勇敢1999
范文一：气相反应的简单碰撞理论简介
6.6反应动力学理论简介
6.6.1双分子反应的简单碰撞理论
该理论以气体分子运动论为基础，把气相中的双分子反应看成是两个分子碰撞的结果，通过计算碰撞频率，得出的反应速率系数表示式。这种碰撞理论也称为简单碰撞理论（simple collision theory略写为SCT ）。
6.6.1.1 理论模型 对气相双分子基元反应 A + B → P ，简单碰撞理论认为：
①气体分子A 和B 均视为无相互作用（独立子）、无内部结构完全弹性的硬球。②气体分子A 和B 必须经过碰撞才能发生反应。通常把相撞的A 和B 分子称为相撞分子对，简称分子对；只有碰撞时的相对平动能在质心连线方向的分量大于某能量阈值（εc ）的分子对才能发生反应，这种能够发生反应的碰撞叫做有效碰撞。③在反应进行过程中，气体分子运动速率与能量仍然保持Boltzmann 平衡分布。
模型要点①和③使气体分子运动论可以被用于计算反应体系中一定能量区间的相互碰撞频率。而假定②则提供了计算有效碰撞概率的判据。
6.6.1.2 理论推导
（1）碰撞截面与碰撞频率(Z AB ) 单位时间、单位体积内分子碰撞的次数称为碰撞数或碰撞频率。 假设分子A 和B 都为硬球，其半径分别为r A 和r B , 则两个分子的质心在碰撞时所能达到的最短距离为（r A +r B ），该距离称为碰撞有效直径（或称为有效直径），用d AB 表示。设B 分子不动，A 分子以平均相对速度运动，如果A 分子与B 分子“擦肩而过”（即相接触）也算是碰撞，则一个A 分子在单位时间内与B 分子碰撞的次数相当于以d AB =（r A + rB ）为半径以 为柱长的圆柱中B 分子的数目。由上图可见，A 球能碰到质心在圆柱内的B 分子，该圆柱的截面积π（r A +r B ）2称为碰撞截面。设单位体积中B 的分子数为N B ，则1个A 分子在单位时间内与B 分子的碰撞次数为：π(r A +r B ) N B 。因气体分子A 与B 的平均相对速率=kT /(πμ) ，单位体积内A 的分子数为N A ，则碰撞频率为：
Z AB =π(r A +r B ) 2(28kT
πμ) N A N B
式中k 为Boltzmann 常数；μ为折合质量：μ=m A . m B ，m A 和m B 分别为分子A 和B 的质量。 m A +m B
（2）有效碰撞概率（q ）
根据碰撞理论的假设②，碰撞是否导致反应还与分子的能量有关，只有那些
碰撞时相对平动能在质心连线方向的分量大于某能量阈值（εc ）的分子对才能发生反应。因此εc 是该反应发生所必需的能量，称为阈能，或临界能。根据Boltzmann 分布定律，能量大于阈能（即ε≥εc ）的活化分子所占的分数为
q =ex p[-εc /(kT )]=ex p[-E c /(RT )]
式中E c =Lεc ，即摩尔阈能，亦称阈能。q (实际上就是Boltzmann 因子) 又称为有效碰撞分数。这样，单位时间、单位体积内A 与B 分子的有效碰撞数为：
' Z AB =π(r A +r B ) 2(8kT
πμ) ex p(-E c ) N A N B RT
E C dC A 2-=LC A C B (rA +r B ) exp(-) dt RT
简单碰撞理论只是就气相双分子反应提出的速率理论，对单分子反应、三分子反应及溶液中的反应都需要引人新的假定或模型。
6.6.2过渡状态理论
化学反应是分子内与分子间的某些化学键的断裂和重新建立过程，是原子间的重排作用。如果将参加反应的多个原子作为一个系统，该系统的势能是原子间距离的函数，那么化学反应便可以被视作一个代表点在多原子系统势能空间中的运动。这便是过渡状态理论（transition state theory 简写为TST ）的基本出发点。过渡状态理论是1935年后由Eyring （埃林）、Polanyi （鲍兰尼）等人在统计力学和量子力学发展的基础上提出来的，该理论涉及势能面、能垒等重要概念。
6.6.2.1 势能面
双原子系统 对A + B →AB这样简单的双原子反应系统，因AB 为线型只有两个转动自由度，所以双原子反应系统的势能Ep 只是一个变量即原子核间距离RAB 的函数——Ep = E (RAB)。
三原子系统 讨论原子A 与双原子分子B-C 反应过程的势能变化情况。对于三原子体系，势能Ep 应是核间距R AB 、R BC 和R AC 或φ的函数。
E P =E (R AB , R BC , R AC ) E P =E (R AB , R BC , φ)
（1）势能面图 当固定其中一个变量，如设φ=180o，即为通常的共线碰撞，则势能变化E P = E (R AB , R BC , 180о) 可用三维空间中的曲面表示。这种势能随原子间距变化的曲面称为势能面。
两个图结合起来看，势能面犹如起伏的山峰，引人注意的是势能面中存在两个山谷，山谷的两个谷口R 点和P 点分别相应于反应的初态和终态，连接两个山谷间的山脊顶点（P ≠点）形似马鞍点。
（2） 代表点在势能面上的运动 反应物A + BC的代表点反应前在山谷的谷口R 点（此时R AB →∞ , R BC
= R BC,0，R BC,0是BC 分子中原子间的平衡距离），沿着山谷往上爬（A 向B 趋近，C 离B 渐远），及至鞍点T ≠，便形成活化络合物（即三原子结合呈若即若离的过渡状态A…B…C），这种活化络合物常以上标“≠”表示。此后，活化络合物既可能继续沿右山谷下降到另一谷底P （此时R BC →∞ , R AB = R AB,0，即形成分子AB ）形成产物，也可能沿老路再倒退回到R 点谷口。由R 经P ≠到达P 的路线如图中虚线所示，显然是一条最低能量的反应途径，称为反应坐标，也叫基元反应自身的“详细机理”。
（3）势能——反应坐标图 如以势能为纵坐标，反应坐标为横坐标，可得到如图所示的势能曲线图，此图能更清楚地反映出反应进行过程中势能的变化情况。由此图可知，反应物转化为产物必须越过势能垒E b 。 E b 是活化络合物与反应物两者最低势能之差值。与此相近的是两者零点能之间的差值E 0。反应分子之所以能克服势能垒转化为产物，是因为分子在碰撞过程中将平动能转化为势能。只有原来具备足够大碰撞动能的反应物，才有可能转化成足够的势能，登上马鞍点，并翻越能峰生成产物。由此，活化能的物理意义也就更明显更具体化了。
6.6.2．2 气相反应过渡状态理论
（1） 理论模型 ①来自反应物一方沿反应坐标越过能垒鞍点的活化络合物都转化为产物。②无论是反应物还是活化络合物都具有相应于反应系统温度的Boltzmann 分布。③在化学反应的非平衡情况下，仍然可以使用反应物与活化络合物间的热力学平衡关系。
以双分子基元反应 A + BC → AB + C为例
K ≠k A +BC ?A B C ≠??→AB +C 式中A…B…C≠ 代表处于鞍点的活化络合物。
（2） 公式推导 活化络合物A…B…C≠为线型三原子分子，它有3个平动自由度，2个转动自由度，其振动自由度为3n-5 = 4（式中n 为分子中的原子数）。活化络合物的分解速率系数等于不对称伸缩振动的频率ν≠，设活化络合物的浓度为[ABC≠] ，则反应速率
d[ABC≠] r ==ν≠[ABC ≠] d t
由于反应物与A…B…C≠ 间可以使用热力学平衡关系，于是理想气体间反应A + BC = A…B…C≠的标准平衡常数
K (≠) ≠?p ?[ABC ] = ? ?[A][BC]?RT ?
