The role of silicon in the corrosion of AA6061 aluminium alloy laser weldments

第42卷第6期2023年6月硅㊀酸㊀盐㊀通㊀报BULLETIN OF THE CHINESE CERAMIC SOCIETY Vol.42㊀No.6June,2023SiC 与耐热钢在高温真空中的界面反应机制研究谢莹莹1,陈㊀毛1,宋子杰1,范冰冰1,张㊀锐1,2,陈勇强1(1.郑州大学材料科学与工程学院,郑州㊀450001;2.洛阳理工学院材料科学与工程学院,洛阳㊀471023)摘要:碳化硅陶瓷可用作镁冶炼还原钢罐的内衬㊂在真空和1200ħ条件下,通过扩散偶试验,对SiC 与耐热钢的界面反应进行了系统研究㊂结果表明,在反应初期,界面反应的主要产物为金属硅化物和石墨,其中分布在界面的片状石墨阻碍了界面反应㊂由于界面上低熔点硅镍化合物的熔化,片状石墨在Ni 的催化作用下转变为纤维状石墨,失去了对碳化硅的保护作用㊂界面反应由固-固反应转变为固-液反应,界面反应过程加快,加速了钢对碳化硅的侵蚀㊂与耐热钢相比,SiC 与纯铁的界面反应速率明显降低,金属熔化所需温度也显著升高㊂减少耐热钢中的Ni 含量,可以有效阻止耐热钢和SiC 之间的反应㊂关键词:SiC;耐热钢;界面;石墨;固相反应中图分类号:TQ174㊀㊀文献标志码:A ㊀㊀文章编号:1001-1625(2023)06-2161-11Interfacial Reaction Mechanism of Silicon Carbide and Heat Resistant Steel in High-Temperature VacuumXIE Yingying 1,CHEN Mao 1,SONG Zijie 1,FAN Bingbing 1,ZHANG Rui 1,2,CHEN Yongqiang 1(1.School of Materials Science and Engineering,Zhengzhou University,Zhengzhou 450001,China;2.School of Materials Science and Engineering,Luoyang Institute of Science and Technology,Luoyang 471023,China)Abstract :Silicon carbide (SiC)ceramics can be used as inner lining of reduction tank for magnesium smelting.The interfacial reaction between SiC and heat resistant steel was systematically investigated by diffusion couple experiment under vacuum and 1200ħ.The results show that at the early stage of reaction,the main products of interfacial reaction are metal silicide and graphite,and the lamellar graphite distributing at the interface hinders the interfacial reaction.However,due to the melting of silicon-nickel compounds with low melting point at interface,the lamellar graphite is transformed into fibrous graphite under the catalysis of Ni,losing its protective effect on silicon carbide.In addition,the interface reaction changes from solid-solid reaction to solid-liquid reaction,and the interfacial reaction process is accelerated,which accelerates the corrosion of silicon carbide by pared with heat resistant steel,the interfacial reaction rate between SiC and pure iron is obviously decreased,and the temperature required for the reaction is obviously increased.Reducing Ni content in heat resistant steel can effectively prevent the reaction between heat resistant steel and SiC.Key words :SiC;heat resistant steel;interfacial;graphite;solid phase reaction收稿日期:2023-02-23;修订日期:2023-03-27基金项目:国家自然科学基金青年项目(52202072)作者简介:谢莹莹(2000 ),女㊂主要从事冶金用耐火材料方面的研究㊂E-mail:2428230514@通信作者:陈勇强,博士,讲师㊂E-mail:chenyq@ 0㊀引㊀言碳化硅(SiC)陶瓷具有高强度㊁高硬度㊁耐磨损㊁耐氧化和良好的高温力学性能等诸多特性,在碳化硅基电子器件的金属化和高温航空航天技术中有着重要应用[1-2]㊂然而,碳化硅陶瓷存在脆性较大㊁难加工和高孔隙率等缺陷,应用范围受到限购[3-5]㊂目前,SiC 与金属通常被复合成复合材料,从而改变了单一陶瓷或单一金属材料应用的局限性,扩大了应用范围[6-7]㊂但是,各组分在复合材料中无论如何连接和重新组合,总会有一定的界面存在㊂因此,SiC 和金属材料的界面结构和反应对碳化硅/金属复合材料的性能和应用起着2162㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷决定性作用[8-9]㊂在皮江法炼镁过程中,镁在1200ħ㊁10Pa条件下被还原[10-11]㊂因此,耐热钢在工业生产中被用作还原罐㊂金属材料本身存在局限性,在高温下会发生蠕变,导致罐体坍塌而无法继续使用㊂因为还原罐的坍塌和变形,一些机械化的操作设备无法使用,只能依靠人工取罐和排渣㊂由Cr24Ni7S制成的传统还原罐寿命约为60天,使用寿命短,这不仅提高了冶炼成本,还严重影响了生产效率㊂有学者提出,在金属罐内安装陶瓷内衬来支撑金属罐,可以延缓金属罐在高温下的蠕变行为㊂据估计,该方法可将还原罐的使用寿命提高三倍以上,但目前该设计尚未应用到实际生产中㊂考虑到常用陶瓷的高温强度㊁高温氧化性能㊁抗热震性能以及生产成本等因素,碳化硅陶瓷可以用作镁冶炼还原罐的衬里材料㊂然而,作为还原罐内衬材料的SiC与Cr24Ni7S在1200ħ㊁10Pa条件下的物理化学相互作用尚未被研究㊂目前的研究主要集中于液态金属对SiC复合材料的侵蚀[12-14],而对于固态金属对SiC的侵蚀机理研究较少[15-16]㊂其他研究学者[17-20]也重点研究SiC与Fe㊁Ti㊁Ni㊁Cr等金属的扩散偶之间的界面反应,而对SiC 