For a given application requirements, you must choose a proper tungsten contact material to make the function of the device get as greater possibility of success in the design process as possible. Besides, adjusting the final properties of addictives, materials particle size and furnace temperatures of the chosen tungsten contact materials are available. And the cost of tungsten contact is cost-effective.

Tungsten contact, generally, its thermal and electrical conductivity will increase and contact wear erosion resistance will decrease as the tungsten content of conductive metal increases, however, contact wear erosion resistance and contact welding becomes a significant concern. On the contrary, contact wear erosion resistance will increase as the refractory metal content increases; what’s more, there is less possibility of tungsten contact welding.

In a word, the selection of tungsten contact materials should take its wear erosion resistance and other properties, and its cost into account.

 

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Tungsten point‘s materials and applications

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Tungsten contacts materials and applications
 

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AC impedance method and polarization curve method were used to study the inhibition effects of environmental friendly inhibitors polyaspartic acid (PASP) and Na2WO4 , alone or in combination, for copper in 3% NaCl solution. The results indicated that both PASP and Na2WO4 were able to inhibit the corrosion of the copper in the 3% NaCl solution. PASP at a concentration of 40 mg/L showed the best inhibition effect for copper, while Na2WO4 gave the optimal inhibition action to copper at a concentration of 350 mg/L. When PASP and Na2 WO4 were formulated as a combined inhibitor, it showed good inhibition effect to copper at a total inhibitor concentration of 40 mg/L, and in this case PASP and Na2 WO4 showed synergistic inhibition effect, with the optimum ratio of PASP to Na2 WO4 to be 1:5. When the total inhibitor concentration of the combined inhibitor rose to 350 mg/L and PASP was mixed with Na2 WO4 at ratios of 7:1, 5:1, 3:1, 1:5, and 1:7, the combined inhibitor still showed good synergistic inhibition effect for copper in the saline water, and the optimum ratio of PASP to Na2 WO4 in this case was 7:1.

 

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The debate on tungsten (W) is fostered by its continuous usage in military munitions. Reports demonstrate W solubilizes in soil and can migrate into drinking water supplies and, therefore, is a potential health risk to humans. This study evaluated the reproductive, systemic and neurobehavioral effects of sodium tungstate (NaW) in rats following 70 days of daily pre-and postnatal exposure via oral gavage to 5, 62.5 and 125 mg/kg/day of NaW through mating, gestation and weaning (PND 0-20). Daily administration of NaW produced no overt evidence of toxicity and had no apparent effect on mating success or offspring physical development. Distress vocalizations were elevated in F(1) offspring from the high dose group, whereas righting reflex showed unexpected sex differences where males demonstrated faster righting than females; however, the effects were not dose-dependent. Locomotor activity was affected in both low and high-dose groups of F(1) females. Low-dose group showed increased distance traveled, more time in ambulatory movements and less time in stereotypic behavior than controls or high dose animals. The high-dose group had more time in stereotypical movements than controls, and less time resting than controls and the lowest exposure group. Maternal retrieval was not affected by NaW exposure. Tungsten analysis showed a systemic distribution of NaW in both parents and offspring, with preferential uptake within the immune organs, including the femur, spleen and thymus. Histopathological evidence suggested no severe chronic injury or loss of function in these organs. However, the heart showed histological lesions, histiocytic inflammation from minimal to mild with cardiomyocyte degeneration and necrosis in several P(0) animals of 125 mg NaW dose group. The result of this study suggests that pre and postnatal exposure to NaW may produce subtle neurobehavioral effects in offspring related to motor activity and emotionality.

 

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The use of tungsten as a replacement for lead and depleted uranium in munitions began in the mid 1990's. Recent reports demonstrate tungsten solubilizes in soil and can migrate into drinking water supplies and therefore is a potential health risk to humans. This study evaluated the reproductive and neurobehavioral effects of sodium tungstate in Sprague-Dawley rats following 70 days of daily pre- and postnatal exposure. Adult male and female rats were orally dosed with diH(2)O vehicle, 5 or 125 mg/kg/day of sodium tungstate through mating, gestation, and weaning (PND 0-20). Daily administration of sodium tungstate produced no overt evidence of toxicity and had no apparent effect on mating success or offspring physical development. Distress vocalizations were elevated in the highest dose group. There was no treatment related effect on righting reflex latencies, however, the males had significantly shorter latencies than the females. Locomotor activity was affected in both the low and high dose groups of F0 females. Those in the low dose group showed increased distance traveled, more time in ambulatory movements, and less time in stereotypic behavior than controls or high dose animals. The high dose group had more time in stereotypical movements than controls, and less time resting than controls and the lowest exposure group. Maternal retrieval was not affected by sodium tungstate exposure and there were no apparent effects of treatment on F1 acoustic startle response or water maze navigation. Overall, the results of this study suggest pre- and postnatal oral exposure to sodium tungstate may produce subtle neurobehavioral effects in offspring related to motor activity and emotionality. These findings warrant further investigation to characterize the neurotoxicity of sodium tungstate on dams and their developing pups.

