>>104
Recently, some causes which bring damages to bone have been made clear.
According to those reports, it has been found out that as UHMWPE used as a material for rubbing parts of artificial joint is low in abrasion-resistance in comparison with cartilage, it's poor in stress-relaxation against impulsive weight.
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>>105
Observing a Charnley type UHMWPE-socket with X-ray, it's abraded by about 0.08 mm every year.
Then, if one granule of UHMWPE-abrasion powders has a span of about 10 μm , 2800 abrasion granules are generated around the joint.
If the quantity of generated abrasion granules is small, as those granules can be digested by macrophages and foreign body giant cells, bad granulation tissues are not formed.
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>>106
But, if large quantities of abrasion granules are generated, as even those cells can not digest generated granules, bad granulation tissues originated in remaining abrasion particles promote necrosis and osteo-injury.
So that, the patient not only gets impossible to walk again but also becomes suffered from intense agony.
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>>107
As most of the 'loosenings' as the most serious complication for artificial joint are caused between bones and osteo-cements, artificial joints without osteo-cements had been developed and they have been clinically used since the 1980's .
To strongly fix this cementless artificial joint on the bone, we must modify the surface of the material so as to be porous and push newly generated osseous tissues into those modified materials.
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>>108
For that, various ways including ways to coat the surface with active ceramics possible to directly join to bones such as hydroxyapatite, methods to screw in and methods to spike, etc are being executed.
But, recently, we have found out that even if these cementless artificial joints are applied to injured parts, the generation of 'loosenings' is not reduced, rather the bone-absorption around an implanted part becomes remarkable.
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>>109
And, it has been reported that large quantities of UHMWPE-abrasion granules are contained in tissues around the implanted part, granulation tissues surrounded by macrophages and foreign body giant cells absorb osseous tissues near those implanted parts, consequently osseous tissues decay.
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>>110
In an international meeting of orthopedics held in September of 1993 , Harris.W bundled up these problems into a concept called 'particle disease' , it was made clear that the most serious problems related to artificial joint at present are originated in abrasion-resistances of UHMWPE .
Since then, problems of UHMWPE-abrasion have been actively dealt with in meetings of orthopedics and bio-material.
However, these problems have never been solved yet ( 2013 ) .
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>>111
・ Present conditions of cartilage for artificial joint ( 2013 )
Bio-joint ( namely a joint in a living body ) functionally relaxes an extreme impulsive weight, uniformly conducts such a weight to bones under cartilages and is durable against abrasion for about 80 years under very low friction.
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>>112
Fluid membranes between articular cartilage and the surface of joint, cancellous bones under cartilages contribute to supporting amazing high performances of bio-joint.
However, it also is sure that functions of joint are gradually lowered due to aging, people who suffer from articular diseases such as deformable hip osteo-arthrists increase.
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>>113
Therefore, it's not rare to reluctantly replace a bio-joint with an artificial joint for recovering lost functions.
In the case of most popularly used artificial hip joint at hip joint at present, a metallic stem such as titanium alloy is inserted into its thighbone-side directly or through osteo-cement, meanwhile a high-polymer hard material such as UHMWPE-cup is combined with its ace tabular side.
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>>114
Correction ;
Therefore, it's not rare to reluctantly replace a bio-joint ( living joint ) with an artificial joint for recovering lost functions.
In the case of most popularly used artificial hip joint
at present ( 2013 ), a metallic stem such as titanium alloy is inserted into its thighbone-side directly or through osteo-cements, meanwhile a high-polymer hard material such as UHMWPE-cup is combined with its acetabular side.
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>>115
But, after a replacement surgery, large quantities of polyethylene abrasion granules are generated between a stem and a cup, besides 'loosenings' originated in osteo-cements and surrounding granulation tissues are caused at very high frequency.
Therefore, in many cases, a secondary replacement is needed within 10 〜 20 years after the surgery. Furthermore, as it's needed to eliminate remarkable quantities of osseous tissues including healthy bones in surgery, considerable loads are brought to the patient.
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>>116
Then, as considerable quantities of osseous tissues have been already lost in secondary surgery, these problems make such surgeries troublesome.
Accordingly, artificial joints are applied to only aged persons at present.
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>>117
By the way, in the case of deforming coxarthropathy ( deforming hip osteo-arthritis ), as its focuses are found out in only partial domains of the surface of joint, we don't have to remove the major part of cartilaginous cancellous trabecular bone group including healthy osseous tissues in performing a surgery.
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>>118
Then, we should develop a surfacial replacement-type artificial articular cartilage to replace only the focus with an artificial material.
In some experiment, an artificial articular cartilage made of polyvinyl alcohol ( PVA ) was applied to a beagle dog.
In this case, a focus originated in femoral head necrosis was replaced with an artificial articular cartilage made of PVA , since then good conditions have been brought to the dog.
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>>119
・ Present conditions of artificial inter-vertebral disk
Main dynamical ( or mechanical ) functions of vertebra are summarized into following three factors.
1. Protections of the spinal cord and nervous components
2. The support of the weight of a body trunk
3. Smooth motions of a body trunk
Namely, bearability and movability are mainly requested of this part.
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>>121
To heal damages on inter-vertebral disk as a main cause of backache, a surgery to remove inter-vertebral disk and an operation to fix lumbar vertebra are mainly performed.
