N2-sorptionsmessungen zur bestimmung der spezifischen oberfläche und der porenverteilung von erhitztem normalbeton

The specific surface and pore size distribution of normal concrete is influenced by temperature effects. Therefore, the specific surface area of concrete specimens has been computed from nitrogen adsorption isotherms after a preceding temperature treatment in a thermal balance. It was found that the specific surface area increases from 2,0 m²/g at 100°C to 4,5 m²/g at 400°C. The mean pore radius decreases from 53 Å to 38 Å. A temperature treatment at 665°C is connected with a further decomposition of concrete and yields a decrease of the specific surface area to 2,4 m²/g and the pore size distribution shifts to larger radii ($\text{r}\text{= 51}\text{A}\text{?}$). Due to sintering processes, at temperatures of 1000°C the porosity of the material is decisively altered and a specific surface area of 1,1 m²/g has been calculated.     

Ultra-high modulus polyethylene. 1 Effect of drawing temperature

Drawing behaviour and the properties of ultra-drawn high density polyethylene have been investigated as a function of the drawing temperature. An optimum temperature has been found for each type of polyethylene, at which the best drawing behaviour is found. It appears that the temperature range for effective drawing (leading to a high draw ratio and high Young's modulus) depends on the molecular weight and its distribution. The temperature range of the effective drawing is shifted towards higher temperatures for polyethylene exhibiting broader molecular weight distribution and higher weightaverage molecular weight. Ultra-high modulus and transport samples have been obtained by drawing high density polyethylene with broad molecular weight distribution ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{～ 20}$ and $\text{M}\text{?}{}_{\mathrm{w}}\text{～ 200 000}$) at higher drawing temperatures. It has been found that in the range of drawing temperatures 80–105°C the modulus of this polyethylene is higher for samples drawn at higher temperatures. Transparent samples with draw ratios of 35–40 and with Young's moduli of 600–650 kbar (at room temperature) have been obtained by drawing the polyethylene at 100°–105°C. We conclude that the high molecular fraction in the polyethylene, forming tie molecules in the drawn material, is responsible for the high modulus, while the low molecular weight fraction facilitates alignment of the long chains and retards the internal voiding (whitening) to a very high draw ratio during drawing at the higher temperatures.     

Anomalous properties and structure of graphite-bromine residue compound at high temperatures

The thermal expansion of the interlayer spacing and the intensity ratio $\text{I(004)}\text{I(002)}$ of the diffraction lines of graphite-bromine residue compounds were measured at temperatures between room temperature and 700°C by using a high temperature X-ray diffractometer. At about 330°C, both the c-spacing and the intensity ratio of diffraction lines were found to show a break. That is, the r-spacing of the residue compound which shows normal linear expansion below 330°C, has a considerably smaller thermal expansion coefficient between 330 and 500°C. Over this temperature, the c-spacing of the residue compound becomes nearly equal to that of original graphite. On cooling, the anomaly in the reverse direction occurs between 330 and 200°C. The intensity ratio of the diffraction lines of the residue compound is smaller below 330°C as compared with that of original graphite, but above 500°C, both are almost the same. The thermal diffusivity and the heat-capacity studies were also performed in the same temperature range. The thermal diffusivity curve shows a break, and the heat-capacity curve has a small hump around 330°C. At temperatures higher than 330°C, both of these properties agree with those of original graphite. The structure of graphite-bromine residue compound and the nature of its change at high temperatures are discussed, and a model to explain all of these peculiar behavior of the residue compound is proposed.     

The significance of heating rate on char yield and char properties in the pyrolysis of cellulose

The carbonization of powdered cellulose was investigated in the temperature range 200–950°C by measuring weight loss, carbon and hydrogen content, BET-adsorption of nitrogen and carbon dioxide, mercury penetration and particle-size distribution. Evidence is presented in support of a kinetic model according to which cellulose decomposition is controlled by dehydration at low temperature and by cleavage/scission at high temperature. Increased char yield and lower $\text{O}\text{C}$ ratio at low heating rate, as well as kinetic investigations into the effect of potential catalysts, support this model. The difference in reaction mechanism according to the heating rate appeared to influence the char properties considerably. Yield in micropore volume and surface area of slowly carbonized cellulose is up to four times larger than that of rapidly heated cellulose. Mercury pore volume, density and particle diameter depend on the heating rate, also. By adsorption of various gases, differences in relative size of the pore openings of different chars can be discerned. Micropore volumes measured with carbon dioxide were as much as seventy times larger than the corresponding volume measured with nitrogen. Thus, it is possible to obtain chars with molecular sieve properties by simple pyrolysis heating schemes.     

