Well, these are two different processes. Sintering is a process of compacting material using both pressure and relatively high temperature which is usually bellow the melting temperature. Calcination is a thermal treatment of solids which aims to heat the material at very high temperature in the absence of air or oxygen (or at least under no gas flow). The purpose of calcination may also be to produce pure powders by eliminating the undesirable compositions.     

Sintering is the process by which a powder compacts transformed to a strong, dense material body upon heating. 

In an alternate definition given: " Sintering is understood to mean any changes in shape which a small particle or a cluster of particles of uniform composition undergoes when held together at high temperature"

American Society for metals has defined the sintering as " The bonding of adjacent surfaces of particles in a mass of metal powders or compact, by heating"

British Standard Association defined it as " A bonding by means of heat of particles in a mass of powder or compact"

The International Powder Metallurgy Glossary defines sintering as " A thermal treatment of a powder compact for the purpose of increasing strength, also the process which occur between surfaces of powder on heating causing adhesion"

Other definitions by  Powder Metallurgy Glossary as " Sintering: A process (operation) which increases the cohesion between the particles in a green or presintered compact or a powder, proceeding (performed) at elevated temperature, but not above the melting point of the main component.

The first three of these definitions refer to some kind of surface effect, the third and fourth definitions are divergent with respect to the mechanism of bonding; adhesion or cohesion.

Calcination is a heat treatment in order to decompose the materials especially carbonate to its oxide state, where the name originated, for example in my research i calcinate the CaCO3 , SrCO3 or BaCO3 at its decomposition temperature in order to obtain CaO, SrO or BaO thus the temperature it will determined by the decomposition temperature. on other hand Sintering object is to form the desired phase and the temperature is not fixed and normally will determined by phase diagrams and the stability region of the desired phase and normally is consist if more heat treatment time than of the calcination one.

As described by others calcinations and sintering both process are related to the heat treatment of ceramics with little difference

CALCINATION

After mixing or milling of oxides powders, ceramic bodies were calcined in granulated powder form. During the calcination step the solid state reaction takes place between the constituents resulting in the desired phase. Proper calcinations at the right temperature are therefore necessary to obtain the best electrical and mechanical properties.

Because calcinations of lead based, bismuth based materials at high temperature could lead to lead and bismuth loss, resulting in detrimental effects on the electrical properties.

SINTERING (DENSIFICATION)

After compaction the ceramics, was densified by sintering. The green bodies should have a certain minimum density before they can be sintered. The desired shape and minimum green density can be provided by various techniques like dry pressing, wet pressing, and cold isotatic pressing (CIP), slip casting, and extrusion.

In the sintering process, reactions between the un-reacted constituent phases (if any) take place at high temperatures.

Sintering commonly refers to a process involving the heat treatment of powder compacts at elevated temperatures, usually at T>0.5Tm K, in the temperature range where diffusional mass transport is appreciable. Successful sintering usually results in a dense polycrystalline solid.

Ceramic processing is based on the sintering of powder compacts rather than melting/solidification/cold working because (a) ceramics melt at high temperatures, (b) as solidified microstructures cannot be modified through additional plastic deformation and recrystallisation due to brittleness of ceramics, (c) the resulting coarse grains would act as fracture initiation sites,(d) low thermal conductivities of ceramics (

Calcination comes from cals, the latin  word for lime (related words: calcium, calcite). It designated the way to obtain quicklime. Since it corresponds to a chemical decomposition, as already pointed out by Dr. Rasekh, CaCO3 -> CaO + CO2, any process used to produce a new phase at high temperature (or simply to remove surface water - from hydrated groups - for example) is also designated a calcination process. In a very broad sense, calcination is a chemical process.

Sintering is instead a physical process: it decreases the free energy of the system (the surface energy). The neck between particles can be viewed as a 'negative' surface and they will therefore be filled by matter. This filling process is performed by the diffusion of species (either in the solid, liquid or vapor phases), the reason why sintering is only observed at high temperatures. In some (few) cases, the sintering process is not accompaigned by shrinkage (no densification), but in the majority of the cases, sintering is observed with densification. This gives the idea that sintering is a densification process, which is normally true, but it can also be observed in some systems without densification.

In many situations, one is performing a sintering process in which some chemical reactions are still present. In these cases, it will be better to say that one is performing a firing process (firing covers all the phenomena).

calcination is also used to mean a thermal treatment process in the absence or limited supply of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction.

Sintering is the process of compacting and forming a solid mass of material by heat and/or pressure without melting it to the point of liquefaction.

calcination: is to heat a substance to a high temperature but below the melting or fusing point, causing loss of moisture, reduction or oxidation, and the decomposition of carbonates and other compounds.

Sintering : is thermal treatment of fine-grained material at a temperature below the melting point of the main constituent, for the purpose of increasing its grain size and strength by bonding together the particles.

Calcination is a heat treatment in order to decompose the materials and to achieve the desired phase through heat treatment above the decompose temperature of at least one of the reactant and below their melting point.

Sintering (post-calcination process) is performed at a temperature below the melting point of the desired phase in order to improve crystal quality by minimizing defects, enhance grain growth (reducing the total area of grain boundary) and to achieve maximum possible density.  

Dear Prof. Nabeel A. Bakr

السلام عليكم ورحمة الله وبركاته

peace be upon you

Calcination is one of the most common processes used in the ceramics industry among many others. The most common application for Calcining is the decomposition of calcium carbonate to calcium oxide and carbon dioxide, in order to create cement. The product of calcination is usually referred to as “calcine,” regardless of the actual minerals undergoing thermal treatment. Calcination is carried out in furnaces or reactors (sometimes referred to as kilns or calciners) of various designs including many of the furnaces offered by CM such as kilns, box furnaces, and more sophisticated production batch furnaces like our CM 100 series.

