What is Tungsten Alloyed With?

Tungsten heavy alloys, also called WHAs, Virtually all commercial WHAs are two-phase materials, with the principal phase being nearly pure tungsten in association with a binder phase containing transition metals plus dissolved tungsten.
WHA provides a very high density, as is apparent when compared to other metals, as shown in the table as follows:


WHAs was once referred to as “tungsten heavy metals,” but that nomenclature has been largely abandoned so as to avoid confusion with toxic heavy metals such as Pb, Hg, and others with which WHAs have no relation. While the primary selection is made on the basis of very high density, WHA provides tungsten alloy manufacturers a unique set of associated engineering benefits which includes:
• Low toxicity, low reactivity surface character
• Ability to be custom manufactured in a wide range of sizes and shapes
• Readily recycled for economy and environmental friendliness.
• Strength comparable to many medium carbon steels
• Ability to be machined with common shop tools and techniques
• High elastic stiffness
• Low CTE in combination with relatively high thermal conductivity

Due to these characteristics, as an ideal material, WHA is widely used for new mass property applications as well as the replacement of Pb or U in existing applications.

As a consequence, WHAs display a unique property set derived from both components — their fundamental properties resulting from those of the principal tungsten phase. The selection of a WHA for a given application is typically made on the basis of very high density — whether gravimetric or radiographic.

Tungsten heavy alloys are distinctly different from related materials such as pure tungsten metal and cemented carbides (most commonly WC-Co). Only very rarely could one material be used as a substitute for another. WHA provides many of the properties of pure W, yet in a form that provides:
• Lower fabrication cost due to the reduced sintering temperature,
• A greater range of both size and shape can be manufactured due to full density attainment via liquid phase sintering (LPS) as opposed to final densification by post-sinter thermomechanical processing,
• Generally improved machinability,
• Preservation of desirable properties of pure tungsten.

Tungsten heavy alloys are not related to “tungsten (T grade) steels.” In difference to pure W however, tungsten heavy alloys are not high temperature materials. Elevated temperature properties of WHA are strongly influenced by the lower melting temperature binder phase.
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Why is Boron Nitride Slippery?

Most people want to learn more about the 'soft' and 'slippery' crystalline nature of boron nitride, because of this special property, Hot Pressed Boron Nitride is used in lubricants and cosmetic preparations.

Firstly, we must know the definition of boron nitride.
What is Boron nitride?
Boron nitride (BN) was first found in 1840's by an English chemist, W.H.Balmain, by using molten boric acid and potassium cyanide, but unfortunately, he found that this new compound was un‐stable and required many methods to obtain a stable boron nitride.

For nearly a hundred years studies on boron nitride remained in laboratory scale due to the technical difficulties of different production techniques and high cost of the material which is obtained with these synthetic methods but in 1950's Carborundum and Union Carbide companies tried to obtain high purity boron nitride powder on an industrial scale and fabricated shaped parts of boron nitride for commercial applications with sophisticated hot pressing techniques.


What are the Properties of hexagonal boron nitride?

There are the main boron nitride properties as follows:
Non toxicity,
Easily machinability- non-abrasive and lubricious,
Chemical inertness,
Non-wetting by most molten metals,
High thermal conductivity,
Low thermal expansion,
Good thermal shock resistance,
High electrical resistance,
Low dielectric constant and loss tangent,
Microwave transparency.

Hexagonal boron nitride is being widely used because of its unique combination of properties which include:
Chemical inertness (corrosion resistance against acids and molten metals),
High temperature stability (melting point near 2600ºC),
Low density (2.27 g.cm-3 theoretical density),
Stability in air up to 1000ºC (in argon gas atmosphere up to 2200ºC and in nitrogen up to 2400ºC), Stability to thermal shock,
Easy workability of hot-pressed shapes,
Excellent electrical insulating character
Very high thermal conductivity.

