问题 问答题 简答题

试述X射线粉末衍射法物相定性分析过程及注意的问题。

答案

参考答案:

物相定性分析过程:

1.用粉末照相法或粉末衍射仪法获取被测试样物相的衍射图样;

2.通过对所获衍射图样的分析和计算,获得各衍射线条的2θ、d及相对强度大小;

3.使用检索手册,查寻物相PDF卡片号;

4.若是多物相分析,则在3步完成后,对剩余的衍射线重新根据相对强度排序,重复3步骤,直至全部衍射线能基本得到解释。

注意问题:

1.对试样分析前,尽可能详细了解样品来源、化学成分、工艺状况,观察外形、颜色等性质,为物相分析的检索工作提供线索;

2.尽可能根据试样的各种性能,在许可的条件下将其分离成单一物相后进行衍射分析;

3.尽可能避免衍射线重叠,提高粉末照相或衍射仪的分辨率;

4.d值处理精度要求高,检索时只允许小数点后第二位才能出现偏差;

5.特别要重视低角度区域的衍射实验数据;

6.多物相混合实验时,应耐心检索,力求全部数据都能合理解释;

7.物相定性分析过程中,尽可能与其他的相分析实验手段结合起来,互相配合,互相印证。

单项选择题


Phyllis Wheatley is regarded as America’s first black poet. She was born in Senegal, Africa, about 1753 and brought to America aboard a slave ship at about the age of seven. John and Susannah Wheatley bought her for three pounds at a slave auction in Boston in 1761 to be a personal servant of Mrs. Wheatley. The family had three other slaves, and all were treated with respect. Phyllis was soon accepted as one of the family, which included being raised and educated with the Wheatley’s twin 15-year-old children, Mary and Nathaniel. At that time, most females, even from better families, could not read and write, but Mary was probably one of the best educated young women in Boston. Mary wanted to become a teacher, and in fact, it was Mary who decided to take charge of Phyllis’s education. Phyllis soon displayed her remarkable talents. At the age of twelve she was reading the Greek and Latin classics and passages from the Bible. And eventually, Mrs. Wheatley decided Phyllis should become a Christian.
At the age of thirteen Phyllis wrote her first poem. She became a Boston sensation after she wrote a poem on the death of the evangelical preacher George Whitfield in 1770. It became common practice in Boston to have "Mrs. Wheatley’s Phyllis" read poetry in polite society. Mary married in 1771, and Phyllis later moved to the country because of poor health, as a teacher and caretaker to a farmer’s three children. Mary had tried to interest publishers in Phyllis’s poems but once they heard she was a Negro they weren’t interested.
Then in 1773 Phyllis went with Nathaniel, who was now a businessman, to London. It was thought that a sea voyage might improve her health. Thirty-nine of her poems were published in London as Poems on Various Subjects, Religious and Moral. It was the first book published by a black American. In 1775 Phyllis wrote a poem extolling the accomplishments of George Washington and sent it to him. He responded by praising her talents and inviting her to visit his headquarters. After both of her benefactors died in 1777, and Mary died in 1778, Phyllis was freed as a slave. She married in 1778, moved away from Boston, and had three children. But after the unhappy marriage, she moved back to Boston, and died in poverty at the age of thirty.

The word "extolling" is closest in meaning to ______.

A.welcoming

B.stating

C.bemoaning

D.praising

单项选择题