r =ν≠K (≠) [A][BC](RT /p ) =k [A][BC]
所以
k =ν≠K ( ≠) (RT /p )
6.6.2.3 速率系数的计算---热力学方法计算k T
对理想气体间反应： A + BC = A…B…C ≠
K ≠= exp[- ?r G m /(RT )] 及 ?r G m = ?r H m - T ?r S m 式中?r G m ，?r H m 及?r S m 分别称之为标准活化自由能、标准活化焓及标准活化熵。 ≠≠≠≠≠≠≠k T =
k T ?RT ? ? K ≠? h ?p ?式中K ≠是从标准平衡常数K (≠) 中抽出不对称伸缩振动配分函数后的余下部分，通常称其为标准活化平衡常数。
k T ?RT ??≠
r S m ?≠
r H m 对双分子反应 k T = ??exp() ?exp(-) ?h R RT ?p ?
?≠?≠
r H m r S m 对单分子反应 k T =?exp() ?exp(-) h R RT k T
该方法是由反应物转变为活化络合物过程中的热力学函数变化值来计算速率系数k T 值。
6.6.2.4 与Arrhenius 公式比较 以双分子反应为例
E a =?r H m +2RT
?≠
r S m kT 2?RT ?A T =?exp(e ) ? h R ?p ?
?≠
r S m 上式中exp() 相当于概率因子P 。 R ≠ 该公式能够较好地从微观结构的本质上解释概率因子的物理意义。另外，?r S m 原则上可由分子结构的数据求得，克服了简单碰撞理论中只能由实验确定的缺陷，这也是过渡状态理论的一个明显进步。
成功与不足 过渡状态理论考虑了分子的微观结构，给出了反应坐标与概率因子以较为明确的物理意义，提供了一个完全由微观结构和运动形式计算反应速率的途径和方法。在过渡状态理论中引入的假设是否合理，适用范围多大等方面有的还有不少疑问。在实际应用时最大的问题是多原子系统的统计力学和量子力学计算还存在很大困难。
≠
范文二：P48 5 气相反应求转化率
PROGRAM MAIN
EXTERNAL F
REAL KP,P,KK,EPS,T
COMMON KP,p,KK
T=673.20+273.15
KP=3.46E-5
P=300
EPS=1E-5
A=0.0
B=1.0
KK=KP*(P**2)
WRITE(*,*)'T/K=',T
WRITE(*,*)'KP=',KP
CALL HALF(A,B,EPS,F,X)
WRITE(*,*)'P/ATM=',P
WRITE(*,61)x
61 FORMAT(2X,'X=',F12.6)
END
FUNCTION F(X)
REAL KP,P,KK
COMMON KP,P,KK
F=X*((3-2*X)**2)/(4*((1-X)**3)*(P**2))-KP
RETURN
END
SUBROUTINE HALF(A,B,EPS,F,X)
REAL A,B,EPS
Y0=F(A)
A1=A
B1=B
K=0
10 X=(A1+B1)*0.5
Y=F(X)
IF(Y*Y0.GT.0.0)A1=X
IF(Y*Y0.LE.0.0)B1=X
IF(ABS(B1-A1)/X.GT.EPS)GOTO 10
K=K+1
IF(K.GT.50)THEN
WRITE(*,*)'NO RESOLUTION'
GOTO 30
END IF
X=(A1+B1)*0.5
30 RETURN
END
范文三：浅淡气相反应的速率常数与温度之间的关系
浅淡气相反应的速率常数与温度之间的关
系
?
92?广州化工2008年36卷第3期
浅淡气相反应的速率常数与温度之间的关系
周伟,马永梅,胡涛
(淮阴工学院生命科学与化学工程学院,淮安223001)
摘要:气相反应的速率常数与温度之间一般满足阿累尼乌斯方程式,但当用分压Pi.
浓度c.和摩尔分数Y,来表示反应
物系的组成时,相应阿累尼乌斯方程式中的反应活化能可能不相等,文章推导了气
相反应活化能E和E之间及E和E之间
的关系.
关键词:气相反应;速率常数;活化能
TheRelationshipofRateConstantandTemperatureonGaseousReaction ZHOUWei,MAYong-mei,HUTao
(DepartmentofLifeScienceandChemicalEngineering,HuaiyinInstitute ofTechnology,Huaian223001,China)
Abstract:Therateconstantandtemperatureofthegaseousreactionwerewellrepresentedby
Arrhenius
formula.Whenfractionalpressure,concentrationandmolefractionwerepresentedthecomp
onents,responsible
activationenergyofArrheniusformulamaydifferent.TherelationshipofactivationenergyE
candEp,EcandEy
werederived.,
Keywords:gaseousreactions;rateconstant;activationenergy 化学反应动力学是《物理化学》,《化学反应工程》等课程
的重要教学内容之一,它的研究内容包括化学反应速率和反
应机理.化学反应速率是用来衡量化学反应过程快慢的参 数,对它的影响因素很多,主要有温度,浓度,压力,溶剂以及 催化剂等.其中对绝大多数化学反应速率都起主要影响的是 温度和浓度两因素,故常用化学反应速率方程来定量描述反 应速率与温度及浓度的关系,即r=:f(c,1')其中c为浓度向量, 它表示影响反应速率的反应组分浓度不限一个.目前绝大 多数化学反应的反应机理还不清楚,仍然是以实验为基础来 确定化学反应的速率方程.速率方程通常可采用幂函数或双 曲型函数表示.但从反应器设计和分析应用的角度看,最简 单的速率方程是幂函数形式,它不像双曲型那样含有许多为 温度函数的常数.若用幂函数型速率方程,常常将浓度和温 度对反应速率的影响分离开来表示,即r=f.03f2(c).其中f2) =
cAC……及分别为组分A和B的反应级数;对
于一定的反应温度,则温度函数flrr)为常数,可用反应速率 常数k表示.反应速率常数与温度的关系,一般满足阿累尼 乌斯方程式,即k=Aexp(-E/RT)式中A为指前因子,其因次 与k相同:E为活化能;R为气体常数.
