Abstract:Abstract:The present work investigates the use of magnesium hydroxide, produced by magnesia hydration, as a fire retardant in polymers. The hydration was carried out in an autoclave, at temperature of 130°C for 1 hour, and the product was further submitted to cominution in a jet mill. The solids were characterized with regard to their chemical composition, particle size distribution, surface area and morphology. The performance evaluation of the hydroxide as a flame retardant for a copolymer of nylon 6-6,6 was… Show more
“…Depending on the application aimed at, MgO hydroxylation can be either valuable or undesired and, in both cases, the knowledge of how this process occurs can be highly useful. The hydroxylation process must be efficient for the production of fertilizers [1,18], animal and human nutrition [1,27], watertreatment input [1,28], medicaments [1,27,28], fast-hardening Sorel and MgO-based cements [1,[29][30][31] and anti-flame agents for polymer composites [32][33][34] and generates particles of controllable size distribution, specific surface area and shape at competitive costs. On the other hand, it must be avoided or at least minimized in applications to refractory [10,13,14,16,[35][36][37][38][39][40] and abrasive [1] materials and optic and electronic devices.…”
Section: Production Of Different Grades Of Polycrystalline Mgomentioning
confidence: 99%
“…8j). Studies have demonstrated this reaction can produce other compounds, as aluminum-magnesium double layered hydroxide, known as hydrotalcite [36,45,47,48], or particles of suitable morphology to act as mechanical reinforcement in polymeric composites [27,32,33,34].…”
“…Depending on the application aimed at, MgO hydroxylation can be either valuable or undesired and, in both cases, the knowledge of how this process occurs can be highly useful. The hydroxylation process must be efficient for the production of fertilizers [1,18], animal and human nutrition [1,27], watertreatment input [1,28], medicaments [1,27,28], fast-hardening Sorel and MgO-based cements [1,[29][30][31] and anti-flame agents for polymer composites [32][33][34] and generates particles of controllable size distribution, specific surface area and shape at competitive costs. On the other hand, it must be avoided or at least minimized in applications to refractory [10,13,14,16,[35][36][37][38][39][40] and abrasive [1] materials and optic and electronic devices.…”
Section: Production Of Different Grades Of Polycrystalline Mgomentioning
confidence: 99%
“…8j). Studies have demonstrated this reaction can produce other compounds, as aluminum-magnesium double layered hydroxide, known as hydrotalcite [36,45,47,48], or particles of suitable morphology to act as mechanical reinforcement in polymeric composites [27,32,33,34].…”
“…Magnesium hydroxide has found several industrial applications typically ranging from pulp and paper production to the fields of pharmaceutical and wastewater treatment, for example. In recent years, there has been observed also a growing interest concerning the use of magnesium hydroxide powders as flame retardant and smoke‐suppressing additives to produce polymers 1, 2. The application of magnesium hydroxide as a flame retardant requires a very high quality Mg(OH) 2 powder with regard both to chemical purity and physical properties of the solid such as particle size, surface area, morphology, etc.…”
The kinetics of magnesia hydration to produce magnesium hydroxide is crucial for process design and control, and for the production of an Mg(OH) 2 powder with desirable particle morphology. In this study, highly pure magnesia has been hydrated in a batch reactor. The effects of the following variables were evaluated experimentally: temperature (308-363 K), reaction time (0.5-5 h), initial slurry density (1-25%wt) and particle size in the ranges −212 + 75 µm and −45 + 38 µm. Experimental data indicate increasing magnesia hydration rates with increasing temperature, as expected. In addition, it has been observed that the hydration of magnesia increases significantly up to about 4-5%wt initial slurry density, stabilising afterwards. On the other hand, the reaction was almost unaffected when magnesia with different particle sizes were hydrated because of similar specific surface areas involved. A reaction mechanism to explain the oxide dissolution and the hydroxide precipitation has been proposed, assuming no significant change in the initial solids size and dissolution rate as the controlling step. The calculated activation energy value of 62.3 kJ mol −1 corroborates the mechanism proposed in this study and compares well with values previously reported in the literature.
“…HM is a relevant magnesium material that has broad applicability, from flame retardant for polymers to neutralizing agent for effluent treatment. Its use as neutralizing agent is increasing in some countries because magnesium hydroxide has a high alkalinity (27%) when compared to traditional agents (calcium and sodium hydroxide) [19,20,21,22].…”
This paper aims to evaluate the kinetics of hydroxylation for two distinct magnesias from Brazilian mineral sources regarding their purity: A -92.44wt% and B -98.20wt% of MgO. The magnesias were characterized and hydroxylated in a CSTR (1,0L) under: 80°C, stirring rate of 950rpm and 30%w/w of solids, in triplicate. The results showed that the presence of natural impurities in caustic magnesia (Fe, Mn, Al, Ca) hindered the advance of the reaction, but not at the beginning, when the hydroxylation was similar for both samples, what is associated with the similar values of their surface area. The reaction stabilization was observed after two hours for both samples: Sample A -35.15%; Sample B -46.43%. The natural impurities of caustic magnesia influenced the development of hydroxylation after 30 minutes, causing a retardant effect probably due to their behavior as a physical-chemical barrier, hindering the ions diffusion though the solid matrix.
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