与合金之间的高温反应,特别是对真空条件下的高温反应研究较少[20-22]㊂本文将Cr24Ni7S和SiC组成的扩散偶置于模拟皮江法炼镁的环境中(1200ħ㊁10Pa),详细研究了SiC/钢界面反应和侵蚀过程㊂对不同时间段的样品进行采样和分析,并利用XRD㊁SEM㊁TEM/EDS等方法对其微观结构进行了详细表征和分析,以期为碳化硅陶瓷衬里在皮江法炼镁中的应用提供理论指导㊂1㊀实㊀验1.1㊀材料及样本制备试验中使用的碳化硅(华盛碳化硅有限公司)的主要成分是SiC和SiO2㊂碳化硅陶瓷的主要物理性能如表1所示㊂ZG30Cr24Ni7钢(Cr24Ni7S)的材质与常规镁冶炼还原罐相同,主要成分如表2所示㊂另外,选择纯度为99.9%的铁进行对照试验㊂表1㊀碳化硅陶瓷的物理特性Table1㊀Physical properties of SiC ceramicProperty IndexFlexural strengthσ/MPa522ʃ5Bulk density/(g㊃cm-3) 2.98ʃ0.14Apparent porosity/%14.01ʃ0.21Diffusivity(25ħ)/(mm2㊃s-1) 4.8ʃ0.3Thermal conductivity(25ħ)/(W㊃m-1㊃K-1)18.3ʃ4.8Thermal expansion coefficient(25ħ)/% 5.6ˑ10-6表2㊀ZG30Cr24Ni7钢的主要成分Table2㊀Main composition of ZG30Cr24Ni7steelComposition Cr Ni C Si Mn P N S Mass fraction/%23.76 6.910.29 1.03 1.960.040.120.03首先将SiC和Cr24Ni7S钢分别加工成20mmˑ20mmˑ5mm和5mmˑ5mmˑ5mm的试样㊂通过粗磨㊁细磨去除表面氧化皮,再经过金相抛光得到表面光滑的样品㊂最后将SiC和金属样品的抛光表面拼接在一起,形成紧密接触的扩散偶㊂1.2㊀试验设备和程序利用可视化高温相变仪(TA-16A,CTJZH,中国)观察SiC与金属界面反应过程中的形态变化㊂该设备主体为卧式管式炉,由硅钼棒加热,最高加热温度为1600ħ,且配有真空和气体保护系统,样品可在真空环境或大气保护下进行测试㊂此外,该设备配备了专业的摄像设备和专用软件系统,可以观察样品在不同加热温度下的形态变化,并按照设定的时间进行拍照㊂在利用辅助光源的情况下,从室温到1600ħ都可以达到同样的成像效果㊂本试验所采用镁冶炼生产条件为:真空度保持在10Pa左右,试验温度设定在1200ħ㊂试验前,将制备第6期谢莹莹等:SiC 与耐热钢在高温真空中的界面反应机制研究2163㊀好的扩散偶样品装入设备的炉管中,调整样品角度㊁光源和摄像机位置,以保证观察到清晰的样品图像㊂打开真空泵,将炉膛内的压力调至10Pa㊂将加热程序和摄影参数输入计算机,依次点击启动任务开始加热,设备开始运行㊂以10ħ/min 的速率升温至1200ħ,并分别保温1㊁2㊁4和8h 得到样品㊂1.3㊀界面和微观结构表征将样品嵌入树脂中,然后用金刚石线切割器(STX-202A,中国沈阳科晶自动化设备有限公司)纵向切割㊂用金相砂纸对样品进行细磨,并对抛光后的组织进行分析㊂通过光学显微镜(OM,Axioscope,德国)观察Cr 24Ni 7S 的显微组织结构演变㊂利用X 射线衍射仪(XRD-6100,SHIMADZU,日本)分析样品的物相组成,扫描速度为4(ʎ)/min㊂使用扫描电子显微镜(SEM,JEOL JSM-7001F,Japan)在15kV 加速电压下,观察样品的微观结构以及SiC 和Cr 24Ni 7S 之间的反应界面㊂利用能谱仪(EDS,Ultim Extreme,Oxford,德国)对界面反应产物的元素组成和分布进行了检测㊂利用透射电子显微镜(TEM,JEOL JEOM 2100,日本)对物质的微观结构进行进一步观察和表征㊂2㊀结果与讨论2.1㊀SiC 与Cr 24Ni 7S的界面反应过程图1㊀在界面反应过程中碳化硅陶瓷和Cr 24Ni 7S 接触角随时间和温度的变化曲线Fig.1㊀Contact angle of SiC ceramics and Cr 24Ni 7S varies with time and temperature during interfacial reaction 图1显示了由SiC 和Cr 24Ni 7S 组成的扩散偶从50ħ加热到1200ħ,并在1200ħ保持8h 的界面反应过程,整个反应过程在真空度为10Pa 的条件下进行,与皮江法镁冶炼的条件相同㊂图2为在界面反应过程中碳化硅陶瓷和Cr 24Ni 7S 接触角(θ)随时间和温度的变化图像㊂从图1可以看出,在温度升高到1000ħ之前接触角没有明显变化㊂然而,当温度达到1000ħ时,接触角出现较大的波动,表明在界面上发生了化学反应,导致界面失稳,接触角随之变化㊂当温度继续升高到1200ħ时,接触角的变化幅度逐渐变小,表明界面反应趋于平衡㊂当保温时间为90min 时,接触角开始急剧增加,此时Cr 24Ni 7S 与SiC 接触面处部分出现熔化,导致金属块倾斜,如图2(c)所示㊂随着保温时间的延长,Cr 24Ni 7S 在接触面处出现大面积的熔化,使Cr 24Ni 7S 试样左右摆动(图2(d)),与碳化硅陶瓷的接触角也出现不连续的剧烈波动㊂然而,当保温时间超过240min 时,接触角趋于稳定,这是因为与SiC 接触的Cr 24Ni 7S 已全部熔化,界面不再变化,而远离界面的Cr 24Ni 7S 则没有继续熔化,如图2(f)所示㊂在1200ħ㊁10Pa 的高温条件下,耐热钢与SiC 接触反应后会出现熔化现象,此时耐热钢中的组织结构和物相也发生了变化㊂样品的物相变化通过XRD 来分析,结果如图3所示㊂从图3(a)可以看出,原始的Cr 24Ni 7S 中主要含有Fe㊁Cr 和CrFeNi 相,这是耐热钢熔点高㊁强度高㊁抗高温蠕变性能好的原因㊂当Cr 24Ni 7S 与SiC 发生接触反应后,界面处主要的第二相是金属硅化物,如Fe 3Si [23]和CrFe 8Si,样品顶部上部主要为金属相和金属碳化物㊂出现这种现象可能是由于硅镍相和硅铁相具有较低的反应焓,在SiC 与Cr 24Ni 7S 的界面上优先生成了Fe 3Si㊁Ni 3Si [24]和石墨,而铬元素更容易与C 结合形成碳化物[25]㊂硅以金属硅化物的形式在界面处富集,而C 则在金属试样内部扩散,导致熔融试样的顶部和底部形成不同的物相㊂图3(b)表明,SiC 与耐热钢反应后,SiO 