Key to a proper calcining process is the absence or limited supply of air or oxygen applied to  and other solid materials to bring about a thermal decomposition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials.

Calcining is often confused with Sintering and Annealing process and indeed there is some conceptual overlap in these.  Calcining is generally used more broadly than simply removing CO2 from carbonates. It It involves decomposition of any suitable salt to form an oxide, including carbonates, nitrates, hydroxides, sulfates, and others.

Sintering of traditional ceramics, including pottery, tile, sanitary ware, dinnerware, etc., takes place in the presence of a viscous liquid, and it typically includes chemical changes as well. For instance, the clay in the original material decomposes.

Annealing of metals is used to reduce the strength and hardness and increase the ductility. It can take place in air or in neutral or reducing atmospheres, but usually is done in air. Annealing of glass is used to reduce internal stresses arising from molding and other processes. It always is done in air.

Examples of calcination processes include the following:

decomposition of carbonate minerals, as in the calcination of limestoneto drive off carbon dioxide;

decomposition of hydrated minerals, as in the calcination of bauxiteand gypsum, to remove crystalline water as water vapor;

decomposition of volatile matter contained in raw petroleum coke;

heat treatment to effect phase transformations, as in conversion of anataseto rutile or devitrification of glass materials

removal of ammoniumions in the synthesis of zeolites.

https://cmfurnaces.com/annealing-sintering-and-calcining-processes/

Good luck

Both 'Sintering' and 'Calcination' are heat treatment used in metallurgy . Sintering is shaping metals/Polyimide powder into compact in dies and its assembly at room temperature without pressure followed by uniform heat treatment . calcination is used in recovery of metals from its ores/minerals , roasting/ heating is conducted in the furnace in the absence of oxygen with decomposition

calcination is a heat treatment at a temperature where all phase transformations are carried out. on the other hand, sintering is a thermal treatment of a product at a defined temperature to obtain a material with the desired characteristics

During the sintering process, the atoms in the solid materials diffuse across the grain boundaries of the particles, fusing the particles together without changing their properties and creating one solid piece.

Calcination normally referred to the heat treatment to make the sample more pure. More precisely, other substance is removed/burn during calcination that leads to the desired phase of materials without impurity.

sintering is a heating process up to a given temperature. this temperature depends on the transformation of a liquid phase or the bond of grains of a material. it is about 2/3 of the melting temperature. for adequate shrinkage it would be necessary to carry out dilatometry tests: ATD, ATG DSC. The calcination is to bring the material to the release temperature of undesirable substances such as CO2

Excellent answers. However, I would like to insist on some aspects:

1. In relation to the sintering process, if the original material is constituted by two or more components, the densification of the mixture is achieved thanks to the adhesion of the particles of one component with those of another and the intra-diffusion that has place among the constituent elements, especially in the case of crystals, which is also highly favored by the increase in temperature to values ​​close to the lowest of the melting points of the different constituents. For example, during the manufacture, by means of powder metallurgy techniques, of an aluminum matrix composite reinforced with bagasse ash from sugarcane, the aluminum powder and the ash are mixed and compacted. To densify the material, propitiate hardness, etc., the composite is subjected to a sintering process at a temperature slightly lower than the melting point of aluminum, in this case in an inert atmosphere. The subsequent properties of the composite depend among other factors on the speed and time of heating, but above all on the affinity of the constituents materials, their ability to adhere to one another and the intra-granular diffusion between the different components that It takes place, which as it was said before is highly favored by the temperature, and that consists in the penetration of the small particles of one of the elements in the structure of the other.

2. With regard to the calcination process, this can be understood as the burning of the material up to a certain temperature, after which some or some components will no longer be present, since they were volatilized, and others have been transformed. Continuing with the example of the aluminum matrix composite with additions of bagasse ash from sugarcane as reinforcement material. During the production of the ash from the burning of the sugarcane bagasse up to 800 °C, calcite and crystalline quartz are obtained, with a subsequent heating of the ash until 1 000 °C calcium oxide and cristobalite are obtained, evidently between 800 and 1000 °C there has been a phase change. It should be noted that the final products of the calcination not only depend on the temperature and time of calcination, but are also strongly determined by the speed of the cooling process. Precisely these processes of obtaining crystalline or amorphous phases, are strongly linked with the speed of the cooling process.

Both the calcination and sintering are heat treatments. The heating temperature is usually kept 2.3rd of the melting point of the constituents. In that sense, they are similar but they differ according to their purpose or goal. Hence, calcination may be defined as the heat treatment process to achieve the desired phase through decomposing the material by heating above the decomposing temperature of at least one of the reactants but definitely below their melting points as said above.

The main purpose of calcination is: (i) to remove a volatile substance, (ii) to cause loss of moistures, reduction or oxidation, (iii) to create a new phase, and (iv) to increase particle size or reduce the surface area of the particles.

Sintering is also heat treatment and simply defined as the process of densification. The purpose of sintering are: (i) to improve crystal quality by minimizing defects, (ii) To reduce the total area of grain boundary by increasing the grain growth, (iii) to increase the strength by removing voids in the material, and (iv) to increase the cohesion or adhesion. However, both the calcination and sintering temperatures are usually kept 2/3rd of their melting points

Both the process, consist of transformation of minerals / phase changes in minerals in original rock /ores . In general sintering has been done on at higher temperature above 1200 deg and calcination is at quite lower temperature. 800 deg. In refractory, sintering term is general used (refractory process required higher temperature (1600-1800 deg)

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