Steady state types for CSTR. Heterogeneous system liquid - liquid

For a heterogeneous liquid - liquid system in which an exothermal reaction takes place, the topology and stability of the steady states of CSTR are investigated. It is shown that the thermal effect of the reaction, the magnitude of the energy barrier and the intensity of mass transfer strongly influence the type of steady state that arises. In this case, a change in the topological picture occurs through degenerate steady states.

Joining with Reactive Nano-Multilayers: Influence of Thermal Properties of Components on Joint Microstructure and Mechanical Performance

Reactive nano-multilayers (RNMLs), which are able to undergo a self-heating exothermal reaction, can, e.g., be utilised as a local heat source for soldering or brazing. Upon joining with RNMLs, the heat produced by the exothermal reaction must be carefully adjusted to the joining system in order to provide sufficient heat for bond formation while avoiding damaging of the joining components by excessive heat. This heat balance strongly depends on the thermal properties of the joining components: a low thermal conductivity leads to heat concentration within the joining zone adjacent to the RNML, while a high thermal conductivity leads to fast heat dissipation into the components. The quality of the joint is thus co-determined by the thermal properties of the joining components. This work provides a systematic study on the influence of the thermal properties upon reactive joining for a set of substrate materials with thermal conductivities ranging from very low to very high. In particular, the evolution of the microstructure within the joining zone as a function of the specific time-temperature-profile for the given component material is investigated, focusing on the interaction between solder, RNML foil and surface metallisations, and the associated formation of intermetallic phases. Finally, the specific microstructure of the joints is related to their mechanical performance upon shear testing, and suggestions for optimum joint design are provided.

High-Pressure Synthesis and Chemical Bonding of Barium Trisilicide BaSi3

BaSi3 is obtained at pressures between 12(2) and 15(2) GPa and temperatures from 800(80) and 1050(105) K applied for one to five hours before quenching. The new trisilicide crystallizes in the space group I 4 ¯ 2m (no. 121) and adopts a unique atomic arrangement which is a distorted variant of the CaGe3 type. At ambient pressure and 570(5) K, the compound decomposes in an exothermal reaction into (hP3)BaSi2 and two amorphous silicon-rich phases. Chemical bonding analysis reveals covalent bonding in the silicon partial structure and polar multicenter interactions between the silicon layers and the barium atoms. The temperature dependence of electrical resistivity and magnetic susceptibility measurements indicate metallic behavior.

Reactive Joining of Thermally and Mechanically Sensitive Materials

Reactive joining, i.e., utilization of an exothermal reaction to locally generate the heat required for soldering or brazing, represents an emerging technology for flexible and benign joining of heat-sensitive materials, e.g., for microelectromechanical systems (MEMS) applications. However, for successful reactive joining, precise control of heat production and heat distribution is mandatory in order to avoid damaging of the components during the process. For the exemplary case of borosilicate glass, the reactive joining process for a both thermally and mechanically sensitive material is developed. Employing various nondestructive and destructive testing methods, typical problems which can occur upon reactive joining are identified, e.g., exposure of the joining zone to excessive temperatures, experience of thermal shock by the substrate due to sudden temperature increase, and generation of residual stresses in substrate and soldering zone. Utilizing the results of nondestructive and destructive testing, procedures for successful reactive joining of borosilicate glass, silicon and aluminum oxide are provided.

ANALYSIS OF PROPERTIES OF CONCRETE USING SEA SHELLS CRUSHEDPOWDER AS ADMIXTURE

The tremendous increment of demand on concrete made admixture one of major component. As admixtures help in enhancement of concrete physical and chemical admixture. In this paper analysis of sea shells as chemical admixture is studied and verified the strength of concrete and temperature emitted due to chemical reaction to the normal Portland cement. As sea shells contain calcium carbonate, CaCo3 as major composition, as calcium is one major component that helps in densifying and hardening of bones in all living things. The flexural and compressive strength has gradually increased; the transmission temperature and reduction time of exothermal reaction has reduced. Hence seashell acts as great admixture.

ANALYSIS OF PROPERTIES OF CONCRETE USING MANUFACTURE SAND AS FINE AGGRIGATES

Aggregate in concrete acts as structural filler, these place a crucial than simple statement implies it is the material that the cement paste coats and blind together. Now a day’s using river sand is prohibited by government, as these cause soil erosion. In this paper analysis of properties of concrete using manufacture sand as course aggregate is studied and verified the strength of concrete and temperature emitted due to chemical reaction to the normal Portland cement. Using manufacture sand as course aggregate the temperature emitted due to exothermal reaction of concrete has reduced. Although the compressive strength of the concrete has reduced compared to normal concrete where no admixtures were used to enhance the properties of concrete.

ANALYSIS OF PROPERTIES OF CONCRETE USING SAFETY MATCHES POWDER AS ADMIXTURE

Recently admixtures had made a major importance in the concrete manufacturing. These admixtures materials ranged from blood in the history to the recent retarding agents. In this paper analysis of properties of concrete using safety matches powder as admixture is studied and verified the strength of concrete and temperature emitted due to chemical reaction to the normal Portland cement. Using safety matches powder the temperature emitted due to exothermal reaction of concrete has reduced. This gives better results hence we can use this safety matches powder as an admixture where the reacting temperature and the emitting temperature place a crucial role in construction and maintenance.