# Study on Heat Transfer Performance and Anti-Fouling Mechanism of Ternary Ni-W-P Coating
## 3 Results
### Transient States of Calcite, Aragonite, and Vaterite  
In order to explore the nucleation selectivity of CaCO\({}_{3}\) fouling on the different surface of specimens, three different-crystal forms of CaCO\({}_{3}\) (calcite, aragonite, and vaterite) were investigated. As shown in Figure 11a, the plane triangle of [CO\({}_{3}\)] is perpendicular to the threefold axis and arranged as layer-structure. The direction of [CO\({}_{3}\)] triangle in the identical layer is the same while the direction of them in the adjacent layer is the opposite. Ca, distributed alternately with [CO\({}_{3}\)], perpendicular to  
Figure 10: **(a)** Heat transfer coefficient of specimens after being fouled; **(b)** Thermal conductively of specimens varied with the temperature; **(c)** Thermal conductively of specimens varied with tungsten content. the threefold axis is also arranged as layer-structure and in the form of cubic closest packing (CCP). Its coordination number is 6 and the Ca constitute [CaO\({}_{6}\)] octahedral with 8 [CO\({}_{3}\)]. The structure of aragonite is isomorphic with calcite. Ca in aragonite is organized in the structure of hexagonal closest packing (HCP) (Figure 11b). Ca, as well as [CO\({}_{3}\)] triangles, are well arranged in layer-structure parallel to the aragonite (001). Both of them are arranged alternately along the c axis and [CO\({}_{3}\)] layers [47]. There are six [CO\({}_{3}\)] around each Ca and 9 angular top oxides of them are connected to the Ca, forming the nine-fold coordination. In Figure 11c, a hexagonal lattice [CO\({}_{3}\)] groups formed by Ca is distributed along the hexagonal axis. The number of coordination per cell is at least 12 [48]. Figure 11d1 shows the PDOS of calcite. It can be viewed that the peaks of 3p orbit of calcite are at \(-\)19, \(-\)18, \(-\)8 eV and the peaks of 4s orbit is at \(-\)38 eV. On the bonding of Ca-[CO\({}_{3}\)], 3p orbit of Ca and the 2s orbit of O have obvious resonance at \(-\)18 eV. Additionally, resonances are established by the 2p orbit of C and the 3p orbit of Ca at \(-\)18 eV, indicating that they are likewise bonded. Comparing with the PDOS in Figure 11d1,d2, we can find that the orbit peaks of the two phases are virtually similar, which manifest that the bond strength and type of them are near-identical [49]. In Figure 11d2, the resonance peaks of the 2s orbit of O and the 3p orbit of Ca at \(-\)18 eV are sharper than that of the calcite. This is because the difference of the coordination number of Ca with [CO\({}_{3}\)] in the two different-crystal structures. Their coordination number is 6 and 9, respectively. From the PDOS of vaterite in Figure 11d3, it is clearly observed that the resonance region shifts to the negative direction obviously and 2s orbit of C resonates with the 4s orbit of Ca at \(-\)42 eV. Meantime, 2p orbit of C contributes to 3p orbit of Ca at \(-\)24 and \(-\)22 eV, which proves that Ca have a stronger effect on C in the vaterite phase structure and leads to multi-orbit bonding of Ca-[CO\({}_{3}\)]. Antibonding orbits in vaterite move to the negative direction as a whole compared with calcite and aragonite, showing that the bonding effect in vaterite decreases. Figure 11: _Cont._  
The geometry optimization in Dmol\({}^{3}\) module was used to minimize the energy of super-cell. Meantime, electronic exchange was disposed with the Perdew-Burke-Ernzerhof (PBE) [35; 36] function of Generalized Gradient Approximation (GGA) when minimizing the energy. The total energy of different-crystal nucleation of Ca\({}^{2+}\) and [CO\({}_{3}\)]\({}^{2-}\) was computed in Table 5. As shown in Figure 12b, it displays an energetic profile for potential energy surface of calcite, vaterite, and aragonite by relative energy \(E\). The energy of nucleation of calcite, aragonite, and vaterite formed by the Ca\({}^{2+}\) and [CO\({}_{3}\)]\({}^{2-}\) decreases. The corresponding decreased energy of a single molecule are 2.13 eV, 2.68 eV, and 2.43 eV, respectively.