Especially, the latter treatment is frequently executed owing to improvements in instrument, conditions after the operation also comparatively become stable.
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>>121
But, movability is partially lost due to the operation to fix vertebra.
Consequently, as extreme stresses are brought to non-fixed neighboring inter-vertebral disks, we must take bad influences into consideration.
It's desirable to develop artificial inter-vertebral disks for giving both bearability and movability with no pains to an injured vertebra again.
Provisionally, developments of artificial inter-vertebral disk have been being carried out for 30 years until now.
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>>122
But, most of them are conceptual researches on biomechanics of vertebra.
Namely, though there are many theoretical reports to show dynamical characters required of artificial inter-vertebral disk and to propose new inter-vertebral materials, we can't find out cases in which such ideas were actually applied to a living body so much.
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>>123
In most of the artificial inter-vertebral disks used until now, a material like polyethylene is inserted between metallic plates.
Failures originated in dislocations and deviations from regular positions have been reported until now.
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>>124
In particular, if an artificial inter-vertebral disk deviates or is dislocated from the vertebral body,
as serious complications are caused, goals to develop artificial inter-vertebral disks are focused on following two points, namely,
( 1 ) the stable settlement of the part on the vertebral body
( 2 ) the physiological movabilities of the implanted inter-vertebral disk
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>>125
An artificial inter-vertebral disk made of PVA which had been developed by Gen & others was implanted into the vertebral body of a beagle dog.
The condition after one year from the surgery was good.
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>>125
• Present conditions of artificial ligament
Damages in ligaments of knee are frequently found out in athletes and sportspersons.
Recently, as the population of sportspersons increases, cases which receive such a damage also gradually increase.
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>>127
In general, as damages in ligaments of knee especially damages in anterior cruciate ligament are not naturally healed, it's needed to perform a surgical operation for healing such an injury.
If such damages are left, serious troubles can be caused in not only returns to sports but also daily life.
In general, 〈 suture ＋ the transplantation of own tendon into the injured part 〉is performed to heal this damage.
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>>128
But, complications originated in picking own tendon such as fall in muscular strength, pains and nervous paralyses are caused, consequently, a long time is required to return to sports, the decline in performance also is inevitable.
In the past, some types of artificial ligaments made of non-absorbent polyester had been produced.
But, stable effects have never been realized yet because of rejections in a living body and in-durability against stress for a long term.
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>>129
Progresses in regenerative medicine enable developments of various artificial organs.
For now, regenerative medical approaches for an injured ligament have been scarcely performed, as there are no effective treatments for this damage, it's one of the most urgent subjects.
A ligament is a tissue in which respective components are closely bound and this is a comparatively simple tissue of fibrous blasts and collagens.
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>>130
However, this organ still includes many unknown points from viewpoints of molecular biology and systematic engineering.
Because, as each tissue itself is very tiny, it's difficult to separate it into cellular units, furthermore characters proper to cells constituting a ligament have never been made clear yet.
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>>131
About one hundred and fifty thousand reconstructive surgeries for injured anterior cruciate ligament are performed a year in USA , about thirty 〜 fifty thousand reconstructive surgeries for it are performed a year in Japan.
It's probable that considerable numbers of cases including surgeries for ligaments except for anterior cruciate ligaments are executed.
Developments of new artificial ligaments combined with bio-activated matters will give remarkable influences on medical and industrial fields.
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>>132
• Future Works
At present, there are various absorbent materials to heal fracture, they are clinically applied to respective situations.
Then, PDS ( Poly Dioxanone ), TMC ( Tri Methylene Carbonate ) or PDLLA ( Poly DL Lactic Acid ) are applied to parts at comparatively low strength.
Meanwhile, PLLA ( Poly L Lactic Acid ) is applied to parts at which high initial strength is required.
Furthermore, various ideas ( for example, introductions of molecular orientations and formations of composites ) are taken into consideration to improve such an initial strength.
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>>133
By the way, materials to join bones for healing fracture at present are as follows.
To sustain the osteo-strength of more than 200 MPa for about 3 months,
for example, composites of poly-lactic acid, co-polymers of lactic acids and glycolic acids with hydroxyapatites are uni-axially stretched.
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>>134
Then,
200 MPa ; the strength of human cortical bone against compression & bending
About 3 months ; the minimum term until a broken bone is naturally healed
Poly Lactic Acid, co-polymer of lactic acid and glycolic acid ; degradable and absorbable high-polymers in vivo
Hydroxyapatite ; this matter is excellent in affinity with osseous tissue , with molecular mass of more than one hundred thousand
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>>135
But. as pointed out previously, the degree to maintain strength with initial strength and hydrolysis has been partially improved, however after four months from the implantation namely after the initial strength gets 0 , implanted materials are still left in the living body without completely being resolved and absorbed. From now, we must solve these problems.
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>>136
〈 Artificial Joint 〉
Since the success in the Charnley-type artificial hip joint with UHMWPE ( Ultra High Molecular Weight PolyEthylene ), UHMWPE s have been applied to most of rubbing parts of artificial joints.
But, UHMWPE-abrasion-granules generated due to frictions and abrasions cause necroses and decays of tissues around an artificial joint, besides the 'loosening' of the artificial joint.
