Humans are increasingly required to harvest green solar energy in order to reduce energy bills and save the environment from the excessive use of fossil resources. In this article, the microstructures of both commercial non-colored anodized Al and commercial blackened anodized Al were studied using optical and scanning electron microscopy in order to interpret the results of their use as solar absorbing surfaces. Microscopic examination showed that the thickness of the anodization layers of the non-colored anodized Al and the blackened anodized Al were approximately 11 µm and 14 µm, respectively, and they were perfectly adhered to the mother Al. The corrosion rate of all studied Al surfaces was investigated using the potentiodynamic polarization technique in 3.5% NaCl as the corrosive medium. The blackened anodized Al surface exhibited the highest corrosion resistance, which made it the best surface for solar heating systems. Moreover, raw Al, matte black painted Al, and blackened anodized Al were tested as selective surfaces for solar radiation in different weather conditions. Our results demonstrated the superiority of the blackened anodized Al in terms of the ability to absorb solar radiation, in addition to its higher corrosion resistance properties. In experimental testing, temperature values higher than 90 °C were reached several times. A gain of an extra 5 °C was achieved when using a double-glazed cover in comparison with a single-glazed setup. In conclusion, we highly recommend using a commercial blackened anodized Al surface to manufacture solar absorbing heaters, owing to its similarity in solar radiation absorptivity with the commercial matte black painted Al, excellent corrosion resistance, superior endurance upon long-term exposure to solar radiation, light weight, low price, and availability. Additionally, the light reflectance % test demonstrated the characteristics of the used solar selective surfaces.

In this study, a novel slow-release fertilizer (SRF) consisting of kaolinite and K₂SO₄ was prepared, employing the process of mechanochemical milling in a planetary ball mill. To obtain the optimum milling time and speed, several samples were made at fixed mass ratios of kaolinite: K₂SO₄ (3:1). The milling rotational speed ranged from 200 to 700 rpm for 120 min. Different milling times ranging from 60 to 180 min at fixed 600 rpm milling speed were also investigated to evaluate the incorporation of K₂SO₄ and to measure the liberation of K⁺ and SO₄²⁻ ions into solution. The properties of the studied samples were analyzed by Fourier transformation infrared spectrometry (FTIR), thermal gravimetric analysis (TGA), and ion chromatography (IC). The mechanochemical process is a green chemistry procedure that is successfully applied to incorporate K₂SO₄ into the amorphous kaolinite structure. The slow-release performance was evaluated by determining the K⁺ and SO₄²⁻ content in the aqueous solution upon leaching. The optimum released amount of K⁺ after 24 h was 32 mg L⁻¹ for the milling conditions of 180 min and 700 rpm, indicating that K₂SO₄-kaolinite has good slow-release properties. The novel SRF is cost-effective, environmentally friendly, and improves the fertilizer’s efficiency in many agricultural applications.

The Sun is a huge and clean energy source that must be relied upon to reduce greenhouse gases and promote the renewable and sustainable energy transition. In this paper, the testing of Al, Cu, and Fe metals with different thicknesses, both bare and painted matte black, was investigated for solar water heating systems. The used technique was a direct contact flat solar heating system (DCFSHS). Many experiments were run to assess this system in terms of metals’ thicknesses and their thermal conductivities as well. Thicknesses of around 0.35 mm and 1 mm of Cu gave almost similar feedback. Maximum temperatures in the range of 93–97 °C were achieved during the autumn season in Amman, Jordan, while it was approximately 80 °C in winter. It has been confirmed that high water temperatures can be obtained in all used metals, regardless of their thermal conductivities. It was also found that a white color of the solar heater case inner wall leads to an increase in water temperature of approximately 4 °C in comparison to a black color. Furthermore, a light reflectance % test in the wavelength range of 240–840 nm for the studied metals, with both bare and black-painted surfaces, gave a superb result that was in line with the obtained results of the DCFSHS. Our innovative system design for solar water heating is due to improvements in many aspects, such as design, production costs, environment, and weight.