Translate this page into:
Anti-hygroscopic surface modification of ammonium nitrate (NH4NO3) coated by surfactants
⁎Corresponding author at: School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, Jiangsu, China. bahaelzaki@njust.edu.cn (Baha I. Elzaki)
-
Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Ammonium nitrate surface is extremely hygroscopic, due to high energy on its surface which increases the potential of the molecules to absorb moisture from the surrounding environment. Ammonium nitrate particles were modified using second coating process with myristic acid in the different amount. The hygroscopicity was tested for ammonium nitrate with and without coating. Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) were used to characterize the surface of coated and uncoated ammonium nitrate. Meanwhile, the method determined mass ratio of coating layer was improved to achieve more accuracy. In addition, focused ion beam technique was used to determine the thickness of coating layer. The results indicated that by using second coating modification method of surfactant adsorption, the anti-hygroscopicity performance of coated samples was significantly improved. The result showed that the decline of the absorption moisture rate was 40.57%, and the mass ratio of the coating layer was 1.42%. These results suggest that the second coating process employed could provide the well fundamental for the further anti-hygroscopic surface modification of ammonium nitrate particles coated by surfactants.
Keywords
Ammonium nitrate (AN)
Anti-hygroscopic
Coating
Modification surface
Surfactant
1 Introduction
Ammonium nitrate (AN) has wide applications as both a fertilizer and composites of a variety of energetic materials, mainly industrial explosives (Nagayama et al., 2014; Zygmunt and Buczkowski, 2007). AN is available, low price, and easy to synthesize (Rolf, 1972; Kajiyama et al., 2013). In comparison, ammonium perchlorate (AP) has a significant harm to the environment when used as the oxidizer (Lewis et al., 2010; Liu et al., 2004; Kohga and Handa, 2016). Therefore AN will become a possible replacement after treatment its drawbacks such as hygroscopicity, phase transitions, and low burning rate (Tan et al., 2017; Chaturvedi and Dave, 2013; Kwok et al., 2004; Videla et al., 2017; Gezerman and Çorbacıoglu, 2014; Nagayama et al., 2015). However, AN is extremely hygroscopic, due to high energy on it is surface increases the potential of the molecules to absorb moisture, and it can cause agglomeration and deliquesces in moist atmospheres greater than critical relative humidity. There is an undesirable property for the application of AN as an oxidizer in solid propellants (Nagayama et al., 2015; Lafci et al., 1988; Wei and Cai, 2012; Jos and Mathew, 2016).
Many researches on surface modification of AN have been carried out to improve anti-hygroscopicity, such as using a physical coating by paraffin wax, stearic acid, mineral oil coated on the surface of the AN particles, forming a hydrophobic layer physical coating method is simple, convenient, easy, and safety in manufacturing (Damse, 2004). In addition; the chemical coating was used to reduce hygroscopicity of AN by surfactants, coupling agents and other functional groups in organic molecules. Although chemical coating method used less dosage and strong binding force, the molecular weight of coating materials is relatively small, low hydrophobic properties (Malash and Hashem, 2005; Zhang et al., 2009). Furthermore, the encapsulation method was used to form a capsule like coating layer on the surface of AN particles. Although the encapsulation method is a new method, and protect the particles from the external humidity, this approach has disadvantages such as the polymer adhesive not dispersed and used some brittle polymer susceptible to cracking during the drying (Zhang and Yang, 2004; Yu Zhicheng, 2013). From the above, the AN anti-hygroscopic was studied by using a different coating materials and coating methods, obtained under certain conditions, absorption moisture rate a large decline-coated sample, although greatly modified anti-hygroscopicity of AN, however, many challenges are remaining (Elzaki and Zhang, 2016). For instance, the index evaluation of the AN hygroscopic effect did not precisely mention the mass ratio of the coating layer. Moreover, the hygroscopicity test conditions of AN coated remain unclear. As example, the time of moisture absorption is quite short, while both the particle size of AN and the size of weighing bottle are unknown, as well as the process of coated AN by surfactant materials have not been thoroughly mentioned, particularly the coating time and temperature.
In this study, we achieved the modification and characterization of the AN particles by coating with alcohol and acid surfactant groups with hydrophobic tails from C14 to C22. Taguchi orthogonal array (TOA) L9(34) was employed to investigate certain factors affecting the coating process before optimizing our formula regarding fixed reaction temperature, time of fixed reaction temperature, the amount of surfactant, and time of decreasing temperature. Furthermore, the surface morphologies of AN particles were observed by electronic scanning microscope, the surface of coated AN particles was assayed by FTIR spectra and Focused Ion beam (FIB) was employed to determine the thickness of coating layer. The results were found useful for surface modification of AN particles, which improved the anti-hygroscopicity of ammonium nitrate particles.
2 Experimental procedures
2.1 Materials
Table 1 shown that the materials and specifications used in this work.
| Name | Purity% | Manufacturer |
|---|---|---|
| Ammonium nitrate | ≥99.0 | Kecheng Fine Chemical CO. Ltd, China |
| chloroform | ≥99.0 | Shanghai Ling Feng Chemical Reagent Co. LTD, China |
| cyclohexane | ≥99.5 | Kelong Chemical Reagent, Chengdu, China |
| Acetonitrile | ≥99.0 | Sinopharm Chemical Reagent Co., Ltd, Shanghai, China |
| 1-Teteradecanol | ≥97.0 | Aladdin Industrial Corporation, Shanghai, China |
| Cetylalcohol | ≥98.0 | Kelong Chemical Reagent, Chengdu, China |
| 1-Octadecylalcohol | ≥99.0 | Aladdin Industrial Corporation, Shanghai, China |
| Arachidylalcohol | ≥95.0 | Meryer Chemical Technology Co. Ltd. Shanghai, China |
| Behenyl alcohol | ≥98.0 | Meryer Chemical Technology Co. Ltd. Shanghai, China |
| Lauric acid | ≥98.5 | Kelong Chemical Reagent, Chengdu, China |
| Myristic acid | ≥97.0 | Aladdin Industrial Corporation, Shanghai, China |
| Palmitic acid | ≥99.0 | Kelong Chemical Reagent, Chengdu, China |
| Stearic acid | ≥99.0 | Kelong Chemical Reagent, Chengdu, China |
| Arachidic acid | ≥99.0 | Meryer Chemical Technology Co. Ltd. Shanghai, China |
| Behenic acid | ≥85.0 | Meryer Chemical Technology Co. Ltd. Shanghai, China |
2.2 First coating method by single surfactant
Physical coating method was improved to modify the surface of AN particles (Damse, 2004; Hu Kunlun et al., 2006). 6 g of AN coated by 2 g of surfactant materials in the mixture of solvents consist of 15 ml chloroform and 15 ml cyclohexane. Choosing the solvents for coating has been based on the solubility of surfactant materials, and AN insoluble in solvents. The reaction was started with stirring at constant temperature 60 °C. After 2 h the heating was stopped, and then the temperature was gradually decreased within 8 h to 30 °C, at this stage the water of bath heating was changed, and when the temperature reached to 25 °C. AN coated was filtered by vacuum filter, and dried at a certain temperature with considering the melting and boiling point of each surfactant materials. Finally, the hygroscopicity test was carried out under the conditions 5 g AN 60 × 30 mm weighing bottle at temperature of 35 °C, humidity (67.5%), and time of absorption rate tested 24 h.
