥撒效應(yīng)”同時(shí)壓強(qiáng)指數(shù)降至-0.065,使復(fù)合改性雙基推進(jìn)劑(CMDB)在4～12 MPa范圍產(chǎn)生平臺(tái)燃燒,同時(shí)壓強(qiáng)指數(shù)降至0.18,是高效的含能催化劑[1]。

為使含能催化劑具有更多的候選物質(zhì),利用四唑化合物1,1′-二羥基-5,5′-聯(lián)四唑(1,1′-BTO)[6]的酸性,通過(guò)復(fù)分解反應(yīng),合成了1,1′-二羥基-5,5′-聯(lián)四唑的鈷鹽(1,1′-BTOCo)、銅鹽(1,1′-BTOCu)和鉛鹽(1,1′-BTOPb)。通過(guò)DSC和TG研究三種鹽的熱分解行為,分別用Kissinger法[7]和Ozawa法[8-9]計(jì)算得到熱分解表觀活化能、指前因子、機(jī)理函數(shù)和動(dòng)力學(xué)方程,進(jìn)而計(jì)算其自加速分解溫度(TSADT)、熱爆炸臨界溫度(Tbpo)和熱力學(xué)參數(shù),初步評(píng)價(jià)其熱安全性,為其在燃燒催化劑中的應(yīng)用提供理論基礎(chǔ)。

2 實(shí)驗(yàn)部分

2.1 試劑與儀器

1,1′-BTO,實(shí)驗(yàn)室自制,制備方法見文獻(xiàn)[6]。

DSC: 823e差示掃描量熱儀,瑞士METTLER TOLED公司。升溫速率均為5,10,15,20 K·min-1,氮?dú)鈿夥?流速30 mL·min-1,樣品質(zhì)量(0.2000±0.02) mg。TG: TGA/SDTA851e熱分析儀,瑞士METTLER TOLED公司。升溫速率為15 K·min-1,氮?dú)鈿夥?流速30 mL·min-1,樣品質(zhì)量(0.2000±0.02) mg。

2.2 金屬鹽的合成

1,1′-BTOCo: 常溫下,1,1′-BTO(0.51 g,0.003 mol)完全溶解于水中,攪拌下加入CoSO4·7H2O(0.68 g,0.003 mol),過(guò)濾得固體,乙醇和水洗進(jìn)行提純,過(guò)濾烘干,得粉色固體0.29 g,收率43.15%。IR(KBr,ν/cm-1): 1607,1437,1253,1183,1013,573; 元素分析(C2N8O2,%): 計(jì)算值,C 14.29,N 66.67; 實(shí)測(cè)值,C 14.15,N 65.97。

1,1′-BTOCu: 1,1′-BTO(0.51 g,0.003 mol)完全溶解于水中,加入CuSO4·5H2O(0.84 g,0.003 mol),用同樣方法處理得淡綠色固體0.36 g,收率51.28%。IR(KBr,ν/cm-1): 1627,1439,1259,1190,1010,748,662; 元素分析(C2N8O2·2H2O,%): 計(jì)算值,C 11.76,H 1.96,N 54.90; 實(shí)測(cè)值,C 11.68,H 2.01,N 53.47。

1,1′-BTOPb: 1,1′-BTO(0.51 g,0.003 mol)完全溶解于水中,攪拌下加入自制Pb(NO3)2(0.76 g,0.003 mol)水溶液,同樣方法處理得白色固體0.42 g,收率56.00%。IR(KBr,ν/cm-1): 1628,1406,1232,1169,991,728,578; 元素分析(C2N8O2·H2O,%): 計(jì)算值,C 12.90,H 1.08,N 60.22; 實(shí)測(cè)值,C 12.73,H 1.12,N 59.69。

X射線熒光光譜測(cè)定,1,1′-BTOCo,1,1′-BTOCu,1,1′-BTOPb中分別含有金屬Co、Cu、Pb。三種鹽等質(zhì)量測(cè)試,理論值: CoO 25.65,CuO 27.18,PbO 47.17; 實(shí)測(cè)值: CoO 25.80,CuO 28.85,PbO 44.59。