Mechanical/thermal dewatering of lignite. Part 3: Physical properties and pore structure of MTE product coals

The mechanical thermal dewatering (MTE) process has been shown to effectively dewater high moisture content low rank coals via the application of mechanical force at elevated temperatures.Using mercury intrusion porosimetry (MIP) as an investigative tool, this study examines how MTE processing conditions, such as temperature and pressure, affect the compressibility, pore size distribution, apparent (skeletal) density and shrinkage behaviour of three low rank coals sourced from Australia, Greece and Germany. As both pore filling and sample compression occurred at high mercury intrusion pressures, all MIP data were corrected for compression effects by using compressibility values derived from mercury extrusion data.The MTE process is shown to produce a low porosity coal, which, depending upon the processing conditions used, undergoes further shrinkage upon oven drying at 105 °C. An increase in MTE temperature (above about 85 °C) led to an increase in mesopore volume, which is caused by a hardening of the coal structure, leading to pore volume retention and a consequent reduction in percent shrinkage on oven drying. The increase in measured mesopore volume is also associated with an increase in measured surface area.The reverse trend is seen with increasing MTE pressure, where both the macro and mesopore volume decrease with pressure, causing the percent shrinkage to increase accordingly. This effect may be due to an increase in capillary forces caused by a decrease in the average pore diameter. The percent shrinkage increased up to a pore volume of about 0.1 cm³/g, beyond which no further reduction in pore volume was achieved. The decrease in mesopore volume is also associated with a decrease in measured surface area.Compressibility values derived from mercury extrusion data show that the MTE process has little impact on the network strength of the skeletal network structure of all three coals investigated. Likewise, the skeletal density remained relatively unchanged.The reduction in water content, pore volume and the changes in shrinkage behaviour under increasingly severe MTE conditions are suggestive of the physical changes that accompany increased coalification (rank) within the lignitic range.     

Recrystallization kinetics of isotactic polypropylene (α-form)

The recrystallization kinetics of isotactic polypropylene (i-PP) (α-form) in the usual melting temperature region (155°–170°C) has been studied by calorimetric and dilametric techniques. The recrystallization is possible over a large range of temperatures also when the residual crystallinity is very low ($\text{? 1\%}$). Low values of the Avrami exponents independent of T_r (n ≤ 1.6), have been found, although the residual crystallinity shows a large variation (1–35%).     

Pulsed n.m.r. of cis-polyisoprene: 1

Proton spin-spin (T₂), and spin-lattice (T₁) relaxation time measurements are reported for six monodisperse cis-polyisoprenes ($\text{M}\text{?}{}_{\mathrm{n}}$ from 2000 to 200 000) over the temperature range from ?50° to 170°C. At low temperatures (?30° to 10°C) T₁ and T₂ are determined by the short range segmental motions but above 10°C T₂ is sensitive to the long range motions. When $\text{M}\text{?}{}_{\mathrm{n}}\text{? 30 000 T}{}_2$ becomes influenced by the presence of entanglements which produce a transient network structure and this confers on the spin-spin relaxation a pseudo-solid-like response. Similar behaviour is observed in crosslinked networks produced by irradiation. The results are discussed in terms of the types of motion occurring in amorphous polymers above T_g and the analogy with dynamic mechanical measurements is discussed.     