 

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The potential for adverse health effects of using tungsten and its alloys in military munitions are an important concern to both civilians and the US military. The toxicological implications of exposure totungsten, its alloys, and the soluble tungstate (Na(2)WO(4)) are currently under investigation. To examine tungstate toxicity, a series of experiments to determine its in vitro effects on cells of the immune system were performed. We identified alterations in isolated human peripheral blood lymphocytes (PBL) treated in vitro with sodium tungstate (0.01, 0.1, 1.0, and 10 mM). Analyses of apoptosis with annexin V and propidium iodide revealed a dose- and time-dependent increase in the quantity of cells in early apoptosis after tungstate exposure. Reductions in the number of cells entering into the cell cycle were also noted. Exposure of PBL to tungstate (1 mM) and Concanavalin A (ConA) for 72 h reduced the number of cells in S and G(2)/M phases of the cell cycle. There were alterations in the numbers of cells in G(0)/G(1), S, and G(2)/M phases of the cell cycle in long-term THP-1 (acute leukemic monocytes) cultures treated with tungstate (0.01, 0.1, 1.0, and 10 mM). Gel electrophoresis,silver staining, and LC-MS/MS showed the cytoplasmic presence of histone H1b and H1d after 72 h oftungstate exposure. The addition of tungstate to cultures resulted in significant reductions in the quantity of interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha), and IL-6 produced by stimulated [CD3/CD28, ConA, or lipopolysaccharide (LPS)] and tungstate-treated lymphocytes. Taken together, these data indicate that tungstate increases apoptosis of PBL, alters cell cycle progression, reduces cytokine production, and therefore warrants further investigation.

Decomposition of ammonium paratungstate under non-oxidizing atmosphere:

The first stage： 90~180℃，lose crystal water：
5(NH4)2O·12WO3·5H2O=5(NH4)2O·12WO3·H2O+4H2O↑

The second stage: 180 ~ 260 ℃, ammonia loss:
5(NH4)2O·12WO3·H2O=3(NH4)2O·12WO3·3H2O+4NH3↑
Ammonium metatungstate（AMT）

The third stage, 260 ~ 350 ℃, further of lose water and ammonia, ammonium tungsten bronze occurred (ATB):
3(NH4)2O·12WO3·3H2O＝(NH4)2O·12WO3+4NH3↑+5H2O↑

Fourth stage: 350 ~ 450 ℃, ammonia begins to decompose to generate hydrogen and nitrogen:
2NH3 =N2 ↑ + 3H2 ↑
This phase chemical reactions may be
(NH4)2O·12WO3 + H2＝12(NH4)xWO3+H2O+(2-x)NH3↑
(NH4)xWO2.8~3.0

Fifth stage: 450 ~ 550 ℃, ATB decomposition output WO3 and WO2.9

Sixth stage: 550 ~ 650 ℃, decomposition products in addition to small amounts of ATB, there are WO3, WO2.9 and tungsten oxide WO2.72 etc., even WO2.



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Ammonium paratungstate (or APT) is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O. Its shape is like sheet or needle.  It is insoluble in water and alcohol. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate.

Ammonium paratungstate content is listed as below:

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Ammonium paratungstate hydrogen reduction preparing tungsten powder combines the calcination of raw material powder and hydrogen reduction of tungsten oxide. It reduces the intermediate process and improves producing efficiency.

During the process of preparing tungsten powder by ammonium paratungstate hydrogen reduction, reduction temperature and time affects the producing or tungsten powder. Raising reduction temperature and extending reduction time will make the size of tungsten powder bigger and the completion of tungsten powder crystal. Extend the reduction time will make the gaseous phase transport more active. The fine tungsten oxide particles will deposit on the large tungsten powder particles. Thus enlarge the size of grain size.

Compared to the traditional preparing method, tungsten powder prepared by ammonium paratungstate hydrogen reduction has higher property and green strength. 



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