2的峰强度明显减弱,同时出现了碳元素的衍射峰㊂在真空条件下,SiO 2易与SiC 发生反应并分解[26-27],从而降低界面处的SiO 2含量㊂Park 等[28-29]认为,对于SiC /金属界面反应,相平衡原理和质量守恒原则是影响新生相形成顺序的主要因素㊂由于碳化硅/金属界面反应的局部平衡,反应产物中不可能生成单质Si,所以硅化物和碳是碳化硅与金属反应的主要反应产物[30]㊂2164㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷图2㊀在界面反应过程中碳化硅陶瓷和Cr 24Ni 7S 接触角随时间和温度的变化Fig.2㊀Contact angle of SiC ceramics and Cr 24Ni 7S varies with time and temperature during interfacialreaction 图3㊀SiC 和Cr 24Ni 7S 反应前后的XRD 谱Fig.3㊀XRD patterns of SiC and Cr 24Ni 7S before and after reaction ㊀㊀图4是Cr 24Ni 7S 与SiC 反应前后的金相照片㊂从图4(a)可以看出,原始的Cr 24Ni 7S 内部是奥氏体组织㊂铬元素主要分布在晶粒内部,镍元素和硅元素在晶界处富集,少量的碳元素分布在基体中㊂然而,当Cr 24Ni 7S 与SiC 反应后,耐热钢的组织结构和元素分布都发生了变化㊂如图4(b)所示,在熔化的样品中没有观察到奥氏体组织,基体中出现白色的第二相㊂通过高倍物镜观察,发现这些白色相呈现不同的尺寸和形状,随机分布在基体上㊂根据图3中的XRD 结果,这些白色物质可能是富铬相㊂此外,由于Cr 24Ni 7S 熔化后部分高熔点金属元素从基体中析出并形成一些新的物相,如出现铬元素的富集,导致基体不同位置的耐蚀性不一致,腐蚀后的颜色也不一致㊂对熔化后的样品进行SEM 和能谱分析,结果如图5所示㊂基体中主要的第二相是白色的富硌相和灰色的富镍相㊂此外,基体中含有较多的硅元素,主要以硅镍化合物的形式存在㊂从Ni Si 相图可知,Si Ni 二元体系的共晶温度为1143ħ,生成的Si Ni 相大多是低熔点化合物[31]㊂例如,NiSi 相的液相温度只有992ħ[32]㊂因此,Ni Si 相的形成是界面融化的原因㊂基体中白色的富铬区最有可能是Cr 23C 6[15],铬元素第6期谢莹莹等:SiC与耐热钢在高温真空中的界面反应机制研究2165㊀与碳元素反应具有较低的反应焓,碳元素的增多可能是基体中铬元素析出的主要原因㊂通过上文分析可知,碳化硅与耐热钢反生应生成的主要产物是金属硅化物㊁碳化物以及单质碳㊂因此,在真空条件下,耐热钢与碳化硅的反应如式(1)所示㊂SiC+Steel(Fe,Cr,Ni)ң(Cr,Ni)x Fe y Si z+Cr x C y+C(1)图4㊀Cr24Ni7S熔化前后的金相照片Fig.4㊀Metallography of Cr24Ni7S before and aftermelting2166㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷图5㊀熔融金属样品的SEM 照片和元素分布Fig.5㊀SEM image and elemental distribution of molten metal sample ㊀㊀一般来说,Cr 24Ni 7S 的熔点在1500ħ左右,1200ħ时不会出现熔化现象㊂为了确定Cr 24Ni 7S 熔化的原因,本文对Cr 24Ni 7S 反应前后样品的熔点进行了分析㊂图6为Cr 24Ni 7S 熔化前后的DTA 曲线㊂原始的Cr 24Ni 7S 样品在1250ħ前没有明显的吸热峰,表明其熔点在1250ħ以上㊂而反应后的样品在1139.8ħ时表现出强烈的吸热峰,表明样品在该温度下已开始熔化㊂参考相图可以看出,在由Fe㊁Cr㊁Ni㊁C 和Si 组成的二元相图中,只有Fe C 和Ni Si 二元体系的熔点低于1200ħ㊂通过检测发现样品中碳元素的含量是初始样品碳含量的10倍,而硅元素的含量只增加了32.6%,因此导致耐热钢熔点降低的主要元素是碳㊂本文以纯铁为参照样品对耐热钢熔化的原因进一步分析㊂用纯铁代替Cr 24Ni 7S 进行重复试验,结果如图7所示㊂当试样温度上升到1000ħ时,接触角开始波动,接触表面上发生化学反应,这与Cr 24Ni 7S 的试验现象一致㊂然而,纯铁在1200ħ甚至1300ħ长时间保温都不会发生熔化,这可能是因为体系内缺少熔点较低的硅镍化合物㊂但是,当温度升高到1400ħ并且保持10min 后,样品的底部首先出现熔化,并且整个金属样品在短时间内发生完全熔化㊂这可能是因为界面反应生成的碳元素逐渐扩散到样品内部,使纯铁转化为具有一定碳含量的碳钢,耐热钢的熔点降低到1400ħ左右并发生熔化,这与Cr 24Ni 7S 从底部向顶部逐渐熔化的过程有明显差别㊂图6㊀Cr 24Ni 7S 熔化前后的DTA 曲线Fig.6㊀DTA curves of Cr 24Ni 7S before and aftermelting 图7㊀在界面反应过程中碳化硅陶瓷和铁接触角随时间和温度的变化Fig.7㊀Contact angle of SiC ceramics and Fe varies with time and temperature during interfacial reaction ㊀㊀图8为在界面反应过程中碳化硅陶瓷和Fe 接触角随时间和温度的变化图像㊂从图8可以看出,在温度升高到1400ħ之前,长时间的保温并会使纯铁发生熔化㊂当温度逐渐升高到1400ħ过程中,纯铁样品的仍保持最初的形状,如图8(c)所示㊂但是随着在1400ħ的保温时间延长,纯铁在短时内整体熔化㊂说明第6期谢莹莹等:SiC 与耐热钢在高温真空中的界面反应机制研究2167㊀该样品在1400ħ因达到熔点而发生了熔化,这与之前观察到的耐热钢逐层熔化现象有着本质差别㊂图8㊀在界面反应过程中碳化硅陶瓷和Fe 接触角随时间和温度的变化Fig.8㊀Contact angle of SiC ceramics and Fe varies with time and temperature during interfacial reaction 2.2㊀Cr 24Ni 7S 在1200ħ、10Pa 条件下对SiC 的侵蚀过程图9为碳化硅复合材料在1200ħ㊁10Pa 条件下,与耐热钢反应2h 前后的微观形貌㊂对碳化硅样品进行试验之前,需将其表面打磨和抛光,如图9(a)所示㊂SiC 样品表面光滑,并且有一些不规则的孔隙,这些孔隙是在烧结过程中形成的㊂然而,碳化硅表面经耐热钢侵蚀后变得非常粗糙(图9(b)),表面分布大量的纤维状结构㊂对图9(b)中区域1进行放大,如图9(c)所示,可以看到一层直径约100nm 的纳米线附着在碳化硅表面㊂根据EDS 分析(图9(d))结果可知,这些纳米线的主要成分是C,可能是由碳化硅分解形成的碳转变而来㊂对被腐蚀后的SiC 表面取样进行TEM 分析,结果如图10所示㊂SiC 