Borate have been used widely in various materials due to its physical and chemical properties such as flame retardant, heat resistance, high hardness, high strength, wear resistance and light weight[1]. Among them, magnesium borate was mainly used in luminous materials, flame retardant materials, coatings and other materials due to its high stability, chemical stability and low cost[2–5]. The results show that the morphology and particle size of the sample has a great influence on its properties. For example, the flame retardancy of nano α-4CaO·5B2O3·7H2O with spherical-like, pupal-like, and sheet-like morphology is enhanced sequentially[6]; the flame-retardant properties of BaO·4B2O3·5H2O nanoribbons and nanosheets increases sequentially[7]; the flame retardancy of 2MgO·B2O3·1.5H2O with nanowire morphology is superior to that of sample with nanorod morphology[8]; among zinc borate (Zn8[(BO3)3O2(OH)3]:Eu3+) phosphors with six different morphologies, zinc borate phosphors with hexahedral morphologies exhibit the strongest luminescence intensity[9]. Therefore, the synthesis and properties research of borate with different morphologies and particle sizes have received increasing attention.
MgBO2(OH)(2MgO·B2O3·H2O) is a kind of translucent mineral widely distributed in nature. MgBO2(OH) with different morphologies and particle sizes has been prepared using hydrothermal and ion thermal methods, and its properties have been studied. For example, Liu et al.[10] obtained nanospherical-like MgBO2(OH):Eu3+, Y3+ with good luminescent properties by hydrothermal method, indicating that MgBO2(OH) is a good luminescent material matrix. Sun[11] and Liu et al.[12] synthesized hierarchical porous MgBO2(OH) microspheres by hydrothermal method, and the results showed that this sample has potential application prospects as an efficient adsorbent for removing Congo red (CR) or other organic dyes from wastewater. Zhang et al.[13] prepared porous MgBO2(OH) nanospheres by ionic thermal method, which have potential advantages in dye adsorption and heterogeneous catalysis. The above results indicate that MgBO2(OH) has good properties in luminescence, mechanics, adsorption and other aspects.
Thermodynamic properties can provide information about the stability and reactivity of the substances, playing a very important role in scientific research and industrial production. In the past few decades, researchers have carried out many studies on the thermodynamic properties of borates using calorimetry. For example, Konings R.J.M et al.[14] measured the standard molar enthalpies of formation of CsBO2; Wang et al.[15] determined the standard molar formation enthalpies of BaB8O11(OH)4·3H2O and MB8O11(OH)4·xH2O (M = Ca, Sr, Ba); Liang et al.[16] determined the standard molar enthalpies of formation of 2ZnO·2B2O3·3H2O and ZnB4O7; the standard molar enthalpies of formation of alkali metal and alkaline earth metal hydrated borates such as lithium borate[17], sodium borate[19], potassium borate[19, 22], calcium borate[18, 23, 24], barium borate[25] and strontium borate[26] were tested by Gao[17–20] and Liu et al.[6, 21]. At present, a few studies on the thermodynamic properties of hydrated magnesium borate have been reported, such as MgO·3B2O3·3.5H2O[27], 2MgO·3B2O3·17H2O[28] and 2MgO·B2O3·1.5H2O[29]. Research has shown that the thermodynamic properties of materials are related to their morphology and particle size. For example, Liu et al.[30] found that the standard molar formation enthalpy of formation of nano Ca[B6O9(OH)2]·3H2O with sheet-like, ellipsoidal-like and flower-like morphologies decreased(more exothermic enthalpy) sequentially; Geng et al.[31] found that the standard molar enthalpy of 2CaO·B2O3·H2O increases(less exothermic enthalpy) with the decrease of its particle size; Guo et al.[32] found that the standard molar formation enthalpy of Zn3B10O18·14H2O increases (less exothermic enthalpy) with the decrease of its particle size.
Zhu et al.[33] determined the thermodynamic properties of MgBO2(OH) nanowhiskers, but there have been no comparative studies on the thermodynamic properties of MgBO2(OH) with different morphologies. In this paper, the MgBO2(OH) with three different morphologies were prepared by hydrothermal method, and the standard molar enthalpies of formation of MgBO2(OH) with different morphologies were measured, and the influence of morphologies on their thermodynamic properties was analyzed.