Ceramics in Space

 CERAMICS IN SPACE

The inherent brittleness of ceramics is the main reason why they are unsuitable as structural material for most applications. However, ceramics do stand out in many highly specific aspects, especially when it comes to high temperatures and chemical stability. In this article, we explore the crucial roles of ceramics in spacecraft and how they save the day where metals falter.

Thermal protection system in spacecrafts:

One of the more common use cases for ceramics in spacecraft is as part of the thermal protection system. To understand why a ceramic material is the ideal candidate for this application, it is important to look closely at the different heat dissipation mechanisms.

            When a spacecraft enters any kind of atmosphere at orbital speeds, it experiences significant surface heating through atmospheric drag. This holds even true for the relatively thin Martian atmosphere, which has only 1% of Earth’s atmospheric density. The heat absorbed by the spacecraft can then take two ways: it can be radiated into the environment or conducted into the interior of the spacecraft, as indicated in the figure 1.




Radiation would be a favourable way for the spacecraft designer to get rid of the absorbed heat, since the environment is hardly affected by the radiated heat, while the spacecraft could disintegrate and/or melt if too much heat is accumulated during the entry phase.

            However, the efficiency of radiation is tied to the fourth power of the surface temperature. This means that it plays hardly any role for surface temperatures most materials can comfortably handle but becomes the dominant heat transfer/cooling mechanism at temperatures above ~1000 K. You may be familiar with this temperature range as virtually all solid materials start to visibly glow red around here .

Specialized coatings are the key :

            The conduction of the heat into the spacecraft is the less favourable way to handle the surface heating because of the temperature limitations of all used materials within the spacecraft. There is only so much heat the spacecraft can absorb before the material limits are exceeded and catastrophic failures may occur.


Engineers came up with a smart solution that utilises both heat transfer mechanisms. For example, the heated surface of the space shuttle orbiter is covered with a good heat-insulating material, namely silica (silicon dioxide). In addition, a black borosilicate coating is applied to this material in order to maximise the radiation emission properties of the surface. This way, up to 95% of the encountered heat is shed away immediately, leaving only 5% of the heat to be absorbed by the interior of the tiles.

            The entire lower surface of the space shuttle orbiters is covered with these black tiles, consisting out of a silica fibre system with a volume content of only 6%. The remaining volume is filled with air. Each tile is marked with an identification number to ensure the correct maintenance and assembly in its unique position. The tiles are bonded to the underlying aluminium structure with a silicon rubber “glue”.

            Other thermal protection systems, such as abrasive systems, also use insulating materials, which are deliberately being eroded by the excessive heat. By design, the abrasive systems can only be used once before they require a complete replacement. In contrast, the silica tiles are reusable, despite their impressive peak service temperature of about 1900 K during the reentry phase.



  SPACE SHUTTLE TILES 


      SHUTTLE INSULATION PLATE

                For especially strongly heated areas, like leading edges of aerodynamic structures, thermal insulation can be insufficient, requiring active cooling. In this case, there is no insulating ceramics layer but a relatively thin, thermally conductive material in place.

                The atmospheric entry phase is not the only operational phase where a spacecraft is subjected to considerable surface heating. Simply being exposed to the sunlight in space can raise the surface temperature quickly up to about 500 K.

                Against this, the space shuttle orbiters were protected by the same silica tiles using a white coating, consisting of a mixture of silica compounds and aluminium oxide, to maximize the surface reflectivity and absorb only a miniscule fraction of the incident solar energy flux.

Spacecraft windows :

                Glass-ceramics are a little more familiar to most of us, if by another name: Gorilla Glass, which is commonly seen in smartphones today. It’s an Aluminosilicate glass formed by letting molten glass nucleate around ceramic dopant particles that are only soluble at high temperatures. When it cools, this gets you somewhere between 50 and 99% crystallinity, according to Corning. The resultant material is very little like a glass except for its transparency. When tempered, the balance between tension and compression makes the stuff tough as hell. Glass-ceramics also play well with electrically conductive coatings, and engineers use that feature on spacecraft windows to keep them free of condensation and ice.



Carbon fiber showing off its flexibility and luster. Carbon fiber wraps lend enormous tensile strength to applications like aircraft fairings and spacecraft landing legs, while contributing little total mass.

Spacecraft windows are a great application of materials science. One way of making space-worthy windows is fused silica, which is 100% pure fused silicon dioxide. Another crazy window material is aluminum oxynitride, which is actually a transparent ceramic we use to make things bulletproof. In a video produced by one manufacturer of aluminum oxynitride bulletproofing products , 1.6 inches of AlON was sufficient to completely stop an armor-piercing .50 cal round. AlON and fused silica both start out as a fine powder called frit, which is tamped into a mold and then just baked at the most unearthly temperatures into a single piece of transparent, super-hard material.