2.3 Second coating method by composite surfactant materials
2.3.1 Select solvents and surfactants
In order to select a suitable solvents and surfactants for second coating process, the global survey of the solubility of ammonium nitrate and surfactant materials (alcohols, acids, amines and amine surfactant groups with different hydrophobic tails C12-C22) were tested in our research group for different solvents at different temperatures 20, 25, 30, 35, 40, 45, 50, 55 and 60 °C and results indicated that the suitable surfactant for first coating were cetylalcohol or stearic acid or stearyl alcohol because these surfactant materials have good performance of anti-hygroscopicity and a little soluble (less than 0.015 g/30 ml) in the solvent of second coating (acetonitrile) (Hou Ying, 2016, 2017). In addition, the experiment of solubility had done for selective surfactant materials (cetylalcohol, stearyl alcohol, stearic acid and myristic acid) in acetonitrile at 20 °C and the results shown in Table 2 below.
| No. | Surfactant | Solubility g/100 ml (Tested) | Solubility g/30 ml (calculated) |
|---|---|---|---|
| 1 | Cetylalcohol | 0.0099 | 0.0030 |
| 2 | Stearyl alcohol | 0.0073 | 0.0022 |
| 3 | Stearic acid | 0.0091 | 0.0027 |
| 4 | Myristic acid | 1.0305 | 0.3092 |
From Table 2, it was found that the solubility of cetylalcohol, stearyl alcohol and stearic acid in acetonitrile will suitable for first coating because very little amount dissolve in solvent of second coating and the exactly amount of first coating layer of cetylalcohol, stearyl alcohol, and stearic acid will dissolve are 4.44%, 3.26 and 4.0%, respectively. Therefore, the first coating layer surfactant will be by stearic acid or cetylalcohol, because they have a good performance of anti-hygroscopicity and less amount dissolve in the second coating solvent.
2.3.2 Determination of the amount of surfactant for second coating
From the micelles formation principle of the surfactant in solution, the surface tension decreases to the lowest value when the concentration of the surfactant reaches the critical micelle concentration (CMC), and the amount of the surfactant is increased again. A large number of micelles formed, the formation of micelles can be used in a single molecule adsorption on the surface of the ammonium nitrate coating so that you can consider the amount of surfactant dosage slightly higher than the CMC value as a basis for calculation. Based on the study of this subject group (Adamson and Gast, 1967), CMC value has been determined by experimental using myristic acid in acetonitrile, with particular critical micelle concentration as shown in Fig. 1 below.
From the data was shown in Fig. 1, the critical micelle concentration of myristic acid in 30 ml acetonitrile at 20 °C was 0.23 g, which can be used as the initial dosage of the experimental. The amount of myristic acid before micelle formed 0.15 g and amount of myristic acid after micelle formed 0.30 g.
2.3.3 Determination of other process conditions
Cetylalcohol or stearic acid were used as a first coating layer in mixture solution solvents of chloroform and cyclohexane, using coating processing procedure same as the procedure in Section 2.2, which got the best results of coating AN with surfactant materials. The first coating of AN by cetylalcohol or stearic acid will produce significant sample as stock (20 g) and then will take 5 g to test the moisture absorption rate, if the result is meet the specification of second coating, the remaining amount will use as starting material for second coating process.
The myristic acid (C14-acid) can be used as a second coating layer with different amount 0.15, 0.23 and 0.3 g, according to CMC determined in Section 2.3.2.
The volume of the solvent solution used in the first coating was 30 ml according to the suspension system, the corresponding solvent will use is 30 ml, and the temperature of is 20 °C due to the solubility and CMC determination test.
The modified ammonium nitrate particles will treat by using filtration and drying process.
The performance of second coating by surfactant was measured in moisture absorption test conditions: 5 g of AN in 60 × 30 weighing bottle, the temperature was 35 °C, relative humidity is 67.5% and absorption time is 24 h.
2.4 Evaluation and characterization of results
Ammonium nitrate samples coated with surfactant materials and the anti-hygroscopicity performance of coating will be assessed by evaluated and characterized the results. The evaluation indexes are mainly increasing the decline of the moisture absorption and the mass ratio of coating layer, and the main characterization methods are scanning electron microscopy observation, infrared characterization and focused ion beam technique.
2.4.1 Measurement of moisture absorption rate
The moisture absorption rate of ammonium nitrate is the rate of changing on the moisture absorption rate of samples before and after test the hygroscopicity of coating ammonium nitrate (Tortorelli, 1998). According to GJB770B-2005 “hygroscopicity - dryer balance method” (GJB770B, 2005), in this study, 5 g of AN sample will put in 60 × 30 mm weighing bottle without a cap will be placed into a desiccator containing saturated solution of strontium chloride (relative humidity 67.5%) the temperature at 35 °C for 24 h. The sample will be scaled up from 5 g to 20 g AN and the test conditions will be used to measure the moisture absorption rate: the relative humidity is 92% by using the saturated solution of potassium nitrate in the bottom glass desiccator inside oven constant temperature at 35 °C, the amount of modified AN is 20 g put inside the 60 × 30 mm weighing bottle without cover and time of absorption rate tested 24 h. The following equation will be calculated the moisture absorption rate (HR):
HR- moisture absorption rate, %.
M0- The weight of sample before absorbed moisture, g
M- The weight of the sample after absorbed moisture, g
Meanwhile, according to the above methods, the ammonium nitrate samples will be measured moisture absorption rate and uncoated blank sample, the decline of the moisture absorption rate calculated by the following equation:
A-decline of moisture absorption rate, %.
HR1- absorption rate of AN sample, %.
HR- absorption rate of coated AN sample, %.
