NaLaMgWO₆ powder is the matrix of LED phosphor powder. LED is becoming the future development direction of the illumination source with the series advantages, such as low voltage and power consumption, high reliability, long life, environmentally friendly and energy-efficient. Phosphor plays an important role in the field of LED lighting. Tungstate is typically self-activated luminescent material, the stable emission spectrum, very wide intrinsic luminescence band, occupying most of the visible light region, thus strongly influence the emission band position. Therefore, ammonium paratungstate (APT) as the typical tungstate, is a matrix material with excellent light-emitting property, and can be used for preparing NaLaMgWO₆  phosphor powder which is applied in LED. The steps as following:

1. Weighing NaNO₃, La(NO₃)₃, magnesium acetate and APT at a certain proportion, and dissolving them in deionized water, then adding citric acid to prepare a solution named A; the molar ratio of citric acid : NaNO₃ is (0.05~0.2):1;
2. Adjusting the pH value of solution A to neutral value;
3. The solution A is carried out a hydrothermal treatment, and then removed for centrifugation, washing and drying to obtain a sample powder;
4. Sintering the powder sample to solid phase, to obtain the NaLaMgWO₆ powder. The solid-phase sintering conditions supposed to be: raising the temperature at the rate of 1~2℃/min from room temperature to 200~300℃, and then continually raising to 500-800℃ at 3~5℃/min, holding for 3~8 hours then cooling down.

Fluorination catalyst plays a central role in the reaction of gas phase catalytic fluorinated halogenated olefins, a method that using ammonium paratungstate (APT) and chromium hydroxide to prepare fluorination catalyst is proposed in this paper.



Steps like bellows:
1. Mixing the chromium hydroxide and APT a certain mass percentage, and pressing to obtain the precursor of product;
2. Calcining the catalyst precursor obtained in step 1 in the nitrogen atmosphere at 300℃~500℃ for 6~15 hours. In the calcination, a large amount of volatile compounds will be produced, and mainly is ammonia, making catalyst of high surface area, pore volume, thus enhancing the activity of catalyst;
3. Carrying out activation in the atmosphere of hydrogen fluoride and hydrogen (mixed gas mixed at a molar ratio of 10:1) at the temperature of 200℃~ 400℃ for 6 ~15 hours; in this process, all or part of the tungsten 6 will be reduced to tungsten;
4. Carrying out activation at 200℃~400℃ again, the atmosphere should be the mixed gas of hydrogen fluoride and chlorine at molar ratio of 10:1, for 6~15 hours, thus to get fluorination catalyst.

There is an experiment chooses WC-10(CoNi) tungsten carbide as an object of study. In order to test the anti-corrosion, it adds different content of Co in the binder and finds that Cr element effectively increases the anti-corrosion of tungsten carbide and the hardness increases with the increasing content of Cr. Another study is about corrosion behavior with WC-9Ni-0.57Cr carbide simulation in seawater, the study found that in deep-sea high pressure, corrosive environments on corrosion resistance is concerned, compared to conventional WC-Co carbide system to Ni-Cr alloy as the binder phase has better corrosion resistance.

Recently, some foreign scholars have also studied the correlation titanium carbide (TiC), tantalum carbide (TaC) and chromium carbide (Cr3C2) added impact on the corrosion resistance of the alloy. They believe that an appropriate amount of such reinforcement TiC ceramic composite materials can improve toughness of the alloy, and TiC and TaC has excellent chemical stability, only some of the acid is dissolved in, super acid and alkaline oxide solution: While Cr dissolved in the bonding phase accordingly in its surface layer of passive film is formed, it will not change the strength of the premise, significantly reduce the current density, and the higher the ratio of Cr alloy and Co, the passivity of alloy becomes higher. Furthermore, adding aluminum (Al) in the binder is also a new attempt of researchers. Theoretically, Al can be formed of metal bond compound (Co3Al), will make a fundamental change in the binder phase from the structure and performance, the amount can be increased to improve the content of Al alloy high temperature oxidation resistance and corrosion resistance.

The latest research has progressed to the development of adhesive-free alloy, which is free or very little binder metal content, high hardness (up 95HRA above), corrosion and oxidation resistance is also very good, but its flexural strength and fracture toughness is lower, which is difficult for machining. Overall, for the study of the corrosion of cemented carbide mainly includes three aspects, one is to replace the binder phase, and the second is to strengthen the binder phase by adding elements, hard phase grain refinement, the third is the development of adhesive-free tungsten carbide.

Conventional tungsten carbide is composed of hard phase WC and the binder Co. Due to Co has good wettability on WC, tungsten carbide has high hardness, high density, high strength and excellent chemical stability, which can be widely used in some wear parts and cutting tools machining. But as binder, Co has poor anti-corrosion, especially for scour corrosion so that to add some other elements with good anti-corrosion or to find new binder becomes the new directions of related researchers. The principle of Co oxidation corrosion of WC and Co is formed of two electrodes in the electrochemical etching solution, to form a closed loop enclosing an electrolyte. WC as a catalyst to promote the electrolytic solution boundaries O₂, producing O^2-, forming a cathode; Co as the anode is oxidized and causes the corrosion.

The Common nickel (Ni) can effectively take place of the cohesive effect of cobalt (Co) and improve the anti-corrosion of tungsten carbide. But tungsten carbide hardness (HRA) affected its formation, as compared to the original cobalt tungsten carbide decreased 0.5-1 times, only 70-80% strength cobalt tungsten carbide, which is only suitable for less demand in strength, wear resistance situations. In addition, add chromium (Cr) in the binder is also a kind of common method to improve anti-corrosion of tungsten carbide. It can remarkably decrease the corrosion rate of tungsten carbide in corrosive conditions, refine tungsten carbide grains and strengthen the binder phase, which not only improve the anti-corrosion of tungsten carbide, but also promote other properties.

