Microstructure and Mechanical Properties of CaCO_3 Whisker-reinforced Cement

Composite Portland cement （PC） played an important role in various kinds of construction engineering owing to low hydration heat,low-cost,and application of solid industrial waste,but its brittleness and low strength limited its use in stress-bearing locations.The aim of this study is to improve the toughness and fracture resistance by incorporating CaCO3 whisker in cement matrix.Effect of different content of calcium carbonate whiskers on the mechanical properties of PC was investigated.The results showed that the flexural strength,impact strength and split tensile strength were increased by 39.7%,39.25% and 36.34% at maximum,respectively.Microstructure and elements of the whiskers in hardened cement were observed and analyzed by SEM/EDS.The mechanisms of the reinforcement of CaCO3 whisker on cement were also discussed,and the conclusion was that the improvement could be correlated to energy-dissipating processes owing to crack bridging,crack deflection,and whisker pull-out at the crack tips.

Influence of CaCO_3 Whisker Content on Mechanical and Tribological Properties of Polyetheretherketone Composites

The mechanical and tribological properties of polyetheretherketone （PEEK） composites filled with CaCO3 whisker in various content of 0～45% （wt pct） were investigated. The composite specimens were prepared by compression molding. Tribological testing of composites in dry wear mode against carbon steel ring was carried out on a MM200 block-on-ring apparatus. Data on neat PEEK were also included for comparison. It was observed that inclusion of CaCO3 whisker affected the most mechanical properties and the friction and wear in a beneficial way. With an increase in CaCO3 whisker content, friction coefficient continuously decreased but the trends in wear performance varied. The specific wear rate showed minima as 1.28×10^-6 mm^3/Nm for 25% CaCO3 whisker inclusion followed by a slow increase for further CaCO3 whisker addition. In terms of friction applications, when the tribological and mechanical properties are combined, the optimal content of CaCO3 whisker in the filled PEEK should be recommended as 15% to 20%. Fairly good correlations are observed in friction coefficient vs bending modulus and wear rate vs bending strength, confirming that the bending properties prove to be the most important tribology controlling parameters in the present work.

我国CaCO_3填料表面改性及在塑料中的应用

介绍了我国CaCO_3填料改性聚烯烃,聚氨酯和聚氯乙烯等塑料的方法和机理。结果表明:CaCO_3颗粒的形状和粒径、CaCO_3在塑料中的分布状态,CaCO_3与树脂之间的界面状态、制品制备工艺条件,以及相容剂和表面改性剂的种类、分子量大小和分子结构等因素塑料的拉伸强度、断裂伸长率、硬度、亲水性、熔体流动指数、密度和白度等性能的改善起着十分重要的作用。

微波法合成红色荧光粉CaCO_3:Eu^(3+)

采用微波法合成了红色荧光粉CaCO_3:Eu^(3+)。通过SEM,XRD和PL-PLE光谱等对样品的性能进行了表征和分析。同时,研究了微波功率对样品发光性能的影响。结果表明:样品在不同功率下会生成球霰石型的花片状、方解石型的立方体和文石型的针状等不同晶型的碳酸钙,颗粒的分散性好。波谱分析说明,掺杂Eu^(3+)作为发光中心进入到CaCO_3晶格中,其激发光谱主要由200～300 nm的Eu^(3+)—O^(2-)电荷迁移跃迁形成,属于宽带激发,在319,395,465,535 nm等处有窄的激发峰出现。在发射光谱中,由于磁偶极跃迁~5D_0→~7F_1受到不同晶体场的作用而分裂为593和589 nm两个峰,最强的发射峰为614 nm,对应于Eu^(3+)的电偶极跃迁~5D_0→~7F_2,属于纯正的红色发光。此外,随着微波功率的提高,基质的晶型逐渐由花片状的球霰石向针状的文石型过渡,样品的红色发射强度也逐渐增强。

中国北方四剖面CaCO_3含量变化及其反映的古降水量

中国北方自西向东的4个剖面,各地层CaCO3的含量呈现逐渐减少的规律。科尔沁剖面和延长剖面、西宁盘子山剖面CaCO3含量曲线表现出的特征为:在每一个古土壤单元的下部一定深度内CaCO3曲线都表现为一个明显的峰;新疆塔勒德剖面的各古土壤的CaCO3含量表现为表层比中、下部要高。利用CaCO3淀积深度恢复出来的部分区域的古降水量显示,末次间冰期期间盘子山剖面的古降水量大为352mm,延长剖面和科尔沁剖面的古降水量大约为500～550mm;末次冰期的间冰阶阶段科尔沁剖面的古降水量大致为320～360mm;延长剖面古降水量大约为443mm;全新世以来盘子山剖面的古降水量大约为306mm,延长剖面和科尔沁剖面的古降水量大约为320～380mm。这些数据可为半定量恢复地质历史时期古环境状况提供依据。

Mechanical properties of calcium carbonate whisker-reinforced high-strength cement mortar

