下载文档原格式
饱和状态下水泥浆体的微观结构冰冻损伤模型刘琳;孙伟;陈惠苏;叶光;钱智炜【摘要】为了研究水转化为冰所带来的体积膨胀对水泥浆体的微观结构的危害,量化微观结构的内部损伤,建立了一个饱水状态下水泥浆体的冰冻破坏模型.首先使用模拟水泥浆体微观结构的数值模型(HYMOSTRUC)生成一个模拟结构,根据这个模拟结构中的孔结构,分析水分在孔隙中发生的相转变;将含有冰、水和水化产物的水泥浆体微观模拟结构转变为三维格构结构,并把水分发生相变时产生的体积膨胀引入其中,从而分析格构结构的受力及断裂;最后得到水泥浆体微结构内部微裂缝的分布.该模型真实反映了冰冻作用对微观结构的破坏,模拟结果显示微裂缝产生在由水转变为冰的孔隙周围的抗拉强度低的固相水化产物中.%In order to investigate the microstructural change of cement paste caused by the volume expansion of water-to-ice change and to quantify the internal damage of the microstructure, a numerical frost damage model of saturated cement paste is proposed. A virtual microstructure of cement paste is first obtained by use of a numerical model namely HYMOSTRUC (hydration, morphology and structure). Then according to the pore structure of the virtual microstructure of cement paste, the phase change of water in pores is analyzed. The next is to convert the microstructure of cement paste containing ice, water and hydration products into a three-dimensional (3D) lattice structure. The volumetric expansion of water-to-ice is imposed in the 3D lattice structure. Thus the fracturing process of the 3D lattice structure is obtained and the distribution of micro-cracks in the microstructure of cement paste is revealed. The modeling shows that themicro-cracks occur in the hydration products of low tensile strength around the pores filled with ice.【期刊名称】《东南大学学报（自然科学版）》【年(卷),期】2011(041)005【总页数】6页(P1059-1064)【关键词】饱水水泥浆体;微观结构;冰冻破坏;三维格构结构【作者】刘琳;孙伟;陈惠苏;叶光;钱智炜【作者单位】东南大学材料科学与工程学院,南京,211189;东南大学江苏省土木工程材料重点实验室,南京,211189;荷兰代尔夫特理工大学土木与地球科学学院微观材料实验室,Delft 2628CN;东南大学材料科学与工程学院,南京,211189;东南大学江苏省土木工程材料重点实验室,南京,211189;东南大学材料科学与工程学院,南京,211189;东南大学江苏省土木工程材料重点实验室,南京,211189;荷兰代尔夫特理工大学土木与地球科学学院微观材料实验室,Delft 2628CN;荷兰代尔夫特理工大学土木与地球科学学院微观材料实验室,Delft 2628CN【正文语种】中文【中图分类】TU528水泥基复合材料在受到冰冻(或冻融循环)作用后性能的劣化是关系到寒冷地区混凝土结构耐久性和服役寿命的重要因素之一.混凝土的抗冻性和冻结破坏的机理在过去几十年中一直是一个热点问题，许多学者先后提出了不同的混凝土冰冻破坏机理.主要有静水压和渗透压理论学说［1］、冰的结晶压理论学说［2-3］和微冰透镜理论学说［4］.虽然对冰冻引起的混凝土破坏机理有不同的理解，但最根本原因是液态水转变为冰晶体时产生了9%的体积膨胀.而混凝土受冻破坏后的各种性能变化(如弹性模量降低、强度下降、传输性能增加及质量损失等)，都是由材料本身微观结构劣化造成的.而引起这个微观结构劣化的重要原因之一，正是水与冰在其内部孔隙中发生相变并伴随体积变化造成的.为了深入理解在冰冻作用时水泥基复合材料的孔隙中的水分发生相变带来的危害和材料内部微观结构的损伤过程，本文建立了一个饱水状态下水泥浆体的冰冻破坏模型.从水泥浆体的微观结构出发，抓住冰在孔隙中的成核与生长过程，将水由液态转变为固态时的体积膨胀转换为力学因素，分析水泥浆体微观结构内部的受力及分布，量化水泥浆体的内部损伤，从而建立一个水泥浆体微观结构劣化的数值模型.1 破坏机理在温度降低过程中，冰晶体首先在大孔中形成，然后随温度继续降低，大孔中的冰向小孔中生长［2-3］.在不同温度条件下，可形成冰的最小孔半径［2］，即式中，ΔT为从冰点到当前温度的温度差，ΔT=Tm-T，Tm为大块冰的冰点，T为当前温度，K;δ为冰与孔壁之间的水膜厚度，μm;γ为冰与水之间的界面能，J/m2;ΔS为每单位体积冰溶解为水的熵，MPa/K.当含水材料受冻时，微观结构的破坏机理主要与孔的大小有关.当温度低于冰点时，较大毛细孔中的水首先转变为冰发生体积膨胀，而孔隙周围的固相抑制孔内物质的膨胀，使得孔隙周围的固相承受一定的应力(见图1).固相中每点处的应力的大小和方向与该点所在的位置到达孔的距离、孔的形状、固相和冰的弹性模量、剪切模量、抗拉强度等因素有关.当固相所承受的局部拉应力大于其局部抗拉强度时，即产生微裂缝.当温度继续降低时，冰在更小的孔隙中生长(见图2).根据结晶压理论，小孔中的冰受到来自孔壁的压力［2，5］，即式中，κE，κM分别为冰的自由端和冰与孔壁接触处曲率.在孔壁施加给冰一定作用力的同时，也受到来自冰的大小相等方向相反的作用力.文献［5］模拟了随着温度降低，由冰的结晶压引起的水泥浆体微观结构的破坏过程.本文研究在较大孔径中由水转变为冰时体积膨胀所引起的水泥浆体的微观结构损伤.对于饱水状态的水泥浆体，由于其内部微观结构的复杂性，表现为孔隙大小不一、形状变化多样、固相的构成组分多样(未水化水泥颗粒和各种水化产物)等，因此，很难仅使用图1所示的概念模型反映真实的微观结构破坏.本文试图建立能够量化微观结构破坏，从本质上把握由水转变为冰的体积膨胀所带来的微观结构损伤的结构模型.图1 由膨胀性产物引起的破坏机理示意图图2 冰在小孔中的结晶［5］2 模型的建立在水泥浆体低温受冻过程中，当温度低于冰点时，冰首先在受冻表面的孔中形成，然后冰晶体在微观结构内部的含水孔隙中生长.由于孔中的水分由液态转变为固态时产生9%的体积膨胀，使得水泥浆体内部承受一定的应力，这个内应力使得水泥浆体产生了内损伤.水泥浆体微观结构的冰冻破坏过程模拟流程图如图3所示.首先，将冰冻过程中的连续温度变化离散为一系列的小温度区间(ΔTk，k=1，2，…，n)，每2 个相邻温度区间之间具有一定的温度差;由水泥浆体的微观结构得到其孔结构信息，分析处于不同温度区间时水泥浆体孔隙中的液态水与结晶态冰的转化过程，即冰的成核与生长过程.在得到冰晶体在孔隙中的三维分布后，把受冻后的水泥浆体微观结构转变为三维格构结构.最后，把这个冰冻后的水泥浆体三维格构结构作为研究对象，计算水泥浆体中的内应力大小及分布.当局部区域固相所承受的内应力大于其抗拉强度时，格构结构发生局部断裂，表现为微裂缝，水泥浆体内部发生损伤.图3 模拟水泥浆体微观结构冰冻破坏流程图2.1 水泥浆体模拟结构由图3可知，在模拟水泥浆体微观结构的受冻破坏过程中，首先需要通过实验或计算机模拟得到水泥浆体的微观结构.由Micro-CT［6］、聚焦离子束［7］等实验手段得到的水泥浆体微观结构虽然可靠性较高，但往往受到分辨率的限制，且比难操作.目前世界上模拟水泥浆体微观结构的计算机模型主要有 HYMOSTRUC3D ［8-10］，CEMHYD3D［11］和Mic［12］等.本文借助 HYMOSTRUC3D 模型得到水泥浆体的模拟微观结构.HYMOSTRUC3D模型假设所有水泥颗粒为球形，在水泥水化过程中，生成水化硅酸钙和氢氧化钙2种水化产物，其中氢氧化钙被转变为等体积的水化硅酸钙产物包裹于未水化水泥颗粒外部.包裹于未水化水泥颗粒外部的水化产物又分为内部水化产物和外部水化产物2种.水泥浆体的水化程度是水泥粒径分布、化学组分、水灰比、反应温度以及时间的函数［8-10］.本文用HYMOSTRUC3D模型模拟水灰比为0.4的普通波特兰水泥(型号42.5N)水化至一定程度的微观结构.水泥所含主要矿物成分为C3S(64%)，C2S(13%)，C3A(8%)和 C4AF(9%)，表观细度为420 m2/kg.模拟试样尺寸为100 μm×100μm ×100 μm，水泥最小粒径为1 μm.将水泥浆体的模拟微观结构用三维像素形式表示出来，在分辨率为0.5 μm/像素的条件下，水化程度为0.69的水泥浆体微观结构如图4所示.考虑现有计算机的计算能力，本文采用边长为25 μm模拟结构(见图4)，是从所生成的边长为100 μm的模拟结构中截取而来.每个像素用不同的数值表示，0，1，2，3分别表示孔相、未水化水泥颗粒相、内部水化产物相和外部水化产物相.模拟微观结构中的孔相是指充满水的毛细孔.水泥浆体在低温受冻时，冰的产生与生长就是发生在这些充满水的毛细孔中.图4所示模拟微观结构中的孔结构如图5所示.图4 水泥浆体模拟微观结构图(水灰比 0.4;水化程度 0.69)图5 水泥浆体模拟孔结构图(水灰比 0.4;水化程度 0.69)2.2 冰在孔结构中的生长由式(1)可知，在温度降低过程中，冰晶体首先在大孔中形成，随着温度的降低，大孔中的冰晶体向小孔中生长［2-3］.当ΔT=0.27 ℃时，在直径为0.5 μm的孔中有冰生成.本文假设水泥浆体沿x轴方向左边表面为受冻面，冰晶体首先在这个表面上的孔中生成，然后向孔隙内部生长.由于是在微观层次研究冰的生长，因此不考虑温度梯度的影响.用燃烧算法［13］来模拟冰的内部生长过程.模拟所得到的温度等于冰点时水泥浆体的模拟孔结构(见图6).此时，与受冻面上冰连通的孔隙中的水全部变为冰，而不连通的孔隙中的水仍然保持液态.图6所示孔结构的体积占整个微观结构总体积的4.7%(因所截取的微观结构的大小不同而有所变化)，孔隙中有97.6%的水转变为冰.在得到孔中水和冰的分布信息后，根据含有液态水、晶体态冰和固相水化产物(包括未水化水泥颗粒、内部和外部水化产物)的水泥浆体微观结构生成与之相对应的格构结构，并运用格构结构断裂模型分析微裂缝的产生. 图6 冰冻后水泥浆体模拟孔结构图(水灰比 0.4;水化程度 0.69)2.3 水泥浆体三维格构结构断裂模型格构结构由一系列格构单元(lattice element)组成，每个单元均能承受一定的力学荷载.格构结构断裂模型在水泥基复合材料领域得到广泛应用，如预测水泥浆体在微观尺度的力学性能［14-15］、分析混凝土的受力破坏［16］等.本文使用该模型预测水泥浆体在冰冻作用下的局部断裂.水泥浆体格构结构的断裂模型可以分为以下几个步骤实现:①格构结构的生成;② 格构单元力学性能的确定;③格构单元受力分析及断裂过程.2.3.1 格构结构的生成文献［15］详细介绍了四角形格构结构的建立方法.以二维情况为例，如图7(a)所示，首先生成一个方格网络(grid)，每个方格网表示为一个元件(cell).元件中含有子元件(sub-cell)，子元件与元件边长的比值定义为随机度(randomness).随机度的取值在0～1之间，随机度表示材料微观结构的无序程度，若随机度为0，对应的材料是理想均匀材料，随机度为1，对应的材料是完全无序的非均质材料.定义好所有元件与子元件后，在子元件中随机生成一个节点(node)，相邻2个节点则构成一个格构单元 (lattice element).假如元件所在的位置是孔相，则不在此元件中生成节点.这样所生成的格构结构能够反映材料的力学性能［15］.然而，在含有冰晶体的水泥浆体中，冰的生成不但产生体积膨胀，而且会承受一定的应力.因此，不能仅将水泥浆体中的固相水化产物(包括未水化水泥颗粒、内部和外部水化产物)作为基本元件来建立格构结构，而需要将冰冻过程中形成的冰晶体作为新的元件引入结构中，这样新的节点和格构单元随之产生.如图7(b)所示，在冰相的元件上需要生成新的节点.由于冰晶体与水泥浆体中的固相水化产物的性质有很大不同，因此并不能简单地连接冰节点与固相节点形成新的格构单元.要在冰与固相的连接处再插入一个新的节点形成2个格构单元，一个格构单元具有冰的性质，另一个格构单元具有固相水化产物的性质.根据上述四边形格构结构的建立方法，一个模拟水泥浆体的三维格构结构如图8所示.图8中随机度为0的格构单元表示在已结冰的孔隙中形成的冰单元，随机度为1的格构单元表示由固相水化产物构成的单元.在此情况下，共有36.1万个固相水化产物梁单元和1.4万个冰晶体梁单元生成.图7 四角形格构结构生成示意图图8 由冰晶体和固相水化产物组成的水泥浆体格构结构(水灰比 0.4;水化程度 0.69) 2.3.2 格构单元性能的确定水泥浆体格构结构的基本组成单元是由冰或者水泥水化产物组成的格构单元，这些单元具有各自的形状参数、弹性模量、剪切模量和抗拉强度.本文假设所有格构单元都是圆柱形梁单元，单元长度等于2个节点之间的距离，横截面面积等于垂直于长度方向的表面面积［17］.图8所示格构结构中每个梁单元的横截面面积取值为0.25 μm2.据表1所列的四相节点，格构结构的梁单元共可分为7种类型，每种类型由其两端的格构节点的相(相1和相2)共同决定(见表2).表3列出了这7种类型的格构单元的力学性能.由冰晶体组成的梁单元不会受到拉应力的作用(类型7)，因此未考虑其抗拉强度.假如冰晶体不受到压应力作用，其与周围固相表面相接触的节点即会与固相分离，冰晶体进入自由伸缩状态.表1 梁单元的力学性能［18-21］ GPa80内部水化产物 30 12.0 0.24外部水化产物 22 8.9 0.15冰10 5.0固相弹性模量剪切模量抗拉强度未水化水泥 135 52.0 1.表2 格构单元组分类型类型格构节点相1 格构节点相2未水化水泥未水化水泥内部水化产物I(类型2) 内部水化产物内部水化产物外部水化产物O(类型3) 外部水化产物外部水化产物混合相U-I(类型4) 未水化水泥内部水化产物混合相U-O(类型5) 未水化水泥外部水化产物混合相I-O(类型6) 内部水化产物外部水化产物冰晶体(类型7)未水化水泥U(类型1)冰冰表3 格构单元的力学性能［18-21］ GPa格构单元组分类型弹性模量剪切模量抗拉强度类型 1 135 52.0 1.80类型 2 30 12.0 0.24类型 3 22 8.9 0.15类型 4 49 20.0 0.24类型 5 38 15.0 0.15类型 6 25 10.0 0.15类型7 10 5.02.3.3 格构单元受力分析及断裂过程由于本文所考虑的内应力主要来源于水转变为冰时所产生的体积膨胀，在格构结构中表现为冰晶体梁单元的长度变化，为相变之前的03倍.由冰组成的梁单元长度的伸长，使与之相衔接的其他类型的梁(类型1～类型6)受到不同程度的挤压或拉伸，从而产生了内应力.由于水泥浆体微观结构的复杂性，梁单元的分布错综复杂，从而使部分梁单元承受拉应力，部分承受压应力.假设梁单元只会受拉破坏，承受拉应力的梁单元在其所受应力大于其抗拉强度时(见表3)，该梁单元断裂.在水泥浆体不受到外部强加荷载的条件下，格构结构的边界条件设定为自由膨胀.3 模拟结果在所截取的水灰比0.4、水化程度0.69、边长25 μm的水泥浆体微观结构中，孔隙率为4.7%.当受到冰冻作用温度ΔT=0.27℃时，孔隙中有97.6%的水转变为冰.由水转变为冰所带来的体积膨胀，致使水泥浆体的三维格构结构中的部分梁单元断裂.通过对具有36.1万个固相水化产物梁单元和1.4万个冰晶体梁单元的格构结构受力分析发现，有275个梁单元断裂，在梁单元断裂位置产生微裂缝;微裂缝的形状表现为钱币型，面积为0.25 μm2(见图9)，微裂缝随机分布于微观结构中.图10为水泥浆体中微裂缝和冰梁单元的分布.看似随机分布的微裂缝，实际上具有一定的规律性，所有的微裂缝都分布在冰梁单元的周围.这是因为在充满冰的孔隙周围的固相所承受的应力较大，而远离冰的固相所承受的应力较小.在断裂的275个梁单元中，274个梁单元的抗拉强度为0.15 GPa(表3中类型3、类型5和类型6)，这说明断裂首先发生在抗拉强度低的薄弱地带，即在外部水化产物中首先产生微裂缝.因此，由本文所提出的水泥浆体的冰冻破坏模型的模拟结果可以得出，当水泥浆体受到冰冻作用时，破坏首先发生在由水转变为冰的孔隙周围的抗拉强度低的固相水化产物中.图9 微裂缝在水泥浆体中的分布图10 微裂缝和冰单元在水泥浆体中的分布4 结论本文从水泥浆体的微观结构出发，把握冰在孔隙中的生长过程，将水由液态转变为固态时的体积膨胀转换为力学因素，通过三维格构结构断裂模型分析水泥浆体的内部损伤，建立了一个预测水泥浆体微观结构劣化的数值模型.以水灰比为0.4、水化程度为0.69、边长为25 μm的普通波特兰水泥浆体的模拟结构为例，在0.5μm/像素的条件下计算得到其孔隙率为4.7%.当温度ΔT=0.27℃时，这个模拟结构的孔隙中共有97.6%的水转变为冰.这个含有液态水、结晶态冰和固相水化产物的模拟微观结构转变为含有37.5万个梁单元的三维格构结构后，由于水转变为冰的体积膨胀9%，使得内部产生随机分布的微裂缝.从模拟结果可以看出，该模型真实反映了冰冻作用对微观结构的破坏，并且破坏首先发生在由水转变为冰的孔隙周围的抗拉强度低的固相水化产物中.