Lesson 44: All about ceramic in phones and hi-tech devices
Hey Dear MIUIers!
Hello and welcome to our new MIUI Device Classroom thread. It's time for our knowledge growth again. Our previous lesson was made by @rahul_09 and he taught us All About Power Banks. If you haven't seen it, you should definitely do it! And today I will try to guide you through ceramic and use of it in mobile and hi-tech devices. Let the lesson begin!
The word ceramic itself is derived from the Greek word κεραμικος (keramikos), which means "having to do with pottery". This term covers inorganic nonmetallic materials that are hardened by baking at high temperatures. Before the high technologies came into our lives this word has been always associated with traditional clays - materials made into pottery, dinnerware, building materials like bricks, tiles and the like. However, since those times we've discovered new ceramic materials, which are not simple clays, but more complex and advanced materials. These new types of ceramic are called "advanced ceramic" and are widely used in nearly every aspect of our lives, including cars, aerospace, defence, environmental, fiber-optic, medical and other technologies. Do you know what other technologies use advanced ceramic? It's cellular phones and smartphones and personal computers.
Did you know?
NASA's space shuttles have around 34,000 ceramic tiles, each. Those are used for protecting from heat produced when space ships re-enter Earth atmosphere.
Advanced ceramics are made of various types of materials including traditional silicate-based and other types as well. But generally they are classified based on the composition type:
1. Oxides: alumina, zirconia.
2. Non-oxides: carbides, borides, nitrides, silicides and silicates.
3. Composites: combinations of two previous types.
Depending upon the group the ceramic is included into, it will exhibit different properties. Different primary chemical element also impacts different properties to the ceramic.
Properties of ceramic and where they are used
Each material used in technologies nowadays needs to have some unique properties. They make the material most suitable for using in a certain place for a certain purpose. Let's have a look on ceramic properties making it be an irreplaceable thing here or there.
Superconductivity is a phenomenon occurring in some materials. It can be characterized by zero electrical resistance and exclusion of the interior electromagnetic field. Superconductivity allows creating most powerful electromagnets we know.
It's the least studied property of ceramic. Why? Because nobody knows the exact reason for it to be present. All we know now is ceramic materials show superconductivity under some conditions (extremely low temperature for example).
Superconductivity: A magnet levitates above a piece of superconductor cooled to -196°C.
Semiconductors are solids, whose electrical conductivity can be controlled in a very wide range, either permanently or dynamically. They are super-important in technology and are essential in all modern electrical devices from PCs to phones and others. Semiconductors are used in integrated circuits, CPUs, GPUs... Well, everywhere actually.
As for ceramics having semiconductivity properties, they are mainly oxides of transition elements, for example Zinc Oxide (ZnO). One of the most common use for this property is varistors. Generally, varistor is an electrical resistor with "negative resistance". While the voltage passing through them is "normal", they show high resistance up to several megaohms. But when the voltage grows and reaches some threshold varistor's electrical resistance drops significantly. This property allows varistors to dissipate a lot of energy. They also self reset - when voltage comes to normal again, resistance grows to the standard value. Varistors are most often used for surge-protection.
Polycrystalline ceramic also changes its electrical resistance while various gases are passed over it. So this type of ceramic is also used for making gas sensors.
Different varistors made of ceramic
Piezoelectricity, pyroelectricity, ferroelectricity
Many ceramic materials have the property of piezoelectricity. Piezoelectricity means that materials develop a voltage difference between two faces when compressed or vibrating, linking the electrical and mechanical responses. Such materials are used in electronics that rely on quartz resonators, where electricity produces mechanical motion (powering the device) and the mechanical motion in turn is used for producing electrical signal. Another way of using this property is building piezoelectric ceramic speakers. This is the main type of speakers currently used in smartphones, portable electronics etc. More than that, piezoelectric cantilever speaker in Mi MIX was also possible to be produced thanks to this property of ceramics.
Mi Mix piezoelectric cantilever ceramic speaker
Pyroelectricity means generating electrical potential while heated or cooled. All pyroelectric ceramics are also piezoelectric materials and can be used to interconvent between thermal, mechanical and electrical forms of energy. This property of ceramics is useful for producing motion sensors - tiny rise of the temperature when someone enters the room produces electrical signal, which is then transmitted to the controlling unit.
Movement sensor. Works thanks to pyroelectrical properties of the material it is made of
Pyroelectricity can be observed most strongly in materials displaying ferroelectric effect. Ferroelectric materials have a spontaneous polarization, which goes reverse while an electric field is applied. Barium titanate and lead zirconate titanate (these are the two representatives of advanced ceramics) have both piezoelectric and ferroelectric properties. They are used in the manufacture of capacitors, high-frequency loudspeakers, transducers for sonar, and actuators for atomic force and scanning tunneling microscopes.
