题干

某可充电的锂离子电池以LiMn2O4为正极,嵌入锂的碳材料为负极,含Li+导电固体为电解质。放电时的电池反应为:Li+LiMn2O4==Li2Mn2O4。下列说法正确的是

A:放电时,LiMn2O4发生氧化反应

B:放电时,正极反应为:Li++LiMn2O4+e-==Li2Mn2O4

C:充电时,LiMn2O4发生氧化反应

D:充电时,阳极反应为:Li++e-==Li

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C

同类题1

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圆珠笔头的制造难度有多大

任志方

    ①圆珠笔头分为笔尖上的球珠和球座体。油性圆珠笔头的圆珠由黄铜、钢或者碳化钨制成;水性圆珠笔头的圆珠则采用不锈钢、硬质合金或氧化铝等材料制成。由这些材料制成的圆珠笔,要满足在同一个角度下,连续不断地书写800米且不出现断线的情况才算合格。

    ②其中,球珠用的碳化钨的硬度比钢的硬度高数倍,仅比金刚石的稍微差一点。其制造工艺和轴承滚珠的类同,主要是采用滚珠旋压成型技术,用钢丝冲剪,或成型锻压成小方块,再磨成圆珠,需要专用的滚珠凹模座,它的精度与旋压力、转速有关。

    ③这一产品真正的设计难点在于怎样把这么小的圆球,在极大的生产数量下,做到相同的尺寸。这里的高精度、高互换性是基于整个制造体系的严谨得到的。

    ④笔头的另外一部分,直径仅有2.3毫米的球座体,无论是生产设备还是原材料,此前都长期掌握在瑞士、日本等国家手中。关键部位的尺寸精度要求在两微米之内,表面粗糙度要求为0.4微米,在笔头最顶端的地方,也就是放小圆珠的地方,厚度仅有0.3毫米到0.4毫米。由于后期要进行高精度的加工,既要容易切削,加工时又不能开裂,对不锈钢原材料提出了极高的性能要求。

    ⑤圆珠笔头对加工精度的要求极高,由于笔头上不仅有小球珠,里面还有5条引导墨水的沟槽,生产加工中一个小小的偏差都会影响书写的流畅度和笔的使用寿命,笔尖的开口厚度不到0.1毫米,还要考虑到书写角度和压力,球珠与笔头、墨水沟槽位必须搭配得“天衣无缝”,加工误差不能超过0.003毫米。以来自瑞士公司的笔头一体化生产设备为例,生一产个小小的圆珠笔头需要20多道工序

(摘自《齐鲁晚报》2017年1月12日 有删节)

同类题4

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    I was sure that I was to be killed. I became terribly nervous. I searched in my pockets to see if there were any cigarettes, which had escaped their search. I found one and because of my shaking hands, I could barely get it to my lips. But I had no matches, they had taken those. I looked through the bars at my jailer. He did not make eye contact with me. I called out to him “Have you got a light?” He looked at me, shrugged and came over to light my cigarette. As he came close and lit the match, his eyes inadvertently(不经意地)locked with mine. At that moment, I smiled. I don't know why I did that. Perhaps it was nervousness, perhaps it was because, when you get very close, one to another, it is very hard not to smile. In any case, I smiled. In that instant, it was as though a spark jumped across the gap between our two hearts, our two human souls. I know he didn't want to, but my smile leaped through the bars and generated a smile on his lips, too. He lit my cigarette but stayed near, looking at me directly in the eyes and continuing to smile.

    "I kept smiling at him, now aware of him as a person and not just a jailer. And his looking at me seemed to have a new dimension too. “Do you have kids?” he asked. “Yes, here, here.” I took out my wallet and nervously fumbled for the pictures of my family. He, too, took out the pictures of his family and began to talk about his plans and hopes for them. My eyes filled with tears. I said that I feared that I'd never see my family again, never have the chance to see them grow up. Tears came to his eyes, too. "Suddenly, without another word, he unlocked my cell and silently led me out. Out of the jail, quietly and by back routes, out of the town. There, at the edge of town, he released me. And without another word, he turned back toward the town.

    “My life was saved by a smile.” Yes, the smile― the unaffected, unplanned, natural connection between people. I really believe that if that part of you and that part of me could recognize each other, we wouldn't be enemies. We couldn't have hate or envy or fear!