Effect of carbon fiber paper made from carbon felt with different yard weights on the performance of low temperature proton exchange membrane fuel cells

This study employed fuel cell gas diffusion layers (GDLs) consisting of carbon fiber paper made from carbon fiber felt with different yard weights in proton exchange membrane fuel cells (PEMFCs), and investigated the relationship between the yard weight of the carbon fiber paper and the fuel cell performance and thickness of the gasket. In this paper we discuss the relationship between carbon fiber felt with different yard weights and fuel cell performance and also explore the effect of carbon fiber paper thickness, air permeability, surface resistivity, and structural study. We focused on the material used for the gas diffusion layer in this study. Carbon fiber paper made in-house in this study contained 10 wt% (all percentages are by weight unless otherwise noted) phenolic resin. When the tested area was 25 cm², the test temperature was 40 °C, the gasket thickness was 0.06 mm, and the yard weight 70 g m⁻², fuel cell current density was 1968 mA cm⁻² at a load 0.3 V. When the gasket thickness was 0.36 mm and yard weight was 190 g m⁻², fuel current density was 1710 mA cm⁻² at a load of 0.3 V.     

Preparation and adsorptive properties of cellulose-based activated carbon tows from cellulose filaments

A series of cellulose-based activated carbon tows were prepared in a vertical tube furnace in the presence of reactive mixed gases after pretreatment with complex inorganic flame-retarding reagents under different burn temperatures and delivery speeds. The cross and vertical sectional surface states of activated carbon tows were observed with a SEM instrument. The surface characteristic, BET surface area, pore volume and pore radius of activated carbon tows were measured with N₂ at 77 K with a Quantachrome Autosorb-6 Sorption System. The adsorptive properties of gases and organic solvents on activated carbon tows (ACT) and granular activated carbon (GAC) were also determined.     

杜拉纤维对钢筋混凝土抗压强度、碳化及钢筋腐蚀影响的实验研究

鉴于过去杜拉纤维对钢筋混凝土中钢筋腐蚀影响研究较少的现状,从杜拉纤维对钢筋混凝土的抗压强度、碳化等方面的影响进行了研究,同时用电化学的方法对加入杜拉纤维对钢筋腐蚀影响进行了探讨。结果表明:a)加入杜拉纤维对混凝土试块抗压强度提高不明显,而对钢筋腐蚀有一定的抑制作用,随杜拉纤维掺量增加,钢筋腐蚀电位增加;b)随杜拉纤维掺量增加,钢筋混凝土表面碳化深度减小。     

Carbonization behaviour of modified synthetic mesophase pitches

Stabilization of naphthalene-derived synthetic mesophase pitch was achieved by controlled oxidation or reaction with phenanthrenequinone (PHQ) in order to suppress the swelling during high-temperature treatments. The modified pitches were characterized and their carbonization behaviour was studied by thermogravimetry-mass spectrometry. The results show that naphthenic groups are involved in the stabilization process. PHQ reacts via cycloaddition reactions, yielding oxygen-containing non-planar structures, a feature that accounts for the loss of anisotropic properties of the final material.     

Carbon foam derived from various precursors

A series of carbon foams was developed by using low-cost precursors, such as coal, coal tar pitch and petroleum pitch. The properties of the resultant carbon foams cover a wide range, e.g., bulk density, 0.32-0.67 g/cm³, compressive strength, 2.5-18.7 MPa, isotropic and anisotropic microstructure, etc. The investigation of foaming mechanism and the relationship between properties and structure indicate that the fluidity and dilatation of the foaming precursors significantly affect the foaming performance and foam structure. Raw coal samples were foamed directly without pretreatment in this work. However, for the pitch based foaming precursor, a thermal pretreatment is necessary to adjust its thermoplastic properties to meet the foaming requirement. The mechanical strength of carbon foam is found to be related to not only the foam cell structure, but also the fluidity and anisotropic domain size of the foaming precursors. In addition, the micro and mesopore structure in carbon foam matrix was investigated by gas adsorption and it was found that it also affects the strength of carbon foam and is related to the fluidity of foaming precursor.     