表面的腐蚀产物主要是各种形态的碳,如石墨片(图10(a))㊁碳纳米线(图10(b))和碳纳米管(图10(c))㊂通过分析碳纳米管的衍射图像,可以发现纳米管为立方晶体结构㊂图10(d)是由图10(e)中a 区域的反傅里叶变化得到的㊂在Fe /Ni 等金属的催化作用下,无定形碳通过原子重排形成碳纳米线,转换界面上分布着大量位错,由无序状态转变为规则的晶体结构㊂纳米线沿着(100)平面生长,生长机制可能是固-液-固(S-L-S)[33]㊂从图9(e)可以看出,碳纳米线的形成与末端的金属有关㊂从EDS 图谱(图10(f))来看,末端金属的主要成分是Ni,还含有Fe 和Cr㊂从文献[34]中可以知,金属具有催化碳纳米形成的作用,但是不同的金属对碳的形态有不同的影响㊂Fe 可以促进片状石墨的形成,而Ni 有助于碳纳米线的形成[34]㊂为了确定Cr 24Ni 7S 对碳化硅陶瓷的腐蚀机制,本文对扩散偶的侵蚀界面进行了分析㊂图11和图12是SiC 陶瓷分别与Cr 24Ni 7S 和纯铁在1200ħ㊁10Pa 条件下反应2h 后的微观界面图㊂从图11(a)可以看出,SiC 被纯铁腐蚀后,在界面处出现了明显碳过渡区㊂这是因为SiC 和纯铁反应形成了FeSi 3,并且生成的C 除部分溶解在金属基体中[35],大部分仍残留在界面处㊂许多结果[36-37]已经证实Fe 与碳化物在高温下反应会生成石墨㊂然而,当SiC 被Cr 24Ni 7S 腐蚀时,其腐蚀界面与纯铁有很大不同,如图12(a)所示㊂在相同条件下,SiC 被Cr 24Ni 7S 腐蚀的情况更为严重,形成的腐蚀层也更大㊂图11(a)和图12(a)的明显区别是,图11(a)界面处形成了不规则的界面侵蚀区域,金属和生成的碳交错分布在一起,没有明显的界面㊂这是因为耐热钢在反应过程中,界面处最先出现熔化,生成的碳部分溶解到金属中,Fe㊁Ni 等金属原子也逐渐向SiC 界面扩散㊂因此,Cr 24Ni 7S 比纯铁对SiC 的侵蚀速率更高,主要是因为反应界面处生成液相,以及碳及金属原子在2168㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷液体中快速扩散㊂图9㊀试验前后碳化硅复合材料的微观结构演变Fig.9㊀Microstructural evolution of SiC composites before and aftertest 图10㊀在1200ħ㊁10Pa 条件下,2h 后侵蚀产物的TEM 图像Fig.10㊀TEM images of corrosion products at 1200ħ,10Pa for 2h.第6期谢莹莹等:SiC 与耐热钢在高温真空中的界面反应机制研究2169㊀图11㊀SiC 复合材料与铁在1200ħ㊁10Pa 条件下腐蚀2h 后的腐蚀层SEM 照片和EDS 谱Fig.11㊀SEM image and EDS spectra of corrosion layer of SiC composite with iron after corrosion at 1200ħ,10Pa for 2h 图12㊀SiC 复合材料与Cr 24Ni 7S 在1200ħ㊁10Pa 条件下腐蚀2h 后的腐蚀层SEM 照片和EDS 谱Fig.12㊀SEM image and EDS spectra of corrosion layer of the SiC composite with Cr 24Ni 7S after corrosion at 1200ħ,10Pa for 2h3㊀结㊀论1)在1200ħ㊁10Pa 的条件下,SiC 与Cr 24Ni 7S 能够发生剧烈的界面反应,生成金属硅化物和无定形碳单质㊂由于硅镍相的熔点较低,硅镍相在界面处熔化后使界面反应由固-固界面转变为固-液界面㊂液相的2170㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷存在促进了原子的扩散,导致耐热钢从界面处向外逐渐熔化㊂2)在固-液界面处,无定形碳在金属Ni的催化作用下转化为碳纳米线,生长机制是固-液-固机制㊂随着保温时间的延长,纳米线逐渐聚集并长大,导致界面处的碳层消失㊂3)纯铁与SiC在相同的反应条件下,只能形成片层状石墨,而且界面处没有液相生成,样品在温度升高到某一数值时发生整体熔化㊂Ni是导致耐热钢与SiC反应并在低温下逐步熔化的关键因素㊂参考文献[1]㊀LI T,ZHANG Y L,LI J C,et al.Improved mechanical strength and oxidation resistance of SiC/SiC-MoSi2-ZrB2coated C/C composites by anovel strategy[J].Corrosion Science,2022,205:10.[2]㊀LIU G W,ZHANG X Z,YANG J,et al.Recent advances in joining of SiC-based materials(monolithic SiC and SiC f/SiC composites):joiningprocesses,joint strength,and interfacial behavior[J].Journal of Advanced Ceramics,2019,8(1):19-38.[3]㊀CAO L,WANG J,LIU Y,et al.Effect of heat transfer channels on thermal conductivity of silicon carbide composites reinforced with pitch-basedcarbon fibers[J].Journal of the European Ceramic Society,2022,42(2):420-431.[4]㊀GOMEZ E,ECHEBERRIA J,ITURRIZA I,et al.Liquid phase sintering of SiC with 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1.1 Metals and Non-metalsWords and termsdefinite－确定的、明确的defect－缺陷plastic deformation塑性变形stress concentrator 应力集中点self-strengthening自强化the tip of a crock裂纹尖端☐Among numerous properties possessed by materials，their mechanical properties，in the majority of cases，are the most essential and therefore，they will be given much consideration in the book．☐在一些主要应用场合，机械性能是材料的各种性能中最重要的性能，因此，本书中将重点讨论。

