Gas pycnometry

density and volume measurement technique......

1. Material Characterization Topic Gas pycnometry Nosheen Maryam Awan M13- 329 6 th Semester

2. Gas Pycnometry “ Pycnometry ” Is a G reek word “ puknos ” meana to measure the density and volume. It is Reliable and absolute method of measuring. Based on B oyle’s law (volume-pressure relationship). Regularly shaped, granular, powder, porous and non-porous samples can be used. Gas pycnometer s also called Helium pycnometers . A gas displacement method for measuring the volume . It can be performed in less than 20 minutes.

3. Gas Pycnometry Principle of operation:  valve a  opens and Inert gas flows into the sample chamber On seeing equilibrium is reached valve  b  opens and Gas flows into second chamber for volume measurement  4. Again e quilibrium is reached 5. Sample weight divided by Volume determines the density. 6 . Then valve   c is   openend and pressure vented off to open atmosphere.

4. Gas Pycnometry Kinds of pycnometers : Constant-volume pycnometer Variable-volume pycnometer Comparative pycnometer Constant-volume pycnometer Valves are opened, sample is placed into the sample chamber , and pycnometer is filled with gas. There is a absolute pressure transducer for measuring the initial gas pressure in the pycnometer ( P i ), while closing the valve “M”.

5. Gas Pycnometry 3 . T o separate the sample chamber from tank valve “Z” is closed and valve “M” is opened and some gas is sent into the tank. 4. Now v alve “M” is closed and gas pressure in the tank is measured ( P j ); and 5. On opening the v alve “Z ” gas will expand from the tank to the sample chamber (or vice versa ), when the gas expansion is completed, then final gas pressure is measured ( P f ). V s = V ◦c + V ◦t τ τ = P f − P j / P f − P i

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7. Gas Pycnometry Variable-volume pycnometer Now sample is placed in the sample chamber , and piston is placed at an initial position 2. Opening the valve, and fill the pycnometer with gas. 3. Close the valve and measure the initial gas pressure in the pycnometer ( P i) with the help of absolute pressure transducer. 4 . F or measuring the final pressure ( P f), t he piston is moved to another position. V s= V ◦c + V ◦p τ τ = - [ Pmin / Pmax – Pmin ]

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9. Gas Pycnometry Comparative pycnometer T he piston chamber and the volume controller are set such as their internal volume is minimum , the sample is placed in the chamber, open the valve, and fill the pycnometer with gas. Close the valve so that there is no difference in the gas pressures in the sample chamber and the tank. Pulled the piston is to a maximum position. And then adjust the volume controller, again to see that there is no difference in the gas pressures of sample chamber and the tank.

10. Gas Pycnometry 5. T he internal volume of the volume controller ( V r ) can be determined . V s = V c − ( V t / Vp ) V r

11. Gas Pycnometry Equipments available:-

12. Gas Pycnometry Advantages Simple method Relatively inexpensive instrument Fastness Less manpower necessary Adjustable gas flow rates Easy to read digital display Non-destructive technique

13. Gas Pycnometry Disadvantages In some cases, they are expensive. ( o n industrial scale) N ot suitable for expensive samples because large sample volumes are required Difficult to clean and dry Applications Used for characterizing catalysts, carbons, metal powders, soils, ceramics, pharmaceutical ingredients, petroleum coke, cement, cosmetics etc. Density of viscous materials can also be determined.

14. Gas Pycnometry Article:- Use of gas pycnometry for estimating the iron content in mineral samples. Hematite iron ore Helium gas pycnometry ( The helium gas pycnometer is typically consists of two chambers of known volumes that are connected by an expansion valve .   One chamber is used where sample is placed, and the other is used where the gas expansion happens.)   V ca   = S ample chamber volume,  V ce   = Expansion chamber volume, and V s   = Volume of the solid(sample).

15. Gas Pycnometry O nly hematite (Fe 2 O 3 ) and quartz (SiO 2 ) were assumed to be present in the sample, rest of components (especially Al 2 O 3 , CaO , K 2 O, and MgO ) represented less than 5% by weight of most of the studied samples . Thus, the mass of hematite ( m he ) plus the mass of quartz ( m si ) results in the solid mass of the sample ( m s ) as follows: mhe+msi = ms T he total volume of the solid sample is a volumetric fraction  ϕ

16. Gas Pycnometry Because the hematite mass fraction ( f he ), which is  f he  =  m he / m s  m= ρ∗ V so, specific gravities of the pure constituents ( ρ he  =  5.2 g/cm 3   and ρ si  = 2.65 g/cm 3 ) and the mean density of the sample obtained experimentally by helium gas pycnometry . Fe(%)=0.70⋅fh⋅ 100 The factor 0.70 shows the Fe fraction present in hematite ore.

17. Gas Pycnometry Sample ρ s  (g/cm 3 ) Fe 2 O 3  (%) – Pic Fe (%) – Pic Fe (%) – CA Absolute difference 1 4.1916 75.0 52.5 48.6 −3.9 2 3.6079 54.1 37.9 34.1 −3.8 3 3.9019 65.4 45.8 43.90 −1.9 4 3.5671 52.4 36.7 33.8 −2.9 5 4.2244 76.0 53.2 50.4 −2.8 6 4.3911 80.9 56.6 53.90 −2.7 7 3.0446 26.4 18.5 17.20 −1.3 8 2.9473 20.6 14.4 12.2 −2.2 9 3.0495 26.7 18.7 16.2 −2.5 10 2.7303 6.0 4.2 2.49 −1.7 Table 1. Comparison of the Fe contents estimated by pycnometry [Fe(%) – Pic] and those obtained by chemical analysis [Fe(%) – CA].

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