特殊形貌碳酸镁用途、制备及表征

碳酸镁大致可分为水合碳酸镁和碱式碳酸镁,是制备镁盐系列产品的重要原料。随着镁质材料的开发,功能化特殊形貌碳酸镁必将是一个重要发展方向。相转移过程贯穿于碳酸镁合成过程中,不同晶型和形貌的碳酸镁可以通过控制相转移过程获得。不同的反应条件和操作方式决定了相转移的热力学基础和动力学过程。棒状/针状三水碳酸镁可在较低温度下得到;碱式碳酸镁是纳米片状晶体的组装体,合成条件影响其外在形貌。较详细介绍了碳酸镁的用途及制备方法和制备碳酸镁过程中的相转移过程,最后对碳酸镁的表征手段予以介绍。     

碱式碳酸镁微球的反应结晶过程

碱式碳酸镁是一种重要的化工产品和原料。实验提供一种反应结晶直接制备碱式碳酸镁微球的方法,考察了搅拌时间、反应温度和反应物浓度对产物形貌和粒度的影响,分析了其形成机制。结果表明,采用控制搅拌时间的方法,制备出粒度在10～43 μm、变异系数为28%～43%的尺寸可控、形态良好的碱式碳酸镁微球。通过对结晶过程晶型晶貌研究发现,氯化镁和碳酸钠反应首先生成无定形物,逐步相转移为结晶相。研究表明,搅拌作用对无定形物相转移具有显著影响。在搅拌过程中,以产生晶核过程为主,在静置状态下,以无定形物生长在已有晶体过程为主,搅拌时间对晶体粒度和形貌起到调控作用。     

碳酸镁水合物在283~363 K范围内的晶体组成及晶型

研究了由MgSO4和Na2CO3在283~363 K反应沉淀得到的碳酸镁水合物的组成和形貌随反应温度的变化规律,并对产品进行了表征. 结果表明,在283~313 K间,可得到棒状三水碳酸镁(MgCO3×3H2O);当温度升高到323 K时,产物由棒状三水碳酸镁变为球形碱式碳酸镁,且随着反应温度升高,球形碱式碳酸镁的直径增大. MgSO4的初始浓度和Na2CO3滴加速率对三水碳酸镁晶体形貌有明显的影响.     

花瓣状纳米氢氧化镁及氧化镁的微波辅助合成

在微波辅助下,以硫酸镁、NH₃•H₂O-NH₄Cl缓冲溶液为原料,通过均相沉淀反应制备了纳米氢氧化镁,经煅烧又得到了纳米氧化镁。采用X射线衍射（XRD）、透射电镜（TEM）、扫描电镜（SEM）、热重分析（TG）等分别对纳米氢氧化镁和氧化镁的结构、形貌及热稳定性进行了分析测试。结果表明,纳米氢氧化镁的结晶性能较好,其形貌为由厚度约40 nm的纳米片团聚而成的花瓣状;纳米氧化镁亦保持了氢氧化镁花瓣状形貌。并对微波辅助下纳米氢氧化镁形成的可能机理进行了初步探讨。     

超临界水快速连续制备纳米磷酸铁锂正极材料

建立了超临界水快速连续合成磷酸铁锂纳米颗粒的工艺。研究了反应物浓度、反应温度和反应压力等因素对磷酸铁锂颗粒的大小、结晶度和形貌的影响并解释了相关机理,采用扫描电镜（SEM）、动态光散射（DLS）粒度分析和X射线衍射（XRD）等手段表征了目标产物的颗粒大小、形貌和结晶度。结果表明,在所研究的过程参数范围内,均获得了纳米尺度的磷酸铁锂。在超临界范围内,提高反应温度会使颗粒尺寸变大,但粒度分布更加均匀;预热温度对磷酸铁锂的结晶度有明显的影响,升高预热温度有利于提高磷酸铁锂纳米颗粒的结晶度;较高的反应压力、较低的反应物浓度有利于得到更小的纳米颗粒。在反应温度为380 ℃、预热温度为405 ℃、反应压力为27 MPa、二价铁离子浓度为0.015 mol/L条件下,获得了平均粒度为105 nm的高结晶度、橄榄石状的球形磷酸铁锂颗粒。     