参考文献(References)［1］Metha P K，Monteiro P J M.Concrete:microstructure，properties and materials［M］.3rd ed.New York:McGraw-Hill，2006.［2］Scherer G W.Crystallization in pores［J］.Cement and Concrete Research，1999，29(8):1347-1358.［3］Scherer G W，Valenza J.Mechanisms of frost damage［C］//Materials Science of Concrete.Westerville，OH，USA，2005:209-246. ［4］Setzer M J.Micro-ice-lens formation in porous solid［J］.Journal of Colloid and Interface Science，2001，243(1):193-201.［5］Liu L，Ye G，Schlangen E，et al.Modeling the internal damage of saturated cement paste due to ice crystallization exposed to low temperature［J］.Cement and Concrete Composites，2011，33(5):562-571. ［6］Promentilla M A B，Sugiyama T，Hitomi T，et al.Quantification of tortuosity in hardened cement pastes using synchrotron-based X-ray computed microtomography［J］.Cement and Concrete Research，2009，39(6):548-557.［7］Trtik P，Münch B，Lura P.A critical examination of statistical nanoindentation on model materials and hardened cement pastes basedon virtual experiments［J］.Cement and Concrete Composites，2009，31(10):705-714.［8］van Breugel K.Simulation of hydration and formation of structure in hardening cement-based materials［D］.Delft，The Netherlands:Faculty of Civil Engineering and Geosciences，Delft University of Technology，1991. ［9］Chen H S，Stroeven P，Ye G，et al.Influence of boundary conditions on pore percolation in model cement paste ［J］.Key Engineering Materials，2006，302/303:486-492.［10］Ye G.Experimental study and numerical simulation of the development of the microstructure and permeability of cementitious materials［D］.Delft，The Netherlands:Faculty of Civil Engineering and Geosciences，Delft University of Technology，2003.［11］Bentz D P，Garboczi E J.Percolation of phases in a three-dimensional cement paste microstructure model［J］.Cement and Concrete Research，1991，21(2/3):325-344.［12］Bishnoi S，Schrivener K L.A new platform for modeling the hydration of cements［J］.Cement and Concrete Research，2009，39(4):266-274.［13］Stauffer D.Introduction to percolation theory［M］.London:Taylor and Francis，1985.［14］Tan L.Failure mechanisms in hydrating cement particle systems ［D］.Delft，The Netherlands:Faculty of Civil Engineering and Geosciences，Delft University of Technology，2007.［15］Qian Z，Schlangen E，Ye G，et al.Prediction of mechanicalproperties of cement paste at microscale ［J］.Materiales de Construccion，2010，60(297):7-18.［16］Schlangen E.Experimental and numerical analysis of fracture processes in concrete［D］.Delft，The Netherlands:Faculty of Civil Engineering and Geosciences，Delft University of Technology，1993. ［17］Bolander J E，Sukumar N.Irregular lattice model for quasistatic crack propagation［J］.Physical Review B，2005，71(9):094106-1-094106-12. ［18］Manzano H，Dolado J S，Ayuela A.Elastic properties of the main species present in Portland cement pastes［J］.Acta Materialia，2009，57(5):1666-1674.［19］Qian Z，Ye G，Schlangen E，et al.3D lattice fracturemodel:application to cement paste at microscale ［J］.Key Engineering Materials，2011，452/453:65-68.［20］Sanahuja J，Dormieux L，Chanvillard G.Modeling elasticity of a hydrating cement paste［J］.Cement and Concrete Research，2007，37(1):1427-1439.［21］Petrovic J J.Review mechanical properties of ice and snow［J］.Journal of Materials Science，2003，38(1):1-6.。
高三英语学术研究方法创新思路探讨单选题30题及答案1. In academic research, a hypothesis is a(n) _____.A. proven factB. educated guessC. random thoughtD. unimportant idea答案：B。
在学术研究中，假设是有根据的推测。
选项A，假设不是已被证实的事实；选项C，假设不是随机的想法；选项D，假设在学术研究中很重要，不是不重要的想法。
2. A research question in academic studies should be _____.A. broad and vagueB. narrow and specificC. unanswerableD. unrelated to the topic答案：B。
学术研究中的研究问题应该是具体且有针对性的。
选项A，宽泛和模糊的问题不利于深入研究；选项C，无法回答的问题没有研究价值；选项D，与主题无关的问题不符合要求。
3. In academic research, data collection is often done through _____.A. guessingB. imaginationC. observation and surveysD. making assumptions答案：C。
在学术研究中，数据收集通常通过观察和调查进行。
选项A，猜测不能用于数据收集；选项B，想象不能作为数据收集的方法；选项D，做假设不是数据收集的方法。
4. A literature review in academic research is mainly to _____.A. show off one's knowledgeB. find existing research on the topicC. fill up pagesD. repeat what others have said答案：B。
Chapter 2 Boiler第二章锅炉Air heater 空预器Commissioning 试运行Anchor 支座，固定Compressor 压缩机、压气机Anhydrous ammonia 无水氨Condenser 凝汽器Anthracite 无烟煤Containment 反应堆安全壳Atomized 雾化Convection 对流Austenitic 奥氏体钢Coolant 制冷剂Auxialiary 辅助机械Coordinated 坐标，定位Axis 轴Corten低合金耐腐蚀钢Bagasse 甘蔗渣Counterflow 逆流（换热器）Bare tube 光管Creep strength 蠕变强度Bark 树皮Criterion 标准Beam 梁，横梁Critical pressure 临界压力Bituminous coal 烟煤Culm 煤屑Blade 叶片Cyclone furnace 旋风炉Blast 鼓风Debris 残骸、有机残留物Blowdown 排污Decane 癸烷Boiler 锅炉Decay 分解Bulk 大块的Deposited 沉积，沉淀的Burner zone 燃烧器区域Deterioration 恶化Butane 丁烷Diesel oil 柴油Calcination 煅烧Differential 差动，微分Capacity 出力Distillate 馏出物Carbon steel 碳钢Distortion 变形Cerium 铈Division wall 分隔墙，双面水冷壁Chromium 铬Drainage 疏水Circulating fluidized bed CFB 循环流化Drum 汽包床锅炉Coal char 煤焦Dwell time 保留时间Cogenerator 热电联产机组Economizer 省煤器Combustion 燃烧Embrittlement 脆性，脆化Equalization 均衡，平衡Ingress进口，入口Erosive 侵蚀的，腐蚀的In-line 顺列Ethane 乙烷Inorganic 无机的Evaluate 评估，评价Ion 离子Evaporate 蒸发Jurisdiction 权限Excess air 过量空气Lignite 褐煤Extended surface 扩展受热面Lime 石灰Fatigue 疲劳Limestone 石灰石Feedwater 给谁Low alloy 低合金钢Ferrite 铁素体Low-volatile 低挥发分的Fin 鳍片，肋片Margin 裕量，安全系数Flange 法兰Matrix 矩阵Flue gas 烟气Membrane 膜Fouling 沾污Methane 甲烷Furnace 炉膛Mill 磨煤机Generator 发电机Molecule 分子Geological 地质的Molten 熔化Girth 环形Nitric oxide 氮氧化物Govern 控制、调节Nonpressure 非承压的Gravity 重力Nontoxic 无毒的Header 联箱，集箱Organisms 有机体Helical 螺旋状的Oxidation 氧化Helium 氦Peat 泥煤Heterogeneous 不均匀的Pendants superheat platen悬吊式屏式过热器Hopper 斗，料斗Pentane 戊烷Husk 壳，外壳Petrochemical 石油化工制品Hydraulic 水力的，液压的Petroleum 石油制品Ignite 点火Plasma spray coating 等离子喷涂Impurity 杂质Platen 屏Inert 惰性Polymer 聚合物Inferior 低级的，劣质的Pores 气孔，小孔Ingredients 成分Porosity多空的Potassium 钾Slurry 水煤浆Prandtl numbers 普朗特数Sodium 钠Prefabricated 预制的Solvents 溶剂Premium fuel 优质燃料Sootblower 吹灰器Pressure loss 压力损失Sour gas 含硫气体Primary air 一次风Specification 规格Propane 丙烷Stable ignition 稳定着火Proximate analysis 工业分析Stanton number 斯坦顿数Pulp 纸浆Saturated 饱和的Pyrites 黄铁矿Straw 稻草Radius 半径，范围Steam line blowing 蒸汽管路吹灰Rare earth element 稀土元素Steams 茎，杆Recuperator 间壁式换热器Stress corrosion 应力腐蚀Regenerator 回热器，蓄热器Structural formula 结构式Regulate 控制，调节Stud 双头螺栓Repercussions 反应Subbituminous 贫煤，次烟煤Reservoirs 储气罐Suction 真空，负压Residuale fuel oil 渣油Sulphur 硫Resonant 共振Superheater 过热器Retract缩回Swamp 沼泽Reynolds number 雷诺数Sweet gas 无硫气Rigid 刚性的，紧密地Switchgear 配电装置，开关装置Rollers 辊子Temperature-entropy 温熵图Scale 水垢，Tenacious 黏的Seal 密封Thermodynamics 热力学Sedimentary 沉积Tube bundles 管束Serpentine tube 蛇形管Tubular 管状的Shale 页岩Turbine 汽轮机Silica 二氧化硅V elocity 速度Silt 淤泥V ertical spidle mill 中速磨，立轴磨Single-phase 单相V essel 容器Skin casing 外护板Viscosity 黏度Slag 结渣V olumetric expansion 体膨胀Vulnerable 易损的，薄弱的DEH 数字电液系统Wear磨损DNB 偏离核态沸腾Welded 焊接FDF 送风机Wingwall屏式凝渣管FGD 烟气脱硫Yttrim 釔FSSS 炉膛安全检测保护系统Abbreviations HRB 回热锅炉AFBC 常压流化床燃烧IDF 引风机AFCO 燃料自动切断IGCC 整体煤气化联合循环AFWC 给水自动切断LMTD 对数平均温差ASME 美国机械工程师协会MFT 主燃料切断ATM 标准大气压MUF 锅炉补给水BFP 锅炉给水泵NWL 正常水位BUT 按钮OFA 火上风，燃尽风BWC锅炉水浓度PFBC 增压流化床燃烧BYP 旁路SSC 刮板除渣机CFBB 循环流化床锅炉TGA 热重分析仪MCR 最大连续蒸发量UBC 未燃烧DAS 数据采集系统WFGD 湿法烟气脱硫2.1 IntroductionBoilers use heat to convert water into steam for a variety of applications. Primary among these are electric power generation and industrial process heating. Steam has become a key resource because of its wide availability, advantageous properties and non toxic nature. The steam flow rates and operating conditions can vary dramatically; from 1000lb/h (0.1kg/s) in one process use to more than 10 million lb/h (1260kg/s) in large electric power plant; from about 14.7 psi (1 bar) and 212ºF in some heating applications to more than 4500 psi (310bar) and 1100ºF (593℃) in advanced cycle power plant.2.1 简介SSC锅炉利用热量使水转变成蒸汽以进行各种利用。