In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural strength,split tensile strength and work of fracture are measured.Microstructures and micromechanical behaviors are investigated using scanning electron microscopy.The strengthening and toughening mechanisms and the efficiency of whisker-reinforced high-strength cement mortar are discussed.The results show that the addition of CaCO3 whiskers brings positive effects on the high-strength cement mortar.The strengthening and toughening mechanisms are whisker-cement coalition debonding,whisker peeling,whisker impact breakage and whisker bridging.Crack deflection is one efficient mechanism,but it is hard to be achieved in high-strength cement mortar.And the interfacial bonding strength between whiskers and the cement mortar matrix should be appropriately weak to introduce more crack deflection mechanisms to strengthen and toughen the cement mortar efficiently.

纳米CaCO_3对PE–HD/CF复合材料力学性能的影响

针对高密度聚乙烯(PE–HD)/碳纤维(CF)二元复合材料随CF含量的增加,拉伸强度和弯曲强度增大、冲击强度却逐渐下降的情况,在二元体系中添加纳米CaCO3制得PE–HD/CF/CaCO3三元复合材料,对比分析了两种复合材料的力学性能,并采用扫描电子显微镜对三元复合材料的冲击断面进行观察。结果表明,纳米CaCO3的加入使得三元复合材料的拉伸强度略有降低,但弯曲强度和冲击强度在一定范围内增大;当纳米CaCO3含量为10份时,复合材料的综合力学性能最佳。

CaCO_3改性对UV固化木器涂料性能的影响

在木器漆应用领域,UV涂料与传统涂料相比以明显优势,逐渐成为当下主流,同时也引领着未来的发展。但UV也有其缺陷,笔者着重于利用CaCO_3对木地板UV涂料进行改性,并对其力学性能和光学性能进行测试研究,旨在寻找一种具有较高性能的木质地板改性UV涂料。

PP/CaCO_3复合过滤板失效分析

介绍PP/CaCO3 复合过滤板在使用过程中存在的质量问题 ,如表面黄斑、熔接痕、小凸台成型不好、表层剥离、板内有气孔及易脆断等 ,着重从成型工艺和刚性填料对过滤板相结构、性能的影响上来分析这些问题 。

CaCO_3在CaCO_3-CuO和CaCO_3-Bi_2O_3体系中的分解动力学

用恒温热重法研究了CaCO_3在CaCO_3-CuO和CaCO_3-Bi_2O_3体系中的分解动力学,求出CaCO_3的分解方程式。实验结果表明:在上述两体系中,CaCO_3的表观分解活化能均为120 kJ·mol^(-I),并初步分析了CaCO_3的分解机理。

晶须CaCO_3超重力法制备及其在PVC中的应用

采用超重力碳化法,使用H3PO4作为添加剂,控制反应温度为80℃,制备出了平均直径为0.4～0.7μm,平均长径比为10～15左右的晶须CaCO3粒子。XRD分析表明,所制得的晶须CaCO3由文石相和方解石相组成,文石相质量分数为88.75%。晶须CaCO3/PVC复合材料力学性能的测试结果表明,晶须CaCO3的填充对PVC复合材料有显著的增强作用,复合材料的缺口冲击强度与未加晶须CaCO3之前相比提高到217%,拉伸强度和弯曲弹性模量也有不同程度的提高。综合来看,晶须CaCO3粒子与PVC的质量比(6～10)∶100为宜。

Synthesis and Structural Analysis of LDH-SO4-CO3 Whisker

High-quality LDH-SO4-CO3 whiskers were synthesized via liquid precipitation method using MgSO4·7 H2 O and Al2(SO4)3·18 H2O as precursors and Na2CO3-NaHCO3 buffer solution as precipitant. The influence of buffer solution concentration on the characteristics of the samples was investigated. The asgrown whiskers were characterized by X-ray diffraction, transmission electron microscopy, and BrunauerEmmett-Teller N2 specific surface area measurements. The results show that the buffer solution concentration has significant impact on whiskers with intercalated structure. The LDH-SO4-CO3 whiskers with well-defined geometry, distinct intercalated structure, decent quality, and excellent dispersing capability can be obtained under the following conditions: buffer solution volume ratio of 45%, reaction temperature of 83°C, and reaction time of 182 h. The obtained whiskers are well-crystallized and exhibit homogeneous morphology consisting of fiber bars.

Serviceability and Reinforcement of Low Content Whisker in Portland Cement

In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanical properties of portland cement were investigated. The experimental results show that CaCO3 whiskers have a good stability and serviceability in cement, and should not significantly alter the rheological properties of the cement paste. The flexural and compressive strength of portland cement reinforced by CaCO3 whiskers was increased by 33.3% and 12.83%, respectively.

