Abstract:
The inventive method for dispersing a dry powder sample in a dispersion chamber consists in vacuuming the chamber with respect to the environment, in dispersing a dry powder in the chamber, by means of a suction generated by the rupture of a membrane which is torn.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and device for dispersing a sample of dry powder in a dispersion chamber. 
     BACKGROUND OF THE INVENTION 
     There is known, for example through the U.S. Pat. No. 4,868,128, a method of dispersing a sample of dry powder in a dispersion chamber comprising:
         sealed closure of the said dispersion chamber,   the placing of the sample in means of introducing dry powder into the dispersion chamber,   putting the chamber under negative pressure with respect to a surrounding environment,   dispersion of the dry powder in the chamber by suction thereof inside.       

     In addition, the device described in the above mentioned patent comprises:
         a dispersion chamber connected to a negative-pressure source and situated in a surrounding environment,   means of opening and/or sealed closure of the said dispersion chamber, and   means of introducing the sample of dry powder into the said dispersion chamber.       

     Unfortunately, this method and this device cause an ordered dispersion of the grains constituting the dry powder because of the existence of a flow and this involves segregation within the dispersed granular materials, preventing a certain homogeneity of dispersion of the grains on a surface. 
     BRIEF SUMMARY OF THE INVENTION 
     The aim of the invention is to mitigate the drawbacks of the prior art by procuring an invention making it possible to avoid this segregation and permitting homogeneous, preferably single-layer, distribution of the grains dispersed on the surface. 
     To resolve this problem, there is provided according to the invention a method as indicated at the start, also comprising
         explosion of a membrane that ruptures, this membrane serving as the above mentioned introduction means and being interposed between the said surrounding environment and the interior of the said dispersion chamber,   entry of a fluid composing the surrounding environment through the ruptured membrane, and   entrainment by this fluid of the dry powder placed on the membrane, inside the dispersion chamber in an evenly dispersed manner.       