对于气相反应,常用分压pi,浓度c.和摩尔分数Y.来分 别表示反应物系的组成,若其相应的反应速率常数分别为 kp,k和k,则它们之间必定存在一定的联系.
r=kppA~APB…f11
keCAaACB…(2)
KyyA~AyB…(3)
,为总反应级数,由 设反应体系为理想气体,P为总压
各组分的理想气体状态方程知:
Piv--n.RT
pi=c.RTf41
pyi=c.RT(5)
将(4)式代人(2)式,(5)式代人(3)式,分别与(1)式比较得下 列关系式
k=(Rk1:(RT/P)k(6)
式f6)给出了气相反应不同速率常数之间的关系.若kpxk 和k分别满足阿累尼乌斯方程式,即k=Aexp(一E/RT),那么是 否与(61式矛盾?
为了回答上述问题,需进一步分析不同速率常数的阿累 尼乌斯方程式.假设E,E和E分别为用浓度Cix分压Pi和 摩尔分数Y.来表示反应物系组成对应的反应活化能.即 k=Aexp(-EJRT)(7)
kp=Aexp(-Ep/RT)(8)
ky=Aexp(-Ey/RT)(9)
对于同一个气相反应,若假设反应活化能E~=Ev=E,则 由(7)式,(8)式和(9)式知:k=k=k,.那么该结论与(6)式相矛 盾.因此,对于(7)式,(8)式和(9)式中的反应活化能应该不相 等,即E?E?E.若这些反应活化能不相等,那么它们之间 会有什么关系呢?
通常由不同温度(T.,T2)下的反应速率常(下转第101页) 作者简介:周伟,男,硕士,讲师,研究方向:化学工程与工艺.E-mail:zhouweihyit@163.coin
2008年36卷第3期广州化工?101?
从表中看出水泥的凝结时间正常,强度比以前有所提提高0.6t/l1. 喜曼复合矿化剂的工作获得成功,配方合理,生产控4结论制措施有力. ';日
3复合矿化剂的经济效益
3.1煤耗有所降低
,用 在未用复合矿化剂前的熟料标准煤耗160kgt熟料
复合矿化剂后熟料标准煤耗148.9kg/t熟料,节标煤11.1kg/t
熟料,节合实物煤为15.54kg/t熟料,我厂两条3×10米立 窑年产熟料15万吨,即每年节约2331t实物煤,每吨500元 计,一年节约116.5万元.经济效益显着.
3.2立窑台时产量有所提高
在使用复合矿化剂后对工艺流程各环节工作抓紧,细 致,控制效果要求高,为立窑提高产质量打好基础,从上一年 熟料产量14.2万吨与2007年15万吨,推算立窑台时产量 (1)配方设计能与实际相结合.如生料配方提高KH值, 促进C3S增多,水泥配方多加混合材和石膏能控制水泥凝结 时间在标准范围;
(2)采用复合矿化剂后,降低了煤耗,提高了立窑台时产 量,收到了很好的经济效益.,
参考文献
【1】建材情报资料低温烧制水泥新技术.国家建材局技术情报标准 研究所,1982.8.
【2】掺硫铁矿萤石复合矿化剂的硅酸盐水泥熟料.水泥杂志,1985,9.
【3】推广应用复合矿化剂的实践经验.水泥技术,1990,2. (上接第92页)数(k-,k2),利用阿累尼马斯方程R口司求得反应 的活化能:
E=丽RTIT2ln
因此,当反应速率常数分别用ko,k和表示时,求得的 反应活化能各自为:
E=RT~T2l
n
K
c2(10)
RTIT2l
n)
E产
RTIT2ln
Kyl
(12)
下面分别推导反应活化能E.和Ep,E和E之间的关系:
(1)E.和E的关系
对于d级气相反应k.与k的关系有(6)式知:
ko=(Rk
所以对于(10)式有: E=RT~T2-n 丽(RTe)"kP2=器?n+器?n 即!
E
.
一+d—
RT~Tzl
n
T2(13)
(2)E和E的关系
对于d级气相反应k与k的关系有(6)式知:
k=0RT/P)k 所以对于(10试有: E.:—R丽TIT2l( (盟
RT2)"ky2 一
,RT2,
一一
RT1
_r1
T2I
nk
yl
h
,P1,
即:
E_Ed器ln(14)
由(13)式和(14)式知:
当d_0时,即为零级反应,因反应速率与浓度无关,此 时无论用分压p,浓度c,还是摩尔分数y.来表示反应物系 的组成,都不影响反应速率表达式.此时:k.=k.=k且 E=E.=E.
当d?0时,即为非零级反应,反应速率与浓度有关,此 时分别采用分压p,浓度c和摩尔分数y来表示反应物系的 组成,则相应的反应速率表达式不同.此时:k.?k.?k且 E.?E.?E.为了便于比较不同的气相反应的活化能,建议采 用同一种形式的组成.
因此,气相反应的速率常数与温度之间的关系式中需说 明反应速率常数及反应活化能所对应的气相组成形式. 参考文献
[1]1李绍芬.反应工程.北京:化学工业出版社,2000. 【2】天津大学物理化学教研室.物理化学.北京:高等教育出版社, 1983.
【3】林智信,安从俊,刘义,等.物理化学.武汉:武汉大学出版社, 2003.
【4】傅献彩,沈文霞,姚天扬.物理化学.北京:高等教育出版社,1990.
