Tuesday, September 3, 2013

Rare Earth Hexaborides For Cathode Poisoning Resistant CRTs?

Even though they are a fairly dated discovery, are rare earth based hexaboride cathode coatings made possible ultra-long-life cathode ray tubes in color television sets and even hi-fi thermionic vacuum tubes?  

By: Ringo Bones 

Though now virtually forgotten when virtually every consumer electronic devices we have are solid state based – including the now “affordable” organic light emitting diode (OLED) video display monitors, there was a time when cathode poisoning was of grave concern – like back in the days when the first programmable digital computers still use thermionic vacuum tubes. But as thermionic vacuum tubes returned in the high end audiophile scene, and given there are certain cathode ray tube based color television sets manufactured in the mid 1990s that are still running, could the concept of cathode poisoning – in a strange twist of fate – inspire consumer electronic companies to design longer lasting thermionic vacuum tubes, even ones rivaling the longevity of solid state transistors and integrated circuits? 

Back in the 1950s, when vacuum tube technicians were still concerned with their tubes developing “sleeping sickness” whenever it was kept in soft-start mode for a prolonged period of time in radar and digital computer applications, cathode poisoning was of a grave concern on how to prolong the life of their banks upon banks of vacuum tubes when they are mostly switched to low current mode in switching applications. In short, cathode poisoning is the failure mode of a thermionic vacuum tube where the emissive layers degrade slowly with time and much more quickly when the cathode is overloaded with too high a current – which usually results in weakened emission and diminished power of the vacuum tubes or brightness of the cathode ray tubes – i.e. CRTs. Given what every “thermionic vacuum tube experts” had learned through such first hand events, were there any progress made in prolonging vacuum tube life and making cathode poisoning less of a concern? 

Various rare earth borides had been used to prolong the life of thermionic vacuum tubes but there’s no news yet on how they affect sound quality of vacuum tubes when used in audio applications. Like boride cathode vacuum tubes that use lanthanum hexaboride and cerium hexaboride as coating of some high-current cathodes. Hexaborides show low work function around 2.5 eV. They are also resistant to cathode poisoning. Cerium hexaboride cathodes show low evaporation rate at 1,700 Kelvin than lanthanum hexaboride, but becomes equal at 8,800 Kelvin and higher. Cerium hexaboride cathodes have one and one half times the lifetime of lanthanum hexaboride cathodes due to its higher resistance to carbon contamination. Hexaboride cathodes are about 10 times as bright as the tungsten ones and have lifetimes up to 10 to 15 times longer. They are used in electron microscopes, microwave vacuum tubes, electron lithography, electron beam welding, X-Ray vacuum tubes and free electron lasers. However, these materials tend to be expensive. Other useful rare earth based hexabordes with long lives are yttrium hexaboride, gadolinium hexaboride and samarium hexaboride. 

Even though rare earth based hexaboride cathode coatings for thermionic vacuum tube devices may not yet be a hit in the hi-fi audio world sound quality wise, but I think these might have contributed in making extra long life CRTs or cathode ray tubes in television sets. Back in 1995, I’ve bought a 14-inch Goldstar color TV manufactured by LG Collins Electronics Manila, Inc. It’s a model CN-14A146 with serial number 60524212 which I bought for around 150 US dollars and it is still running until this very day. I wonder if this particular Goldstar 14-inch color TV uses a rare earth based hexaboride cathode coated CRT? 

Monday, August 19, 2013

The James Webb Space Telescope: A Rare Earth Telescope?

Slated to replace the now aging Hubble Space Telescope, is the James Webb Telescope deserve the moniker “Rare Earth Telescope” due to the amount of rare earth elements needed to make it do its cosmic exploration?

By: Ringo Bones 

Insiders from Lockheed Martin often joked that its rare earth element content equals that of three Predator drones, but why does the James Webb Space Telescope need such prodigious amounts of rare earth elements to do its intended function in exploring the cosmos? Well, maybe it has to do on where the new space telescope will be finally situated. 

