Correlation of the reactivity,the active surface area and the total surface area of thin films of pyrolytic carbon

Using thin films of pyrolytic carbon the rate of the reaction with oxygen has been measured over the temperature range 625–740°C and at pressures of oxygen from 6–100 torr. The active surface area (ASA) of the films was measured from the total concentration of strongly-bound complexes with oxygen on the surface and the relative total surface area (TSA) was measured by low-temperature adsorption of nitrogen. A maximum in reactivity and in ASA was observed for films of average thickness of about 20 nm with a TSA of about 30 m² g^?1. At the maximum the ASA and TSA were essentially equal. The results are interpreted in terms of the mechanism of formation of pyrolytic carbon in the initial stages.     

Polymers for the immobilization of whole cells and their application in biotechnology

Immobilization of whole cells has become an efficient tool for biosynthesis, biotransformation and analysis. High cell density, high operational stability, easy handling, propably in continuous systems, and multiple reuse are important advantages of immobilized cells. In comparison to other methods like adsorption, crosslinking and encapsulation, the entrapment within a polymeric network is the most widely applied technique in heterogeneous biocatalysis. For immobilizing mammalian cells nearly exclusively the adsorption onto micorcarriers is used. Requirements for the polymers to be used in such immobilized cell systems are discussed in detail.     

Properties of products based on aluminum titanate and alumina

Conclusions Aluminum titanate containing additions of alumina and aluminum phosphate is a promising material for making articles with a low or practically zero coefficient of thermal expansion at temperatures of up to 500°C.It is of interest to do further work to find materials based on aluminum titanate, alumina and aluminum phosphate with zero coefficients of expansion in various temperature ranges.The addition of alumina and aluminum phosphate confers an adequate strength to the components of aluminum titanate, a high spalling resistance (including metal resistance) with a refractoriness of the order of 1930°C.     

The effect of catalyst preparation on the performance of magnesium fluoride supported ruthenium

The effect of different ruthenium precursors on the structure and catalytic properties of the Ru/MgF₂ system was studied with such methods as IR, XPS, EPR and catalytic test reactions. The adsorption of probe molecules (CO and O₂) revealed a greater ability to transfer an electron from ruthenium in the case of samples obtained from Ru₃(CO)₁₂ than in the case of samples obtained from RuCl₃. Besides, metallic crystallites of different size were obtained depending on the precursor used. Namely, the average cluster size was 1.5 times smaller for carbonyl samples in comparison with chloride ones. Both series of preparations were active in redox or acid-base reactions. The activities of the carbonyl samples were higher than those of the chloride catalysts, particularly in reactions that require the presence of acid centers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Coulometric Titration of Iodine Values in Fats and Oils

Standard methods for the determination of iodine values of oils involve direct addition of halogen elements to the double bond. Since the reaction proceeds slowly there is a risk of substitution. A direct coulometrical titration method has been investigated.     

Efficiency of transport-dump systems when working fireclay deposits

Conclusions The article recommends the method of determining the basic parameters of the transport-dump systems for working fireclays; the maximum height of the overburden shelf needed, the required length of working front and the useful volume of mining the clays.With all-year-round working in the mines the use of the excavator ERG-35/1000 in combination with the swing chute OSh-105/1500 is desirable with a height of overburden work of up to 13 m; above 13 m it is more economical to use the excavator ERG-350/1000 in combination with the bridge OMSh-65/1200.     

Adhesion Effects of Intermediate Layers on the Densification of Ceramic Powders

In the ceramic technology the first step to produce sintered bodies is the manufacturing of powders which then are densified. The adhesion mechanisms between the single particles and the agglomerates produced from them determine the densification process. Starting from theoretical considerations adhesion mechanisms, such as solid bridge formation, adhesive bonding and glide-promoting effects, are discussed in principle. Subsequently, the effects of surface-active substances on the densification behaviour of clay-ceramics and oxide-ceramic bodies are discussed. Further, the evaluation of the action of additives to the powder mixtures on the microstructure of the compacts, such as porsity and texture, leads to a compaction equation which describes the transition from the powder pile to a densified green body.     

Cationic latex interaction with pulp fibers. II. Modification of sheet properties by styrene butadiene latex with quaternized amino groups

Unbeaten kraft fibers covered with experimental cationic latexes were formed into sheets in which direct fiber-fiber bonds are replaced by polymeric bonds. The effect on sheet properties—breaking length, elongation at break, folding endurance, opacity, and light scattering—was evaluated as a function of latex composition. The composition was altered by either the ratios of styrene to butadiene in the polymer or by mixing soft film-forming and hard nonfilming latex. It is shown that, regardless of latex composition and mechanical properties of the polymeric film, all the latexes can modify the sheet properties to a similar extent, providing that the sheets are heated above the polymer's glass transition temperature. An improvement of tensile strength is accompanied by increased elongation. As a probable mechanism of reinforcement, it is suggested that the polymer acts as a filler of the fiber's surface irregularities, thus providing a larger contact area between fibers and an improved stress transfer between them.     

Mechanisms of antioxidant action: The effect of spin traps during the processing and photooxidation of PVC

It is demonstrated by the use of spin traps that during the early stages of thermal processing of PVC considerable concentrations (> 3 × 10^?6 mol g^?1) of free radicals are produced which are primarily responsible for the initial products (hydroperoxides, unsaturation, and hydrogen chloride) previously shown to be formed in the polymer. From a semiquantitative analysis of these products, it is estimated that more than 50% of the radicals are formed from hydroperoxides and the rest by mechanoscission of the polymer chain. The spin traps are effective processing stabilizers in combination with a tin maleate HC1 scavenger. One of them (2-methyl-2-nitroso propane, MNP) has also been shown to be a photoantioxidant.