2023年学术学位英语翻译句子练习合集1. This experiment aims to investigate the effects of climate change on plant growth.本实验旨在研究气候变化对植物生长的影响。
2. The results of the study suggest that there is a positive correlation between exercise and mental health.研究结果表明运动与心理健康之间存在正相关关系。
3. The research findings are consistent with previous studies in the field.研究结果与该领域的先前研究一致。
4. The study hypothesizes that increased pollution levels will lead to a decline in air quality.该研究假设污染水平的增加将导致空气质量下降。
5. The data analysis revealed a significant difference in test scores between the experimental group and the control group.数据分析显示实验组和对照组的测试成绩存在显著差异。
6. The researchers collected data through surveys and interviews with participants.研究人员通过调查和访谈参与者收集数据。
7. The study provides valuable insights into the factors influencing consumer behavior.该研究对影响消费者行为的因素提供了有价值的见解。
Specialisation can be seen as a response to the problem of an increasing accumulation of scientific knowledge. By splitting up the subject matter into smaller units， one man could continue to handle the information and use it as the basis for further research. But specialisation was only one of a series of related developments in science affecting the process of communication. Another was the growing professionalisation of scientific activity. No clear-cut distinction can be drawn between professionals and amateurs in science： exceptions can be found to any rule. Nevertheless， the word “amateur” does carry a connotation that the person concerned is not fully integrated into the scientific community and， in particular， may not fully share its values. The growth of specialisation in the nineteenth century， with its consequent requirement of a longer， more complex training， implied greater problems for amateur participation in science. The trend was naturally most obvious in those areas of science based especially on a mathematical or laboratory training， and can be illustrated in terms of the development of geology in the United Kingdom. A comparison of British geological publications over the last century and a half reveals not simply an increasing emphasis on the primacy of research， but also a changing definition of what constitutes an acceptable research paper. Thus， in the nineteenth century， local geological studies represented worthwhile research in their own right； but， in the twentieth century， local studies have increasingly become acceptable to professionals only if they incorporate， and reflect on， the wider geological picture. Amateurs， on the other hand， have continued to pursue local studies in the old way. The overall result has been to make entrance to professional geological journals harder for amateurs， a result that has been reinforced by the widespread introduction of refereeing， first by national journals in the nineteenth century and then by several local geological journals in the twentieth century. As a logical consequence of this development， separate journals have now appeared aimed mainly towards either professional or amateur readership. A rather similar process of differentiation has led to professional geologists coming together nationally within one or two specific societies， where as the amateurs have tended either to remain in local societies or to come together nationally in a different way. Although the process of professionalisation and specialisation was already well under way in British geology during the nineteenth century， its full consequences were thus delayed until the twentieth century. In science generally， however，the nineteenth century must be reckoned as the crucial period for this change in the structure of science. 51. The growth of specialisation in the 19th century might be more clearly seen in sciences such as ________. （A）sociology and chemistry （B）physics and psychology （C）sociology and psychology （D）physics and chemistry 52. We can infer from the passage that ________. （A）there is little distinction between specialisation and professionalisation （B）amateurs can compete with professionals in some areas of science （C）professionals tend to welcome amateurs into the scientific community （D）amateurs have national academic societies but no local ones 53. The author writes of the development of geology to demonstrate ________. （A）the process of specialisation and professionalisation （B）the hardship of amateurs in scientific study （C）the change of policies in scientific publications （D）the discrimination of professionals against amateurs 54. The direct reason for specialisation is ________. （A）the development in communication （B）the growth of professionalisation （C）the expansion of scientific knowledge （D）the splitting up of academic societies 答案及试题解析 DBAC 51.（D） 根据第⼆段第三、四句，19世纪开始的专门化要求更长时间、更复杂的培训，⽇益增长的专门化给参与科学活动的业余爱好者带来了更⼤的问题。
学术英语写作P73--76练习答案[Original Source] (A totalitarian) society…can never permit either the truthful recording of facts, or the emotional sincerity, that literary creation demands….Totalitarianism demands… the continuous alteration of the past, and in t he long run…a disbelief in the very existence of objective truth. (written by George Orwell)[Version C] Orwell believed that totalitarian societies must suppress literature and free expression because they cannot survive the truth, and thus they claim it does not exist.(1) Deep waters that were once off limits to oil explores are suddenly accessible, partly because of advances in floating rigs.Deep water exploring oil had once been impossible before, but now it becomes practicable in part because the floating rigs have developed much.(2) A liver cell has a different job from a blood cell and proteins to match.肝细胞与血液细胞分工不同，而且与之匹配的蛋白质也不同。
Concrete international /April 2009 59By leo KAhlConcrete contractors sometimes refuse to substitute industrial byproducts for a portion of the portland cement in a mixture over fears that they will increase construction times by retarding setting and strength gain. CeraTech, Inc., has developed a line of products that not only contain between 30 and 95% industrial waste stream materials but also speed up setting times and early strength gain. One of the products, Great-White TM , is specially formulated for use with volumetric, mobile concrete mixers. The use of a mobile mixer allows concrete to be placed almost immediately after mixing so workers have the full 20 to 30 minutes to place,consolidate, and finish the concrete before the material reaches initial set.Durable anD sustainableMinimizing the extraction of raw materials and extending the lives of existing structures are critical components of sustainability. Because of the flexible base chemistry used to make its cements, CeraTech is able to use locally available byproducts including fly ash, wood ash, crushed glass, and recycled concrete to produce its products. The raw materials used in its manufacture result in concrete that has a tan or brown color while fresh and that later fades to tan or gray.GreatWhite contains 88% byproducts, but allows the return of repaired or replaced areas, such as roads, bridges, runways, or parking garages, to service in as little as 2 to 3 hours. The product has also been shown to reduce alkali-silica reaction, in some cases allowing theFast and GreenCement for rapid setting and strength-gaining applications is alsoenvironmentally friendlyuse of local aggregates rather than having to transport acceptable aggregates from great distances.The amount of water added to the concrete is mainly used to control workability. A proprietary activator solution is used to start the strength development process. CeraTech has also developed a modifier that works with the activator to accommodate a broad range