Unlike the Hubble Space Telescope, which is situated in low Earth orbit 250 miles or 400 kilometers above us, the James Webb Space Telescope will be situated 1-million miles from the Earth so any fixing by NASA astronauts in case of a post launch in-space field repairs will be much, much harder than the Hubble fix in low Earth orbit by EVAing astronauts back in the early 1990s. The unfurling of the James Webb Space Telescope’s over-sized mirrors and heat shield 1 million miles in space must go as planned or it will become a sad multi-billion US dollar astronomical blunder. 

In order for the James Webb Space Telescope to achieve reliability in the hostile vacuum and near absolute zero cold of outer space, its servo motors are especially made with advanced proprietary samarium rare earth magnets that can still reliably function at 2.7 Kelvin – the average temperature of the hard vacuum of outer space. These servo motors not only unfurl the over-sized mirrors once the space telescopes arrive in a point in space 1-million miles away from Earth but also the aluminized gold plated mylar heat shield that would protect the James Webb Space Telescope’s main mirror from the relentless unfiltered glare of the Sun. 

Monday, January 21, 2013

Minami Torishima Island: Japan’s Latest Geopolitically Contentious Rare Earth Metals Strike?

In an attempt to wean the country’s over-dependence on Mainland China for rare earth needs, is Japan’s latest rare earth strike on the Minami Torishima Island too geopolitically contentious?

By: Ringo Bones

From recycling obsolete consumer electronic equipment to prospecting the seabed of the country’s territorial waters, Japan has for the past few years seems to be in a mad dash to wean itself from the People’s Republic of China when it comes to meeting its rare earth metal needs. But is the latest find on Minami Torishima Island might just too geopolitically contentious for Japan and other countries desperate to get its rare earth metal needs other than Mainland China?

Upon hearing sketchy reports of Japanese rare earth explorations of the Minami Torishima Island – also known as Marcus Islands – via CB radio “DX-ing” a few days ago, it seems like Minami Torishima Island is a place forgotten by Google search because the “instant search results feature” of the famed search engine can’t even redirect “confused online researchers” who don’t know how to spell the said Japanese in its accepted Roman letter spelling who are just recently looking for facts about Minami Torishima Island.

Even on the entry on Wikipedia, the island seems to be a 21st Century geographical obscurity in itself. Minami Torishima Island also known as Marcus Island is located 1,848 kilometers South-East of Tokyo – quite veritably for all intents and purposes in international waters in the middle of the Pacific Ocean. And as of late, the island is claimed by two East-Asian regional superpowers – namely Japan and The People’s Republic of China. And anytime soon, either the island’s native inhabitants or some other countries would be voicing their sovereignty on the contentious island, making the situation akin to a real-life version of the TV series Last Resort.

The latest exploratory results of a Japanese rare earth metals mining firm on the said island have shown that the seabed surrounding the island contains commercially viable deposits of dysprosium – a rare earth metal vitally important for the manufacture of tiny, powerful magnets for use in motors of modern computer main memory drives and other indispensible contemporary hi-tech applications. But will Japan’s bid to wean itself form Mainland Chinese sourced rare-earth metals creates more regional geopolitical harm than good?

Even if Japan will win an internationally recognized claim on the Minami Torishima Island – otherwise known as the Marcus Island – it will only be just a first of the very difficult hurdles that it will overcome in extracting the economically viable deposits of dysprosium in the island’s seabed. First of all, the economically viable dysprosium ore – literally beige colored mud ooze – on the island’s seabed lies on average 3,000 to 5,000 meters below the Pacific Ocean. And given that there’s this 1970 UN General Assembly declaration that deep-sea minerals were the common heritage of mankind, Japan could end up sharing some of the profits with the Beijing government, and with a preexisting dispute with the People’s Republic of China over the Senkaku Islands, this situation could get ugly fast.

International law rigmaroles aside, Japan’s rare earth metals mining operations on the Minami Torishima Island – if it ever gets the green light – could and might soon attract ship-borne environmental picketing from the world’s leading environmental pressure groups like Greenpeace. This scenario has a high probability of certainty because every commercially viable rare earth metal ores that have been currently so far tend to be weakly to strongly radioactive due to the fact that that rare earth metals’ actinide homologues - like thorium and uranium - also occurs naturally in these ores, which is the main reason why mine tailings of rare earth metal mining and refining facilities can be significantly radioactive – at levels that can certainly pose a clear and present health risk to humans who come close to it.