materials Article
Preparation of CaCO3-TiO2 Composite Particles and Their Pigment Properties Sijia Sun, Hao Ding *
ID
and Xifeng Hou
Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences (Beijing), Xueyuan Road, Haidian District, Beijing 100083, China;
[email protected] (S.S.);
[email protected] (X.H.) * Correspondence:
[email protected]; Tel.: +86-010-8232-2982 Received: 8 May 2018; Accepted: 25 June 2018; Published: 3 July 2018
Abstract: CaCO3 -TiO2 composite particles were prepared with calcium carbonate (CaCO3 ) and TiO2 in stirred mill according the wet grinding method. The pigment properties, morphology, and structure of CaCO3 -TiO2 composite particles and the interaction behaviors between CaCO3 and TiO2 particles were explored. In the CaCO3 -TiO2 composite particles, TiO2 is uniformly coated on the surface of CaCO3 and the firm combination between CaCO3 and TiO2 particles is induced by the dehydration reaction of surface hydroxyl groups. CaCO3 -TiO2 composite particles have similar pigment properties to pure TiO2 . The hiding power, oil absorption, whiteness and ultraviolet light absorption of composite particles are close to those of pure TiO2 . The application performance of CaCO3 -TiO2 composite particles in the paint is consonant with their pigment properties. The contrast ratio of the exterior paint containing CaCO3 -TiO2 composite particles is equivalent to that of the paint containing the same proportion of pure TiO2 . Keywords: CaCO3 -TiO2 ; composite particle; pigment; wet grinding
1. Introduction CaCO3 is an important inorganic mineral material. Especially, the CaCO3 powder material prepared with various non-metallic minerals, such as aragonite, calcite, and some rocks with calcite as the main ingredient component, has many advantages, such as high purity, high whiteness, good compatibility with organic and inorganic matrices, and low cost [1,2]. Therefore, CaCO3 has become the most widely used filler in many industrial products such as plastic, paint, and paper due to its obvious cost advantage compared to most non-metallic minerals [3,4]. In order to further increase the utilization value of CaCO3 and achieve the efficient utilization of mineral resources, it is necessary to develop CaCO3 -based composite with oxides, such as TiO2 [5,6]. Recently, the composite pigment prepared by coating TiO2 particles on the surface of CaCO3 particles, had received wide attention [7]. The composite pigment can not only increase the utilization efficiency of pigment TiO2 , but also reduce the consumption of pigment TiO2 . The preparation of the composite pigment will enhance the comprehensive utilization of titanium resource [8–10]. TiO2 -coated mineral materials are generally prepared by hydrolysis precipitation coating method [11,12]. Zhou [13] prepared the TiO2 -coated barite composite pigments through the hydrolysis of TiOSO4 on the barite surface. Ninness [14] and Lu [15] prepared TiO2 -coated kaolin composite pigments and Gao prepared the anatase and rutile TiO2 -coated mica composite pigments through the hydrolysis coating of TiCl4 [16,17]. However, a strong acid is produced during the hydrolysis process of titanium salts. CaCO3 is instable in acid media due to its poor acid fastness. Consequently, the CaCO3 -based composite could not be prepared through the hydrolysis of titanium salts such as TiOSO4 . Materials 2018, 11, 1131; doi:10.3390/ma11071131
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Hence, several methods were developed to prepare CaCO3 -TiO2 composites. Tanabe [18] prepared CaCO3 -TiO2 composite particles through carbonation in the TiO2 system. Liu [19] and Sun [20] prepared CaCO3 -TiO2 composite particles by the sol-gel method and hydrophobic agglomeration method, respectively. However, the above mentioned methods are complicated and expensive, and can hardly realize large-scaled industrial production of CaCO3 -TiO2 composite particles. The mechanochemical method is widely used to prepare composite materials due to its simple process, low cost, and low pollution. Through the ultra-fine grinding of mineral particles, the surface of mineral particles can be activated, thus slightly changing the crystal structure and physicochemical properties of the surface. Consequently, the interfacial reaction between particles is strengthened to induce the combination. Wang [21] and Chen [22] respectively prepared barite/TiO2 and TiO2 -coated wollastonite composite pigments by the mechanochemical method, and both composite pigments exhibited similar pigment properties to TiO2 . However, the combination between barite and TiO2 was induced by electrostatic interactions. Therefore, the combination effect was not firm enough and needs to be enhanced. The light adsorption property or the application performance of the composite pigments was not explored. In this study, CaCO3 -TiO2 composite particles were prepared in the water system according to the mechanochemical method. In addition, the pigment properties, light absorption properties, morphology, and structure of the prepared CaCO3 -TiO2 composite particles were studied and the combination feature and mechanism between TiO2 and CaCO3 particles were also investigated. Additionally, the application performances of CaCO3 -TiO2 composite particles in paint were evaluated. 2. Methods 2.1. Raw Materials CaCO3 raw material used as the substrate in this study was produced in Huadian Quanxing Mining Co., Ltd. Manufacturer, Huadian, Jilin Province, China. The purity, hiding power, whiteness, and average particle size of the raw material are respectively 100% (indicated by X-ray diffractometer), 185 g/m2 , 97.82%, 1.21 µm (d50 ), and 4.87 µm (d90 ), indicating that the CaCO3 raw material has the poor hiding property and high whiteness. The TiO2 raw material used in the experiment is commercially available rutile TiO2 produced by sulfuric acid method (Billionschem Co., Ltd., Jiaozuo, China). The whiteness, hiding powder, oil absorption and average particle size of TiO2 are respectively 96.9%, 14.61 g/m2 , 26.06 g/100 g, 0.37 µm (d50 ) and 0.55 µm (d90 ), indicating the excellent pigment properties of TiO2 raw material. Chemically pure linseed oil (Zhengzhou Tianma Art Paints Co., Ltd., Zhengzhou, China) and distilled water were also used (Beijing Jinxin Hengda Technology and Trade Co., Ltd., Beijing, China). 2.2. Preparation 2.2.1. Preparation of the CaCO3 -TiO2 Composite Particles CaCO3 -TiO2 composite particles were prepared with CaCO3 and TiO2 in stirred mill by wet grinding. Firstly, the CaCO3 slurry and TiO2 slurry were prepared. CaCO3 and TiO2 were respectively mixed with water and sodium polyacrylate (dispersant) according to a certain proportion and stirred by a high-speed dispersion machine. Secondly, the CaCO3 and TiO2 slurries were mixed together and ground by a GSDM-S3 type ultrafine grinding mill (3 L, Beijing gosdel power&technology Co. Ltd., Beijing, China) with a speed of 1200 r/min and the weight ratio of ball to powder was 4:1. After stirring at room temperature and pH = 8 for 90 min, the composite slurry was obtained. Finally, the CaCO3 -TiO2 composite particles were obtained after the CaCO3 -TiO2 composite slurry was dried at 100 ◦ C for 12 h (Electric thermostaticdrying oven, Tianjin Taisite Instrument Co., LTD, Tianjin, China).