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

In order to improve the drying efficiency of lignite and restrain the moisture re-adsorption of dewatered coal, the drying characteristics of typical Chinese lignite, the re-adsorption performances of dewatered samples and the change in pore structure throughout the entire processes were investigated in this study. Lignite samples with four different particle size fractions were dried in a fixed-bed reactor in the temperature range 60–160°C. The re-adsorbing moisture behaviors of dewatered coal samples containing different water contents were investigated at temperatures of 20–40°C and humidities of 55–95%. The changes in the pore structure of raw coal and different dried samples were measured by mercury intrusion porosimetry (MIP) and the relations between their re-adsorption performance and change in pore structure were explored. The moisture removal yields of lignite increased with an increase in drying time and temperature and was close to 100% above 120°C and over 100% after holding 40 and 15 min at temperatures of 140 and 160°C due to the release of CO₂ from the decomposing carboxyl group in the coal matrix. The re-adsorbed moisture content in dewatered coal was influenced by drying temperature and coal particle size through varying pore structure. The temperature and relative humidity in the re-adsorbing process were the main factors that influenced the moisture re-adsorption capacity of dewatered lignite, in which the re-adsorbing temperature mainly operated by varying the bonding ability of water on the surface of dewatered coal, and the relative humidity was connected with the pore structure as well. The mesopore was the main factor that influenced the re-adsorption of dewatered coal and the re-adsorption of moisture in dewatered coal at 100°C was highest due to the narrow range of the pore radius and because the relative volume ratio of 5 to 50 nm mesopore (above 91%) was high. The water loss yield of lignite with smaller particle size was higher due to its larger pore volume and surface area, but its re-adsorption capacity was lower because of lower volume ratio of 5 to 50 nm mesopore volume in dewatered coal obtained from the smaller size lignite.     

Catalytic graphitization of carbons by borons

Boron is known as a unique graphitization catalyst, because it accelerates the homogeneous continuous graphitization process of the entire carbon without any formation of specific carbon components such as graphitic carbon. This study uses various amounts of boron and several kinds of carbon in an attempt to reveal whether the boron exhibits other kinds of catalytic effect. For the non-graphitizing phenol-formaldehyde resin carbon, a boron addition of 1 wt % accelerates the homogeneous continuous graphitization process of the entire carbon at heat-treatment temperatures from 1800 to 2600 °C. As the amount was increased to 5 and 10 wt %, the boron catalysed the formation of specific turbostratic carbon (no three-dimensional ordered structure, d₀₀₂ 3.38 Å, L_c 200 Ź) at 2200 °C, and graphitic carbon (three-dimensional ordered structure, $\text{d}{}_{002}\text{3.36}\text{A}\text{?}\text{, L}{}_{\mathrm{c}}\text{1000}\text{A}\text{?}$) above 2400 °C, besides the homogeneous effect, which was enhanced by increased heat-treatment temperature and an increase in the amount of boron. For the graphitizing 3,5-dimethylphenol-formaldehyde resin carbon, only the homogeneous acceleration was catalysed by 1 wt % boron. Additions of 5 and 10 wt % boron resulted in the formation of graphitic carbon above 2400 °C in addition to the homogeneous effect observed above 1800 °C. Turbostratic carbon was never found. The catalytic mechanisms for these effects are discussed.     

Electrical resistivity of carbon films

The electrical resistivity along 500 Å thick carbon films has been measured from 1.2 to 1100°K. The electrical resistivity measurements at high temperature indicate a change in the structure of the film beginning at about 670°K. In the theory of non-crystalline solids by Mott, the temperature dependence of the electrical conductivity σ, at low temperature, is given by In $\text{σ = A —BT}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ where A and B are constants. Whereas previous investigators have shown general agreement with Mott's relation, the present result at low temperature shows deviation from the In σ α $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ relation.     

Flow equations for graphite

In analyzing erosion of graphite at high strain rate (~10⁷ sec^?1) and temperature (~4000°C), it is necessary to have some approximation for the constitutive equation. Data for graphite from static and low strain rate experiments were successfully correlated using the equation $\text{gekT}\text{DbG}\text{= C′(}\text{σ}\text{G}\text{)}{}^{\mathrm{n}}$ which describes the flow of many metals and crystalline ceramics. Solution of the above equation for several specific cases of interest in hypersonic rain erosion at high temperature gives values for flow stress of from 2 to 10 kbar. Changes in temperature of about 500°C or strain rate by a factor 100 shift this value by more than 50%.     