of ambient and application temperatures.A minimum section thickness of 3 in. (75 mm) is suggested when 1 in. (25 mm) coarse aggregate is used. This can be reduced to 1.5 in. (38 mm) when using 1/2 in. (13 mm) coarse aggregate. Concrete containing GreatWhite is proportioned similar to that of portland cement-based concrete mixtures. By varying the cement content, strengths from 1400 to 4500 psi (9.6 to 31 MPa) can be achieved in 2 hours. This gives volumetric concrete producers the opportunity to provide solutions across a broad spectrum of applications, from sidewalk replacement for store fronts on Main Street to slab replacements for runways and freeways.A typical mixture containing the cement includes 1.5 to 2 parts fine aggregate and 2 to 3 parts 1 in. (25 mm)nominal maximum size coarse aggregate for each part of GreatWhite cement by weight. The water content varies depending on the application and the amount of early strength required. Mixtures with proportions similar to these produce compressive strengths around 2800 psi (19 MPa) in 2 hours and 9800 psi (68 MPa) at 28 days. Flexural strength also develops rapidly, with values typically over 350 psi (2.4 MPa) in 2 hours and 980 psi (6.8 MPa) at 28 days. These mixtures are also very60 April 2009 / Concrete internationalThe deteriorated section of U.S. 101 in Gilroy, CA, shown in this photo was selected to be replaced using concrete containing GreatWhite TM cement. Traffic was diverted to the adjacent lane starting at 8:00 p.m. so the 12 x 15 ft (3.7 x 4.6 m) section of 9 to 11 in. (230 to 280 mm) thick concrete pavement could be sawcut into manageable chunks that were removed with a backhoeBy 1:00 a.m., the existing pavement had been removed so the base could be prepared. Workers were installing a polyethylene vapor barrier to mitigate water intrusion from the base and act as a bond breaker between the adjoining slabs. At this time, the volumetric mixer containing the separated ingredients wasbrought to the site. For this application, additional activator was brought in seperate containers to the site to top off the smalltank on the mixerPlacement of the concrete began at 1:20 a.m. The mixer was calibrated off site prior to the placement. This is standard practice before the equipment is dispatched, and Caltrans has specific practices for calibrating volumetric equipment before any project is started. Because of the desire to gain significant concrete strength before the lane was reopened to traffic, the water content of the concrete was tightly controlled. Severalinternal vibrators were used to ensure proper consolidationAt 1:35 a.m., a vibrating screed was used to quickly strike off the concrete. Because the concrete reaches initial set in only 20 to 30 minutes, this process was started as quickly as possible—even before the entire panel of concrete was in place. Ambient temperature during the placement was 55 to 60 °F (13 to 16 °C)Concrete international /April 2009 61durable, producing no mass loss after 50 cycles of the ASTM C672 scaling resistance test and retaining 100% of their dynamic modulus of elasticity after 300 cycles of the ASTM C666 rapid freezing-and-thawing resistance test. Other desirable properties for a repair material include a coefficient of thermal expansion complementary to the host concrete being repaired (typically between 4.5 and 5.5 x 10-6 in./in./°F [8.5 x 10–6 m/m/°C]) and a modulus ofelasticity of 5400 ksi (37.2 GPa). At a concrete temperature of 72 °F (22 °C), initial set is reached 20 to 30 minutes after mixing, with final set occurring 30 to 40 minutes after mixing. The material, however, can be applied on surfaces between 30 and 120 °F (–1 and 49 °C). It is self-curing, eliminating the need for curing compounds or polyethylene sheets under most ambient conditions, but it should be covered with curing blankets if ambient or surface temperatures dip below 32 °F (0 °C) or if exposed to other extreme conditions.example appliCationIn September 2008, the California Department ofTransportation (Caltrans) used concrete produced with GreatWhite cement to replace a deteriorated section of U.S. 101 Southbound in Gilroy, CA. The cement was loaded in the volumetric mixer from 2200 lb (1000 kg)Super Sacks ®, was transported to the site, and then mixed and dispensed into the repair section. The cement isavailable in 75 lb (34 kg) waterproof bags for smaller uses or in bulk quantities for larger applications.The accompanying series of photos and captionsillustrates the speed with which repairs such as these can be accomplished using this material.Selected for reader interest by the editors.—CeraTech, Inc.CIRCLE 51Leo Kahl is Vice president of Marketing for CeraTech, inc. he serves as the technical communications interface for the company and has over 30 years of industrial and consumer marketing and product develop-ment experience in industries ranging from defense systems, automotive, telecom,manufacturing, and construction materials.By 1:45 a.m., concrete placement was complete and finishing operations were well underway. Although the fast setting time of the cement means crews must be ready to work quickly once placement begins, the use of the volumetric mixer adds a great degree of flexibility in the start time for the placement. There is no need to worry about the concrete arriving before the site has been prepared and also no waiting around for a concrete truck ifwork goes smoother and faster than expectedThe final finishing step was to use a grooving tool on the surface of the patch. This step was completed at 2:00 a.m., only 40 minutes after the start of placing concrete. Trial batches performed prior to the repair were used to establish theconcrete’s strength as a function of time. The repaired section of road was opened to traffic by 6:00 a.m., in time for the morning rush hour。
Chapter 2 Boiler第二章锅炉Air heater 空预器Commissioning 试运行Anchor 支座，固定Compressor 压缩机、压气机Anhydrous ammonia 无水氨Condenser 凝汽器Anthracite 无烟煤Containment 反应堆安全壳Atomized 雾化Convection 对流Austenitic 奥氏体钢Coolant 制冷剂Auxialiary 辅助机械Coordinated 坐标，定位Axis 轴Corten低合金耐腐蚀钢Bagasse 甘蔗渣Counterflow 逆流（换热器）Bare tube 光管Creep strength 蠕变强度Bark 树皮Criterion 标准Beam 梁，横梁Critical pressure 临界压力Bituminous coal 烟煤Culm 煤屑Blade 叶片Cyclone furnace 旋风炉Blast 鼓风Debris 残骸、有机残留物Blowdown 排污Decane 癸烷Boiler 锅炉Decay 分解Bulk 大块的Deposited 沉积，沉淀的Burner zone 燃烧器区域Deterioration 恶化Butane 丁烷Diesel oil 柴油Calcination 煅烧Differential 差动，微分Capacity 出力Distillate 馏出物Carbon steel 碳钢Distortion 变形Cerium 铈Division wall 分隔墙，双面水冷壁Chromium 铬Drainage 疏水Drum 汽包Circulating fluidized bed CFB 循环流化床锅炉Coal char 煤焦Dwell time 保留时间Cogenerator 热点联产机组Economizer 省煤器Combustion 燃烧Embrittlement 脆性，脆化Equalization 均衡，平衡Ingress进口，入口Erosive 侵蚀的，腐蚀的In-line 顺列Ethane 乙烷Inorganic 无机的Evaluate 评估，评价Ion 离子Evaporate 蒸发Jurisdiction 权限Excess air 过量空气Lignite 褐煤Extended surface 扩展受热面Lime 石灰Fatigue 疲劳Limestone 石灰石Feedwater 给谁Low alloy 低合金钢Ferrite 铁素体Low-volatile 低挥发分的Fin 鳍片，肋片Margin 裕量，安全系数Flange 法兰Matrix 矩阵Flue gas 烟气Membrane 膜Fouling 沾污Methane 甲烷Furnace 炉膛Mill 磨煤机Generator 发电机Molecule 分子Geological 地质的Molten 熔化Girth 环形Nitric oxide 氮氧化物Govern 控制、调节Nonpressure 非承压的Gravity 重力Nontoxic 无毒的Header 联箱，集箱Organisms 有机体Helical 螺旋状的Oxidation 氧化Helium 氦Peat 泥煤Heterogeneous 不均匀的Pendants superheat platen悬吊式屏式过热器Hopper 斗，料斗Pentane 戊烷Husk 壳，外壳Petrochemical 石油化工制品Hydraulic 水力的，液压的Petroleum 石油制品Ignite 点火Plasma spray coating 等离子喷涂Impurity 杂质Platen 屏Inert 惰性Polymer 聚合物Inferior 低级的，劣质的Pores 气孔，小孔Ingredients 成分Porosity多空的Potassium 钾Slurry 水煤浆Prandtl numbers 普朗特数Sodium 钠Prefabricated 预制的Solvents 溶剂Premium fuel 优质燃料Sootblower 吹灰器Pressure loss 压力损失Sour gas 含硫气体Primary air 一次风Specification 规格Propane 丙烷Stable ignition 稳定着火Proximate analysis 