MgCO3·3H2O晶须的制备及其生长机制的研究

Study on preparation and growth mechanism of MgCO3·3H2O whiskers

以MgCl2·6H2O和NH4HCO3为原料,CH3COONa·3H2O为形貌控制剂,采用沉淀结晶法制备MgCO3·3H2O晶须,考察了不同添加量的CH3COONa·3H2O对晶须结晶过程和形貌的影响,并研究了晶须在该体系中的生长机制。结果表明:当体系中加入质量分数为0.23%的CH3COONa·3H2O时可以成功制备长径比约为30的棒状MgCO3·3H2O晶须,CH3COONa·3H2O的存在促进了MgCO3·3H2O晶须的形成。该体系中晶须的生长过程:首先形成无定形的4MgCO3·Mg(OH)2·4H2O,之后无定形4MgCO3·Mg(OH)2·4H2O逐渐转变为MgCO3·3H2O并生长成较大长径比的棒状MgCO3·3H2O晶须。这是因为CH3COONa·3H2O电离产生的Na+选择性吸附在MgCO3·3H2O晶体轴向的(101)晶面,抑制了该晶面生长,而径向晶面生长速率未受到影响,从而促使无定形MgCO3·3H2O生长成棒状晶须。

MgCO3·3 H2 O whiskers was prepared with MgCl2·6 H2 O and NH4 HCO3 as raw materials and as CH3 COONa·3 H2 O morphology control agent by precipitation crystallization method.The effects of different amounts of CH3 COONa·3 H2 O on the crystal and morphology of MgCO3·3 H2 O and the growth mechanism of whiskers in the system were investigated.The results showed that the rod-shaped MgCO3·3 H2 O whiskers with a length to diameter ratio of 30 can be successfully prepared when the amount of CH3 COONa·3 H2 O added was 0.23%(mass fraction).CH3 COONa·3 H2 O may be beneficial to the formation of whiskers,and the growth mechanism of which was proposed:firstly,amorphous 4 MgCO3·Mg(OH)2·4 H2 O was formed,and then they gradually transformed into MgCO3·3 H2 O and grown into rod-shaped whiskers.The Na+ produced by CH3 COONa·3 H2 O were selectively adsorbed on the(101) crystal plane of the axial direction of MgCO3·3 H2 O crystal,which inhibited the growth of the crystal plane,and the radial growth was not significantly affected,which promoted amorphous MgCO3·3 H2 O grew into the rod whiskers.