Oxidation of carbon derived from phenolic resin

The oxidation of carbon derived from phenolic resin and heat-treated at temperatures ranging from 1000 to 2400°C for 1 hr was studied in a flowing oxygen atmosphere at temperatures between 424 and 692°C. The heat-treatment alters the crystallite size, L_c, from 10.7 to 21.4 Å; the interlayer spacing, d₀₀₂, from 3.74 to 3.52 Å and the surface area from 0.22 to 1.34 m²/g. $\text{L}{}_{\mathrm{a}}\text{L}{}_{\mathrm{c}}$ ratio ranges from 1.62 to 2.22 and appears to be independent of heat treatment temperature and oxidation level. The surface area of the carbon and its change with oxidation were found to be sensitive to the heat treatment process. Heat treatments at 1000 and 1400°C produce carbon with surface area which increases by nearly two orders of magnitude after 10% oxidation. The oxidation rate decreases with increasing heat treatment temperature with the largest change between 1000 and 1400°C. Samples heat-treated at different temperatures give slightly different activation energies with an average value of 41.5 kcal/mole.     

Crystallographic changes characterizing the Curie transition in three ferroelectric copolymers of vinylidene fluoride and trifluoroethylene: 1. As-crystallized samples

Copolymers of vinylidene fluoride/trifluoroethylene of molar composition $\text{65}\text{35}$, $\text{73}\text{27}$ and $\text{78}\text{22\%}$ respectively, are ferroelectric and undergo a Curie transition to the paraelectric state at high temperatures. In contrast to the irregular structure found earlier for the $\text{52}\text{48}\text{mol}\text{\%}$ copolymer, the structures of these three compositions in the low-temperature state are all well ordered and analogous to that of β-poly(vinylidene fluoride): they consist of molecular chains in a polar trans conformation whose order is improved with increasing vinylidene fluoride content, packed pseudo-hexagonally in unit cells whose dimensions decrease with increasing vinylidene fluoride content. In their paraelectric phase, the chains assume a partly disordered conformation consisting of irregular TG, T? and TT sequences and are packed on an expanded pseudo-hexagonal lattice. The Curie transitions were found to occur over a broad temperature range, encompassing ～30°C, and in the case of the $\text{78}\text{22}\text{mol}\text{\%}$ copolymer to extend into the melting region; they were also found to exhibit hysteresis by occurring at much lower temperatures upon cooling than upon heating.     

Effect of low-temperature oxidation on the composition of Athabasca bitumen

The effect of low temperature oxidation on the composition of Athabasca bitumen was examined. Oxidation temperatures in the range 125–135 °C and extents of oxidation up to 100mg $\text{O}{}_2\text{g}$ bitumen were investigated. The aromatics concentration was observed to decline steadily and the concentration of asphaltenes to increase, during oxidation. The saturates were unaffected by low-temperature oxidation. The resins concentration displayed a strange behaviour, first dropping and then increasing to a maximum and again dropping as oxidation proceeded.     

Catalytic effect of potassium on the rate of char-CO2 gasification

The effect of potassium on the rate of char-CO₂ gasification at 800 °C was investigated. The instantaneous rate depends on both catalyst concentration ($\text{K}\text{C}$) and the internal porous structure of the solid. At low values of $\text{K}\text{C}$ atomic ratio, the rate increases sharply with the addition of catalyst. As catalyst concentration is increased, the rate first levels off and then decreases. The levelling off is attributed to the saturation of the surface with catalytic sites. The subsequent decrease in rate seems to be due to the plugging of micropores by catalyst deposits. The reaction rate changes significantly during gasification and drops sharply before gasification is completed. The drop in rate before total conversion can be explained by catalyst accumulation and pore plugging.     

Oxidation of carbonaceous matter—I: Elemental analysis (C,H, O) and IR spectrometry

Products of various elemental composition ($\text{1.56 ? (}\text{H}\text{C}$) at ? 0.45 and $\text{0 < (}\text{O}\text{C}$) at < 0.45) were oxidized under an air flow at various temperatures (from 150 to 280°C) and for various times (from half an hour to one week). When plotted in a Van Krevelen diagram ($\text{H}\text{C}$ vs $\text{O}\text{C}$), their elemental composition follows an oxidation path, the slope of which depends only on the original ($\text{O}\text{H}$) atomic ratio and on the oxidizing temperature. Oxidation reactions have an “apparent activation energy” of 20–40 kcal/mole. Cross-linking may be due either to ether bonding or to hydrogen bonding as indicated by IR spectrometry. The final product, named “oxychar”, has a constant composition ($\text{H}\text{C ～}\text{-}\text{O}\text{C}\text{～- 0.5}$).     

