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| Zirconia Technology, Products and Applications |
| To cater the need of growing zirconia ceramics markets & user industries world wide, RGe manufacturers,exports/supply following type of engineered zirconium oxide products: |
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| Zirconium Oxide Technology & Applications of Zirconia Powders |
Developed by RGe / Zirox Technologies-India |
| Zirconia from India / India zirconium oxide / Nano zirconia |
| Introduction |
In order to meet the stringent requirements of the modern technologies involving steel and chemical industries, power generation, automobile, defence, refractory-metallurgical, optical, bio ceramic, nuclear and space programs, materials are required which can withstand very high temperature and pressure, possess superior mechanical as well as thermal properties, show resistance to oxidation and corrosion. Traditional metals and metallic alloys do not posses these characteristics particularly at high temperatures.
Engineered ceramics based on zirconia and zirconia toughened alumina are attracting the attention of scientists and business houses all over the world because of their excellent high temperature mechanical properties, thermal shock resistance, wear and oxidation resistance, low thermal conductivity and reasonable match in thermal expansion coefficient to that of metals.
Different grades of high quality zirconia powders such as monoclinic, partially stabilized (PSZ) teragonal, fully stabilized cubic zirconia compositions doped with CaO, MgO, Y2O3, CeO2 and Scandia as stabilizing oxides are key ingredients for the development of high temperature zirconia ceramics as well as thermal barrier and wear resistant ceramic coatings.
Tetragonal zirconia powders has also been found useful in the development of zirconia toughened alumina (ZTA) ceramics having superior strength, toughness and wear resistance when compared to conventional alumina ceramics being extensively used at present. Such ceramics are considered suitable for armour applications. ZTA abrasion wheel outperforms the pure alumina variety by a factor of 8. Hence the development of zirconia powders and sintered ceramics has been identified as a high priority area.
Extensive R&D programs are therefore, being progressed at RGe for the production of monoclinic zirconia, different grades of partially stabilized zirconia (YPSZ) fully stabilized cubic zirconia (YSZ) and tetragonal zirconia polycrystalline (TZP) ceramic powders and sintered ceramics have been developed for a wide range of defence and civil sector applications. |
| Types of zirconia powders |
| Monoclinic, partially stabilized tetragonal & fully stabilized cubic zirconia powders |
| Zirconia exhibits three well-defined polymorphs, the monoclinic, tetragonal and cubic phases. The monoclinic phase is stable up-to about 1170’C where it transforms to the tetragonal phase, which is stable up-to 2370’C, when the cubic phase exists up-to the melting point of 2680’C. Monoclinic, tetragonal and cubic zirconia are generally prepared by addition of stabilizing oxides such as MgO, CaO, Y2O3, Scandia and CeO2 in zirconia powders and subjecting the material to appropriate processing parameters. |
| Yttria Tetragonal Zirconia Polycrystal |
Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia powder is a specialty material for structural ceramic applications. Y-TZP is completely ( nearly 100%) tetragonal in structure & is partially stabilized with 3 mol% of Yttria (Y2O3). Zirconia Yttria blends of approximately 3% are called tetragonal zirconia polycrystal or TZP, and have the finest grain size.
Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia powder possess material density above 6.0 g/cc, maximum working temperature of 2000 C. Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia powder attributes the highest flexural strength when processed using a HIP (Hot Isostatic Pressing). Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia imparts flexural values around 900 MPa and 1400 MPa (HIP’d). The hardness is 13-13.5 GPa, Fracture Toughness is 8.0 MPa-m1/2 and Thermal expansion (C.T.E.) is 10.2 x E6/ degree C). The excellent mechanical properties of Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia powder are result of very small grain size, extremely low porosity & transformation toughening.
The main advantages in using Y-TZP ceramics for structural applications are high strength & toughness at higher temperatures, corrosion resistance, light weight and wear resistance, which results in improved component performance and energy savings. As cutting tools and wear resistant materials, TZP contribute to high productivity. Plasma sprayed zirconia coatings on metal substrates are gaining importance as an easy replacement for pure metals and alloys by ceramic coated components in increasing their life and improving their performance in several industries where wear and tear and the temperature capability of the metals are limited.