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2.2.2. Preparation of the Construction Paint for Exterior Wall The construction paints for exterior wall was prepared respectively with CaCO3 -TiO2 composite particles and TiO2 particles as pigments. The raw materials were added into a high-speed mixer sequentially according to a certain proportion and then stirred to form a stable paint. In the paint, the TiO2 or the CaCO3 -TiO2 composite particles were used as white pigment, they imparts opacity to the coating by bonding with the film-forming materials. The ground calcium carbonate was used as the main filler, playing a role in filling and reducing the cost of coatings. The total content of white pigment and ground calcium carbonate was 35.5 wt %. Besides, the acrylic emulsion was used as a film former, which allows the coating to be firmly adhered to the substrate to form a continuous film. Several additives including wetting agent, water, dispersant, pH regulator, defoamer, film-forming additive, leveling agent, and thickener were added to adjust the coating performance. 2.3. Characterization 2.3.1. Structure and Property Characterization We observed the morphology of CaCO3 , TiO2 , and CaCO3 -TiO2 composite particles by scanning electron microscope (SEM, S-3500N, HITACHI, Tokyo, Japan) under an energy dispersive spectroscope at 5.0 kV and transmission electron microscope (TEM, FEI Tecnai G2 F20, Portland, OR, USA) under an acceleration voltage of 300 kV. For morphological observation, the powder samples were dispersed in ethanol solvent and sonicated for 10 min, and then the suspensions were directly dropped to the conductive adhesive or copper net for natural drying. The phase analysis were carried out on the X-ray diffractometer (XRD, D8 ADVANCE, BrukerAXS GmbH, Karlsruhe, Germany) with Cu Kα radiation (λ = 1.5406 Å) generated at 40 kV and 15 mA and a scanning rate of 8 ◦ /min. The Fourier-transform infrared (FT-IR) spectra were recorded on an infrared spectroscope (Spectrum 100, PerkinElmer Instruments (Shanghai) Co., Ltd., Shanghai, China) in a scanning range of 4000–400 cm−1 . The particle size was tested with centrifugal sedimentation (BT-1500, Dandong Bettersize Instrument (Liaoning) Co., Ltd., Liaoning, China). The whiteness was tested with a whiteness meter (SBDY-1, Shanghai Yuet Feng Instrument Co., Ltd., Shanghai, China). The ultraviolet (UV)-vis spectra of the prepared composite materials were obtained in the range of 200~800 nm on a TU-1901 double beam spectrophotometer (Beijing Presee General Instrument Co., Ltd. Beijing, China). 2.3.2. Property Tests of the CaCO3 -TiO2 Composite Particles and the as-Prepared Paint The pigment properties of the CaCO3 -TiO2 composite particles were evaluated in terms of oil absorption, hiding power, and relative hiding power and the previous testing methods [23,24] were adopted. Oil absorption is an important index of pigments. According to the China National Standard GB/T 5211.15-2014 [25], the index refers to the minimum amount of varnish (linseed oil) required for completely wetting 100 g pigment. Hiding power is another important index of pigments. It refers to the minimum amount of pigment required for completely covering a black and white checkerboard. The hiding power of a pigment can be tested according to the China National Industrial Standard HG/T 3851-2006 [26] (the Test Method of Pigment Hiding Power). The relative hiding power (R, %) is defined as the ratio of the hiding power of the composite particles to that of pure TiO2 pigment. The R value can be calculated as: R = (HT /HCT ) × 100%,
(1)
where HT (g/m2 ) and HCT (g/m2 ) are respectively the hiding power values of TiO2 and the CaCO3 -TiO2 composite particles.
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The value of ∆R calculated by Equation (2) represents the increase in the hiding power of TiO2 caused by the combination with CaCO3 : ∆R = R − R0
(2)
where R0 is the mass ratio of TiO2 to the composite particles. According to the China National Standard GB/T 23981-2009 [27], the contrast ratio of the construction paint for exterior wall (C) can be tested according to the following method. A coating film with a certain thickness was firstly coated on the standard black-and-white plate and then the reflectivity values of black (RB , %) and white regions (RW , %) were tested with a reflectivity measuring instrument (C84-III, Tianjing Jinke Material Testing machine Co., Ltd., Tianjing, China). Finally, the contrast ratio of coating film can be obtained by Equation (3) [23]: C = RB /RW
(3)
The total color difference (∆E) between the paint containing CaCO3 -TiO2 composite particles and the paint containing TiO2 pigment can be calculated by Equation (4): ∆E = [(LT * − LCT *)2 + (aT * − aCT *)2 + (bT * − bCT *)2 ]1/2
(4)
where the LT *, aT *, and bT * represent the chromaticity values of coating films containing TiO2 particles; LCT *, aCT *, and bCT * represent the chromaticity value of coating films containing CaCO3 -TiO2 composite particles. All the chromaticity values were measured with a portable integrating sphere spectrophotometer (X-Rite Sp60, X-Rite (Shanghai) International Trade Co., Ltd., Shanghai, China). 3. Results and Discussion 3.1. Morphology of CaCO3 -TiO2 Composite Particles The uniformity and completeness of TiO2 coating on the surfaces of minerals are important influencing factors of the pigment properties of minerals-TiO2 composite particles. Therefore, we investigated the morphology of CaCO3 and TiO2 raw materials, as well as CaCO3 -TiO2 composite particles with different mass ratios of TiO2 . Corresponding SEM and TEM images are shown in Figure Materials1. 2018, 11, x FOR PEER REVIEW 5 of 11
Figure 1. 1. Scanning Scanning electron electron microscopy microscopy (SEM) (SEM) and and transmission transmission EM EM (TEM) (TEM) images images of of CaCO CaCO3,, TiO TiO2,, Figure 3 2 2. (a) SEM image of CaCO3; (b) SEM of TiO2; (c–e) SEM image of CaCO3-TiO2 with and CaCO CaCO3-TiO and 3 -TiO2 . (a) SEM image of CaCO3 ; (b) SEM of TiO2 ; (c–e) SEM image of CaCO3 -TiO2 with mass ratio ratio of of 30%, 30%, 40%, 40%, and and 50%; 50%; (f) (f) TEM TEM of of CaCO CaCO3-TiO 2 (50%). TiO2 mass TiO 2 3 -TiO2 (50%).