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>>137
Accordingly, recently, improvements in abrasion-resistance in UHMWPE (＝ durability against abrasion ) is strongly requested.
Though this improvement in abrasion-resistance is the most important subject for artificial joint, ways to improve those troubles have been scarcely found out.
At present, we are being urged to overcome this trouble.
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>>138
〈 Artificial Articular Cartilage 〉
An artificial articular cartilage can be applied to an injured part comparatively early, besides, it's possible to apply it to the young generation and to keep various healthy functions with it.
For example, PVA ( Poly-Vinyl Alcohol )-hydrogel has been studied as a main material composing an artificial articular cartilage.
As this material contains waters, it has lubricative effects similar to those of living articular cartilage.
So, it's expected to keep a low frictional state with it.
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>>139
Following two points are especially important to apply artificial articular cartilage to clinical fields.
(a) ways to settle it on the osteo-ground
(b) dynamical suitabilities including functionalities in wide sense
First, about (a), according to some researches, it has been made clear that if a titanium fiber mesh (＝ porous artificial bone) is used as a material to bond PVA-hydrogels to osseous tissues, newly generated bones get into respective holes of the TFM ( Titanium Fiber Mesh ), so that the adhesion of osseous tissues with TFMs is rigidly fixed.
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>>140
And, if a PVA-solution at high concentration sufficiently permeates the TFM with injection molding method and the permeated solution is varied to a gel, a strong bond between PVA and TFM can be realized.
Namely, PVA-hydrogel can be regarded as a material for artificial articular cartilage which is very effective in the settlement of it on an osteo-ground.
Furthermore, this is very effective against the deterioration in vivo too.
Accordingly, we should advance researches of artificial articular cartilage on this material.
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>>141
〈 Artifivial Inter-vertebral Disk 〉
The same as the case of artificial articular cartilage, Gen and others produced a material to settle an artificial inter-vertebral disk on a living vertebral body by pouring a PVA-solution into respective holes of TFM with an injection molding machine.
From now, we need to demonstrate the usefulness of the new type of artificial inter-vertebral disk through experiments in vivo and aim at clinical application of it.
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>>142
〈 Artificial Ligament 〉
Followings are provisional aims in this field at present.
・ If mechanical stimuli and various cytokines are given to ligamental cells, reactions to those stimuli and supplies appear.
We need to establish ways to culture ligamental cells at higher cellular activated state on those reactions.
・ Polymers containing heparins with respective cytokine-bonding capacities are used to design matrices which enable cell-multiplication, vascular induction.
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>>143
Furthermore, we need to prepare following materials to compose tissues with sufficient strength.
・ Collagen-gels to which dynamical stimuli such as periodic stresses and magnetic stimuli are given.
・ Hybrid artificial ligaments with which artificial high-polymers such as polylactic acid fibers and elastin-like protein-based polymers ※ are combined.
※ They were developed by Urry SR and others ( Queensland university of technology, Australia ) with genetic modification methods.
First, transplanting this artificial ligament into a rabbit, we must demonstrate that its functions are sustained.
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>>144
• Achievemental levels of respective aims
It's desirable that materials introduced here are developed as medical high-polymer biomaterials which are gentle to living body.
Concretely, following researches should be supported.
〈 Materials to fix bones for healing fracture 〉
・ Developments of degradable & absorbable materials in vivo for fixing bones which are equal to metallic materials for fixing in reliability.
・ To raise initial elastic degrees of those materials to that of cortical bone.
・ After those initial strengths get 0 , they should be quickly degraded and absorbed into the living body.
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>>145
〈 Artificial Joint 〉
As the replacement with an artificial joint brings remarkable stresses to the patient, we should develop an artificial joint which works for a long term of 30 〜 50 years with no troubles after the surgery.
〈 Artificial Articular Cartilage 〉
Artificial joints have considerably contributed to healing of deforming coxarthrosis.
But, as its durable spans are short ( 10 〜 20 years ), they are not suitable to patients at young generation.
And, we need to develop a surfacial replacement-type artificial articular cartilage which is clinically applicable to the replacement of a chondral surface.
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>>146
〈 Artificial Inter-vertebral Disk 〉
Developments of artificial inter-vertebral disks which are similar to living inter-vertebral disks namely have both bearability and movability.
〈 Artificial Ligament 〉
Recent progresses of tissue-engineering and regenerative medicine have partially produced clinically applicable organs.
But, for now, regenerative medical fruits on ligament are scarcely found out.
Namely, there are limits in healing of injured ligament at the present medicine.
Accordingly, the establishment of ways to heal on tissue-engineering is urgent in this case ( in 2013 ).
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• The waste disposal by thermo-plasma 〜 〈 1 〉
1. Preface
It's regarded that thermal plasma is useful to waste-disposal due to following characters.
1 ）As thermo-plasma is at high energy, high density and high temperature,
its speed for processing & reaction is quick.
2 ）Because of its high temperature, we can synthesize compositions at quasi-stable phase and in-equilibrium phase by properly quenching.
3 ）We can quickly start up & shut down the process because of conveying-heat at high speed on thermal plasma.
4 ）A small quantity of gas is sufficient to perform a processing by thermal plasma, so exaust gases can be kept at low quantity.
>>150
And, following processes are realized as practical uses for waste disposal.