2.3 結(jié)果與討論

1,1′-BTOCo、1,1′-BTOCu、1,1′-BTOPb在升溫速率為5，10，15，20 K·min-1下的DSC曲線如圖1、圖3和圖5所示。升溫速率為15 K·min-1下1,1′-BTOCo、1,1′-BTOCu、1,1′-BTOPb的TG-DTG曲線如圖2、圖4和圖6所示。從DSC曲線可知,三種鹽各自隨著升溫速率的增加,DSC放熱峰向高溫方向移動(dòng)。1,1′-BTOCo的TG曲線(圖2)在475 K之前有一定質(zhì)量損失,但對(duì)應(yīng)DSC曲線(圖1)無(wú)吸熱峰,所以為失去游離水階段; 1,1′-BTOCu 的TG曲線(圖4)在400 K之前有明顯質(zhì)量損失,對(duì)應(yīng)DSC曲線(圖3)有吸熱峰,所以為失去結(jié)晶水水階段; 1,1′-BTOPb的TG曲線(圖6)在370 K之前有明顯質(zhì)量損失,對(duì)應(yīng)DSC曲線(圖5)有吸熱峰,所以為失去結(jié)晶水水階段。

圖11,1′-BTOCo在不同升溫速率下的DSC曲線

Fig.1DSC curves of 1,1′-BTOCo at different heating rates

圖215 K·min-1時(shí)1,1′-BTOCo的TG-DTG曲線

Fig.2TG-DTG curves of 1,1′-BTOCo at 15 K·min-1

圖31,1′-BTOCu在不同升溫速率下的DSC曲線

Fig.3DSC curves of 1,1′-BTOCu at different heating rates

圖415 K·min-1時(shí)1,1′-BTOCu的TG-DTG曲線

Fig.4TG-DTG curves of 1,1′-BTOCu at 15 K·min-1

圖51,1′-BTOPb在不同升溫速率下的DSC曲線

Fig.5DSC curves of 1,1′-BTOPb at different heating rates

圖615 K·min-1時(shí)1,1′-BTOPb的TG-DTG曲線

Fig.6TG-DTG curves of 1,1′-BTOPb at 15 K·min-1

3 結(jié)果與討論

3.1 動(dòng)力學(xué)參數(shù)計(jì)算

不同升溫速率下(5、10、15,20 K·min-1)三種鹽到熱分解特征參數(shù),見表1。用Kissinger法[7]和Ozawa法[8-9]求得表觀活化能(EK和EO)、指前因子(AK),見表1。

對(duì)于炸藥的熱分解,用非等溫法做熱分解動(dòng)力學(xué)研究時(shí),常用的Ozawa公式為[8-9]:

(1)

式中,α為炸藥反應(yīng)深度,%;R為理想氣體常數(shù),8.314 J·mol-1·K-1;β為升溫速率,K·min-1;T為溫度,K;A為指前因子, s-1;EO為表觀活化能,J·mol-1·K-1;F(α)為機(jī)理函數(shù)的積分形式。

若選擇相同的α,lgβ與1/T呈線性關(guān)系,由直線的斜率計(jì)算活化能,并用來(lái)求解熱分解的機(jī)理函數(shù)。

根據(jù)Doyle法[9],式(1)可以變換為:

(2)

在式(2)中,對(duì)于任何熱分解的機(jī)理函數(shù),lgF(α)與1/T呈線性關(guān)系。對(duì)于某個(gè)假設(shè)的反應(yīng)機(jī)理函數(shù),若通過(guò)Doyle法求解得到的熱分解活化能與Ozawa法求得的活化能接近,且線性相關(guān)系數(shù)好,由此獲得熱分解的反應(yīng)機(jī)理函數(shù)[10]。

表1不同升溫速率下DSC曲線得到的參數(shù)值

Table1The parameters determined by DSC curves at different heating rates

compoundβ/K·min-1Te/KTp/KΔHd/J·g-1Kissinger'smethodEK/kJ·mol-1AK/s-1Ozawa'smethodEO/kJ·mol-11,1'-BTOCo5511.26539.261181.3610503.04548.331603.1115508.98554.931835.0720528.26559.471173.29162.351.83×1015164.821,1'-BTOCu5527.61547.881173.2910533.29556.751228.8215539.96559.811564.8520542.98563.761342.24217.952.58×1020208.101,1'-BTOPb5529.34558.731491.6710534.19561.151274.1415539.39568.281113.3320543.91572.821189.17223.524.24×1020239.56

Note:Teis extrapolated onset temperature;Tpis the first temperature of exothermic peak; ΔHdis decomposition enthalpy;Ais pre-exponential constant;Eis Apparent activation energy; Subscript K, data obtained by Kissinger′s method; Subscript O, data obtained by Ozawa′s method.