▪consideration 考虑，需要考虑的事项，报酬☐All critical parts and elements，of which a high reliability （可靠性）is required，are made of metals, rather than of glass，plastics or stone.☐由于各种关键零部件的可靠性要求高，均用金属而不是玻璃、塑料或石头制造。

▪is required 翻译时将英文中的被动语态，改译为汉语中的主动语态。

▪rather than 而不是☐As has been given in Sec.1-1，metals are characterized by the metallic bond（金属键），where positive ions （正离子）occupy the sites of the crystal lattice （晶格）and are surrounded by electron gas（电子云）．☐正如Sec1-1中所说，金属主要由金属键组成（其特征主要……）。

有机硅涂料（silicone coating）Research progress of organosilicon coatingsSilicone is the first widely used elements of the organic polymer compound, has excellent performances due to its unique chemical structure, widely used in various fields of national economy, but also plays an important role in the paint industry. Silicone coatings are organosilicon polymer and silicone modified polymer as main film coating material, it has excellent heat resistance, electrical insulation, corona resistance, radiation resistance, moisture resistance and weather resistance, stain resistance, monk water and chemical corrosion resistance and other properties, in recent years in the improvement and application performance of the products have been the rapid development of.1 silicone resin coating made of organic silicon resin film material, mainly heat-resistant, weather resistant silicone anti-corrosion coating, scratch resistant transparent silicone coating, release and moisture-proof coatings and radiation resistant coatings and other varieties.Coating with silicone resin with three methyl chlorosilane (CH3 SiCl3), two methyl two chloro silane [(CH3) 2SiCl2], three (C6H5SiCL3) phenyl chlorosilane, two phenyl chlorosilane two [(C6H5) 2SiCl2] and methyl phenyl chlorosilane CHO two (C6H5) SiCl2 as raw materials for hydrolysis polycondensation prepared. The effect of monomer structure, number and proportion of functional groups on properties of coatings is very important. The types of organic groups connected on silicon atoms also affect the properties of resins. Differentorganic groups can make organosilicon resins exhibit different properties. For example, when the organic group is methyl silicone resin, with thermal stability, releasability, hydrophobicity and arc resistance; for phenyl, given the oxidation stability of silicone resin, crystalline polymer can be destroyed in a certain range;As the vinyl group, the curing property of organosilicon resin can be improved, and coupling property is brought into being; when phenyl ethyl is used, the compatibility of organosilicon resin and organic substance can be improved. The base can be introduced in the siloxane backbone, increase its compatibility with alkyd resin and polyester resin; introducing phenylene and two phenyl ether subunit, biphenyl subunit of aromatic subunit and silicon carbon boron polymers, radiation resistance, the temperature can reach 300 to 500 DEG C; the backbone structure for the Si-N bond is silicone polymer, its thermal stability at 400 deg. In practical application, different organosilicon monomers can be selected according to the requirements, and different organic groups are induced in the organosilicon resin.Chenguang Research Institute of chemical industry with a viscosity of 20 ~ s, 40mPa - hydroxy silicone oil (CH3) and 2SiCl2 methyl triethoxysilane as raw material, control of nR / NSI is 1.3 ~ 1.4, the quality of 2SiCl2 (CH3) and hydroxyl silicone oil ratio was 7O:3O, and the drop of water way at the temperature of 50 1H hydrolysis. Get the methyl silicone resin has good hardness and elasticity, can be used for flame retardant coatings were prepared by metal film resistors. Chinese Academy of sciences so CH3SiCl3 as the main raw material,acetone and xylene as the solvent, soluble trapezoid with narrow molar mass distribution of poly methyl silicone resin was synthesized by the high temperature coating resin with a certain amount of aluminum powder, RTV silicone rubber prepared by 250 DEG C, old 1000 h, its flexibility, oil resistance and resistance have good corrosion resistance. HeFei University of Technology siloxane silicate four functional groups with three functional groups, through strict control of total hydrolysis reaction, the base material is prepared with silicate and silicone polymer properties, the binder and filler and other auxiliary materials according to a certain proportion of organic silicon heat-resisting coating made of.2 modified silicone resin coating while the silicone resin has many excellent properties, but also has some problems: the general need for high temperature (150 ~ 200 DEG C) curing, curing time, the construction of large area is not convenient; adhesion to the substrate, organic solvent resistance, high temperature mechanical strength of the film is not good, the price more expensive etc.. In order to overcome these shortcomings, organic silicone resin was used to modify the organic resin. Modified silicone resin usually has the advantages of two resins, which can make up for some deficiencies in the performance of the two resins, thereby improving performance and expanding application fields. There are two kinds of modification methods, physical mixing and chemical modification. The effect of chemical modification is better than that of physical blending. Chemical modification is mainly on the end or side chain of polysiloxane chain, and then react with other polymers to produce block, graft or interpenetrating polymer networks, thus obtaining newproperties. In the coatings industry, silicone modified organic resins are mainly alkyd resins. Acrylic resin, epoxy resin, etc..2.1 silicone modified alkyd resin coatingSilicone modified alkyd resin coatings is not only an alkyd resin paint film curing at room temperature and physical and mechanical properties, and has the advantages of good heat resistant silicone resin, UV aging resistance and good water resistance characteristics, coating is an excellent comprehensive performance. The first modification was to add the silicone resin directly to the alkyd reaction kettle that reached the end point,The weatherability of alkyd resin is improved greatly. Another modification is to prepare reactive organosilicon oligomers to react with free hydroxyl groups on alkyd resins, and also to use organosilicon oligomers as polyols and alkyd resins for polycondensation. The alkyd resin modified by chemical reaction has better weatherability. Hunan University prepared by alcoholysis hydroxyl alkyd prepolymer and end to hydrolysis or different functional silicone prepolymer prepared by polycondensation reaction synthesis (A B) silicone alkyd type n block copolymer, and the copolymer as base material made of varnish; comprehensive performance of the varnish excellent, not only has the alkyd resin varnish film flexibility, room temperature curing, impact strength and advantages of good adhesion, but also greatly improve the heat resistance, ageing resistance and anti corrosion properties of water medium.2.2 silicone modified acrylic resin coatingSilicone modified acrylic resin coating has excellent weatherability. It has the advantages of light retention, color retention, easy powdering and good gloss. It is widely used for pre coating of metal sheets, painting of machine equipment and weatherproof decoration and decoration of interior and exterior walls of buildings. Silicone modified acrylic resin has two types, solvent and emulsion, of which silicone acrylic latex coating has excellent weatherability, stain resistance, chemical resistance, is an environmentally friendly green paint. Hubei University uses a water-soluble radical initiator, with hydrogen containing silicone oil and butyl acrylate as raw material, the excellent performance of silicone / acrylic emulsion was synthesized by emulsion polymerization method; the emulsion has good acid and alkali. High and low temperature resistance and electrolyte stability, the coatings prepared with it have good weatherability and stain resistance. Ji'nan Chemical Research of acrylate monomer and D4 and vinyl seven methyl siloxane ring four as raw material, by adding a certain amount of grafting agent, using a batch of polyacrylate stable synthesis of polysiloxane emulsion. Sichuan Province Building Materials Industry Research Institute by pre emulsification process, the activity of silicone and acrylate monomer by emulsion copolymerization by organosilicon modified acrylic emulsion coating prepared with the emulsion of stain resistance, excellent comprehensive performance.Fudan University with vinyl silicone monomer and acrylate, methyl acrylate and acrylic acid hydroxy ester monomer polymerization by seed emulsion was stable with excellentproperties of silicone modified acrylate emulsion. Acrylic silicone resin was modified by organosilicon monomer in Zhejiang University, and silicone acrylic emulsion coating was prepared. Polysiloxane polyacrylate interpenetrating network coating synthesis of Chongqing University, the coating is colorless and transparent, high hardness, strong adhesion, acid deposition, heat aging and has good permeability, can