Engineers Develop Environmentally Friendly Ceramic Composites by Hydrothermal Densification

By Liam CritchleyFeb 14 2017

A distinguished professor and his research team from Rutgers University have developed an eco-friendly concrete using a reactive hydrothermal liquid-phase densification (rHLPD) process, otherwise known as low-temperature solidification.

Richard Riman, the inventor of the concrete, has previously been granted many patents for a plethora of novel materials, with the aim of creating a ‘materials valley’- a series of spin-off companies, where the success of one company starts-up another. His first patent, an energy efficient technology that harnesses low temperature to create bonds between different materials, has set the platform and has been used to produce over 30 materials to date.

This patented technology harnesses low-temperature and water-based reactions to produce materials that could only be made at temperatures exceeding the decomposition range of plastics. Instead, these materials can be made at temperatures lower than 240 °C (464 degrees Fahrenheit, 513.15 K), with many being produced at room temperature.

The rHLPD technology can be used with a multitude of materials including ceramics, plastics and metals to produce processed composites that can mimic the properties of other materials, such as wood, bone, seashells and steel. All of the composite materials are produced under sustainable conditions, carry a low CO₂ footprint and are environmentally friendly.

Riman proffered this idea years ago, but at the time the drive for eco-friendly products was not there. In environmentally conscious times, it was decided that now would be the perfect time to launch his new material into the commercial marketplace.

Riman is now producing, via his company Solidia Technologies, environmentally friendly cement and concrete that can capture carbon and reduce greenhouse emissions. The cost of these materials is the same as standard Portland cement. The ability to price match with conventional materials, allows the technology to be dropped straight into the industry without the need for a large capital expenditure.

These environmentally friendly materials can be applied to a wide range of industries and applications. These materials have a superior strength and durability and can reduce the carbon footprint by up to 70% against conventional materials, which can be as much as 528.3 gallons a year.

The rHLPD Process

Conventional processing methods, such as slip-casting, dip coating and sol-gel (to name a few), are first utilized to produce a porous matrix with interconnected pores, which can be produced in a range of shapes and sizes depending on the requirement of the material.

The porous matrix is then infiltrated with a liquid-solvent mixture containing soluble, reactive cations and/or anions. This is followed by a hydrothermal reaction that partially dissociates the matrix and forms reaction products that fill the pore space.

The hydrothermal reaction kinetics allow for processing temperatures of 100 - 300°C. The process requires a reaction product with a molar volume greater than that of the matrix, as the reaction front moves into the pore to fill it.

The pores also act as crystallizing templates, where the reaction products can nucleate homogeneously and epitaxially grow from the pore solution. The pores act as a confinement network to grow the crystals by controlled and uniform growth.

Looking Inside the Composite

This eco-friendly composite is composed of two main precursor materials - barium hydroxide, Ba(OH)₂, which is the infiltrating species and titanium dioxide, TiO₂, which acts as the porous framework. The material formed is pure-phase barium titanate, BaTiO₃, with water, which is a by-product. There can also be a presence of unreacted titanium dioxide in the material, which is encapsulate by the barium titanate - so the structure can also be perceived as BaTiO₃[TiO₂].

Temperatures and reaction times, like any reaction, play a major part in the composite formed. That being said, all samples, independent of these parameters, achieve a crystallinity of at least 95 wt% (88 mol%) with a tetragonal unit cell. Only 2-4 wt% is believed to be unreacted titanium dioxide.

Barium titanate has previously been stipulated to be weaker than its composite counterparts. However, by this process, the composites can exhibit a flexural strength between 49 - 172 MPa and are similar in strength to composites produced by conventional methods. Composites produced at the higher temperature ranges (240 °C) exhibit a higher degree of densification and an increased crystal growth.

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