Porous Nanostructured Gadolinium Aluminate for High-Sensitivity Humidity Sensors

This paper presents the synthesis of gadolinium aluminate (GdAlO3), an oxide compound with a perovskite structure, for applications as a capacitive and/or resistive humidity sensor. Gadolinium aluminate was synthesized by the sol-gel self-combustion method. This method allowed us to obtain a highly porous structure in which open pores prevail, a structure favorable to humidity sensors. Most of the materials studied as capacitive/resistive humidity sensors have significant sensitivities only with respect to one of these types of sensors. In the case of the studied gadolinium aluminate with p-type electric conductivity, the relative humidity of the air has a significant influence on both capacitive and resistive types of electric humidity sensors. The capacity increases about 10,000 times, and the resistance decreases about 8000 times as the relative humidity increases from 0 to 98%. The investigated gadolinium aluminate can be used successfully to obtain high-sensitivity capacitive and/or resistive humidity sensors.

Chemical Composition of Clays for Pottery in Malaysia: A Review

Pottery in Malaysia is been known for its utilized functions and unique properties. Clays as the pottery’s raw materials are a major factor that affecting the quality and reliability of some pottery products. Observations on clays’ elements and phases are very helpful for productions of the good pottery. Hence, in this review, chemical compositions of clays in terms of elements and phases structures are discussed. Basically, the most elements found in clays are Si, Al, Fe, Ti, K and Ca. Depends on location, the concentrations for those clays elements in Malaysia are at range of 24.8 – 32.4 for Si, 10.8 – 19.0 for Al, 0.09 – 2.12 for Fe, 0.08 – 1.13 for Ti and 0.45 – 3.39 for K. Several studies reported, they exist in form of oxide compound which are SiO2, Al2O3, Fe2O3, TiO2, MgO, CaO, Na2O, K2O and P2O5. The percentages of elements in clays do not only determine the clays characteristics, but also influence the physical, mechanical and chemical properties of the end product. Increase of major element like silica arises the melting point, lowers the fluidity, and enhances the hardness and tensile strength. Meanwhile, increase alumina content enables the green body to withstand the sintering temperature and also increase the hardness of the pottery.

Upcycling of Wastewater Sludge Incineration Ash as a 3D Printing Technology Resource

Recycling of usable resources from waste must be prioritized to adhere to the circular economy policy implemented worldwide. This study aims to use wastewater sludge incineration ash (WSIA), which is a by-product of wastewater sludge treatment processes, in the 3D printing industry as a sustainable material. First, we explored the stability of incinerated ash generated from a wastewater treatment facility in Seoul by evaluating its physical (water content, organic matter content, and particle size) and chemical (oxide compound composition) characteristics. Composition ratios of the predominant oxides of silicon (SiO2), aluminum (Al2O3), phosphorous (P2O5), iron (Fe2O3), and calcium (CaO) were stable for 6 months. This finding indicates the potential for the incinerated ash to be commercially viable as a powder-bed 3D printed geopolymer. We then examined the optimal ratio of admixtures between the incinerated ash and ultrarapid hardening cement and the following post-treatment process method as a curing stage. The composite material made with 25% WSIA exhibited stability during the curing stage using alkaline solutions, and its compressive strength and water absorption were in accordance with the values recommended by the Korean Standard for decorative concrete blocks (KS F 4038). Additionally, a geopolymer prototype with 25% incinerated ash was produced. To support efficient upcycling of WSIA, long-term environmental and functional monitoring of the final product, effects of incinerated ash particle sizes, and post-treatment process times were further investigated to reduce costs.

Structural and electronic properties of Cu4O3 (paramelaconite): the role of native impurities

Hybrid density functional theory has been used to study the phase stability and formation of native point defects in Cu4O3. This intermediate copper oxide compound, also known as paramelaconite, was observed to be difficult to synthesize due to stabilization issues between mixed-valence Cu1+ and Cu2+ ions. The stability range of Cu4O3 was investigated and shown to be realized in an extremely narrow region of phase space, with Cu2O and CuO forming readily as competing impurity phases. The origin of p-type conductivity is confirmed to arise from specific intrinsic copper vacancies occurring on the 1+ site. Away from the outlined stability region, the dominant charge carriers become oxygen interstitials, impairing the conductivity by creating deep acceptor states in the electronic band gap region and driving the formation of alternative phases. This study further demonstrates the inadequacy of native defects as a source of n-type conductivity and complements existing experimental findings.

Development of PE/PCL Bilayer Films Modified with Casein and Aluminum Oxide

The studied samples were prepared from polyethylene (PE) polymer which was coated with modified polycaprolactone (PCL) film in order to obtain bilayer films. Thin PCL film was modified with casein/aluminum oxide compound to enhance vapor permeability as well as mechanical and thermal properties of PE/PCL films. Casein/aluminum oxide modifiers were used in order to achieve some functional properties of polymer film that can be used in various applications, e.g., reduction of water vapor permeability (WVTR) and good mechanical and thermal properties. Significant improvement was observed in mechanical properties, especially in tensile strength as well as in water vapor values. Samples prepared with aluminum oxide particles indicated significantly lower values up to 60%, and samples that were prepared with casein and 5% Al2O3 showed the lowest WVTR value.