be used as anti weathering materials of rock friction moment.HH silicone acrylic resin developed by Shanghai Academy of building research is suitable for the preparation of weather resistant coatings with high weatherability for more than 15 years. HeFei University of Technology with TEOS hydrolysis condensation part to polysiloxane with hydroxyl acrylic resin was prepared by organic silicone modified acrylic resin; the resin in acid and alkali resistance, salt resistance, solvent resistance and impact strength has significantly improved compared with that of pure polysiloxane, and high temperature resistance is obviously improved acrylic resin. Jiangsu architectural materials research and Design Institute introduced a certain amount of organosilicon functional group in the synthesis of acrylic resin, and prepared the solvent modified silicone resin coating with high weatherability. The Chinese Academy of Sciences of Lanzhou Institute of Chemical Physics with hydroxyl terminated poly two methyl siloxane, in two under the action of azo isobutyronitrile, and methacrylic acid (ester) monomers by solution copolymerization, silicon rubber modified acrylic resin, the resin has good heat resistance.2.3 silicone modified epoxy resin coatingThe modification of epoxy resin with organosilicon can not only reduce the internal stress of epoxy resin, but also increase the toughness of epoxy resin and improve its heat resistance. The poly (two siloxane) modified novolac epoxy resin has greatly reduced the internal stress and improved the cracking resistance index of the Institute of chemistry of Chinese Academy of sciences. Wuhan Research Institute of materials protection and the compatibility with epoxy resin and reactive silicone oligomer polycondensation of the prepared silicone modified epoxy resin has advantages of both epoxy resin and silicone resin, not only improve the heat resistance, but also has good corrosion resistance. Two point fourModification of styrene acrylate emulsion with organosilicon modified styrene acrylic emulsion coating can obviously improve its weatherability, gloss, elasticity and durability. Shanghai University of Engineering Science by graft copolymerization of synthetic silicone modified styrene acrylic emulsion has the excellent properties of silicone and acrylic resin coating, good elasticity, the elongation was significantly higher than that of styrene acrylic emulsion coating. Silicone modified styrene acrylate emulsion building coating was prepared by adding a certain amount of organic silicone to styrene acrylic emulsion polymerization in Shanghai traffic science and technology university,The coating has good water resistance, scouring resistance and durability.2.5 silicone modified other resin coatingSilicone modified polyurethane coatings are widely used in Aircraft Skins, large tank surfaces, building roofs and cultural relics protection. The Chinese Academy of Sciences of Lanzhou Institute of Chemical Physics with hydroxyl terminated poly two methyl siloxane and alcohol solution of castor oil modified polyurethane prepolymer was modified, the curing rate of the blend is improved after the film adhesion, hardness, heat resistance is also improved. It also uses organosilicon modified urushiol resin as base material to prepare paint with resistance to boiling water and water vapor permeability. It can be used for corrosion protection of equipment for a long time. Shanghai Research Institute of building science by using epoxy resin, acrylic resin, silicone resin copolymer in the main chain introduced special hydrophilic functional groups made of water soluble epoxy silicone acrylic resin, the resin has excellent physical and mechanical properties, and has good resistance to aging. Anti ultraviolet and anti-corrosion properties. The coatings made of this resin are basically non-toxic, easy to construct, good in coating properties and good in decorative effect. In the research of Chenguang Chemical Research Institute, copolymerization of styrene, methyl methacrylate, acrylonitrile and organosilicon was used to develop a kind of impregnating agent for electronic devices.3 silicone rigid wear-resistant coatingStudy of organosilicon hard coating on silica sol as Q chain components, functional silicon or carbon functional silane to alkyl chain as a T component, in the presence of water, alcohol and acid catalyst by hydrolysis and polycondensation are partof TQ type silicon resin pre silicon containing hydroxyl polymer solution. By adjusting the variety of RSi (OR ') 3 and the ratio of silica sol to the additive, the variety and solvent of the additive, we can make a kind of hard and wear-resistant coating with various properties. The viscosity of organosilicon coating is usually 4~25 m, Pa, s, and the solid content is 20% ~ 30%. After coating on the surface of the substrate, the remaining silicon hydroxyl groups are condensed under heating condition to form a network structure of hardened wear-resistant layer.Silicone reinforced wear-resistant coating is superior to UV curing acrylic resin hardening coating in both wear resistance and weather resistance. Transparent plastics processed by organosilicon stiffening coatings have been widely used as glasses, car lampshades, instrument scales, compact discs and special architectural windows.4 ConclusionWith the further research, development and improvement of new materials, the performance of silicone coating will be more excellent to meet the different needs of different industries or fields. With the improvement of people's life and beautify the demands for living rooms and buildings, silicone coating with excellent weatherability and stain resistant performance in the decoration of building has a broad application prospect; and, with the increasing awareness of environmental protection silicone coatings towards non pollution, green environmental protection development direction.Refractory paint TK-000Product ingredients: refractory paint TK-000 series by silicone resin as the main raw material, the product features: high temperature of 800 DEG, acid and alkali resistance, good blackness, high hardness, good weatherability. Application: metal, iron surface coating. For example the fireplace. Through the international quality standard: SGS non-toxic inspection standard. Viscosity: 65 + 5KU/30 C color the following 2 points: black, light adjustable hardness: H-2H dry conditions: 150 DEG C * 30 'solid content: 54% + 2% adhesion: 100% (iron) leveling: good feeling: good complementary series: silicone special solvent construction method: spraying standard packing: canned note: as the climate is different, that day water should be used in different products, more details please contact the company or the dealer.According to the characteristics of low surface energy and low viscosity of organosilicon polymer itself, it is more suitable for practical application and modified in preparation process. The range of application of modified silicone resin is wider and better, which has been proved by the development trend.The above is from the coating process. Chemical industry press. ISBN7-5025-1434-1/TQ.786) part of the third chapter silicone coating: if you can borrow this book, it might be of greater help to you;Preparation of silicone resin, usually more than two or more than two units for hydrolysis, raw materials in the following article is given. When the hydrolysis conditions are different,the composition of the intermediate product and the amount of the ring formation of the hydrolysis product are often greatly different, even though the formula is the same. Effects of various factors on hydrolysis:1. Influence of pH value of hydrolysis medium(1) acid medium; (2) neutral medium; (3) alkaline medium;2. The influence of water content in hydrolysis medium: the amount of water needed for reaction is lower than that of silane reaction, which forms the gradual hydrolysis and polycondensation reaction, limiting the formation of ring. The hydrolysis of excess water is the opposite.3, the influence of the solvent in the hydrolysis medium4 、 the influence of equipment agitation speed in hydrolysis5, the influence of temperature on hydrolysis, the higher temperature when hydrolysis, the molecular movement of components is intense, the chance of collision with each other is increased, which is beneficial to the growth of CO polycondensation, low temperature,Otherwise.Formulation formulation related factors: depending on the resin type, this factor varies:(1) the average degree of substitution of alkyl hydrocarbons(D.S.); (2) the average mass of% (including SiOx, phenyl, methyl); after a lot of chemists' careful research experience, there is a data range;Modified resin: it has the advantage of two kinds of resin, and makes up for the disadvantage of silicone resin, and makes it more suitable for coating application. General organic silicone modified organic resin: alkyd resin, polyester resin, epoxy resin, acrylic resin, polyurethane resin, phenolic resin and so on;Two methods of modification: cold spelling (physical method); chemical method;。

