You are browsing the archives of 2012 July.

Many of the same materials used in semiconductor processing are being applied to textile materials. Credit: Jur, NCSU.

The notion of ceramics going together with fabrics is a little counterintuitive. Mixing the hard stuff with soft threads? But, it’s true, and sort of like peanuts on top of an ice cream sundae—a great combination can occur. Actually, it’s really not all that counterintuitive if one considers just one application developed years ago that must have seemed a little hard to believe when it was introduced: fiberglass.

There are several groups of researchers that have been experimenting with blending ceramic materials and fabrics, yielding applications that range from the relativey simple to the extremely novel and robust.

For example, at the simple end of the spectrum, shirts are now available that claim to permanently incorporate sunblocking materials into their threads. That seems great to me. As a runner and someone who has already had one run-in with cancer, I am very watchful (if not a little paranoid) about sun exposure and wear long sleeve shirts outdoors (even when swimming). Cotton or cotton-blends seem to do a good job of blocking the sun, but hold perspiration like a sponge. As an alternative, I tried wearing some of the lightweight synthetic “wicking” shirts designed for sports, but I always wondered whether the meshy material was blocking all of the UV rays.

That was before I ran across Coolibar long sleeve athletic shirts. Coolibar claims to be the first company to “develop UPF 50+ apparel and hats using a proprietary fabric with zinc oxide that cannot be absorbed by the skin, cannot wear or wash off and safely deflects all UV rays.” Coolibar also makes attire with another UPF 50 fabric that contains TiO₂. (The UPF designation is the fabric corollary to the SPF system for sunscreens.) Coolibar says its fabrics have been evaluated by an independent lab following testing and labeling standards established by ASTM (D6544 and D123) and the American Association of Textile Chemists and Colorists. I just purchased several of these shirts and look forward to testing them during the rest of the summer.

Coolibar’s apparel is an example of ceramic science joining up with textiles that is easy to understand. A bigger stretch is some of the work being conducted at North Carolina State University, and reported in the new August issue of ACerS’ Bulletin, where researchers are experimenting with some novel ceramic surface treatments of textiles.

One NCSU group is using atomic layer disposition to expand the boundary of traditional textiles by exploiting the conducting and semiconducting properties of ceramic nanoscale materials. Jesse S. Jur and Gregory N. Parsons, professors at NCSU, discuss in one of the Bulletin stories how ALD-processing can be used for the fabrication of electronic devices using textiles. They note, for example, that ALD can be used to create building blocks for responsive sensors. “The nanoscale surface coverage of ALD offers the ability to fabricate device layers that take advantage of the high surface area and strategic structure-property relations available through the use of a textile substrate,” Jur and Parsons report. “This is important in the formation of responsive materials with electrical behavior that changes when flexed or exposed to certain chemicals, that is, fabrics that act as platforms for all-fiber-based electronic devices.” Jur and Parsons detail some of the materials being examined as well as the challenges to scaling up high-throughput ALD techniques, and they sketch a future where applications for surface-modified textiles (woven and nonwoven) go well beyond traditional clothing, furnishings and protective coverings.

Another Bulletin story, by Tiina Nypelö and Orlando J. Rojas, focuses on the combination of ceramic materials and cellulose to create new types of functionalized fibers. Nypelö, a postdoctoral student, and Rojas, another NCSU professor, report on the use of coatings of clay, calcium carbonate, TiO₂, silica and magnetic particles on emerging cellulose-based materials. They describe organic-inorganic hybrid fibers that could be used for flexible, printed electronics, circuit board bases, sensors, actuators and resistance temperature detectors as well as conductive, magnetic and piezoelectric films.

Thus, from shirts to sensors, it seems that the emerging ceramics–fabrics mashup isn’t all that odd, and, the benefits loom large.

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Here is what we are hearing:

Prematech Advanced Ceramics adds technical and marketing strength with hiring of Bruce Gretz

PremaTech Advanced Ceramics, a leader in the design, engineering and machining of high-purity silicon carbides and other advanced ceramic materials and components, has named Bruce Gretz senior technical salesperson. In that capacity, Gretz is responsible for developing new business opportunities from customers requiring adaptive ceramics used in semiconductor, aerospace & defense, R&D, life sciences, commercial and microwave applications. “I am pleased that Bruce is helping us build upon more than 30 years of industry leadership,” says Harvey Clough, PremaTech’s general manager. “His combination of management and sales experience puts us in a strong position to retain established customers while attracting new ones in these challenging times.” Prior to joining PremaTech, Gretz worked in engineering management for a variety of software development and systems integration companies on the East and West Coasts. He began his career with Rockwell International’s Allen-Bradley Division. Gretz holds a Bachelor of Science in Mechanical Engineering from Cornell University.

