Basic Research On Additive-assisted Preparation Of Mgo Whiskers

There are abundant reserves of salt lake magnesium resources in Qinghai Province,China.Using MgCl₂ from salt lakes?that is MgCl₂·6H₂O?to prepare Mg O whiskers is one of the important ways to efficiently use magnesium resources.Mg CO₃·3H₂O whiskers are usually used as precursors to prepare Mg O whiskers.When the precursor is prepared by the precipitation crystallization method,it is easy to obtain disordered and agglomerated crystals because the reaction proceeds in an aqueous medium.Therefore,the quality of the calcined Mg O whiskers is poor.Generally,adding additives when preparing Mg CO₃·3H₂O whiskers can increase the aspect ratio and dispersibility of the product.However,the current research on the preparation of Mg CO₃·3H₂O whiskers shows that the effects of various additives are different,and the effects of different additives need to be compared.The growth mechanism of whiskers in the corresponding system is not yet clear.It is important for the preparation of high-quality Mg O whiskers to understand the influence of additives on the preparation of Mg CO₃·3H₂O whiskers and the growth mechanism of whiskers.In this paper,MgCl₂·6H₂O and NH₄HCO₃ were used as raw materials,and different additives were added when preparing Mg CO₃·3H₂O whiskers.And then obtained Mg O whiskers after calcined precursors.The specific research content is as follows:?1?In the preparation of Mg CO₃·3H₂O whiskers,the effects of different additives on the crystallization effect,morphology and size of Mg CO₃·3H₂O were investigated.The results showed that the Mg CO₃·3H₂O crystal obtained without additives had a small aspect ratio and uneven size.In the presence of disodium hydrogen phosphate?DSP?,the size of the obtained Mg CO₃·3H₂O crystal became larger?the length was about 20³5 ?m,and the aspect ratio was about 15²5?.However,there was a partial beam-like structure in the product due to DSP entered Mg CO₃·3H₂O and changed the crystal structure.When polyethylene glycol?PEG?was used as an additive,the crystallinity of the product deteriorated and the aspect ratio also decreased.PEG molecules were wrapped on the surface of amorphous particles and crystals,which hindered the growth of crystals.When cetyltrimethylammonium bromide?CTAB?was added,the Mg CO₃·3H₂O whiskers were well crystallized and dispersed,and the aspect ratio was slightly increased but not obvious.However,when sodium dodecyl sulfate?SDS?and sodium acetate?Na Ac?were used as additives,the length and aspect ratio of the whiskers increased,and the dispersibility was good,which were effective promoted the formation of whiskers.?2?The formation process of Mg CO₃·3H₂O whiskers with SDS and Na Ac as additives was studied,and the composition and morphology of the corresponding products at different reaction times were analyzed.When Na Ac was used as an additive,it first produced amorphous 4Mg CO₃·Mg?OH?2·4H₂O,and then transformed into amorphous Mg CO₃·3H₂O.Na+ produced by Na Ac adsorbed on the?101?plane of the Mg CO₃·3H₂O crystal axis,which hindered the growth of the crystal plane.The growth of radial crystal planes,such as?001?,was not affected.Therefore,Mg CO₃·3H₂O whiskers with large aspect ratio were obtained.When SDS was used as an additive,a spherical layer of 4Mg CO₃·Mg?OH?2·4H₂O was obtained through a spherical micelle template.Then the micelles ruptured due to reduced SDS concentration,and the lamellar spherical structure was transformed into amorphous Mg CO₃·3H₂O.SDS promoted the growth of amorphous Mg CO₃·3H₂O in the?101?direction into whiskers with a large aspect ratio.?3?The results of research on the preparation of Mg O whiskers by the precursor decomposition method showed that the morphology of the precursor whiskers was not significantly damaged.Mg O whiskers with a diameter of 1² ?m and an aspect ratio of 20⁴0 were successfully prepared.