微波水热法用于制备纳米氧化锌粉体的研究

以氯化锌和氢氧化钠为原料,采用微波水热法制备了纳米氧化锌粉体,并采用X射线衍射（XRD）和透射电镜（TEM）对粉体的粒度、形貌、纯度进行了表征。通过单因素实验考察了反应温度、微波反应时间、微波功率、锌离子与氢氧根的浓度比等因素对氧化锌粉体的产率和粒径的影响,再通过正交试验得到最优制备条件。最佳制备工艺条件：锌离子与氢氧根的浓度比为1∶1.2、反应温度为 120 ℃、反应时间为 10 min、微波功率为500 W。在此条件下所得氧化锌粉体的晶型为六方晶相,产率达到93.5%,平均粒度约70 nm,粒径分布较窄,结晶完整。     

十二烷基苯磺酸钠作为添加剂制备球形碱式碳酸镁

在十二烷基苯磺酸钠(SDBS)的辅助下,利用六水氯化镁和无水碳酸钠在2个阶段不同温度下的反应直接合成碱式碳酸镁微球。利用XRD、SEM等表征方法研究了反应温度、热解温度、搅拌速率和搅拌时间等条件对产物的影响。结果表明:反应温度为70℃、热解温度为120℃、搅拌时间为60 s时,可得到球形度高、颗粒均匀、颗粒粒径约为25μm的碱式碳酸镁微球。反应温度、热解温度、搅拌时间、搅拌速率均对球形碱式碳酸镁的尺寸和微观形貌起到调节作用。     

碳酸镁晶体演变过程研究(Ⅱ)

本文采用低温水溶液法制备出棒状三水碳酸镁晶体,通过对制备产品进行恒温水浴加热,研究制备产物的物相及形貌的演变过程,发现晶体物相由三水碳酸镁向四水碱式碳酸镁转变,同时,晶体形貌经历了棒状一片状的变化过程.在此基础上,进一步从晶体结构、晶体稳定性及能量角度分别分析了三水碳酸镁晶体向四水碱式碳酸镁晶体演变的本质.     

聚焦单模微波辐射法制备Pr-TiO_2纳米簇及其光学性能的研究

以钛酸丁酯和硝酸镨为原料,将溶胶-凝胶法制备的纳米Pr-TiO_2颗粒采用Discover聚焦单模微波进行微波处理。采用XRD、SEM、TEM考察了微波辐射温度、时间及功率对其晶型结构、表观形貌及光催化性能的影响。结果表明:当微波辐射温度为120℃,功率为100 W,辐射20 min时得到晶型结构比较完善的锐钛矿纳米Pr-TiO_2,并且在此条件下对甲基橙的降解率最高,光催化性能最强。对其形貌进行分析可知,所制备的纳米Pr-TiO_2为花球状的纳米簇,并且此结构是由片层结构组装而成,所制备的Pr-TiO_2纳米簇为多晶结构。利用聚焦单模微波法拓宽了TiO_2的光响应范围,提高了可见光的利用率。。     