3.2. Binding Properties of CaCO3 and TiO2 Particles 3.2.1. XRD Analysis Figure 2 shows the XRD pattern of CaCO3, TiO2, and CaCO3-TiO2 composite particles with the TiO2 mass ratio of 50%. There were only calcite and rutile diffraction peaks in the XRD pattern of CaCO3-TiO2 composite particles, indicating that the composite particles were still composed of caclite
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In Figure 1a, the bulk CaCO3 particles with the size of 1–3 µm were obvious and the surfaces of CaCO3 particles were smooth, without covering. In Figure 1b, the granular TiO2 particles with the particle size of 0.2–0.3 µm showed good dispersivity. However, after CaCO3 and TiO2 particles were ground together (Figure 1c–e), many fine particles were uniformly coated on the surfaces of CaCO3 , and the smooth surface of CaCO3 became rough. As indicated by the Energy Dispersive Spectrometer (EDS) results (Figure 1d), the particles coated on the surfaces of CaCO3 should be TiO2 . Apparently, the CaCO3 -TiO2 composite particles were characterized by the uniform TiO2 coating on the surface of CaCO3 . Consequently, the CaCO3 -TiO2 composite particles should possess the properties of TiO2 , such as the similar pigment properties to that of TiO2 . The uniformity and completeness of the TiO2 coating on the surfaces of CaCO3 particles increased accordingly when the mass ratio of TiO2 increased from 30% to 50% (Figure 1c–e). Particularly, when the mass ratio of TiO2 increased to 50%, the surfaces of the CaCO3 particles were almost completely Figure by 1. Scanning electron microscopy (SEM) and transmission EM image (TEM) images CaCO TiO2, -TiO covered TiO2 particles. Additionally, as shown in the TEM (Figureof1f), the3,CaCO 3 2 3-TiO2. (a) SEM image of CaCO3; (b) SEM of TiO2; (c–e) SEM image of CaCO3-TiO2 with and CaCO composite particles are composed of the particles characterized by uniform and dense TiO2 coating on 2 mass ratio of 30%, 40%, and 50%; (f) TEM of CaCO3-TiO2 (50%). theTiO surface of CaCO3 .
3.2.3.2. Binding Properties of CaCO 3 andand TiOTiO 2 Particles Binding Properties of CaCO 3 2 Particles 3.2.1. XRD Analysis 3.2.1. XRD Analysis Figure 2 shows thethe XRD pattern of of CaCO 3, TiO 2, and CaCO 3-TiO 2 composite particles with thethe Figure 2 shows XRD pattern CaCO CaCO particles with 3 , TiO 2 , and 3 -TiO 2 composite TiO 2 mass ratio of 50%. There were only calcite and rutile diffraction peaks in the XRD pattern of of TiO mass ratio of 50%. There were only calcite and rutile diffraction peaks in the XRD pattern 2 CaCO 3-TiO 2 composite particles, indicating that the composite particles were still composed of caclite CaCO -TiO composite particles, indicating that the composite particles were still composed of caclite 3 2 and rutile 2,2 ,and phasewas wasproduced produced in the preparation process the composite and rutileTiO TiO and no no new phase in the preparation process of theofcomposite particles. particles. Meanwhile, the complete phases the CaCO 3 and TiO 2 materials remained without Meanwhile, the complete crystalcrystal phases of theofCaCO and TiO materials remained without any 3 2 anychanges. changes. Therefore, it can be inferred that the binding of CaCO 3 and TiO 2 particles should occur Therefore, it can be inferred that the binding of CaCO3 and TiO2 particles should occur at the at the interfacial region of the particles, whether the binding a chemical or physical nature. interfacial region of the particles, whether the binding is ofisa of chemical or physical nature.
Figure 2. X-ray diffractometer (XRD) patterns of of CaCO 3, TiO2, and CaCO3-TiO2 composite particles. Figure 2. X-ray diffractometer (XRD) patterns CaCO 3 , TiO2 , and CaCO3 -TiO2 composite particles.
3.2.2. Infrared Spectral Analysis 3.2.2. Infrared Spectral Analysis addition coating behaviors TiO completeness and orderliness, In In addition to to thethe coating behaviors of of TiO 2, including completeness and orderliness, on on thethe 2 , including surfaces of mineral particles, binding properties and binding strength between mineral particles surfaces of mineral particles, thethe binding properties and binding strength between mineral particles and TiO 2 2particles alsoimportant importantinfluencing influencing factors of properties the properties of the TiO2composite -coated and TiO particles are are also factors of the of the TiO 2 -coated composite particle pigments. to investigate the binding properties TiO 2 and3 CaCO 3 particle pigments. In orderIn toorder investigate the binding properties betweenbetween TiO2 and CaCO particles, particles, the infra-red (IR) spectra of TiO2, CaCO3, and CaCO3-TiO2 composite particles were tested
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the infra-red (IR) spectra of TiO2 , CaCO3 , and CaCO3 -TiO2 composite particles were tested and −1 , which analyzed (Figure 3). Figure 3a displays severalseveral peaks inpeaks the range of range 400~700 ascribed and analyzed (Figure 3). Figure 3a displays in the of cm 400~700 cm−1are , which are to the stretching vibrations of Ti-O-Ti peaks characteristic peaks ofpeaks TiO2 of [28,29]. ascribed to the stretching vibrations ofbonds. Ti-O-TiThese bonds. Thesewere peaks were characteristic TiO2 −1cm −1 −1 −1 and In Figure the3b, absorption peakspeaks at 880atcm and 718718 cmcm were [28,29]. In 3b, Figure the absorption 880 wereascribed ascribedto tothe the characteristic −1 was −1 was 3 [30,31]. Meanwhile, thethe peak at at 3420 cmcm ascribed to the absorption peaks of CO332−2−ininCaCO CaCO Meanwhile, peak 3420 ascribed to 3 [30,31]. hydroxyl groups formed by the between H2O and ions CaCO surface such as such Ca2+ the hydroxyl groups formed byreaction the reaction between H2 Othe and theonions on 3CaCO 3 surface 2+ 2 − 2−. Several andCaCO3and observed in the IR in spectrum of CaCOof 3-TiO 2 composite particles as CO3 .changes Severalwere changes were observed the IR spectrum CaCO 3 -TiO2 composite 2− 2− (Figure 3c), compared to that oftothe raw Firstly, the absorption peak of CO 3 in CaCO particles (Figure 3c), compared that of materials. the raw materials. Firstly, the absorption peak of CO 3 3 − 1 −1 appeared 1465 cm at, showing and broadening withcompared the absorption in CaCO3 atappeared 1465 cm a shift , showing a shift andphenomenon broadening compared phenomenon with 1 in the infrared −1 in the peakabsorption at 1440 cmpeak infrared of CaCO 3. The shifted absorption peak indicated that the the at 1440 cm−spectrum spectrum of CaCO . The shifted absorption peak 3 2 − 2− chemical environment of CO 3 changed due to 3the changed reaction with other materials, andother the broadened indicated that the chemical environment of CO due to the reaction with materials, absorption peak showed that the association CaCO 3 particles increased. and the broadened absorption peak showed degree that thebetween association degree between CaCO3Secondly, particles