Next-Gen Spaceships using 3D - Printed Ceramics :

            Engineers have always liked ceramic parts – they are strong, lightweight and handle heat better than many metals, ideal for crafting parts for airplanes or rockets. Heat-shielding tiles on the space shuttle were made from ceramics, for example.

            Now researchers have used a 3D printer to make customized ceramic parts that have also overcome the Achilles’ heel of ceramic objects: their tendency to crack.

            "If you go very fast, about 10 times speed of sound within the atmosphere, then any vehicle will heat up tremendously because of air friction," said Tobias Schaedler, senior scientist at HRL Laboratories in Malibu, Calif. "People want to build hypersonic vehicles and you need ceramics for the whole shell of the vehicle."

            Schaedler and colleagues at HRL invented a resin formulation that can be 3-D printed into parts of virtually any shape and size.

            The printed resin can then be fired, converting it into a high strength, fully dense ceramic. The resulting material can withstand ultrahigh temperatures in excess of 1,700 degrees Celsius (3,092 Fahrenheit) and is 10 times stronger than similar materials.

Ceramics are much more difficult to work with than plastics or metals because they cannot be cast or machined easily, according to Schaedler, who is an author on the new study appearing today in the journal Science.

            But Schaedler's team figured out how to trick ceramics into behaving like plastic."We have a pre-ceramic resin that you can print like a polymer, then you fire the polymer and it converts to a ceramic," he said. "There is some shrinkage involved, but it's very uniform so you can predict it."

            The big picture is that this method could help rocket and satellite designers who have to make lots of special small parts that are capable of resisting the heating that occurs during high velocity air friction, as well as high temperatures generated by the exhaust during takeoff.

Silicon Nitride Ceramics possesses ideal Properties :

            The electrical conductivity of materials used for the specimen holders must not interfere with the coil’s electromagnetic fields. Moreover, the specimen holders must exhibit extreme resistance to heat. The advanced silicon nitride ceramics used here offer all of the material properties required to meet these specifications.

Comments

Post a Comment

Popular posts from this blog

Into the world of Piezoelectric Ceramics

Image
 Good morning! If your world’s anything like mine, ceramics just woke you from a peaceful sleep. Chances are, your clock or clock radio has an alarm buzzer made from an advanced piezoelectric ceramic. This unusual ceramic vibrates with a loud noise when electricity is applied. If your clock has a quartz mechanism, as most clocks and watches now do, a tiny slice of vibrating piezoelectric quartz ceramic is the timekeeper. However, in this case, the vibrations are so rapid and small that you can’t hear them. Most people have never heard of piezoelectric ceramics, but piezoelectrics are the secret behind a wide variety of products ranging from underwater sonar (submarine searchers) to medical ultrasonic scans to “smart” skis. What are Piezoelectric Ceramics?      Piezoelectric ceramics are known for what are called the piezoelectric and reverse piezoelectric effects. The piezoelectric effect causes a crystal to produce an electrical potential when it is subjected to m...
Read more

Tempered glass : a basic idea

Image
  You may have heard about tempered glass before, seen it as an advertised feature in gadget specifications or in the form of screen protectors for mobile devices. But what is tempered glass exactly? What makes it different from standard glass or plastic screen protectors? Most importantly, what will tempered glass offer you as a consumer and it is worth the money? The main difference between standard glass and tempered glass – is in the way they are made. Tempered glass is created by heating and then quickly cooling the material – and thus comes with a different structure. One of the main characteristics of tempered glass is that it breaks differently from standard glass. Whereas normally, glass would break into big uneven pieces, tempered glass shatters into small even pieces. This gets rid of the danger of sharp edges and makes it a much safer option should something happen – for this reason, tempered glass is often referred to as “safety glass”. How a tempered glass is better t...
Read more

How a computer chip is manufactured - an overview

Image
  Start with sand The process of creating a computer chip begins with a type of sand called silica sand, which is comprised of silicon dioxide. Silicon is the base material for semiconductor manufacturing and must be pure before it can be used in the manufacturing process. Silicon ingot Multiple purification and filtering processes are performed in order to deliver electronic-grade silicon, which has a purity of 99.9999%. A purified silicon ingot, which weighs around 100kg, is shaped from melted silica and made ready for the next step. Cut wafers The circular silicon ingot is sliced into wafers as thin as possible while maintaining the material’s ability to be used in the fabrication process. The silicon wafers are then refined and polished in order to provide the best possible surface for the following fabrication steps. Building the chip The base structure of a processor that the transistors are built into is silicon. Silicon is known as a  semiconductor  because it doe...
Read more