Thin foils

Beryllium windows and foils

Foils from beryllium are used in apparatus and for nuclear-physical experiments. Industrial foils are made by the method of a hot rolling in protective coverings. The traditional technology of beryllium foil rolling has some disadvantages, which with decrease of foil thickness worsen their qualities. It leads to quick increase of thin foil cost, less than 50 mkm in thickness.

There have been elaborated the method of receiving of thin beryllium foils by ion-plasma method in the laboratory of IPT INP. There has been precipitated beryllium layer of necessary thickness (15 mkm and more) on the bearer from metal, after that the formed foil is separated. Depending on bearer form foil is like a ribbon or circle with specified diameter.

Beryllium foils are used as protective windows of detectors passed X-radiation with low energy. For suitable fastening round windows are provided with circular belt from copper. Magnetron method allows receiving without additional processing ready-made vacuum compact X-rayed windows up to 1 inch in diameter with a mirror surface and high mechanic characteristics (fig. 2.).

Fig.2 Beryllium windows, diameter is 30 mm

Fig.3 Microstructure of beryllium foil. (The figure of dr. R. Dickerson, LANL, USA)

A high quality of beryllium windows is provided by a number of factors among which the main one is a low content of mixtures in the target material. The concentration of beryllium in targets after stepwise distillation of storage is 99.992 %. For keeping this beryllium purity in precipitated foil a deep purification of argon from chemically active mixtures in the facility of a magnetron type dispersed getter is used.

Magnetron foils have a high modulus of elasticity. Its small-grained structure promotes to this. Grain sizes do not exceed 0.3 mkm (fig. 3).

Direction of beryllium crystallite growth on immovable substrate practically coincides with normal to the surface. You can see it in fig. 4, where a foil structure in cross section is shown. The foil texture with the aid of uninterrupted substrate moving at foil precipitation is changed for solidity increase of beryllium windows. Crystallites have an incline to normal in foil formed on moving substrate (fig. 5).
The industrial vacuum magnetron facility for receiving windows from beryllium foil has been elaborated and manufactured. Speed of window precipitation is 10 mkm/h. The window thickness is controlled by the duration of the forming process. There have been executed 8 cycles of precipitation of round beryllium windows in 20-mkm thickness, from 5 to 40 mm diameters without target replacement on the facility.

Foil from beryllium alloy

Beryllium alloys represent a practical interest connected with their special physical and mechanic qualities. Anyway a high fragility of beryllium materials make difficult using of a method of plastic storage processing for receiving thin foils and other wares. Besides with some metals for example with aluminum, beryllium does not form solid solutions or compounds. Materials from such immiscible components are not enough homogeneous and this decreases their value.

Fig.4 Crystallite orientation cross section of beryllium foil precipitated on immovable be-arer

Fig.5 Inclined orientation of crystallites in beryllium foil, precipitated on movable be-arer (a = 16╟).

There has been elaborated the technology and equipment for manufacturing of thin foil by magnetron method and volume foil elements from beryllium materials in the laboratory of IPT INP. Foils formed by magnetron method have a number of advantages in compare with foils received by plastic processing of alloys.

Beryllium-aluminum foils and volume elements

Foil consisted from beryllium and aluminum can be used in X-rayed windows passed radiation with low energy. In compare with traditional beryllium windows beryllium-aluminum foil is cheaper. Its application is expedient in spite of small reduce of X-rayed transparence which is connected with re-emission of the first quanta on the main line of aluminum (1.5 keV).
The ribbon is formed from atom mixture consisted of beryllium and aluminum according to magnetron technology at simultaneous dispersion of targets from beryllium and aluminum. Metals are precipitated on moving bearer of cylindrical form up to receiving of a layer of definite thickness. After metal precipitation process foil is separated from bearer (fig. 6).

Fig.6 Beryllium-aluminum foil

Fig.7 Installation for beryllium material pre-cipitation

Foil has high mechanic qualities, increased modulus of elasticity and small-grained microstructure with crystallites of 0.1-0.3 mkm. Beryllium concentration in foil is set constant or variable according to foil thickness, receiving homogeneous or multi-layer ribbon. The thickness and composition of foil is easily controlled.

Geometric form of the bearer defines the form of foil, which is received by magnetron precipitation. At the same time it is possible to receive volumetric elements, for example, cone from beryllium and aluminum. The most important thing in the technology is that beryllium and aluminum cones received by magnetron method have a small-grained isotopic and homogeneous structure without connected seam. If it is necessary it is possible to make multi-layer volumetric element with a variable on wall thickness by beryllium concentration.

A sample of magnetron installation for fine foil receiving from beryllium and aluminum in a form of a ribbon in 65 cm length and 6 cm wide has been designed and produced (fig. 7). The speed of metal precipitation on the bearer is 0.15 mkm/min.

Foils and elastic elements from beryllium bronze

Fine foil from beryllium bronze (copper and beryllium alloy) is used particularly for producing of electroconductive elastic elements. The plastic processing of initial alloy at thickness decrease of foil becomes difficult and the material obtains the quality of anisotropy.

Elaborated in the laboratory of IPT INP magnetron method gives the possibility to obtain foil from beryllium bronze at target dispersion from copper and beryllium and metal precipitation on the moving bearer. To the end of the process of foil forming it is separated from the bearer.

Foil represents homogeneous and isotopic ribbon. It is also possible to obtain ribbons with multi-layer structure or ribbons with a variable on material thickness with beryllium concentration. Foil acquires necessary physical qualities owing to changing of its structure.

Thin foil from beryllium bronze has a small-grained microstructure with size of grains 0.1-0.3 mkm. It gives to foil high mechanic qualities with higher modulus of elasticity. Thickness and qualities of foil are easily controlled during the process.

Using bearers of different geometric forms at foil precipitation, it is possible to produce volume elastic elements from beryllium bronze. Springs, which are obtained during this process, can have a flat, conic, hemispheric and another form. As foil, springs have a small-grained structure with a high elasticity and can be homogeneous or with a variable composition on section. If it is necessary it is possible to carry out the additional thermal processing of wares, which will form the definite phase composition and qualities of beryllium bronze.

The sample of magnetron facility for receiving of thin foil from beryllium bronze in the form of a ribbon 65 cm length, 6 cm wide has been designed and manufactured (fig. 7). Precipitation speed of foil ribbon on the bearer is 0.15 mkm/min.