Comonomer effect on the mechanical and morphological behavior on the calcite‐filled PP,CoPP, and TerPP

Comonomer effect on the mechanical and morphological behavior of the calcite (stearic acid coated calcium carbonate)‐filled polypropylene (PP), poly(propylene‐random‐ethylene) copolymer (CoPP), and poly(propylene‐co‐ethylene‐co‐1‐butene) terpolymer (TerPP) composites were investigated by using dumbbell bar and film specimens. The tensile properties of the calcite‐filled PP, CoPP, and TerPP composites exhibited lower values than those of the pure polymers (calcite‐unfilled polymers), whereas the complex viscosity of the calcite‐filled polymers exhibited slightly higher values than that of the pure polymers. Mechanical properties studied by using various strain rates and draw ratios rationalized in terms of comonomer units and contents in various PP systems. Morphological behavior of the specimens stretched at various strain rates and draw ratios was investigated by using SEM microphotographs and the mechanism of the formation of air holes was proposed. The air hole initiated from crack propagation and followed by dewetting between the calcite surface and the polymer interface in the weakened region. The crack propagated along the transverse direction; then the air hole developed parallel to the machine direction with fibril structure of the resin in PP and CoPP systems. However, TerPP composite exhibited no cracks in the beginning of the elongation, but the air hole was initiated due to dewetting; then its enlargement was exhibited by broken fibril structure of the resin. In the final stage of stretching, the air hole was dominated by merging of the neighboring air holes. Thus, different comonomer units, which are the small content of ethylene and 1‐butene in CoPP and TepPP, are responsible for these systems behaving in a different manner on the mechanical and morphological properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2041–2053, 2002     

Rheology and morphology of poly(vinyl acetate) + calcite films

We have studied mechanical and rheological behavior of poly(vinyl acetate) (PVAC) composites filled with calcite as a function of filler particle geometry, particle size distribution, and active surface area. Detailed morphological characteristic were investigated. Tensile properties of PVAC composites were evaluated in the composition range 5–20 wt% calcite. The elongation at break decreases as consequence of matrix mobility restriction by filer particles. By contrast, the strength at break increases as a result of fewer stress concentration points produced by small calcite particles. Large calcite particles decrease the strength of the PVAC composite because of lack of structural continuity. Failure is then dominated by the dewetting. Understanding the deformation as it relates to structure, mechanism of failure, and strength of interactions makes development of improved PVAC composites for adhesives possible.     

Adsorption of new hydrophobic polyacrylamide on the calcite surface

A hydrophobic polyacrylamide (HPAM) was synthesized by aqueous free‐radical chain polymerization to understand the adsorption action of the polymer on the calcite during operating stimulation. The polymer was designed as acrylamide (AM)/2‐acrylamide‐2‐methylpropanesulfonic acid (AMPS)/2‐methacryloyloxyethyl 12‐alkyl dimethyl ammonium bromide (MADA). The structure of the polymer was characterized by Fourier transform infrared spectroscopy. The adsorption properties of the polyacrylamide onto pure calcite was investigated. When we compared the ζ potentials of the calcite particles in the presence and absence of HPAM, the adsorbed amount was affected by different factors, and the adsorption behaviors were examined to determine the adsorption layer. The results of the ζ potential measurements indicated that the particles were negatively charged between pHs of 6 and 12, and the presence of HPAM did not reverse that. Equilibrium adsorption studies showed that the adsorbed amount was affected by the concentration of HPAM, liquid‐to‐solid ratio, calcite particle size, concentration of background ions, and temperature, which were related the adsorption behaviors of HPAM. Hydrogen bonds between HPAM and calcite were important because the adsorbed amount was significantly reduced when the hydrogen bonds were broken by urea. It is necessary to develop a more active reagent that can break the hydrogen bonds and improve the effect of hydraulic fracturing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45314.     

