Zirconia – Page 4 – Zirconium Metal

How to tell the Zirconia from Diamonds?

Diamond is the product of adamas finishing, which is the hardest and simplest gemstone in the world. It is a natural crystal with a cubic structure made of carbon. The bigger the diamond, the rarer it is. Diamond often contains 0.05%-0.2% impurity elements, among which N and B are the most important. The pure diamond is colorless and transparent, which presents different colors due to the mixing of trace elements.

Natural diamonds are expensive due to their scarcity, especially the larger ones. However, artificial diamonds (synthetic diamonds) are difficult to achieve large size gemstones. Generally, synthetic diamonds are used in cutting and polishing tools. Therefore, in order to meet the design needs of jewelry and some products, there are usually some substitutes, such as glass, artificial spinel, artificial sapphire, zircon, scheelite, strontium titanate, cubic zirconia and so on. Among them, cubic zirconia is very close to diamond in terms of its optical and hardness properties and is the most common diamond substitute.

The cubic zirconia was first developed by the Soviets, also known as Soviet Stone. Cubic zirconia in cubic crystals is rare in nature and is usually synthesized artificially. Synthetic cubic zirconia is a hard, colorless and optically immaculate crystal, and it has been a replacement for diamonds since 1976 because of its low cost, durability and its resemblance to diamonds. Cubic zirconia is known as a “fake” diamond or CZ diamond. The following is a brief analysis of the difference between diamonds and “fake” diamonds and how they are identified.

Difference in hardness

Natural diamonds have a Mohs hardness of 10 and are difficult to process, and the cubic zirconia has a Mohs hardness of 8.5 to 9.0, while quartz sand is 7 and stainless steel is only 5.5. Therefore, the treatment of gem-level cubic zirconia can meet the requirements of daily use and is easier to process.

Differences in dispersion

The dispersion of cubic zirconia was 0.060, which is higher than that of diamond, so cubic zirconia looks more brilliant than diamonds.

The index of refraction

Cubic zirconia has a refractive index of 2.176, which is slightly lower than diamond’s 2.417. Depending on the refractive index, cubic zirconia cuts slightly differently from a diamond, which can be seen under a magnifying glass.

Color

Completely colorless diamonds are very rare, and usually, they are pale yellow. However, the cubic zirconia can be made into diamonds of the highest grade, or D-grade color. A variety of trace elements can also be added to the cubic zirconia to render it in different colors to meet customers’ demand for colored gems.

The crystals of different colors can be obtained by adding different metal oxides to the raw materials. For example, cerium: yellow, orange, red; chromium: green; neodymium: purple; erbium: pink; titanium: golden brown.

Specific gravity

Cubic zirconia is 1.7 times heavier than a diamond, so they can be distinguished by differences in specific gravity, but can only be used to separate unencrusted gems.

The heat-transfer capability

The thermal conductivity of cubic zirconia and diamond are two extremes. Cubic zirconia is a good insulator and can be used as an insulator for jet engines, while diamond is one of the best heat conducting bodies, its heat-conducting ability surpasses copper.

Stanford Advanced Materials supplies high-quality zirconia products to meet our customers’ R&D and production needs. Please visit http://www.samaterials.com for more information.

How is the Zirconia Ceramic Made?

As the most important type of advanced ceramics, zirconia ceramic material is an important basic material for the development of the modern high-tech industry. Zirconia is widely used in the market, and its specific applications include the solid fuel cell, automobile exhaust treatment, dental materials, ceramic cutting tools, and zirconia fiber core plug.

However, as mobile 5G era approaches at any time, zirconia ceramics become the hot spot of the industry again due to its characteristics such as warm feeling, anti-scratch and wear resistance, no signal shielding, and excellent heat dissipation performance.

Zirconia is insoluble in water, sulfuric acid, hydrochloric acid, and nitric acid. It is slightly soluble in hydrofluoric acid and concentrated sulfuric acid when heated. Pure zirconia is an insulator at room temperature. Adding a stabilizer can increase its conductivity and show ionic conductivity at high temperatures. There are three crystal types of zirconia. The crystal parameters and the schematic diagram of the structure of the three crystal types are shown below.

Zirconia ceramics have high hardness, wear resistance, high-temperature thermal stability and impact resistance. The preparation of high-performance zirconia ceramics depends on high-quality zirconia powder and optimized sintering process parameters.

