Zeolite/Cerium Oxide Coat-on Activated Alumina Ball for Arsenite Removal via Fixed- Bed Continuous Flow Adsorption Column

Arsenite (As(III)) has threatened human life for ages. It is a necessity to remove As(III) from the contaminated water before general use. With the improvement of adsorption, higher As(III) removal can be achieved. This study aimed to develop zeolite/cerium oxide coat-on activated alumina ball adsorbent (CeZ-ball) with the aid of PVA binder and apply it to a fixed-bed continuous flow column for As(III) adsorption. The coating percentage of CeZ-ball was studied. Cerium ions leaching from CeZ-ball were monitored throughout the 2,880-min-column run to confirm the stability of CeZ attached to an activated alumina ball. Surface area, pH point of zero charge, and structural property of CeZ-ball were characterized. An average CeZ coating of 83.3% and rare leaching of cerium proved the coating method. The models proposed by Yoon-Nelson provided the most satisfactory fit with the breakthrough curve (r2 = 0.985, MPSD = 2.547, and q0 = 3.481 mg·g–1) under experimental conditions of the flow rate of 5 mL·min–1, As(III) influent concentration of 1 mg·L–1, and CeZ-ball weight of 40 g. The half-time of breakthrough (τ) was 1,228.739 min. The effects of the key parameters, including initial adsorbent weight, initial flow rate, and initial As(III) concentration, were investigated for the performance of As(III) adsorption. Simulated from the Yoon-Nelson model, the τ increased as well as the adsorbent weight but decreased as the flow rate increased, thus impacting the As(III) concentration. With the optimal condition, the fixed-bed continuous column with CeZ-ball could be used in As(III) removal from contaminated water.

Observation of Tribological Wear on PEEK Shaft with Artificial Defect under Radial Rolling Sliding Point Contact

This paper’s aim is to develop the tribological repair method in PEEK (Poly-ether-ether-ketone) polymer mechanical parts with surface damage. The radial rolling sliding contact tests were carried out by using a machined PEEK shaft with an artificial defect as surface damage. An alumina ball and a PTFE composite pin contacted a PEEK shaft specimen under cyclic compressive stress with friction. The particle as solid lubricant from a PTFE composite pin filled up the crevice of the artificial defect. After that, the artificial defect was covered with the deformed microgrooves on the PEEK shaft surface. Due to adhesion by compressive stress and friction, the crevice of the artificial defect was closed. In a running-in process, the artificial defect could be reduced by the adhesion repair.

Tribological Performance of Porous Ti–Nb–Ta–Fe–Mn Alloy in Dry Condition

The tribological properties of a novel porous Ti–Nb–Ta–Fe–Mn alloy with 0%, 30%, and 60% porosity were evaluated for biomedical applications. The tribotesting was performed using a ball-on-disc under dry conditions, using an alumina ball and 1 N of a load. The coefficient of friction at the early stage of the porous samples was lower than that of the bulk, 0.2 and 0.7, respectively, but the samples with 30% porosity shift toward the bulk value after a variable number of cycles, while the samples with 60% remained stable after 100,000 cycles. The wear rate of the specimen with 60% porosity was twice as low as that of the bulk. The results are explained by shift in wear mechanism associated with the modified bearing ratio of the porous surface and by the accumulation of wear debris inside the pores, which prevented the development of three-body abrasion.

Hardness and Wear Resistance of Dental Biomedical Nanomaterials in a Humid Environment with Non-Stationary Temperatures

