Halloysite clay tubes have 50 nm diameter and chemically different inner and outer walls (inner surface of aluminum oxide and outer surface of silica). Due to this different chemistry, the selective etching of alumina from inside the tube was realized, while preserving their external diameter (lumen diameter changed from 15 to 25 nm). This increases 2-3 times the tube lumen capacity for loading and further sustained release of active chemical agents such as metals, corrosion inhibitors, and drugs. In particular, halloysite loading efficiency for the benzotriazole increased 4 times by selective etching of 60% alumina within the tubes' lumens. Specific surface area of the tubes increased over 6 times, from 40 to 250 m(2)/g, upon acid treatment.

Long-lasting anticorrosive coatings for steel have been developed on the basis of halloysite nanotubes loaded with three corrosion inhibitors: benzotriazole, mercaptobenzothiazole, and mercaptobenzimidazole. The inhibitors' loaded tubes were admixed at 5-10 wt % to oil-based alkyd paint providing sustained agent release and corrosion healing in the coating defects. The slow 20-30 h release of the inhibitors at defect points caused a remarkable improvement in the anticorrosion efficiency of the coatings. Further time expansion of anticorrosion agent release has been achieved by the formation of release stoppers at nanotube ends with urea-formaldehyde copolymer and copper-inhibitor complexation. The corrosion protection efficiency was tested on ASTM A366 steel plates in a 0.5 M NaCl solution with the microscanning of corrosion current development by microscopy inspection and studying paint adhesion. The best protection was found using halloysite/mercaptobenzimidazole and benzotriazole inhibitors. Stopper formation with urea-formaldehyde copolymer provided an additional increase in corrosion efficiency as a result of the longer release of inhibitors.

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In this work, we report a simple fabrication method for metal nanoparticles and nanorods on halloysite supports. Silver nanorods of 15 nm diameter were synthesized by thermal decomposition of silver acetate within halloysite lumen. Nanorods had crystalline nature with [111] axis oriented ∼ 68° from the halloysite tubule main axis. Linear arrays from gold, iron, cobalt and palladium nanoparticles on halloysite external surface were also synthesized by chemical and thermal reduction method. Samples were analyzed by high-resolution transmission electron microscopy and field-emission scanning electron microscopy. These in situ syntheses offer a simple method for large scale fabrication of metallic nanorods and core-shell ceramic nanocomposites, which can be used as antimicrobial additives in plastic composites, nanoelectronic and optical materials with biocompatibility and environmentally friendly. Antimicrobial thin films were prepared based on halloysite-silver nanocomposites and tested on E. Coli and S Aureus bacterial culture. Antibacterial performance of the nanocomposite material was superior to the other conventional antimicrobial additives (silver doped bioactive glasses and carbon nanotubes). Radiation protection coatings based on fabricated nanocomposite materials is under development.

Fly ash is a byproduct of the combustion of pulverized coal, which has found an application as a supplementary cementitious material that offers several benefits such as improved workability, durability, and improved long-term strength to concrete. The requirements for sampling frequency of this material are laid out in ASTM C311, Standard Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for Use in Portland-Cement Concrete. The article analyzes the composite sampling frequency and provides insight into how changing it would affect the ability to capture changes in fly ash properties. The analysis is based on data collected using the current composite sampling requirements during the calendar year of 2016 from four power plants located in the United States. Fly ash properties included in the analysis are the sum of silica, alumina, iron oxide content, sulfur trioxide content, loss on ignition (LOI), fineness, and the strength activity index at 7-days and 28-days. The statistical analysis shows that reducing the composite sampling frequency to monthly, instead of every 2,900 Mg (3,200 tons), would not affect the ability to properly identify the properties of fly ash. This conclusion is supported by the observation that the parameters show small variability throughout the year and that those dependent on plant operational changes (such as fineness and LOI) are monitored on site at an even higher frequency, daily or every 360 Mg (400 tons).