硫酸溶液中方解石表面CO2气泡的生长过程

用高速摄像仪对方解石与硫酸反应产生CO2气泡的过程进行了系统研究,分析了硫酸浓度和方解石颗粒尺寸对CO2气泡产生量、气泡生长速率、脱附直径、数量分布、方解石颗粒表观比重及方解石与硫酸反应后的表面形态等的影响。结果表明, CO2气泡在方解石表面的生长非常迅速,在反应时间一定时,CO2气泡产生量与硫酸浓度成反比,浓度越高产生的气泡越少,且随硫酸浓度增加,气泡生长速率越来越大,而脱离直径越来越小。绝大部分生成的CO2气泡会迅速脱离方解石表面。随着反应进行,硫酸浓度越高,相同时间内方解石表面可统计气泡数量越少,但在表面残留CO2气泡的直径越大。酸浓度过高不利于CO2气泡在方解石表面的吸附。方解石与硫酸反应后表面粗糙度增加,可增大表面对气泡的吸附作用。     

Interactions in the system isotactic polypropylene–calcite

Interaction in the system isotactic polypropylene–calcite was investigated using X-ray diffraction and transmission electron microscopy. Calcite acts as a weak nucleation agent for polypropylene crystallization and its activity could be increased or decreased by a suitable surface treatment. Investigation of the morphology on the polypropylene–calcite interface using calcite single crystals disclosed the tendency of polypropylene for epitaxial crystallization along preferred substrate crystallographic directions. This tendency was analogous to polymer crystallization on other ionic crystals.     

The mechanochemical route of vaterite synthesis using sodium hexametaphosphate as an inorganic additive

Vaterite is a metastable phase of CaCO₃ and was prepared mechanochemically for the first time with the assistance of sodium hexametaphosphate (SHMP). First, CaCO₃ was prepared without SHMP and was characterized using X-ray diffraction (XRD) to study the effect of milling times and speeds on the polymorphs of product. The results indicate that the reaction is complete at 60 minutes producing only calcite. Additionally, amorphous CaCO₃ (ACC) was obtained at a milling speed of 300 rpm, while calcite was obtained at 600 and 1000 rpm. Then, the effect of SHMP concentration on the fraction of vaterite was investigated, and the vaterite fraction increased with increasing SHMP amount. Subsequently, the effect of milling speed in the presence of 0.8 g of SHMP was studied, and the vaterite fraction increased with decreasing milling speed. Finally, gentler manual milling was employed, and the effect of the amount of added SHMP on vaterite formation was evaluated. The results confirmed that vaterite increased with increasing amounts of SHMP, and that vaterite formed more readily via manual milling than via mechanical milling. Observations with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that calcite and vaterite particles formed by mechanical milling were irregular agglomerates composed of primary nanoparticles while calcite particles formed by manual milling were irregular microparticles. Moreover, vaterite readily aggregated into spherical particles as the amount of SHMP increased. To investigate the reaction process and mechanism, the ethanol-washed product was characterized using XRD, SEM/EDS and TEM/SAED. The results demonstrate that ACC and calcite were concomitant during the milling process, and ACC transformed into vaterite during subsequent water washing.     

Effects of acidic calcium phosphate concentration on mechanical strength of porous calcite fabricated by bridging with dicalcium phosphate dihydrate

Porous calcium carbonate (CaCO₃) has attracted attention as an artificial bone substitute. We previously reported that interconnected porous calcite block can be fabricated when calcite granules are exposed to acidic calcium phosphate (ACaP) under loading conditions. Dicalcium phosphate dihydrate (DCPD) formed on the surface of the calcite granules caused bridging of the calcite granules with one another and formed an interconnected porous calcite block with DCPD. In this study, the effect of the ACaP concentration on the mechanical strength of the interconnected porous calcite was studied under loading conditions. When the ACaP concentration was increased, the amount of DCPD increased and the compressive strength of the porous calcite increased to approximately 2 MPa. The interconnected porous structure was maintained regardless of the ACaP concentration. No statistically significant difference was observed for the porosity, which was approximately 50%, based on the concentration of ACaP. Therefore, we concluded that the amount of precipitated DCPD can be regulated by the concentration of ACaP solution, and the mechanical strength of the porous calcite can be regulated by the amount of the precipitated DCPD.     

High-rate calcium removal using the Hyperkinetic Vortex Crystallization (HVC) process for reuse of electronics wastewater

The Hyperkinetic Vortex Crystallization (HVC) process using hydrodynamic cavitation technology was investigated to remove high calcium levels from the effluent of the fluoride removal process used in a semiconductor manufacturing company. Due to low alkalinity in the effluent of this wastewater, addition of sodium carbonate was necessary. The relatively stable effluent calcium concentration of 8.0-52.8 mg/L was achieved although the influent calcium concentration severely fluctuated in the range of 173-371 mg/L. A calcium removal efficiency of 84.5-97.0% was determined with the HVC process. To confirm the cavitation effect, the calcium removal process was operated with and without the use of the VRTX cavitation system. The calcium removal efficiency increased from 63.5% to 91.7% when the VRTX unit was operating. The change of the calcite shape from plate to a spherical form by VRTX application was also observed. This can enhance calcium removal because of the larger specific surface area for adsorption of newly produced colloidal calcites. The conversion of the calcite shape to spherical would also prevent (limit) formation of calcite scale in the inner wall of pipes and reactors.     