Superior Technical Ceramics launches new website

Superior Technical Ceramics is thrilled to launch its new website. “Our goal is always to provide superior service, and we think that this new site will make it easier for customers to see how our services can help them” commented Simon Doran, Sales Manager. “I was really happy when I saw the new site. It’s elegant, simple, and functional; exactly what our home on the web needs to be.” STC has been recognized as a “legacy” company in the material area since its start in 1898. Our commitment to materials development and continuous improvement set us apart from most of our competition. STC has complete in-house capabilities to assist with design, engineer, tool and manufacture of technical ceramics to customer requirements. Superior Technical Ceramics invests in state-of-the-art equipment and in highly skilled, knowledgeable employees to produce the industry’s best components. Through the use of ISO 9001:2008, AS9100, 5S and lean practices and policies, STC achieves the control and quality necessary to compete, cost effectively, worldwide.

Fooken taking over as H.C. Starck’s new head of R&D

On Sept. 1, 2012, Michael Fooken will take over the research and development activities for the H.C. Starck Group in Goslar (Germany). Fooken has extensive experience in the field of research and development in the chemical industry. Over the past 12 years, he has held various global positions within the Honeywell Group, including head of research for the Fine Chemicals Division. Before that he spent many years in production as well as in research and development. Fooken studied chemistry at the University of Münster (Germany) and earned his doctorate in electrochemistry in 1995. He holds more than 20 patents in the fields of energy storage materials and inorganic salts. Dr. Fooken is 47 years old, married, and has two children. His predecessor, Gerhard Gille, is retiring on Oct. 31, 2012, after more than 20 years at the company.

MTC introduces expert custom brazing services

Morgan Technical Ceramics announced that its Wesgo Metals site in Hayward, Calif., now offers custom brazing services, including active metal brazing, a process that allows metal to be bonded directly to ceramic without metallization. Active metal brazing eliminates several steps in the joining process and creates an extremely strong, hermetic seal. MTC uses active metal braze alloys, a process is especially beneficial in medical, aerospace and oil exploration applications. MTC has developed several braze alloy compositions, which will directly bond ceramic to metal or even graphite and diamond. Applications include brazing industrial diamonds onto ceramics or metal components for heat spreaders or ceramic windows, as well as brazing graphite to substrates such as titanium for incredibly stable ion traps. Alloy compositions vary and include those designed for use in a variety of settings, from very low temperatures to very high temperature applications, around 500 to 1,000°C. MTC selects the alloy to meet the specific service temperature conditions as well as the requirements of all the components to be joined. MTC’s high end brazing services are used in the medical market for implantable hearing aids and minimally invasive surgical tools. For the aerospace industry, MTC offers compositions of ceramics ideal for brazing to metals for use in the extremely high temperatures found in modern day jet engines. Applications here include ceramic nozzles for turbine engines, new turbine vane systems and super alloy engine parts.

Mettler Toledo offers in-process-control white paper

New high-resolution weigh modules from Mettler Toledo offer surprisingly fast and simple solutions for 100% in-process-control. They can be used to check completeness of parts, kits or modules as well as quality of surfaces where material is added or subtracted. Mettler Toledo now offers a white paper that explains how weigh modules are applied for in-line testing with high throughput rates. Traditional methods for in-process-control and end-of-line-control use electrical resistance, optical imaging, spectrometry, light beam and mechanical sizing. It wasn’t until recently, that weighing technology was used in spot checking mode. This was mostly due to the design of traditional balances and scales, which didn’t fit seamlessly into machines and instruments. It also wasn’t obvious that dimensions, coatings, shapes or completeness could indirectly be checked while looking at weight deviations or differences.

Rockwood opens new lithium hydroxide facilities in North Carolina

Rockwood Lithium has inaugurated its expanded manufacturing facility in Kings Mountain, N.C. The company is leveraging a $28.4-million investment from the Recovery Act to expand its North Carolina lithium production facility with a new lithium hydroxide plant as well as its production operations in Silver Peak, Nev. In addition a new technology center containing new lab facilities, offices, and seminar rooms was opened. The new plant will produce 5,000 metric tons of lithium hydroxide a year enough for about 500,000 electric cars. The company, a subsidiary of New Jersey-based Rockwood Holdings Inc., was awarded the grant because of its potential to advance battery technology for electric cars, said Chris Johnson, project manager for the DOE. Steffen Haber, president of Rockwood Lithium added that the new research and development center will add to the existing facilities to explore new materials for lithium containing batteries as well as for other industrial applications.