工业分析Stanton number 斯坦顿数Pulp 纸浆Saturated 饱和的Pyrites 黄铁矿Straw 稻草Radius 半径，范围Steam line blowing 蒸汽管路吹灰Rare earth element 稀土元素Steams 茎，杆Recuperator 间壁式换热器Stress corrosion 应力腐蚀Regenerator 回热器，蓄热器Structural formula 结构式Regulate 控制，调节Stud 双头螺栓Repercussions 反应Subbituminous 贫煤，次烟煤Reservoirs 储气罐Suction 真空，负压Residuale fuel oil 渣油Sulphur 硫Resonant 共振Superheater 过热器Retract缩回Swamp 沼泽Reynolds number 雷诺数Sweet gas 无硫气Rigid 刚性的，紧密地Switchgear 配电装置，开关装置Rollers 辊子Temperature-entropy 温熵图Scale 水垢，Tenacious 黏的Seal 密封Thermodynamics 热力学Sedimentary 沉积Tube bundles 管束Serpentine tube 蛇形管Tubular 管状的Shale 页岩Turbine 汽轮机Silica 二氧化硅Velocity 速度Silt 淤泥Vertical spidle mill 中速磨，立轴磨Single-phase 单相Vessel 容器Skin casing 外护板Viscosity 黏度Slag 结渣V olumetric expansion 体膨胀Vulnerable 易损的，薄弱的DEH 数字电液系统Wear磨损DNB 偏离核态沸腾Welded 焊接FDF 送风机Wingwall屏式凝渣管FGD 烟气脱硫Yttrim 釔FSSS 炉膛安全检测保护系统Abbreviations HRB 回热锅炉AFBC 常压流化床燃烧IDF 引风机AFCO 燃料自动切断IGCC 整体煤气化联合循环AFWC 给水自动切断LMTD 对数平均温差ASME 美国机械工程师协会MFT 主燃料切断ATM 标准大气压MUF 锅炉补给水BFP 锅炉给水泵NWL 正常水位BUT 按钮OFA 火上风，燃尽风BWC锅炉水浓度PFBC 增压流化床燃烧BYP 旁路SSC 刮板除渣机CFBB 循环流化床锅炉TGA 热重分析仪MCR 最大连续蒸发量UBC 未燃烧DAS 数据采集系统WFGD 湿法烟气脱硫2.1 IntroductionBoilers use heat to convert water into steam for a variety of applications. Primary among these are electric power generation and industrial process heating. Steam has become a key resource because of its wide availability, advantageous properties and non toxic nature. The steam flow rates and operating conditions can vary dramatically; from 1000lb/h (0.1kg/s) in one process use to more than 10 million lb/h (1260kg/s) in large electric power plant; from about 14.7 psi (1 bar) and 212ºF in some heating applications to more than 4500 psi (310bar) and 1100ºF (593℃) in advanced cycle power plant.2.1 简介SSC锅炉利用热量使水转变成蒸汽以进行各种利用。
A Study on theExpansion of Benzoxazine-Based PhenolicResinHatsuo Ishida*and Hong YeeLowThe NSF Center for Molecular and Microstructure of Composites (CMMC),Department of Macromolecular Science,Case Western Reserve University,Cleveland,Ohio 44106Received April 8,1996;Revised Manuscript Received November 26,1996XABSTRACT:Benzoxazine-based phenolic resin has recently attracted a great deal of attention due to its versatile properties.This paper explores yet another interesting shown by this class of phenolic resin:volumetric expansion upon It is the volumetric expansion of the benzoxazine resin is mostly due to the of molecular influenced by inter-and intramolecular hydrogen bonding.The role bonding on the volumetric expansion has been studied by systematically changing the used in the benzoxazine monomer synthesis.In comparison to the other known expanding compounds,this resin has been shown to have a high potential for structural/engineering applications.The homopolymers of this resin have a high glass transition temperature (T g ).IntroductionShrinkage of a resin occurs during the polymerization of monomers which are transformed into high molecular weight polymers.In a fiber-reinforced composite,this shrinkage imposes some internal pressure onto the fiber so that physical bonding is enhanced.1,2The shrinkage could also lead to tension in the matrix depending on the fiber content.However,shrinkage in almost all thermosetting resins is so high that it causes residual stress,warping,premature debonding of the fiber from the matrix,fiber buckling,and delamination in fiber-reinforced composites.Presently,most existing ther-mosets cure with volumetric shrinkages of 3-15%.An example is the widely used epoxy resin,which under-goes volumetric shrinkage of 2-7%upon curing.Shrink-age of an adhesive can induce residual stresses that are relieved by debonding from the substrate.Residual stresses also result in optical distortion.This will be a concern in using adhesives to join parts such as in an optical telescope.Methyl methacrylate end-capped dig-lycidyl ether of Bisphenol-A has been widely used as the matrix for dental fillings;however,the shrinkage of this resin upon curing has been a major problem in the dental industry.Due to volumetric shrinkage,problems arise in the molding industry because of nonuniformity in the dimensions of the molded parts.Some thermosetting resins are difficult to mold without using fillers.For example,the molding of a phenolic resin requires fillers such as cellulose flour,wood flour,and,more commonly,mineral fillers to reduce shrink-age.7However,these fillers can be abrasive to the mold surface,and the different acidic or basic nature of these fillers can affect the curing rate.The disadvantages of resin shrinkage and its effect on the final properties and performance of polymers and composites are well documented in the literature.Extensive research has been carried out to reduce the problems of resin shrinkage.Various fillers are incor-porated into the matrix and molding conditions are modified to reduce resin shrinkage.Unfortunately,no one has been able to eliminate this problem,but only to reduce it.In the early 1970s,Bailey et al.3-6introduced a series of spiroortho compounds that expand upon curing.Unfortunately,these materials by themselves found few useful applications.Other disadvantages include com-plicated synthesis procedures and low glass transition temperatures (T g )of the polymers.Many research groups have tried to incorporate the spiroortho com-pound as an additive into epoxy resins in an attempt to reduce shrinkage and improve the mechanical proper-ties.A copolymer of bisnorbornenyl spiroorthocarbonate and an epoxy was used by Lim and co-workers 8as a matrix for a carbon fiber-reinforced composite.They found that the resulting composite had higher impact strength and higher shear strength than that of epoxy -carbon fiber composites.He and co-workers 9,10also tried to incorporate bisnorbornenyl spiroorthocarbonate into an epoxy resin and found that with a 25%bisnor-bornenyl spiroorthocarbonate content,the mixture ex-panded.They also found that the copolymer with zero shrinkage gave no optical distortion when compared to the copolymers that expand or shrink.However,in the same study,they found that the T g s and thermal resistance of the copolymers decreased with increasing amounts of bisnorbornenyl spiroorthocarbonate.They concluded that the bisnorbornenyl spiroorthocarbonate by itself has poor mechanical properties,and thus incorporating this compound into epoxy resin causes a decrease in the tensile strengths,elongations at break,and Young’s moduli of the copolymers.Shimbo et al.11,12also reported that T g s of the copolymers of spiroortho-ester and epoxy decreased with increasing amounts of spiroorthoester,in agreement with He’s finding.Shim-bo concluded that the reduction in internal stress with an increasing amount of spiroorthoester was not due to the expansion of this material,but rather the reduction in the T g s of the copolymers.This can be rationalized by Ishida and Nigro’s 13work,where it was found that the gelation of the copolymer occurs after consumption of the majority of the spiroortho compound.Hence,any volumetric expansion from the spiroortho compound prior to gelation cannot be appreciated and thus shrink-age stresses may still be present.Furthermore,the spiroortho compounds were polymerized from a crystal-line monomer to an amorphous polymer,with some expansion occurring due to the phase transformation.As a result of the shortcomings of the spiroortho compounds,they have not been used as engineering polymers.X Abstract published in Advance ACS Abstracts,February 1,1997.10991997,30,1099-1106S0024-9297(96)00539-6CCC:$14.00©1997American Chemical SocietyRecently a benzoxazine-based phenolic resin was reported by Ishida and Allen16to have near-zero volu-metric shrinkage upon curing.However,the cause