Thermo-plasma is being used for large general waste disposal such as process to melt down burnt ash.
We can prevent heavy metals which are included in burnt ash issued from incinerators for urban garbages from melting and can turn them to be harmless by resolving dioxin through the thermo-plasma.
Besides, plasma-melting technology is practically used for medical waste disposal.
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>>151
In such a system, wastes are thermally decomposed at anoxia condition, disused material carbides, hypodermic needles and phials, etc are turned to be stable slags by heating through plasma.
And, thermal plasma is being used to re-cycle dusts which are issued in great quantities from iron-manufacturing and steel-making factories too.
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>>152
Dusts from an electric furnace are about equal to 1 〜 2 % of thrown raw materials, those dusts contain valuable metals such as Zn, Pb, Cr, etc.
Processing those dusts through thermo-plasma, we can withdraw Zn and Pb at the high pressure of steam from the top of the furnace, other metals such as Fe, Cr, Ni at melted state from the bottom of the furnace.
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>>153
Furthermore, processes to withdraw platinum-groups from abandoned catalysts for motor-vehicle, processes to re-withdraw aluminum from alumidolos resulted from melting and casting aluminum by melting through arc-plasma have been developed.
As the above, thermo-plasma has already been practically used in various fields for waste-disposal.
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>>154
Besides, thermo-plasma was widely used as a heat source at high temperature in the field of material-processing, for example, plasma-spraying.
But, only characters at high temperature of thermo-plasma are used in most of these applied examples.
Furthermore, thermo-plasma has a fascinating property called 〝high chemical activation″ too.
Properly using charged particles and radicals in the thermal plasma together with its high chemical activation, new processes for waste-disposal also will be developed.
These processes are shown in the following.
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2.1 The decomposition of CFC ( Chloro-Fluoro-Carbon )
To resolve environmental problems originating in CFCs , it's required to suppress the release of CFCs into the atmosphere by properly decomposing CFCs.
The plasma-method, the combustion-method, the cement kiln-method, the oxygen-hydrogen flame-method, etc were acknowledged as valid technologies to decompose CFCs in countries signing the Montreal protocol.
In the case of the method for decomposing CFCs by plasma, methods using arc-discharge, microwave-discharge and corona-discharge have been practically used.
Here, the method for decomposing CFCs by RF-plasma with steam is shown.
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>>156
A plant to decompose CFCs by high-frequency ( RF ) thermal plasma with steam is put in I city of Japan.
This plant can decompose CFCs at 70 kg/h by generating the 100 %-steam plasma from the 200 kW-power under the 200 torr-pressure.
The total reaction to decompose CFC-11 ( CCl3F ) through steam-plasma is as follows.
CCl3F ＋ 2 ( H2O ) → CO2 ＋ 3 ( HCl ) ＋ HF
( 1 )
In the case without steam, disproportionations to generate CCl2F2 and CClF3 and demerization reactions to generate C2Cl3F and C2Cl3F3 appear, and the generation of soot also is confirmed.
To suppress these side-effects is one of the advantages on the use of steam-plasma.
When CFCs are decomposed through steam-plasma, HF and HCl also are generated.
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>>157
Letting these decomposed gases through water, HF and HCl can be removed as solutions.
And, the water temperature can be lowered into below 80 ℃ by directly passing decomposed gas through water, so that the re-composition of dioxin can be suppressed.
After that process, issued gases are purified in a scraba or a building to remove active carbons.
In the case of PLASCON-plasma process in Australia, CFCs are decomposed by supplying steam into a DC plasma jet. http://www.plascon.com.au/
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>>158
The system can decompose CFC-12 ( CF2Cl2 ) at 40 L/min through the 150 kW plasma jet, if the ratio of supply-quantity to the power of plasma is set up below 6 mol/kWh, CF3Cl generated from side-effects can be suppressed.
In particular, the use of steam as plasma-gas can more effectively suppress the generation of CF3Cl and CF4 compared with the use of oxygen.
And, in Germany, a pilot plant to decompose CFCs through DC-plasma jet of 100 % steam has been developed.
「Hazardous Waste Destruction」 http://www.youtube.com/watch?v=atFPpBWl31o
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>>159
2. The waste disposal by steam plasma
2.2 The decomposition of halon
Halon is a kind of CFC including bromine, the matter has been used for computer-rooms, electric rooms and fire-extinguishing equipments in forbidden places of the use of water such as parking areas.
But, as halon was specified as a matter to cause environmental destruction, the production of this matter has been stopped.
However, methods to properly process abandoned halons also have never been established ( in 2011 ).
The decomposition of halon is costly, technologically more difficult than that of CFC .
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>>160
In such a situation, the method to process halon by thermal plasma has been regarded as one of the efficient methods to decompose halon.
※ As about 98 % of managed halons correspond to halon 1301 ( CBrF3 ), the establishment of method to process halon 1301 is an emergency subject.
The decomposition of halon is being carried out through steam RF plasma shown in a previous section.
It has been achieved to decompose halon 1301 at 50 kg/h under the same condition as that of CFC .
The total reaction of halon 1301 with steam-plasma is as follows.
CBrF3 ＋ 2 ( H2O ) → CO2 ＋ 3 ( HF ) ＋ HBr
( 2 )
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>>161
The research to decompose halon with techniques of PLASCON stated in the above also is being continued.