2.4.2 Determination method of the mass ratio of coating layer
The determination method of the mass ratio of the coating layer will be improved to achieve more accuracy than previous literature (Yu Zhicheng, 2013) as following steps:
Firstly: a filter paper of 18 cm diameter was wetted with deionized water.
Secondly: the filter paper placed into an oven for 1 h at the temperature 100 °C, then the filter paper was weighed (WB).
Thirdly: the sample of the coated AN after absorption humidity was dissolved in deionized water, and filtered through a tapered funnel, and the filter paper was washed several times with deionized water, and placed in an oven at 100 °C for 1 h.
Finally, the filter paper was weighed again (WA).
The mass ratio of the coating layer was calculated by the following equation:
W- mass ratio of coating layer, %.
M0- The weight of coated sample before absorbed moisture, g
M1- The weight of coating layer, g = WA − WB.
2.4.3 Fourier transform infrared (FTIR) characterization
The changing on the surface of ammonium nitrate particles after coating by surfactant materials will be characterized by using Fourier transform infrared (FTIR). The infrared spectra of the sample can be obtained by the measurement of the position and intensity of the infrared absorption peaks reflects and the characteristics of the molecular functional group. FTIR is a spectroscopic technique that has been used for analyzing the fundamental molecular structure or identifying unknown structure of the molecular (Lu Li-yuan, 2010). FTIR characterization method has been used to analyze the difference of the characteristic peaks of the molecular of the samples before and after the coating. Furthermore, the results will be analyzed in order to characterize whether the surfactants will be coated surface of AN particles. From the infrared spectrum can reflect change in peaks will happen according to the absorption peaks of some characteristic absorption peaks of the ammonium particles on the spectrum are weakened or disappeared, and the new characteristic absorption peak is refers to the absorption peak of the coating material. The coated AN particles with cetylalcohol, stearic acid, stearyl alcohol, and blank AN characterized by Fourier transform infrared spectroscopy (FTIR). IR spectra will be recorded in the range 400–4500 cm−1 on FTIR spectrophotometer (Thermo Scientific Nicolet, I S10, Thermo Fisher USA) using KBr pellets.
2.4.4 Scanning electron microscopy (SEM) observation
Scanning electron microscopy (SEM) used to characterize the surface morphology of the sample by use a very fine focus of the high-energy electron beam on the sample scan, to stimulate a variety of physical information. SEM will capable of observing the particle size of the sample particles, the surface morphology of the particles, the surface bump, surface roughness, and also will be obtained crystal-related information such as crystal morphology, dislocations, and steps such as the direction and type, not crystal surface defects, crystal growth trajectories and directions (Rao et al., 1989; Wei, 2008). In this study, the surface of coated AN samples will be observed with scanning electron microscopy (JEOL JSM 6380LV, Japan), based on the SEM pictures of AN/cetylalcohol, AN/stearic acid, AN/Stearyl alcohol and AN without coated will be observed the surfaces morphology to examine the surface of ammonium nitrate particles in details. The difference between the surface morphology of the coated particles and the surface morphology of the particles without coating were compared to determine the effect of the coating.
2.4.5 Focused ion beam (FIB) technique
Focused ion beam (FIB) is a technique used particularly the semiconductor industry, materials science and increasingly in biological field for site-specific analysis deposition and ablation materials (Giannuzzi, 2006). A FIB setup is a scientific instrument that resembles a scanning electron microscope (SEM). However, while the SEM uses a focused beam of electrons to image the sample in the chamber. FIB can also be incorporated in a system with both electron and ion beam columns, allowing the same feature to be investigated using either of the beams. FIB should not be confused with using a beam of focused ions for direct write lithography (such as in proton beam writing). In this study the FIB was used to determine the thickness of coating.
2.5 Taguchi orthogonal array (TOA)
A L9 (34) TOA was used in the current study to define the optimal conditions regarding the selected factors to AN/cetylalcohol and AN/stearic acid with hygroscopicity (HR), the mass ratio of the coating layer, and decline of moisture absorption rate. The design involved four factors at three levels as showed in Table 3. These factors were A: fixed temperature of the coating process, time of fixed temperature of the coating process, the amount of surfactant, and time of reducing temperature and the assessed index by the decline of the moisture absorption rate. As showed in Table 3; the L9 (34) array had 9 rows and four columns at three levels.
| Factors | Levels | ||
|---|---|---|---|
| 1 | 2 | 3 | |
| A: Fixed temperature of coating process (°C) | 55 | 60 | 65 |
| B: Time of fixed temperature of coating process (h) | 1.5 | 2 | 2.5 |
| C: Amount of Surfactant (g) | 1 | 1.5 | 2 |
| D: Time of reducing temperature (h) | 7 | 8 | 9 |
3 Results and discussion
3.1 Anti- hygroscopicity performance of coating AN by alcohol surfactant
The performance of modified ammonium nitrate particles was indicated by the decline of the moisture absorption rate and the mass ratio of the coating layer. Table 4 showed the anti-hygroscopicity performance AN coated by alcohol surfactants with different length of hydrophobic tail from C14 to C22. The data recorded in hygroscopicity test showed the cetylalcohol was the best one of alcohol surfactant group used as a coating of AN whereas the moisture absorption rate of modified AN by cetylalcohol was were decreased and significantly changed from 11.37% (AN blank) to 07.20% with a mass ratio of coating layer of 0.45%, and the highest decline of absorption rate of 36.68%. While stearyl alcohol and arachidylalcohol were 18.65% and 18.29%, with the mass ratio of coating layer were 1.23% and 1.81% respectively. The lowest performance of alcohol surfactant group coated AN were recorded by myristyl alcohol and behenyl alcohol with the decline of the absorption moisture rate were 14.78% and 17.94%, the mass ratios of coating layer were 1.07% and 1.57% respectively. These results fit to be a basis for surface modification of ammonium nitrate particles to improvement the anti-hygroscopicity.
