5.1 Objective:

The objective of this experiment is to compare the compaction properties (e.ge densification, green density and %age porosity) of BaCO₃ +MgO system and sintered properties (e.g. densification sintered density and %age porosity) of different compositions.

5.2 Introduction:

In liquid phase sintering a mixture of two or more powders is sintered at a temperature below the melting point of the high-melting constituent but above that of the low-melting constituent. In liquid phase sintering, densification takes place under the effect of surface tension (low surface tension, better wetting properties). Particle is rapidly drawn together and air is expelled. Resultant liquid phase can be disappeared by diffusion or by peritectic reaction.

 Liquid phase sintering is characterized by a rapid change in properties and densification, removal of porosity quickly completed. Materials produced by the process of liquid phase sintering are referred to as the high density (low porosity) materials. It must not be thought that all liquid phase sintered materials are dense, as porosity may be extremely difficult to remove and diffusion may be slow in complex alloys. This is particularly so if coarse sized pores are present in the as pressed state and the liquid content at temperature is of a minor proportion. In this case the effect of surface tension is reduced and porosity will remain after sintering is complete. Liquid phase sintering applies to pre-mixed powders. If the constituent are mixed properly, the behavior on sintering depend on the wetting properties of the two metals.

Mechanism of liquid phase sintering, it can be explained by three overlapping action.

(1)   The liquid phase allows rearrangement and rapid shrinkage of the solid materials.

(2)    Dissolution and re-precipitation occurs with densification.

(3)    Coalescence occurs when the liquid phase disappears.

5.3 Apparatus Used:

Figure 5.1: Hydraulic press (Carver)

1. Powder of BaCO₃ and MgO

2. Glass beakers of 100ml volume                                                         

3. Solvent binder

4. Heating furnace with max. Temperature 1200◦C

5.4 Procedure:

 Prepare 5 sample of BaCO₃+MgO powder of 1.5g each,

(i)                 MgO =1.3g +BaCO₃=0.2g

(ii)                MgO=1.1g +BaCO₃=0.4g   

(iii)             MgO=0.9g  +BaCO₃ =0.6g                               

(iv)             And powder mixture (ii) are divided into two subsample S₁ and S₂

(v)               And powder mixture (iii) are divided into two subsample S₃  and S₄

Calculate the theoretical volume of MgO and BaCO₃ powders by using the formula of Volume (V) πr²h =mass/density. Density of BaCO₃=4.2g/cm³, MgO=3.6g/cm³.Calculate the theoretical densities of each (i), (ii), and  (iii) powder mixtures and also calculate the theoretical density of (ii) subsample of S₁ and S₂ and (iii) subsample of S₁ and S_2. Add a amount of 4-5 drops of solvent (ethanol) into each powder mixtures to aid in compaction. Mix thoroughly with the help of stainless steel rod so that sample powders should be completely mixed.

Cold compaction:

Clean all part of die with the help of ethanol. Lubricate the inner walls of die orifice with 2% ethanol. Use 10,000-15,000 psi load for all samples. Apply pressure and maintain for 10 sec. Remove the pellets from die and reweight the pellets. Measure the green densities of these pellets. Calculate densification of these pellets (densification=green density/theoretical density). Calculate the %age porosity of green compacts.  (%age porosity=1-green density/actual density). Compare the green density, densification, and %age of porosity of MgO+BaCO₃ samples.

 Liquid phase sintering:

Place the sample pellets into the furnace. Select sintering cycle in such a way that first hold at 150◦c for 10 min, second hold at 450◦c for 15 min and third hold at 850◦c for 25 min and finally furnace cooled. And draw a graph between temperature and time. Take out the sintered pellets from the furnace with the help of tongs. Calculate and compare the sintered densities, %age porosity and densification of sintered pellets

 

 5.5 Compaction:

Figure 5.1:  Muffle furnace (Nebertherm)

  Observation and calculation:                                    

          Load (10,000-15,000)

         Diameter of die =1.3cm                                              

        Area of die =1.32cm²                                                                        

                                                                                                                                                                                                                                                                                        

Pellets	Mass of pellets    G		Pressure   Psi		Dia of pellets   Cm	Height of pellets    Cm	Vol.of pellets     cm3	Green density    g/cm3	Theoretical density     g/cm3		%age of porosity	Densification
i	1.5		10,000-15,000		1.3	0.759	1.00740	1.48	3.679		59.77	0.4023
ii S1	0.7		10,000-15,000		1.3	0.315	o.418	1.67	3.761		55.59	0.4440
iii S2	0.897		10,000-15,000		1.3	0.356	0.4725	1.693	3.761		54.98	0.4501
iv S3	0.9	10,000-15,000		1.3		0.329	0.4366	2.06	3.847	46.45		0.5355
V S4	0.6	10,000 -15,000				0.214	0.2840	2.418	3.846	37.12		0.6287

5.6 Liquid phase sintering:

Pellet	Mass of pellet      G	Pressure      Psi	Dia of pellets   Cm	Height of pellets    Cm	Vol.of pellets	Sintered density    g/cm3		Theoretical density     g/cm3		%age of porosity	Densification
i	1.164g	NIL	1.3	0.795	1.05	1.109		3.685		69.90	0.3014
ii s1	0.538	NIL	1.264	0.349	0.4384	1.226		3.761		67.40	0.3259
iii s2	0.604	NIL	1.286	0.357	0.4636	1.304		3.761		65.32	0.3463
Iv S3	0.679	NIL	1.283	0.33	0.4356		1.55		3.847	59.70	0.4052
V S4	0.5078	NIL	1.284	0.261	1.157		0.4385		3.847	88.61	0.1140

5.7 Result:

 The compaction of BaCO₃-MgOsystem and find out the green density, theoretical density, %age porosity and densification. Sintering of Liquid phase sintering of BaCO₃-MgO System and find out the all samples of sintered density, theoretical density, %age of porosity and densification.