for the expansion or near-zero shrinkage is not well un-derstood.In addition to the near-zero volumetric shrink-age,these resins have been shown to overcome most of the shortcomings of conventional phenolic resins and to have excellent processibility.15Thus,this paper will examine the effects of different amines on the volumet-ric changes upon polymerization of this series of ben-zoxazine resins.Experimental SectionBenzoxazine monomers were synthesized according to the procedure of Ning and Ishida.14Various benzoxazine mono-mers were prepared from Bisphenol-A and various primary amines:methylamine,ethylamine,propylamine,isopropyl-amine,butylamine,tert-butylamine,cyclohexylamine,and aniline.The compounds will be referred to as B-m,B-e,B-p, B-ip,B-b,B-t,B-c,and B-a,respectively.The benzoxazine monomer contains an oxazine ring that opens into a phenolic structure upon polymerization:R in the structure denotes the radical of amine and R′the substituent of the phenolic group.In this paper,the difunc-tional benzoxazines were synthesized using a bifunctional phenol;therefore the monomer contains two oxazine rings that are available for polymerization.Crude reaction products containing the benzoxazine monomer were purified by washing with3N NaOH solution at least three times,followed by distilled water,and then drying over sodium sulfate.For B-a, B-c,and B-t,the purified compounds were recrystallized in diethyl ether.The purity of the compounds was determined from1H-NMR spectra.Pure monomers were used for density measurements.Purified monomeric materials were used for a stepwise thermal curing from150to195°C for a total of4h.All samples were cured without adding catalyst.Care was taken to ensure that all cured samples were free of bubbles.Density was used to evaluate the shrinkage or expansion of the monomers and polymers.Density measurements were per-formed according to ASTM D792(Method A)for all cured polymers.The temperature of the water bath was kept constant at24(1°C for all density measurements by water displacement.A10mL pycnometer was used to measure the density of the monomers.All monomers were in the amor-phous state.The densities of the amorphous monomers and polymers are shown in Table3.Molecular modeling was performed on a Silicon Graphics workstation using Sybyl6.0software.Charges of the struc-tures were calculated by Pullman’s method,17where theσand πorbital contributions are included.Energies of the molecules, bond lengths,and bond angles were evaluated after the molecules were energy minimized.The monofunctional ben-zoxazine dimer constructed from the X-ray crystal structure by Dunkers and Ishida18was used to evaluate the hydrogen bonding.FTIR spectra were taken on a Michelson Bomem FTIR spectrometer.The T g of the cured polybenzoxazine was measured using Rheometrics RMS-800a dynamic mechanical spectrometer with a2000g cm force rebalance transducer.This experiment was carried out as temperature sweep from20to200°C at a heating rate of2°C/min,a frequency of1Hz,and a strain of 0.05%.Isothermal curing was performed using a parallel plate fixture with a gap of0.8mm.The tests were run at a frequency of1Hz and a strain of5%.Results and DiscussionVolumetric shrinkage of a typical resin occurs during the curing process because molecules move from a van der Waals distance of separation to a covalent distance of separation.Small molecules are sometimes released as byproducts during the polymerization process;for instance,in a condensation polymerization of resole-formaldehyde resin,water molecules are released,thus further reducing the volume in the resulting polymer. When the polymerization reaction is completed,the material is cooled from the curing temperature,which is normally at an elevated temperature,to room tem-perature,with further thermal shrinkage occurring (Figure1a).It has been reported that only the shrink-age that occurs when cooling from T g to room temper-ature has any significant effect on the material prop-erties.11,12An explanation for this is that any volumetric changes,and thus any built-up stresses,can be relaxed above T g since molecules are readily mobile at these temperatures.However,any stresses caused by cooling from T g to room temperature cannot be relaxed as molecules are nearly immobile in the glassy state.Since the volumetric relaxation is retarded,the shrinkage will be transformed into residual stress.There are two ways that the volumetric shrinkage can be reduced or re-versed:(i)if there is a volumetric expansion during polymerization in such a way as to overcome the shrinkage caused by the difference in the thermal expansion coefficients of the monomer and polymer,as shown in Figure1b,or(ii)if the thermal expansion coefficient of the polymer is lower than that of the monomer so that the volumetric expansion caused by the thermal expansion coefficient difference overcomes the shrinkage during the isothermal polymerization,as shown in Figure1c.According to the polymerization mechanism proposed by Dunkers and Ishida,18the oxazine ring opens by breaking a C-O bond of the oxazine ring.During this process a covalent bond is broken and the benzoxazine molecule transforms from a closed-ring structure to a linear open-chain structure as shown in Scheme1.The open-chain intermediate then reacts with another mono-mer molecule and breaks a C-H bond that is ortho to the phenolic OH on the aromatic ring of the second molecule.Both O-H and C-ring bonds are formed as a result of polymerization.Thus,a total of two covalent bonds are rearranged(C-O of oxazine and C-ring of Mannich base,-CH2-N-CH2-);one covalent bond is formed(O-H),and a van der Waals distance is lost when two monomers merge.Data from molecular modeling show that the lengths of the C-O bond of the oxazine ring and the aromatic C-H bond are almost constant for all compounds,regardless of the amine groups.The calculated values are presented in Table 1.The O-H bonds that formed during ring-opening polymerization are shorter than the C-H bond that breaks and their bond lengths are independent of the amine groups as shown in Table2from the molecular modeling data.The C-ring bond of the Mannich base, on the other hand,is longer than the C-O bond that breaks upon polymerization,and this is true for all the benzoxazines.The slight increase in the bond length of the linear open-chain structure compared to the closed ring of the monomer may be because the strain is released in the open-chain structure.This rationale was used by Bailey et al.1-4for the expansion of the spiroortho compounds.However,in the case of benzox-azine resins,the size of the oxazine ring does not changeScheme11100Ishida and Low Macromolecules,Vol.30,No.4,1997much regardless of the starting compounds.In addition, the benzoxazine ring is a six-membered ring,meaning that the strain energy is almost negligible.Further-more,the fact that the volumetric expansion is different among the different amine-based benzoxazines indicates that the expansion may not be solely due to the strain that is released in the open-chain structure.It should be mentioned that the comparison is made in this paper between amorphous monomer and amorphous polymer. Thus,the volumetric expansion due to the crystalline-to-amorphous transition is not involved.If this transi-tion is included in the comparison,as is typically done in the spiroortho compound studies,the apparent volu-metric expansion of benzoxazine resins would be higher. In order to understand the effects of the amine groups on the volumetric shrinkage or expansion,the benzox-azine compounds are divided into three groups based on the amine structure:(i)the cyclic amines,B-a and B-c;(ii)the aliphatic amines B-m,B-e,B-p,and B-b; and(iii)the steric amines,B-e,B-ip,and B-t.Cyclic Amines.As shown in Table3,the density measurements of the amorphous monomers and amor-phous polymers indicate that B-a expands about0.40% and B-c a nearly identical0.43%.From the results of molecular modeling listed in Tables1and2,the bonds that break and form upon polymerization are slightly shorter for B-a when compared to those of B-c.There-fore,the contribution from the bond length can be eliminated.Dunkers and Ishida18found that the poly-benzoxazines form both inter-and intramolecular hy-drogen bonding.Figure2shows the two possible intramolecular hydrogen bonds in the dimer structure of benzoxazine.In Figure2a,the hydroxyl proton hydrogen bonds with the nitrogen of the Mannich bridge and forms a six-membered ring.On the other hand, Figure2b shows that the hydroxyl proton hydrogen bonds with an adjacent hydroxyl group of the dimer.ItabcFigure1.