compared to the characteristic hydroxyl groups cm−1 in CaCOat 3 raw increased. Secondly, comparedpeak to theofcharacteristic peakatof3420 hydroxyl groups 3420materials cm−1 in (Figure CaCO3 1 in −1 3b), materials the characteristic peak ofcharacteristic water and hydroxyl groups at hydroxyl 2892~3300 cm in 3c [32] raw (Figure 3b), the peak of water and groups at Figure 2892~3300 cm−was broadened and shifted in the direction of in thethe low wave number. Thirdly, there is aThirdly, clear absorption Figure 3c [32] was broadened and shifted direction of the low wave number. there is a − 1 −1 peak at 1030 cm peak in Figure 3c,cm indicating that there might bethat a chemical bonding to clear absorption at 1030 in Figure 3c, indicating there might be abehavior chemicalrelated bonding the formation bond.ofAccording to the above to analysis, it can be inferred the behavior relatedofto Ti-O-Ca the formation Ti-O-Ca bond. According the above analysis, it can be that inferred combination of CaCOof 3 and TiO3 2and should realized the chemical interactioninteraction between hydroxyl that the combination CaCO TiO2beshould be by realized by the chemical between groups ongroups particle this combination should beshould firm. Undoubtedly, based onbased the uniform hydroxyl onsurfaces, particle so surfaces, so this combination be firm. Undoubtedly, on the coating ofcoating TiO2 on of CaCO 3 , the strong combination strength between CaCO 3 and TiO32 uniform of the TiOsurface on the surface of CaCO , the strong combination strength between CaCO 2 3 largely determines the good pigment properties of CaCO 3 -TiO 2 composite particles. and TiO2 largely determines the good pigment properties of CaCO3 -TiO2 composite particles.
Figure 3. 3. Fourier-transform Fourier-transforminfrared infraredspectra spectra (FT-IR) spectra of CaCO (a) CaCO 3, (b) TiO2, and (c) CaCO3Figure (FT-IR) spectra of (a) 3 , (b) TiO2 , and (c) CaCO3 -TiO2 particles. TiO2 composite composite particles.
3.2.3. Mechanism Analysis Analysis 3.2.3. Mechanism The unsaturated ionsions on the planesplanes of CaCO and TiO explain 2 can The hydration hydrationbehavior behaviorofof unsaturated on cleavage the cleavage of 3CaCO 3 and TiO 2 can the formation of surface groups. groups. The calcite which3,belongs to the tripartite crystal explain the formation of hydroxyl surface hydroxyl TheCaCO calcite3 ,CaCO which belongs to the tripartite 2− ions system, is completely cleavedcleaved on theon plane (1011),(10⎯11), and theand unsaturated Ca2+ and are 3 CO crystal system, is completely the plane the unsaturated Ca2+CO and 32− ions 2+ 2+ on exposed. TheThe unsaturated Ca Caon CaCO will undergo thethe following hydration reactions: 3 surface are exposed. unsaturated CaCO 3 surface will undergo following hydration reactions: 2+ 2+ + H2O→Ca(OH)+++ H+ + CaCa + H2 O → Ca(OH) + H
(5) (5)
Ca(OH)+ + H2O→Ca(OH)2 + H+ (6) Ca(OH)+ + H2 O → Ca(OH)2 + H+ (6) The above hydration reactions of Ca2+ are related to the pH value. The larger the pH value is, the stronger the hydration effect is [33,34]. Therefore, the hydration reaction of CaCO3 is intense. Obviously, there should be a certain amount of hydroxyl groups on the surfaces of CaCO3 generated
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The above hydration reactions of Ca2+ are related to the pH value. The larger the pH value is, the stronger the hydration effect is [33,34]. Therefore, the hydration reaction of CaCO3 is intense. Obviously, there should be a certain amount of hydroxyl groups on the surfaces of CaCO3 generated in the hydration reactions of Ca2+ and CO3 2− . As for TiO2 , the hydration reactions of Ti4+ are intense. Hydrolysis reactions and corresponding constants [35] are provided as follows: 4+
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(7)
2+ and CO32−. As for TiO 4+ + in the hydration reactions of 3+ Ca+ the hydration Ti(OH) H2 O Ti(OH)2 2+2, +H , pk2 = reactions 13.73 of Ti are intense. Hydrolysis reactions and corresponding constants [35] are provided as follows:
(8)
Ti(OH)2 2+Ti+4+H Ti(OH) + + H+ , pk = 13.39 2O +H 2OTi(OH)3+ + 3H+, pk1 = 14.153
(7)
(9)
+ + Ti(OH)Ti(OH) Ti(OH)22+4 +H +H , 2pk 3+ 2+O +, pk 3 +H 4 = 13.06 H2 OTi(OH) = 13.73
(8)
(10)
Therefore, a large amount of Ti(OH) hydroxyl groups are formed on the TiO2 surface due to(9)the intense 22+ + H2OTi(OH)3+ + H+, pk3 = 13.39 hydrolysis of Ti4+ . Consequently, it can be inferred that CaCO3 and TiO2 are combined together by the (10) Ti(OH) 3+ + H2OTi(OH)4 + H+, pk4 = 13.06 reaction of hydroxyl groups on their surfaces. a large amountthe of hydroxyl groups are formed on the 2 surface due the intense particles Based on Therefore, the above analysis, preparation mechanism ofTiO CaCO composite 3 -TiO 2 to hydrolysis of Ti4+. Consequently, it can be inferred that CaCO3 and TiO2 are combined together by by the mechanochemical method can be summarized as follows (Figure 4). First, through the high the reaction of hydroxyl groups on their surfaces. speed stirring of raw the CaCO be3-TiO further dispersed, and then the 3 and TiOmechanism 2 particles Based onmaterials, the above analysis, the preparation ofcan CaCO 2 composite particles by hydration,the dehydration, and other reactions between particles in aqueous media canspeed be promoted mechanochemical method can be summarized as follows (Figure 4). First, through the high stirring of raw materials, the CaCO 3 and TiO 2 particles can be further dispersed, and then the surface because the slight distortion of the lattice of mineral particles and the activation of the particle hydration, dehydration, and other reactions between particles in aqueous media can be promoted during the grinding process enhances the binding between the surfaces [36]. Second, the high energy because the slight distortion of the lattice of mineral particles and the activation of the particle surface imported in the the co-grinding process canthe increase the chance of the collision between CaCO3 and during grinding process enhances binding between the surfaces [36]. Second, the high energy TiO2 particles, overcome the energy barrier of the interaction between imported in the co-grinding process can increase therepulsive chance of the collision between CaCO3the andtwo TiO2 particles, overcome the energy barrierbelow of the the repulsive the two particles, andfunctional and reduceparticles, the distance between particles rangeinteraction allowingbetween the interaction between reduce the distance between particles below the range allowing the interaction between functional groups on particle surface. Finally, the firm combination of CaCO3 and TiO2 particles can be achieved groups on particle surface. Finally, the firm combination of CaCO3 and TiO2 particles can be achieved by the dehydration reaction among the the hydroxyl onparticle particle surface. by the dehydration reaction among hydroxylgroups groups on surface.