Study of the AlCl3 catalytic activity on aromatic hydrocarbons—II: Mesophase formation

When naphthalene is carbonized in the presence of AlCl₃, polymerization and disproportionation reactions mainly occur up to approximately 300°C. Then, when the temperature is further increased, the catalyst gives rise to additional processes which are accompanied by H₂ evolution. Mesophase formation is observed at relatively low temperatures. After the catalyst removal the obtained mesophase seems to be stable in a wide temperature interval. Unusually low $\text{C}\text{H}$ ratios and high aliphatic hydrogen contents were observed in the catalytically formed mesophase. These properties are probably responsible for the solubility behaviour in conventional solvents. It is thought that the polymerization and disproportionation processes referred to above lead to the formation of high molecular weight nearly planar molecules, which contain fully aromatic and tetralin-like rings in their structures. These molecules would then be able to enter into the stacking process leading to the mesophase formation.     

Change of pore properties during carbonization of coking coal

Porosimetry, sorption and density measurements are reported on two caking bituminous coals, West Virginia Jewel No. 2 medium volatile and a Pennsylvania Pittsburgh seam high volatile C, for final carbonization temperatures between 400 and 1000°C. Samples were not confined and heating rates of 3 and 8.2°/min were employed. The medium volatile samples exhibit pronounced maxima in pore volume, pore surface area and porosity between 600 and 800°C. These temperatures are considerably greater than the characteristic temperature and the temperature at which maximum dilation occurs. The high volatile C coal does not exhibit well defined maxima. Results are interpreted in terms of pore development mechanisms. A mathematical model for pore development is proposed and shown to correlate satisfactorily, the pore volume and surface area measurements.     

Comparison of the unperturbed dimension of polystyrene for endothermal and exothermal heats of dilution within the same system

Light scattering measurements for two samples of polystyrene (I, M_w = 2.15 × 10⁵; II, M_w = 2.5 × 10⁶) were performed in the iso-refractive mixed solvent dimethoxymethane-diethyl ether. For sample I the temperature dependence of the second osmotic virial coefficient A₂ was determined for three constant compositions of the mixed solvent. In the range ?30° to +25°C the three curves run practically parallel and exhibit a maximum at approximately ?10°C. For the volume fraction of 0.7 diethyl ether in the mixed solvent, an endothermal theta-temperature θ₊ was found at ?27.0° ± 1.5°C and θ_?, the exothermal theta-temperature, at ?5.0 ± 1°C. The investigation of sample II in the abovementioned solvent confirmed the observed θ_?-temperature and displayed a higher exothermicity compared with I. Similarly to the temperature variation of A₂, the chain dimensions of II, determined from the angular dependence of the scattered light, run through a maximum. The unperturbed dimensions in the mixed solvent are found to be: $\text{r}{}_{\mathrm{w}}\text{= 448 ± 5}\text{A}\text{?}$ at θ₊ = ?27°C and $\text{r}{}_{\mathrm{w}}\text{= 443 ± 5}\text{A}\text{?}$ at θ_? = ?5°C, as compared with $\text{r}{}_{\mathrm{w}}\text{= 420 ± 10}\text{A}\text{?}$ at θ₊ = +33°C in cyclohexene. The inter-relation of the chain expansion coefficient and A₂ is quantitatively described by the Zimm-Stockmayer-Fixman equation over the entire range of heats of dilution.     

Random-coil configurations of alicyclic polyformals

A sample of poly (trans-1,4-cyclohexylene-dimethylene-oxymethylene oxide) (PTCDM) was synthesized by condensation of trans-1,4-cyclohexane dimethanol and paraformaldehyde using p-toluene sulphonic acid as catalyst. A fraction having M_n=6500 and a melting point of 86°C was isolated and purified; its n.m.r. spectrum does not change with temperature in the range 20°–50°C which indicates a rigid distribution of methylene substituents in the cyclohexane ring; its dipole moment, measured in benzene solution at several temperatures between 20° and 60°C, yielded values of $\text{D}{}_{\mathrm{n}}\text{=}\text{[μ}{}^2\text{]}\text{nm}{}^2\text{=0.17–0.21}$ and a temperature coefficient dln $\text{{gm}{}^2\text{}}\text{d}\text{T}\text{= 5.5 × 10}{}^{\mathrm{?3}}\text{K}{}^{\mathrm{?1}}$, similar to those reported in the literature for acyclic polyformals. Agreement between experimental and calculated (using rotational isomeric states theory) values is satisfactory.