As a thermal conductor, BN ranks with stainless steel at cryogenic temperatures and with beryllium oxide, BeO, at elevated conditions; above 700ºC, the thermal conductivity of hexagonal boron nitride exceeds that of toxic BeO.

The particular interest are its good dielectric properties (dielectric constant is 4, i.e half of that of α-Al2O3 ), also high dielectric strength and its ability to lubricate over a wide range of temperatures.

Its small coefficient of friction is retained up to 900ºC, whereas other solid lubricants like graphite and molybdenum disulphide are burnt away at lower temperatures.

Because of its high temperature stability and inertness against carbon and carbon monoxide up to 1800ºC it is as a refractory ceramic superior to the nitride ceramics Si3N4 and AlN and the oxide ceramics magnesium oxide, CaO, zirconia. ,

Due to its non-wetting properties it is stable to attack by molten glass, molten silicon, boron, nonoxidizing slags, molten salts (borax, cryolite) and reactive metal melts (e.g Al, Fe, Cu, Zn).

Because of its poor sinterability, dense shapes of hexagonal boron nitride are obtained almost exclusively by hot-pressing.

It must be recognized that the most chemical and physical properties of axial hot-pressed BN shapes depend on the nature and the amount of additives used for densification (up to 6 wt. % of B2O3, metal borates or SiO2 ).

Further some thermal (coefficient of expansion, thermal conductivity) and mechanical (flexural strength, Young's modulus) property values vary according to the direction of hot-pressing, BN being similar to graphite in respect of anisotropy.

By hot-pressing isostatic of canned boron nitride powder, theoretically dense and pure hot pressed boron nitride shapes without texture and with improved properties can nowadays be obtained.
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The Fourth Generation Light Source -LED

LED is called the fourth generation light source, with energy-saving, environmental protection, safety, long life (up to 100,000 hours), low power consumption, low heat, high brightness, waterproof, miniature, shock-proof, easy dimming, beam concentration, easy maintenance and other characteristics. It meets the requirements of energy saving, green and efficient era. It can be widely used in various fields such as indication, display, decoration, backlight, general lighting and so on.

LED is essentially a PN junction, through the P region hole and N region electron compound to produce photons, electrical energy directly converted to light energy, is a cold light source. But the traditional incandescent lamp is the electric heating filament, the electric energy transforms into the thermal energy, then transforms from the thermal energy to the light energy. So the efficiency of LED is much higher than that of incandescent lamps.

The LED industry chain includes upstream epitaxial manufacturing, midstream chip preparation, electrode fabrication, cutting and test sorting, downstream product packaging. Epitaxial films are in the upper reaches of the industry, including three major fields: raw materials, substrate materials and equipment. Epitaxial film growth is the highest technology content of lighting industry, and has the greatest impact on the final product quality and cost control.

Most of the LED epitaxial wafers are III-V compound semiconductor single crystals, such as gallium arsenide, aluminum nitride, gallium nitride, gallium phosphide, gallium arsenide phosphide, phosphorus compounds (blue-green light), aluminum calcium indium nitrogen (quaternary LED, red-yellow light), and other single crystals. The raw materials used to prepare these single crystals include indium, high-purity gallium, organometallic gallium, aluminum, etc. Epitaxial growth depends mainly on growth technology and equipment. The main method of fabricating epitaxial wafers is metal organic chemical vapor deposition (MOCVD), which is very difficult to fabricate.

The substrate material is the basis of LED illumination and epitaxial growth. Different substrate materials need different epitaxial growth technology, which affects chip processing and device packaging. Therefore, the technical route of substrate materials will affect the technical route of the entire industry, which is the key of each technical link. At present, Al2O3 (sapphire), SiC, Si, GaN, GaAs, ZnO, ZnSe and so on can be used as substrate materials, but the most widely used commercial Al2O3 (sapphire) and SiC.

