The best tungsten electrode for a specific application depends on factors such as the type of welding, the welding material and the welding current. However, some commonly used tungsten electrodes include:

1. Thoriated tungsten electrode: usually used for DC welding of stainless steel, nickel alloy and titanium. They have good arc starting and stability properties.

2. Tungsten-cerium electrode: suitable for AC and DC welding, often used for welding carbon steel, stainless steel, nickel alloy and titanium. They have good arc starting properties and low burnout rates.

3. Lanthanum Tungsten Electrodes: These are versatile electrodes suitable for AC and DC welding of carbon steel, stainless steel, nickel alloys and titanium. They have good arc stability and long service life.

4. Zirconium tungsten electrode: usually used for AC welding of aluminum and magnesium alloys. They have good resistance to contamination and provide a stable arc.

It is important to consult a welding expert or refer to specific welding application guides to determine the best tungsten electrode for a specific welding task.

Tungsten is no stronger than diamond. Diamond is one of the hardest materials known and is characterized by exceptional hardness and strength. It is composed of carbon atoms arranged in a specific crystal structure, which gives it unique properties.

Tungsten, on the other hand, is a very dense and strong metal with a high melting point, but it is not as hard as diamond. Tungsten is commonly used in applications that require high strength and heat resistance, such as the production of high-performance tools, electrical contacts, and the aerospace industry.

In summary, while tungsten is a strong and durable material, it is not as hard as diamond. Diamond remains one of the hardest and most durable materials known to man.

Tungsten has an extremely high melting point of 3,422°C (6,192°F), making it one of the highest melting points of all elements. However, there are some substances and conditions that can melt tungsten:

1. Tungsten itself: Tungsten can be melted using extremely high temperatures generated by specialized equipment such as electric arc furnaces or other advanced heating methods.

2. Tungsten-rhenium alloy: Adding a small amount of rhenium to tungsten can lower the melting point of the alloy. This alloy is used in certain high temperature applications where a lower melting point is required.

3. Tungsten can also be melted in the presence of certain reactive gases or under specific conditions in a controlled environment.

Generally speaking, melting tungsten requires extreme conditions due to its high melting point, which is generally not easy to achieve.