**1. Introduction**

Many metals are widely used in construction and other industrial fields. Corrosion problems, which limit the long-term use of metals such as iron, zinc, and their alloys, are one of the greatest challenges in the metals industry. Carbon steel (C-steel) is a common steel alloy that is used extensively in a variety of applications, such as installation, transportation, mining, and construction [1–7]. C-steel has a carbon content ranging from 0.12% to 2.0% (*w*/*w*), which increases the strength and hardness of steel objects, as well as their corrosion resistance [1–7]. Metal corrosion protection is the most difficult problem that many engineers and chemists face [1–4]. Many studies have been conducted to protect steel bodies and other metal alloys from damage caused by aggressive corrosion [1–7]. Organic coatings are one of many coating applications used to protect various steel bodies and

**Citation:** Howyan, N.A.; Al Juhaiman, L.A.; Mekhamer, W.K.; Altilasi, H.H. Comparative Study of Protection Efficiency of C-Steel Using Polystyrene Clay Nanocomposite Coating Prepared from Commercial Indian Clay and Local Khulays Clay. *Metals* **2023**, *13*, 879. https://doi.org/ 10.3390/met13050879

Academic Editors: Changdong Gu and Renato Altobelli Antunes

Received: 15 February 2023 Revised: 12 April 2023 Accepted: 18 April 2023 Published: 2 May 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

<sup>1</sup> Chemistry Department, King Saud University, Riyadh 145111, Saudi Arabia

other metallic substrates from corrosion due to their good barrier properties. Recently, scientists have attempted to prepare nanocomposite materials by interacting polymer coating materials with nanosized particles (e.g., metallic, organic, and inorganic nanofillers, and many nanoscale additives) that are added to improve the barrier, mechanical, and thermal properties of these polymer coatings [7–12]. Some filler nanoparticles are SiO2, TiO2, ZrO2, Fe2O3, Al2O3 [10,11], and clay derivatives (e.g., organic and inorganic clay) [11–19].

A nanocomposite is described as a mixture of two or more different materials, at least one of which has nanostructural dimensions between 1 and 100 nm. Clay and polymer or monomer molecules can be combined to create nanocomposite materials, or they can be made via a variety of other methods [20–23]. According to the degree of silicatelayer separation and the strength of the interfacial tension between the polymer matrix and clay layers, polymer organoclay nanocomposites are divided into three categories: intercalated nanocomposites, exfoliated nanocomposites, and conventional composites [21]. Due to their superior properties as compared with pure polymers, polymer organoclay nanocomposites (PCNs) have been used in several applications in numerous fields. These characteristics include flame resistance, thermal stability, barrier properties, mechanical properties, chemical resistance, and optical qualities [13,14]. Additionally, many studies have examined the coating characteristics of polymers and assessed the impact of adding clay to various polymers and epoxy coating [13,16–19,23,24].

Montmorillonite clay (MMT), which belongs to the Smectite group, is used for intercalation or exfoliation with the polymer matrix in PCN application [12,21]. MMT is a very soft layered silicate with the following chemical formula:
