Document:

<PAGE>   1
                                                                   EXHIBIT 10.17

Assignment Agreement made May 26, 2000 between UCAR Graph-Tech Inc., a Delaware
corporation ("ASSIGNOR"), and UCAR Carbon Company Inc., a Delaware corporation
("ASSIGNEE").

RECITALS:

WHEREAS a Memorandum of Understanding was made on April 12, 2000 between the
ASSIGNOR and Mazarin Mining Corporation Inc. ("MAZARIN") with respect to a
graphite deposit located at Lac Knife in the Province of Quebec, Canada and to
an acquisition by the ASSIGNOR or a company to be owned by or affiliated to the
ASSIGNOR of an Equity Investment (as this term is defined at section 1
hereinafter) in the share capital of MAZARIN (the "MOU");

WHEREAS the ASSIGNEE is an affiliate of the ASSIGNOR as the term affiliate is
defined in the MOU;

WHEREAS the ASSIGNOR and the ASSIGNEE wish to enter into an agreement whereby
the rights, interests and benefits under the MOU with respect to the transfer,
assignment and conveyance of the rights, benefits and interests of the ASSIGNOR
provided for in the MOU but only as they concern the Equity Investment as above
described are assigned, transferred and conveyed to the ASSIGNEE;

WHEREAS the ASSIGNOR and the ASSIGNEE wish to hereby consign in writing the
terms and conditions of their agreements as to said assignment, transfer and
conveyance;

NOW THIS AGREEMENT WITNESSES AS FOLLOWS:

1.       ASSIGNMENT. For good and valid consideration, of which the ASSIGNOR
         acknowledges receipt and for which release and discharge is hereby
         given, the ASSIGNOR assigns, transfers and conveys its rights, benefits
         and interests with respect to the acquisition of an equity investment
         in the share capital of MAZARIN as provided for in the MOU, in
         particular at section 6 of its recitals, at its section 10 and at its
         Appendix "B" (the "Equity Investment") to the ASSIGNEE, who accepts
         such assignment, transfer and conveyance.

2.       ASSUMPTION. The ASSIGNEE hereby agrees to be bound by the provisions of
         the MOU as they concern the Equity Investment and assume the ASSIGNOR'S
         obligations, undertakings, representations and warranties as they
         relate specifically to said Equity Investment and as if the ASSIGNEE,
         in this regard, had signed the MOU, in the place of the ASSIGNOR.

3.       NOTICES. Any notice or other communication to be given hereunder may be
         effectively given to a party by delivering the same at the addresses
         hereinafter set forth or by sending the same by prepaid registered
         mail, prepaid courier or telecopy to such party at such addresses and
         numbers. Any notice so mailed shall be deemed to have been received on
         the third (3rd) business day following the mailing thereof and if given
         by delivery or telecopy the same shall be deemed to have been received
         upon delivery or upon
<PAGE>   2
         transmission. The mailing and telecopy address of the parties for the
         purposes hereof shall be:

         3.1      If to the ASSIGNOR:

                  UCAR GRAPH-TECH INC.
                  11709, Madison Avenue
                  Lakewood, Ohio 44107
                  USA

                  Attention:
                  Facsimile: (216) 529-3888

         3.2      If to the ASSIGNEE:

                  UCAR CARBON COMPANY INC.
                  3102 West End Avenue, Suite 1100
                  Nashville, Tennessee 37203
                  USA

                  Attention:
                  Facsimile: (615) 760-7785

         Any party may from time to time notify the other in accordance with the
         provisions hereof of any change of address which thereafter, until
         changed by like notice, shall be the address of such party for the
         purposes of this agreement. In the event of actual or threatened postal
         interruption, notice shall be made by delivery or telecopy. Receipt of
         a courtesy copy of any notice or other communication shall not be a
         condition to the effectiveness thereof.

4.       INVALID OR UNENFORCEABLE PROVISIONS. If any provision of this agreement
         is judicially determined to be invalid or unenforceable, the remainder
         of this agreement shall not be affected thereby and shall be applied
         and construed as if such invalid or unenforceable provision had been
         omitted.

5.       FURTHER ASSURANCES. Each party shall do such acts and shall execute
         such further documents, conveyances, deeds, assignments, transfers and
         the like and will cause the doing of such acts and will cause the
         execution of such further documents as are within its powers as any
         other party may in writing at any time and from time to time reasonably
         request to be done and/or executed, in order to give full effect to the
         provisions of the present agreement.