Stanford Advanced Materials provides high-purity organometallic compounds for epilayers, substrate materials, photoresist for chip fabrication, high-temperature molybdenum, tungsten drying pots and furnace assemblies and fixtures in MOCVD processes (these high-temperature materials have high thermal conductivity and electrical conductivity, up to 2000 degrees Celsius). It has the characteristics of low thermal expansion coefficient, high strength and stability, and epoxy resin for chip packaging.

What is Tantalum Organic Complex Compound

The most important of tantalate is potassium and sodium salts.
Potassium tantalate has K 2O:Ta2O 5 from 3:7 to 10:3. The most common stable tantalate is potassium tantalate (K2O.Ta 2O 5); six potassium tantalate (4K2O.3Ta 2O 5). Tantalum potassium salt is soluble in water, but partial salt solubility is smaller, KTaO 3 at 25 DEG C when the solubility is 4.87 * 10-5mol/L.

Sodium tantalate has Na 2O:Ta2O 5 as 4:3, 7:5, 1:1, 1:3 and 2:7, such as NaTaO 3, Na 5TaO 5, 4Na 2O. It is 5. yuan. The solubility of sodium in water and caustic soda solution is very small, the solubility of 25 C NaTaO 3 salt is 5.5 * 10-5mol/L.

Tantalum organic complex compound
The tantalum complex is mainly tannic acid, its color is lemon yellow, and it is precipitated from weak acidic solution (pH=3~4) after boiling.

Tantalum alkoxide

Tantalum alkoxide quinquevalent is highly volatile, these alkoxides can be without distillation under the pressure of 6.67~1333Pa. The boiling point of tantalol is influenced by the length of the chain.

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List of Tantalum Compounds

Tantalum carbide
TaC is a dark brown powder. Its melting point is 3880 degrees, boiling point is 5500 degrees, and its density is 14.4g/cm3. It has good chemical stability and can only be dissolved in nitric acid and hydrofluoric acid mixed solution. Tantalum carbide is not easy to oxidize in air when it is below 1000~1100. It is easy to produce nitrides under the action of nitrogen or ammonia.

Tantalum hydride
The hydrides of tantalum are very stable at ambient temperature. When heated to 1000~1200 C in high vacuum, hydrogen is released from decomposition.

Tantalum hardly occurs with hydrogen below 350, and the reaction speed increases with the increase of temperature. The solubility of hydrogen in tantalum decreases with increasing temperature. Under certain temperature and pressure, the maximum hydrogen content in tantalum is equal to H/Ta 0.02~0.08 (TaH 0.2~ TaH 0.8).

Tantalum nitride
The nitrides of tantalum have three kinds of TaN, Ta 2N and Ta 3N 5. TaN is a gray powder with blue, melting point 2980~3090 C, density 14.4g/cm3, insoluble in nitric acid, hydrofluoric acid and sulfuric acid, but dissolving in hot alkaline solution and releasing ammonia or nitrogen. Tantalum nitride generates oxide and releases nitrogen gas when heated in air.

Tantalum boride
Tantalum boride has TaB and TaB 2. The density of TaB is 14.0g/cm3, the specific resistance is 100 uomega.Cm, the melting point of TaB 2 is 3200 C, the density is 11.7g/cm3, the specific resistance is 86.5 muomomega.Cm, and it is not corroded by hydrochloric acid and water, but it can be decomposed slowly by hot sulfuric acid and hydrofluoric acid.

Tantalum selenate
The selenide of tantalum is TaSe 2, the specific resistance is 2.23 x 10-3 Omega.Cm, the relative friction coefficient at room temperature air is 0.08, the oxidation temperature in the air is 600 degrees C, and the decomposition temperature in the vacuum is 900.

Tantalum silicone
The main silicide of tantalum is TaSi 2, and there are also some other compounds, such as Ta 2Si and Ta 5Si 3. TaSi 2 melting point 2200 C, density 8.83g/cm3.
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