Erasmus : Transparent Alumina was first showcased in a Star Trek movie, and used in saving humpback whales. When a powerful alien spaceship approaches earth in this movie, it tries to communicate with the whales but finds a deadly silence, as the humpback whales are extinct at that time.
Captain Kirk and his crew travel back in time to find humpback whales. To transport them into the future they need to put them in an enclosure full of seawater. But, to transport this much water mass, glass or Perspex is not strong enough to cope with the water pressure. Transparent alumina was invented as a material with metallic characteristics: strength and elasticity, easy to work with and tool, but with the aesthetic characteristics of transparency.
Humpback Whales Star Trek IV
Erasmus :“It would be interesting to see whether posterity gives us synergies between future technologies such as transparent alumina composites and new directions for humanity such as oceanic colonisation.”
If humans begin to colonise the oceans using some of our predicted future tech, there will be a need for transparent, corrosion resistant, super strong windows. However, in a hostile environment like the sea, corrosion resistance and strength are likely to be paramount.
Erasmus : More obviously, the Star Trek application for transparent alumina is the production of see through windows for space ships. Glass could not stand the lateral pressure, is less flexible, less forgiving of mechanical impact or shock and would have less heat resistance. In short, not suitable for spaceship windows especially where they might be banged about a bit or exposed to extremes of temperature on exposure (or not) to solar radiations.
Kinkajou : “Is such a thing as transparent alumina possible?”
Erasmus : Perhaps! Most metals possess characteristics related to their position in the periodic table. Metal atoms possess outer electron shells that can be readily shared between adjacent metal atoms. This allows photons of many different energy levels to be captured and reflected; giving metals a characteristic reflection or shine.
Transparent Armor Glass
Methods around this issue allowing photons to pass through the alloy or composite material without interacting with the material include:
- doping the metal structure with another mixture of appropriate electron capturing atoms
- New alloys which interact poorly with visible or infrared light. Many materials may only be transparent at particular wavelengths only.
- New composite materials: e.g. ceramics
- New structures with nano-islands of materials allowing light to penetrate the interstices
- New structures such as nanotubes allowing light to travel down the interstices
- New techniques in manufacturing.
- New polymers or polymer combinations.
- Monocrystalline lattices e.g. diamonds: a high density tight lattice of carbon atoms.
- Finally, exotic states of excited matter
Kinkajou : Do we really need all these methods of achieving transparency?
Erasmus :The world is a big place and different problems need different solutions. In applications, such as in "Star Trek", the ability to withstand pressure and increased flexibility would allow the design and construction of the most amazing aquariums and fish tanks, and would allow these structures to be fairly impact tolerant.
Kinkajou : So back to the example of transparent metals. Any problems?
Erasmus :The problem lies in that much of the malleability or elasticity of metal is probably related to the shared electron shell in the metal or metal alloy. If the electron shells are restricted in their mobility or interactiveness, the material would likely become more brittle and less elastic. This would limit the alloy’s characteristics of strength and elasticity, while gaining transparency.
The earth has been in existence for billions of years and has been a natural if perhaps crude chemical laboratory for all of this time. You would instinctively believe that if the earth has not produced a naturally occurring transparent metal composite or alloy, that perhaps, such a thing may not be possible.
Perhaps the answer lies in industrial grade manufacturing of transparent grade natural silica composites, perhaps better known as gemstones. Alternatively, perhaps humans could outdo nature by inventing a composite of nanodiamond in a carbon polymer matrix.
Glass : The Early Competitor of Transparent Alumina
Kinkajou : Tell us about glass?
Erasmus : Glass may be brittle, but it also does not corrode or oxidize. A glass window a hundred years old still functions as much it ever did.
Glass allows infrared energy to pass through, but is not very heat tolerant, especially to rapid temperature changes.
Glass was not invented by humans. Glass occurs accidentally in fires built over beach sand, (silica) at the right temperature and also in lightning strikes. Ancient Humans just identified and became intrigued by this substance and over time learned to make it themselves and learned how to manufacture or work with glass in the construction of many common things that we take for granted today.
It took a long time between identifying glass and then understanding how to commercialize its industrial production on a cheap efficient commercial scale.
I can’t even begin to imagine what our world would be like without glass.
Float Glass Factory
Materials for Transparency
Kinkajou : “Do we really need transparent alumina?” asks Kinkajou.
Erasmus : Perhaps not. A transparent alumina window will probably be dust in the wind within a hundred years as “rust” eats the alloy away. Seawater poses an even more unforgiving environment, with the naturally occurring chemicals assisting oxidation or corrosive electrolytic processes. I would probably not want to walk in front of a transparent alumina seawater whale tank more than a decade old. However, perhaps our children will go to the stars in a spaceship with silica polyalloy coated nanodiamond matrix carbon polymer windows.