In the case of decomposition of CF2ClBr with steam, if the ratio of supplied quantity to plasma-power is below 10 mol/kWh , un-decomposed halons can be ignored.
And, HBr, HF and HCl can be removed as solutions by making decomposed gases alkaline.
However, a defect in ways to make decomposed gas alkaline is that the facility for drainage tends to be large-scale.
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>>162
Recently ( about 2011 ), the dry-thermal decomposing-method is being considered to withdraw bromides and fluorines generated as decomposed CFC-gases by reacting them with solid-alkaline materials such as calcium oxide and magnesium oxide.
The system for waste-disposal without water-processing like this is economically advantageous.
The total reaction of halon 1301 with burnt lime is as follows.
CBrF3 ＋ 2 ( CaO ) → CO2 ＋ 3/2 ( CaF2 ) ＋ 1/2 ( CaBr )
( 3 )
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>>163
One of the features of dry-thermal decomposing-method is to solidify fluorines & bromines resulted from the decomposition of halon into CaF2 & CaBr2 and efficiently withdraw those solidified matters.
2.3 The decomposition of tire
The process to re-use combustion heat resulted from the burning of abandoned tires has been regarded as one of the ways to process abandoned tires.
But, in this case, the generation of harmful issued gases such as NOx, CHx and SOx, etc is inevitable, and heavy-metals such as Hg, Zn, Cd also are contained in those issued gases.
So, way to synthesize fuel-gas through thermal decomposition is more suitable than burning for processing abandoned tires.
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>>164
In particular, when the thermal decomposition of abandoned tires is carried out through thermal plasma, the fuel-gas of C2H2, CH4, C2H4, H2, CO, etc can be efficiently synthesized.
The mixed gas of argon or argon-hydrogen is used as a plasma-gas and the steam is supplied into the lower stream of plasma-jet at 3 kg/h in this process.
Processing tires turned to be like dusts in about 500 μm through 80 kW of plasma-jet at 1.5 〜 4 kg/h , fuel-gases equal to 4 〜 7 MJ/m＾3 can be synthesized.
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>>165
It's important to control the generated quantity of ZnO , SOx , NOx in processing abandoned tires.
The process with thermal plasma can suppress the issued quantity of SOx and NOx so as to be below 100 〜 200 ppm , can gather ZnO through a filter.
So, the process to decompose abandoned tires through thermal plasma also is remarkable.
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>>166
3. The waste disposal by plasma at reduction mode
3.1 A way to turn molten flying dusts to be harmless
About fifty million tons of urban garbages a year are issued in this country, 70 % of them are burnt.
Several % of high volatile heavy-metals such as Pb and Zn are contained in burnt flying dusts which are generated in garbage dumps.
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>>167
Flying dusts gathered by devices for collecting dusts such as electric dust-collector of incinerator and bug-filter are specified as specially managed general wastes, four kinds of methods for processing are set to those flying dusts on the executive law for waste disposal.
One of them is a molten slugging-method.
This is a way to melt flying dusts down at high temperature ( about 1200 〜 1500 ℃ ) and withdraw molten dusts turned to be like slug.
And, although dioxin at high concentration is contained in the flying dust, the molten slugging-method can decompose dioxin.
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>>168
When flying dusts or burnt main dusts are molten down, heavy metals and salts contained in those dusts with low boiling point are volatily diffused and dusts like heavy metals which are more concentrated than flying dusts appear.
These are called molten flying dusts and are equal to about several % of the quantity of molten flying dusts.
As molten flying dusts contain heavy metals which have higher concentration than that of original burnt flying dusts, more rigorous way for handling than that of burnt flying dusts is required.
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>>169
At present ( about 2011 ), molten flying dusts are being buried under managed places for disposal through processes to stabilize such as cement-slugging, drug-slugging.
But, as these molten flying dusts contain heavy metals at higher concentration than usual flying dusts and salts such as NaCl and KCl in large quantities, it's very hard to maintain the stability after slugging-process.
Furthermore, wet processing-methods using acid, alkaline chemicals eventually need large quantities of waters.
So that, the cost for chemicals tends to be expensive and the facility for drainage also tends to be large-scale.
Therefore, the development of compact and low-costed technology for processing molten flying dusts without water-processing has been desired.
One of the solutions for that is a processing-method to make molten flying dusts to be harmless through RF-thermal plasma with hydrogen.
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>>170
Putting molten flying dusts in the RF-thermal plasma at high temperature reduction mode, those dusts are immediately evaporated and decomposed.
Then, heavy metals such as Pb, Zn contained as oxides in molten flying dusts are turned into metallic atoms in the plasma.
Taking these decomposed products separately or as bulks out of the lower stream of plasma, we can separate pure and harmless ashes from heavy metals.
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>>171
To separate-withdraw flying dusts decomposed in RF-plasma, it's needed to control its process for condensing.
Respective temperatures of condensation are calculated out on the degree of super-saturation which is an important parameter related to the generation of nucleus during condensation.
This implies that hydrogen has significant influence on the temperature of condensation for ZnO .
Metals with low boiling point make aggregations on those surfaces of particles composing matters with high boiling point in burnt flying dusts or molten flying dusts.