6.       ENTIRE AGREEMENT. This agreement, with respect to its specific subject
         matter, together with any agreements and other documents to be
         delivered pursuant hereto constitutes the only and entire agreement
         between the parties pertaining to the subject matter hereof and
         supersedes all prior agreements, negotiations, discussions and
         understandings, written or oral between the parties. There are no
         representations, warranties, conditions, other

                                       2
<PAGE>   3
         agreements or acknowledgments, whether direct or collateral, express
         or implied, that form part or affect this agreement.

7.       ENGLISH LANGUAGE. The parties have expressly required that this
         agreement and all documents and notices relating hereto be drafted in
         English. Les parties aux presentes ont expressement exige que la
         presente convention et tous les documents et avis qui y sont afferents
         seront rediges en anglais.

8.       GOVERNING LAW. This agreement evidences a binding agreement between the
         parties and shall be governed by and construed in accordance with the
         laws of Ontario and the federal laws applicable therein.

9.       RECITALS. The recitals form an integral part of the present agreement.

IN WITNESS WHEREOF the parties hereto have executed this agreement in as of the
date first above written,

                                             THE ASSIGNOR

                                             UCAR GRAPH-TECH INC.

                                             Per:  /s/ John J. Wetula
                                                   ------------------------
                                                   (Authorized signature)

                                                   President
                                                   ------------------------
                                                   (Position)

                                             THE ASSIGNEE

                                             UCAR CARBON COMPANY INC.

                                             Per:  /s/ Craig S. Shular
                                                   -------------------------
                                                   (Authorized signature)

                                                   EVP-CFO
                                                   -------------------------
                                                   (Position)

                                       3
<PAGE>   4

                                     CONSENT

Mazarin Mining Corporation Inc. ("MAZARIN"), a Quebec corporation, hereby
declares that it has examined the present agreement, is satisfied of its content
and, to the extent this may be required, consents to the assignment, transfer
and conveyance described therein in accordance with its terms and conditions.

IN WITNESS WHEREOF, MAZARIN has executed the present consent in Quebec City, as
of the date first above written.

                                                MAZARIN MINING CORPORATION INC.

                                                Per:/s/ J. Bonneau
                                                    -------------------------
                                                    (Authorized signature)

                                                    President - C.E.O.
                                                    -------------------------
                                                    (Position)

                                                Per:/s/ Robert Dutil
                                                    -------------------------
                                                    (Authorized signature)

                                                    Chairman
                                                    -------------------------
                                                    (Position)

                                       4<PAGE>   1

                                                                 EXHIBIT 10(tt)

                               FIRST AMENDMENT TO
                    1999 AMENDED AND RESTATED LOAN AGREEMENT

First Union National Bank
300 Main Street
Stamford, Connecticut 06904
(Hereinafter referred to as the "Bank")

Novametrix Medical Systems Inc.
5 Technology Drive, P.O. Box 690
Wallingford, Connecticut 06492
     ("Novametrix")

NTC Technology, Inc.
c/o Novametrix Medical Systems Inc.
5 Technology Drive, P.O. Box 690
Wallingford, Connecticut 06492
     ("NTC")

Children's Medical Ventures, Inc.
541 Main Street
South Weymouth, Massachusetts 02190
("CMV"; Novametrix, NTC and CMV being,
individually and collectively "Borrower")

This First Amendment to 1999 Amended and Restated Loan Agreement (the
"Amendment") is entered into as of April 28, 2000, by and between Bank and
Borrower, each of which are corporations organized under the laws of Delaware.
The Amendment amends that certain 1999 Amended and Restated Loan Agreement,
entered into as of June 30, 1999, by and between Bank and Borrower (said
agreement being hereinafter referred to as the "Agreement").

                                    RECITALS

Bank is the holder of, inter alia: (i) a certain 1999 Substitute Promissory Note
that certain First Allonge to 1999 Substitute Promissory Note by and between the
Borrower and Bank,

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<PAGE>   2

dated as of even date herewith, in the original principal amount of up to
$8,000,000.00, as amended (hereinafter referred to as the "Line of Credit
Note"); (ii) a certain 1999 Term Promissory Note in the original principal
amount of $4,800,000.00, dated as of June 30, 1999, from the Borrower to the
Bank (hereinafter referred to as the "1999 Term Note"); (iii) a certain 1998
Term Promissory Note executed and delivered by Novametrix and NTC, dated
December 11, 1998, in the original principal amount of $3,000,000.00, as
modified by Allonge No. 1 to 1998 Term Promissory Note, dated as of June 30,
1999, executed by Borrower and the Bank (as modified, hereinafter referred to
as the "1998 Term Note"; the Line of Credit Note, the 1999 Term Note and the
1998 Term Note being sometimes collectively referred to as the "Notes"); and
certain other Loan Documents, including the Agreement; and

Borrower and Bank have agreed to modify the terms of the Agreement by, inter
alia, replacing certain provisions contained therein with those contained in
this Agreement, as more particularly hereinafter set forth.

