Hydrostatic powder pressing

Porosimetry The determination of the open pore volume in a material. Example Mercury porosimetry, where mercury is hydrostatically forced into the pores and the weight change is measured. Porosimetry can be used in the specification of sputtering targets formed by powder pressing processes. 

Many of the difficulties encountered in dry-pressing can be avoided by some form of isostatic-pressing. Ideally, this simply involves the application of hydrostatic pressure to powder in a flexible container. Powder movement is minimal and side-walls are absent. In practice shapes are often produced by the use of rigid mandrels as illustrated in Fig. 3.4. Powder is weighed into a rubber bag with a rigid mouth and a mandrel is then inserted and makes a seal with the mouth. Pressures of 20-280 MPa ( 200-2800 atm) can be applied through either liquid or gas media. The pressure must be released slowly since the air originally... 

Isostatic compaction Powder encased in flexible mold is pressed equally from all directions by pressure transmitted to the mold by a liquid medium. Isostatic molding, isostatic pressing Hydrostatic molding chambers, automatic isostatic presses... 

Cold Isostatic Pressing. In isostatic pressing, the powder is filled into flexible molds made of rubber or elastomers and subjected to hydrostatic pressure. The pressure is commonly in the range of 200 to 400 MPa. As a result of the uniform pressure, a much higher uniformity in density is achieved. Isostatic pressing has gained much... 

Isostatic pressing involves the application of hydrostatic pressure to a powder in a flexible container. The advantage of applying pressure in all directions is that there is more uniform compaction of the powder and more complex shapes can be produced than with uniaxial pressing. Isostatic pressing can be performed either with or without applied heat. 

There are many variations on using the cold isostatic press (CIP) here we just emphasize some basic themes. Figure 23.3 illustrates the so-called wet-bag CIP process. Powder is weighed into a rubber bag and a metal mandrel is inserted that makes a seal with the mouth of the rubber bag. The sealed bag is placed inside a high-pressure chamber that is filled with a fluid (normally a soluble oil/ water mixture) and is hydrostatically pressed. The pressures used can vary from about 20 MPa up to IGPa depending upon the press and the application. For production units the pressure is usually <400 MPa. Once pressing is complete, the pressure is released slowly, the mold is removed from the pressure chamber, and the pressed component is removed from the mold. 

The transformation process of p phase can be accelerated under ciystals deformation and pressure [140], For example the partial transformation of P to y can be caused at room temperature through crushing of sample in hydraulic press. It accelerates probably nuclei formation of this phase as the result of crystals shearing. From the other side when the powdered sample of p phase is exposed to the hydrostatic pressure of 900 MPa no transformation is observed, becanse y has lower... 

Isostatic pressing is a compaction technique through the application of a uniform hydrostatic pressure to the powder confined in a flexible rubber container. There are two modes of isostatic pressing (i) wet-bag pressing and (ii) dry-bag pressing. In wet-bag isostatic pressing, the powder is filled in a flexible rubber mold, which is then submerged into a pressure vessel filled with oil as fluid, as shown... 

Next, the green body is compacted at high temperature, whereupon the ceramic powder particles, previously only loosely bound mechanically or by binders, bind chemically. Standard processes for this are sintering, hot pressing, and hot isostatic pressing (hip) [126]. While sintering is done without external load, the other processes superimpose uniaxial or hydrostatic stresses. 

High-purity BP powders are prepared by hydroisostatic pressing. Boron and red phosphor were mixed in a fused silica tube evacuated to less than 10 torr and sealed. The ampule was hydrostatically pressed to 1300°C under pressure of 1.8 ton/cm for 2 h. The BP powders thus prepared are far purer than commercial ones. The specimens were sintered at 1300°C at a hydrostatic pressure of 2 ton/cm for 1 h (28). 

Specified quantities of copper powder have been pressed from both sides in the die block with feeding chamber of 30.5 mm diameter at 50 MPa load without any lubricant. In this way samples were obtained of dimensions 030.5x3.5 mm and porosity 30%. For futher compaction already obtained compacts have been placed in the elastic matrices made of natural rubber and placed in the pressure chamber filled with the mixture of rape seed oil with methyl alcohol. Hydrostatic densification was carried out at 315 MPa through 15 minutes. Sintering was carried out at the atmosphere of dissociated ammonia NH at temperature 1223 K through 1 hour. In this way a set of 40 specimens of dimensions 030x3 was prepared. Specimens from this first series featured porosity within 9 - 15% range. 

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