(a)Density changes of a typical shrinking material upon curing:“a”)volumetric shrinkage during curing;“b”) total volumetric shrinkage.T r)room temperature,T g)glass transition temperature,and T c)curing temperature.(b) Density changes of an expanding material upon curing:“a”)volumetric expansion during curing;“b”)total volumetric expansion.(c)Density changes of an expanding monomer with the thermal expansion coefficient of the monomer higher that the polymer“a”)volumetric shrinkage during curing;“b”) net volumetric expansion.Table1.Calculated Bond Lengths of the Oxazine Ringof the Monomer aamine C-O C-H N-Rmethyl 1.396 1.085 1.481ethyl 1.392 1.084 1.487n-propyl 1.392 1.084 1.488isopropyl 1.397 1.085 1.492butyl 1.392 1.084 1.488tert-butyl 1.396 1.084 1.497aniline 1.394 1.083 1.415cyclohexyl 1.396 1.085 1.492a The C-O and C-H are the bonds that break upon polymer-ization.R represents the amine.All bond lengths are in ang-stroms.Table2.Calculated Bond Lengths of the Open-RingStructure of a Dimer aamines O-H C-ring C-H N-CH2N-R methyl0.951 1.535 1.101 1.488 1.483 ethyl0.952 1.536 1.101 1.491 1.487 n-propyl0.952 1.535 1.101 1.491 1.488 isopropyl0.951 1.534 1.085 1.494,1.488 1.494 butyl0.952 1.536 1.102 1.490 1.488 tert-butyl0.951 1.536 1.086 1.493 1.499 aniline0.950 1.538 1.102 1.484 1.416 cyclohexyl0.948 1.539,1.544 1.101 1.493,1.487 1.495a The O-H,C-ring,and the C-H are formed upon polymeri-zation.N-CH2and N-R are from the Mannich bridge.R represents the amine.All bond lengths are in angstroms. Table3.Room Temperature Densities of the Amorphous Benzoxazine Monomers and AmorphousPolybenzoxazinesaminedensity ofmonomer(g/cm3)density ofpolymer(g/cm3)%shrinkage(-)or%expansion(+) methyl 1.159 1.122+3.20 ethyl 1.109(1×10-3 1.104(2×10-3+0.41n-propyl 1.076(1×10-3 1.084(2×10-3-0.76 isopropyl 1.063(7×10-4 1.071(6×10-4-0.72 butyl 1.067(1×10-3 1.076(2×10-3-0.82tert-butyl 1.078 1.061+1.58 aniline 1.200 1.195-0.40 cyclohexyl 1.123(3×10-3 1.118(6×10-4+0.43Macromolecules,Vol.30,No.4,1997Benzoxazine-Based Phenolic Resin1101can be seen that the latter causes a larger unoccupied volume in the structure.Although the population and stability of the individual hydrogen bonding have not been resolved,both types of hydrogen bonding would cause the molecule to curl,and appear to hinder tight packing.The strength of this hydrogen bonding is directly dependent on the electronegativity of the amine group that is attached to the nitrogen.For aniline-based benzoxazine,the benzene ring that is attached to the nitrogen atom has delocalized electrons,causing the electron cloud around the nitrogen atom to be lower compared to the cyclohexyl group,where the electrons are localized.Thus,the nitrogen atom of the B-a compound should have weaker hydrogen bonding to the O-H groups compared to B-c.However,in the hydrogen-bonded structure,the nitrogen will have a partial positive charge,and in the case of aniline-based poly-benzoxazine,the delocalized electrons in the benzene ring can stabilize the nitrogen and thus the hydrogen bond is more stable in the B-a polybenzoxazine.The strength of hydrogen bonding of B-a and B-c can be qualitatively evaluated from the FTIR spectra shown in Figure3c.Hydrogen-bonded hydroxyl groups,fromboth inter-and intramolecular interactions,appear between3600and2500cm-1.Ordinary intermolecu-larly hydrogen-bonded OH groups should appear around 3400cm-1while the strong intramolecularly hydrogen-bonded OH gives rise to a very broad band and often multiple bands below3000cm-1.Obviously,the inter-molecular interactions will have a significant effect on the density since the density of a material is a direct consequence of the packing of molecules.Even though the relative intermolecular interactions could not be determined precisely,the OH band around3400-3300 cm-1of B-a appear to be broader and stronger than that of B-c polybenzoxazine.In spite of the possibly stronger and more stable hydrogen bonding in the B-a polyben-zoxazine,the volumetric expansion of the B-a and B-c benzoxazines is comparable.This is probably due to a combined steric effect that compensates for the expected difference in expansion.Aliphatic Groups.In Table3,B-m benzoxazine shows the highest volumetric expansion of3.2%,fol-lowed by B-e benzoxazine,which has a volumetric expansion of0.41%.On the other hand,B-p and B-b benzoxazines show volumetric shrinkages of0.72and 0.82%,respectively,which are still considerably lower than most thermosets.The relationship of volumetric shrinkage versus the number of carbon atoms in the aliphatic group is plotted in Figure 4.Volumetric expansion is found to decrease with increasing length of aliphatic chains in the amine moieties.The strength of hydrogen bonding and thus the hydrogen bond length is dependent on the electron density of the nitrogen.The higher the electron density on the nitrogen atom,the stronger the hydrogen bond. It appears that there is a drastic decrease in volumetric expansion from methylamine to ethylamine,with the effect of chain length becoming insignificant for chains longer than the propyl group.Since all of these materi-als are amorphous in their monomeric and polymeric states,the study of intermolecular interactions by molecular modeling is beyond the scope of this paper. Therefore,this study limits itself to the intramolecular interactions from the molecular modeling.The FTIR spectra of the aliphatic amine-based polybenzoxazines are shown in Figure3a,b.As can be seen,the regionsabFigure2.Conformation of the dimer after energy minimiza-tion.abcFigure3.(a)FTIR spectra of B-m and B-e polybenzoxazines. The broad band between3600and2500cm-1indicates the presence of a hydrogen-bonded OH group.(b)FTIR spectra of the B-p and B-b polybenzoxazines.