Y-TZP ceramics are generally produced by alloying zirconia with yttria. Similar zirconia compositions based on alloying with ceria have become commercially available and considered superior to Y2O3 doped TZP particularly for applications in low temperature humid environments.
TZP Zirconia is established in ceramics as being both fracture-tough & hard at room temperature. Zirconia’s fine (sub-micron) grain size enables excellent surface finishes & ability to hold sharp edges. Although it retains many properties including corrosion resistance at extremely high temperatures, zirconia does exhibit structural changes due to reversal crystal transformations that some times limit its use to perhaps only 500°C. It also becomes electrically conductive as this temperature is approached. . TZP Zirconia exhibit the highest toughness at room temperature, because they are nearly 100% tetragonal. Y-TZP or tetragonal zirconia polycrystal is one of the recently developed materials whose unusual combination of properties are revolutionizing industries and opening new vistas for future technologies.
The Y-TZP Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia powder’s fine grain size makes it ideal for creating sharp blades which, because of excellent wear resistance, remain razor sharp. Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia powder, due to its excellent strength, translucency, and tooth-like color, is a popular dental restoration material, used as single-unit copings and multiple-unit frameworks in fixed partial dentures. Y-TZP (Yttria Tetragonal Zirconia Polycrystal) zirconia powder is used in tooling and process applications for its strength, superior toughness, and excellent abrasion resistancy.
Structural ceramics available for the dental restoration market includes a class of materials based on transformation toughened zirconias (TZZ’s). Magnesia-partially stabilized zirconia (Mg-PSZ) and yttria-tetragonal zirconia polycrystals (Y-TZP) both belong to the family of TTZ’s. Fully sintered Mg-PSZ zirconia, Y-TZP zirconia, HIPed Y-TZP zirconia as well as a grade of “Bisque Fired” Y-TZP material . These materials offer: Excellent Biocompatibility, Ultra High Purity, Near-Zero Porosity, Fine Grained Microstructure, Good Surface Finish and High Fracture Toughness for dental restorations that include caps, crowns, bridges, inlays and onlays.
Apart from Yttira , Zirconia is commonly blended with either magnesia( MgO),Calcia(CaO) or Ceria (CeO2) as dopant/stabilizer in order to facilitate transformation toughening. This induces a partial cubic crystal structure instead of fully tetragonal during initial firing, which remains metastable during cooling. Upon impact, the tetragonal precipitates undergo a stress induced phase transformation near an advancing crack tip. This action expands the structure as it absorbs a great deal of energy, and is the cause of the high toughness of this material. Reforming also occurs dramatically with elevated temperature and this negatively affects strength along with 3-7% dimensional expansion. The amount of tetragonal can be controlled by additions of the blends above to balance toughness against loss of strength.
For applications which requires optimum electrical, mechanical and thermal properties of zirconia sintered products & ceramic coatings, precursors containing various amounts of stabilizing oxides CaO, MgO, Y2O3, CeO2 etc. are required. Ideally the stabilizing additives should be uniformly distributed on an atomic scale. In practice, the actual distribution of the stabilizing oxides depends on the method of powder preparation.
Mg Partially stabilized zirconia ( Mg PSZ), Cream colored blends with approximately 10% MgO, called partially stabilized zirconia (PSZ), are high in toughness, and retain this property to elevated temperatures. They are somewhat lower in cost but also have larger grain structure
Cubic zirconia or YSZ or fully stabilized zirconia, the single crystal optically clear form of ZrO2 has a relatively low fracture toughness and strength, but very high thermal shock resistance.