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Juan Nino, associate professor at the University of Florida, describes his research at an NSF workshop for principle investigators in June. The NSF is sponsoring another workshop in August early-career faculty and postdoctoral researchers. Credit: ACerS.

If you are an assistant professor or postdoctoral associate with research experience, you may want to set aside a few days in August to attend a NSF-sponsored workshop designed to enhance career development for future leaders in ceramic materials research and education.

Senior faculty and junior faculty peers from the international scientific community with expertise in ceramic materials will come together for an intensive two-day technical and professional development workshop. The workshop will touch on areas of research, best practices for training and teaching students and collaborative research opportunities worldwide.

The event will be Aug. 23-24, 2012 at the Westin Arlington Gateway Hotel in Arlington, Va. It is being organized by University of Arizona assistant professor, Erica Corral. (Corral’s research activities were highlighted in the August issue of The Bulletin, by the way.)

Space is limited, so registration is required. To register or for more information, contact Erica Corral at elcorral@email.arizona.edu.

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When high-temperature superconducting oxides were discovered in the mid-1980s, it was thought that they would revolutionize electric power delivery. They might still, however, the physics of these intriguing materials has made them tricky to engineer for applications. One problem that persists is the tendency of high-temperature superconducting cuprates, such as YBCO, to have weakly linked grain boundaries, which diminishes the global critical current density.

The weak linking can be overcome by controlling the grain misorientation angle with textured substrates. Another way would be to find a material with high enough local intragrain critical current densities. The ferropnictide family of compounds show some promise in this regard. (The pcnitides are the Group Va compounds in the period table of the elements: N, P, As, Sb and Bi.) The ferropcnitide family of superconducting compounds, in particular, are interesting because of their high critical temperatures and some interesting physics related to their multiband superconductivity and antiferromagnetism.

For example, the pcnitide compound, BaFe₂As₂ (Ba-122), is of interest because its magnetic and superconducting properties are in a range that makes them useful for applications. There has been a fair amount of research on cobalt-doped Ba-122 (electron-doped). A disadvantage is that this compound has the problem mentioned above, namely intrinsically weak linking of its grain boundaries. However, the critical current density is less sensitive to grain misorientation than is seen in the cuprate compounds. Thus, there is strong interest in studying polycrystalline ferropcnitides.

ACerS member, Eric Hellstrom, and his team at Florida State University recently published a paper in Nature Materials reporting on superconductivity in potassium-doped Ba-122 (hole-doped) wire and bulk material.

The surprising result is that the global critical current density is much higher in K-doped Ba-122 than the Co-doped version. The abstract gets right to the point: “Here we present a contrary and very much more positive result in which untextured polycrystalline (Ba_0.6K_0.4)Fe₂As₂ bulks and round wires with high grain boundary density have transport critical current densities well over 0.1MA cm^-2 (self field, 4.2 K).”

How “much more positive?” They report critical current densities that are “more than 10 times higher than that of any other round untextured ferropnitide wire and 4-5 times higher than the best textured flat wire,” which they say are “high enough to be interesting for applications.”

The improvement is attributed to enhanced grain connectivity, which in turn, arises from several factors relating to the material’s microstructure, and therefore, processing. Three factors are singled out.

First, the polycrystals were synthesized by chemical reaction, which could be done at temperatures that are low enough to prevent the formation of unfavorable secondary phases like FeAs. Secondary phases have been shown to wet the grain boundaries and block current.

Second, the synthesis process is done under high-pressure conditions, which yields a nearly 100 percent dense material and very good intragranular connectivity.

Third, the material is very fine-grained with grain sizes of approximately 200 nanometers. This means that planar grain boundaries are rare and the anisotropy values are low, which makes the vortex stiffness high. Why does this matter? Even though most of the vortices span grain boundaries, with this material, very little of any vortice actually resides in the grain boundary.

In the paper, the authors suggest that there may be some compound-related factors involved, too, citing a higher critical current density as a function of magnetic field for the K-doped Ba-122 than for the Co-doped material, which could be related to hole- vs. electron-doping.

For full details see “High intergrain critical current density in fine-grain (Ba0.6K0.4)Fe2As2 wires and bulks,” Weiss, et al., Nature Materials (doi: 10.1038/NMAT3333).