There probably is a need for transparent strong yet elastic polymers, but corrosion resistance would be paramount in demanding mission critical applications in the future,” Our current building materials met our needs admirably and very cost efficiently.
However, as usual demand drives innovation. It would only take a single change in our lives to drive innovation and cost performance efficiencies. For example. A sudden spike in shipbuilding demand for corrosion and pressure resistant transparent panels, could fuel innovation or technological development
Erasmus :“It would be interesting to see whether posterity gives us synergies between future technologies such as transparent nanodiamond polymers and oceanic colonization.”
If humans begin to colonize the oceans using some of our predicted future tech, there will be a need for transparent, corrosion resistant, super strong windows. However, in a hostile environment like the sea, corrosion resistance and strength are likely to be paramount.
Kinkajou : So tell me about the examples you have given before. What about new composite materials? For example, ceramics.
Erasmus :This sounds really difficult and technical, but there are examples of ceramics that are very familiar to us indeed.
- The most obvious examples are gemstones. These are “transparent” ceramics. Synthetic Sapphires and rubies are both made from-crystalline aluminum oxide (Al2O3), the base mineral being called corundum. Color is caused mainly by the presence of Impurities. For example chromium contamination usually tints these gems “red”.
- Many ceramics could even be said to be made with transparent alumina, as aluminium is fundamental to their structure.
Transparent Solar Voltaic Solar Concentrator
Kinkajou : What about composite materials: e.g. what most of us normal people would call “ceramics “
Erasmus : Most ceramic materials have a crystalline structure with the size of crystalline micro islands at around the frequency of visible light. If the wavelength of the light attempting to pass though the microcrystalline or nanocrystalline islands is similar to the sizes of crystalline islands, the light is scattered and the materials becomes opaque.
If the micro-islands or nano-islands can be uniformly reduced in size below the wavelength of the light attempting to pass through the ceramic, the material may acquire transparent properties. The issue then becomes the processing of the materials to control the sizes of the microcrystalline islands, either through milling, heat / pressure processing, or combination with other materials.
The method involving reduction of the micro-island or nano-island material island particle sizes to well below the wavelength of visible light (~ 0.5 µm or 500 nm) , could eliminate much of the light scattering resulting from light interacting with crystalline micro-islands or nano-islands,, resulting in a translucent or even transparent material Heating and pressure treatment tends to reduce the sizes of the intercrystalline islands resulting in tough clear materials, the best example being gemstones.
Recent nanoscale technology has, however, made possible the production of (poly) crystalline transparent ceramics such as alumina Al2O3, Yttria Alumina Garnet (YAG), and neodymium-doped, Yttria Alumina Garnet Nd: YAG.
Mixtures of materials can have quite different properties to the individual constituents. Significant increases in strength (2–5 times), toughness (1–4 times), and creep resistance have been observed in systems including SiC/Al2O3, SiC/Si3N4, SiC/MgO, and Al2O3/ZrO2.
Nanocomposites of yttria and magnesia have also been produced.
Clear ceramics have industrial uses due to their properties. YAG is used extensively in LASER processes due to their transparency, heat tolerance and temperature change tolerance. These can include lenses, amplifiers, optical windows or base host materials.
Other applications of transparent YAG ceramics include:
- Transparent armor windows,
- Night vision devices (NVD) and
- Nose cones for heat seeking missiles
- Domes for Infrared or radio frequency transmitters,
Due to the extreme temperatures associated with the environment of military aircraft and missiles, the ceramic composites must also possess excellent thermal stability.
Synthetic ruby lasers and YAG lasers are still in use Medical surgery in multiple sites and applications in the body. Laser applications can be found in eye lenses recontouring to avoid the need to wear glasses, removing tattoos, removing telangiectasias and skin blemishes at both the small blood vessels or capillary level.
The strengthening mechanisms observed vary depending on the material system, and there does not appear to be any general consensus regarding strengthening mechanisms, even within a given system. There is trade-off between optical performance, type of optical transmission (e.g. IR or visible light wavelengths), mechanical strength, mechanical ductility, corrosion resistance and heat resistance.
Kinkajou : Wow! What about exotic states of matter? What the hell does that mean?
Scientists have made: “aluminum” transparent by bombarding the metal with a very powerful soft x-ray laser.
They did this by knocking out an electron from every aluminum atom in the material being worked with, using a short pulse from the laser. The bombarded sample of aluminum turned nearly transparent to extreme UV radiation. This transparent aluminum essentially is new state of matter. (Natural aluminum does not have properties of transparency).
Unfortunately, the effect occurred only for very short times (Femtoseconds), using very high energy levels and affecting very small areas, such as target sizes the size of a human hair cross-section.
The significance of this finding is that materials function quite differently at different operating conditions such as temperature (i.e. very hot or very cold).
Building the Future.