This method with plasma for reduction can decompose or separate particles of dusts turned to be gas-like, atom-like from the mixture of various matters.
And, this can separately withdraw respective components by controlling post-processes for cohesion.
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>>172
We carried out some experiments with a device for processing molten flying dusts.
This device was composed of a RF-plasma torch and a thermostat.
The thermostat as a component heated up matters to check the correlations of temperatures with collected matters in the lower stream of plasma.
In this case, flying dusts are led from the center of plasma torch to the nozzle for supplying, and the temperature of the thermostat for heating is optionally set up.
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>>174
In particular, in the case of argon-hydrogen plasma, the quantity of contained heavy metals such as Pb, Zn is little in the range at high temperature above 700 〜 900 ℃ , meanwhile matters containing much heavy metals are withdrawn in the range at low temperature below 700 〜 900 ℃ .
The quantity of heavy metals contained in matters withdrawn in this range at high temperature was very little ( Pb ; 0.04 wt% , Zn ; 0.05 wt% ).
So, the system to process molten flying dusts by hydric RF-plasma is promising as a compact and low-costed technology for processing.
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>>175
3.2 The processing of coal flying dusts
The fundamental research on the separation of components from coal flying dusts is being carried out ( about 2010 〜 2011 ).
The purpose of this research is to separate-withdraw silicon components with processing main components of coal flying dusts such as SiO2 and Al2O3 through argon-hydric plasma-jet.
Processing the mixture of SiO2 - Al2O3 through argon-plasma or argon-hydric plasma, the thermal decomposition or the reducing reaction of SiO2 is selectively caused.
So that, Si and SiO are obtained as evaporative matters, Al2O3 is left as a heated substance.
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>>176
The reducing-reaction of SiO2 selectively happens and Si and SiO evaporate from the heated substance through argon-hydric plasma.
At the same time, the reducing reaction of Al2O3 also is partially caused, then Al and Al2O evaporate.
However, its speed of reaction is very slow, the quantity of evaporated matters is quitely little.
So that, the purity of silicon components withdrawn as evaporated substances becomes high.
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4. The waste disposal by plasma at oxidative mode
4.1 The processing of low-level radioactive waste
Incombustible miscellaneous solid wastes of low-level radioactive wastes which were issued from nuclear power plants have remained un-treated.
The system to process low-level radioactive wastes with furnace for inducting meltdown by plasma is considered for the stabilization and the reduction of these wastes.
Ways such as cutting, compressing and melting, etc have been presented as methods to reduce volumes of waste, a more idealized method to process wastes with melting is expected to have the maximum ratio of reducing volume, even if various wastes are processed through this method, an uniform matter must be obtained.
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>>178
The combination of RF-plasma with inductive furnace for heating of these methods to process with meltdown can process various wastes as a lump regardless of combustibility or incombustibility.
Furthermore, because oxidative plasma is used for processing in this method, it's possible to rapidly burn-decompose incombustible wastes through the method.
Therefore, at present ( about 2011 ), this method is being regarded as a validest way for processing.
The DC-plasma method has been used for reducing volume until now.
Although the oxygen-rich burning has been supported to be effective for burning incombustible matters, the exhaustion of electrodes was remarkable in this method.
And, the meltdown by inductive heating is not suitable for processing concretes and glasses.
Accordingly, the combination of RF-plasma with inductive furnace for heating will be able to compensate for above defects.
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4.1 The processing of abandoned ion-exchange resin
The system to process abandoned ion-exchange resins with oxygen-plasma is being developed ( at 2011 ).
This is a way to reduce the volume and stabilize of ion-exchange resins which are generated in reactors for cleaning radionuclides, through oxygen-plasma.
A part of metallic materials composing a reactor which are corroded under high temperature reaches the reactor core as ion through coolant, and another part of those materials reaches the core as suspended matter respectively.
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And, corroded products radio-activated by the irradiations of neutrons circulate in the system, adhere to pipings as clads.
Most of elements composing those clads are Fe, meanwhile the ratio of 60CO and 54Mn for contributing to radio-activity is high.
These nuclides are originated in CO , Ni and Fe composing stainless steel, stellite and inconel, etc which are materials to compose a nuclear power plant.
In particular, the radioactive half-life of 60CO is long compared with other nuclides, its energy of γ-ray is high.
So, it's difficult to handle this element.
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Steams generated in a reactor are condensed through a device for returning water after driving the turbine.
Corroded products generated in the upper stream of the device for returning water are removed through ion-exchange resins in a purifier returning water.
Accordingly, powdered ion-exchange resins clean up radioisotopes activated in a reactor, so that those resins adsorb radio-activated CO and others.
Abandoned ion-exchange resins are generally stored in facilities. But, as it's hard to keep places for storing those matters, it's desired to reduce the volume and stabilize of those matters.
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Because abandoned ion-exchange resins are in-combustible, it's hard to usually burn-reduce the volume of those.
Accordingly, the volume of low-level abandoned resins are reduced by burning those resins together with miscellaneous wastes, and they are stored as uniform solid matters through cement-slugging in facilities or are disposed.
Meanwhile, most of high level abandoned resins are stored at half-processed in the tank of the facility.
The same as that, ways to process abandoned resins generated during the disposition have never been found out ( about 2011 ).
