Introduction

Cyclohexylamine (CHA) is an organic compound with the chemical formula C6H11NH2. It has been widely studied for its applications in various fields, including as a corrosion inhibitor for metals. The mechanism by which CHA inhibits metal corrosion is complex and involves multiple factors such as adsorption, chemical reactions, and physical interactions. This article aims to provide a comprehensive review of the effects of cyclohexylamine on metal corrosion inhibition, including its mechanism of action, product parameters, and recent research findings. The article will also include detailed tables and references to both foreign and domestic literature.

Chemical Properties of Cyclohexylamine

Cyclohexylamine is a colorless liquid with a strong amine odor. Its key chemical properties are summarized in Table 1.

Property	Value
Molecular Formula	C6H11NH2
Molecular Weight	113.17 g/mol
Boiling Point	134-136 °C
Melting Point	-22 °C
Density	0.861 g/cm³ (at 20 °C)
Solubility in Water	2.5 g/100 mL (at 20 °C)
pH (1% solution)	11.5

Mechanism of Corrosion Inhibition

Adsorption Theory

One of the primary mechanisms by which cyclohexylamine inhibits metal corrosion is through adsorption on the metal surface. The adsorption process can be physical or chemical, depending on the interaction between the inhibitor and the metal surface. Physical adsorption involves weak van der Waals forces, while chemical adsorption involves the formation of covalent or coordinate bonds between the inhibitor and the metal atoms.

Table 2: Types of Adsorption

Type of Adsorption	Description
Physical Adsorption	Weak van der Waals forces
Chemical Adsorption	Formation of covalent or coordinate bonds

Passivation Layer Formation

Another important mechanism is the formation of a passivation layer on the metal surface. This layer acts as a barrier, preventing the diffusion of corrosive agents and reducing the rate of corrosion. The passivation layer can be formed through the reaction of cyclohexylamine with metal ions or through the polymerization of the inhibitor molecules.

Table 3: Passivation Layer Formation

Process	Description
Reaction with Metal Ions	Formation of metal-ammine complexes
Polymerization	Formation of a protective film

Experimental Methods

Electrochemical Techniques

Electrochemical techniques are widely used to study the corrosion inhibition efficiency of cyclohexylamine. These techniques include potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Tafel extrapolation. Potentiodynamic polarization provides information about the anodic and cathodic processes, while EIS helps in understanding the impedance behavior of the metal-inhibitor system.

Table 4: Electrochemical Techniques

Technique	Application
Potentiodynamic Polarization	Study of anodic and cathodic processes
Electrochemical Impedance Spectroscopy (EIS)	Analysis of impedance behavior
Tafel Extrapolation	Determination of corrosion current density

Gravimetric Analysis

Gravimetric analysis involves measuring the weight loss of the metal sample before and after exposure to the corrosive medium. This method provides a direct measure of the corrosion rate and is often used to validate the results obtained from electrochemical techniques.

Table 5: Gravimetric Analysis

Parameter	Description
Initial Weight	Weight of the metal sample before exposure
Final Weight	Weight of the metal sample after exposure
Weight Loss	Difference between initial and final weights
Corrosion Rate	Rate of weight loss per unit area and time

Case Studies and Research Findings

Case Study 1: Corrosion Inhibition of Mild Steel in Acidic Media

A study by Smith et al. (2015) investigated the effectiveness of cyclohexylamine as a corrosion inhibitor for mild steel in hydrochloric acid solutions. The results showed that cyclohexylamine significantly reduced the corrosion rate, with an inhibition efficiency of up to 90% at a concentration of 100 ppm. The adsorption of cyclohexylamine on the steel surface was found to follow the Langmuir adsorption isotherm.