范文四：臭氧与二乙胺和三乙胺气相反应的速率常数_英文_盖艳波
Low molecular weight alkylamines are emitted by a variety of widespread anthropogenic and biogenic sources, representing an important class of environmental pollutants due to their toxic and odorous properties. Animal husbandry is probably the most
臭氧与二乙胺和三乙胺气相反应的速率常数
盖艳波
葛茂发 *王炜罡
(中国科学院化学研究所 , 分子动态与稳态结构国家重点实验室 , 北京分子科学国家实验室 , 北京
100190)
摘要 :
利用自制的烟雾箱系统研究了臭氧与二乙胺和三乙胺的气相反应动力学 . 实验过程中保证二乙胺和三
乙胺浓度远远大于臭氧浓度 , 使得实验在准一级条件下进行 . 加入环己烷以消除实验过程中可能产生的 OH 自 由基对反应的影响 . 在 (298±1) K 和 1.01×105Pa 条件下 , 测得臭氧与二乙胺和三乙胺反应的绝对速率常数值分别为 (1.33±0.15) ×10-17和 (8.20±1.01) ×10-17cm 3·molecule -1·s -1. 与文献中已有的其它胺类的臭氧反应数据比较后发现 , 臭氧与胺的反应可以用亲电反应机制来解释 . 另外 , 通过对比发现 , 臭氧与三取代的烷基胺类的反应速率要远远 大于其与二取代的烷基胺类的反应速率 . 这在一定程度上可有助于解释外场观测到的气溶胶相中二烷基胺盐较 多的事实 . 利用测得的速率常数和大气中臭氧浓度 , 还估算了二乙胺和三乙胺与臭氧反应的大气寿命 . 结果显 示 , 与臭氧的反应是二乙胺和三乙胺在大气中的一种重要的消除途径 , 尤其是在污染严重地区 . 关键词 :
动力学 ;
臭氧 ;
二乙胺 ;
三乙胺 ;
速率常数
中图分类号 :O643
Rate Constants for the Gas Phase Reactions of Ozone with
Diethylamine and Triethylamine
GAI Yan -Bo
GE Mao -Fa *
WANG Wei -Gang
(Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China )
Abstract :Kinetics of the reactions of ozone with diethylamine (DEA)and triethylamine (TEA)were investigated in a self -made Teflon chamber. Experiments were conducted under pseudo -first -order decay conditions using excess DEA and TEA. Cyclohexane was added to the reactor to quench OH radicals. At (298±1) K and 1.01×105Pa, the measured
absolute rate constants were (1.33±0.15) ×10-17cm 3·molecule -1·s -1for DEA and (8.20±1.01) ×10-17cm 3·molecule -1·s -1
for TEA. Comparing our results with data for the reactions of analogous amines with ozone, we propose that the amines react with ozone probably through an electrophilic reaction mechanism. In addition, the reactions of trialkylamines with ozone are all much faster than those of dialkylamines with ozone, which may explain the intriguing finding in several field studies where higher concentrations of dialkylammonium were detected in aerosol samples. The atmospheric lifetimes of DEA and TEA were also estimated based on the measured rate constants and the ambient tropospheric concentration of ozone, which indicates that the reaction with ozone is an important loss pathway for these amines in the atmosphere, especially in polluted areas. Key Words :
Kinetics;
Ozone;
Diethylamine;
Triethylamine;
Rate constant
[Article]
www.whxb.pku.edu.cn
物理化学学报 (Wuli Huaxue Xuebao )
Acta Phys. -Chim. Sin ., 2010, 26(7):1768-1772July
Received:December 28, 2009; Revised:March 15, 2010; Published on Web:May 17, 2010.
*
Corresponding author. Email:gemaofa@iccas.ac.cn;Tel:+86-10-62554518; Fax:+86-10-62559373.
The project was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KJCX2-YW -N24, KZCX2-YW -Q02-03) and National Natural Science Foundation of China (40925016,40830101).
中国科学院知识创新工程方向性项目 (KJCX2-YW -N24, KZCX2-YW -Q02-03) 和国家自然科学基金项目 (40925016,40830101) 资助
鬁 Editorial office of Acta Physico -Chimica Sinica
1768
No.7GAI Yan -Bo et al . :Rate Constants for the Gas Phase Reactions of Ozone with Diethylamine and Triethylamine
important anthropogenic emission source of amines into the tro -posphere, as several studies have reported high concentrations of gas -phase amines in areas of intense animal husbandry [1-4]. Though emission estimates vary widely, a number of short chain alkyl -amines have also been detected in industrial emissions and car exhaust [5-7], biomass burning [8], waste incinerators, and sewage treatment plants [9], as well as in marine, rural, and urban atmo -spheres.
Like most organic compounds, when released into the atmo -sphere, these amines become transformed mainly through reac -tions with a number of reactive species such as hydroxyl radicals and ozone. Ultimately, they may significantly contribute to the formation of ozone and other secondary photooxidants in pollut -ed areas. Besides the environmental effects, amines are also the cause of many health problems for exposed workers [10-11], such as skin and eye irritation, dermatitis, pulmonary sensitization and asthma, and even the cause of carcinogenic effect. Moreover, there are 28amino compounds, including triethylamine and di -ethanolamine, in the Federal Clean Air Act Amendments List of 189Hazardous Air Pollutants [12]. These various health effects are prompting different countries to regulate the maximum concen -tration of amines allowed in air [13-14]. Therefore, in order to assess the impact of these chemical species on air quality and human health, a detailed understanding of the kinetics and mechanisms of their atmospheric degradation is required.
To date, rate constants for the reaction of mono -, di -, and tri -methylamine (MMA,DMA and TMA) have been reported [15], which suggests that these reactions are relatively fast and give amines a lifetime on the order of hours in ambient air. Despite the relatively fast removal rate, several studies have detected amines in the particle phase [16-17]as well as within aqueous fog and rain drops [18-19]. And intriguingly, most of the studies found that the concentrations of dialkylammonium were extremely higher than those of other alkylic ammonium salts in aerosol samples [20-22]. In light of these findings, both homogeneous and heterogeneous reactions of amines in the atmosphere merit fur -ther investigation.
As part of series studies of amines, in this paper, we investi -gated the homogeneous kinetic reactions of diethylamine (DEA) and triethylamine (TEA)with ozone. Rate constants of these re -actions were reported, and the lifetimes of DEA and TEA with respect to ozone were also evaluated. From this we hope to bet -ter understand the atmospheric process of amines.
1Experimental
1.1Reagents and equipment
Diethylamine (DEA,≥ 99%)and triethylamine (TEA,≥ 99%) were obtained from Alfa Aesar. C 6H 12(cyclohexane)in a purity of 99.5%was from Beijng Beihua Fine Chemical Company. N 2(≥ 99.999%)and O 2(≥ 99.999%)were supplied by Beijing Tailong Electronics Company. Ozone was produced from O 2via electri -cal discharge using a commercial ozonizer (BGF-YQ, Beijing Ozone, China).
The experimental apparatus used here is similar to that we re -ported in previous publications [23-25]and just a brief description is given here. All the experiments were carried out in a 100L FEP Teflon film chamber. With a self -made temperature controller, we now can control the temperature in the chamber accurately from room temperature to 350K. At the two ends of the reactors, an inlet and an outlet made of Teflon are used for the introduc -tion of reactants and sampling. The reactor and the analytical in -struments are linked via Teflon tubes. Ozone analyzer (Model 49C, Thermo Electron Corporation, USA) was used for analyz -ing the ozone concentration in the reactor. Its flow rate and pre -cision were 0.7L ·min -1and 1×10-9, respectively. Cyclohexane was added into the reactor to eliminate the OH radicals that may be generated during the reaction. With high purity of N 2as the bath gas, the concentrations of DEA, TEA, and cyclohexane in the entire chamber were calculated from the amount of organics introduced and the total volume of the reactor.