Effects of stearic acid coated talc,CaCO3, and mixed talc/CaCO3 particles on the rheological properties of polypropylene compounds

The effect of the stearic acid coated fillers and their geometry on the shear/dynamic viscosity and complex viscosity has been investigated using polypropylene (PP) compounds filled with stearic acid uncoated and coated talc, calcite, and mixed talc/calcite particles. The viscosity was measured over a wide range of shear rates (10^?8 to 10³) using a capillary, cone‐plate and sandwich rheometer. Overall, the rheological properties of the compounds exhibited different behavior upon different filler systems, stearic acid involvement, shear stress or strain, and frequencies due to stearic acid involvement. This implies that the stearic acid lowers the interfacial force between the filler surface and the resin matrix, followed by a favorable processing. In addition, at very low shear stresses, the viscosity of talc(un) compounds was higher than calcite(un) ones; at very high shear stresses, on the other hand, talc compounds became lower than calcite(un) compounds. This is interpreted as due to the different geometry between talc and calcite. The yield value as a function of shear stress was observed for all filler systems and exhibited lower than that obtained from the extrapolation. Furthermore, the Cox–Merz relation between the complex and shear viscosity for both the stearic acid uncoated and coated compounds is found not valid. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2105–2113, 2004     

准东煤燃烧中矿物质转化行为的CCSEM研究

在沉降炉中进行了准东煤的燃烧实验,利用计算机控制扫描电镜技术(computer controlled scanning electron microscopy,CCSEM)研究了煤中矿物质的转化行为。研究表明煤中主要矿物为方解石、高岭石、含铁类物质以及未分类矿物,燃烧后灰中石英、铁的氧化物、白云石的含量急剧增加,未分类矿物和方解石的含量下降。同时对3种重要致渣元素Na、Fe、Ca在燃烧前后的矿物转化行为及颗粒粒径分布进行了详细研究。     

Controlled Crystallization of Calcite Under Surface Electric Field Due to Polarized Hydroxyapatite Ceramics

We examined effects of surface electric fields for the crystallization of calcite on polarized hydroxyapatite ceramics with and without polyacrylic acid (PAA) as soluble additive. Both on negatively and positively charged surfaces without PAA, the only precipitates were rhombohedra calcite crystals with the face of the {10.4} plane favorably oriented parallel to the surfaces. This oriented growth was explained by the nucleation theory in the presence of an external electric field. However, the addition of PAA drastically changed the situation of the calcite crystals, i.e., the crystallites were the hemispheric aggregates of calcite needles with a facetted rhombohedral {10.4} end face and flat island-shaped aggregates of ones with a rough (00.1) end face having a triangular shape. The calcite needles grew along the crystallographic [00.1] axis. This oriented growth was explained by epitaxy on the PAA–Ca²⁺ complexes adsorbing on the surfaces. The morphology of the PAA–Ca²⁺ complex assemblies adsorbing on the surfaces before the calcite nucleation was an important factor to control the structure of calcite aggregates formed following. This morphology was controlled by properties of the surface electric field and the spatial distribution of the negatively and positively charged sites in the PAA–Ca²⁺ complexes.     

Transformation of calcareous oil-shale circulating fluidized-bed combustion boiler ashes under wet conditions

The hydration and transformation of Ca-rich kerogenous oil-shale (kukersite) ashes, formed in circulating fluidized bed (CFB) combustion furnaces, were investigated during a one-year experiment. During the first stages the process was characterized by rapid hydration of free lime hydration into portlandite and dissolution of anhydrite and periclase, whereas the formation of (crystalline) ettringite was somewhat delayed. During the final process, ettringite and portlandite that are unstable under atmospheric conditions were replaced by stable calcite and Ca-sulphate.     

