Effect of K/Al Molar Ratio on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites

A metakaolinite-based geopolymer binder was prepared by using calcined claystone as the main raw material and potassium as the alkaline activator. Chamotte was added (65 vol%) to form geopolymer composites. Potassium hydroxide (KOH) was used to adjust the molar ratio of K/Al and the effect of K/Al on thermo-mechanical properties of geopolymer composites was investigated. This study aimed to analyze the effect of K/Al ratio and exposure to high temperatures (up to 1200 °C) on the compressive and flexural strengths, phase composition, pore size distribution, and thermal dilatation. With an increasing K/Al ratio, the crystallization temperature of the new phases (leucite and kalsilite) decreased. Increasing content of K/Al led to a decline in the onset temperature of the major shrinkage. The average pore size slightly increased with increasing K/Al ratio at laboratory temperature. Mechanical properties of geopolymer composites showed degradation with the increase of the K/Al ratio. The exception was the local maximum at a K/Al ratio equal to one. The results showed that the compressive strength decreases with increasing temperature. For thermal applications above 600 °C, it is better to use samples with lower K/Al ratios (0.55 or 0.70).

Melting Process and Viscosity of Bohemian Historical Glasses Studied on Model Glasses

Analyzing the chemical composition of archaeological glasses can provide an insight into their provenance and raw materials used in their making. However, to the authors’ knowledge, the historical production process itself and melting characteristics of the glasses have not yet been extensively investigated. The main focus of this paper is to describe the melting process of three main types of Bohemian historical glasses: Gothic (14th–1st half of 16th c.); Renaissance (16th–17th c.); and Baroque (end of 17th–18th c.). The model glasses were prepared from natural raw materials and processes that take place during melting were investigated using optical microscopy, SEM-EDS, XRD, and DTA-TG methods. Furthermore, the viscosity of model glasses and thermal dilatation was measured and used to calculate the reference viscosity points. The results illustrate the complexity of historical glass melting, as well as the technological progress between different periods.

Compatibility assessment of solid ceramic electrolytes and active materials based on thermal dilatation for the development of solid-state batteries

Assembling an all ceramic solid-state battery (ACSSB) using inorganic oxide electrolytes is challenging. The battery must have a continuous layered structure with a thin dense electrolyte separator and interfaces between...

Thermo-osmotic metamaterials with large negative thermal expansion

Negative thermal expansion (NTE) is important for compensation of thermal dilatation effects and has significant applications in high-precision devices and instruments. Several materials with intrinsic negative expansion exist but are...

Multi-Scale Contact Localization and Dynamic Instability Related to Brake Squeal

Friction-induced vibrations (brake squeal) produced during braking applications have been one of the major problems in the transportation for many years. It can be the most troublesome for passengers because of its high frequency and acoustic pressure. The role of frictional contact surface geometry on the occurrence of squeal was investigated recently by some researchers. However, it has never been systematically studied at different scales simultaneously. Contact localizations are induced on the one hand by macro effects such as thermal dilatation (macroscopic scale) and on the other hand, by the heterogeneity of third body (tribolayer) generated by friction (mesoscopic scale). The aim of this paper is to investigate the effect of contact localization at both scales through stability analysis on a simplified pad on disc system. The model has been developed numerically by the finite element method (FEM) to introduce a non-uniform contact at macroscopic and mesoscopic scales. The results showed a strong dependency between squeal frequencies and effective contact zone at macroscopic and mesoscopic scales for the investigated configuration. Especially, it is found that squeal frequencies depend on the contact area at a macroscopic scale whereas the probability of occurrence of squeal frequency strongly relies on mesoscopic contact distribution.

Linear thermal expansion of the building stone from plutonic massifs of the Vardar zone of Serbia

Thermal properties of the building stone used for cladding and flooring, especially in exteriors, are significant for durability and lifespan of buildings' surfaces covered with it, but also their aesthetic properties in the sense of integrity. Linear thermal expansion of natural stone units is determined in laboratory examinations, aiming to provide the value of yield between the units as free space for their dilatation and contraction upon temperature oscillations. Where this space is not provided, diurnal changes, especially temperature increase, create stone expansion and tension which can lead to deformations of stone units and mar units' and covered surfaces' integrity and aesthetics. Data on linear thermal expansion values of natural stone, especially from Serbia, are very rare in the literature, so our aim is to contribute to this type of knowledge. Examination of thermal dilatation of stone originating from eight plutonic massifs in External Vardar zone of Serbia has shown that the values are very small, parts of millimetres, and lower than those of the similar rock types originating from China, Brazil and Eastern Serbia. A clear grouping of the values of thermal expansion of the stone according to the genetic groups to which the plutons belong to can be observed. Mineral composition, grain size and presence of metallic minerals in samples have shown no clear influence on thermal dilatation values, but fabric inhomogeneity appears to cause the increase of these values.

IDENTIFIKACIJA ZVUČNIH IMPULSA KOD FRIŽIDERA ZA UPOTREBU U DOMAĆINSTVU

This paper presents a new visualization method of complex sound sources in combined fridge freezers. Measurement method with sixty array microphones in free sound field conditions is used. Laboratory acoustic measurements using an algorithm of the complex sound sources visualization are performed. With this method, sound effects are successfully identified, localized and calculated. The individual crack noises emitted as a result of thermal dilatation of different types of material in the transitional cooling modes of the household refrigerator.