This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Properties of Refractories”.
1. Which of the following properties is not associated with refractory metals?
a) High fusion temperature
b) High heat resistance
c) Good Corrosion resistance
d) High thermal coefficient of expansion
Explanation: Refractories are heat resistant materials capable of withstanding high temperatures of up to 2150oC. They have developed good heat, corrosion, and abrasion resistance. They also possess a high fusion temperature. However, they have a low thermal coefficient of expansion.
2. Firebrick is an important raw material of refractory metals, which is made from ______
Explanation: Refractories are ceramic materials capable of withstanding high temperatures. They are formed by firebrick obtained from fireclay, along with other materials. However, non-clay refractories are being developed for specific requirements.
3. What kind of refractory can bauxite be grouped as?
a) Acid refractory
b) Basic refractory
c) Neutral refractory
d) Silica refractory
Explanation: Basic refractories are those which are rich in periclase or magnesia, sometimes with calcium, chromium, and other irons. The presence of silica in these may pose a threat to their performance. Magnesia and bauxite are examples of basic refractories.
4. Silica refractories are also known as ______ refractories.
Explanation: Silica containing refractories are referred to as silica or acid refractories. They possess a high-temperature capacity to withstand loads. The common types of acid refractories are silica, aluminum silica, alumina, and silimanite.
5. What is the fusion temperature of aluminum silica?
Explanation: Aluminum silica containing 46% Al2O3 and 54% SiO2 has an approximate fusion temperature of 1780oC. This refractory is a common type of acid refractory ceramic material. Silimanate and alumina have an approximate fusion temperature of 1900oC and 2050oC respectively.
6. Which of the following is an example of a neutral refractory?
Explanation: Chromite, along with graphite, is a common neutral refractory material. Chromite has an approximate fusion temperature of 2180oC while that of graphite is 3000oC. Dolomite and magnesia are basic refractories, whereas silica is an acid refractory.
7. What is the fusion temperature of Magnesia?
Explanation: Magnesia is a type of basic refractory material which has an approximate fusion temperature of 2800oC. The fusion temperature for silica is 1700oC while that for chromite is 2180oC. Basic refractories find applications in open hearth furnaces.
8. How much of alumina in weight percent is added to silica refractories?
a) 0.2 – 1.0
b) 1.1 – 1.5
c) 1.6 – 1.8
d) > 2.0
Explanation: Under the presence of alumina, silica refractories show a negative effect. Therefore they are limited to 0.2 – 1.0 wt %. These refractories are generally resistant to silica-rich slags.
9. Mullite is an example of ______ refractory.
Explanation: Special refractories are those materials having high purity and low porosity. Examples of special refractories are beryllia, zirconia, and mullite. These special refractories are comparatively expensive compared to the other types.
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