论文-探究晶体结晶

晶体是什么

晶体(crystal)是由原子、分子或离子有序排列组成的固体。晶体都有组成框架，这些框架向三维方向延伸。由于框架内部的“单元”有序而且重复排列，所以晶体有标致准确的外形。这在大型晶体上体现得尤为明显。许多大型晶体有平整的面和分明的角。

日常生活中我们经常见到晶体，比如食盐、白糖、雪，还有许多宝石，等等。

有许多物质虽然看起来像晶体，实际上不是，它们是多晶体(polycrystal)。多晶体由许多小晶体杂乱无章地排列而成。常见的多晶体有冰、许多金属、陶瓷、玻璃等。

晶体如何结晶

晶体是在物态转变时形成的，气态、液态转变成固相时形成晶体，固态之间也可以直接产生转变。

液态转固态（蒸发结晶法）

顾名思义，蒸发结晶法通过蒸发溶液中的溶剂，只令溶质保留，从而得到结晶。

2.液态转固态（冷却热饱和法）

冷却热饱和法首先将溶剂加热，再将其冷却并达到过饱和状态，使得超出饱和部分的晶体结晶。

3. 气态转固态（升华法）

升华法首先将晶体加热升华为气态，再降低温度，使其达到过饱和状态，而后经过冷凝生长成为晶体。

实验

目的：获取结晶

方法：冷却热饱和法

步骤：

按5：1的比例往奶锅中加入白糖和自来水，然后中火加热并搅拌内容物，直到水煮开且无法看见糖。此时的溶液清澈、呈淡黄褐色、微稠。
将溶液倒入一个玻璃杯，从杯口伸入一根竹签并用夹子固定（签头不要触到瓶底）。将玻璃杯在室温下静置直到玻璃杯与溶液都达到室温。
将玻璃杯放入冰箱上层静置。
只需静静等待二至三天，因为结晶的速度非常快。

注意事项

往水中加入糖的数量只能多（多于5：1）不能少，不然无法结晶。这个实验我做了两次，第一次实验失败，原因就在于加入糖不够多，因此在冰箱中放置数天也无法结晶。
竹签不能触到瓶底。

结果

冰箱中静置二至三天后，杯壁上几乎结满了晶体。将竹签抽出，竹签浸入溶液的部分被结晶覆盖。结晶形似冰霜，晶莹剔透。有的部分看得出分明的细小棱角，有的部分看上去光滑，摸起来微微粗糙。

感想

通过这次实验，我第一次真切地体会了自然的精致与细微，不同于以往所体会到的。这是我第一次真切地明白，世界上居然存在虽然如此细小，但结构精巧、别具一格的物质。它们会生长，会变化，会“消失”得无影无踪，似乎具有独特的生命。日后，我可以对它们多加了解、做更多有关的实验，探寻它们的美妙。在我的努力下，我一定会成功。

图片：

室温下静置三十分钟后

论文-探究晶体结晶

放入
冰箱数小时后

论文-探究晶体结晶

放入冰箱第二天

论文-探究晶体结晶

放入冰箱第三天

论文-探究晶体结晶

放入冰箱第五天

论文-探究晶体结晶

参考资料：

www.thoughtco.com

-What Is a Crystal? (https://www.thoughtco.com/what-is-a-crystal-607656)

-A Guide to Growing Great Crystals (https://www.thoughtco.com/how-to-grow-great-crystals-602157)

www.baidu.com

-晶体-百度百科（https://baike.baidu.com/item/%E6%99%B6%E4%BD%93/944670?fr=aladdin）

完成于2017年8月22日

Article about crystallization

What are crystals?

Crystals are solids that are formed by orderly-arranged atoms, molecules or ions. Crystals are formed by lattices which extend out in three-dimensions. For the units inside the lattices are arranged orderly and repeatedly, many crystals have exquisite and well-defined shape. This is especially obvious on large-sized crystals. Many of them have flat faces and well-defined angles.

We usually meet crystals in our daily lives, such as table salt, sugar, snow, many gemstones etc. Nevertheless, some solid materials that look like crystals are not actually crystals. They are polycrystals. They are formed by many little crystals but without order. Common polycrystals are ice, many metal samples, ceramics and glass.

2. What is the process of crystallization?

Crystals are formed when phase changes, especially when gas or liquid phase change into solid phase. Substance of solid phase can turn into crystal too (related to isotopes).

a) Liquid phase to solid phase (evaporate method)

As the term suggests, the evaporate method achieves the crystal by evaporating over-saturated solution.

b) Liquid phase to solid phase (cooling over-saturated solution method)

This method needs to heat over-saturated solution. When it is boiled, stop heating and let it cool down. It can also be put in the fridge. Before long, the crystallizing procedure will begin.

c) Gas phase to solid phase (sublimation method)

This method is a little like method b). This method sublimates crystals into gas phase and then cools the gas down. The gas eventually condensates into crystals.

3. My experiment

Goal: Achieve crystals

Method: cooling over-saturated solution

Steps:

a) Add sugar and water （5 to 1 ratio）to a milk pot. Heat it (medium heat) and keep mixing the solution until water is boiled and sugar cannot be seen. The solution at this moment looks clear, a little thick and slightly biscuits.

b) Pour the boiled solution into a glass, soak a thin wooden stick in it. Fix it with clips and do not let the end of the stick attach to the bottom of the glass. Cool the glass and the solution to room temperature.

c) Place the glass on the upper layer of the fridge.

d) The waiting time will be 2 to 3 days. The crystallization procedure is quite fast.

4. Kind reminder

a) Sugar which is added into the water cannot be less than 5 to 1 ratio, or the crystallization cannot succeed. I did this experiment two times and failed the first time because I did not add enough sugar into the water.

b) The end of the stick must not attach to the bottom of the glass.

5. Results

After 2 to 3 days in the fridge, the glass’s walls are nearly full of crystals. Pull out the stick and I see the part of the stick which soaks into the solution is covered by crystals (a bit like a popsicle). The crystals look like anomalous ice, transparent, glisten under the light. Some are a clear vision of small edges and angles and some look like a smooth surface but slightly rough when touching.

6. My thoughts

Through this experiment, I experienced the exquisite of nature for the first time, different from the other phenomena I experienced before. This is the first time I see these substances with my own eyes. Although these substances are tiny, they are well-structured and delicated-created. They can grow, change and disappear. In the future, I can learn more about them and do more relevant experiments, seek for their beauty. With my effort, I will succeed.

Images:

Thirty minutes under room temperature

论文-探究晶体结晶