根據(jù)升溫速率分別為5,10,15,20 K·min-1時(shí),1,1′-BTOCo熱分解曲線,分別求出反應(yīng)深度α所對(duì)應(yīng)的反應(yīng)溫度T。根據(jù)公式(1)和實(shí)驗(yàn)數(shù)據(jù)對(duì)lgβ與1/T進(jìn)行線性擬合,由直線斜率計(jì)算得表觀活化能EO,見表2。根據(jù)公式(2)用Doyle法對(duì)假設(shè)的炸藥分解反應(yīng)的機(jī)理函數(shù)相應(yīng)lgF(α)與1/T進(jìn)行線性回歸分析,結(jié)果見表3。線性擬合結(jié)果表明,1,1′-BTOCo在反應(yīng)深度為0.2～0.6的階段,熱分解屬于相邊界反應(yīng)(一維),R1,n=1機(jī)理。反應(yīng)機(jī)理的微分形式為f(α)=α,熱分解動(dòng)力學(xué)方程為:

(3)

(4)

用同樣的方法得到1,1′-BTOPb的表觀活化能EO,見表6,并進(jìn)行線性回歸分析,計(jì)算結(jié)果見表7。線性擬合結(jié)果表明,鉛鹽熱分解第一階段,即反應(yīng)深度為0.3～0.5的階段,熱分解屬于一維擴(kuò)散,1D,D1減速型α-t曲線機(jī)理。反應(yīng)機(jī)理的微分形式為f(α)=α2,熱分解動(dòng)力學(xué)方程為:

(5)

3.2 熱爆炸臨界溫度

自加速分解溫度(TSADT)的計(jì)算,依據(jù)表1,按照文獻(xiàn)[7,10-11],由式(6)計(jì)算得β→0時(shí)的Te0和Tp0。

(6)

式中,βi為試樣升溫速率,K·min-1;To0、Te0和Tp0分別為β→0時(shí)的T0、Te和Tp值,K。

表21,1′-BTOCo的熱分解反應(yīng)活化能計(jì)算數(shù)據(jù)

Table2Calculated data of the activation energy for thermal decomposition reaction of 1,1′-BTOCo

compoundαT/Kβ=5K·min-1β=10K·min-1β=15K·min-1β=20K·min-1rEO/kJ·mol-11,1'-BTOCo0.2526.32536.32545.82545.820.9981158.780.25529.23539.32548.82548.820.9978160.060.3531.90542.15551.48551.480.9974161.480.35534.48544.98553.82553.820.9969162.880.4536.98547.48556.48556.480.9964164.260.45539.32549.98558.82558.820.9959164.400.5541.73552.48561.15561.150.9954166.780.55544.07554.98563.48563.480.9948167.840.6546.57557.65566.15566.150.9941168.59average163.90

Note:αis depth of reaction;Eis apparent activation energy; Subscript O, data obtained by Ozawa′s method.

表31,1′-BTOCo的lgF(α)-1/T的線性擬合結(jié)果

Table3Liner fitting results of lgF(α)-1/Tfor 1,1′-BTOCo

compoundβ/K·min-1interceptslopeDoyle'smethodr2Ed/kJ·mol-1Ad/s-1Ozawa'smethodEO/kJ·mol-11,1'-BTOCo516.5185-9210.16670.9799167.671.41×10151015.8778-9040.33600.9785164.576.61×10141516.4833-9479.43930.9772172.572.51×10152017.0773-9855.66270.9776179.429.55×1015163.90average171.062.57×1015

Note:Adis pre-exponential constant;Eis apparent activation energy; Subscript d, data obtained by Doyle′s method; Subscript O, data obtained by Ozawa′s method.