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Photographs of the mechanically strong and biocompatible hydroxyapatite/t-ZrO₂ composite scaffolds prepared by microwave sintering at 1,300°C (a, b), 1,400°C (c, d) and 1500°C (e, f). Credit: Jang et al.; Science and Technology of Advanced Materials.

A group of Korean researchers at Soonchunhyang University who have been working on developing various types of a bone-like scaffolds to help regenerate defective or damaged bone tissue say they have found a fairly uncomplicated mixed-material candidate for use in situations where mechanical strength is a factor but the dimensions are fairly small, such as in fingers and toes. The scaffold is composed of hydroxyapatite and zirconium dioxide. They say the key to making this combination work together—each has separate beneficial characteristics but different coefficients of thermal expansion—is carefully engineering the interface between the two materials and microwave sintering.

Sample of electrospun artificial cancellous-type scaffold. Credit: Kim and Lee; Sci. Technol. Adv. Mater

The group, led by Byong-Taek Lee, has been creating a variety of bone scaffold structures for several years. For example, in 2011, they reported on the clever use of electrospinning to engineer a candidate for artificial cancellous bone, a spongy, soft and weak type of bone tissue found, for example, at the expanded heads of long bones and in the interior of vertebrae.

In contrast to cancellous bone, “compact” or cortical bone is harder, denser and stiffer and provides more structural support for organs and joints and, ultimately, the whole body. This time Lee’s group focused on a substitute for this tougher bone for use in bone graft applications.

Bone grafts have become fairly common in dental reconstruction efforts (to build support for dental implants) and are also used in complicated bone fractures and situations where small amounts of bone are missing or have necessarily been removed. Generally speaking, the graft serves as a temporary support that is gradually replaced by the host’s bone tissue.

Currently, the most widely used materials for bone grafts are tissues taken from elsewhere on the individual or from a cadaver. However, there are drawbacks to both of these sources, and the biomedical materials community in recent years has been active in developing alternative materials and scaffolds for grafting. The search is on among many groups looking for the “ideal” artificial graft materials and several tests have been made using scaffolds of hydroxyapatite, bioactive glass and other ceramic materials.

It is not clear whether there will ever be a single ideal graft material, especially if the composition can be customized based for a specific site. However, at a minimum, any substitute material will have to be fairly light and strong, will have to be porous to allow cell growth and fluid penetration, and will have to encourage bone cell growth (not to mention growth of vascular and neural tissues).

As mentioned above, this recent work in Korea has to do with combining two well known materials, hydroxyapatite and ZrO₂. A news release from the National Institute for Materials Science notes that, “While hydroxyapatite encourages bone cell ingrowth, when it is porous like natural bone, it is mechanically weak. The second material, zirconium dioxide, is stronger but cells do not grow on it.”

The question they faced was how to create a scaffold from these very different materials (with normally incompatible coefficients of thermal expansion) without cracking and damaging the structure during the sintering process. In their paper published in the journal Science and Technology of Advanced Materials, “Microwave sintering and in vitro study of defect-free stable porous multilayered HAp-ZrO₂ artificial bone scaffold” (doi:10.1088/1468-6996/13/3/035009), the researchers say their goal was “to fabricate a bone preform that can be strong enough to maintain a reasonable load during the natural healing period, and at the same time offers extensive porous space for the bone regeneration to take place throughout the whole scaffold.”

The solution they discovered is to carefully build up hydroxyapatite on the exterior of a ZrO₂ core, using a gradient zone between the two, and then sinter using a microwave oven instead of a conventional furnace. In particular, they credit the gradient region with resolving the potential thermal expansion problems.

In their paper, the researchers say the microwave sintering “ensures sufficient sintering within a short time… In this method, the heating rate is relatively high and the dwelling time is significantly shortened, which hinders undesired reactions and, hence, preserves the biocompatibility of the intended materials.“

After creating test structures and confirming their strength and porosity, the team seeded the composite with cells and found that they indeed grew successfully, divided as hoped and after several days covered the entire surface. They also found that the cells completely filled the pores and penetrated the ceramic structures.

There is no word about what the group’s next steps are.

I would like to note that the topic of bone repairs and creating scaffolds for tissue regeneration will be thoroughly covered at ACerS’ upcoming Innovations in Biomedical Materials 2012 conference scheduled for Sept. 10-13 in Raleigh, N.C. The tracks in this meeting include

• Uses of Bioactive Glass in New Treatments

• Three-Dimensional Scaffolds for Tissue Regeneration

• Blood Vessel and Nerve Guide

• Malleable Bone Void Fillers (Bone Cements or Putty) and

• Composites.

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