【作者】 陈春钰；

【导师】 贡雪东； 王风云；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2013， 博士

【摘要】 本论文运用pH曲线法和分子动力学(MD)方法研究了工业循环冷却水系统中七种常用的含N有机膦系化合物：氨基亚甲基膦酸(AMP)、氨基二亚甲基膦酸(NDP)、氨基三亚甲基膦酸(NTMP),乙二胺四亚甲基膦酸(EDTMP)、丁二胺四亚甲基膦酸(TDTMP)、己二胺四亚甲基膦酸(HDTMP)和二乙烯三胺五亚甲基膦酸(DTPMP)的阻垢性能及其作用机理。通过pH曲线实验评定有机膦酸分子对CaCO3的阻垢能力；采用MD方法模拟了目标分子对CaCO3三种晶型的阻垢机理,并与pH曲线实验结果相比较,验证理论模型及MD模拟条件的合理可靠性；在上述相同模拟细节条件下分别系统地研究了目标分子对BaSO4、Ca10(PO4)6(OH)2、CaSO4及水分子存在条件下CaCO3的阻垢机理。pH曲线实验结果表明,在温度75±2℃条件下,搅拌速度500r/min, Ca2+浓度为8mmol/L的标准水样中,除了AMP和NDP以外其余五种膦酸分子均在低浓度时对此条件水样有高效、稳定、良好的阻垢效果,当NTMP、EDTMP、TDTMP、HDTMP和DTPMP的用量分别是5μmol/L、1μmol/L、0.8μmol/L、0.5μmol/L和0.2μmol/L时,阻垢效果良好,几乎完全抑制了此浓度下CaCO3的形成,得到有机膦系化合物的阻CaCO3垢效果排序为：DTPMP> HDTMP> TDTMP> EDTMP> NTMP> NDP≈AMP。对这七种阻垢剂与CaCO3三种晶型相互作用的MD研究表明,目标分子与方解石、文石及球霰石各晶面的结合能均为负值,相互作用是放热过程,主要是静电相互作用起主导,影响远远大于范德华作用力。总的修正结合能表明有机膦系分子对碳酸钙垢的阻垢效果强弱排序为DTPMP> HDTMP> TDTMP> EDTMP> NTMP>>NDP> AMP,与pH曲线实验结果基本一致,说明在此条件下的MD计算模拟是合理可行的。作用机理研究结果表明,膦酸基团个数越多阻垢效果越好,而骨架碳链长度的影响与CaCO3的晶型有关：在与方解石相互作用时,碳链越长阻垢效果越好；而对文石和球霰石,骨架长度的影响相对不明显。以HDTMP为例研究了阻垢剂中的膦酸基团与晶面的相互作用细节,结果表明膦酸基团中的氧原子与晶面上的Ca2+形成了强静电相互作用,占据了原本游离态CO32-在晶面上的活性生长空间,阻碍了晶格的正常生长,从而抑制了晶体的形成。同时测量了膦酸基团作用在晶面上的O原子与晶面Ca2+的有效距离,发现与实际中的Ca-O离子键长相接近,推断添加的阻垢剂与晶面间形成了Ca-O离子键。计算出晶面Ca2+与膦酸基团上氧原子的对关联函数g(r),也可以看出,七种有机膦酸分子的最高峰值均在2.5A左右,与实际的Ca-O离子键长相接近,进一步推测晶面上的Ca2+与有机膦酸分子中的O原子形成了离子键,即存在静电相互作用。根据周期性键链(PBC)理论模型讨论了水分子在方解石阶梯(011)面上的吸附,结果表明水分子主要聚集在边界A(Ca2+层与CO32-层形成的阶梯钝角边缘)和拐点B(CO32-层与Ca2+层形成的阶梯边缘锐角拐角点)位置上,测量出的二面角角度分别为129.4°和63.2°。再以HDTMP为例进一步探讨阶梯晶面的活性吸附点,发现膦酸基团也作用在A和B这两个位置,推测阶梯边缘和拐角点是阶梯晶面的最佳活性生长位置,这结果与PBC理论相符合。同时,根据上述研究将方解石(104)面切割为四种不同终端的阶梯面,分析目标分子与四种不同阶梯面的相互作用。以其中Ca-CO3面为例具体给出目标分子与晶面的作用细节,可以看出也主要作用在阶梯面的阶梯拐点(S位置),这也符合晶体生长PBC理论,说明S位置是Ca-CO3晶面的活性生长点。比较膦酸分子在四种不同晶面的作用,发现除了S位置,晶面的终端拐角点也是优先生长位置。同时比较DTPMP与这四个面的结合能,发现C03> CO3-Ca> Ca-CO3> Ca,即四个面的稳定性与之相反。以相同方法及条件对目标分子与BaSO4、Ca10(PO4)6(OH)2、CaSO4及水分子存在条件下CaCO3晶体的主要生长面进行MD研究,结果表明除AMP和NDP以外其余五种分子均能不同程度的与上述各无机盐晶型紧密结合。根据修正结合能数据,得到膦酸分子对BaSO4垢抑制作用强弱为TDTMP> DTPMP> EDTMP> HDTMP> NTMP> NDP> AMP;对HAP和CaSO4的抑制作用排序均为DTPMP> HDTMP> TDTMP> EDTMP> NTMP>NDP>AMP,与碳酸钙结果一致,说明在抑制上述三种Ca类晶型时结果是相似的。测量出的Ca-O和Ba-O距离,平均值都在2.3-2.5A之间,也说明有机膦酸分子中的O原子与晶面的金属阳离子形成了离子键,即静电相互作用力,是结合作用的主导力量。同时,比较了同一膦酸分子与不同晶面的结合能,结合能越大说明晶面越不稳定,更容易发生晶格转换,生长速度也更快。更多还原