| No. | Surfactants | Hygroscopicity (HR) % | Mass ratio of coating layer % | Decline % |
|---|---|---|---|---|
| – | AN blank | 11.37 | – | – |
| 1 | Myristyl alcohol | 09.69 | 1.07 | 14.78 |
| 2 | Cetylalcohol | 07.20 | 0.45 | 36.68 |
| 3 | Stearyl alcohol | 09.25 | 1.23 | 18.65 |
| 4 | Arachidyl alcohol | 09.29 | 1.81 | 18.29 |
| 5 | behenyl alcohol | 09.33 | 1.57 | 17.94 |
3.2 Orthogonal optimization experiment of AN coated by cetylalcohol
Table 5 and Fig. 2 showed that the orthogonal experiment of the process factors ranges value among them, RC > RD > RB > RA. This process has four factors affecting on the improvement of the anti-hygroscopicity of the ammonium nitrate particles coated with cetylalcohol: fixed temperature of the coating process, time of fixed temperature of the coating process, the amount of surfactant, the time of decreasing temperature. As shown in Fig. 2, the optimum process conditions of ammonium nitrate particles coated with cetylalcohol to reduce hygroscopicity, A3B3C2D2, namely fixed reaction temperature 65 °C, time of fixed reaction temperature 2.5 h, the amount of surfactant1.5 g, the time of decreasing temperature 8 h. The actual best coating process conditions, the optimum conditions for the A1B2C2D2, fixed temperature of coating process 60 °C, time of the temperature of coating process 2.0 h, the amount of surfactant 1.5 g, the time of decreasing temperature 8 h.
| No. | A | B | C | D | Hygroscopicity (HR) % | Mass ratio of coating layer% | Decline % |
|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 1 | 1 | 09.70 | 0.82 | 14.69 |
| 2 | 1 | 2 | 2 | 2 | 07.34 | 0.95 | 35.44 |
| 3 | 1 | 3 | 3 | 3 | 08.42 | 1.27 | 25.95 |
| 4 | 2 | 1 | 2 | 3 | 08.01 | 1.5 | 29.55 |
| 5 | 2 | 2 | 3 | 1 | 10.03 | 1.41 | 11.79 |
| 6 | 2 | 3 | 1 | 2 | 08.42 | 1.13 | 25.95 |
| 7 | 3 | 1 | 3 | 2 | 08.70 | 0.55 | 23.48 |
| 8 | 3 | 2 | 1 | 3 | 08.36 | 1.22 | 26.47 |
| 9 | 3 | 3 | 2 | 1 | 08.26 | 0.87 | 27.35 |
| k1 | 25.36 | 22.57 | 22.37 | 17.94 | |||
| k2 | 22.41 | 24.57 | 30.78 | 28.29 | |||
| k3 | 25.77 | 26.42 | 20.41 | 27.32 | |||
| R | 3.36 | 3.85 | 10.37 | 10.35 |
It can be seen from Table 6 that the average decline of moisture absorption rate of the coated sample at theoretical optimum point of the experiment was 24.44%, with average mass ratio of coating layer was 0.85%, while the average decline of moisture absorption rate of the actual optimum point of the experiment is 35.15%, the average mass ratio of coating layer was 1.22%. The anti-hygroscopicity performance of actual optimum point was better than the theoretical best point. Therefore, the optimum coating conditions of the anti-hygroscopic surface modification of ammonium nitrate coated by cetylalcohol were as follows: fixed temperature of coating process was 55 °C, time of fixed temperature of coating process was 2 h, the amount of surfactant was 1.5 g, and time of reducing temperature 8 h. The optimum results were as follows: the decline of moisture absorption rate was 35.15% and the mass ratio of coating layer was 1.22% under the moisture absorption test conditions; temperature was 35 °C, relative humidity was 68% and time was 24 h.
| No. | Process conditions | Moisture absorption rate (%) | Average mass ratio of coating layer (%) | Blank AN (%) | Decline (%) | Average decline (%) |
|---|---|---|---|---|---|---|
| 1 | Theoretical optimum result | 09.03 | 0.85 | 12.10 | 25.37 | 24.44 |
| 2 | 08.07 | 10.74 | 24.86 | |||
| 3 | 08.26 | 10.74 | 23.09 | |||
| 1 | Actual optimum result | 07.81 | 1.22 | 12.10 | 35.45 | 35.15 |
| 2 | 07.31 | 10.74 | 31.93 | |||
| 3 | 06.65 | 10.74 | 38.08 | |||
3.3 Anti- hygroscopicity performance of coating AN by acid surfactants
The performance of modified ammonium nitrate particles was indicated by the decline of the moisture absorption rate and the mass ratio of the coating layer. Table 7 showed that the anti-hygroscopicity performance AN coated by acid surfactants with different length of hydrophobic tail from C14 to C22. The data from hygroscopicity test indicated the modified AN by stearic acid was found the best one of acid surfactant group used as a coating of AN with decreased of moisture absorption rate from 11.37% (AN blank) to 08.64% with a mass ratio of coating layer of 0.67%, and the highest decline of absorption rate of 24.01%. While palmitic acid and behenic acid were 18.29% and 17.06%, with the mass ratio of coating layer were 0.97% and 1.55% respectively. The lowest performance of acid surfactant group coated AN were recorded by myristic acid and arachidic acid with the decline of the absorption moisture rate were 11.87% and 04.84%, the mass ratio of coating layer were 0.83% and 1.03% respectively.
| No. | Surfactants | Hygroscopicity (HR) % | Mass ratio of coating layer % | Decline % |
|---|---|---|---|---|
| – | AN-Blank | 11.37 | – | – |
| 1 | Myristic acid | 10.02 | 0.83 | 11.87 |
| 2 | Palmitic acid | 09.29 | 0.97 | 18.29 |
| 3 | Stearic acid | 08.64 | 0.67 | 24.01 |
| 4 | Arachidic acid | 10.82 | 1.03 | 04.84 |
| 5 | Behenic acid | 09.43 | 1.55 | 17.06 |
3.4 Orthogonal optimization experiment of AN coated by stearic acid
Table 8 and Fig. 3 showed that the orthogonal experiment of the process factors ranges value among them, RC > RD > RA > RB. This process has four factors affecting on the improvement of the anti-hygroscopicity of the ammonium nitrate particles coated with stearic acid: fixed reaction temperature, time of fixed reaction temperature, the amount of surfactant, the time of decreasing temperature. As shown in Fig. 3, the optimum process conditions of ammonium nitrate particles coated with stearic acid to reduce hygroscopicity, A1B2C2D2, namely fixed temperature of coating process 55 °C, time of fixed temperature of coating process 2.0 h, amount of surfactant 1.5 g, the time of decreasing temperature 8 h. The actual best coating process conditions, the optimum conditions for the A1B2C2D2, fixed temperature of coating process 55 °C, time of fixed temperature of coating process 2.0 h, the amount of surfactant 1.5 g, the time of decreasing temperature 8 h.