氨基酸调控无水碳酸镁晶体结晶试验研究

无水碳酸镁晶体作为一种新型无机功能材料引起了研究者们的广泛关注。以氯化镁为原料,碳酸钠为沉淀剂,合成了无水碳酸镁晶体,再以甘氨酸、组氨酸、丙氨酸及L-天门冬氨酸四种不同种类氨基酸作为添加剂,调控其结晶的粒度及形貌。采用X射线衍射仪、扫描电子显微镜、激光粒度分析仪对合成产物进行表征,分析不同种类氨基酸对合成的无水碳酸镁晶体物相结构和形貌的影响。结果表明:在组氨酸调控下合成的无水碳酸镁结晶纯度高,生成的产物中n(Mg²⁺)∶n(CO^2-₃)为1∶0.94;L-天门冬氨酸调控合成的晶体纯度次之;甘氨酸和丙氨酸调控合成的晶体中掺杂大量碱式碳酸镁晶体。在组氨酸、L-天门冬氨酸、甘氨酸及丙氨酸四种氨基酸调控作用下,晶体结晶形貌依次呈凸面球三角形状、近球状、球状及不规则状,且无水碳酸镁晶体粒径分布均呈先上升后振荡下降最后小粒径拖尾的趋势。以上研究结果为无水碳酸镁晶体的仿生合成提供了参考。     

Effect of particle size of hydromagnesite on properties of calcium aluminate cement bonded corundum based castables

Calcium aluminate cement was premixed with hydromagnesite having different particle sizes, as a calcium magnesium aluminate cement precursor, to investigate the influence of particle size of hydromagnesite on the volume stability and thermo-mechanical properties of corundum based castables after firing at 1550 °C. The impact of particle size of hydromagnesite on the phase composition and microstructure evolution of fired castables matrix were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results demonstrate that hydromagnesite with smaller particle size has a better volumetric stability and thermo-mechanical properties of castables, because of the more homogeneously distributed micro-pores, and smaller size MA and CA₆ resulted from the more uniformly distributed hydromagnesite in castables.     

Preparation and thermal properties of polyethylene terephthalate/huntite–hydromagnesite composites

In this report, it was aimed to the improve thermal stability of polyethylene terephthalate (PET) by adding huntite/hydromagnesite minerale. PET/huntite/hydromagnesite composites were prepared by adding various proportions of huntite/hydromagnesite to PET. The chemical structures of the composites were characterized by Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) analysis. Thermal properties of the composites were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Glass‐transition temperatures and char yields increased with the increase of the huntite/hydromagnesite content in the composites. The surface morphologies of the composites were investigated by a scanning electron microscopy. The obtained results proved that the composite system is more thermally stable than the pure PET itself. POLYM. COMPOS., 37:3275–3279, 2016. © 2015 Society of Plastics Engineers     

水菱镁石在专用化学品生产中应用探讨

对水菱镁石在专用化学品生产中的应用进行了研讨。介绍了水菱镁石的化学组成、性能参数和矿床资源。探讨了水菱镁石在镁质阻燃剂、烟气脱硫剂、镁肥和动物饲料添加剂生产方面应用的可行性。     

Use of Turkish huntite/hydromagnesite mineral in plastic materials as a flame retardant

In this study, the flame retardancy properties of huntite/hydromagnesite mineral in plastic compounds were investigated for potential electrical applications. Before the production of composite materials, huntite/hydromagnesite minerals were ground to particle sizes of 10, 1, and 0.1 μm. Phase and microstructural analysis of huntite/hydromagnesite mineral powders were undertaken using XRD and SEM‐EDS preceding the fabrication of the composite materials. The ground minerals with different particle size and content levels were subsequently added to ethylene vinyl acetate copolymer to produce composite materials. After fabrication of huntite/hydromagnesite reinforced plastic composite samples, they were characterized using DTA‐TG, FTIR, and SEM‐EDS. Flame retardancy tests were undertaken as a main objective of this research. The size distribution and the mineral content effects are measured regarding the flame retardancy of the polymer composites It was concluded that the flame retardant properties of plastic composites were improved as the mineral content increased and the size was reduced. POLYM. COMPOS., 31:1692–1700, 2010. © 2010 Society of Plastics Engineers.     

