Refractory Metals
Ultrafine Hard Materials
By using nanoscale tungsten carbide particles as hard material components, it is possible to improve the properties of hard metals substantially. With these particles the hardness and toughness of both tools and wear parts can be enhanced. Researchers at H.C. Starck have already succeeded in producing WC powders in grain sizes of 100 nm using stably running and reproducible processes. The following table shows the available standard powder qualities:
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WC quality |
DN 3-0 |
DN 3-5 |
DN 4-0 |
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Specific surface |
3 m²/g |
3.5 m²/g |
4.0 m²/g |
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Primary grain size |
130 nm |
115 nm |
100 nm |
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The powders have a high sintering stability and can be processed into hard metals using conventional technologies. Due to the high specific surface areas, other properties of the nanostructured WC powders are also gaining in importance. For example, there is broad potential in heterogeneous catalysis. In this connection, H.C. Starck has developed a WC DN 5-0 grade that will soon be ready for launching. |
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High CV Tantalum Powder Paste
Paving the Way for Extremely Small Capacitors
The miniaturization of electronic components means that higher capacitance must be accommodated in ever smaller volumes of tantalum capacitors. This requirement can only be realized with tantalum powders having very high specific surface area. Pressing these extremely fine powders is a challenge because of their poor flowability, and the resulting electrodes have low mechanical strength.
Anodes less than 250 microns thick, like those used in microchip and multi-anode capacitors (low ESR), are difficult to produce with current pressing technologies.
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A new technique developed by H.C. Starck produces thin Ta anodes with tantalum powder paste and stencil printing on tantalum foil. Since the flowability of the pastes is significantly better than that of the powders, this process delivers anodes with thickness < 50 microns in almost any 2D shape.
In addition the mechanical stability of the printed anodes is superior to those of pressed anodes. Moreover, the pastes of these otherwise highly reactive metal powders can be handled more safely. |
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Niobium and Tantalum Doping
Single-phase microstructures are often an essential prerequisite for maximizing material performance. For example, homogeneous doping with niobium oxide and tantalum oxide on an atomic level is required in many cases for the production of catalysts, ferrites and electroceramics. This can be achieved by using H.C. Starck’s water-soluble niobium ammonium oxalate (NAmOx) and tantalum oxalate compounds.
The doping of ferrites with NAmOx influences grain growth during their production. Properties such as energy loss, electrical resistance and magnetic permeability are positively affected. Battery manufacturers use NAmOx as a dopant to increase the conductivity of cathode materials in lithium ion batteries.
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The addition of NAmOx also helps to considerably reduce the sintering temperature in the production of dielectrics.
H.C. Starck´s alkaline, alkaline earth and transition metal niobates and tantalates, e.g. potassium niobate (KNbO3), nickel niobate (NiNb2O6) and magnesium niobate (MgNb2O6) have various applications. For example, KNbO3, produced by H.C. Starck, is used as a dopant in piezoceramics. |
Crystal structure of NH4[Nb(O)(C2O4)2(H2O)2] x 3 H2O |
Ultra-high Capacitance Tantalum Powders
The increasing miniaturization of electronic components also drives the development of smaller and smaller capacitors. Higher and higher electronic capacitance must be accommodated in an ever smaller volume, which directly correlates with the surface area of the anode, the main element of a capacitor. These anodes primarily consist of pressed and sintered tantalum powders with very high surface areas. With today’s conventional methods to produce Ta powder, such as sodium reduction of K2TaF7, it is becoming increasingly difficult to obtain high-surface powders economically and in sufficiently high qualities.
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H.C. Starck researchers have developed a magnesium reduction of tantalum oxide as a new approach to high-performance tantalum powders.
With this process it is possible to obtain metal powders with surface areas of > 5 m²/g and thus to develop the next generation of tantalum capacitors. |
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