Method of making a protective material and articles made therefrom

Abstract

A method of preparing a protective material is shown. In one aspect the method includes the steps of providing a powder mixture of solid particles having a size in the range of colloidal up to 100 μm. The particles have a ceramic or mineral composition. Then a liquid is provided to form an external phase of a suspension when mixed with the powder, to yield a solids volume concentrating greater then 0.5. The solid powder liquid mixture forms a thixotropic-dilatant liquid material. The rheological curve of the TDLM is adjusted to suit the application, resulting in thixotropic properties at low strain rates and dilatant properties at higher strain rates to yield a material that solidifies upon impact. The rheological curve is adjusted by one or more of additives, material composition and gravity mixing. In another aspect protective articles made from TDLM are provided.

We claim:  
     
         1 . A method of preparing a protective material comprising the steps of: 
 providing a powder mixture of solid particles having a particle size in the range of colloidal size up to 100 μm, said solid particles being of ceramic and/or mineral composition;    providing a liquid to form an external phase of a suspension when mixed with said powder with a solids volume concentration of greater than 0.5;    mixing said powder and said liquid together to form a thixotropic-dilatant liquid material TDLM;    adjusting the rheological curve of said material; and    producing a TDLM having a dependence of viscosity on strain rate which is thixotropic or constant at lower strain rates and dilatant at higher strain rates wherein said TDLM solidifies on impact.    
     
     
         2 . A method as claimed in  claim 1  wherein said solid particles in the powder mixture are selected from the group of fused silica, silica, quartz, alumina, vermiculate, mica or other crystalline and/or amorphous materials.  
     
     
         3 . A method as claimed in  claim 1  further including adding admixtures of alkaline and/or acid substances, or industrial surfactants.  
     
     
         4 . A method as claimed in  claim 1  wherein said step of providing said powder further comprises wet grinding said solid particles in a suspension.  
     
     
         5 . A method as claimed in  claim 1  wherein said step of wet grinding the solid particles results in a particle size distribution in the range from colloidal to 100 μm with a solid particles volume concentration of C V >0.80 and colloidal fractions content of C V >0.005, all having a specific surface of >0.5 m 2 /g (larger than 0.5 m 2 /g).  
     
     
         6 . A method as claimed in  claim 4  further including the step of drying said suspension.  
     
     
         7 . A method as claimed in  claim 1  wherein said step of mixing said liquid and said powder comprises gravitational mixing.  
     
     
         8 . A method as claimed in  claim 1  further including adding organic fluids to permit applications of said TDLM to be used at temperatures below 0° C.  
     
     
         9 . A method as claimed in  claim 7  wherein said step of gravitational mixing/treatment comprises slowly rotating a volume of said material in a rotating volume with rotational velocity of 1-60 revolutions/min for at least 12 hours.  
     
     
         10 . A method as claimed in  claim 1  wherein said step of adjusting the rheological curve further comprises adjusting the solids volume concentration of said material by adjusting the proportions of said powder or said liquid in said material.  
     
     
         11 . A method as claimed in  claim 1  wherein said step of adjusting the Theological curve further comprises extending a period of gravitational mixing/treatment by at least 24 hours.  
     
     
         12 . An armour material comprising: 
 at least two layers including an outer layer and an inner layer;    the outer layer consisting of a thixotropic-dilatant liquid material having a first rheological curve;    the inner layer consisting of a thixotropic-dilatant liquid material having a second Theological curve;    wherein the first rheological curve has a critical shear stress at a higher shear rate than the second curve.    
     
     
         13 . An armour material comprising: 
 a layer of thixotropic-dilatant liquid material; and    a projectile resistant material that is not rigidly fixed, in contact with said layer, to disperse and redistribute shear forces caused by a projectile across an area within said layer.    
     
     
         14 . An armour material as claimed in claims  12  or  13  further including at least one containment structure for containing said layers of thixotropic-dilatant liquid material therein.  
     
     
         15 . An armour material as claimed in claims  12  or  13  wherein the layers containing TDLM are hermetically enclosed to prevent liquid evaporation and changes of rheological properties.  
     
     
         16 . An armour material as claimed in  claim 14  further including a valve on said containment structure for controlled pressure release of gasses arising in the containment structure.  
     
     
         17 . An armour material as claimed in  claim 12  comprising cells with rigid walls containing the said TDLM structures wherein side walls of cells are made of hard and strong materials and are rigidly fixed to increase armour protection.  
     
     
         18 . An armour material as claimed in  claim 12  wherein the front wall has a coating with a coefficient of heat emission <0.3 (e.g. Ni, etc.) to reflect heat radiation.  
     
     
         19 . An armour material as claimed in  claim 12  wherein some layers are made of metal and carbon containing materials to improve protection from ioning radiation.  
     
     
         20 . A method for long term storage of the protective materials as claimed in claims  12  or  13  comprising slowly rotating or otherwise gravitational stirring said material while said materials are being tested.