This study discusses a quantitative fatigue evaluation of polymer–ceramic composites for dental restorations, i.e., commercial material (Filtek Z550) and experimental materials Ex-nano (G), Ex-flow (G). Their evaluation is based on the following descriptors: microhardness, scratch resistance, and sliding wear. In order to reflect factors of environmental degradation conditions, thermal fatigue was simulated with a special computer-controlled device performing algorithms of thermocycling. Specimens intended for the surface strength and wear tests underwent 104 hydrothermal fatigue cycles. Thermocycling was preceded by aging, which meant immersing the specimens in artificial saliva at 37 °C for 30 days. Microhardness tests were performed with the Vickers hardness test method. The scratch test was done with a Rockwell diamond cone indenter. Sliding ball-on-disc friction tests were performed against an alumina ball in the presence of artificial saliva. A direct positive correlation was found between thermocycling fatigue and microhardness. The dominant mechanism of the wear of the experimental composites after thermocycling is the removal of fragments of the materials in the form of flakes from the friction surface (spalling). Hydrothermal fatigue is synergistic with mechanical fatigue.

Titanium-Based Sintered Alloy with Improved Wear Resistance

Titanium sintered alloys have a special use in the technique because they have multiple advantages. Titanium and its alloys are characterized by remarkable physic-chemical, mechanical and technological properties. However, there are several such properties that have a lower value, such as friction behavior. Titanium and its alloys are recognized as having low wear resistance. Titanium alloyed with certain elements, such as tin or graphite, can lead to alloys with improved wear properties, with the specification that graphite does not exceed 1%. The technology of manufacturing titanium-based alloys is specific to powder metallurgy, but it also has some originality by choosing special sintering cycles. The paper aims to present a tribological characterization of the sintered TiAl alloy; the method uses the disc of the alloy that has been researched in contact with an alumina ball. The paper presents a detailed analysis of the wear tests carried out for four types of specimens obtained by different methods.

Comparison of alumina ball size distribution in two white cement grinding units using Swebrec function

The results of characterizing the alumina ball size distribution in two mills of a crushing and grinding plant are shown. The mills were unloaded and the ball charge was screened in order to establish the ball size distribution. For both mills, the balls retained during the unloading were compared to the balls retained at the beginning of the process, and additionally, they were compared to the results obtained by the Swebrec adjusted distribution model. In both cases, the experimental data have had a good fit with this model. This practice is important in order to establish the best ball charge at the beginning of the operation and the ball recharge in the steady state.

Wear Behavior of Graphene-Reinforced Alumina–Silicon Carbide Whisker Nanocomposite

In the present work, the tribological properties of graphene-reinforced Al2O3-SiCw ceramic nanocomposites fabricated by spark plasma sintering were studied against alumina ball. Compared with pure ceramic, the wear resistance of these nanocomposites was approximately two times higher regardless of the applied load. It was confirmed by Raman spectroscopy that the main factor for the improvement of the wear resistance of the Al2O3-SiCw/Graphene materials was related to the formation of protecting tribolayer on worn surfaces, which leads to enough lubrication to reduce both the friction coefficient, and wear rate.

Tribological Properties of Spark Plasma Sintered NiCr–Cr2AlC Composites at Elevated Temperature

In this work, layered ternary Cr2AlC powders with high purity and a size of 0.5–1 μm were synthesized by solid-state reaction method. NiCr–Cr2AlC composites have been prepared by spark plasma sintering (SPS) process. The composites' tribological properties were evaluated against alumina ball under dry sliding condition from room temperature to 600 °C. Compared with unmodified NiCr alloy, Cr2AlC addition has an effect on reduction of friction coefficient of NiCr–Cr2AlC composites at the temperatures up to 400 °C. Especially, in comparison with NiCr alloy, the wear rates of NiCr–Cr2AlC composites significantly decrease from 10−4 mm3/(N·m) to 10−5–10−6 mm3/(N·m) from room temperature to 600 °C (except for 200 °C). The NiCr–20 wt % Cr2AlC composite exhibited excellent tribological properties with a friction coefficient of 0.3–0.4 and a wear rate of about 10−6 mm3/(N·m) from 400 °C to 600 °C. Through the analysis of scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS), it is clarified that effective improvement of tribological properties of NiCr–Cr2AlC composites is attributed to a glaze layer consisting of NiO, Cr2O3, Al2O3, and NiCr2O4, which is formed by tribo-oxidation during wear process.