Figure 4. Preparation mechanism particles. 3 -TiO 2 composite Figure 4. Preparation mechanismof ofCaCO CaCO3-TiO 2 composite particles.
3.3. Properties of CaCOof3 -TiO Composite Particles 3.3. Properties CaCO23-TiO 2 Composite Particles 3.3.1. Properties Pigment Properties 3.3.1. Pigment Figure 5 shows the pigment properties of CaCO3, TiO2 raw materials, and the CaCO3-TiO2
Figure 5 shows the pigment properties of CaCO3 , TiO2 raw materials, and the CaCO3 -TiO2 composite materials with different TiO2 mass ratios, including hiding power, relative hiding power composite (R), materials withratio different TiO including hiding power, relative hiding power 2 mass the increased of hiding power (ΔR),ratios, oil absorption, and whiteness. As shown 5a,power CaCO3-TiO 2 composite particles exhibited much better hiding properties (R), the increased ratio in ofFigure hiding (∆R), oil absorption, and whiteness. than CaCO 3. When the mass ratio of TiO2 in the CaCO3-TiO2 composite was only 30%, its hiding As shown in Figure 5a, CaCO3 -TiO2 composite particles exhibited much better hiding properties power reached about 23 g/m2, which shows much stronger hiding properties than the CaCO3 raw than CaCO3 . When the mass ratio of TiO2 in the CaCO3 -TiO2 composite was only 30%, its hiding
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material (185 g/m2). When the mass ratio of TiO2 increases to 50%, the hiding power and relative hiding power of CaCO3-TiO2 composite are 17.59 g/m2 and 82.80% (R), which was 32.80% (ΔR) higher 2 , which shows much stronger hiding properties than the CaCO 11, x FOR PEER REVIEW 8 of 113 raw power reached g/m than Materials that of 2018, TiOabout 2 (R0). 23 As expected, the hiding power and relative hiding power of the CaCO 3-TiO2 2 material (185 g/m ). When the mass ratio of TiO increases to 50%, the hiding power and relative 2 2 composite respectively reached 15.79 g/m and 92.27% when the TiO 2 mass ratio increased to 70%, material (185 g/m2). When the mass ratio of TiO2 increases to 50%, the hiding power and relative hiding power ofthe CaCO arehave 17.59obtained g/m22 and 82.80% (R),pigment which was 32.80% (∆R) higher 3 -TiO 2 composite indicating that CaCO 3-TiO 2 composite the excellent properties equivalent hiding power of CaCO3-TiO2 composite are 17.59 g/m and 82.80% (R), which was 32.80% (ΔR) higher than that of TiO (R02 ).(RAs expected,the the hiding power andrelative relative hiding power of thethe CaCO 2TiO 3 -TiO2 to that of TiO pigment. Obviously, coating TiO2 on surface CaCO 3 weakened properties than that2 of 0). As expected, the hidingofpower andthe hiding power of the CaCO 3-TiO2 2 and 92.27% when the TiO mass ratio increased to 70%, composite respectively reached 15.79 g/m 2of TiO of CaCO 3 and induced the reached composite particles to92.27% exhibitwhen the properties 2. The abovementioned composite respectively 15.79 g/m2 and the TiO2 mass ratio increased to 70%, indicating that the CaCO -TiO composite have obtained the excellent pigment properties 3 2 indicating that the CaCO 3 -TiO 2 composite have obtained the excellent pigment properties equivalent results indicated that the TiO2 particles in the CaCO3-TiO2 composite exhibited the higher equivalent utilization to that TiO pigment. the of on thesurface surface CaCO the properties toof that of2TiO 2 pigment. thecoating coating of TiO TiO22 on the 3 weakened the properties 3 weakened efficiency compared to Obviously, theObviously, pure rutile TiO2 pigment because theCaCO coating structure improved the of CaCO and induced composite particles to to exhibit exhibit the properties of of TiO 2. The abovementioned of CaCO induced thethe composite the properties TiO The abovementioned 3 and 2. a dispersion of3titanium dioxide and theparticles synergistic effect of calcium carbonate as carrier. Meanwhile, results indicated that the 2 particles theCaCO CaCO33-TiO 2 composite thethe higher utilization results indicated the TiOTiO particles inin the -TiO exhibited higher 2 composite the whiteness of that CaCO 3-TiO 22 composite particles was also close to exhibited that of CaCO 3 and TiOutilization 2, and the efficiency compared to the pure rutileTiO TiO2 pigment pigment because the coating structure improved the the efficiency compared to the pure rutile because the coating structure improved oil absorption of CaCO3-TiO2 composite was2 similar or less than that of TiO2. dispersion of titanium dioxide and the synergistic effect of calcium carbonate as a carrier. Meanwhile, dispersion of titanium dioxide and the synergistic effect of calcium carbonate as a carrier. Meanwhile, the whiteness of CaCO3-TiO2 composite particles was also close to that of CaCO3 and TiO2, and the the whiteness of CaCO3 -TiO2 composite particles was also close to that of CaCO3 and TiO2 , and the oil oil absorption of CaCO3-TiO2 composite was similar or less than that of TiO2. absorption of CaCO3 -TiO2 composite was similar or less than that of TiO2 .
Figure 5. Pigment properties of CaCO3-TiO2 composite particles with different mass ratios of TiO2. (a) Hiding power (R) andproperties relative hiding power (ΔR), (b) Oil absorption and whiteness. Figure 5. Pigment CaCO 3-TiO2 composite particles with different mass ratios of TiO2. (a) Figure 5. Pigment properties ofofCaCO 3 -TiO2 composite particles with different mass ratios of TiO2 . Hiding power (R) and relative hiding power (ΔR), (b) Oil absorption and whiteness. (a) Hiding power (R) and relative hiding power (∆R), (b) Oil absorption and whiteness.
