The Jubilee Church located in Rome, Italy, is made of self-cleaning concrete that helps keep the surface shiny white.

Now, scientists are taking the fight to the streets by developing "smart" building materials designed to clean the air with a little help from the elements.

Using technology already available for self-cleaning windows and bathroom tiles, scientists hope to paint up cities with materials that dissolve and wash away pollutants when exposed to sun and rain.

"Among other things, we want to construct concrete walls that break down vehicle exhausts in road tunnels," said Karin Pettersson, a spokeswoman for Swedish construction giant Skanska. "It is also possible to make pavings that clean the air in cities."

The Stockholm-based company is part of a $1.7 million Swedish-Finnish project to develop catalytic cement and concrete products coated with titanium dioxide, a compound often used in white paint and toothpaste that can become highly reactive when exposed to ultraviolet light.

This is the idea: UV rays hitting the titanium dioxide trigger a catalytic reaction that destroys the molecules of pollutants, including nitrogen oxides, which are emitted in the burning of fossil fuels and create smog when combined with volatile organic compounds.

Exposure to high levels of nitrogen oxides can trigger serious respiratory problems, including lung damage.

The catalytic reaction also prevents bacteria and dirt from sticking to a surface, making them easily removed by a splash of water or rain.

Bo-Erik Eriksson, head of research at Cementa, another company participating in the Swedish-Finnish project, said the byproducts of the reaction, called photocatalysis, are benign, though it depends on what substances are involved: Organic compounds are broken down into carbon dioxide and water, while the nitrogen oxides yield nitrate salts.

Research in the field has been made possible by the revolution in nanotechnology -- science dedicated to building materials from the molecular level. The catalytic properties of titanium dioxide become active when it is applied in a very thin layer, or in microscopic particles.

A range of self-cleaning products coated with titanium dioxide, including windows and ceramic tiles, are already on the market but the focus has mostly been on their practical value rather than the environmental impact.

In Rome, the Dives in Misericordia church, designed by U.S.-based architect Richard Meier, is made of self-cleaning concrete that helps keep the surface shiny white. In Japan, several modern buildings including the Marunouchi Building in downtown Tokyo, are covered with photocatalytic tiles to reduce discoloring from pollution.

"Now we have to change and think of the product not just for architectural purposes, but also for environmental purposes," said Francesco Galimberti, spokesman for Italcementi, maker of the concrete for the church in Rome.

In a test in 2003, the company coated 75,000 square feet of road surface on the outskirts of Milan with photocatalytic cement. It found nitrogen oxide levels were reduced by up to 60 percent, depending on weather conditions.

A similar experiment in France found nitrogen oxide levels were 20 percent to 80 percent lower in a wall plastered with photocatalytic cement than one with regular cement.

Encouraged by such results, the European Union last year earmarked $2.27 billion for a project to develop "smart" construction materials that would break down nitrogen oxides and other toxic substances, such as benzene.

However, researchers admit they're still not sure how much of an impact the technology could have on air pollution outside of controlled test environments.

"Now we want to find out if it works optimally and economically and make sure it has a long-lived effect that does not disappear after a couple of years," said Eriksson of Cementa.

Cost is another issue. Galimberti said Italcementi's products are 30 percent to 40 percent more expensive than regular concrete, and using the external air quality as a selling point doesn't necessarily appeal to builders with tight budgets. The company's sales pitch is that self-cleaning materials will save money in the long run.

However, some scientists caution it's too soon to declare a titanium dioxide-fueled war on pollution.

"Trying to clean up air pollution seems to me to be a stretch," said Reynaldo Barreto, a chemistry professor at Purdue University in Indiana. "It doesn't mean it can't be done. But there's an awful lot of air and not a whole lot of surface."

2005/09/22

Realizing the Potential of Color in 3D Printing

By Marc R. Tremblay, Ph.D.
Introduction
3D Printers have now been around for a number of years and they are starting to reach critical mass, with thousands of units installed throughout the world. With numerous vendors, the technology envelope continues to be pushed and capabilities that were once reserved for RP equipment costing several hundred thousand dollars are now appearing in 3D Printers costing $25,000 to $50,000.

A more recent capability, which has continued to evolve in recent years, is the ability to print full color parts. This can be achieved with some 3D Printers based on ink-jet technology, such as those offered by Z Corporation and potentially other "jetting" technologies in the future. With the recent launch of its Spectrum Z^(TM)510 3D Printer, the company has now released its 3rd generation of color printers. The breakthrough color quality achieved with this new generation of printers, which is coupled with software designed specifically to exploit the potential of color, should propel color into mainstream usage by designers, engineers, architects and others.

In the end, color is really about better communication, better designs and a better understanding of what a final product will look like before expensive production steps have been taken. Very few would argue that the monochrome part on the right of Figure 1 conveys as much information about its complexity as the color version on the left. Let’s consider some of the many potential applications for color in the 3D Printing process, including concept models, communication and analysis.

