Calorimetric Investigation of Grafting of Styrene and Methylmethacrylate onto Air-Preirradiated Polyethylene

All existing and widely used methods for measuring reaction rate of polymerization processes suffer from basic disadvantages including indirect measurement, insufficient accuracy and limited applicability. Their unsuitability is especially pronounced in the investigation of graft copolymerization reactions in which the accuracy of measurement could be affected even by the different properties of individual polymer samples. In this work a new method, calorimetry, free of mentioned disadvantages is generally proposed for investigation of polymerization processes and particularly its application to radiation induced grafting of styrene and methylmethacrylate onto polyethylene is demonstrated. Experimental results showed the possibility of calorimetry to measure the grafting rate continuously and directly in the whole conversion range with the accuracy much better than with any other method used so far. It was concluded that styrene grafting is non-diffusion-controlled, whereas methylmethacrylate grafting is not diffusion- independent. With both monomers the reaction kinetics was found to be dependent on the type of polyethylene a s a consequence of different mechanisms, i. e. in the initiation step two different species, peroxy radicals and peroxides, take part. Its concentration is different in two types of polyethylene used. In the case of high density polyethylene both active species participate in the initiation process equally, according to their different nature. However, in low density polyethylene the concentration of peroxy radicals is negligible compared to that of peroxides and therefore peroxides have dominating role in the initiation step of grafting reaction. The change of the viscosity of reaction medium in the course of reaction as well as the structure of polymer in the case of high density polyethylene influence the kinetics of grafting reaction

Thermodynamically self-consistent non-stochastic micromagnetic model for the ferromagnetic state

In this work, a self-consistent thermodynamic approach to micromagnetism is presented. The magnetic degrees of freedom are modeled using the Landau-Lifshitz-Baryakhtar theory, that separates the different contributions to the magnetic damping, and thereby allows them to be coupled to the electron and phonon systems in a self-consistent way. We show that this model can quantitatively reproduce ultrafast magnetization dynamics in Nickel.Comment: 5 pages, 3 figure

Minimising the impact of scale-dependent galaxy bias on the joint cosmological analysis of large scale structures

We present a mitigation strategy to reduce the impact of non-linear galaxy bias on the joint ‘3 × 2pt’ cosmological analysis of weak lensing and galaxy surveys. The Ψ-statistics that we adopt are based on Complete Orthogonal Sets of E/B Integrals (COSEBIs). As such they are designed to minimize the contributions to the observable from the smallest physical scales where models are highly uncertain. We demonstrate that Ψ-statistics carry the same constraining power as the standard two-point galaxy clustering and galaxy-galaxy lensing statistics, but are significantly less sensitive to scale-dependent galaxy bias. Using two galaxy bias models, motivated by halo-model fits to data and simulations, we quantify the error in a standard 3 × 2pt analysis where constant galaxy bias is assumed. Even when adopting conservative angular scale cuts, that degrade the overall cosmological parameter constraints, we find of order 1σ biases for Stage III surveys on the cosmological parameter S8 = σ8(Ωm/0.3)α. This arises from a leakage of the smallest physical scales to all angular scales in the standard two-point correlation functions. In contrast, when analysing Ψ-statistics under the same approximation of constant galaxy bias, we show that the bias on the recovered value for S8 can be decreased by a factor of ∼2, with less conservative scale cuts. Given the challenges in determining accurate galaxy bias models in the highly non-linear regime, we argue that 3 × 2pt analyses should move towards new statistics that are less sensitive to the smallest physical scales

Calvet Microcalorymetry - a New Suitable Method for Investigation of Polymerization Reactions

The method of Calvet microcalorimetry was used to follow the course of the spontaneous polymerization of styrene. Comparison of this method with widely used point-by-point methods has been performed and the great advantages of calorimetry are shown. Calorimetry measures continuously and directly the reaction rate independently from the physical state of the sample using only one sample for the whole conversion range. The accuracy and sen,sitivity achieved are better than those achieved with other methods. On the basis of these advantages Calvet microcalorimetry can be recommended as very promising method for the investigation of polymerization kinetics

Termination Reaction in the Anionic Polymerization of Methacrylonitrile

The anionic polymerization of methacrylonitrile initiated by triethylphosphine in dimethylformamide was studied. Experimental evidence for two mechanisms of termination reaction was obtained. By addition of water or alcohol in polymerizing system the rate of polymerization and molecular weight of polymethacrylon1itrile decrease, which proves the termination reaction to be bimolecular and proceed by interaction of the active carbanion with water or alcohol. The rate constant for termination of free anions with water was determined, k~,0 = 2.2 x 102 dm3 moP s-1• The termination reaction could not be excluded by purification and prolonged drying of all components of the system, which indicates that the second mechanism of termination is operative as well. Conductivity measurements gave evidence for a monomolecular spontaneous reaction leading to deactivation of the anion

Development and recent progress on ammonia synthesis catalysts for Haber–Bosch process

Due to its essential use as a fertilizer, ammonia synthesis from nitrogen and hydrogen is considered to be one of the most important chemical processes of the last 100 years. Since then, an enormous amount of work has been undertaken to investigate and develop effective catalysts for this process. Although the catalytic synthesis of ammonia has been extensively studied in the last century, many new catalysts are still currently being developed to reduce the operating temperature and pressure of the process and to improve the conversion of reactants to ammonia. New catalysts for the Haber–Bosch process are the key to achieving green ammonia production in the foreseeable future. Herein, the history of ammonia synthesis catalyst development is briefly described as well as recent progress in catalyst development with the aim of building an overview of the current state of ammonia synthesis catalysts for the Haber–Bosch process. The new emerging ammonia synthesis catalysts, including electride, hydride, amide, perovskite oxide hydride/oxynitride hydride, nitride, and oxide promoted metals such as Fe, Co, and Ni, are promising alternatives to the conventional fused‐Fe and promoted‐Ru catalysts for existing ammonia synthesis plants and future distributed green ammonia synthesis based on the Haber–Bosch process