(c)FTIR spectra of the B-a and B-c polybenzoxazines.1102Ishida and Low Macromolecules,Vol.30,No.4,1997of inter-and intramolecular hydrogen-bonded hydroxyl groups of the B-m and B-e are much stronger than that of the B-p and B-b polybenzoxazines.The relationship between the hydrogen bond length and the length of the aliphatic group of a series of model dimers is plotted in Figure5a,paring Figure4 to Figure5a,there is an opposite trend in the hydrogen bond length and the percentage volumetric change of the aliphatic amine-based benzoxazines.In Figure5b, the hydrogen bond length of the H---OH also increases with increasing aliphatic chain,although there is an almost negligible decrease from ethylamine to propyl-amine.Both Figure5a and Figure5b show that there is a dramatic change from the methyl to the ethyl group, and the changes became very small from ethyl to butyl.However,Figure4shows that the decrease of volumetric expansion becomes constant after the propyl group.This is because the effect of intermolecular interaction has not been considered in the molecular modeling.It should be mentioned that the above discussion is based on the assumption that both OH---N and H---OH hydrogen bonds exist in all the benzoxazines,which have been observed qualitatively in the FTIR spectra. The hydrogen bond length increases as the number of aliphatic carbons increases,indicating the reduction of the hydrogen bond strength.Logically,one would expect the density to increase as the hydrogen bonding becomes stronger,which is the case for most organic molecules.The water molecule is an exception to this trend.It is known that the most favorable hydrogen bonding in the ice crystals results in a lower density than the liquid water.19The hydro-gen bond length calculations and density measurements seem to imply that the polybenzoxazines may behave like the water molecules,although we have considered only intramolecular hydrogen bonding in this paper.It is important to mention that the analysis in this paper is restricted to the intramolecular hydrogen bonding, which tends to force the molecule to curl rather than extend.Such a conformation might be unfavorable for tight packing,leading to a larger volume occupied.As mentioned earlier,all polybenzoxazines show inter-and intramolecular hydrogen bonding in the FTIR spectra.The aliphatic amine-based polybenzoxazines are no exception.Evidence of intermolecular hydrogen bonding in the aliphatic amine-based polybenzoxazines complicates the explanation.Furthermore,as the ali-phatic amine becomes longer,the amine portion of the structure becomes more mobile and can more easily attain the lowest energy of conformation,resulting in a better packing of the polymer chains.Steric Effect of Amine Groups.The steric effect of the amine group attached to the nitrogen can have a significant effect on the conformations of the polymer chain such that the hydrogen bonding will be affected. The steric effect may be accessed by comparing the B-e, B-ip,and B-t benzoxazines.B-t benzoxazine with the bulkiest amine shows the greatest volumetric expan-sion,while B-ip shows a slight shrinkage as can be seen in Table3.The volumetric expansion decreases from B-e to B-ip but increases from B-ip to B-t.In addition to the steric effect from the ethyl to the tert-butyl group, there is also an inductive effect from the increasing number of carbon atoms from B-e to B-t,which may explain the increase in shrinkage from B-m to B-ip. However,the steric effect may be stronger when com-paring B-ip and B-t,thus causing an increase in expansion.Isothermal Curing.Isothermal curing at150°C, followed by density measurement at room temperature, was carried out for the as-synthesized sample in order to follow the volumetric changes at room temperature as a function of the extent of cure.All benzoxazines show a decrease in density,and thus expansion in volume,as a function of cure time until about6or7h, when the volume changes level off.Since all samples experienced the same thermal history,the decrease of the density can be explained by the degree of cure.As curing proceeds,more cross-linked chains are formed.A higher cross-link density is believed to result in higher free volume at room temperature.20However,in most polymers this increase in the free volume as T g increasesFigure4.Volumetric expansion as a function of the increas-ing length of the aliphatic amine.1represents the methylamine-based benzoxazine,2represents the ethylamine based-benzoxazine,and so forth.abFigure5.(a)Hydrogen bond lengths between the N and OHas a function of increasing length of aliphatic amine,frommethylamine(1)to butylamine(4).(b)Hydrogen bond lengthsbetween the H and OH as a function of increasing carbon inthe aliphatic amine,from methylamine(1)to butylamine(4).Macromolecules,Vol.30,No.4,1997Benzoxazine-Based Phenolic Resin1103has not been reported to overcome the polymerization shrinkage.A dilatometric experiment was carried out using a calibrated dilatometer with mercury as the volumetric transfer agent.To eliminate the effects of thermal expansion,the material was cured isothermally at150°C.The volumetric changes were recorded at this temperature for a pregelled sample.The volumetric changes of the isothermal curing were followed by a dilatometric experiment with the purified B-e benzox-azine,and the results are shown in Figure6.The measurements were taken5min after the dilatometer containing the sample and mercury was immersed in a 150°C oil bath for establishing temperature equilibri-um.The volumetric changes were recorded in situ during the course of curing.It can be seen that there is a volumetric decrease throughout the16h of curing. After normalizing the amount of volumetric change to the initial volume,this volumetric decrease is ap-proximately3%.The small volumetric decrease at150°C during curing can be understood as the monomers move from a van der Waals distance to a covalent distance of separation.However,the effect of hydrogen bonding on the volume will become more significant as the cured polymer is cooled down to room temperature.A comparison of the B-a and B-c polybenzoxazines from the isothermal curing and room temperature measurement also shows that B-c benzoxazine expands slightly more than B-a benzoxazine.A plot of density changes at room temperature as a function of cure time for B-a and B-c polybenzoxazines is shown in Figure7. In Figure8,the room temperature densities of the aliphatic amine benzoxazines are plotted as a function of curing time.B-m polybenzoxazine shows the highest decrease in density as a function of isothermal curing. B-e and B-p polybenzoxazines show almost no change in density as curing proceeds,while B-b shows only a slight decrease in density.B-p and B-b benzoxazines show volumetric shrinkage according to the density measurements of purified monomers and stepwise cured polymers.The comparison of B-e,B-ip,and B-t ben-zoxazines is presented in Figure9.There is an expan-sion as a function of cure time,with B-t showing the highest amount of expansion.However,B-ip has a higher volumetric expansion than B-e.It should be noted that benzoxazines are cured by means of thermal polymerization without using any catalyst and that as-synthesized benzoxazine monomers contain open rings,dimers,and oligomers that may help the ring opening and thus accelerate the polymerization process.Therefore,isothermal curing was also carried out for purified B-m and B-b benzoxazines,and the plots are shown in Figures10and11,respectively.For B-m polybenzoxazine,it was found that the purified form has a lower density than the as-synthesized form.Both the purified and as-synthesized B-m polybenzoxazines show expansion as a function of the curing time.On the other hand,the purified form of B-b polybenzoxazine has a higher density than the as-synthesized form although both show expansion as a function of curing time. The effect of isothermal curing at different tempera-tures was determined for purified B-b benzoxazine.The curing temperatures and their durations are presented in Table4.Different curing times were employed for each curing temperature in order to ensure that allFigure6.Dilatometry experiment:volumetric changes at 150°C as a function of curing time for B-e benzoxazine.Figure7.Room temperature density changes of the isother-mal curing of as-synthesized(O)B-a and([)B-c benzoxazine.Figure8.Room temperature density changes as a function of curing time for the as-synthesized aliphatic amine-based benzoxazines:B-m(O),B-e(0),B-p([),and B-b(2).Figure9.Room temperature density of isothermally cured B-e(O),B-ip([),and B-t(1).1104Ishida and Low Macromolecules,Vol.30,No.4,1997。