In consideration of Bank's continued extension of credit and the agreements
contained herein, the parties agree as follows:

This Amendment amends the Agreement.

This Amendment applies to the Loan and all Loan Documents.

This Amendment and the Loans contemplated and covered herein are subject to that
certain Intercreditor Agreement by and between the Bank and Webster Bank, a
Connecticut banking association with a place of business at 80 Elm Street, New
Haven, CT 06510 ("Webster"). The parties acknowledge and agree that Borrower has
previously entered into a Loan Agreement and related loan documents (the
"Webster Loan Documents"), including executing and delivering to Webster a
certain Term Promissory Note in the original principal amount of $4,800,000.00,
dated as of June 30, 1999 (the "Webster Note").

Relying upon the covenants, agreements, representations and warranties contained
in this Amendment and in the Agreement, Bank is willing to modify the terms on
which it will extend credit to Borrower as set forth in the Agreement, as more

                                      E-9
<PAGE>   3
particularly set forth herein, and Bank and Borrower agree as follows:

ACKNOWLEDGMENT OF BALANCE. Borrower acknowledges that the most recent Commercial
Loan Invoice sent to Borrower with respect to the Obligations under the Notes is
correct.

FINANCIAL COVENANTS. (a) The FUNDED DEBT TO EBITDA RATIO provision set forth in
the Financial Covenants section of the Agreement shall be deleted and the
following inserted in its place:

        FUNDED DEBT TO EBITDA RATIO. Beginning April 30, 2000 and for the
        following three fiscal quarters, Borrower shall maintain a ratio of
        Funded Debt to EBITDA of not more than 2.25 to 1.00. Beginning April 30,
        2001 and for the following three fiscal quarters, Borrower shall
        maintain a ratio of Funded Debt to EBITDA of not more than 1.50 to 1.00.
        At all times thereafter, Borrower shall maintain said ratio of not more
        than 1.00 to 1.00. This covenant shall be tested on a rolling four
        quarter basis. "Funded Debt" shall mean, as applied to any person or
        entity, the sum of all indebtedness for borrowed money including,
        without limitation, capital lease obligations, subordinated debt
        (including debt subordinated to the Bank), and unreimbursed drawings
        under letters of credit, or any other monetary obligation evidenced by a
        note, bond, debenture or other agreement of that person or entity.
        "EBITDA" shall mean earnings before interest, taxes, depreciation and
        amortization.

        (b) The FIXED CHARGE COVERAGE RATIO provision set forth in the Financial
Covenants section of the Agreement shall be deleted and the following inserted
in its place:

        FIXED CHARGE COVERAGE RATIO. Beginning April 30, 2000 and for the
        following three fiscal quarters, Borrower shall maintain a Fixed Charge
        Coverage Ratio of not less than 1.50 to 1.00. Beginning April 30, 2001
        and for all fiscal quarters thereafter, Borrower shall maintain a Fixed
        Charge Coverage Ratio of not less than 1.75 to 1.00. This covenant shall
        be tested on a rolling four quarter basis. "Fixed Charge Coverage" shall
        mean the sum of net income plus taxes,

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<PAGE>   4

        depreciation, amortization, and interest expense less capital
        expenditures not financed divided by the sum of interest expense and
        scheduled amounts repaid on long term debt and capital lease
        obligations during the prior four fiscal q quarters.

PREPAYMENT. The Bank hereby waives, in connection with the period ending April
30, 2000 only, Borrower's obligation pursuant to the Prepayment section of the
Agreement to pay an amount equal to 35% of Excess Cash Flow. Such obligation
shall, however, be in full force and effect for all subsequent periods.

LINE OF CREDIT NOTE. All references in the Loan Documents to the Line of Credit
Note shall be understood to mean the Line of Credit Note, as amended by that
certain First Allonge to 1999 Substitute Promissory Note by and between the
Borrower and Bank, dated as of even date herewith, in the original principal
amount of up to $8,000,000.00.

ACKNOWLEDGMENT. The Bank hereby acknowledges the closing of a transaction by and
between Novametrix and GE Marquette Medical Systems, Inc. ("Marquette") as more
particularly set forth in that certain Unit Purchase and Master Agreement dated
as of March 16, 2000 by and between Novametrix and Marquette (the "UPMA").