小学上册英语第6单元真题(含答案)英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.We have a ________ (家庭聚会) every year.2.What is the term for a young quokka?A. KitB. PupC. CalfD. Chick答案:c3.I have a _____ (跳绳) that I use to exercise. 我有一根用来锻炼的跳绳。

4.The garden is full of ________ (植物).5.The __________ (历史的启示) can spark innovation.6.The chemical symbol for barium is ______.7.What is the opposite of "clean"?A. DirtyB. WetC. SmallD. Tall答案:A Dirty8.I enjoy _______ (看书) at the library.9.The ant can lift objects many times its _______.10.What is the capital of Mozambique?A. MaputoB. BeiraC. NampulaD. Tete答案: A11.Which fruit is red and often mistaken for a vegetable?A. BananaB. TomatoC. OrangeD. Grape答案: B12.The process of hydrolysis uses ______ to break bonds.13.What do you call the season when leaves fall from trees?A. SpringB. SummerC. FallD. Winter答案:C14.She likes to swim in the ___. (lake)15.My cousin is very __________ (有条理的) in her studies.16.Vinegar is an example of an _______.17.The sun rises in the ______ (east).18.She is drawing a ________ (图画).19.The _____ (lettuce) grows quickly in cool weather.20.What is the name of the famous American author known for his adventure novels?A. Mark TwainB. Ernest HemingwayC. F. Scott FitzgeraldD. John Steinbeck答案:A21. A ______ is a type of animal that can run very fast.22.The vegetables are very ___. (fresh)23. (20) River is known as the "Yellow River." The ____24.The ______ (小鸟) chirps cheerfully in the ______ (早晨).25. A sunny day is great for flying a __________. (风筝)26.The _______ can help create a sustainable environment.27.The ________ (文化节) highlights traditions.28.Baking soda is a common ______ used in baking.29.The capital of Armenia is ________ (亚美尼亚的首都是________).30. A polymer is a large molecule made up of many ________.31.The ______ is known for her support of the arts.32.I saw a _______ (蝴蝶) resting on a flower.33.The capital of Libya is _____.34.I like to visit the ______.35. A _______ (小水獺) plays in the river.36.What do you call the art of making paper flowers?A. OrigamiB. QuillingC. PapercraftD. Floral Design答案: A37.The process of combining two or more elements to form a compound is called_______.38.What do you call a fruit that is usually red and grows on a vine?A. PotatoB. TomatoC. CarrotD. Cucumber答案: B39.The _______ (鲸鱼) sings beautiful songs.40.The __________ is a famous city known for its canals. (威尼斯)41.My favorite animal is the _________ (大象).42.I love to visit ______ (自然保护区) to learn about wildlife and conservation efforts. It’s important to protect our planet.43. A ______ is a geographical area characterized by its unique features.44.I have a pet _____ that likes to chase balls.45._____ (落叶树) lose their leaves in the winter.46. A chemical reaction can create a new _______.47.I tell my __________ about my day. (妈妈)48.The process of turning a liquid into a gas is called ______.49.Abraham Lincoln was the ________ president of the United States.50.What do you call the study of the Earth?A. GeographyB. GeologyC. BiologyD. History答案: A51.In a chemical reaction, the substances that are produced are called _____.52.What is the term for the outer layer of the Earth?A. CoreB. MantleC. CrustD. Surface答案:c53.My brother loves going to ____ (amusement parks).54.ayas are famous for their ________ (雪山). The Hima55.I see a spider on the ___. (wall)56.I enjoy ________ (旅行) with my family.57.The term "viscosity" refers to a liquid's _______ to flow.58.Chemical reactions can be affected by _____, concentration, and surface area.59.In a chemical equation, reactants are found on the ______.60.The _____ is known for its spiral shape.61.I want to ________ (learn) English.62.My _____ (邻居) is very nice.63.The __________ (历史的协作) encourages partnership.64.George Washington was the commander of the Continental ________.65. A _______ (小孔雀) displays its feathers proudly.66.I have a toy _______ that can jump high and far, bringing me joy.67. A chemical reaction can produce a precipitate from ______.68.In ancient Rome, people used to watch _____ (gladiator) fights in the arena.69.I enjoy _______ (参加) sports activities.70.The __________ is essential for understanding the geology of an area.71. Age marks the beginning of human ________ (文明). The Suez72. A ________ (有机农业) avoids chemicals.73.My friend is a ______. He loves to read comics.74. A _____ can tell us about the history of our solar system.75.The birds are ______ in the bright blue sky. (flying)76. A ____ hops quickly and has large ears.77.I like to _______ (写作) stories.78.Hawaii is a group of ________ (夏威夷是一组________) in the Pacific Ocean.79.The antelope leaps gracefully across the _____.80.What is the capital of the Solomon Islands?A. HoniaraB. SuvaC. TarawaD. Funafuti答案: A. Honiara81.The _____ (小兔) hops in the grass.82.I like to ___ new things. (discover)83.The ______ is a symbol of peace.84.The __________ (历史的探索) invites curiosity.85.In a covalent bond, atoms share ______.86.The __________ (国家公园) protects natural beauty.87.The tortoise is much _________ than the hare. (慢)88.I think it's essential to be respectful to __________.89.Photosynthesis is how plants make their own ________.90.What is the freezing point of water?A. 0 degrees CelsiusB. 32 degrees CelsiusC. 100 degrees CelsiusD. 50 degrees Celsius答案:A.0 degrees Celsius91. A ____ is often found swimming in ponds and has smooth skin.92. A _______ can be used to demonstrate the principles of physics.93.The capital of Macedonia is __________.94.The country famous for chocolate is ________ (以巧克力闻名的国家是________).95.I love watching the ________ (星星) at night.96.What is the name of the famous novel written by George Orwell?A. Brave New WorldB. Moby DickC. 1984D. Animal Farm答案: C97.What is the capital of Iceland?A. OsloB. ReykjavikC. HelsinkiD. Copenhagen答案:B98.My brother is passionate about __________ (科学).99. A polymer is a large molecule made of many ______. 100.________ (生态影响) shapes landscapes.。