用水菱镁石作为烟气脱硫剂的建议

针对我国水菱镁石的资源特点、化学组成和物性参数,参照用矿物型镁质材料诸如水镁石、菱镁矿做烟气脱硫剂的研究实例,根据水菱镁石可溶于任何无机酸的特性,提出了在镁法烟气脱硫中用水菱镁石做烟气脱硫剂的建议,并探讨了它的发展前景。     

Fabrication of hydrophobic surface with hierarchical structure on Mg alloy and its corrosion resistance

A hydrotalcite/hydromagnesite conversion coating with hierarchical structure has been fabricated on a Mg alloy substrate by in situ hydrothermal crystallization method. A MgO layer existing between the hydrotalcite/hydromagnesite film and the substrate was formed prior to the hydrotalcite/hydromagnesite film during the crystallization process. After surface treatment with silane coupling agent, the surface of conversion coating changes from hydrophilic to hydrophobic. Scanning electron microscopy (SEM) revealed that the silylated conversion coating with hierarchical structure maintains the original rough surface of which was composed of numerous micro-scale flakes and beautiful flower-like protrusions. Polarization measurements have shown that the hydrophobic conversion coating exhibited a low corrosion current density value of 0.432 μA/cm², which means that the hydrophobic conversion coating can effectively protect Mg alloy from corrosion. Electrochemical impedance spectroscopy (EIS) showed that the impedance of the hydrophobic conversion coating was 9000 Ω. It means that the coating served as a passive layer with high charge transfer resistance.     

Fire-proof silicate coatings with magnesium-containing fire retardant

A formula for an environmentally friendly and safe fire-proof paint was developed based on a potassium silicate aqueous solution with addition of a magnesium-containing fire retardant. The predominant use in paint of magnesium-containing fire retardant such as hydromagnesite compared to brucite and magnesite was demonstrated. It was established that a paint containing 5.5 wt% of hydromagnesite provides the first group of fire resistance for a wooden surface. The high fire resistance of the paint with this formula is proven by the high intumescence ratio (150%) and low weight losses (8.4%) after tests in a ceramic tube. When the paint is heated, a gradual loss of weight is detected, which is related to the characteristics of the hydromagnesite structure and helps to obtain an effectively foamed protective layer that prevents the diffusion of combustible gases and flame.     

加压碳化法制备碱式碳酸镁新工艺研究

碱式碳酸镁是一种性能优良的填充剂和分散剂,目前主要采用白云石碳化法或苦土粉-硫酸-碳酸氢铵法生产,流程复杂,污染严重。研究了在加压条件下以氢氧化镁浆液和二氧化碳气体为原料制备碱式碳酸镁新工艺。考察了反应温度、反应时间、二氧化碳分压对产品质量的影响。采用扫描电子显微镜（SEM）、X射线衍射仪(XRD)和热重-差热分析仪（TG-DTA）对产品的形貌、晶体结构及热失重进行了表征。结果表明,在反应温度为120 ℃,二氧化碳分压为0.22 MPa,反应时间为3 h时,可得到纯度较高、形貌为规则的六方薄片状的产品。     

The effectiveness of magnesium carbonate‐based flame retardants for poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐ethyl acrylate)

In this report we outline recent work on the evaluation of magnesium carbonate‐based flame retardants for polymers commonly used in halogen‐free flame retardant wire and cable applications: poly(ethylene‐co‐vinyl acetate) (EVA) and poly(ethylene‐co‐ethyl acrylate) (EEA). Natural magnesium carbonate (magnesite), synthetic magnesium carbonate (hydromagnesite), and hydromagnesite/huntite blends were combined with EVA or EEA and tested for flame retardancy effectiveness with the cone calorimeter. The flammability results showed that the effectiveness of these carbonates was polymer dependent, suggesting that polymer degradation chemistry played a role in the flammability reduction mechanism. Hydromagnesites were, in general, more effective in reducing flammability, being comparable in performance to magnesium hydroxide. Finally, we report some polymer–clay (organically treated montmorillonite and magadiite) + magnesium carbonate flame retardant results which showed that the nanocomposite yielded mixed results. Specifically, the polymer–clay nanocomposite samples did not always yield the greatest reductions in peak heat release rate. Copyright © 2007 John Wiley & Sons, Ltd.