Why it is so special in the big family of cement?

Bircball with his partner, from the Imperial Chemical Company (ICI), create their own type cement which have no big hole( $>100\mu m$ ) in its slurry, named Macro-Defect-Free cement（无宏观缺陷水泥）.

The outstanding advantage of it, of course, give it a large E (Young's Modulus), a large Fracture toughness（断裂韧度）, etc. Because of these strange proporties, it can even be used to make springs.

It is composed as following, shear agitation at low temperature and pressure, to get it.

things compose the MDF cement

Where does it shine?

There are too many platforms for it to demonstrate its superiority, this text will just name a few of them below.

$\mathbb{A}.$ Electromagnetic shielding performance（电磁屏蔽性能）: can easily mix with iron powder ( $r<100\mu m$ ), their successfully interaction make this new cement get a good sheilding characteristic.

$\mathbb{B}.$ Biological property（生物性能）: can interact mildly with certain cells, which make it have the biological portability.

$\mathbb{C}.$ Low temperature non-cracking property（低温不易碎裂特性）: don't like the common cement, it gives larger $K_{IC}$ （应力集中系数）and lower Thermal conductivity （热传导系数）even when the tempreture is 77K, which make it more hard in the low temperature.

$\mathbb{D}.$ Of course, it is very hard: the common cement have E(Young's Modulus) 5MPa, but here, the value can be 200MPa!

Dig in? the electromagnetic shielding performance.

Step 1: skin effect（趋肤效应）!

skin effect of E wave

When the electromagnetic field go through the metal mesh（金属网络结构）, it will die out exponentially, hence the field is gatherd in the skin of the metal. That what is called the skin effect.

Some brief explanations are given below:

E wave be conciled

When there is a field with large frequency $\nu$ , it will produce large anti-electromagnetic field (Faraday's Law), which offsetting themselves well, just because the truth that only in a closed loop can the induced current be generated by the counter electromotive force（仅闭合回路中的反电动势才可产生感生电流）, the field inside the metal will be canceled out better.

The electromagnetic wave is "large" at the outside "skin"

That is, the larger the frequency of the E wave is, the more complete the shielding function of the metal will be.

Step 2: The Good modification of MDF cement（良好的改性）

It is lucky that if MDF is mixed with the second phase material（第二相材料）, its machenical parameter will not be change greatly, that means, if mixed it with metal, it will get both hardness and electromagnetic shielding performance.

Step 3: Application of its electromagnetic shielding performance.

Make the shielding material to protect equipment such as computers, motors and transmission lines from electromagnetic waves.

Electromagnetic shielding chamber

Some interesting use? the Biological property.

Get to know some interesting things:

$\alpha$ .From the intramuscular transplantation in mice（老鼠肌内移植实验）by Williams (Williams D F. McNamara A. et al JMat Sci.1981.19 ;637), it is confirmed that the interaction between MDF cement and muscle tissue can delay the cycle of cellular inflammatory response（细胞炎性反应的周期）.

$\beta$ .Modification with PEEK（PEEK生物相容性改性）, PEEK is a chemical material named polyetheretherketone（聚醚醚酮）. As shown below.

PEEK

Is there any strange connection between them?

PEEK with biology use

From the experiment, if mix it with the MDF cement, the new cement will have no cytotoxicity and mutagenesis（无细胞毒性及诱变作用）, and it is expected to be the next bone transplantation material, maybe, a new type of Bone cement（骨水泥）?

Bone cement

Bone transplant opration

Referance: 李北星.无宏观缺陷水泥基复合材料的性能，应用与湿敏性 Wikipedia. cement Baidubaike_PEEK 生物材料表面改性与生物相容性.中国科学院深圳先进技术研究院 Wikipedia.skin effect m.baidu baidubaike_无宏观缺陷水泥 wenku.todgo.com