Study On Preparation Of One Dimensional Nano Magnesium Borate （Mg₂B₂O₅） From Desalinated Concentrated Seawater And Its Application

The one-dimensional（1-D）magnesium borate nanomaterials,such as nanorods,nanowires,nanobelts etc,are widely employed in military affairs,transportation and aerospace field due to its light weight,high toughess,strength and modulus.While,lots of factors,such as time-consuming,high sintering temperature and cost which confine the development of 1-D magnesium borate materials.In this work,a novel homogeneous precipitation and ternary molten salts process are introduced to prepare 1-D Mg₂B₂O₅ by using desalinated concentrated seawater which contains MgCl₂,MgSO₄,NaCl and KCl,NaCl,KCl and reaction byproduct of Na₂SO₄ act as ternary molten salts,this process overcomes the above mentioned limitation factors.The main results were as following:Desalinated seawater with 27.4 Bh was obtained by simulation of solar evaporation with boric acid as raw material,sodium hydroxide as precipitant to form slurry.In this process,Mg₂（OH）₃Cl、Na₂SO₄ and Na₂B₄O₅（OH）₄·8H₂O were produced.Dried the slurry,the powder was obtained by ball-milling the mixture.The powder was characterized by DTA techniques,the results showed that the formation temperature of Mg₂B₂O₅ in ternary molten salts was 540 °C and melting point of ternary molten salts was 738 °C,weight-loss ratio is 37.28 %.Chemical reaction was confirmed by thermodynamic calculation during calcination process for preparing Mg2B2O5 1-D nanomaterial.During the calcination process,the The effect of calcined temperature,heating rate and calcined time on the growth direction,structure,composition and morphology evolution of as-prepared samples were discussed.The results showed that calcined temperature,calcined time,and heating rate had great effect on morphology evolution but had no effect on structure.Calcined temperature and time can affect growth direction and heating rate can influnce the composition.The optimized preparation conditions were 780 °C of calcination temperature,5 °C min-1 of heating rate and 2 h calcinated time.The Micro dimension of the as-prepared sample had an average diameter of 100 nm-150 nm and length over 5 μm.XPS,SEM,HRTEM,FT-IR and BET were further employed to character the as-prepared samples.Furthermore,desalinated seawater with different Bh were also stiudied to synthesize magnesium borate 1-D nanomaterial,and the results proved the formated nanorod morphology,in according well with the above results but had some difference such as homogeneity and size.The growth mechanism of synthesizing magnesium borate 1-D nanomaterial using desalinated seawater was briefly discussed,and the conclusion on the growth mechanism was paralled growth model.Compared with ternary molten salts process for preparing Mg2B2O5 1-D nano material,calcined temperature,formation temperature of Mg2B2O5 in NaCl molten salt,point of molten salt inreased by 40 °C、84 °C and 64 °C respectively.Natural seawater methods were also investigated.Natural seawater were empolyed to synthesize Mg₂B₂O₅ nanorods which was added purification unit,size distribution of nanorods were different.So it was clear that ternary molten salts process to synthesize Mg₂B₂O₅ 1-D nanomaterial using desalinated seawater possesses obvious advantage.The as-prepared nanorods surface modified by KH550 reinforced nylon-6 composite was studied,the results showed that tensile,bending and impact strength of the composite were improved with increased the content of modified Mg₂B₂O₅ nanorods in nylon-6 composite.