Preparation of high-quality zirconia powder

The preparation methods of high-quality zirconia powder mainly include the physical method and the chemical method. The physical methods include high-temperature spray pyrolysis, spray induction coupled plasma pyrolysis and freeze-drying; chemical methods include gas phase, liquid phase, and solid-phase method. Among them, the liquid phase synthesis method has high efficiency, fine powder particle quality, and simple equipment, so it has been widely used.

The sintering method

Sintering process parameters include sintering temperature, sintering pressure and sintering time. Ceramic materials with very different microstructures and properties can be obtained when the same ceramic materials adopt different sintering processes. At present, the sintering process of zirconia ceramics at home and abroad has pressureless sintering, hot pressing sintering, hot isostatic sintering, and discharge plasma sintering. Pressureless sintering, also known as traditional atmospheric sintering, is the sintering of a prefabricated ceramic body under atmospheric pressure and high-temperature conditions; hot press sintering is a sintering method for applying axial pressure to the powder in the mold; spark plasma sintering (SPS), also known as plasma-activated sintering, is a new rapid sintering technology.

Stanford Advanced Materials supplies high-quality zirconia powder and related products to meet our customers’ R&D and production needs. Please visit http://www.samaterials.com for more information.

How Does the Fused Zirconia Work in Modern Industry?

Zirconia and zirconite are the main raw materials of zirconia in nature. Pure zirconia is a white solid that will appear grey or light yellow when it contains impurities, and various other colors can be displayed by adding a developer. Pure zirconium oxide is a kind of advanced refractory raw material with a melting temperature of about 2900 ℃. Zirconia usually contains a small amount of hafnium oxide, which is difficult to separate but has no obvious effect on the properties of zirconia.

Zirconia has three crystalline forms: monoclinic, tetragonal and cubic. The zirconia at room temperature only appears in monoclinic phase, and it will be transformed into the tetragonal phase when heated to 1100 ℃ or so, and it will turn into a cubic phase when heated up to a higher temperature. Due to large volume changes when the monoclinic phase changes to the square phase, and large volume changes in the opposite direction when cooling, it is easy to cause product cracking, which limits the use of pure zirconia at high temperatures. However, the tetragonal phase can be stabilized at room temperature after adding stabilizer, so the volume mutation will not occur after heating, which greatly expands the application range of zirconia.

Refractory materials and casting

There are two main refractory markets for the fused zirconia. The first is the cast steel refractories in the steel industry, particularly for the production of isostatic pressure molding products, which include intermediate flow slots and ladle outlets and immersion nozzles.

The second major market is the refractory produced by the electric melting and burning method in the special glass industry. Zirconia gives the molten glass good resistance to high temperature and corrosion. As there is no reaction area, there is no gravel in the glass. Aluminum-zirconium silicon refractories are graded by the content of zirconia, which is determined by the content of zirconia in the product.

Investment casting

For fused zirconia, investment casting is another major specialized market. For example, zirconia is commonly used as a model coating for the casting of special products such as aerospace engines, turbine engines, and golf clubs. Zirconite is used in investment casting because it can form actual contact with hot metal alloy to protect the die from thermal shock.

Abrasive substance

The polishing tools used in the ceramic industry, such as grinding wheel pieces and non-metal blades used in stone cutting, are made into coarse abrasive particles by mixing zirconia and alumina according to a certain formula, and then made into a grinding wheel or coated on the surface of grinding tool after thermal processing. This method can be used to polish steel and metal alloys.

Advanced ceramics and special products

For stable zirconia, the roasting control board for electronic components is a major market. Stable zirconia is also used in oxygen sensors and fuel cell partitions because it has the ability to allow oxygen ions to move freely in the crystalline structure at high temperatures, and the high ionic conductivity makes it one of the most promising materials for electrical ceramics. Chemical-grade zirconia is often used in electric melting products, and other special product markets include vacuum pumps and high-value components, special tool parts and brake lining. Fully stable cubic phase yttrium stabilized zirconia is used in the jewelry industry as a cheap alternative to diamonds.

Stanford Advanced Materials supplies high-quality zirconia products to meet our customers’ R&D and production needs. Please visit http://www.samaterials.com for more information.