Concept Models
3D Printers have been used for years for producing concept models that are used in the early stages of a design process, where most iterations take place. Since many products – especially consumer products – have multiple colors and labels along with packaging designed to catch the eye, it is vital to capture this design element since it accounts for such a large portion of the final appearance of a product. Historically, companies have resorted to painting their models, a process that is often tedious and time consuming. To view packaging and labels, which make a much more complex use of color, companies have typically relied on computer renderings.

A number of vendors offer different color materials, and it is possible to print each individual component in a different color, although this process can prove cumbersome. For the past few years, full color capabilities have been offered on some 3D Printers based on ink-jet technology. These printers can print a full range of color in a manner that is similar to 2D color printers. The trade-off has generally been on color crispness and detail. Because of this, these full color capabilities gained traction in some industries, but the color fidelity did not quite match the standards required in others, especially with consumer goods.

A new generation of color 3D Printers released earlier this year and based on ink jet technology has eliminated the tradeoff and reached new levels in color quality. Early signs indicate that the imaginary “barrier” for color has finally been broken, as is illustrated by the Reebok shoe sole shown in Figure 2, which was printed on a 3D Printer. Designers at Fisher Price, one of the world’s leading toy manufacturers, were able to release three product concepts directly to manufacturing in the first month of owning their new color 3D Printer. The decision was based on viewing 3D models that were printed, rather than painted, in color – a first for the company.

In another example, a company selling soft drinks can now design and print various versions of can labels directly onto the model of the can itself, with enough detail to read the ingredient list or see the bar code (Figure 3). With this level of detail, important decisions can be made without needing to resort to more costly and time consuming alternatives.

Communication
One very important thing to understand about color on a 3D Printer is that the definition of color is fundamentally different than that of a regular paper printer. With 2D printers, a monochrome device can put black words on white paper. In 3D printing, the same operation requires a color printer, since the output of a monochrome 3D printer is a monochrome object, usually white.

What this means is 3D color printing opens a whole new range of applications, even for users who do not need full color parts. These applications include:

Engineering Labels
No one would consider producing a CAD drawing without some form of engineering label to provide information about the drawing. The same goes for a 3D part – without any label on the part, much information is lost. Consider the casing in Figure 4. Out of context, very little information can be derived from this part. Now consider the same part, but with an engineering label. One can quickly see what the part name is, what scale it has, when it was printed, who designed it, etc.

Part Annotation and Mark-Up
Consider the parts shown at the top of Figure 5. At first glance, it is difficult to tell what has changed in the latest iteration of the part, which is one the right. Now consider the part at the bottom of the Figure. In this case, the additional changes are very easy to identify. This is another example of the usefulness of color, i.e. a quick and simple way to annotate and mark-up parts.

Manufacturing Steps
Another powerful use for color is the ability to convey information about manufacturing steps when a design is complete and needs to be transferred to manufacturing (or a supplier). Figure 6 shows a transmission housing designed by Caterpillar. Once the part has been cast, several additional manufacturing steps are required. By using color, it is very easy to highlight surfaces that need to be machined, holes that need to be drilled, etc.

An even simpler use of color is to identify the order in which a complex assembly will be assembled, e.g., blue first, red second and yellow last.

Other Communication Applications include highlighted edges on a part for emphasis or additional treatment, such as de-burring. Designers can get creative and start adding visual effects like shadows onto a part to enhance communication. The possibilities are limited only by the designer’s imagination.

Analysis
Data analysis is another area where color can tremendous value. Sometimes it is not possible to properly visualize the output of an FEA analysis if only looking at the data on the screen. Furthermore, it can be difficult to share this information in a meeting if there are no parts to pass around. Examples of analytical output that can be applied to a 3D model include: thermal analysis, stress/strain analysis (Figure 7), geological analysis, etc.

Software
To fully exploit the potential of color, one must be able to easily produce the data files that need to be printed. There are a number of file formats that support color (VRML, PLY, etc) and in some cases, texture maps, and most CAD tools can export these files. STL exports are more prevalent and tend to be of better quality, but the STL format does not support color.

In these instances, it is important to be able to add color to a monochrome part to be able to take advantage of the benefits described in this paper. With this in mind, a software program called ZEdit^(TM) was developed by Z Corp.’s development team. This software tool lets the user:
. Color parts (whole part, a bounded region such as a face, or an individual triangle)
. Place a texture map on the part (jpg, bmp)
. Annotate or “mark-up” a part with circles, arrows and text
. Place engineering labels on a part

Once the file has been prepared, a process that is mostly automatic, the task of enhancing the part with color is actually quite straightforward and intuitive. For example, one could wrap a label around a bottle and then trim it to a surrounding feature in just a few mouse clicks (Figure 8).

Conclusion
In 3D Printing, color has arrived and is here to stay. One just needs to look at the history of television, laser printing, inkjet printing, scanning and others to see the obvious parallels. Our world is inherently a color one. We’ve looked at a number of useful applications for 3D Printers with full color capabilities. We have also shown that in the absence of a need to color a part or model, color can still add value by enabling a host of other capabilities, such a labeling and annotation.