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| Speacility of TZP Zirconia |
| Zirconia (TZP) offers chemical and corrosion resistance to temperatures well above the melting point of Alumina. In its pure form crystal structure changes limit mechanical applications, however stabilised Zirconias produced by addition of Calcium, Magnesium or Ytrium Oxides can produce very high strength, hardness and particularly toughness. |
| Special characteristics of zirconia |
| High temperature capability up to 2400ºC ,High density ,High strength and fracture toughness ,High hardness and wear resistance ,Low thermal conductivity (20% that of Alumina) ,Good chemical resistance ,Ionic conductivity |
| Technology absorbed by RGe and its advantages |
Fine to sub-micronized and nano crystalline particle technology for producing different grades of zirconia powders such as monoclinic, Tetragonal polycrystalline( TZP) and yttria partially stabilized( YPSZ) and fully stabilized cubic ceramic powders (YSZ) has been developed by RGe. This generates pure, stoichiometric, chemically homogeneous & nano crystalline submicron size zirconia powders in a reproducible manner. This is a wet process based on treating of the aqueous salt solutions of desired constituents. Zirconia powders sinterable at low temperatures are prepared by this process repeatedly.. Ceramic components developed using these powders have shown considerably high strength and fracture toughness. Zirconia powders synthesized at RGe have been found suitable for providing thermal barrier and wear resistant ceramic coatings by plasma spray deposition process on metallic structural components used in high temperature corrosive environments. Zirconia ceramics for structural applications are prepared by consolidating high quality powders under precisely controlled processing conditions to produce materials with superior properties.
Zirconia powders produced by RGe attain homogeneous distribution of stabilizing oxides such as MgO, CaO, Y2O3 and CeO2 and repeated consistency is guaranteed in physico-chemical characteristics. The zirconia production process as adopted by RGe has adequate control on chemical homogeneity, purity and other physical-chemical characteristics of the powders such as purity, homogeneity, particle size, shape, surface area etc. which are prime requirements to achieve improved finished products.
The values of transformable tetragonal phase in partially stabilized and tetragonal zirconia polycrystalline powders and ceramics are dependent on crystallite size. Values of fracture toughness, strength and hardness of sintered ceramics increase with the content of transformable tetragonal phase and are maximum when the crystallite size reaches the critical value. In this respect care must be taken to optimize the firing cycle since the matrix is required to reach the high density in order to give the necessary mechanical constraint to zirconia particles. On the other hand the zirconia particle must be grown to sufficient size, that it is meta-stable and therefore transformable but preferably does not exceed the critical diameter when spontaneous transformation from tetragonal to monoclinic phase occurs.
Critical particle size is dependent on the concentration of dopant on powders. Extensive data have been generated for optimizing the dopant concentration, critical crystallite size and transformable tetragonal phase in zirconia powders. The zirconia powders developed at RGe effectively satisfy the requirements for the development of critical ceramic components and protective ceramic coatings for a large number of applications as structural materials suitable for use in high temperature, hostile environments. The excellent properties of ceramic components and coatings are attributed to the physico-chemical characteristics of the starting powders such as purity, stoichiometry as well as ultrafine, spherical, dense and agglomerate free particles with compositional homogeneity. |
| Properties of zirconia ceramics |
| Important mechanical and thermal properties of different compositions of zirconia powders prepared by fine particle are suitable for producing zirconia ceramics having a combination of strength, toughness and chemical resistance and therefore considered suitable for applications in harsh environments under severe loading conditions. Such TZP zirconia powders have been found suitable for the development of zirconia toughened alumina (ZTA) ceramics having superior strength, toughness and wear resistance when compared to conventional alumina. |
| Applications of zirconia |