LOAN AGREEMENT.  All references in the Loan Documents to the Agreement shall be
understood to mean the Agreement, as amended by this Amendment.

ACKNOWLEDGMENTS AND REPRESENTATIONS. Borrower acknowledges and represents that
the Agreement and other Loan Documents, as amended hereby, and the Webster Loan
Documents, are in full force and effect without any defense, counterclaim, right
or claim of set-off; that, after giving effect to this Amendment, no default or
event that with the passage of time or giving of notice would constitute a
default under the Loan Documents or the Webster Loan Documents has occurred, all
representations and warranties contained in the Loan Documents and in the
Webster Loan Documents are true and correct as of this date, all necessary
action to authorize the execution and delivery of this Amendment has

                                      E-11
<PAGE>   5

been taken; and this Amendment is a modification of an existing obligation and
is not a novation.

COLLATERAL. Borrower acknowledges and confirms that there have been no changes
in the ownership of any collateral pledged to secure the Obligations (the
"Collateral") since the Collateral was originally pledged; Borrower acknowledges
and confirms that the Bank has, subject only to the Intercreditor Agreement,
existing, valid first priority security interests and liens in the Collateral;
and that such security interests and liens shall secure Borrower's Obligations
to Bank, including any modification of the Note or Loan Agreement, if any, and
all future modifications, extensions, renewals and/or replacements of the Loan
Documents.

CONDITIONS PRECEDENT. In addition to the Conditions Precedent identified in the
Agreement, the obligations of Bank to make any advances pursuant to the Loan
Documents or this Amendment (including, without limitation, under the Line of
Credit Note) are subject to the following conditions precedent: ADDITIONAL
DOCUMENTS. Receipt by Bank of such additional supporting documents as Bank or
its counsel may reasonably request. STOCK PURCHASE DOCUMENTS. Receipt and review
to Bank's reasonable satisfaction of the documents executed in connection with
the transaction contemplated by the UPMA. PAYMENT OF COMMITMENT FEE. Borrower
shall have paid to the Bank a one time commitment fee of $1,250.00 for the
amendments to the Loan as contemplated herein (including, without limitation, to
the Line of Credit Note). PREPAYMENT. Borrower shall have prepaid $1,000,000.00
of principal on each of the 1999 Term Note and the Webster Note. CONSENT AND
AMENDMENT. The Borrower shall have obtained the consent of Webster Bank to the
modifications to the Loan and the Loan Documents contemplated hereby and
Webster Bank's agreement to the inclusion of the increased amount under the
Line of Credit Note as a Loan (and not an Other Loan, as each of these terms is
defined in the Intercreditor Agreement) for purposes of the Intercreditor
Agreement; Webster Bank shall have executed an amendment to the Intercreditor
Agreement

                                      E-12
<PAGE>   6

reflecting the foregoing. CERTIFICATE OF GOOD STANDING. Bank shall
have received from Borrower a certificate from the Secretary of State of the
state of Borrower's incorporation or organization, as applicable, as to the
good standing of Borrower. CERTIFICATE OF INCUMBENCY AND AUTHORIZATION. Bank
shall have received from Borrower a certificate of an appropriate officer of
Borrower as to the incumbency and signatures of the officers of Borrower
executing the Loan Documents and as to the adoption of resolutions authorizing
the amendments to the Loan Documents including, without limitation, the
increase to the amount of the Line of Credit Note. OPINION OF COUNSEL. Bank
shall have received a written opinion of the counsel of Borrower acceptable to
Bank that includes confirmation of the following: (a) The Borrower is duly
organized and validly existing under the laws of the jurisdictions where
Borrower is organized and has full power and authority to undertake the
activities contemplated by the Loan; There have been no changes, since June 30,
1999, to the Charter Documents or Operating Agreements of Borrower. (b) The
Loan Documents, as modified by documents executed in connection with this
Amendment, create a perfected lien on and security interest in the Collateral
(as defined in the Loan Documents). (c) The accuracy, as of the date hereof, of
the representations set forth in the Agreement in the Representations
Subparagraphs entitled "Authorization; Non-Contravention"; "Compliance with
Laws" as to the transaction contemplated by this Amendment and the documents
pertaining thereto; and "Organization and Authority." (d) This Amendment and
other Loan Documents executed in connection herewith have been duly executed
and delivered by Borrower and constitute the legal, valid and binding
obligations of Borrower, enforceable in accordance with their terms. (e) No
registration with, consent of, approval of, or other action by, any federal,
state or other governmental authority or regulatory body to the execution and
delivery of this Agreement, the borrowing under this Agreement or other Loan
Documents, is required by law, or, if so required, such registration has been
made, and consent or approval given or such other appropriate action taken. (f)
The Loan and its terms do not violate any laws including, without limitation,
any usury laws of the jurisdictions where Borrower and any

                                      E-13
<PAGE>   7

Collateral are located; such other matters and opinions as the Bank reasonably
requests.

