Images of Tungsten Oxides and Tungsten Metal

Electron-microscopical images of tungsten oxides and tungsten metal, formed during hydrogen reduction of WO3. The reason for the significant change in form of the powder particles is a result of a chemical vapour transport (CVT) of tungsten via the volatile tungsten hydroxide WO2(OH)2; by courtesy of Prof. Roland Haubner; Vienna University of Technology.tungsten oxides,tungsten metal

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Barrel Shapes

There are some barrel shapes we can chose in the market of dart.

The barrel forms is the main part of a dart. When we are speaking of "buying a (new) dart" we mean getting a new dart barrel. Nowadays barrels are available in almost every possible shape, with a wide selection of knurl or rings on the surface for a comfortable and safe grip.

It's not possible to say which one is the "right" one. Based on a very theoretical reasoning the long cylindrical barrel could be the best of them because it is the slimmest and allows the tightest grouping. But this reasoning doesn't help you when you are not able to handle such a barrel. Selecting the right shape is a matter of personal preference. Choose what feels comfortable for you. This is much more important than an abstract or "academic" reasoning about theoretical advantages or disadvantages of some shapes.

 

 

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How to Buy a Dart (I)

Here is a checklist of what you should pay attention to when you shop for a set of darts.

The supermarket is not proper places for buying darts. Some of these facilities sell darts (steel and soft) now and then, often combined with boards. In 99 percent of all cases this stuff is just plainly useless. If it's soft then the boards tend to have weird dimensions and poor quality (segments will break often with no replacement available). If it is steel then the boards are often paper boards which only last for a couple of darts. The darts supplied with these packages are the cheapest things possible, and in this case cheap doesn't mean low price, it means worthless.

The darts supplied with these packages are the cheapest things possible, and in this case cheap doesn't mean low price, it means worthless.Find a shop that has specialized in darts. If you can't find such a shop then look for a fisherman, hunting or weapon shop. Sometimes these facilities sell dart stuff (at least in Europe), and if they have a board where you can try their darts then you are in business. Pubs and bars where darts is played are also possible places to buy darts.

Take enough time to try different darts. You should spend at least 1 hour for trying different shapes/weights. If the shop doesn't give you this opportunity then it isn't a good shop.

When trying the darts don't judge by what you are hitting with them. Only judge by how the dart is feeling. This is important because when you are trying new darts it is very likely that you are more concentrated and careful than usual. This will result in better hits, but it's not because the dart is so good.

When trying different darts then first try a couple of darts and make the first preselection. For instance, try new sets of darts that look promising. Don't forget to try darts that look very odd for you, or shapes different from the ones you are used to! Prejudice is not the best thing when you are shopping for a new set of darts, you might find the perfect set where you wouldn't have expected it. One you have filtered out about 4 "candidates" you should go on further examining them, filtering half of them out. Then you have 2 sets left to decide which one to buy (most probably this will be the same dart in two adjacent weights).

If you can't get sure which set to buy then buy none of them, not both. If you find it unpleasant to tell the shopkeeper that you won't buy anything after he patiently assisted you in your 2-hour session at the shop then buy a couple of shafts or flights you'll need anyway sooner or later. In long term this will only kill your round-the-corner dart shop which will hurt you more when you discover that you are out of shafts the day before that deciding league match of the season.

 

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Tungsten Oxides Colours (I)

There are several tungsten oxides, but only four of them are of major importance. They all have attractive colours: the yellow WO3, the dark blue W20O58 (WO2.9), the violet W18O49 (W2.72) and the chocolate brown WO2. So-called higher tungsten oxides are structurally related to both the WO3 and W20O58 structures and exhibit chemical formulas between WO2.99 and WO2.889. They belong to the group of non-stoichiometric tungsten oxides, and are of interest mainly to structural chemists. They exhibit colours from yellow to green to very dark blue. The colour changes are a result of a slight loss of oxygen which generates an additional valence state in the WO3 parent structure, either W5+ or W4+. Cation-to-cation charge transfer between the parent W6+ and a reduced ion is responsible for the change in colour.
 
Tungsten oxides are important starting materials for the production of tungsten metal powder by hydrogen reduction. These oxides are formed out of ammonium paratungstate by a thermal decomposition process called “calcination” and are depending on the decomposition conditions (more or less reducing), a mixture of different higher tungsten oxides, including amorphous oxide phases. As described before, they exhibit colours between yellow and dark blue (TBO,“Tungsten Blue Oxide”).
 
 
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The Causes of Tungsten Oxides’Colours

The colours of tungsten oxides are due to light absorption and selective reflection (and/or transmission). This is called subtractive colouration. The colour of the oxides changes with the electronic properties of the oxides which, perse, are a result of the crystal symmetry of the solid. Changes in size, crystallinity or temperature can significantly change the colour, as demonstrated in this article. Chemical vapour transport of tungsten renders the preparation of single crystals of tungsten oxides, but also tungsten metal, to further exploit their interesting structural, optical and electronic properties.
 
 
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