问题 问答题 简答题

简述盐酸化学清洗锅炉的步骤?

答案

参考答案:

(1)水冲洗;

(2)碱洗:(0.2%~0.5%)磷酸钠+(0.1%~0.2%)磷酸氢二钠+0.05%表面活性剂的混合液来进行。温度80~90℃,时间8~24h,于液水冲洗;

(3)酸洗:在碱洗水冲洗合格后进行酸洗,一般配5%盐酸+(0.2%~0.4%)缓蚀剂,温度50~55℃,时间6~8h;

(4)漂洗:酸洗结束后,用除盐水冲洗后,再用0.1%~0.2%的稀柠檬酸漂洗,调pH3.5~4.0,温度60~70℃,循环至溶液中,铁离子达到平衡;

(5)钝化:漂洗后,直接在漂洗液中加盐酸调pH5.0左右(或氨水调pH9~10),然后加入(0.5%~1.0%)亚硝酸并维持浓度。温度50±5℃,循环4~6h,立即排出。

15(Lb3F3015).影响疲劳极限的因素有哪些?

答案:影响疲劳极限的因素很多,通常内在因素有材料本身的强度、塑性、组织结构、纤维方向和材料内部缺陷等。外界因素主要为零件的工作条件、表面光洁度等。金属材料本身的强度和塑性好,其抗疲劳断裂的能力就大,但材料内部存在夹杂,表面光洁度低,有刀痕或磨裂等,都容易引起应力集中而使疲劳极限下降;此外在酸碱盐的水溶液等腐蚀性介质中工作的金属制品,由于表面易腐蚀,其腐蚀产物嵌入金属内也会造成应力集中,而使疲劳极限下降。

单项选择题
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The structure and workings of the university are ever changing. The university of the past is not like the university of the present and the university of the present will not be like the university of the future. This “adaptation” to the times is what can make some universities great or make some universities among the worst in the nation.

In the past the university was very set in their ways. They did things the way they wanted them done. They paid no attention to the rest of the society and the way the ones paying the bills wanted them done. In the past the professors would lecture endlessly to the students, which often left the students bored and with no idea what was really said to them in the lecture. This is no way to try and teach students; students need interaction with the professors that are paid to teach them. As Paulo Freire believed there needs to be communication between the students and the professors and the class should not be totally memorization. This is the way that things were done in the past.

In the present many universities have either changed or are changing the way that they run their universities. The universities now are taking on many of the modern educational beliefs in order to make changes in the teaching methods. Universities are breaking down many of the divides between majors that they offer. By breaking these barriers the universities are becoming less specialized and more diverse. This goes along with the ideas of Berry who believes that the schools are over-specialized and that the universities are now just machines that are merely meant to produce workers. In the past few years the colleges have been lowering the standards of admission, which in turn lowers the standards of all the schools below the college level. The universities are now on the right track by increasing the standards of admission into their colleges.

小题1:In the author’s view, what can decide a university’s quality?

A.What its structure is like.

B.How its workings are run.

C.What times it belongs to.

D.Whether it’ll adjust itself.小题2:Which of the following is NOT a feature of universities in the past?

A.They were run in a fixed way.

B.They ignored the needs of society.

C.They had lower standards of admission.

D.Professors lacked interaction with students.小题3:What is the author’s main attitude towards universities in the present?

A.Positive.

B.Doubtful.

C.Passive.

D.Uncertain.小题4:What would the author most probably focus on in the following part of this passage?

A.Universities in the future.

B.The standards of schools.

C.The admission into some colleges.

D.Other changes of teaching methods.