JOINT AND SEVERAL OBLIGATIONS.  The obligations of the Borrower hereunder and
under the Loan Documents shall be joint and several.

MISCELLANEOUS. This Amendment shall be construed in accordance with and governed
by the laws of the State of Connecticut without reference to conflicts of laws
principles. This Amendment and the other Loan Documents constitute the sole
agreement of the parties with respect to the subject matter thereof and
supersede all oral negotiations and prior writings with respect to the subject
matter thereof. No amendment of this Amendment, no other amendment to the
Agreement, and no waiver of any one or more of the provisions hereof or thereof
shall be effective unless set forth in writing and signed by the parties hereto.
The illegality, unenforceability or inconsistency of any provision of this
Amendment shall not in any way affect or impair the legality, enforceability or
consistency of the remaining provisions of this Amendment, the Agreement, as
modified hereby, or the other Loan Documents. The Agreement, as modified by this
Amendment, and the other Loan Documents are intended to be consistent. However,
in the event of any inconsistencies among the Agreement, as modified by this
Amendment, and any of the Loan Documents, the terms of the Notes, and then the
Agreement, as modified by this Amendment, shall control. This Amendment may be
executed in any number of counterparts and by the different parties on separate
counterparts. Each such counterpart shall be deemed an original, but all such
counterparts shall together constitute one and the same agreement. The terms
"Loan Documents" and "Obligations" shall have the meanings of such terms as
defined in the Agreement. Additional terms used in this Amendment which are
capitalized and not otherwise defined herein shall have the meanings ascribed
to such terms in the Loan Documents. Without limiting the generality of the
foregoing, the term "Loan Documents" does not include any swap

                                      E-14
<PAGE>   8

agreements (as defined in 11 U.S.C. Section 101); the term "Obligations" shall
include, without limitation, all obligations under any swap agreements as
defined in 11 U.S.C. Section 101 between Borrower and Bank whenever executed.

CONNECTICUT PREJUDGMENT REMEDY WAIVER. EACH BORROWER ACKNOWLEDGES THAT THE
TRANSACTIONS REPRESENTED BY THIS AMENDMENT ARE COMMERCIAL TRANSACTIONS AND
HEREBY VOLUNTARILY AND KNOWINGLY WAIVES ANY RIGHTS TO NOTICE OF AND HEARING ON
PREJUDGMENT REMEDIES UNDER CHAPTER 903a OF THE CONNECTICUT GENERAL STATUTES OR
OTHER STATUTES AFFECTING PREJUDGMENT REMEDIES, AND AUTHORIZES THE BANK'S
ATTORNEY TO ISSUE A WRIT FOR A PREJUDGMENT REMEDY WITHOUT COURT ORDER, PROVIDED
THE COMPLAINT SHALL SET FORTH A COPY OF THIS WAIVER.

WAIVER OF JURY TRIAL.  THE PARTIES ACKNOWLEDGE THAT THEY HAVE IRREVOCABLY
WAIVED ANY RIGHT THEY MAY HAVE TO JURY TRIAL WITH REGARD TO A DISPUTE.

PLACE OF EXECUTION AND DELIVERY. Borrower hereby certifies that this Agreement
and the Loan Documents were executed in the State of Connecticut and delivered
to Bank in the State of Connecticut.

                                      E-15

<PAGE>   9

IN WITNESS WHEREOF, Borrower and Bank, on the day and year first written above,
have caused this Agreement to be executed under seal.

                             NOVAMETRIX MEDICAL SYSTEMS INC.

                             By: /s/ William J. Lacourciere
                                -----------------------------
                                name:  William J. Lacourciere
                                title: President and Chief Executive Officer

                             NTC TECHNOLOGY, INC.

                             By: /s/ Thomas M. Haythe
                                -----------------------------
                                name:  Thomas M. Haythe
                                title: President

                             CHILDREN'S MEDICAL VENTURES, INC.

                             By: /s/ Joseph A. Vincent
                                -----------------------------
                                name:  Joseph A. Vincent
                                title: Vice President

                            FIRST UNION NATIONAL BANK

                             By: /s/ John H. Frost
                                ------------------------------
                                name:  John H. Frost
                                title: Vice President

                                      E-16

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