The applications of zirconia ceramics are amazingly large, diverse and include cutting tools, forming dies, wear parts, bearings, seals, valves, nuclear fuels, nose cones and tiles for space shuttles and missiles, pollution control devices, gas and humidity sensors, thermal barrier coatings, medical prosthesis, dental reconstruction, optical fibers and electrical devices. Monolithic zirconia bricks and zirconium oxide coatings are already being used widely by steel makers in other countries. Thermal barrier ceramic coatings based on various types of partially and fully stabilized zirconias have been proved suitable for petrol and diesel engines, turbine and even in most demanding aviation engines. Zirconia powders are also applied to Precision ball valve (balls and seats) Pump seals, valves and impellors, high density grinding media ,Oxygen sensors ,Thread guides ,,Fuel cell membranes ,Cutting blades, Radio frequency heating suseptors, Medical prostheses
High hardness of zirconia can be put to use for wear resistance of mechanical parts. Abrasion resistant coatings can also be developed for machinery components facing extremely hostile conditions of wear. Zirconia can have a very high hardness when prepared under exacting conditions with attention to heat treatment. Zirconia happens to be the first monolithic ceramics to have overcome the universal brittleness. Additional information about applications may be availed upon request. |
| Application of zirconia based on Mechanical and Physical Properties |
| The fundamental properties of zirconia ceramics which are of interest to the engineer or designer are: |
| • high strength, • high fracture toughness, • high hardness, • wear resistance, • good frictional behaviour, • non-magnetic, • electrical insulation, • low thermal conductivity, • corrosion resistance in acids and alkalis, • modulus of elasticity similar to steel, • coefficient of thermal expansion similar to iron. |
| Zirconium oxide or zircon oxide, ZrO2 developed by RGe finds applications in advanced ceramics and are compatible to injection molding, slip casting, tape castings, uniaxial isostatic pressing. Following are the applications of TZP / FYSZ / Monoclinic zirconia powders based on different properties. |
| Zirconia ceramics Based on chemical & physical properties |
| Zirconia Structural ceramics precision parts including Pump components, bearing, seals, valves, and various industrial parts-e.g. optical Fibre zirconia ferrules, zirconia sleeves for connectors Zirconia capillary. |
| Zirconia Bio ceramics alike Body implants-hip joints, bone replacements, dental ceramics - zirconia blanks / zirconia blocks. |
| Zirconia Low wear ceramics are Grinding medias, mill linings, engine components-cams, tappets, valves, piston crowns/liners, thread guides, printer heads |
| Zirconia Forming dies like Copper extrusion and wire drawing dies, Gaging and fixturing zirconia ceramics, Zirconium Oxide Weld Box Rolls, Seam Guides, Impeder Wear Strips, zirconia guide rolls for non-ferrous rod mills, Pinch and guide weld box rolls in welded tube mills, Seam guides and impeder wear strips on welded tube mills. |
Metal filtration : Use of zirconia honeycomb structure
Zirconium oxide Cutting tools including blades, scissors, shears, cutting & drilling tools.
Cubic zirconia Gemstones: ZrO2 single crystal-synthetic diamond can be made in various colours
Zirconia in Glass: Camera lenses / measuring instruments/use in fiberglass
Zirconia Jewelry: ZrO2 in various colours |
| Zirconia ceramics Based on utilizing electronic properties |
Zirconia possesses low thermal conductivity and is an ionic conductor above 600ºC. This has lead to applications in oxygen sensors and high temperature fuel cells.
Zirconia Oxygen Sensors (8 mol% Y2O3 solid electrolyte) for automobile emission control (stabilized ZrO2 with Pt electrodes).This exhaust monitor controls fuel air ratio entering engine. Control of high temperature furnaces by flue gas monitoring & Control of O2 in steel making.
Zirconia Fuel cells : This uses stabilized zirconia as oxygen ion conductor, particularly with a clean fuel e.g. hydrogen.
H2 from electrolysis of water: This is reverse of fuel cells.
MHD electrodes : Magneto hydrodynamic generators. This process involves passing an electrically charged gas at high speed through magnetic field generating a direct current. ZrO2 electrodes have been used successfully.
Zirconia Filters, Transducers, Filters in TV, radio, mobile phones, hearing aids, stereo pick up Elements, microphones
zirconia Resonators : Acceleration sensors.
Zirconia Buzzer elements: Clocks, watches, telephones, securuiy systems, house hold Appliances, ultrasonic applications, cleaning ashing, soldering, drilling, welding, underwater detection(fish, depth etc)
zirconia Other PZT: Electric motors-automobile application (windshield wipers, widow winders etc.)
