Question

Read the following sentences related to glass packaging materials.
A. Breaking point of silicate glass is 70 MPa.
B. The purpose of including cullet in glass bottle manufacture is for decolorizing.
C. Annealing is the temperature at which stresses in the glass are relieved in a few minutes.
D. The three main colors of glass used to produce containers are flint or clear, amber or brown, and green.
E. Thermal stresses can be reduced by minimizing the temperature gradient from the hot to the cold side, decreasing the glass thickness, and avoiding sharp corners.
Choose the correct answer from the options given below:

• A. A and B only
• B. C and D only
• C. A, C, D and E only
• D. B and E only

Hint:

Cullet is added to glass batches solely to lower the melting temperature and reduce energy consumption. Knowing that Statement B is false allows you to easily eliminate options A and D.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Glass is a silicate-based inorganic, non-crystalline solid widely used in food packaging due to its inertness, barrier properties, and reusability.
Understanding its mechanical properties, manufacturing additives, and thermal stress behaviors is essential to evaluating glass as a packaging material.

Step 2: Detailed Explanation:
Let us analyze each statement:
- Statement A: Pristine silicate glass has a high theoretical strength, but practical silicate glass has surface microcracks that reduce its practical tensile breaking strength to around 50 to 70 MPa. (True)
- Statement B: Cullet is crushed recycled glass added to the glass furnace.
Its primary purpose is to lower the melting temperature of the batch, which saves energy and extends furnace life, not to act as a decolorizer. Decolorization is achieved by adding trace minerals like selenium or cobalt. (False)
- Statement C: Annealing is the process of controlled heating and cooling of glass to relieve internal mechanical stresses formed during molding, typically occurring over a few minutes in a lehr. (True)
- Statement D: The three primary commercial colors of glass containers are flint (clear), amber (brown, which provides UV protection), and green. (True)
- Statement E: Thermal shock and stress are minimized by keeping glass walls thin and uniform, avoiding sharp corners (which act as stress concentrators), and reducing temperature gradients across the glass wall. (True)
Thus, statements A, C, D, and E are correct, while B is incorrect.

Step 3: Final Answer
The correct option is (C).