| No. | A | B | C | D | Hygroscopicity (HR) % | Mass friction of coating layer% | Decline % |
|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 1 | 1 | 09.99 | 0.59 | 12.14 |
| 2 | 1 | 2 | 2 | 2 | 07.96 | 1.14 | 29.99 |
| 3 | 1 | 3 | 3 | 3 | 09.68 | 1.32 | 14.86 |
| 4 | 2 | 1 | 2 | 3 | 08.70 | 1.29 | 23.48 |
| 5 | 2 | 2 | 3 | 1 | 09.92 | 1.35 | 12.75 |
| 6 | 2 | 3 | 1 | 2 | 09.57 | 0.54 | 15.83 |
| 7 | 3 | 1 | 3 | 2 | 09.86 | 0.61 | 13.28 |
| 8 | 3 | 2 | 1 | 3 | 09.89 | 1.12 | 13.02 |
| 9 | 3 | 3 | 2 | 1 | 09.32 | 0.39 | 18.03 |
| k1 | 19.00 | 16.30 | 13.66 | 14.31 | |||
| k2 | 17.35 | 18.59 | 23.83 | 19.70 | |||
| k3 | 14.78 | 16.24 | 13.63 | 17.12 | |||
| R | 4.22 | 2.35 | 10.20 | 5.39 |
It can be seen from Table 9 that the average decline of moisture absorption rate of the coated sample at theoretical optimum point of the experiment was 25.92%, with average mass ratio of coating layer was 0.73%, while the average decline of moisture absorption rate of the actual optimum point of the experiment was 30.73%, the average mass ratio of coating layer was 0.91%. The anti-hygroscopicity performance of actual optimum point is better than the theoretical optimum point. Therefore, the optimum coating conditions for the anti-hygroscopic surface modification of ammonium nitrate coated by stearic acid were as follows: fixed temperature of coating process was 55 °C, time of fixed temperature of coating process was 2 h, the amount of surfactant was 1.5 g, and time of reducing temperature 8 h. The optimum results were as follows: the decline of moisture absorption rate was 30.73% and the mass ratio of coating layer was 0.91% under the moisture absorption test conditions; temperature was 35 °C, relative humidity was 68% and time was 24 h.
| No. | Process conditions | Moisture absorption rate (%) | Average mass ratio of coating layer (%) | Blank AN (%) | Decline (%) | Average decline (%) |
|---|---|---|---|---|---|---|
| 1 | Theoretical optimum result | 08.12 | 0.73 | 10.99 | 26.11 | 25.92 |
| 2 | 07.70 | 10.84 | 28.97 | |||
| 3 | 08.38 | 10.84 | 22.69 | |||
| 1 | Actual optimum result | 07.69 | 0.91 | 10.99 | 30.03 | 30.73 |
| 2 | 07.58 | 10.84 | 30.07 | |||
| 3 | 07.36 | 10.84 | 32.10 | |||
3.5 Single factors experiment of AN/cetylalcohol
The effect of fixed temperature of coating process: Based on the optimum coating process conditions obtained from the orthogonal optimization experiment results were shown in Table 6, the fixed temperature of coating process was changed to 50, 55, 60, 65 and 70 °C and other processing conditions unchanged. The effect of fixed temperature of coating process on the decline of the moisture absorption rate and the mass ratio of the coating layer, as can be seen from Table 10 at the same cetylalcohol amount, time of fixed temperature of coating process and time of reducing the temperature. Increasing fixed temperature of coating process lead to increase the decline of the moisture absorption rate at the high coating performance of anti-hygroscopicity at 60 °C. Then increasing fixed temperature of coating process lead to decrease the ant-hygroscopicity performance of coating ammonium nitrate particle. The effect of fixed temperature on the mass ratio of the coating layer increasing the temperature lead to decreased the mass ratio of the coating layer at 60 °C the lowest obtained was 0.45% and then increasing temperature lead to increase the mass ratio of the coating layer. According to the effect of temperature on the adsorption process of surfactants at the solid-liquid interface, it is known that the solubility of the surfactant in the solvent increases with increasing temperature (van Os et al., 2012). As the temperature of the coating reaction increases, the solubility of cetylalcohol in the solvent increases, and the cetylalcohol molecules dispersed in the solvent are fully adsorbed on the surface of AN particles in the form of free single molecules, so that the surface of the coated particles is more uniform and compact, and the coating effect can be improved. However, when the surfactant dosage is fixed, the solvent vaporization may cause the surfactant concentration to increase in a short time when the solvent boils. The surface of the ammonium nitrate particles is uncoated, the effect is not good, and the anti-hygroscopicity effect of the coated sample is deteriorated.
The effect of time of fixed temperature of coating process: According to the optimum coating process conditions obtained from the orthogonal optimization experiment results were shown in Table 6, the time of fixed temperature of coating process was changed to 1, 1.5, 2.0, 2.5 and 3.0 h. The effect time of fixed temperature of coating process on the decline of the moisture absorption rate and the mass ratio of the coating layer, as can be seen from Table 11 at the same fixed temperature of the coating process, cetylalcohol amount and time of reducing the temperature. The highest value of decline recorded 36.68% at two h. There is no effect on the mass ratio of the coating layer by the time of reaction because the mass ratio of coating layer changes randomly with increasing the number of surfactant materials. The adsorption process of surfactant molecules dispersed in the solvent on the surface of solid particles is a dynamic process of adsorption and desorption (Lucassen-Reynders, 1981). As the reaction time increases, the contact between the surfactant molecules and the ammonium nitrate particles increases, and adsorption are continuously performed on the surface of the particles. The coated surface of the coated particles is denser and more uniform, the coating effect is good, and the decline of moisture absorption rate increases. When the reaction time becomes longer, the content of the surfactant coated on the particle surface increases slightly, but it may not be conducive to the stable and uniform coating layer, and the effect of subsequent treatment makes the coated sample anti-hygroscopicity effect lower and decline of moisture absorption rate smaller.