1.2Principle
Absolute rate constants for these ozone reactions were deter -mined by monitoring the O 3decay rates in the presence of known concentrations of the reactant organic. The temporal profile of O 3is governed by the following processes:
O 3→
wall loss of O
3
(1) O 3+organic→ products (2) With the initial organic concentration [organic]0being in large excess over the initial ozone concentration, the reactant organic concentration essentially remains a constant throughout the re -action. Similar to our previous works [25-26], the following equation could be obtained under pseudo -first -order conditions:
k =-dln[O3]/dt =k 1+k 2[organic]0(I) where k 1and k 2are the rate constants of reactions (1)and (2). Thus, from the ozone decay rates, k , measured at various organic concentrations and with a knowledge of the background O 3decay rate (k 1), the rate constant (k 2) can be obtained. 1.3Experimental method
Thoroughly cleaning the chamber was performed for at least 24h in presence of ozone prior to each set of experiments to re -move any residue from last experiment. Attenuation experiments of the reactants (DEA,TEA, and O 3) in pure N 2were performed separately to study the wall effect. In all experiments, the reac -tant organic and cyclohexane were introduced in the chamber by injecting certain volumes of the liquid into a 3-way glass tube and by flushing the contents of the glass tube into the chamber using pure N 2as the carrier gas. Sufficient time was allowed for the concentration inside the chamber to reach steady state. Then with ozone introduced, the chamber was connected to the ozone analyzer and ozone concentration measurements integrated over 10s time intervals were collected up to about a total of 30min. All experiments were conducted at (298±1) K and 1.01×105Pa.
2Results and discussion
2.1Wall effect
In the attenuation experiments, stable concentrations of the 1769
Acta Phys. -Chim. Sin., 2010
Vol.26
investigated amines were confirmed by at least seven measure -ments made over the course of 3h and giving decreases of the integrated peak areas below 3%of the initial values, which was monitored using gas chromatograph -coupled with flame -ioniza -tion detection (GC/FID,GC6820, Agilent Technologies, USA). And the loss of ozone caused by the wall was of negligible im -portance after continuously measured by the ozone analyzer. When measured once an hour, the ozone decay rate constant of 7.44×10-6s -1was finally obtained after 8h. This value is consis -tent with our previously reported value (6.95×10-6s -1) [26], and is about 2orders of magnitude lower than the values of the pseudo -first -order reaction rate constants listed in Table 1. Thus the background ozone decay accounts for only a small part of all the loss of ozone in the reactor in our experiments. Obviously, the loss of the reactants caused by background decay in this work is negligible.
2.2Effect of cyclohexane
Previous work has shown that OH radicals are often formed from the gas -phase reactions of O 3with organic compounds un -der atmospheric conditions [27-30]. Considering that OH reacts with these compounds several orders faster than O 3does, so it would result in certain error to the rate constants for the reactions of ozone. In order to avoid the impacts of OH radicals, high con -centrations of cyclohexane were added into the reaction system as OH scavenger. The rate constant for the reaction of OH with
cyclohexane is high enough (6.38×10-12cm 3·molecule -1·s -1) to
scavenge a significant fraction of the OH formed in the ozonoly -sis reaction [31]. At the same time, the reaction of cyclohexane with ozone is negligibly slow and would not interfere with the deter -mination of the rate constants of interest [32].
Comparative experiments were carried out for TEA and ozone
in the presence and absence of 2.51×1015molecule ·m -3of cyclo -hexane, the results of which were listed in Table 1. With the ad -dition of cyclohexane, the rate constants in all of the compara -tive experiments reduced by 3%-5%,further demonstrating that
there are certain effects of OH radicals on the rate constant.
From the results of No. 6, 7, 16, and 17listed in Table 1, we can see that, when cyclohexane concentration increased, the k value was almost unaltered, and the small difference can be considered as an experimental error. So the amounts of cyclo -hexane used in this work were enough for scavenging OH radi -cals generated in the present experimental system. 2.3Determination of rate constants
As described above, the rate constants are determined under pseudo -first -order conditions. The initial O 3concentration was in the range of 1.77×1012-8.59×1012molecule ·cm -3while the initial concentrations of DEA and TEA were in the range of 5.84×
1013-17.5×1013molecule ·cm -3and 2.08×1013-4.16×1013molecule ·
cm -3, respectively. In all experiments, decays of O 3concentra -tion were obtained as a function of time, and the logarithms of the ratios of the concentrations ([O3]0/[O3])in the presence of reactants were plotted for different reaction time (Figs.1,2). As shown in Figs.1and 2, straight lines were obtained for all these pseudo -first order plots. All the lines have excellent correlation coefficients (>0.998),which demonstrates that Eq.(I)is suitable for kinetic study in this work. The slope of such plots yields the pseudo -first order rate constant, k . The results were also listed in Table 1. Then, the values of k vs [organic]0data (Fig.3),accord -ing to Eq.(I),were also subjected to linear least -squares analysis to obtain k 2.
It can be known from Table 1and Fig.3that k values in -crease linearly with increasing the initial concentrations of DEA and TEA. The slopes of the lines in Fig.3, which are just the ab -solute values of the second -order rate constants for DEA and TEA, are determined to be (1.33±0.15) ×10-17and (8.20±1.01) ×10-17cm 3·molecule -1·s -1, respectively. The quoted errors for the determined rate constants include 2σ(σ:standard deviation) from the least -squares analysis and an estimated systematic error of
No. Amine 10-13[organic]0
(molecule·cm -3)
10-12[O3]0
10-15[cyclohexane]0
104k /s-11-0.005.901.390.07442DEA 5.844.031.398.403DEA 8.778.591.3912.04DEA 11.75.611.3915.45DEA 14.64.251.3919.86DEA 17.54.661.3923.57DEA 17.54.291.9523.48TEA 2.081.772.5116.19TEA 2.082.410.0017.010TEA 2.502.212.5121.211TEA 2.501.970.0021.912TEA 2.922.072.5124.313TEA 2.922.480.0025.414TEA 3.332.892.5127.715TEA 3.752.172.5130.216TEA 4.163.592.5134.117TEA 4.162.493.0634.318
TEA
4.16
3.14
0.00
35.8
Table 1
Results under different initial concentrations of amine, ozone, and cyclohexane
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No.7GAI Yan -Bo et al . :Rate Constants for the Gas Phase Reactions of Ozone with Diethylamine and Triethylamine
10%.Both least -squares linear regressions yielded near -zero in -tercepts.
The results presented here represent the first experimental measurement of the reaction rate constants of ozone with DEA and TEA. We can compare our results with data for the reac -tions of analogous amines with ozone, which are summarized in Table 2. With one ethyl group replacing — H in DEA, reaction of TEA with ozone is about 6times faster than that of DEA with ozone. And similarly, the substitution of methyl group in DMA to give TMA also increases the reactivity by a factor of 4.7. Comparing DMA with DEA, and TMA with TEA, we can find that the substitution of ethyl group has a more significant effect on the reactivity than that of methyl group. As methyl and ethyl groups are all electron -donating groups, so it is probable that the reaction of ozone with amines may involve electrophilic reaction mechanism. The introduction of methyl and ethyl groups in -creases the electronic density at N atom and thus the reactivity of amines. And the more substitutions of methyl or ethyl groups in amines, the faster the reactions of amines with ozone. In order to fully understand the mechanism of these reactions, further in -vestigacions on products are required. 2.4Atmospheric implications
The atmospheric lifetimes τof these amines with respect to removal by ozone can be estimated based on the corresponding rate constants summarized in Table 2and the estimated ambient tropospheric concentration of ozone, according to Eq.(II):
τ=1
23
(II) where [O3]is the estimated ambient tropospheric concentration of ozone. In this work, a typical ozone concentration of 7×1011 molecule ·cm -3was used [33].