【Abstract】 In this dissertation, the functionary mechanisms of seven organic phosphonate inhibitors (AMP, NDP, NTMP, EDTMP, TDTMP, HDTMP and DTPMP) in the indrustrial circulating cooling water system have been investigated by the pH curve method (pHCM) and molecular dynamics (MD) method. The effect of seven phosphonates on the growth of CaCO3has been evaluated by the pHCM. And MD simulation has been used to study the interaction of the objects on three polymorphs of CaCO3crystal. The results are compared with the pHCM conclusions to validate the rationality and dependability of MD computational simulation. Afterwards, the same simulative conditions are used to study the inhibiting effect of the objects on BaSO4, Ca10(PO4)6(OH)2and CaSO4.The experimental results of the pHCM show that the objects at the low concentration except AMP and NDP have a steady and favorable inhibitory effect at the temperature of75±2℃. The greatest inhibition concentrations of the five phosphonates are5μmol/L (NTMP),1μmol/L (EDTMP),0.8μmol/L (TDTMP),0.5μmol/L (HDTMP) and0.2μmol/L (DTPMP), respectively. It is shown that the inhibition effect of CaCO3precipitation is AMP≈NDP<NTMP<EDTMP<TDTMP<HDTMP<DTPMP.The interactions of organic phosphonates on the three polymorphs of CaCO3crystal are simulated by MD method. The results show that the binding energies of calcite, aragonite and vaterite are negative, namely the interaction is exothermic. It also indicates that the strong electrostatic interactions between the oxygen atoms in phosphonic functional groups and the Ca2+ions of crystal surfaces play a dominant role in their adsorption, whereas the van der Waals interactions play a very small role in the non-bonded interaction. The corrected binding energies are obtained to discuss the inhibitor effectiveness:DTPMP> HDTMP> TDTMP> EDTMP> NTMP>>NDP> AMP, according with the previous pHCM experimental data. It proves that the MD modeling method in these conditions is a useful and reasonable tool in the pursuit of an atomistic understanding of interactions between surfaces and additive molecules. The results also clearly indicate the important of the number of phosphonate groups and the length of the backbone methylene chain connecting the two N atoms. In total, the greater the number of the-PO32-groups and the longer the length of the backbone chain, the better the inhibition of precipitation. But the backbone chain effect of aragonite and vaterite is unconspicuous. The Ca-0(P) distances are all close to2.5A in accordance with the Ca-0bond length from experiment. And the strongest adsorption peak at almost2.5A also shows the formation of Ca-0electrovalent bond between the calcium ions of crystal surfaces and the oxygen atoms of phosphonate groups.According to the periodic bond chains (PBC) theory, MD simulation has been employed to study the adsorption of water molecules onto the stepped calcite (011) surface. The results show that the great mass of water molecules are coordinated to the edge calcium ions and the oxygen atoms on the step edge labeled A or at the corner of the surface labeled B. Their interfacial angles are separately129.4°and63.2°. It suggests that the step edge and the corner are the optimal binding sites. Then, the interaction of HDTMP on the stepped surface is considered as an example. It is found that HDTMP closes with the calcium ions at the B site in accordance with the adsorption of water molecules. Based on the above study, the calcite (104) surface is divided into four different stepped surfaces, terminated by either calcium ions or carbonate groups. The results of the interaction of phosphonates with the four stepped surfaces also suggest that the step edge and the corner are the optimal binding sites. Compared with the binding energies of DTPMP on the four surfaces, it is found the stability of the surfaces:Ca> Ca-CO3> CO3-Ca> CO3.The same method and conditions are used to investigate the inhibition mechanism of the seven phosphonates on the surfaces of BaSO4, HAP and CaSO4. The results indicate that the organic compounds except AMP and NDP can close well with all the surfaces. Based on the corrected binding energies, the inhibition effect of organic phosphonates on BaSO4is TDTMP> DTPMP> EDTMP> HDTMP> NTMP> NDP> AMP different with the conclusion of CaCO3. And the effect on HAP and CaSO4is DTPMP> HDTMP> TDTMP> EDTMP> NTMP> NDP> AMP according with CaCO3.The average of Ca-0and Ba-O distances is almost2.3-2.5A which suggests the formation of Ca-0and Ba-O electrovalent bonds.更多还原