Tensile property and interfacial dewetting in the calcite filled HDPE, LDPE, and LLDPE composites

Mechanical properties and complex melt viscosity of unfilled and the calcite (calcium carbonate: CaCO₃) filled high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE) composites using dumbbell bar and film specimens are studied. In addition, the formation of air holes between calcium carbonate and the resin matrix was investigated from the phase morphology and interfacial behavior between the above constituents upon stretching using scanning electron microscopy. The tensile stress and the complex melt viscosity of the calcite filled (50%) polyethylene composites were higher than that of unfilled ones, implying that the reinforcing effect of calcium carbonate. The crack was initiated up to first 50% elongation along the transverse direction and the formation of air holes was originated by dewetting occurring through machine direction in the interface between calcium carbonate surface and HDPE. The propagation mechanism of the air hole formation was proposed to firstly originate by dewetting up to 300% elongation, and enlarged not only by breaking of a superimposed fibril structure, but also by merging effect air holes between fibrous resin matrix. However, the crack propagation was not observed at the very beginning elongation for the calcite filled LDPE and LLDPE systems. Less fibril structure was observed in LLDPE, then LDPE composites. The observed shape and the average size of the air holes were different from system to system. This sort of different interfacial behavior and mechanical properties may arise from different configuration of polyethylene.     

方解石包覆-酸反应浮沉试验及机理

本工作系统研究了硫酸浓度、聚乙烯醇(PVA)种类及浓度、甲基异丁基甲醇(MIBC)浓度和十二烷基磺酸钠(SDS)浓度对PVA包裹的方解石颗粒与稀硫酸反应时方解石上浮情况的影响,并针对酸浓度、PVA浓度和MIBC浓度三因素开展正交试验。研究结果表明,包覆-酸反应方法可实现方解石颗粒的上浮。当方解石颗粒为1 mm时的最佳包覆-酸反应条件为PVA包覆剂型号为P139546,浓度为2.4wt%、硫酸浓度为2.0wt%、MIBC用量为40 mg/L,在此条件下方解石上浮率能达到84.9%;此外,PVA浓度与硫酸浓度是影响方解石包覆-酸反应浮沉的主要因素。     

Effects of humidity on calcite block fabrication using calcium hydroxide compact

Calcite has attracted attention as an artificial bone replacement material and as a precursor for the fabrication of carbonate apatite, which is also an artificial bone replacement material. In this study, the effect of humidity on calcite block fabrication was investigated using calcium hydroxide (Ca(OH)₂) compact. Ca(OH)₂ compact and Ca(OH)₂ paste compact were exposed to CO₂ at room temperature under 0%, 50%, and 100% humidity for two weeks. No carbonation was observed when Ca(OH)₂ compact was exposed to CO₂ under 0% humidity. In contrast, Ca(OH)₂ compact transformed into pure calcite under 100% humidity. Forty percent of the Ca(OH)₂ compact transformed into calcite under 50% humidity, while 30% of the Ca(OH)₂ paste compact transformed into calcite. Interestingly, the diametral tensile strength of the Ca(OH)₂ paste compact was four times higher than that of the Ca(OH)₂ compact when both were exposed to CO₂ under 100% humidity, despite the paste compact׳s lower conversion into apatite. After exposure to CO₂, SEM observations revealed that in the case of the paste compact, the Ca(OH)₂ powder was bridged with a precipitate, whereas in the case of Ca(OH)₂ compact, no precipitate was found. Results obtained in this study demonstrated that carbonation of the Ca(OH)₂ compact at room temperature was the result of a dissolution–precipitation reaction. Ca(OH)₂ powder was dissolved into water to supply the Ca²⁺, and CO₃²⁻ was supplied for the calcite precipitation from the interaction of CO₂ and water. Excess humidity from the paste compact was the key to the precipitation of the calcite bridge. The presence of the calcite bridge resulted in a higher mechanical strength for the calcite block.     