The effect of cetylalcohol amount: Based on the optimum coating process conditions obtained from the orthogonal optimization experiment results were shown in Table 6, the amount of cetylalcohol was changed to 1, 1.5, 2.0, 2.5 and 3.0 g. The effect of the cetylalcohol amount on the decline of the moisture absorption rate and the mass ratio of the coating layer, as can be seen from Table 12 at the same fixed temperature of the coating process, time of fixed temperature and time of reducing the temperature. The highest value of decline recorded 36.68% at 1.5 g, and then the decline of the moisture absorption rate was gradually decreased after that by increasing the amount of surfactant. The mass ratio of the coating layer was directly proportional to increase the number of surface materials. According to the adsorption model of surfactant at the solid-liquid interface, as the concentration of surfactant molecules increases, the adsorption amount of surfactant molecules on the solid surface increases (Lucassen-Reynders, 1981). Cetylalcohol is dissolved in mixture of chloroform and cyclohexane. Hydrophilic polar groups are adsorbed on the surface of AN particles through hydrogen bonds. Hydrophobic non-polar groups point to the periphery of ammonium nitrate molecules. A uniform hydrophobic film is formed to achieve anti-hygroscopicity properties (van Os et al., 2012). When the dosage of cetylalcohol increase, the molecular concentration of cetylalcohol dissolved in the solvent gradually increases, the surfactant molecules adsorbed on the surface of ammonium nitrate particles also increase, and the mass ratio of the coating on the surface of ammonium nitrate particles keeps increasing. Therefore, as the solvent concentration increases, the moisture absorption rate of the coated sample decreases continuously. However, when the concentration of the surfactant in the solvent exceeds a certain amount, the surfactant molecules may be adsorbed on the surface of the particles in the form of micelles (Holmberg et al., 2002), which may leave gaps in the coating layer and it is difficult to uniformly adsorption on the surface of the particles; on the other hand, may be due to the continuous increase in the surface adsorption of ammonium nitrate particles, excessive surfactant particles on the surface of the coating easily filtered, drying process caused by adhesion and mechanical damage. Therefore, when the amount of surfactant exceeds a certain value, there is a decrease in the moisture absorption rate of coated AN particles.
The effect of the time of decreasing temperature: According to optimum coating process conditions obtained from the orthogonal optimization experiment results were shown in Table 6, the time of decreasing temperature was changed to 5, 6, 7, 8 and nine h. The effect of the time of decreasing temperature on the decline of the moisture absorption rate and the mass ratio of the coating layer, as can be seen from Table 13 at the same fixed temperature of the coating process, cetylalcohol amount and time of fixed. While the time increased, the decline in the moisture absorption rate increased to a higher value 36.68% at eight h and then the increasing the time lead to decrease the decline of the moisture absorption rate. The effect of the time of decreasing temperature on the mass ratio of coating layer also was studied. Moreover, the results were indicated that when the time increased the mass ratio of the coating layer was decreased to a lower value 0.46% at 8 h, and then the increasing the time lead to increase the mass ratio of the coating layer. The mass ratio of the coating gradually decreases and the anti-hygroscopic effect gradually increases. However, after a certain period of time, the coating by surfactant is basically completed, the entire coating process system tends to be stable, the coating condition on the surface of the particles is basically unchanged, and the coating effect no longer changes.
| No. | Temperature (°C) | Hygroscopicity (HR) % | Mass ratio of coating layer % | Decline % |
|---|---|---|---|---|
| 0 | Blank AN | 11.37 | / | / |
| 1 | 50 | 8.49 | 1.13 | 25.35 |
| 2 | 55 | 8.15 | 0.78 | 28.30 |
| 3 | 60 | 7.2 | 0.45 | 36.68 |
| 4 | 65 | 9.6 | 1.34 | 15.56 |
| 5 | 70 | 9.85 | 1.75 | 13.34 |
| No. | Time of reaction (h) | Hygroscopicity (HR) % | Mass ratio of coating layer % | Decline % |
|---|---|---|---|---|
| 0 | Blank AN | 11.37 | / | / |
| 1 | 1.0 | 9.98 | 0.73 | 12.17 |
| 2 | 1.5 | 9.24 | 0.59 | 18.74 |
| 3 | 2.0 | 7.20 | 0.45 | 36.68 |
| 4 | 2.5 | 9.72 | 0.99 | 14.47 |
| 5 | 3.0 | 9.44 | 0.97 | 16.98 |
| No. | Amount of surfactant (g) | Hygroscopicity (HR) % | Mass ratio of coating layer % | Decline % |
|---|---|---|---|---|
| 0 | Blank AN | 11.37 | / | / |
| 1 | 1.0 | 9.08 | 0.37 | 20.15 |
| 2 | 1.5 | 7.20 | 0.45 | 36.68 |
| 3 | 2.0 | 8.71 | 0.61 | 23.38 |
| 4 | 2.5 | 8.85 | 0.80 | 22.19 |
| 5 | 3.0 | 9.82 | 0.99 | 13.65 |
| No. | Time of decreasing temperature (h) | Hygroscopicity (HR) % | Mass ratio of coating layer % | Decline % |
|---|---|---|---|---|
| 0 | Blank AN | 11.37 | / | / |
| 1 | 5 | 8.98 | 0.79 | 21.02 |
| 2 | 6 | 8.37 | 0.71 | 26.33 |
| 3 | 7 | 8.22 | 0.58 | 27.75 |
| 4 | 8 | 7.20 | 0.45 | 36.68 |
| 5 | 9 | 8.45 | 0.97 | 25.66 |
3.6 The performance of second coating process
The results of second coating process as shown in Table 14 indicated that the first coating of cetylalcohol has been destroyed by solvent of the second coating that very clear from the decline of moisture absorption rate results of second coating when compared with decline of moisture absorption rate of first coating we found that the decline of moisture absorption rate of first coating was decreased. The results of second coating by different amount of myristic acid (0.15, 0.23 and 0.30 g) for ammonium nitrate coated by stearic acid (first coating), showed that when the amount of myristic acid were 0.30 g and 0.15 g of myristic acid the decline of moisture absorption rate was decreased from 32.10% to 19.52% and 22.69–21.73%, respectively. Best performance of second coating when the decline of moisture absorption rate of first coating (AN/stearic acid) was increased from 28.97% to 36.75%, by using 0.23 g of myristic acid as second coating material were quite significant compared to those reported in previous studies, and the mass ratio of coating layer was 1.5% (Xu Ce and Yuejun, 2017). The modified coating sample was significantly reduced the absorption moisture rate and the coated samples before and after the modified by second coating.