Electrical properties variation
Some crystalline ceramic materials conduct electricity while being below so called "transition temperature" and break circuit when reaching it. These materials are used for self-controlled heating elements. The most common place where you can find them is rear-windows of your cars - they are the part of the defrost system in those.
Rear-window defrost system
And what can we see about ceramics?
The properties i described above are all rather well known. But not visible to a general consumer like me and you. They are all hidden somewhere under the enclosure. We have to believe ceramics is there. But the best way to understand something is to see it by our eyes. So we are coming to a moment that can be seen, touched, scratched and investigated in tons of other ways. The housing, the body of our phones (not only phones) is now also sometimes made of ceramic. Let's speak about it.
The first tech product to use ceramic housing was the watch. IWC (International Watch Company) is often named as one of the first brands initiated the use of ceramics in watch making.
Certina and IWC produced watches with ceramic bodies/bezels
Ceramics is a very lightweight material. It is scratch-resistant and smooth. These features are what makes ceramics a good housing material. Wide variety of ceramic materials was tested for this, but as of now there is one most commonly used type of advanced ceramic. It's the Zirconium oxide (zirconium dioxide actually, ZrO2), also known as zirconia.
Zirconia ceramics are structured in a martensite-type transformation mechanism of stress induction. This provides the ability to absorb highest amounts of stress relative to other ceramic materials. This type of ceramics shows the highest mechanical strength and toughness at room temperature - the temperature most devices are used at. Zirconia is also corrosion, chemicals and wear resistant. Its thermal expansion coefficient is close to steel, which makes it even better to replace metallic parts. More than that, it also dissipates heat better than any other non-metallic material. Zirconia is 8.5 on the Mohs scale of mineral hardness, compared to 4.5 for normal steel and 7.5 to 8 for hardened steel and 10 for diamond
Pure zirconia at room temperature occurs in the monoclinic form and looks like a white powder. It is stable up to 1170 degrees and transforms to the tetragonal structure above this temperature. At 2370 degrees it transforms to the cubic phase.
Atoms of elements in zirconia have two types of bondings - ionic and covalent. This combination makes zirconia a mechanically strong material and gives it property called ductility. Although zirconia is stronger than many metals it is more brittle. To overcome brittle behaviour, ceramic fibers made with a special process are embedded - they form fiber bridges and increase fracture toughness. Zirconia ceramic is also radio-transparent and doesn't interfere with the signals your smartphone sends or receives. This allows us to get rid of plastic parts, which were previously included for antennas to be able to work. More than that, zirconia can also be transparent or colored with any color. Possibly, it will replace screen glasses soon.
Different types of circonia-made parts. Pay attention, they are of different colours
Which of Xiaomi devices are made of ceramics?
And here is my favourite part of the lesson - is Xiaomi somewhere at the top of the hi-tech companies or is it somewhere behind them? The answer is known - Xiaomi is leading! :)
Let's see, which of the Xiaomi's devices have ceramic parts? The simplest answer would be - all of them as we already know that each technological product nowadays includes ceramic parts in its circuits. But let's only count the devices with ceramic bodies.
The first product with ceramic body Xiaomi released was its Mi 5 Pro on April 6, 2016. It was the first try to use ceramics not only inside, but also outside the device - it had a black-coloured ceramic body and looked gorgeous.
Mi 5 Pro with black ceramic body
Few months later that year, on August 31 they also started selling the first smartwatch in Xiaomi family - Huami Amazfit with a ceramic scratch-resistant bezel.
Huami Amazfit smart watch
And finally, on October 25 and at CES 2017 Xiaomi presented 2 variants of the concept smartphone with tons of innovations - Mi MIX. Mi MIX body is also made of ceramic. However, opposite to the two products above it exists in two colour variations - black and white (remember, we discussed that zirconia ceramic can be of different colours). But it's not only the body that is made of ceramic. This device is also packed with piezoelectric cantilever speaker, which only could be created thanks to ceramics.
Two different colour variations of Mi Mix - with Black and White bodies
Does anybody of you, the readers, have any ideas, what will be the next Xiaomi device using ceramic in it? Maybe anything other than body or bezel? Share your ideas in comments if you have any.
This is the end of our today's lesson. Hope you liked it and know a little more about the devices and things around us. As for me I am looking forward to learn more from the Device Team members next week. Are you?
Thanks @BharatG for giving me the idea about the topic.
Thanks also go to @marcus_keong and @Candicesu for all the motivation, kindness and suggestions.
Forbes, Ortech Ceramics, Wikipedia, Quora, Science Direct, PubChem, New World Encyclopedia and others
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