F-在方解石表面的吸附及其对方解石表面性质的影响

氟元素主要存在于磷矿和萤石等矿物中,这些矿物中都伴生有方解石脉石矿物,在浮选分离的弱酸条件下,矿物表面的F^-会部分溶出并吸附到矿物表面,从而影响矿物表面性质。本文研究了F^-在方解石表面的吸附及其对方解石表面性质的影响机理。结果表明,在矿浆pH 值为5.5时,F^-以化学吸附的方式吸附在方解石表面,随着吸附时间的增加吸附量逐渐增加,90 min时方解石对F^-的吸附达到平衡。在油酸钠(NaOL)为捕收剂时,F^-的存在会降低方解石表面的疏水性。通过Zeta电位测试、溶液化学计算和X射线光电子能谱仪(XPS)分析表明,F^-会和方解石表面的Ca²⁺反应生成CaF₂沉淀,占据方解石表面的Ca位点,降低NaOL在方解石表面的吸附量。     

Synergetic effects of temperature and magnetic field on the aragonite and calcite growth

The effects of temperature and magnetic field on aragonite and calcite growth were investigated in a stirred-tank crystallizer, using the constant-composition technique. At room temperature without magnetization, the calcite seeds grew but the aragonite did not. When the growth rates of the aragonite and calcite seeds were measured in the presence of a magnetic field at temperatures above room temperature, the synergetic effects were significant but with differing effects on the different seeds. The cluster-transformation mechanism was used to explain the growth rate data. Finally, the aragonite growth rate data were compared with data obtained in a fluidized bed.     

Comparison of sintering and compressive strength tendencies of a model coal mineral mixture heat-treated in inert and oxidizing atmospheres

The chemical interactions responsible for sintering in a coal mineral mixture were investigated in air and in N₂. A mineral mixture was made up by mixing kaolin, pyrite, quartz, calcite, hydromagnesite, FeCO₃ and anatase in a fixed ratio. The mineral mixture was pelletized and heat-treated up to 1100 °C in order to evaluate sintering by recording the compressive strength values and visual assessment with scanning electron microscopy (SEM). Chemical interactions responsible for the trends in the compressive strength results were investigated with simultaneous thermogravimetric and differential thermal analysis (TG/DTA), as well as X-ray diffraction. The results indicated that the formation of anhydrite (CaSO₄) was responsible for increased mechanical strength in the mineral mixture pellets heated in air at temperatures higher that 400 °C. CaSO₄ formed from the reaction of the decomposition products of pyrite and calcite (SO_x and CaO). The TG/DTA results also indicated that the reaction with pyrite in air caused the decomposition of calcite in the mixture at a lower temperature than was observed for calcite only. The pellets heated in N₂ did not increase in mechanical strength during heat-treatment due to the lack of CaSO₄ formation in the inert atmosphere. However, SEM analysis indicated that sintering did occur at the higher temperatures in N₂. A decrease was observed in the compressive strength values obtained in air at temperatures from 900 °C to 1100 °C. Reasons for the decreased compressive strengths may include increased porosity, decomposition of CaSO₄, and changes in the characteristics of the aluminosilicate phases.     

方解石颗粒尺寸对白云质灰岩中碱白云石反应的影响

探讨了白云质灰岩中方解石基质对Na＋在岩石中迁移及其对碱白云石反应的影响。采用图像分析法测定不同白云质灰岩样本中方解石颗粒的尺寸,采用N2吸附法测定岩石孔径分布,采用火焰光度计测定养护在80℃、1 mol／L NaOH溶液中岩石柱内部的Na＋含量,采用X-射线内标法定量分析白云质灰岩中碱白云石反应（ ADR）生成的水镁石含量。结果表明,白云质灰岩TS-1、TS-2、GS-2及FHS-1中方解石颗粒中位径分别为4μm、12μm、15μm和33μm;方解石颗粒越小,迁移到岩石内部的Na＋含量越高,岩石中白云石的碱白云石反应程度越高。     

Dolomite,wollastonite and calcite as different CaO sources in anorthite-based porcelain

Anorthite-based porcelain was fabricated by using ball clay, quartz, alumina, feldspar and three different sources of CaO as raw materials. The effect of CaO sources such as dolomite, wollastonite and calcite on the mechanical, thermal and aesthetical properties of anorthite-based porcelain was investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were also carried out to analyze the microstructure. Anorthite was formed as major phase in all the samples fired at their optimum sintering temperatures (1200, 1215 and 1230 °C). The sample with dolomite had the highest bulk density but the smallest flexural strength due to formation of substantial glassy phase. The maximum flexural strength (～110 MPa) was reached in the sample containing wollastonite, which was mainly attributed to the favorable microstructure. Anorthite as the single crystalline phase was found in the sample with calcite and the sample showed the lowest thermal expansion coefficient and the highest whiteness, which was similar to bone china in appearance.