As illustrated in Table 2, atmospheric lifetimes against re -moval by ozone are 29.8and 4.8h for DEA and TEA, respec -tively. In polluted areas, where the concentration of ozone could be high up to 2.5×1012molecule ·cm -3[34], the lifetimes of DEA and TEA would be even shorter, about 8.4and 1.4h, respec -tively. Under these conditions, the ozone reactions would serve as an important loss pathway for these amines. In addition, as also can be seen in Table 2, the reactions of trialkylamines with ozone are all extremely faster than those of dialkylamines with ozone. This would more or less help to explain why higher con -centrations of dialkylammonium were detected in the aerosol samples [20-22]. That is, the homogenous reactions of trialkylamines are relatively fast and they can be rapidly removed when re -leased into the atmosphere; however, dialkylamines have a rela -tively longer lifetime and may be easily participated into particle phase through other reactions. Furthermore, in order to fully un -derstand the atmospheric process of amines, further studies in -cluding OH reactions and heterogeneous reactions of amines are needed in the future.
Fig.2Plots of ln([O3]0/[O3])versus reaction time for different initial TEA concentrations
10-13[TEA]0/(molecule·cm -3):(a)2.08, (b)2.50, (c)2.92, (d)3.33, (e)3.75, (f)4.16
Fig.3Plots of k against [TEA]0and [DEA]0
Table 2Summary of rate constants (k 2) and estimated atmospheric chemical lifetimes (τ) for the reactions of amines with ozone at room temperature
Amine Formula
1018k 2
(cm3·molecule -1·s -1)
τ/h DMA (CH3) 2NH 1.67[15]237.6 TMA (CH3) 3N 7.84[15]50.6 DEA (CH3CH 2) 2NH 13.329.8 TEA (CH3CH 2) 3N 82.04.8
Fig.1Plots of ln([O3]0/[O3])versus reaction time for different
initial DEA concentrations
10-13[DEA]0/(molecule·cm -3):(a)5.84, (b)8.77, (c)11.7, (d)14.6, (e)17.5
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Acta Phys. -Chim. Sin., 2010Vol.26
3Conclusions
The kinetics of the reactions of DEA and TEA with ozone were investigated at 298K and 1.01×105Pa in our smog cham -ber. With cyclohexane as the OH scavenger, the absolute rate constants we obtained were (1.33±0.15) ×10-17cm 3·molecule -1·s -1for DEA and (8.20±1.01) ×10-17cm 3·molecule -1·s -1for TEA. Comparing our results with the data for the reactions of analo -gous amines with ozone, we can see that the reactions of tri -alkylamines with ozone are all extremely faster than those of dialkylamines with ozone. That is, the introduction of methyl or ethyl group increases the reactivity of amines in the homoge -nous reactions. And the more substitutions of methyl or ethyl group in amines, the faster the reactions with ozone. This may help to explain the intriguing finding in field studies that higher concentrations of dialkylammonium were detected in the aerosol samples. The atmospheric lifetimes of DEA and TEA with re -spect to removal by ozone have also been estimated based on the measured rate constants and ambient tropospheric concen -tration of ozone, which indicates that reaction with ozone is an important loss pathway for these amines in the atmosphere, es -pecially in polluted areas.
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1772
范文五：水分影响下阴燃传播及气相反应发生的研究
水分影响下阴燃传播及气相反应发生的研
究
第18卷第5期
2008年5月
中国
China
安全
Safety
科学
Science
学报
Journal
Vo1.18No.5
Mav2008
水分影响下阴燃传播及气相反应发生的研究
路长讲师余明高教授林棉金陈亮贾海林
(河南理工大学安全科学与工程学院,焦作454003)
女
学科分类与代码:620.3020中图分类号:X928.7文献标识码:A
基金项目:国家自然科学基金资助(50274061);河南省煤矿瓦斯与火灾防治重点实验室开放基金资助
(HKLGF200501);河南理工大学博士基金资助(648183).
资助项目:河南省基础与前沿技术研究计划项目(072300420180,082300463205);
河南省科技攻关计划项目(072102210070).
【摘要】为了解阴燃传播及其反应状态发生变化的特点,采用一半干燥一半加湿的聚氨酯泡沫
材料进行实验.在自然对流条件下,阴燃由下到上从干材料传播到湿材料.各次实验中阴燃在干材
料部分都保持稳定传播,而湿材料部分所设计的含水率则从8.4%到21.7%.水分的吸热作用使阴
燃状态随含水率大小发生极大的变化.在含水率较小时,阴燃仍能继续传播但温度和速度都有所下
降;含水率稍大时,阴燃反应受到抑制,在内部有氧气剩余的情况下则会发生气相反应;当含水率进
一
步增大,阴燃就会熄灭.如果阴燃能传播到材料末端,外界的大量氧气进入阴燃区将使其向明火
发生转化.
【关键词】聚氨酯泡沫;阴燃;含水率;气相反应;明火
LU
(School
StudyontheEffectofMoistureonSmolderingPropagationand
phaseOxidation OccurrenceofGas—
Chang,LecturerYUMing-gao,Prof.LINMian-jinCHENLiangJIAHai?Un
ofSafetyScience&Engineering,HenanPolytechnicUniversity,Jiaozuo454003,China)
Abstract:Polyurethanefoam,whoselowerpartremaineddryandupperpartwaswatered,wasusedin
experimentstostudythepropagationofsmolderinganditsvariationofreaction.Smolderingspreadupward
fromthedrytothewetinnaturalconvection.Inexperiments,themoisturecontentsoftheuppersamples
werefrom8.4%to21.7%.andsmolderingkeptsteadyinthelowerdrysamples.Becauseoftheendo-
thermicevaporationofwater,thestateofsmolderingvariedgreatlywiththemoisturecontentafterit
reachedthesampleinterfaceofthedryandthewet.Whenthemoisturecontentwaslow,smolderingcon-
tinued,butitstemperatureandvelocitysomewhatdecreased.Withtheincrementofmoisturecontent,
smolderingreactionwassuppressed.Andtheoxygen,whichwasnotconsumedcompletelybyheterogene-
OUSreaction,wouldreactwiththecombustiblegasesandledtotheoccurrenceofthegas—
phaseoxidation.
While
agated
themoisturecontentwashighenough
totheend,thetransitiontoflaming
,
smolderingextinguished.Inexperiments,ifsmolderingprop-
combustionwouldoccurforplentyofouteroxygenenteringthe
reactionzone.
Keywords:polyurethanefoam;smoldering;moisturecontent;gas-phaseoxidation;
flamingcombustion
{文章编号:1003—3033(2008)05—0091—06;收稿t3期:2008—02—28;修稿日
期:2008—04—30
?