| No | First coating surfactant | Decline of first coating | Amount of myristic acid (g) | Absorption moisture rate (%) | Mass ratio of coating layer (%) | Decline (%) | Average |
|---|---|---|---|---|---|---|---|
| 0 | / | / | / | 10.74 | / | / | |
| 1 | Cetylalcohol | 23.09 | 0.15 | 8.39 | 0.65 | 21.88 | 20.90 |
| 2 | 29.70 | 0.15 | 8.60 | 0.55 | 19.92 | ||
| 3 | 30.17 | 0.23 | 8.37 | 1.44 | 22.07 | 22.82 | |
| 4 | 31.93 | 0.23 | 8.21 | 1.20 | 23.56 | ||
| 6 | 24.86 | 0.30 | 8.75 | 0.87 | 18.53 | 18.72 | |
| 7 | 38.08 | 0.3 | 8.71 | 0.93 | 18.90 | ||
| 0 | / | / | / | 10.84 | / | / | |
| 1 | Stearic acid | 22.69 | 0.15 | 8.51 | 1.04 | 21.49 | 21.73 |
| 2 | 22.23 | 0.15 | 8.46 | 1.44 | 21.96 | ||
| 3 | 28.97 | 0.23 | 6.77 | 1.50 | 37.55 | 40.57 | |
| 4 | 30.07 | 0.23 | 6.26 | 1.33 | 41.71 | ||
| 5 | 31.17 | 0.23 | 6.28 | 1.42 | 42.46 | ||
| 7 | 30.07 | 0.30 | 8.59 | 0.78 | 20.76 | 19.52 | |
| 8 | 32.10 | 0.30 | 8.86 | 0.85 | 18.27 | ||
Best performance of second coating when the decline of moisture absorption rate of first coating (AN/stearic acid) was increased from 28.97% to 40.57%, by using 0.23 g of myristic acid as second coating material were quite significant compared to those reported in Previous studies as summarized in Table 15. According to modification surface of ammonium nitrate particles in this study, these results are an improvement over the properties found in current reports available in the literature. According to these results, the decline of moisture absorption rate was 40.57% of second coating and mass ratio of coating layer was 1.42%.
| No. | Method | Absorption Moisture Rate (%) | Mass Ratio of Coating Layer (%) | Absorption Moisture Test Conditions | Decline (%) | Reference (year) |
|---|---|---|---|---|---|---|
| 1 | Chemical coating | 10.92 | – | T = 20 °C, RH = 88%, t = 8 h | 15.08 | Zhang (2009) |
| 2 | Chemical coating | 19.1 | 0.2 | T = 25 °C, RH = 92.5%, t = 8 h | 7.0 | Zhang Xudong and Yang (2010) |
| 3 | liquid phase separation | 0.33 | – | T = 30 °C, RH = 75%, t = 24 h | 30.6 | Wei and Cai (2012) |
| 4 | precipitation polymerization | 8.78 | 0.48 | T = 35 °C, RH = 92%, t = 24 h | 28.35 | Yu Zhicheng (2013) |
| 5 | Phase separation | – | 1.54 | T = 20 °C, RH = 86%, t = 18 h | 75 | Xiulian et al. (2014) |
| 6 | Spray-dried | – | – | T = 25 °C, RH = 83%, t = 30 min | did not deliquesce | Nagayama (2015) |
| 7 | Surface adsorbed-coating | 6.3 | 1.01 | T = 35 °C, RH = 92%, t = 24 h | 29.7 | Hou (2017) |
| 8 | precipitation Polymerization | 6.9 | 1.4 | T = 35 °C, RH = 67.5%, t = 24 h | 25.8 | Xu Ce (2017) |
| 9 | second coating by surfactants | 6.44 | 1.42 | T = 35 °C, RH = 67.5%, t = 24 h | 40.57 | This work |
3.7 SEM observations
In order to observe the surface morphology of coating ammonium nitrate particles and compare with blank ammonium nitrate particles, the coated sample of ammonium nitrate particles characterized by using scanning electron microscopy. The SEM observations with a different scale bar of 100 µm, 50 µm, and 10 µm Electron micrographs for the surface morphology of AN/cetylalcohol, AN/stearic and AN particles were demonstrated in Figs. 4, 5 and 6 respectively. The SEM pictures showed the surface morphology of the AN coated by cetylalcohol (Fig. 4) which showed a clear difference in the surface morphology, which was smooth and without cracking in the surface coating layer. In contrast, the surface of AN coated by stearic acid particles was not smooth, also have to crack in the surface, this clear showed in Fig. 5(c), and ammonium nitrate without coating (Fig. 6). Almost all of the particles in the AN coated by cetylalcohol, and AN/stearic acid samples were liked AN particle shape without coating. In addition, adhesion between particles cannot be seen in all samples this explains no caking and agglomeration happened after coating AN particles.
3.8 FTIR spectra characterization
Surface modified of AN/cetylalcohol, AN/stearic acid, and ammonium nitrate particles without coating were monitored by using the FTIR technique to provided information about the vibration state of absorbed surfactant materials and hence the nature of surface complexes as depicted in figures below. It is observed that upon the surface modification of AN and surfactant materials, two peaks appear in the region 3000–2800 cm−1, which are attributed to CH3 stretching vibrations in Figs. 7 and 8. Whereas, these peaks were not observed in the FTIR recorded for blank AN. It was important to note that a medium intense peak is observed at 1703 cm−1 for modified AN particles by stearic acid. This peak originated mainly due to carbonyl group C⚌O stretching of the stearic acid in Fig. 8. FTIR spectrum results showed that cetylalcohol and stearic acid existed on the surface of AN particles.
3.9 FIB characterization
Focused ion beam scanning electron microscopy (FIB-SEM) nanotomography (Holzer et al., 2004) has been identified as a method of choice to resolve the structure sufficiently as typical pore and particle diameters are well below 100 nm, and FIB-SEM imaging for these materials has been demonstrated successfully. FIB-SEM tomography is a serial sectioning technique combined with the usual SEM imaging. A focused ion beam mills slices off a block of material that are being analyzed. The objective of this experiment to determine the thickness of coating layer on the surface on ammonium nitrate particles, SEM-FIB technique of optimum process ammonium nitrate coating sample shows in Fig. 9. The data from SEM-FIB technique showed that the thickness of coating layer of ammonium nitrate particle has two different thickness 1.679 µm and 0.873 µm those two thicknesses less than the numerical thickness 2.133 µm. Thus, to verify the thickness of coating layer need more hypothesis will be studied in further.
4 Conclusions
Ammonium nitrate particles were coated with the alcohol and acid surfactant groups (C14-C22) and coated ammonium nitrate particles were modified by using second coating, in order to suppress the hygroscopicity. Our findings were listed below:
The surface of ammonium nitrate was modified by using second coating process by surfactant. The anti-hygroscopic effect of the coated sample with stearic acid after modified by myristic was the best and the decline of moisture absorption rate was 40.57% at 35 °C and 68% relative humidity, and the mass ratio of the coating layer was 1.42%. These results provide new ideas and methods for further improving the anti-hygroscopicity performance of ammonium nitrate particles coated by surfactants.
Investigated the relationship between the processing, performance and structure by using alcohol and acid surfactant groups with different hydrophobic tails C14-C22.
The optimized modification process of coating ammonium nitrate was successfully prepared as a result of TOA analysis using the best performance surfactant in each surfactant group (cetylalcohol and stearic acid).
