Zheng Mao Ye

Effect of Sr/Ba Ratio on Dielectric Properties of BSTN Ceramics

The phase composition of (1-x)BaO·xSrO·0.7TiO2·0.3Nb2O5 (BSTN) composite ceramics was analyzed by XRD, and the effect of Sr/Ba ratio on the dielectric properties of BSTN was investigated by impedance analyzer. The results showed that any sample with different x value contained two phases-the perovskite phase and the tungsten bronze phase. The dielectric constants of BSTN basically decreased while the tanδ increased with the increase in x value. Both dielectric constant and tanδ decreased with the applied frequency increased for the same x value. There were two Curie points for BSTN composite ceramics. The first one belonging to the perovskite phase decreased with the increase in x value, but the second one belonging to the tungsten bronze phase kept almost constant at about 300°C.

Study on Effect of Carbonation Curing for Cement Minerals and Clinker

As an advanced technology, carbonation reaction could dispose of industrial solid residues and sequestrate CO2 gas, save resources and protect environment. In this study, Major minerals of cement were high-temperature burned using pure chemical reagents ( the burning temperature of C3S, C2S, C3A, C4AF were 1550°C,1400°C,1330°C, 1350°C). Forming and unforming main cement minerals and clinker were carbonated under the condition of CO2 partial pressure P=0.2MPa, T =25°C, CO2 gas concentration c>99.9% and water/soild w/s=0.12kg/kg. The change of minerals and the effect of carbonation were tested. The experimental results showed that carbonation reaction could been occured in four cement minerals (C3S, C2S, C3A and C4AF), and CaCO3 crystals appeared in these minerals. The sequence of carbonation degree of minerals were C3S﹥C2S﹥C4AF﹥C3A. 0.168g and 0.125g CO2 gas could been sequestrated by 1 gramme of C3S and C2S in carbonated curing respectively, and 0.1301g and 0.1464 g CO2 gas could been sequestrated by 1 gramme of formed and powdery clinker. After carbonated curing, clinker samples had high early strength and good soundness, 2h strength was 24.65 MPa and 3d strength was 41.65 MPa.

Redispersible Polymer Powder-Modified Sulphoaluminate Cement Mortar

The super-softening property of redispersible polymer powder can improve the flexibility of cement-based materials while guarantees other work performances. In this study, the influences of different mixing amounts of redispersible polymer powders on the compressive strength, flexural strength, flexural compression ratio and bonding strength of sulphoaluminate cement mortar were investigated. The microscopic morphological structure of redispersible polymer powder-modified sulphoaluminate cement mortar was also observed through SEM to analyse the influence mechanism. Results show that, with the mixing amount of 2.0%, the compressive strength of cement mortar was improved. This mixing amount also increased the 28d flexural strength to 8.21 MPa (5.0% improvement) and 14d bonding strength to 5.6 MPa (27.3% improvement). Addition of more redispersible polymer powder resulted in the increase in flexural compression ratio because the powder particles formed water-insoluble continuous polymer colloidal film in hardened paste. This film generated a network with cement dydration products throughout the paste, consequently promoting the flexibility of cement.

The Change of Stress on Marine Concrete Covered with Barnacles

Barnacle is a major creature in marine fouling organisms, it increases static load and dynamic load of marine structures. In this paper, the change of stress on marine concrete surface covered with barnacles is studied. Moreover, a simplified model is established. The result shows that the stress of seawater increases by 0.53 times on the concrete surface, which is covered with barnacles.

Study of Frost Resistance of 50 Years Concrete Exposed to Saline Areas

The Hong Run petrochemical oil depot is located in a saline area in the north of Weifang.This area is severe cold in winter and has large temperature span throughout a year. Due to the areas rigorous environmental conditions, concrete with 50 years durability and strength grade of C40 was fabricated with the ordinary Portland cement, high performance superfine mineral powder and high performance pumping agent. Tests using the onsite concrete samples show that concrete mechanical properties meet the design requirements. After 300 freezing and thawing cycles including accelerated freezing thawing method and single-side freezing thawing method, the quality loss rate and relative dynamic modulus both comply with the design requirements. This suggests that the sample concrete has excellent frost resistance ability.

