Thursday, January 29, 2015

Question: What Do You Get When You Cross Science and History?

Answer:  Exciting news if you’re an ancient history buff! 

Researchers in Italy have found a way to read ancient scrolls thought to be irreparably damaged in the Mt. Vesuvius explosion that destroyed or damaged Pompeii and Herculaneum in 79 A.D.


According to a recent article in ECN, the scrolls were recovered from a Roman villa that may have belonged to Julius Caesar’s father-in-law.  This is an exciting development since some of the scrolls may have been written by known Greek and Roman writers.  Some of the scrolls may have already been 100 years old at the time of the eruption.

Using a modified version of CT X-ray technology, researchers have been able to discern letters in the rolled-up scrolls.   


CT stands for Computer Tomography.  Tomography is the method by which images are sliced.  The 2D slices are converted and assembled into 3D images, which is where the computer comes in.  We’ve all seen them….Here is an example of another use in an historical application – a CT image of King Tut’s head obtained in early 2005.

Image Credit


Okay, back to Italy…..The 300 or so scrolls in the villa were originally recovered in the late 1700's.  They are extremely fragile, but interestingly enough, instead of being burned to a crisp, the scrolls were carbonized by the hot gases from Mt. Vesuvius. 

Anyway, this is a great example of what happens when cross-fertilization occurs between two different disciplines – science and history.  We all win. 

I’m looking forward to reading more about the scrolls, and what they might reveal about life almost 2000 years ago in present-day Italy.  Good science is hard to beat, eh?  

High Voltage Diodes for X-ray Power Supplies

Oh, and by way of mentioning high voltage diodes, they are useful in high voltage power supplies that power x-ray systems.  Diode requirements varying, depending on the X-ray application. Industrial x-ray applications use high voltage, high current diodes like the Z- or K-body diodes.  Medical and dental x-ray apps typically use high voltage, low current diodes like M- or X-body diodes. 

If you're not sure what diodes you need, contact VMI.  We'll help you make the best choice for your application. 


Wednesday, January 28, 2015

A Diode Gets New Clothes - Or One Way High Voltage Diodes Are Passivated

In today’s engineering meeting a specific step in the diode glassing process was discussed.  Several experiments have been underway, the goal of which is to evaluate equipment that may be incorporated into the process.

Mostly the equipment under consideration would help to quantify material properties such as viscosity of glass.    

Glass-passivated High Voltage Diode
Glass application in diode manufacturing is a tricky business.  Over the years, many of the best engineers and some of the biggest diode companies in the world have devoted almost unlimited resources in optimizing glass application.  Their expertise and research led to many breakthroughs, 

Glass passivation is what enables the diode to block high reverse voltages.  Without it, arcing would take place between junctions because the distances between junctions are so small – less than 10 mils normally.  Glass passivation provides extremely high isolation voltage.  A high voltage diode is much more likely to arc between leads than between junctions, especially if the reverse voltage is higher than 5kV, and it's running in air (isolation voltage is air is, conservatively, 10kV/in).        
The passivation process starts with the application of glass slurry to stacks of metallurgically bonded, multi-
junction diode stacks.  The glass is allowed to dry, then fired in a high temperature furnace. Sounds simple, doesn't it?
Some of the technical difficulties relating to glass has to do with how much solvents evaporate over time.  It’s an integral function.  Coupled with the fact that glass does not like to stay suspended in liquid indefinitely, some level of mixing has to occur.  There are other factors at play also, but mixing, and the level of solvents present directly impact glass viscosity.  Glass viscosity impacts the ability of the glass to adhere to the die stacks and the overall shape it dries in, whether it slides around the diode and pools at the bottom, or pulls back from the edges.  It's a wonderful, infinitely fascinating material to work with!
But, back to the meeting.....the experimental results were discussed in great detail.  It was great listening to the experts, and from a bystander’s perspective, it’s amazing what information can be gathered from the right piece of equipment used in the right place, and in the right hands.

But the most important lesson from a glass-properties newbie is, we have a great team!  They're smart, funny, hardworking, and open-minded.  It's a pleasure working with them.