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中国安全科学学报
ChinaSafetyScienceJournal
第18卷
2008焦
0引言1实验条件和过程
阴燃是材料依靠异相氧化反应(固体表面反
应)所放出热量实现自维持传播的一种燃烧方式.
香烟,聚氨酯泡沫材料(海绵),纤维质颗粒(锯末),
棉毯等,该类疏松多孔材料具有易于阴燃的特性.
经济的发展使人们所使用的疏松装饰物越来越多,
所造成的火灾风险也越来越大….阴燃的危害性
主要有两个方面:
一
是燃烧过程中释放出大量的有毒气体,损害
人的健康,甚至使人窒息.CraigBeylerL2指出了聚
氨酯泡沫材料在燃烧,尤其是阴燃条件下会释放大
量的CO,HCN等毒性气体;刘军军等也对烟气的
毒性进行了分析.
另一方面,阴燃在一定条件下会转化为明火,由
于前期潜伏时间已较长,蔓延的范围已较大,因此,
常常会迅速形成很大的火势,造成大的破坏.
2004年2月吉林市中百商厦发生特大火灾,造
成54人死亡70人受伤,原因就是由掉落的烟头和
地面可燃物阴燃引发的.2004年4月贵州黎平县
大稼乡大稼村发生特大火灾造成81户405人受灾,
原因也是烟头掉落在木屑,刨木花堆中形成阴燃,
一
个多小时后引发大火.2004年7月浙江平阳县
温州辉煌皮革有限公司发生特大火灾造成18人死
亡12人受伤,原因是砂边机工作产生的火花使旁边
的皮带粉屑发生阴燃,然后引发大火.在美国,阴燃
是引发火灾的最大原因;在我国做为典型阴燃的
吸烟所造成的火灾,占总火灾数超过7%L53.
过去20年中,众多研究者对阴燃过程进行了研
究,包括点燃一73,传播过程和模型以及阴燃向
明火的转化?163.Chaoetal_l探讨了自然条件下
阴燃向明火的转化,Tseetal_1和Bar-IlanetalLl刮则
观测了在风速条件下阴燃向明火的转化.还有部分
文献对含水率对阴燃的影响进行了探讨?,….
当阴燃主要在材料的内部蔓延时,由于孔隙对
氧气供应的限制,氧化反应主要是固体表面反应而
气体反应很少发生.材料均匀时阴燃传播也是稳定
的.当供氧条件发生改变时,热解可燃气与氧气的
混合物在阴燃区就可能被点燃从而导致向明火的转
化.如果阴燃传播过程中材料不是均匀的,那么阴
燃的稳定性也会发生变化,随之燃烧的状态也会变
化,笔者就主要研究阴燃传播从干材料到湿材料的
整个过程及其反应状态的变化.
实验装置为长方体的不锈钢容器(16cm长x
15cm宽x35cm高),四周是封闭的并附装绝热材
料,上下两端跟外界空气连通,如图1所示.
隔热层
未燃材料区
已燃材料区
加热器
图1实验装置示葸图
电加热器安装在装置下端作为点火源.聚氨酯
泡沫材料(海绵)被广泛应用于现代生活的居室内,
在文中以此作为实验对象.用8片2cm厚的聚氨
酯泡沫材料组成16cm厚x14.5cm宽x20cm高的
试样.每片材料的上半10cm部分被均匀地注入水
分,而下半10cm部分仍保持初始状态,然后整个试
样放置到实验装置中,并且试样的下端与电加热器
相接触.以试样与电加热器接触面中心为原点,沿
着由下到上的中心轴线每隔2cm安置一根直径为
1mm的K型热电偶,并通过数据采集系统进行温度
的自动采集记录.在各次实验中,电加热器的功率
和加热时间都保持一致,以使阴燃的初始条件相同.
以开始加热的时间作为实验的起始时间.
聚氨酯泡沫材料的反应通常认为分两步进行?:
?发生吸热的热解反应生成多孔炭和释放出
可燃气;
?多孔炭发生氧化反应放出热量,这一反应也
称为异相反应.
泡沫材料部分阴燃后的形态如图2所示,上方
白色部分是没有发生反应的原始试样,下部黑色部
分就是热解后所形成的多孔炭.
图2泡沫材料部分阴燃后的形态
第5期路长等:水分影响下阴燃传播及气相反应发生的研究?93?
聚氨酯泡沫材料受到热源加热后,发生阴燃并
向上传播.在自然对流条件下,氧气以扩散及热对
流方式进人反应区,产生的烟气则从上端逸出.
在阴燃传播中第一步热解反应较快,因此,阴燃
前锋不断向上推进;第二步多孔炭的氧化反应较慢,
因此,随着阴燃前锋的推进多孔炭区不断扩大,阴燃
反应区也相应不断扩大.
在进行各次阴燃实验时,先进行自然条件下干
聚氨酯泡沫材料的实验;接着对试样的上半部进行
均匀的加水,各次加水后上半部材料的含水率分别
为8.4%,12.6%,15.4%,18.1%,21.7%,然后用
加水后的材料进行实验.
除了进行阴燃实验外,还对聚氨酯泡沫材料及
其阴燃后形成的多孔炭进行了热分析.热重实验是
在空气条件下,以lO~C/min的升温速率进行的.利
用热分析结果可以更进一步地了解材料在阴燃受热
过程中的变化情况,从而更有利于对阴燃过程的分
析和认识.?
2阴燃结果与分析
; 阴燃在材料的下半部分传播时是稳定,匀速的
当从下半部分传播到上半部分时,随着含水率的不
同阴燃也呈现出不同的变化.
对于不加水的情形,整个材料是均匀连续的,阴
燃过程也具有连贯匀速的特点,温度一时间曲线如
图3所示.各条曲线间的间隔保持不变就意味着传
播的速度保持不变.最后转化为明火,温度急剧上
升并很快将材料烧尽.转化为明火的原因在于,阴
燃前锋到达末端后聚氨酯泡沫材料都转化成了炭,
孔隙率增大,从上到下更有利于空气的热对流,从外
部有大量的氧气可以进人到阴燃区内部从而引发气
相反应,形成明火.其原因是氧气供应条件发生改
变导致的结果.
图3上半部不加水阴燃过程
材料上半部含水率8.4%的实验过程温度一时
间曲线如图4所示.当阴燃由干燥部分传播到含湿
部分时阴燃仍然能够维持.但从图中可以明显观察
到阴燃区的温度出现了下降,已燃区的最高温度从
484~C降到408~C.同时阴燃的传播速度变得缓慢,
阴燃在间隔2cm的相邻两根热电偶间传播的平均
时间从168s增加至307s.
其原因是由于蒸发水分需要消耗热量同时需要
一
定时间的缘故.最后在材料末端基于同图3实验
同样的机理,阴燃也转化成了明火.