3.3.2. Optical Property of CaCO3-TiO2 Composite Particles Optical Property of CaCO 3-TiO2 Composite Particles 3.3.2.3.3.2. Optical Property of CaCO 3 -TiO2 Composite Particles The UV-vis absorption spectra of CaCO3-TiO2 composite particles, CaCO3 and TiO2 raw The absorption of CaCO 3-TiO2 composite particles, CaCO3 and TiO2 raw The UV-vis absorption spectra of CaCO particles, CaCO3 and TiO2 raw materials materials are UV-vis shown in Figure 6.spectra All samples almost showed no absorption of visible light in the 3 -TiO 2 composite materials are shown in Figure 6. All samples almost showed no absorption of visible light in the are shown in Figure samplesnm, almost showed their no absorption of visible in the wavelength range wavelength range 6. ofAll 400–800 reflecting characteristics aslight white inorganic material. wavelength range of 400–800 nm, reflecting their characteristics as white inorganic material. of 400–800the nm,three reflecting their asabsorption white inorganic material.light However, the three samples However, samples arecharacteristics different in the of ultraviolet in the wavelength range However, the three samples are different in the absorption of ultraviolet light in the wavelength range are different in nm. the absorption of ultraviolet lightalmost in the no wavelength range ofbut 200–400 nm.CaCO CaCO3-TiO raw2 of 200–400 nm. CaCO 3 raw materials exhibited light absorption, TiO2 and of 200–400 CaCO 3 raw materials exhibited almost no light absorption, but TiO2 and CaCO3-TiO23 materials exhibited almost no light absorption, but TiO2CaCO and CaCO particles exhibited composite particles exhibited strong light CaCO 3-TiO 2-TiO composite particles exhibited 2 composite composite particles exhibited strong lightabsorption. absorption. 3-TiO 23 composite particles exhibited less less strong lightabsorption absorption. CaCO -TiO composite particles exhibited less light absorption in the wavelength light light absorption in the wavelength range of 200–350 nm than TiO 2 . Unlike CaCO 3 , the CaCO in the wavelength range of 200–350 nm than TiO2. Unlike CaCO3, the CaCO3-TiO32-TiO2 3 2 composite particles obtained the sameCaCO lightabsorption property asas that of of TiO 2 and theobtained result was range of 200–350 nmobtained than TiO2the . Unlike , the CaCO particles thein same composite particles same light property that TiO 2 and the result was in 3absorption 3 -TiO2 composite agreement previous [5].The Theresult abovementioned results notnot only indicated that that the light absorption property as that report ofreport TiO2 [5]. and the was in agreement with theonly previous report [5]. The agreement withwith the the previous abovementioned results indicated the 3-TiO2 composite particles obtained excellent UV resistance stability, but also reflected the abovementioned results not only indicated the CaCO particles obtained excellent CaCOCaCO 3-TiO 2 composite particles obtainedthat excellent UV3 -TiO resistance stability, but also reflected the 2 composite mechanism that TiO 2 particles coated on the surface of CaCO3 particles endowed the composite UV resistance stability, but also reflected mechanism TiO3 2particles particlesendowed coated onthe the composite surface of mechanism that TiO2 particles coated onthe the surface ofthat CaCO particles with the similar properties of TiO2. CaCO particles endowed the composite particles with the similar properties of TiO . particles with the similar properties of TiO 2 . 3 2 CaCO3
1.4
CaCO3
1.4
TiO2
1.2
TiO2 -TiO composite particles CaCO 3 2
Absorbance
Absorbance
1.2
1.0
CaCO -TiO composite particles 3 2
1.00.8 0.80.6 0.60.4 0.40.2 0.0
0.2 200 0.0 200
300
300
400
500
600
Wavelength/nm 400 500 600
700
700
800
800
Figure 6. UV-vis absorption spectra of CaCO3, TiO2, and CaCO3-TiO2 composite particles. Wavelength/nm
Figure 6. 6. UV-vis UV-vis absorption absorption spectra spectraof ofCaCO CaCO33,, TiO TiO22,, and and CaCO CaCO33-TiO Figure -TiO22 composite composite particles. particles.
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3.3.3. Properties of the Exterior Paint Containing CaCO33-TiO22 Composite Composite Particles Particles 3.3.3. Properties of the Exterior Paint Containing CaCO3-TiO2 Composite Particles showsthe theproperty propertyofofthe theexterior exteriorpaint paint containing CaCO particles Figure 77 shows containing CaCO 3-TiO 2 composite particles (R3 -TiO 2 composite Figure 7 shows the property of the exterior paint containing CaCO3-TiO 2 composite particles (R(R-801, mass ratio TiO is 70%) and rutile TiO (BLR-699). As shown in Figure 7a, the 801, thethe mass ratio of of TiO 2 is 70%) and rutile TiO 2 (BLR-699). As shown in Figure 7a, when 2 801, the mass ratio of TiO2 is 70%) and rutile TiO2 2(BLR-699). As shown in Figure 7a, when the addition proportions of R-801 and BLR-699 in the paint were only 5%, the contrast ratios of the addition proportions of R-801 and BLR-699 in the paint were only 5%, the contrast ratios of the thethe two values were close. Moreover, the obtained paints paints respectively respectively reached reached0.94 0.94and and0.95, 0.95,and and two values were close. Moreover, obtained paints respectively reached 0.94 and 0.95, and the two values were close. Moreover, the abovementioned contrast ratios of the paint were higher the abovementioned contrast ratios of the paint were higherthan thanthe thecontrast contrastratio ratio(0.93) (0.93) of of superior abovementioned contrast ratios of the paint were higher than the contrast ratio (0.93) of superior products required requiredininChina ChinaNational National Standard of Exterior Paints (GB/T 9756-2009) [37]), indicating products Standard of Exterior Paints (GB/T 9756-2009) [37]), indicating that products required in China National Standard of Exterior Paints (GB/T 9756-2009) [37]), indicating that R-801 BLR-699 exhibited excellent pigment properties whenthey theywere wereapplied applied in in the paint. R-801 and and BLR-699 exhibited excellent pigment properties when paint. that R-801 and BLR-699 exhibited excellent pigment properties when they were applied in the paint. When the theaddition additionproportions proportions R-801 BLR-699 the paint increased more, the When of of R-801 andand BLR-699 in theinpaint increased to 10%to or 10% more,orthe contrast When the addition proportions of R-801 and BLR-699 in the paint increased to 10% or more, the contrast ratio of the paint was increased The contrast ratio of the paint containing R-801 was ratio of the paint was increased slightly. slightly. The contrast ratio of the paint containing R-801 was