     Other embodiments of the method according to the invention are indicated in the accompanying claims. 
     Another object of the invention is a device as indicated at the start for implementing the method described above. 
     This device is characterised in that the introduction means comprise a membrane that is interposed between the said surrounding environment and the inside of the said dispersion chamber and on which the sample is disposed, the said membrane being arranged to rupture at a predetermined pressure difference between the said surrounding environment and the said inside of the dispersion chamber. 
     Other embodiments of the device according to the invention are indicated in the accompanying claims. 
     Other characteristics, details and advantages of the invention will emerge from the description given below, non-limitingly and making reference to the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic view of a particular embodiment of the device according to the invention. 
         FIG. 2  is a schematic view of a variant embodiment of the device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a particular embodiment of the device comprising a vacuum pump  1 , a pressure gauge  2 , means of introducing a sample into the dispersion chamber  11 , in the form of a sample support membrane  4 , on which provision is made for disposing a sample of dry powder  5 , and a surface (surface to be treated  12 ) on which the sample of dry powder is to be dispersed. The dispersion chamber  11  consists of a cylinder  10 , a top cover  6  and a bottom  14 . These elements  10 ,  6  and  14  can be assembled in order to form a dispersion chamber. On the bottom  14 , a seal  7  is placed on which the cylinder  10  must be placed for assembly. Above the cylinder  10 , provision is made for placing another seal  7  before closing the dispersion chamber by means of the cover  6 . In addition, clamping means, for example of the type with closure column  9  and butterflies  8 , ensure a seal by pushing the cover  6  and bottom  1  onto the seals on each side of the cylinder  11 . The clamping means  8  and  9  and sealing means  7  therefore form the opening and/or sealed closure means of the device according to the invention. In addition, when the partial vacuum is produced, the cover  6  and bottom  14  exert an even greater pressure on the seals. The cover  6  and bottom  14  therefore grip the cylinder  10  sealingly. 
     The device that is described above is an apparatus for dispersing a sample of dry powder  5  by explosion in a vacuum dispersion chamber  11 . This technique allows the dispersion of micrometric or nanometric grains of dry powder  5  on a surface positioned in the bottom of the dispersion chamber  11 , the surface to be treated  12 . 
     This dispersion is carried out by separating and setting in movement the sample of dry powder  5  without producing an ordered movement of the grains making up the dry powder  5 , in the dispersion chamber  11 . This condition of not generating an ordered movement of the material (a flow) is essential since a flow generates segregation within the dispersed granular materials, which is very detrimental in the context of the subsequent analyses. 
     In order to perform the dispersion operation, a low-intensity explosion is generated. This explosion is generated by the rupture of the sample-holding membrane  4 , the membrane  4  being interposed between a surrounding environment  13  and the dispersion chamber  11  in which an at least partial vacuum was previously established. 
     The non-ordered movement of the sample of dry powder  5  is effected by a turbulent filling of the dispersion chamber  11  with ambient air  13  or any gas. This gas or the ambient air  13  is then used as a carrier of the material within the dispersion chamber  11 . 
     This explosion and the filling of the dispersion chamber  11  with ambient air  13  or any gas gives rise to an unexpected phenomenon. The grains making up the sample of dry powder  5  have a tendency to push against one another and to form an homogeneous cloud of material within the dispersion chamber  11 . 
     The sample of dry powder  5  is recovered for the purpose of analysis by a process of natural sedimentation of the grains in the dispersion chamber  11  on the surface to be treated  12 . 
     In addition, when the surrounding pressure in the dispersion chamber is re-established owing to the rupture of the membrane  4 , the butterflies prevent a lifting of the cylinder  10  and maintain the seal in order to prevent a loss of sample  4 . 
     In order to use the device illustrated in  FIG. 1 , it is possible to proceed in the following manner. The surface to be treated  12  is disposed on the bottom base of the dispersion chamber  11 , the dispersion chamber  11  is closed, by depositing the cylinder  10  on the bottom seal  7 . The top cover  6  pivots on the right hand closure column  9  and will be placed in its compression position. The top and bottom seals  7  are compressed by butterfly screws ( 8 ) bolted onto the two lateral columns  9 . 
     When the procedure for preparing the dispersion chamber  11  has ended, the membrane sample holder  3  is placed in the opening provided for this purpose on the top cover  6 , and the membrane sample holder  3  is fixed by pressing on the fixing ring of the membrane sample holder  3 . 
     The sample of dry powder  5  is disposed on the membrane  4  of the sample support previously fixed to the membrane sample holder  3 . 
     A vacuum is produced in the dispersion chamber  11  by actuating the vacuum pump  1 , which sucks out the air, the sample support membrane  4  will then tension; the pressure gauge  2  makes it possible to monitor the change in internal pressure in the dispersion chamber  11 . When the pressure reaches the required level in the dispersion chamber  11  two cases may be envisaged: 
     Firstly, the sample support membrane  4  is intact and the explosion is effected by means of a punch  15  that perforates the sample support membrane  4 , manually or automatically, thus initiating the explosion. 
     Secondly, the sample support membrane  4  can be sized so as to rupture automatically when the tension created by the difference in pressure existing between its two faces exceeds a given strength threshold of the membrane. This makes it possible to automate the procedure of exploding the sample support membrane  4 . 
     The rupture of the sample support membrane  4  causes an opening in the dispersion chamber  11 , which gives rise to an entry of ambient air  13  or of any gas or fluid sucked in by the vacuum previously prevailing inside the dispersion chamber. 
     The entry of the fluid in the dispersion chamber  11  is accompanied by a complete suction of the sample of dry powder  5  inside the dispersion chamber  11 . Turbulence inherent in the filling process in the dispersion chamber  11  disperses the grains making up the sample of dry powder  5 . 
     After a length of time sufficient to permit the natural sedimentation of the sample of dry powder  5  in the dispersion chamber  11 , the treated surface  12 , on which a uniform single layer of material has been deposited with an entirely random distribution of the particles, is removed. 
     The device according to  FIG. 2  is differentiated from that in  FIG. 1  by a simplification of the construction of the dispersion chamber  11 , where the cylinder  10  and cover  6  are produced in one piece. The device also comprises a removable tubular capsule  16 . This can be introduced into the top orifice of the dispersion chamber  11 , in a sealed manner by virtue of its rim in the form of a collar  17  provided with a seal. The capsule is, at its top end, open to the surrounding environment. Its bottom end is provided with the membrane  4  that supports the sample to be dispersed. This bottom end projects inside the chamber. 
     This arrangement affords an easy placement of the sample in the capsule whilst the latter is not yet on the device. The capsule can easily be handled and replaced with another after dispersion of the sample that it contains. In addition, when the membrane ruptures the dispersion takes place at a distance from the cover  6 , which assists total dispersion of the powder. 
     In the example embodiment according to  FIG. 2 , a punch has been shown, driven in movement in a linear motion towards and away from the membrane, in a motorised fashion. In the present case the punch is a solenoid rod driven by an electromagnet  18 . 
     In the example illustrated in  FIG. 2  a feed tube  19  is provided for the surrounding fluid around the orifice where the capsule  16  is housed. This tube is, at its top end, open towards the outside. It also contains, in its tubular cavity, gas ionisation means  20  known per se and depicted schematically, for example an electromagnetic coil. When the membrane  4  ruptures, there is a suction of gas from the outside, through the feed tube  19 . This gas is then ionised by passing in front of the ionisation means  20 . The effect of this ionisation is to promote further the mutual repulsion of the particles of powder and therefore to obtain an even better random dispersion of the powder on the surface to be treated  12 . 
     Naturally the present invention is in no way limited to the embodiments described above and many modifications can be made thereto without departing from the scope of the accompanying claims.