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A method with RF-plasma at decompression ( 0.25 〜 0.9 torr ) also is one of the efficient ways to process abandoned ion-exchange resins.
This method can decrease secondary wastes such as tar and soot through complete oxidation by oxygen-atoms and radicals.
These active particles directly interact with ion-exchange resins and decomposed gases from those resins to pull hydrogens out of an alkyl group, and they oxidize hydro-carbons through cutting into c-c coupling.
So that, those resins are transformed into gases such as CO, CO2, H2O and the volume of them are reduced.
And, metallic ions such as CO sticking to exchange bases of resins are left as oxides in reduced remnants.
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The method to process abandoned ion-exchange resins by this decompression way has following advantages because that is at low temperature compared with burning.
・ It's possible to decrease the shift of radioactive nuclides into gas-phase.
・ It's possible to reduce the quantity of issued gas because this method is a direct oxidative process by oxygen-plasma.
In a demonstrative test-device, processing ion-exchange resins of 4L for three hours,
the ratio of reducing volume was about 90 % .
Then, supplying oxygen into the system at 50 L/min , the RF-plasma was realized under the condition at 450 Hz , 10 kW .
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And, a method to process abandoned ion-exchange resins by oxygen-thermal plasma under atomospheric pressure also is being considered to increase the speed of processing.
It has been reported that abandoned ion-exchange resins were processed at 4 kg/h through the oxygen-plasma generated by a transition arc-discharge ( 42 kW ).
In this case, the mixture ratio of positive ion-exchange resins and negative ion-exchange resins was 50 : 50 .
This processing by plasma was carried out together with glasses of 25 kg ( Na2O - Al2O3 - 2SiO2 ) to trap radioactive nuclides sticking to ion-exchange resins.
In this method to process, ion-exchange resins are supplied from the upper part of the system and they are dropped into the glass molten through arc-discharge.
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And, a comparison of batch-processing with continuous processing has been carried out.
Batch-processing is a method to process ion-exchange resins put in a melting pot by an arc-discharge of 24 kW.
In this case, ion-exchange resins of 100 cm＾3 were processed, the ratio of reduced volume of 65 % on positive ion-exchange resins ( IRN 77 ) and the ratio of reduced volume of 90 % on negative ion-exchange resins ( IRN 78 ) were obtained respectively.
The condition of continuous processing was set up same as that of batch processing, IRN 77 was processed at 200 g/min , IRN 78 was processed at 63 g/min respectively.
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The ratio of reduced volume in this case didn't depend on the speed to supply ion-exchange resins so much.
That ( the ratio of reduced volume ) of IRN 77 was equal to about 60 % , and that of IRN 78 was equal to about 90 % .
This result was approximately equal to that of batch processing.
But, as the heating of batch processing can't be uniform, it's hard to control issued gases in this case.
Meanwhile, in the case of continuous processing, it's comparatively easy to control the composition of issued gas.
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As the method to process abandoned ion-exchange resins by thermal plasma is basically a kind of burning process by oxygen in plasma, oxygen or air is used as a plasma-gas for processing.
※ When using air, we should pay attention to the generation of NOx .
And, as COs sticking to ion-exchange resins are roughly gathered up to resins after processing, they are not shifted into gas-phase almostly.
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The method to process ion-exchange resins under atmospheric pressure with blowing oxygen into plasma-jet also is being considered ( about 2011 ).
As time for processing goes, the weight of resins substantially decreases.
So, the ratio of reduced mass of 90 〜 95 % can be obtained for about 20 〜 40 minutes on the process.
And, from the result of infrared absorption spectrum, it has been confirmed that strong acid ion-exchange resin has a character that as time goes, the peak on sulfonic acid group decreases and that peak completely vanishes by the processing of 20 minutes.
Furthermore, it also has been confirmed that CO sticking to ion-exchange resin is divided into CO 0 and CO3O4 , Cs turns to be Cs2SO4 .
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4.3 The Decomposition of PCB
The process to decompose PCB in oxidative mode with oxygen plasma or air plasma is being considered ( about 2011 ).
For example, a system to process liquid wastes by plasma-jet has been realized to load on a heavy-duty trailer.
※ PCB can be decomposed with supplying PCB into a plasma-jet of 327 kW at 0.4 kg/min through this method.
And, in the PLASCON-system stated previously, a plant to process PCB by blowing PCB itself together with oxygen into the system has been completed.
This PLASCON-system can process PCB at 40 〜 50 kg/h by reacting oil including PCB with oxygen through the DC-plasma jet of 150 kW .
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Weakquakes had occurred on both ends of Japan within a short time just before a large-scale earthquake happened in Italy at the beginning of April of 2009 .
Then, it also was pointed out that there are non-local correlations on tectonic movements of the earth.
※ Some told that the case in Italy might be related to heliacal neutrinos or neutrino-beams.
By the way, the same as situations in other countries, large quantities of untreated radioactive wastes are still kept to be buried under ground of this country too.
And, a neutrino-detector called SK is put under the area neighboring to Hida.
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5. The separation of matters by reactive thermal plasma
5.1 The separation of matters by hydric plasma
The 'high chemical activation' possessed by thermal plasma is suitable for the separation of components from mixture.
Generally, hydrogen is used for the reaction of high chemical active plasma.
And, hydrogen is used as a plasma-gas for arc-melting too.