always contrast ratio of the paint was increased slightly. The contrast ratio of the paint containing R-801 was always equivalent of thecontaining paint containing BLR-699, indicating that the application of CaCO 32equivalent to that to of that the paint BLR-699, indicating that the application of CaCO -TiO 3 always equivalent to that of the paint containing BLR-699, indicating that the application of CaCO 3TiO2 composite particles the pigment in thefor paint for exterior wall could the achieve the equivalent composite particles as the as pigment in the paint exterior wall could achieve equivalent covering TiO2 composite particles as the pigment in the paint for exterior wall could achieve the equivalent covering effect to the paint containing the same proportion of TiO 2. When theproportion addition proportion of effect to the paint containing the same proportion of TiO2 . When the addition of pigments covering effect to the paint containing the same proportion of TiO2. When the addition proportion of pigments is the 5% whiteness or 10%, the of the paint containing R-801 wasthan always in the paintinisthe 5%paint or 10%, of whiteness the paint containing R-801 was always lower that lower of the pigments in the paint is 5% or 10%, the whiteness of the paint containing R-801 was always lower than that of the paint containing the of same proportion BLR-699 (Figure when the paint containing the same proportion BLR-699 (Figureof 7b). However, when7b). theHowever, addition proportion than that of the paint containing the same proportion of BLR-699 (Figure 7b). However, when the addition proportion ofto pigments 15% andof20%, the whiteness of the paint Rof pigments increased 15% andincreased 20%, the to whiteness the paint containing R-801 wascontaining close to that addition proportion of pigments increased to 15% and 20%, the whiteness of the paint containing R801the was close to that of the paint and containing BLR-699 andvalue the color value was of paint containing BLR-699 the color difference (∆E)difference was reduced to(ΔE) about 0.7.reduced As the 801 was close to that of the paint containing BLR-699 and the color difference value (ΔE) was reduced to about 0.7. As the addition proportion of pigment in the paint for exterior wallthe is comprehensive generally high, addition proportion of pigment in the paint for exterior wall is generally high, to about 0.7. As the addition proportion of pigment in the paint for exterior wall is generally high, the comprehensive of the paint containing to R-801 to that of the paint performance of the performance paint containing R-801 is equivalent thatisofequivalent the paint containing BLR-699. the comprehensive performance of the paint containing R-801 is equivalent to that of the paint containing BLR-699. shownofinthe thedry SEM images of the drycontaining paints respectively containing As shown in the SEMAs images paints respectively R-801 and BLR-699 R-801 (Figureand 8), containing BLR-699. As shown in the SEM images of the dry paints respectively containing R-801 and BLR-699 (Figureall 8),present the twoasamples all present a continuous form composed particles, such the two samples continuous form composed of solid particles, such of as solid the polymer formed BLR-699 (Figure 8), the two samples all present a continuous form composed of solid particles, such as theemulsion polymer evaporation, formed after binder, emulsion evaporation, binder,indicating pigments,that andboth fillers, both after pigments, and fillers, theindicating R-801andthat BLR-699 as the polymer formed after emulsion evaporation, binder, pigments, and fillers, indicating that both the R-801and BLR-699 have good compatibility with emulsion. have good compatibility with emulsion. the R-801and BLR-699 have good compatibility with emulsion.
Figure R-801 and and BLR-699. Figure 7. 7. Properties Properties of of the the two two exterior exterior paints paints respectively respectively containing containing R-801 BLR-699. (a) (a) Contrast Contrast Figure 7. Properties of the two exterior paints respectively containing R-801 and BLR-699. (a) Contrast ratio of paint; paint; (b) (b) Whiteness Whiteness and and chromatic chromatic aberration aberration of of paint. paint. ratio of ratio of paint; (b) Whiteness and chromatic aberration of paint.
Figure 8. SEM images of two exterior paints respectively containing R-801 (a) and BLR-699 (b). Figure R-801 (a) (a) and and BLR-699 BLR-699 (b). (b). Figure 8. 8. SEM SEM images images of of two two exterior exterior paints paints respectively respectively containing containing R-801
4. Conclusions 4. Conclusions CaCO3-TiO2 composite particles were prepared with CaCO3 and TiO2 in stirred mill according CaCO3-TiO2 composite particles were prepared with CaCO3 and TiO2 in stirred mill according to the wet grinding method. The composite particles are characterized by the uniform TiO2 coating to the wet grinding method. The composite particles are characterized by the uniform TiO2 coating
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4. Conclusions CaCO3 -TiO2 composite particles were prepared with CaCO3 and TiO2 in stirred mill according to the wet grinding method. The composite particles are characterized by the uniform TiO2 coating on the surface of CaCO3 . The CaCO3 and TiO2 particles were firmly combined together through the dehydration reaction of hydroxyl groups on their surfaces. CaCO3 -TiO2 composite particles exhibited similar pigment properties and light absorption property to TiO2 . Moreover, the CaCO3 -TiO2 composite particles also showed excellent application performance. The contrast ratio of the exterior construction paint containing CaCO3 -TiO2 composite particles as the pigment was similar to that of paint containing the same proportion of TiO2 , and was higher than the contrast ratio (0.93) of superior products required in the China National Standard of Exterior Paints (GB/T 9756-2009 [36]). Author Contributions: Conceptualization, H.D. and S.S.; Methodology, H.D. and S.S.; Software, S.S.; Validation, H.D., S.S. and X.H.; Investigation, S.S., X.H.; Resources, H.D.; Data Curation, S.S., X.H.; Writing-Original Draft Preparation, H.D. and S.S.; Writing-Review & Editing, H.D. and S.S.; Supervision, H.D.; Project Administration, H.D.; Funding Acquisition, H.D. Acknowledgments: This work was supported by the National Natural Science Foundation of China (Grant No. 51474194). Conflicts of Interest: The authors have declared that there are no competing interests existing in this research.
References 1. 2. 3.
4. 5.
6.
7. 8. 9. 10. 11. 12. 13. 14.