Some aspects of structural transformations taking place in organic mass of Ukrainian coals during heating. Part 1. Study of structural transformations when heating coals of different caking capacity

The structure of the plastic layer in coals of different caking capacity was studied using the X-ray method and the influence of the plastic layer structure on the mechanism of coke formation was determined. It is shown that the transportation of the plastic mass in the gas-saturated zone of the plastic layer has a decisive influence on the decrease in volume of the coal charge and on obtaining a denser residue during carbonization. When heating poorly caking and non-caking coals an increase in the charge volume takes place.Using the quantitative X-ray phase analysis an ordered phase amount (C_cryst) was found in solid residues of carbonization and the parameters d₀₀₂, L_c and L_a were determined. It is shown that the gas-saturated zone is generated in the plastic layer only when structural transformations in coals take place at the pre-plastic stage without changing the ratio between the number of carbon atoms in the ordered and non-ordered phases. The transition of well caking coal into the plastic state is accompanied by the activation of segmental and conformal movement of side chains and separate macromolecular fragments of the coal organic mass. In the course of grain swelling of non-caking coal its crystallites degrade. The conclusions drawn on the basis of X-ray studies were confirmed by the EPR-spectroscopy of residues corresponding to plastic zones in coals of different caking capacity.     

Carbonization of petroleum feedstocks II: Chemical constitution of feedstock asphaltenes and mesophase development

The characterization of the asphaltene fractions of a range of petroleum feedstocks by FT-IR, ¹H and ¹³C NMR spectroscopy indicated distinct differences in the molecular structure of the asphaltenes. Some of these differences could be related to the variations in the size of the principal optical texture of the semi-cokes produced by carbonization. The principal optical texture size was observed to increase steadily with the increasing hydrogen aromaticity of the asphaltenes over the whole range of the feedstocks used. There was no consistent correlation, however, between the carbon aromaticity of the asphaltenes and the optical texture size. The correlation between the hydrogen aromaticity and the principal optical texture size was attributed to structural differences among the asphaltenes that are critically important for the mesophase development.     

Changes of porosity during carbonization of bituminous coals: effects due to pores with radii less than 2500 nm

Based on both available reports and the results of experimental studies, the pores in coal chars have been divided into three groups. The first group comprises of pores with radii <7.5 nm, the second one consists of the pores with radii in the range 7.5≤r≤2500 nm and the third group consists of the pores with r>2500 nm. Based on the results of the experimental study conducted for ten Polish bituminous coals, the set of equations describing volume changes of the pores with r≤2500 is derived and discussed for slow carbonization of selected coals up to 1000 °C. The equations describe both the transformation processes of the primary pores and the formation and development of new pores depending on the final temperature of carbonization and properties of the parent coal. These properties include the Gieseler temperatures of softening and resolidification as well as the characteristics of the chemical structure of coal organic matter. The impact of the coal's organic matter contraction and the coal's total mass loss on the pore volume (cm³/g) are also taken into account.     

The mechanism of coking pressure generation I: Effect of high volatile matter coking coal, semi-anthracite and coke breeze on coking pressure and plastic coal layer permeability

One of the most important aspects of the cokemaking process is to control and restrain the coking pressure since excessive coking pressure tends to lead to operational problems and oven wall damage. Therefore, in order to understand the mechanism of coking pressure generation, the permeability of the plastic coal layer and the coking pressure for the same single coal and the same blended coal were measured and the relationship between them was investigated. Then the ‘inert’ (pressure modifier) effect of organic additives such as high volatile matter coking coal, semi-anthracite and coke breeze was studied. The coking pressure peak for box charging with more uniform bulk density distribution was higher than that for top charging. It was found that the coking pressure peaks measured at different institutions (NSC and BHPBilliton) by box charging are nearly the same. The addition of high volatile matter coking coal, semi-anthracite and coke breeze to a low volatile matter, high coking pressure coal greatly increased the plastic layer permeability in laboratory experiments and correspondingly decreased the coking pressure. It was found that, high volatile matter coking coal decreases the coking pressure more than semi-anthracite at the same plastic coal layer permeability, which indicates that the coking pressure depends not only on plastic coal layer permeability but also on other factors. Coking pressure is also affected by the contraction behavior of the coke layer near the oven walls and a large contraction decreases the coal bulk density in the oven center and hence the internal gas pressure in the plastic layer. The effect of contraction on coking pressure needs to be investigated further.