Effect of Redispersible Powders on Frost Resistance of Sulphoaluminate Cement Mortar

Frost Resistance of rapid hardening sulphoaluminate cement was modified with redispersible powders. Frost resistance and strength of sulphoaluminate cement mortar were tested. With the help of SEM and mercury porosimetry, the morphology of the hydrates and the micro-structure of the mortar were observed. The frost resistance mechanism of redispersible powders in the mortar is analyzed. The results show that the frost resistance of sulphoaluminate cement mortar could be improved significantly by mixing redispersible powders. The optimal content of redispersible powders is 0.9%.

Study on the Properties of Fiber Reinforced Sulphoaluminate Cement Mortar

The effects of wood fiber and polypropylene fiber on the mechanical performance, drying shrinkage and moisture loss of sulphoaluminate cement (SAC) mortar were studied. The experimental results show that wood fiber and polypropylene fiber can both improve the flexural strength of the mortar and reduce drying shrinkage ratio and moisture loss at different ages. Polypropylene fiber can also improve the late compressive strength of the mortar. Adding 0.3% mass fraction of wood fiber, the drying shrinkage ratio and moisture loss of the motar reach minimum values. The drying shrinkage ratio reduces to 0.029% at 28d. Moisture loss reduces to 0.4%. Adding 0.5% mass fraction of polypropylene fiber, the drying shrinkage ratio and moisture loss of the motar also reach minimum values. The drying shrinkage ratio reduces to 0.03% at 28d and moisture loss reduces to 0.39%.

Research on the Performance of Ba-Bearing Aluminoferrite Cement

This paper discussed the main clinker minerals and their optimal proportion of Ba-bearing aluminoferrite cement. The results show that the optimal sintering temperature is 1365°C. In XRD patterns, the diffraction peak of C2.75B1.25A3 and C4AF nearly disappear when the harden cement slurry hydrated for 3d at absent of gypsum. At the same time, a large numbers of hydration products like BaSO4 and CxAHy which including CAH10, C2AH8, C4AH19 and so on, appear in XRD patterns. So the hydration rate of Ba-bearing aluminoferrite cement is fast and the degree of hydration is high. These hydration products come into being a stable structural frame so that 3d compressive strength of the clinker can reach to 73.3MPa.

Application of Second Law of Fick in NaCl Attack of Sulphoaluminate Cement

The standard diffusion calculating model is one of the models widely used to predict the concrete construction life in chloride environment. According to test results, the surface concentration and the initial concentration of chloride ion on sulphoaluminate cement sample was analyzed by mathematical method. Life prediction model in chloride environment was built. According to the model, the sulphoaluminate cement construction life will be 51.5 years when the thickness of cement protective layer is 40mm.

Synthesis and Characterization of Nanocrystalline Mg4Nb2O9 by the Modified Sol-Gel Method

Nanosized and highly reactive magnesium niobate Mg4Nb2O9 were successfully synthesized by a sol-gel method as potential candidates for use in microwave applications as a low-temperature co-fired ceramic (LTCC). The Nb-Mg-citric acid solution was evaporated resulting in a dry gel that was calcined in the temperature ranging from 550°C to 850°C for crystallization in air atmosphere. The crystallization process from the gel to the crystalline Mg4Nb2O9 was followed by thermal analysis and during calcinations phase evolution of the powders was studied using X-ray diffraction (XRD) technique. Particle size and morphology were examined by high resolution scanning electron microscopy (HR-SEM). At 850°C the corundum-like phase of magnesium niobate was obtained in air atmosphere with an average particle diameter of 80 nm approximately calculated from the HR-SEM images.