Effects of Soil Texture and CaCO_3 on Turnover of Organic Material in Chao Soils

Decomposition experiments of 14C-labelled sickle alfalfa in chao soils of different texture and these soils after removal of CaCO3 were carried out under field and laboratory conditions respectively. The amount of residual 14C in, or 14CO2 evolved from, the soils at intervals after the beginning of decomposition were measured and the distribution of native and labelled C between particle size fractions isolated from these soils was edtermined. Results showed that contents of both labelled (14C) and non-labelled (12C) carbon decreased with increasing particle size. The enrichment factor for 14C was higher than that for 12C in the clay fraction, the reverse being true for the silt enrichment factors. The effect of soil texture on the decomposition of plant material could not be observed in chao soils when the clay content was lower than 270g kg-1, while it became obvious once CaCO3 was removed from these soils. The decomposition rate of plant material in the soil from which the native CaCO3 was removed was correlated significantly to both the clay content of the soil and the application rate of CaCO3. A preliminary correction equation describing the effect of clay and CaCO3 on the decomposition of organic material in chao soil was derived from the results obtained.

IN SITU PROCESSING OF Al_(2)O_(3) WHISKERS REINFORCED Ti-Al INTERMETALLIC COMPOSITES

In situ Al2O3 whiskers reinforced Ti-Al intermetallic composites were fabricated at ~1200℃ by reaction sintering of cold-consolidated fillets consisting mainly of Ti, Al, and different additives. The phases and microstructures of the sintered composites were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The process of synthesis was investigated using differential thermal analysis (DTA). The effects of processing parameters and additives on the microstructures of the composites and the development of whisker were examined. It is found that the morphology of the whisker is strongly influenced by the additives, the exothermal reaction process, and the processing parameters.

Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

Study on Microstructures of Micron Si_3N_4 Composite Ceramic with Addition of Nano SiC and SiC Whisker

The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a small amount of α Si 3N 4 and α SiC, and amorphous phase. Most of Si 3N 4 grains were equiaxed crystal and also there were some bulky columnar ones. Most of SiC particles and SiC whiskers distributed at the Si 3N 4 grain boundaries and a few of smaller SiC particles in the Si 3N 4 grains. Most of amorphous structure was in the junction of several Si 3N 4 grains and thin amorphous layer was observed only at a few of Si 3N 4 boundaries. Failured cracks propagated mainly along the boundaries of the Si 3N 4 grains and partially passed through Si 3N 4 grains. The path of crack propagating might change, branching and twisting of the cracks might occur when the expanding crack meet the SiC particle and/or SiC whisker. Effect of the microstructure on strength and toughness of the composite ceramic was briefly discussed.

Direct synthesis of single-phase α-CaSO4·0.5H2O whiskers from waste nitrate solution

Single-phaseα-CaSO4·0.5H2O whiskers were directly synthesized from waste Ca(NO3)2 solution using a hydrothermal method,and HNO3 was synchronously regenerated.The effects of reaction temperature and Ca^2+concentration on the phase composition and morphology of products were determined by X-ray diffraction and optical microscopy.On the basis of the experimental results,the formation diagram ofα-CaSO4·0.5H2O was plotted within the range of 5–35 g·L^-1 Ca^2+and 115°C–150°C.In addition,the conditions of the direct synthesis ofα-CaSO4·0.5H2O were determined.Well-crystallized,single-phaseα-CaSO4·0.5H2O whiskers with high aspect ratios(length,1785μm;diameter,10.63μm;aspect ratio,168)and HNO3(70.25 g·L^-1)were obtained at the optimal conditions of 25 g·L^-1 Ca^2+and 125°C.

Liquid precipitation and microstructure of Mg6Al2(OH)15NO3CO3·4H2O whiskers

High-quality LDH-NO_3-CO_3 whiskers were synthesized via a liquid precipitation method using Mg(NO_3)_2·6H_2O and Al(NO_3)_3·9H_2O as raw materials and Na_2CO_3-NaHCO_3 buffer solutions as precipitant. The whiskers were characterized by X-ray diffraction, transmission electron microscope, and Brunauer-Emmett-Teller N_2 surface area measurement. The influence of buffer solution concentration on the characteristics of the sample was investigated. The results show that the buffer solution concentration has significant impact on whiskers with intercalated structure. Overall, LDH-NO_3-CO_3 whiskers with well-defined geometry, distinct intercalated structure, high quality, and good dispersion capability can be obtained under the following conditions: buffer solution volumetric ratio of 60%, reaction temperature of 55°C, and reaction time of 269 h.

P123/Mg^(2+)水溶液中CaCO_3结晶及形貌的调控研究

在三嵌段共聚物P123与Mg2+的混合水溶液中,通过控制反应条件对CaCO3的微粒形貌进行调控。探讨了Mg2+浓度、反应时间、反应温度及P123浓度对CaCO3粒子形貌和晶型的影响。采用扫描电子显微镜(SEM)、X射线粉末衍射仪(XRD)对合成样品进行了表征。结果表明,Mg2+与Ca2+的质量比对CaCO3粒子形貌和晶型具有重要的影响。