Goo : So maybe in Star trek they could build a transparent nuclear fusion reactor. You could look inside and keep an eye on how it was working.Kinkajou : Astounding, Goo. I’m not sure why it might be a good idea. However, I think the amount of energy leaking out of the nuclear fusion reactor may indeed make it a very bad idea. Sort of looking directly into the sun at a distance of a few meters.
Erasmus : Yet, consider one step further. If we can take advantage of the extra dimensions of the universe inherent in our understanding of space and time, perhaps we could coax energy storage out of the nuclear reactor, gated by the transparent “alumina “, ( or whatever else we could manage), allowing bursts of energy to be released such as in advanced sci-fi weaponry. Ion cannons, Phasors, Disrupters and Plasma particle Beams may rewrite our ability to defend our universe. Force shields may also be possible if we can gate the energy into storage pockets. The ability to allow our instruments to see inside these pocket universes may be essential for monitoring energy storage, leakage and release.
Kinkajou : Bizarre!
Dr AXxxxx : Learn about it when modern weaponry vaporizes you into ash. There is nothing like imminent death to focus your attention on the possibilities at hand.
GemStones : Not Glass , but Metals
Kinkajou : Any other transparent materials you have come across?
Erasmus : Yes. There is a group of compounds called spinels, which are transparent. For example, Magnesium aluminate spinel (MgAl2O4) or Aluminium Oxynitride spinel (Al23O27N5
Transparent spinel (MgAl2O4) ceramic, is superior to glass or sapphire, when used for applications such as high-energy laser windows and lightweight armor. Excellent transmission in visible wavelengths and mid-wavelength infrared (0.2-5.0Âµm) occur when these chemical composites are combined with selected materials.
Sapphire Crystals are made from single-crystal aluminum oxide (sapphire – Al2O3). Sapphire is a transparent ceramic. It is very strong, but lacks full transparency throughout the 3–5 micrometer mid-infrared range.
This material is often combined with Yttria which is fully transparent from 3–5 micrometers. However, Yttria lacks sufficient strength, hardness, and thermal shock resistance for exacting applications, such as Lasers or aerospace applications. Not surprisingly, a combination of these two materials in the form of the yttria-alumina garnet (YAG) has proven to be one of the top performers in the field. Other composites such as Neodymium-doped YAG (Nd: YAG) have also proven to be valuable in solid-state lasers.
Alternative materials, such as yttrium oxide, offer better optical performance, but inferior mechanical durability.
Ruby crystals in ruby lasers consist of single-crystal sapphire alumina (Al2O3) also. These are structured in rods doped with a small concentration of chromium Cr, typically in the range of 0.05%. The end faces are highly polished with a planar and parallel configuration.
Ruby Transparent Gem
Glass which is a non-crystalline ceramics can also be used as host materials for lasers. This material is cheaper, more readily milled in terms of size and shape. Glass copes poorly with heat load, being essentially a poor heat conductor. This means that it not as useful as transparent alumina or YAG in continuous and high repetition-rate applications.
Glass can also fluoresce under energy load. This means that it will be more difficult to obtain continuous wave laser operation (CW), relative to the same lasing ions in crystalline solid laser hosts.
Several types of glass are used in transparent armouring applications such as
- Normal plate glass (soda-lime-silica),
- borosilicate glass, and
- Fused silica: fused silica glass, is crystal clear, lightweight and high strength.
- A lithium disilicate based glass-ceramic, for use in transparent armor systems. It has all the workability of an amorphous glass, but upon recrystallization it demonstrates properties similar to a crystalline ceramic.
Some transparent ceramic composites have unusual penetration resistance. The advantage of using composites for armouring relates to their low weight for a given level of protection. Armor must defeat the attack but also provide a multi-hit capability with minimized distortion of surrounding areas. Night vision equipment works at specific frequencies of light, and armor would need to work with such equipment, providing appropriate optical windows for this type of equipment.
Existing transparent armor systems typically have many layers, separated by polymer (e.g. polycarbonate) interlayers which assist with thermal tolerance and cracking control. Other transparent materials have been investigated for armouring applications. These include transparent nylons, polyurethane, and acrylics.
Military armouring requires transmission of light around the visible (0.4–0.7 micrometers) and mid-infrared (1–5 micrometers) regions of the spectrum.
Kinkajou : What about novel manufacturing techniques? Erasmus : One new technique involves combustion to generate spherical nanoparticles of yttrium, aluminium and neodymium. Combining these shapes or producing other shapes such as tubes may allow new materials with new properties to be manufactured.
Kinkajou : So what do you think, Goo?
Goo :Transparency is a property that enhances the human world. But there is a need for transparency with other properties: strength, elasticty or corrosion resistance if the human race is to meet a variety of needs in a variety of niches. Transparency will also allow the passage of energy from within to without containment, or vice versa. Lasers can fire out and energy can be kept in.