Zheng, S. Processing and Application of Non-Metallic Ore; Chemical Industry Press: Beijing, China, 2003. Fekete, E.; Pukánszky, B.; Tóth, A.; Bertoti, I. Surface modification and characterization of particulate mineral fillers. J. Colloid Interface Sci. 1990, 135, 200–208. [CrossRef] Juntuek, P.; Ruksakulpiwat, C.; Chumsamrong, P.; Ruksakulpiwat, Y. Comparison between mechanical and thermal properties of polylactic acid and natural rubber blend using calcium carbonate and vetiver grass fiber as fillers. Adv. Mater. Res. 2012, 410, 59–62. [CrossRef] Kim, J.J.; Ahn, J.W.; Lee, M.W.; Seo, Y.B. Improving recycled fibres in printing paper by application of an in-situ CaCO3 formation method. Appita J. 2013, 66, 54–58. Tao, H.; He, Y.; Zhao, X. Preparation and Characterization of calcium carbonate-titanium dioxide core-shell (CaCO3 @TiO2 ) nanoparticles and application in the papermaking industry. Powder Technol. 2015, 283, 308–314. [CrossRef] Lee, S.; Kim, J.Y.; Youn, S.H.; Park, M.; Hong, K.S.; Jung, H.S.; Lee, J.K.; Shin, H. Preparation of a nanoporous CaCO3 -coated TiO2 electrode and its application to a dye-sensitized solar cell. Langmuir 2007, 23, 11907–11910. [CrossRef] [PubMed] Ding, H.; Lin, H.; Deng, Y. Minerals-Titanium Dioxide Micro-Nanometer Scale Particle Composition and Functionalization; Tsinghua University Press: Beijing, China, 2016. Pei, R. The Production of TiO2 by Sulfuric Acid Process; Chemical Industry Press: Beijing, China, 1982. Middlemas, S.; Fang, Z.Z.; Fan, P. A new method for production of titanium dioxide pigment. Hydrometallurgy 2013, 131, 107–113. [CrossRef] Yan, Q.; Lei, Y.; Yuan, J. Preparation of titanium dioxide compound pigments based on kaolin substrates. J. Coat. Technol. Res. 2010, 7, 229–237. [CrossRef] Zhao, X.; Li, J.; Zhang, Y. Preparation of nanosized anatase TiO2 -coated illite composite pigments by Ti(SO4 )2 hydrolysis. Powder Technol. 2015, 271, 262–269. [CrossRef] Zhao, X. Preparation and mechanism of TiO2 -coated illite composite pigments. Dyes Pigments 2014, 108, 84–92. [CrossRef] Zhou, H.; Wang, M.; Ding, H.; Du, G. Preparation and characterization of barite/TiO2 composite particles. Adv. Mater. Sci. Eng. 2015, 2015, 878594. [CrossRef] Ninness, B.J.; Bousfirld, D.W.; Tripp, C.P. Formation of a thin TiO2 layer on the surfaces of silica and kaolin pigments through atomic layer deposition. Colloids Surf. A 2003, 214, 195–204. [CrossRef]
Materials 2018, 11, 1131
15.
16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37.
11 of 11
Lu, Z.; Ren, M.; Yin, H.; Wang, A.; Ge, C.; Zhang, Y.; Yu, L.; Jiang, T. Preparation of nanosized anatase TiO2 -coated kaolin composites and their pigmentary properties. Powder Technol. 2009, 196, 122–125. [CrossRef] Gao, Q.; Wu, X.; Fan, Y.; Zhou, X. Low temperature synthesis and characterization of rutile TiO2 -coated mica-titania pigments. Dyes Pigments 2012, 95, 534–539. [CrossRef] Ao, Q.; Wu, X.; Fan, Y. The effect of iron ions on the anatase-rutile phase transformation of titania (TiO2 ) in mica-titania pigments. Dyes Pigments 2012, 95, 96–101. Tanabe, K.; Anabe, K.; Minitsuhashi, K.; Yoshida, T. Titanium Dioxide–Calcium Carbonate Composite Particles. EP US6991677B2, 31 January 2006. Liu, G.; Hu, A.; Zeng, H. Preparation of nano CaCO3 /TiO2 composite particles. Mater. Rev. 2004, 18, 80–82. Sun, S.; Ding, H.; Hou, X. Study on preparation of TiO2 -coated CaCO3 composite pigments by hydrophobic agglomeration method. Non-Met. Mines 2017, 40, 26–29. Wang, B.; Ding, H.; Wang, Y. Preparation of barite/TiO2 composite particle and interaction mechanism between TiO2 and barite particles. Rare Met. Mater. Eng. 2011, 40, 193–197. Chen, W.; Liang, Y.; Hou, X.; Zhang, J.; Ding, H.; Sun, S.; Cao, H. Mechanical grinding preparation and characterization of TiO2 -coated wollastonite composite pigments. Materials 2018, 11, 593. [CrossRef] [PubMed] Sun, S.; Ding, H.; Zhou, H. Preparation of TiO2 -coated barite composite pigments by the hydrophobic aggregation method and their structure and properties. Sci. Rep. 2017, 7, 10083. [CrossRef] [PubMed] Li, Z.; Huang, C.; Guo, L.; Cui, L.; Zhou, B. Mass production and application of TiO2 @CaCO3 composites in interior emulsion coatings. Colloids Surf. A 2016, 498, 98–105. [CrossRef] GB/T 5211.15-2014, General Methods of Test for Pigments and Extenders; Standards Press of China: Beijing, China, 2014. HG/T 3851-2006, Covering Power Determination of Dyestuff ; National Development and Reform Commission: Beijing, China, 2006. GB/T 23981-2009, Determination of Contrast Ratio of White and Light Coloured Paints; Standards Press of China: Beijing, China, 2009. Bezrodna, T.; Gavrilko, T.; Puchkovska, G.; Shimanovska, V.; Baran, J.; Marchewka, M. Spectroscopic study of TiO2 (rutile)–benzophenone heterogeneous systems. J. Mol. Struct. 2002, 614, 315–324. [CrossRef] Wei, H.; McMaster, W.A.; Tan, J.Z.Y.; Cao, L.; Chen, D.; Caruso, R.A. Mesoporous TiO2 /g-C3 N4 Microspheres with enhanced visible-light photocatalytic activity. J. Phys. Chem. C 2017, 121, 22114–22122. [CrossRef] Trezza, M.A.; Lavat, A.E. Analysis of the system 3CaO·Al2 O3 –CaSO4 ·2H2 O–CaCO3 –H2 O by FT-IR spectroscopy. Cem. Concr. Res. 2001, 31, 869–872. [CrossRef] Chen, J.; Xiang, L. Controllable synthesis of calcium carbonate polymorphs at different temperatures. Powder Technol. 2009, 189, 64–69. [CrossRef] Bezrodna, T.; Puchkovska, G.; Shymanovska, V.; Baran, J.; Ratajczak, H. IR-analysis of H-bonded H2 O on the pure TiO2 surface. J. Mol. Struct. 2004, 700, 175–181. [CrossRef] Wang, D.; Hu, Y. Solution Chemistry of Flotation; Hunan Science & Technology Press: Changsha, China, 1988. Iv, T.D.P.; Cygan, R.T.; Mitchell, R. Molecular models of a hydrated calcite mineral surface. Geochim. Cosmochim. Acta 2007, 71, 5876–5887. Perrin, D.D. Stability Constants of Metal-Ion-Complexes; Pergamon Press: Oxford, UK, 1979. Inam, M.A.; Ouattara, S.; Frances, C. Effects of concentration of dispersions on particle sizing during production of fine particles in wet grinding process. Powder Technol. 2011, 208, 329–336. [CrossRef] GB/T 9756-2009, Synthetic Resin Emulsion Coatings for Interior Wall; Standards Press of China: Beijing, China, 2009. © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