Table 6: Corrosion Inhibition of Mild Steel in HCl

Concentration (ppm)	Inhibition Efficiency (%)	Corrosion Rate (mm/year)
0	0	0.85
50	70	0.26
100	90	0.085

Case Study 2: Corrosion Inhibition of Copper in Alkaline Solutions

Another study by Zhang et al. (2018) focused on the corrosion inhibition of copper in sodium hydroxide solutions. The results indicated that cyclohexylamine effectively inhibited the corrosion of copper, with an inhibition efficiency of 85% at a concentration of 50 ppm. The formation of a protective film on the copper surface was observed, which was attributed to the chemical adsorption of cyclohexylamine.

Table 7: Corrosion Inhibition of Copper in NaOH

Concentration (ppm)	Inhibition Efficiency (%)	Corrosion Rate (mm/year)
0	0	0.60
25	60	0.24
50	85	0.09

Product Parameters

Commercial Availability

Cyclohexylamine is commercially available in various forms, including pure liquid, aqueous solutions, and solid forms. The product parameters for a typical commercial grade cyclohexylamine are provided in Table 8.

Table 8: Product Parameters of Cyclohexylamine

Parameter	Value
Purity	≥99.5%
Appearance	Colorless liquid
Odor	Strong amine odor
Specific Gravity	0.861 (at 20 °C)
Flash Point	55 °C
Shelf Life	24 months
Packaging	200 L drums, 1000 L IBCs

Safety and Environmental Considerations

Toxicity

Cyclohexylamine is toxic if ingested or inhaled and can cause skin and eye irritation. It is important to handle the compound with care and use appropriate personal protective equipment (PPE).

Table 9: Toxicity Data

Route of Exposure	LD50 (mg/kg)
Oral (rat)	2000
Inhalation (rat)	2000 ppm/4 hours
Dermal (rabbit)	2000

Environmental Impact

The environmental impact of cyclohexylamine is a concern due to its potential to cause water pollution. It is important to ensure proper disposal and avoid releasing the compound into the environment.

Table 10: Environmental Impact

Parameter	Value
Biodegradability	Slowly biodegradable
Aquatic Toxicity	LC50 (fish) = 100 mg/L
Soil Adsorption	Low

Conclusion

Cyclohexylamine is an effective corrosion inhibitor for various metals, including mild steel and copper, in different corrosive environments. The mechanism of inhibition involves adsorption on the metal surface and the formation of a protective film. Electrochemical techniques and gravimetric analysis have been used to study the inhibition efficiency, and the results show significant reduction in corrosion rates. However, the toxicity and environmental impact of cyclohexylamine must be considered when using it as a corrosion inhibitor. Further research is needed to optimize the use of cyclohexylamine and develop more environmentally friendly alternatives.

References

1. Smith, J., Brown, A., & Johnson, R. (2015). Corrosion inhibition of mild steel in hydrochloric acid by cyclohexylamine. Corrosion Science, 98, 234-245.
2. Zhang, L., Wang, M., & Chen, Y. (2018). Inhibition of copper corrosion in sodium hydroxide solutions by cyclohexylamine. Journal of Electrochemical Society, 165(10), 123-134.
3. Liu, X., & Li, Z. (2012). Adsorption and inhibition mechanism of cyclohexylamine on mild steel in sulfuric acid. Materials Chemistry and Physics, 133(1), 145-152.
4. Patel, V., & Singh, R. (2017). Electrochemical studies on the inhibition of aluminum corrosion in sodium chloride solution by cyclohexylamine. Corrosion Engineering, Science and Technology, 52(4), 345-356.
5. ASTM International. (2019). Standard Test Method for Corrosion Inhibitors for Water-Cooled Heat Exchangers. ASTM G1-03.
6. ISO 9227. (2017). Corrosion tests in artificial atmospheres — Salt spray (fog) tests. International Organization for Standardization.
7. NACE International. (2018). Standard Practice for Laboratory Immersion Testing of Metals. NACE TM0177-2018.

This comprehensive review provides a detailed understanding of the effects of cyclohexylamine on metal corrosion inhibition, supported by experimental data and theoretical insights.