Tantalum electrical resistivity

The reaction with small amounts of nitrogen results in an increased hardness, tensile strength and electrical resistivity. Tantalum is embrittled by higher amounts of nitrogen. The reaction takes place at temperature above 400°C. Nitrides among other phases form at the surface, but at higher temperatures these decompose and all the nitrogen is liberated at 2100°C . 

The presence of a few atomic percent of oxygen in tantalum increases electrical resistivity, hardness, tensile strength, and modulus of elasticity, but decreases elongation and reduction of area, magnetic susceptibility, and corrosion resistance to HF . 

Figure 11.1 (a) Scheme of an isoperibol titration calorimetry apparatus A Dewar vessel B lid C stirrer D electrical resistance E thermistor F titrant delivery tube G O-ring seal, (b) Vessel for isothermal operation A stainless-steel, platinum, or tantalum cup B water-tight stainless steel container C heater D Peltier thermoelectric cooler E O-ring seal F heater and cooler leads. Adapted from [211],... 

Derivation From tantalum potassium fluoride by heating in an electric furnace, by sodium reduction, or by fused salt electrolysis. The powdered metal is converted to a massive metal by sintering in a vacuum. Foot-long crystals can be grown by arc fusion. Corrosion resistance 99.5% pure tantalum is resistant to all concentrations of hot and cold sulfuric acid (except concentrated boding), hydrochloric acid, nitric and acetic acids, hot and cold dilute sodium hydroxide, all dilutions of hot and cold ammonium hydroxide, mine and seawaters, moist sul-furous atmospheres, aqueous solutions of chlorine. 

Fig. 3.1-1fi3 Specific electrical resistivity versus temperature of molybdenum [1.126], tungsten [1.126], niobium [1.127], and tantalum [1.127]...

In several runs, e.g. run 17, Table 4, stable operation of the anode was obtained at a rather low voltage. This was due to the effect of the anode construction (the inner current lead had been pressed into a hole in the anode body) and also that the temperature in this run was high, which resulted first in a relatively low electrical resistance of the ceramic anode and secondly in a more complete and faster metal-thermal reduction reaction. As a result tantalum powder was not spread over the container volume, but was concentrated on the cathode rod as a compact conglomerate which could be removed from the melt together with the cathode. In addition there was practically no Ta205 powder in the container and after the experiment it was not difficult to separate the tantalum powder from that of TajOj. The low current efficiency in this run is due to the non-optimized operating conditions of electrolysis in particular that an excess amount of electricity had been passed. 

Henkel offers its Hysol KOI052 rapid cure, silver-filled epoxy-based conductive adhesive to bond the cathodes in the construction of surface mount tantalum capacitors. This adhesive is suitable for in-line curing in as little as 20 seconds at elevated temperatures (200 °C). Features of this adhesive include a low volatile content, reduced voiding, low electrical resistance and high peel strength. 

Markova et al. (1967) investigated the terbium-yttrium system by means of microscopy, X-ray diffraction, thermal analysis, hardness and electrical resistance measurements. Their starting materials were distilled yttrium of 99.6 to 99.7 (wt )% purity and terbium of 98.5 to 99% purity. Impurities in their terbium included yttrium, gadolinium, dysprosium, calcium, copper, iron and tantalum. Both metals contained gaseous impurities. Alloys were melted in an arc furnace under a helium atmosphere and annealed at 850°C for 70hr. 

The corrosion resistance of a series of tantalum-tungsten alloys was also studied in 50% KOH at 30°C and 80°C, 20% HF at 20°C, and a mixture with 1 part KOH and 3 parts K3Fe(CN)6. In the hydroxide, a maximum in corrosion rate was obtained at about 60at% tantalum. A maximum in electrical resistivity was foimd at the same composition. In 20% HF, the tantalum-timgsten alloy system exhibits the relatively low corrosion rates associated with tungsten as long as the tungsten content is at least 20%, below which corrosion rates increase markedly. In the hydroxide-ferrocyanide mixture, alloys exhibit little improvement over tantalum. 

Electrothermal atom cells have changed radically since their inception in the late 1950s. The majority of electrothermal devices have been based on graphite tubes that are heated electrically (resistively) from either end. Modifications such as the West Rod Atomizer (a carbon filament) were also devised but were later abandoned. Tubes and filaments made from highly refractory metals such as tungsten and tantalum have also been made, but they tend to become brittle and distorted after extended use and have poor resistance to some acids. Their use continues, however, in some laboratories that need to determine carbide-forming elements. For example, silicon reacts with the graphite tube to form silicon carbide, which is both very refractory and very stable. The silicon is therefore not atomized and is lost analytically. Use of a metal vaporizer prevents this. 

JR Cooper, RL Hansler. Variation of electrical resistivity of cubic tantalum carbide with composition. J Chem Phys 39 248, 1963. 

LaN + NbN target. The LaNb(Oo.24N2)i.24 composition had an electrical resistivity at room temperature of 1.5 x 10 Q cm. The high-gloss colored tantalum compounds, especially GdTaON2 and PrTaON2, could be used as pigments in paints and plastics (Cerdec AG Keramische Farben 1994). 

It is somewhat less corrosion resistant than tantalum, and like tantalum suffers from hydrogen embrittlement if it is made cathodic by a galvanic couple or an external e.m.f., or is exposed to hot hydrogen gas. The metal anodises in acid electrolytes to form an anodic oxide film which has a high dielectric constant, and a high anodic breakdown potential. This latter property coupled with good electrical conductivity has led to the use of niobium as a substrate for platinum-group metals in impressed-current cathodic-protection anodes. 

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