This set of Casting Questions and Answers for Campus interviews focuses on “Fire Clays, Illite and Kaolinite”.
1. Which of the following materials presents in clay which imparts plasticity in it?
Explanation: Clay generally contains phyllosilicates which are mainly responsible for imparting plasticity in the clay material. It can also include other materials which impart plasticity and harden-ability when the clay is dried or fired. Combined phases in clay material can also contain materials that do not impart any plasticity.
2. Which of the following components of soil are acts as chemical sponges in the soil?
a) Clay minerals
Explanation: Clay minerals are quite stable and are an important part of the soil. Clay minerals are also called as chemical sponges which basically hold water content and dissolved nutrients from other mineral particles. This results due to the presence of unstable electric charges on the surface of clay particles, in which opposite charges attract to each other.
3. The attraction of clay minerals with water is a surface phenomenon which is called absorption.
Explanation: Clay minerals have the ability to attract water particles and this attraction is a surface phenomenon which is called as adsorption, which is completely different from absorption process because the ions and water molecules do not get inside the clay particles and they remained to adhere to the clay grains, that’s why the process is called as adsorption.
4. Kaolinite clay mineral generally adsorbs fewer ions than that of other clay minerals.
Explanation: Kaolinite clay mineral is a weathering product of feldspars and it commonly has white and powdery appearance. Kaolinite name is derived from a region named kaolin in china using the local clay mineral. It is extensively used in ceramics industries because it is electrically balanced but adsorbs fewer ions than that of other clay minerals.
5. The layer structure of kaolinite mineral totally consists of three tetrahedral silicate sheets.
Explanation: The kaolinite minerals normally include kaolinite, nacrite and halloysite which are the most common but important clay minerals in nature that are widely used in industries. They consist one to one layered structure, in which each layer include one tetrahedral silicate sheet and one octahedral silicate sheet.
6. Which of the following members of clay minerals is formed by the decompositions of micas?
Explanation: Vermiculite is a very important and essential member of clay minerals which is normally formed by the decompositions of micas and occurs as completely large crystals of mica like appearance. It has a layer structure which basically consists of water particles and exchangeable cations which are mainly magnesium ions.
7. Which of the following types of clay mineral includes potassium in the layer structure?
Explanation: Illite is a clay mineral which has potassium in the interlayer structure. The size and coordination number of potassium are like that it fits tightly in the hexagonal ring of oxygen of the tetrahedral sheets. This makes the structure a strong interlocking ionic bond which packs the individual layers together and restricts the water particles from immersing the interlayer site.
8. Palygorskite and sepiolite clay minerals generally have similar fibrous structures.
Explanation: Palygorskite and sepiolite clay minerals have similar fibrous structures or morphologies, but palygorskite shows more structural variety. Both the clay minerals are magnesium silicates, but palygorskite has less magnesium and more aluminium than sepiolite. Structurally, both the clay minerals include blocks and ribbon like sheets extending in a specific direction.
9. Ball clay is a type of clay which has zero percent moisture or water content in it.
Explanation: Ball clay normally has water content nearly about 28 percent. To decrease moisture content, they are stored in drying sheds. Then the clay is shredded into small pieces which are further dried by the use of hammer mill. Extracted scrap material from the hammer mill is blended with water to form a slurry mixture for further use.
10. Repeated freezing and melting of fire clay can improve the plasticity of the clay material.
Explanation: First the fire clay is taken to the processing plant and then weathered for a long period of time, depending on the type of fire clay. Freezing and melting break the clay material and results in improved plasticity. Then the clay material is crushed and dried in mechanical dryers to remove the moisture content. Mostly, the rotary dryers fired with natural gas are used for drying the fire clay.
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