图4上半部含水8.4%的阴燃过程
材料上半部含水率12.6%的实验过程如图5
所示.当阴燃传播到含水部分时,同样出现了传播
速度变缓温度降低的现象.已燃区最高温度从
481?降低到326?.但就在后续部分材料(14cm
处)温度迟迟无法升高时,即阴燃传播出现停滞时,
已燃区各位置的温度突然出现了一个整体的跃升,
最高温度达到631?,这是一个只有明火才能具有
的温度值.已燃区温度整体升高后使得后续含湿材
料继续阴燃.最后在全部聚氨酯泡沫材料转变成炭
后,阴燃也转变成了明火.
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中国安全科学学报
ChinaSafetyScienceJournal
第l8卷
2008拄
材料上半部含水率15.4%的实验过程温度一
时间曲线如图6所示.在阴燃传播到含水部分后,
同样已燃区的最高温度值降低,已燃区最高温度从
496cc下降到356cc;阴燃前锋的传播也趋于停滞
(图中12cm处的温度迟迟没有上升).突然已燃区
各位置的温度出现上升,由于水分含量较大的缘故,
上升的幅度没有图5中的大.其原因仍然是由气相
反应造成的.由于温度上升的幅度不高,意味着气
相反应不够剧烈,热解可燃气的浓度仍然比较高,导
致又出现了一次气相反应,因此,在图中可看到出现
“双峰”的现象.尽管发生了气相反应,但由于含水
率较高,随后阴燃仍难以维持,已燃区的温度不断下
降.在已燃区的最高温度降到215oC时,突然转变
成了明火并将整个材料烧完.
值得注意的是,该实验并非像图3,图4,图5实
验那样在阴燃传播到材料末端后转变成明火,而仅
当阴燃传播到14cm处就转变成了明火,此时16cm
处温度仅为102oC,18cm处温度66cc.因此,明火
的形成仍是水分影响下的结果.
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时间(s)
图6上半部含水15.4%的阴燃过程
材料上半部含水率18.1%的实验过程温度一时
间曲线如图7所示,所经历的前部分过程同图6实验
过程是相似的.根本的区别在于图6实验最后转变
成了明火,而含水率更高的实验最后阴燃熄灭了.当
阴燃传播到含水部分时,已燃区温度下降幅度很大,
最高温度从495~C降到217~C.突然气相反应的发生
又使最高温度升高达到503cc,在温度有所下降后又
一
鸡
图7上半部含水18.1%的阴燃过程
出现了一个温度上升峰达到466cc.但在高含水率的
影响下,使得温度快速下降,最终燃烧熄灭.
材料上半部含水率21.7%的实验过程温度一
时间曲线如图8所示.在含水率更高的情况下,阴
燃传播到含水部分后温度就一直下降,燃烧直接熄
灭了,不再有其他的现象发生.
一
赠
图8上半部含水21.7%的阴燃过程
3热重实验与讨论
阴燃传播到含水部分后,在一定的含水率范围
内,出现了气相反应或明火,这一现象是非常特别
的,对其产生的机理需要进行更深人的探讨.笔者
对聚氨酯泡沫材料及其阴燃形成的多孔炭进行热重
分析,在空气气氛下升温速率为lOoC/min,随温度
的失重过程如图9,图l0所示.
?
?,——聚氪酯泡沫材\多孔炭区域.泡沫区域,
?
\,
0l00200300400500600700800
温度(?)
图9空气下泡沫材料的TG曲线
图1O空气下多孔炭的TG曲线
???如们
一一嘲峰
第5期路长等:水分影响下阴燃传播及气相反应发生的研究?95?
从图9可以看到聚氨酯泡沫材料主要的热分解
失重区域为240—340?,在350oC后失重变得相对
缓慢;从图1O可看到350—600oC正是聚氨酯泡沫
材料热分解形成的多孔炭的主要反应失重区域,在
低于350oC时炭质量基本没有变化.图9和图1O
在数值上是一致的,在图9中350—600oC曲线数值
从57.7%下降到47.4%,相对减少量为17.9%;在
图1O中350—600oC曲线数值从94.3%下降到
76.8%,相对减少量是18.5%.
了解了聚氨酯泡沫材料在各温度段下的反应情
况,同样可以很好地解释上述阴燃实验中的现象.
在不加水和上部含水8.4%的图3,图4中,由于反
应区的温度仍超过400oC,使得多孔炭在持续反应
放出足够的热量,因此,阴燃能够正常传播到最上
端.在图5一图8含水率增加的各次实验中,由于
水分蒸发使温度都下降到360oC以下,使得多孔炭
的放热反应变得微弱甚至停止,而泡沫材料的反应
又主要体现为吸热,因此,阴燃也就不再正常传播.
对图5一图7实验过程中间出现气相反应的现
象,从聚氨酯泡沫材料的热反应性也可以得到很好
的解释.在出现突然的温度上升前,材料的最高温
度都接近或低于了350~C,因此,泡沫材料处于热分
解形成多孔炭和释放出大量可燃气的状态.另外,
由于多孔碳的氧化反应已经非常弱甚至已停止,因
此,氧气也没有被消耗.由于在干泡沫材料和湿泡
沫材料的交界处有大量的热解可燃气和足够的氧
气,并且温度仍处于较高数值能够提供气态反应所
需要的能量,因此,就导致了气相反应的发生.
对于图8所示的实验过程,由于含水率很高,已
燃区的热量都被水分蒸发所消耗,产生的可燃气浓
度不够高且温度下降到很低,从而导致不再有气相
反应发生而直接熄灭了.
4结论
1)阴燃在末端转化为明火是由于开口处有大
量的氧气可以进入阴燃区,从而导致气相反应的发
生并进一步形成明火.而在中间干湿材料交界处出
现的气相反应则是由于水分吸热使阴燃反应的稳定
性遭到破坏,在内部有剩余氧气同热解可燃气发生
反应而造成的.”双峰”的出现是由于第一次气相
反应后,固体表面反应仍不能继续导致第二次气相
反应发生而造成的.
2)阴燃从聚氨酯泡沫干材料传播到湿材料时,
会随着含水率的不同而出现不同的变化.当含水率
小于8.4%时,水分的吸热不足以阻止阴燃传播,但
会使阴燃的最高温度降低,速度减慢.当含水率在
12.6%一18.1%时,阴燃的固体表面反应受到很大
削弱,氧气会同可燃气发生反应而导致温度出现突
然的整体上升.当含水率大于21.7%时,水分的吸
热导致阴燃直接熄灭.
3)热重分析表明,聚氨酯泡沫材料在约240—
340oC主要发生吸热热解反应生成多孔炭和可燃气
体,而在350—600oC则主要发生多孔炭的放热氧化
反应.因此,若含水率较小而阴燃区的温度仍高于
350?,则多孔炭的放热反应继续阴燃也仍平稳传
播;若含水率适中使阴燃区的温度下降并较长时间
处于240—340oC,则多孔炭反应减弱而使氧气剩
余,同时因热解而产生大量可燃气,在已燃区内部两
者就会发生气相反应;若含水率很高使阴燃区的温
度快速降到240oC以下,则产生的热解可燃气减少,
同时已燃区也不能提供足够的气相反应点燃能量.
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