Tungsten electrode material having strong electron emission ability, high elastic modulus, low vapor pressure and other good properties, so often as thermal electron emitting material used in various different areas. It also as an important part used in TIG welding, plasma welding and cutting. The minimum amount of pure tungsten electrode is 99.5%. It has a higher electron work function, so it is difficult to arcing and arc beam is instability. Besides the service life is short. The shortages of pure tungsten electrodes greatly limited its application.

Tungsten electrode in order to meet the development of modern industry, from the production process and raw materials employs a lot of analysis and breakthroughs. For example, base on the shortage of pure tungsten electrode some researchers have produced a new type tungsten electrode-rare earth tungsten electrode. Rare earth tungsten electrode uses tungsten as substrate, doped with some rare earth oxides which have low electron work function, common rare earth tungsten electrodes including: thoriated tungsten electrodes, ceriated tungsten electrodes, lanthanated tungsten electrodes, zirconiated tungsten electrodes and so on. Different types rare earth tungsten electrodes having different properties can select them according to the welding material and current conditions.

With welding industry continuous development, the reliability and stability of the electrode made more stringent requirements, on this basis, invented a new tungsten electrode type-composite rare earth electrodes. The study found arcing performance and properties of the composite electrode materials are better than rare earth tungsten electrodes, and ternary composite tungsten electrode property is better than binary composite tungsten electrode.

At present, China has less research on rare earth tungsten electrode and composite rare earth tungsten electrode. Besides, the production process of them is not mature, lacking large-scale development and promotion. China has rich resources of tungsten ore and rare earth resources, we have the advantage for large-scale electrodes production, if tungsten electrode materials research and development, China's tungsten electrode industry will be able to grab opportunities in the global market, has broad market prospects.

As we know, different type and shape of tungsten electrode you used will influence the arc quality and welding performance that you will achieve. This article will brief introduce the performance and usage tip of different tungsten electrode shape. 

A balled tip is generally used on a pure tungsten electrode. Besides, it is suggested for use with the AC process on sine wave and conventional squarewave TIG welders. What’s more the diameter of the balled end should not exceed 1.5 times the diameter of the tungsten electrode. Because a larger sphere at the tip of the electrode can reduce arc stability and/or fall off and contaminate the weld.

A pointed or truncated tip is generally used on pure tungsten electrode, ceriated tungsten electrode, lanthanated tungsten electrode and thoriated electrode. And a pointed or truncated tip of electrode should be used for inverter AC and DC welding processes. To process electrode tip to a pointed or truncated shape should use a grinding wheel specially designated for tungsten grinding which can avoid contamination and one that is made of borazon or diamond which can resist tungsten’s hardness. Note: if you are grinding thoriated tungsten, make sure you control and collect the dust, have an adequate ventilation system at the grinding station and that you follow manufacture’s warnings, instructions and MSDS sheets. What’s more, during grinding should put the tungsten electrode straight on the wheel versus at a 90-degree angle to ensure that the grind marks run the length of the electrode. So it will reduce the presence of ridges on the electrode that could create arc wandering or melt into the weld puddle, causing contamination.

Generally, when welding with lower currents on thinner materials, it is best to use the pointed tungsten electrode. Because A pointed tungsten allows the welding current to transfer in a focused arc and helps prevent thinner metals, such as aluminum, from becoming distorted. However, using pointed tungsten for higher current applications is not recommended. Because, at the higher current it can blow off the tip of the electrode and cause weld puddle contamination. So at the higher current, truncated tip will more suitable than pointed shape.

In any application, different type and shape of tungsten electrode has distinct advantages and disadvantages. That’s why, regardless of type of material you are TIG welding or whether you are using an AC or DC process, it is always important to choose tungsten electrode shape and type. Doing so can maximize your TIG welding success and is one of the best defenses against contamination and rework.

In addition, it is necessary that consider the glass transition temperature of the temperature and pressure of the main component of the binder, temperature and pressure temperature closer to the glass transition temperature, the better the viscous flow of the binder can form a good lubricating film on the particle surface, effectively reducing inter particle internal friction and external particles and mold wall friction, effectively increasing the density of tungsten and copper compacts. When temperature and pressure temperature exceeds the glass transition temperature of the binder, the binder near the melting point, viscosity decreases, lubrication is no longer obvious, friction coefficient rises, effectively suppress power drops down so that the compact density decreases.

Theoretically, for pressing pressure, the density of material by PM is increasing with the increasing pressing pressure. However, increasing the pressure is having some limitations, first of all it is necessary to subject to the applicable conditions of tolerance and mold equipment. Besides, the pressure should be chose according to the impact on tungsten copper compacts. By contrast green density at room temperature and pressure different pressing force, both of which are rising as the pressing pressure, green density increases. But at the same compaction pressure units, the density of tungsten copper green by warm compacting process is higher than the density of tungsten-copper compacts by cold compacting process. This is due to the molding temperature and pressure present in the adhesive film surface of the particles can effectively reduce the particle relative displacement resistance when pressing the powder particles are better able to transmit pressure, increasing the effective pressing pressure, which will help increase the density of compacts.

Furthermore, in the process of warm compacting process, the yield strength and hardening rate of metal powder grains decrease, which increases the plastic deformation of powder particles and is beneficial for improving the density of green. Concerning powder compacting law, many experts and scholars propose some famous equation of repression, combined with the requirements of production equipment as well as the relative performance of tungsten copper required, thereby rational use of temperature and pressure molding process to improve its green density.