[Ashutosh]

isotopes has same chemical properties but different physical properties.therefore it is difficult to separate them.
    then,How it possible to separate 235 U and 238  U by using UF6
    thanks for answering.


   

[Demotivator]

You said it yourself. They have different physical properties based on weight,
So, a series of gas centrifuges are used to spin the UF6 at high speed to separate the isotopes.
Another technology is gaseous diffusion at high pressure through semiporous membranes.

[Simon Gunson]

The UF6 (uranium hexaflouride) gaseous centrifuge process was first developed by Nazi scientists at the university of Keil in 1942 under Prof Kurt Clusius. It was subsequently developed on a large scale by Dr Paul Harteck of the Heereswaffenamt (HWA) A-bomb project during WW2 for the production of U235. It is thus now known as the "Harteck process."

South Africa and Pakistan both used the Harteck process after WW2 to develop uranium A-bombs. Pakistan now has 20 A-bombs. Iran is currently developing the same harteck process developed by Nazi Germany.

Uranium-oxide powder (Yellow Cake) which has mostly non radioactive U238, is mixed with flouric acid to make uranium hexaflouride. This gas compound is spun at up to 500rpm and the containment bowl is heated from below which boils enriched U235 to the top. Electro-magnets then sluce the enriched material from the top. Thus they are sometimes called Isotope sluces.

Japanese nuclear scientists also used thermal difusion techniques of allowing UF6 to rise inside a column around a cylinder and depositing U235 on the walls of the cylinder.

Yet another method developed by the japanese during WW2 was with cyclotrons where the UF6 was accelerated and then deflected by magnets such that the U238 flung off at one angle and the U235 at another angle.

The Nazi gaseous centrifuge project was discovered by British espionage through project Epsilon in Stockholm. Allied bombing of Hamburg in 1943 destroyed the Nazi uranium enrichment plant. It shifted to Freiburg under the codename "Volmers Furniture Factory," which was also bombed. From there it shifted to Austria under the codename "Angora Farm" and was yet again bombed.

From November 1943 the Nazis began shipping uranium ore to Japan by submarine for enrichment at what is now North Korea. US Army archives at NARA indicate the Japanese successfully test blasted at least one uranium A-bomb before the war ended.

In Germany the chief designer of the Nazi A-bomb was Prof Kurt Deibner  

Large contracts were awarded in Nazi Germany during 1944 for manufacture of Harteck centrifuges.

These centrifuges had nothing to do with heavy water from Norway, where the sabotage of the Voermark plant and later sinking of the Telemark ferry did nothing to hamper uranium enrichment.

Heisenberg worked on nuclear reactors for the Kaiser Wilhelm Geselschaft (KWA) and by the end of the war had not been able to moderate nuclear reaction though he had developed a very crude reactor at a cave in Hechingen. Heisenberg was not involved with the A-bomb project.

In October 1944 top Nazi scientists with the discreet sanction of the SS approached General Electric Corporation (GEC) to negotiate the surrender of Germany to Western Allies. Nazi Germany was close to deploying a nuclear bomb, but the Nazis realised this would not stop the Red Army.

Before the end of the War several tons of Uranium and radium were either buried around Garminsch Partikirchen (and smuggled out post war) or dumped in the River Issar.
 

[jdurg]

Actually, the Uranium Oxide powder is mixed with fluoric acid to produced UF4 which is a solid crystalline substance.  UF4 is then reacted with fluorine gas to produce the volatile UF6.