Then, hydrogen is effective for refinements such as the devaporization from molten metals, the separation-removal of impurities.
Deacidifying, decarbonization and denitrogenization from molten steels, deacidifying, decarbonization from Ta and the refinement of Mo from molybdenum mineral deposites are being studied as processes to refine metals with the high chemical activation of hydrogen in thermo-plasma ( about 2011 ).
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The withdrawing of Ta from a scrap of abandoned Ta-condensers is known as an application of hydric plasma to waste-disposal.
As Ta-condensers inserted into computers contain manganese and oxygen, efficient processes to deoxidize, de-manganize are needed to reuse them.
In particular, as Ta is one of the uneven distributed resources, an used Ta-condenser can be a precious secondary resource of Ta .
It has been realized to reduce concentrations of nitrogen, Fe, Ni as well as oxygen, Mn as impurities into about 100 mass ppm with only single manufacturing process through arc-melting process by hydric plasma.
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The withdrawing of Zr from Zircoloy-scrap also has been carried out by hydric plasma.
Zr is utilized as Zircoloy to compose fuel-covering pipes of a nuclear reactor.
The scrap of large quantities of cutoffs and defective products which are generated in manufacturing of covering pipes also can be regarded as a secondary resource of Zr .
Zircoloy contains Fe, Sn, Ni, Cr, it has been attained to reduce Fe, Ni, Cr into 10 mass ppm and Sn into 100 mass ppm through arc-melting by hydric plasma ( about 2010 〜 2011 ).
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In these processes, hydrogens dissociated in a plasma play important roles to remove impurities from metals.
But, its concrete mechanisms have never been made clear ( at 2011 ) .
For example, Mimura and others explained that temporal loose couplings of Fe and H like clusters are formed, so that the separation of Fe from molybdenum mineral deposite can be effectively carried out through hydrogen.
And, as suggested in a process to manufacture superfine particles with hydric arc, the compulsory vaporization-model of dissociated hydrogens also is considered as one of the factors.
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This compulsory vaporizing action is a model that the generation of superfine particles is originated in reaction heat which is caused through recoupling-releasing processes of supersaturatively molten hydrogens in a liquid metal ( such as magma ).
Ohno and Uda asserted that speeds of vaporization for respective metals originated in this compulsory vaporizing action can be calculated out of a parameter Rp expressed with the following formula.
Rp ＝ ( − Δ H/L )・( nH2〈T〉／ nH2〈273K〉)
( 4 )
Then,
Δ H ; reactive heat to re-combine hydric atoms at temperature T
L ; latent heat to vaporize metals at T
nH2〈T〉; numerical density of hydric molecules at T
nH2〈273K〉; numerical density of hydric molecules at 273K
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In the process to manufacture superfine particles of inter-metallic compounds with hydric arc, it's possible to control the composition of generated superfine particles through hydrogens in the plasma.
The higher the concentration of hydrogens in the plasma becomes, the more the composition of Ti in superfine particles of intermetallic compounds which are generated from the mixture of raw materials ( such as Ti , Si ) put on the positive pole ( anode ) gets.
As the pressure of steam of Ti is equal to about 1/10 of that of Si , the quantity of evaporation of Ti must be promoted to synthesize superfine particles of intermetallic compounds of TiSi2 .
Namely, we can control the composition of generated superfine particles by the concentration of hydrogen in an arc.
In this case, same results can be derived from the combination of Mo & Si or V & Si .
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Accordingly, we have known that hydrogens contained in plasma play same role as a kind of catalyst to promote the evaporation of specific metals.
Considered causes are shown as follows.
( 1 ) Compulsory vaporizing actions by hydrogens dissociated in plasma
( 2 ) The increase of vaporized quantity because of thermal conductive ratio raised by hydrogens
( 3 ) The generation of intermediate products such as hydric-products
( 4 ) The change of activated quantity by hydrogens fusing into molten metal
The relation of the reactive parameter shown in formula ( 4 ) with the coefficient of separation derived from the composition of superfine particles has been made clear.
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The coefficient of separation of the arc with hydrogen of 20 % is far different from that with hydrogen of 50 % .
This implies that the mechanism to promote the vaporization through hydric-arc is not originated in ( 1 ) and ( 2 ) .
So, it can be supposed that the promotion of vaporizing specific metals through hydrogens in a plasma is originated in ( 3 ) or ( 4 ) .
However, because intermediate products such as hydrite-products composed of molten metals ( including magma ) and hydrogens in plasma are unstable, it's difficult to experimentally examine them.
And, it also is hard to calculate out the change on activated quantities of a molten metal by hydrogens.
※ Magma also can be often regarded as a kind of molten metal.
By the way, technologies to make underground-tunnels and to deeply dig strata to the mantle by melting rocks through direct-current plasma have been developed.
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5. The separation of matters by reactive thermal plasma
5.2 The separation of matters by chloric plasma
Hydrogens have mainly been used to cause plasma-reactions with applying 'high chemical activation' of thermal plasma until now ( about 2010 〜 2011 ) .
But, we have very few informations about plasma-reactions related to hydrogens such as thermo-dynamical data to realize such reactions ( for example, melting points, boiling points and steam-pressures of hydrogenated matters, etc ).
Therefore, it's difficult to theoretically study such processes.
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