表41′-BTOCu的熱分解反應(yīng)活化能計(jì)算數(shù)據(jù)

Table4Calculated data of the activation energy for thermal decomposition reaction of 1,1′-BTOCu

compoundαT/Kβ=5K·min-1β=10K·min-1β=15K·min-1β=20K·min-1rEO/kJ·mol-11,1'-BTOCu0.25537.57545.98550.40553.480.9993205.010.3539.57547.98552.15555.820.9993205.700.35541.23549.65553.90557.480.9992206.440.4542.73551.32555.40558.820.9990207.300.45544.07552.65556.65560.150.9988208.160.5545.32553.98557.90561.480.9986208.930.55546.48555.15558.90562.820.9983209.49average207.29

表51,1′-BTOCu的lgF(α)-1/T的線性擬合結(jié)果

Table5Liner fitting result of lgF(α)-1/Tfor 1,1′-BTOCu

compoundβ/K·min-1interceptslopeDoyle'smethodr2Ed/kJ·mol-1Ad/s-1Ozawa'smethodEO/kJ·mol-11,1'-BTOCu520.7760-11391.66080.9986207.382.45×10191020.1870-11246.71020.9993204.741.29×10191521.7567-12201.37420.9988222.126.61×10202020.8558-11775.46120.9980214.371.15×1020207.29average212.157.08×1019

表61,1′-BTOPb的熱分解反應(yīng)活化能計(jì)算數(shù)據(jù)

Table6Calculated data of the activation energy for thermal decomposition reaction of 1,1′-BTOCu

compoundαT/Kβ=5K·min-1β=10K·min-1β=15K·min-1β=20K·min-1rEO/kJ·mol-11,1'-BTOPb0.30552.15559.15564.15566.820.9994234.550.35554.57561.65566.40569.150.9992237.570.40556.98564.15568.90571.480.9989239.240.45559.23566.65571.40573.820.9986239.920.50561.57568.98573.90576.150.9982240.43average238.34

表71,1′-BTOPb的lgF(α)-1/T的線性擬合結(jié)果

Table7Liner fitting results of lgF(α)-1/Tfor 1,1′-BTOCu

compoundβ/K·min-1interceptslopeDoyle'smethodr2Ed/kJ·mol-1Ad/s-1Ozawa'smethodEO/kJ·mol-11,1'-BTOPb522.9920-13257.47430.9920241.353.47×10211022.3470-13065.49960.9932237.851.62×10211522.2574-13126.77810.9892238.971.95×10212023.7608-14044.27300.9914255.677.76×1022238.34average243.465.37×1021

又根據(jù)TSADT=Te0,計(jì)算可得1,1′-BTOCo的TSADT=534.46 K,Tp0=527.31 K; 1,1′-BTOCu的TSADT=527.56 K,Tp0=526.50 K; 1,1′-BTOPb的TSADT=525.87 K,Tp0=568.32 K。

爆炸臨界溫度(Tbpo)的計(jì)算,根據(jù)Zhang-Hu-Xie-Li法,將表2中Ozawa法得到的EO和Tp0代入式(7)。

(7)

計(jì)算可得1,1′-BTOCo的Tbpo=542.22 K,1,1′-BTOCu的Tbpo=539.11 K,1,1′-BTOPb的Tbpo=580.00 K。

3.3 熱力學(xué)參數(shù)

計(jì)算熱力學(xué)參數(shù),包括自由能ΔG≠,活化焓ΔH≠和活化熵ΔS≠,根據(jù)文獻(xiàn)[12]按式(8)～(10)計(jì)算:

(8)

ΔH≠=Ek-RTp0

(9)

ΔG≠=ΔH≠-Tp0ΔS≠

(10)

式中,kB為Boltzmann常數(shù),1.3807×10-23J·K-1;h為Plank常數(shù),6.626×10-34J·K-1;EK為表觀活化能,J·mol-1;AK為指前因子,s-1。

計(jì)算可得1,1′-BTOCo的ΔG≠=139.92 kJ·mol-1,ΔH≠=157.97 kJ·mol-1,ΔS≠= 34.23 J·mol-1; 1,1′-BTOCu的ΔG≠=143.51 kJ·mol-1,ΔH≠=213.56 kJ·mol-1,ΔS≠=132.98 J·mol-1; 1,1′-BTOPb的ΔG≠=141.34 kJ·mol-1,ΔH≠= 218.79 kJ·mol-1,ΔS≠=136.28 J·mol-1。

4 結(jié) 論

(2) 三種鹽的自加速分解溫度和熱爆炸臨界溫度數(shù)值均較高,且焓變較大,說(shuō)明三種鹽熱安定性好,尤其是常溫下不易發(fā)生熱分解。對(duì)于表觀活化能,1,1′-BTOCo<1,1′-BTOCu<1,1′-BTOPb; 對(duì)于指前因子,1,1′-BTOCo<1,1′-BTOCu<1,1′-BTOPb。

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