The single factors effect on the coating process was investigated such as the effect of fixed temperature of the coating process, the effect of the cetylalcohol amount, the effect of the time of fixed temperature and the effect of time of decreasing temperature.
The surface of AN particles modified by stearic acid has cracked and hollow. In contrast, the surface of AN particles modified by cetylalcohol was solid and smooth.
The thickness of coating layer was characterized by using FIB technique.
The cetylalcohol showed a promising coating surfactant material for ammonium nitrate, and it should be subjected to further investigations as anti-hygroscopicity.
References
- Adamson, A.W., Gast, A.P., 1967. Physical chemistry of surfaces.
- Review on thermal decomposition of ammonium nitrate. J. Energ. Mater.. 2013;31(1):1-26.
- [Google Scholar]
- Coating methods for surface modification of ammonium nitrate: a mini-review. Materials. 2016;9(7):502.
- [Google Scholar]
- Effects of calcium lignosulfonate and silicic acid on ammonium nitrate degradation. J. Chem.. 2014;2014
- [Google Scholar]
- Introduction to Focused Ion Beams: Instrumentation, Theory, Techniques and Practice. Springer Science & Business Media; 2006.
- GJB770B, 2005. Hygroscopic- Drier Balance Method People's Republic of China National Military Standard.
- Surfactants and Polymers in Aqueous Solution. Wiley Online Library; 2002.
- Three-dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography. J. Microsc.. 2004;216(1):84-95.
- [Google Scholar]
- Hou Ying, Y.J.Z., 2016. Study on the hygroscopicity of several surfactant coating materials. In: Proceedings of the National Symposium on Green Manufacturing and Applied Technology for Fine Chemicals.
- Preliminary Study on the Anti- Hygroscopicity of Materials for Coating Ammonium Nitrate Particles. Nanjing University of Science & Technology; 2017. Master Dissertation
- Hou, W.B, Z.Y., 2017. Study on anti-hygroscopicity of modified ammonium nitrate particles by the fatty acid surfactant (M. Sc. Dissertation). Nanjing University of Science and Technology.
- Test and study on the modification of ammonium nitrate by coating its surface. Explosive Mater.. 2006;35:14-17.
- [Google Scholar]
- Ammonium nitrate as an eco–friendly oxidizer for composite solid propellants: promises and challenges. Crit. Rev. Solid State Mater. Sci. 2016:1-29.
- [Google Scholar]
- Thermal characteristics of ammonium nitrate, carbon, and copper (II) oxide mixtures. J. Therm. Anal. Calorim.. 2013;113(3):1475-1480.
- [Google Scholar]
- Preparation of combined ammonium perchlorate/ammonium nitrate samples by freeze drying. J. Energ. Mater. 2016:1-16.
- [Google Scholar]
- Investigation of factors affecting caking tendency of calcium ammonium nitrate fertilizer and coating experiments. Fertilizer Res.. 1988;18(1):63-70.
- [Google Scholar]
- Chemical dynamics of aluminum nanoparticles in ammonium nitrate and ammonium perchlorate matrices: enhanced reactivity of organically capped aluminum. J. Phys. Chem. C. 2010;115(1):70-77.
- [Google Scholar]
- Effects of nanometer Ni, Cu, Al and NiCu powders on the thermal decomposition of ammonium perchlorate. Propellants Explos. Pyrotech.. 2004;29(1):34-38.
- [Google Scholar]
- Study on the interaction mechanism of modified ammonium nitrate by octadecylamine. Initiators Pyrotech.. 2010;02(03):41-44.
- [Google Scholar]
- Anionic Surfactants: Physical chemistry of Surfactant Action. Vol vol. 11. Marcel Dekker; 1981.
- Improving the properties of ammonium nitrate fertilizer using additives. Alexandria Eng. J.. 2005;44(4):685-693.
- [Google Scholar]
- Differential scanning calorimetry analysis of crystal structure transformation in spray-dried particles consisting of ammonium nitrate, potassium nitrate, and a polymer. J. Therm. Anal. Calorim.. 2014;118(2):1215-1219.
- [Google Scholar]
- Moisture proofing of spray dried particles comprising ammonium nitrate/potassium nitrate/polymer. Propellants Explos. Pyrotech.. 2015;40(4):544-550.
- [Google Scholar]
- Scanning electron microscopy of ammonium nitrate prills in relation to their application in ammonium nitrate-fuel oil systems. Fuel. 1989;68(9):1118-1122.
- [Google Scholar]
- Rolf, F.-M., 1972. Production of ammonium nitrate. U.S. Patent 3,690,820.
- Effect of mixing methods on the thermal stability and detonation characteristics of ammonium nitrate and sodium chloride mixtures. Propellants Explos. Pyrotech.. 2017;42(11):1315-1324.
- [Google Scholar]
- Tortorelli, L.J., 1998.Ammonium nitrate particulate fertilizer and method for producing the same. Google Patents.
- Physico-Chemical Properties of Selected Anionic, Cationic and Nonionic Surfactants. Elsevier; 2012.
- Phenomenological model of the effect of organic polymer addition on the control of ammonium nitrate caking. Powder Technol.. 2017;315:114-125.
- [Google Scholar]
- Study on Anti-moisture and Anti-caking Technology of Solid Propellant with Oxidant. Nanjing University of Science & Technology; 2008. Master Dissertation
- Study on surface modification of ammonium nitrate. In: Advanced Materials Research. Trans Tech Publ.; 2012.
- [Google Scholar]
- Study on absorbing moisture by polystyrene - coated ammonium nitrate. Bonding. 2014;35(4):76-78.
- [Google Scholar]
- Xu Ce, J.X., Yuejun, Zhang, 2017. Studies on anti-hygroscopicity modification of ammonium nitrate coated by usingpoly-(meth)acrylates (M. Sc. Dissertation).
- Ammonium nitrate reactively coated with ethylenediamine and its application in azide polyether propellants. Chin. J. Explos. Propellants. 2010;33(4):14-18.
- [Google Scholar]
- Coating and Modification of Ammonium Nitrate Particles. China: Nanjing University of Science & Technology; 2013. Master Dissertation
- Surface modification of phase stabilized ammonium nitrate and its application in solid composite propellants. Chin. J. Explos. Propellants. 2009;1:002.
- [Google Scholar]
- Study on surface properties of coated ammonium nitrate. Energ. Mater.-Chengdu. 2004;12(1):1-5.
- [Google Scholar]
- Influence of ammonium nitrate prills' properties on detonation velocity of ANFO. Propellants Explos. Pyrotech.. 2007;32(5):411-414.
- [Google Scholar]