材料英文单词Materials English Words。

In the field of materials science and engineering, there are numerous English words that are commonly used to describe different types of materials, their properties, and their applications. Understanding these words is essential for anyone working in this field, whether they are researchers, engineers, or students. In this document, we will explore some of the most important English words related to materials and provide explanations for their meanings and usage.1. Metal。

Metal is a material that is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity. Examples of metals include iron, copper, aluminum, and gold. Metals are widely used in various industries, such as construction, automotive, and electronics.2. Alloy。

An alloy is a mixture of two or more elements, at least one of which is a metal. Alloys often have enhanced properties compared to pure metals, such as increased strength, hardness, and corrosion resistance. Common examples of alloys include steel, brass, and bronze.3. Polymer。

介绍钢铁英文作文英文：Steel is a type of alloy made from iron and carbon, with other elements such as manganese, silicon, and phosphorus added to enhance its properties. It is one of the most widely used materials in the world, with applications in construction, transportation, and manufacturing.Steel has a high strength-to-weight ratio, making it ideal for use in buildings, bridges, and vehicles. It is also durable and resistant to corrosion, making it suitable for use in harsh environments. Additionally, steel can be easily formed and shaped, allowing for a wide range of designs and applications.One example of steel's versatility is its use in the construction of skyscrapers. The Empire State Building, for instance, is made primarily of steel, with over 57,000 tonsof the material used in its construction. Steel's strength and durability make it an ideal choice for supporting tall buildings and withstanding the forces of wind and earthquakes.Another example of steel's usefulness is its role in the automotive industry. Cars and trucks rely heavily on steel for their frames, engines, and other components. The strength and durability of steel help ensure the safety of passengers in the event of a crash, while its light weight helps improve fuel efficiency.Overall, steel is an essential material that has played a crucial role in shaping our modern world. Its strength, durability, and versatility make it an ideal choice for a wide range of applications, and it will likely continue to be a key material in construction, transportation, and manufacturing for years to come.中文：钢铁是一种由铁和碳组成的合金，加上其他元素如锰、硅和磷等，以增强其性能。

钢铁类型外贸英语作文Title: Exploring Steel Types in International Trade。

In the realm of international trade, steel holds a significant position due to its widespread usage in various industries. Understanding different types of steel iscrucial for effective trade negotiations and transactions.In this essay, we will delve into the classification ofsteel types and their relevance in foreign trade.Firstly, let's address the primary classification of steel: carbon steel and alloy steel. Carbon steel, as the name suggests, primarily consists of iron and carbon, with the carbon content ranging from 0.04% to 2.1% by weight. This type of steel is further divided into low, medium, and high carbon steel based on carbon content. Low carbon steel, with carbon content typically below 0.3%, is commonly usedin construction and manufacturing due to its affordability and ease of shaping. Medium carbon steel (carbon content between 0.3% and 0.6%) finds applications in automotivecomponents and machinery parts, offering a balance between ductility and strength. On the other hand, high carbonsteel (carbon content above 0.6%) is renowned for its hardness and wear resistance, making it suitable for tools and blades.Alloy steel, on the other hand, is composed of ironwith significant additions of other elements such as manganese, silicon, nickel, chromium, and vanadium. These alloying elements impart specific properties to the steel, such as increased strength, corrosion resistance, and heat resistance. Alloy steels are further categorized into various subtypes based on their alloying elements and properties. For instance, stainless steel, containing chromium and often other elements like nickel or molybdenum, exhibits excellent corrosion resistance and is extensively used in kitchen utensils, architectural facades, andsurgical instruments.In the realm of international trade, the classification of steel types is instrumental in determining trade tariffs, quality standards, and product specifications. For instance,certain countries impose tariffs based on the carbon content of imported steel, incentivizing the importation of low carbon steel for applications such as construction where strength requirements are not as stringent. Additionally, quality standards such as those set by organizations like the International Organization for Standardization (ISO) ensure that traded steel meets specific criteria for composition, mechanical properties, and dimensional tolerances, fostering trust and reliability in international transactions.Moreover, understanding the properties and applications of different steel types enables traders to identify market demands and opportunities. For instance, in regions with a booming automotive industry, there may be a higher demand for medium carbon alloy steel for manufacturing components such as gears and shafts. Conversely, in coastal areas with high humidity and salt exposure, there may be a greater need for corrosion-resistant stainless steel for marine applications.Furthermore, advancements in steel manufacturingtechnology have led to the development of specialized steel grades tailored to specific industries and applications. For instance, advanced high-strength steel (AHSS) has gained traction in the automotive sector due to its exceptional strength-to-weight ratio, contributing to vehicle lightweighting and fuel efficiency. Similarly, electrical steel with low core loss and high magnetic permeability is indispensable in electrical power distribution and transformer manufacturing.In conclusion, steel's versatility and ubiquity in various industries make it a cornerstone of international trade. Understanding the classification, properties, and applications of different steel types is paramount for navigating the complexities of foreign trade negotiations, adhering to quality standards, and capitalizing on market opportunities. As global industries continue to evolve, the role of steel in international trade is poised to remain indispensable, driving economic growth and innovation across borders.。

生物学英语复试题及答案一、选择题1. Which of the following is not a characteristic of living organisms?A. Growth and developmentB. ReproductionC. ResponsivenessD. Inertia2. What is the basic unit of life?A. CellB. TissueC. OrganD. Organ system3. What is the process of photosynthesis?A. The conversion of light energy into chemical energyB. The conversion of chemical energy into light energyC. The conversion of heat energy into chemical energyD. The conversion of chemical energy into heat energy4. What is the primary function of chlorophyll in plants?A. To absorb light energyB. To store chemical energyC. To release oxygenD. To produce water5. What is the main component of the cell membrane?A. ProteinsB. LipidsC. CarbohydratesD. Nucleic acids二、填空题6. The genetic material of all living organisms is either__________ or __________.7. The process by which organisms adapt to their environment is called __________.8. In eukaryotic cells, the organelles that are responsible for energy production are __________.9. The basic structural and functional unit of a protein is the __________.10. The process of an organism developing from a fertilized egg into a mature individual is known as __________.三、简答题11. Explain the role of DNA in the cell.12. Describe the process of cellular respiration.13. What are the main differences between prokaryotic and eukaryotic cells?四、论述题14. Discuss the importance of biodiversity and the threats itfaces.五、翻译题15. Translate the following sentence into English:“细胞分裂是生物体生长和发育的基本过程。