Transparent ceramics has emerged as an entity promising variety of applications across industries. The article aims to explore unique properties and the most recent advancements in the regime of transparent ceramics. We will also discuss on the how to convert opaque to transparent ceramic and methodologies to achieve the same.
Transparent Ceramic: A detailing
Transparent ceramic constitutes a group of advanced ceramic that are generous on passing light through their body. They lack the impurities in its lattice that causes scattering of light .Transparent ceramics are manufactured through advanced techniques.
Composition of transparent ceramic
The major reason of transparency of ceramic as already cited is attributed to the arrangement of atoms in crystal lattice. The common transparent ceramics are made up of Oxides, Carbides and Nitrides. The most popular and widely used are alumina transparent ceramic and the spinel of magnesium aluminate. Another interesting such ceramic is yttrium-based garnet of alumina.
As already discussed, it’s no easy to manufacture transparent ceramic, the reason why the process of manufacturing is termed advanced. High temperature and pressure sintering of ceramic give rise to the formation of transparent ceramic. A dense and intense crystal lattice are formed because of the process.
Often spark plasma sintering abbreviated as SPS is applied to produce transparent ceramic. The process uses pulsed current on the ceramic powder. This method aids sintering on a rapid note that also retards the growth of grains in the lattice. The process guarantees ceramic with increased transparency with good mechanical strength and thermal stability.
Properties of Transparent ceramic
Transparent ceramic has a huge set of desired properties that makes them attractive for several applications. The notable properties are not only transparency; they have high thermal conductivity and resistance to chemicals. The hardness of the transparent ceramics makes them useful for window panes and Armor applications. The favouring nature to infrared and visible spectrum of light helps them function as laser materials, optical ceramics and scintillators.
The thermal stability and corrosion resistances constitute the reason why they are often used as furnace liners and cutting materials.They are also deployed in biomedical applications, implants and tissue replacement.
Application of transparent ceramic
- The doping of Nd3+ in transparent ceramic offers interesting spectroscopic and light emission benefits. The lasers made of this ensure continuous emission to a wide range offering transmission in short time.
- Transparent ceramics is an integral constituent in protective equipments such as armours, bullet proof windows and vehicle shields. They offer good hardness and higher stability without compromising on the visibility front.
- PCB’s use transparent ceramics as substrates for their property of electrical insulation and heat conductivity.
- They are also used in manufacture of entities that enhance diagnostic capability such as quality lenses
Some best transparent ceramic examples
Yttrium Nano composite clear ceramic
Yttrium Oxide is known for their transmittance to infrared, UV and visible spectrum of light. Although the mechanical properties are moderate, they offer lesser radiation coefficient. These composites are superior in their temperature and shock resistance properties.
Alumina transparent ceramics
The ALON functions in UV, middle infrared and visible spectrum ranges. They have hardness in the range of 19.5 GPa and has bending strength ranging from 350 – 700 MPa. AlON is comparable to sapphire in terms of hardness and possesses superior mechanical properties. Traditional methods can be one option to prepare the complex AlON ceramics.
MgO based transparent ceramics
MgO ceramics caters to infrared range which help them better function as windows of furnace and detectors of infrared. They have high thermal conductivity, comparatively lesser density and good light transmittance.
MgAl2O4 ceramic
The optical properties of MgAl2O4 makes the material highly transparent with a melting point of greater than 2000 degC. They are being used as protective masks for military applications as this would help in transferring 0.2 – 6 m wide band light.
What does Opaque Ceramic signify?
The opaque nature of the ceramic is because of the grain boundaries, grains and pores they have. Ceramics are polycrystalline material having lesser refraction coefficient. This is because of the grains or the boundaries scattering the light. The usage of strict composition control, reducing porosity and imparting homogeneity makes the ceramic transparent.
Cubic symmetry often Favors transparent ceramic. Non-cubic such as h-BN can also bring the ability to pass light and hence impart translucency in the material. Coming to cubic silicon Carbide they are also prepared under high temperature and pressure but little submissive to diamond.
How to transform Opaque ceramic to Transparent?
There are various influential factors that is overlooked in the manufacturing of Transparent ceramic. Aspects like the raw material nature, sintering process, the microstructure of the material and post manufacturing is important.
Raw Material nature
Crystal structure or the speciality of lattice
Structure contributes to the nature of ceramic. For example, cubic polycrystalline ceramic scatters light almost like that of normal glasses. The crystals of other geometry such as tetragonal and trigonal has less transmittance as the quality deteriorates at grain boundaries.
Purity of the Raw material
Generally transparent ceramic is pure. The light dispersion is impacted by the weak points. So, keeping the particle homogeneous and well dispersed is the key to produce transparent ceramic.
Dispersion Property
Dispersion is equally important; the particle should form agglomerates during the sintering mechanism that decreases the light pass through.
The process of Sintering
Sintering medium
Vacuum is often favoured to produce Transparent ceramic. Other mediums such as air gets trapped inside the ceramic compromising on the transparency. Generally transparent ceramic of Alumina, Yttrium oxide, Zirconia etc is formed under vacuum conditions.
Firing temperature and Additive
Optical ceramic is often manufactured at temperature fixed based on the nature of raw material. The firing temperature should be fixed on the viability and the property expected. Additives ensure to decrease the sintering temperature. They can retard the formation of grain boundary, take off voids and helps to densify the material.
Post manufacturing methods
Surface Properties
Surface finish is important to impart reflection or transmittance. The transparency often decreases with increase in surface roughness.
Ceramic Glaze
Clear glaze ceramic or transparent glaze in simple terms is something that doesn’t give opacity. Glaze refers to the coating that is applied to a ceramic to make it look extremely appealing. The transparent glaze is a subject to its raw material and the impurity it has. The more the impurity, the glaze becomes translucent ceramic glaze with less permeability to light.
The raw material for ceramic glazes is metal oxides, the fluxes help in the liquefaction of the ceramic. Glaze combinations can differ depending upon the property expected. Colourful glazes such as pink glaze are also getting lot of compliments these days. This glaze provides functional surfaces distinct from the outer body uplifting the overall look of the product.
Pic: Al2O3 con 6 glazes at the left with lesser flow coefficient due to high Al2O3 and SiO2 content
결론
A brief overview on transparent ceramic is written. Transparent ceramic is an advanced ceramic of at most importance in today’s era due to its superior benefits. It caters to advancement in engineering and science. The very nature of ceramic varies depending upon the raw material used, sintering process and lattice formed.