Zirconia PLZT: optical shutter-military uses-eye protection from nuclear flash
Zirconia Catalyst: : CeO2-ZrO2 in various mixtures with other addition (also CO-
precipitated forms) provide high and low oxygen storage capacities (OSC) these materials are applied to ceramic honeycomb (cordierite) to form an exhaust catalyst. Catalysts for various chemical reaction both as single oxide, mixed oxide and support alkyation, condensation, cracking, hydration, esterification, hydrogenation, isomerisation, oxidation etc. |
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| Zirconia ceramics Based on Utilizing Mechanical , Refractory & other Properties |
| Zirconia is applied where high melting point, high refractive index, chemical inertness, high strength & Toughness, excellent wear resistant properties are desired. |
| Zirconia Ceramic stains: Compounding of Zirconium –vanadium blues, Greens & Yellows, Zirconium –Praseodymium yellow stains, Zirconium germinate (Zr GeO4) ZrTiO4 Stains, Iron Corals & pinks, Inclusion Pigments, Frits & Enamels |
| Zirconia finds applications in ZrO2-Al2O3 abrasives, erosion & corrosion resistant refractories for Glass furnace & special Cast refractories, Refractory Cements, Castables, Mortars, Setter sands, insulating materials, kiln furniture, crucibles, Saggers Nozzles, Slide gates Investment Casting, Foundry & Metallurgical Coating/Washes, Mill liners, Applications requiring an inert material with high melting point and low thermal conductivity. Abrasives, tribological applications, Bearing /friction/brake lining and pads |
| Zirconia Coatings |
Thermal barrier coatings as used in gas turbines and on piston crowns in large diesel engines; low friction and anti-seizure coatings as used in lubricant free bearings; wear resistant or "hard-facing" coatings as used for the treatment of valves in internal combustion engines and finally corrosion resistant coatings as used in the chemicals industry. Zirconia coating can be done by Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD) and Chemically Formed Processes (CFP) with other techniques e.g. thermal spraying, High Velocity Oxy-Fuel (HVOF), plasma spraying, flame spraying together with Plasma Transferred Arc (PTA) routes
Thermal Barrier Coatings finds applications In Gas turbine engines, rotors turbine blades , ceramic blades, plasma sprayed ceramic layer, Desirable properties of the ceramic barrier coating include a high thermal expansion coefficient, low thermal conductivity, chemical stability in the gas turbine environment and thermal shock resistance. Low co-efficient of thermal expansion/CTE are added features.
TBC deposition with t-phase / t-ZrO2 / tetragonal zirconia like 3YSZ ,3 MOL% YSZ ,7YSZ,8YSZ, 8 MOL% YSZ,Y-PSZ,PYSZ,TZY,Y-TZP is common. , Thermal barrier coatings or TBC’s attributes nano structured heat resistant high temperature coatings, ceramic coatings, protective coatings to components of aeronautics and automobile engines specially air craft engines, jet engines, aero engines, combustion chambers of gas turbine, turbine blades, guide vanes, air foil vanes ,diesel engine to extend component life.
Ke words: Plasma sssisted CVD, Plasma-spraying coatings, bond coat, TGO process, vapour deposition, electron beam, ceramic coatings process, vapour deposition ceramic coatings, bonded coatings high temperature coatings, low multilayer ceramets,matrix,ceramic-polymer,7% Y2O3 stabilised ZrO2 TBC's, PLASMA SPRAY, PLASMA SPRAYED, APS, EB-PVD, EB PVD, electronic beam physical vapour deposition, AGGREGATES, AGGLOMERATES, PLASMA ASSISTED CVD, |
| Zircon oxide in bio ceramics |
| Zirconia crowns/ dental zirconia blanks / blocks |
| Zircon oxide dental crowns and bridges let light through– just like natural teeth. The opaque metal framework of the usual crowns and bridges stops the light. The zircon framework and the thin ceramic-layer match the color of natural teeth perfectly and the light permeability can be also retained. |
| EXTREMEly stable |
| Zircon oxide ensures extreme stability and long durability and these performance qualities have been recognised by automobile maker for use in brakes, and valves of engines.Hearing prostheses, artificial joints and implants. |
| 100 % ANTI-ALLERGIC |
| Zircon oxide is the only material that makes a 100% metal free prosthetic supply possible. The material is biological neutral/biocompatible, there is no problem of resonance and it is especially mucous membrane and fabric friendly. Furthermore zircon oxide – unlike the most prosthesis with metallic frameworks – does not conduct cold, heat or power! |
| Test characteristics as follows: |
- good functional stability, strength ,significantly enlarged estethic effects ,excellent biocompatibility reduced formation of fur , high chemical and biological stability
- popular – mainly in the front region ,lets the x-ray shine through ,
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| Team RGe |
RGe may be contacted at its head quarters:
F-8, PHASE III, RIICO INDUSTRIAL AREA, Beawar 305901. Rajasthan – India.
Tel +91 1462 512340, fax +91 1462 226966, Mobile +91 9414009700
Email: ssr@zirox.co.in, zirox50@gmail.com .
Website: www.zirox.co.in |
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